Mercaptopurine metabolism and risk of relapse in childhood lymphoblastic leukaemia

Discovery of therapeutic targets in cancer using chromatin accessibility and transcriptomic data

Most cancer types lack targeted therapeutic options, and when first-line targeted therapies are available, treatment resistance is a huge challenge. Recent technological advances enable the use of assay for transposase-accessible chromatin with sequencing (ATAC-seq) and RNA sequencing (RNA-seq) on patient tissue in a high-throughput manner. Here, we present a computational approach that leverages these datasets to identify drug targets based on tumor lineage. We constructed gene regulatory networks for 371 patients of 22 cancer types using machine learning approaches trained with three-dimensional genomic data for enhancer-to-promoter contacts. Next, we identified the key transcription factors (TFs) in these networks, which are used to find therapeutic vulnerabilities, by direct targeting of either TFs or the proteins that they interact with. We validated four candidates identified for neuroendocrine, liver, and renal cancers, which have a dismal prognosis with current therapeutic options.

Impact of Mercaptopurine Metabolites on Disease Outcome in the AIEOP-BFM ALL 2009 Protocol for Acute Lymphoblastic Leukemia

In the maintenance phase of Associazione Italiana di Ematologia e Oncologia Pediatrica (AIEOP)- Berlin-Frankfurt-Muenster (BFM) acute lymphoblastic leukemia (ALL) 2009 protocol, mercaptopurine (MP) is given at the planned dose of 50 mg/m2 /day; however, dose adjustments are routinely performed to target patients' white blood cells to the optimal range of 2,000-3,000 cells/μL. Pediatric patients with ALL (n = 290, age: median (1st-3rd quartile): 4.8 (3.0-8.1) years; boys: 56.9%) were enrolled mainly in 4 medium-large Italian pediatric hospitals; 14.1% of patients relapsed after a median (1st-3rd quartile) follow-up time of 4.43 (3.82-5.46) years from maintenance beginning. MP metabolites (thionucleotide (TGN) and methyl-derivatives (MMPN)) were measured in the erythrocytes of 387 blood samples of 200 patients by high performance liquid chromatography with ultraviolet detection. Single-nucleotide polymorphisms (SNPs; (rs1800462, rs1800460, and rs1142345 in TPMT gene, rs116855232 in NUDT15, rs1127354, rs7270101, rs6051702 in ITPA, and rs2413739 in PACSIN2) were characterized by Taqman SNP genotyping assays. Cox proportional hazard models did not show an impact of TGN levels and variability on relapse. In contrast, after multivariate analysis, relapse hazard ratio (HR) increased in children with ALL of the intermediate risk arm compared with those in standard risk arm (3.44, 95% confidence interval (CI), 1.31-9.05, P = 0.012), and in carriers of the PACSIN2 rs2413739 T allele compared with those with the CC genotype (heterozygotes CT: HR, 2.32, 95% CI, 0.90-5.97, P = 0.081; and homozygous TT: HR, 4.14, 95% CI, 1.54-11.11, P = 0.005). Future studies are needed to confirm the lack of impact of TGN levels and variability on relapse in the AIEOP-BFM ALL trials, and to clarify the mechanism of PACSIN2 rs2413739 on outcome.

Metal-decorated γ-graphyne as a drug transporting agent for the mercaptopurine chemotherapy drug: a DFT study

In recent years, carbon-based two-dimensional (2D) materials have gained popularity as the carriers of various anticancer therapy drugs, which could reduce the crucial side effects by directly applying the drugs to the intended tumor cells. In this study, through first-principles density functional theory simulations, we have investigated the adsorption properties of a famous cancer chemotherapy drug called mercaptopurine (MC) on a 2D γ-graphyne (GYN) monolayer. Analyzing the geometric and electronic properties, we can summarize that the MC interaction with the pristine GYN is weak, with a small adsorption energy of -0.15 eV, which is too low for potential applications. Therefore, we have decorated the GYN monolayer with biocompatible metals such as Al, Ag, and Cu to trigger the adsorption capacity. The Al- and Cu-decorated GYN offered improved adsorption towards MC compared to the pristine case. The drug release from these metal-decorated systems was examined by creating an acidic environment. In addition, the desorption temperature of the drug from the system was also evaluated using ab initio molecular dynamics simulations. The calculations demonstrated that the Al-decorated GYN is a potential vehicle for MC drug delivery because of the favourable adsorption energy of -0.63 eV, charge transfer of 0.17e and desorption temperature above 270 K. The current research will stimulate the investigation of other low-dimensional carbon materials for drug-delivery applications.

Is Monitoring of the Intracellular Active Metabolite Levels of Nucleobase and Nucleoside Analogs Ready for Precision Medicine Applications?

Nucleobase and nucleoside analogs (NAs) play important roles in cancer therapy. Although there are obvious individual differences in NA treatments, most NAs lack direct relationships between their plasma concentration and efficacy or adverse effects. Accumulating evidence suggests that the intracellular active metabolite levels of NAs predict patient outcomes. This article reviewed the relationships between NA intracellular active metabolite levels and their efficacy or adverse effects. The factors affecting the formation of intracellular active metabolites and combination regimens that elevate intracellular active metabolite levels were also reviewed. Given the mechanism of NA cytotoxicity, NA intracellular active metabolite levels may be predictive of clinical outcomes. Many clinical studies support this hypothesis. Therefore, the monitoring of intracellular active metabolite levels is beneficial for individualized NA treatment. However, to perform clinical monitoring in practice, well-designed studies are needed to explore the optimal threshold or range and the appropriate regimen adjustment strategies based on these parameters.

[Practical management during maintenance therapy of pediatric acute lymphoblastic leukemia: Recommendations of the French Society for Childhood and Adolescent Cancer and Leukemia (SFCE)]

Maintenance therapy is the last phase of treatment for acute lymphoblastic leukemia in children and adolescents. Although maintenance therapy is associated with toxicities and specific management issues, it is an essential phase of treatment that reduces the risk of relapse. The objective of this work is to propose a guide for the initiation, administration, and monitoring of maintenance therapy, and for the management of food, schooling, leisure, community life, risk of infection and links with family medicine.

The Thiopurine Tale: An Unexpected Journey

Exactly 70 years ago [1951] mercaptopurine was discovered by Gertrude Elion as a novel treatment option for acute leukaemia. A total of three thiopurines (also thioguanine [1950] and azathioprine [1957]) were developed over time. These immunosuppressive drugs were also successfully introduced a few decades later to prevent rejection of transplanted organs and to treat several autoimmune diseases. For her discovery of thiopurines and other antimetabolite drugs, in 1988 Elion was rewarded, together with George Hitchings and James Black, with the Nobel Prize in Physiology or Medicine. Important steps have been made in recent years to unravel its metabolism, mode of action and pharmacogenetics. Today thiopurine [based] therapy remains an essential immunosuppressive approach in treating patients with inflammatory bowel disease.

Naturally occurring, natural product inspired and synthetic heterocyclic anti-cancer drugs

This chapter describes the importance and activity of a huge number of commercially available naturally occurring, natural product derived or synthetic heterocyclic anti-cancer drugs.

