Association between busulfan exposure and outcome in children receiving intravenous busulfan before hematopoietic stem cell transplantation

Population Pharmacokinetic Modeling for Twice-Daily Intravenous Busulfan in a Large Cohort of Pediatric Patients Undergoing Hematopoietic Stem Cell Transplantation-A 10-Year Single-Center Experience

Reaching target exposure of busulfan-based conditioning prior to hematopoietic stem cell transplantation is vital for favorable therapy outcomes. Yet, a wide inter-patient and inter-occasion variability in busulfan exposure has been reported, especially in children. We aimed to identify factors associated with the variability of busulfan pharmacokinetics in 124 consecutive patients transplanted at the University Children's Hospital Zurich between October 2010 and February 2020. Clinical data and busulfan plasma levels after twice-daily intravenous administration were analyzed retrospectively by population pharmacokinetic modeling. The volume of distribution correlated with total body water. The elimination rate constant followed an age-dependent maturation function, as previously suggested, and correlated with the levels of serum albumin. Acute lymphoblastic leukemia reduced busulfan clearance by 20%. Clearance significantly decreased by 17% on average from the start to the third day of busulfan administration, in agreement with other studies. An average reduction of 31% was found in patients with hemophagocytic lymphohistiocytosis and X-linked lymphoproliferative disease. In conclusion, we demonstrate that in addition to known factors, underlying disease and serum albumin significantly impact busulfan pharmacokinetics in pediatric patients; yet, substantial unexplained variability in some patients remained. Thus, we consider repeated pharmacokinetic assessment essential to achieve the desired target exposure in twice-daily busulfan administration.

Predicting busulfan exposure in patients undergoing hematopoietic stem cell transplantation using machine learning techniques

PURPOSE

This study aimed to establish an optimal model to predict the busulfan (BU) area under the curve at steady state (AUCss) by using machine learning (ML).

PATIENTS AND METHODS

Seventy-nine adult patients (age ≥18 years) who received BU intravenously and underwent therapeutic drug monitoring from 2013 to 2021 at Fujian Medical University Union Hospital were enrolled in this retrospective study. The whole dataset was divided into a training group and test group at the ratio of 8:2. BU AUCss were considered as the target variable. Nine different ML algorithms and one population pharmacokinetic (pop PK) model were developed and validated, and their predictive performance was compared.

RESULTS

All ML models were superior to the pop PK model (R2 = 0.751, MSE = 0.722, 14 and RMSE = 0.830) in model fitting and had better predictive accuracy. The ML model of BU AUCss established through support vector regression (SVR) and gradient boosted regression trees (GBRT) had the best predictive ability (R2 = 0.953 and 0.953, MSE = 0.323 and 0.326, and RMSE = 0.423 and 0.425).

CONCLUSION

All the ML models can potentially be used to estimate BU AUCss with the aim of facilitating rational use of BU on the individualized level, especially models built by SVR and GBRT algorithms.

The Importance of New EBMT Criteria on the Diagnosis of Veno-Occlusive Liver Disease in Children

BACKGROUND

Early recognition and specific therapy facilitate a favorable disease course in hepatic venous-occlusive disease (HVOD) following hematopoietic stem cell transplantation (HCT). Diagnostic and classification criteria, published by the European Society for Blood and Marrow Transplantation (EBMT), better account for clinical differences in disease presentation in pediatric populations.

OBJECTIVES

To compare the course of HVOD in children before and after the implementation of new EBMT criteria.

MATERIAL AND METHODS

The study retrospectively evaluates 26 HVODs in 179 children treated in a single HCT unit (Slovakia) comparing the period of 2014-2017 using the Baltimore and modified Seattle criteria with the period of 2018-2021, when new EBMT criteria were adopted.

RESULTS

No difference in HVOD incidence (11.2% vs. 14.8%, p = 0.46) and in time of diagnosis post-HCT (15.6 days vs. 15.7 days, p = 0.75) was found. With EBMT criteria we observed more frequent anicteric disease at diagnosis (50% vs. 87.5%, p = 0.04), lower serum bilirubin at diagnosis (3.4 mg/dL vs. 1.23 mg/dL, p = 0.045), and non-significant trends of shorter defibrotide treatment (21.7 days vs. 15.6 days, p = 0.73), decreased mortality (30% vs. 6.2%, p = 0.10) and shorter hospitalization (73.1 days vs. 59.6 days, p = 0.54).

CONCLUSIONS

Different time periods around the implementation of new criteria are evaluated, underling that pediatric EBMT criteria for post-transplant HVOD diagnosis appear more sensitive.

External Evaluation of Population Pharmacokinetic Models of Busulfan in Chinese Adult Hematopoietic Stem Cell Transplantation Recipients

Objective: Busulfan (BU) is a bi-functional DNA-alkylating agent used in patients undergoing hematopoietic stem cell transplantation (HSCT). Over the last decades, several population pharmacokinetic (pop PK) models of BU have been established, but external evaluation has not been performed for almost all models. The purpose of the study was to evaluate the predictive performance of published pop PK models of intravenous BU in adults using an independent dataset from Chinese HSCT patients, and to identify the best model to guide personalized dosing.

Methods: The external evaluation methods included prediction-based diagnostics, simulation-based diagnostics, and Bayesian forecasting. In prediction-based diagnostics, the relative prediction error (PE%) was calculated by comparing the population predicted concentration (PRED) with the observations. Simulation-based diagnostics included the prediction- and variability-corrected visual predictive check (pvcVPC) and the normalized prediction distribution error (NPDE). Bayesian forecasting was executed by giving prior one to four observations. The factors influencing the model predictability, including the impact of structural models, were assessed.

Results: A total of 440 concentrations (110 patients) were obtained for analysis. Based on prediction-based diagnostics and Bayesian forecasting, preferable predictive performance was observed in the model developed by Huang et al. The median PE% was -1.44% which was closest to 0, and the maximum F₂₀ of 57.27% and F₃₀ of 72.73% were achieved. Bayesian forecasting demonstrated that prior concentrations remarkably improved the prediction precision and accuracy of all models, even with only one prior concentration.

Conclusion: This is the first study to comprehensively evaluate published pop PK models of BU. The model built by Huang et al. had satisfactory predictive performance, which can be used to guide individualized dosage adjustment of BU in Chinese patients.

The Correlation Between Busulfan Exposure and Clinical Outcomes in Chinese Pediatric Patients: A Population Pharmacokinetic Study

Aims: The aims of the study were to 1) establish a population pharmacokinetic (Pop-PK) model for busulfan in Chinese pediatric patients undergoing hematopoietic stem cell transplantation (HSCT) and then estimate busulfan exposure and 2) explore the association between busulfan exposure and clinical outcomes.

Methods: A total of 128 patients with 467 busulfan concentrations were obtained for Pop-PK modeling using nonlinear mixed effect model (NONMEM) software. Sixty-three patients who received the 16-dose busulfan conditioning regimen were enrolled to explore the correlations between clinical outcomes and the busulfan area under the concentration–time curve (AUC) using the Cox proportional hazards regression model, Kaplan–Meier method and logistic regression.

Results: The typical values for clearance (CL) and distribution volume (V) of busulfan were 7.71 L h⁻¹ and 42.4 L, respectively. The allometric normal fat mass (NFM) and maturation function (Fmat) can be used to describe the variability in CL, and the fat-free mass (FFM) can be used to describe the variability in V. Patients with AUCs of 950–1,600 µM × min had 83.7% (95% CI: 73.3–95.5) event-free survival (EFS) compared with 55.0% (95% CI: 37.0–81.8) for patients with low or high exposure (p = 0.024). The logistic regression analysis results showed no association between transplant-related toxicities and the busulfan AUC (p > 0.05).

Conclusions: The variability in busulfan CL was related to the NFM and Fmat, while busulfan V was related to the FFM. Preliminary analysis results suggested that a busulfan AUC of 950–1,600 µM × min was associated with better EFS in children receiving the 16-dose busulfan regimen.

Development of a Population Pharmacokinetic Model of Busulfan in Children and Evaluation of Different Sampling Schedules for Precision Dosing

We develop a population pharmacokinetic model to describe Busulfan pharmacokinetics in paediatric patients and investigate by simulations the impact of various sampling schedules on the calculation of AUC. Seventy-six children had 2 h infusions every 6 h. A two-compartment linear model was found to adequately describe the data. A lag-time was introduced to account for the delay of the administration of the drug through the infusion pump. The mean values of clearance, central volume of distribution, intercompartmental clearance, and peripheral volume of distribution were 10.7 L/h, 39.5 L, 4.68 L/h and 17.5 L, respectively, normalized for a Body Weight (BW) of 70 kg. BW was found to explain a portion of variability with an allometric relationship and fixed exponents of 0.75 on clearance parameters and 1 on volumes. Interindividual variability for clearance and volume of distribution was found to be 28% and 41%, respectively, and interoccasion variability for clearance was found to be 11%. Three sampling schedules were assessed by simulations for bias and imprecision to calculate AUC by a non-compartmental and a model-based method. The latter was found to be superior in all cases, while the non-compartmental was unbiased only in sampling up to 12 h corresponding to a once-daily dosing regimen.

