The repurposing strategy was applied herein to evaluate the effects of
lopinavir, an aspartic
protease inhibitor currently used in the treatment of HIV-infected individuals, on the globally widespread opportunistic human fungal pathogen Candida albicans by using in silico, in vitro and in vivo approaches in order to decipher its targets on fungal cells and its antifungal mechanisms of action.
Secreted aspartic proteases (Saps) are the obviously main target of
lopinavir. To confirm this hypothesis, molecular docking assays revealed that
lopinavir bound to the Sap2 catalytic site of C. albicans as well as inhibited the Sap hydrolytic activity in a typically dose-dependent manner. The inhibition of Saps culminated in the inability of C. albicans yeasts to assimilate the unique
nitrogen source (
albumin) available in the culture medium, culminating with fungal growth inhibition (IC50 = 39.8 µM). The antifungal action of
lopinavir was corroborated by distinct microscopy analyses, which evidenced drastic and irreversible changes in the morphology that justified the fungal death. Furthermore, our results revealed that
lopinavir was able to (i) arrest the yeasts-into-hyphae transformation, (ii) disturb the synthesis of neutral
lipids, including
ergosterol, (iii) modulate the surface-located molecules, such as Saps and
mannose-,
sialic acid- and
N-acetylglucosamine-containing
glycoconjugates, (iv) diminish the secretion of hydrolytic
enzymes, such as Saps and
esterase, (v) negatively influence the biofilm formation on
polystyrene surface, (vi) block the in vitro adhesion to epithelial cells, (vii) contain the in vivo
infection in both immunocompetent and immunosuppressed mice and (viii) reduce the Sap production by yeasts recovered from kidneys of infected animals. Conclusively, the exposed results highlight that
lopinavir may be used as a promising repurposing drug against C. albicans
infection as well as may be used as a lead compound for the development of novel antifungal drugs.