Pharmacogenomic testing in paediatrics: clinical implementation strategies

Pharmacogenomics (PGx) relates to the study of genetic factors determining variability in drug response. Implementing PGx testing in paediatric patients can enhance drug safety, helping to improve drug efficacy or reduce the risk of toxicity. Despite its clinical relevance, the implementation of PGx testing in paediatric practice to date has been variable and limited.

As with most paediatric pharmacological studies, there are well‐recognised barriers to obtaining high‐quality PGx evidence, particularly when patient numbers may be small, and off‐label or unlicensed prescribing remains widespread. Furthermore, trials enrolling small numbers of children can rarely, in isolation, provide sufficient PGx evidence to change clinical practice, so extrapolation from larger PGx studies in adult patients, where scientifically sound, is essential.

This review paper discusses the relevance of PGx to paediatrics and considers implementation strategies from a child health perspective. Examples are provided from Canada, the Netherlands and the UK, with consideration of the different healthcare systems and their distinct approaches to implementation, followed by future recommendations based on these cumulative experiences.

Improving the evidence base demonstrating the clinical utility and cost‐effectiveness of paediatric PGx testing will be critical to drive implementation forwards. International, interdisciplinary collaborations will enhance paediatric data collation, interpretation and evidence curation, while also supporting dedicated paediatric PGx educational initiatives. PGx consortia and paediatric clinical research networks will continue to play a central role in the streamlined development of effective PGx implementation strategies to help optimise paediatric pharmacotherapy.

Towards personalised medicine in autoimmune hepatitis: Measurement of thiopurine metabolites results in higher biochemical response rates

BACKGROUND & AIMS

Patients with autoimmune hepatitis (AIH) usually receive maintenance therapy with thiopurines, such as azathioprine (AZA) or mercaptopurine. Genetic polymorphisms in AZA metabolism can lead to variations in thioguanine nucleotide (TGN) and 6-methylmercaptopurine, both of which can cause adverse drug reactions (ADRs). In inflammatory bowel disease, a therapeutic TGN range (225-450 pmol/8x10⁸ erythrocytes) has been identified to optimise effectiveness. We evaluated the benefits of a personalised medicine approach to thiopurine dosing, in comparison to standard weight-based dosing.

METHODS

A retrospective matched cohort study of 214 patients with AIH who were seen at King's College between 1999-2019 was performed. Metabolite levels were measured in 109 patients. The control group included 105 patients on weight-based thiopurine dosing with no metabolite monitoring.

RESULTS

Biochemical response (BR) occurred more frequently at 6-month follow-up in patients with metabolite monitoring compared to those on a weight-based regimen (77% vs. 60%, p = 0.008). This remained true with data analysis based on clinicians who measure metabolites and those who do not (BR at 6 months: 84% vs. 64%, p = 0.016). Patients with BR had TGN levels within the therapeutic range of 225-450 pmol/8x10⁸ erythrocytes significantly more often than those who failed to achieve or lost BR (40% vs. 13%, p <0.0001). Moreover, TGN levels within the pre-defined therapeutic range predicted more stable disease within 6 months of testing compared to levels outside the range (p <0.0001). A high proportion of patients with sub-therapeutic TGN levels (75-225 pmol/8x10⁸ erythrocytes) remained in BR (75% vs. 81%, p = 0.589) with fewer ADRs (44% vs. 86%, p = 0.0002) when compared to patients with therapeutic TGN levels.

CONCLUSION

A strategy of personalised medicine using metabolite levels can optimise treatment regimens in AIH, resulting in fewer ADRs whilst maintaining BR.

LAY SUMMARY

This study looked to see if measuring the breakdown products of a medication used in autoimmune hepatitis increases the chances of gaining good control of the disease, when compared to a group of patients who were on a dose of this medication based on their weight. A group of 214 patients with autoimmune hepatitis were split into 2 groups: roughly half had their medication dose adjusted according to measurements of breakdown products in the blood, whilst the other half received their weight-based dose as normal. The results confirmed that using a personalised approach and checking drug breakdown products resulted in fewer side effects and potentially improved control of disease.

Allopurinol use during pediatric acute lymphoblastic leukemia maintenance therapy safely corrects skewed 6-mercaptopurine metabolism, improving inadequate myelosuppression and reducing gastrointestinal toxicity

BACKGROUND

Inadequate myelosuppression during maintenance therapy for acute lymphoblastic leukemia (ALL) is associated with an increased risk of relapse. One mechanism is skewed metabolism of 6-mercaptopurine (6MP), a major component of maintenance therapy, which results in preferential formation of the hepatotoxic metabolite (6-methyl mercaptopurine [6MMP]) with low levels of the antileukemic metabolite, 6-thioguanine nucleotides (6TGN). Allopurinol can modify 6MP metabolism to favor 6TGN production and reduce 6MMP.

METHODS

Patients in maintenance were considered for allopurinol treatment who had the following features: (a) Grade ≥3 hepatotoxicity; (b) Grade ≥2 nonhepatic gastrointestinal (GI) toxicity; or (c) persistently elevated absolute neutrophil count (ANC) despite >150% protocol dosing of oral chemotherapy.

RESULTS

From 2013 to 2017, 13 ALL patients received allopurinol: nine for hepatotoxicity, five for inadequate myelosuppression, and three for nonhepatic GI toxicity (four met multiple criteria). Allopurinol was well tolerated, without significant adverse events. Allopurinol resulted in a significant decrease in the average 6MMP/6TGN ratio (mean reduction 89.1, P = .0001), with a significant increase in 6TGN (mean 550.4, P = .0008) and a significant decrease in 6MMP (mean 13 755, P = .0013). Patients with hepatotoxicity had a significant decrease in transaminase elevation after starting allopurinol (alanine transaminase [ALT] mean decrease 22.1%, P = .02), and all with nonhepatic GI toxicity had improved symptoms. Those with inadequate myelosuppression had a significant increase in the time with ANC in goal (mean increase 26.4%, P = .0004).

CONCLUSIONS

Allopurinol during ALL maintenance chemotherapy is a safe, feasible, and effective intervention for those who have altered metabolism of 6MP causing toxicity or inadequate myelosuppression.

Effects of NT5C2 Germline Variants on 6-Mecaptopurine Metabolism in Children With Acute Lymphoblastic Leukemia

6-mercaptopurine (6-MP) is widely used in the treatment of acute lymphoblastic leukemia (ALL), and its cytotoxicity is primarily mediated by thioguanine nucleotide (TGN) metabolites. A recent genomewide association study has identified germline polymorphisms (e.g., rs72846714) in the NT5C2 gene associated with 6-MP metabolism in patients with ALL. However, the full spectrum of genetic variation in NT5C2 is unclear and its impact on 6-MP drug activation has not been comprehensively examined. To this end, we performed targeted sequencing of NT5C2 in 588 children with ALL and identified 121 single nucleotide polymorphisms nominally associated with erythrocyte TGN during 6-MP treatment (P < 0.05). Of these, 61 variants were validated in a replication cohort of 372 children with ALL. After considering linkage disequilibrium and multivariate analysis, we confirmed two clusters of variants, represented by rs72846714 and rs58700372, that independently affected 6-MP metabolism. Functional studies showed that rs58700372 directly altered the activity of an intronic enhancer, with the variant allele linked to higher transcription activity and reduced 6-MP metabolism (lower TGN). By contrast, rs72846714 was not located in a regulatory element and instead its association signal was explained by linkage disequilibrium with a proximal functional variant rs12256506 that activated NT5C2 transcription in-cis. Our results indicated that NT5C2 germline variation significantly contributes to interpatient variability in thiopurine drug disposition.