Therapeutic Drug Monitoring of Conditioning Agents in Pediatric Allogeneic Stem Cell Transplantation; Where do We Stand?

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established curative treatment that has significantly improved clinical outcome of pediatric patients with malignant and non-malignant disorders. This is partly because of the use of safer and more effective combinations of chemo- and serotherapy prior to HSCT. Still, complications due to the toxicity of these conditioning regimens remains a major cause of transplant-related mortality (TRM). One of the most difficult challenges to further improve HSCT outcome is reducing toxicity while maintaining efficacy. The use of personalized dosing of the various components of the conditioning regimen by means of therapeutic drug monitoring (TDM) has been the topic of interest in the last decade. TDM could play an important role, especially in children who tend to show greater pharmacokinetic variability. However, TDM should only be performed when it has clear added value to improve clinical outcome or reduce toxicity. In this review, we provide an overview of the available evidence for the relationship between pharmacokinetic parameters and clinical outcome or toxicities of the most commonly used conditioning agents in pediatric HSCT.

Clinical outcomes of individualized busulfan-dosing in hematopoietic stem cell transplantation in Chinese children undergoing with therapeutic drug monitoring

To identify relationships between busulfan (Bu) exposure and outcomes of a cohort pediatric patients receiving hematopoietic stem cell transplantation (HSCT), along with a targeted busulfan-based conditioning regimen. We retrospectively evaluated targeted busulfan concentrations in 53 pediatric patients (age 0.4-16 years) who received busulfan 4 times daily according to recommended weight-based doses in a single-center analysis between 2018 and 2020. In this trial, individual busulfan pharmacokinetics were performed following dose 5 of the conditioning regimen. Twenty four of 53 patients (45.3%) studies did not require dose adjustments. Equal number of patients (24/53) required one dose adjustments while two-dose adjustment applied for 5 of 53 (9.4%). Twenty-one percent of the patients exhibited ll-lV aGVHD. The incidence of veno-occlusive disease (VOD) was in 3.8% of the 53 patients, while incidence of hemorrhagic cystitis (II-III) reached to 9.7%. Engraftment was successful in 98% of the 53 patients with relapse in 2% of cases. The probability of overall survival and disease-free survival at day 100 was 96% and 94%, respectively. In conclusion, therapeutic drug monitoring (TDM) and individualization of Bu dosage are essential to improve the efficacy and safety of busulfan-based regimen in Chinese pediatric HSCT recipients.

Is Salivary Busulfan the Cause of Oral Mucositis and the Changes in Salivary Antioxidant Enzymes After Hematopoietic Cell Transplantation?

BACKGROUND

To determine whether the busulfan (Bu) present in saliva during hematopoietic cell transplantation (HCT) conditioning correlates with oral mucositis and the changes in salivary antioxidant enzymes.

METHODS

Bu levels in the plasma and saliva of 19 patients who received HCTs were quantified. Salivary flow and salivary superoxide dismutase and catalase activities were measured during HCT. For the toxicity analysis of salivary Bu, an in vitro assay was conducted by exposing human keratinocytes to artificial saliva containing Bu.

RESULTS

Plasma and salivary Bu concentrations were very similar (rho = 0.92, P < 0.001). Salivary Bu concentration correlated with the degree of oral mucositis severity (rho = 0.391, P = 0.029) and was inversely proportional to salivary superoxide dismutase and catalase activities (rho = -0.458, P = 0.036; rho = -0.424, P = 0.043, respectively). Cells exposed to Bu-containing saliva had fewer viable cells (P < 0.01) and more apoptotic cells (P = 0.001) than those exposed to non-Bu-containing saliva.

CONCLUSIONS

Bu found in saliva during HCT conditioning was correlated with severe oral mucositis and the reduction in salivary antioxidative activity. Furthermore, Bu can be toxic to keratinocytes.

Comparing Dried Blood Spots and Plasma Concentrations for Busulfan Therapeutic Drug Monitoring in Children

BACKGROUND

Busulfan (Bu) is one of the conditioning regimen components for pediatric hematopoietic stem cell transplantation. Bu therapeutic drug monitoring (TDM) is essential for a successful treatment outcome and toxicity evasion. Dried blood spot (DBS) sampling is a rapid and simple method for Bu TDM, compared with conventional plasma sampling. This study evaluated the feasibility of using the DBS method for Bu TDM. The hematocrit (Hct) and conditioning day were also examined for their impact on the DBS method's performance.

METHODS

Venous blood collected from 6 healthy volunteers was diluted, using their plasma into 4 samples of varying Hct values. Each sample was spiked with Bu calibrators (300, 600, and 1400 ng/mL), prepared using DBS and dried plasma spot (DPS) sampling and analyzed using a validated liquid-chromatography tandem-mass spectrometry method. Clinical blood samples (n = 153) from pediatric patients (n = 15) treated with Bu (mainly from doses 1, 2, 5, and 9) were used to prepare paired volumetric DBS and DPS samples. A Bland-Altman plot and Deming regression were used to define the agreement between the paired DBS and DPS measurements. Passing-Bablok regression analyses investigated the effects of Hct and conditioning day on the linearity between both methods.

RESULTS

In vitro analyses showed good agreement between DBS and DPS measurements, with a mean difference of -5.4% and a 95% confidence interval on the limits of agreement of -15.3% to 4.6%. Clinical samples showed good correlation (Pearson correlation coefficient = 0.96; slope = 1.00) between the DBS and DPS methods. The DBS method met the clinical acceptance limits for clinical samples, with a bias <±20%. Bland-Altman plots showed good agreement, with only 5.8% of paired measurements exceeding the limits of agreement (±1.96 SD), although within its 95% confidence interval. Hct observations ranged from 21.7% to 34.7% and did not affect Bu concentrations measured from DBS in either the in vitro or in vivo studies.

CONCLUSIONS

These results show that DBS is a useful method for Bu TDM, provided samples are analyzed on the collection day. DBS sampling offers advantages over traditional plasma sampling in infants and younger children because only small volumes of blood are required.

The analysis of GSTA1 promoter genetic and functional diversity of human populations

GSTA1 encodes a member of a family of enzymes that function to add glutathione to target electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. GSTA1 has several functional SNPs within its promoter region that are responsible for a change in its expression by altering promoter function. This study aims to investigate distributions of GSTA1 promoter haplotypes across different human populations and to assess their impact on the expression of GSTA1. PHASE 2.1.1 was used to infer haplotypes and diplotypes of six GSTA1 promoter SNPs on 2501 individuals from 26 populations classified by the 1000 Genomes Project into five super-populations that included Africa (N = 660), America (N = 347), East Asia (N = 504), Europe (N = 502), and South Asia (N = 488). We used pairwise FST analysis to compare sub-populations and luciferase reporter assay (LRA) to evaluate the impact of each SNP on activation of transcription and interaction with other SNPs. The distributions of GSTA1 promoter haplotypes and diplotypes were significantly different among the different human populations. Three new promoter haplotypes were found in the African super-population. LRA demonstrated that SNPs at -52 and -69 has the most impact on GSTA1 expression, however other SNPs have a significant impact on transcriptional activity. Based on LRA, a new model of cis-elements interaction is presented. Due to the significant differences in GSTA1 diplotype population frequencies, future pharmacogenomics or disease-related studies would benefit from the inclusion of the complete GSTA1 promoter haplotype based on the newly proposed metabolic grouping derived from the LRA results.

Mucopolysaccharidosis Type I: Current Treatments, Limitations, and Prospects for Improvement

Mucopolysaccharidosis type I (MPS I) is a lysosomal disease, caused by a deficiency of the enzyme alpha-L-iduronidase (IDUA). IDUA catalyzes the degradation of the glycosaminoglycans dermatan and heparan sulfate (DS and HS, respectively). Lack of the enzyme leads to pathologic accumulation of undegraded HS and DS with subsequent disease manifestations in multiple organs. The disease can be divided into severe (Hurler syndrome) and attenuated (Hurler-Scheie, Scheie) forms. Currently approved treatments consist of enzyme replacement therapy (ERT) and/or hematopoietic stem cell transplantation (HSCT). Patients with attenuated disease are often treated with ERT alone, while the recommended therapy for patients with Hurler syndrome consists of HSCT. While these treatments significantly improve disease manifestations and prolong life, a considerable burden of disease remains. Notably, treatment can partially prevent, but not significantly improve, clinical manifestations, necessitating early diagnosis of disease and commencement of treatment. This review discusses these standard therapies and their impact on common disease manifestations in patients with MPS I. Where relevant, results of animal models of MPS I will be included. Finally, we highlight alternative and emerging treatments for the most common disease manifestations.

