Abstract:
Invasive fungal lung infections caused by Aspergillus spp., Candida spp. and Cryptococcus spp. affect patients on immunosuppressive therapies, and have alarmingly high mortality rates. Antifungal drug treatments for fungal lung infections are complicated by sub-therapeutic concentrations in lung tissues, drug-drug interactions and drug resistance. An inhalable antifungal drug therapy is a promising alternative to currently used oral or intravenously administered drugs, and could lead to a safer, more effective antifungal treatment of fungal lung infections. Scytinostroma sp., a previously uncharacterised white rot fungus, produces a volatile antifungal metabolite. Due to the volatile nature of this metabolite, it could be ideal for the development of an inhalable therapy to treat fungal lung infections. The aim of this project was to determine if a volatile antifungal metabolite produced by Scytinostroma sp. is a suitable candidate for the treatment of pulmonary fungal infections. Antifungal culture optimisation revealed that the expression of Scytinostroma sp. antifungal metabolites were highly inducible by growth on media supplemented with Candida albicans spent culture. These antifungal metabolites were found to have a broad spectrum of antifungal activity against clinically relevant fungi, including C. albicans and Aspergillus fumigatus isolated from patients with fungal lung infections. However, fungal minimum inhibitory concentration and mammalian cytotoxicity assays showed that Scytinostroma sp. antifungal metabolites may also be highly toxic toward mammalian cells. An antifungal metabolite was purified from crude Scytinostroma sp. extracts using preparative high performance liquid chromatography (HPLC). Gas chromatography mass spectrometry (GC-MS) analysis of the purified antifungal HPLC fraction identified isovelleral: a known fungal sesquiterpene with potent antifungal activity and mammalian cytotoxicity. Due to the evidence of high mammalian cytotoxicity in this project and in previous studies, it was concluded that isovelleral is unlikely to be a suitable candidate for the development of an inhalable antifungal drug therapy. Future biodiscovery efforts could benefit from the use of spent medium to induce antimicrobial metabolites, and a targeted HPLC purification using cultures with induced and no antifungal activity. Furthermore, the findings in this project could prompt new investigations into the ecological roles of isovelleral.