Simultaneous UPLC-MS/MS Determination of 6-mercaptopurine, 6-methylmercaptopurine and 6-thioguanine in Plasma: Application to the Pharmacokinetic Evaluation of Novel Dosage forms in Beagle Dogs

BACKGROUND

6-Mercaptopurine (6-MP) is widely used to treat pediatric acute lymphoblastic leukemia (ALL). Mini-tablets of 5 mg per tablet were developed for precision individual therapy for children and individuals with poor thiopurine S-methyltransferase (TPMT) or nucleoside diphophate-linked moiety X-type motif 15 (NUDT15) metabolism. This study investigated the pharmacokinetic profiles of mini-tablets and conventional tablets with an improved ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method.

METHODS

After giving 8 healthy beagle dogs 50 mg 6-MP in different dosage forms, plasma samples collected at different time points were analyzed for pharmacokinetic evaluation. The samples were precipitated by methanol with 0.05% formic acid and separated on a Waters Atlantis T3 column (2.1 × 150 mm, 3 μm particles) using 0.1% formic acid in water and methanol at a flow rate of 0.4 mL/min in 4 min.

RESULTS

This method showed good linearity, accuracy, precision and stability with a detection range of 5.0-500.0 ng/mL for 6-MP, 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TG). The main parameters, half-life of apparent terminal disposition, maximum observed plasma concentration, total AUC extrapolated to infinity, AUC since initiation of the experiment, mean residence time, distribution volume and clearance were 1.62 ± 0.87 hours, 90.58 ± 60.43 ng/mL, 151.20 ± 94.18 ng·h/mL, 292.06 ± 184.02 ng·h2/mL, 1.90 ± 0.92 hours, 864.08 ± 538.52 L, and 432.75 ± 360.64 L/h for conventional tablets and 1.70 ± 1.10 hours, 84.15 ± 39.50 ng/mL, 147.70 ± 51.80 ng·h/mL, 300.92 ± 124.48 ng·h2/mL, 2.07 ± 0.50 hours, 756.90 ± 324.00 L, and 340.75 ± 125.81 L/h for minitablets, respectively. Paired t-tests showed no significant difference in any of the evaluated pharmacokinetic parameters between the two types tablets (P > 0.05).

CONCLUSION

Two dosage forms showed the same pharmacokinetic characteristics. This developing, novel formulation will help to provide a more accurate and optimal dosing regimen of 6-MP for humans in the future.

A mathematical model of white blood cell dynamics during maintenance therapy of childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia is the most common malignancy in childhood and requires prolonged oral maintenance chemotherapy to prevent disease relapse after remission induction with intensive intravenous chemotherapy. In maintenance therapy, drug doses of 6-mercaptopurine (6-MP) and methotrexate (MTX) are adjusted to achieve sustained antileukemic activity without excessive myelosuppression. However, uncertainty exists regarding timing and extent of drug dose responses and optimal dose adaptation strategies. We propose a novel comprehensive mathematical model for 6-MP and MTX pharmacokinetics, pharmacodynamics and myelosuppression in acute lymphoblastic maintenance therapy. We personalize and cross-validate the mathematical model using clinical data and propose a real-time algorithm to predict chemotherapy responses with a clinical decision support system as a potential future application.

Use of Allopurinol to Mitigate 6-Mercaptopurine Associated Gastrointestinal Toxicity in Acute Lymphoblastic Leukemia

An essential component of acute lymphoblastic leukemia (ALL) therapy is the prolonged maintenance phase with daily 6-mercaptopurine (6-MP) as the cornerstone. While 6-MP is generally well-tolerated, some patients suffer from significant side effects such as gastrointestinal (GI) toxicity, including hepatitis, hypoglycemia, nausea, and pancreatitis, which can substantially limit the tolerated dose of 6-MP. These toxicities are thought to result from skewed metabolism of 6-MP leading to an accumulation of the 6-methylmercaptopurine (6-MMP) metabolite. Here, we describe current knowledge behind the use of allopurinol to modify 6-MP metabolism and improve tolerance to therapy. This method has been successfully used in adults with inflammatory bowel disease refractory to purine therapy and has been modified for use in children with GI toxicities related to 6-MP in maintenance therapy for ALL. Use of allopurinol for 6-MP related toxicities should be reserved for patients in which an alternative cause of signs or symptoms has been excluded and for whom non-pharmacologic measures have failed. When allopurinol is used, simultaneous dose reduction of 6-MP is required to avoid severe myelosuppression and related side effects, though overall combination therapy appears to be well-tolerated and effective when instituted appropriately.

Thiopurines' Metabolites and Drug Toxicity: A Meta-Analysis

Many questions remain unanswered regarding therapeutic drug monitoring (TDM) utility with thiopurines. This study aims to establish a relationship between thiopurines' metabolites and drug toxicity. We performed a systematic review with inclusion of studies evaluating the relationship between thiopurines' metabolites and drug toxicity. Meta-analysis of mean difference (MD), correlations and odds ratio (OR) was performed. We identified 21,240 records, 72 of which were eligible for meta-analysis. Levels of 6-thioguanine nucleotides (6-TGN) were higher in patients with leukopenia (MD 127.06 pmol/8 × 10⁸ RBC) and gastrointestinal intolerance (MD 201.46 pmol/8 × 10⁸ RBC), and lower in patients with hepatotoxicity (MD -40.6 pmol × 10⁸ RBC). We established a significant correlation between 6-TGN and leukocytes (r = -0.21), neutrophils (r = -0.24) and alanine aminotransferase levels (r = -0.24). OR for leukopenia in patients with elevated 6-TGN was 4.63 (95%CI 2.24; 9.57). An optimal cut-off of 135 pmol/8 × 10⁸ RBC for leukopenia was calculated (sensitivity 75.4%; specificity 46.4%). 6-methylmercaptopurine ribonucleotides (6-MMPR) were significantly associated with hepatotoxicity (MD 3241.2 pmol/8 × 10⁸ RBC; OR 4.28; 95%CI 3.20; 5.71). Levels of 6-MMPR measured in the first 8 weeks of treatment were associated with leukopenia. We conclude that TDM could be used to prevent thiopurines' toxicity. As optimal metabolites level may vary according to indication, physicians may adapt posology to decrease toxicity without compromising efficacy.

When Multiple Objective Measures of Medication Adherence Indicate Incongruent Adherence Results: An Example with Pediatric Cancer

Previous research suggests that children and adolescents with acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LBL) often have difficulty adhering to complex treatment regimens during the maintenance phase of therapy. Measurement of treatment adherence can be done via objective (e.g., electronic monitoring (EM), pharmacological assays) or subjective methods (patient, parent, or physician reports). This paper provides an illustration of recommended strategies for comparing discrepancies between two objective measures of medication adherence (e.g., behavioral adherence using electronic monitoring versus pharmacological adherence using 6-mercaptopurine (6MP) metabolite data) within a relatively large cohort of pediatric patients with ALL or LBL (N = 139) who had longitudinal data for both measures of medication adherence over a 15-month period. Additionally, individual- and family-level factors such as gender, socioeconomic status, household environment, and dose intensity will be examined to identify possible sources of discrepancies between adherence measures. This information will provide practical advice for physicians, healthcare providers, and psychologists in identifying nonadherence and the caveats therein so patients achieve the best possible health outcomes.

