Maintenance therapy of childhood acute lymphoblastic leukemia revisited-Should drug doses be adjusted by white blood cell, neutrophil, or lymphocyte counts?

Metronomic chemotherapy in hematology: Lessons from preclinical and clinical studies to build a solid rationale for future schedules

Metronomic chemotherapy (mCHEMO), based on frequent, regular administration of low, but pharmacologically active drug doses, optimizes antitumor efficacy by targeting multiple targets and reducing toxicity of antineoplastic drugs. This minireview will summarize preclinical and clinical studies on cytotoxic drugs given at weekly, daily, or at continuous metronomic schedules alone or in combination with novel targeted agents for hematological malignancies, including lymphoma, multiple myeloma, and leukemia. Most of the preclinical in vitro and in vivo studies have reported a significant benefit of both mCHEMO monotherapy and combinatorial regimens compared with chemotherapy at the maximum tolerated dose. However, the combination of mCHEMO with targeted drugs is still little explored in the hematologic clinical setting. Data obtained from preclinical studies on low dose metronomic chemotherapy in hematological malignancies clearly suggested the possibility to clinically investigate more tolerable and effective strategies for the treatment of patients with advanced hematological malignancies, or at least for those frail and elderly patients, who are not eligible or resistant to standard treatments.

Bioequivalence study followed by model-informed dose optimization of a powder for oral suspension of 6-mercaptopurine

BACKGROUND

6-Mercaptopurine (6MP) is the mainstay chemotherapy for acute lymphoblastic leukemia (ALL) and is conventionally available as 50 mg tablets. A new 6MP powder for oral suspension (PFOS 10 mg/mL) was developed recently by IDRS Labs, India, intended for pediatric use. A comparative pharmacokinetics of PFOS with T. mercaptopurine was conducted to determine the dose equivalence.

METHODS

An open-label, randomized, two-treatment, two-period, two-sequence, single oral dose, crossover, bioequivalence study was conducted on 51 healthy adult subjects. Post hoc, a population pharmacokinetic (PopPK) model was developed using the healthy volunteer data to perform simulations with various PFOS doses and select a bioequivalent dose. Further, to confirm the safety of PFOS in pediatrics, a simulation of 6MP and 6-thioguanine exposures was performed by incorporating the formulation-specific parameters derived from the healthy volunteer study into the PopPK model in childhood ALL available in literature.

RESULTS

The 6MP PFOS had 47% higher oral bioavailability compared to the reference product. Simulations using a two-compartmental PopPK model with dissolution and transit compartments showed that 40 mg of PFOS was found to be equivalent to 50 mg tablets. The simulated 6-thioguanine nucleotide concentrations in children using the dose adjusted for PFOS were between 114 and 703.6 pmol/8 × 108 RBC, which was within the range reported in pediatric ALL studies.

CONCLUSION

6MP PFOS 10 mg/mL should be administered at a 20% lower dose than the tablet to achieve comparable exposure. 6MP PFOS addresses an unmet medical need for a liquid formulation of 6MP in the Indian subcontinent.

Maintenance Treatment in Acute Lymphoblastic Leukemia: A Clinical Primer

Cure rates in pediatric acute lymphoblastic leukemia (ALL) currently approach 90% in the developed world. Treatment involves 6-8 mo of intensive multi-drug chemotherapy followed by 24 mo of maintenance treatment (ALL-MT). The cornerstone of ALL-MT is the daily administration of oral 6-mercaptopurine (6MP), a purine analogue. 6MP is combined with weekly oral methotrexate (MTX), an antifolate drug, to augment therapeutic activity. Some protocols include additional chemotherapy drugs (such as vincristine and corticosteroids) during MT. The objective of ALL-MT is to ensure uninterrupted treatment at the highest tolerated doses of 6MP and MTX. This requires periodic adjustments of 6MP and MTX doses throughout treatment. Tolerance is determined through regular clinical assessments and careful monitoring of blood counts. Tolerated drug doses vary widely among patients, influenced by genetic and non-genetic factors, and require individualized dosing. Suboptimal treatment intensity in ALL-MT is associated with inferior outcomes and results from failure to treat at highest tolerated drug doses and/or interruptions in treatment due to non-adherence or toxicity. Management of MT thus requires close supervision to ensure treatment adherence, periodic drug dose modifications, and treatment to tolerance, while minimizing treatment interruptions due to toxicity. The review highlights these challenges and discusses approaches and strategies for the management of MT, focusing on the Indian context.

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.

