Abstract 2819: Temsirolimus inhibits colon cancer growth in vitro and in vivo
Authors: Manabu Kaneko, Hiroaki Nozawa, Nelson H. Tsuno, Kazushige Kawai, Kazuhito Sasaki, Kumiko Hongo, Masaya Hiyoshi, Eiji Sunami, Koki Takahashi, Joji Kitayama
Journal: Cancer Research (2012)

Abstract Objective: Temsirolimus (CCI-779), an ester of the macrocyclic immunosuppressive agent sirolimus, is a cytostatic cell cycle inhibitor with antitumor properties. Temsirolimus inhibits the mammalian target of rapamycin (mTOR), a serine-threonine kinase involved in the initiation of mRNA translation, and has been shown to inhibit the growth of a variety of tumor cells. However, there have been only a few reports concerning the effect of temsirolimus on colon cancer cells. In the present study, we aimed to investigate the mechanisms of antitumor activity of temsirolimus in colon cancer cells in in vitro and in vivo studies. Methods: Two human colon cancer cell lines, CaR1 and LOVO, were treated with temsirolimus at a range of concentrations. Cell proliferation, cell cycle and apoptosis indices were evaluated to assess antitumor effects in vitro. The effect of temsirolimus on the proliferative activity was investigated by the MTS assay. The cell cycle was evaluated by flow-cytometry after staining of cell with PI. Apoptosis was analyzed by flow-cytometry after double-staining of cells with AnnexinV/PI. PI3K/AKT/mTOR pathway related proteins were measured by Western blot analysis. The in vivo effects of temsirolimus on tumor cell growth were examined using subcutaneous xenograft mouse model. Temsirolimus treatment (0, 0.1, 1, 10 mg/kg, 3 days/week, i.p.) was started when tumor reached approximately 100-200 mm3, and repeated three weeks. Tumor volume was calculated using the following equation: Volume (mm3) = Length x Width2 x 1/2. Results: Temsirolimus decreased the ability of colon cancer cells to proliferate in vitro in time and dose dependent manners. Furthermore, temsirolimus induced G1 cell cycle arrest, but did not induce apoptosis. Western blot analysis revealed that temsirolimus downregulated phospho-S6K, which phosphorylates the S6 protein of the 40S ribosomal subunit and leads to initiation of protein synthesis. In murine xenograft model, temsirolimus reduced tumor volume in a dose-dependent manner. After three weeks treatment, the average tumor volume in the vehicle group was about four times larger than that in the group receiving temsirolimus at a dose of 10mg/kg. Conclusions: Temsirolimus suppressed the proliferation of colon cancer cells in vitro through induction of G1 cell cycle arrest and downregulation of phospho-S6K. The tumor suppressive effect of the mTOR inhibitor was reproduced in an in vivo model. Our present findings indicate that mTOR signaling is a potential target of colon cancer, and the mTOR inhibitor temsirolimus may be a promising agent for colon cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2819. doi:1538-7445.AM2012-2819