Dihydroxyphenyl-substituted thiosemicarbazone: A potent scaffold for the development of metallo-ß-lactamases inhibitors and antimicrobial.

The superbug infection mediated by metallo-ß-lactamases (MßLs) has grown into anemergent health threat, and development of MßL inhibitors is an ideal strategy to combat the infection. In this work, twenty-five thiosemicarbazones 1a-e, 2a-e, 3a-e, 4a-d, 5a-d and 6a-b were synthesized and assayed against MßLs ImiS, NDM-1 and L1. The gained molecules specifically inhibited NDM-1 and ImiS, exhibiting an IC50 value in the range of 0.37-21.35 and 0.45-8.76 µM, and 2a was found to be the best inhibitor, with an IC50 of 0.37 and 0.45 µM, respectively, using meropenem (MER) as substrate. Enzyme kinetics and dialysis tests revealed and confirmed by ITC that 2a is a time-and dose-dependent inhibitor of ImiS and NDM-1, it competitively and reversibly inhibited ImiS with a Ki value of 0.29 µM, but irreversibly inhibited NDM-1. Structure-activity relationship disclosed that the substitute dihydroxylbenzene significantly enhanced inhibitory activity of thiosemicarbazones on ImiS and NDM-1. Most importantly, 1a-e, 2a-e and 3a-b alone more strongly sterilized E. coli-ImiS and E. coli-NDM-1 than the MER, displaying a MIC value in the range of 8-128 µg/mL, and 2a was found to be the best reagent with a MIC of 8 and 32 µg/mL. Also, 2a alone strongly sterilized the clinical isolates EC01, EC06-EC08, EC24 and K. pneumonia-KPC-NDM, showing a MIC value in the range of 16-128 µg/mL, and exhibited synergistic inhibition with MER on these bacteria tested, resulting in 8-32-fold reduction in MIC of MER. SEM images shown that the bacteria E. coli-ImiS, E. coli-NDM-1, EC24, K. pneumonia-KPC and K. pneumonia-KPC-NDM treated with 2a (64 µg/mL) suffered from distortion, emerging adhesion between individual cells and crumpled membranes. Mice tests shown that monotherapy of 2a evidently limited growth of EC24 cells, and in combination with MER, it significantly reduced the bacterial load in liver and spleen. Docking studies suggest that the 2,4-dihydroxylbenzene of 2a acts as zinc-binding group with the Zn(II) and the residual amino acids in CphA active center, tightly anchoring the inhibitor at active site. This work offered a promising scaffold for the development of MßLs inhibitors, specifically the antimicrobial for clinically drug-resistant isolates.

Hydroxamate and thiosemicarbazone: Two highly promising scaffolds for the development of SARS-CoV-2 antivirals.

The emerging COVID-19 pandemic generated by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has severely threatened human health. The main protease (Mpro) of SARS-CoV-2 is promising target for antiviral drugs, which plays a vital role for viral duplication. Development of the inhibitor against Mpro is an ideal strategy to combat COVID-19. In this work, twenty-three hydroxamates 1a-i and thiosemicarbazones 2a-n were identified by FRET screening to be the potent inhibitors of Mpro, which exhibited more than 94% (except 1c) and more than 69% inhibition, and an IC50 value in the range of 0.12-31.51 and 2.43-34.22 µM, respectively. 1a and 2b were found to be the most effective inhibitors in the hydroxamates and thiosemicarbazones, with an IC50 of 0.12 and 2.43 µM, respectively. Enzyme kinetics, jump dilution and thermal shift assays revealed that 2b is a competitive inhibitor of Mpro, while 1a is a time-dependently inhibitor; 2b reversibly but 1a irreversibly bound to the target; the binding of 2b increased but 1a decreased stability of the target, and DTT assays indicate that 1a is the promiscuous cysteine protease inhibitor. Cytotoxicity assays showed that 1a has low, but 2b has certain cytotoxicity on the mouse fibroblast cells (L929). Docking studies revealed that the benzyloxycarbonyl carbon of 1a formed thioester with Cys145, while the phenolic hydroxyl oxygen of 2b formed H-bonds with Cys145 and Asn142. This work provided two promising scaffolds for the development of Mpro inhibitors to combat COVID-19.

