The Mce3R Regulon Is Required for 6-Azasteroid Potentiation of Anti-TB Drug Activity

Cholesterol is important for <i>Mycobacterium tuberculosis (Mtb)</i> survival and persistence in the host. We describe a series of 6-azasteroids tested as cholesterol analogs, that are synergistic inhibitors of <i>Mtb</i> viability. The analogs improve <i>Mtb</i> killing efficacy by isoniaizid and bedaquiline, two approved drugs for the treatment of drug-sensitive and drug-resistant <i>Mtb</i>, respectively. In addition, the 6-azasteroids work with existing TB drugs under anaerobic conditions and lower their MICs by greater than 10-fold, suggesting they will work in hypoxic conditions found in infected lungs. <div><br><div>Our work provides strong evidence for an expanded repertoire of cholesterol utilization in <i>Mtb</i> infection that extends beyond the commonly accepted role of cholesterol in nutrition and primary energy generation. We discovered that a stress-resistance regulon (Mce3R) is required for the synergistic activity of 6-azasteroids. Moreover, we demonstrate that cholesterol catabolism is not required for the activity of these inhibitors. Earlier Cirillo, Jacobs and coworkers, established that the <i>mel2</i> operon residing in the Mce3R regulon is important for persistence and dissemination of <i>Mtb</i> infection in mice (DOI: 10.1128/IAI.01481-08). Thus, an important role of cholesterol utilization for survival of <i>Mtb</i> infection is stress resistance.</div><div>Importantly, we demonstrate that this stress-resistance pathway is vulnerable to small molecule targeting. </div></div>