INDUCTION OF DNA-DAMAGE, INHIBITION OF DNA-SYNTHESIS AND SUPPRESSION OF C-MYC EXPRESSION BY THE ANTHRACYCLINE ANALOG, IDARUBICIN (4-DEMETHOXY-DAUNORUBICIN) IN THE MCF-7 BREAST-TUMOR CELL-LINE

Purpose: Studies were designed to elucidate the basis for the antiprol iferative activity of the anthracycline antibiotic, idarubicin (4-deme thoxy-daunorubicin) in MCF-7 breast tumor cells. Methods: Growth inhib ition was evaluated using the MTT tetrazolium dye assay, induction of DNA strand breaks was determined by alkaline elution, inhibition of DN A synthesis was assessed by measuring the incorporation of labelled th ymidine into DNA, modulation of the expression of the c-myc oncogene w as determined by Northern blotting and the induction of apoptosis was evaluated by alkaline unwinding, static field gel electrophoresis, ter minal end labelling and assessment of cell morphology. Results: MCF-7 cells were relatively sensitive to idarubicin, with an IC50 value for growth inhibition of approximately 0.01 mu M. While DNA strand breakag e was not evident below a concentration of 0.1 mu M idarubicin, where growth inhibition exceeded 70%, both the inhibition of DNA synthesis a nd suppression of c-myc expression closely paralleled the profile of a ntiproliferative activity for idarubicin. Finally, while exposure to i darubicin resulted in a substantial loss of viable cells within 48-72 h, there was no morphological evidence of apoptotic body formation. Th e absence of apoptosis in cells exposed to idarubicin was supported by studies demonstrating the absence of DNA fragmentation using gel elec trophoresis, alkaline elution and in situ DNA end-labelling assays. Co nclusions: The results of these studies extend previous results from t his laboratory indicating an association between suppression of c-mye expression, inhibition of DNA synthesis and growth arrest by topoisome rase II inhibitors, as well as the lack of induction of apoptotic cell death by topoisomerase II inhibitors in MCF-7 breast tumor cells.