Rapid and sensitive liquid chromatography-tandem mass spectrometry method for determination of protein-free pro-drug treosulfan and its biologically active monoepoxy-transformer in plasma and brain tissue

Safety and Efficacy of High-Dose Chemotherapy with TreoMel 200 vs. TreoMel 140 in Acute Myeloid Leukemia Patients Undergoing Autologous Stem Cell Transplantation

(1) Background: Treosulfan and melphalan (TreoMel)-based high-dose chemotherapy (HDCT) has shown promising safety and efficacy as a conditioning regimen for acute myeloid leukemia (AML) patients undergoing autologous stem cell transplantation (ASCT). However, despite intensive first-line induction treatment and upfront consolidation with HDCT and ASCT, AML relapse rates are still high, and further efforts are needed to improve patient outcomes. The aim of this study was to compare two melphalan dose schedules in regard to the safety of TreoMel HDCT and patient outcomes. (2) Methods: We retrospectively analyzed the safety and efficacy of two melphalan dose schedules combined with standard-dose treosulfan in AML patients undergoing HDCT and ASCT at the University Hospital of Bern, Switzerland, between August 2019 and August 2023. Patients received treosulfan 42 g/m2 combined with either melphalan 140 mg/m2 (TreoMel 140) or melphalan 200 mg/m2 (TreoMel 200). Co-primary endpoints were progression-free survival (PFS), overall survival (OS), as well as safety profile. (3) Results: We included a total of 51 AML patients: 31 (60.8%) received TreoMel 140 and 20 (39.2%) TreoMel 200. The patients' basal characteristics were comparable between both cohorts. No significant differences in the duration of hospitalization or the adverse event profile were identified. There were no statistically significant differences in relapse (0.45 vs. 0.30, p = 0.381) and mortality rates (0.42 vs. 0.15, p = 0.064) between the melphalan 140 mg/m2 and 200 mg/m2 cohorts, nor for PFS (HR: 0.81, 95% CI: 0.29-2.28, p = 0.70) or OS (HR: 0.70, 95% CI: 0.19-2.57, p = 0.59) for the TreoMel 140 vs. TreoMel 200 cohort. (4) Conclusions: A higher dose of melphalan (TreoMel 200) was well tolerated overall. No statistically significant differences for patient outcomes could be observed, possibly due to the relatively small patient cohort and the short follow-up. A longer follow-up and prospective randomized studies would be required to confirm the safety profile and clinical benefit.

Treosulfan Exposure Predicts Thalassemia-Free Survival in Patients with Beta Thalassemia Major Undergoing Allogeneic Hematopoietic Cell Transplantation

A toxicity-reduced conditioning regimen with treosulfan, fludarabine, and thiotepa in patients with high-risk β-thalassemia major has significantly improved hematopoietic stem cell transplantation (HCT) outcomes. However, complications resulting from regimen-related toxicities (RRTs), mixed chimerism, and graft rejection remain a challenge. We evaluated the dose-exposure-response relationship of treosulfan and its active metabolite S, S-EBDM, in a uniform cohort of patients with β-thalassemia major to identify whether therapeutic drug monitoring (TDM) and dose adjustment of treosulfan is feasible. Plasma treosulfan/S, S-EBDM levels were measured in 77 patients using a validated liquid chromatography with tandem mass spectrometry method, and the pharmacokinetic parameters were estimated using nlmixr2. The influence of treosulfan and S, S-EBDM exposure, and GSTA1/NQO1 polymorphisms on graft rejection, RRTs, chimerism status, and 1-year overall survival (OS), and thalassemia-free survival (TFS) were assessed. We observed that treosulfan exposure was lower in patients with graft rejection than those without (1,655 vs. 2,037 mg•h/L, P = 0.07). Pharmacodynamic modeling analysis to identify therapeutic cutoff revealed that treosulfan exposure ≥1,660 mg•hour/L was significantly associated with better 1-year TFS (97% vs. 81%, P = 0.02) and a trend to better 1-year OS (90% vs. 69%, P = 0.07). Further, multivariate analysis adjusting for known pre-HCT risk factors also revealed treosulfan exposure <1,660 mg•h/L (hazard ratio (HR) = 3.23; 95% confidence interval (CI) = 1.12-9.34; P = 0.03) and GSTA1*B variant genotype (HR = 3.75; 95% CI = 1.04-13.47; P = 0.04) to be independent predictors for inferior 1-year TFS. We conclude that lower treosulfan exposure increases the risk of graft rejection and early transplant-related mortality affecting TFS. As no RRTs were observed with increasing treosulfan exposure, TDM-based dose adjustment could be feasible and beneficial.

