2',3'-Dideoxycytidine (ddC), which is currently used as an HIV treatment, is a potent carcinogen in mice. Gavage exposures with ddC (500- 1000mg/kg) for 3-6 months result in a high incidence of lymphomas of T- cell origin in NIH-Swiss and B6C3F1 mice. Molecular genetic analyses of these lymphomas were performed in an attempt to provide information that could be useful for extrapolation between species and the assessment of human risks associated with ddC treatment. In order to map the potential involvement of tumor suppressor genes, allelotypes of 16 B6C3F1 lymphomas were generated with simple sequence repeat or microsatellite markers on each chromosome. The most frequent losses of heterozygosity (LOH) were observed with markers on chromosomes 12 (38%), 2 (31%) and 4 (25%). Additional studies indicated telomeric locations for the chromosome 12 and 2 loci but candidate genes for these regions are not apparent. In contrast, the chromosome 4 losses were consistent with a region containing the MTS1 and MTS2 genes which are cyclin dependent kinase inhibitors. Mutation screening of these genes in the ddC-lymphomas by Southern analysis and direct sequencing is in progress. Since the p53 tumor suppressor gene is inactivated in some human and mouse lymphomas including those induced by 1,3-butadiene, ddC-lymphomas were examined for p53 mutations. Southern analysis revealed a homozygous p53 deletion in one of 63 lymphomas. In addition, p53 point mutations in three tumors were identified by single strand conformation analysis and direct sequencing. Finally, activating mutations in the K- and N-ras proto- oncogenes were examined since they are common in some mouse lymphomas. Single strand conformation analysis and direct sequencing revealed six K-ras and a single N-ras alteration in this series of 63 ddC-induced lymphomas.
