Once-daily intravenous busulfan given with fludarabine as conditioning for allogeneic stem cell transplantation: study of pharmacokinetics and early clinical outcomes

Busulfan with 400 centigray of total body irradiation and higher dose fludarabine: An alternative regimen for hematopoietic stem cell transplantation in pediatric acute lymphoblastic leukemia

BACKGROUND

Hematopoietic stem cell transplantation can be curative for children with difficult-to-treat leukemia. The conditioning regimen utilized is known to influence outcomes. We report outcomes of the conditioning regimen used at the Alberta Children's Hospital, consisting of busulfan (with pharmacokinetic target of 3750 μmol*min/L/day ±10%) for 4 days, higher dose (250 mg/m2 ) fludarabine and 400 centigray (cGy) of total body irradiation.

PROCEDURE

This retrospective study involved children receiving transplant for acute lymphoblastic leukemia (ALL). It compared children who fell within the target range for busulfan with those who were either not measured or were measured and fell outside this range. All other treatment factors were identical.

RESULTS

Twenty-nine children (17 within target) were evaluated. All subjects engrafted neutrophils with a median [interquartile range] time of 14 days [8-30 days]. The cumulative incidence of acute graft-versus-host disease was 44.8% [95% confidence interval, CI: 35.6%-54.0%], while chronic graft-versus-host disease was noted in 16.0% [95% CI: 8.7%-23.3%]. At 2 years, the overall survival was 78.1% [95% CI: 70.8%-86.4%] and event-free survival was 74.7% [95% CI: 66.4%-83.0%]. Cumulative incidence of relapse was 11.3% [95% CI: 5.1%-17.5%]. There were no statistically significant differences in between the group that received targeted busulfan compared with the untargeted group.

CONCLUSION

Our conditioning regiment for children with ALL resulted in outcomes comparable to standard treatment with acceptable toxicities and significant reduction in radiation dose. Targeting busulfan dose in this cohort did not result in improved outcomes.

Optimal Once-Daily Busulfan Administration in Pediatric Patients: A Simulation-Based Investigation of Intravenous Infusion Times

Purpose

Pediatric patients receiving hematopoietic stem cell transplantation undergo regular administration of intravenous busulfan as a conditioning regimen. Once-daily regimen of busulfan has been proposed as a more convenient alternative to the traditional regimen, but it may increase the risk of toxicity such as veno-occlusive disease (VOD). The study aims to evaluate the pharmacokinetics (PKs) of once-daily regimens and investigate appropriate intravenous infusion times to reduce the risk of toxicity.

Patients and methods

Once-daily busulfan dosing regimens for pediatric patient were reviewed and selected including EMA- and FDA-based once-daily dosing regimens. We generated busulfan PK data of virtual pediatric patients using a previously developed population PK model. PK profiles and proportion of patients achieving the referenced maximum concentration (Cmax) and exposure to busulfan were used to evaluate the appropriateness of both infusion time and dosing regimens.

Results

Predicted PK profiles and exposure of busulfan showed relatively similar distributions for all once-daily dosing regimens. Most patients exceeded the referenced Cmax possibly associated with a high risk of VOD with all once-daily regimens when applied with 3 hours of infusion.

Conclusion

While intravenous infusion of once-daily busulfan is typically administered over 3 hours, our findings emphasize the necessity of considering sufficient infusion times to ensure safe drug utilization and prevent toxicity, which will aid in optimal busulfan use in pediatric oncology.

INSPIRED Symposium Part 4B: Chimeric Antigen Receptor T Cell Correlative Studies-Established Findings and Future Priorities

Chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of B cell malignancies, with multiple CAR T cell products approved for numerous indications by regulatory agencies worldwide. However, significant work remains to be done to enhance these treatments. In March 2023, a group of experts in CAR T cell therapy assembled at the National Institutes of Health in Bethesda, Maryland at the Insights in Pediatric CAR T Cell Immunotherapy: Recent Advances and Future Directions (INSPIRED) Symposium to identify key areas for research for the coming years. In session 4B, correlative studies to be incorporated into future clinical trials and real-world settings were discussed. Active areas of research identified included (1) optimizing CAR T cell product manufacturing; (2) ensuring adequate lymphodepletion prior to CAR T cell administration; (3) overcoming immunoregulatory cells and tumor stroma present in the tumor microenvironment, particularly in solid tumors; (4) understanding tumor intrinsic properties that lead to CAR T cell immunotherapy resistance; and (5) uncovering biomarkers predictive of treatment resistance, treatment durability, or immune-related adverse events. Here we review the results of previously published clinical trials and real-world studies to summarize what is currently known about each of these topics. We then outline priorities for future research that we believe will be important for improving our understanding of CAR T cell therapy and ultimately leading to better outcomes for patients.

Busulfan induces steatosis in HepaRG cells but not in primary human hepatocytes: Possible explanations and implication for the prediction of drug-induced liver injury

BACKGROUND

The antineoplastic drug busulfan can induce different hepatic lesions including cholestasis and sinusoidal obstruction syndrome. However, hepatic steatosis has never been reported in patients.

OBJECTIVES

This study aimed to determine whether busulfan could induce steatosis in primary human hepatocytes (PHH) and differentiated HepaRG cells.

METHODS

Neutral lipids were determined in PHH and HepaRG cells. Mechanistic investigations were performed in HepaRG cells by measuring metabolic fluxes linked to lipid homeostasis, reduced glutathione (GSH) levels, and expression of genes involved in lipid metabolism and endoplasmic reticulum (ER) stress. Analysis of two previous transcriptomic datasets was carried out.

RESULTS

Busulfan induced lipid accumulation in HepaRG cells but not in six different batches of PHH. In HepaRG cells, busulfan impaired VLDL secretion, increased fatty acid uptake, and induced ER stress. Transcriptomic data analysis and decreased GSH levels suggested that busulfan-induced steatosis might be linked to the high expression of glutathione S-transferase (GST) isoenzyme A1, which is responsible for the formation of the hepatotoxic sulfonium cation conjugate. In keeping with this, the GST inhibitor ethacrynic acid and the chemical chaperone tauroursodeoxycholic acid alleviated busulfan-induced lipid accumulation in HepaRG cells supporting the role of the sulfonium cation conjugate and ER stress in steatosis.

CONCLUSION

While the HepaRG cell line is an invaluable tool for pharmacotoxicological studies, it might not be always an appropriate model to predict and mechanistically investigate drug-induced liver injury. Hence, we recommend carrying out toxicological investigations in both HepaRG cells and PHH to avoid drawing wrong conclusions on the potential hepatotoxicity of drugs and other xenobiotics.

