Colon Cancer Chemoprevention by Ursodeoxycholic Acid

描述(申请人提供)：我的主要目标是发展成为结肠癌化学预防领域的独立研究员。我的长期研究目标是阐明熊去氧胆酸在结肠癌方面发挥抗癌作用的机制。 我们已经证明，补充胆酸促进了偶氮甲烷诱导的大鼠结肠肿瘤的发展。相比之下，饮食中的熊去氧胆酸(UDCA)抑制了肿瘤的形成，并抑制了胆酸诱导的肿瘤促进作用。为了研究UDCA抗癌作用的机制，初步研究表明，UDCA在mRNA和蛋白水平上都抑制了ACF间质细胞中COX-2基因的表达，并减少了COX-2的免疫染色。此外，来自人类结肠癌的HCA-7细胞对脱氧胆酸(DCA)的反应表现出COX-2的上调。DCA是初级胆汁酸胆酸的主要代谢物，是一种有效的促胆汁酸肿瘤物质。相反，UDCA抑制了DCA诱导的Hca-7细胞中COX-2的上调，进一步支持了我们的假设，即UDCA的化学预防作用至少部分涉及UDCA抑制结肠癌COX-2表达的能力。因此，Hca-7细胞对UDCA的反应与在AOM模型中观察到的COX-2抑制类似。因此，这些细胞将是一个理想的体外模型，以剖析与COX-2在结肠癌发生中的失调有关的分子事件。它们还将使我们能够确定UDCA抑制COX-2表达的潜在机制，从而抑制肿瘤的发生。在我们的特定目标中，我们建议阐明DCA上调COX-2的信号转导途径和调节成分，而UDCA抑制这种诱导。 目前的项目非常符合我的长期研究目标，即评估这种化学预防胆汁酸的分子靶点。我们在这项提案中的发现也可能确定潜在的斑点，我们将在未来的人类ACF研究中验证这些斑点。

DESCRIPTION (provided by applicant): My primary goal is to develop into an independent investigator in the field of colon-cancer chemoprevention. My long-term research objectives are to elucidate the mechanisms by which ursodeoxycholic acid exerts anticarcinogenic effects with respect to colon cancer. We have demonstrated that supplemental dietary cholic acid promoted the development of azoxymethane-induced rat colonic tumors. In contrast, dietary ursodeoxycholic acid (UDCA) inhibited tumorigenesis and suppressed cholic acid-induced tumor promotion. To examine the mechanisms by which UDCA causes anticarcinogenic effects, preliminary studies in the proposal demonstrated that UDCA inhibited Cox-2 gene expression at both the mRNA and protein levels and decreased Cox-2 immunostaining in stromal cells within the ACF. Furthermore, HCA-7 cells derived from a human colon cancer, demonstrated up-regulation of Cox-2 in response to deoxycholic acid (DCA). DCA is the major metabolite of the primary bile acid cholic acid, and is a potent tumor promoting bile acid. In contrast, UDCA inhibited DCA-induced Cox-2 up-regulation in HCA-7 cells, further supporting our hypothesis that the chemopreventive actions of UDCA involve, at least in part, the ability of UDCA to inhibit Cox-2 expression in colon cancer. HCA-7 cells, therefore, manifest a similar response to UDCA with respect to Cox-2 inhibition as observed in the AOM model. These cells will, therefore, serve as an ideal in vitro model to dissect the molecular events involved in Cox-2 dysregulation in colonic carcinogenesis. They will also allow us to identify potential mechanisms by which UDCA acts to inhibit Cox-2 expression, and thereby suppress tumorigenesis. In our Specific aims we propose to elucidate the signal transduction pathways and regulatory components by which DCA up-regulates Cox-2, while UDCA suppresses this induction. The current project fits well into my long-term research objectives to evaluate the molecular targets of this chemopreventive bile acid. Our findings in this proposal will also likely identify potential blomarkers that we will validate in a future study involving human ACF.