Medical Conferences

2016

 

Evaluation of the In Vitro Activity Profile of Omadacycline Against Haemophilus influenza

 B. D. VanScoy, H. Conde, K. Tanaka, S. M. Bhavnani, J. N. Steenbergen, P. G. Ambrose

 

In Vitro Protein Binding with Omadacycline, a First in Class Aminomethylcycline Antibiotic

Stephen Villano, Evan Tzanis, S. Ken Tanaka

 

 Effect of Food on the Bioavailability of Omadacycline in Healthy Volunteers

Evan Tzanis, Amy Manley, Stephen Villano, S. Ken Tanaka, Steven Bai, Evan Loh

 

In Vitro Intracellular Activity of Omadacycline Against Legionella pneumophila

J. Dubois, M. Dubois, J. F. Martel, S.K. Tanaka

 

Population Pharmacokinetics of Omadacycline Following Intravenous and Oral Administration and Evaluation of Phase 3 Sparse PK Sampling Strategies

Scott A. Van Wart, Amy Manley, Sujata M. Bhavnani, Ken Tanaka, Evan Loh, Evan Tzanis, Paul G. Ambrose

 

Activity of Omadacycline Against Clinical Isolates of Neisseria gonorrhoeae, Including Ciprofloxacin-Resistant Isolates

D. Sweeney, D. Hall, D. Shinabarger, C. Pillar

 

Post-antibiotic Effect of Omadacycline against Target Pathogens

R. Hinshaw, L. Stapert, D. Shinabarger, C. Pillar

 

In Vitro Activity of Omadacycline against E coli Biofilms

D. Diehl, N. Bionda, N.C. Cady, A.D. Strickland, S.K. Tanaka

 

ASMMicrobe 2016 Poster 567 Omadacycline Spectrum 2003-2015

M.M. Traczewski, S.D. Brown

 

Chilton - Effects of omadacycline on gut microbiota populations and Clostridium difficile germination, proliferation and toxin production in an in vitro model of the human gut

 Introduction:  Omadacycline is a potent aminomethycycline antibiotic with activity against Gram-positive bacteria, including MSSA/MRSA and S. pneumoniae, Gram-negative bacteria, and atypical bacteria. It is currently in phase 3 clinical trials for acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia. We have used a well validated, clinically reflective model of the human gut to investigate the effects of omadacycline exposure on the normal gut microbiota, and subsequent potential for induction of simulated C. difficile infection (CDI).

 

Dubois - In Vitro Bacterial and Intracellular Activity of Omadacycline Against Legionella pneumophila

 Background: Omadacycline (OMC) is the first aminomethylcycline in late stage clinical development for community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infection (ABSSI) as once-daily oral and IV formulations. In vitrobacterial activity and intracellular activities using human monocytes against a variety of L. pneumophilaserogroup 1 were investigated.

Methods: The in vitroactivity of OMC was compared with that of doxycycline (DO), azithromycin (AZ), erythromycin (ER), levofloxacin (LE), and moxifloxacin (MO) against a total of 90 L. pneumophilaserogroup 1 by microdilution procedure using buffered yeast extract broth containing Legionellagrowth supplement (BYE). A pre-test to determine if antibiotic activity was impacted artificially by Legionellasupplement or iron was done by testing 3 ATCC quality control isolates on BYE, BYE without iron, and cation-adjusted Mueller-Hinton Broth (MH). The intracellular activity of OMCwas compared against a total of 3 ER-resistant and 2 ER-susceptible strains of L. pneumophilaserogroup 1. The intracellular activity was determined by exposing human monocytes, U937 cell line, with intracellular L. pneumophila to antibiotic at 1X the extracellular MIC of each strain during either 2 or 6 days of exposure. Counts of CFU/mL were performed daily in duplicate using the BYE agar with charcoal.

Results: Against tested L. pneumophila serogroup 1, the MIC50/90of MO, LE, OMC, AZ, ER, and DO was 0.008/0.016, 0.016/0.016, 0.25/0.25, 0.12/0.5, 0.25/1 and 1/1 mg/L in BYE, respectively. Pilot tests suggested that the MIC values of OMCand DO obtained in BYE for L. pneumophilamay be artificially elevated (5-to 7-fold increase) due to the media effects. A significant reduction of more than 3 log10CFU/mL or 99.9% of ER-susceptible or ER-resistant L. pneumophilagrown in monocytes was observed after4 to 6 days of continuous exposure to OMC at 1X the MIC. A regrowth of L. pneumophilain monocytes was observed after 1 day of ER exposure, after 3 days of AZ and DO exposure, and after 4 days of LE exposure, however this regrowth was not observed with OMCand MO.After drug wash-out at day 2 of drug exposure, OMC followed byMO, DO, LE, and AZ, slowed substantially the regrowth of L. pneumophilatested strains in human monocytes, whereas a rapid regrowth occurred for ER-treated culture.

Conclusions: This data demonstrating good bacterial activity and human monocytes penetration, suggest that OMCmay have use in infections caused by L. pneumophila and highlights the potential utility of this oral and IV agent for the treatment of CABP.

 

Flamm - OmadacyclineActivity Tested Against European Bacterial Isolates from a Combined 2010-2011 Global Surveillance Program

Background: Omadacyclineis a broad spectrum aminomethylcycline in late stage clinical development for the treatment of acute bacterial skin and skin structure infections and community-acquired pneumonia that is being evaluated as both oral and intravenous, once-daily formulations. It has excellent activity against Gram-positive and Gram–negative pathogens including tetracycline resistant organisms. The results from testing omadacycline and comparator agents against clinical isolates collected during 2010-2011 from the European region of a global surveillance study are presented.

Material/methods: More than 20,000 Gram-positive and –negative isolates were selected from patients in 45 medical centers in 14 European countries and Israel. Only one isolate per infection episode per patient was included. A central monitoring laboratory confirmed isolate identity using standard bacteriologic algorithms, the VITEK 2 System, or molecular characterization if necessary. Antibacterial susceptibility testing was performed by broth microdilutionper CLSI guidelines. EUCAST breakpoints were used to determine susceptibility rates.

Results: The omadacycline MIC50/90for all Staphylococcus aureus was 0.12/0.25 mg/L. Against MRSA, omadacycline (MIC90, 0.25 mg/L) and tigecycline (MIC90, 0.25 mg/L; 100.0% susceptible) were the most potent antimicrobials tested while susceptibility to multiple agents including erythromycin (32.9%), clindamycin (67.7%), and levofloxacin (12.0%) were compromised. Omadacycline and tigecycline exhibited potent activity against Enterococcus faecalis and E. faecium (MIC90 values at ≤0.25 mg/L). The MIC50 and MIC90 for omadacycline (0.06/0.06 mg/L) and tigecycline (≤0.03/0.06 mg/L) against Streptococcus pneumoniae, were the lowest among the agents tested and demonstrated activity against ceftriaxone and levofloxacin resistant isolates. Omadacycline and tigecycline MIC values for S. pneumonia were 16-fold lower than ceftriaxone (MIC90, 1 mg/L) and levofloxacin (MIC90, 1 mg/L). Omadacycline was potent against the β-haemolytic streptococci, MIC90 0.12 mg/L. All β-haemolytic streptococci were susceptible to tigecycline, β-lactams, linezolid, daptomycin, and vancomycin, however resistance to levofloxacin (95.0% susceptible), erythromycin (81.4% susceptible), clindamycin (92.5% susceptible), tetracycline (45.7% susceptible) and doxycycline (49.5% susceptible) occurred. The MIC50 and MIC90 for omadacycline for the Enterobacteriaceae was 1 and 8 mg/L, respectively. Omadacycline was less potent against Klebsiella pneumonia (MIC50/90, 2/8 mg/L [86.8% inhibited at ≤4 mg/L]); ESBL-phenotype MIC 50/90, 2/8 mg/L [78.3% inhibited at ≤4 mg/L]) and more potent against Escherichia coli (MIC50/90, 0.5/2 mg/L; ESBL-phenotype MIC50/90, 1/4 mg/L [97.9% inhibited at ≤4 mg/L]).

Conclusions: Omadacycline was active against a broad spectrum of Gram-positive and –negative pathogens including MRSA, Enterococci, β-haemolytic streptococci, S. pneumonia including MDR isolates, and Enterobacteriaceae. Further evaluation in clinical trials is warranted.

 

Hawser - Bactericidal activity of omadacycline, a novel aminomethylcycline

Background: Omadacycline (OMC) is the first of a new class of tetracyclines, the aminomethylcyclines, and is being developed as a once-daily oral and IV treatment for acute bacterial skin and skin structure infection (ABSSSI) and community-acquired bacterial pneumonia (CABP). The objective of the present study was to evaluate the bactericidal activity of OMC compared with other antibacterial agents. Materials/methods: Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were determined against 85 bacterial isolates following CLSI guidelines. A subset of isolates was further investigated with time-kill studies (TK), where bactericidal activity was defined as a 3-log reduction in viable count (99.9% kill) over 24 hours. Results: OMC showed low MICs against the test isolates, including antibiotic-resistant strains. MBC data indicated bactericidal activity against streptococci, M. catarrhalis, and H. influenzae but bacteriostatic activity against enterococci, S. aureus, and E. coli. TK studies generally confirmed the MBC data with omadacycline being rapidly bactericidal against H. influenzae and S. pneumoniae. Bactericidal activity was species and strain dependent, and time to achieve 99.9% killing for these isolates varied between 3.1 to 20.4 hours. Conclusion: Omadacycline demonstrated good activity against the pathogens tested with particularly strong bactericidal activity against H. influenzae, M. catarrhalis, and S. pneumoniae. The spectrum and rapidity of the bactericidal activity of omadacycline was comparable to tigecycline. The inhibitory and bactericidal activity of omadacycline was not affected by resistance to other antimicrobials.

 

Kim - Activity and Efficacy of Omadacycline against Clostridium difficile

 Introduction: Omadacycline (OMC) is a new aminomethylcycline in Phase 3 clinical development for the oral and intravenous treatment of acute bacterial skin and skin structure infections (ABSSSI) and community acquired bacterial pneumonia (CABP). OMC has broad-spectrum activity against Gram-positive, Gram-negative, and atypical bacteria.

Material and methods: OMC was tested in vitro against 27 clinical isolates of C. difficile (Cd) using both broth microdilution and agar dilution methods according to CLSI guidelines. The efficacy of OMC was determined in the hamster model of CDAD (ViviSource Laboratories, Inc., Waltham MA). Male LGV-Golden Syrian Hamsters were pretreated with a subcutaneous (SC) dose of clindamycin (10 mg/kg) and infected 24 hours later by oral gavage with a suspension of a 48 hour culture of Cd ATCC 43596, resulting in an inoculum of approximately 1.3 x 107 CFU/hamster. At 24 hours post infection, animals were treated PO with OMC (50 mg/kg/day), vancomycin (VAN 50 mg/kg/day) or vehicle for 5 days.

Results: The MIC90 for OMC against Cd was 0.06 mg/L by broth dilution and 0.12 mg/L by agar dilution, and OMC was more active than doxycycline (MIC90 = 0.5 mg/L by broth and 1 mg/L by agar). Against the infection model strain, OMC was as active as tigecycline, metronidazole, and VAN (MIC = 0.06 mg/L for all drugs). Day 2 post infection, 100% of OMC treated animals were alive, compared to 40% and 0% for VAN and vehicle control animals. For the OMC-treated animals, survival declined to 60% by Day 3 and remained at 60% until declining to 40% on Day 13 and to 0% by Day 16. Animals treated with VAN that survived the initial 2 days began to die by Day 11 (30% survival) and all animals succumbed to infection by Day 14. Overall, the median survival for OMC treated animals was 12 days compared to 2 days for VAN.

Conclusion: OMC exhibited potent in vitro activity against C. difficile and efficacy in the hamster model of CDAD and might offer potential for the treatment of C. difficile infections.

 

Tanaka - Effect of Age and Gender on the Pharmacokinetics of Oral and IV Omadacycline, A New Class of Aminomethylcyclines

Background: Omadacycline is the first of a new class of antibiotics, the aminomethylcyclines, currently in phase 3 clinical development as a once daily oral and intravenous (IV) formulation for CABP and ABSSSI. Two phase 1 studies were undertaken to evaluate the effect of age and gender on the pharmacokinetic (PK) of omadacycline after oral and IV administration in healthy volunteers.

Methods: Both were double-blind and placebo-controlled studies of single oral doses of omadacycline in subjects randomized in a 3:1 ratio to omadacycline or placebo. Study 1 included 4 subject groups: A) young males; B) young females; C) elderly males; D) elderly females. After an 8-hour overnight fast, each group received placebo or omadacycline 200 mg. Study 2 included healthy young male and female subjects who received a single 200 mg oral or 100 mg IV dose of omadacycline or placebo. Blood samples were obtained pre-dose, and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 18, 24, 48, 72 and 96 hours post-dose to determine PK parameters.

Results: In Study 1 (23 subjects), a high degree of consistency was observed for the PK characteristics of a single 200 mg oral dose. No significant difference in drug exposure was observed between fasting young and elderly subjects. Both young and elderly females exhibited greater mean AUCinf values than corresponding young and elderly male subjects (14.6 mg*h/L vs. 9.4 mg*h/L for all female and all male subjects; ratio 0.64, 90% CI: 0.52, 0.80). For elderly vs. young subjects, the mean ratio was 1.13 (90% CI: 0.91, 1.41). In Study 2 (24 subjects), evaluation of PK profiles showed a high degree of consistency between males and females who received a 200 mg oral dose of omadacycline. The AUCinf ratio of males to females was 1.02 (2-sided 90% CI 0.69, 1.50). The geometric mean half-life was 17.2 hours for the males and 11.4 hours for the females. The AUCinf for IV omadacycline exhibited more variability in female (18.4%) than in male subjects (4.9%) but the 90% CI for mean AUCinf ratio for males to females was within the specified range (ratio 0.77, 90% CI: 0.67, 0.89). Omadacycline oral and IV formulations were well tolerated with no unexpected safety or tolerability adverse events.

Conclusion: After a single oral administration of 200 mg of omadacycline, female subjects demonstrated higher mean AUCinf compared to male subjects. However, the exposure in females did not differ significantly after a single IV dose. No effect of age on omadacycline absorption and PK profile was observed. Thus, no dosage adjustment on the basis of patient age or gender is necessary.

 

Tanaka - A Pooled Analysis of Two Randomized Multicenter, Evaluator-Blind Studies Comparing the Safety and Efficacy of Omadacycline and Linezolid for the Treatment of Complicated Skin and Skin Structure Infections

Background: Omadacycline is the first of a new class of antibiotics, the aminomethylcyclines, currently in clinical development as a once daily oral and intravenous (IV) formulation for community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSI). A phase 2 and a truncated phase 3 study in patients with complicated skin and skin structure infections (cSSSI) were conducted. Both studies compared the safety and efficacy of omadacycline, a broad-spectrum agent with activity against methicillin-resistant Staphylococcus aureus (MRSA). Results from these two studies were pooled to evaluate the effect of omadacycline on safety, tolerability, and efficacy.

Material/Methods: Patients were randomized 1:1 to omadacycline 100 mg IV once a day (QD) with an option to transition to 200 mg or 300 mg orally QD or linezolid 600 mg IV twice daily (BID) with an option to transition to 600 mg orally BID and treated for 7-14 days. Patients in both studies were evaluated at the test of cure visit.

Results: A total of 377 patients randomized to either omadacycline or linezolid, with 359 patients in the intent-to-treat population (ITT), 179, and 180, respectively. Mean age was 43.7 years with omadacycline and 41.9 years with linezolid. For the ITT population at the test of cure visit, 156 (87.2%) patients on omadacycline had clinical success compared to 146 (81.1%) patients on linezolid. In the clinically evaluable (CE) population, clinical success occurred in 156 (97.5%) patients on omadacycline compared to 146 (94.2%) on linezolid. In the microbiologically evaluable (ME) population, microbiological success occurred in 123 (97.6%) patients with omadacycline compared with 112 (97.4%) patients with linezolid. Adverse event rates for both omadacycline and linezolid were comparable; 58% in the omadacycline group and 62.8% in the linezolid group experienced an adverse event. Gastrointestinal adverse events were the most frequent for omadacycline (28.5%) and linezolid (26.1%).

Conclusions: In this analysis, the success rates for omadacycline and linezolid in the treatment of cSSSI were comparable in the ITT, ME, and CE populations at the test of cure visit. Pooled analyses support a favorable and comparable tolerability profile for both omadacycline and linezolid. These data further support the development of omadacycline as a broad spectrum, once a day, oral and IV treatment for serious community-acquired infections.