Total Body Irradiation Forever? Optimising Chemotherapeutic Options for Irradiation-Free Conditioning for Paediatric Acute Lymphoblastic Leukaemia

Total-body irradiation (TBI) based conditioning prior to allogeneic hematopoietic stem cell transplantation (HSCT) is generally regarded as the gold-standard for children >4 years of age with acute lymphoblastic leukaemia (ALL). Retrospective studies in the 1990's suggested better survival with irradiation, confirmed in a small randomised, prospective study in the early 2000's. Most recently, this was reconfirmed by the early results of the large, randomised, international, phase III FORUM study published in 2020. But we know survivors will suffer a multitude of long-term sequelae after TBI, including second malignancies, neurocognitive, endocrine and cardiometabolic effects. The drive to avoid TBI directs us to continue optimising irradiation-free, myeloablative conditioning. In chemotherapy-based conditioning, the dominant myeloablative effect is provided by the alkylating agents, most commonly busulfan or treosulfan. Busulfan with cyclophosphamide is a long-established alternative to TBI-based conditioning in ALL patients. Substituting fludarabine for cyclophosphamide reduces toxicity, but may not be as effective, prompting the addition of a third agent, such as thiotepa, melphalan, and now clofarabine. For busulfan, it's wide pharmacokinetic (PK) variability and narrow therapeutic window is well-known, with widespread use of therapeutic drug monitoring (TDM) to individualise dosing and control the cumulative busulfan exposure. The development of first-dose selection algorithms has helped achieve early, accurate busulfan levels within the targeted therapeutic window. In the future, predictive genetic variants, associated with differing busulfan exposures and toxicities, could be employed to further tailor individualised busulfan-based conditioning for ALL patients. Treosulfan-based conditioning leads to comparable outcomes to busulfan-based conditioning in paediatric ALL, without the need for TDM to date. Future PK evaluation and modelling may optimise therapy and improve outcome. More recently, the addition of clofarabine to busulfan/fludarabine has shown encouraging results when compared to TBI-based regimens. The combination shows activity in ALL as well as AML and deserves further evaluation. Like busulfan, optimization of chemotherapy conditioning may be enhanced by understanding not just the PK of clofarabine, fludarabine, treosulfan and other agents, but also the pharmacodynamics and pharmacogenetics, ideally in the context of a single disease such as ALL.

Total Body Irradiation or Chemotherapy Conditioning in Childhood ALL: A Multinational, Randomized, Noninferiority Phase III Study

Total body irradiation (TBI) before allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric patients with acute lymphoblastic leukemia (ALL) is efficacious, but long-term side effects are concerning. We investigated whether preparative combination chemotherapy could replace TBI in such patients.

Predicting the presence and mechanism of busulfan drug-drug interactions in hematopoietic stem cell transplantation using pharmacokinetic interaction network-based molecular structure similarity and network pharmacology

PURPOSE

This study aimed to predict the presence and mechanism of busulfan drug-drug interactions (DDIs) in hematopoietic stem cell transplantation (HSCT) using pharmacokinetic interaction (PKI) network-based molecular structure similarity and network pharmacology.

METHODS

Logistic function models were established to predict busulfan DDIs based on the assumption that an approved drug tends to interact with the drug used in HSCT (DH) if structurally similar to the drugs in the PKI network of the DH. The PKI network of the DH represented the association between drugs and the proteins related to the PK of the DH. The most appropriate model was applied to predict busulfan DDIs in HSCT. Candidate targets for busulfan DDIs and their interacting were identified by network pharmacology.

RESULTS

Six of the top ten predicted busulfan DDIs were clinically relevant and involved voriconazole, fludarabine, itraconazole, cyclophosphamide, metronidazole, and melphalan. Candidate targets for these DDIs were CYP450s (3A4, 2B6, 2C9, and 2C19), GSTs (GSTA1, GSTP1, GSTT1, and GSTM1), and ABC transporters (ABCB1, ABCC1, ABCC2, and ABCC3), in the targets of drug-induced liver injury (DILI). The networks of interacting proteins and candidate targets indicated the regulatory potential of pregnane X receptor (PXR), as a nuclear receptor. Enrichment analysis showed the metabolism of drugs and xenobiotics, glutathione metabolism, and bile secretion associated with busulfan DDIs and DILI.

CONCLUSIONS

This study has successfully predicted busulfan DDIs in HSCT through PKI-based molecular structure similarity. The mechanism of busulfan DDI and DILI was attributed mostly to CYP450s, GSTs, and ABC transporters, and PXR was identified as a potential target.

Review of the Pharmacokinetics and Pharmacodynamics of Intravenous Busulfan in Paediatric Patients

We aimed to review the pharmacokinetics (PK) of intravenous busulfan in paediatric patients, identify covariate factors influencing exposure, investigate evidence of changes in PK behaviour over time, and correlate exposure with efficacy and toxicity outcomes. A literature review was undertaken of original research published between 2007 and 2019, investigating the PK and pharmacodynamics (PD) of intravenous busulfan in patients ≤ 18 years of age. The review identified 41 publications characterising the PK, and 45 publications describing the PD, of busulfan. Median typical clearance (CL) was 0.22 L/h/kg and median typical volume of distribution was 0.69 L/kg. Patient weight, age, glutathione-S-transferase A1 (GSTA1) genotype and busulfan dosing day/time were the most commonly identified factors affecting CL. Of nine studies investigating changes in CL, seven reported reduced CL over the 4-day course of treatment. Exposure monitoring methods and therapeutic targets were heterogeneous across studies. Relationships between busulfan exposure and patient outcomes were observed in five studies. One study observed a cumulative area under the concentration-time curve over all days of treatment of between 78 and 101 mg/L·h, and two studies observed an average concentration at first dose of < 600 ng/mL improved overall survival, transplant-related mortality, or relapse. One study observed increased sinusoidal obstructive syndrome with maximum busulfan concentration > 1.88 ng/mL. Patient weight, age and GSTA1 genotype are important covariates to consider when individualising busulfan therapy. Reduced busulfan CL over time may need to be accounted for, particularly in patients not receiving phenytoin co-therapy. Standardised monitoring of busulfan exposure over the entire course of treatment and further investigation of the role of busulfan metabolites and pharmacogenomics is warranted.

Pharmacokinetic analysis for model-supported therapeutic drug monitoring of busulfan in Japanese pediatric hematopoietic stem cell transplantation recipients

This prospective observational study analyzed the pharmacokinetics of busulfan in Japanese children and evaluated the predicting accuracy of previous pediatric PPK models of busulfan. This study enrolled five patients (aged 2-12 years, BW 14-48 kg) receiving a busulfan-based conditioning regimen for hematopoietic stem cell transplantation at our hospital between January 2017 and December 2018. All patients received a 2-hour intravenous busulfan infusion four times daily for a total of 16 doses. After the infusions, 51 plasma samples were collected with the plasma busulfan concentration measured by liquid chromatography-tandem mass spectrometry. PPK model fitting was analyzed using the (%MPE) and the (%MAPE). Limited sampling strategies for estimating busulfan AUC were also evaluated. High interpatient variability was observed in the PK parameters. The most suitable PPK model that reflected our data was McCune's two-compartment model (%MPE -8.7, %MAPE 19.3). A combination sampling method using the busulfan concentration at 2 and 6 hours after the start of the first busulfan dose was found to be able to estimate AUC_4 day . These results provide useful information on busulfan therapeutic drug monitoring in the Japanese pediatric population.

Population pharmacokinetics of busulfan in Saudi pediatric patients undergoing hematopoietic stem cell transplantation

Background Busulfan is an antineoplastic drug that is used widely as part of a conditioning regimen in pediatric patients undergoing hematopoietic stem cell transplantation. It has a narrow therapeutic index and highly variable pharmacokinetics; therefore therapeutic drug monitoring is recommended to optimize busulfan dosing. Objective To study the population pharmacokinetics of busulfan in Saudi pediatric patients to optimize its dosing. Settings King Abdullah Specialist Children's Hospital in Riyadh, Saudi Arabia. Methods This pharmacokinetic observational study was conducted between January 2016 and December 2018. All pediatric patients receiving IV busulfan and undergoing routine therapeutic drug monitoring were included. Population pharmacokinetics modeling was conducted using Monolix2019R1. Pharmacokinetic data of busulfan in children. Results The study included 59 patients and 513 samples. The mean ± SD age was 6.10 ± 3.17 years, and the dose administered was 0.994 ± 0.15 mg/kg. The mean ± SD Cmax and area under the curve (AUC) were 900.60 ± 402.8 ng/mL and 1031.14 ± 300.75 µM min, respectively. Based on our simulations, the European Medicines Agency recommended dose were adequate for most patient's groups to achieve the conventional target of an AUC_0-tau of 900-1350 µM min. For patients in the lower weight group < 9 kg, higher doses were need at 1.2 mg/kg. With regards to the newly proposed target of AUC 78-101 mg h/mL, all of the doses we tested had low probability of achieving it. Conclusions Most of our patients had less than a proportional increase in busulfan concentration suggesting autoinduction. The high interindividual variability and autoinduction make dose adjustments challenging and AUC at steady state difficult to predict from the first dose. One approach to improve dose predictions is to use Bayesian dosing software. Based on our simulations, the European Medicines Agency recommended doses were adequate for most patient groups, except those in the lower (< 9 kg) and higher weight groups (> 34 kg).

