Hans‐Joachim Müller

Pegylated asparaginase (OncasparTM) in children with ALL: drug monitoring in reinduction according to the ALL/NHL‐BFM 95 protocols

Hypersensitivity reactions are relevant adverse effects of asparaginase therapy. Therefore, children treated with native Escherichia coli asparaginase in induction therapy of acute lymphoblastic leukaemia (ALL) or non‐Hodgkins lymphoma (NHL) were switched to the pegylated enzyme for reinduction under drug monitoring. Seventy children, including four patients with allergic reactions during induction, were given one dose of OncasparTM 1000 U/m2 intravenously. Activity was determined every third or fourth day until it dropped below the limit of quantification. In current reinduction protocols [ALL/NHL‐Berlin–Frankfurt–Münster (BFM) 95 trials], four doses of 10 000 U/m2E. coli asparaginase deplete asparagine for about 2–3 weeks, therefore activities of ≥ 100 U/l up to day 14 and ≥ 50 U/l up to day 21 were targeted. In 66 patients without an allergic reaction during induction, the mean activity was 606 ± 313 U/l, 232 ± 211 U/l and 44 ± 50 U/l after 1, 2 and 3 weeks respectively. In 44/66 patients, activity was ≥ 100 U/l after 14 d. A rapid decline in activity was seen in the remaining 22 patients, including 8/22 patients who showed no activity after 1 week. Toxicity was low and comparable to the native enzymes but, in contrast to about 30% of hypersensitivity reactions with conventional reinduction therapy, no allergic reaction was seen. Substituting 4 × 10 000 U/m2 asparaginase medac for one dose of 1000 U/m2 OncasparTM was safe and well tolerated. Comparable pharmacokinetic treatment intensity was achieved in about two‐thirds of patients.

Pharmacokinetics of native Escherichia coli asparaginase (Asparaginase medac) and hypersensitivity reactions in ALL‐BFM 95 reinduction treatment

Repeated asparaginase treatment has been associated with hypersensitivity reactions against the bacterial macromolecule in a considerable number of patients. Immunological reactions may range from anaphylaxis without impairment of serum asparaginase activity to a very fast decline in enzyme activity without any clinical symptoms. Previous investigations on a limited number of patients have shown high interindividual variability of asparaginase activity time courses and hypersensitivity reactions in about 30% of patients during reinduction treatment. Therefore, monitoring of reinduction treatment was performed prospectively in 76 children with newly diagnosed acute lymphoblastic leukaemia (ALL). According to the ALL‐Berlin–Frankfurt–Münster (BFM) 95 protocol, 10 000 U/m2 body surface area of native Escherichia coli asparaginase (Asparaginase medac) was given on d 8, 11, 15 and 18. In 45/76 children, trough and peak activities were determined with every dose, and also on d 4 and d 11 after the last administration. Data on asparaginase activity were not available from the remaining 31 patients, but information with regard to hypersensitivity reactions only was given. Eighteen out of 76 patients (24%) suffered a clinical hypersensitivity reaction; however, no silent inactivation was observed. Activity in the therapeutic range of greater than 100 U/l for at least 14 d was determined in 43 of the 45 patients who were analysed for enzyme activity.

Comparison of intramuscular therapy with Erwinia asparaginase and asparaginase Medac: pharmacokinetics, pharmacodynamics, formation of antibodies and influence on the coagulation system

Asparaginase comes from different biological sources and the various preparations have different pharmacokinetic properties, and their tendency to induce side‐effects is different. Erwinia asparaginase (ASNase) has a shorter half‐life than the Escherichia coli preparations, and it has been reported to be less immunogenic than the E. coli preparations and to induce fewer coagulation disorders. Children with newly diagnosed acute lymphoblastic leukaemia (ALL) were included in this study. Twenty‐seven patients were treated with Erwinia ASNase (induction therapy 30·000 IU/m2/d i.m. for 10 d, and re‐induction therapy 30·000 IU/m2 twice a week for 2 weeks) and 15 were treated with ASNase Medac (induction therapy 1·000 IU/m2/d i.m. for 10 d, and re‐induction therapy 5·000 IU/m2 i.m. twice a week for 2 weeks). Blood samples were drawn to determine enzyme activity, l‐asparagine, anti‐asparaginase antibodies, and coagulation parameters. After i.m. administration, Erwinia ASNase displayed a protracted absorption phase compared to ASNase Medac. The mean bioavailability after i.m. administration was 27% for Erwinia ASNase and 45% for ASNase Medac respectively. Mean trough enzyme activities during induction therapy were Erwinia ASNase 1748 IU/l and ASNase Medac 272 IU/l, and during re‐induction therapy Erwinia ASNase 83 IU/l and ASNase Medac 147 IU/l. We conclude that in this setting, therapy with ASNase Medac resulted in sufficient treatment during both phases of therapy, whereas treatment with Erwinia ASNase resulted in unnecessarily intense therapy during the induction phase and insufficient treatment during the re‐induction phase. There was no significant difference in the incidence of antibody formation, and therapy with Erwinia ASNase resulted in a more pronounced influence on the coagulation parameters than therapy with ASNase Medac.

