Novel therapy for the metastatic prostate cancer forms by using a combination of gefitinib, tamoxifen and etoposide

Abstract

2130

Current treatments for prostatic cancer (PC) are generally curative for the majority of patients diagnosed with localized and androgen-dependent forms; however, the progression to the androgen-independent and metastatic disease states is often accompanied by the recurrence of PC. Therefore, the development of a novel combination therapy more effective against anti-androgen- and chemotherapy-refractory PC forms is highly desirable for prostate cancer patients. In this study, we evaluated, for the first time, the antiproliferative and cytotoxic effects induced by a combination of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, gefitinib with other chemotherapeutic drugs including estrogen receptor (ER-β) antagonist (tamoxifen), and topoisomerase II inhibitor (etoposide) on metastatic prostate cancer cells. The results from growth tests and flow cytometric analyses revealed that each drugs alone or at lower concentrations in combination with others inhibited the growth of EGF-, EGF plus 17β-estradiol (E2) and serum-stimulated androgen-sensitive LNCaP-C33 and androgen-independent LNCaP-C81, DU145 and PC3 cells. The antiproliferative effect of gefitinib and tamoxifen, alone or in combination, on EGF plus E2-stimulated PC3 was mediated via a blockade of the PC3 cells in the G1 phase of cell cycle while etoposide induced a G2 arrest. Furthermore, the growth inhibitory effect induced by gefitinib and tamoxifen was also accompanied by the down-regulation of telomerase expression and up-regulation of cell cycle inhibitor proteins, p21^Cip1 and p27^kip1. Importantly, the combined gefitinib, tamoxifen and etoposide also caused a higher rate of apoptotic death of prostate cancer cells compared to single agents. The cytotoxic effect induced by this tri-combination of drugs in PC3 cells appears to be mediated at least, in part, via the mitochondrial pathway through the depolarization of the mitochondrial membrane and release of cytochrome c and reactive oxygen species into cytosol. This was also accompanied by the cellular ceramide accumulation and activation of caspase cascades and DNA fragmentation. These findings indicate that the combined use of inhibitors of EGF-EGFR and ER-β signaling with other chemotherapeutic agents as etoposide which acting by increasing the cellular ceramide levels and caspase activation represents a promising strategy for a more effective treatment of metastatic prostate cancer forms.