Chemotherapy in Childhood Acute Lymphoblastic Leukemia In vitro cellular drug resistance and pharmacokinetics

Sammanfattning: The aims of the studies described in this thesis were to investigate the pharmacokinetics of and cellular resistance to chemotherapy as causes of treatment failure in childhood acute lymphoblastic leukemia (ALL).Leukemic cells from 370 children with newly diagnosed ALL were tested by the Fluorometric Microculture Cytotoxicity Assay to measure their resistance to each of ten standard cytotoxic drugs. In the high-risk group, increased in vitro resistance to each of the drugs dexamethasone, etoposide and doxorubicin was associated with a worse clinical outcome. Combining the results for these drugs yielded a drug resistance score, showing a relative risk of relapse in the most resistant group that was 9.8 times higher than in the most sensitive group. In the standard-risk and intermediate-risk groups, final evaluation must await longer follow-up.The new cytotoxic agent CHS 828 was equally active in vitro in samples from children with acute myeloblastic leukemia (AML) and ALL, with 50% cell kill at concentrations achievable in vivo. In AML samples CHS 828 also displayed high frequencies of synergistic interactions with four standard drugs. The well-known differences in clinical outcome between Down´s syndrome (DS) and non-DS children with acute leukemia may partly be explained by our finding of differences in drug resistance at the cellular level.Pharmacokinetic studies were performed at the start of induction treatment of ALL. Doxorubicin was assayed by reversed-phase liquid chromatography with fluorometric detection, and vincristine by high performance liquid chromatography with electrochemical detection. Plasma doxorubicin concentrations were measured in 107 children after 23 h of a 24-h infusion. The median steady-state concentration in children 4-6 years old, a group known to have a favorable outcome of treatment, was about 50% higher than in those 1-2 and >6 years old Vincristine pharmacokinetics was evaluated in 98 children. There was no correlation between age and total body clearance or any other pharmacokinetic parameters.In vitro testing of cellular drug resistance might be useful in predicting the outcome in high-risk ALL. The further exploration of CHS 828 in childhood leukemia seems warranted. There is no pharmacokinetic rationale for the common practice of administering relatively lower doses of vincristine to adolescents than to younger children.