Effects of long-term feeding with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in C57BL/ByA and Eμ-pim-1 mice

The heterocyclic amine PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, has been shown to be carcinogenic in rats producing colon and mammary carcinomas. There is, so far, only a single long-term study report on PhIP carcinogenicity in mice. However, this study focuses on the lymphoma induction only. Whether PhIP induces tumors in other organs in mice after long-term exposure is yet to be established. To contribute to the knowledge about the long-term effects of PhIP feeding the remaining animals from a 7 months feeding study (0.03% PhIP) were put on standard diet and followed up to 18 months. The results confirmed that PhIP is a potent mouse lymphomagen. In addition, treatment with 0.03% PhIP in the diet for the first 7 months of a life-time study (18 months) gave rise to very few and sporadic tumors in other tissues, indicating weak, if any, carcinogenicity of PhIP to organs other than the lymphatic system under the present study design.