Outcomes from hematopoietic stem cell transplantation following treosulfan-based conditioning: A clinical and pharmacokinetic analysis.

BACKGROUND: The aims of this study are to report our experience with treosulfan-based conditioning regimens for patients with non-malignant hematologic conditions, correlating clinical outcomes at different time points post-transplant with treosulfan exposure (AUC). METHODS: This study was a single-center observational study investigating overall survival (OS), disease-free survival (DFS), and event-free survival (EFS) end-points post-transplant. The consequences of treosulfan AUC with respect to toxicity, correction of underlying disease, and long-term chimerism were also explored using pharmacokinetic analysis. RESULTS: Forty-six patients received 49 transplants with treosulfan and fludarabine-based conditioning between 2005 and 2023. Twenty-four patients also received thiotepa. Donor chimerism was assessed on either whole blood or sorted cell lines at different time points post-transplant. Thirty-nine patients received treosulfan pharmacokinetic assessment to evaluate cumulative AUC, with five infants receiving real-time assessment to facilitate daily dose adjustment. OS, DFS, and EFS were 87%, 81%, and 69%, respectively. Median follow-up was 32.1 months (range 0.82-160 months) following transplant. Lower EFS was associated with patient age (<1 year; p = .057) and lower cumulative treosulfan dose (<42 g/m2; p = .003). Stable donor chimerism in B-cell, NK-cell, and granulocyte lineages at 1-year post-transplant were more prevalent in patients receiving thiotepa conditioning. Two infants required daily dose adjustment to treosulfan to avoid high AUC. CONCLUSIONS: Excellent clinical outcomes and stable chimerism were observed in this patient series. The addition of thiotepa conferred no significant toxicity and trended toward sustained ongoing donor engraftment. Correlating treosulfan AUC with long-term patient outcomes is required.

Validation of a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of N,N-dimethylacetamide and N-monomethylacetamide in pediatric plasma.

N,N-dimethylacetamide is an excipient used in intravenous busulfan formulations, a drug used in hematopoietic stem cell transplantation conditioning. The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of N,N-dimethylacetamide, and its metabolite N-monomethylacetamide in plasma from children receiving busulfan. A 4 µl aliquot of patient plasma was extracted using 196 µl 50% methanol solution and quantified against calibrators prepared in the extraction solvent given negligible matrix effects across three concentrations. 9 [H2 ]-N,N-dimethylacetamide was used as an internal standard. Separation of N,N-dimethylacetamide and N-monomethylacetamide was achieved using a Kinetex EVO C18 stationary phase (100 mm × 2.1 mm × 2.6 µm) running an isocratic mobile phase of 30% methanol containing 0.1% formic acid at a flow of 0.2 ml/min over 3.0 min. The injection volume was 1 µl. Calibration curves for N,N-dimethylacetamide and N-monomethylacetamide were linear up to 1200 and 200 µg/L, respectively, with a lower limit of quantification 1 µg/L for both analytes. Calibrator accuracy and precision were within ± 10% of the test parameters across four concentration levels. Analytes were stable over 14 days at three different storage conditions. This method was successfully applied to measure N,N-dimethylacetamide and N-monomethylacetamide concentrations in a total of 1265 plasma samples from 77 children.

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, AUC0→∞ ) 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 AUC0→∞ 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 AUC0→∞ (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 AUC0→∞ were not influenced by patient disease.

Challenges associated with test dose pharmacokinetic predictions of high dose melphalan exposure in patients with multiple myeloma.

AIM: To evaluate the accuracy of melphalan test dose pharmacokinetic (PK) predictions of the subsequent high dose (HDM) area under the concentration-versus-time curve (AUC) and to identify sources of prediction error (PE). METHODS: A prospective multicentre PK study was conducted in 40 myeloma patients of median age 60 (range:35-71) years using a 20 mg/m2 test dose administered 1-3 days prior to HDM (predominantly 180 mg/m2). PK data were collected post the test and high doses to compare predicted versus actual AUCs determined using the trapezoidal rule. Test and high dose infusion concentration, volume and duration and the time from preparation to infusion were compared using the paired Wilcoxin rank sign test. The impact of Melphalan administration parameters on PE was evaluated using the Mann-Whitney test. The predictive capacity of a previously published population PK (PopPK) model was also examined. RESULTS: Predicted HDM AUC was within 15% of the observed values in only 63% of patients when analysed using the trapezoidal rule and 70% of patients using PopPK. Test dose infusion concentration, volume, duration and time from preparation to infusion were significantly lower than for HDM (p < 0.005). Test dose administration within 15 min of reconstitution (n = 5) was associated with significantly lower PE than administration times of 16-60 min (n = 22), p < 0.05. Test and HDM infusion concentrations were lower in patients with large PE (> ± 15%), but the differences were not significant (p = 0.078, 0.228, respectively). CONCLUSION: Test dose PK has the potential to predict subsequent HDM exposure to achieve a target AUC once melphalan administration parameters are optimised to account for stability issues in the formulation.

Quantification of vincristine and tariquidar by liquid chromatography-tandem mass spectrometry in mouse whole blood using volumetric absorptive microsampling for pharmacokinetic applications.

A liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of vincristine and tariquidar in 10 µL of mouse whole blood using volumetric absorptive microsampling devices. Samples were extracted from the devices and quantified against calibrators prepared in a human blood plasma matrix. Separation of vincristine and tariquidar was achieved using a Shimpack XR ODS III C18 stationary phase and H2 O and methanol mobile phase solvents containing 0.1% formic acid, running a gradient elution at a flow rate of 0.2 mL/min over 6.0 min. The method was linear up to 1200 ng/mL (R2 > 0.99 for both analytes), with calibrator accuracy within ± 15% of the nominal concentrations and analyte coefficient of variance <15% for both vincristine and tariquidar. Pharmacokinetic assessment of both analytes was successfully applied in mice as both single-agent therapy and combination therapy over a 24-h period, and a 2.3-fold increase in vincristine drug exposure was observed in combination with tariquidar. This study validates the use of this approach for longitudinal analysis of drug exposure in animal studies.