High melphalan exposure is associated with improved overall survival in myeloma patients receiving high dose melphalan and autologous transplantation.

AIM: High dose melphalan (HDM) and autologous stem cell transplantation (ASCT) retains a central role in the treatment of myeloma. The aim of this study was to determine whether HDM exposure (area under the concentration vs. time curve, AUC), is significantly associated with transplant outcomes. METHODS: Melphalan concentrations were measured in six to 11 plasma samples collected after HDM (median 192 mg m(-) (2) ) to determine melphalan AUC for a total of 114 patients. Binary logistic regression was used to assess whether melphalan AUC was associated with severe (≥ grade 3) oral mucositis. Multivariate Cox regression was used to assess whether melphalan AUC was significantly associated with time to progression, progression-free survival and overall survival (OS). RESULTS: Melphalan AUC ranged from 4.9 to 24.6 mg l(-1)  h, median 12.84 mg l(-1) h. Melphalan AUC above the median was a risk factor for severe mucositis (HR 1.21, 95% CI 1.06, 1.38, P = 0.004) but was also associated with significantly improved overall survival (OS) (HR 0.40, 95% CI 0.20, 0.81, P = 0.001), with an estimated median survival of 8.50 years vs. 5.38 years for high vs. low AUC groups. Multivariate analysis did not identify melphalan AUC as being significantly associated with time to progression or progression-free survival. CONCLUSIONS: This large scale pharmacodynamic analysis of HDM demonstrates that high melphalan exposure is associated with improved survival, with an acceptable increase in transplant toxicity. These results suggest studies targeting a higher AUC are warranted in patients undergoing HDM and ASCT for myeloma.

Development and Validation of a High Pressure Liquid Chromatography-UV Method for the Determination of Treosulfan and Its Epoxy Metabolites in Human Plasma and Its Application in Pharmacokinetic Studies.

Treosulfan (l-threitol-1,4-di-methanesulfonate) is a prodrug of a bifunctional alkylating agent that is being used increasingly in pediatric bone marrow transplantation regimens. The activation pathway is a complex reaction, which consists of two consecutive reactions leading to epoxybutane derivatives which are responsible for DNA alkylation. A simple, sensitive high performance liquid chromatography method for the determination of the sum of treosulfan and its epoxy metabolites by UV detection after derivatization with sodium diethyldithiocarbamate in human plasma was developed and validated. Plasma samples containing treosulfan and epoxy metabolites were converted into thiocarbamate derivative with 10% sodium diethyldithiocarbamate. Dinitrobiphenyl was used as an internal standard. The analysis was carried out using a reversed phase C18 column with a mobile phase consisting of methanol-water (65:35, v/v) at a flow rate of 1 mL/min. The eluent was monitored at 254 nm. The standard calibration curve was established between 2.5 and 50 µg/mL, with a correlation coefficient of 0.9987. Intra- and interday precision and accuracy of the method was <8% and met the analytical criteria. Pharmacokinetic parameters were determined in six children who received intravenous treosulfan (dose range 12-24 g/m(2)) in combination with fludarabine prior to blood or marrow transplantation.

Population pharmacokinetics of mycophenolic acid in children and young people undergoing blood or marrow and solid organ transplantation.

AIMS: To characterize the population pharmacokinetics of mycophenolic acid (MPA) and evaluate dose regimens using a simulation approach and accepted therapeutic drug monitoring targets in children and young people undergoing blood or marrow, kidney and liver transplantation. METHODS: MPA concentration-time data were collected using an age specific sampling protocol over 12h. Some patients provided randomly timed but accurately recorded blood samples. Total and unbound MPA were measured by HPLC. NONMEM was employed to analyze MPA pharmacokinetic data. Simulations (n= 1000) were conducted to assess the suitability of the MPA dose regimens to maintain total MPA AUC(0,12h) within the range 30 and 60mg l(-1) h associated with optimal outcome. RESULTS: A two-compartment pharmacokinetic model with first-order elimination best described MPA concentration-time data. Population mean estimates of MPA clearance, inter-compartmental clearance, volumes of distribution in the central and peripheral compartments, absorption rate constant and bioavailability were 6.42 l h(-1) , 3.74 l h(-1) , 7.24 l, 16.8l, 0.39h(-1) and 0.48, respectively. Inclusion of bodyweight and concomitant ciclosporin reduced the inter-individual variability in CL from 54.3% to 31.6%. Children with a bodyweight of 10kg receiving standard MPA dose regimens achieve an MPA AUC below the target range suggesting they may be at a greater risk of acute rejection. CONCLUSIONS: The population pharmacokinetic model for MPA can be used to explore dosing guidelines for safe and effective immunotherapy in children and young people undergoing transplantation.