Results of a phase II clinical trial of 6-mercaptopurine (6MP) and methotrexate in patients with BRCA-defective tumours

BACKGROUND

Tumour cells with BRCA1/2 gene mutations demonstrate increased sensitivity to platinum and poly (ADP-ribose) polymerase (PARP) inhibitors. 6-mercaptopurine (6MP) was found to selectively kill BRCA-defective cells in a xenograft model as effectively as the PARP inhibitor AG014699, even after these cells acquired resistance to a PARP inhibitor or cisplatin.

METHODS

This phase II single-arm trial investigated the activity of 6MP 55-75 mg/m2 per day, and methotrexate 15-20 mg/m2 per week in advanced breast or platinum-resistant ovarian cancer patients with a BRCA1/2 germline mutation, who had progressed after ≥1 previous line of chemotherapy. The primary outcome was objective response including stable disease (SD) as an assessment of clinical benefit rate (CBR), at 8 weeks, by RECIST v1.1. Secondary outcomes included overall survival (OS) and progression-free survival (PFS).

RESULTS

In total, 67 evaluable patients were recruited; 55 ovarian and 11 breast cancer patients. In total, 21 patients had SD (31%), one had a partial response (1.5%); CBR was 33% at 8 weeks. In total, 12/67 patients (18%) had SD at 16 weeks. In total, five ovarian cancer patients had SD for over 200 days. Median OS was 10.3 months (95% CI 6.9-14.5), median PFS 1.9 months (1.7-2.8).

CONCLUSIONS

The overall activity of 6MP and methotrexate in these patients was low; however, there was a small group of patients who appeared to derive longer-term clinical benefit.

TRIAL REGISTRATION

NCT01432145 http://www.ClinicalTrials.gov.

Stopping immunosuppressive treatment in autoimmune hepatitis (AIH): Is it justified (and in whom and when)?

BACKGROUND

Initial treatment of autoimmune hepatitis (AIH) with prednisolone ± azathioprine is based on randomised controlled trials. Many patients receive long-term immunosuppressive treatment to prevent disease relapse; this strategy has a weaker evidence base.

AIM

To consider whether immunosuppressive treatment (IST) withdrawal in AIH is justified and to develop a rationale for patient selection.

METHODS

We reviewed published papers between 1972 and 2018, which addressed the outcomes of IST withdrawal and/or complications of IST in AIH.

RESULTS

(1) AIH relapse rates after withdrawal of IST vary between 25% and 100%. There is heterogeneity in these studies regarding relapse definition, IST duration prior to withdrawal and criteria for biochemical and histological remission prior to withdrawal. (2) Factors associated with relapse following IST withdrawal include: (a) absence of an identifiable initial disease trigger, (b) presence of other autoimmune diseases, (c) longer time to biochemical remission and (d) elevated serum transaminases on treatment withdrawal. Reports of associations between relapse and age, IST duration and failure of histological remission have been inconsistent. (3) Continued IST reduces risk of AIH relapse over at least 5 years. However, there is no evidence that routine (as opposed to selective) long-term IST improves disease outcome. (4) Patients with AIH have an increased risk of extrahepatic cancer, notably non-melanoma skin cancer, to which long-term IST may contribute. Long-term corticosteroid therapy is associated with weight gain, low-trauma fractures, diabetes and possibly vascular disease.

CONCLUSIONS

While further studies are needed, evidence supports a strategy of IST withdrawal in some patients with AIH who have achieved remission.

Quantification of Thiopurine Nucleotides in Erythrocytes and Clinical Application to Pediatric Acute Lymphoblastic Leukemia

Background:

Concentrations of 6-thioguanine (6TG) nucleotides and 6-methylmercaptopurine (6MMP) nucleotides in RBCs were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This assay was validated for clinical use and was applied to blood samples from patients taking mercaptopurine (6MP).

Methods:

RBCs were hemolyzed and deproteinized using perchloric acid, followed by heating for the hydrolysis of nucleotides, and the resultant base was measured using LC-MS/MS. Precision, recovery, linearity, matrix effect, and limit of quantification was validated for clinical application. Our results were compared with another institution's established LC-MS/MS assay. We measured the concentrations of 6TG and 6MMP in RBCs of pediatric patients with acute lymphoblastic leukemia (ALL), and the clinical impact of those metabolites was investigated.

Results:

The imprecision coefficient of variations of 6TG and 6MMP were 5.7%–8.1%, and the bias was within 5%. Lower limits of quantification were set at 54 ng/mL for 6TG and 1036 ng/mL for 6MMP. Correlation coefficients for 6TG and 6MMP were 0.997 and 1.0 in a comparison study. For clinical proof-of-concept, 74 blood samples were collected from 37 pediatric ALL patients receiving maintenance therapy. Concentration of 6TG ranged from 16.1 to 880 pmol/8 × 10⁸ RBCs and that of 6MMP from 55 to 20,937 pmol/8 × 10⁸ RBCs. The 6MP metabolites were not correlated with WBC or absolute neutrophil count. On the other hand, the higher 6MMP level was associated with elevated alanine aminotransferase and aspartate aminotransferase.

Conclusions:

In this study, an assay for the quantification of 6TG and 6MMP in RBCs was established and applied to pediatric ALL patients. Interindividual variability in 6MP metabolite concentrations was considerable and associated with elevation of liver enzymes, which may be useful in the clinical monitoring of 6MP maintenance therapy in pediatric ALL patients.

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.

Measuring Medication Adherence in Pediatric Cancer: An Approach to Validation

Objective

This study described the prospective relationship between pharmacological and behavioral measures of 6-mercaptopurine (6MP) medication adherence in a multisite cohort of pediatric patients diagnosed with cancer ( N  = 139).

Methods

Pharmacological measures (i.e., metabolite concentrations) assessed 6MP intake. Behavioral measures (e.g., electronic monitoring) described adherence patterns over time.

Results

Three metabolite profiles were identified across 15 months: one group demonstrated low levels of both metabolites (40.8%) consistent with nonadherence and/or suboptimal therapy; two other groups demonstrated metabolite clusters indicative of adequate adherence (59.2%). Those patients whose metabolite profile demonstrated low levels of both metabolites had consistently lower behavioral adherence rates.

Conclusions

To our knowledge, this was the first study to prospectively validate a pharmacological measure of medication adherence with a behavioral adherence measure in a relatively large sample of pediatric patients with cancer. Using multiple methods of adherence measurement could inform clinical care and target patients in need of intervention.

NUDT15 Variants Cause Hematopoietic Toxicity with Low 6-TGN Levels in Children with Acute Lymphoblastic Leukemia

Purpose

We aimed to identify the impact of NUDT15 variants on thiopurine intolerance and 6-thioguanine nucleotide (6-TGN) levels in Korean children with acute lymphoblastic leukemia (ALL).

