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p16 gene deletions are present in about 70% of primary paediatric T-cell acute lymphoblastic leukaemia (T-ALL) and 20% of common/precursor B-cell ALL cases. It is not clear what the impact of the frequent p16 deletions is within the subgroup of T-lineage ALL. We studied the relationship between p16/p19(ARF) deletions, using fluorescence in situ hybridization. and in vitro drug resistance and prognosis in childhood T-ALL at diagnosis. The cellular drug resistance was measured with the methyl thiazol tetrazoliumbromide assay using a panel of drugs and the thymidylate synthase inhibition assay for methotrexate. There was a complete overlap of individual LC50 values of p16 gene homozygously deleted and p16 germ-line cases for most of the nine classes of drugs tested. The only difference was for dexamethasone: the p16-deleted group was more sensitive than the germ-line p16 group (P = 0.030). The homozygously deleted p16 T-ALL patients (n = 34) treated with the modern multiagent chemotherapy schemes of the Dutch Childhood Leukaemia Study Group ALL-VII/-VIII or Co-operative ALL-92/-97 protocols have a significantly lower 5-year disease-free survival (DFS) than germ-line p16 T-ALL (n = 25) (65.1 +/- 9.1% vs. 95.5 +/- 4.4%, P-log (rank) = 0.021). Hence, this study identifies a subpopulation of primary childhood T-ALL that appears to have an extremely high DFS, However, the observed differences in outcome do not seem to be related to intrinsic resistance for the tested drugs.

Background. To investigate late cardiotoxicity in childhood acute lymphoblastic leukemia (ALL) survivors after induction treatment with or without daunorubicin (DNR; 25 mg/m(2), i.v., weekly, x4, cumulative dose 100 mg/m(2)). Procedure, Cardiac function was assessed in 90 event-free survivors of childhood ALL, 11.4-17.8 years (median 14.8 years) after treatment according to the DCLSG protocol ALL V. In this protocol patients were randomized to receive (group B) or not to receive (group A) DNR 25 mg/m(2)/week i.v. during the first 4 weeks of induction treatment. Age at diagnosis was 1.2-14.9 years (median 4.5 years). The cardiac evaluation consisted of a history, physical examination, electrocardiogram (ECC), 24 hr ambulatory EGG, and echocardiography. Results. Electrocardiographic data, arrhythmias, left ventricular dimensions, left ventricular contractility, wall stress, and diastolic function were within normal limits in both groups. No difference could be shown between data from group A (n = 40) and group B (n = 50). Conclusions. No late cardiac damage was demonstrated in childhood ALL survivors after induction treatment including a cumulative dose of 100 mg/m(2) DNR, compared to survivors who received the same treatment but without DNR. DNR 100 mg/m(2) given in 4 doses of 25 mg/m(2)/week appears to be a safe dose in induction treatment of ALL. 2000 Wiley-Liss, Inc.

Treatment failure in childhood acute lymphoblastic leukaemia (ALL) might be associated with methotrexate (MTX) resistance. Little is known about MTX resistance in relapsed ALL. In this study, we determined ex vivo MTX resistance in precursor-B ALL at relapse (rALL) and determined possible defects in MTX membrane transport and polyglutamylation. Using the in situ thymidylate synthase inhibition assay, 21 rALL samples were threefold more MTX resistant than 63 initial precursor-B ALL samples, both after short-term and after continuous MTX exposure (P < or = 0.01). [3H]-MTX membrane transport did not differ between eight rALL and 25 precursor-B ALL samples. Incubation for 24 h with 1 microM [3H]-MTX resulted in a trend towards a lower accumulation of MTX in 20 relapsed than in 83 initial samples of precursor-B ALL samples (906 vs. 1364 pmol/109 cells; P = 0.07). Accumulation of long-chain MTX polyglutamates (MTX-Glu4-6) did not differ between relapsed and newly diagnosed samples (746 and 889 pmol/109 cells; P = 0.1). Activities of the enzymes involved in polyglutamylation (folylpolyglutamate synthetase and folylpolyglutamate hydrolase) did not differ between rALL and untreated c/pre-B-ALL. This study demonstrates that leukaemic cells of children with relapsed precursor-B ALL are relatively MTX resistant, but that this MTX resistance is not associated with major impairments in MTX uptake or polyglutamylation.

Multidrug resistance (MDR), which is cross-resistance to structurally and functionally unrelated drugs such as anthracyclines, epipodophyllotoxins and vinca alkaloids, is a major cause of treatment failure in malignant disorders. Known mechanisms of MDR are overexpression of the ATP-dependent membrane proteins P-glycoprotein (P-gp) and muitidrug resistance protein (MRP1), or an increased detoxification of compounds mediated by glutathione (GSH) or GSH related enzymes. MRP1 appeared to transport drugs conjugated to GSH and also unmodified cytostatic agents in presence of GSH. The relation between MRP1, GSH and enzymes involved in GSH metabolism or GSH dependent detoxification reactions recently has drawn a lot of attention. Coordinated induction of MRP1 and GSH related enzymes is reported in malignant cells after exposure to cytostatic agents. Besides MRP1, a number of MRP1 homologs are identified, named MRP2, MRP3, MRP4, MRP5 and MRP6. The relation between MDR and expression of these MRP1 homologs is currently under research. In human Acute Myeloid Leukemia (AML) the expression of MRP1 appears to be of potential importance. We demonstrated that AML blasts of patients express MRP1 protein and MRP1 and MRP2 mRNA. Furthermore a functional flow cytometric assay was developed to determine MRP functional activity. Since GSH and related enzymes have shown to play a critical role in MRP1 mediated transport of several anticancer drugs, both mechanisms should be studied in relation with each other. Further work on these interwoven mechanisms is needed to improve our understanding of MDR in leukemia.

The Dutch Childhood Leukemia Study Group (DCLSG) has implemented eight protocols for the treatment of childhood acute lymphoblastic leukemia (ALL) (ALL I to VIII) during the period from 1972 to 1995. They were based on St. Jude's Total Therapy (ALL II to VI) and the risk-adapted intensive therapy (ALL VII and VIII) developed by the BFM Group, respectively, and included seven randomized studies. In study ALT, I (N = 43, 1972 to 1973), no effect was observed after the addition of daunorubicin to vincristine/prednisone pulses during maintenance treatment. In study ALL II (N = 143, 1973 to 1975) the addition of cyclophosphamide to maintenance treatment with 6-mercaptopurine/methotrexate increased toxicity and mortality without increasing the event-free survival rate. In study ALL III (N = 148; 1975 to 1979) for non-high-risk patients (defined as initial leukocyte count