In vivo enhancement of genomic instability in minisatellite sequences of mouse C3H/10T½ cells transformed in vitro by X-rays[superscript 1]

The level of genomic instability was determined during tumor development in vivo. Genomic rearrangements, a marker of genomic instability, was measured mouse C3H/10T½ cells transforned in vitro by X-rays with a DNA fingerprinting assay. Three transformed clones isolated from type III foci were divided into two groups. Cells from the first group were injected s.c. into syngeneic and nonimmunosuppressed C3H mice. After 3 to 5 months, the tumors were excised, and the neoplastic cells were isolated and subcloned. Cells from the second group were incubated in vitro for 25 passages (about 6 months) to approximate the number of cell divisions occurring in the tumor, and then they were subcloned. DNA was extracted from subclones grown in vitro and in vivo and analyzed with the DNA fingerprinting assay. A high frequency of genomic rearrangements (50-100%) was found in subclones derived from tumors that arose in vivo, whereas the frequency was very low (