Hexadecylphosphocholine (Miltefosine) Has Broad-Spectrum Fungicidal Activity and Is Efficacious in a Mouse Model of Cryptococcosis

Abstract

ABSTRACT The alkyl phosphocholine drug miltefosine is structurally similar to natural substrates of the fungal virulence determinant phospholipase B1 (PLB1), which is a potential drug target. We determined the MICs of miltefosine against key fungal pathogens, correlated antifungal activity with inhibition of the PLB1 activities (PLB, lysophospholipase [LPL], and lysophospholipase-transacylase [LPTA]), and investigated its efficacy in a mouse model of disseminated cryptococcosis. Miltefosine inhibited secreted cryptococcal LPTA activity by 35% at the subhemolytic concentration of 25 μM (10.2 μg/ml) and was inactive against mammalian pancreatic phospholipase A2 (PLA 2 ). At 250 μM, cytosolic PLB, LPL, and LPTA activities were inhibited by 25%, 51%, and 77%, respectively. The MICs at which 90% of isolates were inhibited (MIC 90 s) against Candida albicans , Candida glabrata , Candida krusei , Cryptococcus neoformans , Cryptococcus gattii , Aspergillus fumigatus , Fusarium solani , Scedosporium prolificans , and Scedosporium apiospermum were 2 to 4 μg/ml. The MICs of miltefosine against Candida tropicalis ( n = 8) were 2 to 4 μg/ml, those against Aspergillus terreus and Candida parapsilosis were 8 μg/ml (MIC 90 ), and those against Aspergillus flavus ( n = 8) were 2 to 16 μg/ml. Miltefosine was fungicidal for C. neoformans , with rates of killing of 2 log units within 4 h at 7.0 μM (2.8 μg/ml). Miltefosine given orally to mice on days 1 to 5 after intravenous infection with C. neoformans delayed the development of illness and mortality and significantly reduced the brain cryptococcal burden. We conclude that miltefosine has broad-spectrum antifungal activity and is active in vivo in a mouse model of disseminated cryptococcosis. The relatively small inhibitory effect on PLB1 enzyme activities at concentrations exceeding the MIC by 2 to 20 times suggests that PLB1 inhibition is not the only mechanism of the antifungal effect.