Population Pharmacokinetics of Melphalan in a Large Cohort of Autologous and Allogeneic Hematopoietic Cell Transplantation Recipients: Towards Individualized Dosing Regimens

High Melphalan Exposure Increases the Risk of Graft-Versus-Host Disease in Pediatric Patients Undergoing Alpha-Beta T-Cell Depleted Haploidentical Transplantation

BACKGROUND

Melphalan is often used as the backbone agent for conditioning prior to A/B-T-cell depleted (A/B-TCD) hematopoietic cell transplant (HCT) due to lower rates of organ toxicity compared to busulfan or total-body irradiation, albeit with significant mucosal injury. Traditional dosing based on body-surface-area (BSA) may result in non-optimal melphalan exposure among certain patient subsets.

OBJECTIVES

As mucosal injury is linked to initiation of alloreactivity, we hypothesized that high exposure of melphalan predicted via a pharmacokinetic (PK) model would be associated with an increased risk of acute graft-versus-host disease (aGVHD).

STUDY DESIGN

We performed an analysis of 85 patients who underwent A/B-TCD haploidentical HCT on 2 prospective trials using melphalan-based conditioning for treatment of malignancy at 3 centers from 2015 to 2024. Most patients (61.2%) received a total dose of melphalan at 140 mg/m2 using actual body weight; others received a dose adjusted for obesity or age <2 years. We analyzed outcomes based on whether melphalan exposure was above or below the median exposure for the group.

RESULTS

The 100-day cumulative incidences of engraftment syndrome (ES), grade II-IV aGVHD, and grade III-IV aGVHD were 34.2%, 24.8%, and 17.1%, respectively. The 3-year cumulative incidence of chronic GVHD (cGVHD), non-relapse mortality (NRM), and relapse were 17.5%, 8.7%, 21.8%, respectively. The 3-year cumulative incidence of disease-free survival (DFS) and severe GVHD-relapse-free survival (GRFS) were 71.4% and 55.6%, respectively. ES was significantly associated with the subsequent development of aGVHD, both grade II-IV (41.4% vs. 17.3% in those with and without ES, P = .01) and grade III-IV (34.5% vs. 8.5% in those with and without ES; P = .003). Chronic GVHD occurred at significantly higher rates in patients with prior Grade II-IV (66.7% vs. 0% for Grade 0-I; P < .001) and Grade III-IV aGVHD (75% vs. 4.3% for Grade 0-II; P < .001). Compared to non-obese patients, the PK model predicted lower melphalan exposure (P = .02) in obese patients where adjusted ideal body weight was utilized, suggesting overcorrection of the dose. There was no impact of melphalan exposure on immunologic rejection. The median melphalan exposure was 6.81 mg*hr/L (range, 4.4-8.8). Compared to a melphalan exposure ≤6.8 mg*hr/L, a melphalan exposure >6.8 mg*hr/L was associated with a higher incidence of ES (48.8% vs. 19.1%; P = .005), grade II-IV aGVHD (39.3% vs. 10.1%; P = .002), and grade III-IV aGVHD (31.5% vs. 2.5%; P < .001). The 3-year incidence of cGVHD was 27.2% in those with high predicted melphalan exposure compared to 7.4% for low exposure (P = .03); with no difference in 3-year NRM incidence (9.2% vs. 7.7%; P = .82) or 3-year relapse incidence (16.8% vs. 27.6%; P = .31) for high compared to low exposure. However, GRFS was significantly worse in patients with high exposure (46.4%) vs. low exposure (64.6%; P = .02).

CONCLUSIONS

High melphalan exposure predicted by a validated population PK model is associated with an increased likelihood of developing ES and subsequently acute and chronic GVHD. Given that a substantial number of patients already require adjustment of standard BSA-based dosing for young age or obesity, a prospective trial of model-based dosing to individualize melphalan exposure is warranted to confirm these results.

Influence of Obesity on the Efficacy and Toxicity of Patients Undergoing Autologous Hematopoietic Cell Transplantation for Lymphoma

Hematopoietic cell transplantation requires higher doses of chemotherapy, and practices of adjusting the weight because of concerns of organ toxicity are common. This retrospective analysis of 239 adult recipients of autologous hematopoietic cell transplantation for lymphoma assessed the effect of obesity on transplantation outcomes.

BACKGROUND

Prior data evaluating the impact of obesity in autologous hematopoietic cell transplantation (AHCT) for lymphomas have provided differing results when assessing overall (OS) and progression-free survival (PFS). Impact on survival outcomes have been described, but direct comparison of discrete toxicities is lacking.

PATIENTS AND METHODS

We retrospectively compared outcomes with patients divided between 3 groups: nonobese patients (n = 129), obese patients dosed on adjusted body weight (AdjBW) (n = 32), and obese patients dosed on total body weight (TBW) (n = 78).

RESULTS

In multivariate analysis of OS with the nonobese group as the comparator, outcomes trended worse in obese patients dosed on AdjBW (HR 1.22, 95% CI 0.52-2.85) but were improved in obese patients dosed on TBW (HR 0.19, 95% CI 0.04-0.85, P = .012). PFS of obese patients dosed on AdjBW vs. the nonobese group was comparable (HR 1.19, 95% CI 0.63-2.24), but improved in obese patients dosed on TBW (HR 0.45, 95% CI 0.23-0.89, P = .021). Notably, no differences were noted between groups in gastrointestinal, infectious, renal, or hepatic toxicities.

CONCLUSION

In summary, our data suggest that recipients of AHCT for lymphoma should be dosed on TBW to maximize curative outcomes with no apparent increase in toxicities.

