A synthetic diterpene analogue inhibits mycobacterial persistence and biofilm formation by targeting (p)ppGpp synthetases

Bacterial persistence coupled with biofilm formation is directly associated with failure of antibiotic treatment of TB. We have now identified 4-(4,7-DiMethyl-1,2,3,4-tetrahydroNaphthalene-1-yl)Pentanoic acid (DMNP), a synthetic diterpene analogue, as a lead compound that was capable of suppressing persistence and eradicating biofilms in Mycobacterium smegmatis. By using two reciprocal experimental approaches – DrelMsm and DrelZ gene knockout mutations versus relMsm and relZ overexpression technique – we showed that both RelMsm and RelZ (p)ppGpp synthetases are plausible candidates for serving as targets for DMNP. In vitro, DMNP inhibited (p)ppGpp synthesizing activity of purified RelMsm in a concentration-dependent manner. These findings, supplemented by molecular docking simulation, suggest that DMNP targets the structural sites shared by RelMsm, RelZ and presumably by a few others as yet unidentified (p)ppGpp producers, thereby inhibiting persister cell formation and eradicating biofilms. Therefore, DMNP may serve as a promising lead for development of antimycobacterial drugs.