Efficacy of the Echinocandin Caspofungin against Disseminated Aspergillosis and Candidiasis in Cyclophosphamide-Induced Immunosuppressed Mice

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Abstract
The in vivo efficacy of the echinocandin antifungal caspofungin acetate (caspofungin; MK-0991) was evaluated in models of disseminated aspergillosis and candidiasis in mice with cyclophosphamide (CY)-induced immunosuppression. Caspofungin is a 1,3-β- d -glucan synthesis inhibitor efficacious against a number of clinically relevant fungi including Aspergillus and Candida species. Models of CY-induced transient or chronic leukopenia were used with once daily administration of therapy initiated 24 h after microbial challenge. Caspofungin was effective in treating disseminated aspergillosis in mice that were transiently leukopenic (significant prolongation of survival at doses of ≥0.125 mg/kg of body weight and a 50% protective dose [PD 50 ] of 0.245 mg/kg/day at 28 days after challenge) or chronically leukopenic (50 to 100% survival at doses of ≥0.5 mg/kg and PD 50 s ranging from 0.173 to 0.400 mg/kg/day). Caspofungin was effective in the treatment and sterilization of Candida infections in mice with transient leukopenia with a 99% effective dose based on reduction in log 10 CFU of Candida albicans /gram of kidneys of 0.119 mg/kg and 80 to 100% of the caspofungin-treated mice having sterile kidneys at caspofungin doses from 0.25 to 2.0 mg/kg. In Candida -infected mice with chronic leukopenia, caspofungin was effective at all dose levels tested (0.25 to 1.0 mg/kg), with the log 10 CFU of C. albicans /gram of kidneys of caspofungin-treated mice being significantly lower (>99% reduction) than that of sham-treated mice from day 4 to day 28 after challenge. Also, 70 to 100% of the caspofungin-treated, chronic leukopenic mice had sterile kidneys at caspofungin doses of 0.5 to 1.0 mg/kg from day 8 to 28 after challenge. Sterilization of Candida infections by caspofungin in the absence of host leukocytes provides compelling in vivo evidence for fungicidal activity against C. albicans . Further human clinical trials with caspofungin against serious fungal infections are in progress.