MONOCYTES MITIGATE PLASMA-TREATED WATER-INDUCED CYTOTOXICITY IN HEAD AND NECK CANCER CELLS

Aim: Plasma-treated water solutions (PTWS), enriched with longlived reactive oxygen and nitrogen species (RONS), represent a tumor-selective therapeutic strategy. This study evaluated PTWS cytotoxicity in head and neck cancer (HNC) cells and the modulatory role of monocytes in the tumor microenvironment. Methods: FaDu and SAS HNC cells and HaCaT epithelial cells were treated with PTWS oxy 20′ or air 20′ for 24 h. Cell death, ROS, and lipid peroxidation were assessed. SAS and FaDu cells were co-cultured with CD14+ monocytes and exposed to PTWS. Results: SAS cells were most sensitive (~65% death; ~35% late apoptotic, ~30% non-apoptotic), with 2-fold ROS increase and lipid peroxidation of ~27% (air) and ~56% (oxy). FaDu cells showed intermediate sensitivity (~20% air, ~50% oxy), modest ROS increase, and <10% lipid peroxidation. Ha-CaT cells displayed low cytotoxicity (<30%) with minimal ROS and no lipid peroxidation. Monocytes alone showed 18% (air) and 59% (oxy) death. In co-culture, monocyte mortality reached ~99%, reducing SAS cell death by ~50% via apoptosis attenuation and abolishing lipid peroxidation. In FaDu cells, co-culture slightly reduced death, induced early apoptotic arrest, and decreased lipid peroxidation to ~1%. Conclusions: monocytes act as key modulators of PTWS response, protecting HNC cells while undergoing extensive death, highlighting a TME-dependent limitation of PTWS efficacy.