G-quadruplexes form and are functional in dermatophytes

Abstract

Over one billion people are affected by skin infections caused by dermatophytes each year. Although often only considered an inconvenience, fungal skin infections are notoriously difficult to treat, and if fungi enter wounds, they can lead to fungal sepsis and death. This problem is soon to worsen following the emergence of terbinafine-resistant Trichophyton indotineae globally. Therefore, it is essential that we identify new methods to treat such infections. Four-stranded secondary structures in DNA and RNA called G-quadruplexes (G4s) have arisen as novel therapeutic targets to treat bacterial and viral infections, given that ligands stabilising these structures (G4 ligands) can inhibit G4-regulated processes, such as transcription and replication. However, their effects on pathogenic fungi are poorly understood. QUMA-1 and Thioflavin-T (ThT) assays demonstrated that G4s could form in Trichophyton spp. RNA and DNA, respectively. The G4 ligands PhenDC3 and RHPS4 were found to have antifungal activity against Trichophyton mentagrophytes and Trichophyton interdigitale as determined via biomass measurements, the quantification of absorbance at 560 nm and AlamarBlue assays. The production of secondary metabolites by Trichophyton spp. is poorly understood. AntiSMASH results identified numerous putative biosynthetic gene clusters in Trichophyton spp., and incubation with either PhenDC3 and RHPS4 was found to impact the secondary metabolite profile of T. mentagrophytes and T. interdigitale. This research revealed three significant findings: first, G4s could form in dermatophyte DNA and RNA; second, specific G4 ligands displayed antifungal potential; and third, stabilising G4s can alter the metabolite profile of both T. mentagrophytes and T. interdigitale. These are the first observations implicating G4s in dermatophyte biology, but we need to conduct more comprehensive studies into determining the metabolite profile following the stabilisation of G4s and how they are regulated.