Pharmacogenetics influence treatment efficacy in childhood acute lymphoblastic leukemia

Management of CNS Disease in Pediatric Acute Lymphoblastic Leukemia

PURPOSE OF REVIEW

The treatment of acute lymphoblastic leukemia (ALL) is one of the success stories of pediatric oncology, but challenges and questions remain, including the optimal approach to the treatment of central nervous system (CNS) leukemia. It is unclear why some children with ALL develop CNS leukemia and others do not, and there remains debate regarding optimal regimens for prophylaxis, upfront treatment, and the treatment of CNS relapses. These topics are especially important since both cranial radiation therapy (CRT) and intensive intrathecal therapy carry risks of both short- and long-term adverse effects. In this review, we aim to identify areas of ongoing debate on this topic, review the biology of CNS leukemia, and summarize clinical trial data that address some of these questions.

RECENT FINDINGS

Both retrospective and meta-analyses have demonstrated that few patients with ALL benefit from CRT as a component of CNS-directed treatment for de novo disease, allowing cooperative groups to greatly limit the number of patients undergoing CRT as part of their initial ALL regimens. More recent efforts are focusing on how best to assay for low levels of CNS disease at the time of diagnosis, as well as the biological drivers that may result in CNS leukemia in certain patients. Progress remains to be made in the identification and treatment of CNS leukemia in pediatric ALL. Advancements have occurred to limit the number of children undergoing CRT, but much has yet to be learned to better understand the biology of and risk factors for CNS leukemia, and novel approaches are required to approach CNS relapse of ALL.

Supportive methods for childhood acute lymphoblastic leukemia then and now: A compilation for clinical practice

Survival of childhood acute lymphoblastic leukemia has significantly improved over the past decades. In the early years of chemotherapeutic development, improvement in survival rates could be attained only by increasing the cytostatic dose, also by modulation of the frequency and combination of chemotherapeutic agents associated with severe short- and long-time side-effects and toxicity in a developing child's organism. Years later, new treatment options have yielded promising results through targeted immune and molecular drugs, especially in relapsed and refractory leukemia, and are continuously added to conventional therapy or even replace first-line treatment. Compared to conventional strategies, these new therapies have different side-effects, requiring special supportive measures. Supportive treatment includes the prevention of serious acute and sometimes life-threatening events as well as managing therapy-related long-term side-effects and preemptive treatment of complications and is thus mandatory for successful oncological therapy. Inadequate supportive therapy is still one of the main causes of treatment failure, mortality, poor quality of life, and unsatisfactory long-term outcome in children with acute lymphoblastic leukemia. But nowadays it is a challenge to find a way through the flood of supportive recommendations and guidelines that are available in the literature. Furthermore, the development of new therapies for childhood leukemia has changed the range of supportive methods and must be observed in addition to conventional recommendations. This review aims to provide a clear and recent compilation of the most important supportive methods in the field of childhood leukemia, based on conventional regimes as well as the most promising new therapeutic approaches to date.

A GRIN3A polymorphism may be associated with glucocorticoid-induced symptomatic osteonecrosis in children with acute lymphoblastic leukemia

Aim: To evaluate the association between candidate genetic polymorphisms and glucocorticoid-induced osteonecrosis in Arab children treated for acute lymphoblastic leukemia. Methods: A total of 189 children treated for acute lymphoblastic leukemia were genotyped for four SNPs with allele discrimination assays. The incidence and timing of radiologically confirmed symptomatic grade 4 osteonecrosis were classified based on the Ponte di Legno toxicity working group consensus definition. Results: Thirteen children developed grade 4 osteonecrosis (6.8%), of whom 12 received the intermediate/high-risk treatment protocol. GRIN3A variant allele carriers had to stop dexamethasone therapy earlier resulting in significantly shorter duration of dexamethasone treatment (mean [95% CI]: 75.17 [64.28-86.06] vs 85.90 [81.22-90.58] weeks; p = 0.054) and lower cumulative dose (mean [95% CI]: 1118.11 [954.94-1281.29] vs 1341.14 [1264.17-1418.11] mg/m^2; p = 0.011). Conclusion: This is the first pharmacogenomics evaluation of the association between GRIN3A variants and glucocorticoid-induced osteonecrosis in Arab children.

Implementation of Pharmacogenetics to Individualize Treatment Regimens for Children with Acute Lymphoblastic Leukemia

Despite major advances in the management and high cure rates of childhood acute lymphoblastic leukemia (ALL), patients still suffer from many drug-induced toxicities, sometimes necessitating dose reduction, or halting of cytotoxic drugs with a secondary risk of disease relapse. In addition, investigators have noted significant inter-individual variability in drug toxicities and disease outcomes, hence the role of pharmacogenetics (PGx) in elucidating genetic polymorphisms in candidate genes for the optimization of disease management. In this review, we present the PGx data in association with main toxicities seen in children treated for ALL in addition to efficacy, with a focus on the most plausible germline PGx variants. We then follow with a summary of the highest evidence drug-gene annotations with suggestions to move forward in implementing preemptive PGx for the individualization of treatment regimens for children with ALL.

Successful Management of l-Asparaginase-Associated Pancreatitis With Octreotide and Pegylated Asparaginase in 2 Patients With Acute Lymphoblastic Leukemia: Is There a Different Rare Warning Sign of Hypoglycemia for l-Asparaginase-Associated Pancreatitis?

l-Asparaginase (l-Asp) is a critical component of chemotherapy for acute lymphoblastic leukemia (ALL). However, toxic effects associated with l-Asp, such as hepatic dysfunction, pancreatitis, hypercholesterolemia, and hyperglycemia, have occurred. In addition, acute pancreatitis is a significant life-threatening adverse event associated with ALL. We describe 2 patients with ALL who had l-Asp-associated pancreatitis (AAP), with one patient presenting with hyperglycemia and the other presenting with hypoglycemia during induction treatment. When octreotide was administered to both of these patients, the clinical findings and laboratory data were improved. AAP was not repeated after treatment with pegylated asparaginase. Although AAP has a high risk of mortality and morbidity in childhood, APP treatment with appropriate agents, such as octreotide, can be successful.

Role of TPMT and ITPA variants in mercaptopurine disposition

PURPOSE

To explore the levels of thioguanine incorporated into DNA (DNA-TG), and erythrocyte levels of 6-thioguanine nucleotides (Ery-TGN) and methylated metabolites (Ery-MeMP) during 6-mercaptopurine (6MP)/Methotrexate (MTX) therapy of childhood acute lymphoblastic leukemia (ALL) and the relation to inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT) gene variants.

