The in-vitro uptake of four anthracyclines into leukemic cells was investigated. The accumulation was found to be dependent on the extracellular anthracycline concentration in a linear fashion. The steady state intracellular drug level was reached very quickly and was found to be correlated to the extracellular pH-value in the range between 6.4 and 7.4. Intracellular anthracycline accumulation was restricted in a leukemic subline (F 4-6 R), which was found to be 86 times more resistant to doxorubicin compared with its wild tpye (F 4-6). The importance of the initial uptake phase of anthracyclines into leukemic cells raises the question whether long-term "cardioprotective" anthracycline application schedules will retain the same antileukemic effect as conventional bolus injection.
