Flow cytometric study of idarubicin and daunorubicin accumulation and the effect of verapamil in leukemic cell lines and fresh cells from patients with acute non-lymphoblastic leukemia

By using flow cytometry, the intracellular accumulation (Acc) of idarubicin (IDA) and daunorubicin (DNR) and the effect of verapamil (VRP) on both anthracycline accumulation (VRP) index) were studied in leukemic cell lines (K562 and HL60 and their two DNR-resistant subclones) and fresh leukemic cells. IDA accumulated more than DNR in both parental (K562: p < 0.03 and HL60: 0.09) and resistant cell lines ( p < 0.01 for both cell lines) irrespective of whether or not they were treated with VRP. VRP index was higher for DNR than for IDA ( p < 0.05). Similar results were observed in fresh leukemic blasts from 25 patients with ANLL (IDA Acc superior to DNR Acc: p < 0.0001; higher VRP index for DNR than for IDA: p < 0.01). The higher Acc of IDA than DNR seen in fresh leukemic cells could explain the better clinical efficacy of IDA reported in patients with ANLL.