 

Tanaka - Single and Multiple Dose Pharmacokinetics and Tolerability of Intravenous Omadacycline in Healthy Volunteers

 Background: A first in class aminomethylcycline antibiotic, omadacycline, is undergoing clinical development for the treatment of acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP) as a once daily oral and intravenous (IV) formulation. Two phase 1 studies in healthy volunteers examined the pharmacokinetic (PK) profile and tolerability of omadacycline after single- and multiple-dose administration.

Methods: Both studies were randomized, double-blind, and placebo-controlled in healthy male subjects. In Study 1, subjects were randomized to receive a single omadacycline dose of 25, 50, 100, 200, 300, 400 or 600 mg as a 30- or 60-minute IV infusion. In Study 2, subjects received a 30-minute IV infusion of omadacycline 200 mg once daily x 7 days. Blood samples were obtained pre-dose and at frequent intervals over 72 hours to determine plasma omadacycline levels for PK calculations. Monitoring consisted of adverse events, vital signs, physical examination, laboratory tests, and an electrocardiogram.

Results: In Study 1, 41 subjects were treated with omadacycline and had PK data available. After a single IV dose, a dose-dependent increase was exhibited for mean AUC0-24 (0.9 to 24.9 mg*h/L) over the range from 25 to 600 mg. Mean Cmax was 0.3 to 2.6 mg/L for 25 to 200 mg doses infused over 30 minutes and 2.6 to 4.5 mcg/mL for doses infused over 60 minutes, respectively. For the majority of doses, mean half-life ranged from 17 to 21 hours. In Study 2, 20 subjects were treated in 2 cohorts with omadacycline and had PK data available. Among the 2 cohorts, mean Cmax on Day 1 was 2.9 and 2.7 mg/L and on Day 7 was 3.5 and 3.3 mg/L, and, mean AUC0-24 on Day 1 was 12.1 and 11.0 mg*h/L and Day 7 was 17.8 and 17.2 mg*h/L. AUC0-24 on Day 7 was approximately 1.5-1.6 fold higher than Day 1. For all of the AUC measures, the coefficient of variation ranged from 8.7% to 13.8%. In Study 1, no GI adverse events were recorded. In Study 2, 5 (12.2%) episodes of mild or moderate nausea and 1 (2.4%) of vomiting were reported, but there were no discontinuations due to any adverse event. No unexpected safety issues were reported.

Conclusion: After IV administration, omadacycline demonstrated a well-tolerated, dose-proportional, and linear PK profile over a dosage range from 25 to 600 mg together with a low incidence of GI adverse events, which contrasts with other tetracycline-derived antibiotics.

 

Van Wart - Population Pharmacokinetics of Omadacycline Following Intravenous or Oral Administration to Phase 1 Subjects

Introduction:  Omadacycline, a novel aminomethylcyline synthesized by chemical modification of minocycline, is active against both Grampositive and Gram-negative organisms.

• Omadacycline is available for both intravenous (IV) and oral administration and is currently in phase 3 of development for treatment of acute bacterial skin and skin structure infections or community-acquired bacterial pneumonia.

• A population pharmacokinetic (PPK) analysis was conducted to characterize the time-course of omadacycline in plasma and excretion into the urine of healthy volunteers following IV and/or oral administration, as well as to evaluate the impact of formulation differences and food on the rate and extent of omadacycline absorption.

Materials and Methods:

Data

• The population PK analysis was conducted in NONMEM 7.2 using plasma PK data from 319 subjects (including 18 with cirrhosis) who participated in 10 Phase 1 clinical trials.

• Subjects were administered omadacycline freebase or tosylate salt as IV (50 or 100 mg), oral capsule (50 to 600 mg) or tablet (150 to 300 mg) doses; food was consumed at varying times within a 4 hour window prior to or after oral dosing across studies.

• Serial PK samples collected in each study were assayed using LC-MS/MS (lower limit of quantitation of 20 ng/mL) to determine plasma omadacycline concentrations.

Population Pharmacokinetic Analysis

• Both 2- and 3-compartment (CMT) models with zero-order input and first-order elimination were first evaluated using only IV data.  The models were parameterized using total clearance (CL), central volume (Vc), distribution clearances (CLd1 and CLd2), and peripheral volumes (Vp1 and Vp2). Interindividual variability (IIV) for PK parameters was described using an exponential model; an additive plus constant coefficient of variation model was used for residual error.

• The population PK model was then modified to simultaneously fit the data obtained after IV or oral dosing

 Oral bioavailability (F) and first-order absorption rate (ka) and their IIV were estimated.  An absorption lag-time or transit absorption compartments were also explored to better account for the delay in the onset of oral

absorption.  Interoccasion variability (IOV) was also estimated for ka.  Omadacycline oral formulation differences, as well as the timing of meals relative to dose administration, were explored as covariates on both F and ka.  Subject covariates such as age, weight, BMI, creatinine clearance (CLcr), etc. were then analyzed using stepwise forward selection (α=0.01) and backward elimination (α=0.001).

• Lastly, plasma and urine PK data (6 subjects only) were co-modeled to independently estimate renal (CLR) and non-renal (CLNR) clearance, and a prediction corrected visual predictive check (PC-VPC) was performed to evaluate final model fit.

Results:

Pharmacokinetic Analysis Population

• The PK analysis population (N = 319) was 81.2% male and 75.2% Caucasian. The mean (SD) age was 32.8 (11.0) years, weight was 75.8 (10.9) kg, and CLcr was 107 (19.6) mL/min/1.73 m2 and ranged from 52.8 to 185 mL/min/1.73 m2.

Final Population Pharmacokinetic Model

• A 3-CMT model with zero-order IV input, or first-order oral absorption with 2 transit CMTs to provide delayed absorption, best characterized omadacycline PK (Figure 1 and Table 1).  Observed plasma concentrations agreed well with the population (r2=0.74) and individual post-hoc (r2=0.96) predictions (Figure 2) and PC-VPCs (Figure 3) showed a reasonable fit by formulation.

• Non-renal CL was 5.72 L/hr, while renal CL was linearly related to CLcr (4.62 L/hr at the median of 109 mL/min/1.73 m2) for the range of renal function studied.

• Body size was not predictive of Vc (24.3 L) but steady-state volume of distribution (225 L) indicated extensive tissue distribution.

• Cirrhosis did not impact total CL, although Vc was 74.4% lower relative to healthy subjects.

• F was determined using absolute time of food consumption relative to dosing (AMTIME) via a Hill-type function which estimated F for consuming food exactly at dosing (F0) , the maximal increase in F in the absence of food (Fmax) and the AMTIME at which Fmax decreased by 50% (AMTIME50)

• F was more sensitive to food consumption pre-dose (Figure 4); F was <3% when omadacycline was administered just prior to a meal and 27-30% when meals were restricted to 2-4 hours post-dose.

Conclusions:

A PPK model including significant covariate effects for omadacycline was developed using Phase 1 data. This model provided the basis for recommending food consumption be restricted to at least 4 hours prior to or 2 hours after administration of an oral omadacyline dose.

• Although only a limited range of renal function has been studied to date, this PPK model will be further updated after including additional omadacycline PK from individuals with moderate or severe renal impairment and used to support dosing guidelines for renal impairment.

 

Villano - Omadacycline, an Aminomethylcycline Antibiotic, Has No Effect on QT/QTc Intervals in Healthy Subjects

Background: Omadacycline (OMC), a first-in-class aminomethylcycline, is a once daily oral and intravenous (IV) broad spectrum antibiotic that is undergoing clinical development for treatment of serious bacterial infections. The objective of this study was to evaluate the effect of single therapeutic and supratherapeutic IV doses of omadacycline on ventricular repolarization and the relationship between plasma concentrations of omadacycline and QTc intervals.

Methods: This was a single dose, double-dummy, randomized, crossover study. Healthy adult volunteers were randomized to one of four treatment sequences: OMC 100 mg IV, OMC 300 mg IV, moxifloxacin 400 mg oral or placebo. Baseline ECGs were obtained one day prior to the first treatment at timepoints to match those obtained post-dose. After dosing, 12-lead Holter monitoring was recorded over 24 hours, and omadacycline plasma concentrations were measured at set timepoints over 96 hours. The primary ECG parameter of interest was the placebo- and baseline-adjusted QTcF value (ddQTcF) at each defined post-dose timepoint.

Results: 64 subjects were enrolled (mean age 28 years, 63% male). Mean AUC0-24 and Cmax were dose proportional for omadacycline 100 mg and 300 mg and were consistent with previous studies. OMC did not increase QTcF as demonstrated by one-sided 95% upper confidence bounds on ddQTcF <10 msec at all post-dose timepoints – the largest value was 1.53 msec for OMC 100 mg (6 hours post-dose) and 0.83 msec for OMC 300 mg (2 hours post-dose). Assay sensitivity was confirmed by increases in ddQTcF >5 msec at multiple timepoints for moxifloxacin. There was no relationship between OMC plasma concentrations and ddQTcF. The most common adverse event (AE) was infusion site pain (all mild intensity): 6% for OMC 100 mg and 11% for OMC 300 mg. There were no serious AEs. Within one hour after dosing, mean peak increases in heart rate were observed for OMC (17 bpm for 100 mg and 24 bpm for 300 mg) vs. 3 bpm for placebo and 5 bpm for moxifloxacin; the changes were asymptomatic and became comparable across all groups by 12-24 hours after dosing.

Conclusion: Omadacycline at doses of 100 mg and 300 mg IV did not increase QTcF.

2015

Activity of Omadacycline Tested against Streptococcus pneumoniae from a Global Surveillance Program (2014)

Streptococcus pneumoniae is the most common bacterial pathogen causing pneumonia. Bacterial resistance occurring in S. pneumoniae is a serious problem to many of the commonly used oral agents. As antimicrobial resistance among S. pneumoniae extends beyond the β- lactams to include macrolides and fluoroquinolones, the choice of appropriate therapies becomes limited. Further, multidrug resistance leads to increased morbidity and mortality. Thus it is important to choose the appropriate initial empiric therapy. Omadacycline (PTK 0796; [7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline]) is a novel tetracycline antibacterial agent, which is currently under clinical development for use as both an oral and intravenous formulation against acute bacterial skin and skin structure infections, community-acquired pneumonia, and urinary tract infections. Omadacycline has broad spectrum activity against Gram-positive, Gram-negative, atypical and anaerobic bacteria, including those with multi-drug resistance (MDR). In this report, the activity of omadacycline and comparator agents were tested against S. pneumoniae selected from a 2014 global surveillance program and compared to the results of a 2010 surveillance program. Omadacycline was highly active against S. pneumoniae (MIC90 , 0.06-0.12 µg/mL).

  • The activity of omadacycline was similar for the North American and European regions in both 2014 and 2010.
  • Omadacycline was highly active against ceftriaxone non-susceptible, Pen-R, macrolideR, quinolone-R and MDR subgroups of S. pneumoniae.
  • S. pneumoniae resistance rates to doxycycline, azithromycin, and TMP/SMX continue to be high for both North America and Europe.

 

 

Activity of Omadacycline Tested against Enterobacteriaceae Causing Urinary Tract Infections from a Global Surveillance Program (2014)

Urinary tract infections (UTI) are common infections that occur in the community and healthcare settings. The most common cause of bacterial UTI is Escherichia coli. In the healthcare setting, bacterial resistance to commonly prescribed antibacterials is an issue. Extended-spectrum β-lactamases and carbapenemases may occur, thus limiting β-lactam options. Further clones such as E. coli ST-131 may occur which are often also resistant to other antibacterial classes such as the fluoroquinolones. The resistance to oral agents in the community setting and the emergence of the ESBL positive E. coli into the community indicate an urgent need for new alternatives to treat UTI. Omadacycline (PTK 0796; [7-dimethylamino, 9-(2,2-dimethyl-propyl) aminomethylcycline]) is a novel tetracycline antibacterial agent, which is currently under clinical development for use as both an oral and intravenous formulation against acute bacterial skin and skin structure infections, community-acquired pneumonia, and urinary tract infections. Omadacycline has broad spectrum activity against Grampositive, Gram-negative, atypical and anaerobic bacteria, including those with multi drug resistance (MDR). In this study, the activity of omadacycline and comparator agents was evaluated against isolates causing UTI in 2014. These results were compared to those from a 2010 global surveillance program.

  • Omadacycline was active against a wide-range of Enterobacteriaceae isolates causing UTI from North America and Europe between 2010 and 2014.
  • Omadacycline was active (MIC90 ≤4 µg/mL) against E. coli regardless of ESBL status. A similar level of activity was observed with Klebsiella species isolated in North America (MIC90, ≤4 µg/mL) however there was less activity observed in Klebsiella isolates from Europe in 2014 (MIC90, ≥8 µg/mL). Omadacycline was least active against Proteus/Providencia/Morganella species.
  • Further clinical study with omadacycline in the treatment of UTI caused by Enterobacteriaceae is indicated.

 

 

Activity of Omadacycline Tested against Staphylococcus aureus from a Global Surveillance Program (2014)

Omadacycline (PTK 0796; [7-dimethylamino, 9-(2,2-dimethylpropyl)-aminomethylcycline]) is a novel tetracycline antibacterial agent, which is currently under clinical development for use as both an oral and intravenous formulation against acute bacterial skin and skin structure infections, community-acquired pneumonia, and urinary tract infections. Omadacycline has broad spectrum activity against Gram-positive, Gram-negative, atypical and anaerobic bacteria, including those with multi-drug resistance (MDR). Staphylococcus aureus are extremely common causes of infection including serious infections in the hospital environment. S. aureus is a major cause of acute bacterial skin and skin structure infections and bloodstream infections with methicillin-resistant strains (MRSA) accounting for approximately 50% of S. aureus. In this report, we evaluated the activity of omadacycline tested by reference methods against S. aureus causing community- and hospital-acquired infections in North America and Europe in comparison to data collected in the 2010 global surveillance program.

  • The potent in vitro activity of omadacycline remains unchanged between 2010 and 2014, and was similar for North American and European isolates including MRSA (CA-MRSA or HA-MRSA).
  • Resistance to clindamycin, erythromycin, and levofloxacin was higher in MRSA than in MSSA.
  • Susceptibility for a number of agents tended to be lower in HA-MRSA compared to CA-MRSA.
  • The potent activity of omadacycline against S. aureus indicates that omadacycline merits further study in serious community-acquired infections, such as ABSSSI and CABP, where MDR may be a concern.

 

 

Quality Control Parameters for Broth Microdilution and Agar dilution Susceptibility Tests of Omadacycline (formerly PTK-0796) against B. fragilis ATCC 25285, B. thetaiotaomicron ATCC 29741, E. lenta ATCC 43055, and C. difficile ATCC 700057 Using Fresh Media

Omadacycline is the first aminomethylcycline to enter clinical development. OMC is being developed globally as an intravenous and oral, once daily monotherapy therapy for ABSSSI and CABP. OMC was designed to overcome tetracycline resistance mechanisms and has been shown to have potent in vitro activity and in vivo efficacy against the key pathogens of ABSSSI and CABP, including isolates resistant to standards of care. The IV and oral formulations are bioequivalent and neither shown the dose-limiting nausea and vomiting exhibited by other tetracycline derivatives.

 

 

Omadacycline (formerly PTK-0796) In Vitro Spectrum of Activity and Confirmation of Disk Mass Using Fresh Media for MIC Testing

  • Omadacycline has broad spectrum activity with potent activity against the primary pathogens causing acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia.
  • There was no evidence of a resistant subpopulation amongst the highly susceptible species, while some Enterobacteriaceae and P. aeruginosa were not susceptible to OMC.
  • Fresh media is important for broth dilution testing.
  • Zone diameters correlate well with MICs.
  • The 30 mg disk was chosen based on testing 15, 30, and 60 mg disk masses giving the best dynamic range without overly large zones against highly susceptible organisms.

 

 

Quality Control Parameters for Omadacycline Minimum Inhibitory Concentration (MIC) Susceptibility Tests.

Omadacycline is the first aminomethylcycline to enter clinical development. OMC is being developed globally as an intravenous and oral, once daily monotherapy therapy for ABSSSI and CABP. OMC was designed to overcome tetracycline resistance mechanisms and has been shown to have potent in vitro activity and in vivo efficacy against the key pathogens of ABSSSI and CABP, including isolates resistant to standards of care. The IV and oral formulations are bioequivalent and neither shown the dose-limiting nausea and vomiting exhibited by other tetracycline derivatives.

 

 

In Vitro Activity of Omadacycline Against Legionella pneumophila.

Based on the in vitro results of this study, omadacycline exhibits potent extracellular activity against L. pneumophila and warrants further study as a potential antimicrobial agent for the treatment of pneumonia caused by L. pneumophila.