Pharmacokinetic-pharmacodynamic modeling of maintenance therapy for childhood acute lymphoblastic leukemia

In the treatment of childhood acute lymphoblastic leukemia (ALL), current protocols combine initial high-dose multiagent chemotherapy with prolonged oral therapy with 6-mercaptopurine (6MP) and low-dose methotrexate (MTX) maintenance therapy. Decades of research on ALL treatment have resulted in survival rates of approximately 90%. However, dose-response relationships vary widely between patients and insight into the influencing factors, that would allow for improved personalized treatment management, is insufficient. We use a detailed data set with measurements of thioguanine nucleotides and MTX in red blood cells and absolute neutrophil count (ANC) to develop pharmacokinetic models for 6MP and MTX, as well as a pharmacokinetic-pharmacodynamic (PKPD) model capable of predicting individual ANC levels and thus contributing to the development of personalized treatment strategies. Here, we show that integrating metabolite measurements in red blood cells into the full PKPD model improves results when less data is available, but that model predictions are comparable to those of a fixed pharmacokinetic model when data availability is not limited, providing further evidence of the quality of existing models. With this comprehensive model development leading to dynamics similar to simpler models, we validate the suitability of this model structure and provide a foundation for further exploration of maintenance therapy strategies through simulation and optimization.

[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.

Maintenance therapy for acute lymphoblastic leukemia: basic science and clinical translations

Maintenance therapy (MT) with oral methotrexate (MTX) and 6-mercaptopurine (6-MP) is essential for the cure of acute lymphoblastic leukemia (ALL). MTX and 6-MP interfere with nucleotide synthesis and salvage pathways. The primary cytotoxic mechanism involves the incorporation of thioguanine nucleotides (TGNs) into DNA (as DNA-TG), which may be enhanced by the inhibition of de novo purine synthesis by other MTX/6-MP metabolites. Co-medication during MT is common. Although Pneumocystis jirovecii prophylaxis appears safe, the benefit of glucocorticosteroid/vincristine pulses in improving survival and of allopurinol to moderate 6-MP pharmacokinetics remains uncertain. Numerous genetic polymorphisms influence the pharmacology, efficacy, and toxicity (mainly myelosuppression and hepatotoxicity) of MTX and thiopurines. Thiopurine S-methyltransferase (encoded by TPMT) decreases TGNs but increases methylated 6-MP metabolites (MeMPs); similarly, nudix hydrolase 15 (encoded by NUDT15) also decreases TGNs available for DNA incorporation. Loss-of-function variants in both genes are currently used to guide MT, but do not fully explain the inter-patient variability in thiopurine toxicity. Because of the large inter-individual variations in MTX/6-MP bioavailability and metabolism, dose adjustments are traditionally guided by the degree of myelosuppression, but this does not accurately reflect treatment intensity. DNA-TG is a common downstream metabolite of MTX/6-MP combination chemotherapy, and a higher level of DNA-TG has been associated with a lower relapse hazard, leading to the development of the Thiopurine Enhanced ALL Maintenance (TEAM) strategy-the addition of low-dose (2.5-12.5 mg/m²/day) 6-thioguanine to the 6-MP/MTX backbone-that is currently being tested in a randomized ALLTogether1 trial (EudraCT: 2018-001795-38). Mutations in the thiopurine and MTX metabolism pathways, and in the mismatch repair genes have been identified in early ALL relapses, providing valuable insights to assist the development of strategies to detect imminent relapse, to facilitate relapse salvage therapy, and even to bring about changes in frontline ALL therapy to mitigate this relapse risk.

Thiopurine Enhanced ALL Maintenance (TEAM): study protocol for a randomized study to evaluate the improvement in disease-free survival by adding very low dose 6-thioguanine to 6-mercaptopurine/methotrexate-based maintenance therapy in pediatric and adult patients (0-45 years) with newly diagnosed B-cell precursor or T-cell acute lymphoblastic leukemia treated according to the intermediate risk-high group of the ALLTogether1 protocol

Background

A critical challenge in current acute lymphoblastic leukemia (ALL) therapy is treatment intensification in order to reduce the relapse rate in the subset of patients at the highest risk of relapse. The year-long maintenance phase is essential in relapse prevention. The Thiopurine Enhanced ALL Maintenance (TEAM) trial investigates a novel strategy for ALL maintenance.

Methods

TEAM is a randomized phase 3 sub-protocol to the ALLTogether1 trial, which includes patients 0–45 years of age with newly diagnosed B-cell precursor or T-cell ALL, and stratified to the intermediate risk-high (IR-high) group, in 13 European countries. In the TEAM trial, the traditional methotrexate (MTX)/6-mercaptopurine (6MP) maintenance backbone (control arm) is supplemented with low dose (2.5–12.5 mg/m²/day) oral 6-thioguanine (6TG) (experimental arm), while the starting dose of 6MP is reduced from 75 to 50 mg/m²/day. A total of 778 patients will be included in TEAM during ~ 5 years. The study will close when the last included patient has been followed for 5 years from the end of induction therapy. The primary objective of the study is to significantly improve the disease-free survival (DFS) of IR-high ALL patients by adding 6TG to 6MP/MTX-based maintenance therapy. TEAM has 80% power to detect a 7% increase in 5-year DFS through a 50% reduction in relapse rate. DFS will be evaluated by intention-to-treat analysis. In addition to reducing relapse, TEAM may also reduce hepatotoxicity and hypoglycemia caused by high levels of methylated 6MP metabolites. Methotrexate/6MP metabolites will be monitored and low levels will be reported back to clinicians to identify potentially non-adherent patients.

