Repurposing the non-steroidal anti-inflammatory drug diflunisal as an adjunct therapy with amphotericin B against mucoralean fungi.

Introduction. Mucormycosis is an aggressive, angioinvasive infection associated with high morbidity and mortality. The disease remains difficult to treat, with limited available antifungal drugs. Consequently, there is an urgent need to develop alternate therapeutics against mucormycosis. In an earlier study, we demonstrated that the non-steroidal anti-inflammatory drug diflunisal impacted the actin cytoskeleton and quorum sensing and inhibited the formation of filopodia-/cytoneme-like extensions in Rhizopus arrhizus.Hypothesis. The non-steroidal anti-inflammatory drug diflunisal could exhibit potential antifungal activity.Aim. This study aimed to investigate the plausible antifungal activity of diflunisal against a range of medically important Mucorales and its combination effect with antifungal drugs.Methodology. The antifungal activity of diflunisal against Rhizopus arrhizus, Lichtheimia corymbifera, Rhizomucor pusillus, Cunninghamella bertholletiae, Mucor indicus, Mucor irregularis and Apophysomyces elegans was evaluated by broth microdilution assay. Allied salicylates were also screened. A combination assay with amphotericin B deoxycholate and posaconazole was performed by fractional inhibitory concentration test.Results. Exposure to diflunisal inhibited Rhizopus arrhizus spore germination in a dose-dependent manner. MICs of diflunisal against different Mucorales ranged from 64 to 2048 µg ml^-1. Remarkably low levels of diflunisal (0.03-2 µg ml^-1), depending on the strain/species tested, improved the antifungal activity of amphotericin B against mucoralean fungi by twofold (ΣFIC ≈ 0.5-0.508; P<0.01). Field-emission scanning electron micrographs further confirmed these observations. MICs of posaconazole were unchanged by this compound.Conclusion. Considering that amphotericin B remains the first-line drug against mucormycosis and exhibits dose-dependent side effects in clinical practice, especially nephrotoxicity, the observed additive interaction at remarkably low, clinically achievable levels of diflunisal demonstrates its potential utility as an adjunct therapy against mucoralean fungi.