Limited Sampling Strategies Supporting Individualized Dose Adjustment of Intravenous Busulfan in Children and Young Adults

BACKGROUND

Therapeutic drug monitoring (TDM) for busulfan supports dose adjustment during conditioning for stem cell transplantation. The authors aimed to develop and validate limited sampling strategies (LSS) of 4-5 samples for a precise estimation of the area under concentration (AUC)-time curve of busulfan, in plasma as an alternative to an intensive sampling strategy (ISS) requiring 9-10 samples.

METHODS

ISS TDM data from 297 patients (≤18 years of age) were used. AUCLSS was calculated using the trapezoidal rule and multiple linear regression (MLR). Unlike more complex modeling methods, MLR does not require sophisticated software or advanced training of personnel. MLR coefficients were estimated in the development subset containing randomly selected 50% of the records and were then used to calculate the AUCLSS of the remaining records (the validation subset). The agreement between dose adjustment recommendations (DAR) based on ISS and LSS, in the validation subset, was evaluated by a Bland-Altman analysis. A DAR deviating from an ISS-based reference by <15% was deemed acceptable.

RESULTS

Twelve LSSs were acceptable. Sampling at 0, 120, 180, and 240 minutes after the start of the second infusion (LSS15) yielded the best performance, with DAR deviating from the reference by <10% for 95% of cases; the AUCLSS was determined as follows: AUCLSS = 74.7954 × C(0) + 81.8948 × C(120) + 38.1771 × C(180) + 138.1404 × C(240) + 54.1837. This LSS and LSS13 performed similarly well in an independent external validation.

CONCLUSIONS

MLR-based estimates of AUCLSS provide DARs that deviate minimally from the reference. LSSs allow the reduction of patient discomfort, a ∼50% reduction of TDM-related workload for nursing staff and blood loss and a ∼25% reduction in laboratory workload. These benefits may encourage wider use of busulfan TDM, supporting safe and efficacious personalized dosing.

Busulfan Pharmacokinetics and Precision Dosing: Are Patients with Fanconi Anemia Different?

It is well known that pharmacokinetics (PK)-guided busulfan (BU) dosing increases engraftment rates and lowers hepatotoxicity in patients undergoing hematopoietic cell transplantation (HCT). However, there are no published PK data in patients with Fanconi anemia (FA), who are known to have baseline DNA repair defect and related inherent sensitivity to chemotherapy. In our prospective, multi-institutional study of alternative donor HCT for FA using chemotherapy-only conditioning, we replaced the single dose of total-body irradiation with BU at initial doses of 0.8 to 1.0 mg/kg and 0.6 to 0.8 mg/kg given i.v. every 12 hours for 4 doses. Patients received the first dose of i.v. busulfan on day -8, and blood levels for PK were obtained. PK samples were drawn following completion of infusion. BU PK levels were collected at 2 hours, 2 hours and 15 minutes, and 4, 5, 6, and 8 hours from the start of infusion. The remaining 3 doses of BU were given on days -7 and -6. Thirty-seven patients with available BU PK data with a median age of 9.2 years (range, 4.3 to 44 years) are included in the final analyses. The overall BU PK profile in patients with FA is similar to non-FA patients after considering their body weight. In our cohort, a strong correlation between BU clearance and weight supports current practice of per kilogram dosing. However, not surprisingly, we show that the disease (ie, host) sensitivity related to FA is the main determinant of total dose of BU that can be safely administered to patients in this high-risk population. On the basis of our results, we propose an optimal BU concentration at steady-state level of ≤350 ng/mL (equivalent to total cumulative exposure of 16.4 mg*h/L for 4 doses over 2 days) for patients with FA undergoing HCT. To our knowledge, this is the first and largest report of prospective BU PK in patients with FA undergoing HCT, providing an optimal BU target cutoff to achieve stable donor engraftment while avoiding excessive toxicity.

Personalized pharmacokinetic targeting with busulfan in allogeneic hematopoietic stem cell transplantation in infants with acute lymphoblastic leukemia

Individual busulfan (BU) dosing based on pharmacokinetic (PK) data is preferable for hematopoietic stem cell transplantation (HSCT) conditioning, but information on BU PK in infants is scarce. We report BU PK data on HSCT conditioning for infants with KMT2A-gene-rearrangement-positive acute lymphoblastic leukemia (MLL-r ALL). Infants showed wide variation in BU PK indices, such as clearance (CL) and volume of distribution (V_d) value, which are distributed more widely among those who received oral, rather than intravenous (IV), BU. Because the steady state concentration (C_ss) fluctuates readily in infants, dose re-adjustment based on PK at the initial administration was important even if the initial dose was determined by a PK test. HSCT can be performed safely within the C_ss range of 600-900 ng/mL per dose, although it was difficult to fit within the therapeutic index of BU. The clinical outcome of engraftment, graft-versus-host disease, adverse events, including sinusoidal obstruction syndrome, and survival did not correlate with the BU PK data, which paradoxically suggests that remaining within this C_ss range helped minimize transplant-related toxicities, while securing engraftment in infants with MLL-r ALL.

Use of busulfan in conditioning for allogeneic hematopoietic stem cell transplantation in adults: a survey by the Transplant Complications Working Party of the EBMT

A survey was carried out among EBMT centers about the use of busulfan for conditioning in allogeneic stem cell transplantation. Of 109 responding centers, 106 used busulfan for conditioning, 102 in conventional myeloablative doses, and 93 in reduced doses (RIC). The route of administration was mostly intravenous, but ~10% of the centers gave the drug orally. The number of doses in i.v. administration varied and was in myeloablative conditioning mostly one (50 centers) or four (43 centers) doses a day. Seventeen of the 106 centers used pharmacokinetics for dose adjustment in myeloablative conditioning, nine in RIC. The details of pharmacokinetic monitoring varied markedly. Three quarters of the centers reported adjusting the dose based on obesity in myeloablative conditioning and about 60% in RIC. The most common method for dose calculation was ideal body weight + 0.25 × (actual body weight - ideal body weight). In conclusion, the present survey showed marked heterogeneity in the current practices of busulfan administration for conditioning. The impact of the heterogeneity is not well known. Due to this and the scarcity of support from controlled clinical studies, no clear guidelines can be presented, but some prevailing policies to be recommended were identified.

Retrospective cohort study comparing the outcomes of intravenous busulfan vs. total-body irradiation after single cord blood transplantation

Limited to inadequate stem-cell doses, cord blood transplantation (UCBT) is accompanied by increased graft failure and delayed haematopoietic recovery. The conditioning regimen is critically important for engraftment, and numerous trials have been undertaken comparing the outcomes of IV Bu and TBI, but there are no comparative data for UCBT. We conducted a retrospective multicentre study to analyse the outcomes of IV Bu and TBI in UCBT patients with haematologic malignancies. Between 1 May, 2008 and 31 Mar, 31 2018, a total of 331 patients from the China Umbilical Cord Blood Transplantation Corporation (IV Bu, n = 131; TBI, n = 200) were evaluated. The cumulative incidence of neutrophil engraftment was 91.6% in the IV Bu/Cy cohort and 98.0% in the Cy/TBI cohort (P < 0.001). The median times to neutrophil engraftment were 16 and 19 days (P < 0.001), respectively. Multivariate analysis showed no statistical difference for nonrelapse mortality (hazard ratio [HR], 1.11; 95% confidence interval [CI], 0.66 to 1.86; P = 0.695), relapse (HR, 0.90; 95% CI, 0.50 to 1.60; P = 0.713) and overall survival (HR, 0.94; 95% CI, 0.61 to 1.44; P = 0.763) between the two conditioning regimens. Our results show that both IV Bu and TBI are valid myeloablative conditioning regimens for haematologic malignancy patients treated with UCBT.

Hematopoietic Stem Cell Transplantation for Mucopolysaccharidoses: Past, Present, and Future

Allogenic hematopoietic stem cell transplantation (HSCT) has proven to be a viable treatment option for a selected group of patients with mucopolysaccharidoses (MPS), including those with MPS types I, II, IVA, VI, and VII. Early diagnosis and timely referral to an expert in MPS are critical, followed by a complete examination and evaluation by a multidisciplinary team, including a transplantation physician. Treatment recommendations for MPS are based on multiple biological, sociological, and financial factors, including type of MPS, clinical severity, prognosis, present clinical signs and symptoms (disease stage), age at onset, rate of progression, family factors and expectations, financial burden, feasibility, availability, risks and benefits of available therapies such as HSCT, enzyme replacement therapy (ERT), surgical interventions, and other supportive care. International collaboration and data review are critical to evaluating the therapeutic efficacy and adverse effects of HSCT for MPS. Collaborative efforts to assess HSCT for MPS have been ongoing since the first attempt at HSCT in a patient with MPS reported in 1981. The accumulation of data since then has made it possible to identify early outcomes (ie, transplantation outcomes) and long-term disease-specific outcomes resulting from HSCT. The recent identification of predictive factors and the development of innovative regimens have significantly improved the outcomes of both engraftment failure and transplantation-related mortality. Assessment of long-term outcomes has considered a variety of factors, including type of MPS, type of graft, age at transplantation, and stage of disease progression, among others. Studies on long-term outcomes are considered a key factor in the use of HSCT in patients with MPS. These studies have shown the effects and limitations of HSCT on improving disease manifestations and quality of life. In this review, we summarize the efficacy, side effects, risks, and cost of HSCT for each type of MPS.

