ABSTRACT
A series of bis(4-pentylpyridinium) compounds with a variety of spacers between the pyridinium headgroups was synthesised, and the antifungal activity of these compounds was investigated. Lengthening the alkyl spacer between the pentylpyridinium headgroups from 12 to 16 methylene units resulted in increased antifungal activity against C.â neoformans and C.â albicans, but also resulted in increased hemolytic activity and cytotoxicity against mammalian cells. However, inclusion of an ortho-substituted benzene ring in the centre of the alkyl spacer resulted in decreased cytotoxicity and hemolytic activity, while maintaining antifungal potency. Replacement of the alkyl and aromatic-containing spacers by more hydrophilic ethylene glycol groups resulted in a loss of antifungal activity. Some of the compounds inhibited fungal PLB1 activity, but the low correlation of this inhibition with antifungal potency indicates PLB1 inhibition is unlikely to be the predominant mode of antifungal action of this class of compounds, with preliminary studies suggesting they may act via disruption of fungal mitochondrial function.
Subject(s)
Antifungal Agents/chemistry , Antifungal Agents/pharmacology , Aspergillus fumigatus/drug effects , Candida albicans/drug effects , Cryptococcus neoformans/drug effects , Pyridinium Compounds/chemistry , Pyridinium Compounds/pharmacology , A549 Cells , Animals , Antifungal Agents/chemical synthesis , Aspergillosis/drug therapy , Candidiasis/drug therapy , Cryptococcosis/drug therapy , Dogs , Hemolysis/drug effects , Humans , Madin Darby Canine Kidney Cells , Microbial Sensitivity Tests , Pyridinium Compounds/chemical synthesis , Structure-Activity RelationshipABSTRACT
Miltefosine has antifungal properties and potential for development as a therapeutic for invasive fungal infections. However, its mode of action in fungi is poorly understood. We demonstrate that miltefosine is rapidly incorporated into yeast, where it penetrates the mitochondrial inner membrane, disrupting mitochondrial membrane potential and leading to an apoptosis-like cell death. COX9, which encodes subunit VIIa of the cytochrome c oxidase (COX) complex in the electron transport chain of the mitochondrial membrane, was identified as a potential target of miltefosine from a genomic library screen of the model yeast Saccharomyces cerevisiae. When overexpressed in S. cerevisiae, COX9, but not COX7 or COX8, led to a miltefosine-resistant phenotype. The effect of miltefosine on COX activity was assessed in cells expressing different levels of COX9. Miltefosine inhibited COX activity in a dose-dependent manner in Cox9p-positive cells. This inhibition most likely contributed to the miltefosine-induced apoptosis-like cell death.
