High-performance liquid chromatographic assay of metabolites of thioguanine and mercaptopurine in capillary blood.

The main metabolites of the cytotoxic drugs thioguanine (6TG) and mercaptopurine (6MP) can be measured conveniently in red blood cells (RBC). Isolation of RBC, however, is laborious and requires some milliliters of blood. This HPLC assay allows measurements of thiopurine metabolites in very small blood samples obtained from the finger-tip. The metabolites, derivatives of 6TG and methylmercaptopurine (6MeMP), were extracted and hydrolized with perchloric acid to liberate the corresponding base. 6MeMP is completely transformed under these conditions to 4-amino-5-(methylthio)carbonyl imidazole. The chromatographic separation of 6TG and this imidazole was performed in a single run under isocratic conditions within 10 min using a 70 mm column. The quantification limit was 0.5 nmol/ml for 6TG and 3 nmol/ml blood for 6MeMP. The accuracy was 83% for 6TG (CV=3%) over the concentration range of 0.5-20 nmol/ml blood and 102% (CV=4%) for 6MeMP over the range of 3-150 nmol/ml blood. The intra-assay CV ranged from 5.4 to 7.4% for 6TG and from 6.2 to 10.6% for 6MeMP. The inter-assay CV was 7.5 and 9.5% in a pooled blood sample. The levels in RBC in whole blood were nearly coincident with those obtained in separated RBC, isolation of RBC therefore is not necessary for these measurements, if the drugs are given per os in the day before blood sampling. The concentration of 6MeMP nucleotides is more dependent on the given 6MP dose than the concentration of 6TG nucleotides. Intraindividual variations were small at unchanged drug doses, interindividual metabolite concentrations were highly variable.

Thioguanine offers no advantage over mercaptopurine in maintenance treatment of childhood ALL: results of the randomized trial COALL-92.

The German cooperative study group for childhood acute lymphoblastic leukemia (COALL-92) was designed to examine the clinical effectiveness of thioguanine (TG) versus mercaptopurine (MP) in maintenance treatment of childhood acute lymphoblastic leukemia (ALL) in a randomized multicenter trial. TG and MP are prodrugs and have to be converted intracellularly to 6-thioguanine nucleotides (TGNs) for cytostatic activity. TG is converted into TGN in fewer steps and has been shown to be more cytotoxic in equimolar doses in vitro compared with 6-MP. Therefore, a higher effectiveness of TG in maintenance treatment was postulated. Of 521 patients enrolled into the protocol, 474 were randomized to receive either MP or TG during maintenance therapy in a daily oral dose. After a median observation time of 6.6 years, the probability of event-free survival was 79% +/- 3% for the MP group (238 children) and 78% +/- 3% in the TG group (236 patients). In spite of TGN levels, exceeding those of the MP group 7 times, treatment with TG did not improve the outcome but was more complicated to handle due to a specific toxicity profile of prolonged myelosuppression with marked thrombocytopenia. Therefore, MP should remain the preferred drug for maintenance treatment of ALL, unless other studies demonstrate superiority of TG in larger trials or selected patient groups.

Outcome of treatment in childhood acute lymphoblastic leukaemia with rearrangements of the 11q23 chromosomal region.

BACKGROUND: The prognosis and optimum treatment of childhood acute lymphoblastic leukaemia (ALL) with abnormalities of chromosomal band 11q23 are controversial. We aimed to identify prognostic factors that might help in planning future therapy, and to assess the effectiveness of haemopoietic stem-cell transplantation in patients with the t(4;11) translocation, which is associated with a particularly poor outcome. METHODS: We reviewed data on 497 children and young adults who had ALL with various 11q23 abnormalities, including the translocations t(4;11), t(9;11), and t(11;19). All patients were treated with intensive chemotherapy, with or without haemopoietic stem-cell transplantation in first complete remission, by 11 study groups and single institutions from 1983 to 1995. FINDINGS: Age was the most important prognostic factor. In a Cox's proportional-hazard model stratified by 11q23 abnormalities, infants younger than 1 year fared significantly worse than patients 1 year of age or older (hazard ratio for event-free survival 1 84 [95% CI 1 38-2 47], p=0 0001). Among infants, any category of 11q23 abnormality conferred a dismal outcome, whereas in older patients, t(4;11) and t(9;11) were associated with a worse outcome than were other 11q23 changes. In the largest subgroup--256 patients with t(4;11)--any type of transplantation was associated with significantly worse disease-free survival (1 61 [1 10-2 35], p=0 014) and overall survival (1 76 [1 08-2 45], p=0 004) compared with chemotherapy only. Even transplantation with stem cells from HLA-matched related or HLA-matched unrelated donors tended to be associated with a worse outcome than chemotherapy alone. INTERPRETATION: The prognosis of acute lymphoblastic leukaemia with an 11q23 abnormality is particularly dismal in infants. Allogeneic transplantation with haemopoietic stem cells from an HLA-matched related donor does not seem to improve the clinical outcome in patients with t(4;11)-positive leukaemia.