Detection of somatic DNA alterations in azoxymethane-induced F344 rat colon tumors by random amplified polymorphic DNA analysis

Colon carcinogenesis induced in rats by azoxymethane (AOM) is a useful expe rimental model as it mimics the human adenoma-carcinoma sequence and allows the study of dietary variation and of the effects of chemopreventive subst ances. Alterations of specific oncogenes and tumor suppressor genes (APC an d K-ras) play roles at different stages of this carcinogenesis process. Rec ently, it has been suggested that genomic instability is the necessary step for the generation of multiple mutations underlying the occurrence of canc er. We studied the frequency of K-ras and microsatellite instability (MSI) in 30 colorectal tumors induced by AOM (30 mg/kg) in F344 rats. We also use d the random amplified polymorphic DNA (RAPD) method to identify genomic al terations in chemically induced aberrant crypt foci (ACF), adenomas and ade nocarcinomas. K-ras mutations were identified in 16.7% of the cases (5/30; 9% in adenomas and 37.5% in adenocarcinomas) and MSI in 20% (6/30) of the t umors (only one sample exhibited instability at more than one locus). Of 21 primers used for the RAPD assay, six were very informative, All the analyz ed tumors (16/16) showed at least one RAPD profile with lost or additional bands compared with the normal mucosa, A lower level of genomic alteration was present in the ACF analyzed (7/10), In conclusion, K-ras and MSI are no t often involved in the AOM carcinogenesis in the rat, whereas extensive ge nomic instability is always present and can be detected using the RAPD anal ysis.