Combined Inhibition of Epidermal Growth Factor Receptor and Cyclooxygenase-2 Leads to Greater Anti-tumor Activity of Docetaxel in Advanced Prostate Cancer

The epidermal growth factor receptor (EGFR) and cyclooxygenase-2(COX-2) play a critical role in disease progression, relapse and therapeutic resistance of advanced prostate cancer (PCa). In this paper, we evaluated, for the first time, the therapeutic benefit of blocking EGRF and/or COX-2 (using gefitinib and NS-398, respectively) in terms of improving the efficacy of the conventional clinical chemotherapeutic drug docetaxel in vitro and vivo. We showed that EGFR and COX-2 expression was higher in metastatic than non-metastatic PCa tissues and cells. Docetaxel, alone or in combination with gefitinib or NS-398, resulted in a small decrease in cell viability. The three drug combination decreased cell viability to a greater extent than docetaxel alone or in combination with gefitinib or NS-398. Docetaxel resulted in a modest increase in apoptotic cell in metastatic and non-metastatic cell lines. NS-398 markedly enhanced docetaxel-induced cell apoptosis. The combination of the three drugs caused even more marked apoptosis and resulted in greater suppression of invasive potential than docetaxel alone or in association with gefitinib or NS-398. The combination of all three drugs also resulted in a more marked decrease in NF-ΚB, MMP-9 and VEGF levels in PC-3M cells. These in vitro findings were supported by in vivo studies showing that docetaxel in combination with gefitinib and NS-398 was significantly more effective than any individual agent. Based on previous preclinical research, we conclude that simultaneously blocking EGFR and COX-2 by gefitinib and NS-398 sensitizes advanced PCa cells to docetaxel-induced cytotoxicity.