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Celecoxib (Celebrex®) is a cyclooxygenase-2 (COX-2) selective inhibitor that has been proposed to be effective as an anti-tumor agent in several types of human cancer. Human, animal, and in-vitro studies have been conducted to determine the mechanism of cell death and the possible therapeutic use of anti-inflammatory drugs in the treatment of cancer because many cancer types exhibit increased expression of COX-2, including colon cancer. This research examined the anti-tumor properties of celecoxib on HT-29 colon carcinoma cells grown in a three dimensional agarose model. This model is permissive, unlike monolayer culture models, and is not affected by contact growth inhibition. Cells are suspended in agarose as single cells, where they can then form colonies of cells over the course of 1 - 2 weeks. Direct observation of the mitotic activity of each cell can then be observed as single cells develop into colonies. Furthermore, dead cells can be identified by using Trypan blue exclusion.

The IC50 for celecoxib in monolayer in the HT-29 cell line was found to be 55 μg/ml. In the agarose method, lower concentrations of 2.5, 5, and 10 μg/ml were examined which approach celecoxib blood levels in humans (200 mg single oral dose, range from 0.5 - 2 μg/ml plasma, highly variable (H.-H. S. Chow et al., J. Pharm. Biomed. Analysis 34 (2004) 167-174)). In control cells, 89% of the cells developed colonies, and 10% remained single cells. For treatments of 2.5, 5, and 10 μg/ml, respectively, 21, 57, and 76% remained as single cells. The number of dead single cells (as measured by trypan blue exclusion) was respectively, from control to 10 μg/ml: 2, 6, 19, and 56%, indicating both an antimitotic activity, as well as a cytotoxic component (Student’s t-test, p<0.05 for all treatments compared to control). As the number of single cells increased, there was a concomitant decrease in colonies formed. While the number of colonies decreased, there was an increase in the number of dead cells in the colonies relative to control. Additionally, colonies that formed were smaller in size reflecting fewer cells in the colony when compared to control. In conclusion, celecoxib shows significant cell growth inhibitory as well as a cytotoxic activity against HT-29 cells cultured in agarose. The decreased cytotoxic effect relative to mitotic activity inhibition may explain why celecoxib does not completely block polyp formation in certain cancer patients.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA