Disposition of treosulfan and its active monoepoxide in a bone marrow, liver, lungs, brain, and muscle: Studies in a rat model with clinical relevance

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.

Metformin pretreatment ameliorates busulfan-induced liver endothelial toxicity during haematopoietic stem cell transplantation

The success of Haematopoietic cell transplantation (HCT) is often limited by regimen-related toxicity (RRT) caused by conditioning regimen drugs. Among different conditioning drugs, busulfan (Bu) and treosulfan (Treo), although widely used in HCT, exhibit different toxicity profiles, the mechanism of which is still unclear. Here we investigated the effects of Bu and Treo in endothelial cells. While both Bu and Treo induced DNA damage in endothelial cells, we observed Bu alone to induce oxidative stress and sustained activation of phospho-ERK1/2, leading to apoptosis. However, Treo-treated cells exhibited no oxidative stress/apoptosis of endothelial cells. Screening of pharmacological inhibitors of both ROS and p-ERK revealed that metformin effectively ameliorates Bu-mediated toxicity in endothelial cells. In Balb/c mice, we observed a significant reduction in bone marrow endothelial cells in Bu-treated mice compared to Treo-treated mice. Further, liver sinusoidal endothelial cells (LSEC) was damaged by Bu, which is implicated in liver vasculature and their functional capacity to uptake FITC-albumin. However, Treo-treated mice liver vasculature was morphologically and functionally normal. When mice were pretreated with metformin followed by Bu, LSECs damage was ameliorated morphologically and functionally. Bone marrow transplants done on these mice did not affect the engraftment of donor cells.

Evaluation of treosulfan cumulative exposure in paediatric patients through population pharmacokinetics and dosing simulations

AIM

To investigate the pharmacokinetics (PK) of intravenous treosulfan in paediatric patients undergoing haematopoietic stem cell transplantation (HSCT) for a broad range of diseases and to explore the impact of different dosing regimens on treosulfan exposure (area under the concentration-time curve, AUC_0→∞ ) through dosing simulations.

METHODS

A prospective multicentre PK study was conducted using treosulfan concentration data (n = 423) collected from 53 children (median age 3.5, range 0.2-17.0 years) receiving three daily age-guided doses (10-14 g/m² ). Population PK modelling was performed using NONMEM software, utilising a stepwise forward selection backward elimination method and likelihood-ratio test for screening covariates to describe PK variability. Monte Carlo simulation was used to generate patient PK data for 10 000 virtual paediatric patients and cumulative AUC_0→∞ values were evaluated using age, body surface area (BSA) and model-based dosing regimens, targeting 4800 mg*h/L.

RESULTS

Treosulfan concentration data were described using a one-compartment PK model with first-order elimination. Population mean (95% CI) estimates for clearance (CL) and volume of distribution (V) were 16.3 (14.9-18.1) L/h and 41.9 (38.8-45.1) L, respectively. Allometrically scaled body weight was the best covariate descriptor for CL and V, and maturational age further explained variability in CL. Dosing simulations indicated that in young patient groups (<2 years), a model-based dosing regimen more accurately achieved the target AUC_0→∞ (58.3%) over the age (42.6%) and BSA-based (51.3%) regimens.

CONCLUSION

Treosulfan disposition was described through allometric body weight and maturational age descriptors. Model-informed dosing is recommended for patients under 2 years. Treosulfan PK parameters and AUC_0→∞ were not influenced by patient disease.

Comparison of Melphalan Combined with Treosulfan or Busulfan as High-Dose Chemotherapy before Autologous Stem Cell Transplantation in AML

Simple Summary

Different consolidation strategies are available for acute myeloid leukemia (AML) patients fit for intensive treatment. For favorable- or intermediate-risk AML, high-dose chemotherapy (HDCT) followed by autologous stem cell transplantation (ASCT) is one of these options. Busulfan plus melphalan is a frequently used and efficient HDCT regimen, but it bears neurotoxic potential and may cause irreversible alopecia, amongst other toxicities. Thus, improving HDCT regimens with lesser toxicity, albeit at comparable anti-leukemic efficacy, is wishful. We combined treosulfan with its more favorable toxicity profile with melphalan for HDCT and compared these patients with a group receiving busulfan/treosulfan. Whereas disease-free and overall survival did not differ significantly, the treosulfan regimen compared favorably, with the absence of neurotoxicity and irreversibly alopecia. Treosulfan serum levels by mass cytometry demonstrated considerable interindividual biovariability. Further studies should explore treosulfan/melphalan for HDCT/ASCT in AML, aiming to improve the quality of life of AML survivors and offer safer consolidation strategies.