Accurate Prediction of Initial Busulfan Exposure Using a Test Dose With 2- and 6-Hour Blood Sampling in Adult Patients Receiving a Twice-Daily Intravenous Busulfan-Based Conditioning Regimen

This study aimed to predict the area under the curve (AUC) of the initial busulfan dose using a test dose with the sparse sampling scheme in adult patients who underwent hematopoietic cell transplant. A test dose of 0.8 mg/kg busulfan was used 2 days before twice-daily intravenous busulfan-based conditioning regimens were administered. The AUC and the clearance (CL) were calculated for both the test dose and the first dose (AUC_T , CL_T , AUC_1, and CL₁ ) by noncompartmental analysis. The sparse sampling schemes of the test dose were developed by Bayesian method based on the population pharmacokinetic model. The optimal sparse sampling schemes were determined by evaluating the mean prediction error, the root mean square error, the absolute mean prediction error, and Bland-Altman plot. The mean AUC₁ was 7.20 ± 1.48 mg • h/L, which ranged from 4.70 to 9.46 mg • h/L. The AUC₁ was below the therapeutic concentration of 7.38 mg • h/L in 45% (9 of 20) of the patients. The CL_T of 3.05 ± 0.56 mL/min/kg was not significantly different with the CL₁ of 3.03 ± 0.69 mL/min/kg (P = .901). A sampling scheme at 2 and 6 hours after the test dose was developed to predict the AUC_T (mean prediction error of 1.64%, root mean square error of 6.17%, and absolute mean prediction error of 4.94%). Additionally, the Bland-Altman plot showed that the 2-sampling scheme provided an acceptably accurate prediction of the AUC₁ . A test dose with a 2-sampling scheme was sufficient to personalize the initial busulfan dosing in hematopoietic cell transplant recipients.

Therapeutic Drug Monitoring of Busulfan for the Management of Pediatric Patients: Cross-Validation of Methods and Long-Term Performance

BACKGROUND

Busulfan (Bu) is an alkylating agent used as part of the conditioning regimen in pediatric patients before hematopoietic stem cell transplantation. Despite intravenous (IV) administration and dosing recommendations based on age and weight, reports have revealed interindividual variability in Bu pharmacokinetics and the outcomes of hematopoietic stem cell transplantation. In this context, adjusting doses to Bu's narrow therapeutic window is advised. We aimed to assess the utility of therapeutic drug monitoring (TDM) of Bu in children, the reliability of Bu quantification methods, and its stability in plasma when stored for up to 5 years.

METHODS

Eighteen patients from our TDM center (252 samples) were included. All of them received a 2-hour Bu IV infusion 4 times daily for a total of 16 doses. The first dose of Bu was age/weight-based, and the subsequent doses were adjusted from third or fifth dose onward based on the estimated first dose pharmacokinetic parameters to target steady-state concentrations (Css) of 600-900 ng/mL. The performance of our unit's high-performance liquid chromatography with tandem mass spectrometry method was assessed using a quality control (QC, 35 series) chart. International, multicenter, cross-validation test (n = 21) was conducted to validate different analytical methods. To assess Bu stability, regression analyses and Bland-Altman plots were performed on measurements at repeated time points on samples stored at -80°C for up to 5 years.

RESULTS

We observed a 4.2-fold interindividual variability in Bu Css after the first dose, with only 28% of children having a Css within the target range. During the 4 days of conditioning, 83% of children had their doses modified according to TDM recommendations. This achieved a Css within the target range in 75% of the children. Routine QC measurements were generally within the ±15% range around theoretical values, showing the optimal robustness of our center's analytical method. Two of the 21 Bu TDM centers returned inadequate results during cross-validation testing; both used a UV detection method. Storage at -80°C led to a fall in Bu content of 14.9% ± 13.4% at 2-4 years and of 20% ± 5% by 5 years (roverall = 0.92).

CONCLUSIONS

We conclude that TDM is an effective method of achieving targeted Bu levels in children. QC programs are crucial to monitoring and maintaining the quality of an analytical method.

Maximal concentration of intravenous busulfan as a determinant of veno-occlusive disease: a pharmacokinetic-pharmacodynamic analysis in 293 hematopoietic stem cell transplanted children

Veno-occlusive disease (VOD) is a severe adverse reaction to busulfan-containing regimens used in the preparation of children for hematopoietic stem cell transplantation (HSCT). We conducted a retrospective analysis of data to examine determinants of VOD in children who received IV busulfan for HSCT conditioning. Busulfan PK parameters as well as various indices (maximal concentration-Cmax, area under the concentration-time curve-AUC) were estimated using a validated Bayesian approach. The influence of available PK, demographic, and clinical variables on the incidence of VOD was evaluated by using logistic regression and classification and regression tree (CART) analyses. Among the 293 patients included, the mean age was 6.5 years and the mean actual body weight was 26.3 kg. The incidence of VOD was 25.6%. Busulfan Cmax as well as weight <9 kg or age <3 years were identified as independent predictors of VOD in logistic regression analysis. CART analysis identified busulfan Cmax over the entire regimen as the strongest predictor of VOD. This study suggests that busulfan-associated VOD is in part a concentration-dependent reaction. In addition, the youngest children showed the highest risk of VOD. These findings may have important implications for busulfan dosing and therapeutic drug monitoring practice in HSCT children.

Incorporation of GSTA1 genetic variations into a population pharmacokinetic model for IV busulfan in paediatric hematopoietic stem cell transplantation

AIMS

The aim of this study is to develop a population pharmacokinetic (PopPK) model for intravenous busulfan in children that incorporates variants of GSTA1, gene coding for the main enzyme in busulfan metabolism.

METHODS

Busulfan concentration-time data was collected from 112 children and adolescents (median 5.4 years old, range: 0.1-20) who received intravenous busulfan during the conditioning regimen prior to stem cell transplantation. Weight, sex, baseline disease (malignant vs. non-malignant), age, conditioning regimen and GSTA1 diplotypes were evaluated as covariates of pharmacokinetic parameters by using nonlinear mixed effects analysis. The ability to achieve the target AUC_24h (3600-6000 μM min^-1 ) was assessed by estimating the first dose based on the present PopPK model and by comparing the results with other available models in children.

RESULTS

A one-compartment model with first-order elimination best described the data. Allometric scaling of weight and a factor of busulfan metabolism maturation were included in the base model. GSTA1 diplotypes were found to be a significant covariate of busulfan clearance, which was 7% faster in rapid metabolizers and 12% slower in poor metabolizers, in comparison with normal ones. Busulfan doses calculated using the parameters of the proposed PopPK model were estimated to achieve the target AUC in 85.2% of the cases (95% CI 78.7-91.7%).

CONCLUSION

This is the first PopPK for busulfan that successfully incorporated GSTA1 genotype in a paediatric population. Its use may contribute to better prediction of busulfan exposure in children and adolescents since the first dose, by tailoring the dose according to the individual metabolic capacity.

Pharmacokinetics-adapted Busulfan-based myeloablative conditioning before unrelated umbilical cord blood transplantation for myeloid malignancies in children

Unrelated umbilical cord blood transplantation (UCBT) is an alternative to provide transplants in children with acute leukemia or myelodysplastic syndrome who lack a related donor. Intravenous Busulfan (Bu) combined with therapeutic drug monitoring-guided dosing has been increasingly used, with more predictable bioavailability and better outcomes comparing to oral Bu. There is still an important variation in Bu pharmacokinetic between patients that is associated with an increased risk of toxicity and graft failure. The objective of the study was to analyze the impact of first-dose pharmacokinetic adapted myeloablative conditioning regimen of intravenous Bu on the different outcomes after transplantation. Data of 36 children who underwent allogeneic HSCT with Bu plus a second alkylating agent at Sainte Justine Hospital in Montreal, Canada, between December 2000 and April 2012 were analyzed. For children with high risk myeloid malignancies receiving an UCBT, first dose Bu pharmacokinetic seems to be a significant prognostic factor, influencing neutrophil (100% vs 67.9%) and platelet recovery (95.5% vs 70.5%), non-relapse mortality (0% vs 18.6%), EFS (64% vs 28.6%) and OS (81.3% vs 37.5%) for a first-dose steady-state concentration (Css) <600ng/mL vs >600ng/mL, respectively. These data reinforce the importance of Busulfan therapeutic drug monitoring-guided dosing in pediatric HSCT patients, particularly in the context of UCBT.

