Anthracycline pharmacodynamics and pharmacokinetics in acute myeloid leukemia

Abstract

The goal of this thesis has been to study pharmacodynamics and pharmacokinetics of anthracyclines in acute myeloid leukemia (AML) with the ultimate goal to improve chemotherapy:

1. By studying the relation between daunorubicin (DNR) and idarubicin (IDA) uptake in vitro and in vivo and apoptosis in vitro in leukemic cells isolated from patients with AML. We studied the intracellular concentrations of DNR and IDA and apoptosis in leukemic cells after a one hour pulse incubation with increasing concentrations of anthracyclines. A clear concentration-response relationship was found between intracellular anthracycline concentrations and apoptosis although there was a large interindividual variation. Furthermore, the intracellular concentrations of DNR in vivo, directly after DNR infusion, were approximately tenfold lower than the concentrations needed to induce effective apoptosis in vitro. A significant correlation was found between in vivo intracellular concentrations and clinical remission. We also found a significant relation between apoptosis induction by IDA in vitro and clinical remission. The results indicate that the intracellular anthracycline levels in vivo are suboptimal and treatment protocols that increase the intracellular levels of anthracyclines should be considered.

2. By studying DNR metabolism in leukemic cells isolated from patients with AML. The metabolism of DNR in leukemic cell extracts from 25 AML patients was determined and related to the expressions of carbonyl reductase 1 (CR1) and aldo-keto reductase 1A1 (AKR1A1). We found a large interindividual variation (up to 47-fold) in the leukemic cells ability to convert DNR to its main metabolite daunorubicinol (DOL) and the metabolic rate was significantly correlated with CR1 expression. Zeraleone analogue-5, a specific inhibitor of CR1, significantly inhibited reduction of DNR. Our results support that CR1 is the most important enzyme for DNR metabolism in leukemic cells.

3. By studying the effect of the leukemic cell burden on plasma levels of DNR. Plasma and mononuclear cells were isolated from 40 patients with AML at the end of DNR infusion, after 5 h, and 24 h after the start of the DNR infusion. We found a weak and significant inverse correlation between the white blood cell count (WBC) and plasma levels of DNR. By using a population based pharmacokinetic model we found a significant correlation between the WBC count and volume of distribution (Vd). This study suggests that the leukemic cell burden lowers plasma levels of anthracyclines although further studies are needed to investigate if patients with a high WBC would benefit from higher doses of anthracyclines.

4. By comparing the uptake mechanisms of different anthracyclines in leukemic cells. The mechanisms behind anthracycline uptake are not completely understood. In this study we compared the uptake of five anthracyclines; DNR, doxorubicin (DOX), epirubicin (EPI), idarubicin (IDA), and pirarubicin (PIRA) by leukemic cells and investigated the possible involvement of specific carriers. HL-60 cells were incubated for one hour with the anthracyclines under various conditions and then the cellular uptake was determined. DNR, IDA, and PIRA had the highest intracellular accumulation. The uptake of DOX, DNR, and IDA was significantly reduced at 0° C. Suramin, a purinergic-2-receptor inhibitor, strongly inhibited the uptake of all anthracyclines except PIRA and dipyridamole, a nucleoside transport inhibitor, only inhibited the uptake of DNR. The addition of nucleosides reduced the uptake of DNR, IDA and PIRA.

The results of this study indicate that anthracyclines may have different uptake mechanisms. Furthermore, our data also suggest that the uptake might be carrier mediated with a possible involvement of the nucleoside transporter family.