METHODS

Blood samples were drawn during 6MP/MTX maintenance therapy from 132 children treated for ALL at Rigshospitalet, Copenhagen. The samples were analysed for thiopurine metabolites and compared to TPMT (rs1800460 and rs1142345) and ITPA (rs1127354) genotypes.

RESULTS

Median DNA-TG (mDNA-TG) levels were higher in TPMT and ITPA low-activity patients as compared to wildtype patients (TPMTLA 549 vs. 364 fmol/µg DNA, p = 0.007, ITPALA 465 vs. 387 fmol/µg DNA, p = 0.04). mDNA-TG levels were positively correlated to median Ery-TGN (mEry-TGN)(rs = 0.37, p = 0.001), but plateaued at higher mEry-TGN levels. DNA-TG indices (mDNA-TG/mEry-TGN) were 42% higher in TPMTWT patients as compared to TPMTLA patients but no difference in DNA-TG indices was observed between ITPAWT and ITPALA patients (median 1.7 vs. 1.6 fmol/µg DNA/ nmol/mmol Hb, p = 0.81). DNA-TG indices increased with median Ery-MeMP (mEry-MeMP) levels (rs = 0.25, p = 0.001).

CONCLUSIONS

TPMT and ITPA genotypes significantly influence the metabolism of 6MP. DNA-TG may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than cytosolic metabolites. Prospective trials are needed to evaluate the usefulness of DNA-TGN for individual dose adjustments in childhood ALL maintenance therapy.

Predictors of hepatotoxicity and pancreatitis in children and adolescents with acute lymphoblastic leukemia treated according to contemporary regimens

BACKGROUND

Hepatotoxicity and pancreatitis are common treatment-related toxicities (TRTs) during contemporary treatment regimens for acute lymphoblastic leukemia (ALL). Limited detailed data from Children's Oncology Group (COG) regimens has been previously reported to enable identification of patient and treatment risk factors for these toxicities and their impact on outcomes.

PROCEDURE

We analyzed a retrospective pediatric ALL cohort treated at a single institution according to COG regimens from 2008 to 2015. The primary endpoint was cumulative incidence of study-defined "severe" hepatotoxicity (Common Terminology Criteria for Adverse Events [CTCAE] Grade ≥ 4 transaminitis or Grade ≥ 3 hyperbilirubinemia) and clinically significant pancreatitis (any grade). Pancreatitis was additionally classified using the Ponte di Legno (PdL) toxicity criteria. Secondary endpoints were chemotherapy interruptions, early disease response (end of induction [EOI] minimal residual disease [MRD]), and event-free survival (EFS).

RESULTS

We identified 262 patients, of whom 71 (27%) and 28 (11%) developed hepatotoxicity and pancreatitis, respectively. Three cases of pancreatitis did not fulfill PdL criteria despite otherwise consistent presentations. Both TRTs occurred throughout therapy, but approximately 25% of hepatotoxicity (18/71) and pancreatitis (8/28) occurred during induction alone. Both obesity and age (≥10 years) were identified as predictors of hepatotoxicity (subdistribution hazard ratio [SHR] obesity = 1.75, 95% confidence interval [95% CI] 1.04-2.96; SHR age ≥10 = 1.9, 95% CI 1.19-3.10) and pancreatitis (SHR obesity = 2.18, 95% CI 1.01-4.67; SHR age ≥ 10 = 2.76, 95% CI 1.19-6.39, P = 0.018). Dose interruptions were common but neither toxicity influenced EOI MRD nor EFS.

CONCLUSIONS

Obese and/or older children are particularly at risk for hepatotoxicity and pancreatitis, and may benefit from toxicity surveillance and chemoprotective strategies to prevent or mitigate associated morbidity.

Consensus Guideline for Use of Glucarpidase in Patients with High-Dose Methotrexate Induced Acute Kidney Injury and Delayed Methotrexate Clearance

An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop high‐dose methotrexate (HDMTX)‐induced nephrotoxicity and delayed methotrexate excretion. This guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of a HDMTX infusion.

Acute kidney injury due to high‐dose methotrexate (HDMTX) is a serious, life‐threatening toxicity that can occur in pediatric and adult patients. Glucarpidase is a treatment approved by the Food and Drug Administration for high methotrexate concentrations in the context of kidney dysfunction, but the guidelines for when to use it are unclear. An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop HDMTX‐induced nephrotoxicity and delayed methotrexate excretion. The guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of an HDMTX infusion. For an HDMTX infusion ≤24 hours, if the 36‐hour concentration is above 30 µM, 42‐hour concentration is above 10 µM, or 48‐hour concentration is above 5 µM and the serum creatinine is significantly elevated relative to the baseline measurement (indicative of HDMTX‐induced acute kidney injury), glucarpidase may be indicated. After a 36‐ to 42‐hour HDMTX infusion, glucarpidase may be indicated when the 48‐hour methotrexate concentration is above 5 µM. Administration of glucarpidase should optimally occur within 48–60 hours from the start of the HDMTX infusion, because life‐threatening toxicities may not be preventable beyond this time point.

Implications for Practice.

Glucarpidase is a rarely used medication that is less effective when given after more than 60 hours of exposure to high‐dose methotrexate, so predicting early which patients will need it is imperative. There are no currently available consensus guidelines for the use of this medication. The indication on the label does not give specific methotrexate concentrations above which it should be used. An international group of experts was convened to develop a consensus guideline that was specific and evidence‐based to identify the population of patients who would benefit from glucarpidase.

ABCB1 genetic variants in leukemias: current insights into treatment outcomes

Despite improvements in treatment of different types of leukemia, not all patients respond optimally for a particular treatment. Some treatments will work better for some, while being harmful or ineffective for others. This is due to genetic variation in the form of single-nucleotide polymorphisms (SNPs) that affect gene expression or function and cause inherited interindividual differences in the metabolism and disposition of drugs. Drug transporters are one of the determinants governing the pharmacokinetic profile of chemotherapeutic drugs. The ABCB1 transporter gene transports a wide range of drugs, including drugs used in leukemia treatment. Polymorphisms in the ABCB1 gene do affect intrinsic resistance and pharmacokinetics of several drugs used in leukemia treatment protocols and thereby affect the efficacy of treatment and event-free survival. This review focuses on the impact of three commonly occurring SNPs (1236C>T, 2677G>T/A, and 3435C>T) of ABCB1 on treatment response of various types of leukemia. From the literature available, some of the genotypes and haplotypes of these SNPs have been found to be potential determinants of interindividual variability in drug disposition and pharmacologic response in different types of leukemia. However, due to inconsistencies in the results observed across the studies, additional studies, considering novel genomic methodologies, comprehensive definition of clinical phenotypes, adequate sample size, and uniformity in all the confounding factors, are warranted.

