In silico identification and experimental validation of hits active against KPC-2 β-lactamase

Exploiting the Carboxylate-Binding Pocket of β-Lactamase Enzymes Using a Focused DNA-Encoded Chemical Library

β-Lactamase enzymes hydrolyze and thereby provide bacterial resistance to the important β-lactam class of antibiotics. The OXA-48 and NDM-1 β-lactamases cause resistance to the last-resort β-lactams, carbapenems, leading to a serious public health threat. Here, we utilized DNA-encoded chemical library (DECL) technology to discover novel β-lactamase inhibitors. We exploited the β-lactamase enzyme-substrate binding interactions and created a DECL targeting the carboxylate-binding pocket present in all β-lactamases. A library of 106 compounds, each containing a carboxylic acid or a tetrazole as an enzyme recognition element, was designed, constructed, and used to identify OXA-48 and NDM-1 inhibitors with micromolar to nanomolar potency. Further optimization led to NDM-1 inhibitors with increased potencies and biological activities. This work demonstrates that the carboxylate-binding pocket-targeting DECL, designed based on substrate binding information, aids in inhibitor identification and led to the discovery of novel non-β-lactam pharmacophores for the development of β-lactamase inhibitors for enzymes of different structural and mechanistic classes.

PoSSuM v.3: A Major Expansion of the PoSSuM Database for Finding Similar Binding Sites of Proteins

Information on structures of protein-ligand complexes, including comparisons of known and putative protein-ligand-binding pockets, is valuable for protein annotation and drug discovery and development. To facilitate biomedical and pharmaceutical research, we developed PoSSuM (https://possum.cbrc.pj.aist.go.jp/PoSSuM/), a database for identifying similar binding pockets in proteins. The current PoSSuM database includes 191 million similar pairs among almost 10 million identified pockets. PoSSuM drug search (PoSSuMds) is a resource for investigating ligand and receptor diversity among a set of pockets that can bind to an approved drug compound. The enhanced PoSSuMds covers pockets associated with both approved drugs and drug candidates in clinical trials from the latest release of ChEMBL. Additionally, we developed two new databases: PoSSuMAg for investigating antibody-antigen interactions and PoSSuMAF to simplify exploring putative pockets in AlphaFold human protein models.

Ehretia Species Phytoconstituents as Potential Lead Compounds against Klebsiella pneumoniae Carbapenemase: A Computational Approach

The evolution of antibiotic-resistant carbapenemase has negatively impacted the management of critical healthcare-associated infections. K. pneumoniae carbapenemase-2- (KPC-2-) expressing bacteria have developed resistance to conventional therapeutic options, including those used as a last resort for life-threatening diseases. In this study, Ehretia species phytoconstituents were screened for their potential to inhibit KPC-2 protein using in silico approaches. Molecular docking was used to identify strong KPC-2 protein binding phytoconstituents retrieved from the literature. The best-docked conformation of the ligands was selected based on their glide energy and binding interactions. To determine their binding free energies, these hit compounds were subjected to molecular mechanics with generalized born and surface area (MM-GBSA) in the PRIME module. Pharmacological assessments of the ligands were performed to evaluate their drug-likeness. Molecular dynamic (MD) simulations were used to analyze the conformational stability of the selected druglike compounds within the active site of the KPC-2 protein. Overall, a total of 69 phytoconstituents were compiled from the literature. Fourteen of these compounds exhibited a stronger binding affinity for the protein target than the reference drugs. Four of these top hit compounds, DB09, DB12, DB28, and DB66, revealed the highest efficacy in terms of drug-likeness properties. The MD simulation established that among the druglike compounds, DB66 attained stable conformations after 150 ns simulation in the active site of the protein. We concluded that DB66 from Ehretia species could play a significant role in therapeutic efforts against KPC-2-expressing bacteria.

Structural Comparisons of Cefotaximase (CTX-M-ase) Sub Family 1

The cefotaximase or CTX-M, family of serine-β-lactamases represents a significant clinical concern due to the ability for these enzymes to confer resistance to a broad array of β-lactam antibiotics an inhibitors. This behavior lends CTX-M-ases to be classified as extended spectrum β-lactamases (ESBL). Across the family of CTX-M-ases most closely related to CTX-M-1, the structures of CTX-M-15 with a library of different ligands have been solved and serve as the basis of comparison within this review. Herein we focus on the structural changes apparent in structures of CTX-M-15 in complex with diazabicyclooctane (DABCO) and boronic acid transition state analog inhibitors. Interactions between a positive surface patch near the active site and complementary functional groups of the bound inhibitor play key roles in the dictating the conformations of active site residues. The insights provided by analyzing structures of CTX-M-15 in complex with DABCO and boronic acid transition state analog inhibitors and analyzing existing structures of CTX-M-64 offer opportunities to move closer to making predictions as to how CTX-M-ases may interact with potential drug candidates, setting the stage for the further development of new antibiotics and β-lactamase inhibitors.

