Distinct subpopulations of head and neck cancer cells with different levels of intracellular reactive oxygen species exhibit diverse stemness, proliferation, and chemosensitivity

Head and neck squamous cell carcinoma (HNSCC) is driven by cancer-initiating cells (CIC), but their maintenance mechanisms are obscure. For hematopoietic stem cells, low levels of intracellular reactive oxygen species (ROS^Low) is known to help sustain stemness properties. In this report, we evaluated the hypothesis that ROS^Low character conferred CIC properties in HNSCC. Sphere cultures define CIC in HNSCC cell populations (HN-CIC). We found that ROS^Low cells in HN-CIC defined in this manner were more numerous than in parental HNSCC cells. Further, ROS^Low cells frequently coexpressed CIC surface markers such as memGrp78 and Glut3. Exploiting flow cytometry to sort cells on the basis of their ROS level, we found that isolated ROS^Low cells displayed relatively more CIC properties, including quiescence, chemoresistance, in vitro malignant properties, and tumorigenicity. Pharmacological depletion of ROS modulators in cisplatin-treated HN-CIC reduced CIC properties, enhancing cell differentiation and enhancing cisplatin-induced cell death. Overall, our work defined cell subpopulations in HNSCC on the basis of differential intracellular ROS levels, which associated with stemness and chemoresistance properties. On the basis of our findings, we suggest that strategies to promote intracellular ROS levels may heighten the efficacy of conventional chemotherapy used for HNSCC treatment.