Assessment of brain-to-blood drug distribution using liquid chromatography

Delivery of already existing and new drugs under development to the brain necessitates passage across the blood-brain barrier (BBB) with its tight intercellular junctions, molecular components and transporter systems. Consequently, it is critical to identify the extent of brain permeation and the partitioning across the BBB. The interpretation of brain-to-blood ratios is considered to be a significant and fundamental approach for estimating drug penetration through BBB, the brain-targeting ability and central nervous system (CNS) pharmacokinetics. Among the different bioanalytical techniques, liquid chromatography with various detectors has been widely used for determination of these ratios. This review defines the different approaches for sample preparation, extraction techniques and liquid chromatography procedures concerned with the determination of drugs in blood and brain tissues and the assessment of brain-to-blood levels. These approaches are expanded to cover the analysis of several drug classes such as CNS-acting drugs, chemotherapeutics, antidiabetics, herbal medicinal products, radiopharmaceuticals, antibiotics and antivirals. Accordingly, stability in biological matrices and matrix effects are investigated. The different administration/formulation effects and the possible deviations in these ratios are also disscussed.

Pre-formulation investigations for establishing a protocol for treosulfan handling and activation

INTRODUCTION

Treosulfan is an alkylating agent that is used for the treatment of ovarian cancer and for conditioning prior to stem cell transplantation. It is a prodrug that is activated non-enzymatically to two active epoxides.

OBJECTIVES

To optimize a protocol for both in vivo samples handling and in vitro drug preparation. Treosulfan stability was tested in biological fluids at different conditions as well as for its cytotoxicity on cell lines.

RESULTS

Plasma samples can be safely frozen for a short period up to 8 h, however; for longer periods, samples should be acidified. Urine samples and cell culture media can be safely frozen regardless their pH. For in vitro investigations, incubation of treosulfan at 37 °C for 24 h activated 100% of the drug. Whole blood acidification should be avoided for the risk of hemolysis. Finally; treosulfan cytotoxicity on HL-60 cells has increased following pre-incubation for 24 h at 37 °C compared to K562 cell line.

CONCLUSION

The stability profiling of treosulfan provided a valuable reference for handling of biological samples for both in vivo and in vitro studies. These results can be utilized for further investigations concerning the drug kinetics and dynamics in addition to the development of new pharmaceutical formulations.

Relationship between exposure to treosulfan and its monoepoxytransformer - An insight from population pharmacokinetic study in pediatric patients before hematopoietic stem cell transplantation

Treosulfan (TREO), a structural analog of busulfan, is currently studied as a myeloablative agent in conditioning regimens before hematopoietic stem cell transplantation in pediatric patients. High exposure to TREO (>1650 mg∗h/mL) might be related to early toxicity, especially skin toxicity and mucositis. The aim of the present study was to investigate a potential relationship between exposure to TREO and its monoepoxytransformer (S,S-EBDM), as well as variability of the pharmacokinetics of these entities by means of a population pharmacokinetic approach with a non-linear mixed-effects analysis. The study included data from 14 children with malignant and non-malignant diseases treated with TREO in daily doses 10-14 g/m². The parent-metabolite population pharmacokinetic model was developed in NONMEM 7.3 software. Upon the constructed model, an extensive simulation was performed to assess the correlation between exposure to TREO and S,S-EBDM. It was found that TREO and S,S-EBDM pharmacokinetics was best described with 2-compartmental and 1-compartmental linear models, respectively. The vast majority (>65%) of TREO was transformed to S,S-EBDM. Overall, a considerable interpatient variability of pharmacokinetic parameters was observed, especially the clearance of S,S-EBDM. A weak correlation was found between the exposure to TREO and S,S-EBDM (r = 0.1681, p < 0.0001). Also, patients with an exposure to TREO above 1650 mg∗h/mL were most likely to have also a high exposure to S,S-EBDM (35.38 μM∗h vs. 43.14 μM∗h, p < 0.0001). In summary, a parent-metabolite population pharmacokinetic model for TREO and S,S-EBDM was developed for the first time. It was shown that there is a weak correlation between exposure to TREO and S,S-EBDM. Therefore therapeutic drug monitoring of not only prodrug but also its active epoxide might be needed.

Clinical bioanalysis of treosulfan and its epoxides: The importance of collected blood processing for valid pharmacokinetic results

Currently, there is an urgent need to establish the optimal dosing of TREO in conditioning prior to hematopoietic stem cell transplantation, especially in children. For that purpose, pharmacokinetic analyses are ongoing within clinical phase II and III trials. In this paper, HPLC methods for determination of prodrug treosulfan and/or its biologically active epoxides in human plasma or serum are reviewed for the first time, including the spectrum of analytes being quantified, detection type, and derivatization methodology. The major focus is addressed to the stability of TREO and its monoepoxide related with different strategies of patients' blood processing, e.g. blood pH lowering to different values, no pH adjustment; centrifugation of blood immediately after collection or within a few hours later. This issue is crucially important for the robust bioanalysis because the epoxytransformation of TREO is a nonenzymatic, highly pH and temperature-dependent reaction. In-depth analysis of the literature results demonstrates that some methodologies of blood treatment could produce the systematic underestimation of TREO concentrations. Consequently, the drug clearance and volume of distribution will be overestimated, which might false the association of the drug exposure with the regimen-related toxicity and clinical outcomes. The paper indicates the deficiencies of the blood processing strategies and offers hints for their refinement. The provided information ought to be important in the current investigations of the personalized TREO pharmacokinetics.

