Impact of conditioning regimen in allogeneic hematopoetic stem cell transplantation for children with acute myelogenous leukemia beyond first complete remission: a pediatric blood and marrow transplant consortium (PBMTC) study

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.

Busulfan systemic exposure and its relationship with efficacy and safety in hematopoietic stem cell transplantation in children: a meta-analysis

Background

Busulfan (Bu) is a key component of several conditioning regimens used before hematopoietic stem cell transplantation (HSCT). However, the optimum systemic exposure (expressed as the area under the concentration-time curve [AUC]) of Bu for clinical outcome in children is controversial.

Methods

Research on pertinent literature was carried out at PubMed, EMBASE, Web of science, the Cochrane Library and ClinicalTrials.gov. Observational studies were included, which compared clinical outcomes above and below the area under the concentration-time curve (AUC) cut-off value, which we set as 800, 900, 1000, 1125, 1350, and 1500 μM × min. The primary efficacy outcome was notable in the rate of graft failure. In the safety outcomes, incidents of veno-occlusive disease (VOD) were recorded, as well as other adverse events.

Results

Thirteen studies involving 548 pediatric patients (aged 0.3–18 years) were included. Pooled results showed that, compared with the mean Bu AUC (i.e., the average value of AUC measured multiple times for each patient) of > 900 μM × min, the mean AUC value of < 900 μM × min significantly increased the incidence of graft failure (RR = 3.666, 95% CI: 1.419, 9.467). The incidence of VOD was significantly decreased with the mean AUC < 1350 μM × min (RR = 0.370, 95% CI: 0.205–0.666) and < 1500 μM × min (RR = 0.409, 95% CI: 0182–0.920).

Conclusions

In children, Bu mean AUC above the cut-off value of 900 μM × min (after every 6-h dosing) was associated with decreased rates of graft failure, while the cut-off value of 1350 μM × min were associated with increased risk of VOD, particularly for the patients without VOD prophylaxis therapy. Further well-designed prospective and multi centric randomized controlled trials with larger sample size are necessary before putting our result into clinical practices.

Comparison of conditioning regimens for autologous stem cell transplantation in children with acute myeloid leukemia: A nationwide retrospective study in Japan

BACKGROUND

Indications for hematopoietic stem cell transplantation (HSCT) have decreased with the improvement in chemotherapy for pediatric acute myeloid leukemia (AML) in the last decade. We conducted reevaluation of autologous HSCT (AHSCT) to compare myeloablative conditioning (MAC) regimens for pediatric AML without the need for consideration of toxicities caused by allogeneic immune reactions.

PROCEDURE

This retrospective study analyzed the clinical outcomes of 220 children with AML who underwent consecutive AHSCT between 1989 and 2002 in Japan by the national prospective registry. The transplantation outcomes of various conditioning regimens were compared.

RESULTS

The median follow-up period of the survivors was 160 months. The clinical outcomes of busulfan + cyclophosphamide ± etoposide or busulfan + melphalan regimens were significantly superior compared with other busulfan-based and total body irradiation-based regimens (leukemia-free survival [LFS]: 68% vs 42% and 55%, P = 0.001; overall survival [OS]: 74% vs 49% and 61%, P < 0.001). Multivariate analysis showed that busulfan + cyclophosphamide ± etoposide and busulfan + melphalan regimens were independent favorable factors for LFS (hazard ratio: 0.46; P < 0.001) and OS (hazard ratio: 0.40; P < 0.001) compared with the other busulfan-based regimen, and both age 2 years or older and advanced stage at AHSCT were independent poor predictors for LFS and OS, simultaneously.

CONCLUSION

Busulfan + cyclophosphamide ± etoposide and busulfan + melphalan regimens exhibited superior antileukemic effects compared with other BU-based myeloablative regimens.