Comparison of fludarabine/melphalan (FluMel) with fludarabine/melphalan/BCNU or thiotepa (FBM/FTM) in patients with AML in first complete remission undergoing allogeneic hematopoietic stem cell transplantation - a registry study on behalf of the EBMT Acute Leukemia Working Party

Conditioning protocols for patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT) are being developed continuously to improve their anti-leukemic efficacy and reduce their toxicity. In this study, we compared the conditioning protocol of fludarabine with melphalan 140 mg/m2 (FluMel) with conditioning protocols based on this same backbone but with an additional alkylating agent i.e., either fludarabine/BCNU (also known as carmustine)/melphalan (FBM), or fludarabine/thiotepa/melphalan (FTM) 110 mg/m2. We included 1272 adult patients (FluMel, n = 1002; FBM/FTM, n = 270) with acute myeloid leukemia (AML) with intermediate/poor cytogenetic risk in first complete remission (CR) from the registry of the EBMT Acute Leukemia Working Party. Despite patients in the FBM/FTM group were older (64.1 years vs. 59.8 years, p < 0.001) and had a worse Karnofsky performance score (KPS < 90, 33% vs. 24%, p = 0.003), they showed a better overall survival (OS) (2 y OS: 68.3% vs. 58.1%, p = 0.02) and less non-relapse mortality (NRM) (2 y NRM: 15.8% vs. 22.2%, p = 0.009) compared to patients treated with FluMel. No significant differences were observed in relapse incidence (RI) (2 y RI: 24.9% vs. 23.7%, p = 0.62). In conclusion, the addition of a second alkylating agent (BCNU/carmustine or thiotepa) to FluMel as FBM/FTM conditioning, improves OS in AML patients in first CR with intermediate/poor risk cytogenetics after allo-HCT.

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.

Individualized busulfan dosing improves outcomes compared to fixed-dose administration in pre-transplant minimal residual disease-positive acute myeloid leukemia patients with intermediate-risk undergoing allogeneic stem cell transplantation in CR

Pre-transplant minimal residual disease (MRD) impacts negatively on post-transplant relapse risk in acute myeloid leukemia (AML). Therapeutic drug monitoring by calculating area under the curve (AUC) was developed to optimize busulfan (Bu) exposure. Here, we compared post-transplant outcomes after individualized versus fixed busulfan dosage in intermediate-risk AML who achieved CR prior to allograft focusing on pre-transplant flow-MRD. Eighty-seven patients (median, 56 years) with intermediate-risk AML and pre-transplant flow-MRD ("different from normal") were included. Thirty-two patients received individualized busulfan; 54 fixed dosages. Individualized dosage was adjusted in 25/32 patients: increased, n = 18/25 (72%); decreased: n = 7/25 (28%). After median follow-up of 27 months, we observed lower 3-year relapses (6%, 2%-19% vs. 35%, 23%-49% p = 0.02), improved 3-year leukemia-free survival (LFS) (78%, 54%-91% vs. 55%, 40%-70% p = 0.009) and - overall survival (OS) (82%, 60%-93% vs. 69%, 54%-81% p = 0.05) after individualized compared to fixed Bu. Non-relapsed mortality (NRM) and acute graft versus host disease (GvHD) were not different. In multivariate analysis, fixed Bu showed unfavorable impact on OS (hazard ratio [HR] 4.6, p = 0.044), LFS (HR 3.6, p = 0.018) and relapses (HR 3.6, p = 0.033). Fixed Bu also had unfavorable impact on LFS (3.6, 1.1-12.6, p = 0.041) in pre-transplant MRD-positive patients. Individualized, AUC-based, busulfan is associated with lower relapses in intermediate-risk AML patients allografted in CR and may overcome pre-transplant MRD-positivity.

Iron Chelation with Deferasirox Suppresses the Appearance of Labile Plasma Iron During Conditioning Chemotherapy Prior to Allogeneic Stem Cell Transplantation

During conditioning chemotherapy prior to allogeneic haematopoietic stem cell transplantation (HSCT), non-transferrin-bound iron and its chelatable form, labile plasma iron (LPI), regularly appear in the blood of patients at high levels of transferrin saturation (TfS). As these free iron species potentially favor infection and mediate transplantation-associated toxicities, chelation therapy could be an approach to improve outcome after transplantation. However, data addressing iron chelation in the immediate peritransplantation period are sparse. In this study, we investigated the influence of iron chelation with deferasirox during conditioning chemotherapy on the appearance of LPI, the incidence of infection and toxicities, and the tolerability of this treatment in the peritransplantation period. We conducted this single-center prospective observational study in 25 adults with iron overload (serum ferritin >1000 µg/L) undergoing allogeneic HSCT after myeloablative busulfan-based conditioning chemotherapy. Patients received iron chelation with deferasirox (14 mg/kg) from the start of conditioning until day 3 post-transplantation. Iron parameters, including LPI, were obtained at the chelator's trough level daily until day 0 and then on days 4, 7, and 14. Data on infection (bacteremia or invasive fungal disease) and toxicity, as well as the tolerability of deferasirox, were collected until the end of the follow-up period on day 28. Data were analyzed descriptively. TfS levels exceeded 70% in median on 6 days (range, 4 to 10 days) and in 63.6% (range, 36.4% to 90.9%) of the samples per patient, although in 19 of 25 patients (76%), no elevated LPI values were detected during the intake of deferasirox despite high TfS levels. Only 6 patients (24%) showed mildly increased LPI values (≤0.5 units) during the intake of deferasirox, 3 of whom had presented with elevated LPI values before the start of conditioning. Deferasirox was well tolerated, and no aggravation of toxicities was observed. Infection occurred in 5 patients (20%), including 3 of the 6 patients with elevated LPI values despite chelation therapy. In the present study, we demonstrate that iron chelation with deferasirox safely suppresses the appearance of LPI and might decrease the incidence of infection, whereas the impact on transplantation-associated toxicities remains to be elucidated.

Haploidentical Hematopoietic Stem Cell Transplantation in Thalassemia

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only established treatment that is potentially curative, but it is limited by the availability of donors and the medical condition of the patient. To expand the donor pool to include haploidentical related donors, we introduced a program consisting of a pharmacologic pre transplant immune suppression phase (PTIS) and two courses of dexamethasone (DXM) and fludarabine (FLU) followed by pre transplant conditioning with intravenous FLU busulfan (BU) and post transplant graft-vs.-host disease (GvHD) prophylaxis with cyclophosphamide (CPM), tacrolimus, and mycophenolate mofetil. We transplanted 83 consecutive transfusion-dependent patients with thalassemia; the 3-year projected overall and event-free survival is over 96.0%, and there have been no secondary graft failures. Of the first 31 patients, we had two graft failures, both of them occurring in patients with extremely high titers of anti-donor-specific human leukocyte antigen (HLA) antibodies [anti-donor specific antibodies (DSAs)], but after adjusting the PTIS to include bortezomib (BORT) and rituximab (RIX) for patients with high titers of anti-DSAs and using pharmacologic dose guidance for BU, we had no graft failures in the last 52 patients. Six (7.0%) of 83 patients developed severe GvHD. We conclude that this is a safe and efficacious approach to allogeneic HSCT in thalassemia.

