Regressive Effects of Various Chemopreventive Agents on Azoxymethane‐induced Aberrant Crypt Foci in the Rat Colon

Regressive effects of four chemopreventive agents [5‐hydroxy‐4‐(2‐phenyl‐(E)‐ethenyl)‐2(5Hfura‐none (KYN‐54), S‐methyl metbanethiosulfonate (MMTS), chlorogenic acid (CA), and piroxicam] on azoxymethane (AOM)‐induced aberrant crypt foci (ACF) in the colon of male F344 rats were examined by dietary exposure. At six weeks of age, 60 rats of groups 1 through 5 received subcutaneous injections of AOM (15 mg/kg body weight) once a week for three weeks. Twelve weeks after the first carcinogen injection, wben the occurrence of ACF was maximal, the rats in groups 2 through 5 were started on diet containing the test chemicals as follows: group 2, KYN‐54 (0.02%); group 3, MMTS (0.01%); group 4, CA (0.025%); and group 5, piroxicam (0.0125%). Group 1 (20 rats) was kept on the basal diet alone, and group 6 (12 rate) served as an untreated control. Rats in each group were killed at 6, 12, 18, or 24 weeks after the start of the experiment, and the yield of ACF in the colon of each group at 18 or 24 weeks was compared with that at 12 weeks. The number of ACF per rat colon of each group at 18 or 24 weeks was smaller than that at 12 weeks. The reduction rates at 18 weeks were 7% in group 1 (AOM alone), 11% in group 2 (AOM+KYN‐54), 10% in group 3 (AOM+MMTS), 51% in group 4 (AOM + CA) (P 0.01), and 33% in group 5 (AOM+piroxicam) (P<0.02), while at 24 weeks they were 12%, 26%, 51% (P<0.002), 43% (P <0.05), and 70% (P <0.001), respectively. These results indicate that chemopreventive agents for large bowel carcinogenesis, i.e., KYN‐54, MMTS, CA, and piroxicam, are not only able to prevent the development of ACF, but also can regress ACF, which are regarded as precursor lesions of colorectal cancer.