A Series of Pyrazolo-Quinazoline Amines Inhibits the Cytochrome bd Oxidase in Mycobacterium tuberculosis

The Mycobacterium tuberculosis cytochrome bcc:aa₃ (cyt-bcc:aa₃) oxidase is a validated drug target for tuberculosis treatment. In addition to telacebec (Q203), a clinical-stage drug candidate, several preclinical cyt-bcc:aa₃ inhibitors have been reported. However, the bactericidal potency of cyt-bcc:aa₃ inhibitors is limited by cytochrome bd oxidase (cyt-bd), an alternative terminal oxidase. We developed a high-throughput whole-mycobacteria assay to identify new cyt-bd 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 M. tuberculosis, retains activity against a panel of M/XDR M. tuberculosis clinical isolates, and also shows efficacy against nontuberculous mycobacteria (NTM). Mode of action studies validated the cyt-bd 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.