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.

A randomized phase III study of pretransplant conditioning for AML/MDS with fludarabine and once daily IV busulfan ± clofarabine in allogeneic stem cell transplantation

Pretransplant conditioning with Fludarabine (Flu)-Busulfan (Bu) is safe, but clofarabine (Clo) has improved antileukemic activity. Hypothesis: Flu+Clo-Bu (FCB) yields superior progression-free survival (PFS) after allogeneic transplantation. We randomized 250 AML/MDS patients aged 3–70, Karnofsky Score ≥80, with matched donors, to FCB (n = 120) or Flu-Bu (n = 130), stratifying complete remission (CR) vs. No CR, (NCR). HCT-CI scores varied, from 0 to 10. All evaluable patients engrafted. Median follow-up was 66 months (interquartile range: 58–80). Three-year relapse incidence (RI), 25% with FCB, vs. 39% with Flu-Bu (p = 0.018), offset by higher non-relapse mortality, 22.6% (95%CI: 16–30.2%) vs. 12.3% (95%CI: 6.5–19%). Three-year PFS was 52% (95%CI: 44–62%) (FCB), vs. 48% (95%CI: 41–58%) (Flu-Bu). FCB benefited CR patients less, NCR patients age ≤ 60 had 3-year 34% RI (95%CI: 19–49%) (FCB) vs. 56% (95%CI: 38–70%) after Flu-Bu (p = 0.037). NCR patients >60 years had 3-year RI 10.0% (FCB), vs. 56.0%, after Flu-Bu (p = 0.003). Bayesian regression analysis including treatment-covariate interactions showed FCB superiority in NCR patients with low HCT-CI (0–2). Serious adverse event profiles were similar for the regimens. Conditioning with FCB did not improve PFS overall, but improved disease control in NCR patients, mandating confirmatory trials. Remission status and HCT-CI should be considered when using FCB.

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.

Fludarabine/busulfan versus busulfan/cyclophosphamide as myeloablative conditioning for myelodysplastic syndrome: a propensity score-matched analysis

Myeloablative conditioning with fludarabine/busulfan (Flu/Bu4) prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT) is effective for acute myeloid leukemia. However, the effectiveness of Flu/Bu4 for myelodysplastic syndrome (MDS) remains poorly understood. Therefore, we retrospectively analyzed nationwide registry data in Japan from 2006 to 2018 and compared transplant outcomes of adult MDS patients receiving Flu/Bu4 and busulfan/cyclophosphamide (Bu4/Cy) using propensity score (PS) matching. The primary endpoint was overall survival (OS). Among 2,482 MDS patients, 153 patients were assigned each to the Flu/Bu4 and Bu4/Cy groups. The 3-year OS rates were 52.7% (95% confidence interval [CI], 43.8-60.8%) and 49.5% (95% CI, 40.8-57.6%) in the Flu/Bu4 and Bu4/Cy group, respectively (P = 0.548). The 3-year progression-free survival (P = 0.858), the cumulative incidence of relapse (P = 0.536), and cumulative incidence of non-relapse mortality (P = 0.684) were not significantly different between the two groups. According to the findings of subgroup analyses, no patient had a favorable OS when using either of the two regimens. In conclusion, although our PS-matched cohort mainly comprised older patients who had a low hematopoietic cell transplantation-comorbidity index and low-risk disease status, Flu/Bu4 could be an alternative to Bu4/Cy for MDS patients prior to allo-HSCT.

Pharmacokinetically guided, once-daily intravenous busulfan in combination with fludarabine for elderly AML/MDS patients as a conditioning regimen for allogeneic stem cell transplantation

The efficacy of pharmacokinetically (PK) guided, once-daily administration of busulfan (BU) was evaluated in elderly patients with acute myeloid leukemia/myelodysplastic syndrome (AML/MDS). Twenty-one patients (median age 61) received 30 mg/m² fludarabine for 6 days and BU for 4 days, starting from 3.2 mg/m² and subsequently adjusted to the target area under the curve (AUC) of 6000 µmol-min/L. The median AUC of day 1 (AUC1), AUC4, and their average were 4871.3, 6021.0, and 5368.1 µmol-min/L, respectively. Veno-occlusive disease/sinusoidal obstructive syndrome (VOD/SOS) occurred in five patients (24%) but all recovered well. Four patients (20%) had non-infectious pulmonary complications (NIPCs). Patients with high AUC1 had frequent gastrointestinal adverse events, but similar incidence of VOD/SOS and NIPCs. Two-year overall survival (OS), non-relapse mortality (NRM), and relapse rates were 44.4%, 28.6%, and 29.1%, respectively. Patients with high AUC1 had significantly high NRM (57.1% vs. 14.3%, P = 0.04) and inferior OS (14.3% vs. 60.1%, P = 0.002), while patients with high AUC4 had a significantly low relapse rate (8.3% vs. 55.6%, P = 0.02). In conclusion, once-daily BU and a PK-guided dose intensification were beneficial for reducing relapse in elderly patients with AML/MDS. However, caution should be exercised as rapid BU dose elevation may contribute to NRM.

Dose individualization of intravenous busulfan in pediatric patients undergoing bone marrow transplantation: impact and in vitro evaluation of infusion lag-time

OBJECTIVES

To apply therapeutic drug monitoring and dose-individualization of intravenous Busulfan to paediatric patients and evaluate the impact of syringe-pump induced Busulfan infusion lag-time after in vitro estimation.

METHODS

76 children and adolescents were administered 2 h intravenous Busulfan infusion every 6 h (16 doses). Busulfan plasma levels, withdrawn by an optimized sampling scheme and measured by a validated HPLC-PDA method, were used to estimate basic PK parameters, AUC, Cmax, kel, t1/2, applying Non-Compartmental Analysis. In vivo infusion lag-time was simulated in vitro and used to evaluate its impact on AUC estimation.

KEY FINDINGS

Mean (%CV) Busulfan AUC, Cmax, clearance and t1/2 for pediatric population were found 962.3 μm × min (33.1), 0.95 mg/L (41.4), 0.27 L/h/kg (33.3), 2.2 h (27.8), respectively. TDM applied to 76 children revealed 6 (7.9%) being above and 25 (32.9%) below therapeutic-range (AUC: 900-1350 μm × min). After dose correction, all patients were measured below toxic levels (AUC < 1500 μm × min), no patient below 900 μm × min. Incorporation of infusion lag-time revealed lower AUCs with 17.1% more patients and 23.1% more younger patients, with body weight <16 kg, being below the therapeutic-range.

