Abstract 2127: Silibinin modulates the inflammatory signals on colon cancer stem cells and provides protective effect against colitis-associated colon tumorigenesis

The inflammatory milieu of the colon cancer stem cell (CSC) niche is an important growth regulator for both CSC and progenitor cell population. The inflammatory signals such as cytokines arising in CSC niche, due to the presence of inflammatory cells, also network with other regulatory pathways to influence the expansion of both cell types. Activation of interleukin (IL)-mediated signaling cascade in colon enterocytes also regulates cell survival in colitis-associated tumorigenesis and provides an autocrine/paracrine amplification loop in colorectal cancer (CRC). Also, myeloid cells in the lamina propria of mice subjected to colitis-associated CRC produce cytokines that stimulate the proliferation of adjacent pre-malignant intestinal epithelial cells. Recent studies have also identified IL-4/ 6 as critical NF-κB-dependent pro-tumorigenic cytokines, produced by lamina propria myeloid cells that stimulate survival and proliferation of pre-malignant intestinal epithelial cells via oncogenic transcription factor STAT-3. Together, these studies suggest that blocking inflammatory milieu could be a rational approach to control CRC. We found that silibinin, a non-toxic CRC chemopreventive agent, strongly decreases colonosphere formation and that this effect on colon CSC is mediated via blocking of IL-4/ 6 signaling in CRC cell lines. Silibinin also caused a strong decrease in IL-4/ 6 induced transcriptional activation of STAT-3 and NF-κB, which was associated with decreased mRNA levels of various CSC regulatory molecules, and associated markers and transcription factors. Next, we used a colitis-related AOM/DSS-induced colon tumorigenesis model to assess the role of inflammatory conditions on colon CSC generation and expansion, and their modulation by silibinin. In this model, male BALB/c mice were given a single i.p. injection of a colonic genotoxic carcinogen AOM (10 mg/kg body wt) followed by colitis inducing synthetic sulfate polysaccharide (DSS) at 2% (w/v) in drinking water for 7 days, which resulted in severe colonic inflammation, followed by cryptic dysplasia and carcinoma. In silibinin group, starting 5 weeks before AOM, mice were gavaged orally with 600 mg/kg of siliphos (silibinin) and continued till study end. Post necropsy, our results indicated that silibinin feeding provided the protective effect as evidenced by minimal inflammation in entire length of colon, absence of large macroadenomas (>2-3mm) in the colon, and no significant change in colon length as observed in AOM/DSS control colons which had shortened in length. Also importantly, while rectal bleeding and rectal prolapse incidence was frequently observed in AOM/DSS controls, such incidences were minimal in silibinin-fed mice. Together, these results further support the translational relevance of silibinin in human CRC control. Citation Format: Alpna Tyagi, Ranganatha Somasagara, Sushil Kumar, Komal Raina, Chapla Agarwal, Rajesh Agarwal. Silibinin modulates the inflammatory signals on colon cancer stem cells and provides protective effect against colitis-associated colon tumorigenesis. [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 2127. doi:10.1158/1538-7445.AM2014-2127