Abstract 3908: Id1/Id3 Knockdown increases Chemosensitivity of Colorectal Cancer

Abstract

Abstract Objective: The inhibitor of DNA binding/differentiation (Id) proteins belong to the helix-loop-helix transcriptional regulatory factors, and play important roles in tumor development. Recently, overexpression of Id-1 has been associated with more aggressive and metastatic cancers in various cancer types, as well as implicated in resistance to chemotherapy, and thus, its down-regulation has been shown to lead to increased chemotherapy-induced apoptosis. Previously, we have demonstrated that simultaneous targeting of Id1 and Id3 inhibited proliferation, migration, adhesion, and metastatic growth of colorectal cancers. In the present study, we aimed to evaluate the role of Id in chemosensitivity of colorectal cancer cells, and for this purpose, human colon cancer cells with downregulated expression of Id1/Id3 were treated with oxaliplatin, and the changes in the sensitivity to chemotherapy as well as the mechanisms underlying it were investigated. Methods: Id1 and Id3 were stably and simultaneously knockdown in human colorectal cancer cell line HT29 by means of RNA interference. Both Id1 and Id3 were double-knockdown since they are known to functionally compensate each other, and the downregulation of either is not enough for the inhibition of their effects. Parental HT29 cells and the empty vector (mock) transfectants were used as control. Oxaliplatin, one component of FOLFOX6, which is one of the standard treatment protocols for colorectal cancer, was chosen as the chemotherapeutic agent. The chemosensitivity was investigated as follows: the proliferative activity was analyzed by the MTS assay, the induction of apoptosis, by the flow-cytometry after double-staining of the cells with AnnexinV/PI. Induction of autophagy was investigated by flow-cytometry after staining of the cells with acridine orange for the detection of AVOs. The changes of the cell cycle were investigated by flow-cytometry after staining of the cells with propidium iodide (PI). Results: Id double-knockdown resulted in increased chemosensitivity to oxaliplatin, as observed by the reduced proliferative ability compared with parental and mock cells. And the reduced proliferative activity was associated with the arrest of cell to the G2-M phase of the cell cycle, and the increased cell apoptosis. The chemosensitivity of Id double-knockdown cells seemed to be associated with decreased ability to induce autophagy in response to the chemotherapeutic agent. Conclusions: Id1, 3 double-knockdown resulted in increased chemosensitivity of colorectal cancer cells to oxaliplatin, dependent on the cell cycle arrest and apoptosis induction. And the decreased ability to induce autophagy seemed to be a mechanism responsible for this effect. From these results, we concluded that Id proteins play an important role in the chemoresistance of colorectal cancer, and downregulation of Id should be a promising strategy to improve chemosensitivity of Id expressing cancers. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. 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 3908.