Optimizing high dose melphalan

Melphalan, has been a major component of myeloma therapy since the 1950s. In the context of hematopoietic cell transplantation (HCT), high dose melphalan (HDM) is the most common conditioning regimen used due to its potent anti-myeloma effects and manageable toxicities. Common toxicities associated with HDM include myelosuppression, gastrointestinal issues, and mucositis. Established approaches to reduce these toxicities encompass dose modification, nausea prophylaxis with 5HT3 receptor antagonists, cryotherapy, amifostine use, and growth factors. Optimization of melphalan exposure through personalized dosing and its combination with other agents like busulfan, or bendamustine show promise. Propylene glycol-free melphalan (Evomela) represents a novel formulation aiming to enhance drug stability and reduce adverse effects. This review explores strategies to enhance the efficacy and mitigate the toxicity of HDM in multiple myeloma. Future directions involve exploring these strategies in clinical trials to improve the safety and efficacy of HDM, thereby enhancing outcomes for multiple myeloma patients undergoing autologous HCT.

Association between busulfan exposure and survival in patients undergoing a CD34+ selected stem cell transplantation

Busulfan is an alkylating drug routinely used in conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT). A myeloablative conditioning regimen, including busulfan, is commonly used in patients undergoing T-cell depletion (TCD) and allo-HCT, but data on optimal busulfan pharmacokinetic (PK) exposure in this setting are limited. Between 2012 and 2019, busulfan PK was performed to target an area under the curve exposure between 55 and 66 mg × h/L over 3 days using a noncompartmental analysis model. We retrospectively re-estimated busulfan exposure following the published population PK (popPK) model (2021) and correlated it with outcomes. To define optimal exposure, univariable models were performed with P splines, wherein hazard ratio (HR) plots were drawn, and thresholds were found graphically as the points at which the confidence interval crossed 1. Cox proportional hazard and competing risk models were used for analyses. 176 patients were included, with a median age of 59 years (range, 2-71). Using the popPK model, the median cumulative busulfan exposure was 63.4 mg × h/L (range, 46.3-90.7). The optimal threshold was at the upper limit of the lowest quartile (59.5 mg × h/L). 5-year overall survival (OS) with busulfan exposure ≥59.5 vs <59.5 mg × h/L was 67% (95% CI, 59-76) vs 40% (95% CI, 53-68), respectively (P = .02), and this association remained in a multivariate analyses (HR, 0.5; 95% CI, 0.29; 0.88; P = .02). In patients undergoing TCD allo-HCT, busulfan exposure is significantly associated with OS. The use of a published popPK model to optimize exposure may significantly improve the OS.

A rapid and sensitive LC-MS/MS method for simultaneous determination of melphalan and its monohydroxy and dihydroxy metabolites in human plasma

As a hydrolysis mediated drug in vivo, the pharmacokinetics of melphalan are highly variable in patients. Few methodologies could simultaneously measure the concentrations of melphalan and its hydrolyzed metabolites in plasma. The aim of this study was to develop a simple, rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of melphalan and its hydrolyzed metabolites, monohydroxy melphalan (MOH melphalan) and dihydroxy melphalan (DOH melphalan). A simple protein precipitation was employed for sample preparation and melphalan-d8 was used as internal standard. Baseline separation of target analytes was achieved using an XSelect HSS T3 column (2.1 × 50 mm, 5 µm) with a gradient elution at a flow rate of 0.5 mL/min in 5 min. The monitored transitions were m/z 305.1 → 287.7 for melphalan, m/z 287.1 → 228.0 for MOH melphalan, m/z 269.3 → 251.8 for DOH melphalan, and m/z 313.1 → 295.7 for melphalan-d8. The method was fully validated in accordance with the FDA guideline. The calibration curves were established over the range of 5.22-5220 ng/mL for melphalan, 7.94-1588 ng/mL for MOH-melphalan, and 15.0-3000 ng/mL for DOH-melphalan with the regression coefficients greater than 0.99. The intra- and inter-day coefficients of variation for the analytes were ≤11.0% and all the biases were less than 8.3%. The method has been successfully applied to the quantification of melphalan and its metabolites in clinical plasma samples obtained from hematopoietic stem cell transplantation patients who received a dose of melphalan for pre-transplant conditioning.

Evaluation of Melphalan Exposure in Lymphoma Patients Undergoing BEAM and Autologous Hematopoietic Cell Transplantation

High-dose melphalan is one of the main cytotoxic DNA alkylating agents and is used in many transplantation conditioning regimens. Studies have shown a wide range of drug exposure when a traditional weight-based dose of melphalan is used. The optimal melphalan dose in BEAM (carmustine, etoposide, cytarabine, and melphalan), which results in maximum efficacy with acceptable toxicity, is unknown. In this pharmacokinetic (PK) analysis of 105 patients with lymphoma undergoing treatment with BEAM and autologous hematopoietic cell transplantation, we initially estimated melphalan exposure as area under the curve (AUC) by a noncompartmental analysis and subsequently compared it with a newly developed 2-compartment population-PK model. The 2 models correlated closely with each other. We found that the traditional fixed weight-based dosing of propylene glycol-free (captisol-enabled) melphalan in BEAM results in a wide variation in exposure as estimated by both models. Higher melphalan exposure was significantly associated with increased metabolic toxicities but did not seem to impact progression-free survival. Although our study suggests a melphalan AUC of 8 mg·h/L as a potential target in BEAM, larger prospective studies using personalized PK-directed melphalan dosing are needed to determine the optimal melphalan exposure in lymphomas.