Phenotypic and in silico studies for a series of synthetic thiosemicarbazones as New Delhi metallo-beta-lactamase carbapenemase inhibitors

Abstract

The past two decades have been marked by a global spread of bacterial resistance to β-lactam drugs and carbapenems derivatives are the ultimate treatment against multidrug-resistant bacteria. β-lactamase expression is related to resistance which demands the development of bacterial resistance blockers. Drug inhibitor combinations of serine-β-lactamase and β-lactam were successful employed in therapy despite their inactivity against New Delhi metallo-beta-lactamase (NDM). Until now, few compounds are active against NDM-producing bacteria and no specific inhibitors are available yet. The rational strategy for NDM inhibitors development starts with in vitro assays aiming to seek compounds that could act synergistically with β-lactam antibiotics. Thus, eight thiosemicarbazone derivatives were synthesized and investigated for their ability to reverse the resistant phenotype in NDM in Enterobacter cloacae. Phenotypic screening indicated that four isatin-beta-thiosemicarbazones showed Fractional Inhibitory Concentration (FIC) ≤ 250 µM in the presence of meropenem (4 µg/mL). The most promising compound (FIC= 31.25 µM) also presented synergistic effect (FICI = 0.34). Docking and molecular dynamics studies on NDM-thiosemicarbazone complex suggested that 2,3-dihydro-1H-indol-2-one subunit interacts with catalytic zinc and interacted through hydrogen bonds with Asp124 acting like a carboxylic acid bioisostere. Additionally, thiosemicarbazone tautomer with oxidized sulfur (thione) seems to act as a spacer rather than zinc chelator, and the aromatic moieties are stabilized by pi–pi and cation–pi interactions with His189 and Lys221 residues. Our results addressed some thiosemicarbazone structural changes to increase its biological activity against NDM and highlight its scaffold as promising alternatives to treat bacterial resistance.

Communicated by Ramaswamy H. Sarma

Keywords:

• Metallo-β-lactamase
• NDM inhibitor
• bacterial resistance
• thiosemicarbazone
• phenotypic assay
• molecular modeling
• drug discovery

Disclosure statement

All authors have declared no conflict of interest.

Author’s contributions

Silvio Cunha and Danilo Santana synthesized the entire series of derivatives with structure elucidation. Humberto F. Freitas and Joice Reis initiated the idea and design of the biology and computational parts. Jonatham Moreira and Carolina Xavier carrying out in vitro phenotypic screening and molecular docking. Samuel R. Pita performs the Molecular Dynamic simulations. All authors contributed to data analysis and manuscript writing in their corresponding parts.

Additional information

Funding

This study received financial support from the Brazilian National Research Council (grant number 309360/2019-6), the Bahia State Foundation for Research Support (FAPESB; grant code PPSUS 0014/2018). The authors (Jonatham Moreira and Humberto F. Freitas) would like to thank the Coordination for the Improvement of Higher Education Personnel agency (CAPES, Finance Code 001) and Samuel Pita thanks to Bahia Research Foundation (FAPESB, grant numbers JCB-0039/2013 and RED-008/2013).