Trichomonacidal Activity of 3,3′-Diindolylmethane (DIM) Is Additive to Metronidazole (MTZ) In Vitro, Supporting Future Oral/Topical Use ^†

New, safe, well tolerated, and versatile anti-trichomonal agents for oral and topical use are needed to combat spreading resistance of Trichomonas vaginalis to metronidazole (MTZ). Diindolylmethane (DIM) is a non-toxic, cruciferous indole under pharmaceutical development for treatment of cervical and prostatic pre-cancers. Present work reports anti-trichomonal activity of DIM with IC₅₀ hundreds of times below the DIM concentration provided in a clinic-ready, sustained-release, vaginal-topical formulation (BR-DIM-VC™ 2%) which has passed vaginal tolerance testing in rabbits. Present in vitro findings against T. vaginalis exhibit additive effects of DIM with MTZ, significantly reducing the IC₅₀ for MTZ (p < 0.05). Combinatorial activity with MTZ was demonstrated using DIM dissolved in DMSO and in a novel self-emulsifying lipid-based formulation, BR-9001, showing a statistically significant enhanced effect of BR-9001 over DIM (DMSO) (p < 0.05). Improved bio-delivery of DIM from BR-9001 confirmed DIM’s concentration-dependent trichomonacidal activity. Performed in triplicate, the anti-parasitic results are: IC_{50 DIM-DMSO} = 91.8 µM, IC_{50 BR-9001} = 30.65 µM *, IC_{50 MTZ} = 2.34 µM, IC_{50 MTZ(0.75uM)+DIM(37.5uM)} = 1.6 µM * and IC_{50 MTZ(0.75uM)+BR9-001(37.5uM)} = 0.8 µM *, * = p < 0.05.

Considering the nonexistent therapeutic alternatives for trichomonosis treatment in patients with hypersensitivity to 5-nitroimidazoles or against resistant cases, the combined use of DIM + MTZ for oral and topical administration provides a promising new therapeutic opportunity.