Background: WCK 5222 (Phase 1 completed in US) is being developed for the treatment of serious Gram-negative infections including MBL-producing MDR enterics and PA strains and carbapenem hydrolyzing oxacillinases associated with Acinetobacter. Pan β-lactamase stable ZID enhances the activity of FEP against wild type Gram-negatives as well as MBL producing pathogens based on complementary PBP binding (SR Palwe et al., 3169, ASM Microbe, 2016). Impact of this novel mechanism of action on WCK 5222 PK-PD attributes was assesed through FEP and ZID PBP binding studies, time-kill and Phase 1 PK simulating IVPM and neutropenic mouse lung eradication studies.
Methods: ZID IC50 for PBPs of EC, KP and PA were determined by Bocillin FL-based competition experiment. MBL inhibition by ZID was ruled out through nitrocefin-based colorimetric method. MICs and time-kill studies were undertaken by standard methods. NDM-producing EC M44 and KP 13443 and PA 13437 (VIM-10) were evaluated in a single compartment IVPM and PA S814 (NDM; FEP-ZID MIC- 32 µg/mL) in neutropenic lung infection model. Lung eradication study was initiated by intranasal infection ( 6.0 log CFU/lung) and 1 day therapy was initiated 2h post infection employing various regimen. IVPM was initiated with 5.64 - 6.8 log CFU/mL. Clinical exposures of FEP (1-2 g) and ZID (750 mg-2g) were simulated. CFUs and drug concentrations were estimated for 24h.
Results: ZID showed specific and high PBP2 affinity [IC50s (mg/L): EC- 0.06, KP- 0.08 and PA-0.26]. FEP showed primacy to PBP3 with IC50s in the range of 0.13-0.19 mg/L. In time-kill studies, FEP+ZID (8+4 mg/L or 8+8 mg/L) provided >2 log kill for all the pathogens. In IVPM studies, stand alone FEP at 2g TID (Cmax 120-140 mg/L, AUC 1068 µg.h/mL), lacked cidality, where as ZID at 1g BID/TID (Cmax 70 mg/L, AUC 380/534 µg.h/mL) showed transient cidality. However, FEP‑ZID combination demonstrated rapid initial cidality with >1 log kill till 24h at BID or TID doses. In lung infection study, FEP+ZID (50+8.33q2h) exerted >2 log kill wheras carbapenem failed to eradicate.
Conclusion: Complementary PBP binding by WCK 5222 constituents triggered rapid and pronounced cidality in IVPM and caused in vivo eradication of MBL-expressing pathogens at clinical or sub-clinical exposures of FEP & ZID.
M. Bartolomé Cañellas,
U. Aniruddha, Wockhardt Ltd.,: Employee , Salary
S. Bhagwat, Wockhardt Ltd.,: Employee and Shareholder , Salary
M. Patel, Wockhardt Ltd.,: Employee and Shareholder , Salary
G. Bou, Wockhardt Ltd.,: Grant Investigator , Research grant
O. Antonio, Wockhardt Ltd.,: Grant Investigator , Research grant
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