Abstract

(1) Background: High-dose chemotherapy (HDCT) before autologous stem cell transplantation (ASCT) in acute myeloid leukemia (AML) patients predominantly combines busulfan with cyclophosphamide or melphalan. Treosulfan compares favorably regarding lower inter-individual bioavailability and neurotoxicity, but so far, had not been studied before ASCT in AML. (2) Methods: This single-center study investigated AML patients undergoing ASCT in CR1 between November 2017 and September 2020. The first 16 patients received busulfan 16 mg/kg b.w. (days −5 to −2) and melphalan 140 mg/m² (day −1) (BuMel). In a subsequent (TreoMel) cohort, 20 patients received treosulfan 14 g/m² (days −4 to −2) and melphalan. Plasma concentrations of busulfan and treosulfan were determined by mass spectrometry. (3) Results: Neutrophil engraftment and platelet recovery were similar, and PFS and OS were comparable. In only the BuMel cohort, patients reported central nervous toxicities, including seizures (6%) and encephalopathy (12%). The mean AUC for busulfan was 1471.32 μM*min, and for treosulfan it was 836.79 mg/L*h, with ranges of 804.1–2082 μM*min and 454.2–1402 mg/L*h. The peak values for busulfan ranged between 880.19–1734 μg/L and for treosulfan between 194.3–489.25 mg/L. (4) Conclusions: TreoMel appears to be safe and effective for pre-ASCT treatment in AML patients. Due to considerable interindividual biovariability, pharmacologic monitoring may also be warranted for the use of treosulfan.

Treosulfan-induced myalgia in pediatric hematopoietic stem cell transplantation identified by an electronic health record text mining tool

Treosulfan is increasingly used as myeloablative agent in conditioning regimen prior to allogeneic hematopoietic stem cell transplantation (HSCT). In our pediatric HSCT program, myalgia was regularly observed after treosulfan-based conditioning, which is a relatively unknown side effect. Using a natural language processing and text-mining tool (CDC), we investigated whether treosulfan compared with busulfan was associated with an increased risk of myalgia. Furthermore, among treosulfan users, we studied the characteristics of given treatment of myalgia, and studied prognostic factors for developing myalgia during treosulfan use. Electronic Health Records (EHRs) until 28 days after HSCT were screened using the CDC for myalgia and 22 synonyms. Time to myalgia, location of pain, duration, severity and drug treatment were collected. Pain severity was classified according to the WHO pain relief ladder. Logistic regression was performed to assess prognostic factors. 114 patients received treosulfan and 92 busulfan. Myalgia was reported in 37 patients; 34 patients in the treosulfan group and 3 patients in the busulfan group (p = 0.01). In the treosulfan group, median time to myalgia was 7 days (0–12) and median duration of pain was 19 days (4–73). 44% of patients needed strong acting opiates and adjuvant medicines (e.g. ketamine). Hemoglobinopathy was a significant risk factor, as compared to other underlying diseases (OR 7.16 95% CI 2.09–30.03, p = 0.003). Myalgia appears to be a common adverse effect of treosulfan in pediatric HSCT, especially in hemoglobinopathy. Using the CDC, EHRs were easily screened to detect this previously unknown side effect, proving the effectiveness of the tool. Recognition of treosulfan-induced myalgia is important for adequate pain management strategies and thereby for improving the quality of hospital stay.

Computational Approaches in Preclinical Studies on Drug Discovery and Development

Because undesirable pharmacokinetics and toxicity are significant reasons for the failure of drug development in the costly late stage, it has been widely recognized that drug ADMET properties should be considered as early as possible to reduce failure rates in the clinical phase of drug discovery. Concurrently, drug recalls have become increasingly common in recent years, prompting pharmaceutical companies to increase attention toward the safety evaluation of preclinical drugs. In vitro and in vivo drug evaluation techniques are currently more mature in preclinical applications, but these technologies are costly. In recent years, with the rapid development of computer science, in silico technology has been widely used to evaluate the relevant properties of drugs in the preclinical stage and has produced many software programs and in silico models, further promoting the study of ADMET in vitro. In this review, we first introduce the two ADMET prediction categories (molecular modeling and data modeling). Then, we perform a systematic classification and description of the databases and software commonly used for ADMET prediction. We focus on some widely studied ADMT properties as well as PBPK simulation, and we list some applications that are related to the prediction categories and web tools. Finally, we discuss challenges and limitations in the preclinical area and propose some suggestions and prospects for the future.

