Enantiomeric separation and determination of absolute stereochemistry of asymmetric molecules in drug discovery—Building chiral technology toolboxes

The application of Chiral Technology, or the (extensive) use of techniques or tools for the determination of absolute stereochemistry and the enantiomeric or chiral separation of racemic small molecule potential lead compounds, has been critical to successfully discovering and developing chiral drugs in the pharmaceutical industry. This has been due to the rapid increase over the past 10-15 years in potential drug candidates containing one or more asymmetric centers. Based on the experiences of one pharmaceutical company, a summary of the establishment of a Chiral Technology toolbox, including the implementation of known tools as well as the design, development, and implementation of new Chiral Technology tools, is provided.

1723. MK-3866, a metallo-β-lactamase inhibitor, is not subject to efflux in Pseudomonas aeruginosa

Background

Metallo-beta (β)-lactamases (MBLs) are in the class B group of β-lactamases due to zinc ions in the active site that are required for enzymatic activity. MK-3866 is a small molecule MBL inhibitor (MBLi) that restores antibacterial activity against resistant MBL-expressing gram-negative bacteria. Efflux is an important mechanism of antibiotic resistance in Pseudomonas aeruginosa (Pa). Imipenem (IMI) is not subject to efflux and neither is relebactam (REL), a β-lactamase inhibitor (BLi) of class A and C β-lactamases that is approved in combination with IMI/cilastatin. An efflux assay was devised to characterize MBLis for potentiation of IMI or cefepime (FEP) in isogenic strain pairs of efflux wild-type and multiply efflux deleted (MED) strains of Pa. Our objective was to determine if MK-3866 and related analogs are subject to efflux in Pa.

Methods

Bacterial isolates were engineered to demonstrate the ability of MBLis to be effluxed by introducing IMI metallo-β-lactamase-1 (IMP-1) (by electroporation) or Verona integron-encoded metallo-β-lactamases (VIM-1, VIM-2) (utilizing the cloning vector pFlp2) into isogenic MED and wild-type (WT) Pa isolates. Susceptibility testing was performed with IMI or FEP at a fixed concentration equal to the Pa Clinical and Laboratory Standards Institute susceptibility breakpoint for each and including a fixed 4 µg/mL of REL to inhibit class A or C enzymes, referred to as the SLICE assay. The concentration of MK-3866 and analogues required to restore susceptibility to either antibiotic in WT and MED strains was assessed.

Results

MICs to the combination of MK-3866/REL/IMI or MK-3866/REL/FEP vary by ≤4-fold between the WT and MED strain of each isogenic strain pair (Table 1). In contrast, large differential MIC values (efflux ratios) can be seen for the MK-3866 analogues A and B, with more moderate efflux ratios observed for other analogues. The exact efflux ratio depended on the MBL studied and the antibiotic partner.

Conclusion

MK-3866 showed a low potential for efflux whether IMP-1, VIM-1, or VIM-2 was expressed, in contrast to analogues of MK-3866 which exhibited differentials from nominal to extreme (≥ 128-fold) between efflux WT versus MED isolates.

Disclosures

Katherine Young, M.S., Merck & Co., Inc.: Stocks/Bonds Asra Mirza, MS, Merck & Co., Inc.: Stocks/Bonds Carl Balibar, PhD, Merck & Co., Inc.: Stocks/Bonds Shuzhi Dong, PhD, Merck & Co., Inc.: Stocks/Bonds Frank Bennett, PhD, Merck & Co., Inc.: Stocks/Bonds Jinlong Jiang, PhD, Merck & Co., Inc.: Stocks/Bonds Haiqun Tang, PhD, Merck & Co., Inc.: Stocks/Bonds Claire Tudge, PhD, Merck & Co., Inc.: Stocks/Bonds Jack Scott, PhD, Merck & Co., Inc.: Stocks/Bonds Dexi Yang, PhD, Merck & Co., Inc.: Stocks/Bonds Alexander Pasternak, PhD, Merck & Co., Inc.: Stocks/Bonds.