Quinolinyl sulfonamides and sulphonyl esters exhibit inhibitory efficacy against New Delhi metallo-ß-lactamase-1 (NDM-1).

The "superbug" infection caused by metallo-ß-lactamases (MßLs) has grown into anemergent health threat, and development of effective MßL inhibitors to restore existing antibiotic efficacy is an ideal alternative. Although the serine-ß-lactamase inhibitors have been used in clinical settings, MßL inhibitors are not available to date. In this work, thirty-one quinolinyl sulfonamides 1a-p and sulphonyl esters 2a-o were synthesized and assayed against MßL NDM-1. The obtained molecules specifically inhibited NDM-1, 1a-p and 2a-o exhibited an IC50 value in the range of 0.02-1.4 and 8.3-24.8 µM, respectively, and 1e and 1f were found to be the most potent inhibitors, with an IC50 of 0.02 µM using meropenem (MER) as substrate. Structure-activity relationship reveals that the substitute phenyl and the phenyl with a halogen atom more significantly improve inhibitory effect of quinolinederivatives on NDM-1. 1a-p restored antimicrobial effect of MER on E. coli with NDM-1, EC01 and EC08, resulting in a 2-64-fold reduction in MIC values. Most importantly, 1e synergized MER and significantly reduced the load of EC08 in the spleen and liver of mice after a single intraperitoneal dose. Docking studies suggested that the endocyclic nitrogen of the quinoline ring, and exocyclic nitrogen of the sulfonamide functional group are coordinate with Zn(II) ion at active sites of NDM-1. Cytotoxicity assays indicated that 1e had low cytotoxicity. This work offers potential lead compounds for further development of the clinically useful inhibitor targeting NDM-1.

Hydroxamates as a potent skeleton for the development of metallo-ß-lactamase inhibitors.

Bacterial resistance caused by metallo-ß-lactamases (MßLs) has become an emerging public health threat, and the development of MßLs inhibitor is an effective way to overcome the resistance. In this study, thirteen novel O-aryloxycarbonyl hydroxamates were constructed and assayed against MßLs. The obtained molecules specifically inhibited imipenemase-1 (IMP-1) and New Delhi metallo-ß-lactamase-1, exhibiting an IC50 value in the range of 0.10-18.42 and 0.23-22.33 µM, respectively. The hydroxamate 5 was found to be the most potent inhibitor, with an IC50 of 0.1 and 0.23 µM using meropenem and cefazolin as substrates. ICP-MS analysis showed that 5 did not coordinate to the Zn(II) ions at the active site of IMP-1, while the rapid dilution, thermal shift and MALDI-TOF assays revealed that the hydroxamate formed a covalent bond with the enzyme. Cytotoxicity assays indicated that the hydroxamates have low toxicity in MCF-7 cells. This work provided a potent scaffold for the development of MßLs inhibitors.

N-acylhydrazones confer inhibitory efficacy against New Delhi metallo-ß-lactamase-1.

The expression of ß-lactamases, especially metallo-ß-lactamases (MßLs) in bacteria is one of the main causes of drug resistance. In this work, an effective N-acylhydrazone scaffold as MßL inhibitor was constructed and characterized. The biological activity assays indicated that the synthesized N-acylhydrazones 1-11 preferentially inhibited MßL NDM-1, and 1 was found to be the most effective inhibitor with an IC50 of 1.2 µM. Analysis of IC50 data revealed a structure-activity relationship, which is that the pyridine and hydroxylbenzene substituents at 2-position improved inhibition of the compounds on NDM-1. ITC and enzyme kinetics assays suggested that it reversibly and competitively inhibited NDM-1 (Ki = 0.29 ± 0.05 µM). The synthesized N-acylhydrazones showed synergistic antibacterial activities with meropenem, reduced 4-16-fold MIC of meropenem on NDM-1- producing E. coli BL21 (DE3), while 1 restored 4-fold activity of meropenem on K. pneumonia expressing NDM-1 (NDM-K. pneumoniae). The mice experiments suggested that 1 combined meropenem to fight against NDM-K. pneumoniae infection in the spleen and liver. Cytotoxicity assays showed that 1 and 2 have low cytotoxicity. This study offered a new framework for the development of NDM-1 inhibitors.