Antimicrobial Effects of Tol-463 on Neisseria Gonorrhoeae

Background:  Neisseria gonorrhoeae (NG), a common sexually transmitted bacterial pathogen, quickly develops resistance to antibiotics, limiting our ability to treat gonorrhea and highlighting the need for new therapeutic options.  TOL-463, a boric acid (BA) based vaginal anti-infective enhanced with ethylenediaminetetraacetic acid (EDTA), has shown antibacterial/antifungal activity and is in clinical development for treatment of lower genital tract infections.  The objective of this study was to evaluate the in vitro antimicrobial activity of TOL-463 against NG.

Methods:  NG reference strains exhibiting low (F18) and high (SPL4) antibiotic resistance profiles were grown in liquid media in shaking 96-well plates at 37° under 5% CO₂.  Phosphate buffered saline (PBS), EDTA alone, BA alone, or TOL-463 (EDTA-BA combined) were co-incubated with each strain to determine optimal drug concentrations.  Penicillin and ciprofloxacin alone or in combination with EDTA and TOL-463 were also tested to evaluate synergistic antibacterial effects.  At designated time points from 0 h to 24 h, co-cultures were serially diluted and plated.  Colonies were counted and reported as colony forming units (CFUs) per ml.

Results: A ≥4-log reduction in CFUs was observed with 1% EDTA and TOL-463 by 5 h compared to PBS control.  Optimal (1%) EDTA and TOL-463 concentrations inhibited NG growth at the same rate or faster than the reference minimum inhibitory concentration of penicillin or ciprofloxacin for each strain.  Furthermore, suboptimal penicillin and ciprofloxacin concentrations in combination with 1% EDTA or TOL-463 resulted in a ≥4-log reduction in CFUs compared to antibiotic controls.

Conclusions: TOL-463 has antimicrobial activity equal to or better than traditional antibiotics and enhances the inhibitory capacity of these drugs in vitro at suboptimal concentrations.  TOL-463 may have potential for augmenting treatment of antibiotic resistant NG.