Carglumic acid and mesalazine as potential anti-mycobacterial agents: a spectroscopic study for repurposing drugs against <i>Mycobacterium tuberculosis</i> targeting its essential enzyme ThyX

<i>Mycobacterium tuberculosis (M.tb</i>) needs a key enzyme called ThyX to make thymidylate, which is essential for DNA replication and cell survival. In our previous study, carglumic acid (CGA) and mesalazine (MSZ) emerged as promising candidates from a Food and Drug Administration-approved drug library, selected through <i>in silico</i> screening. Our current investigation delves into the impact of CGA and MSZ on ThyX's biophysical properties. Utilizing fluorescence quenching, thermal, chemical denaturation, characterization, and circular dichroism spectroscopy, we probed the interaction between ThyX and the drugs. Our results confirm that both CGA and MSZ effectively quench ThyX's intrinsic fluorescence via a static quenching mechanism, leading to structural alterations in the protein. In subsequent <i>in vitro</i> and <i>ex vivo</i> studies, we determined that MSZ and CGA exhibit minimum inhibitory concentrations of 6.25 and 3.12 µg/mL, respectively, against <i>M.tb</i>. Notably, the survival of <i>M.tb</i> within RAW macrophages significantly decreased upon treatment with CGA and MSZ compared to untreated controls. In summary, our findings support the potential repurposing of CGA and MSZ as anti-tuberculosis (TB) drugs. Further validation in animal and clinical models is essential to assess their suitability for TB treatment.IMPORTANCEThyX (<i>Rv2754c</i>), flavin-dependent thymidylate synthase, is a crucial enzyme required by <i>Mycobacterium tuberculosis</i> for DNA replication and RNA maturation, making it a potential drug target to explore novel anti-tuberculosis (TB) treatments. Given the essentiality of ThyX, it was screened against Food and Drug Administration-approved drugs using molecular docking screening, and carglumic acid (CGA) and mesalazine (MSZ) were selected as potential inhibitors. To validate and explore their anti-mycobacterial potential, molecular dynamic simulation of these drugs in the presence of ThyX was carried out, and these studies were validated using <i>in vitro</i> biophysical characterization to establish their binding kinetics and effects of these drugs on the stability and structural changes of ThyX. Lastly, <i>in vitro</i> and <i>ex vivo</i> anti-mycobacterial activity of CGA and MSZ establish them as probable candidates for management of TB.