Context: The compound 4,7-dimethoxy-5-(2-propen-1-yl)-1,3-benzodioxole (apiole) has been isolated from several different plant species, including Petroselinum sativum. Our recent study found that apiole is a chemical derivative of 4,7-dimethoxy-5-methyl-l,3-benzodioxole (SY-1), which has been isolated from dried Antrodia camphorata (AC ) fruiting bodies, a traditional Chinese medicine with antitumor properties.Aims: Our previous in vitro study demonstrated that apiole inhibits the growth of human colon (COLO 205) cancer cells through the arrest of the cell cycle in G0/G1 phase. The in vivo antitumor effects of apiole were evaluated in this study.Setting and Design: Apiole was administered to mice at 1-30 mg/kg body weight through intraperitoneal (I.P.) injection three times per week... (defined as a dosage of 1×-30×).Materials and Methods: The in vivo antitumor effects of apiole were evaluated in mice with xenografts of COLO 205 cells.Statistical Analysis: All of the data are reported as the means ± S.E. Comparisons were performed with a one-way analysis of variance (ANOVA) followed by a Fisher′s least significant difference test. Significance was defined as P < 0.05.Results: Apiole (> 1×) markedly decreased the growth of COLO 205 human colon cancer cell tumor xenografts in an athymic nude mouse model system through the up-regulation of cell cycle regulators, such as p53, p21/Cip1, and p27/Kip1. The apiole-induced increase in G0/G1 phase cell cycle regulators was also associated with a significant decrease in the expression of cyclins D1 and D3. Surprisingly, statistically significantly higher tumor volumes were observed in mice that received 5× apiole compared with 30× apiole-treated mice (P < 0.05). No gross signs of toxicity were observed (e.g., body weight changes, general appearance, or individual organ effects) in any group.Conclusions: Our results show, for the first time, the promising antitumor effects of apiole against colon tumors in an in vivo xenograft model.