Materials and Methods

Genotyping of NUDT15 was tested in 258 patients with ALL registered at Samsung Medical Center. Patients were classified into normal-activity (wild-type), intermediate-activity (heterozygous variant), and low-activity groups (homozygous or compound heterozygous variant). Clinical and laboratory features during the first year of maintenance therapy were investigated.

Results

A total of 182 patients were included in the final analysis. There were five (2.7%), 46 (25.3%), and 131 (72.0%) patients in low-, intermediate-, and normal-activity groups, respectively. The lowest 6-mercaptopurine (6-MP) dose (mg/m²/day) was administered to the low-activity group (low-activity group 7.5 vs. intermediate-activity group 24.4 vs. normalactivity group 31.1, p < 0.01) from three months to a year after beginning maintenance therapy. The low-activity group experienced the longest duration of therapy interruption during the first year (low-activity group 169 days vs. intermediate-activity group 30 days vs. normal-activity group 16 days, p < 0.01). They also showed the lowest blood cell counts and had a longer duration of leukopenia (low-activity group 131 days vs. intermediate-activity group 92 days vs. normal-activity group 59 days, p < 0.01). 6-TGN level and its ratio to 6-MP dose were lowest in the low-activity group.

Conclusion

NUDT15 variants cause hematopoietic toxicity with low 6-TGN levels. NUDT15 genotyping should be conducted before administering thiopurine, and dose adjustments require caution regardless of 6-TGN levels.

NUDT15 polymorphisms alter thiopurine metabolism and hematopoietic toxicity

Widely used as anticancer and immunosuppressive agents, thiopurines have narrow therapeutic indices owing to frequent toxicities, partly explained by TPMT genetic polymorphisms. Recent studies identified germline NUDT15 variation as another critical determinant of thiopurine intolerance, but the underlying molecular mechanisms and the clinical implications of this pharmacogenetic association remain unknown. In 270 children enrolled in clinical trials for acute lymphoblastic leukemia in Guatemala, Singapore and Japan, we identified four NUDT15 coding variants (p.Arg139Cys, p.Arg139His, p.Val18Ile and p.Val18_Val19insGlyVal) that resulted in 74.4-100% loss of nucleotide diphosphatase activity. Loss-of-function NUDT15 diplotypes were consistently associated with thiopurine intolerance across the three cohorts (P = 0.021, 2.1 × 10(-5) and 0.0054, respectively; meta-analysis P = 4.45 × 10(-8), allelic effect size = -11.5). Mechanistically, NUDT15 inactivated thiopurine metabolites and decreased thiopurine cytotoxicity in vitro, and patients with defective NUDT15 alleles showed excessive levels of thiopurine active metabolites and toxicity. Taken together, these results indicate that a comprehensive pharmacogenetic model integrating NUDT15 variants may inform personalized thiopurine therapy.

Comparative pharmacogenetic analysis of risk polymorphisms in Caucasian and Vietnamese children with acute lymphoblastic leukemia: prediction of therapeutic outcome?

AIMS

Acute lymphoblastic leukemia (ALL) is the most common of all paediatric cancers. Aside from predisposing to ALL, polymorphisms could also be associated with poor outcome. Indeed, genetic variations involved in drug metabolism could, at least partially, be responsible for heterogeneous responses to standardized leukemia treatments, hence requiring more personalized therapy. The aims of this study were to (a) to determine the prevalence of seven common genetic polymorphisms including those that affect the folate and/or thiopurine metabolic pathways, i.e. cyclin D1 (CCND1-G870A), γ-glutamyl hydrolase (GGH-C452T), methylenetetrahydrofolate reductase (MTHFR-C677T and MTHFR-A1298C), thymidylate synthase promoter (TYMS-TSER), thiopurine methyltransferase (TPMT*3A and TPMT*3C) and inosine triphosphate pyrophosphatase (ITPA-C94A), in Caucasian (n = 94, age < 20) and Vietnamese (n = 141, age < 16 years) childhood ALL and (b) to assess the impact of a multilocus genetic risk score (MGRS) on relapse-free survival (RFS) using a Cox proportional-hazards regression model.

RESULTS

The prevalence of MTHFR-677TT genotype was significantly higher in Caucasians (P = 0.008), in contrast to the prevalence of TYMS-TSER*3R/3R and ITPA-94AA/AC genotypes which were significantly higher in Vietnamese (P < 0.001 and P = 0.02, respectively). Compared with children with a low MGRS (≤ 3), those with a high MGRS (≥ 4) were 2.06 (95% CI = 1.01, 4.22; P = 0.04) times more likely to relapse. Adding MGRS into a multivariate Cox regression model with race/ethnicity and four clinical variables improved the predictive accuracy of the model (AUC from 0.682 to 0.709 at 24 months).

CONCLUSION

Including MGRS into a clinical model improved the predictive accuracy of short and medium term prognosis, hence confirming the association between well determined pharmacogenotypes and outcome of paediatric ALL. Whether variants on other genes associated with folate metabolism can substantially improve the predictive value of current MGRS is not known but deserves further evaluation.

Model-Based Individualized Treatment of Chemotherapeutics: Bayesian Population Modeling and Dose Optimization

6-Mercaptopurine (6-MP) is one of the key drugs in the treatment of many pediatric cancers, auto immune diseases and inflammatory bowel disease. 6-MP is a prodrug, converted to an active metabolite 6-thioguanine nucleotide (6-TGN) through enzymatic reaction involving thiopurine methyltransferase (TPMT). Pharmacogenomic variation observed in the TPMT enzyme produces a significant variation in drug response among the patient population. Despite 6-MP's widespread use and observed variation in treatment response, efforts at quantitative optimization of dose regimens for individual patients are limited. In addition, research efforts devoted on pharmacogenomics to predict clinical responses are proving far from ideal. In this work, we present a Bayesian population modeling approach to develop a pharmacological model for 6-MP metabolism in humans. In the face of scarcity of data in clinical settings, a global sensitivity analysis based model reduction approach is used to minimize the parameter space. For accurate estimation of sensitive parameters, robust optimal experimental design based on D-optimality criteria was exploited. With the patient-specific model, a model predictive control algorithm is used to optimize the dose scheduling with the objective of maintaining the 6-TGN concentration within its therapeutic window. More importantly, for the first time, we show how the incorporation of information from different levels of biological chain-of response (i.e. gene expression-enzyme phenotype-drug phenotype) plays a critical role in determining the uncertainty in predicting therapeutic target. The model and the control approach can be utilized in the clinical setting to individualize 6-MP dosing based on the patient's ability to metabolize the drug instead of the traditional standard-dose-for-all approach.

Review article: The pharmacokinetics and pharmacodynamics of drugs used in inflammatory bowel disease treatment

BACKGROUND

The following review is a compilation of the recent advances and knowledge on the behaviour of the most frequently used compounds to treat inflammatory bowel disease in an organism.

RESULTS

It considers clinical aspects of each entity and the pharmacokinetic/pharmacodynamic relationship supported by the use of plasma monitoring, tissue concentrations, and certain aspects derived from pharmacogenetics.

