Abstract 4362: Plk1 is overexpressed in retinoblastoma and its inhibition by siRNA or small-molecule inhibitor results in growth arrest and apoptosis

Abstract

Abstract Retinoblastoma (RB) is a pediatric cancer of the retina where current chemotherapeutic regimens are broad spectrum with significant side effects. Molecular target-based approaches for RB therapy are absent and may be rational for this disease. We performed a siRNA library screen for growth inhibition of human Y79 RB cells. Knockdown of Plk1 or AURKA (but not other mitotic regulatory factors) lead to greater than 90% cell growth inhibition and prompted further investigation. We determined Plk1 expression in retinoblastoma and normal retina tissue by immunohistochemistry. We also determined the effects of siRNA-mediated Plk1 knockdown and small molecule-mediated Plk1 inhibition on Y79 and Weri-Rb1 cell growth using a tetrazolium dye-based assay. Effects on proliferation and cell cycle distribution were determined by flow cytometric analysis of EdU incorporation and DNA content. Activation of DNA damage response and apoptosis was determined by western blot analysis of phospho-H2AX, cleaved caspase-3, and PARP. We observed moderate and high Plk1 protein expression in several human retinoblastoma tumor samples as compared to minimal or low expression found in normal retinal tissue. Increased Plk1 expression was observed in RB cell lines as compared to normal retina cells. 10 nM Plk1 siRNA and 30 nM BI-2536 potently inhibited Y79 and Weri-Rb1 cell growth and significantly decreased cell viability. A decrease in S phase EdU incorporation and proliferation and an increase in G1 phase population was observed in flow cytometric analysis of Plk1 inhibited RB cells. A significant increase in phospho-H2AX, cleaved caspase-3, and cleaved PARP protein levels was observed in Y79 and Weri-Rb1 cells treated with Plk1 siRNA or BI-2536. These results suggest that Plk1 may be a rational target for RB therapy and encourages preclinical studies in animal models of RB. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4362.