# Novel C5α-substituted carbapenems enhance Mycobacterium abscessus killing via selective target binding and reduced hydrolysis by BlaMab

## TL;DR

New C5α-modified carbapenems show improved effectiveness against Mycobacterium abscessus infections by better targeting bacterial proteins and resisting breakdown.

## Contribution

The study introduces novel C5α-substituted carbapenems with enhanced antibacterial activity and resistance to BlaMab hydrolysis.

## Key findings

- JDB/NA-1-157 effectively kills Mab with low MICs and high binding affinity to key enzymes.
- JDB/NA-1-208 resists BlaMab hydrolysis but shows poor efficacy alone, though synergistic when combined with other β-lactams.

## Abstract

Mycobacterium abscessus (Mab) poses significant clinical challenges and underscores the urgent need for safer and more effective treatments, including β-lactams. Among currently available carbapenems, imipenem is widely used to treat Mab infections by combining with other antibiotics. Commercial carbapenems share a common scaffold with C2 modifications, whereas this study focuses on novel carbapenem candidates with C5α modifications. We evaluated their antibacterial activity against Mab ATCC 19977 and clinical isolates, as well as their acylation of peptidoglycan target receptors (L,D-transpeptidases [LDTs] and penicillin-binding proteins [PBPs]) and the β-lactamase enzyme BlaMab. In vitro studies of two C5α-modified carbapenems, JDB/NA-1-157 and JDB/NA-1-208, revealed distinct antibacterial effects. JDB/NA-1-157 demonstrated potent bacterial killing with low minimum inhibitory concentrations (MICs; 0.125–8 mg/L) and near-complete eradication within 5 days, surpassing the efficacy of the standard-of-care regimen (amikacin + clarithromycin + imipenem). In contrast, JDB/NA-1-208 exhibited poor bacterial killing, with high MICs (16–256 mg/L) and limited efficacy in time-kill studies. However, JDB/NA-1-208 showed synergistic killing when combined with other β-lactams. Mechanistically, JDB/NA-1-208 is not a substrate for BlaMab, while JDB/NA-1-157 is, albeit with low catalytic efficiency. This is supported by the observation that the addition of avibactam did not enhance synergy with JDB/NA-1-157. The substantial bacterial killing effect of JDB/NA-1-157 is attributed to its high binding affinity for PBP-B, PBP-lipo, PonA2, D,D-carboxypeptidase, and LDT1–2. These findings highlight the potential of novel C5α-modified carbapenems, particularly JDB/NA-1-157, as promising therapeutic candidates for Mab infections.