Intravenous Busulfan Compared with Total Body Irradiation Pretransplant Conditioning for Adults with Acute Lymphoblastic Leukemia

Total body irradiation (TBI) has been included in standard conditioning for acute lymphoblastic leukemia (ALL) before hematopoietic cell transplantation (HCT). Non-TBI regimens have incorporated busulfan (Bu) to decrease toxicity. This retrospective study analyzed TBI and Bu on outcomes of ALL patients 18-60 years old, in first or second complete remission (CR), undergoing HLA-compatible sibling, related, or unrelated donor HCT, who reported to the Center for International Blood and Marrow Transplant Research from 2005 to 2014. TBI plus etoposide (25%) or cyclophosphamide (75%) was used in 819 patients, and intravenous Bu plus fludarabine (41%), clofarabine (30%), cyclophosphamide (15%), or melphalan (13%) was used in 299 patients. Bu-containing regimens were analyzed together, since no significant differences for patient outcomes were noted between them. Bu patients were older, with better performance status; took longer to achieve first CR and receive HCT; were treated more recently; and were more likely to receive peripheral blood grafts, antithymocyte globulin, or tyrosine kinase inhibitors. With median follow-up of 3.6 years for Bu and 5.3 years for TBI, adjusted 3-year outcomes showed treatment-related mortality Bu 19% versus TBI 25% (P = .04); relapse Bu 37% versus TBI 28% (P = .007); disease-free survival (DFS) Bu 45% versus TBI 48% (P = .35); and overall survival (OS) Bu 57% versus TBI 53% (P = .35). In multivariate analysis, Bu patients had higher risk of relapse (relative risk, 1.46; 95% confidence interval, 1.15 to 1.85; P = .002) compared with TBI patients. Despite the higher relapse, Bu-containing conditioning led to similar OS and DFS following HCT for ALL.

Treosulfan and Fludarabine Conditioning for Hematopoietic Stem Cell Transplantation in Children with Primary Immunodeficiency: UK Experience

We previously published results for 70 children who received conditioning with treosulfan and cyclophosphamide (n = 30) or fludarabine (n = 40) before undergoing hematopoietic stem cell transplantation (HSCT) for primary immunodeficiency (PID). Toxicity was lower and T cell chimerism was better in the patients receiving fludarabine, but cohort numbers were relatively small and follow-up was short. Here we report outcomes of 160 children who received homogeneous conditioning with treosulfan, fludarabine, and, in most cases, alemtuzumab (n = 124). The median age at transplantation was 1.36 years (range, .09 to 18.25 years). Donors included 73 matched unrelated, 54 1 to 3 antigen-mismatched unrelated, 12 matched sibling, 17 other matched family, and 4 haploidentical donors. Stem cell source was peripheral blood stem cells (PBSCs) in 70, bone marrow in 49, and cord blood in 41. Median duration of follow-up was 4.3 years (range, .8 to 9.4 years). Overall survival was 83%. No patients had veno-occlusive disease. Seventy-four patients (46%) had acute GVHD, but only 14 (9%) greater than grade II. Four patients underwent successful retransplantation for graft loss or poor immune reconstitution. Another patient experienced graft rejection and died. There was no association between T cell chimerism >95% and stem cell source, but a significant association was seen between myeloid chimerism >95% and use of PBSCs without an increased risk of significant GVHD compared with other sources. All 11 patients with severe combined immunodeficiency diagnosed at birth were alive at up to 8.7 years of follow-up. Long-term studies are needed to determine late gonadotoxic effects, and pharmacokinetic studies are needed to identify whether specific targeting is advantageous. The combination of treosulfan, fludarabine, and alemtuzumab is associated with excellent results in HSCT for PID.

Population pharmacokinetics analysis of intravenous busulfan in Chinese patients undergoing hematopoietic stem cell transplantation

There are several reports describing population pharmacokinetic (popPK) models of busulfan (BU). However, limited information is available in Chinese hematopoietic stem cell transplantation (HSCT) patients. The present study aimed to establish a popPK model of intravenous BU in Chinese HSCT patients for individualized drug therapy. The popPK model of BU was developed from a total of 284 concentration-time points from 53 patients. The effects of demographic and biochemical covariates were investigated by nonlinear mixed effect model (NONMEM) software. Plots, visual predictive check (VPC), bootstrap and normalized prediction distribution error (NPDE) were performed to determine the stability and the reliability of the final model. A one-compartment model with first-order elimination process was confirmed as the final structural model for BU. For a typical patient whose body surface area (BSA) is 1.7 m² , the population typical values of CL and Vd were 11.86 L/h, and 48.2 L, respectively. The result suggested BSA showed significant influence on CL and Vd (P<.001). Plots revealed the final model was performing a goodness fit. The steady rate verified by bootstrap was 100%, relative deviation was less than 4.00%, estimated value of final model was in the 95% confidence interval (CI). The VPC results showed the observed values were almost all positioned within the 5th and 95th CIs. The mean and variance of the NPDE were 0.0363 (Wilcoxon signed-rank test, 0.298) and 0.877 (Fisher variance test, 0.134; SW test of normality, 0.108), respectively. The global adjusted P value was 0.305, which indicated that the prediction of the BU popPK model was adequate. A physician-friendly Microsoft Excel-base tool was implemented using the final popPK model for designing individualized dosing regimens.

GSTA1 diplotypes affect busulfan clearance and toxicity in children undergoing allogeneic hematopoietic stem cell transplantation: a multicenter study

Busulfan (BU) dose adjustment following therapeutic drug monitoring contributes to better outcome of hematopoietic stem cell transplantation (HSCT). Further improvement could be achieved through genotype-guided BU dose adjustments. To investigate this aspect, polymorphism within glutathione S transferase genes were assessed. Particularly, promoter haplotypes of the glutathione S transferase A1 (GSTA1) were evaluated in vitro, with reporter gene assays and clinically, in a pediatric multi-center study (N =138) through association with BU pharmacokinetics (PK) and clinical outcomes. Promoter activity significantly differed between the GSTA1 haplotypes (p<0.001) supporting their importance in capturing PK variability. Four GSTA1 diplotype groups that significantly correlated with clearance (p=0.009) were distinguished. Diplotypes underlying fast and slow metabolizing capacity showed higher and lower BU clearance (ml/min/kg), respectively. GSTA1 diplotypes with slow metabolizing capacity were associated with higher incidence of sinusoidal obstruction syndrome, acute graft versus host disease and combined treatment-related toxicity (p<0.0005). Among other GST genes investigated, GSTP1 313GG correlated with acute graft versus host disease grade 1-4 (p=0.01) and GSTM1 non-null genotype was associated with hemorrhagic cystitis (p=0.003). This study further strengthens the hypothesis that GST diplotypes/genotypes could be incorporated into already existing population pharmacokinetic models for improving first BU dose prediction and HSCT outcomes. (N^o Clinicaltrials.gov identifier: NCT01257854. Registered 8 December 2010, retrospectively registered).

GSTA1 Genetic Variants and Conditioning Regimen: Missing Key Factors in Dosing Guidelines of Busulfan in Pediatric Hematopoietic Stem Cell Transplantation

Busulfan (Bu) is a key component of conditioning regimens used before hematopoietic stem cell transplantation (SCT) in children. Different predictive methods have been used to calculate the first dose of Bu. To evaluate the necessity of further improvements, we retrospectively analyzed the currently available weight- and age-based guidelines to calculate the first doses in 101 children who underwent allogenic SCT in CHU Sainte-Justine, Montreal, after an intravenous Bu-containing conditioning regimen according to genetic and clinical factors. The measured areas under the curve (AUCs) were within target (900 to 1500 µM/min) in 38.7% of patients after the administration of the first dose calculated based on age and weight, as locally recommended. GSTA1 diplotypes linked to poor Bu metabolism (G3) and fludarabine-containing regimens were the only factors associated with AUC within target (OR, 4.7 [95% CI, 1.1 to 19.8, P = .04]; and OR, 9.9 [95% CI, 1.6 to 61.7, P = .01], respectively). From the 11 methods selected for dose calculation, the percentage of AUCs within the target varied between 16% and 74%. In some models G3 was associated with AUCs within the therapeutic and the toxic range, whereas rapid metabolizers (G1) were correlated with subtherapeutic AUCs when different methods were used. These associations were confirmed by clearance-prediction analysis, in which GSTA1 diplotypes consistently influenced the prediction errors of the methods. These findings suggest that these factors should be considered in Bu dose prediction in addition to the anthropometric data from patients. Furthermore, our data indicated that GSTA1 diplotypes was a factor that should be included in future population pharmacokinetic models, including similar conditioning regiments, to improve the prediction of Bu exposure after its initial dose.