Non-infectious chemotherapy-associated acute toxicities during childhood acute lymphoblastic leukemia therapy

During chemotherapy for childhood acute lymphoblastic leukemia, all organs can be affected by severe acute side effects, the most common being opportunistic infections, mucositis, central or peripheral neuropathy (or both), bone toxicities (including osteonecrosis), thromboembolism, sinusoidal obstruction syndrome, endocrinopathies (especially steroid-induced adrenal insufficiency and hyperglycemia), high-dose methotrexate-induced nephrotoxicity, asparaginase-associated hypersensitivity, pancreatitis, and hyperlipidemia. Few of the non-infectious acute toxicities are associated with clinically useful risk factors, and across study groups there has been wide diversity in toxicity definitions, capture strategies, and reporting, thus hampering meaningful comparisons of toxicity incidences for different leukemia protocols. Since treatment of acute lymphoblastic leukemia now yields 5-year overall survival rates above 90%, there is a need for strategies for assessing the burden of toxicities in the overall evaluation of anti-leukemic therapy programs.

NUDT15 and TPMT genetic polymorphisms are related to 6-mercaptopurine intolerance in children treated for acute lymphoblastic leukemia at the Children's Cancer Center of Lebanon

BACKGROUND

Interindividual variability in thiopurine-related toxicity could not be completely explained by thiopurine S-methyltransferase (TPMT) polymorphisms, as a number of patients who are homozygous wild type or normal for TPMT still develop toxicity that necessitates 6-mercaptopurine (MP) dose reduction or protocol interruption. Recently, few studies reported on an inherited nucleoside diphosphate-linked moiety X motif 15 (NUDT15) c.415C>T low-function variant that is associated with decreased thiopurine metabolism and leukopenia in childhood acute lymphoblastic leukemia (ALL) and other diseases.

PROCEDURES

The aim of this study is to measure the frequency of TPMT and NUDT15 polymorphisms and assess whether they are predictors of MP intolerance in children treated for ALL. One hundred thirty-seven patients with ALL of whom 121 were Lebanese were evaluated. MP dose intensity was calculated as the ratio of the tolerated MP dose to planned dose during continuation phase to maintain an absolute neutrophil count (ANC) dose above 300 per μl.

RESULTS

One patient was NUDT15 heterozygous TC and tolerated only 33.33% of the planned MP dose, which was statistically significantly different from the median-tolerated MP dose intensity of the rest of the cohort (76.00%). Three patients had the TPMT*3A haplotype and tolerated 40.00-66.66% of the planned MP dose, which was also statistically significantly different from the rest of the cohort.

CONCLUSIONS

This is the first report on the association of TPMT and NUDT15 polymorphisms with MP dose intolerance in Arab patients with ALL. Genotyping for additional polymorphisms may be warranted for potential gene/allele-dose effect.

Polymorphisms in the ABCB1 gene and effect on outcome and toxicity in childhood acute lymphoblastic leukemia

The membrane transporter P-glycoprotein, encoded by the ABCB1 gene, influences the pharmacokinetics of anti-cancer drugs. We hypothesized that variants of ABCB1 affect outcome and toxicity in childhood acute lymphoblastic leukemia (ALL). We studied 522 Danish children with ALL, 93% of all those eligible. Risk of relapse was increased 2.9-fold for patients with the 1199GA variant versus 1199GG (P=0.001), and reduced 61% and 40%, respectively, for patients with the 3435CT or 3435TT variants versus 3435CC (overall P=0.02). The degree of bone marrow toxicity during doxorubicin, vincristine and prednisolone induction therapy was more prominent in patients with 3435TT variant versus 3435CT/3435CC (P=0.01/P<0.0001). We observed more liver toxicity after high-dose methotrexate in patients with 3435CC variant versus 3435CT/TT (P=0.03). In conclusion, there is a statistically significant association between ABCB1 polymorphisms, efficacy and toxicity in the treatment of ALL, and ABCB1 1199G>A may be a new possible predictive marker for outcome in childhood ALL.

Mercaptopurine/Methotrexate maintenance therapy of childhood acute lymphoblastic leukemia: clinical facts and fiction

The antileukemic mechanisms of 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy are poorly understood, but the benefits of several years of myelosuppressive maintenance therapy for acute lymphoblastic leukemia are well proven. Currently, there is no international consensus on drug dosing. Because of significant interindividual and intraindividual variations in drug disposition and pharmacodynamics, vigorous dose adjustments are needed to obtain a target degree of myelosuppression. As the normal white blood cell counts vary by patients' ages and ethnicity, and also within age groups, identical white blood cell levels for 2 patients may not reflect the same treatment intensity. Measurements of intracellular levels of cytotoxic metabolites of 6MP and MTX can identify nonadherent patients, but therapeutic target levels remains to be established. A rise in serum aminotransferase levels during maintenance therapy is common and often related to high levels of methylated 6MP metabolites. However, except for episodes of hypoglycemia, serious liver dysfunction is rare, the risk of permanent liver damage is low, and aminotransferase levels usually normalize within a few weeks after discontinuation of therapy. 6MP and MTX dose increments should lead to either leukopenia or a rise in aminotransferases, and if neither is experienced, poor treatment adherence should be considered. The many genetic polymorphisms that determine 6MP and MTX disposition, efficacy, and toxicity have precluded implementation of pharmacogenomics into treatment, the sole exception being dramatic 6MP dose reductions in patients who are homozygous deficient for thiopurine methyltransferase, the enzyme that methylates 6MP and several of its metabolites. In conclusion, maintenance therapy is as important as the more intensive and toxic earlier treatment phases, and often more challenging. Ongoing research address the applicability of drug metabolite measurements for dose adjustments, extensive host genome profiling to understand diversity in treatment efficacy and toxicity, and alternative thiopurine dosing regimens to improve therapy for the individual patient.

Genetic polymorphisms in candidate genes predict increased toxicity with methotrexate therapy in Lebanese children with acute lymphoblastic leukemia

BACKGROUND

The aim of this study is to analyze polymorphisms in genes involved in 6-mercaptopurine detoxification (TPMT); methotrexate (MTX) metabolism including ABCB1 (or MDR1), ABCC2, SLC19A1 (or RFC1), and SLCO1B1; and the MTX effect mainly MTHFR and TYMS, and to assess whether these polymorphisms are predictors of treatment toxicity and/or MTX clearance.

