The anti-mycobacterial activity of the cytochrome bcc inhibitor Q203 can be enhanced by small-molecule inhibition of cytochrome bd

Ping Lu,Holger Lill,Martijn Kremer,Amer H Asseri,Dirk Bald,Roy Ummels,Janneke Maaskant

doi:10.1038/s41598-018-20989-8

Abstract

Mycobacterial energy metabolism currently attracts strong attention as new target space for development of anti-tuberculosis drugs. The imidazopyridine Q203 targets the cytochrome bcc complex of the respiratory chain, a key component in energy metabolism. Q203 blocks growth of Mycobacterium tuberculosis at nanomolar concentrations, however, it fails to actually kill the bacteria, which may limit the clinical applicability of this candidate drug. In this report we show that inhibition of cytochrome bd, a parallel branch of the mycobacterial respiratory chain, by aurachin D invoked bactericidal activity of Q203. In biochemical assays using inverted membrane vesicles from Mycobacterium tuberculosis and Mycobacterium smegmatis we found that inhibition of respiratory chain activity by Q203 was incomplete, but could be enhanced by inactivation of cytochrome bd, either by genetic knock-out or by inhibition with aurachin D. These results indicate that simultaneously targeting the cytochrome bcc and the cytochrome bd branch of the mycobacterial respiratory chain may turn out as effective strategy for combating M. tuberculosis.

Highlights

Tuberculosis (TB) chemotherapy has averted 49 million deaths globally between 2000 and 2015, but important treatment gaps still persist[1]
We explore if small-molecule inhibition of cytochrome bd can enhance the activity of a cytochrome bcc inhibitor, Q203, against M. tuberculosis
In line with previously reported results[30], treatment of the M. tuberculosis H37Rv strain used in our laboratory with Q203 resulted in only a marginal decrease of colony forming units (Supplementary Figure 1)

Summary

Introduction

Tuberculosis (TB) chemotherapy has averted 49 million deaths globally between 2000 and 2015, but important treatment gaps still persist[1]. The regulatory approval of the ATP synthase inhibitor bedaquiline (BDQ), the first within 40 years for a TB drug, validated the oxidative phosphorylation pathway in Mycobacterium tuberculosis as target for treatment of tuberculosis[2,3,4,5]. Q203, the lead compound of the imidazopyridine amide class of drugs, targets the cytochrome bcc complex[12], a variant of the cytochrome bc[1] complex (complex III) found in the respiratory chain of mycobacteria and other actinobacteria[13]. Cytochrome bd facilitates metabolic adaptation of certain M. tuberculosis laboratory strains, including the reference strain H37Rv, to imidazopyridine-type cytochrome bcc inhibitors[29] These adapted strains displayed considerably elevated minimal inhibitory concentrations (MICs) for Q203, effectively evading growth inhibition by these drugs[29]. We explore if small-molecule inhibition of cytochrome bd can enhance the activity of a cytochrome bcc inhibitor, Q203, against M. tuberculosis

Methods

Results

Conclusion