An isocratic fluorescence HPLC assay for the monitoring of l-asparaginase activity and l-asparagine depletion in children receiving E. colil-asparaginase for the treatment of acute lymphoblastic leukaemia.

A novel assay for the determination of l-asparaginase activity in human plasma is described that is based on the HPLC quantitation of l-aspartic acid produced during enzyme incubation. Methods for monitoring l-asparagine depletion are also described. Chromatography of l-aspartic acid, l-asparagine and l-homoserine (the internal standard) involved derivatization with o-pthaldialdehyde, then separation from other amino acids on a Phenomenex Luna C(18) column using a 1 mL/min flow rate and a mobile phase consisting of di-potassium hydrogen orthophosphate propionate buffer, pH 6, with 10% methanol and 10% acetonitrile. Fluoresence detection was at excitation/emission wavelengths of 357/455 nm. Under these conditions l-aspartic acid, l-asparagine and l-homoserine had retention times of 3.5, 9.8 and 17.7 min, respectively. The l-asparaginase assay was linear from 0.1 to 10 U/mL activity and interday precision and accuracy were less than 13%. The limit of quantitation was approximately 0.03 U/mL. The assay utility was established in 12 children who received E. coli l-asparaginase as treatment for acute lymphoblastic leukaemia.

Variability in the pharmacokinetics of intravenous busulphan given as a single daily dose to paediatric blood or marrow transplant recipients.

AIM: To examine inter- and intrapatient variability in the pharmacokinetics of intravenous (i.v.) busulphan given as a single daily dose to children with malignant (n = 19) and nonmalignant (n = 21) disease. METHODS: Busulphan (120 mg m(-2), 130 mg m(-2) or 3.2 mg kg(-1)) was administered over median 2.1 h. Blood samples (4-10) were collected after the first dose, busulphan concentrations were measured and pharmacokinetic parameters, including clearance (CL) and area under the concentration-time curve (AUC), were determined using the Kinetica software (Innaphase). Interpatient variability was assessed as percent coefficient of variation (% CV). Intrapatient variability was assessed by calculating percent differences between observed full dose AUC and AUC predicted from an initial 65 mg m(-2) dose in 13 children who had busulphan pharmacokinetic monitoring. RESULTS: Clearance of i.v. busulphan in 40 children was 4.78 +/- 2.93 l h(-1) (% CV 61%), 0.23 +/- 0.08 l h(-1) kg(-1) (% CV 35%) and 5.79 +/- 1.59 l h(-1) m(-2) (% CV 27%). Age correlated significantly (p < 0.001) with CL (l h(-1)) and CL (l h(-1) kg(-1)), but not with CL (l h(-1) m(-2)). AUC normalized to the 130 mg m(-2) dose ranged from 14.1 to 56.3 mg l(-1) x h (% CV 37%) and also did not correlate with age. Interpatient variability in CL (l h(-1) m(-2)) was highest in six children with immune deficiencies (60%) and lowest in seven children with solid tumours (14%). Intrapatient variability was <13% for nine (of 13) children, but between 20 and 44% for four children. CONCLUSIONS: There is considerable inter- and intrapatient variability in i.v. busulphan CL (l h(-1) m(-2)) and exposure that is unrelated to age, especially in children with immune deficiencies. These results suggest that monitoring of i.v. busulphan pharmacokinetics is required.

Amphotericin B dose optimization in children with malignant diseases.

