New antibacterial agents targeting mycobacterial the ATP synthase

Background: A set of 700 compounds found active after the whole cell screening of 20,000 compounds library against Mycobacterium tuberculosis H37Rv was screened in the ATP synthase assay. Three compounds showed promising IC50 and were further evaluated in the time kill assay and combination studies with first line anti-TB drugs against M tuberculosis H37Rv. The compounds were tested for cytotoxicity against HepG-2 cell lines Methods & Materials: ATP synthase assay was performed using the inverted membrane vesicles of Mycobacterium smegmatis for the screening of the 700 compounds by estimating the ATP production. In-vitro activities of the selected compounds were done by microdilution method, cell toxicity profile using MTT assay in HepG2 cell line, in vitro time kill assay and combinational studies with first line drugs. Results: Three compounds C1-C3 showing promising inhibitory activity (IC50 values 0.13-4.0 M) in the in-vitro ATP synthase inhibition assay also exhibited potent anti-mycobacterial activity (MIC-0.06-2.0 g/ml). These compounds were nontoxic in HepG2 cell line, Compound C1 was bactericidal at 8X MIC (1 g/ml) and exhibited synergistic activity with rifampicin. Conclusion: ATP synthase screening of whole cell active compounds from IIIM repository led to the identification of three compounds showing good inhibitory activity against ATP synthase. All the compounds displayed promising anti-mycobacterial potential with no detected toxicity against mammalian cell line. Compound (C1) showed synergistic activity with rifampicin, which forms the backbone of anti-TB therapy. These compounds represents novel chemotypes against ATP synthase and can be taken up for medicinal chemistry efforts.