Ammonium salts of carbamodithioic acid as potent vaginal trichomonacides and fungicides

• Ammonium salts of carbamodithioic acid were designed to inhibit free thiols.
• Anaerobes like sperm, T. vaginalis, C. albicans and S. aureus were found susceptible.
• Drug-resistant and -susceptible strains were equally susceptible.
• A unique scaffold is discovered for development as vaginal microbicides.

Chemical attenuation of the reactive oxygen species (ROS)-sensitive anaerobes Trichomonas vaginalis, which is the most prevalent non-viral sexually transmitted infection, and two often coexisting vaginal infections, namely Candida albicans and Staphylococcus aureus, which are opportunistic reproductive tract infections, was attempted with novel ammonium salts of carbamodithioic acid through inhibition of free thiols. In vitro and in vivo efficacies of the designed compounds were evaluated as topical vaginal microbicides. Five compounds showed exceptional activity against drug-resistant and -susceptible strains with negligible toxicity to host (HeLa) cells in vitro in comparison with the standard vaginal microbicide nonoxynol-9 (N-9), without disturbing the normal vaginal flora (i.e. Lactobacillus). The compounds significantly inhibited the cytopathic effects of Trichomonas on HeLa cells in vitro with efficacies comparable with metronidazole (MTZ); however, their efficacy to rescue host cells from co-infection (protozoal and fungal) was greater than that of MTZ. The compounds inhibited β-haemolysis of red blood cells caused by Trichomonas and were found to be active in vivo in the mouse subcutaneous abscess assay. Some compounds rapidly immobilized human sperm. A mechanism involving inhibition of free thiols and consequently the cysteine proteases of T. vaginalis by the new compounds has been proposed. Thus, a unique scaffold of antimicrobial agents has been discovered that warrants further investigation for development as contraceptive vaginal microbicides.