MATERIALS AND METHODS

This study included 127 Lebanese acute lymphoblastic leukemia patients, of whom 117 were treated following the St Jude's Children Research Hospital protocol. Genotyping was performed using real-time PCR or restriction fragment length polymorphism. MTX levels were measured using a polarization fluorescence assay from Roche. MTX clearance was estimated on the basis of all available MTX levels measured after high-dose MTX treatment during the consolidation phase.

RESULTS

Five variants in four genes (MTHFR, ABCB1, ABCC2, and TYMS) were shown to be associated with toxicity, but neither was associated with MTX pharmacokinetic parameters. For instance, during the consolidation phase, a statistically significant association was found between MTHFR rs1801133 variant allele carriers and a decrease in hemoglobin levels [odds ratio (OR)=3.057; 95% confidence interval (CI): 1.217; 7.680]. In addition, a statistically significant association was found among neutropenia (absolute neutrophil count<500) and variant allele carriers of ABCB1 rs1045642 (OR=5.174; 95% CI: 1.674; 15.989) and ABCB1 rs1128503 (OR=3.364; 95% CI: 1.257; 9.004), respectively. ABCC2 rs717620 variant allele carriers needed significantly more time to reach a MTX level below 0.1 µmol/l (β=5.122; 95% CI: 1.412; 8.831). During the continuation phase, a statistically significant association was found between ABCC2 rs717620 and TYMS 28-bp tandem repeats carriers with the need to decrease weekly MTX doses (β=-4.905; 95% CI: -9; -0.809 and β=-5.770; 95% CI: -10.138; -1.403), respectively.

CONCLUSION

Genotyping for MTHFR, ABCB1, ABCC2, and TYMS polymorphisms may be useful in identifying patients at risk of increased MTX toxicity and the need for dose optimization before treatment initiation.

Genomic profiling of thousands of candidate polymorphisms predicts risk of relapse in 778 Danish and German childhood acute lymphoblastic leukemia patients

Childhood acute lymphoblastic leukemia survival approaches 90%. New strategies are needed to identify the 10-15% who evade cure. We applied targeted, sequencing-based genotyping of 25 000 to 34 000 preselected potentially clinically relevant single-nucleotide polymorphisms (SNPs) to identify host genome profiles associated with relapse risk in 352 patients from the Nordic ALL92/2000 protocols and 426 patients from the German Berlin-Frankfurt-Munster (BFM) ALL2000 protocol. Patients were enrolled between 1992 and 2008 (median follow-up: 7.6 years). Eleven cross-validated SNPs were significantly associated with risk of relapse across protocols. SNP and biologic pathway level analyses associated relapse risk with leukemia aggressiveness, glucocorticosteroid pharmacology/response and drug transport/metabolism pathways. Classification and regression tree analysis identified three distinct risk groups defined by end of induction residual leukemia, white blood cell count and variants in myeloperoxidase (MPO), estrogen receptor 1 (ESR1), lamin B1 (LMNB1) and matrix metalloproteinase-7 (MMP7) genes, ATP-binding cassette transporters and glucocorticosteroid transcription regulation pathways. Relapse rates ranged from 4% (95% confidence interval (CI): 1.6-6.3%) for the best group (72% of patients) to 76% (95% CI: 41-90%) for the worst group (5% of patients, P<0.001). Validation of these findings and similar approaches to identify SNPs associated with toxicities may allow future individualized relapse and toxicity risk-based treatments adaptation.

Pharmacogenetically based dosing of thiopurines in childhood acute lymphoblastic leukemia: influence on cure rates and risk of second cancer

BACKGROUND

Previous studies have indicated that patients with thiopurine methyltransferase (TPMT) low activity (TPMT(LA)) have reduced risk of relapse but increased risk of second malignant neoplasm (SMN) compared to patients with TPMT wild-type (TPMT(WT)) when treated with 6 MP maintenance therapy starting doses of 75 mg/m(2)/day. To reduce SMN risk, 6MP starting doses were reduced to 50 mg/m(2)/day for patients with TPMT heterozygosity in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL2000 protocol.

PROCEDURE

We explored the pattern of SMN and relapse in the NOPHO ALL2000 protocol (n = 674) and NOPHO ALL92 protocol (n = 601) in relation to TPMT pheno- and/or genotype.

RESULTS

The overall risk of any event did not differ significantly between the two protocols. However, in event pattern analyses considering only the patients with TPMT(LA) who experienced relapse or SMN, the risk of SMN versus leukemia relapse was significantly lower in the ALL2000 cohort for patients with a 6MP starting dose <75 mg/m(2)/day when compared to the patients in ALL92 (relapse (n = 11) and SMN (n = 0) in ALL2000 versus relapse (n = 5) and SMN (n = 4) in ALL92, P = 0.03). Furthermore, the 8-year cumulative incidence of relapse for patients with TPMT(LA) was significantly higher in the ALL2000 compared to the ALL92 cohort (19.7% (11.6-33.3%) vs. 6.7% (2.9-15.5%), P = 0.03).

CONCLUSION

This study indicates that reducing 6MP starting dose for patients with TPMT(LA) may reduce SMN risk but lead to a relapse risk similar to that of patients with TPMT(WT).

SMYD2 is highly expressed in pediatric acute lymphoblastic leukemia and constitutes a bad prognostic factor

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy. Although several clinical characteristics can be associated with worse prognosis, more robust biological markers still remains uncovered. SMYD2, a member of SMYD protein family, regulates the activity of several proteins through methylation. In this study, we performed quantitative real time PCR to compare the expression of SMYD2 in 83 pediatric ALL patients and non-neoplastic bone marrow samples (BMS). The study revealed that SMYD2 expression is altered in ALL BMS and its high expression was correlated with a bad prognosis. Moreover, we also revealed that SMYD2 expression level significantly decreases in patients that respond to chemotherapy treatment.

Host genetic variants of ABCB1 and IL15 influence treatment outcome in paediatric acute lymphoblastic leukaemia

BACKGROUND

Host germline variations and their potential prognostic importance is an emerging area of interest in paediatric ALL.

METHODS

We investigated the associations between 20 germline variations and various clinical end points in 463 children with ALL.

