A semi-mechanistic model based on glutathione depletion to describe intra-individual reduction in busulfan clearance.

AIM: To develop a semi-mechanistic model, based on glutathione depletion and predict a previously identified intra-individual reduction in busulfan clearance to aid in more precise dosing. METHODS: Busulfan concentration data, measured as part of regular care for allogeneic hematopoietic cell transplantation (HCT) patients, were used to develop a semi-mechanistic model and compare it to a previously developed empirical model. The latter included an empirically estimated time effect, where the semi-mechanistic model included theoretical glutathione depletion. As older age has been related to lower glutathione levels, this was tested as a covariate in the semi-mechanistic model. Lastly, a therapeutic drug monitoring (TDM) simulation was performed comparing the two models in target attainment. RESULTS: In both models, a similar clearance decrease of 7% (range -82% to 44%), with a proportionality to busulfan metabolism, was found. After 40 years of age, the time effect increased with 4% per year of age (0.6-8%, P = 0.009), causing the effect to increase more than a 2-fold over the observed age-range (0-73 years). Compared to the empirical model, the final semi-mechanistic model increased target attainment from 74% to 76%, mainly through better predictions for adult patients. CONCLUSION: These results suggest that the time-dependent decrease in busulfan clearance may be related to gluthathione depletion. This effect increased with older age (>40 years) and was proportional to busulfan metabolism. The newly constructed semi-mechanistic model could be used to further improve TDM-guided exposure target attainment of busulfan in patients undergoing HCT.

Clinical Trial Simulation To Optimize Trial Design for Fludarabine Dosing Strategies in Allogeneic Hematopoietic Cell Transplantation.

Optimal fludarabine exposure has been associated with improved treatment outcome in allogeneic hematopoietic cell transplantation, suggesting potential benefit of individualized dosing. A randomized controlled trial (RCT) comparing alternative fludarabine dosing strategies to current practice may be warranted, but should be sufficiently powered for a relevant end point, while still feasible to enroll. To find the optimal design, we simulated RCTs comparing current practice (160 mg/m2 ) to either covariate-based or therapeutic drug monitoring (TDM)-guided dosing with potential outcomes being nonrelapse mortality (NRM), graft failure, or relapse, and ultimately overall survival (covering all three aforementioned outcomes). The inclusion in each treatment arm (n) required to achieve 80% power was calculated for all combinations of end points and dosing comparisons. The trial requiring the lowest n for sufficient power compared TDM-guided dosing to current practice with NRM as primary outcome (n = 70, NRM decreasing from 21% to 5.7%). We conclude that a superiority trial is feasible.

Sialic Acid-Engineered IL4-10 Fusion Protein is Bioactive and Rapidly Cleared from the Circulation.

PURPOSE: Modulating sialylation of therapeutic glycoproteins may be used to influence their clearance and systemic exposure. We studied the effect of low and high sialylated IL4-10 fusion protein (IL4-10 FP) on in vitro and in vivo bioactivity and evaluated the effect of differential sialylation on pharmacokinetic parameters. METHODS: CHO cell lines producing low (IL4-10 FP lowSA) and high sialylated (IL4-10 FP highSA) fusion protein were generated. Bioactivity of the proteins was evaluated in an LPS-stimulated whole blood assay. Pharmacokinetics were studied in rats, analyzing plasma levels of IL4-10 FP upon intravenous injection. In vivo activity was assessed in an inflammatory pain mice model upon intrathecal injection. RESULTS: IL4-10 FP lowSA and IL4-10 FP highSA had similar potency in vitro. The pharmacokinetics study showed a 4-fold higher initial systemic clearance of IL4-10 FP lowSA, whereas the calculated half-life of both IL4-10 FP lowSA and IL4-10 FP highSA was 20.7 min. Finally, both IL4-10 FP glycoforms inhibited persistent inflammatory pain in mice to the same extent. CONCLUSIONS: Differential sialylation of IL4-10 fusion protein does not affect the in vitro and in vivo activity, but clearly results in a difference in systemic exposure. The rapid systemic clearance of low sialylated IL4-10 FP could be a favorable characteristic to minimize systemic exposure after administration in a local compartment.

