Epigallocatechin-3-gallate targets cancer stem-like cells and enhances 5-fluorouracil chemosensitivity in colorectal cancer

Resistance to cytotoxic chemotherapy is a major cause of mortality in colorectal cancer (CRC) patients. A small subset of cancer cells, termed “cancer stem cells” (CSCs), are believed to be key contributors of chemoresistance and tumor recurrence. Recently, epigallocatechin-3-gallate (EGCG), an active catechin present in green tea, has been shown to suppress CSC growth in various cancers, but whether it can specifically target CSCs and subsequently sensitize chemoresistant CRC cells to standard of care chemotherapeutic treatments remains unknown. Herein, we investigated the chemosensitizing effects of EGCG in 5-fluorouracil (5FU)-resistant (5FUR) CRC cells and spheroid-derived CSCs (SDCSCs), and interrogated the underlying molecular mechanisms responsible for its chemopreventive activity. EGCG enhanced 5FU-induced cytotoxicity and inhibited proliferation in 5FUR cell lines through enhancement of apoptosis and cell cycle arrest. The 5FUR cells showed higher spheroid forming capacity compared to parental cells, indicating higher CSC population. EGCG treatment in these cells resulted in suppression of SDCSC formation and enhanced 5FU sensitivity to SDCSCs. Furthermore, EGCG suppressed Notch1, Bmi1, Suz12, and Ezh2, and upregulated self-renewal suppressive-miRNAs, miR-34a, miR-145, and miR-200c, which are some of the key pathways targeted in 5FUR CRC cells. These findings were validated in vivo, wherein EGCG treatment resulted in inhibited tumor growth in a SDCSC xenograft model. Collectively our data provide novel and previously unrecognized evidence for EGCG-induced sensitization to 5FU through targeting of CSCs in CRC. Our data highlight that in addition to its chemopreventive ability, EGCG may serve as an adjunctive treatment to conventional chemotherapeutic drugs in CRC patients.