Mercaptopurine metabolite levels are predictors of bone marrow toxicity following high-dose methotrexate therapy of childhood acute lymphoblastic leukaemia

High-dose methotrexate (HD-MTX) courses with concurrent oral low-dose MTX/6-mercaptopurine (6MP) for childhood acute lymphoblastic leukaemia (ALL) are often followed by neutro- and thrombocytopenia necessitating treatment interruptions. Plasma MTX during HD-MTX therapy guides folinic acid rescue to prevent toxicities, but myelosuppression can also be prevented by pre-HD-MTX 6MP dose reductions. Accordingly, we monitored pre-HD-MTX erythrocyte levels of methylated 6MP metabolites (Ery-MeMP) and of thioguanine nucleotides (Ery-6TGN) as well as DNA-incorporated thioguanine nucleotides (DNA-TGN) in circulating leucocytes to identify patients at highest risk of post-HD-MTX myelosuppression. In multiple linear regression analyses of neutrophil and thrombocyte nadir values (adjusted for gender, age, risk group and 6MP dose) after 48 HD-MTX courses in 17 childhood ALL patients on MTX/6MP maintenance therapy, the pre-HD-MTX DNA-TGN levels in neutrophils (P < 0.0001), Ery-MeMP (P < 0.0001) and Ery-6TGN (P = 0.01) levels were significant predictors of post-HD-MTX neutrophil nadirs, whereas Ery-MeMP (P < 0.0001) was the only predictor of post-HD-MTX thrombocyte nadir. In conclusion, pre-HD-MTX 6MP metabolite levels may be applicable for 6MP dose adjustments to prevent HD-MTX-induced myelosuppression.

Optimal chemotherapy for leukemia: a model-based strategy for individualized treatment

Acute Lymphoblastic Leukemia, commonly known as ALL, is a predominant form of cancer during childhood. With the advent of modern healthcare support, the 5-year survival rate has been impressive in the recent past. However, long-term ALL survivors embattle several treatment-related medical and socio-economic complications due to excessive and inordinate chemotherapy doses received during treatment. In this work, we present a model-based approach to personalize 6-Mercaptopurine (6-MP) treatment for childhood ALL with a provision for incorporating the pharmacogenomic variations among patients. Semi-mechanistic mathematical models were developed and validated for i) 6-MP metabolism, ii) red blood cell mean corpuscular volume (MCV) dynamics, a surrogate marker for treatment efficacy, and iii) leukopenia, a major side-effect. With the constraint of getting limited data from clinics, a global sensitivity analysis based model reduction technique was employed to reduce the parameter space arising from semi-mechanistic models. The reduced, sensitive parameters were used to individualize the average patient model to a specific patient so as to minimize the model uncertainty. Models fit the data well and mimic diverse behavior observed among patients with minimum parameters. The model was validated with real patient data obtained from literature and Riley Hospital for Children in Indianapolis. Patient models were used to optimize the dose for an individual patient through nonlinear model predictive control. The implementation of our approach in clinical practice is realizable with routinely measured complete blood counts (CBC) and a few additional metabolite measurements. The proposed approach promises to achieve model-based individualized treatment to a specific patient, as opposed to a standard-dose-for-all, and to prescribe an optimal dose for a desired outcome with minimum side-effects.

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.

Pediatric perspective on pharmacogenomics

The advances in high-throughput genomic technologies have improved the understanding of disease pathophysiology and have allowed a better characterization of drug response and toxicity based on individual genetic make up. Pharmacogenomics is being recognized as a valid approach used to identify patients who are more likely to respond to medication, or those in whom there is a high probability of developing severe adverse drug reactions. An increasing number of pharmacogenomic studies are being published, most include only adults. A few studies have shown the impact of pharmacogenomics in pediatrics, highlighting a key difference between children and adults, which is the contribution of developmental changes to therapeutic responses across different age groups. This review focuses on pharmacogenomic research in pediatrics, providing examples from common pediatric conditions and emphasizing their developmental context.

Relationship between azathioprine dosage and thiopurine metabolites in pediatric IBD patients: identification of covariables using multilevel analysis

BACKGROUND

Previous studies have reported no or only a very poor correlation between 6-methylmercaptopurine/6-thioguanine nucleotide (6-MeMPN/6-TGN) and azathioprine (AZA) dose in the treatment of inflammatory bowel disease (IBD). However, metabolite levels are often repeatedly measured yielding a hierarchical data structure that requires more appropriate data analysis.

METHODS

This study explored the relationship between the weight-based dosage of AZA and metabolites levels in 86 pediatric IBD patients using multilevel analysis. Other covariates related to patient characteristics and treatment were evaluated.

RESULTS

This is the first study to demonstrate positive correlations between AZA dose and 6-TGN and 6-MeMPN levels and 6-MeMPN/6-TGN ratio (P < 0.001) in IBD children. Other novel predictors of metabolites were reported. Younger children exhibited lower 6-TGN and 6-MeMPN levels, probably suggesting age-related differences in metabolism and/or absorption of thiopurines. Coadministration of infliximab resulted in a significant increase in 6-TGN levels (P = 0.023). Moreover, alanine aminotransferase values positively correlated with 6-MeMPN levels (P = 0.032). The duration of AZA therapy, gender, and thiopurine methyltransferase activity were associated with metabolite levels. The wide interindividual variability in metabolite levels that accounted for 67.7%, 48.6%, and 49.4% of variance in the 6-TGN and 6-MeMPN levels and the ratio, respectively, were confirmed.

CONCLUSIONS

The reliable AZA dose-metabolites relationship is useful for clinicians to guide the dosing regimen to maximize clinical response and minimize side effects or to consider alternative therapies when patients have preferential production of the toxic 6-MeMPN. These results may be of potential interest for optimizing thiopurine therapy to achieve safe and efficacious AZA use in pediatric IBD patients.

Clinical significance of azathioprine metabolites for the maintenance of remission in autoimmune hepatitis

Azathioprine (AZA) is used to maintain remission in autoimmune hepatitis (AIH), but up to 18% of patients are unresponsive. AZA is a prodrug, and the formation of active thioguanine nucleotide (TGN) metabolites varies widely. We aimed to assess the relationship between AZA metabolite concentrations (i.e., TGNs and methylmercaptopurine nucleotides [MeMPNs]), thiopurine methyltransferase (TPMT) activity, therapeutic response, and toxicity in adult patients with AIH prescribed a stable dose of AZA for the maintenance of remission. Red blood cell (RBC) TGNs and MeMPNs were measured in serial blood samples over a 2-year period. The average TGNs (avTGNs) and MeMPNs (avMeMPNs) concentrations for each patient were used for analysis. Therapeutic response was defined as the ability to maintain remission, defined as a normal serum alanine aminotransferase (ALT) level (ALT <33 IU/mL). Patients who maintained remission (n = 53), compared to those who did not (n = 17), tended to be on lower doses of AZA (1.7 versus 2.0 mg/kg/day; P = 0.08), but had significantly higher concentrations of avTGN (237 versus 177 pmol/8 × 10(8) RBCs; P = 0.025). There was no difference in MeMPN concentrations or TPMT activities between the two groups. There was a negative correlation between ALT and avTGN (r(s) = -0.32; P = 0.007). An avTGN concentration of >220 pmol/8 × 10(8) RBCs best predicted remission, with an odds ratio of 7.7 (P = 0.003). There was no association between TGN, MeMPN, or TPMT activity and the development of leucopenia. Two patients developed AZA-induced cholestasis and the avMeMPN concentration was higher in those patients, compared to those who did not (14,277 versus 1,416 pmol/8 × 10(8) RBCs).