Population Pharmacokinetics of Fludarabine in Children and Adults during Conditioning Prior to Allogeneic Hematopoietic Cell Transplantation.

BACKGROUND: Fludarabine is often used as an important drug in reduced toxicity conditioning regimens prior to hematopoietic cell transplantation (HCT). As no definitive pharmacokinetic (PK) basis for HCT dosing for the wide age and weight range in HCT is available, linear body surface area (BSA)-based dosing is still used. OBJECTIVE: We sought to describe the population PK of fludarabine in HCT recipients of all ages. METHODS: From 258 HCT recipients aged 0.3-74 years, 2605 samples were acquired on days 1 (42%), 2 (17%), 3 (4%) and 4 (37%) of conditioning. Herein, the circulating metabolite of fludarabine was quantified, and derived concentration-time data were used to build a population PK model using non-linear mixed-effects modelling. RESULTS: Variability was extensive where area under the curve ranged from 10 to 66 mg h/L. A three-compartment model with first-order kinetics best described the data. Actual body weight (BW) with standard allometric scaling was found to be the best body-size descriptor for all PK parameters. Estimated glomerular filtration rate (eGFR) was included as a descriptor of renal function. Thus, clearance was differentiated into a non-renal (3.24 ± 20% L/h/70 kg) and renal (eGFR × 0.782 ± 11% L/h/70 kg) component. The typical volumes of distribution of the central (V1), peripheral (V2), and second peripheral (V3) compartments were 39 ± 8%, 20 ± 11%, and 50 ± 9% L/70 kg respectively. Intercompartmental clearances between V1 and V2, and V1 and V3, were 8.6 ± 8% and 3.8 ± 13% L/h/70 kg, respectively. CONCLUSION: BW and eGFR are important predictors of fludarabine PK. Therefore, current linear BSA-based dosing leads to highly variable exposure, which may lead to variable treatment outcome.

Simultaneous quantification of busulfan, clofarabine and F-ARA-A using isotope labelled standards and standard addition in plasma by LC-MS/MS for exposure monitoring in hematopoietic cell transplantation conditioning.

In allogeneic hematopoietic cell transplantation (HCT) it has been shown that over- or underexposure to conditioning agents have an impact on patient outcomes. Conditioning regimens combining busulfan (Bu) and fludarabine (Flu) with or without clofarabine (Clo) are gaining interest worldwide in HCT. To evaluate and possibly adjust full conditioning exposure a simultaneous analysis of Bu, F-ARA-A (active metabolite of Flu) and Clo in one analytical run would be of great interest. However, this is a chromatographical challenge due to the large structural differences of Bu compared to F-ARA-A and Clo. Furthermore, for the bioanalysis of drugs it is common to use stable isotope labelled standards (SILS). However, when SILS are unavailable (in case of Clo and F-ARA-A) or very expensive, standard addition may serve as an alternative to correct for recovery and matrix effects. This study describes a fast analytical method for the simultaneous analysing of Bu, Clo and F-ARA-A with liquid chromatography-tandem mass spectrometry (LC-MS/MS) including standard addition methodology using 604 spiked samples. First, the analytical method was validated in accordance with European Medicines Agency guidelines. The lower limits of quantification (LLOQ) were for Bu 10µg/L and for Clo and F-ARA-A 1µg/L, respectively. Variation coefficients of LLOQ were within 20% and for low medium and high controls were all within 15%. Comparison of Bu, Clo and F-ARA-A standard addition results correspond with those obtained with calibration standards in calf serum. In addition for Bu, results obtained by this study were compared with historical data analysed within TDM. In conclusion, an efficient method for the simultaneous quantification of Bu, Clo and F-ARA-A in plasma was developed. In addition, a robust and cost-effective method to correct for matrix interference by standard addition was established.