Biological characteristics of primary tumors induced by polyoma virus in hamsters

Abstract Eleven primary subcutaneous tumors induced by polyoma virus in hamsters were analyzed for morphology, growth capacity in vitro , transplantability and karyology. In most cases, cultures prepared from these tumors grew for a few generations and then degenerated with loss of a majority of cells; from the few surviving cells, a population emerged that was able to grow indefinitely in vitro . The initial explanted population differed from that which emerged from the degenerative phase in its susceptibility to the toxic activity of 3,4‐benzo (a)pyrene and in its high MTD (median tumor dose) values (10 5 –10 6 cells) when transplanted in adult hamsters. The MTD decreased to 10 2 –10 3 cells with prolonged growth in vitro . Cultures derived from the transplanted tumors grew permanently in vitro and had low MTD values. All the tumors were aneuploid with a prevalent near‐diploid mode and remained so even after prolonged growth in vitro . No common karyotypic changes were observed, but in 4/8 tumors there was a chromosome marker longer than the X. The long chromosome of the various lines differed in the arm ratios. The occurrence of monosomy and trisomy of pairs ≠1 and ≠21 was not random in 4/8 primary tumors. A comparison with previous studies of hamster embryo cells infected in vitro with polyoma virus indicates that there is a strong parallelism in the biological properties and progression toward neoplasia between cell populations infected in vivo or in vitro by the virus.