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Down-regulation of miR-221 inhibits proliferation of pancreatic cancer cells through up-regulation of PTEN, p27(kip1), p57(kip2), and PUMA.

Pancreatic cancer is the fourth leading cause of cancer related death in the US and exhibits aggressive features with short survival rate and high mortality. Therefore, it is important to understand the molecular mechanism(s) involved in the aggressive growth of pancreatic cancers, and further design novel targeted therapies for its treatment with better treatment outcome. In the present study, we found that the expression of miR-221 was significantly up-regulated in pancreatic cancer cell lines and tumor tissues compared to normal pancreatic duct epithelial cells and normal pancreas tissues. Moreover, we found that the pancreatic cancer patients with high miR-221 expression had a relatively shorter survival compared to those with lower expression, suggesting that miR-221 could be an oncogenic miRNA and a prognostic factor for poor survival of patients. Interestingly, transfection of miR-221 inhibitor suppressed the proliferative capacity of pancreatic cancer cells with concomitant up-regulation of PTEN, p27(kip1), p57(kip2), and PUMA, which are the tumor suppressors and the predicted targets of miR-221. Most importantly, we found that the treatment of pancreatic cancer cells with isoflavone mixture (G2535), formulated 3,3'-diindolylmethane (BR-DIM), or synthetic curcumin analogue (CDF) could down-regulate the expression of miR-221 and consequently up-regulate the expression of PTEN, p27(kip1), p57(kip2), and PUMA, leading to the inhibition of cell proliferation and migration of MiaPaCa-2 and Panc-1 cells. These results provide experimental evidence in support of the oncogenic role of miR-221 and also demonstrate the role of isoflavone, BR-DIM, and CDF as potential non-toxic agents that are capable of down-regulation of miR-221. Therefore, these agents combined with conventional chemotherapeutics could be useful in designing novel targeted therapeutic strategy for the treatment of pancreatic cancer for which there is no curative therapy.