MicroRNAs are endogenous posttranscriptional modulators that negatively control the expression of their target genes and play an important role in the development and progression of many
malignancies, including
colorectal carcinoma. In particular, expression of microRNA-21 (miR-21) is greatly increased in
chemotherapy-resistant (CR)
colon cancer cells that are enriched in undifferentiated
cancer stem/stem-like cells (CSCs/CSLCs). We hypothesize that miR-21 plays a critical role in regulating differentiation of CR
colon cancer cells. Indeed, we observed that downregulation of miR-21 in CR
colon cancer cells (HCT-116 or HT-29) by antisense miR-21 induced differentiation, as evidenced by marked increases in
cytokeratin-20 (CK-20) expression and
alkaline phosphatase activity. These changes were accompanied by a significant reduction in the expression of colon CSC/CSLC marker CD44, colonosphere formation, and
T-cell factor/
lymphoid enhancer factor (TCF/LEF) activity but increased the expression of proapoptotic programmed cell death 4 gene. Induction of differentiation greatly increased sensitivity of CR
colon cancer cells to the growth inhibitory properties of all three regimens tested:
5-fluorouracil +
oxaliplatin (FUOX), difluorinated
curcumin (CDF), and the combination of CDF and FUOX. However, the magnitude of inhibition of growth by either CDF (75%) alone or CDF + FUOX (80%) was much higher than that observed with only FUOX (40%). Growth inhibition by CDF and CDF + FUOX in differentiating CR
colon cancer cells was associated with a 98% to 99% reduction in the expression of CD44 and
epidermal growth factor receptor (EGFR). However, down-regulation of CK-20 in CR
colon cancer cells produced no significant change in cellular growth in the absence or presence of FUOX, when compared with the corresponding controls. The current observation suggests that CDF and CDF + FUOX are highly effective in inhibiting growth and reducing colon CSCs/CSLCs in anti-miR-21-induced differentiating CR
colon cancer cells and supports our contention that differentiation enhances susceptibility of CR
cancer cells to conventional and nonconventional therapeutic regimen.