Abstract: AIM: To investigate the effect and the mechanism of thymoquinone in the growth inhibition of human colon cancer in vitro and in vivo. METHODS: After human colon cancer SW480 cells were treated with different concentrations of thymoquinone, the cellular proliferation was detected by Cell Counting Kit-8 (CCK-8) assay. The flow cytometry (FCM) was used to determine apoptosis in SW480 cells. Western blotting was used to detect the protein expression of NF- B, Bcl-2 and Survivin. SW480 cells were injected subcutaneously into nude mice to establish xenograft model, and the mice were randomized into two groups (n= 10): Control group, feed with 1% ethanol; Test group, thymoquinone (3 mg/mouse) was given by intragastric intubation. All treatment lasted for two weeks, thrice per week. Eight weeks after implantation, tumor weight and inhibition rate were evaluated respectively after the mice were sacrificed. Immunohistochemistry was used to detect the positive expression of NF- B, Bcl-2 and Survivin in the tumors. RESULTS: Thymoquinone induced a higher percentage of growth inhibition and apoptosis in SW480 cell when compared with the control. The expression of NF- B, Bcl-2 and Survivin were down-regulated in human colon cell line SW480 after treatment of thymoquinone. The treatment of thymoquinone showed significant decrease (P<0.05) in tumor weight relative to untreated control, and the positive expression of NF- B, Bcl-2 and Survivin in the tumors of test group was significantly lower than those in control group. CONCLUSION: Thymoquinone has the antitumor effect to the human colon cancer both in vitro and in vivo, and the effect may be related to the down-regulation of NF-κB and its regulated molecules such as Bcl-2 and Survivin proteins.

Key words: Thymoquinone, Colon cancer, NF- B