Discussion

TEAM provides a novel strategy for maintenance therapy in ALL with the potential of improving DFS through reducing relapse rate. Potential risk factors that have been considered include hepatic sinusoidal obstruction syndrome/nodular regenerative hyperplasia, second cancer, infection, and osteonecrosis. Metabolite monitoring can potentially increase treatment adherence in both treatment arms.

Trial registration

EudraCT, 2018–001795-38. Registered 2020-05-15,

Clinicaltrials.gov, NCT04307576. Registered 2020-03-13, https://clinicaltrials.gov/ct2/show/NCT04307576

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09522-3.

Salivary parameters and their correlation with neutrophil counts in children with acute lymphoblastic leukemia

BACKGROUND

Chemotherapy for Acute Lymphoblastic Leukemia (ALL) is known to render children immuno-deficient. A concomitant suppression of local defence mechanisms, such as saliva may further aggravate the adverse consequences of chemotherapy. The present study was conducted to evaluate alterations in salivary flow rate, pH and buffering capacity and to correlate these parameters with Absolute Neutrophil Counts (ANC).

METHODS

A cohort of 43 patients, aged 3-12 years were evaluated for the aforementioned parameters at baseline, post-induction and post-consolidation phases. Salivary collection was done and ANC was measured from routine haematological reports.

RESULTS

A decrease in the salivary parameters was observed at the end of Induction phase as compared to baseline, with a statistically significant decrease in unstimulated salivary flow rates (p < 0.01). Statistically significant positive correlations were found between ANC and salivary flow rate (p = 0.005), pH (p < 0.00) and buffering capacity (p < 0.00). On testing the significance of these correlations, all the values for these parameters were found to be statistically significant.

CONCLUSION

Salivary parameters showed derangements over the phases of chemotherapy, with maximum decrease at the end of induction phase. The positive correlations of salivary parameters with ANC of the subjects may be considered indicative of a concomitant immunological compromise in these children.

Prevalence of non-adherence and non-compliance during maintenance therapy in adults with acute lymphoblastic leukemia and their associations with survival

OBJECTIVES

Explore patient adherence and physician compliance to protocol guidelines during maintenance therapy, including the association with survival in adults with acute lymphoblastic leukemia (ALL).

METHODS

Blood counts, aminotransferase levels and prescribed 6-mercaptopurine (6MP)/methotrexate (MTX) doses were compared with the protocol guidelines to assess compliance. Non-adherence to the prescribed medication was confirmed in patients with unmeasurable 6MP metabolite levels and suspected in patients with low 6MP metabolites concurrent with aminotransferase and white blood cell count within normal ranges, while potential intermittent non-adherence was defined by >1.9 fold fluctuating 6MP metabolites.

RESULTS

Physicians' non-compliance with insufficient dose increments of 6MP/MTX despite white blood cell counts above the target level comprised a median of 20.1% (interquartile range 9.7-39.3%) of the observed time in maintenance therapy, yet no association to relapse was found (P = .17). Non-adherence to 6MP was confirmed in 9.8% (5 of 51 patients), suspected in an additional 9.8% (5 of 51 patients), and intermittent non-adherence was suspected in 52.6% (20 of 38 patients).

CONCLUSION

Although no association between non-compliance and leukemic relapse was found, likely due to lack of power, increased attention to this phase of ALL therapy is indicated.

Outcome of young adult patients with very-high-risk acute lymphoblastic leukemia treated with pediatric-type chemotherapy - a single institute experience

BACKGROUND/PURPOSE

Adult patients of acute lymphoblastic leukemia (ALL) with very high-risk (VHR) characteristics have an inferior outcome, and allogeneic hematopoietic stem cell transplantation (HSCT) is usually performed. In contrast, VHR pediatric patients can be treated effectively with minimal residual disease (MRD)-guided pediatric protocols and HSCT are not always needed.

METHODS

We retrospectively reviewed young adult ALL VHR patients treated with the pediatric-type (TPOG-ALL-2002 VHR) regimen in our institute from 2008 to 2019 and compared the event-free survival (EFS) with patients treated with an adult-type regimen (Hyper-CVAD alternating with high dose methotrexate and cytarabine).

