Purpose: Colorectal cancer (CRC) is one of the most common causes of cancer-associated mortality worldwide, but it is truly a preventable disease. Accumulating evidence indicates that several dietary botanicals, including curcumin and boswellic acids, have potent anti-inflammatory and anti-tumorigenic properties. However, the molecular mechanisms underlying the anti-cancer potential of these compounds remain poorly understood. More recent data suggest that the chemopreventive effects of these botanicals may in part be mediated through regulation of key cancer-related microRNAs (miRNAs), and their downstream gene targets. This study aimed to determine whether curcumin and 3 acetyl-11-keto-β-boswellic acid (AKBA) exert their anti-tumorigenic effects through modulation of specific miRNAs in CRC cell lines and a xenograft mouse model.

Experimental Design: We first determined the effects of curcumin and AKBA on cellular proliferation, apoptosis and cell cycle dynamics in a panel of CRC cell lines. Next, we used Illumina's Human HT-12 V4 array gene expression arrays to systematically identify specific gene signaling pathways regulated by curcumin and AKBA. Subsequently we used combined bioinformatics and in-silico approaches to identify miRNAs and molecular pathways activated by curcumin and AKBA individually, and their combination. We determined the functional role of curcumin and AKBA-related miRNAs in CRC cell lines, and validated these findings for the chemopreventive efficacy of curcumin and AKBA in a xenograft animal model.

Results: Both curcumin and AKBA inhibited cellular proliferation, induced apoptosis and cell cycle arrests in all CRC cell lines, and these effects were significantly enhanced with combined vis-à-vis individual treatments with the botanicals. Gene-expression arrays revealed that curcumin and AKBA regulated key cell cycle controlling genes including: cMYC, CCND1, CCNE1 and CDK4. Combined bioinformatics and in-silico analysis identified apoptosis, proliferation and cell cycle regulatory signaling pathways as the key modulators of curcumin and AKBA-induced anti-cancer effects, and further discovered miR-27a and miR-34a as the most significantly differentially expressed miRNAs following treatment with the two botanicals. In support of our in vitro findings, mouse xenograft experiments further confirmed that both curcumin and AKBA suppressed tumor size and volume in mice, and that these effects were orchestrated through modulation of miR-27a and miR-34a expression in the animal model.

Conclusion: We provide novel mechanistic evidence for the chemopreventive effects of curcumin and AKBA through regulation of specific miRNAs in CRC. The enhanced anti-tumorigenic effect by combined treatment with these botanicals provides a potential rationale for the use of such diet-based botanicals for the chemoprevention of this malignancy.

Citation Format: Shusuke Toden, Yoshinaga Okugawa, Keun Hur, Thomas A. Jascur, Constanze Burhrmann, Durgha Nattamai, Esperanza Anguiano, Mehdi Shakibaei, C. Richard Boland, Ajay Goel. Novel evidence for chemopreventive effects of curcumin and boswellic acid through regulation of mir-27a and mir-34a in human colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4119. doi:10.1158/1538-7445.AM2014-4119