Inhibiting mycobacterial tryptophan synthase by targeting the inter-subunit interface

Katherine A Abrahams,Jorge Esquivias,Fátima Ortega-Muro,Lluís Ballell,Joaquín Rullas,Esther Pérez-Herrán,Nicholas J Loman,Elena Jiménez,Klaus Fütterer,Carlos Alemparte,David Barros,Patrick J Moynihan,Gurdyal S Besra,Jonathan A G Cox

doi:10.1038/s41598-017-09642-y

Katherine A Abrahams, Jorge Esquivias + Show 12 more

Open Access

https://doi.org/10.1038/s41598-017-09642-y

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Abstract

Drug discovery efforts against the pathogen Mycobacterium tuberculosis (Mtb) have been advanced through phenotypic screens of extensive compound libraries. Such a screen revealed sulfolane 1 and indoline-5-sulfonamides 2 and 3 as potent inhibitors of mycobacterial growth. Optimization in the sulfolane series led to compound 4, which has proven activity in an in vivo murine model of Mtb infection. Here we identify the target and mode of inhibition of these compounds based on whole genome sequencing of spontaneous resistant mutants, which identified mutations locating to the essential α- and β-subunits of tryptophan synthase. Over-expression studies confirmed tryptophan synthase as the biological target. Biochemical techniques probed the mechanism of inhibition, revealing the mutant enzyme complex incurs a fitness cost but does not prevent inhibitor binding. Mapping of the resistance conferring mutations onto a low-resolution crystal structure of Mtb tryptophan synthase showed they locate to the interface between the α- and β-subunits. The discovery of anti-tubercular agents inhibiting tryptophan synthase highlights the therapeutic potential of this enzyme and draws attention to the prospect of other amino acid biosynthetic pathways as future Mtb drug targets.

Highlights

Drug discovery efforts against the pathogen Mycobacterium tuberculosis (Mtb) have been advanced through phenotypic screens of extensive compound libraries
According to a WHO survey in 20152, Mtb was shown to be responsible for 10.4 million new cases of TB, which included 480,000 new cases of multi-drug resistant (MDR)-TB, with an estimated 1.8 million deaths and 400,000 deaths resulting from co-infection with HIV
GSK continuously screens the new chemical diversity in its compound collection in search for new hits with anti-tubercular potential. As part of these efforts, we have recently identified two new chemical scaffolds with in vitro activity against Mtb: sulfolanes, represented by compound 1 and indoline-5-sulfonamides, represented by compounds 2 and 3 (Fig. 1)

Summary

Introduction

Drug discovery efforts against the pathogen Mycobacterium tuberculosis (Mtb) have been advanced through phenotypic screens of extensive compound libraries. Such a screen revealed sulfolane 1 and indoline-5-sulfonamides 2 and 3 as potent inhibitors of mycobacterial growth. The discovery of anti-tubercular agents inhibiting tryptophan synthase highlights the therapeutic potential of this enzyme and draws attention to the prospect of other amino acid biosynthetic pathways as future Mtb drug targets. In 2013, GlaxoSmithKline (GSK) published a collection of 177 non-cytotoxic compounds, known as the ‘TB box set’, with activity against Mtb H37Rv7 This set has been extended to include a total of 227 compounds[8] and has led to a broad effort of target assignment. The target assignment of the tryptophan synthase highlights the plausibility of amino acid biosynthesis pathways as suitable and underexploited Mtb drug targets

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