A monovalent SMAC mimetic as a potential host-directed therapy for tuberculosis.

Abstract

Tuberculosis (TB) caused by the Mycobacterium tuberculosis complex (MTBC) is the leading cause of death from a single infectious agent worldwide. Current antibiotics fail against drug-resistant strains, highlighting the urgent need for novel therapies. Host-directed therapy (HDT), which enhances host immunity rather than targeting pathogens directly, offers a promising solution. In this study, we use the in vitro cells infection assays and in vivo mouse infection model to identify the effects of a monovalent second mitochondria-derived activator of caspases (SMAC) mimetic named BI82 against mycobacterial infections. Here, we demonstrate that BI82 potently inhibits M. bovis growth in Raw264.7 macrophages, bone marrow-derived macrophages, and peripheral blood mononuclear cells, while exhibiting synergy with rifampicin. BI82 also significantly restricts M. tuberculosis growth in ex vivo whole-blood assays from both tuberculosis patients and healthy donors. Mechanistically, BI82 degrades cellular inhibitor of apoptosis protein 1 (cIAP1), promoting infected cell apoptosis as evidenced by elevated cleaved caspase-3 and phosphorylated MLKL levels. Caspase inhibition abrogates BI82's anti-mycobacterial effects, confirming apoptosis as the primary therapeutic pathway. In a mouse model, oral BI82 treatment degraded cIAP1, reduced M. bovis burden in lungs and spleens, alleviated lung lesions, and increased CD3⁺ T cells with elevated CD4/CD8 ratios. Notably, different SMAC mimetics showed pathogen-specific efficacy profiles, with monovalent compounds (BI82, LCL161) demonstrating superior activity compared to bivalent Birinapant against M. bovis. This study highlights BI82's unique apoptosis-dependent mechanism and broad-spectrum potential against mycobacterial infections, including drug-resistant TB, positioning it as a promising HDT candidate.