In this study, rational dosing guidelines for amphotericin B-deoxycholate (AmB) are proposed for children. AmB steady-state trough concentrations (C(ss,trough)) and plasma creatinine concentrations (C(creat)) were measured in 83 children (age: 10 months to 18 years) receiving prophylactic AmB therapy (1 mg/kg/day). Maximum tolerable AmB C(ss,trough) were identified by determining the probability of large (>24%, 75th percentile) increases in C(creat) after 6 days of AmB for a series of C(ss,trough) ranges. Dose requirements were determined using a concentration-targeting approach. The 0.76-1.05 mg/l C(ss,trough) range provided the maximum concentrations that still had a low probability (p < 0.29) of adverse renal effects. 1 mg/kg/day AmB produces C(ss,trough) within this range for children weighing 25-45 kg. Lighter children (10-25 kg) require higher AmB doses (1.25-1.5 mg/kg/day) to achieve target C(ss,trough), while heavier children (45-55 kg) require lower doses (0.75 mg/kg/day). These starting dose guidelines may require individualization and prospective evaluation.

Population pharmacokinetics of melphalan in paediatric blood or marrow transplant recipients.

AIM: To develop a population pharmacokinetic model for melphalan in children with malignant diseases and to evaluate limited sampling strategies for melphalan. METHODS: Melphalan concentration data following a single intravenous dose were collected from 59 children with malignant diseases aged between 0.3 and 18 years. The data were split into two sets: the model development dataset (39 children, 571 concentration observations) and the model validation dataset (20 children, 277 concentration observations). Population pharmacokinetic modelling was performed with the NONMEM software. Stepwise multiple linear regression was used to develop a limited sampling model for melphalan. RESULTS: A two-compartment model was fitted to the concentration-vs.-time data. The following covariate population pharmacokinetic models were obtained: (i) Clearance (l h(-1)) = 0.34.WT - 3.17.CPT + 0.0377.GFR, where WT = weight (kg), CPT = prior carboplatin therapy (0 = no, 1 = yes), and GFR = glomerular filtration rate (ml min(-1) 1.73 m(-2)); (ii) Volume of distribution (l) = 1.12 + 0.178.WT. Interpatient variability (coefficient of variation) was 27.3% for clearance and 33.8% for volume of distribution. There was insignificant bias and imprecision between observed and model-predicted melphalan concentrations in the validation dataset. A three-sample limited sampling model was developed which adequately predicted the area under the concentration-time curve (AUC) in the development and validation datasets. CONCLUSIONS: A population pharmacokinetic model for melphalan has been developed and validated and may now be used in conjunction with pharmacodynamic data to develop safe and effective dosing guidelines in children with malignant diseases.

Plasma protein distribution and its impact on pharmacokinetics of liposomal amphotericin B in paediatric patients with malignant diseases.

OBJECTIVE: This study investigates the association of liposomal amphotericin B (L-AmB) with plasma proteins and its impact on the pharmacokinetics of L-AmB in paediatric patients with malignant diseases. METHODS: Paediatric oncology patients (n = 39) who received multiple-doses of L-AmB were recruited into this study. The association of the drug with plasma lipoprotein was investigated using single vertical spin density gradient ultracentrifugation and quantitated with a validated HPLC assay. The unbound amphotericin B (AmB) in the plasma was separated by ultrafiltration and determined with a validated LC/MS/MS assay. RESULTS: The ex vivo lipoprotein distribution of L-AmB found that 68.3 +/- 11.8% of the drug was associated with the high density lipoprotein (HDL) fraction, which demonstrated a significant inverse correlation with posterior Bayesian estimates of L-AmB clearance (r = -0.690, p < 0.01). The average of unbound fraction of AmB in plasma of patients administered with L-AmB was 0.005, but its relationship with L-AmB clearance did not reach a statistical significance. CONCLUSION: L-AmB displays different lipoprotein distribution profile from that of the conventional AmB formulation, with L-AmB preferentially associated with HDL in plasma. The inverse correlation of L-AmB clearance to its HDL distribution contributes to the difference in the pharmacokinetic profile of L-AmB.

Population pharmacokinetics of liposomal amphotericin B in pediatric patients with malignant diseases.

