Susceptibility of melanized and nonmelanized Cryptococcus neoformans to the melanin-binding compounds trifluoperazine and chloroquine

Cryptococcus neoformans is an opportunistic fungal pathogen which becomes heavily melanized in the presence of phenolic substrates such as L-dopa. Various drugs are known to bind to melanin with high affinity, including the antipsychotic agent trifluoperazine and the antimalarial agent chloroquine. We hypothesized that drugs which bind melanin may have different toxicities for melanized and nonmelanized C. neoformans cells. The effects of trifluoperazine and chloroquine or C. neoformans were determined by measuring cell viability after exposure to these drugs. Cell viability was measured by CFU determination and flow cytometry with propidium iodide staining. Melanized cells were more susceptible than nonmelanized cells to the fungicidal effects of trifluoperazine. Chloroquine had no fungicidal effect on either melanized or nonmelanized C. neoformans under the conditions studied. Flow cytometry of trifluoperazine-treated C. neoformans cells stained with the mitochondrial stain dihydrorhodamine 123 revealed fluorescence changes consistent with mitochondrial damage. Our results indicate that melanized and nonmelanized C. neoformans cells can differ in susceptibility to certain drugs and suggest that strategies which target melanin may be productive for antifungal-drug discovery.