CONCLUSIONS

TDM, applied successfully to 76 children, confirmed the need for Busulfan dose-individualization in paediatric patients. Infusion lag-time was proved clinically significant for younger, low body-weight patients and those close to the lower therapeutic-range limit.

Busulfan-containing conditioning regimens in allogeneic hematopoietic stem cell transplantation for acute lymphoblastic leukemia: A Taiwan observational study

Background

Allogeneic stem cell transplantation (allo‐HSCT) is the ultimate cure for acute lymphoblastic leukemia (ALL).

Aim

This study was performed to compare the outcomes of ALL patients receiving busulfan (Bu) with cyclophosphamide (Cy)‐based or total body irradiation (TBI)‐based regimen in a Chinese population.

Methods

We enrolled 224 adult patients with ALL who received allo‐HSCT at National Taiwan University Hospital between 1997 and 2016.

Results

The median age at transplantation was 33 years. Before allo‐HSCT, 75.9% of patients attained first or late complete remission. A total of 141 patients (62.9%) received Bu/Cy‐based conditioning, either myeloablative (MA) or reduced‐intensity stem cell transplantation (RIST), and 83 patients received a TBI‐based regimen (MA‐TBI). Patients receiving the MA‐Bu regimen had longer relapse‐free survival (RFS) than those receiving the MA‐TBI regimen (median, 24.1 vs. 6.7 months, p = .044). There was no difference in overall survival (OS, MA‐Bu vs. MA‐TBI vs. RIST‐Bu: 39.4 vs. 28.2 vs. 13.1 months, p = .276), treatment‐related mortality (TRM), or incidences of grade 3–4 acute graft‐versus‐host disease (GvHD). Among patients receiving identical GvHD prophylactic regimens, there was no difference between MA‐Bu and MA‐TBI groups regarding the incidence of grade 3–4 acute GvHD, grade 2–4, and all‐grade chronic GvHD. In subgroup analysis, patients receiving oral busulfan had comparable RFS and OS to the intravenous busulfan group (p = .436 and p = .236, respectively), but a higher TRM (25% vs. 9.8%, p = .016). In the multivariable analysis, disease status before allo‐HSCT was the only risk factor impacting RFS and OS.

Conclusion

In summary, patients receiving Bu/Cy‐based or TBI‐based regimens as conditioning had similar results in terms of OS, TRM, and acute GvHD, whereas the use of myeloablative Bu/Cy resulted in a better RFS. A Bu‐based regimen could be an alternative conditioning choice for patients who are ineligible to receive TBI. Prospective and randomized controlled trials are warranted to validate the long‐term outcomes.

Adding melphalan to fludarabine and a myeloablative dose of busulfan improved survival after allogeneic hematopoietic stem cell transplantation in a propensity score-matched cohort of hematological malignancies

Fludarabine and a myeloablative dose of busulfan (Flu/Bu4) can improve prognosis after allogeneic hematopoietic stem cell transplantation (HSCT) with melphalan (Mel). We investigated the prognostic impact of adding Mel to Flu/Bu4 by comparing between Flu/Bu4/Mel and Flu/Bu4 groups. This study included 846 propensity score (PS)-matched patients who received either Flu/Bu4/Mel (n = 423) or Flu/Bu4 (n = 423) from 2394 patients enrolled in a multicenter prospective registry, from January 2010 to December 2016. The primary endpoint (5-year overall survival [OS]), and the prognostic impact of adding Mel was evaluated using Cox regression analysis. The study population median age was 58 (interquartile 50-64) years and 61.0% were male. Patient characteristics were well-balanced between groups. Five-year OS was 34.2% (95% confidence interval [CI]: 27.3-41.1%) and 30.1% (24.8-35.6%) in the Flu/Bu4/Mel and Flu/Bu4 groups, respectively (log-rank P = 0.019). The adjusted hazard ratio of adding Mel was 0.77 (95% CI: 0.62-0.96) (P = 0.022) for the 5-year OS, and this attributed to a lower incidence of 5-year relapse (0.71, 0.56-0.90, P = 0.005) and relapse associated mortality (0.73, 0.57-0.95, P = 0.018). There was no statistical difference in 5-year non-relapse mortality between groups (log-rank P = 0.855). Flu/Bu4/Mel was associated with better 5-year OS compared to Flu/Bu4 in a PS-matched cohort after allogeneic HSCT.

Optimization of Busulfan Dosing Regimen in Pediatric Patients Using a Population Pharmacokinetic Model Incorporating GST Mutations

Purpose

The aim of this study was to develop a novel busulfan dosing regimen, based on a population pharmacokinetic (PPK) model in Chinese children, and to achieve better area under the concentration-time curve (AUC) targeting.

Patients and Methods

We collected busulfan concentration-time samples from 69 children who received intravenous busulfan prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT). A population pharmacokinetic model for busulfan was developed by nonlinear mixed effect modelling and was validated by an external dataset (n=14). A novel busulfan dosing regimen was developed through simulated patients, and has been verified on real patients. Limited sampling strategy (LSS) was established by Bayesian forecasting. Mean absolute prediction error (MAPE) and relative root mean Squared error (rRMSE) were calculated to evaluate predictive accuracy.

Results

A one-compartment model with first-order elimination best described the data. GSTA1 genotypes, body surface area (BSA) and aspartate aminotransferase (AST) were found to be significant covariates of Bu clearance, and BSA had significant impact of the volume of distribution. Moreover, two equations were obtained for recommended dose regimens: dose (mg)=34.14×BSA (m²)+3.75 (for GSTA1 *A/*A), Dose (mg)=30.99×BSA (m²)+3.21 (for GSTA1 *A/*B). We also presented a piecewise dosage based on BSA categories for each GSTA1 mutation. A two-point LSS, two hours and four hours after dosing, behaved well with acceptable prediction precision (rRMSE=1.026%, MAPE=6.55%).

Conclusion

We recommend a GSTA1-BSA and BSA-based dosing (Q6 h) based on a PPK model for personalizing busulfan therapy in pediatric population. Additionally, an optimal LSS (C_2h and C_4h) provides convenience for therapeutic drug monitoring (TDM) in the future.

