Interaction between the cytostatic effects of quercetin and 5-fluorouracil in two human colorectal cancer cell lines

Therapy with 5-fluorouracil (5-FU) as a single agent has only limited success in palliative treatment of cancer of the large bowel. In the current study, the effect of quercetin on the action of 5-FU in the human colorectal cancer cell lines COLO 320 DM and COLO 205 was evaluated using the MTT and clonogenic assays. Both assays were used in order to discriminate between cell growth inhibition and actual cell kill. As single agents as well as in combination, considerably higher concentrations of 5-FU and quercetin were required in the clonogenic assay to obtain detectable effects than in the MTT assay. In the MTT assay, but not in the clonogenic assay, a synergistic interaction between quercetin and 5-FU was found for COLO 320 DM cells. Our results therefore indicate that this interaction between quercetin and 5-FU mainly takes place at the level of growth inhibition. It is concluded that the cytostatic action of a combination of quercetin and 5-FU in COLO 320 DM cells is superior to that of the single agents.