Acidic plasma-activated povidone-iodine induces copper-dependent oxidative death in oral squamous cell carcinoma...

Oral squamous cell carcinoma (OSCC) requires therapeutic strategies that preserve oral function while providing effective tumor control. Here we demonstrate that non-thermal plasma (NTP) irradiation of a clinically established povidone-iodine solution generates a potent cytotoxic formulation termed plasma-activated povidone-iodine (PAI). PAI selectively reduced viability of OSCC cell lines (SAS, HSC-2, HSC-4) compared with normal fibroblasts. Mechanistically, PAI activity strictly depended on its acidic pH (3.0 or below) and hydrogen peroxide (H₂O₂) generated during NTP irradiation. Neutralization or freeze-drying abolished both H₂O₂ content and cytotoxicity, indicating that reactive oxygen species are essential mediators. Unlike plasma-activated media, whose effects are predominantly iron-dependent, PAI-induced cytotoxicity required intracellular monovalent copper (Cu⁺). The Cu⁺ chelator tetrathiomolybdate suppressed ROS accumulation, glutathione depletion, lipid peroxidation, and cell death, whereas classical ferroptosis or apoptosis inhibitors failed to rescue viability. PAI increased intracellular Cu⁺ levels and triggered oxidative damage including γH2AX induction; however, the resulting death program was mechanistically distinct from apoptosis, ferroptosis, and cuproptosis. Our findings reveal a previously unrecognized Cu⁺-dependent oxidative pathway initiated by PAI. This study establishes an accessible iodine-based platform that harnesses metal-driven redox chemistry for selective OSCC elimination.