Combined Inhibition of Epidermal Growth Factor Receptor and Cyclooxygenase-2 as a Novel Approach to Enhance Radiotherapy

Abstract

Targeting epidermal growth factor receptor (EGFR) is a promising approach to increasing radiosensitivity of head and neck cancers but treatment resistance remains an important clinical problem. We hypothesize that combined EGFR and cyclooxygenase-2 (COX-2) inhibition, using small molecule inhibitors erlotinib and celecoxib, respectively would further increase the antitumor activity of radiotherapy. The effects of combinations of celecoxib, erlotinib and ionizing radiation (IR) on cell growth, cell cycle progression and apoptosis of head and neck cancer cell lines were assessed in vitro by cell viability, clonogenic survival, flow cytometry and Annexin V assays and in vivo. The effects of celecoxib, erlotinib and IR on primary and downstream molecular targets were analyzed by immunoblotting & ELISA assays. Compared to single or double agent approaches, concurrent celecoxib, erlotinib and IR was the most effective regimen at reducing clonogenic survival, increasing apoptosis and inhibiting tumor growth in vivo. Concurrent treatment with celecoxib and erlotinib +/- IR inhibited multiple prosurvival proteins including p-ERK1/2, p-EGFR, p-AKT, p-STAT3, COX-2 and PGE-2. The combination of celecoxib, erlotinib and IR is a promising strategy to overcoming resistance to combined EGFR inhibition and IR alone.