Population pharmacokinetics of treosulfan and development of a limited sampling strategy in children prior to hematopoietic stem cell transplantation

Purpose

There is an increasing interest in use of treosulfan (TREO), a structural analogue of busulfan, as an agent in conditioning regimens prior to hematopoietic stem cell transplantation (HSCT), both in pediatric and adult populations. The aim of this study was to develop a population pharmacokinetic model and to establish limited sampling strategies (LSSs) enabling accurate estimation of exposure to this drug.

Methods

The study included 15 pediatric patients with malignant and non-malignant diseases, undergoing conditioning regimens prior to HSCT including TREO administered as a 1 h or 2 h infusion at daily doses of 10, 12, or 14 g/m². A population pharmacokinetic model was developed by means of non-linear mixed-effect modeling approach in Monolix® software. Multivariate regression analysis and Bayesian method were used to develop 2- and 3-point strategies for estimation of exposure to TREO.

Results

Pharmacokinetics of TREO was best described with a two-compartmental linear model with proportional residual error. Following sampling schedules allowed accurate estimation of exposure to TREO: 1 h and 6 h or 1 h, 2 h, and 6 h for a TREO dose 12 g/m² in a 1 h infusion, or at 2 h and 6 h or 2 h, 4 h, and 8 h for a TREO dose of 12 g/m² and 14 g/m² in a 2 h infusion.

Conclusions

A two-compartmental population pharmacokinetic model of TREO was developed and successfully used to establish 2- and 3-point LSSs for accurate and precise estimation of TREO AUC_0→∞.

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.

Transport of treosulfan and temozolomide across an in-vitro blood-brain barrier model

In vitro, treosulfan (TREO) has shown high effectiveness against malignant gliomas. However, a first clinical trial for newly diagnosed glioblastoma did not show any positive effect. Even though dosing and timing might have been the reasons for this failure, it might also be that TREO does not reach the brain in sufficient amount. Surprisingly, there are no published data on TREO uptake into the brain of patients, despite extensive research on this compound. An in-vitro blood-brain barrier (BBB) model consisting of primary porcine brain capillary endothelial cells was used to determine the transport of TREO across the cell monolayer. Temozolomide (TMZ), the most widely used cytotoxic drug for malignant gliomas, served as a reference. An HPLC-ESI-MS/MS procedure was developed to detect TREO and TMZ in cell culture medium. Parallel to the experimental approach, the permeability of TREO and the reference substance across the in-vitro BBB was estimated on the basis of their physicochemical properties. The detection limit was 30 nmol/l for TREO and 10 nmol/l for TMZ. Drug transport was measured in two directions: influx, apical-to-basolateral (A-to-B), and efflux, basolateral-to-apical (B-to-A). For TREO, the A-to-B permeability was lower (1.6%) than the B-to-A permeability (3.0%). This was in contrast to TMZ, which had higher A-to-B (13.1%) than B-to-A (7.2%) permeability values. The in-vitro BBB model applied simulated the human BBB properly for TMZ. It is, therefore, reasonable to assume that the values for TREO are also meaningful. Considering the lack of noninvasive, significant alternative methods to study transport across the BBB, the porcine brain capillary endothelial cell model was efficient to collect first data for TREO that explain the disappointing clinical results for this drug against cerebral tumors.

Treosulfan-based conditioning regimens for allogeneic haematopoietic stem cell transplantation in children with non-malignant diseases

An increasing number of children with non-malignant diseases can be cured by allogeneic haematopoietic stem cell transplantation (HSCT). Treosulfan (L-treitol-1,4-bis-methanesulfonate) is being used more frequently for conditioning, owing to its' lower toxicity profile compared with conventional myeloablative regimens. A retrospective analysis was performed of children registered in the EBMT database, who received treosulfan before HSCT between January 2005 and 2010, to identify possible dose-related toxicity and determine the incidence of engraftment, treatment-related mortality and overall survival (OS). Results from 316 transplants from 11 different countries are presented. Ninety-five (30%) were under 1 year of age at the time of transplant. OS was 83% and event-free survival was 76%; 3-year OS and event-free survival of infants below 1 year were 79% and 73%, respectively. No association was found with age at transplant, dose of treosulfan given, other agents used in combination with treosulfan, donor type, stem cell source, or second or subsequent transplant. In this report of the largest number of children to date receiving treosulfan for non-malignant diseases, treosulfan is shown to be a safe and effective agent even for those under 1 year of age at the time of transplant. Further prospective studies are needed using precisely defined protocols with pharmacokinetic monitoring and detailed chimerism analysis. In addition, long-term studies will be vital to determine long-term effects, for example, on fertility in comparison with other regimens.