Fungal infections have been increasing during the last decades. Scedosporium and Lomentospora species are filamentous fungi most associated to those infections, especially in immunocompromised patients. Considering the limited options of treatment and the emergence of resistant isolates, an increasing concern motivates the development of new therapeutic alternatives. In this context, the present study screened the Pathogen Box library to identify compounds with antifungal activity against Scedosporium and Lomentospora. Using antifungal susceptibility tests, biofilm analysis, scanning electron microscopy (SEM), and synergism assay, auranofin and iodoquinol were found to present promising repurposing applications. Both compounds were active against different Scedosporium and Lomentospora, including planktonic cells and biofilm. SEM revealed morphological alterations and synergism analysis showed that both drugs present positive interactions with voriconazole, fluconazole, and caspofungin. These data suggest that auranofin and iodoquinol are promising compounds to be studied as repurposing approaches against scedosporiosis and lomentosporiosis.

Mucorales are a group of non-septated filamentous fungi widely distributed in nature, frequently associated with human infections, and are intrinsically resistant to many antifungal drugs. For these reasons, there is an urgent need to improve the clinical management of mucormycosis. Miltefosine, which is a phospholipid analogue of alkylphosphocholine, has been considered a promising repurposing drug to be used to treat fungal infections. In the present study, miltefosine displayed antifungal activity against a variety of Mucorales species, and it was also active against biofilms formed by these fungi. Treatment with miltefosine revealed modifications of cell wall components, neutral lipids, mitochondrial membrane potential, cell morphology, and the induction of oxidative stress. Treated Mucorales cells also presented an increased susceptibility to SDS. Purified ergosterol and glucosylceramide added to the culture medium increased miltefosine MIC, suggesting its interaction with fungal lipids. These data contribute to elucidating the effect of a promising drug repurposed to act against some relevant fungal pathogens that significantly impact public health.

Mucormycosis is considered concerning invasive fungal infections due to its high mortality rates, difficult diagnosis and limited treatment approaches. Mucorales species are highly resistant to many antifungal agents and the search for alternatives is an urgent need. In the present study, a library with 400 compounds called the Pandemic Response Box^® was used and four compounds were identified: alexidine and three non-commercial molecules. These compounds showed anti-biofilm activity, as well as alterations in fungal morphology and cell wall and plasma membrane structure. They also induced oxidative stress and mitochondrial membrane depolarization. In silico analysis revealed promising pharmacological parameters. These results suggest that these four compounds are potent candidates to be considered in future studies for the development of new approaches to treat mucormycosis.

The emergence of infections caused by Scedosporium/Lomentospora and Mucorales species poses a major clinical challenge due to their intrinsic resistance to multiple antifungal drugs and the limited number of therapeutic options available. In this study, we evaluated the antifungal activity of synthetic organic compounds and characterized the mechanisms of antifungal activity. Eight compounds were initially screened against Scedosporium aurantiacum and Rhizopus oryzae. Compounds 2, 3, and 4 inhibited more than 60% of fungal growth and were selected for further characterization. Antifungal susceptibility assays revealed that compound 2 exhibited the strongest activity, with minimum inhibitory concentrations ranging from 12.5 to 25 μg/mL, whereas compounds 3 and 4 showed MIC values between 50 and 100 μg/mL. All compounds displayed fungistatic activity and significantly impaired fungal germination and biofilm development. Drug interaction analyses demonstrated additive or synergistic effects when the compounds were combined with clinically used antifungals. Investigations revealed that the compounds induced alterations in the fungal cell surface, including reductions in neutral lipids and chitin, increased membrane permeability, disruption of sterol-enriched membrane microdomains, and ultrastructural abnormalities. Exogenous ergosterol partially reversed the activity of compounds 2 and 3, suggesting interactions with membrane sterols. In silico toxicity prediction indicated generally favorable safety profiles. In summary, these findings identify synthetic organic compounds as promising scaffolds for antifungal drug discovery and highlight their potential to target fungal membrane and cell wall integrity in resistant filamentous pathogens.