Population pharmacokinetic approach for evaluation of treosulfan and its active monoepoxide disposition in plasma and brain on the basis of a rat model

PURPOSE

Efficacy of treosulfan, used in the treatment of marrow disorders, depends on the activity of its monoepoxy-(EBDM) and diepoxy compounds. The study aimed to describe the pharmacokinetics of treosulfan and EBDM in the rat plasma and brain by means of mixed-effects modelling.

METHODS

The study had a one-animal-per-sample design and included ninty-six 10-week-old Wistar rats of both sexes. Treosulfan and EBDM concentrations in the brain and plasma were measured by an HPLC-MS/MS method. The population pharmacokinetic model was established in NONMEM software with a first-order estimation method with interaction.

RESULTS

One-compartment pharmacokinetic model best described changes in the concentrations of treosulfan in plasma, and EBDM concentrations in plasma and in the brain. Treosulfan concentrations in the brain followed a two-compartment model. Both treosulfan and EBDM poorly penetrated the blood-brain barrier (ratio of influx and efflux clearances through the blood-brain barrier was 0.120 and 0.317 for treosulfan and EBDM, respectively). Treosulfan plasma clearance was significantly lower in male rats than in females (0.273 L/h/kg vs 0.419 L/h/kg).

CONCLUSIONS

The developed population pharmacokinetic model is the first that allows the prediction of treosulfan and EBDM concentrations in rat plasma and brain. These results provide directions for future studies on treosulfan regarding the contribution of transport proteins or the development of a physiological-based model.

Treosulfan Pharmacokinetics and its Variability in Pediatric and Adult Patients Undergoing Conditioning Prior to Hematopoietic Stem Cell Transplantation: Current State of the Art, In-Depth Analysis, and Perspectives

Treosulfan is a prodrug that undergoes a highly pH- and temperature-dependent nonenzymatic conversion to the monoepoxide {(2S,3S)-1,2-epoxy-3,4-butanediol 4-methanesulfonate [S,S-EBDM]} and diepoxide {(2S,3S)-1,2:3,4-diepoxybutane [S,S-DEB]}. Currently, treosulfan is tested in clinical trials as an alternative to busulfan in conditioning prior to hematopoietic stem cell transplantation (HSCT). Of note, the optimal dosing of the prodrug is still unresolved, especially in infants. In this paper, the pharmacokinetics of treosulfan, together with its biologically active epoxides, is comprehensively reviewed for the first time, with the focus on conditioning prior to HSCT. Most of the insightful data presented in this review comes from studies that have been conducted in the last 3 years. The article widely discusses the volume of distribution and total clearance of treosulfan. In particular, the interindividual variability of these key parameters in infants, children above 1 year of age, and adults is analyzed, including possible covariates. A clinically important aspect of the formation rate-limited elimination of S,S-EBDM and S,S-DEB is described, including the correlation between the exposure of the prodrug and S,S-EBDM in children. The significance of the elimination half-life of treosulfan and its epoxides for successful conditioning prior to HSCT is also raised. Furthermore, the organ disposition of treosulfan and S,S-EBDM in rats is discussed in the context of the clinical toxicity and myeloablative activity of treosulfan versus busulfan. Moreover, perspectives for future therapeutic drug monitoring of treosulfan are presented. The review is intended to be helpful to pharmacists and doctors in the comprehension of the clinical pharmacokinetics of treosulfan.

