Progressive genomic instability in the FVB/KrasLA2 mouse model of lung cancer

Alterations in DNA copy number contribute to the development and progression of cancers and are common in epithelial tumors. We have used array Comparative Genomic Hybridization (aCGH) to visualize DNA copy number alterations across the genomes of lung tumors in the KrasLA2 model of lung cancer. Copy number gain involving the Kras locus, as focal amplification or whole chromosome gain, is the most common alteration in these tumors, and with a prevalence that increased significantly with increasing tumor size. Furthermore, Kras amplification was the only major genomic event among the smallest lung tumors, suggesting that this alteration occurs early during the development of mutant Kras driven lung cancers. Recurring gains and deletions of other chromosomes occur progressively more frequently among larger tumors. These results are in contrast to a previous aCGH analysis of lung tumors from KrasLA2 mice on a mixed genetic background, in which relatively few DNA copy alterations were observed regardless of tumor size. Our model features the KrasLA2 allele on the inbred FVB/N mouse strain, and in this genetic background there is a highly statistically significant increase in level of genomic instability with increasing tumor size. These data suggest that recurring DNA copy alterations are important for tumor progression in the KrasLA2 model of lung cancer, and that the requirement for these alterations may be dependent on the genetic background of the mouse strain. The KrasLA2 allele, originally on a C57BL6/129svJae mixed background, was backcrossed into the FVB/N background for more than 10 generations in order to minimize the effect of genetic heterogeneity on lung tumor development. Mice were sacrificed at 6 months of age.