Description:
<jats:title>Abstract</jats:title>
<jats:p>Background:</jats:p>
<jats:p>The standard treatment for locally advanced rectal carcinomas consists of preoperative chemoradiotherapy (CT/RT), followed by radical surgery. However, the clinical response to this treatment strategy is very heterogeneous. To determine the molecular basis of disparate response, we recently profiled a series of responsive and resistant rectal cancers using gene expression microarrays and identified a set of differentially expressed genes. One gene that was significantly over-expressed in the resistant tumors was TCF7L2 (also known as TCF4), the main downstream effector of the Wnt signaling pathway. The aim of this study was to understand its role in treatment response by testing the hypothesis that RNAi-mediated silencing of TCF7L2 sensitizes tumor cells to radiation therapy.</jats:p>
<jats:p>Methods:</jats:p>
<jats:p>The colorectal cancer cell line SW480, which is relatively resistant to radiation, was transfected with two different shRNA-vectors targeting TCF7L2, and a non-silencing control. Subsequently, stable single cell clones were established, and knockdown efficiency was analyzed by Western blot analysis. For each vector, individual clones were irradiated at 2, 4, 6 and 8 Gy. Colonies were counted after 10 days to calculate the respective surviving fractions.</jats:p>
<jats:p>Results:</jats:p>
<jats:p>TCF7L2 protein levels were reduced to ∼ 34% for shRNA_1, and ∼ 29% for shRNA_2. This led to a ∼ 1.6-fold growth inhibition (plating efficiency) compared to the non-silencing control. Importantly, RNAi-mediated silencing of TCF7L2 significantly reduced colony-formation after radiation (dose reduction factors of ∼ 1.5 and ∼ 2.0 at 37% survival for shRNA_1 and shRNA_2, respectively). These results were validated in a second cell line (HT29). In addition, we analyzed global gene expression profiles after RNAi to analyze the global transcriptomic changes induced by silencing TCF7L2.</jats:p>
<jats:p>Conclusion:</jats:p>
<jats:p>TCF7L2 is over-expressed in rectal carcinomas resistant to chemoradiotherapy. RNAi-mediated silencing of this gene caused a significant growth inhibition and, importantly, radiosensitization of colorectal cancer cells. Thus, TCF7L2 might represent a potential molecular target to sensitize a priori resistant tumor cells. Additionally, these data provide first evidence that the Wnt signaling pathway might not only be central for the development of colorectal cancers, but also for the resistance to therapy.</jats:p>
<jats:p>Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 487.</jats:p>