A population pharmacokinetic model of liposomal amphotericin B (L-AmB) in pediatric patients with malignant diseases was developed and evaluated. Blood samples were collected from 39 pediatric oncology patients who received multiple doses of L-AmB with a dose range from 0.8 to 5.9 mg/kg of body weight/day. The patient cohort had an average age of 7 years (range, 0.2 to 17 years) and weighed an average of 28.8 +/- 19.8 kg. Population pharmacokinetic analyses were performed with NONMEM software. Pharmacokinetic parameters, interindividual variability (IIV), between-occasion variability (BOV), and intraindividual variability were estimated. The influence of patient characteristics on the pharmacokinetics of L-AmB was explored. The final population pharmacokinetic model was evaluated by using a bootstrap sampling technique. The L-AmB plasma concentration-time data was described by a two-compartment pharmacokinetic model with zero-order input and first-order elimination. The population mean estimates of clearance (CL) and volume of distribution in the central compartment (V1) were 0.44 liters/h and 3.12 liters, respectively, and exhibited IIV (CL, 10%) and significant BOV (CL, 46% and V1, 56%). The covariate models were CL (liters/h) = 0.44 . e(0.0152.(WT-21)) and V1 (liters) = 3.12.e(0.0241.(WT-21)), where WT is the patient's body weight (kg) centered on the study population cohort median of 21 kg. Model evaluation by the bootstrap procedure indicated that the full pharmacokinetic model was robust and parameter estimates were accurate. In conclusion, the pharmacokinetics of L-AmB in pediatric oncology patients were adequately described by the developed population model. The model has been evaluated and can be used in the design of rational dosing strategies for L-AmB antifungal therapy in this special population.

Melphalan pharmacokinetics in children with malignant disease: influence of body weight, renal function, carboplatin therapy and total body irradiation.

AIM: To analyse the pharmacokinetics of melphalan in 52 children (0.3-18 years) and determine whether any clinical factors affect the pharmacokinetic parameters Additionally, to examine whether a test melphalan dose can predict the pharmacokinetics of a full dose, when there are 5 intervening days of carboplatin therapy. METHODS: Melphalan concentrations were measured in 14 blood samples collected from each child following doses ranging from 30 to 180 mg m(-2). The pharmacokinetics were analysed with Kinetica 4.0. RESULTS: Children who did not have carboplatin (n = 27) had median melphalan clearance (CL) of 15.5 l h(-1) m(-2) (interquartile range: 12.4-19.9 l h(-1) m(-2)) and steady state volume of distribution (Vss) of 14.9 l m(-2) (interquartile range: 12.7-18.3 l m(-2)). Children who had carboplatin (n = 25) had 34% lower median CL (10.2 l h(-1) m(-2)) and 18% lower median Vss (12.2 l m(-2)) (P < 0.001). Melphalan elimination was impaired in a separate group of three children given concomitant carboplatin and etoposide. Stepwise multiple linear regression indicated that weight, carboplatin, glomerular filtration rate (GFR) and total body irradiation (TBI) significantly affected CL, while weight and carboplatin influenced Vss. A test dose (10 mg m(-2)) tended to underpredict the area-under-the-concentration-vs.-time-curve for a full (180 mg m(-2)) dose in 19 individuals given carboplatin. CONCLUSIONS: In children, melphalan CL is influenced by weight, carboplatin, TBI and GFR. Vss is influenced by weight and carboplatin.

HeLa cells cocultured with peripheral blood lymphocytes acquire an immuno-inhibitory phenotype through up-regulation of indoleamine 2,3-dioxygenase activity.

The mechanisms by which tumour cells escape recognition by the immune system or subvert antitumour effector responses remain poorly understood. In the course of investigating the potential of costimulatory signals in anticancer immunotherapy strategies, we have observed that HeLa cells (a human cervical carcinoma cell line) cocultured with peripheral blood lymphocytes (PBL) acquire the capacity to inhibit PBL proliferation in response to interleukin-2 (IL-2). This immuno-inhibitory phenotype was further shown to result from induction of the tryptophan-catabolizing enzyme, indoleamine 2,3-dioxygenase (IDO), by interferon-gamma (IFN-gamma) secreted from cocultured allo-reactive PBL. This enzyme has recently been shown to be a critically important modulator of immunological responses, most notably through the capacity to protect allogeneic concepti from alloreactive maternal lymphocytes. While the cytostatic consequences of IDO activity in tumour cells has received attention, the data presented in this report support the hypothesis that IDO activity may also act to impair antitumour immune responses.