Effects of verapamil on in vitro intracellular accumulation and retention of daunorubicin in blast cells from patients with acute nonlymphocytic leukemia

The effects of verapamil on the intracellular pharmacokinetics of daunorubicin (DNR) in blast cells from the bone marrows of patients with acute nonlymphocytic leukemia (ANLL) were studied to determine whether verapamil was capable of enhancing intracellular accumulation and retention of DNR in ANLL, as has been observed in murine P388 cells resistant to DNR. Seventeen marrows from ANLL patients were studied, 13 of which were from patients who were considered to be clinically refractory to DNR. We took care to include such patients in this study since, in the P388 model, verapamil enhancement of DNR uptake is observed only in cells resistant to DNR. Intracellular accumulation of DNR was studied by exposing blast cells to DNR (1 microgram/mL) +/- verapamil (6.6 mumol/L) for up to 4 hours. Following a 2-hour exposure of cells to DNR +/- verapamil, intracellular retention of DNR was studied by incubating the cells in DNR-free medium for 3 hours. Intracellular DNR/10(6) cells was quantified by fluorometry. In 12 of 15 patient marrows, verapamil failed to enhance intracellular accumulation of DNR. Three patient marrows had a very small increment in DNR uptake in response to verapamil (approximately 14% greater than DNR alone) that was significant (P less than .05) by paired t test. Intracellular retention of DNR (t 1/2) and the area under the intracellular DNR v time curve (AUC) were studied in 17 patients marrow specimens. No significant alterations in these parameters were observed in response to verapamil. These data indicate either that verapamil did not substantially enhance DNR uptake or retention in blast cells obtained from ANLL patients who are clinically resistant to DNR, or that the frequency of DNR-resistant cells (ie, verapamil-responsive cells) among the blast cells obtained from these patients was too low to influence the population mean of intracellular DNR as measured in these studies.