Mo1904 Curcumin Inhibits Epithelial-to-Mesenchymal Transition and Enhances 5-Fluorouracil Sensitivity by Targeting Specific miRNAs in Chemoresistant Colorectal Cancer

Background: Resistance to chemotherapy is one of the major causes of mortality in colorectal cancer (CRC) patients. Chemoresistance has been linked to a subset of ‘cancer cells with stem cell-like' properties undergoing epithelial-to-mesenchymal transition (EMT). Emerging evidence indicates that microRNAs (miRNAs) play a critical role in regulating pathways involved in cancer stemness including polycomb repressive complexes (PRC) and EMT. Curcumin, a potent anti-inflammatory and anti-cancer botanicalmodulates multiple miRNAs, and has been shown to enhance chemosensitivity of chemotherapeutic drugs, such as 5fluorouracil (5FU). However, the molecular mechanisms underlying chemoresistance and the involvement of specific miRNAs and the downstream gene targets mediating EMT and regulation of PRC proteins in CRC remains unclear. Aim: We determined whether curcuminmediated chemosensitization manifests through regulation of specific miRNAs that regulate EMT and polycomb complexes in 5FU-resistant CRC cells. Methods: We first established 5FU resistant (5FUR) CRC cell lines by culturing HCT116 and SW480 cells to increasing concentrations of 5FU for several months. Thereafter, we examined the effects of curcumin (2.5-30 μM) on cellular proliferation, apoptosis, cell-cycle dynamics, and migration in parental and 5FUR cells. Next, we systematically explored the role of curcumin in a subset of putative EMT and PRC-related miRNAs in 5FUR cells. Finally, we validated the chemosensitizing effects of curcumin in a xenograft mice model. Results: Curcumin treatment resulted in inhibited proliferation and migration, increased apoptosis and G2/M arrest in all cell lines, but combined treatment with curcumin and 5FU demonstrated significant synergistic effects in 5FUR cell lines. Interestingly, curcumin upregulated the expression of EMT and PRC related tumor suppressive miR-101, 200b, 200c, 141 and 34ain 5FUR cells. We identified that curcumin suppressed EMT in 5FUR cell lines by down-regulating ZEB1, and inhibited PRC-mediated transcription by targeting EZH2, BMI1 and SUZ12, which dictate cancer Mechanistic investigations revealed that ectopic expression of miR-200c enhanced 5FU sensitivity by down-regulating ZEB1 and BMI1 expression, while siRNA knockdown of miR-200c further enhanced 5FU resistance in 5FUR cells. In addition, we successfully demonstrated this phenomenon in a xenograft model, wherein curcuminmediated 5FU sensitization significantly suppressed tumor growth in these animals. Conclusion: We provide novel mechanistic evidence for curcumin-mediated enhancement of 5FU chemosensitivity through suppression of EMT and PRC in 5FUR cells via coordinated modulation of specific-miRNAs that control cancer stemness. This study highlights the potential therapeutic usefulness of curcumin as a potential adjunct in chemoresistant CRC patients.