The aim of this study was to investigate the potential applications of 5,5-diphenyl-2-thiohydantoin-N10 (DPTH-N10) in the treatment of human colon cancer. Subcultured human colon cancer cell line, COLO-205, was used for examining the antiproliferation effect of DPTH-N10 on colon cancer. Thymidine incorporation and cell count were conducted to examine the antiproliferation effect of DPTH-N10. Western blot analysis was performed to examine the protein levels of cell cycle-related proteins. DNA fragmentation assay was performed to examine the occurrence of apoptosis. DPTH-N10 at a range of concentrations (0-30 microM) inhibits the proliferation but did not cause the cell death of COLO-205, indicating that it may have an inhibitory effect on the cell proliferation in COLO-205. The apoptosis was observed in COLO-205 when the DPTH-N10 concentrations were higher than 30 muM. Western blot analysis showed that the protein level of the cell cycle inhibitory protein, p21, in COLO-205 increased after DPTH-N10 treatment. Immunoprecipitation showed that the formation of the cyclin-dependent kinase (CDK)2-p21 complex was increased in the DPTH-N10-treated COLO-205. Kinase assay further demonstrated that the CDK2 activity was decreased in the DPTH-N10-treated COLO-205. DPTH-N10 caused growth inhibition in COLO-205 by inhibiting DNA synthesis and activating apoptosis. The findings from our previous in vitro studies in DPTH-N10-induced anti-angiogenic effect and from the present in vitro studies in DPTH-N10-induced antiproliferation effect on colon cancer cell line strongly suggest the potential applications of DPTH-N10 in the treatment of human colon cancer.