  • Omadacycline and doxycycline MICs were 5-7-dilution higher in BYE broth with iron, compared to broth without the iron supplement, indicating that the MIC’s of omadacycline may be artificially elevated in vitro due to media effects.
  • Against Legionella pneumophila all serogroups (n=100), the MICs for omadacycline ranged from =0.08 – 1 mg/L, and were either comparable or up to 2 dilutions lower than the most commonly used drugs for the treatment of Legionellosis, such as azithromycin and erythromycin.
  • Moxifloxacin and levofloxacin are the most active compounds tested followed by telithromycin, omadacycline, azithromycin, erythromycin and doxycycline against L. pneumophila all serogroup, .
  • Against L. pneumophila serogroup 1 which is the most resistant Legionella serogroup to erythromycin and the most usual Legionella serogroup isolated from respiratory tract infections, omadacycline (MIC90=0.25 mg/L) is more active than doxycycline (MIC90=1 mg/L), erythromycin (MIC90=1 mg/L) and azithromycin (MIC90=0.5 mg/L), .
  • L. pneumophila serogroup 2, 3, 4, 5 and 6 (n=10) were less susceptible to omadacycline with a MIC90 of 1 mg/L.
  • Against Legionella pneumophila serogroup 2 to 6, moxifloxacin and levofloxacin still the most active compounds tested followed by telithromycin, azithromycin, erythromycin, omadacycline and doxycycline.
  • Activity of omadacycline has not changed between the 1995-2005 isolates and the 2006-2014 isolates

2013

In Vitro Activity of Omadacycline (OMC) against Biothreat Bacteria

In general, a 4 µg/mL in vitro MIC value supports the progression of an antibiotic into further (in vivo) studies, because this value is reasonably achievable in serum, without regard for tissue accumulation or individual drug performance.

Based on the results of our in vitro testing, OMC should be further tested in vivo against B. anthracis, F. tularensis, Y. pestis, and B. mallei. OMC had MIC values ≤ 4 µg/mL against 100% of the 120 different isolates of these 4 biothreat pathogens.

As a novel aminomethylcycline compound that has been engineered to defeat existing resistance mechanisms of efflux and ribosomal protection, OMC might offer the only viable treatment alternative where current therapies are not indicated due to host drug reactions or resistance. OMC showed broad spectrum in vitro activity against USAMRIID’s collection of biothreat bacteria isolates. OMC efficacy is currently being evaluated in murine infection models for these bacterial agents.

2012

Pharmacokinetics of Omadacycline (PTK0796) in Subjects with Hepatic Impairment

  • Overall, omadacycline exposures were similar in subjects with hepatic impairment, regardless of severity, compared with healthy subjects following IV or oral administration.
  • The pooled analysis of dose normalized omadacycline AUC or Cmax across all study groups showed no clear relationship between exposure to omadacycline and Child-Turcotte-Pugh score.
  • Single doses of omadacycline administered orally and intravenously were safe and well tolerated in the subjects studied.
  • The data from this study suggest no dose adjustment for omadacycline in subjects with hepatic impairment is warranted.

 

Pharmacokinetics of [14C]-labeled Omadacycline (PTK 0796) in Healthy Male Subjects

Background: Omadacycline (OMC), formerly PTK 0796, is a novel aminomethylcyline that has activity against gram positive, gram negative, anaerobic, and atypical organisms. Potential indications include intravenous and oral therapy of CABP and ABSSSI. This study assessed the absorption, distribution, metabolism and excretion, and identification of metabolites, from a single oral dose of [14C]OMC in humans.

Methods: Six healthy male subjects were administered a single oral dose of 300mg [14C]OMC (mean radioactivity 36.6 µCi) under fasting conditions, and observed for 7 days post-dose during which plasma samples, and excreta samples of urine and feces, were collected. Parent plasma OMC concentrations were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. Excretion and mass balance of radioactivity were determined with liquid scintillation; metabolites were characterized by HPLC with radioactivity detection and metabolite identification performed by LC-MS/MS. Safety assessments included hematology, blood chemistry and urinalysis, vital signs, and adverse events.

Results: The maximum OMC plasma concentration was reached between 1 and 4 h; the mean half-life was 17.6 h, the mean apparent clearance was 32.8 L/h and the apparent volume of distribution was 827.8 L. Recovery of the radioactive dose was complete after 7 days (mean 95.5%) and no metabolites were detected. The C-4 epimer of OMC, a spontaneous conversion product present in the oral dose, was observed in all biofluids. The main route of OMC elimination was via the fecal route; feces accounted for 81.1±2.34% of the radioactivity, while 14.4±2.33% of the radioactivity was recovered in urine. Based on prior estimates of 30% oral bioavailability these data suggest that >40% of the absorbed dosed is eliminated in the urine. In plasma, OMC and its C-4 epimer accounted for 100% of the radioactivity exposure. Radiolabeled OMC was safe and well-tolerated.

Conclusion: Oral OMC is excreted in the feces (81.1%) and urine (14.4%) as unchanged drug and as C4-epimer, and does not undergo metabolism in humans.

  • The mass balance achieved in this study on average was 95.5% of the administered OMC radioactivity in the excreta (urine plus feces) of all subjects after 7 days.
  • No metabolites were detected. Several impurities and degradation products were characterized in both the dosing solution and biological samples (plasma, urine and feces).
  • In urine, the % mean total radioactivity administered was 14.4±2.33 with 100% being OMC and its C-4 epimer. This represents 43.2 mg or approximately 40% of the absorbed dose.
  • In feces, the % mean total radioactivity was 81.1±2.34 with 100% being OMC and its C-4 epimer.
  • OMC in plasma reached Cmax between 1 and 4 h. The mean half-life was 17.6 h, the mean apparent clearance was 32.8 L/h and the apparent volume of distribution was 827.8 L.
  • Overall oral administration of OMC 300 mg was safe with acceptable tolerability.

Safety and efficacy of PTK 0796 (Omadacycline) as treatment of complicated skin and soft tissue infection (cSSTI)

Background: Having completed phase 1 and 2 clinical programs, PTK 0796, an aminomethylcycline, broad-spectrum antibacterial agent active against all the leading causes of cSSTI including methicillin-resistant Staphylococcus aureus (MRSA), has begun assessment in phase 3 trials.

Methods: A randomized (1:1), controlled, evaluator-blind, stratified by infection type, trial comparing PTK 0796 (100mg iv; 300mg po QD) to linezoid (LZD; 600mg iv/po BID) was designed to establish non-inferiority between treatment arms regarding efficacy based on clinical assessment immediately after (EOT), and 10-17 days after (TOC) completing therapy in the intent-to-treat (ITT) and clinically evaluable (CE) populations. Subjects were given iv therapy initially with an option to transition to oral formulations of either PTK 0796 or LZD. Moxifloxacin (400 mg QD) was added to LZD treatment if infection due to Gram-negative bacteria was suspected.

Results: The trial was administratively stopped to address alignment with a new FDA guidance on ABSSSI, after 143 of the planned 790 subjects were enrolled. Subjects enrolled at 6 sites with 140 and 127 qualifying for the ITT and CE populations, respectively. A total of 44 (65%) PTK 0796 and 48 (67%) LZD subjects had cellulitis and 14 (21%) PTK 0796 subjects and 14 (19%) LZD subjects (19%) had wound infections. The mean and median duration of therapy were 10.1 and 10.0 days for PTK 0796 and 9.9 and 9.5 days for LZD subjects. MRSA was the most frequently isolated pathogen and success in the CE population occurred in 96.2% (25/26) with PTK 0796 and 93.5% (29/31) with LZD treatment. There were comparable numbers of treatment emergent adverse events (56;82.4% in PTK 0796 and 58;80.6% in LZD) and study-drug related adverse events (41;60.3% in PTK 0796 and 41;56.9% in LZD) across treatment arms. The most common adverse events reported involved the gastrointestinal system and the most common of these was nausea, reported by 18 PTK 0796 and 19 LZD treated subjects.

Conclusions: Results of this phase 3 trial experience are consistent with those of the phase 2 clinical program that also involved patients with cSSTI and showed comparable efficacy and overall safety/tolerability between PTK 0796 and LZD. Although stopped before meeting planned enrolment goals, results in the CE population met the protocol-defined criteria of a 10% margin to conclude non-inferiority between treatments.

  • Although stopped well short of the planned enrollment, the results in this phase 3 trial are consistent with those reported in the phase 2 cSSSI trial and support the conclusion that PTK 0796 (omadacycline) is not inferior to linezolid as a treatment of patients with serious infections involving the skin and adjacent structures.
  • Intravenous and oral formulations of PTK 0796 were well tolerated
  • This experience supports the continued development of PTK 0796 for the treatment of patients with serious infectious diseases.

 

Metabolic Stability of PTK 0796 (Omadacycline)

PTK 0796 (PTK, omadacycline) is a novel aminomethylcycline now in Phase 3 clinical development. An in vitro assessment of the potential for metabolism and/or drug-drug interactions was undertaken.

Objectives. The in vitro stability and interaction of PTK with human cytochrome P450 isozymes was determined to assess the potential for in vivo modification or whether there was a significant potential for drug-drug interactions.

Methods. Metabolism assays were conducted using either pooled human liver microsome preparations, S9, liver cytosol, or recombinant flavin monooxygenases (FMO1, FMO3, FMO5) (BD Bioscience, Woburn, MA). Metabolism of 14C-PTK (5-50 µM) was determined with either NADPH or UDPGA or a combination of both co-factors. Binding of 14C-PTK to liver microsomes was determined by ultracentrifugation. The metabolism of 14C-PTK by human hepatocytes (Celsis, Baltimore, MD) was tested at 2.5 µM and 12.5 µM with 2 x 106 cells/ml at 37°C for 2-24hrs. PTK and metabolites were detected by HPLC with radio-detection. CYP450 induction was determined in primary human hepatocytes (1 x 10^5 cells) incubated with 1-100 µM PTK and substrate probe for 24 and 48hrs. Inhibition of CYP450 isozymes was determined using pooled human microsomes (BD Biosciences, Bedford, MA) with PTK (1-50 µM) and probe concentrations approximating the Km of each probe. Time-dependent inhibition was determined by preincubating microsomes with 1-50 µM . Probe metabolism was determined by LC-MS.

Results. There was no detectable metabolism of omadacycline by human microsomes, hepatocytes, S9 or cytosol, FMO1, FMO3, or FMO5. PTK did not induce activities of CYP 1A2, 2B6, 2C8, 2C9, 2C19, or 3A. There was no or minimal (less than 40% of maximal positive control response) induction of mRNA for CYP 1A1, 1A2, 1B1, 2B6, 2C8, 2C9, 2C19, 2J2, 3A4, or 3A5. There was no significant inhibition of CYP 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, or 3A4/5 activity by PTK without pre-incubation nor time-dependent inhibition of CYP 1A2, 2C9, 2D6, or 3A4/5. There was no significant binding to human microsomes.

Conclusions. In vitro studies indicate that PTK 0796 (omadacycline) is unlikely to undergo significant metabolism in humans. Further, there was no induction or inhibition of CYP enzymes indicating little potential for drug-drug interactions based on these mechanisms.

Key words. PTK 0796, omadacycline, metabolism

  • There was no significant in vitro metabolism, inhibition, or induction of CYP450 isozymes by PTK 0796.
  • Low level induction of mRNA over 48 hours in human hepatocytes was observed but generally to a much lower degree than observed with known inducers.
  • There was no nonspecific binding of PTK 0796 to liver microsomes.
  • The results suggest that PTK 0796 has low potential for clinically significant drug-drug interactions based on interactions with CYP450 enzymes and that PTK 0796 metabolism is unlikely to be a major contributor to systemic clearance.

 

A single-dose study to evaluate the pharmacokinetics, safety, and tolerability of multiple formulations of PTK 0796 in healthy subjects

Objectives: PTK 0796 (omadacycline) is a first in class aminomethylcycline antibiotic with activity against Grampositive, Gram-negative, aerobes and anaerobes, and atypical bacteria. PTK 0796 is being developed for the treatment of Acute Bacterial Skin and Skin Structure Infections (ABSSSI) and Community Acquired Bacterial Pneumonia (CABP) with once daily IV followed by oral dose administration. The bioavailability of two oral formulations (tablets) relative to the IV was investigated to select an optimal oral formulation for Phase 3 Studies. An oral solution was also included as an exploratory investigation.

Methods: This was an open-label, randomized, four period, complete cross-over study in healthy subjects with four treatment conditions (PTK0796 100 mg IV infusion, two 300 mg tablet formulations with different dissolution profiles, and a 300 mg oral solution for comparison to the tablets). A total of 24 subjects between the ages of 18-50 were randomized to the treatment groups. Routine safety and tolerability assessments were performed. Analysis of plasma PTK 0796 concentration was performed using a validated LC/MS/MS method. Results: Twenty subjects completed all periods of the study. No SAEs were reported and only three AEs of mild intensity (dizziness, nausea, vomiting) were experienced by three subjects during the study. There were no clinically relevant changes in laboratory tests following dose administration. Among the oral formulations studied, the oral solution had the fastest rate of absorption as evident by the earlier Tmax. Both 300 mg tablet formulations produced equivalent total exposure relative to the 100 mg IVdose (9960 h*ng/mL) with geometric mean ratios of AUCinf (90% CI) of 1.00 (0.93,1.07) and 0.96 (0.90,1.03), respectively. The absolute bioavailability of the tablets was approximately 34%. Compared to the tablets, the oral solution yielded 19% higher total systemic exposure. The inter-subject variabilities were consistent among the oral formulation groups (~20-25%).

Conclusions: The two 300 mg tablet formulations of PTK 0796 produced equivalent total exposure as measured by AUC relative to the 100 mg IV dose. Single doses of PTK0796 administered orally (as different formulations) and intravenously were safe and well tolerated in the subjects studied.

  • The two 300 mg tablet formulations of PTK 0796 produced equivalent total exposure as measured by AUC relative to the 100 mg IV dose.
  • Single doses of PTK0796 administered orally (as different formulations) and intravenously were safe and well tolerated in the subjects studied.
  • Among the oral formulations studied, the oral solution had the fastest rate of absorption (as evident by the earlier Tmax) and yielded the higher exposure (19% higher AUCinf compared to 100mg IV infusion).

 

Lack of Interaction of PTK 0796 (Omadacycline) with Human Transporter

PTK 0796 (PTK) is a novel aminomethylcycline in Phase 3 development as an IV and oral therapy for bacterial skin infections and community-acquired pneumonia.

Objective: The in vitro interaction of PTK with human drug transporter proteins was determined to establish the potential for drugdrug interactions based on this mechanism of drug uptake and efflux.

Methods: Transport of 14C-PTK by human organic ion transporters was determined in HEK293 cells stably expressing hOAT1, hOAT3, or hOCT2 compared to the parental host cell line HEK-Flp-In. Transport of PTK by organic anion transport polypeptide transporters OATP1B1 and OATP1B3 was assessed similarly in HEK cells stably expressing these transporters. Transport of 14CPTK by P-glycoprotein (P-gp) was determined in Caco-2 cells. Induction of P-gp and multidrug resistance-associated protein-2 (MRP2) was determined in human hepatocytes by mRNA levels. Inhibition of human Breast Cancer Resistance Protein (BRCP), Pgp, and MRP2 was determined in cell lines T8, T0.3, and MDCKII cell lines.

Results: At 25µM14C-PTK, there was no difference in intracellular concentrations with or without hOAT1 or hOAT3. Probenecid did not reduce the accumulation of PTK (8µM) whereas there was a significant effect on the probe substrate. Uptake of PTK into cells was rapid, reaching more than 100 pmol/mg protein within 5min independent of transporters. PTK appears to be a substrate for P-gp, with a Km for efflux of approximately 81.5µM and a Jmax of 1140 pmole·hr-1·cm-1. PTK did not inhibit the function of hOAT3 and at 25µM inhibited hOAT1 by only 30%. Intracellular accumulation of PTK was not affected by hOATP. PTK (100µM) reduced transport of probes for hOATP1B1 and hOATP1B3 by ±10.1%.PTK did not induce P-gp or MRP-2 mRNA. PTK did not inhibit the activity of BRCP, P-gp or MRP-2 up to 50µM.

Conclusion: The potential for drug-drug interactions based on PTK interactions with drug transporters appears to be minimal. PTK does not interact with the transporters tested except P-gp. It is a substrate for P-gp (Km=81.5µM) but is unlikely to act as an inhibitor (no inhibition up to 50µM) nor an inducer of P-gp.

