Combination Therapy to Treat Fungal Biofilm-Based Infections.

An increasing number of people is affected by fungal biofilm-based infections, which are resistant to the majority of currently-used antifungal drugs. Such infections are often caused by species from the genera Candida, Aspergillus or Cryptococcus. Only a few antifungal drugs, including echinocandins and liposomal formulations of amphotericin B, are available to treat such biofilm-based fungal infections. This review discusses combination therapy as a novel antibiofilm strategy. More specifically, in vitro methods to discover new antibiofilm combinations will be discussed. Furthermore, an overview of the main modes of action of promising antibiofilm combination treatments will be provided as this knowledge may facilitate the optimization of existing antibiofilm combinations or the development of new ones with a similar mode of action.

Combination of Miconazole and Domiphen Bromide Is Fungicidal against Biofilms of Resistant Candida spp.

The occurrence and recurrence of mucosal biofilm-related Candida infections, such as oral and vulvovaginal candidiasis, are serious clinical issues. Vaginal infections caused by Candida spp., for example, affect 70 to 75% of women at least once during their lives. Miconazole (MCZ) is the preferred topical treatment against these fungal infections, yet it has only moderate antibiofilm activity. Through screening of a drug-repurposing library, we identified the quaternary ammonium compound domiphen bromide (DB) as an MCZ potentiator against Candida biofilms. DB displayed synergistic anti-Candida albicans biofilm activity with MCZ, reducing the number of viable biofilm cells 1,000-fold. In addition, the MCZ-DB combination also resulted in significant killing of biofilm cells of azole-resistant C. albicans, C. glabrata, and C. auris isolates. In vivo, the MCZ-DB combination had significantly improved activity in a vulvovaginal candidiasis rat model compared to that of single-compound treatments. Data from an artificial evolution experiment indicated that the development of resistance against the combination did not occur, highlighting the potential of MCZ-DB combination therapy to treat Candida biofilm-related infections.

Combining Miconazole and Domiphen Bromide Results in Excess of Reactive Oxygen Species and Killing of Biofilm Cells.

Fungal biofilm-related infections are increasingly occurring. We previously identified a fungicidal antibiofilm combination, consisting of miconazole (MCZ) and the quaternary ammonium compound domiphen bromide (DB). DB eliminates tolerance rather than altering the susceptibility to MCZ of various Candida spp. Here we studied the mode of action of the MCZ-DB combination in more detail. We found that DB's action increases the permeability of the plasma membrane as well as that of the vacuolar membrane of Candida spp. Furthermore, the addition of DB affects the intracellular azole distribution. MCZ is a fungicidal azole that, apart from its well-known inhibition of ergosterol biosynthesis, also induces accumulation of reactive oxygen species (ROS). Interestingly, the MCZ-DB combination induced significantly more ROS in C. albicans biofilms as compared to single compound treatment. Co-administration of the antioxidant ascorbic acid resulted in abolishment of the ROS generated by MCZ-DB combination as well as its fungicidal action. In conclusion, increased intracellular MCZ availability due to DB's action results in excess of ROS and enhanced fungal cell killing.