New natural compounds bind tuberculosis enzyme CYP124

Tuberculosis remains a leading global health threat, made worse by the rise of drug-resistant strains. Scientists are searching for new bacterial targets to overcome resistance, and one promising candidate is the cytochrome P450 of the 124 family, CYP124, from Mycobacterium tuberculosis (CYP124). CYP124 has been implicated in host sterol metabolism and bacterial virulence, and although its precise physiological role was debated, its confirmed ability to metabolize immunomodulatory host sterols gives it clear pharmacological relevance. Under the direction of corresponding author Leonid Kaluzhskiy, the research team set out to find small molecules from natural sources that interact with CYP124. Rather than testing standard drug scaffolds, they screened a focused library of 32 plant-derived and marine natural compounds to search for new, non-azole molecules that could bind and potentially inhibit CYP124. The goal was to identify chemical starting points that link the enzyme’s role in sterol handling to opportunities for therapeutic intervention against multidrug-resistant tuberculosis.

To find CYP124 ligands the team used surface plasmon resonance binding assays and UV-Vis spectral titration screening to measure direct interactions and characteristic spectral changes. From the 32-compound library they identified nine novel non-azole ligands that showed measurable binding to CYP124. Two standout hits were (25S)-5α-cholestane-3β,4β,6α,7α,8,15β,16β,26-octaol (termed 15β-octaol) and henricioside H 2 (HD-4). Both induced characteristic difference spectra and formed long-lived inhibitory complexes with CYP124, with dissociation half-lives of 181 min for 15β-octaol and 65 min for HD-4. Despite these long-lived complexes, inhibitory potency was moderate: IC50 values were approximately 86 μM for 15β-octaol and greater than 100 μM for HD-4. Complementary in silico molecular docking and analysis pinpointed conserved hydrophobic residues in the CYP124 active site that appear critical for binding, suggesting a shared pharmacophore among the ligands. Structural similarity analysis then showed that 37 human endogenous metabolites, including known immunoregulatory sterols, resemble the identified CYP124 ligands.

These findings have several important implications. Identifying nine natural, non-azole ligands establishes a chemical foothold for developing mechanism-based CYP124 inhibitors as potential therapeutics against multidrug-resistant tuberculosis. The long-lived inhibitory complexes formed by 15β-octaol and HD-4 are encouraging because they show the enzyme can be trapped by small molecules, but the moderate IC50 values make clear that chemical optimization is needed to reach the potency required for a drug. The docking results and the conserved hydrophobic residues give medicinal chemists concrete structural features to target, while the similarity to 37 human endogenous metabolites hints at a sterol-mediated interplay at the host-pathogen interface that could be exploited therapeutically or require caution for selectivity. Overall, the study by Leonid Kaluzhskiy and collaborators provides a foundation of assays, chemical hits, and structural hypotheses that can guide further chemistry, biological testing, and eventual evaluation in infection models as part of the long road toward new treatments for resistant tuberculosis.