Key words: PTK 0796, omadacycline, metabolism

  • PTK 0796 (omadacycline) rapidly accumulates within mammalian cells, consistent with its large volume of distribution and rapid distribution from plasma.
  • PTK 0796 is not a substrate for any of the tested transporters tested except P-glycoprotein. The Km value for the association of PTK796 with P-gp transporter was 81.5 µM indicating a rather weak affinity interaction.
  • PTK 0796 is a relatively weak inhibitor of only 400 500 600 796 ry Flux, 2*h)-1 900 1200 1500 1800 C]VAL489 accumulation pmol/µg protein *Uptake experiments conducted over 120 minutes at 37 ⁰C. www.postersession.com PTK 0796 is a relatively weak inhibitor of only hOAT1 (30% at 25µM), with no evidence of significant inhibition of any other transporter tested.
  • PTK 0796 does not induce increased transcription of either P-gp or MRP2 genes. Further, there appears to be no increase in activity of transporters in the presence of PTK 0976.
  • There appears to be no significant interaction of PTK 0796 with the human drug transporters tested suggesting that drug-drug interactions based on transporter activity is unlikely

Antimicrobial Activity of PTK 0796 (Omadacycline) and Comparator Agents Against Contemporary Pathogens Commonly Associated with Community-Acquired Respiratory Tract Infections Collected During 2011 from the European Union

Objectives: To determine the activity of PTK 0796 (omadacycline) and comparator agents against recent (2011) Streptococcus pneumoniae (SPN), Haemophilus influenzae (HI), and Moraxella catarrhalis (MCAT) isolated in the European Union (EU). PTK 0796 is a novel aminomethylcycline which is currently under clinical development for both intravenous and oral formulations. It has excellent activity against pathogens from the respiratory tract and overcomes tetracycline resistance.

Methods: Susceptibility (S) testing for omadacycline and commonly used antimicrobials was performed by Clinical and Laboratory Standards Institute (CLSI) broth microdilution methodology on a total of 1,024 isolates in 2011 from medical centers in the SENTRY Antimicrobial Surveillance Program platform in the EU. S interpretations were performed using CLSI and EUCAST guidelines.

Results: PTK 0796 was very active against SPN independent of S to penicillin (PEN; MIC50/90, 0.06/0.06 mg/L for PEN-S and -resistant [R] strains). PTK 0796 was 16-fold more active than levofloxacin (MIC50/90, 1/1 mg/L) and ceftriaxone (MIC90, 1 mg/L) against SPN. SPN showed high R rates to erythromycin (S, 60.8%) and tetracycline (S, 69.3% CLSI/68.8% EUCAST) even though all isolates had PTK 0796 MIC values ≤0.25 mg/L. PTK 0796 against HI (13.9% beta-lactamase positive) and MCAT (98.5% betalactamase positive) exhibited low MIC values (Table) independent of beta-lactamase production.

  • PTK 0796 (omadacycline) demonstrated potent activity against the key bacterial respiratory pathogens (S. pneumoniae, H. influenzae, and M. catarrhalis).
  • PTK 0796 activity was unaffected by penicillin or tetracycline susceptibility patterns.
  • PTK 0796, which is currently undergoing clinical development for acute bacterial skin and skin structure infections, exhibited activity against key bacterial respiratory pathogens and merits further studies in this clinical indication.

Antimicrobial Activity of PTK 0796 (Omadacycline) Tested against Gram-positive Organisms Isolated from European Hospitals in 2011

Objective: To evaluate the activity of PTK 0796 (PTK) against Gram-positive (GP) cocci causing infections in European (EU) hospitals. PTK (7-dimethylamino, 9-[2,2- dimethyl-propyl]-aminomethylcycline) is a novel antibacterial agent of the tetracycline family, which is under clinical development (IV and oral formulations).

Methods: 2719 strains from 25 medical centers in 10 EU countries, Turkey and Israel were collected in 2011 and tested for susceptibility (S) against PTK, tigecycline (TIG) and many other comparators by CLSI broth microdilution methods. MIC results were interpreted according to EUCAST and CLSI breakpoint criteria. The isolates were collected mainly from skin/skin structure infections, bacteremia and pneumonia, and include S. aureus (1,572; 27.4% oxacillin-resistant [MRSA]), coagulase-negative staphylococci (CoNS; 344, 71.5% oxacillin-resistant [R]), E. faecalis (EF; 270; 0.7% vancomycin [VAN]-R [MIC, ≥8 mg/L]), E. faecium (EFM; 156; 23.7% VAN-R), β-haemolytic streptococci (βHS; 245) and viridans group streptococci (VGS; 132).

Results: PTK was very active against oxacillin-S S. aureus (MSSA) and MRSA with a MIC90 of 0.12 and 0.25 mg/L respectively (see Table 2). PTK activity against S. aureus was eight-fold greater than linezolid and VAN, two-fold greater than daptomycin and similar to TIG. MRSA rates varied from 1.0% in Sweden to 61.5% in Portugal (27.4% overall). The highest PTK MIC value among S. aureus was only 2 mg/L and >99% of strains were inhibited at PTK MIC of ≤0.25 mg/L. CoNS exhibited slightly higher PTK MICs (MIC50/90, 0.12/1 mg/L) compared to S. aureus, with a bimodal distribution. EF (MIC50/90, 0.12/0.25 mg/L) and EFM (MIC50/90, 0.06/0.12 mg/L) were very S to PTK and VAN R did not adversely affect PTK activity against enterococci. VAN-R EFM was detected in 10 of 12 countries, while VAN-R EF was observed only in Germany and Italy (one strain each). βHS and VGS exhibited very low PTK MIC values (MIC50/90, 0.06/0.12 mg/L for all groups).

Conclusions: PTK demonstrated potent activity against a large collection of contemporary (2011) GP clinical isolates. Its activity was similar to that of TIG and was not affected by R to other antimicrobial classes.

  • PTK 0796 (omadacycline) demonstrated very potent activity when tested against a large collection of contemporary (2011) Gram-positive clinical isolates.
  • PTK 0796 activity was similar to that of tigecycline and was not affected by resistance to other antimicrobial classes including tetracyclines.

2011

Omadacycline (PTK796) Mechanism of Action Studies by Using In Vitro Protein Synthesis Inhibition Assay and Molecular Modeling

Background: Omadacylcine (OMC) is a novel aminomethylcycline antibacterial compound. The structural similarity between OMC and tetracyclines (known inhibitors of bacterial protein synthesis) such as tigecycline (TGC), minocycline (MINO) and tetracycline (TET) as well as previous studies suggested that OMC targets bacterial protein synthesis. This study assessed the potency of OMC as compared to TGC, MINO and TET by using an in vitro transcription/translation (IVT) inhibition assay. Computational chemistry studies by structure based design and molecular modeling using alignment and docking techniques provided insight into ligand binding.

Methods: IVT reactions were conducted by using an E. coli S30 extract system and pBESTluc plasmid DNA as a template. Luciferase activity was assayed on LmaxII luminometer. Data analysis was performed using Microsoft Office Excel 2007 and Grafit 5 (v5.0.4). GLIDE docking and Cresset alignment molecular modeling technologies were used to predict binding poses using a Thermus thermophilus X-ray solution, pdb code 1HNW.

Results: IC50 values for TGC, OMC, MINO and TET in the IVT assay were 0.9, 2.8, 3.5 and 13.8 µM, respectively. Percent inhibition values at 10 µM of TGC, OMC, MINO and TET were 99.4, 78.7, 77.6 and 49.9%, respectively. Modeling suggested that secondary amine group of OMC may form a salt bridge with the phosphate on guanine 1053 and a weak hydrophobic interaction with cytosine 1054. In comparison, TGC may form a salt bridge with the phosphate on G1053, a coulombic interaction with the phosphate on U531 and an amide moiety π-stacking with C1054. An alternate pose was also found for both TGC and OMC binding within a cleft coordinating two Mg++ ions in the groove formed by G963, A964, U1052, G1053, G1197, G1198 and U1199.

Conclusions: The results of this sudy confirmed that the mechansim of action of OMC is the inhibition of protein synthesis. The data suggested that OMC was a more efficient inhibitor than MINO and TET although it is a less efficient inhibitor than TGC. Molecular modeling data are consistent with the results of IVT assay.

  • The results of this study confirmed that the mechansim of action of omadacycline is the inhibition of protein synthesis.
  • From comparison of IC50 and % percent inhibition values, the results of this study suggest that omadacycline is a more potent in vitro protein synthesis inhibitor than minocycline and tetracycline while less efficient inhibitor than tigecycline.
  • Based on the molecular modeling, several factors may be at play for tigecycline as compared to omadacycline:
    • the larger surface area of a π interaction between the amide moiety of tigecycline with the pyrimidine of C1054 – the amine salt bridge to guanine phosphate groups is shared by both molecules and is likely equivalent in strength
    • closer inter-atomic proximity of the salt bridge to U531 for the amine in tigecycline
    • one fewer rotatable bond in the side-chain results in lower rotational entropy compared to omadacycline that has four rotatable bonds
    • tigecycline’s amide N-H potentially being locked in an intramolecular hydrogen bond with the phenolic hydroxyl.

In a Phase 2 Complicated Skin and Soft Tissue Infections Trial, Outcomes Assessed Early in the Course of Therapy were Consistent with Outcomes 10-17 Days After Completing Therapy with Either Omadacycline (OMC; PTK796) or Linezolid

Background: A successful phase 2 program studying OMC has been completed that suggested efficacy comparable to linezolid, thus supporting progression to a phase 3 program in patients with serious skin infections. Because of an evolving concern that assessing outcome 10-17 days after completing therapy for cSSTI may poorly correlate with historical trial data used to establish treatment effect of antibacterials in this disease, the early responses in patients with cSSTI randomized to either OMC or linezolid were further assessed.

Methods: A post-hoc analysis was conducted that was aimed at defining: 1) incidence of cessation of spread of infection (no increase in either maximum length or width of infection site inflammation) and absence of fever (core body temp <38.2 C) 1-3 days (24-72 hours) after therapy and 2) reduction of lesion size during the treatment course.

Results: In OMC and linezolid-treated patients respectively, the clinical response rates 10- 17 days after completing therapy were 88.3% (98/111) and 75.9% (82/108) [95% CI for the difference: 1.9, 22.9] in the ITT (intent-to-treat) population, 98.0% (98/100) and 93.2% (82/88) [95% CI for the difference: -1.7, 11.3] in the CE (clinically evaluable) population. The incidence of cessation of lesion size increase and absence of fever at day 1-3 in OMC and linezolid-treated patients, respectively, was 96.8% and 94.4% in the ITT and 96.4% and 93.8% in the CE population. In ITT patients for whom complete data on lesion size were available, mean reduction of maximal lesion dimension was greater for patients treated with OMC than those treated with linezolid evaluated following 24-72 hrs of therapy (31.8%; SE 4.6% for OMC and 6.7%; SE 15.1% for linezolid) and upon completion of therapy (81.1%; SE 3.4% and 63.2%; SE 5.8%). Among ITT subjects who received no systemic antibiotics prior to enrollment, mean reductions were 28.3% (SE 5.1%) for OMC-treated and -6.9% (SE 25.4%) for linezolid-treated patients after 24-72 hrs of therapy. At the end of treatment, mean reduction of lesion size in these patients was 82.7% (SE 4.3%) for OMC-treated and 63.0% (SE 8.0%) for linezolid-treated patients.

Conclusions: Consistent with outcomes assessed 10-17 days after completing therapy, outcome assessed early in the course of therapy with OMC compared favorably to that of linezolid. This phase 2 experience strongly supports continued development of OMC as a treatment of patients with serious skin infections.

Treatment outcomes of cSSTI patients randomized to OMC compared favorably to those measured in linezolid-treated patients. In post-hoc analyses conducted to address recently raised issues about measurement of lesion size and resolution of fever during antibiotic therapy, similar favorable outcomes were evident in OMC-treated subjects.

Results of this phase 2 trial comparing OMC to linezolid support the continued development of omadacycline as a treatment for patients with serious infections involving the skin and adjacent structures.

 

Comparative Efficacy of Omadacycline (PTK796) in Lethal Streptococcus pneumoniae and Staphylococcus aureus Pneumonia Models

Objective: Omadacycline is a novel aminomethylcycline with excellent activity against pulmonary pathogens and overcomes tetracycline resistance. The objective of these studies was to evaluate omadacycline as a clinical candidate to treat Grampositive pneumonias.

Methods: Neutropenic (cyclophosphamide treated) male CD-1 mice were infected intranasally with 50µl containing approximately 7.9 x 107 CFU of Staphylococcus aureus USA300 (SA) diluted in sterile PBS. Neutropenic or immunocompetent male CD-1 mice were also infected intranasally with 50µl containing approximately 6.4 x 106 of Streptococcus pneumoniae PBS1339 (SP) diluted in sterile PBS. Animals were treated with omadacycline, comparator, or saline at 2 hours postinfection (pi) with a single intravenous (IV) dose and survival determined out to 7 days pi.

Results: Omadacycline was more effective than tigecycline and vancomycin in preventing death in both the SA and SP neutropenic pneumonia models at all time points tested (Table 1). Omadacycline was over 3 fold more effective than tigecycline at the early end points tested for both SA and SP, and 1.5-2 fold more effective by 7 days pi. Vancomycin was ineffective at any of the doses tested and at either of the time points for both SA and SP infections. In addition, doxycycline was tested against SA and daptomycin, linezolid, ceftriaxone, and levofloxacin were tested against SP. All these comparators failed by 7 days pi even at the highest doses tested (>18 mg/kg or higher). Omadacycline was more effective than linezolid or levofloxacin and as effective as tigecycline and vancomycin in preventing death in a SP non-neutropenic pneumonia model at 96 hours pi. Omadacycline was over 2 fold more effective in preventing death than vancomycin at day 7 pi.

Conclusion: Omadacycline was successful in protecting neutropenic or non-neutropenic (SP only) mice against a lethal SA or SP pneumonia and was equal or more effective than tigecycline or vancomycin. This data suggests that omadacycline may be considered as a potential candidate for the treatment of Gram-positive pneumonias, particularly in patients with normal immune function.

 

  • In the neutropenic S. pneumoniae pulmonary infection model, omadacycline, tigecycline and ceftriaxone performed well although the long-term efficacy for all drugs was reduced.
  • Omadacycline and the comparator agents all benefited substantially from the presence of an intact immune system. All exhibited substantially reduced dose requirements for efficacy and benefit was observed for long-term survival.
  • Linezolid and levofloxacin were much less effective vs. S. pneumoniae than omadacycline, tigecycline, ceftriaxone, and vancomycin indicating that the pharmacodynamic requirements for efficacy were not achieved by a single intravenous dose in either neutropenic or normal mice. Vancomycin was ineffective in the neutropenic pneumonia model but benefited substantially from an intact immune system.
  • Omadacycline and tigecycline were superior to doxycycline and vancomycin in the S. aureus pulmonary model in neutropenic mice. The inability of the S. aureus isolate to cause a lethal pulmonary infection in non-neutropenic animals, prevented the evaluation of the contribution of the immune system in the treatment of this infection.
  • These results support the development of omadacycline in bacterial pneumonia caused by S. pneumoniae and S. aureus, particularly in patients with normal immune function. The role of the immune system on the response to therapy should be carefully considered in the determination of the pharmacodynamic relationship of drug, pathogen, and host.

In vitro Activity of Omadacycline (PTK796) in Broth Plus Lung Surfactant or Human Serum

Background: Determine the effects of lung surfactant and human serum on the in vitro activity of omadacycline (OMC).

Methods: MICs were performed in three systems. Cation-adjusted Mueller Hinton broth was used according to standard CLSI microdilution procedures, in addition to broth enriched with 1% bovine surfactant, and 25%-50% human serum. The strains included were clinical Gram-positive, (S. aureus, S. pneumoniae), also Gramnegative, (E. coli and H. influenzae), selected to include a range of susceptibilities, and appropriate ATCC controls. Doxycycline (DOXY) and daptomycin (DAPTO) were tested as comparators.

Results: MIC ranges in all three systems are shown below (Table 1).

Conclusions: MICs of omadacycline did not increase with the addition of surfactant or serum for either Gram-positive or Gram-negative organisms. The in vitro activity of DAPTO was markedly affected by surfactant, as well as serum reflecting its high protein binding character. DOXY activity was not affected by surfactant, but exhibited some decreases in activity in the presence of serum. The inhibition of activity of DAPTO by lung surfactant has been suggested as the explanation for its lack of efficacy in pneumonia. (Silverman, JA et al, JID 191:2149-2152. 2005). In contrast, OMC was not affected by surfactant. This finding supports the potential use of OMC in treating pneumonia caused by susceptible bacteria.

  • Omadacycline (PTK796) in vitro activity was not affected by the addition of lung surfactant or serum
  • These results support the potential use of omadacycline in treating pneumonia caused by susceptible bacteria

2010

Efficacy of PTK796 in a Rat MRSA Infected Endocarditis (IE) Model

Background: PTK796 is the first semi-synthetic aminomethylcycline in clinical development. It is active in vitro and in vivo against resistant pathogens, particularly MRSA and VRE. The efficacy of PTK796, tigecycline (TGC) and daptomycin (DAP) were tested using a rat infective endocarditis (IE) model with a MRSA 32 strain.