CONCLUSION

TGN concentrations of >220 pmol/8 × 10(8) RBCs are associated with remission. TGN measurement may help identify inadequate immunosupression. AZA-induced cholestasis was associated with increased MeMPN concentrations.

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.

Estimation of dynamic treatment strategies for maintenance therapy of children with acute lymphoblastic leukaemia: an application of history-adjusted marginal structural models

Childhood acute lymphoblastic leukaemia is treated with long-term intensive chemotherapy. During the latter part of the treatment, the maintenance therapy, the patients receive oral doses of two cytostatics. The doses are tailored to blood counts measured on a weekly basis, and the treatment is therefore highly dynamic. In 1992-1996, the Nordic Society of Paediatric Haematology and Oncology (NOPHO) conducted a randomised study (NOPHO-ALL-92) to investigate the effect of a new and more sophisticated dynamic treatment strategy. Unexpectedly, the new strategy worsened the outcome for the girls, whereas there were no treatment differences for the boys. There are as yet no general guidelines for optimising the treatment. On basis of the data from this study, our goal is to formulate an alternative dosing strategy. We use recently developed methods proposed by van der Laan et al. to obtain statistical models that may be used in the guidance of how the physicians should assign the doses to the patients to obtain the target of the treatment. We present a possible strategy and discuss the reliability of this strategy. The implementation is complicated, and we touch upon the limitations of the methods in relation to the formulation of alternative dosing strategies for the maintenance therapy.

A grounded theory of the process of adherence to oral chemotherapy in Hispanic and caucasian children and adolescents with acute lymphoblastic leukemia

Children and adolescents with acute lymphoblastic leukemia (ALL) receive treatment that relies on daily self- or parent/caregiver-administered oral chemotherapy for approximately 2 years. Despite the fact that pediatric ALL is uniformly fatal without adequate treatment, nonadherence to oral chemotherapy has been observed in up to one third of patients. Little is known about the reasons for nonadherence in these patients. This study used Straussian grounded theory methodology to develop and validate a model to explain the process of adherence to oral chemotherapy in children and adolescents with ALL. Thirty-eight semistructured interviews (with 17 patients and 21 parents/caregivers) and 4 focused group discussions were conducted. Three stages were identified in the process of adherence: (a) Recognizing the Threat, (b) Taking Control, and (c) Managing for the Duration. Doing Our Part was identified as the core theme explaining the process of adherence and involves the parent (or patient) taking responsibility for assuring that medications are taken as prescribed. Understanding the association between taking oral chemotherapy and control/cure of leukemia (Making the Connection) appeared to mediate adherence behaviors.

Disparities in cancer outcomes: lessons learned from children with cancer

Disparities in cancer burden by race/ethnicity have been reported, primarily in adults with cancer. However, there appear to be gaps in the pediatric oncology literature with regards to a comprehensive overview on this topic. Extant literature is used to highlight the results of studies focusing on racial and ethnic disparities in outcome observed in selected childhood cancers. A comprehensive approach is utilized to understand possible underlying causes of disparities in cancer outcomes, and to highlight the gaps that currently exist. This review helps define areas of future research that could help develop targeted, disease-specific approaches to eliminate the disparities.

Treatment non-adherence in teenage and young adult patients with cancer

Adhering to treatment can be a significant issue for many patients diagnosed with chronic health conditions and this has been reported to be greater during the adolescent years. However, little is known about treatment adherence in teenage and young adult (TYA) patients with cancer. To increase awareness of the adherence challenges faced by these patients, we have reviewed the published work. The available evidence suggests that a substantial proportion of TYA patients with cancer do have difficulties, with reports that up to 63% of patients do not adhere to their treatment regimens. However, with inconsistent findings across studies, the true extent of non-adherence for these young patients is still unclear. Furthermore, it is apparent that there are many components of the cancer treatment regimen that have yet to be assessed in relation to patient adherence. Factors that have been shown to affect treatment adherence in TYA patients include patient emotional functioning (depression and self-esteem), patient health beliefs (perceived illness severity and vulnerability), and family environment (parental support and parent-child concordance). Strategies that foster greater patient adherence are also identified. These strategies are multifactorial, targeting not only the patient, but the health professional, family, and treatment regimen. This review highlights the lack of interventional studies addressing treatment adherence in TYA patients with cancer, with only one such intervention being identified: a video game intervention focusing on behavioural issues related to cancer treatment and care. Methodological issues in measuring adherence are addressed and suggestions for improving the design of future adherence studies highlighted, of which there is a great need.

Oral 6-mercaptopurine versus oral 6-thioguanine and veno-occlusive disease in children with standard-risk acute lymphoblastic leukemia: report of the Children's Oncology Group CCG-1952 clinical trial

The Children's Cancer Group 1952 (CCG-1952) clinical trial studied the substitution of oral 6-thioguanine (TG) for 6-mercaptopurine (MP) and triple intrathecal therapy (ITT) for intrathecal methotrexate (IT-MTX) in the treatment of standard-risk acute lymphoblastic leukemia. After remission induction, 2027 patients were randomized to receive MP (n = 1010) or TG (n = 1017) and IT-MTX (n = 1018) or ITT (n = 1009). The results of the thiopurine comparison are as follows. The estimated 7-year event-free survival (EFS) for subjects randomized to TG was 84.1% (+/- 1.8%) and to MP was 79.0% (+/- 2.1%; P = .004 log rank), although overall survival was 91.9% (+/- 1.4%) and 91.2% (+/- 1.5%), respectively (P = .6 log rank). The TG starting dose was reduced from 60 to 50 mg/m(2) per day after recognition of hepatic veno-occlusive disease (VOD). A total of 257 patients on TG (25%) developed VOD or disproportionate thrombocytopenia and switched to MP. Once portal hypertension occurred, all subjects on TG were changed to MP. The benefit of randomization to TG over MP, as measured by EFS, was evident primarily in boys who began TG at 60 mg/m(2) (relative hazard rate [RHR] 0.65, P = .002). The toxicities of TG preclude its protracted use as given in this study. This study is registered at http://clinicaltrials.gov as NCT00002744.

Using adaptive model predictive control to customize maintenance therapy chemotherapeutic dosing for childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a common childhood cancer in which nearly one-quarter of patients experience a disease relapse. However, it has been shown that individualizing therapy for childhood ALL patients by adjusting doses based on the blood concentration of active drug metabolite could significantly improve treatment outcome. An adaptive model predictive control (MPC) strategy is presented in which maintenance therapy for childhood ALL is personalized using routine patient measurements of red blood cell mean corpuscular volume as a surrogate for the active drug metabolite concentration. A clinically relevant mathematical model is developed and used to describe the patient response to the chemotherapeutic drug 6-mercaptopurine, with some model parameters being patient-specific. During the course of treatment, the patient-specific parameters are adaptively identified using recurrent complete blood count measurements, which sufficiently constrain the patient parameter uncertainty to support customized adjustments of the drug dose. While this work represents only a first step toward a quantitative tool for clinical use, the simulated treatment results indicate that the proposed mathematical model and adaptive MPC approach could serve as valuable resources to the oncologist toward creating a personalized treatment strategy that is both safe and effective.