RESULTS

After adjusting for known prognostic factors, variants in two genes were found to be independently associated with poorer EFS: ABCB1 T/T at either 2677 (rs2032582) or 3435 (rs1045642) position (P=0.003) and IL15 67276493G/G (rs17015014; P=0.022). These variants showed a strong additive effect affecting outcome (P<0.001), whereby patients with both risk genotypes had the worst EFS (P=0.001), even after adjusting for MRD levels at the end of remission induction. The adverse effect of ABCB1 T/T genotypes was most pronounced in patients with favourable cytogenetics (P=0.011) while the IL15 67276493G/G genotype mainly affected patients without common chromosomal abnormalities (P=0.022). In both cytogenetic subgroups, increasing number of such risk genotypes still predicted worsening outcome (P<0.001 and=0.009, respectively).

CONCLUSION

These results point to the prognostic importance of host genetic variants, although the specific mechanisms remain unclarified. Inclusion of ABCB1 and IL15 variants may help improve risk assignment strategies in paediatric ALL.

Pharmacogenetics of methotrexate in acute lymphoblastic leukaemia: why still at the bench level?

PURPOSE

The antifolate drug methotrexate (MTX) was introduced into clinical practice about 60 years ago and remains an important component of different acute lymphoblastic leukemia (ALL) treatment protocols. It acts by inhibiting several enzymes in the folate pathway, thereby resulting in the disruption of folate homeostasis. To date, treatment regimens have not been personalized despite there being experimental evidence that gene polymorphisms of folate metabolizing enzymes affect MTX response. The aim of this review was to evaluate the influence of genetic polymorphisms of the enzymes involved in the MTX pathway on ALL treatment outcomes and identify factors underlining the failure to personalize MTX therapy.

METHODS

We conducted a literature search in PUBMED and Google Scholar using the following key words: methotrexate, polymorphism, acute lymphoblastic leukemia, pharmacogenetics, pharmacogenomics and personalized medicine.

RESULTS

The reasons for the failure to personalize MTX therapy may be due to (1) most studies involving single-center, small-sized cohorts, (2) differences in MTX dose across different protocols, (3) failure to consider minimal residual disease as a risk factor for post-induction treatment, (4) differences in outcome criteria between studies and (5) failure to consider the folate levels of a patient before initiation of MTX therapy. Although high-throughput techniques allow the mapping of thousands of genetic polymorphisms in a single run, it remains a major challenge to dissect out folate-metabolizing enzymes which have a high impact on the efficacy and toxicity of MTX and which, therefore, could be the targets for intervention.

CONCLUSIONS

Prospective pharmacogenetic studies which consider all of the above-mentioned factors should be undertaken to facilitate the design of personalized MTX treatment for ALL patients.

Drug cocktail optimization in chemotherapy of cancer

BACKGROUND

In general, drug metabolism has to be considered to avoid adverse effects and ineffective therapy. In particular, chemotherapeutic drug cocktails strain drug metabolizing enzymes especially the cytochrome P450 family (CYP). Furthermore, a number of important chemotherapeutic drugs such as cyclophosphamide, ifosfamide, tamoxifen or procarbazine are administered as prodrugs and have to be activated by CYP. Therefore, the genetic variability of these enzymes should be taken into account to design appropriate therapeutic regimens to avoid inadequate drug administration, toxicity and inefficiency.

OBJECTIVE

The aim of this work was to find drug interactions and to avoid side effects or ineffective therapy in chemotherapy.

DATA SOURCES AND METHODS

Information on drug administration in the therapy of leukemia and their drug metabolism was collected from scientific literature and various web resources. We carried out an automated textmining approach. Abstracts of PubMed were filtered for relevant articles using specific keywords. Abstracts were automatically screened for antineoplastic drugs and their synonyms in combination with a set of human CYPs in title or abstract.

RESULTS

We present a comprehensive analysis of over 100 common cancer treatment regimens regarding drug-drug interactions and present alternatives avoiding CYP overload. Typical concomitant medication, e.g. antiemetics or antibiotics is a preferred subject to improvement. A webtool, which allows drug cocktail optimization was developed and is publicly available on http://bioinformatics.charite.de/chemotherapy.

Physicians compliance during maintenance therapy in children with Down syndrome and acute lymphoblastic leukemia

Children with Down syndrome (DS) and acute lymphoblastic leukemia (ALL) have an inferior prognosis compared with non-DS ALL patients. We reviewed methotrexate (MTX)/mercaptopurine (6MP) maintenance therapy data for children with DS treated according to the Nordic Society of Pediatric Hematology and Oncology (NOPHO) ALL92 or the NOPHO ALL2000 protocols between 1992 and 2007. The 5-year event-free survival probability (pEFS(5 yr)) for the 66 DS patients was inferior to the 2602 non-DS patients (0.50 ± 0.07 vs 0.77 ± 0.01 (P<0.001)). The 48 DS patients in first remission at the beginning of maintenance therapy had pEFS(10 yr) below that of the 522 non-DS control patients (pEFS(10 yr): 0.58 (95% confidence interval (CI) 0.43-0.77) vs 0.83 (95% CI 0.80-0.86), respectively (P<0.0001)). The DS patients received lower median doses of MTX (median: 11.8 vs 15.4 (P<0.0001)) and 6MP (median: 43.6 vs 59.4 (P<0.0001)). In Cox regression analysis, male gender, presence of DS and high median maintenance therapy white blood cell levels (mWBC) were associated with increased risk for relapse. DS-ALL patients with mWBC above or below 3.5 × 10(9)/l (protocol target) had pEFS(10 yr) of 0.31 and 0.72 (P=0.02), and the mWBC hazard ratio for DS-ALL patients was 2.0 (P<0.0005). We conclude that insufficient treatment intensity during maintenance therapy of DS-ALL patients may contribute to their poor prognosis.

Asparaginase-associated pancreatitis in children

l-asparaginase has been an element in the treatment for acute lymphoblastic leukaemia (ALL) and non-Hodgkin lymphoma since the late 1960s and remains an essential component of their combination chemotherapy. Among the major toxicities associated with l-asparaginase therapy are pancreatitis, allergic reactions, thrombotic events, hepatotoxicity and hyperlipidaemia. Acute pancreatitis is one of the most common reasons for stopping treatment with l-asparaginase. Short-term complications of asparaginase-associated pancreatitis include development of pseudocysts and pancreatic necrosis. Long-term complications include chronic pancreatitis and diabetes. The pathophysiology of asparaginase-associated pancreatitis remains to be uncovered. Individual clinical and genetic risk factors have been identified, but they are only weak predictors of pancreatitis. This review explores the definition, possible risk factors, treatment and complications of asparaginase-associated pancreatitis.

