Exploiting the synthetic lethality between terminal respiratory oxidases to kill <i>Mycobacterium tuberculosis</i> and clear host infection

Abstract

The recent discovery of small molecules targeting the cytochrome <i>bc</i>_<i>1</i> :<i>aa</i>_<i>3</i> in <i>Mycobacterium tuberculosis</i> triggered interest in the terminal respiratory oxidases for antituberculosis drug development. The mycobacterial cytochrome <i>bc</i>_<i>1</i> :<i>aa</i>_<i>3</i> consists of a menaquinone:cytochrome <i>c</i> reductase (<i>bc</i>_<i>1</i> ) and a cytochrome <i>aa</i>_<i>3</i> -type oxidase. The clinical-stage drug candidate Q203 interferes with the function of the subunit b of the menaquinone:cytochrome <i>c</i> reductase. Despite the affinity of Q203 for the <i>bc</i>_<i>1</i> :<i>aa</i>_<i>3</i> complex, the drug is only bacteriostatic and does not kill drug-tolerant persisters. This raises the possibility that the alternate terminal <i>bd</i>-type oxidase (cytochrome <i>bd</i> oxidase) is capable of maintaining a membrane potential and menaquinol oxidation in the presence of Q203. Here, we show that the electron flow through the cytochrome <i>bd</i> oxidase is sufficient to maintain respiration and ATP synthesis at a level high enough to protect <i>M. tuberculosis</i> from Q203-induced bacterial death. Upon genetic deletion of the cytochrome <i>bd</i> oxidase-encoding genes <i>cydAB</i>, Q203 inhibited mycobacterial respiration completely, became bactericidal, killed drug-tolerant mycobacterial persisters, and rapidly cleared <i>M. tuberculosis</i> infection in vivo. These results indicate a synthetic lethal interaction between the two terminal respiratory oxidases that can be exploited for anti-TB drug development. Our findings should be considered in the clinical development of drugs targeting the cytochrome <i>bc</i>_<i>1</i> :<i>aa</i>_<i>3</i> , as well as for the development of a drug combination targeting oxidative phosphorylation in <i>M. tuberculosis</i>.