Inhibition of EphB4-ephrin-B2 signaling enhances response to Cetuximab-radiation therapy in head and neck cancers

Purpose: The clinical success of targeted therapies such as cetuximab and radiation (RT) is hampered by the low response rates and development of therapeutic resistance. In the current study, we investigated the involvement of EphB4-ephrin-B2 pro-tumorigenic signaling in mediating resistance to EGFR inhibition and radiation therapy in head and neck cancers. Experimental Design: We used patient-derived xenograft (PDX) models of head and neck squamous cell carcinoma (HNSCC) and HNSCC cell lines to test our hypothesis. Tumor tissues were subjected to PhosphoRTK array, and western blotting to detect changes in EphB4-ephrin-B2 targets. mRNA sequencing and microarray data analysis was performed on PDX tumors and HNSCC cell lines respectively to determine differences in gene expression of molecules involved in tumor cell growth, proliferation, and survival pathways. Effects on cell growth were determined by MTT assay on HNSCC cells downregulated for EphB4/ephrin-B2 expression, with and without EGFR inhibitor and radiation. Results: Our data from locally-advanced HNSCC patients treated with standard of care definitive chemo-RT show elevated EphB4 and ephrin-B2 levels after failure of treatment. We observed significant response towards cetuximab and radiation therapy following EphB4-ephrin-B2 inhibition resulting in improved survival in tumor-bearing mice. Tumor growth inhibition was accompanied by decrease in the levels of proliferation and pro-survival molecules and increased apoptosis. Conclusions: Our findings underscore the importance of adopting rational drug combinations to enhance therapeutic effect. Our study documenting enhanced response of HNSCC to cetuximab-RT therapy with EphB4-ephrin-B2 blockade has the potential to translate into clinic to benefit this patient population.

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