Epinecidin-1 Induces Distinct Oncosis and Pyroptosis Responses in Osteosarcoma Cells and Enhances Methotrexate-associated Cytotoxicity.

Marine antimicrobial peptide epinecidin-1 (epi) is known to have inhibitory effects toward several cancers. In this study, we further evaluated the therapeutic potential of epi in osteosarcoma. We found that epi effectively killed two osteosarcoma cell lines, MG63 and U2OS. Notably, the cytotoxic mechanism in these two cell lines was not classical apoptosis or necroptosis. Rather, epi induced pyroptosis in U2OS cells, and it triggered oncosis in MG63 cells. In both cell lines, epi caused mitochondrial damage accompanied by a redistribution of intracellular calcium, characterized by decreased mitochondrial calcium and increased cytosolic calcium. Increased cytosolic calcium further contributed to mitochondrial dysfunction and cell death. Additionally, epi stimulated gasdermin D cleavage via caspase-1 activation, resulting in pyroptosis. In MG63 cells, increased cytosolic calcium contributed to epi-induced oncosis. Furthermore, the combination of epi with MTX increased intracellular MTX accumulation and resulted in greater cytotoxicity than either treatment alone. We also found that epi inhibits MG63-derived cancer spheres, with increased porimin expression suggesting the potential involvement of oncosis. Overall, this study reveals that epi exerts potent cytotoxic effects on osteosarcoma cancer cell lines and cancer spheres, and it enhances MTX-associated toxicity. Thus, our study suggests that epi can inhibit osteosarcoma via distinct mechanisms, highlighting its promising potential as a therapeutic agent for osteosarcoma.