Specific karyotype changes in cells resistant to colchicine

Two new sublines of Djungarian hamster cells DM-15CHR-1/1 and DM-15CHR-1/5 which are 170--190-fold resistant to colchicine as compared to the initial DM-15 cells have been described. Drug resistance of these cells is unstable: in nonselective conditions the trait is lost at a rate approximately 2.10(-2) per cell per generation. All cells of the two independently derived clonal sublines have the same karyotypic alteration: an additional marker chromosome, the derivative of chromosome 4 carrying homogeneously colored region (HCR) in the long arm. The size of HCR varies in different cells. Its average length is about 4--5% of the total length of all chromosomes. In some cells circular chromosomes or double-minutes were found in addition to the marker chromosome. They consist of the material similar to that of HCR. These data suggest that colchicine-resistance is associated with gene amplification.