Sodium Sulfite as an Oxygen-Depletion-Based Chemical Model of Tumor Hypoxia In Vitro

Hypoxia is a major determinant of tumor progression, yet most chemical hypoxia models rely on HIF stabilization rather than true oxygen depletion. Here, we evaluated sodium sulfite (SS), a direct oxygen scavenger, as an oxygen-dependent in vitro hypoxia model. Cancer cell lines were treated with optimized SS concentrations, and dissolved oxygen levels were monitored for up to 96 h. Cell viability, cell death, cell cycle distribution, morphological alterations, and hypoxia-associated metabolic and redox responses were assessed and compared with conventional hypoxia mimetics. SS reduced dissolved oxygen levels below 1 mg/L in a dose- and time-dependent manner. Based on their oxygen-consumption profiles under SS exposure, cell lines were operationally grouped into sustained and limited oxygen-consuming phenotypes. SS induced moderate cytotoxicity without reducing viability below 50%, caused S-phase accumulation in the sustained oxygen-consuming group and G0/G1 accumulation in the limited oxygen-consuming group, and altered cell morphology. Importantly, SS promoted HIF-1α and HIF-2α nuclear translocation, increased VEGF-A, LDHA, GLUT1, and HK-2 expression, decreased extracellular pH, suppressed eNOS, and enhanced antioxidant capacity more effectively than CoCl₂ or DFO. Together, these findings indicate that SS induces direct oxygen depletion and captures selected signaling, metabolic, and redox-related responses associated with hypoxia. SS therefore represents a simple and accessible oxygen-depletion-based chemical model that may complement conventional hypoxia mimetics for studying selected features of hypoxic adaptation in vitro, although further studies are needed to distinguish oxygen depletion-dependent effects from sulfite-specific contributions.