RESULTS

We identified 16 patients treated with the TPOG and 11 treated with the Hyper-CVAD regimen. Philadelphia chromosome-positive (n = 10) and T-cell immunophenotype (n = 11) are the most common VHR features. Compared with the Hyper-CVAD group, patients treated with the TPOG regimen showed a trend toward better EFS with a hazard ratio (HR) of 0.42 (p = 0.16). Compared with untransplanted patients, HSCT showed a positive trend in the Hyper-CVAD (HR 0.22, p = 0.12) but not in the TPOG group (p = 0.37). Untransplanted patients treated initially with the hyper-CVAD regimen had a significantly worse outcome than the TPOG regimen (HR 4.19, p < 0.05). In the TPOG group, patients with negative MRD at the end of consolidation had a significantly better outcome (HR 0.12, p = 0.03).

CONCLUSION

Young adult VHR patients can be effectively treated with the TPOG-ALL-2002 protocol, and those who achieved MRD negativity before the end of consolidation have a good outcome without allogeneic HSCT.

Dynamics of leucocyte DNA thioguanine nucleotide levels during maintenance therapy of childhood acute lymphoblastic leukemia

PURPOSE

Methotrexate (MTX)/6-Mercaptopurine (6MP)-based maintenance therapy is crucial to cure childhood acute lymphoblastic leukemia (ALL). Cytotoxicity is mediated by incorporation of thioguanine nucleotides (TGN) into DNA (DNA-TG) with higher levels in leucocytes being associated with reduced relapse risk. To further understand the dynamics of DNA-TG formation, we measured DNA-TG levels in leucocyte subsets during maintenance therapy and in the months following its discontinuation.

METHODS

DNA-TG levels were measured in leucocytes (DNA-TG_Total), polymorph nucleated granulocytes (neutrophils, eosinophils, basophils [DNA-TG_PMN]) and mononucleated cells (lymphocytes, monocytes [DNA-TG_MNC]) in 1013 samples from 52 patients on ALL maintenance therapy (951 samples during therapy and 62 samples after therapy discontinuation, respectively).

RESULTS

Median DNA-TG_Total, DNA-TG_PMN and DNA-TG_MNC during maintenance therapy were 539, 563 and 384 fmol/µg DNA, respectively. DNA-TG_PMN displayed more pronounced fluctuation than DNA-TG_MNC (range 0-3084 [interquartile range IQR 271-881] versus 30-1411 [IQR 270-509] fmol/µg DNA). DNA-TG_Total was more strongly correlated with DNA-TG_PMN (r_S = 0.95, p < 0.0001) than DNA-TG_MNC (r_S = 0.73, p < 0.0001). DNA-TG_PMN correlated less with DNA-TG_MNC (r_S = 0.64, p < 0.0001) and to a much lesser extent with absolute neutrophil count (r_S = 0.35, p < 0.0001). Following discontinuation of therapy, DNA-TG_PMN was rapidly eliminated, and not measurable beyond day 22 after discontinuation, whereas DNA-TG_MNC was slowly eliminated, and five patients demonstrated a measurable DNA-TG_MNC more than 365 days after therapy discontinuation.

CONCLUSION

Fluctuations in DNA-TG_Total are predominantly caused by corresponding fluctuations in DNA-TG_PMN, thus DNA-TG_Total measures recent TGN incorporation in these short-lived cells. Measurement of DNA-TG_Total at 2-4 weeks intervals provides a reliable profile of DNA-TG levels.

Effects of germline DHFR and FPGS variants on methotrexate metabolism and relapse of leukemia

Methotrexate (MTX) during maintenance therapy is essential for curing acute lymphoblastic leukemia (ALL), but dosing strategies aiming at adequate treatment intensity are challenged by interindividual differences in drug disposition. To evaluate genetic factors associated with MTX metabolism, we performed a genome-wide association study in 447 ALL cases from the Nordic Society for Pediatric Haematology and Oncology ALL2008 study, validating results in an independent set of 196 patients. The intergenic single-nucleotide polymorphism rs1382539, located in a regulatory element of DHFR, was associated with increased levels of short-chain MTX polyglutamates (P = 1.1 × 10-8) related to suppression of enhancer activity, whereas rs35789560 in FPGS (p.R466C, P = 5.6 × 10-9) was associated with decreased levels of long-chain MTX polyglutamates through reduced catalytic activity. Furthermore, the FPGS variant was linked with increased relapse risk (P = .044). These findings show a genetic basis for interpatient variability in MTX response and could be used to improve future dosing algorithms.

