Modeling Mechanisms of In Vivo Variability in Methotrexate Accumulation and Folate Pathway Inhibition in Acute Lymphoblastic Leukemia Cells

Methotrexate (MTX) is widely used for the treatment of childhood acute lymphoblastic leukemia (ALL). The accumulation of MTX and its active metabolites, methotrexate polyglutamates (MTXPG), in ALL cells is an important determinant of its antileukemic effects. We studied 194 of 356 patients enrolled on St. Jude Total XV protocol for newly diagnosed ALL with the goal of characterizing the intracellular pharmacokinetics of MTXPG in leukemia cells; relating these pharmacokinetics to ALL lineage, ploidy and molecular subtype; and using a folate pathway model to simulate optimal treatment strategies. Serial MTX concentrations were measured in plasma and intracellular MTXPG concentrations were measured in circulating leukemia cells. A pharmacokinetic model was developed which accounted for the plasma disposition of MTX along with the transport and metabolism of MTXPG. In addition, a folate pathway model was adapted to simulate the effects of treatment strategies on the inhibition of de novo purine synthesis (DNPS). The intracellular MTXPG pharmacokinetic model parameters differed significantly by lineage, ploidy, and molecular subtypes of ALL. Folylpolyglutamate synthetase (FPGS) activity was higher in B vs T lineage ALL (p<0.005), MTX influx and FPGS activity were higher in hyperdiploid vs non-hyperdiploid ALL (p<0.03), MTX influx and FPGS activity were lower in the t(12;21) (ETV6-RUNX1) subtype (p<0.05), and the ratio of FPGS to γ-glutamyl hydrolase (GGH) activity was lower in the t(1;19) (TCF3-PBX1) subtype (p<0.03) than other genetic subtypes. In addition, the folate pathway model showed differential inhibition of DNPS relative to MTXPG accumulation, MTX dose, and schedule. This study has provided new insights into the intracellular disposition of MTX in leukemia cells and how it affects treatment efficacy

The role of cranial radiotherapy for childhood T-cell acute lymphoblastic leukemia with high WBC count and Prednisone good response

PURPOSE: The ALL-BFM 90 and AIEOP-ALL 91 studies share the same treatment backbone and have 5-year event-free survival (EFS) rates close to 75%. This study evaluated the impact of differing presymptomatic CNS therapies in T-cell acute lymphoblastic leukemia (T-ALL) patients with a good response to prednisone (PGR) according to WBC count and Berlin-Frankfurt-M\ufcnster (BFM) risk factor (RF). PATIENTS: A total of 192 patients (141 boys; median age, 7.5 years) with T-ALL, PGR, RF less than 1.7, and no CNS leukemia diagnosed between 1990 and 1995 were enrolled onto the ALL-BFM 90 (n = 123) or AIEOP-ALL 91 (n = 69) study. Presymptomatic CNS therapy consisted of cranial radiation (CRT) and intrathecal methotrexate (I.T. MTX) (11 doses) in the BFM study and of extended triple intrathecal therapy (T.I.T.) (17 doses) in the Associazione Italiana Ematologia Oncologia Pediatrica (AIEOP) study. Patients were divided into a low-WBC group (WBC count 100,000/microL). EFS was compared using the log-rank test. RESULTS: For patients treated with CRT and I.T. MTX (BFM group), the 3-year EFS rate was 89.8% (SE = 3.5) for 99 patients in the low-WBC group versus 81.9% (SE = 8.2) in the high-WBC group (difference not significant). Conversely, for patients treated with T.I.T. alone (AIEOP group), the EFS rate was 80.6% (SE = 5.6) in 55 patients with a low WBC count versus 17.9% (SE = 11.0) in 14 patients with a high WBC count (P < .001). CONCLUSION: These data suggest that CRT may not be necessary in PGR T-ALL patients with a WBC count less than 100,000/microL; on the contrary, in patients with a high count, extended T.I.T. may be inferior to CRT and I.T. MTX

Progressive reduction in treatment-related deaths in Medical Research Council childhood lymphoblastic leukaemia trials from 1980 to 1997 (UKALL VIII, X and XI).

In the last 20 years, the survival rate for children with acute lymphoblastic leukaemia (ALL) has markedly improved, largely owing to a decrease in relapses. However, children still die from complications of treatment and these are potentially preventable. We have analysed data from three large consecutive national protocols for ALL from 1980 to 1997 [Medical Research Council United Kingdom ALL (MRC UKALL) trials VIII, X and XI] to compare the incidence and causes of treatment-related deaths (TRD). The percentage of TRD has fallen from 9% to 2% (UKALL VIII to XI), largely as a result of a decrease in fatal infections. Deaths during induction have fallen from 3% to 1%, the main causes of death being bacterial, followed by fungal infection, while other causes, chiefly haemorrhage, have not declined. Remission deaths also decreased from 6% to 1%, particularly those deaths due to measles and pneumocystis carinii. More guidelines for surveillance and treatment of infections have been included within progressively more intensive protocols. Risk factor analysis showed increased TRD in patients with Down's syndrome, high leucocyte count and older age in UKALL XI. In contrast, the introduction of blocks of intensification was not associated with an increased death rate. While improved supportive care has reduced the incidence of TRD, there is still scope for further reduction by prompt treatment of suspected infection. Maintenance of herd immunity remains of vital importance in avoiding deaths from measles