Nrf2 hyperactivation as a driver of radiotherapy resistance and suppressed anti-tumor immunity in head and neck squamous cell carcinoma.

PURPOSE: Alterations in the KEAP1/NFE2L2 (NRF2)/CUL3 pathway occur in ~20% of human head and neck squamous cell carcinomas (HNSCC) and are associated with resistance to standard-of-care therapy. However, this pathway's role in radiotherapy resistance in HNSCC has not been well-studied. EXPERIMENTAL DESIGN: We generated genetically engineered mouse models and developed primary murine cancer cell lines harboring mutations commonly observed in human HNSCC, including inducible activation of PIK3CA and deletion of Trp53, with or without Keap1 loss. Primary tumors were initiated via 4-hydroxytamoxifen injection ± the tobacco carcinogen benzo[a]pyrene (BAP) into the oral buccal mucosa. Tumors were analyzed using Western blotting, immunohistochemistry, RNA sequencing (RNA-seq), and subjected to fractionated radiation therapy to investigate the role of the KEAP1/NRF2 pathway in radioresistance and modulation of the tumor immune microenvironment. RESULTS: BAP exposure accelerated primary tumor formation within one month, with histological analysis confirming invasive squamous cell carcinoma, validated by cytokeratin and differentiation marker expression. Primary cell lines derived from Keap1-haploinsufficient tumors exhibited upregulation of NRF2 target genes and a radioresistant phenotype, which was reversed post-Nrf2 knockdown in vitro. Bulk RNA-seq revealed that Keap1 haploinsufficiency correlated with NRF2 pathway activation, increased myeloid infiltration, and enhanced angiogenic signatures. In vivo, Keap1 haploinsufficiency promoted accelerated tumor growth and decreased survival. Finally, using fractionated radiotherapy, we showed that Keap1 haploinsufficient primary tumors were significantly more radioresistant than Keap1-proficient tumors, regardless of BAP exposure. CONCLUSION: These data demonstrate that Keap1 haploinsufficiency in HNSCC is linked to unfavorable tumor immune microenvironment, aggressive growth, and a radioresistant phenotype.