Methods: IE was induced following transcarotid-transaortic valve indwelling catheterization after i.v. infection with 5 x 105 CFU/rat MRSA 32 strain. At 6 hours and the next 4 days post-infection, animals were randomized to receive: i) saline s.c. qd; ii) PTK796 s.c. bid; iii) TGC s.c. bid; or i.v.) DAP s.c. qd. At 18 h after the last treatment, hearts and spleens were removed and quantitatively cultured. The ends of catheters from the left ventricle were qualitatively cultured.

Results: All dosing regimens significantly decreased bacterial counts in all target tissues (P <0.05). ED50 (the dose at which 50% of the animals showed a 3-log reduction in bacterial load relative to the colony counts in salinetreated controls) of PTK796 (bid), TGC (bid), and DAP (qd) were 2.89, 0.97, and below 2.5 mg/kg, respectively.

Conclusions: PTK796 showed efficacy against MRSA 32 strain-induced IE in rats.

  • The rat infective endocarditis (IE) model provides a good system for evaluating antibiotics used for serious infections
  • PTK796 showed good efficacy against a strain of MRSA (susceptible to all the antibiotics tested) in the IE model, reducing bacterial counts in the heart by over 5 log10 CFU/g at a dose of 5 mg/kg
  • PTK796 was less efficacious than tigecycline in the model, especially in the ratio of total heart sterilization (2/6 for PTK796 at 5 mg/kg vs. 5/6 for the same dose of tigecycline)
  • The efficacy of daptomycin in the model was less than the lowest dose tested; therefore a direct comparison with PTK796 cannot be made
  • The efficacy of PTK796 in this MRSA-induced rat IE model indicates the potential utility of PTK796 in Gram-positive infections

 

 

Studies on the Mechanism of Resistance to PTK796 in Pseudomonas aeruginosa and Klebsiella pneumonia

Background: PTK796 is a novel aminomethylcycline compound that is active against Gram-positive and Gram-negative bacteria. Certain Gram-negatives (e.g., P. aeruginosa) are intrinsically less susceptible to PTK796, whereas in others (e.g., K. pneumoniae), reduced susceptiblity can be mutationally acquired. This study was conducted to provide initial insight into the mechanisms of resistance to PTK796 in P. aeruginosa and K. pneumoniae.

Methods: MICs were determined by broth microdilution using fresh media. Mutants were selected and spontaneous mutation frequency was measured on PTK796-containing plates. Gene expression was analyzed by Taqman RT-PCR.

Results: The MIC profile of P. aeruginosa efflux defective mutants revealed that deletion of the RND-type efflux pump mexXY reduced the MICs of PTK796 from 64 to 4 mg/mL. Inactivation of mxB had no effect; however, inactivation of mexB in the mexXY background caused an additional 4-fold increase in susceptibility. Less susceptible mutants (MIC 64-128 mg/mL) emerged at a frequency of 2.7x10^-8 when the mexXY-deletion mutant was plated on 32 mg/mL of PTK796. The MICs of chloramphenicol and ciprofloxacin were elevated and squence alterations were detected in nfxB gene (MexCD-OprJ repressor) in these mutants. In a less-susceptible strain of K. pneumoniae (MIC 16 mg/mL), the transcriptional activator ramA and the RND-type efflux pump acrAB were constitutively overexpressed as compared with a susceptible strain (MIC 1 mg/mL, typical for K. pneumoniae).

Conclusions: The results of this study suggested that: 1) similar to tigecycline, the inducible MexXY efflux pump is the major pump contributing to intrinsic decreased susceptibility in P. aeruginosa. with a smaller potential contribution from MexAB-OprM. In the absence of MexXY, MexCD-OprJ expressors emerge, indicating PTK796 is a substrate for this pump; 2) efflux is likely to be a primary determinant of acquired reduced susceptibility in K. pneumoniae, as indicated by overexpression of known tigecycline resistance determinants such as ramA and acrAB.

  • Similar to tigecycline, the inducible MexXY efflux pump appears to be the major pump contributing to intrinsic decreased susceptibility to PTK796 in P. aeruginosa, with a smaller potential contribution from MexAB-OprM
  • In the absence of MexXY, MexCD-OprJ expressors emerge, indicating that PTK796 is a substrate for this pump
  • Efflux is likely to be a primary determinant of acquired reduced susceptibility in K. pneumoniae as indicated by overexpression of known tigecycline resistance determinants such as ramA and acrAB. Gene knockouts are required to confirm the role of RamA and AcrAB in the decreased susceptibility to PTK796 in K. pneumoniae

 

 

In Vitro Evaluation of PTK 0796 Activity Tested against Staphylococcus aureus, Including Hospital- and Community-Associated MRSA Strains from the USA and Europe

Background: PTK796 (PTK) is a novel aminomethylcycline currently under clinical development. PTK activity was evaluated against methicillin-susceptible (MSSA) and -resistant S. aureus (MRSA), including multidrug-resistant strains from documented hospital-acquired (HA) infections and community-associated (CA) infection isolates.

Methods: 325 S. aureus were collected from bloodstream, skin and skin structure, CA and HA pneumonia in USA (35 sites) and European (EU, 31) laboratories. The CLSI broth microdilution method (M07-A8) was utilized (9 comparators) applying fresh Mueller-Hinton media when testing PTK and tigecycline. Cefoxitin disks were used to confirm MRSA. CAMRSA genotypes (USA300 [120] and USA400 [5]) were identified by PFGE and SCCmec typing, and PVL genes.

Results: PTK MIC values for all strains were g/ml. PTK (MIC50/90, 0.25/0.5 g/ml), tigecycline (MIC50/90, 0.12/0.25 g/ml; 100% susceptible) and daptomycin (MIC50/90, 0.25/0.5 g/ml; 100% susceptible) exhibited similar activity against SA, while doxycycline (MIC50/90, 0.12/2 g/ml; 92.6% susceptible) showed elevated MIC values. Overall, the tetracycline derivatives were more active than vancomycin (MIC50/90, 1/1 g/ml; 99.7% susceptible) and linezolid (MIC50/90, 2/2 g/ml; 100% susceptible). PTK inhibited 100.0 and 90.9% of EU and USA HA-MRSA at g/ml, respectively. All EU CA-MRSA were inhibited by PTK of 0.5 g/ml, except for one strain; while USA300/400 MRSA strains were very susceptible to PTK (MIC50/90, 0.12/0.25 g/ml). Conclusions

  • Overall, PTK796 was very active against all S. aureus isolates tested in this investigation (MIC50/90) regardless of isolate origin (geographic or hospital/ community) or resistance phenotype to other antimicrobial agents.
  • Among MRSA isolates combined, strains from Europe had slightly higher PTK796 MIC50/90 values (two-fold) compared to isolates from the USA. These results appear to be associated with the decreased susceptibility to doxycycline documented among MRSA isolates from Europe.
  • The in vitro activity established in this study coupled with pharmacokinetic/pharmacodynamic and target attainment results would suggest that PTK796 is a promising antimicrobial agent for the treatment of serious MDR S. aureus infections.

 

 

Antimicrobial Activity of PTK 0796 Tested against Gram-Positive Organisms Causing Bloodstream Infections in 2009

Background: PTK796 (PTK; 7-dimethylamino, 9-(2,2- dimethyl-propyl)-aminomethylcycline) is a novel antibacterial agent of the tetracycline family, which is under clinical development (IV and oral formulations). We evaluated the activity of PTK against Gram-positive (GP) cocci collected from bloodstream infections (BSI) in hospitals worldwide during 2009.

Methods: 3670 strains from 62 medical centers (USA, Europe and Latin America) were collected and tested for susceptibility (S) against PTK, tigecycline (TIG) and 14 other comparators by CLSI broth microdilution methods. The collection includes S. aureus (SA; 1,697; 37.2% MRSA), coagulase-negative staphylococci (CoNS; 640), E. faecalis (EF; 564; 3.0% vancomycin [VAN] resistance [R]), E. faecium (EFM; 368; 48.4% VAN-R), S. pneumoniae (SPN; 211); β-haemolytic streptococci (βHS; 170), viridans group streptococci (VGS; 9) and others (11).

Results: PTK was very active against oxacillin-S (MSSA) and MRSA with a MIC90 of 0.5 µg/ml for both groups (see Table). PTK activity against SA was eight- and four-fold greater than linezolid and VAN, respectively, and similar to daptomycin and TIG. CoNS exhibited slightly higher PTK MIC values (MIC50/90, 0.25/2 µg/ml) compared to SA, with a bimodal distribution. EF (MIC90, 0.5 µg/ml) and EFM (MIC90, 0.25 µg/ml) were very S to PTK and R to VAN did not adversely affect PTK activity against enterococci. SPN, βHS and VGS exhibited very low PTK MIC values (MIC90, 0.12 µg/ml for all groups)

Conclusions: PTK demonstrated potent activity against a large collection of recent (2009) GP isolates from BSI. Its activity was similar to that of TIG and was not affected by R to other antimicrobial classes

  • PTK796 demonstrated potent activity against a large collection of recent (2009) Gram-positive isolates from bacteremias, including MRSA and VRE.
  • PTK796 activity was similar (within one doubling dilution) to that of tigecycline and was not affected by resistance to other antimicrobial classes.
  • These data suggest a potentially important clinical role for PTK796 in the treatment of BSI caused by Gram-positive organisms, include multidrugresistant strains.

 

 

Pharmacokinetics of Intravenous and Oral PTK796, A New Aminomethylcycline Antibiotic

Background: PTK796 is a novel semi-synthetic compound related to the tetracyclines and specifically derived from minocycline. It has activity against MRSA and pathogens expressing tetracycline resistance. PTK796 is being developed for clinical use with both intravenous (IV) and oral (PO) administration. The current proposed therapeutic dose is 100 mg IV or 300 mg PO administered once daily.

Methods: The pharmacokinetics of PTK796 were evaluated in the following studies:

  • Study 1: Single ascending dose of IV PTK796 in healthy males, 25-600 mg (n=5-6 in each dose group, total n=41)
  • Study 2: Crossover study, single dose of IV (100 mg) and oral (300 mg) PTK796 in 16 healthy males or females
  • Study 3: Single dose of IV PTK796 in 6 healthy males and 6 females, 100 mg. Plasma PTK796 concentrations were quantified by a validated LC-MS/MS method with a lower limit of quantitation of 20.0 ng/mL.

Results: Intravenous administration of PTK796 exhibited threecompartment pharmacokinetics, with a rapid initial distribution phase and a large volume of distribution of 300-430 L. The terminal half life of PTK796 was about 18 h and clearance was 11.4 L/h. PTK796 exhibited dose-proportional increases in AUC over the dose range 25-600 mg following IV administration. After oral administration, PTK796 was rapidly absorbed with a median Tmax of 1.8 h (range 1.0 to 3.0 h). The median AUC0-24h after 300 mg PTK796 PO was 5.66 μg*h/mL compared to 5.71 μg*h/mL after 100 mg IV. Based on the median AUC calculation, the oral bioavailability of PTK796 was 33%. In Study 3, the AUC0-24h in females was 7.18±1.03 μg*h/mL and 5.61±0.19 μg*h/mL in males. PTK796 was well tolerated after single IV or PO doses.

Conclusions: PTK796 has dose-proportional pharmacokinetics after intravenous administration. The 100 mg IV and 300 mg PO doses produce comparable exposures. The long half life supports once-daily dosing.

  • PTK796 showed dose-proportional pharmacokinetics after intravenous administration. The 100 mg IV and 300 mg PO doses produced comparable total exposures.
  • The terminal elimination half life supports once-daily dosing.
  • PTK796 administered intravenously and orally was well tolerated

 

 

Identification and Susceptibility of Pathogens Isolated from Patients with Complicated Skin and Skin Structure Infections (cSSSI): Results of a PTK0796 (PTK) Phase 2 Clinical Trial

Background: Paratek conducted a randomized, investigator-blinded Phase 2 clinical trial in adults with cSSSI comparing PTK (100mg IV/200mg oral, QD) with linezolid (LZD) (600mg IV/600 mg oral, Q12h). LZD was supplemented with aztreonam when gram negative infection was suspected. A total of 234 patients were enrolled.

Methods: Patient enrollment isolates were identified and tested at a central laboratory. MICs were determined by broth microdilution using dried panels. Analysis was based on the Clinically Evaluable (CE) population with a pathogen isolated at enrollment (ME).

Results: The predominant pathogen isolated was S. aureus (SA). 67 patients in the PTK arm were clinical successes with 80 isolates of SA (56.3% MRSA) and 59 isolates from 45 clinical successes (67.8% MRSA) in the LZD arm. MIC90s for MRSA and MSSA from each treatment arm were 0.25 µg/ml (PTK) and 2.0 µg/ml (LZD). Other pathogens in the PTK clinical success group included β-hemolytic strep (4 pts, mixed cultures), Gram negative bacteria (5 pts, 4 mixed), E. faecalis (2pts, one mixed), S. hemolyticus (1pt, mixed), and S. constellatus (1pt, only pathogen). In the LZD clinical success group other pathogens included Gram negatives (4 pts , 3 mixed), E. faecium (1pt, mixed), and S. constellatus (2 pts, only pathogen). There were only two clinical failures in the PTK arm, both MSSA (PTK MIC = 0.25 and 0.5 µg/ml, mixed cultures) and three in the LZD arm, 2 MRSA (LZD MIC = 2µg/ml, 1 mixed) and one MSSA (LZD MIC = 2µg/ml, only pathogen).

Conclusions: PTK exhibited excellent efficacy in the Phase 2 trial compared to LZD (CE Success 98% vs 93.2% respectively and ME Success 97.4% vs 93.7%, respectively). S. aureus was the predominant pathogen at enrollment (93.3% from PTK and 87.3% from LZD) the majority of which were MRSA. Susceptibility to PTK and LZD did not differ between MRSA and MSSA and did not differ between treatment arms.

The Phase 2 evaluation of PTK796 in comparison to linezolid indicated that PTK was safe and well tolerated and appeared to be efficacious compared to linezolid. The most common pathogen isolated was S. aureus, the majority of which were MRSA. PTK796 was active against S. aureus, with an MIC90 of 0.25µg/ml. Only two clinical failures occurred in the PTK796 treated group. In neither case was the infection caused by an organism with elevated PTK796 MIC. There were three failures in the linezolid treated group and none of these isolates had elevated MICs to linezolid to account for the lack of success.

2008

Safety and Efficacy of PTK 0796: Results of the Phase 2 Study in Complicated Skin and Skin Structure Infections Following IV and Oral Step Down Therapy

Background: PTK 0796 (PTK) is the first aminomethylcycline in clinical development. A multicenter Phase 2 randomized, investigator blinded, comparative trial in complicated skin and skin structure infections (CSSSI) was completed in January 2008. Patients with CSSSI who required initial intravenous (IV) therapy and met inclusion and exclusion criteria were enrolled at 11 centers in the US and were randomized to receive either PTK (100mg Q24h IV with 200mg Q24h oral step-down) or linezolid (LZD) (600mg Q12h IV with 600mg Q12h oral step-down).

Results: The ITT populations (111 received PTK, 108 received LZD) were comparable in terms of enrollment criteria, disease severity, co-morbidities, and demographics. Mean duration of total treatment and of IV and oral therapy did not differ between PTK (9.9, 4.3, 5.6 days respectively) and LZD (9.7, 4.3, 5.4 days, respectively). The efficacy (clinical success) of PTK was 88.3% for the ITT population compared to 75.9% for LZD. In the clinically evaluable population, the clinical success rates were 98% and 93.2% for PTK and LZD, respectively. Bacterial pathogens were cultured at baseline from ~74% of each treatment group; over 50% had MRSA. Among the microbiologically evaluable patients, there were 2 failures in the PTK group, none was associated with MRSA and 4 failures in the LZD group, 2 of which were associated with MRSA. PTK was well tolerated. There were no discontinuations due to adverse events (AEs) for PTK (vs 2 for LZD) and no drug-related serious AE in either group. In both treatment groups the most common drug-related AEs were gastrointestinal (12 PTK vs 13 LZD). GI events associated with PTK were observed almost entirely during oral therapy, were mild, and did not result in discontinuation of therapy. There were no observed differences between the treatment groups in hematology or serum chemistry parameters.

Conclusions: Based on these results, PTK 0796 is advancing to Phase 3 trials.

In this Phase 2 study of over 200 adults with complicated skin and skin-structure infections, the safety and efficacy of PTK 0796 administered by IV and oral routes was comparable to linezolid (Zyvox™).

