Locked Dimerized CXCL12 Exerts Radiosensitizing Effects in Head and Neck Cancer

ABSTRACT Background Head and neck squamous cell carcinoma (HNSCC) presents significant treatment challenges, particularly in cases unrelated to human papillomavirus (HPV). The chemokine receptor CXCR4, interacting with its ligand CXCL12, plays a crucial role in tumor proliferation, metastasis, and treatment resistance. This study explores the therapeutic potential of engineered monomeric and dimerized CXCL12 variants (CXCL12 1 and CXCL12 2 , respectively) in HNSCC and evaluates potential additive effects when combined with radiation therapy. Methods Clinical HNSCC biopsies were evaluated for CXCR4 expression in both previously untreated and radiorecurrent disease. HNSCC cell lines were then treated with combinations of CXCL12 variants and radiotherapy and interrogated for proliferation, gene expression change, and underlying molecular mechanisms. In vivo studies evaluated the biodistribution of engineered CXCL12 and tested these treatments in humanized cell line‐derived xenograft (CDX) models. Results CXCL12 2 significantly reduced HNSCC cell proliferation and enhanced the effects of radiotherapy, likely through biased agonism at the CXCR4 receptor and upregulation of the KISS1R pathway. In vivo, CXCL12 2 localized to tumor sites and augmented the effects of radiation to inhibit tumor growth. Conclusions CXCL12 2 , in combination with radiation, demonstrates potent anti‐tumor effects in HNSCC. These findings support further clinical investigation of CXCL12 2 to enhance the effects of radiotherapy.