Adriamycin‐induced DNA strand breaks in HeLa and in P388 leukaemia cells detected using in situ nick translation

DNA strand breaks produced by adriamycin (ADR) were measured in HeLa cells and ADR‐sensitive and ‐resistant P388 leukaemia cells, using the in situ nick translation method. The break sites in the DNA were translated artificially in the presence of Escherichia coli DNA polymerase I and ³H‐labelled dTTP, and were visualized by autoradiographic observation of the grains. The DNA strand breaks in the HeLa cells increased in a dose‐dependent manner, compared with findings in the untreated control cells, i.e., 15·2 fold at 20 μg/ml of ADR for 1 h. This level correlated with DNA single‐strand breaks detected by the alkaline elution method. DNA breaks were also noted in the ADR‐sensitive P388 cells, but in the ADR‐resistant cells the level of DNA strand breaks was low. The enhanced cytotoxicity is apparently the consequence of the enhanced potential of ADR to cause breaks in the DNA strands. Our findings show that the survival response of the cells decreases and the level of DNA strand breaks increases following exposure to ADR. ADR resistance may be mediated by a reduction in the level of DNA strand breaks.