Based on these results, PTK 0796 is proceeding to Phase 3 trials in cSSSI, diabetic foot infection and moderate to severe community acquired pneumonia (CAP).

2006

Antistaphylococcal Activity of MK-2764 / PTK 0796 Compared to Other Agents

Background: MK-2764 / PTK 0796 is a new aminomethylcycline with a broad spectrum of activity against gram-positive and gram-negative organisms. The activity of MK-2764/PTK 0796, compared to those of vancomycin (VAN), linezolid (LIN), daptomycin (DAP), clindamycin (CLN), azithromycin (AZI), ceffriaxone (CEF) and levofloxacin (LEVO) against 112 strains of S. aureus was determined.

Method: The 112 strains comprised 24 MSSA and 88 MRSA (the latter including 3 VRSA, including the Hershey strain, and 5 VISA strains). MIC was as recommended by CLSI by agar dilution on M-H agar with added calcium for DAP testing. Inocula were 10^4 cfu/spot and MICs read after overnight incubation at 35 C (a full 24 h for VAN).

Results: MICs (µg/ml) were as follows: All strains, irrespective of phenotypes, were susceptible to MK-2764/PTK 0796, with MICs ranging from 0.06-2 mg/mL. LIN and DAP were also potent against all strains, with MIC ranges between 0.5 - 4 mg/mL and 0.12-4 mg/mL, respectively. VAN MIC ranges against all except the VISA and VRSA strains were 0.5-2 mg/mL and all strains, especially MRSA organisms, showed resistance to B-lactams, CLN, AZI and LEVO.

Conclusions: MK-2764/PTK 0796, a new aminomethylcycline, was potent against all S. aureus strains tested, irrespective of phenotype.

  • MK-2764 was active against all staphylococci tested regardless of their susceptibility to other agents at MICs < 2 µg/ml.
  • If results of pharmacokinetic/pharmacodynamic and animal toxicity and therapeutic studies look positive, MK- 2764 holds promise for treatment of infections caused by drug-resistant S. aureus strains of all phenotypes.
  • MK-2764 is currently undergoing evaluation as an oral agent. Of the orally available antibacterials tested, only linezolid exhibited reasonable activity against these isolates, although less potent in vitro than MK-2764.

 

 

In Vivo Pharmacodynamics of MK-2764 / PTK 0796 Against Various Gram-positive and Gram-negative Bacteria in the Thighs of Neutropenic and Normal Mice

Background: MK-2764 / PTK 0796 (PTK) is an aminomethylcycline antibiotic, derived from the tetracycline class, with potent activity against gram-positive cocci and many Enterobacteriaceae. We used the murine thigh-infection model in neutropenic and normal mice to determine [1] the PK/PD indice driving in vivo efficacy and its magnitude with different bacteria, and [2] the effect of neutrophils on the magnitude of the PK/PD indice. PTK was compared with tigecycline (TG), a glycylcycline antibiotic also derived from the tetracycline class and recently FDA approved, in some experiments.

Methods: Neutropenic and normal mice were exposed to 105.9-7.8 cfu/thigh of 21 strains [3 MSSA, 2 CA-MRSA, 12 S. pneumoniae (SP), 3 E. coli (EC) and 1 K. pneumoniae (KP)] and then treated sc for 24 hrs with PTK. Dose fractionation studies were performed with 4 strains (MSSA, SP, and 2 EC). Dosing in normal and neutropenic mice was compared with SP and KP. Dose-response data using CFUs at 24 hrs were analyzed by an Emax model using non-linear regression. Static doses for each strain were determined. The pharmacokinetics (PK) of PTK were determined by LC/MS/MS assay at doses of 1.25, 5 and 20 mg/ kg. PK/PD indices were calculated using total drug concentrations, as protein binding of PTK is very low.

Results: In vitro MICs ranged from 0.03 to 2 mg/L. PK of PTK was linear for all doses with peak/dose values of 0.10-0.15 and AUC/dose values of 0.84-0.94. 24-hr AUC/MIC was the PK/PD indice that best correlated with efficacy with all 4 strains (R2 = 81-85%). The presence of neutrophils enhanced the activity of PTK with SP more than 6-fold, but KP only about 2-fold. PTK was more potent against EC and KP than TG even though MICs of PTK were 4-fold higher than MICs of TG.

Conclusions: PTK exhibited potent in vivo activity against MSSA, MRSA, SP, EC and KP. The increased potency over TG despite higher MICs suggests that PTK has more favorable PK or PD characteristics

The above studies have characterized the in vivo pharmacodynamic activity of MK-2764 against various strains of S. pneumoniae, S. aureus and a few gram-negative bacilli.

  • MK-2764 produced a modest postantibiotic effect with S. aureus.
  • The 24-hr AUC/MIC was the PK/PD indice most important for efficacy.
  • The magnitude of the 24-hr AUC/MIC required for the various strains of pneumococci was 23.8. This value is very similar to the 24-hr AUC/MIC values obtained with fluoroquinolones, other tetracyclines, clindamycin and macrolides with S. pneumoniae. The 24-hr AUC/MIC values were similar for E. coli, but S. aureus and K. pneumoniae appeared to require a slightly higher AUC/MIC for a static effect.
  • The presence of WBCs had a major impact in reducing the magntiude of the 24-hr AUC/ MIC over 6-fold with one strain of S. pneumoniae.
  • MK-2764 exhibited excellent killing of S. pneumoniae over 24 hours of therapy. Killing of E. coli was modest while the drug was primarily bacteriostatic against S. aureus and K. pneumoniae.
  • Against E. coli and K. pneumoniae, MK-2764 was slightly more potent in vivo than tigecycline, despite being four-fold less active in vitro in two strains selected. This suggests that MK-2764 has more favorable pharmacologic characteristics (eg. longer half-life with resulting higher AUC, lower protein binding, or even more potent pharmacodynamics).

 

 

In Vitro Activity of MK-2764 / PTK 0796 Against Legionella spp.

Background: MK-2764 / PTK 0796 is a novel aminomethycycline with excellent activity against respiratory pathogens. In order t to determine as potential utility in pneumonia, the in vitro activity of MK-2764 / PTK 0796 was determined against Legionella spp.

Methods: The in vitro activity of MK-2764 / PTK 0796 was determined against 45 clinical isolates of Legionella spp. by broth erythromycin, moxifloxacin and gatifloxacin. The species tested included microdilution using buffered yeast extract without charcoal compared to doxycycline, telithromycin, azithromycin, L. pneumophila serogroup 1 to 12 (25 isolates), L. dumoffii (5), L. micdadei (5), L. longbeacheae (5) and one isolate each of five other species.

Results: MK-2764 / PTK 0796 (MIC Results 90 0.25 mg/L) was more active than doxycycline (MIC90 1 mg/L), azithromycin (MIC90 0.5 mg/L) and erythromycin (MIC90 1 mg/L) and was less active than moxifloxacin (MIC <0.03 mg/L), gatifloxacin (MIC <0.03 mg/L) and telithromycin (MIC 0.06 mg/L) against L. pneumophila. L. pneumophila serogroup 5 had one isolate with the highest MK-2764/PTK 0769 MIC of 1.0 mg/L of all the isolates tested. Against other species of Legionella, MK-2764/PTK 0796 (MIC range <0.03-0.25 mg/L) was as active as azithromycin (MIC range <0.03-0.25 mg/L) and telithromycin (<0.03-0.12 mg/L) and more active than doxycycline and erythromycin (MIC range <0.03-1.0 mg/L for both).

Conclusions: These data confirm the interesting activity of this novel aminomethylcycline antibiotic, MK-2764/PTK 0769, against Legionella spp.

 

Pharmacokinetic/Pharmacodynamic Profile of MK-2764 / PTK 0796 against S. pneumoniae in a Murine Pneumonia Model

Background: A leading causative agent of community-acquired pneumonia (CAP), Streptococcus pneumoniae (SPN), has developed resistance to several classes of antimicrobials. class, has demonstrated potent MK-2764 / PTK 0796, a novel aminomethylcycline antibiotic derived from the tetracycline in vitro activity against pulmonary pathogens, including multi-drug resistant SPN.

Methods: The efficacy of MK-2764 was assessed against penicillin-susceptible (PEN-S) characterize the 0.5 to 10 mg/kg after single subcutaneous doses. PK modeling techniques were used to monia model. The pharmacokinetic profile of MK-2764 in serum was described at doses of and penicillin/macrolide-resistant (PEN/MAC-R) SPN isolates in a neutropenic mouse pneufreeMK-2764 drug exposure after various single and multiple dose regimens. Evaluation of PD parameters and estimations of the effective dose by bacterial density measurement were completed. Accumulation of MK-2764 into epithelial lining fluid (ELF) and lung tissue was also measured.

Results: MK-2764 displayed a linear PK profile over the range of 0.5 to 10 mg/kg doses 38.96; k10 (1/hr) 0.107. Potent efficacy of 2 ½ logs bacterial k used in PD studies. Average initial parameters were as follows: V_F (L/kg) 6.99; k01 (1/hr) ill by MK-2764 was achieved after doses of 10 mg/kg/day. For both strains, the static dose was 1 mg/kg. The free AUC/MIC was predictive of the change in bacterial load. Concentration (AUC) ratios for ELF serum and lung tissue serum ranged from 1.1 to 1.4 and 2.3 to 4.4, respectively.

Conclusions: MK-2764 was an effective agent against SPN in this in vivo model and the PD parameter predictive of antibacterial activity was the AUC/MIC. Both ELF and lung tissue concentrations indicated accumulation of MK-2764 in these extravascular compartments. The characteristics of MK-2764 including potent antibacterial activity and accumulation at the site of infection make this a candidate for further evaluation.

  • MK-2764 exhibited activity both in vitro and in vivo against the two SPN isolates. The presence on mefA genotype and penicillin resistance in SPN 100 did not appear to limit or alter the activity of MK-2764 whether in vitro or in vivo versus SPN 22 which is an antibiotic susceptible strain.
  • The pharmacokinetics after single subcutaneous MK-2764 doses of 0.5, 5 and 10 mg/kg were linear and were satisfactorily exemplified using a nonlinear one compartment model.
  • MK-2764 appears to concentrate at the site of infection in this model as demonstrated by the amount of drug entry and accumulation in the extravascular compartment of relevance.
  • MK-2764 produced an overall dose-dependent killing effect. On an exposure basis, the impact of bacterial density decreased proportionally with an increase of AUC/MIC and a potential Cmax/MIC. This relationship was found to be favorably correlated for both SPN isolates. The maximum bacterial kill was observed after doses of approximately 10 mg/kg and approached bactericidal activity (i.e. 2.4-2.7 logs).

 

 

2004

Potent activity of BAY 73-7388, a Novel Aminomethylcycline, Against Susceptible and Resistant Gram-positive and Gram-negative Organisms

Objectives: BAY 73-7388 is the lead compound of a new class of antibiotics, the aminomethylcyclines, which evo l ved from the tetracycline (TET) family. BAY 73-7388 has potent activity against antibiotic-susceptible and resistant gram-positive and gram-negative pathogens.The present study compared the activity in vitro of BAY 73-7388 and 10 other agents including vancomycin (VA N ) , linezolid (LZD), l evo f l o x a c i n (LVX) and TET against recent clinical isolates including methicillin-resistant Staphylococcus aureus ( M R S A ) , VAN-resistant Enterococcus faecium (Efa V R E ) , Enterococcus faecalis ( E f ) ,p e n i c i l l i n - r e s i s t a n t Streptococcus pneumoniae (Spn PENR), Groups A and B beta-haemolytic streptococci (BHS), Escherichia coli ( E c ) , and other pathoge n s . Potential microbiological interactions between BAY 73-7388 and other antibiotics were also assessed.

Methods: Microdilution MIC tests were performed according to NCCLS guidelines.The activity of BAY 73-7388 in the presence of other antibacterial agents was assessed using standard chequerboard MIC methods. TET-resistance determinants were identified using multiplex polymerase chain reaction (PCR).

Results: Susceptibility in vitro (MIC 90 mg/L) for selected agents is shown in the Table below.

Conclusions: BAY 73-7388 has potent activity in vitro against a range of common p a t h o ge n s , including those resistant to currently available antibiotics: most notably MRSA,VRE and penicillin-resistant S.pneumoniae. Chequerboard studies in vitro demonstrate BAY 73-7388 does not affect, and is not affected by, the activity of other antibiotics. (BAY 73-7388 was discovered by Paratek Pharmaceuticals Inc., Boston, MA, and designated PTK 0796.)

BAY 73-7388 is highly active in vitro against a broad spectrum of pathogens, most notably:

  • Methicillin-resistant Staphylococcus aureus
  • Vancomycin-resistant Enterococcus
  • Penicillin-resistant S t reptococcus pneumoniae
  • Escherichia coli
  • Klebsiella pneumoniae
  • Haemophilus influenzae

BAY 73-7388 is active in vitro against organisms which are resistant to multiple classes of antibiotics including:

  • Methicillin-resistant Staphylococcus aure u s and vancomycin-resistant
  • Enterococcus also resistant to tetracyclines, levofloxacin, azithromycin, and clindamycin
  • Penicillin-resistant S t reptococcus pneumoniae also resistant to tetracyclines, cefotaxime, azithromycin, and clindamycin

BAY 73-7388 shows no interaction with ampicillin, cefotaxime, ciprofloxacin, clindamycin, gentamicin, rifampin, or vancomycin.

 

BAY 73-7388 is Highly Efficacious in Animal Models of Intraabdominal Infections Caused by a Range of Aerobic and Anaerobic Organisms, Including VRE

Objective: BAY 73-7388, a novel antibiotic compound from the aminomethylcycline class, has an antibacterial spectrum encompassing gram-positive, gram-negative, and anaerobic bacteria, including those resistant to currently available antibiotics.The efficacy of BAY 73-7388 in 4 different mouse infection models with pathogens causing intra-abdominal infections was compared with that of vancomycin (VA N ) , linezolid (LZD), imipenem (IMI), and metronidazole (MTN). Methods: For systemic infections (sepsis), enterococci (tetracycline [TET]-resistant Enterococcus faecalis, VAN-resistant Enterococcus faecium [VRE]) were administered intraperitoneally, IV treatment was started 30 min postinfection, and survival of the infected mice until day 5 was monitored. In the pouch model using Bacteroides fragilis as infecting pathoge n , therapeutic efficacy of BAY 73-7388 compared with MTN was determined as reduction of colony forming units (CFU).The mouse model of caecal ligation was used as a model for polymicrobial peritonitis after surgical intervention and 10-day survival was monitored. Results: In systemic infections with TET-resistant E.faecalis or E.faecium VRE, efficacy of BAY 73-7388 was superior to VAN or LZD: 100% surv i val was observed at 1 mg/kg BAY 73-7388, 10 mg/kg VAN , and 3 mg/kg LZD. For the E.faecium septicaemia model, 100% survival was found at 15 mg/kg BAY 73-7388, while neither VAN nor LZD treatment resulted in 100% survival, even at 50 mg/kg, the highest dose tested. In the pouch model with B.fragilis, the CFU reduction caused by BAY 73-7388 was superior to MTN (CFU reduction >6 log compared with 4 log at 25 mg/kg, r e s p e c t i ve l y ) .T h e r a py (2 x 10 mg/kg IV on day 1) of intra-abdominal infections and postoperative polymicrobial peritonitis with BAY 73-7388 showed increased surv i val compared with IMI or LZD (80% vs 70% vs 30%, respectively). Conclusions: Against pathogens causing intra-abdominal infections (including VRE and T E T-resistant strains), BAY 73-7388 demonstrated superior therapeutic efficacy compared with VAN, LZD, MTN, or IMI. ( BAY 73-7388 was discovered by Paratek Pharmaceuticals. Inc., Boston, MA, and designated PTK 0796.)

BAY 73-7388 demonstrated superior therapeutic efficacy against pathoge n s causing intra-abdominal infections (including VRE and T E T-resistant strains) compared with VAN, LZD, MTN, or IMI.

  • In a mouse model of enterococcal (tetRes, VRE) septicaemia, efficacy of BAY 73-7388 was superior to vancomycin or linezolid
  • In a mouse model of anaerobic infection with B.fragilis, BAY 73-7388 shows higher potency than metronidazole
  • In a polymicrobial peritonitis mouse model, BAY 73-7388 demonstrates superior efficacy compared with imipenem or linezolid

BAY 73-7388 is a promising agent for the treatment of intra-abdominal infections including those involving strains resistant to currently available antibiotics, eg, VRE.

 

Superior Efficacy of BAY 73-7388, a Novel Aminomethylcycline, Compared with Linezolid and Vancomycin in Murine Sepsis Caused by Susceptible or Multiresistant Staphylococci

Objective: BAY 73-7388 is the first compound selected from the novel class of aminomethylcyclines and was designed to meet an increasing need for additional therapies for bacterial infections, including those resistant to currently available antibiotics. Multiresistant staphylococci are of particular concern in the clinical setting. Therefore, the efficacy of BAY 73-7388 was compared with that of vancomycin (VAN) and linezolid (LZD) in different mouse models of staphylococcal infection.