Gene dose effects of GSTM1, GSTT1 and GSTP1 polymorphisms on outcome in childhood acute lymphoblastic leukemia

Children with acute lymphoblastic leukemia (ALL) react very differently to chemotherapy. One explanation for this is inherited genetic variation. The glutathione S-transferase (GST) enzymes inactivate a number of chemotherapeutic drugs administered in childhood ALL therapy. Two multiplexing methods were applied for genotyping the GSTM1 and GSTT1 genes (distinguishing between 0, 1, or 2 gene copies) and the GSTP1 313 A>G polymorphism, simultaneously. A total of 263 childhood ALL patients were genotyped. No gene dose effect on outcome was demonstrated with either GST polymorphisms. Grouping of GSTM1 and GSTT1 into poor (0 or 1 gene copy)-and good metabolizers (at least 2 gene copies)-showed that the poor metabolizers had a trend toward a better outcome (event-free survival =91.8%) compared with the good metabolizers (event-free survival =83.2%). Similarly, in the adjusted analysis the good metabolizers demonstrated a 2.2-fold higher risk trend of experiencing an event (resistant disease or relapse) compared with the poor metabolizers (P=0.066; hazard ratio =2.248; 95% confidence interval, 0.948-5.327). In conclusion, our results suggest that the combined gene dose of GSTM1 and GSTT1 may influence outcome in childhood ALL.

Liquid chromatography-tandem mass spectrometry quantification of 6-thioguanine in DNA using endogenous guanine as internal standard

Thiopurines are S-substituted antimetabolites that are widely used in the treatment of hematological malignancies and as immunosuppressants. Because of extensive inter-individual variation in drug disposition and the significant toxicity associated with thiopurine therapy, there is a need for improved individualized treatment. We here present a fast and sensitive method for quantifying the pharmacological end-point of thiopurines, 6-thioguanine (TG) in chromosomal DNA. Purine nucleobases are released from DNA, etheno-derivatized with chloroacetaldehyde, separated by HILIC and quantified by tandem mass spectrometry using endogenous chromosomal guanine as internal standard. The method is linear up to at least 10 pmol TG/μg DNA and the limit of detection and quantification are 4.2 and 14.1 fmol TG/μg DNA, respectively. The matrix (DNA) had no effect upon quantification of TG. SPE recovery was estimated at 63% (RSD 26%), which is corrected for by the internal standard resulting in stable quantification. The TG levels found were above the LOQ in 18 out of 18 childhood leukemia patients on 6-mercaptopurine/methotrexate maintenance therapy (median 377, range 45-1190 fmol/μg DNA) with intra- and inter-day RSDs of less than 11%. The method uses 2 μg DNA/sample, which can easily be obtained from these patients.

Pharmacogenetics and individualized therapy in children: immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs

Pharmacogenetic polymorphisms that change the amino acid sequences in coding regions only account for part of the interindividual differences in disease susceptibility and drug response. Additional pharmacogenomic and epigenetic factors are also involved. In children, pharmacogenetic studies are limited, although it has been clear for many years that the interactions between developmental patterns of drug-metabolizing enzymes and transporters have a major impact on dose exposure with age-specific dosage requirements. This article will analyze the factors affecting variability in drug response in children and focus on the pharmacogenetic polymorphisms of immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs. Additional pharmacogenetic and epigenetic studies should be performed to allow the individualization of therapy in children.

Individualized toxicity-titrated 6-mercaptopurine increments during high-dose methotrexate consolidation treatment of lower risk childhood acute lymphoblastic leukaemia. A Nordic Society of Paediatric Haematology and Oncology (NOPHO) pilot study

This study explored the feasibility and toxicity of individualized toxicity-titrated 6-mercaptopurine (6MP) dose increments during post-remission treatment with High-dose methotrexate (HDM) (5000 mg/m(2), ×3) in 38 patients with Childhood (ALL). Patients were increased in steps of 25 mg 6MP/m(2) per day if they did not develop myelotoxicity within 2 weeks after HDM. 6MP could be increased in 31 patients (81%). Toxicity was acceptable and did not differ significantly between groups. Patients receiving 75 mg/m(2) per day had significantly shorter duration of treatment interruptions of 6MP than the remaining patients (P = 0·03). This study shows individualized toxicity-titrated 6MP dosing during consolidation is feasible without increased risk of toxicity.

The impact of CYP3A5*3 on risk and prognosis in childhood acute lymphoblastic leukemia

OBJECTIVES

  Acute lymphoblastic leukemia (ALL) is the most common cancer in childhood; however, little is known of the molecular etiology and environmental exposures causing the disease. Cytochrome P450 3A5 (CYP3A5) plays a crucial role in the catalytic oxidation of endogenous metabolites and toxic substances, including chemotherapeutic agents. The aim of this study was to investigate the role of a single-nucleotide polymorphism (CYP3A5*3 6986A>G), which renders low enzyme activity, in the risk of developing ALL and in the outcome for children with ALL.

PATIENTS AND METHODS

  Six hundred and sixteen childhood patients with ALL and 203 controls were genotyped by allelic discrimination.

RESULTS

  Individuals with the A allele had a 64% increased risk of developing childhood ALL (odds ratio = 1.64; 95% CI, 1.009-2.657). In general, event-free survival (EFS) did not differ in relation to CYP3A5 genotype. However, for patients with T-ALL, presence of the A allele was associated with better prognosis (EFS = 94.1%), while patients with the low-activity GG genotype only had an EFS of 61.5% (P = 0.015). Thus, for patients with T-ALL having no A allele and therefore low expression of CYP3A5, the risk of experiencing an event was almost eight times higher compared to those having at least one A allele (P = 0.045, hazard ratio = 7.749; 95% CI, 1.044-57.52).

CONCLUSIONS

  This study shows that genetics may play a role in the risk of developing childhood ALL and indicates that improved treatment stratification of childhood patients with ALL may require addition of host genetic information.

MicroRNA pharmacogenomics: post-transcriptional regulation of drug response

The field of pharmacogenomics aims to predict which drugs will be most effective and safe for a particular individual based on their genome sequence or expression profile, thereby allowing personalized treatment. The bulk of pharmacogenomic research has focused on the role of single nucleotide polymorphisms, copy number variations or differences in gene expression levels of drug metabolizing or transporting genes and drug targets. In this review paper, we focus instead on microRNAs (miRNAs): small noncoding RNAs, prevalent in metazoans, that negatively regulate gene expression in many cellular processes. We discuss how miRNAs, by regulating the expression of pharmacogenomic-related genes, can play a pivotal role in drug efficacy and toxicity and have potential clinical implications for personalized medicine.

