Preliminary Insight into the Antifungal and Anti-melanogenic Potential of a Xanthenone-based Hit Compound: In Vitro and In Vivo Zebrafish Evaluation

The emergence of multidrug-resistant Candida auris highlights the urgent need for alternative antifungal agents. This study evaluates the biological potential of xanthenones (XA1, XA2, XA3), previously synthesized xanthone derivatives with unexplored bioactivity, focusing on their antifungal efficacy and anti-melanogenic activity. All hydroxathenones were first screened in vitro against a series of pathogens. The active compound was then comprehensively tested against C. auris, with minimum inhibitory concentration (MIC) testing and mechanistic assays conducted to assess membrane permeability disruption, reactive oxygen species (ROS) production, and biofilm inhibition. Cytotoxicity was examined in HaCaT keratinocytes and B16F10 melanoma cells. Anti-melanogenic activity was assessed through in vitro tyrosinase inhibition and melanin quantification, followed by in vivo pigmentation analysis in zebrafish embryos, with kojic acid as a reference standard. The most active analogue, 7-hydroxy-2,3,4,4,4a-tetrahydro-1H-xanthen-1-one (XA3), exhibited an MIC of 100 µg/mL against C. auris. Mechanistic investigations indicated disruption of fungal cell integrity through increased membrane permeability and elevated ROS production, contributing to reduced biofilm formation. Cytotoxicity assays showed acceptable safety profiles, with HaCaT keratinocytes retaining 85% viability at 25 µg/mL and consistent tolerance observed in B16F10 melanoma cells. Additionally, XA3 demonstrated potent anti-melanogenic activity, significantly reducing tyrosinase activity, melanin content, and zebrafish embryo pigmentation, comparable to kojic acid. This study presents the first preliminary report of the biological activity of XA3, highlighting its antifungal and anti-melanogenic effects at distinct concentration ranges. These findings position XA3 as an early-stage hit compound with separate pharmacological properties that require further investigation.