Methods: Murine sepsis was used to compare the efficacy of BAY 73-7388 with VAN and LZD. For systemic infections, Staphylococcus aureus (MSSA), methicillin-and quinolone-resistant Staphylococcus aureus (MQRSA), and methicillin-resistant Staphylococcus epidermidis (MRSE) were administered intraperitoneally, and IV treatment was started 30 min postinfection. Survival of the infected mice was monitored until day 5. For the investigation in immunocompromised animals, mice were rendered neutropenic by 2 injections of 150 and 100 mg/kg cyclophosphamide at days 4 and 1 prior to infection.

Results: In systemic infections with MSSA, BAY 73-7388 was more effective than VAN or LZD, resulting in 100% surv i val at 0.3 mg/kg compared with 10 mg/kg for VAN and LZD. The efficacy of BAY 73-7388 therapy on systemic MQRSA and MRSE infection was also pronounced (100% survival for MQRSA at 3 mg/kg compared with >10 mg/kg for VAN and LZD; 100% survival for MRSE at 1 mg/kg compared with 10 mg/kg and >10 mg/kg for VAN and LZD, respectively). Moreover, in neutropenic mice, BAY 73-7388 was the only curative agent (100% survival for BAY 73-7388 at 50 mg/kg). In contrast, there was 60% survival in the VAN and the LZD groups at the highest dosage tested, 50 mg/kg.

Conclusions: Treatment with BAY 73-7388 is highly effective in systemic staphylococcal infections (susceptible and multiresistant strains) in mice and is superior compared with LZD and VAN. (BAY 73-7388 was discovered by Paratek Pharmaceuticals, Inc., Boston, MA, and designated PTK 0796.)

  • Treatment with the novel aminomethylcycline BAY 73-7388 is highly effective in murine models of staphylococcal infection.
  • The efficacy of BAY 73-7388 is superior to linezolid and va n c o m y c i n in murine models of staphylococcal infection.
  • The efficacy of BAY 73-7388 is not affected by resistance to other antibiotic classes, including methicillin.
  • BAY 73-7388 is a promising agent for the treatment of staphylococcal infections, including those caused by MRSA

 

Activity of BAY 73-7388, a Novel Aminomethylcycline, and Other Novel Antibiotic Classes Against Resistant Bacteria In Vitro

Objectives: The emergence of antibiotic resistance among gram-positive pathogens has impacted the clinical management of these infections. Paratek Pharmaceuticals initiated a programme to apply medicinal chemistry to the core structure of tetracycline (TET) with the goal of creating novel classes of proprietary antibiotics that would (a) be unaffected by the known TET resistance mechanisms and (b) retain the safety and tolerability profile of the TET family. Since there is no cross-resistance between the TETs and other antibiotics, such new agents would be expected to be active against isolates resistant to all other currently available classes.The aim of the programme was to synthesize new agents active against gram-positive, common gram-negative, atypical, and anaerobic bacteria.

Methods: A series of 7-position and 7,9-position derivatives of sancycline were synthesized and tested for activity in vitro a gainst methicillin-resistant Staphylococcus aureus (MRSA) , vancomycin-resistant enterococci (VRE), Enterococcus faecalis, and Streptococcus pneumoniae by microdilution.The presence of TET-resistance determinants was assessed by polymerase chain reaction (PCR) and confirmed by resistance to currently available tetracyclines.

Results: A number of 7-dimethylamino-9-aminomethylcyclines (AMC) and 7-aryl or heteroaryl sancyclines with potent activity in vitro (MIC range, ≤0.06-2.0 mg/L) were identified. Both novel series were more potent against one or more of the resistant strains than currently available antibiotics tested (MIC range, 16-64 mg/L).The AMC derivatives were active against bacteria resistant to TET by both efflux and ribosome-protection mechanisms.

Conclusions: This study identified the AMCs as a novel class of antibiotics evo l ved from TET that exhibit potent activity in vitro against TET-resistant bacteria, including gram-positive bacteria resistant to currently available antibiotics. One agent of this class, BAY 73-7388 (discovered by Paratek Pharmaceuticals, Inc., Boston, MA, and designated PTK 0796) has been chosen for development.

  • The novel classes of aminomethylcyclines and sancyclines designed by medicinal chemistry demonstrate potent activity in vitro against gram-positive bacteria
  • Aminomethylcyclines and sancyclines are not affected by resistance to currently available classes of antibiotics including quinolones, glycopeptides, and tetracyclines (both ribosome protection and efflux resistance mechanisms)

 

BAY 73-7388, a Novel Aminomethylcycline, Exhibits Potent Efficacy in Pulmonary Murine Models of Infection

Objective: With the emergence of resistance to currently available antibiotics in the treatment of infectious diseases, the development of novel antibiotic classes has become of major importance. BAY 73-7388 is the first aminomethylcycline antibacterial agent and is characterised by potent activity in vitro against sensitive and multiantibiotic-resistant gram-positive, gram-negative atypical, and anaerobic bacteria. We have evaluated BAY 73-7388 in several murine pulmonary infection models with a range of pathogens in both neutropenic (Neut) and immunocompetent (IC) mice.

Methods: BAY 73-7388 and reference antibiotics were evaluated in acute, systemic lethal infections caused by multiresistant (res) and susceptible (sus) Streptococcus pneumoniae (SPn); acute, lethal pulmonary SPn infection in Neut mice; chronic, SPn lung model in IC mice; and chronic Haemophilus influenzae (HFlu) infection model in IC mice. In each infection, BAY 73-7388 and other antibiotics were administered IV.

Results: PD50 (survival) and ED50 (bacterial burden) results for BAY 73-7388 and comparators, vancomycin (VAN), linezolid (LZD), ciprofloxacin (CIP), azithromycin (AZI), and doxycycline (DOX), a gainst susceptible and resistant strains of SPn and HFlu (sus) are detailed in the table below.

Conclusions: Overall, BAY 73-7388 performed as well as or better than the currently available therapeutic agents in all the models investigated in this study. (BAY 73-7388 was discovered by Paratek Pharmaceuticals, Inc., Boston, MA, and designated PTK 0796.)

  • BAY 73-7388, a novel aminomethylcycline antibiotic, demonstrated efficacy equal or superior to all five currently available antibiotics tested in immunocompetent mice with systemic infection due to tetracycline-susceptible and -resistant strains of S.pneumoniae.
  • BAY 73-7388 demonstrated efficacy comparable or superior to all five comparator antibiotics in immunocompromised and immunocompetent mice with pulmonary infection due to tetracycline-susceptible and -resistant clinical strains of S.pneumoniae.
  • BAY 73-7388 demonstrated efficacy comparable or superior to all three comparator antibiotics in immunocompetent mice with pulmonary infection due to H.influenzae.
  • In summary, BAY 73-7388 was consistently effective in treating common pulmonary pathogens in four different murine models investigated.

 

BAY 73-7388 Demonstrates Greater Activity than Linezolid in a Range of Murine Models of Skin and Soft Tissue Infection

Objective: BAY 73-7388 is a novel antibiotic compound being developed for the treatment of severe bacterial infections. It is the first compound selected from the novel class of aminomethylcyclines and was designed to meet an increasingly significant need for additional therapies for treatment of infections, including those resistant to currently available antibiotics. The efficacy of BAY 73-7388 in different mouse models of skin and soft tissue infection (SSTI) was compared with that of vancomycin (VAN) and linezolid (LIN).

Methods: Two mouse models were employed to determine the efficacy of BAY 73-7388: (1) infected abscess model (induced by implantation and subsequent infection of Gelfoam (TM)) and (2) infected thigh muscle model in neutropenic mice. Staphylococcus aureus strain DSM11823 (MSSA) was used to infect the respective structures in the skin and soft tissues. Infected abscess bearing mice were treated i.v. bid for 2 days, while thigh muscle infection model mice were treated s.c. 30 min post-infection. CFU reduction of infected tissues and bacterial load in different organs (spread from the infection site) were used as read-out for therapeutic efficacy.

Results: As measured by reduction of bacterial load, therapy of infected abscesses with BAY 73-7388 (CFU reduction >4 log units at 10 mg/kg) was superior to VAN and LIN (no reduction in bacterial load). Furthermore, BAY 73-7388 reduced the overall bacterial load in spleen, liver, lung and heart. In the reduction of organ load, BAY 73-7388 was as efficacious as VAN or LIN. In the mouse thigh muscle infection model, BAY 73-7388 proved to be as least as effective as VAN (2 log CFU reduction) and superior to LIN, which demonstrated no efficacy at the same dose (0.5 log CFU increase).

Conclusions: BAY 73-7388 was clearly more potent than LIN and VAN in the infected abscess model, and more potent than LIN and at least as effective as VAN in the thigh wound model. (BAY 73-7388 was discovered by Paratek Pharmaceuticals, Inc., Boston, MA, and designated PTK 0796.)

  • BAY 73-7388 was clearly more potent than LZD and VAN in the infected abscess model, and more potent than LZD, and at least as effective as VAN in the thigh wound model.
  • BAY 73-7388 is a promising agent for treatment of SSTI, including infections caused by isolates resistant to current classes of antibiotics

 

BAY 73-7388, a Novel Aminomethylcycline, is Highly Active In Vivo in a Murine Model of Pneumococcal Pneumonia

Objectives: BAY 73-7388 is the first antibiotic compound from the novel class, the aminomethylcyclines. BAY 73-7388 is being investigated for the treatment of severe bacterial infections including those caused by strains resistant to current classes of antibiotics. The efficacy of BAY 73-7388 was compared with that of vancomycin (VAN) and linezolid (LIN) in a mouse model of pneumococcal pneumonia.

Methods: For lung infections, Streptococcus pneumoniae (strain L3 TV, Serotype 3) was administered intranasally to 5 mice per group, followed by i.v. antibiotic treatment bid over 2 days. The bacterial counts in the lungs on day 4 were used as read-out. Survival was monitored until day 4 post-infection.

Results: (a) CFU: Bacterial CFU in the lung at day 4 were lower with BAY 73-7388 and VAN in comparison with LIN therapy (reduction in CFU >6 log units at 1 mg/kg BAY 73-7388 vs. no reduction in CFU at the same doses of LIN). A 4.5 log unit CFU reduction was only obtained at a 10 mg/kg dose of LIN. (b) Survival assays: For BAY 73-7388 and VAN all mice survived at the three tested doses (1, 3 and 10 mg/kg). In contrast for LIN 0, 2, and 4 animals survived when tested at the same dose range.

Conclusions: Treatment with BAY 73-7388 is highly effective in an animal model of pneumococcal pneumonia. (BAY 73-7388 was discovered by Paratek Pharmaceuticals, Inc., Boston, MA, and designated PTK 0796.)

  • Treatment with BAY 73-7388 is highly effective in an animal model of pneumococcal pneumonia
  • BAY 73-7388 demonstrated superior efficacy to linezolid as measured by reduction in CFU and survival

2003

The Mechanism of Action of BAY 73-6944/PTK 0796

Background: PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline) is a novel antibacterial agent of the tetracycline family with enhanced activity against gram-positive and gram-negative bacteria. To establish the mechanism of action, PTK 0796 was evaluated for its effects on in vitro macromolecular synthesis (protein, DNA, RNA, and peptidoglycan (pg)), ribosome binding, and an assessment of its killing activity was performed.

Methods: Macromolecular synthesis in viable S. aureus was determined using radiolabeled substrates. Ribosome binding was determined by competition with radiolabeled tetracycline (tet) in in vitro binding assays. Bacterial killing was assessed by standard methods against several gram-positive organisms.

Results: In vitro macromolecular synthesis assays demonstrated that PTK 0796 specifically inhibited protein synthesis, similar to tet. The IC50 was 32 mg/ml for RNA synthesis, >32 mg/ml for DNA synthesis, and 11.5 mg/ml for pg synthesis. PTK 0796 was a better competitor for ribosomal binding than unlabeled tet (IC50 2.32 mM vs 7.4 mM, respectively) in a competitive binding assay using [ 3H]Tet. PTK 0796 exhibited an ability to kill S. aureus and E. faecium beginning within the first 2 hrs and extending through 24 hrs of incubation although not to the extent to be defined as a bactericidal agent.

Conclusions: The antibacterial activity of PTK 0796 is linked to specific inhibition of bacterial protein synthesis. Competitive binding assays demonstrated that PTK 0796 effectively competed with tet for ribosome binding indicating that PTK 0796 shares ribosome-binding sites with tet and has greater affinity for these sites. In addition, PTK 0796 exhibited limited killing activity similar to that described previously for other tests.

PTK 0796 (BAY 73-6944), a novel aminomethylcycline,

  • Exerts its antibacterial activity against tetracycline susceptible and resistant bacteria by inhibition of protein synthesis.
  • In vitro MICs were not affected by tetracycline resistance mechanisms.
  • Exhibited some bacterial killing activity.
  • Protein synthesis was preferentially inhibited and at similar concentrations in the absence and presence of tetracycline resistance determinants.
  • Binds to the tetracycline binding site of bacterial ribosomes.

 

The Activity of BAY 73-6944/PTK 0796 Against Tetracycline Resistance

Background: PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline), a novel antibacterial agent of the tetracycline family, exhibits enhanced activity against gram-positive clinical isolates resistant to approved tetracyclines (tets). Studies were conducted to evaluate the potential emergence of resistance and the mechanism by which PTK 0796 circumvents tet resistance determinants.

Methods: MIC testing was performed according to NCCLS guidelines. Tet resistance determinants (Tet(K), Tet(L), Tet(M)) were identified using multiplex PCR. Single-step mutant selection and passage studies were used to establish the likelihood of emergence of resistance. The influence of efflux was determined in Tet(K) Staphylococcus aureus and ribosome protection by in vitro translation with and without Tet(O).

Results: PTK 0796 has activity against both ribosomal protection and efflux mediated tet resistance. MICs were not significantly affected by the presence of Tet(M) (MIC range of 0.125 to 0.5 mg/ml), presence of Tet(L) or Tet(K) (0.125 to 0.25 mg/ml), compared to susceptible strains.

Conclusions: PTK 0796 overcomes tet resistance mechanisms in gram-positive bacteria as shown by its potent activity against strains resistant to currently marketed tets. This activity was the result of PTK 0796 having low affinity for efflux pumps and greater affinity for ribosome binding than the protection protein. Regardless of the status of tet susceptibility of the test organisms, mutational resistance to PTK 0796 was not observed.

PTK 0796 (BAY 73-6944), a novel aminomethylcycline,

  • Exhibited excellent activity against clinical bacterial isolates with a variety of tetracycline resistance traits.
  • Did not appear to be recognized by the tetracycline efflux pump, Tet(K) when tested in whole cell protein synthesis assays comparing isogenic strains with and without Tet(K).
  • In contrast to minocycline and tetracycline, overcame tetracycline resistance conferred by the ribosomal protection protein, Tet(O), in in vitro translation assays.
  • Did not select single-step resistant mutants in the strains of S. aureus tested. This included strains carrying tetracycline resistance determinants tet(M) and tet(K).
  • Did not select for multi-step resistant mutants in tetracycline sensitive and tetracycline resistant strains of S. aureus in a passage study over 10 days.

These results indicate that PTK 0796 (Bay 73-6944), has superior broad spectrum activity compared to tetracyclines, is not affected by tetracycline resistance, and exhibits a low propensity for resistance selection.

 

BAY 73-6944/PTK 0796: In Vitro Potency and Spectrum of Activity Compared to Ten Other Antimicrobial Compounds

Background PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)- aminomethylcycline), is a novel antibacterial agent of the tetracycline family with potent and enhanced activity against resistant gram-positive and gram-negative pathogens.

Methods Using NCCLS microbroth dilution and agar dilution methodology, the present study was designed to: 1) assess the in vitro activity of PTK 0796 against 1084 clinical isolates representing a broad spectrum of pathogenic bacterial species in comparison with 10 other antimicrobials, and 2) compare the broth microdilution MICs of PTK 0796 with those achieved with agar dilution.

Results MIC90s (µg/ml) for selected groups of isolates and antimicrobials are as follows: MIC90s for gram-negative species range from 1-32 µg/ml. MICs by agar dilution were 1 dilution higher than microbroth dilution MICs.

Conclusions PTK 0796 had excellent activity against gram-positive pathogens. MIC’s were generally ​<0.25 mg/mL (1 mg/mL for CNS) and were relatively consistent between and within species. Activity of PTK0796 was not affected by resistance to reference compounds and was notably active against MRSA, MRSE, VRE, and PRSP. The activity against gram-negative pathogens was more various between species, having better activity against some species (eg E. coli, Enterobacter, Shigella) compared to others (eg P. stuartii, P rettgeri, M. morganii). Agar dilution MICs were higher than broth microdilution MICs for all groups tested.

