Infections caused by carbapenem-resistant (CRE) are increasingly prevalent and have become a major worldwide threat to human health. Carbapenem resistance is driven primarily by the acquisition of β-lactamase enzymes, which are able to degrade carbapenem antibiotics (hence termed carbapenemases) and result in high levels of resistance and treatment failure. Clinically relevant carbapenemases include both serine β-lactamases (SBLs; e.g., KPC-2 and OXA-48) and metallo-β-lactamases (MBLs), such as NDM-1. MBL-producing strains are endemic within the community in many Asian countries, have successfully spread worldwide, and account for many significant CRE outbreaks. Recently approved combinations of β-lactam antibiotics with β-lactamase inhibitors are active only against SBL-producing pathogens. Therefore, new drugs that specifically target MBLs and which restore carbapenem efficacy against MBL-producing CRE pathogens are urgently needed. Here we report the discovery of a novel MBL inhibitor, ANT431, that can potentiate the activity of meropenem (MEM) against a broad range of MBL-producing CRE and restore its efficacy against an NDM-1-producing strain in a murine thigh infection model. This is a strong starting point for a chemistry lead optimization program that could deliver a first-in-class MBL inhibitor-carbapenem combination. This would complement the existing weaponry against CRE and address an important and growing unmet medical need.

The clinical effectiveness of carbapenem antibiotics such as meropenem is becoming increasingly compromised by the spread of both metallo-β-lactamase (MBL) and serine-β-lactamase (SBL) enzymes on mobile genetic elements, stimulating research to find new β-lactamase inhibitors to be used in conjunction with carbapenems and other β-lactam antibiotics. Herein, we describe our initial exploration of a novel chemical series of metallo-β-lactamase inhibitors, from concept to efficacy, in a survival model using an advanced tool compound (ANT431) in conjunction with meropenem.

The clinical effectiveness of the important β-lactam class of antibiotics is under threat by the emergence of resistance, mostly due to the production of acquired serine- (SBL) and metallo-β-lactamase (MBL) enzymes. To address this resistance issue, multiple β-lactam/β-lactamase inhibitor combinations have been successfully introduced into the clinic over the past several decades. However, all of those combinations contain SBL inhibitors and, as yet, there are no MBL inhibitors in clinical use. Consequently, there exists an unaddressed yet growing healthcare problem due to the rise in recent years of highly resistant strains which produce New Delhi metallo (NDM)-type metallo-carbapenemases. Previously, we reported the characterization of an advanced MBL inhibitor lead compound, ANT431. Herein, we discuss the completion of a lead optimization campaign culminating in the discovery of the preclinical candidate ANT2681, a potent NDM inhibitor with strong potential for clinical development.

The diazabicyclooctanes (DBOs) are a class of serine β-lactamase (SBL) inhibitors that use a strained urea moiety as the warhead to react with the active serine residue in the active site of SBLs. The first in-class drug, avibactam, as well as several other recently approved DBOs (e.g., relebactam) or those in clinical development (e.g., nacubactam and zidebactam) potentiate activity of β-lactam antibiotics, to various extents, against carbapenem-resistant Enterobacterales (CRE) carrying class A, C, and D SBLs; however, none of these are able to rescue the activity of β-lactam antibiotics against carbapenem-resistant Acinetobacter baumannii (CRAB), a WHO “critical priority pathogen” producing class D OXA-type SBLs. Herein, we describe the chemical optimization and resulting structure–activity relationship, leading to the discovery of a novel DBO, ANT3310, which uniquely has a fluorine atom replacing the carboxamide and stands apart from the current DBOs in restoring carbapenem activity against OXA-CRAB as well as SBL-carrying CRE pathogens.

The global dissemination of metallo-ß-lactamase (MBL)-producing carbapenem resistant Enterobacterales (CRE) is a serious public health concern. Specifically, NDM (New Delhi MBL) has been a major cause of carbapenem therapy failures in recent years, particularly as effective treatments for serine-ß-lactamase (SBL)-producing Enterobacterales are now commercially available. Since the NDM gene is carried on promiscuous plasmids encoding multiple additional resistance determinants, a large proportion of NDM-CREs are also resistant to many commonly used antibiotics, resulting in limited and sub-optimal treatment options. ANT2681 is a specific, competitive inhibitor of MBLs with potent activity against NDM enzymes, progressing to clinical development in combination with meropenem (MEM). Susceptibility studies have been performed with MEM-ANT2681 against 1,687 MBL-positive Enterobacterales, including 1,108 NDM-CRE. Addition of ANT2681 at 8 μg/ml reduced MEM MIC50/MIC90 from >32/>32 μg/ml to 0.25/8 μg/ml. Moreover, the combination of 8 μg/ml of both MEM and ANT2681 inhibited 74.9% of the VIM-positive and 85.7% of the IMP-positive Enterobacterales tested. The antibacterial activity of MEM-ANT2681 against NDM-CRE compared very favourably to that of cefiderocol (FDC) and cefepime (FEP)-taniborbactam, which displayed MIC90 values of 8 μg/ml and 32 μg/ml, respectively, whereas aztreonam-avibactam (ATM-AVI) had an MIC90 of 0.5 μg/ml. Particularly striking was the activity of MEM-ANT2681 against NDM-positive E. coli (MIC90 1 μg/ml), in contrast to ATM-AVI (MIC90 4 μg/ml), FDC (MIC90 >32 μg/ml) and FEP-taniborbactam (MIC90 >32 μg/ml) which were less effective due to the high incidence of resistant PBP3-insertion mutants. MEM-ANT2681 offers a potential new therapeutic option to treat serious infections caused by NDM-CRE.