Challenges in implementing individualized medicine illustrated by antimetabolite therapy of childhood acute lymphoblastic leukemia

Predicting the response to medical therapy and subsequently individualizing the treatment to increase efficacy or reduce toxicity has been a longstanding clinical goal. Not least within oncology, where many patients fail to be cured, and others are treated to or beyond the limit of acceptable toxicity, an individualized therapeutic approach is indicated. The mapping of the human genome and technological developments in DNA sequencing, gene expression profiling, and proteomics have raised the expectations for implementing genotype-phenotype data into the clinical decision process, but also multiplied the complex interaction of genetic and other laboratory parameters that can be used for therapy adjustments. Thus, with the advances in the laboratory techniques, post laboratory issues have become major obstacles for treatment individualization. Many of these challenges have been illustrated by studies involving childhood acute lymphoblastic leukemia (ALL), where each patient may receive up to 13 different anticancer agents over a period of 2-3 years. The challenges include i) addressing important, but low-frequency outcomes, ii) difficulties in interpreting the impact of single drug or single gene response data that often vary across treatment protocols, iii) combining disease and host genomics with outcome variations, and iv) physicians' reluctance in implementing potentially useful genotype and phenotype data into clinical practice, since unjustified downward or upward dose adjustments could increase the of risk of relapse or life-threatening complications. In this review we use childhood ALL therapy as a model and discuss these issues, and how they may be addressed.

Risk factors for treatment related mortality in childhood acute lymphoblastic leukaemia

BACKGROUND

In spite of major improvements in the cure rate of childhood acute lymphoblastic leukaemia (ALL), 2-4% of patients still die from treatment related complications.

PROCEDURE

We investigated the pattern of treatment related deaths (TRDs) and possible risk factors in the NOPHO ALL-92 and ALL-2000 protocols. Fifty-five TRDs were identified among the 1,645 ALL-92 patients and 33 among the 1,090 ALL-2000 patients.

RESULTS

There was no significant difference in the incidence of TRDs between the two protocols (3.4% vs. 3.2%). Five patients died before initiation of therapy (0.2%), and the overall subsequent risk of induction death and death in first complete remission (CR1) was 1.2% and 1.8%, respectively. Infections were the major cause of death comprising 72% of all cases including 9 deaths from Pseudomonas aeruginosa and 11 deaths from fungal infections. Other causes of death included bleeding or thrombosis (eight patients), tumour burden related toxicities (seven patients) and organ toxicity (seven patients). Female gender (hazard ratio (HR): 2.2, 95% confidence interval (95% CI): 1.4-3.4), high white blood cell count (≥ 200 × 10(9) /L) at diagnosis (HR: 3.5, 95% CI: 1.7-7.1), T-cell disease (HR: 1.9, 95% CI: 1.01-3.7), Down syndrome (HR: 7.3, 95% CI: 3.6-14.9) and haematopoietic stem cell transplantation in CR1 (HR: 8.0, 95% CI: 3.3-19.5) were identified as independent risk factors for TRD.

CONCLUSION

Several TRDs were potentially preventable and future efforts should be directed towards patients at risk.

Cost-effective multiplexing before capture allows screening of 25 000 clinically relevant SNPs in childhood acute lymphoblastic leukemia

Genetic variants, including single-nucleotide polymorphisms (SNPs), are key determiners of interindividual differences in treatment efficacy and toxicity in childhood acute lymphoblastic leukemia (ALL). Although up to 13 chemotherapeutic agents are used in the treatment of this cancer, it remains a model disease for exploring the impact of genetic variation due to well-characterized cytogenetics, drug response pathways and precise monitoring of minimal residual disease. Here, we have selected clinically relevant genes and SNPs through literature screening, and on the basis of associations with key pathways, protein-protein interactions or downstream partners that have a role in drug disposition and treatment efficacy in childhood ALL. This allows exploration of pathways, where one of several genetic variants may lead to similar clinical phenotypes through related molecular mechanisms. We have designed a cost-effective, high-throughput capture assay of ∼25,000 clinically relevant SNPs, and demonstrated that multiple samples can be tagged and pooled before genome capture in targeted enrichment with a sufficient sequencing depth for genotyping. This multiplexed, targeted sequencing method allows exploration of the impact of pharmacogenetics on efficacy and toxicity in childhood ALL treatment, which will be of importance for personalized chemotherapy.

Pharmacogenomics and active surveillance for serious adverse drug reactions in children

Juxtaposing clinical pharmacology with human genetics, pharmacogenomics utilizes a patient’s genetic information to identify genetic variants that have the potential to provide clinically relevant predictions of toxicity and efficacy. The goal is to develop personalized and genetic-based predictions of an individual’s drug response and likelihood of experiencing an adverse drug reaction. The Canadian Pharmacogenomics Network for Drug Safety (CPNDS) has implemented active adverse drug reaction surveillance to monitor and discover genetic markers related to serious adverse drug reactions in the pediatric population. Evidence-based pharmacogenomics research will inform public policy and influence drug benefit–risk decision-making. Regulatory processes and future challenges in pharmacogenomics research will be discussed.

The association of reduced folate carrier 80G>A polymorphism to outcome in childhood acute lymphoblastic leukemia interacts with chromosome 21 copy number

The reduced folate carrier (RFC) is involved in the transport of methotrexate (MTX) across the cell membrane. The RFC gene (SLC19A1) is located on chromosome 21, and we hypothesized that the RFC80 G>A polymorphism would affect outcome and toxicity in childhood leukemia and that this could interact with chromosome 21 copy number in the leukemic clone. A total of 500 children with acute lymphoblastic leukemia treated according to the common Nordic treatment protocols were included, and we found that the RFC AA variant was associated with a 50% better chance of staying in remission compared with GG or GA variants (P = .046). Increased copy numbers of chromosome 21 appear to improve outcome also in children with GA or GG variant. In a subset of 182 children receiving 608 high-dose MTX courses, we observed higher degree of bone marrow toxicity in patients with the RFC AA variant compared with GA/GG variants (platelet 73 vs 99/105 x 10(9)/L, P = .004, hemoglobin 5.6 vs 5.9/6.0 mmol/L, P = .004) and a higher degree of liver toxicity in patients with RFC GG variant (alanine aminotransferase 167 vs 127/124 U/L, P = .05). In conclusion, the RFC 80G>A polymorphism interacts with chromosome 21 copy numbers and affects both efficacy and toxicity of MTX.

