Grape compounds suppress colon cancer stem cells in vitro and in a rodent model of colon carcinogenesis

Background: We have previously shown that the grape bioactive compound resveratrol (RSV) potentiates grape seed extract (GSE)-induced colon cancer cell apoptosis at physiologically relevant concentrations. However, RSV-GSE combination efficacy against colon cancer stem cells (CSCs), which play a key role in chemotherapy and radiation resistance, is not known. Methods: We tested the anti-cancer efficacy of the RSV-GSE against colon CSCs using isolated human colon CSCs in vitro and an azoxymethane-induced mouse model of colon carcinogenesis in vivo. Results: RSV-GSE suppressed tumor incidence similar to sulindac, without any gastrointestinal toxicity. Additionally, RSV-GSE treatment reduced the number of crypts containing cells with nuclear beta-catenin (an indicator of colon CSCs) via induction of apoptosis. In vitro, RSV-GSE suppressed - proliferation, sphere formation, nuclear translocation of beta-catenin (a critical regulator of CSC proliferation) similar to sulindac in isolated human colon CSCs. RSV-GSE, but not sulindac, suppressed downstream protein levels of Wnt/beta-catenin pathway, c-Myc and cyclin D1. RSV-GSE also induced mitochondrial-mediated apoptosis in colon CSCs characterized by elevated p53, Bax/Bcl-2 ratio and cleaved PARP. Furthermore, shRNA-mediated knockdown of p53, a tumor suppressor gene, in colon CSCs did not alter efficacy of RSV-GSE. Conclusion: The suppression of Wnt/beta-catenin signaling and elevated mitochondrial-mediated apoptosis in colon CSCs support potential clinical testing/application of grape bioactives for colon cancer prevention and/or therapy.