ONC201 enhances the cytotoxic effect of cisplatin through ATF3/ATF4/CHOP in head and neck squamous cell carcinoma cells.

Head and neck squamous cell carcinoma (HNSCC) remains a prevalent and challenging cancer to treat due to its genetic heterogeneity. Cisplatin resistance is one of important causes in treatment failure of locally advanced HNSCC. ONC201, a selective dopamine receptor D2 antagonist and mitochondrial ClpP agonist, has emerged as a potential antitumor agent in various malignancies. This study explores the therapeutic potential of ONC201, alone and in combination with cisplatin, in both cisplatin-sensitive and -resistant HNSCC cells, with an emphasis on endoplasmic reticulum (ER) stress-mediated apoptosis. A cisplatin-resistant HNSCC subline (OC2-CR1) was developed via long-term drug exposure. The treatment effectiveness of ONC201 alone and cisplatin in combination on cell viability, DNA damage, reactive oxygen species (ROS) production, and stress response markers were evaluated. ONC201 exhibited potent cytotoxicity in both cisplatin-sensitive and -resistant HNSCC cells, retaining efficacy in OC2-CR1 cells. Combined treatment with ONC201 and cisplatin demonstrated synergistic inhibition of proliferation and migration, with enhanced induction of apoptosis. Mechanistically, ONC201 induced ER stress-mediated cell death via ATF4/CHOP signaling in cisplatin-sensitive cells, while ATF3/CHOP predominated in resistant cells. In vivo, combination therapy significantly suppressed tumor growth in xenograft models, including cisplatin-resistant tumors, without inducing toxicity. Immunohistochemical analysis confirmed activation of CHOP in tumor tissues. Furthermore, clinical correlation revealed that low CHOP expression in OSCC patients was associated with increased recurrence risk and inferior recurrence-free survival significantly. This study provides compelling evidence that ONC201 enhances cisplatin efficacy through distinct, stress-mediated apoptotic pathways in HNSCC. The ability of ONC201 to overcome cisplatin resistance and its synergistic antitumor effects highlight its promise as a candidate for combination therapy. These findings support the translational potential of targeting the ATF3/ATF4/CHOP axis to improve outcomes in patients with cisplatin resistant HNSCC.