Turning the respiratory flexibility of Mycobacterium tuberculosis against itself

Abstract

The Mycobacterium tuberculosis (Mtb) electron transport chain (ETC) has received significant attention as a drug target, however its vulnerability may be affected by its flexibility in response to disruption. Here we determine the effect of the ETC inhibitors bedaquiline, Q203 and clofazimine on the Mtb ETC, and the value of the ETC as a drug target, by measuring Mtb's respiration using extracellular flux technology. We find that Mtb's ETC rapidly reroutes around inhibition by these drugs and increases total respiration to maintain ATP levels. Rerouting is possible because Mtb rapidly switches between terminal oxidases, and, unlike eukaryotes, is not susceptible to back pressure. Increased ETC activity potentiates clofazimine's production of reactive oxygen species, causing rapid killing in vitro and in a macrophage model. Our results indicate that combination therapy targeting the ETC can be exploited to enhance killing of Mtb.

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

“…To unleash the full potential of drugs targeting the Cyt-bc 1 :aa 3 branch, we advocate for the development of Cyt-bd inhibitors. It was previously suggested that interference with oxidative phosphorylation at multiple levels is a promising anti-TB strategy (24). Our data indicate that a drug combination targeting simultaneously the Cyt-bc 1 :aa 3 , the Cyt-bd, and the F 1 F o -ATP synthase may represent the cornerstone of a complementary sterilizing drug combination for the treatment of MDR and XDR tuberculosis.…”

“…A recent study revealed that Q203 and BDQ treatment triggered an increase in oxygen consumption rate (OCR) up to 16 h posttreatment, which is counterintuitive given the capacity of the drugs to interfere with respiration. Interestingly, increase in OCR was only observed at a very high dose of drugs (300× MIC), but not at an intermediate dose (30× MIC) (24). Consequently, we were interested in gaining more mechanistic insight into the ETC adaptations to Q203 and BDQ and their long-term effects on oxygen respiration.…”

Antibiotic efficacy — context matters

“…Targeted metabolomic studies have revealed significant changes in intracellular energy metabolites following antibiotic treatment [29-31], corroborated by live-cell imaging experiments directly measuring transient changes in ATP [32]. Experiments using the Seahorse XF Analyzer have captured real-time increases to cellular respiration by bactericidal antibiotics [33-35], complementing real-time measurements of overflow ROS production using electrochemical [36] or genetically encoded biosensors [33]. Interestingly, integrated analyses of transcriptomic and metabolomic data have revealed TCA cycle activity to be critical for antibiotic lethality, independent from drug uptake [37].…”

“…For instance, penicillin-binding protein disruption by β-lactams stimulates a futile cycle of cell wall synthesis and degradation that depletes cellular resources as part of its toxicity [48,49]. In addition, ATP synthase inhibition by bedaquiline stimulates futile cycling of protons in the respiratory chain [50], which increases oxygen consumption [35] and is lethal to M. tuberculosis [51]. Moreover, genetically induced futile cycling in MazF-mediated RNA degradation has been shown to confer complete protection against β-lactam and quinolone lethality, but potentiate sensitivity to aminoglycosides [52].…”

“…Under normoxia, oxygen participates in aerobic respiration as the terminal electron acceptor for ATP synthesis and produces reactive species as metabolic byproducts [35]. In such conditions, antibiotic efficacy is linked to respiratory activity; for example, deletion of the cytochrome oxidases, which reduces respiration, inhibits drug lethality [34], while deletion of ATP synthase subunits, which increases respiration, enhances lethality [34,69].…”