Treosulfan, Fludarabine, and Low-Dose Total Body Irradiation for Children and Young Adults with Acute Myeloid Leukemia or Myelodysplastic Syndrome Undergoing Allogeneic Hematopoietic Cell Transplantation: Prospective Phase II Trial of the Pediatric Blood and Marrow Transplant Consortium

This multicenter study evaluated a treosulfan-based regimen in children and young adults with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing allogeneic hematopoietic cell transplant (HCT). Forty patients with median age 11 years (range, 1 to 19) underwent allogeneic HCT for AML in first (n = 18), second (n = 11), and third or greater remission (n = 3) or MDS (n = 8) using bone marrow (n = 25), peripheral blood stem cells (n = 5), or cord blood (n = 9). The regimen consisted of body surface area (BSA)-based treosulfan 10 g/m²/day (BSA ≤ .5 m²), 12 g/m²/day (BSA > .5 to 1.0 m²), or 14 g/m²/day (BSA > 1.0 m²) on days -6 to -4; fludarabine 30 mg/m²/day on days -6 to -2; and a single fraction of 200 cGy total body irradiation on day -1. Graft-versus-host disease (GVHD) prophylaxis included tacrolimus and methotrexate for marrow and peripheral blood stem cell and cyclosporine/mycophenolate mofetil for cord blood. One-year overall survival, disease-free survival, and nonrelapse mortality were 80%, 73%, and 3%, respectively. One-year relapse was 38% for AML and 13% for MDS. No serious organ toxicities were observed. All 37 assessable patients engrafted. Cumulative incidences of grades II to IV acute GVHD and chronic GVHD were 22% and 40%, respectively. BSA-based treosulfan dosing resulted in predictable area under the curve and maximum concentration, which is required for dosing without measuring individual pharmacokinetic parameters. Observed differences in pharmacokinetics did not impact disease control or regimen toxicity. This BSA-based treosulfan regimen resulted in excellent engraftment and disease-free survival and minimal toxicity and transplant-related mortality (3%) in children and young adults with AML and MDS.

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.

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.

Hematopoietic Stem Cell Transplantation Activity in Pediatric Cancer between 2008 and 2014 in the United States: A Center for International Blood and Marrow Transplant Research Report

This Center for International Blood and Marrow Transplant Research report describes the use of hematopoietic stem cell transplantation (HSCT) in pediatric patients with cancer, 4408 undergoing allogeneic (allo) and3076 undergoing autologous (auto) HSCT in the United States between 2008 and 2014. In both settings, there was a greater proportion of boys (n = 4327; 57%), children < 10 years of age (n = 4412; 59%), whites (n = 5787; 77%), and children with a performance score ≥ 90% at HSCT (n = 6187; 83%). Leukemia was the most common indication for an allo-transplant (n = 4170; 94%), and among these, acute lymphoblastic leukemia in second complete remission (n = 829; 20%) and acute myeloid leukemia in first complete remission (n = 800; 19%) werethe most common. The most frequently used donor relation, stem cell sources, and HLA match were unrelated donor (n = 2933; 67%), bone marrow (n = 2378; 54%), and matched at 8/8 HLA antigens (n = 1098; 37%) respectively. Most allo-transplants used myeloablative conditioning (n = 4070; 92%) and calcineurin inhibitors and methotrexate (n = 2245; 51%) for acute graft-versus-host disease prophylaxis. Neuroblastoma was the most common primary neoplasm for an auto-transplant (n = 1338; 44%). Tandem auto-transplants for neuroblastoma declined after 2012 (40% in 2011, 25% in 2012, and 8% in 2014), whereas tandem auto-transplants increased for brain tumors (57% in 2008 and 77% in 2014). Allo-transplants from relatives other than HLA-identical siblings doubled between 2008 and 2014 (3% in 2008 and 6% in 2014). These trends will be monitored in future reports of transplant practices in the United States.

Comparison of a fludarabine and melphalan combination-based reduced toxicity conditioning with myeloablative conditioning by radiation and/or busulfan in acute myeloid leukemia in Japanese children and adolescents

BACKGROUND

The relative efficacy of allogeneic hematopoietic cell transplantation (allo-HCT) after reduced toxicity conditioning (RTC) compared with standard myeloablative conditioning (MAC) in pediatric patients with acute myeloid leukemia (AML) has not been studied extensively. To address whether RTC is a feasible approach for pediatric patients with AML in remission, we performed a retrospective investigation of the outcomes of the first transplant in patients who had received an allo-HCT after RTC or standard MAC, using nationwide registration data collected between 2000 and 2011 in Japan.

PROCEDURE

We compared a fludarabine (Flu) and melphalan (Mel)-based regimen (RTC; n = 34) with total body irradiation (TBI) and/or busulfan (Bu)-based conditioning (MAC; n = 102) in demographic- and disease-criteria-matched childhood and adolescent patients with AML in first or second complete remission (CR1/CR2).