The Effect of NUDT15, TPMT, APEX1, and ITPA Genetic Variations on Mercaptopurine Treatment of Pediatric Acute Lymphoblastic Leukemia

Mercaptopurine (MP) is a commonly used maintenance regimen for childhood acute lymphoblastic leukemia (ALL). However, 6-MP has a narrow therapeutic index, which causes dose-limiting toxicities in hematopoietic tissues. Recent studies reported several candidate pharmacogenetic markers such as TPMT, NUDT15, ITPA, and APEX1, which predict the possibility of 6-MP related toxicities. The aim of this study is to evaluate the effect of major variants of these genes on 6-MP intolerances and toxicities in pediatric acute lymphoblastic leukemia (ALL) patients. A total of 83 pediatric ALL patients were included (56 males and 27 females). The NUDT15 c.415C>T (rs116855232), NUDT15 c.55_56insGAGTCG (rs746071566), ITPA c.94C>A (rs1127354), ITPA c.IVS2+21A>C (rs7270101), APEX c.190A>G (rs2307486), and TPMT variants were analyzed by sanger sequencing. Correlations between indexes of 6-MP-related toxicities or 6-MP intolerance (absolute neutrophil count [ANC] at several time point, days of ANC < 1 × 10³/mm³, days of ANC < 0.5 × 10³/mm³, frequency of febrile neutropenia, maximum AST and ALT, 6-MP dose and 6-MP dose intensity during maintenance therapy) and genetic variations were analyzed. The NUDT15 c.415C>T allele carrier showed significantly low 6-MP doses at the final maintenance therapy period than the wild type carrier (p = 0.007). The 6-MP dose intensities at the sixth and final maintenance period were also significantly low in NUDT15 c.415C>T carriers (p = 0.003 and 0.008, respectively). However, indexes for neutropenia, days of febrile neutropenia, maximum AST, and ALT levels were not associated with the presence of c.415C>T as well as other analyzed variants. When analyzing the effect of the coexistence of NUDT15 c.415C>T and ITPA c.94C>A, no significant differences were found between the NUDT15 c.415C>T carrier and carrier with both variations. The NUDT15 c.415C>T was the most useful marker to predict 6-MP intolerance among analyzed variants in our study population. Although we could not find association of those variants with 6-MP induced toxicities and the synergistic effects of those variants, a well-planed larger scale study would be helpful in clarifying new candidates and their clinical effects.

Classification of white blood cells using weighted optimized deformable convolutional neural networks

BACKGROUND

Machine learning (ML) algorithms have been widely used in the classification of white blood cells (WBCs). However, the performance of ML algorithms still needs to be addressed for being short of gold standard data sets, and even the implementation of the proposed algorithms.

METHODS

In this study, the method of two-module weighted optimized deformable convolutional neural networks (TWO-DCNN) was proposed for WBC classification. Our algorithm is characterized as two-module transfer learning and deformable convolutional (DC) layers for the betterment of robustness. To validate the performance, our method was compared with classical MLs of VGG16, VGG19, Inception-V3, ResNet-50, support vector machine (SVM), multilayer perceptron (MLP), decision tree (DT) and random forest (RF) on our undisclosed WBC data set and public BCCD data set.

RESULTS

TWO-DCNN achieved the best performance with the precisions (PREs) of 95.7%, 94.5% and 91.6%, recalls (RECs) of 95.7%, 94.5% and 91.6%, F1-scores (F1s) of 95.7%, 94.5% and 91.6%, area under curves (AUCs) of 0.98, 0.97 and 0.95 for low-resolution and noisy undisclosed data sets, BCCD data set, respectively.

CONCLUSIONS

With accurate feature extraction and optimized network weights, the proposed TWO-DCNN showed the best performance in WBC classification for low-resolution and noisy data sets. It could be used as an alternative method for clinical applications.

DNA-thioguanine nucleotide as a treatment marker in acute lymphoblastic leukemia patients with NUDT15 variant genotypes

Background

Large inter-individual variations in drug metabolism pose a challenge in determining 6-mercaptopurine (6MP) doses. As the last product of 6MP metabolism, DNA-thioguanine nucleotide (DNA-TGN) could reflect the efficacy of 6MP, especially in patients harboring variants in the 6MP metabolism pathway. The aim of this study was to investigate the clinical significance of DNA-TGN monitoring in Korean pediatric acute lymphoblastic leukemia (ALL) patients, focusing on the NUDT15 genotype.

Methods

The subjects of this study were patients who underwent ALL treatment with 6MP. Tests for the NUDT15 and TPMT genotypes were performed, and prospective DNA-TGN and erythrocyte TGN samples were collected after two weeks or more of 6MP treatment. DNA-TGN was quantified using the liquid chromatography-tandem mass spectrometry method.

Results

A total of 471 DNA-TGN measurements in 71 patients were analyzed, which ranged from 1.0 to 903.1 fmol thioguanine/μg DNA. The 6MP intensity demonstrated a significant relationship with DNA-TGN concentration (P<0.001). Patients harboring NUDT15 variants were treated with a lower dose of 6MP (P<0.001); however, there was no significant difference in DNA-TGN concentration when compared to patients carrying wild-type NUDT15 (P = 0.261). These patients also presented higher variation in DNA-TGN levels (P = 0.002) and DNA-TGN/6MP intensity (P = 0.019) compared to patients carrying wild-type NUDT15. DNA-TGN concentration did not show a significant correlation with WBC count (P = 0.093).