Treatment with intravenous busulfan, melphalan, and etoposide followed by autologous stem cell transplantation in patients with non-Hodgkin's lymphoma: a multicenter study from the consortium for improving survival of lymphoma

Several high-dose therapy (HDT) conditioning regimens have been used to treat non-Hodgkin's lymphoma (NHL), such as bis-chloroethylnitrosourea (BCNU)/etoposide/cytosine arabinoside/melphalan (BEAM), BCNU/etoposide/cytosine arabinoside/cyclophosphamide (BEAC), and cyclophosphamide/BCNU/etoposide (CBV). BCNU is an active drug in HDT of NHL, but the supply is limited in some countries, including Korea. Busulfan has been used in allogeneic and autologous stem cell transplantation (ASCT). This phase II study evaluated the efficacy of busulfan/melphalan/etoposide (BuME) as a conditioning regimen for HDT in relapsed or high-risk NHL. The regimen consisted of intravenous busulfan (3.2 mg/kg/day) on days -8, -7, and -6, etoposide (400 mg/m² /day) on days -5 and -4, and melphalan (50 mg/m² /day) on days -3 and -2. A total of 46 patients were included in the study, with 36 (78.3%) achieving a complete response after ASCT. The 2-year progression-free survival (PFS) and overall survival (OS) rates for all patients were 46.7% (95% CI, 31.8-60.4%) and 63.7% (95% CI, 47.7-76.0%), respectively. There was no development of veno-occlusive disease and no treatment-related deaths within 100 days after ASCT. These results indicate that a BuME regimen is well-tolerated and effective for patients with relapsed or high-risk NHL, and may be comparable to some previously used regimens. This regimen may be useful as a substitute for BCNU-containing regimens.

Impact of Adding Antithymocyte Globulin to Posttransplantation Cyclophosphamide in Haploidentical Stem-Cell Transplantation

BACKGROUND

Graft-versus-host disease (GVHD) is a major cause of mortality after allogeneic stem-cell transplantation. Posttransplantation cyclophosphamide (PT/CY) has become standard prophylaxis of GVHD in T-replete haploidentical transplantation. The question is whether adding antithymocyte globulin (ATG) to PT/CY may further reduce the incidence of GVHD compared to PT/CY only.

PATIENTS AND METHODS

We retrospectively studied 268 patients undergoing myeloablative haploidentical transplantation with thiotepa, busulfan, and fludarabine (TBF) conditioning. Sixty-nine patients (26%) received ATG.

RESULTS

In the ATG group, 3% died due to GVHD versus 8% in the no ATG group. The 100-day and 1-year nonrelapse mortality (NRM) was 0% and 19%, respectively, in the whole cohort. On univariate analysis, the 1-year NRM was 8% versus 23% in patients receiving ATG and no ATG, respectively (P = .005). The no ATG group had a higher incidence of acute GVHD at 12 months compared to the ATG group (22% vs. 12%, respectively, P = .029). The ATG group had better overall survival at 12 months compared to the no ATG group (79% vs. 69%, P = .029). On multivariate analysis, adding ATG to PT/CY had no significant impact on any of the outcomes. A low disease risk index was associated with better overall survival and lower NRM, while Hematopoietic Cell Transplantation-Specific Comorbidity Index (HCT-CI) score ≥ 3 was associated with higher NRM.

CONCLUSION

ATG can be safely used as part of the pretransplantation conditioning and does not increase the incidence of relapse or complications after transplantation.

Hematopoietic Stem Cell Transplantation for Severe Thalassemia Patients from Haploidentical Donors Using a Novel Conditioning Regimen

Patients with severe thalassemia commonly have a survival that is significantly shorter than that of the general population. Allogeneic hematopoietic stem cell transplantation (allo-SCT) is the only established treatment that is potentially curative, but it is limited by the availability of donors and the medical condition of the patient. To expand the donor pool to include haploidentical related donors, we introduced a program consisting of a pharmacologic pretransplant immune suppression phase (PTIS) and 2 courses of dexamethasone and fludarabine, followed by pretransplant conditioning with fludarabine-i.v. busulfan and post-transplant graft-versus-host disease (GVHD) prophylaxis with cyclophosphamide, tacrolimus, and mycophenolate mofetil. We transplanted 83 consecutive transfusion-dependent patients with thalassemia (median age, 12 years; range, 1 to 28 years) with a minimum follow-up of 6 months (median, 15 months; range, 7 to 53 months); the 3-year projected overall and event-free survival is over 96%, and there have been no secondary graft failures. Of the first 31 patients, we had 2 graft failures, both of them occurring in patients with extremely high titers of anti-donor-specific HLA antibodies (anti-DSAs), but after adjusting the PTIS to include bortezomib and rituximab for patients with high titers of anti-DSAs and using pharmacologic dose guidance for busulfan, we had no graft failures in the last 52 patients. Six (7%) of 83 patients developed severe GVHD. We conclude that this is a safe and efficacious approach to allogeneic SCT in thalassemia, yielding results comparable to those available for patients with fully matched donors.

A review of bioanalytical methods for chronic lymphocytic leukemia drugs and metabolites in biological matrices

Quantitation of drugs used for the treatment of chronic lymphocytic leukemia in various biological matrices during both pre-clinical and clinical developments is very important, often in routine therapeutic drug monitoring. The first developed methods for quantitation were traditionally done on LC in combination with either UV or fluorescence detection. However, the emergence of LC with mass spectrometry in tandem in early 1990s has revolutionized the quantitation as it has provided better sensitivity and selectivity within a shorter run time; therefore it has become the choice of method for the analysis of various drugs. In this article, an overview of various bioanalytical methods (HPLC or LC-MS/MS) for the quantification of drugs for the treatment of chronic lymphocytic leukemia, along with applicability of these methods, is given.

Therapeutic Dose Monitoring of Busulfan Is Associated with Reduced Risk of Relapse in Non-Hodgkin Lymphoma Patients Undergoing Autologous Stem Cell Transplantation

