Abstract 2593: Procyanidin B2 3,3″-di-O-gallate causes strong efficacy towards prostate cancer stem cells via targeting Notch1 signaling.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Prostate cancer (PCa) is the most common malignancy in US men; statistical estimates for 2012 indicate 241,740 new PCa cases and 28,170 associated deaths. Epithelial cancers including PCa are now recognized as generated and maintained by a small sub-set of undifferentiated cells known as cancer stem cells (CSC) or tumor initiating cells. Importantly, CSC are inherently resistant to chemo- and radio-therapies, and that has been the major reason for the failure of most of the current therapies. Since an early event in carcinogenesis involves expansion of CSC pool, interventions inducing apoptosis or differentiation with a loss of self-renewal capacity of CSC, represent a rational approach for PCa prevention and treatment. In this regard, the present study was aimed to determine whether grape seed extract (GSE), a natural non-toxic chemopreventive agent and its active constituent Procyanidin B2 3,3”-di-O-gallate (B2G2), have the potential to target CSC in PCa. For this, we determined the effect of these agents on the self-renewal capacity of the CSC population of PCa cell lines. The CSC cell populations were isolated and purified based on CD44+ α2β1highsurface markers in PCa cell lines LNCaP, C4-2B, 22Rv1, PC3, and DU145, and then subjected to sphere cluster formation assays, in the absence or presence of (a single or multi-treatments) GSE (5-125 μg/ml) or B2G2 (25-100μM). The percentage of floating spheroids (prostaspheres) generated in the sphere cluster assays after 1-2 weeks were determined. Results indicated that while a single treatment of GSE is not sufficient to reduce either the number or size of generated spheres in the PCa cell lines, multiple treatments with GSE at low dose was sufficient to cause a significant reduction in the number and size of generated spheres. On the other hand, single treatment of PCa cells with B2G2 significantly reduced the number and size of prostaspheres. As formation of spheroids under specific in vitro conditions is a measure of stemness, these results indicate the potential of GSE and B2G2 to target the self-renewal of CSC in PCa cell lines, though B2G2 was found to be more potent in its efficacy. Subsequent mechanistic studies revealed that both agents strongly decreased the constitutive as well as Jagged1 (Notch1 ligand)-induced protein levels of cleaved Notch and its transcriptional target Hes-1 in PCa cells. The implications of such an effect could be important, since the modulation of Notch signaling among stem cells and progenitor cells in PCa results in the expansion of CSC pool together with an increase in proliferative cell population. Together, our results are significant as they show that both GSE and B2G2 interfere with kinetics of CSC pool expansion via targeting Notch-1 regulatory signals, which eventually could help control PCa growth and progression. Citation Format: Alpna Tyagi, Komal Raina, Sushil Kumar, Rajesh Agarwal, Chapla Agarwal. Procyanidin B2 3,3″-di-O-gallate causes strong efficacy towards prostate cancer stem cells via targeting Notch1 signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2593. doi:10.1158/1538-7445.AM2013-2593