Kinetics of in Vitro Guanine- N7-Alkylation in Calf Thymus DNA by (2 S,3 S)-1,2-Epoxybutane-3,4-diol 4-methanesulfonate and (2 S,3 S)-1,2:3,4-Diepoxybutane: Revision of the Mechanism of DNA Cross-Linking by the Prodrug Treosulfan

Prodrug treosulfan, originally registered for treatment of ovarian cancer, has gained a use in conditioning prior to hematopoietic stem cell transplantation. Treosulfan converts nonenzymatically to the monoepoxide intermediate (EBDM), and then to (2 S,3 S)-1,2:3,4-diepoxybutane (DEB). The latter alkylates DNA forming mainly (2' S,3' S)- N-7-(2',3',4'-trihydroxybut-1'-yl)guanine (THBG) and (2 S,3 S)-1,4-bis(guan-7'-yl)butane-2,3-diol cross-link (bis-N7G-BD) via the intermediate epoxide adduct (EHBG). It is believed that DNA cross-linking by DEB is a primary mechanism for the anticancer and myeloablative properties of treosulfan, but clear evidence is lacking. Recently, we have proved that EBDM alkylates DNA producing (2' S,3' S)- N-7-(2',3'-dihydroxy-4'-methylsulfonyloxybut-1'-yl)-guanine (HMSBG) and that free HMSBG converts to EHBG. In this paper, we investigated the kinetics of HMSBG, bis-N7G-BD, and THBG in DNA in vitro to elucidate the contribution of EBDM and DEB to treosulfan-dependent DNA-DNA cross-linking. Calf thymus DNA was exposed to ( A) 100 μM treosulfan, ( B) 200 μM treosulfan, and ( C) DEB at a concentration 100 μM, exceeding that produced by 200 μM treosulfan. Following mild acid thermal hydrolysis of DNA, ultrafiltration, and off-line HPLC purification, the guanine adducts were quantified by LC-MS/MS. Both bis-N7G-BD and THBG reached highest concentrations in the DNA in experiment B. Ratios of the maximal concentration of bis-N7G-BD and THBG to DEB (adduct C_max/DEB C_max) in experiments A and B were 1.7-3.0-times greater than in experiment C. EHBG converted to the bis-N7G-BD cross-link at a much higher rate constant (0.20 h^-1) than EBDM and DEB initially alkylated the DNA (1.8-3.4 × 10^-5 h^-1), giving rise to HMSBG and EHBG, respectively. HMSBG decayed unexpectedly slowly (0.022 h^-1) compared with the previously reported behavior of the free adduct (0.14 h^-1), which revealed the inhibitory effect of the DNA environment on the adduct epoxidation to EHBG. A kinetic simulation based on the obtained results and the literature pharmacokinetic parameters of treosulfan, EBDM, and DEB suggested that in patients treated with the prodrug, EBDM could produce the vast majority of EHBG and bis-N7G-BD via HMSBG. In conclusion, EBDM can produce DNA-DNA lesions independently of DEB, and likely plays a greater role in DNA cross-linking after in vivo administration of treosulfan than DEB. These findings compel revision of the previously proposed mechanism of the pharmacological action of treosulfan and contribute to better understanding of the importance of EBDM for biological effects.

In Vivo Red Blood Cells/Plasma Partition Coefficient of Treosulfan and Its Active Monoepoxide in Rats

BACKGROUND AND OBJECTIVES

Treosulfan is a prodrug applied in the treatment of ovarian cancer and conditioning prior to stem cell transplantation. So far, the bioanalysis of treosulfan in either whole blood or red blood cells (RBC) has not been carried out. In this work, the RBC/plasma partition coefficient (K_e/p) of treosulfan and its active monoepoxide was determined for the first time.

METHODS

Male and female 10-week-old Wistar rats (n = 6/6) received an intraperitoneal injection of treosulfan at the dose of 500 mg/kg body weight. The concentrations of treosulfan and its monoepoxide in plasma (C_p) and RBC were analyzed with a validated HPLC-MS/MS method.

RESULTS

The mean K_e/p of treosulfan and its monoepoxide were 0.74 and 0.60, respectively, corresponding to the blood/plasma partition coefficient of 0.88 and 0.82. The Spearman test demonstrated that the K_e/p of the prodrug correlated with its C_p, but no correlation between the K_e/p and C_p of the active monoepoxide was observed.

CONCLUSIONS

Treosulfan and its monoepoxide achieve higher concentrations in plasma than in RBC; therefore, the choice of plasma for bioanalysis is rational as compared to whole blood. The distribution of treosulfan into RBC may be a saturable process at therapeutic concentrations.

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.