QcrB inhibitor (Fimbrion Therapeutics)

Fimbrion Therapeutics is developing a series of 4-amino-thieno[2,3-d]pyrimidine small molecule inhibitors targeting the QcrB protein (ubiquinol-cytochrome C reductase cytochrome b subunit) in *Mycobacterium tuberculosis*. By inhibiting QcrB, a key component of the mycobacterial respiratory electron transport chain, these compounds disrupt bacterial respiration and deplete ATP levels, resulting in bactericidal activity. This program, in-licensed from intellectual property developed at Washington University and Saint Louis University, is designed to treat both drug-sensitive and multidrug-resistant tuberculosis (MDR-TB) through a novel mechanism of action that avoids cross-resistance with existing antibiotics. As of 2025, the program has demonstrated efficacy in mouse models and received NIH Small Business Innovation Research (SBIR) funding to support its advancement toward clinical development.

Other names

4-amino-thieno[2,3-d]pyrimidine seriesHeterocyclic compound (TB program)QcrB-targeting small molecule