PTK 0796 (BAY 73-6944) a potent new aminomethylcycline antimicrobial agent exhibited excellent activity against strains resistant to other antibiotics

  • Enterococci regardless of vancomycin susceptibility
  • Methicillin susceptible and resistant S. aureus and other staphylococci
  • Streptococci including penicillin resistant S. pneumoniae
  • H. influenzae and M. catarrhalis
  • Also demonstrated activity with MICs at < 4.0 mg/ml against many of the gram negative species including E. coli, E aerogenes, E. cloacae, S. marcescens, Salmonella spp., Shigella spp., and S. maltophilia.

 

In Vitro Activity of BAY 73-6944/PTK 0796 Against Gram-Positive and Gram-Negative Organisms

Background: To address the problem of antibiotic resistance, Paratek scientists have produced PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline), a novel antibacterial agent of the tetracycline family with potent and enhanced activity against resistant gram-positive and gram-negative pathogens.

Methods: The present study compared the in vitro activity of PTK 0796 and 10 agents including, vancomycin, tetracycline, and ciprofloxacin against >200 strains of recent grampositive and gram-negative clinical isolates including methicillin sensitive S. aureus (MSSA), methicillin resistant S. aureus (MRSA), vancomycin resistant E. faecium (EFA VRE), E. faecalis (EF), penicillin resistant S. pneumoniae (SPN PENR), Groups A and B Beta hemolytic Streptococci (BHS), E. coli (EC), and other pathogens. Microdilution MIC tests were performed according to NCCLS guidelines.

Results: As shown in the Table, PTK 0796 exhibited potent activity particularly against antibiotic resistant gram-positive isolates.

Conclusions: PTK 0796 is highly active in vitro against a broad spectrum of pathogens including multiple antibiotic-resistant pathogens, most notably methicillin resistant Staphylococcus aureus, vancomycin resistant Enterococcus, and penicillin resistant S. pneumoniae. The activity of PTK 0796 is not affected by the presence of resistance to tetracycline.

 

PTK 0796 (BAY 73-6944) was highly active in vitro against a broad spectrum of pathogens most notably:

  • Methicillin-resistant Staphylococcus aureus ó Vancomycin-resistant Enterococcus faecium ó Penicillin-resistant Streptococcus pneumoniae
  • Eschericia coli
  • Klebsiella pneumoniae
  • Haemophilus influenzae

PTK 0796 (BAY 73-6944) was active in vitro against organisms which are resistant to multiple classes of antibiotics including:

  • Methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium also resistant to tetracyclines, levofloxacin, azithromycin, and clindamycin enicillin-resistant
  • Streptococcus pneumoniae also resistant to tetracyclines, cefotaxime, azithromycin and clindamycin

 

PTK 0796 (BAY 73-6944) and other Novel Tetracycline Derivatives Exhibiting Potent in vitro and in vivo Activities Against Antibiotic Resistant Gram-Positive Bacteria

Background: Antibiotic resistant bacteria pose a significant health risk because antibiotic treatment is ineffective against infections caused by these organisms. In an effort to combat resistance, Paratek Pharmaceuticals has undertaken a medicinal chemistry effort to create novel tetracycline derivatives as potential agents against multiple antibiotic resistant gram-positive bacteria.

Methods: 7-position and 7,9 position derivatives of sancycline were synthesized and tested for activity in vitro against MRSA, VRE, E. faecalis (Ef), and S. pneumoniae (Spn). Serum effects and COS-1 and CHO-K1 cell cytotoxicity were obtained to aid in the selection of compounds for efficacy testing in vivo using a mouse systemic Spn. infection model.

Results: In vitro MIC screening in vitro identified four 7-dimethylamino-9-aminomethylcyclines (AMCs) and four 7-aryl or heteroaryl sancyclines with potent activity (MIC range 100 mg/ mL). When tested in an infection model in vivo, the compounds demonstrated good efficacy (PD50 range 0.35-0.63 mg/kg) against susceptible Spn.

Conclusions: This study identified two classes of novel tetracyclines which exhibited potent in vitro activity against resistant gram-positive bacteria. The antibacterial activity, absence of cytotoxicity, and demonstrated efficacy in vivo highlights the potential of the AMCs as a novel class of antibacterials, one of which, PTK 0796 has been chosen for development.

  • The two novel classes of tetracycline derivatives presented in this study demonstrated potent activity in vitro against antibiotic resistant gram-positive bacteria.
  • The low serum MICs, low cyctotoxicity and good efficacy in vivo of the 7-dimethylamino-9- aminomethylcyclines (AMCs, 7a-d) highlight the potential of these derivatives as novel agents to combat antibiotic resistance.
  • As a result of this study, the AMC derivative, PTK 0796 (BAY 73-6944) (7a), was chosen for further development.

 

BAY 73-6944/PTK 0796: Effects of Environmental Variation on MICs and Confirmation of Disk Mass

Background: PTK0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)- aminomethylcycline), is a novel antibacterial agent of the tetracycline family with potent and enhanced activity against resistant gram-positive and gram-negative pathogens.

Methods: Using E. coli (EC) ATCC 25922, S. aureus (SA) ATCC 29213, and E. faecalis (EF) ATCC 29212 and NCCLS microbroth dilution (M7-A6) or disk diffusion (M2-A8) methodology, the present study was designed to: 1) determine the effect of varying test conditions (pH 6.0 to 8.0, divalent cation concentrations from 0.25 to 2 X normal range, inoculum size from 103 to 107 CFU/ml, presence or absence of CO2 , and the presence of blood in the test medium) on the in vitro activity of PTK0796; and 2) determine the appropriate disk content of PTK0796 for performing the disk diffusion susceptibility test by comparing zone diameters from 15, 30, and 60 µg disks compared to microbroth dilution MICs against clinical isolates.

Results: No differences in MICs were noted under varying conditions of divalent cation content, or the presence of blood or CO2 . Up to a 4-fold increase in MICs was noted with increases in inoculum size from 103 to 107 CFU/ml for SA and EF. No change was noted for EC. Although stable over a pH range of 7.2 to 7.4, the MICs increased up to 4- fold at pH 6.0. All gram-positive and Haemophilus strains were susceptible at a concentration of £4 µg/ml. Zones of inhibition for the 15, 30, and 60 mg disks generally correlate with MIC’s. The 30 µg disk could be used for all species tested.

Conclusions: When performed within NCCLS guidelines, minor variations in pH, divalent cation concentration, incubation in CO2 , and presence of blood in the test medium had little effect on the in vitro activity of PTK0796. Increasing inoculum size increased MICs by 4-fold for SA and EF but not EC. All disk contents gave good correlations to MICs.

  • PTK 0796 (BAY 73-6944) is a potent new aminomethlycycline antimicrobial agent.
  • All gram positive strains tested and all H. influenzae were susceptible at < 4.0 mg/ml.
  • Many enteric and some non enteric species were also susceptible at < 4.0 mg/ml.
  • Microbroth susceptibility tests on PTK 0796 (BAY 73-6944) were not affected by varying divalent cation content, the addition of lysed horse blood, incubation in a 5% CO2 environment or by pH changes in the broth from pH 7.0 to pH 8.0.
  • Increasing the standard inoculum size from 10 5 to 10 7 caused an increase in the MICs.
  • The 30 mg disk performed satisfactorily for all gram positive species and Haemophilus influenzae.
  • The 30 mg disk also performed satisfactorily for Enterobacteriaceae and non-enteric bacilli, however there was a slightly higher percentage of minor errors with these species.
  • Agar dilution resulted in somewhat higher MICs compared to microbroth

 

Evaluation of BAY 73-6944/PTK 0796 in Experimental Models of Infections Caused by Gram-Positive and Gram-Negative Pathogens

Background: With the emergence of resistance to all commonly used antibiotics in the treatment of infectious diseases, the development of novel antibiotics has become of major importance. PTK 0796 (7- dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline) is a novel antibacterial agent of the tetracycline family that has broad and enhanced antibacterial activity including multi-antibiotic resistant grampositive bacteria. We have evaluated PTK 0796 in various infection models with gram-positive and gramnegative pathogens in both immunocompromised and immunocompetent mice.

Methods: Models (all treated intravenously): systemic S. aureus (immunocompetent, IP inoculation, survival endpoint); MRSA Thigh Wound (neutropenic, intramuscular inoculation, bacterial burden endpoint); systemic E. faecalis (IV inoculation, kidney bacterial burden endpoint); E. coli UTI (intrabladder inoculation, kidney burden endpoint).

Results: In the systemic S. aureus infection, PTK 0796 was equally or more efficacious (PD50 0.4 mg/kg) when compared to minocycline (1.0mg/kg), vancomycin (0.4 mg/kg) and linezolid (3.5 mg/kg). The efficacy of PTK 0796 in the Thigh Wound caused by MRSA was superior to the comparators tested, with a more than 5-fold decrease in the ED50 when compared to vancomycin, linezolid, and minocycline. In the systemic E. faecalis model, PTK 0796 treatment had an ED50 of 4.5 mg/kg compared to >40 mg/kg for linezolid and over >100 mg/kg for both vancomycin and minocycline. In addition to gram-positive infections, we also evaluated PTK 0796 in an E. coli UTI model. When compared to minocycline (ED50 = 11.0mg/kg), PTK 0796 had an ED50 of 4.8 mg/kg.

Conclusions: Overall, PTK 0796 performed better than or equal to the marketed therapeutic agents tested in all the models investigated in this study.

PTK 0796 (BAY 73-6944)

  • When tested in neutropenic mice challenged in the thigh with MRSA, was superior to the comparators studied.
  • In a systemic, E. faecalis model showed greater efficacy than Minocycline, Vancomycin and Linezolid.
  • Was equally efficacious against S. aureus compared to the other comparators tested in a systemic model of infection in immunocompetent mice.
  • Showed equal efficacy to Minocycline in an E. coli urinary tract infection model.

In summary, PTK 0796 (BAY 73-6944) performed better than or equal to the reference therapeutic agents tested in all the models investigated in these studies.

 

The Efficacy of BAY 73-6944/PTK 0796 in Murine Models of Streptococcus pneumoniae Infections

Background: Streptococcus pneumoniae (Spn) is the most frequently isolated organism in community-acquired pneumonia, is a significant cause of hospitalization and mortality, and is becoming increasingly resistant to antibiotics. PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline) is a novel antibacterial agent of the tetracycline family having broad and enhanced activity against susceptible and multi-antibiotic resistant gram-positive bacteria. PTK 0796 was tested in four Spn animal infection models to evaluate its potential as a therapeutic agent.

Methods: Efficacy of PTK 0796 was evaluated in four models: Systemic Immunocompetent (IC) Infection, LRTI Neutropenic (Neut), LRTI Lung Burden (IC), Thigh Wound (Neut).

Results: PD50 and ED50 results for PTK 0796 and comparators, Vancomycin (Vanco), Linezolid (Lin), and Minocycline (Mino) against tetracycline susceptible (Sus) and resistant (Res) strains of Spn

Conclusions: PTK 0796 exhibited excellent efficacy in four Spn infection models. Efficacy was demonstrated in systemic and organ-based infections, in normal and neutropenic animals, and irrespective of in vitro resistance to other antibiotics. PTK 0796 was comparable or superior to antibiotics currently available for the treatment of serious Spn infections

 

Pharmacokinetics of BAY 73-6944/PTK 0796 in Mouse, Rat and Cynomolgus Monkey

Background: PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline) is a novel antibacterial agent of the tetracycline family that exhibits potent and enhanced activity in vitro against resistant and susceptible gram-positive and gram-negative pathogens and efficacy in animal models of infection. The pharmacokinetics (PK) of intravenously (IV) administered PTK 0796 was determined in the mouse, rat, and monkey.

Methods: PTK 0796 was administered as a single IV dose escalating from 5 mg/kg to 40 mg/kg to rats, as a single IV 10 mg/kg dose to mice, and a 25 mg/kg dose to monkeys. Analyses of plasma (all), kidneys (rats), and lungs (rats) were accomplished using LC-MS/ MS.

Results: In all species, PTK 0796 exhibited a bi-exponential decline with a rapid distribution phase and an extended elimination phase. In mouse and rat, the plasma T½ (elim) were 5.6 hr and 3.8 hr, respectively. AUC0-24 in rat and mouse were similar at similar doses, and increased linearly with increasing dose (rat). Time of plasma concentrations above 1 mg/ml ranged from 15 min in mice and 40 min in rats (10 mg/kg) to more than nine hrs in rats (40 mg/kg). In monkeys, plasma T½ (elim) was greater than in rodents (10-11 hrs) and plasma concentrations remained above 1 mg/ml for at least 24 hrs at 25 mg/kg. In rats, the kidney concentrations were more than six-fold greater than in plasma and were linearly related to dose. In the lung, concentrations were found to be 10 to 20-fold that of the plasma and similarly dose related. Time above 1 mg/gram in lung increased with increasing dose (6 hrs to 22 hrs).

Conclusions: PTK 0796 administered IV to mice, rats, and monkeys exhibited similar PK. PTK 0796 plasma PK in all species indicated a rapid distribution and prolonged elimination. Dose escalation studies in rats indicated linear PK in both plasma and tissue, with sustained tissue levels in both kidneys and lungs.

  • In all species, after IV administration, plasma concentrations of PTK 0796 (BAY 73-6944) exhibited a broadly exponential decline with a rapid distribution phase followed by a slower elimination phase.
  • The elimination half life appeared to increase in higher species.
  • When administered as an IV bolus to rats, PTK 0796 (BAY 73-6944) distributed rapidly into tissues; kidneys and lung were found to have concentrations 6 to more than 20 fold that of plasma. Elimination half lives of 4 - 5 hr were observed.
  • In rats, concentrations of PTK 0796 (BAY 73-6944) in tissues appeared to be of microbiologic significance for between 6 and 20 hr, depending on dose.
  • The elimination half life achieved values of 10 hr in the plasma of Cynomolgus monkeys.

 

In Vitro Assessment of Plasma Protein Binding and Metabolic Stability of BAY 73-6944/PTK 0796

Background: PTK 0796 (7-dimethylamino, 9-(2,2-dimethyl-propyl)-aminomethylcycline) is a novel antibiotic of the tetracycline family with potent and enhanced activity against susceptible and resistant strains of both gram positive and gram negative bacteria.

Method: Protein binding of PTK 0796 in mouse, rat, and monkey plasma was estimated using an equilibrium dialysis based method. The metabolic stability of PTK 0796 to the cytochrome P450 enzymes was assessed by incubation for up to 60 minutes with liver microsomes from mice, rats, and monkeys. The sample analysis in both assays was carried out on a High Turbulence Liquid Chromatography based on-line extraction system coupled with a triple quadrupole mass spectrometer. The metabolic stability was assessed by monitoring the disappearance of the parent molecule.

Results: PTK 0796 was found to be substantially unbound in plasma at concentrations ranging from 0.5 mg/ml to 10 mg/ml. At these concentrations, the plasma protein binding for reference tetracyclines (doxycycline and minocycline) ranged from 79-87 %. The data were quite similar across the species. In the presence of liver homogenates from all the species tested in this study, PTK 0796 appears to be metabolically stable with no detectable loss of compound over 60 minutes. These results are consistent with data for tetracyclines such as doxycycline and minocycline which also do not yield any major metabolites and are known to be metabolically stable.

Conclusions: PTK 0796 exhibits little protein binding and metabolism in mouse, rat, and monkey, both of which are considered to be favorable pharmacologic characteristics consistent with potential effectiveness in treating bacterial infections. These characteristics likely contribute to the excellent efficacy in animal models of infection reported elsewhere.

  • PTK 0796 (BAY 73-6944) exhibited minimal protein binding to mouse, rat and monkey plasma at concentrations above 0.1mg/ml. However, at a concentration of 0.1mg/ml, it shows low (14-20%) but appreciablebinding to plasma proteins. Doxycycline and Minocycline are substantially more bound (68-86%) for the concentrations tested in this study.
  • The low plasma protein binding of PTK 0796 (BAY 73-6944) would result in a considerably higher fraction unbound (fu) facilitating better target tissue distribution of this drug.
  • PTK 0796 (BAY 73-6944) is metabolically stable. The results are generally consistent with those reported for Doxycycline and Minocycline, which are known to be only modestly metabolized.
  • This low protein binding and metabolic stability could have a strong positive influence on the pharmacokinetics, pharmacodynamics and toxicity of this drug leading to better potency and efficacy in animal models of infection

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Omadacycline Presentations & Posters - January 5, 2017

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