Intracellular concentrations of anti cancer drugs in leukemic cells in vitro vs in vivo.

A comparison of intracellular concentrations of daunorubicin, doxorubicin and ara-C in myeloid blast cells was carried out in vivo and in vitro. In vivo, blood samples were obtained from 27 patients with acute nonlymphoblastic leukemia during and up to 4 days after drug infusion. Leukemic cells were isolated and drug concentrations were determined by HPLC. Before treatment, leukemic cells from 21 patients were isolated from blood and bone marrow, and in vitro incubations were done with anthracyclines for 1-3 h at concentrations of 0.1-1.0 microM and with ara-C for 1 h to 5 days at concentrations of 0.5-5.0 microM. The cells were cultured for 5 days, during which cell samples were taken for drug determination. The results showed that incubation with 0.2 microM daunorubicin for 1 h and 0.2 microM doxorubicin for 3 h and continuous exposure to 0.5 microM ara-C gave intracellular concentration curves similar to those obtained in vivo. After 5 days' culture, the cytotoxic effect was determined by vital dye staining with fast green, the addition of an internal standard of fixed goose erythrocytes, cytospin centrifugation and counter-staining of living cells with haematoxylin/eosin (DiSC). Incubations at the above-mentioned concentrations exerted a cytotoxic effect of approximately 50%. We conclude that in mimicking the in vivo situation, it is important to consider differences in intracellular pharmacokinetics.