Immunosuppressive and nonimmunosuppressive clyclosporine analogs are toxicto the opportunistic fungal pathogen Cryptococcus neoformans via cyclophilin-dependent inhibition of calcineurin

Cyclosporine (CsA) is an immunosuppressive and antimicrobial drug which, in complex with cyclophilin A, inhibits the protein phosphatase calcineurin. We recently found that Cryptococcus neoformans growth is resistant to CsA a t 24 degrees C but sensitive at 37 degrees C and that calcineurin is requir ed for growth at 37 degrees C and pathogenicity. Here CsA analogs were scre ened far toxicity against C. neoformans in vitro. In most cases, antifungal activity was correlated,vith cyclophilin A binding in vitro and inhibition of the mixed-lymphocyte reaction and interleukin 2 production in cell cult ure. Two unusual nonimmunosuppressive CsA derivatives, (gamma-OH) MeLeu(4)- Cs (211-810) and D-Sar (alpha-SMe)(3) Val(2)-DH-Cs (209-825), which are als o toxic to C. neoformans were identified. These CsA analogs inhibit C. neof ormans via fungal cyclophilin A and calcineurin homologs. Our findings iden tify calcineurin as a novel antifungal drug target and suggest nonimmunosup pressive CsA analogs warrant investigation as antifungal agents.