Zapotin (5,6,2',6'-tetramethoxyflavone), found in the tropical fruit zapote blanco (Casimiroa edulis), is consumed in many parts of the world, including Central America and Asia. Previously, we have demonstrated in vitro chemopreventive activity of extracts derived from the seeds of C. edulis. In the present study, we examined the effects of natural and synthetic zapotin in SW480, SW620, and HT-29 colon cancer cell lines and on the generation of aberrant crypt foci (ACF) using mice. Zapotin treatment (IC50=2.74x10(-7 M)) resulted in a marked suppression of cell proliferation in the HT-29 cells. Cell cycle analysis demonstrated a significant accumulation of cells in the G2-M phase, with a concomitant decrease of cells in the G0-G1 phase, after treatment with zapotin (molecular weight=342.35 g/mol; 1 microM for 18, 24, and 48 h). Zapotin treatment enhanced apoptosis in all of the colon cancer cell lines studied. For the study of ACF, 5-wk-old CF-1 mice were given subcutaneous injections of azoxymethane (AOM; 10 mg/kg body weight, BW) weekly for 2 wk, and zapotin (5 or 10 mg/kg BW; 46 or 92 pmol/kg BW) or vehicle was administered intragastrically 7 days/wk. The mean number of ACF for the control group was 14.0+/-2.3, whereas the mean numbers of ACF in the zapotin-treated groups were 6.2+/-1.7 and 4.6+/-1.4 at doses of 5.0 and 10.0 mg/kg BW, respectively. Loss of hexosaminidase, a lysosomal enzyme active in normal colonic crypts but decreased in up to 95% of ACF, was used as a second biomarker for colon carcinogenesis. Zapotin was found to significantly (P<0.01) prevent loss of hexosaminidase in the colon of AOM-treated mice. The present study is the first to report the potent anticancer activity of zapotin and suggests a role for zapotin both as a chemopreventive and a chemotherapeutic agent against colon cancer.