Nano-combination for Reviving the Activity of Fluconazole against Rhizopus delemar

Background: Rhizopus delemar, the main causative pathogen for the lethal mucormycosis and a severe threat during the COVID-19 pandemic, is resistant to most antifungals, including fluconazole, a known selective antifungal drug. On the other hand, antifungals are known to enhance fungal melanin synthesis. Rhizopus melanin plays an important role in fungal pathogenesis and in escaping the human defense mechanism, thus complicating the use of current antifungal drugs and fungal eradication. Because of drug resistance and the slow discovery of effective antifungals, sensitizing the activity of older ones seems a more promising strategy. Methods: In this study, a strategy was employed to revive the use and enhance the effectiveness of fluconazole against R. delemar. UOSC-13, a compound synthesized in-house to target the Rhizopus melanin, was combined with fluconazole either as is or after encapsulation in poly (lactic-coglycolic acid) nanoparticles (PLG-NPs). Both combinations were tested for the growth of R. delemar, and the MIC50 values were calculated and compared. Results: The activity of fluconazole was found to be enhanced several folds following the use of both combined treatment and nanoencapsulation. The combination of fluconazole with UOSC-13 caused a 5-fold reduction in the MIC50 value of fluconazole. Furthermore, encapsulating UOSC-13 in PLG-NPs enhanced the activity of fluconazole by an additional 10 folds while providing a wide safety profile. Conclusion: Consistent with previous reports, the encapsulation of fluconazole without sensitization showed no significant difference in activity. Collectively, sensitization of fluconazole represents a promising strategy to revive the use of outdated antifungal drugs back in the market.