Oral 6-mercaptopurine versus oral 6-thioguanine and veno-occlusive disease in children with standard-risk acute lymphoblastic leukemia: report of the Children's Oncology Group CCG-1952 clinical trial

The Children's Cancer Group 1952 (CCG-1952) clinical trial studied the substitution of oral 6-thioguanine (TG) for 6-mercaptopurine (MP) and triple intrathecal therapy (ITT) for intrathecal methotrexate (IT-MTX) in the treatment of standard-risk acute lymphoblastic leukemia. After remission induction, 2027 patients were randomized to receive MP (n = 1010) or TG (n = 1017) and IT-MTX (n = 1018) or ITT (n = 1009). The results of the thiopurine comparison are as follows. The estimated 7-year event-free survival (EFS) for subjects randomized to TG was 84.1% (+/- 1.8%) and to MP was 79.0% (+/- 2.1%; P = .004 log rank), although overall survival was 91.9% (+/- 1.4%) and 91.2% (+/- 1.5%), respectively (P = .6 log rank). The TG starting dose was reduced from 60 to 50 mg/m(2) per day after recognition of hepatic veno-occlusive disease (VOD). A total of 257 patients on TG (25%) developed VOD or disproportionate thrombocytopenia and switched to MP. Once portal hypertension occurred, all subjects on TG were changed to MP. The benefit of randomization to TG over MP, as measured by EFS, was evident primarily in boys who began TG at 60 mg/m(2) (relative hazard rate [RHR] 0.65, P = .002). The toxicities of TG preclude its protracted use as given in this study. This study is registered at http://clinicaltrials.gov as NCT00002744.

Thiopurines: factors influencing toxicity and response

Thiopurines are the backbone of current anti-leukemia regimens and have also been effective immunosuppressive agents for the past half a century. Extensive research on their mechanism of action has been undertaken, yet many issues remain to be addressed to resolve unexplained cases of thiopurine toxicity or treatment failure. The aim of this review is to summarize current knowledge of the mechanism of thiopurine action in experimental models and put into context with clinical observations. Clear understanding of their metabolism will contribute to maximizing efficacy and minimizing toxicity by individually tailoring therapy according to the expression profile of relevant factors involved in thiopurine activation pathway.

Very long-term outcome of acute promyelocytic leukemia after treatment with all-trans retinoic acid and chemotherapy: the European APL Group experience

Acute promyelocytic leukemia (APL) is highly curable with the combination of all-trans retinoic acid (ATRA) and anthracycline-based chemotherapy (CT), but very long-term results of this treatment, when CT should be added to ATRA and the role of maintenance treatment, remain uncertain. In our APL93 trial that included 576 newly diagnosed APL patients, with a median follow-up of 10 years, 10-year survival was 77%. Maintenance treatment significantly reduced 10-year cumulative incidence of relapses, from 43.2% to 33%, 23.4%, and 13.4% with no maintenance, maintenance using intermittent ATRA, continuous 6 mercaptopurine plus methotrexate, and both treatments, respectively (P < .001). Maintenance particularly benefited patients with white blood cell (WBC) count higher than 5 x 10(9)/L (5000/microL). Early addition of CT to ATRA significantly improved 10-year event-free survival (EFS), but without significant effect on overall survival (OS). The 10-year cumulative incidence of deaths in complete response (CR), resulting mainly from myelosuppression, was 5.7%, 15.4%, and 21.7% in patients younger than 55, 55 to 65, and older than 65 years, respectively, supporting the need for less myelosuppressive treatments, particularly for consolidation therapy. This study is registered at http://clinicaltrials.gov as NCT00599937.

DNA incorporation of 6-thioguanine nucleotides during maintenance therapy of childhood acute lymphoblastic leukaemia and non-Hodgkin lymphoma

PURPOSE

To explore the DNA incorporation of 6-thioguanine nucleotide levels (DNA-6TGN) during 6-mercaptopurine (6MP) therapy of childhood acute lymphoblastic leukaemia (ALL) and non-Hodgkin lymphoma (NHL) and its relation to erythrocyte levels of their metabolites: 6-thioguanine-nucleotides (E-6TGN), methylated metabolites (E-MeMP), Methotrexate polyglutamates (E-MTX), and to thiopurine methyltransferase activity (TPMT).

METHODS

We studied these metabolites in 229 blood samples from 18 children with ALL (N = 16) or NHL (N = 2) on 6MP/Methotrexate maintenance therapy.

RESULTS

DNA-6TGN levels were significantly correlated to E-6TGN (r (p) = 0.66, p = 0.003) with a trend to reach a plateau at high E-6TGN levels. To explore the relative DNA incorporation of 6TGN in relation to cytosol 6TGN levels, a DNA-6TGN index was calculated as DNA-6TGN/E-6TGN. The DNA-6TGN index was inversely correlated to E-6TGN (r (p) = -0.58, p = 0.012), which implies that with increasing levels of E-6TGN relatively less 6TGN are incorporated into DNA. E-MeMP levels were correlated to the DNA-TGN index (r (p) = 0.60, p = 0.008), indicating that high levels of MeMP result in enhanced DNA-6TGN incorporation, possibly due to inhibition of purine de novo synthesis, mediated by some of the methylated 6MP metabolites.

CONCLUSIONS

DNA-6TGN may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than the previously used erythrocyte 6MP metabolites levels. Prospective clinical trials are needed to evaluate the usefulness of DNA-6TGN for individual dose adjustments.

Oral methotrexate/6-mercaptopurine may be superior to a multidrug LSA2L2 Maintenance therapy for higher risk childhood acute lymphoblastic leukemia: results from the NOPHO ALL-92 study

The importance of maintenance therapy for higher risk childhood acute lymphoblastic leukemia (ALL) is uncertain. Between 1992 and 2001 the Nordic Society for Pediatric Haematology/Oncology compared in a nonrandomized study conventional oral methotrexate (MTX)/6-mercaptopurine (6MP) maintenance therapy with a multidrug cyclic LSA2L2 regimen. 135 children with B-lineage ALL and a white blood count > or =50 x 10/L and 98 children with T-lineage ALL were included. Of the 234 patients, the 135 patients who received MTX/6MP maintenance therapy had a lower relapse risk than the 98 patients who received LSA2L2 maintenance therapy, which was the case for both B-lineage (27%+/-5% vs. 45%+/-9%; P=0.02) and T-lineage ALL (8%+/-5% vs. 21%+/-5%; P=0.12). In multivariate Cox regression analysis stratified for immune phenotype, a higher white blood count (P=0.01) and administration of LSA2L2 maintenance therapy (P=0.04) were both related to an increased risk of an event (overall P value of the Cox model: 0.003), whereas neither sex, age at diagnosis, administration of central nervous system irradiation, nor presence of a day 15 bone marrow with > or =25% versus <25% lymphoblasts were of statistical significance. These results indicate that oral MTX/6MP maintenance therapy administered after the first year of remission can improve the cure rates of children with T-lineage or with higher risk B-lineage ALL.