4-Amino-1,2,4-triazole-3-thione as a Promising Scaffold for the Inhibition of Serine and Metallo-β-Lactamases

The emergence of bacteria that co-express serine- and metallo- carbapenemases is a threat to the efficacy of the available β-lactam antibiotic armamentarium. The 4-amino-1,2,4-triazole-3-thione scaffold has been selected as the starting chemical moiety in the design of a small library of β-Lactamase inhibitors (BLIs) with extended activity profiles. The synthesised compounds have been validated in vitro against class A serine β-Lactamase (SBLs) KPC-2 and class B1 metallo β-Lactamases (MBLs) VIM-1 and IMP-1. Of the synthesised derivatives, four compounds showed cross-class micromolar inhibition potency and therefore underwent in silico analyses to elucidate their binding mode within the catalytic pockets of serine- and metallo-BLs. Moreover, several members of the synthesised library have been evaluated, in combination with meropenem (MEM), against clinical strains that overexpress BLs for their ability to synergise carbapenems.

Targeting the Class A Carbapenemase GES-5 via Virtual Screening

The worldwide spread of β-lactamases able to hydrolyze last resort carbapenems contributes to the antibiotic resistance problem and menaces the successful antimicrobial treatment of clinically relevant pathogens. Class A carbapenemases include members of the KPC and GES families. While drugs against KPC-type carbapenemases have recently been approved, for GES-type enzymes, no inhibitors have yet been introduced in therapy. Thus, GES carbapenemases represent important drug targets. Here, we present an in silico screening against the most prevalent GES carbapenemase, GES-5, using a lead-like compound library of commercially available compounds. The most promising candidates were selected for in vitro validation in biochemical assays against recombinant GES-5 leading to four derivatives active as high micromolar competitive inhibitors. For the best inhibitors, the ability to inhibit KPC-2 was also evaluated. The discovered inhibitors constitute promising starting points for hit to lead optimization.

X-ray Crystallography Deciphers the Activity of Broad-Spectrum Boronic Acid β-Lactamase Inhibitors

Recent decades have witnessed a dramatic increase of multidrug resistant (MDR) bacteria, compromising the efficacy of available antibiotics, and a continual decline in the discovery of novel antibacterials. We recently reported the first library of benzo[b]thiophen-2-ylboronic acid inhibitors sharing broad spectrum activity against β-lactamases (BLs). The ability of these compounds to inhibit structurally and mechanistically different types of β-lactamases has been here structurally investigated. An extensive X-ray crystallographic analysis of boronic acids (BAs) binding to proteins representative of serine BLs (SBLs) and metallo β-lactamases (MBLs) have been conducted to depict the role played by the boronic group in driving molecular recognition, especially in the interaction with MBLs. Our derivatives are the first case of noncyclic boronic acids active against MBLs and represent a productive route toward potent broad-spectrum inhibitors.

First virtual screening and experimental validation of inhibitors targeting GES-5 carbapenemase

The worldwide spread of beta-lactamases with hydrolytic activity extended to last resort carbapenems is aggravating the antibiotic resistance problem and endangers the successful antimicrobial treatment of clinically relevant pathogens. As recently highlighted by the World Health Organization, new strategies to contain antimicrobial resistance are urgently needed. Class A carbapenemases include members of the KPC, GES and SFC families. These enzymes have the ability to hydrolyse penicillins, cephalosporins and carbapenems, while also being less susceptible to available beta-lactam inhibitors, such as clavulanic acid. The KPC family is the most prevalent. It is mostly found on plasmids in Klebsiella pneumoniae, meaning that great amounts of attention, in terms of inhibitor design and structural biology, have been dedicated to it, whereas no efforts have yet been dedicated to GES-type enzymes, despite their ability to rapidly and horizontally disseminate. We herein report the first in silico screening against GES-5, which is the most dangerous GES-type beta-lactamase, using a library of 800K commercially available candidates that all share drug-like properties, such as their MW, logP, rotatable bonds and HBA/HBD atoms. The best screening results were filtered to enrich the number of different chemotypes, and then submitted to molecular docking. The 34 most promising candidates were selected for in vitro validation in biochemical assays against recombinant GES-5. Six hits acted as inhibitors, in the high micromolar range, towards GES-5 and led to the identification of the first, novel chemotypes with inhibitory activity against this clinically relevant carbapenemase.