The Association of Combined GSTM1 and CYP2C9 Genotype Status with the Occurrence of Hemorrhagic Cystitis in Pediatric Patients Receiving Myeloablative Conditioning Regimen Prior to Allogeneic Hematopoietic Stem Cell Transplantation

Hemorrhagic cystitis (HC) is one of the complications of busulfan-cyclophosphamide (BU-CY) conditioning regimen during allogeneic hematopoietic stem cell transplantation (HSCT) in children. Identifying children at high risk of developing HC in a HSCT setting could facilitate the evaluation and implementation of effective prophylactic measures. In this retrospective analysis genotyping of selected candidate gene variants was performed in 72 children and plasma Sulfolane (Su, water soluble metabolite of BU) levels were measured in 39 children following treatment with BU-CY regimen. The cytotoxic effects of Su and acrolein (Ac, water soluble metabolite of CY) were tested on human urothelial cells (HUCs). The effect of Su was also tested on cytochrome P 450 (CYP) function in HepaRG hepatic cells. Cumulative incidences of HC before day 30 post HSCT were estimated using Kaplan–Meier curves and log-rank test was used to compare the difference between groups in a univariate analysis. Multivariate Cox regression was used to estimate hazard ratios with 95% confidence intervals (CIs). Multivariate analysis included co-variables that were significantly associated with HC in a univariate analysis. Cumulative incidence of HC was 15.3%. In the univariate analysis, HC incidence was significantly (p < 0.05) higher in children older than 10 years (28.6 vs. 6.8%) or in children with higher Su levels (>40 vs. <11%) or in carriers of both functional GSTM1 and CYP2C9 (33.3 vs. 6.3%) compared to the other group. In a multivariate analysis, combined GSTM1 and CYP2C9 genotype status was associated with HC occurrence with a hazards ratio of 4.8 (95% CI: 1.3–18.4; p = 0.02). Ac was found to be toxic to HUC cells at lower concentrations (33 μM), Su was not toxic to HUC cells at concentrations below 1 mM and did not affect CYP function in HepaRG cells. Our observations suggest that pre-emptive genotyping of CYP2C9 and GSTM1 may aid in selection of more effective prophylaxis to reduce HC development in pediatric patients undergoing allogeneic HSCT.

Article summary:

(1) Children carrying functional alleles in GSTM1 and CYP2C9 are at high risk for developing hemorrhagic cystitis following treatment with busulfan and cyclophosphamide based conditioning regimen.

(2) Identification of children at high risk for developing hemorrhagic cystitis in an allogeneic HSCT setting will enable us to evaluate and implement optimal strategies for its prevention.

Trial registration: This study is a part of the trail “clinicaltrials.gov identifier: NCT01257854.”

Mortality after hematopoietic stem cell transplantation for severe mucopolysaccharidosis type I: the 30-year University of Minnesota experience

BACKGROUND AND AIM

Mucopolysaccharidosis IH (MPS IH, Hurler syndrome) naturally leads to death within the first decade of life, primarily from cardiac and pulmonary causes. To determine how hematopoietic stem cell transplantation (HSCT) has altered mortality, we analyzed our institution's 30-year experience of patients with MPS IH undergoing HSCT.

METHODS

Using chart review and the National Death Index, we determined survival status of 134 patients (males = 69) with MPS IH transplanted between 9/16/1983 and 7/25/2013 on 12/31/2013. Analysis included descriptive statistics, Kaplan-Meier curves, and regression analysis by Cox proportional hazards model.

RESULTS

Overall survival (95% CI) at one- and 25-years was 70% (62-78%) and 37% (19-55%), respectively. From 2004 onward, overall survival at one- and 8-years was 84% (73-96%) and 81% (69-94%), respectively, compared to 65% (55-74%) and 57% (47-67%) prior to 2004 (Log-rank p = 0.032). Regardless of era, male survival was significantly better than female (HR 0.40, [95% CI: 0.21-0.74], p = 0.004). The cumulative incidence of death (95% CI) at 25 years was 63% (45-81%); incidence of pulmonary-related death was the highest at 27% (10-41%) compared to 8% (0.3-16%) for cardiac, 12% (6-17%) for infectious disease, and 16% (3-27%) from other complications.

CONCLUSIONS

HSCT has increased survival in MPS IH beyond the third decade of life and decreased the incidence of cardiac mortality, but deaths after the third year post-HSCT occur in excess of expected US mortality. It is important to determine if improved transplant strategies since 2004 result in better long-term survival in the current patient population.

Association of busulfan exposure with survival and toxicity after haemopoietic cell transplantation in children and young adults: a multicentre, retrospective cohort analysis

BACKGROUND

Intravenous busulfan combined with therapeutic drug monitoring to guide dosing improves outcomes after allogeneic haemopoietic cell transplantation (HCT). The best method to estimate busulfan exposure and optimum exposure in children or young adults remains unclear. We therefore assessed three approaches to estimate intravenous busulfan exposure (expressed as cumulative area under the curve [AUC]) and associated busulfan AUC with clinical outcomes in children or young adults undergoing allogeneic HCT.

METHODS

In this retrospective analysis, patients from 15 centres in the Netherlands, USA, Canada, Switzerland, UK, Italy, Germany, and Australia who received a busulfan-based conditioning regimen between March 18, 2001, and Feb 12, 2015, were included. Cumulative AUC was calculated by numerical integration using non-linear mixed effect modelling (AUC_NONMEM), non-compartmental analysis (AUC from 0 to infinity [AUC_0-∞] and to the next dose [AUC_0-τ]), and by individual centres using various approaches (AUC_centre). The main outcome of interest was event-free survival. Other outcomes of interest were graft failure or relapse, or both; transplantation-related mortality; acute toxicity (veno-occlusive disease or acute graft versus-host disease [GvHD]); chronic GvHD; overall survival; and chronic-GvHD-free event-free survival. We used propensity-score-adjusted Cox proportional hazard models, Weibull models, and Fine-Gray competing risk regressions for statistical analyses.

FINDINGS

790 patients were enrolled, 674 of whom were included: 274 (41%) with malignant and 400 (59%) with non-malignant disease. Median age was 4·5 years (IQR 1·4-10·7). The median busulfan AUC_NONMEM was 74·4 mg × h/L (95% CI 31·1-104·6), which correlated with the standardised method AUC_0-∞ (r²=0·74), but the latter correlated poorly with AUC_centre (r²=0·35). Estimated 2-year event-free survival was 69·7% (95% CI 66·2-73·0). Event-free survival at 2 years was 77·0% (95% CI 72·1-82·9) in the 257 patients with an optimum intravenous busulfan AUC of 78-101 mg × h/L compared with 66·1% (60·9-71·4) in the 235 patients at the low historical target of 58-86 mg × h/L and 49·5% (29·2-66·0) in the 44 patients with a high (>101 mg × h/L) busulfan AUC (p=0·011). Compared with the low AUC group, graft failure or relapse occurred less frequently in the optimum AUC group (hazard ratio [HR] 0·57, 95% CI 0·39-0·84; p=0·0041). Acute toxicity (HR 1·69, 1·12-2·57; p=0·013) and transplantation-related mortality (2·99, 1·82-4·92; p<0·0001) were significantly higher in the high AUC group (>101 mg × h/L) than in the low AUC group (<78 mg × h/L), independent of indication; no difference was noted between AUC groups for chronic GvHD (<78 mg × h/L vs ≥78 mg × h/L, HR 1·30, 95% CI 0·73-2·33; p=0·37).

INTERPRETATION

Improved clinical outcomes are likely to be achieved by targeting the busulfan AUC to 78-101 mg × h/L using a new validated pharmacokinetic model for all indications.

FUNDING

Research Allocation Program and the UCSF Helen Friller Family Comprehensive Cancer Center and the Mt Zion Health Fund of the University of California, San Francisco.

Clinical pharmacy service practice in a Chinese tertiary hospital

Clinical pharmacy service is focused on the rationality and safety of medication therapy. Clinical pharmacists play an important role in designing therapeutic regimen, preventing medication errors, reducing the incidence of adverse drug reaction, and saving medical costs. Although clinical pharmacy service in China is in its early stage, its development is rapid. In this manuscript, the working model of clinical pharmacists in a Chinese tertiary hospital is introduced, including ward rounds, consultation, stewardship of antimicrobial therapy, drug adverse reaction monitoring, therapeutic drug monitoring, clinical pharmacokinetics and pharmacogenetics, and training system. With the efforts of clinical pharmacists, there will be a significant increase in the optimization of medication therapy and a notable reduction in preventable adverse drug events as well as health-care cost in China.

Personalizing Busulfan-Based Conditioning: Considerations from the American Society for Blood and Marrow Transplantation Practice Guidelines Committee

The Practice Guidelines Committee of the American Society of Blood or Marrow Transplantation (ASBMT) sought to develop an evidence-based review about personalizing busulfan-based conditioning. The Committee sought to grade the relevant published studies (June 1, 2008 through March 31, 2016) according to criteria set forth by the Steering Committee for Evidence Based Reviews from ASBMT. Unfortunately, the published literature was too heterogeneous and lacked adequately powered and sufficiently controlled studies for this to be feasible. Despite this observation, the continued interest in this topic led the Practice Guidelines Committee to develop a list of most frequently asked questions (FAQs) regarding personalized busulfan dosing. This "Considerations" document is a list of these FAQs and their responses, addressing topics of practical relevance to hematopoietic cell transplantation clinicians.

