Roridin E and satratoxin H, macrocyclic trichothecene mycotoxins, induce endoplasmic reticulum stress-dependent apoptosis through ribosome interaction in B16 mouse melanoma cells.

Podostroma cornu-damae, commonly known as the red deer's horn mushroom, is a highly toxic species responsible for severe poisonings characterized by vomiting, diarrhea, dehydration, impaired consciousness, and potentially death. This mushroom is notorious for its content of macrocyclic trichothecene mycotoxins. In our ongoing research aimed at discovering bioactive natural compounds, we isolated thirteen macrocyclic trichothecene mycotoxins (P1-P13) from the methanol extract of a plate culture of P. cornu-damae. The chemical structures of these mycotoxins were elucidated through analysis of nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). While macrocyclic trichothecene mycotoxins have previously been reported to exhibit antifungal, antiviral, and anticancer activities, their anti-melanoma effects have not been documented to date. In this study, we examined the cytotoxicity of isolated mycotoxins (P1-P13) against mouse melanoma (B16F10) cells and explored their underlying molecular mechanisms. Among these isolated compounds, P1 (roridin E) and P5 (satratoxin H) exhibited substantial cytotoxicity, demonstrated by dose-dependent inhibition of cell proliferation, increased expression levels of cleaved caspase-3 and Bax, and elevated intracellular reactive oxygen species (ROS). Importantly, the cytotoxic effects elicited by roridin E and satratoxin H were significantly attenuated following scavenging of ROS by glutathione (GSH). Additionally, molecular docking analysis indicated high binding affinities of both roridin E and satratoxin H toward ribosomal targets. Treatment with these two mycotoxins led to an increased expression of critical endoplasmic reticulum (ER) stress biomarkers, with activation of the unfolded protein response (UPR) signaling pathways involving activating transcription factor 6 (ATF6), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and inositol-requiring enzyme 1 (IRE1). Collectively, our findings suggest that roridin E and satratoxin H induce ER stress-mediated, caspase-dependent apoptosis in melanoma cells. These results highlight the potential of these macrocyclic trichothecene mycotoxins as promising therapeutic candidates for melanoma treatment.