HIGHLY METASTATIC HEPATOCELLULAR CARCINOMAS INDUCED IN MALE F344 RATSTREATED WITH N-NITROSOMORPHOLINE IN COMBINATION WITH OTHER HEPATOCARCINOGENS SHOW A HIGH-INCIDENCE OF P53 GENE-MUTATIONS ALONG WITH ALTEREDMESSENGER-RNA EXPRESSION OF TUMOR-RELATED GENES

The carcinogenic and metastatic processes are thought to consist of a sequence of steps, and animal models featuring highly metastatic lesio ns are clearly necessary to allow analysis of the whole process of tra nsformation from preneoplastic changes to high grade metastatic tumors , and to access effectiveness of therapeutic treatments of advanced ca ncers in vivo. The purpose of the present study was to establish a mod el and to screen for reported genetic alterations in induced lesions, In the present study, it was confirmed that lung metastasis of hepatoc ellular carcinomas (HCCs) induced in male F344 rats by N-nitrosomorpho line (NNM), given in the drinking water at a dose of 120 ppm for 24 we eks, was significantly enhanced by additional carcinogenic pretreatmen ts and that a single i.p. injection of 100 mg/kg body weight N-diethyl nitrosamine (DEN) alone was sufficient for that purpose. Molecular bio logical analyses of the induced lesions revealed point mutations in th e p53 gene in 60.9% of HCCs, and elevated expression of mRNAs for p53, c-myc, c-fos, TGF-alpha, TGF-beta 1, alpha-fetoprotein, GST-P, and GG T, and decreased mRNA expression of EGF and EGFR in HCCs when compared to controls. No obvious association of gene alterations with metastat ic potential of primary tumors was found except for an increase in the incidence of p53 mutations. Since the process of metastasis is though t to be sequential and selective, further comparative analysis of meta static and primary lesions should clarify the mechanisms involved in t he multi-step process of metastasis. (C) 1997 Elsevier Science Ireland Ltd.