Background and Aims: Colorectal cancer (CRC) is the second leading cause of cancer-related mortality rate in the United States, but can be prevented through lifestyle and dietary modifications. Over the last two decades, anti-tumorigenic properties of various botanicals have been studied extensively, and currently selected compounds are being exploited as potential chemopreventive agents. Proanthocyanidins are the most abundant dietary polyphenols present in many fruits and vegetables. Although anti-tumorigenic properties of proanthocyanidins have been investigated substantially, emerging evidence indicates that oligomeric form of proanthocyanidins (OPCs) has more potent anti-tumorigenic properties, but the underlying mechanisms remain unclear. A small subset of cancer cells, termed “cancer stem cells” (CSCs), are believed to be the major contributors of tumor initiation and metastasis. Despite complex molecular network associated with CSCs, several botanicals have shown promising efficacy against CSCs. We aimed to investigate the protective role of OPCs, focusing on CRC CSC formation, using cell lines and animal models. Methods: The effects of OPCs on cellular proliferation, apoptosis and cell-cycle dynamics were examined in a series of in-vitro experiments. Spheroid derived CSCs (SDCSCs) were generated from CRC cell lines to determine whether OPCs can suppress sphere formation capacity. The role of OPCs on major signaling pathways driving self-renewal capability (Hippo-YAP, Polycomb repressive complex (PRC) and intestinal stem cell markers) was systematically assessed. Finally, chemopreventive efficacy of OPCs was tested in a mouse xenograft model. Results: OPCs inhibited cellular proliferation and induced apoptosis in a dose-dependent manner. Cell cycle analysis revealed that OPC-treated CRC cells underwent G2/M arrest and subsequently showed reduced cellular proliferation. Intriguingly, OPCs suppressed SDCSC formation at a significantly low dose, suggesting that these could effectively inhibit CSC formation. Mechanistically, OPCs suppressed Hippo-YAP pathway, a major pathway driving cellular proliferation and stem cell reprogramming, through simultaneous inhibition of multiple Hippo-YAP associated proteins. In CRC cell lines with high YAP expression, OPCs preferentially inhibited YAP, while a downstream regulator TAZ was targeted in cells with low YAP expression. Furthermore, we showed that OPCs suppressed CRC CSC markers (CD44, CD133, ALDH1 and Notch1) and BMI1, EZH2 and SUZ12, key oncogenic PRC subunits. In addition, using SDCSC derived mouse xenograft model, we demonstrated that OPCs significantly inhibited tumor growth. Conclusion: Collectively, our data unravels previously unrecognized mechanisms for OPCs to target CSCs and Hippo-YAP pathway in CRC. These data highlight the therapeutic potential of OPCs as chemopreventive agents through inhibition of CSC formation.

Citation Format: Shusuke Toden, Ajay Goel. Oligomeric proanthocyanidins inhibit Hippo-YAP pathway and prevent colorectal cancer stem cell formation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4311.