Down-regulation of Bcl2 sensitizes radiation resistance prostate cancer cells to ionizing radiation.

Abstract Radiation therapy (RT) is an important treatment for primary prostate cancer (PCa). However, intermediate and high risk patients can relapse and recurrent disease can be resistant to RT. Bcl2 is one of the critical regulators of apoptotic cell death. Previously, we selected from the DU145 cell line (DU) a subset of cells (DUIR) that survive fractionated high dose ionizing radiation (IR) in vitro. In the current work, we have identified Bcl2 as an important regulator that determines IR resistance and IR-induced aggressiveness in PrCa cells. DUIR has undergone epithelial-mesenchymal transition (EMT) as defined by reduced E-cadherin and enhanced vimentin expression. DUIR cells display higher levels of neurotensin receptor 1 (NTR1), neuron specific enolase (NSE) and chromogranin B, resembling a neuroendocrine (NE) phenotype. DUIR survives better than DU when exposed to IR (6-10 Gy) or to zinc-directed toxins, and DUIR grows faster in response graded levels of serum or NT. NTR1 antagonist (SR48692) blocks the response to NT. NT stimulation reduces apoptosis while SR486923 enhances apoptosis in DUIR cells exposed to IR. The expression level of Bcl2 is dramatically higher in DUIR than in DU. To assess the role of Bcl2 in the ability of cells to survive IR, we generated stable cell lines using lentivirus caring Bcl2 specific shRNA. Down-regulation of Bcl2 sensitized the cells to IR, as shown by decreased proliferation, decreased clonogenicity, increased apoptosis (cleaved PARP and caspase 3/7 activity), and increased DNA breakage (γ-H2AX foci), as compared to control cells. Our study indicates that PCa cells that survive high dose IR display an aggressive phenotype characterized by NE and EMT features with resistance to IR or drug induced cell death. The up-regulation of Bcl2 plays an important role in cell survival following IR. These findings define a mechanism of cellular resistance to IR therapy and they suggest that strategies aimed to limit the effects of Bcl2 could be beneficial. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C50. Citation Format: Tao Wang, Robert E. Carraway, Joshua Briggs, Huazhen Chen, Thomas J. FitzGerald. Down-regulation of Bcl2 sensitizes radiation resistance prostate cancer cells to ionizing radiation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C50.