Worldwide approximately 1.7 billion people suffer from fungal diseases. Per year around 1.5 million of these infections result in death of the patient. The emerging resistance of fungal pathogens to the available drugs poses an increasing threat to global health. Hence, there is an urgent need for the development of new kinds of antifungal therapeutics with a novel mode of action.
F901318 is the lead candidate of the novel class of orotomide antifungals with excellent in vitro activity against all the clinically significant Aspergillus spp. F901318 also shows excellent in vivo efficacy in murine models of invasive aspergillosis together with good pharmacokinetics, tissue distribution and oral bioavailability.
In this study we investigated the impact of F901318 treatment on the viability of A. fumigatus.
Susceptibility of A. fumigatus to F901318 was determined using CLSI methodology. Live-cell imaging was used to observe the effect of F901318 on the elongation rate of A. fumigatus germinated spores and hyphae. Confocal microscopy was employed to determine viability of A. fumigatus after exposure to F901318, using fluorescent viability dyes propidium iodide, DiBac and FUN-1. The impact of the drug on A. fumigatus was also determined by quantitation of the intracellular ATP concentration. Furthermore, biomass assays were established to evaluate the ability of A. fumigatus hyphae to recover from treatment with F901318.
A. fumigatus is highly susceptible to F901318 with a minimal inhibitory concentration (MIC) of <0.03 mg/L. In addition, F901318 displays a rapid antifungal effect by inhibiting growing germlings after approx. 30 min. exposure and growing hyphae after approx. 60 min exposure to concentrations just above the MIC. Staining F901318 treated hyphae with the viability dyes showed that F901318 had a detrimental effect on A. fumigatus hyphae which appeared to be irreversible. This was confirmed by growth assays that showed that removal of the compound and supply of fresh medium only allows minimal to no regrowth depending on the concentration of F901318.
Although it is difficult, particularly for filamentous fungi, to definitively conclude that an agent is fungicidal, a combination of approaches indicate that F901318 causes damage to Aspergillus fumigatus hyphae that leads to cell death.