Association Between Busulfan Exposure And Clinical Efficacy And Safety In Children Undergoing Hematologic Stem Cell Transplantation

Objectives:To establish a population pharmacokinetic(Pop-PK)model for busulfan(BU)in children undergoing hematologic stem cell transplantation(HSCT),and evaluate the relationship of BU exposure(expressed as AUC),event-free survival(EFS)and the complication incidences within 100 days after transplantation,thereby preliminarily explore the optimal exposure of BU.Methods:Patients who had been in hematology ward of Children's Hospital of Soochow University and used BU-based conditioning before HSCT from July 2018 to October 2019 were collected.Sparse blood samples after first dose administration of BU were collected.Then we determined BU concentration in plasma using UPLC-MS/MS method.Concentration results and several covariates(such as demographic data and single nucleotide polymorphisms of GSTA1 and GSTP1)were collected to establish BU Pop-PK model using NONMEM.BU exposure,which showed by Area Under Curve(AUC)was reckoned up using Pop-PK model.Then we used COX regression analysis,third-order polynomial model,Kaplan-Meier curve to analyze the association between BU exposure and EFS as well as complication incidences within 100 days after transplantation.Results:(1)We established a well-validated UPLC-MS/MS method for determination of BU plasma concentration.Linearity was good ranged from 0.1 ?g/mL to 10 ?g/mL.Inter-and Intra-batch RSD were below 15%in lower limit of quantitation and all QC samples at low,medium and high level.In addition,the average extract recovery in this method was(97.09±10.50)%.The matrix effects normalized by internal standard were all less than 15%.Method validation suggested applicability in clinical determination.(2)In this study,467 blood samples from 128 pediatric patients were collected for the establishment of BU Pop-PK model.The typical value of the clearance(CL)and distribution volume(V)of BU were 7.71 L/h and 42.4L,respectively.Results confirmed that allometry normal fat mass(NFM)and maturation function(Fmat)can be used to describe the variability of CL,fat free mass(FFM)to describe the variability of V.However,GSTA1 and GSTP1 single nucleotide polymorphism showed no correlation with the pharmacokinetic parameters of BU.(3)63 patients followed by 16-dose BU conditioning were chosen to investigate the association between BU AUC and EFS as well as complication incidences within 100 days after transplantation.In COX proportional risk regression model,grouped BU AUC was associated with EFS(P=0.015),while other factors(age,gender,transplant type,etc.)had no effects.In Kaplan-Meier survival curve analysis,Group AUC 900-1400±M×min showed the longest EFS,followed by Group AUC>1400 ?M×min,and Group AUC<900 ?M×min had the shortest EFS.Moreover,there was a significant difference between Group AUC<900 ?M×min and Group 900-1400 ?M×min(HR=7.1,P=0.008).The result of third-order polynomial model found the lowest incidence when BU AUC was at 1246.7 gMxmin.Although no statistical difference,there was a positive trend in grade ?-?aGVHD(acute graft-versus host disease),grade ?-? OM(oral mucositis)and grade ?-?HC(hemorrhagic cystitis)with the growth of BU AUC,also a lower incidence of grade?-? aGVHD in Group AUC 900-1400 ?M×min.Conclusions:We established a UPLC-MS/MS method for BU plasma concentration determination.The variability of BU CL in pediatric patients with HSCT was related to allometry normal fat mass(NFM)and maturation function(Fmat),the variability of V was related to allometry fat free mass(FFM).The preliminarily analysis results suggested that when BU AUC in the range of 900-1400 ?M×min could be safer and more effective to pediatric HSCT patients,which contributes efforts for studying BU individualized dose administration.