Microfluorimetric analysis of dynamics of genomic changes in Chinese hamster fibroblasts CHL V-79 RJK with multiple drug resistance

Results of a karyological analysis of cells CHL V-79 RJK selected for their resistance to ethidium bromide (EB) causing multidrug resistance (MDR) (subline Vebr-5) were compared with data from the microfluorimetric determination of the DNA content in individual chromosomes of the karyotype. The analysis was performed at the 11th and 88th passages. Karyotyping of Vebr-5 has shown the presence of an additional genetic material (AGM) in the form of homogenously or differentially stained regions (HSR or DSR, respectively) in two chromosomes (Z1 and Z6, loci 1p29-31 and 1q26, respectively). HSR in Z6, in the site of localization of the mdr gene of the wild type had unstable length and structure, which is characteristic of the morphological markers of the amplification of genes of the mdr family. During the long cultivation of Vebr-5 in the presence of EB (88 passages), the instability of HSR (DSR) in Z6 increased. Results of a microfluorimetric analysis of Vebr-5 at the 11th passage have shown a statistically significant increase of the DNA content not only in chromosomes Z1 and Z6 marked by HSR (DSR), but also in three chromosomes (Z5, Z12, and Z13) that have no visual morphological changes. The corresponding analysis at the 88th passage has also revealed nonrandom changes in the DNA content in four more chromosomes, including an increase in Z14 and a decrease in chromosomes 8, Z7, and Z9. A decrease in the DNA content in chromosomes is considered to be the result of a partial loss of genetic material, while its increase is considered to be the result of its translocation and/or amplification. While the coefficient of the variation of the DNA content changes about 9% for large chromosomes, it amounted to about 26% for the small ones, indicating that small chromosomes to have a greater potential for instability than large chromosomes. The obtained data not only confirm, but also enlarge, the concept of the directions and character of the destabilization of the cell genetic apparatus in the process of neoplastic transformation due to MDR acquisition by these cells.