Conclusions

Patients harboring NUDT15 variants demonstrated similar DNA-TGN concentrations even at low doses of 6MP and showed high variability in DNA-TGN. Particularly in patients with NUDT15 variants who need a reduced 6MP dose, DNA-TGN could be applied as a useful marker to monitor the therapeutic effect of 6MP.

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.

An exploration of mercaptopurine/methotrexate tolerance during maintenance therapy in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (6MP) and methotrexate (MTX) cause myelosuppression and interruptions in therapy in children with lymphoblastic leukemia (ALL). Length of time off of therapy is related to poorer outcomes. To date the dose at which most children tolerate these agents without drops in blood counts has not been identified. This study attempts to determine the maximum tolerated dose of both 6MP/MTX.

METHODS

A retrospective chart review of 77 ALL children, median age 4.5 years. Time to first interruption and dose, along with total number of interruptions were collected. Absolute neutrophil and platelet counts recorded at time of interruption. Subgroup analysis of age, sex, diagnosis and risk stratification were also completed. REB approval was gained.

RESULTS

Of the 77 patients that were studied, 9 of them had no treatment interruptions. Descriptive statistics are reported using Strata software. The mean number of interruptions during maintenance was 3.2, the mean time to first interruption was 149.8 days. The mean dose percent of MTX and 6MP at first interruption was 94.4% and 106% respectively. Maintenance therapy was interrupted independent of age, sex, diagnosis or disease risk stratification.

CONCLUSION

Few patients complete maintenance therapy without interruptions at the current dose escalation schedules outlined by the Children's Oncology Group protocols. The interruptions are due in part to intolerance of dose escalations of MTX and 6 MP above 100%. Future research should investigate doses of 6MP and MTX in maintenance therapy in relation to leukemia outcomes.

Pharmacokinetics of tablet and liquid formulations of oral 6-mercaptopurine in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (6MP) is essential to cure childhood acute lymphoblastic leukemia (ALL). A liquid 6MP formulation was recently introduced to facilitate oral 6MP administration, especially to children. Its approval and bioequivalence with 6MP tablet were based on comparative pharmacokinetics in 60 healthy adults. Due to potential pharmacokinetic differences between healthy adults and children with ALL, we compared pharmacokinetics of tablet and liquid 6MP formulations in children with ALL.

METHODS

Pharmacokinetics of 50 mg 6MP tablet (Puri-Nethol^®) and 20 mg/ml 6MP liquid suspension (Xaluprine^®) were compared in a non-blinded, random order, single-dose, cross-over study in 16 children with ALL (eight males). 6MP was administered after a 12 h fast, and 6MP plasma concentrations measured consecutively over seven hours post-dose. Pharmacokinetic outcomes were as follows: Area under the curve (AUC), maximum plasma concentration (C_max), time to maximum plasma concentration (T_max), and terminal half-life (T_½).

RESULTS

Liquid 6MP formulation resulted in a 26% lower AUC (p = 0.02) compared with tablet (median 1215 vs. 1805 h × nmol/l). No significant differences were observed for C_max,T_max and T_½ (p = 0.28, p = 0.09, p = 0.41, respectively). Based on criteria declared by the World Health Organization the results did not establish non-inferiority of liquid 6MP formulation compared with 6MP tablet.

CONCLUSION

Non-inferiority of liquid 6MP formulation compared with 6MP tablet was not demonstrated. Yet, maintenance therapy doses are adjusted by degree of myelosuppression and not by 6MP dose. Thus, in spite of a lower bioavailability, a liquid 6MP formulation is still desirable in a clinical setting, especially for children. However, if shifting between 6MP formulation is indicated, dose adjustments should be anticipated to maintain equivalent treatment intensity in children with ALL. The study is registered on clinicaltrials.gov (NCT01906671). Date of registration: 24.07.13.

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.

Dihydrofolate Reductase Genetic Polymorphisms Affect Methotrexate Dose Requirements in Pediatric Patients With Acute Lymphoblastic Leukemia on Maintenance Therapy

