Inter-individual differences in toxic symptoms and pharmacokinetics of highdose methotrexate (MTX) treatment may be caused by genetic variants in the MTX pathway. Correlations between polymorphisms and pharmacokinetic parameters and the occurrence of hepato-and myelotoxicity were studied. Single nucleotide polymorphisms (SNPs) of the ABCB1, ABCC1, ABCC2, ABCC3, ABCC10, ABCG2, GGH, SLC19A1 and NR1I2 genes were analyzed in 59 patients with osteosarcoma. Univariate association analysis and Bayesian network-based Bayesian univariate and multilevel analysis of relevance (BN-BMLA) were applied. Rare alleles of 10 SNPs of ABCB1, ABCC2, ABCC3, ABCG2 and NR1I2 genes showed a correlation with the pharmacokinetic values and univariate association analysis. The risk of toxicity was associated with five SNPs in the ABCC2 and NR1I2 genes. Pharmacokinetic parameters were associated with four SNPs of the ABCB1, ABCC3, NR1I2, and GGH genes, and toxicity was shown to be associated with ABCC1 rs246219 and ABCC2 rs717620 using the univariate and BN-BMLA method. BN-BMLA analysis detected relevant effects on the AUC 0-48 in the following SNPs: ABCB1 rs928256, ABCC3 rs4793665, and GGH rs3758149. In both univariate and multivariate analyses the SNPs ABCB1 rs928256, ABCC3 rs4793665, GGH rs3758149, and NR1I2 rs3814058 SNPs were relevant. These SNPs should be considered in future dose individualization during treatment.

We carried out a detailed comparative study of the pharmacokinetics and toxicity of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) after high-dose intravenous methotrexate (HD-MTX) in children with acute lymphoblastic leukemia (ALL). Overall, 65 children were treated with 5 g/m2/24 h MTX and 88 children were treated with 2 g/m2/24 h MTX according to ALL-BFM 95 and ALL IC-BFM 2002 protocols (mean age: 6.4 years, range 1.0-17.9 years). A total of 583 HD-MTX courses were analyzed. Serum MTX and 7-OH-MTX levels were measured at 24, 36, and 48 h, and cerebrospinal fluid (CSF) MTX levels were determined 24 h after the initiation of the infusion. The area under the concentration-time curve was calculated. Hepatotoxicity, nephrotoxicity, and bone marrow toxicity were estimated by routine laboratory tests. We investigated pharmacokinetics and toxicity in distinct age groups (< 6 and > 14 years). 5 g/m2/24 h treatments resulted in higher serum and CSF MTX and 7-OH-MTX levels (P < 0.05). The CSF penetration rate of MTX was independent of the MTX dose [2.3% (95% confidence interval: 1.7-2.5%) vs. 2.8% (95% confidence interval: 2.4-3%)]. The CSF MTX concentration was correlated with the 24 h MTX serum level (r = 0.38, P < 0.0001). Repeated treatments did not alter MTX or 7-OH-MTX levels. 7-OH-MTX levels were correlated with nephrotoxicity (r = 0.36, P < 0.0001). Higher MTX levels and toxicity occurred more frequently in children aged older than 14 years (P < 0.05). Therapeutic serum and CSF MTX concentrations can be achieved more reliably with 5 g/m2/24 h treatments. To predict the development of toxicity, monitoring of the level of the 7-OH-MTX is useful. Monitoring of pharmacokinetics is essential to prevent the development of severe adverse events in adolescents.

SummaryHigh-dose methotrexate (HD-MTX) plays an important role in the consolidation therapy of acute lymphoblastic leukaemia (ALL) in many treatment regimens worldwide. However, there is a large interpatient variability in the pharmacokinetics and toxicity of the drug. We investigated the influence of single nucleotide polymorphisms (SNPs) in genes of the folate metabolic pathway, transporter molecules and transcription proteins on the pharmacokinetics and toxicity of MTX and 7-hydroxy-methotrexate (7-OH-MTX). 63 SNPs of 14 genes were genotyped and a total of 463 HD-MTX courses (administered according to the ALL-BFM 95 and ALL IC-BFM 2002 protocols) were analysed. Haematological, hepatic and renal toxicities, estimated by routine laboratory parameters were evaluated. Random forest and regression trees were used for variable selection and model building. Linear mixed models were established to prove the significance of the selected variables. SNPs (rs4948502, rs4948496, rs4948487) of the ARID5B gene were associated with the serum levels of MTX (P < 0Á02), serum levels and area under the curve of 7-OH-MTX (P < 0Á02) and with hypoproteinaemia (P = 0Á004). SLCO1B1 rs4149056 also showed a significant association with serum MTX levels (P < 0Á001). Our findings confirm the association of novel genetic variations in folate-related and ARID5B genes with the serum MTX levels and acute toxicity.

The survival rates in childhood acute lymphoid leukemia (ALL) have improved dramatically; however, patients still suffer from a variety of drug-related toxicities. Individualized therapy regimens promise the least toxic therapy regimen with the best hematologic outcome. Our aim was to investigate whether increased individual glucocorticoid sensitivity due to the N363S polymorphism of the glucocorticoid receptor increased susceptibility to steroid-related toxicities during ALL therapy. A total of 346 pediatric ALL patients were involved in the present study. N363S carrier status was investigated by allele-specific PCR. Clinical and laboratory signs of glucocorticoid-related toxicities, Day 8 prednisone response, and 5-year event-free survival were analyzed and compared retrospectively. Thirty-two of the 346 patients were heterozygous carriers (9.2 %). Hepatotoxicity (31.3 vs. 11.2 %, p = 0.004, carriers and non-carriers, respectively) and glucose metabolism abnormalities (18.8 vs. 3.8 %, p = 0.001, carriers and non-carriers, respectively) were significantly more frequent among carriers. There was no difference in the incidence of hypertension and encephalopathy/psychosis among carriers and non-carriers. Carriers were also more prone to have a combination of toxicities. All 363S carriers were good prednisone responders (100 %) and had significantly better 5-year event-free survival rates (93.1 vs. 71.86 %, p = 0.012), whereas among non-carriers there were more poor prednisone responders (8.28 %) and worse 5-year event-free survival rates. Patients with the N363S polymorphism in the glucocorticoid receptor are more prone to steroid-related toxicity during ALL therapy and should be monitored more closely. Patients with N363S polymorphism of the glucocorticoid receptor may be appropriate candidates for inclusion in the design of individualized therapies.