Efflux pump inhibition by 11H-pyrido[2,1-b]quinazolin-11-one analogues in mycobacteria

Mycobacterium tuberculosis infection causes 1.8 million deaths worldwide, of which half a million has been diagnosed with resistant tuberculosis (TB). Emergence of multi drug resistant and extensive drug resistant strains has made all the existing anti-TB therapy futile. The major involvement of efflux pump in drug resistance has made it a direct approach for therapeutic exploration against resistant M. tuberculosis. This study demarcates the role of 11H-pyrido[2,1-b]quinazolin-11-one (quinazolinone) analogues as efflux pump inhibitor in Mycobacterium smegmatis. Sixteen quinazolinone analogues were synthesized by treating 2-aminopyridine and 2-fluorobenzonitrile with KtOBu. Analogues were tested, and 3a, 3b, 3c, 3g, 3j, 3l, 3m, and 3p were found to modulate EtBr MIC by >4 whereas 3a, 3g, 3i and 3o showed >4 modulation on norfloxacin MIC. 3l and 3o in addition to their very low toxicity they showed high EtBr and norfloxacin accumulation respectively. Time kill curve showed effective log reduction in colony forming unit in presence of these analogues, thus confirming their role as efflux pump inhibitor. Through docking and alignment studies, we have also shown that the LfrA amino acid residues that the analogues are interacting with are present in Rv2333c and Rv2846c of M. tuberculosis. This study have shown for the first time the possibility of developing the 11H-pyrido[2,1-b]quinazolin-11-one analogues as efflux pump inhibitors for M. smegmatis and hence unbolts the scope to advance this study against resistant M. tuberculosis as well.