Miconazole - domiphen bromide: a fungicidal combination treatment against biofilms of various azole-sensitive and azole-resistant Candida spp.

Background: Mucosal biofilm-related Candida infections are very common and can occur for example on genital organs. Such infections are difficult to treat, since miconazole (MCZ), the preferred topical treatment, is only moderately active against biofilms. We discovered a fungicidal combination consisting of MCZ and a quaternary ammonium compound, domiphen bromide (DB), that is active against biofilms of C. albicans and C. glabrata. Here we investigated the activity spectrum of MCZ-DB, the combination's effect in vivo and its mode of action. Materials/methods: Activity against C. albicans, C. auris and C. glabrata biofilm and planktonic stationary cultures was assessed by treating cultures with MCZ, DB or a combination and performing CFU determination after 24h (biofilms) or 2,5h (planktonic cultures) treatment. The in vivo activity of the MCZ-DB combination was examined in a Candida vaginitis rat model during 14 days. The combination treatment's mode of action was studied in planktonic C. glabrata cultures, using a fluorescently labeled ketoconazole derivative (FKD) (1) to investigate the effect of DB on azole uptake and its subcellular localization, via FACS analysis and confocal microscopy, respectively. BCECF-AM staining was used to study DB's effects on C. glabrata vacuolar pH. Results: MCZ-DB leads to a significant CFU reduction as compared to single compound treatments in biofilms of azole-resistant C. albicans isolates, C. auris biofilms and planktonic cultures of C. albicans and C. glabrata in stationary phase. Moreover, the combination treatment significantly reduces the infection burden as compared to single compound treatment in an in vivo vaginitis rat model. Apparently DB (i) enables increased FKD uptake in C. glabrata cells at low doses, (ii) alters cytoplasmic distribution of high FKD doses and (iii) negatively affects vacuolar integrity. Conclusion: Our data reveal that MCZ-DB combination treatment has fungicidal antibiofilm activity against various azole-resistant and azole-sensitive Candida spp., probably because DB increases intracellular MCZ availability. 1 Benhamou R. I., Bibi M., Steinbuch K. B., Engel H., Levin M., Roichman Y., Berman J. and Fridman M. (2017). Real-Time Imaging of the Azole Class of Antifungal Drugs in Live Candida Cells. ACS Chemical Biology, 2017; 12, 1769−1777.