The antidepressant sertraline provides a promising therapeutic option for neurotropic cryptococcal infections

Abstract

Therapeutic treatment for systemic mycoses is severely hampered by the extremely limited number of antifungals. The difficulty of treatment of fungal infections in the central nervous system is further compounded by the poor central nervous system (CNS) penetration of most antifungals due to the blood-brain barrier. Only a few fungistatic azole drugs, such as fluconazole, show reasonable CNS penetration. Here we demonstrate that sertraline (Zoloft), the most frequently prescribed antidepressant, displays potent antifungal activity against Cryptococcus neoformans, the major causative agent of fungal meningitis. In in vitro assays, this neurotropic drug is fungicidal to all natural Cryptococcus isolates tested at clinically relevant concentrations. Furthermore, sertraline interacts synergistically or additively with fluconazole against Cryptococcus. Importantly, consistent with our in vitro observations, sertraline used alone reduces the brain fungal burden at an efficacy comparable to that of fluconazole in a murine model of systemic cryptococcosis. It works synergistically with fluconazole in reducing the fungal burden in brain, kidney, and spleen. In contrast to its potency against Cryptococcus, sertraline is less effective against strains of Candida species and its interactions with fluconazole against Candida strains are often antagonistic. Therefore, our data suggest the unique application of sertraline against cryptococcosis. To understand the antifungal mechanisms of sertraline, we screened a whole-genome deletion collection of Saccharomyces cerevisiae for altered sertraline susceptibility. Gene ontology analyses of selected mutations suggest that sertraline perturbs translation. In vitro translation assays using fungal cell extracts show that sertraline inhibits protein synthesis. Taken together, our findings indicate the potential of adopting this antidepressant in treating cryptococcal meningitis.

Figures

Fig 1

Sertraline is fungicidal against both proliferative and quiescent Cryptococcus cells. (A) H99 cells were inoculated into RPMI media and cultured without any drug (control) or in the presence of fluconazole (FLC; 8 μg/ml) or sertraline (SRT; 10 μg/ml) or a combination of these two drugs. At the indicated time points, aliquots of cell suspensions were transferred and plated onto drug-free agar medium to determine CFU after 2 more days of incubation. Fungal cells proliferated rapidly in the absence of any drugs, but they were gradually cleared with any of the drug treatments. (B) H99 cells were inoculated into PBS buffer and cultured without any drug (control) or in the presence of fluconazole (8 μg/ml) or sertraline (8 μg/ml) or a combination of these two drugs. At the indicated time points, aliquots of cell suspensions were transferred and plated on drug-free medium to determine CFU after 2 more days of incubation. Fungal cells in PBS maintained viability during the tested period.

Fig 2

Sertraline reduces the fungal burden alone or in combination with fluconazole in vivo. Brains (A), kidneys (B) and spleens (C) of mice from different treatment groups were dissected and homogenized. The suspensions were diluted serially, and the fungal burden was determined by calculating CFU. Sertraline alone significantly reduced the brain and the kidney fungal burden, while the drug combination reduced the fungal burden significantly in all three organs. *, P < 0.05; **, P < 0.01; ***, P < 0.001. In brain, the drug combination displayed higher potency compared to either fluconazole or sertraline alone (both P < 0.05). The efficacy of the drug combination is also superior to that of fluconazole alone in kidney (P < 0.001) or that of sertraline alone in spleen (P < 0.001).

Fig 3

Antagonistic effects between sertraline and fluconazole among Candida strains. Six Candida strains, C. albicans SC5314, C. glabrata PAT2ISO3, C. krusei DUMC132.91, C. parapsilosis MMRL1594, C. tropicalis MMRL2017, and C. lusitaniae 2-367, were incubated in RPMI media with the indicated drug treatment. Gradients in columns represent sertraline (shown in micrograms per milliliter); gradients in rows represent fluconazole (shown in micrograms per milliliter). The scale of the fluconazole concentrations was determined based on a previous study (40). Growth was measured by absorbance at 600 nm after 24 h of incubation. Green indicates fungal growth, and black indicates the lack of fungal growth.

Fig 4

Gene ontology analysis of the S. cerevisiae genes involved in sertraline tolerance or susceptibility. Gene ontology (GO) terms for annotated S. cerevisiae genes involved in sertraline resistance (A) or susceptibility (B) were extracted from the GO database and sorted into the immediate subcategories for molecular functions and biological processes. See Table S2 in the supplemental material for the detailed gene list.

Fig 5

Sertraline inhibits translation in a Cryptococcus cell-free system. The cell-free translation system was prepared as described in Materials and Methods. (A) The translation of luciferase in both Cryptococcus and Saccharomyces cell extracts is dependent on the mRNA 5′ terminal cap, designated C, and on the 3′ terminal poly(A) tail, designated A. The cap and poly(A) synergistically stimulate RNA translation in both cell-free systems. (B and C) Water, the solvent DMSO, or sertraline in stock solution was added into reaction mixtures to reach the indicated concentrations. Luciferase protein synthesis by the cell-free translation system was measured based on the relative light units arising from the enzymatic activity of luciferase (B) or the level of [35S]methionine incorporated into the synthesized luciferase polypeptide (C). Both measurements showed that sertraline inhibited translation in a dose-dependent manner.