Differential susceptibility to chemically induced thymic lymphomas in SENCARB and SSIN inbred mice

In the past 20 yr, several inbred strains have been derived from SENCAR outbred mice. These strains display different susceptibility to the induction of papillomas and progression to squamous cell carcinomas (SCC) in the skin after chemical carcinogenesis. In the present study, we showed that one of these strains SENCARB/Pt was highly susceptible to the development of N-methyl-N-nitrosourea (MNU)- and 7,12-dimethylbenz[a]anthracene (DMBA)-induced lymphomas. In contrast, the SSIN/Sprd inbred strain is completely resistant to T-cell lymphomagenesis by both carcinogens. Within 175 d after a single injection of 75 mg/kilogram body weight (kbw) of MNU, SENCARB/Pt mice exhibited a 91.6% incidence of lymphoma. In addition, during an independent tumorigenesis study with repeated doses of intragastric DMBA, SENCARB/Pt mice showed an incidence of 75% lymphoma development 300 d after the last treatment. Histopathological and flow cytometric parameters indicated that the lymphomas were of the T-cell lineage. In order to study the genetics of MNU-induced tumorigenesis, we generated F1 hybrid mice between SSIN/Sprd and SENCARB/Pt mice. Tumor incidence in MNU-injected F1 mice suggested that the high tumor incidence is a dominant trait. Loss of heterozygosity (LOH) analysis in these tumor samples revealed allelic imbalances on chromosomes 15 and 19. Given that these inbred strains are closely related, it is likely that a relatively small number of loci are responsible for the observed differences in susceptibility. Therefore, these SENCAR inbred strains constitute important new tools to study the genetic basis of resistance and susceptibility to chemically induced thymic lymphoma formation.