Discovery of uncompetitive inhibitors of SapM that compromise intracellular survival of Mycobacterium tuberculosis

Paulina Fernández-Soto,Pablo Rodríguez-Fernández,Danilo Solano-Castro,Mark A Travis,Thomas A Jowitt,Joshua Casulli,Jennifer S Cavet,Lydia Tabernero

doi:10.1038/s41598-021-87117-x

Abstract

SapM is a secreted virulence factor from Mycobacterium tuberculosis critical for pathogen survival and persistence inside the host. Its full potential as a target for tuberculosis treatment has not yet been exploited because of the lack of potent inhibitors available. By screening over 1500 small molecules, we have identified new potent and selective inhibitors of SapM with an uncompetitive mechanism of inhibition. The best inhibitors share a trihydroxy-benzene moiety essential for activity. Importantly, the inhibitors significantly reduce mycobacterial burden in infected human macrophages at 1 µM, and they are selective with respect to other mycobacterial and human phosphatases. The best inhibitor also reduces intracellular burden of Francisella tularensis, which secretes the virulence factor AcpA, a homologue of SapM, with the same mechanism of catalysis and inhibition. Our findings demonstrate that inhibition of SapM with small molecule inhibitors is efficient in reducing intracellular mycobacterial survival in host macrophages and confirm SapM as a potential therapeutic target. These initial compounds have favourable physico-chemical properties and provide a basis for exploration towards the development of new tuberculosis treatments. The efficacy of a SapM inhibitor in reducing Francisella tularensis intracellular burden suggests the potential for developing broad-spectrum antivirulence agents to treat microbial infections.

Highlights

Tuberculosis (TB) is still a major global health threat with 10 million people developing active TB and over 1.5 million deaths every y ear[1]
To identify new inhibitors of SapM, we screened four different compound libraries covering a wide range of pharmacological active drugs (LOPAC-1280 and LOPAC-Pfizer), phosphatase inhibitors (Enzo-BML-2834), and in-house compounds from other drug discovery programmes
False positives or negatives are expected as compounds tend to degrade or precipitate after long-term storage in D MSO30, but the number of hits identified in our screening is similar with previous reports using the same libraries[31,32]

Summary

Introduction

Tuberculosis (TB) is still a major global health threat with 10 million people developing active TB and over 1.5 million deaths every y ear[1]. Two recent new drugs, bedaquiline[2] and delamanid[3] were approved for the treatment of multidrug-resistant TB (MDR-TB). Resistance to both drugs was reported in less than a year after clinical u se[4,5], and the number of cases continue to r ise[6,7]. We have reported that SapM can be inhibited using l-ascorbic acid (L-AC) and 2-phospho-l-ascorbic acid (2P-AC), and that inhibition reduced mycobacterial survival in human THP1 macrophages[22]. These are low potency inhibitors with IC50 values > 200 μM

Methods

Results

Conclusion