SNP analysis of Rac1 For personalized ligand interaction

This paper addresses mutational events that give rise to differing response to drugs focusing on Rac1, a protein that has been recognized as a target for drug design for cardiovascular disease due its regulatory role of angiogenesis. Rac1 has been considered with reference to Single Nucleotide Polymorphism (SNP), which has become of great value for personalized medicine. We have considered four variation of Rac1 registered in UNIPROTKB. Two of these variations are due to the environmental or population factors and two are mutation that we have selected because they are located near the binding sites of Rac1. Rac1 has been modelled by Rosetta software and by i-Tasser web server. We have chosen i-Tasser based modelling because the Rac1 structure obtained was more closely resembling crystallography data. In silico model have been used as receptors for docking with a set of 20 morpholines. The results that have been obtained on SNPs shows that a single ligand can react very differently with a mutated structure. Our analysis shows that all mutations that have been considered change Rac1 conformation and increase the accessible surface of Rac1. Our analysis highlights the effect of two sources of genetic variability: single base variation and alternative splicing.

Long-term results of NOPHO ALL-92 and ALL-2000 studies of childhood acute lymphoblastic leukemia

Analysis of 2668 children with acute lymphoblastic leukemia (ALL) treated in two successive Nordic clinical trials (Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL-92 and ALL-2000) showed that 75% of all patients are cured by first-line therapy, and 83% are long-term survivors. Improvements in systemic and intrathecal chemotherapy have reduced the use of central nervous system (CNS) irradiation to <10% of the patients and provided a 5-year risk of isolated CNS relapse of 2.6%. Improved risk stratification and chemotherapy have eliminated the previous independent prognostic significance of gender, CNS leukemia and translocation t(1;19)(q23;p13), whereas the post-induction level of minimal residual disease (MRD) has emerged as a new risk grouping feature. Infant leukemia, high leukocyte count, T-lineage immunophenotype, translocation t(4;11)(q21;q23) and hypodiploidy persist to be associated with lower cure rates. To reduce the overall toxicity of the treatment, including the risk of therapy-related second malignant neoplasms, the current NOPHO ALL-2008 protocol does not include CNS irradiation in first remission, the dose of 6-mercaptopurine is reduced for patients with low thiopurine methyltransferase activity, and the protocol restricts the use of hematopoietic stem cell transplantation in first remission to patients without morphological remission after induction therapy or with high levels of MRD after 3 months of therapy.

Advances in individual prediction of methotrexate toxicity: a review

As the cure rates for haematological malignancies have improved, the exploration of the balance between efficacy and side effects has become a major research target. The antifolate methotrexate is widely used in the treatment of acute lymphoblastic leukaemia, non-Hodgkin lymphoma, and osteosarcoma. Even when given identical methotrexate doses, patients vary significantly in their response and pattern of toxicities. This diversity can, to some extent, be linked to sequence variations in genes involved in drug absorption, metabolism, excretion, cellular transport, and effector targets or target pathways. In the coming years pharmacogenomics is expected to change our approaches to individualised therapy with methotrexate. However, genetic polymorphisms affect the pharmacokinetics and dynamics of all the drugs a patient receive as well as the normal tissues tolerance to a given drug exposure. Thus, although high-throughput techniques will allow mapping of tens of thousands of genetic polymorphisms in one run, it will be a major challenge to dissect out which of these have the strongest impact on efficacy and toxicity and hence should be the targets for intervention. This paper discusses the pharmacology of methotrexate and reviews studies on haematological malignancies that have attempted to predict the risk of toxicity by specific clinical or genetic features.

Methotrexate/6-mercaptopurine maintenance therapy influences the risk of a second malignant neoplasm after childhood acute lymphoblastic leukemia: results from the NOPHO ALL-92 study

Among 1614 children with acute lymphoblastic leukemia (ALL) treated with the Nordic Society for Paediatric Haematology and Oncology (NOPHO) ALL-92 protocol, 20 patients developed a second malignant neoplasm (SMN) with a cumulative risk of 1.6% at 12 years from the diagnosis of ALL. Nine of the 16 acute myeloid leukemias or myelodysplastic syndromes had monosomy 7 (n = 7) or 7q deletions (n = 2). In Cox multivariate analysis, longer duration of oral 6-mercaptopurine (6MP)/methotrexate (MTX) maintenance therapy (P = .02; longest for standard-risk patients) and presence of high hyperdiploidy (P = .07) were related to increased risk of SMN. Thiopurine methyltransferase (TPMT) methylates 6MP and its metabolites, and thus reduces cellular levels of cytotoxic 6-thioguanine nucleotides. Of 524 patients who had erythrocyte TPMT activity measured, the median TPMT activity in 9 patients developing an SMN was significantly lower than in the 515 that did not develop an SMN (median, 12.1 vs 18.1 IU/mL; P = .02). Among 427 TPMT wild-type patients for whom the 6MP dose was registered, those who developed SMN received higher average 6MP doses than the remaining patients (69.7 vs 60.4 mg/m2; P = .03). This study indicates that the duration and intensity of 6MP/MTX maintenance therapy of childhood ALL may influence the risk of SMNs in childhood ALL.

Thiopurine methyltransferase activity is related to the risk of relapse of childhood acute lymphoblastic leukemia: results from the NOPHO ALL-92 study

Myelotoxicity during thiopurine therapy is enhanced in patients, who because of single nucleotide polymorphisms have decreased activity of the enzyme thiopurine methyltransferase (TPMT) and thus more thiopurine converted into 6-thioguanine nucleotides. Of 601 children with acute lymphoblastic leukemia (ALL) who were treated by the NOPHO ALL-92 protocol, 117 had TPMT genotype determined, whereas for 484 patients only erythrocyte TPMT activity was available. The latter were classified as heterozygous, if TPMT activity was <14 IU/ml, or deficient (<1.0 IU/ml). 526 patients had TPMT wild type, 73 were presumed heterozygous, and two were TPMT deficient. Risk of relapse was higher for the 526 TPMT wild type patients than for the remaining 75 patients (18 vs 7%, P=0.03). In Cox multivariate regression analysis, sex (male worse; P=0.06), age (higher age worse, P=0.02), and TPMT activity (wild type worse; P=0.02) were related to risk of relapse. Despite a lower probability of relapse, patients in the low TPMT activity group did not have superior survival (P=0.82), possibly because of an excess of secondary cancers among these 75 patients (P=0.07). These data suggest that children with ALL and TPMT wild type might have their cure rate improved, if the pharmacokinetics/-dynamics of TPMT low-activity patients could be mimicked without a concurrent excessive risk of second cancers.