RESULTS

The incidence of engraftment, early complications, grade II-IV acute graft-versus-host disease (GVHD), and chronic GVHD were similar in each conditioning group. The risk of relapse (25% vs. 26%) and non-relapse mortality (13% vs. 11%) after 3 years did not differ between these groups, and univariate and multivariate analyses demonstrated that the 3-year overall survival (OS) rates after Flu/Mel-RTC and MAC were comparable (mean, 72% [range, 51-85%] and 68% [range, 58-77%], respectively).

CONCLUSIONS

The results suggest that the Flu/Mel-RTC regimen is a clinically acceptable conditioning strategy for childhood and adolescent patients with AML in remission. Although this retrospective, registry-based analysis has several limitations, RTC deserves to be further investigated in prospective trials.

Treatment of Acute Myeloid Leukemia in Adolescent and Young Adult Patients

The objectives of this review were to discuss standard and investigational treatment strategies for adolescent and young adult with acute myeloid leukemia, excluding acute promyelocytic leukemia. Acute myeloid leukemia (AML) in adolescent and young adult patients (AYAs) may need a different type of therapy than those currently used in children and older patients. As soon as AML is diagnosed, AYA patient should be offered to participate in well-designed clinical trials. The standard treatment approach for AYAs with AML is remission induction chemotherapy with an anthracycline/cytarabine combination, followed by either consolidation chemotherapy or stem cell transplantation, depending on the ability of the patient to tolerate intensive treatment and cytogenetic features. Presently, continuing progress of novel drugs targeting specific pathways in acute leukemia may bring AML treatment into a new era.

Reduced-toxicity myeloablative conditioning consisting of 8-Gy total body irradiation, cyclophosphamide and fludarabine for pediatric hematological malignancies

Conventional myeloablative conditioning (MAC) regimens often cause severe regimen-related toxicity (RRT). Furthermore, many patients suffer from poor quality of life in accordance with the increase in long-term survivors. We therefore devised a reduced-toxicity myeloablative conditioning (RTMAC) regimen consisting of 8-Gy total body irradiation (TBI), fludarabine (FLU) and cyclophosphamide (CY) for pediatric hematological malignancies. A retrospective single-center analysis was performed on patients with leukemia or myelodysplastic syndrome (MDS), aged ≤20 years, who had received an 8-Gy TBI/FLU/CY RTMAC regimen followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT). Thirty-one patients underwent first allo-HSCT after an RTMAC regimen. The diagnoses were acute lymphoblastic leukemia (n = 11), acute myeloid leukemia (n = 13), MDS (n = 4), juvenile myelomonocytic leukemia (n = 1) and acute leukemias of ambiguous lineage (n = 2). While 3 patients showed early hematological relapse, the remaining 28 patients achieved engraftments. None of the patients developed grade 4 or 5 toxicities during the study period. The 5-year overall survival and relapse-free survival were 80% [95% confidence interval: CI, 61-91%] and 71% [95% CI, 52-84%], respectively. Our RTMAC regimen would be less toxic and offers a high probability of survival for children with hematological malignancies.

Impact on long-term OS of conditioning regimen in allogeneic BMT for children with AML in first CR: TBI+CY versus BU+CY: a report from the Société Française de Greffe de Moelle et de Thérapie Cellulaire

Allogeneic hematopoietic SCT (HSCT) appears to be an efficient tool to cure high-risk AML in first CR but the choice between BU-based or TBI-based conditioning regimens still remains controversial. In order to analyze the impact of conditioning regimen on long-term survival, we conducted a retrospective analysis from French registry data including all consecutive patients under 18 years old (n=226) from 1980 to 2004 transplanted for AML in CR1 from sibling (n=142) or matched unrelated donors and given either TBI-1200 cGy and CY 120 mg/kg (TBI-Cy, n=84) or BU 16 mg/kg and CY 200 mg/kg (BuCy200, n=142). Patient subgroups were comparable for all criteria except for median age at diagnosis and HSCT and for donor type. Both 5-year OS and disease-free survival (DFS) were significantly better in BuCy200 group (P=0.02 and 0.005, respectively). In multivariate analysis, both HLA matching and BuCy200 appeared as good prognostic factors for treatment-related mortality and DFS. Grade 2-4 acute GvHD and chronic GvHD rates were statistically higher in TBI-Cy group than in Bu-Cy200 one with a RR at 2 (P=0.002). In total, Bu-Cy200 conditioning regimen gives better outcome compared with TBI-Cy irrespective of the stem cell source and the donor type.