New TB lead starves bacteria of vitamin B6 to kill drug‑resistant strains

Tuberculosis remains the top killer among single infectious agents worldwide, and rising multi-drug resistance means new ways to kill Mycobacterium tuberculosis (Mtb) are urgently needed. In work led by corresponding author Alain R. Baulard, researchers characterized a small molecule called BVL3572S — a hydroxamic acid-containing compound — that is bactericidal and potently blocks growth of both extracellular and intracellular Mtb. Rather than working like classic antibiotics that hit a single bacterial machine, BVL3572S attacks the bacterium’s reliance on pyridoxal phosphate (PLP), the active form of vitamin B6 that many enzymes need to function. By interfering with PLP-dependent processes, the compound creates broad metabolic stress in the pathogen. The team combined genetic, biochemical and structural approaches to follow how BVL3572S works and to identify which bacterial proteins it affects, building a case for a new therapeutic strategy that exploits a vitamin B6 vulnerability in Mtb.

To pinpoint BVL3572S’s action, the authors used integrated transcriptomic, genetic, and biochemical analyses. These experiments identified the PLP-dependent aminotransferases HisC (Rv1600) and AlaA (Rv0337c; formerly AspC) as the primary molecular targets, meaning the compound simultaneously disrupts L-histidine and L-alanine biosynthesis. Spontaneous resistance mutants harbored mutations in hisC or alaA. Target engagement was supported by overexpression studies: AlaA overexpression increased resistance in the presence of L-His whereas HisC overexpression paradoxically increased susceptibility. X-ray crystallography revealed a covalent adduct between PLP and BVL3572S within the HisC active site, and the short occupancy of this adduct suggests a futile cycle that sequesters PLP. Isotopic labeling showed widespread perturbation of amino acid biosynthesis consistent with PLP starvation. Stepwise resistance upon supplementation with L-His and L-Ala together or with PLP alone further suggests inhibition of multiple targets. Genome-scale CRISPRi and Tn-seq analyses pointed to downstream disruptions in central metabolism, cell envelope integrity, and redox balance. Finally, consistent with AlaA inhibition, BVL3572S showed strong synergy with D-cycloserine, a second-line antitubercular drug that targets D-alanine synthesis and peptidoglycan assembly.

Taken together, these findings establish BVL3572S as a promising lead that acts through a previously unexploited, multitarget mechanism in Mtb. By forming a covalent PLP–BVL3572S adduct in HisC and affecting AlaA, the compound appears to trigger a cascade of metabolic failures that extend beyond single-enzyme inhibition, effectively inducing PLP starvation and broad biosynthetic stress. That multitarget profile may help explain why resistance arose through stepwise changes and why supplementation experiments can partially reverse the effect — hallmarks of a mechanism that touches core metabolism rather than a single pathway. The observed synergy with D-cycloserine highlights practical opportunities for combination therapy that could strengthen existing regimens, especially against strains resistant to frontline drugs. Overall, the study points to vitamin B6 dependency as a fertile, previously underused vulnerability in Mtb and positions BVL3572S as a candidate for further development toward new treatments for drug-resistant tuberculosis.