Cytogenetic modifications of Friend leukemia cells resistant to adriamycin.

Chromosome analysis was performed on adriamycin-sensitive and resistant Friend leukemia cells. Resistance to ADM is associated with an increased number of metacentric chromosomes. With increasing level of drug resistance additional metacentric chromosomes and several chromosomal markers were observed. Furthermore, the C-banding patterns and the heterochromatin distribution differed in resistant, as compared to sensitive cells. When sensitive cells were exposed to a toxic dose of ADM, multiple chromosomal breaks were observed in 62% of cells. In contrast, when ADM resistant cells were exposed to cytotoxic concentrations, the pulverization phenomenon was not observed and 75-80% of cells were without breaks. This striking difference suggests a different mechanism for cytotoxicity in sensitive and resistant cells.