Duloxetine repositioning: Investigation of antifungal and antibiofilm activity against fluconazole-sensitive and resistant Candida Spp. strains

The increase in fungal infections, the limited therapeutic arsenal, and the emergence of resistance pose a global health problem. Candida spp. stand out as opportunistic pathogens that cause superficial and invasive diseases. Thus, the search for new therapeutic alternatives, such as drug repositioning, is necessary. Duloxetine (DUL), a serotonin-norepinephrine reuptake inhibitor antidepressant used to treat depression, has demonstrated antifungal activity and potentiates the effects of conventional antifungals in vitro. The objective of this study is to evaluate the in vitro activity of duloxetine (DUL) against resistant Candida spp. strains. To this end, the minimum inhibitory concentration (MIC) of DUL alone and in combination with conventional antifungals was determined in order to evaluate the type of interaction between them, as well as the minimum fungicidal concentration (MFC). The activity of DUL against mature and developing biofilms was evaluated, in addition to the possible antifungal mechanism of action. DUL showed MICs of 16 to 128 µg/mL with a fungicidal action profile, and when combined there was synergistic interaction with amphotericin B (AMB). In biofilms, DUL exhibited antibiofilm activity and enhanced AMB activity against developing, but not mature, biofilms. Mechanism of action analysis showed that DUL promoted oxidative stress, evidenced by increased reactive oxygen species (ROS) production, reduced GSH levels, mitochondrial depolarization, and phosphatidylserine externalization, suggesting the activation of the apoptotic pathway as a possible mechanism of cell death. The pro-oxidant effects of DUL were evident in C. albicans strains deficient in antioxidant defenses (cap1Δ and gpx3Δ) compared to the wild-type strain. DUL exhibited antibiofilm activity and enhanced AMB activity against developing, but not mature, biofilms.