A Series of Pyrazolo-Quinazoline Amines Inhibits the Cytochrome <i>bd</i> Oxidase in <i>Mycobacterium tuberculosis</i>

The <i>Mycobacterium tuberculosis</i> cytochrome <i>bcc:aa</i>₃ (cyt-<i>bcc:aa</i>₃) oxidase is a validated drug target for tuberculosis treatment. In addition to telacebec (Q203), a clinical-stage drug candidate, several preclinical cyt-<i>bcc</i>:<i>aa</i>₃ inhibitors have been reported. However, the bactericidal potency of cyt-<i>bcc</i>:<i>aa</i>₃ inhibitors is limited by cytochrome bd oxidase (cyt-<i>bd</i>), an alternative terminal oxidase. We developed a high-throughput whole-mycobacteria assay to identify new cyt-<i>bd</i> inhibitors. Screening 115,398 small molecules identified several new chemical series, including a pyrazolo-quinazoline amine series. Chemical optimization yielded the potent derivative ETX1975-3, which, in combination with Q203, is bactericidal against <i>M. tuberculosis</i>, retains activity against a panel of M/XDR <i>M. tuberculosis</i> clinical isolates, and also shows efficacy against nontuberculous mycobacteria (NTM). Mode of action studies validated the cyt-<i>bd</i> target as the molecular target. While further chemical optimization is required, favorable microbiological, ADMET, and in vivo potency of ETX1975-3 makes it a promising preclinical candidate for tuberculosis and NTM infections.