Optimal administration of busulfan (Bu) is hampered by variable and unpredictable drug metabolism in individual patients. At our institution, Bu was previously administered with fixed weight-based dosing (WBD) in combination with cyclophosphamide (Cy) and etoposide (E) for patients with non-Hodgkin lymphoma (NHL) undergoing autologous stem cell transplantation (ASCT). In 2014, we adopted real-time pharmacokinetic (PK)-guided therapeutic drug monitoring (TDM) of Bu for all NHL patients undergoing Bu-containing ASCT. Here we compare outcomes of NHL patients who underwent ASCT with Bu/Cy/E using WBD and those who did so using TDM of Bu. We studied 336 consecutive adult NHL patients who underwent ASCT with Bu/Cy/E using WBD from January 2007 to December 2013 (n = 258) or TDM from May 2014 to December 2017 (n = 78), excluding patients with mantle cell lymphoma. Clinical outcomes, including relapse, nonrelapse mortality (NRM), progression-free survival (PFS), and overall survival (OS), hepatotoxicity and pulmonary toxicity were compared in the 2 groups. To adjust for differences in baseline characteristics between the groups, propensity-matched cohorts of WBD and TDM patients were also studied. After the first dose of Bu, the dose was increased in 36% of the patients and decreased in 41%. Changes in pulmonary and liver function from baseline to transplantation were not different between the 2 groups, although these changes showed significantly less variability with TDM than with WBD. Relapse was significantly lower and PFS was improved with TDM; 2-year estimates were 19% for TDM and 38% for WBD for relapse (P = .004) and 69% and 55%, respectively, for PFS (P = .038). No significant between-group differences in NRM or OS were seen. In multivariable analysis, TDM remained prognostic for lower risk of relapse (hazard ratio [HR], .52; 95% confidence interval [CI], .30 to .89; P = .018), but did not remain prognostic for PFS (HR, .74; 95% CI, .48 to 1.16; P = .19). Propensity-matched cohorts displayed similar patterns of outcomes. In subset analysis based on disease status at ASCT, TDM was associated with less relapse and better PFS than WBD for patients who underwent transplantation in less than complete remission (CR) compared with those who underwent transplantation in CR. Compared with WBD, PK-directed TDM of Bu reduces the incidence of relapse when used in combination with Cy and E for patients with NHL undergoing ASCT, particularly for patients in less than CR. These data support the continued use of personalized PK-guided dosing for all NHL patients undergoing ASCT with Bu-containing preparative regimens.

Single cord blood transplantation in Japan; expanding the possibilities of CBT

Cord blood (CB) has been an alternative stem cell source for patients with a wide variety of hematological diseases. Cord blood confers the advantages of rapid availability and higher tolerance to two HLA antigen mismatches compared with unrelated donors, and this has increased opportunities for patients who do not have suitable donors or require urgent transplantation. Although the higher rate of engraftment failure remains a serious concern after cord blood transplantation (CBT), the mechanisms underlying this risk have gradually been clarified, which has helped to improve engraftment. Recent studies of CBT and other alternatives have reported comparable outcomes. Moreover, CBT shows promise even when patients are in a non-remission status, which may reflect the potent graft-versus-leukemia effect of CB. Here we compare the most recent outcomes of CBT with those of other stem cell sources and discuss the potential of CB and several outstanding issues that require resolution.

Pharmacokinetics analysis results are similar for oral compared to intravenous busulfan in patients undergoing hematopoietic stem cell transplantation, except for the earlier onset of mucositis. A controlled clinical study

Busulfan is used in myeloablative schemes for hematopoietic stem cell transplantation (HSCT), with monitoring of dosage through the area under the curve (AUC) of the drug plasma concentration (µMol min). In this study, we compared the complete pharmacokinetics of busulfan administered orally (Bu-Oral) and intravenously (Bu-IV). We evaluated 40 patients who underwent HSCT with different types of conditioning regimens. After one dose, in the Bu-Oral group (n = 21), the median AUC was 1174 µMol min (799-4000), reaching a median of 4440 µMol min (3428-7181.5) during conditioning in 24 h. In the Bu-IV group (n = 19), it was 1244.8 µMol min (1001.2-2021), reaching 5598.0 µMol min (3102-8818) during conditioning in 24 h. Measuring plasma concentration of Bu in patients undergoing HSCT is important, regardless of the formulation, and the inclusion of a pre-HSCT test can predict the optimal dose during conditioning. Pharmacokinetics of the oral administration of busulfan, as well as clearance, are extremely variable, and this can potentially compromise the clinical results of the treatment since it makes it difficult to predict clinical results.

Comparison of pediatric allogeneic transplant outcomes using myeloablative busulfan with cyclophosphamide or fludarabine

Busulfan combined with cyclophosphamide (BuCy) has long been considered a standard myeloablative conditioning regimen for allogeneic hematopoietic cell transplantation (HCT), including both nonmalignant conditions and myeloid diseases. Substituting fludarabine for cyclophosphamide (BuFlu) to reduce toxicity without an increase in relapse has been increasingly performed in children, but without comparison with BuCy. We retrospectively analyzed 1781 children transplanted from 2008 to 2014 to compare the effectiveness of BuCy with BuFlu. Nonmalignant and malignant disease populations were analyzed separately. Overall mortality was comparable for children with nonmalignant conditions who received BuFlu or BuCy (relative risk [RR], 1.14, P = .52). Lower incidences of sinusoidal obstruction syndrome (P = .04), hemorrhagic cystitis (P = .04), and chronic graft-versus-host disease (P = .02) were observed after BuFlu, but the influence of the conditioning regimen could not be assessed by multivariate analysis because of the low frequency of these complications. Children transplanted for malignancies were more likely to receive BuFlu if they had higher hematopoietic cell transplantation-comorbidity index scores (P < .001) or their donor was unrelated and HLA-mismatched (P = .004). Nevertheless, there were no differences in transplant toxicities and comparable transplant-related mortality (RR, 1.2; P = .46), relapse (RR, 1.2; P = .15), and treatment failure (RR, 1.2; P = .12). BuFlu was associated with higher overall mortality (RR, 1.4; P = .008) related to inferior postrelapse survival (P = .001). Our findings demonstrated that outcomes after BuFlu are similar to those for BuCy for children, but for unclear reasons, those receiving BuFlu for malignancy may be at risk for shorter postrelapse survival.

Reduced intensity vs. myeloablative conditioning with fludarabine and PK-guided busulfan in allogeneic stem cell transplantation for patients with AML/MDS

Conditioning regimens contribute significantly to outcomes following allogeneic stem cell transplantation (allo-SCT). Reduced-intensity conditioning (RIC) regimens provide lower toxicity at the cost of reduced efficacy compared with myeloablative conditioning (MAC) regimens. However, because pre-transplant prognostic variables often determine the conditioning regimen, studies of RIC vs. MAC have been inconclusive. We present a retrospective analysis of 242 acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) patients, 112 of whom were in 56 pairs matched using propensity scores, to account for variation that may confound clinical outcomes. The uniform conditioning regimens consisted of fludarabine with pharmacokinetic (PK)-guided intravenous busulfan (Bu). The RIC and MAC regimens were dosed at the average daily area under the concentration-vs-time curve (AUC) of 4000 µMol min and 5000-6000 µMol min, or total course AUC of 16,000 µMol min and 20,000-24,000 µMol min, respectively; PK-guided dosing removes overlap in systemic Bu exposure. When patients' data were propensity-matched, there was a trend toward significantly increased full donor chimerism and decreased chronic graft vs. host disease in RIC, and no significant differences in progression free survival and overall survival between RIC and MAC. Our results also elucidate the efficacy of PK-guided-dosing in the setting of allo-SCT for AML and MDS.