We have aimed to determine the effect of polymorphisms in regulatory regions of the DHFR gene in relation to methotrexate (MTX) dose adjustments and drug-induced toxicity in children on maintenance therapy for acute lymphoblastic leukemia (ALL). In total, 41 children diagnosed with ALL were screened for 3 tag-single nucleotide polymorphisms in the DHFR promoter (C-1610G, C-680G/T, A-317G) and an intronic 19-bp insertion/deletion. Genotypes were analyzed in relation to dose requirements and toxicity. The percentage of MTX dose administered (with respect to protocol-recommended values) was affected by DHFR polymorphisms. Carriers of the -680AA genotype displayed a median percentage of 44.08 (interquartile range=34.69), compared with 77.98 (interquartile range=33.90) for CC and CA carriers (P=0.01). The number of counts within white blood cell therapeutic range (2.0 to 3.0×10/L) was higher for -680AA carriers than for CC/CA carriers (P=0.003). With regard to toxicity, carriers of the -680AA genotype displayed more treatment interruptions than CC/CG carriers (P=0.03), as well as more episodes of severe neutropenia (P=0.04) and higher number of blood counts with elevated levels (>400 mg/dL) of lactate dehidrogenase (P=0.04). Overall, our findings suggest that the identification of DHFR polymorphisms in the promoter region of the gene may be helpful in tailoring MTX doses for ALL pediatric patients on maintenance therapy.

Hepatic sinusoidal obstruction syndrome during maintenance therapy of childhood acute lymphoblastic leukemia is associated with continuous asparaginase therapy and mercaptopurine metabolites

BACKGROUND

Hepatic sinusoidal obstruction syndrome (SOS) during treatment of childhood acute lymphoblastic leukemia (ALL) has mainly been associated with 6-thioguanine. The occurrence of several SOS cases after the introduction of extended pegylated asparaginase (PEG-asparaginase) therapy in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL2008 protocol led us to hypothesize that PEG-asparaginase, combined with other drugs, may trigger SOS during 6-thioguanine-free maintenance therapy.

PROCEDURE

In children with ALL treated in Denmark according to the NOPHO ALL2008 protocol, we investigated the risk of SOS during methotrexate (MTX)/6-mercaptopurine (6MP) maintenance therapy that included PEG-asparaginase until week 33 (randomized to two- vs. six-week intervals), as well as alternating high-dose MTX or vincristine/dexamethasone pulses every four weeks.

RESULTS

Among 130 children receiving PEG-asparaginase biweekly, 29 developed SOS (≥2 criteria: hyperbilirubinemia, hepatomegaly, ascites, weight gain ≥2.5%, unexplained thrombocytopenia <75 × 10⁹ l^-1 ) at a median of 30 days (interquartile range [IQR]: 17-66) into maintenance (cumulative incidence: 27%). SOS cases fulfilling one, two, or three Ponte di Legno criteria were classified as possible (n = 2), probable (n = 8), or verified (n = 19) SOS, respectively. Twenty-six cases (90%) occurred during PEG-asparaginase treatment, including 21 (81%) within 14 days from the last chemotherapy pulse compared with the subsequent 14 days (P = 0.0025). Cytotoxic 6MP metabolites were significantly higher on PEG-asparaginase compared to after its discontinuation. Time-dependent Cox regression analysis showed increased SOS hazard ratio (HR) for erythrocyte levels of methylated 6MP metabolites (HR: 1.09 per 1,000 nmol/mmol hemoglobin increase, 95% confidence interval: 1.05-1.14). Six-week PEG-asparaginase intervals significantly reduced SOS-specific hazards (P < 0.01).

CONCLUSIONS

PEG-asparaginase increases cytotoxic 6MP metabolite levels and risk of SOS, potentially interacting with other chemotherapy pulses.

SAMHD1 protects cancer cells from various nucleoside-based antimetabolites

Recently, we demonstrated that sterile α motif and HD domain containing protein 1 (SAMHD1) is a major barrier in acute myelogenous leukemia (AML) cells to the cytotoxicity of cytarabine (ara-C), the most important drug in AML treatment. Ara-C is intracellularly converted by the canonical dNTP synthesis pathway to ara-CTP, which serves as a substrate but not an allosteric activator of SAMHD1. Using an AML mouse model, we show here that wild type but not catalytically inactive SAMHD1 reduces ara-C treatment efficacy in vivo. Expanding the clinically relevant substrates of SAMHD1, we demonstrate that THP-1 CRISPR/Cas9 cells lacking a functional SAMHD1 gene showed increased sensitivity to the antimetabolites nelarabine, fludarabine, decitabine, vidarabine, clofarabine, and trifluridine. Within this Extra View, we discuss and build upon both these and our previously reported findings, and propose SAMHD1 is likely active against a variety of nucleoside analog antimetabolites present in anti-cancer chemotherapies. Thus, SAMHD1 may constitute a promising target to improve a wide range of therapies for both hematological and non-haematological malignancies.

DNA-thioguanine nucleotide concentration and relapse-free survival during maintenance therapy of childhood acute lymphoblastic leukaemia (NOPHO ALL2008): a prospective substudy of a phase 3 trial

BACKGROUND

Adjustment of mercaptopurine and methotrexate maintenance therapy of acute lymphoblastic leukaemia by leucocyte count is confounded by natural variations. Cytotoxicity is primarily mediated by DNA-incorporated thioguanine nucleotides (DNA-TGN). The aim of this study was to establish whether DNA-TGN concentrations in blood leucocytes during maintenance therapy are associated with relapse-free survival.

