Chromosomal and molecular alterations associated with fibrosarcma development in the mouse

By the time solid tumors are clinically observed, many chromosomal changes are present. Observing tumors early in development and following chromosome changes with the progression of tumors may help determine if specific chromosome changes are associated with tumors at different stages of development and if changes are dependent upon a particular inducing agent. As one approach to studying this, silastic disks were implanted subcutaneously into C₃H female mice, and fibrosarcomas developed at the site of the disks. The disks and associated tissue were removed from 28 weeks post— implantation until mature sarcomas were observed. The associated cells or tumors were then both cultured and karyotyped, and direct chromosome preparations were made from 80% of the tumors. G— banding analysis was performed to look for specific structural and numerical chromosomal changes, and C— banding analysis was performed to look for homogeneously staining regions (HSRs). In some cases the animals were treated with X rays (2.5 X 4), in addition to the disk, and the sarcomas analyzed for chromosome changes. The chromosome numbers per cell varied from 38 to 350 in all tumors analyzed. There were wide variations in chromosome number between sarcomas, with much less variation within a particular sarcoma. Double minutes (CMs) and HSRs, both indicative of gene amplification, were present in many tumors at later stages of development (longer times post- implantation of the disk). Consistent ciTromosonwi trends including duplications of chromosomes 10, 16, and 19 were observed in sarcomas from animals that received both the disk IV treatment ard the disk + X ray treatment. Non- specific metacentric chromosomes were observed in many tumors from animals that received the disk treatment alone, and of these 55% were isochromosomes. Aneuploidy was a very early change observed in all tumors analyzed. It occurred even before a histological diagnosis of malignancy could be made with confidence (personal communication, R. J. M. Fry).

Southern analysis of 8 tumor cell lines has shown no correlation between the amplification of the c-myc, c-h-ras, c-raf, c-rel, c-mos, c-myb, c-abl, c-erbA, c-erbB, and c-sis oncogenes and the presence of EMS and/ or HSRs. However, Southern analysis has shown a correlation between the presence of EMS and amplification of the multiple drug resistance (MER) gene. Cells containing EMs were more resistant to methotrexate, cytosine arabinoside (ara C), actinomycin D, and colchicine than tumor cells lacking EMS. Ihe presence or absence of EMS (and thus MER) had no effect on the X ray sensitivities of these fibrosarcoma cell lines.