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.

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.

Epigenetic modification enhances the cytotoxicity of busulfan and4-hydroperoxycyclophosphamide in AML cells

The combination of the DNA-alkylating agents busulfan (Bu) and cyclophosphamide is the most commonly used myeloablative pretransplantation conditioning therapy for myeloid leukemias. However, it is associated with significant nonrelapse mortality, which prohibits dose escalation to control relapse. We hypothesized that combining these two drugs with an epigenetic modifier would increase antileukemic efficacy without jeopardizing patient safety. A preclinical study was performed to determine the synergistic cytotoxicity of Bu, 4-hydroperoxycyclophosphamide (4HC), and the hypomethylating agent decitabine (DAC) in human acute myeloid leukemia (AML) cell lines. Exposure of KBM3/Bu250⁶ (P53-null) and OCI-AML3 (P53-wild-type) cells to Bu+4HC inhibited cell proliferation by ∼35-39%; addition of DAC increased the inhibition to ∼60-62%. The observed synergistic interactions correlated with DNA damage response activation, increased the production of reactive oxygen species, and decreased mitochondrial membrane potential, release of mitochondrial proapoptotic proteins into the cytoplasm, and induction of caspase-dependent programmed cell death. The Bu+4HC+DAC combination further caused chromatin trapping of DNMT1 with a concomitant increase in DNA damage. In contrast, FMS-like tyrosine kinase 3 internal tandem duplications (FLT3-ITD)-positive AML cell lines were not sensitized to Bu+4HC by inclusion of DAC; addition of the FLT3 kinase inhibitor sorafenib sensitized the FLT3-ITD-positive MV4-11 and MOLM13 cell lines to the triple drug combination by inhibiting the FLT3 signal transduction pathway. Our results therefore provide a rationale for the development of personalized conditioning therapy for patients with P53-mutated and FLT3-ITD-positive AML.

Safety and Efficacy of Once-Daily Intravenous Busulfan in Allogeneic Transplantation: A Matched-Pair Analysis

Compared with 4-times-daily infusion of intravenous busulfan (ivBU4), the safety and efficacy of once-daily infusion of ivBU (ivBU1) has not been fully clarified. We have been routinely using ivBU1 in a conditioning regimen in adult patients with myeloid malignancy who undergo allogeneic hematopoietic stem cell transplantation. In this study, a total of 91 patients who received ivBU1 for 2 days (n = 18) or 4 days (n = 73) in our institutions were compared with 273 control patients who received ivBU4, who were matched for age, sex, performance status, disease risk, conditioning regimen, and donor type, selected from the database of the Japanese Society for Hematopoietic Cell Transplantation using optimal matching algorithms. One-year overall survival (56.8% versus 57.1%, P = .94), disease-free survival (51.6% versus 50.8%, P = .73), relapse rate (28.5% versus 26.2%, P = .94), nonrelapse mortality (19.9% versus 23.0%, P = .71), and the incidence of graft-versus-host disease were not significantly different between the ivBU1 and ivBU4 groups. In patients who received ivBU1, neutrophil recovery was slower (median days: 22 versus 17, P = .001), and the incidence of veno-occlusive disease was lower (2.6% versus 17.4%, P = .04). In conclusion, ivBU1 can be safely administered with clinical outcomes similar to those with ivBU4.

Diagnosis of GATA2 haplo-insufficiency in a young woman prompted by pancytopenia with deficiencies of B-cell and dendritic cell development

BACKGROUND

GATA2 deficiency presents with a spectrum of phenotypes including increased susceptibility to viral and bacterial infections, multi-lineage cytopenias, aplastic anemia, leukemic transformation and lymphedema. Allogeneic transplantation is only curative therapy for GATA2 deficiency, but is associated with significant treatment related morbidity and mortality. Given the spectrum of clinical presentation, accurate diagnosis of GATA2 deficiency is necessary to identify patients early in their disease course when allogeneic bone marrow transplantation may be of clinical benefit.

CASE PRESENTATION

In this report, we present a GATA2 mutation diagnosed in 23-year-old woman presenting with pancytopenia, recurring oral blisters, fatigue and chronic pain. We describe markedly low levels of mature B-cells in the blood and bone marrow and the absence of detectable blood dendritic cells with normal serum immunoglobulin levels and normal numbers of marrow plasma cells. She was ultimately diagnosed with GATA2 haplo-insufficiency due to a GATA2 germ-line mutation and underwent a successful allogeneic bone marrow transplant from a 10/10 HLA matched unrelated donor.

CONCLUSIONS

The case illustrates the diagnostic difficulties in identifying GATA2 deficiencies and the importance of family history and genetic testing. GATA2 plays an important role in B-cell and dendritic cell development, and decreased numbers of those cells is a characteristic feature that should prompt consideration of GATA2 deficiency in a patient with pancytopenia. Maturation of B-cells to long-lived plasma cells is relatively unaffected in GATA2 deficiency. Allogeneic stem cell transplantation can correct immune-deficiencies and prevent leukemic transformation in patients with GATA2 deficiency.

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.

Thiotepa-busulfan-fludarabine compared to busulfan-fludarabine for sibling and unrelated donor transplant in acute myeloid leukemia in first remission

Background

A preparatory regimen consisting of thiotepa-busulfan-fludarabine (TBF) has been associated with reduced relapse in patients with haematological malignancies after haploidentical and cord blood transplants; however, few data exist regarding TBF conditioning in sibling (MSD) and unrelated donor (URD) transplants for AML.

Results

Among patients receiving a myeloablative (MAC) regimen, TBF-MAC was associated with significantly lower relapse (HR 0.47, p = 0.005) however higher non-relapse mortality (NRM, HR 2.69, p < 10^–4) as compared to BF. This led to similar leukemia-free (LFS) and overall survival (OS) between the two regimens (LFS: p = 0.6; OS: p = 0.27). When we selected TBF-MAC patients receiving busulfan 9.6 mg/kg, NRM resulted still higher but no more significantly different as compared to BF-MAC with busulfan 12.8 mg/kg (HR 1.53, p = 0.12); despite the lower busulfan dose, relapse remained inferior with TBF-MAC (HR 0.45, p = 0.01), however no difference in survival could be demonstrated (LFS: p = 0.31; OS: 0.82). Among patients receiving a reduced-intensity (RIC) regimen, similar outcome was observed with TBF-RIC and BF-RIC (LFS: p = 0.77; OS: p = 0.88).

Conclusions

TBF-MAC as conditioning regimen for transplant from MSD and URD in AML patients in first remission provided stronger anti-leukemic activity but higher NRM as compared to BF-MAC, thus leading to similar survival. TBF-MAC with busulfan 9.6 mg/kg was associated with low relapse and acceptable NRM, however again with no survival benefit. TBF-RIC and BF-RIC resulted in comparable outcome.

