Candida albicans enhances iron uptake to maintain fluconazole resistance.

Widespread use of fluconazole has led to the emergence of fluconazole-resistant (FR) Candida spp. causing challenges in clinical treatment. Iron, an essential nutrient, affects the levels of ergosterol (a fluconazole target) in fungal membranes. Our lab-generated FR strain (fluconazole minimum inhibitory concentration [MIC] >125 µg/mL) showed a twofold lower MIC (4.66 µg/mL) for the iron chelator deferasirox (DFX), compared to its patent strain CAI4 (DFX MIC 9.34 µg/mL), suggesting a greater sensitivity to iron chelation. A sublethal dose of DFX (2.33 µg/mL) was able to effectively synergize with 125 µg/mL fluconazole to kill the FR strain. Iron estimation revealed significantly enhanced intracellular iron accumulation in the FR strain compared to CAI4. Expression of iron-uptake genes (FRP1, FRE10, and RBT5) was also significantly upregulated in the FR strain, particularly under high iron. FR strain also showed an increase in the levels of cellular ergosterol, along with an increase in the expression of ergosterol biosynthesis genes (ERG11 and ERG9), compared to CAI4, under both low and high iron. The strain further showed increased β-glucan levels and exposure. Additionally, FR strain showed significantly higher survival in high-iron mice compared to low-iron mice, during fluconazole treatment. Finally, we observed a synergistic fungicidal response between 2.33 µg/mL DFX and 125 µg/mL fluconazole, for FR clinical strains. Overall, this suggests that FR C. albicans actively uptakes more iron to maintain cellular conditions needed to support its resistance against fluconazole; and that DFX alone or in conjugation with fluconazole has the potential to overcome fluconazole drug resistance.