METHODS

In this substudy of the NOPHO ALL2008 phase 3 trial done in 23 hospitals in seven European countries (Denmark, Estonia, Finland, Iceland, Lithuania, Norway, and Sweden), we analysed data from centralised and blinded analyses of 6-mercaptopurine and methotrexate metabolites in blood samples from patients with non-high-risk childhood acute lymphoblastic leukaemia. Eligible patients were aged 1·0-17·9 years; had been diagnosed with non-high-risk precursor B-cell or T-cell leukaemia; had been treated according to the Nordic Society of Pediatric Hematology and Oncology ALL2008 protocol; and had reached maintenance therapy in first remission. Maintenance therapy was (mercaptopurine 75 mg/m² once per day and methotrexate 20 mg/m² once per week, targeted to a leucocyte count of 1·5-3·0 × 10⁹ cells per L). We measured DNA-TGN and erythrocyte concentrations of TGN nucleotides, methylated mercaptopurine metabolites, and methotrexate polyglutamates. The primary objective was the association of DNA-TGN concentrations and 6-mercaptopurine and methotrexate metabolites with relapse-free survival. The secondary endpoint was the assessment of DNA-TGN concentration and 6-mercaptopurine and methotrexate metabolites during maintenance therapy phase 2.

FINDINGS

Between Nov 26, 2008 and June 14, 2016, 1509 patients from the NOPHO ALL2008 study were assessed for eligibility in the DNA-TGN substudy, of which 918 (89%) of 1026 eligible patients had at least one DNA-TGN measurement and were included in the analyses. Median follow-up was 4·6 years (IQR 3·1-6·1). Relapse-free survival was significantly associated with DNA-TGN concentration (adjusted hazard ratio 0·81 per 100 fmol/μg DNA increase, 95% CI 0·67-0·98; p=0·029). In patients with at least five blood samples, erythrocyte concentrations of TGN, methylated mercaptopurine metabolites, and methotrexate polyglutamates were associated with DNA-TGN concentration (all p<0·0001).

INTERPRETATION

Our results suggest the need for intervention trials to identify clinically applicable strategies for individualised drug dosing to increase DNA-TGN concentration, and randomised studies to investigate whether such strategies improve cure rates compared with current dose adjustments based on white blood cell counts.

FUNDING

Danish Cancer Society, Childhood Cancer Foundation (Denmark), Childhood Cancer Foundation (Sweden), Nordic Cancer Union, Otto Christensen Foundation, University Hospital Rigshospitalet, and Novo Nordic Foundation.

Measures of 6-mercaptopurine and methotrexate maintenance therapy intensity in childhood acute lymphoblastic leukemia

PURPOSE

Normal white blood cell counts (WBC) are unknown in children with acute lymphoblastic leukemia (ALL). Accordingly, 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy is adjusted by a common WBC target of 1.5-3.0 × 10⁹/L. Consequently, the absolute degree of myelosuppression is unknown for the individual child and we wanted to evaluate this.

METHODS

A median of 22 (range 8-27) 6MP/MTX metabolite samples and 100 (range 25-130) blood counts during therapy and 10 (range 2-15) off therapy were collected in 50 children with ALL. Differences between off-therapy and on-therapy WBCs [including absolute neutrophil (ANC) and lymphocyte counts (ALC)] were used to retrospectively approximate the absolute myelosuppression (="delta-") and association with age, sex and 6MP/MTX doses explored. We applied linear mixed models to estimate on-therapy counts by 6MP/MTX metabolites: DNA-incorporated thioguanine nucleotides (DNA-TGN), erythrocyte thioguanine nucleotides (ery-TGN), erythrocyte-methylated 6MP metabolites (ery-MeMP) and erythrocyte MTX polyglutamates with 2-6 glutamate residues (ery-MTXpg_2-6).

RESULTS

On-therapy WBC was correlated with ANC and ALC (r _s  = 0.84 and r _s  = 0.33, p values <0.001), whereas ANC was weakly correlated with ALC (r _s  = -0.11, p < 0.001), and neither significantly correlated with age. Off-therapy ALC, but not ANC, was strongly correlated with age (r _s  = -0.68 and -0.18, p < 0.001 and p = 0.22). Delta-ALC decreased with increasing age (r _s  = -0.69, p < 0.001). Incorporation of DNA-TGN was positively associated with ery-TGN (p < 0.001), ery-MeMP (p < 0.001) and ery-MTXpg_2-6 (p = 0.047). On-therapy ALC decreased with increasing DNA-TGN level (p < 0.001, model adjusted for off-therapy ALC), whereas on-therapy ANC could not be modeled reliably.

CONCLUSION

Measurements of 6MP/MTX metabolites could supplement blood counts in assessing therapy intensity, but require prospective validation.