Methods

We conducted a registry-based study comparing outcomes of patients with AML in first remission undergoing transplant from MSD or URD prepared with either TBF (n = 212) or BF (n = 2698) conditioning.

Test Dose Pharmacokinetics in Pediatric Patients Receiving Once-Daily IV Busulfan Conditioning for Hematopoietic Stem Cell Transplant: A Reliable Approach?

Intravenous (IV) busulfan test dose pharmacokinetics (PK) has been shown to accurately predict once-daily dose requirements and improve outcomes in adult transplant patients, but there are limited data to support this approach in children. Test doses of busulfan ∼0.8 mg/kg were infused over 2 to 3 hours, followed by serial sampling to 4-6 hours postinfusion in pediatric hematopoietic stem cell transplant recipients (n = 5). Once-daily busulfan doses were calculated based on a myelosuppressive area under the concentration-time curve (AUC) target of ∼3700 to 4000 μmol·min/L and assumed dose-proportionality to the test dose. PK analysis was then repeated at full daily doses within 6-8 days of test dose administration. Plasma PK samples collected under test and full-dose conditions were analyzed using validated commercial assays and noncompartmental methods. In 4 out of 5 patients, PK estimates after once-daily IV busulfan administration differed in comparison to test dose estimates (AUC range -38.2% to +49.7%, clearance range -34.3% to +61.8%). Patients 1, 2, and 3 required increases in remaining daily busulfan doses to achieve AUC targets, and no adjustment was required in patient 4. Patient 5's AUC was 49.7% higher than expected, and he subsequently developed fatal sinusoidal obstruction syndrome. In our experience with pediatric patients, test dose PK failed to reliably predict daily dosing requirements with large discrepancies from predicted AUC targets. This article highlights the necessity for therapeutic drug monitoring of IV busulfan and inadvisability of relying solely on test-dose busulfan PK in pediatric patients. Furthermore, clinicians should consider strategies to expedite dose adjustments in real time.

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.

A novel drug interaction between busulfan and blinatumomab

Busulfan is an alkylating agent used in pre-transplant conditioning for patients undergoing hematopoietic stem cell transplantation. Several factors contribute to variations in busulfan drug disposition including bioavailability, age, liver function, genetic polymorphisms, and concurrent administration of other drugs. Busulfan is metabolized by hepatic oxidation via the cytochrome P450 3A4 system as well as through conjugation with glutathione. Interactions with drugs such as phenytoin, itraconazole, and metronidazole have been reported to alter busulfan clearance and result in sub- or supra-therapeutic concentrations. We report a case of a clinically significant drug interaction between intravenous busulfan and the bifunctional T-cell engager, blinatumomab, observed through busulfan therapeutic drug monitoring. We found that busulfan clearance was reduced resulting in a higher area under the concentration-time curve when it was administered 48 h after blinatumomab. Repeat busulfan pharmacokinetic testing two weeks later demonstrated increased clearance of the drug and a 31% higher dose recommendation.

Similar to other protein therapeutics, cytokine elevations during blinatumomab treatment can lead to cytochrome 3A4 suppression. We hypothesize that the increased busulfan levels observed could be related to a cytokine-mediated CYP3A4 suppression. This represents a unique pharmacologic consideration in hematopoietic stem cell transplantation which would impact several drugs that undergo CYP3A4 metabolism, including calcineurin inhibitors, cyclophosphamide, sirolimus, and triazole antifungals. Additionally, this mechanism of CYP3A4 suppression may be relevant in treatments and disease states where cytokine levels are elevated such as haploidentical stem cell transplantation, graft-versus-host disease, and use of chimeric antigen receptor T-cell therapy.

Pediatric patients undergoing hematopoietic stem cell transplantation can greatly benefit from a novel once-daily intravenous busulfan dosing nomogram

Busulfan, a bifunctional alkylating agent, has been used as a conditioning regimen prior to allogeneic hematopoietic stem cell transplantation (HSCT). The aim of this study was to derive a novel once-daily intravenous (IV) busulfan dosing nomogram for pediatric patients undergoing HSCT using a population pharmacokinetic (PK) model. A population PK analysis was performed using 2183 busulfan concentrations in 137 pediatric patients (age: 0.6-22.2 years), who received IV busulfan once-daily for 4 days before undergoing HSCT. Based on the final population PK model, an optimal once-daily IV busulfan dosing nomogram was derived. The percentage of simulated patients achieving the daily target area under the concentration-time curve (AUC) by the new nomogram was compared with that by other busulfan dosing regimens including the FDA regimen, the EMA regimen, and the empirical once-daily regimen without therapeutic drug monitoring (TDM). A one-compartment open linear PK model incorporating patient's body surface area, age, dosing day, and aspartate aminotransferase as a significant covariate adequately described the concentration-time profiles of busulfan. An optimal dosing nomogram based on the PK model performed significantly better than the other dosing regimens, resulting in >60% of patients achieving the target AUC while the percentage of patients exceeding the toxic AUC level was kept <25% during the entire treatment period. A novel once-daily busulfan dosing nomogram for pediatric patients undergoing HSCT is useful for clinicians, particularly in a setting where TDM service is not readily available or to optimize the dose on day 1.

Therapeutic drug monitoring-guided dosing of busulfan differs from weight-based dosing in hematopoietic stem cell transplant patients

Busulfan (Bu)-based preparative regimens in hematopoietic stem cell transplantation are commonly used. Previous studies have shown that Bu at a fixed dose of 3.2mg/kg/day (FBD) given intravenously decreases variability in drug pharmacokinetics and this decreases the dependency on therapeutic drug monitoring (TDM) of Bu. We compared the Bu dose given using TDM with the FBD of 3.2mg/kg/day. Seventy-three patients with acute leukemia, myelodysplasia, chronic myeloid leukemia, thalassemia major, and sickle cell disease were included. The mean age at transplant was 15years (range 2-55years) with 57% adults. Indication for transplantation was leukemia/myelodysplastic syndrome in 46% of the patients, while the remaining 54% were transplanted for inherited blood disorders. We found that the median FBD was lower than the median TDM dose by 39mg/day with a statistically significant difference (p<0.001) even after adjusting for the weight (median total FBD of 349mg, median TDM dose of 494mg, p<0.0001). Age and underlying condition (malignant vs. nonmalignant) were the main factors affecting Bu clearance (p<0.001 and p<0.07, respectively). TDM remains an important tool for the appropriate dosing of Bu in preparative regimens of hematopoietic stem cell transplantation, especially in populations with genetic admixture.