F2F-202, a Selective Histone Deacetylase 6 (HDAC6) Inhibitor, Behaves as an Arrow with Multiple Tips against Azole-Resistant <i>C. albicans</i> : Modulation of Yeast-to-Hyphae Transition, Trailing Effect, and Oxidative Stress

Fungal infections are increasingly threatening public health due to the onset of multidrug-resistant fungal strains. Accordingly, the incidence of chemoresistant C. albicans strains has steadily increased, along with associated mortality, thus highlighting the need for effective antifungal agents for the treatment of both localized and systemic C. albicans infections. Post-transcriptional modifications are key regulators of fungal virulence, modulating the production of virulence factors, yeast-to-hyphae transition, biofilm formation, and chemoresistance phenomena, whereas fungal histone deacetylases are key regulators of these processes. Herein, we report a potent and selective histone deacetylase 6 inhibitor (named F2F-202, 6) showing synergistic activity in combination with the azole antifungal voriconazole (VRC) through the modulation of fungal histone deacetylase Hda1. Compound 6 showed growth inhibition against the azole-resistant C. albicans ATCC 10231 strain in combination with VRC, combined with a significant reduction of yeast-to-hyphae morphological transition. Moreover, the synergistic combination 6/VRC affected the expression of key genes regulated by Hda1 activity and involved in morphogenesis, namely, Nrg1, Als1, and Hpw1. Additionally, 6 in combination with VRC was able to counteract the VRC-induced upregulation of Erg11, a gene involved in C. albicans azole resistance. Finally, our data suggest that the synergistic combination downregulates Sod1 gene expression at an early point and impairs the antioxidant response. This study offers cues for the development of therapeutic options targeting resistant fungal infections and potentially overcoming the limitations associated with antifungal drugs currently in clinical use.