Novel inhibitors of Mycobacterium tuberculosis GuaB2 identified by a target based high-throughput phenotypic screen.

Jonathan A G Cox,Fernando Ramon,Grace Mugumbate,Carlos Alemparte,Laura Vela-Glez Del Peral,Lluis Ballell,Katherine A Abrahams,Joël Lelièvre,Monika Jankute,Peter Jervis,Gurdyal S Besra,Jorge Esquivias,Stefan Jackenkroll,David Barros,Arancha Perez

doi:10.1038/srep38986

Abstract

High-throughput phenotypic screens have re-emerged as screening tools in antibiotic discovery. The advent of such technologies has rapidly accelerated the identification of ‘hit’ compounds. A pre-requisite to medicinal chemistry optimisation programmes required to improve the drug-like properties of a ‘hit’ molecule is identification of its mode of action. Herein, we have combined phenotypic screening with a biased target-specific screen. The inosine monophosphate dehydrogenase (IMPDH) protein GuaB2 has been identified as a drugable target in Mycobacterium tuberculosis, however previously identified compounds lack the desired characteristics necessary for further development into lead-like molecules. This study has identified 7 new chemical series from a high-throughput resistance-based phenotypic screen using Mycobacterium bovis BCG over-expressing GuaB2. Hit compounds were identified in a single shot high-throughput screen, validated by dose response and subjected to further biochemical analysis. The compounds were also assessed using molecular docking experiments, providing a platform for their further optimisation using medicinal chemistry. This work demonstrates the versatility and potential of GuaB2 as an anti-tubercular drug target.

Highlights

High-throughput phenotypic screens have re-emerged as screening tools in antibiotic discovery
The rate limiting two-step catalysis of Inosine monophosphate (IMP) to xanthosine monophosphate (XMP) conversion by inosine monophosphate dehydrogenase (IMPDH) requires nicotinamide adenine dinucleotide (NAD+) as a cofactor, which is first reduced to NADH by a dehydrogenation reaction, forming an intermediate covalent bond between IMPDH and XMP, followed by a hydrolysis reaction that breaks the covalent attachment and releases XMP12
GuaB2 is the only catalytically active and essential IMPDH shown by transposon site hybridization (TraSH) to be required for viability of Mycobacterium tuberculosis (Mtb)[13,14]

Summary

Introduction

High-throughput phenotypic screens have re-emerged as screening tools in antibiotic discovery. Several crystal structures of GuaB2 from Mtb have recently been determined in complex with substrate, product and cofactors along with a number of new compounds with anti-mycobacterial activity[19,20,21] This enhanced understanding of the biophysics of GuaB2 inhibition can be used for in silico drug discovery and for the assessment of newly discovered anti-mycobacterial compounds targeting GuaB2. Following a high-throughput resistance-based phenotypic screen using a GuaB2 over-expressing strain of M. bovis BCG, we present 7 new inhibitors of Mtb GuaB2, and their subsequent biochemical and in silico assessment. These diverse compounds contribute to a growing pool of GuaB2 inhibitors, laying a foundation for a future medicinal chemistry optimisation programmes and acceleration of GuaB2 as a future anti-tubercular drug target

Methods

Results

Conclusion