Use of an Oral Busulfan Test Dose in Patients Undergoing Hematopoietic Stem Cell Transplantation Treated With or Without Fludarabine

This study investigated the importance of an oral test dose for busulfan (BU) dose adjustment before a conditioning regimen for hematopoietic stem-cell transplantation (HSCT) and the effect of fludarabine (FLU) on the oral BU pharmacokinetics evaluated after the fifth treatment dose (first BU dose on day 2 of treatment). Twenty-eight patients treated with oral BU (1 mg/kg every 6 hours for 4 days) were divided into 2 groups according to the concomitant administration of FLU (n = 15; 30 mg/m² for 5 days) or subsequent administration of cyclophosphamide (CY) (n = 13; 60 mg/kg for 2 days). On the day prior to the beginning of the conditioning regimen, blood samples were collected (0-6 hours) after administration of an oral BU test dose of 0.25 mg/kg. Busulfan was quantified in plasma samples by LC-MS/MS, and the pharmacokinetic parameters were calculated using WinNonlin software. Blood samples were collected between the fifth and sixth treatment dose to confirm the mean plasma steady-state concentration (C_ss ) of BU. The AUC_0-6 and apparent clearance of BU did not differ (P < .05) between the groups receiving FLU and CY. In 81% of the patients who received BU doses adjusted based on the test dose (n = 21), the C_ss was within the target range of 600-900 ng/mL. No association was observed between BU AUC_0-6 and clinical outcome in the study group (n = 28). The results suggest that in concomitant administration of FLU and BU during conditioning regimens for HSCT, changes in BU dose should be considered only after the administration of the fifth BU dose.

European Society for Blood and Marrow Transplantation Analysis of Treosulfan Conditioning Before Hematopoietic Stem Cell Transplantation in Children and Adolescents With Hematological Malignancies

BACKGROUND

Standard myeloablative conditioning regimens for children with hematological malignancies undergoing allogeneic HSCT are based mainly on total body irradiation or busulfan. Their serious short- and long-term side effects warranted the exploration of less toxic alternatives. Treosulfan is increasingly used for adults and children before HSCT due to its potent immunosuppressive and cytotoxic effects combined with low organ toxicity.

PROCEDURE

To further investigate the role of treosulfan conditioning in children, the EBMT Pediatric diseases working party performed a retrospective analysis of 193 children with hematological malignancies (ALL n = 71, AML n = 47, MDS/MPS n = 40, other leukemia/lymphoma n = 25) undergoing allogeneic HSCT following treosulfan between January 2005 and July 2010.

RESULTS

Early regimen-related toxicity was low and mainly gastrointestinal. Veno-occlusive disease and neurological toxicity were rare. There was no association of toxicity with type of disease or treosulfan dose. High-grade early toxicity was not higher in infants or patients undergoing second or later transplantation. Treatment related mortality was low at 14%. Three-year event-free survival was 45 ± 4% and not significantly influenced by number of transplants, however it appeared to be significantly better for infants (P = 0.022). When compared to treosulfan plus fludarabine, the combination of treosulfan, fludarabine and an alkylator (either thiotepa or melphalan) resulted in significantly better overall survival (OS, P = 0.048) and a trend toward better EFS.

CONCLUSIONS

Treosulfan based conditioning is a safe and effective approach for children with hematological malignancies, including and importantly for infants and those patients undergoing second or later transplantation.

Should busulfan therapeutic range be narrowed in pediatrics? Experience from a large cohort of hematopoietic stem cell transplant children

Busulfan, the corner stone of hematopoietic stem cell transplantation regimens, has a narrow therapeutic window. Therapeutic drug monitoring (TDM)-guided dosing to reach the conventional area under the concentration-time curve (AUC) target range of 900-1500 μmol min/L is associated with better outcomes. We report our experience with busulfan TDM in a large cohort of children. The aims were to investigate the relevance of using a more restricted therapeutic range and investigate the association between busulfan therapeutic range and clinical outcome. This study includes 138 children receiving 16 doses of intravenous busulfan, with the first dose assigned based on weight and doses adjusted to a local AUC target range of 980-1250 μmol min/L. Busulfan TDM combined with model-based dose adjustment was associated with an increased probability of AUC target attainment, for both target range: 90.8% versus 74.8% for the conventional target range and 66.2% versus 43.9% for the local target range (P<0.001). The median follow-up was 56.2 months. Event-free survival was 88.5%, overall survival was 91.5% and veno-occlusive disease occurred in 18.3% of patients. No difference was observed for clinical outcomes depending on the selected target range. Pharmacokinetic monitoring and individualization of busulfan dosage regimen are useful in improving target attainment, but using a restricted target range has no impact on clinical outcomes.

Personalizing chemotherapy dosing using pharmacological methods

PURPOSE

Given the toxic nature and narrow therapeutic index of traditional chemotherapeutics, better methods of dose and therapy selection are critical. Pharmacological methods, including pharmacogenomics and pharmacokinetics, offer a practical method to enrich drug exposure, reduce toxicity, and improve quality of life for patients.

METHODS

PubMed and key abstracts from the American Society of Clinical Oncology (ASCO) and American Association for Cancer Research (AACR) were searched until July 2015 for clinical data relating to pharmacogenomic- and/or pharmacokinetic-guided dosing of anticancer drugs.

RESULTS

Based on the results returned from a thorough search of the literature and the plausibility of utilizing pharmacogenomic and/or pharmacokinetic methods to personalize chemotherapy dosing, we identified several chemotherapeutic agents with the potential for therapy individualization. We highlight the available data, clinical validity, and utility of using pharmacogenomics to personalize therapy for tamoxifen, 5-fluorouracil, mercaptopurine, and irinotecan, in addition to using pharmacokinetics to personalize dosing for 5-fluorouracil, busulfan, methotrexate, taxanes, and topotecan.

CONCLUSION

A concerted effort should be made by researchers to further elucidate the role of pharmacological methods in personalizing chemotherapy dosing to optimize the risk-benefit profile. Clinicians should be aware of the clinical validity, utility, and availability of pharmacogenomic- and pharmacokinetic-guided therapies in clinical practice, to ultimately allow optimal dosing for each and every cancer patient.

Chemotherapy-related complications in the kidneys and collecting system: an imaging perspective

Nephrotoxicity is a common adverse effect of many chemotherapeutic agents. The agents most commonly associated with chemotherapy-associated nephrotoxicity are methotrexate, semustine, streptozocin, mithramycin, and cisplatin. Certain chemotherapeutic agents have adverse effects on the kidneys and urothelium that can be visualized radiographically, including cystic change, interstitial nephritis, papillary necrosis, urothelial changes, haemorrhagic cystitis, acute tubular necrosis, and infarction. This review focuses on imaging features identifying complications of chemotherapy in the kidneys and collecting system and provides didactic cases to alert referring clinicians.

TEACHING POINTS

• Nephrotoxicity is a common adverse effect of many chemotherapeutic agents. • Chemotherapies have adverse renal and urothelial effects that can be visualized radiographically. • Crizotinib use can result in the development of complex renal cysts.

Single Daily Busulfan Dosing for Infants with Nonmalignant Diseases Undergoing Reduced-Intensity Conditioning for Allogeneic Hematopoietic Progenitor Cell Transplantation

Busulfan (Bu) is widely used in conditioning regimens for infants undergoing allogeneic hematopoietic progenitor cell transplantation (HPCT), but the best approach to administer Bu in this population is still unknown. Here, we report a single-center experience of the use of a test dose to guide dose adjustment of intravenous (i.v.) Bu therapy in infants. Between 2004 and 2013, 33 infants younger than 1 year with nonmalignant conditions received allogeneic peripheral blood or cord blood HPCT after a reduced-intensity conditioning (RIC) regimen consisting of fludarabine, antithymocyte globulin, and 2 single daily doses of i.v. Bu. Pharmacokinetic results of a test dose of i.v. Bu (.8 mg/kg) were used to determine the dose of 2 single daily i.v. Bu regimen doses, adjusted to target an area under the curve (AUC) of 4000 μMol*minute per day in a first cohort (n = 12) and 5000 μMol*minute in a second cohort (n = 21). The mean Bu clearance in our infant patients was found to be 3.67 ± 1.03 mL/minute/kg, and the test dose clearance was highly predictive of the regimen dose clearance. The mean AUC achieved after the first single daily regimen dose was 3951 ± 1239 in the AUC 4000 cohort and 4884 ± 766 for the AUC 5000 cohort. No patient in either cohort developed hepatic sinusoidal obstructive syndrome or seizures attributable to Bu. Primary graft failure occurred in 4 patients and secondary graft failure occurred in 3, predominantly in the AUC 4000 cohort (6 of 7). Among the engrafted patients (n = 28), 16 achieved full donor chimerism and 9 patients attained stable mixed chimerism. Overall survival of patients at 6 years after transplantation was 59.5% for the AUC 4000 cohort and 85.4% for the AUC 5000 cohort, with primary graft failure in the first cohort being a major contributor to morbidity. Logistic regression analysis showed that the risk of graft failure increased significantly if cord blood hematopoietic progenitor cells were used or if total Bu exposure was below 4000 μMol*minute per day for 2 days. The difference in clinical outcomes between the 2 cohorts supports the conclusion that targeting a higher Bu AUC of 5000 μMol*minute per day for 2 days improves donor engraftment in infants with nonmalignant conditions undergoing RIC HPCT without increasing toxicity. Measuring i.v. Bu pharmokinetics using a test dose allows timely adjustment of single daily regimen doses and optimization of total Bu exposure, resulting in an effective and safe regimen for these infants.