Pharmacokinetic dose adjustment of Erwinia asparaginase in protocol II of the paediatric ALL/NHL-BFM treatment protocols

Native forms of asparaginase stem from different biological sources. Previously reported data from children treated with ErwinaseTM showed significantly lower trough levels and pharmacokinetic dose intensity than after E. coli‐derived preparations. Hence, schedule optimization was initiated to achieve relevant serum activities. 21 children on reinduction therapy received Erwinase on Mondays, Wednesdays and Fridays for 3 weeks (9 × 20 000 IU/m2 i.v.) instead of 4 × 10 000 IU/m2 of E. coli asparaginase (twice weekly for 2 weeks). Asparaginase trough activities were measured as the primary parameter, targeting 100–200 IU/l after 2 d and >50 IU/l after 3 d. Concurrently, asparagine trough concentrations were monitored. The mean trough activity was 156 ± 99 IU/l, with 2/108 samples showing no detectable activity. Regarding trough levels per individual (three or more measurements/patient), means ranged from 52 ± 29 to 276 ± 114 IU/l (20 patients, 106 samples), with nine, six, and five children inside, below, and above the target range, respectively. The mean 3 d trough activity was 50 ± 39 IU/l (20 patients, 51 samples). In 11 of these samples no activity was measurable. Mean trough activities calculated per individual ranged from < 20–84 ± 30 IU/l (14 patients, 42 samples) with seven children below the target limit of 50 IU/l and asparagine concentrations < 0.2–1.5 μm. We concluded that an increased dose of 9 × 20 000 IU/m2 of Erwinia asparaginase within 3 weeks resulted in a pharmacokinetic dose intensity comparable to former observations made with 4 × 10 000 IU/m2 of the E. coli product CrasnitinTM which is no longer marketed. High interindividual variability and the phenomenon of ‘silent’ inactivation necessitate monitoring wherever possible.

Drug monitoring of low-dose PEG-asparaginase (Oncaspartm) in children with relapsed acute lymphoblastic leukaemia

Use of asparaginase (ASNase) in the treatment of relapsed childhood acute lymphoblastic leukaemia (ALL) is associated with a high rate of hypersensitive reactions. ‘Silent’ inactivation may additionally reduce treatment intensity. Therefore, PEG‐ASNase (Oncaspartm), a polyethylene glycol conjugate of the native Escherichia coli‐ASNase, was introduced into the Berlin‐Frankfurt‐Münster (BFM) 96 treatment protocol for relaped ALL under drug monitoring conditions. A single i.v. dose of 500 IU/m2 PEG‐ASNase, substituted for the native ASNases, was administered to supply a plasma activity of 100 IU/l for 1 week. From November 1997 to March 2000, 35 patients from 23 BFM‐associated hospitals, with or without a previous allergic reaction to one or both native preparations, underwent monitoring. After 82 applications, a total of 270 samples were submitted to be tested for ASNase activity. The ASNase activity on the day of the administration and the following day ranged between < 20 and 693 IU/l, with a median of 413 IU/l (53 samples). The median on d 7 ± 1 was 199 IU/l (range <20–421 IU/l; 41 samples) and on d 14 ± 1, 105 IU/l (range <20–188 IU/l; 19 samples). An ASNase activity of > 100 IU/l was seen on d 7 in 36 activity time courses of 52 interpretable applications (69%). Intraindividual variability of activity time courses was low. However, a rapid decrease in ASNase activity after repeated applications was observed in 4 out of 20 children. Previously experienced allergic reactions to native ASNases did not influence PEG‐ASNase pharmacokinetics. PEG‐ASNase is a useful alternative to the native ASNases in children with relapsed ALL. Whenever possible, drug monitoring should be performed to identify patients with ‘silent’ inactivation.

Asparagine synthetase activity in paediatric acute leukaemias: AML‐M5 subtype shows lowest activity

Lack of sufficient cellular activity of asparagine synthetase (AS) in blast cells compared with normal tissue is thought to be the basis of the antileukaemic effect of l‐asparaginase in acute lymphoblastic leukaemia (ALL). Although l‐asparaginase is routinely used in ALL, its role and value in the treatment of acute myelogenous leukaemia (AML) is still being discussed. To evaluate the pharmacological basis for l‐asparaginase treatment, we established pretreatment monitoring of the intracellular AS activity in blast cells of patients with AML and ALL. There was no general difference in AS activity between ALL and AML samples. Significantly lower AS activity, however, was found in the B‐lineage ALL subgroups as well as AML‐M5.

Pegylated asparaginase in combination with high‐dose methotrexate for consolidation in adult acute lymphoblastic leukaemia in first remission: a pilot study

Summary.  The German Multicentre acute lymphoblastic leukaemia (ALL) study group (GMALL) performed a pilot study using pegylated asparaginase (PEG‐ASP) in combination with high‐dose methotrexate as consolidation therapy in the 05/93 protocol. The aim of the study was an intra‐individual comparison of two different doses of PEG‐ASP in 26 patients, with regard to the depletion of asparagine in serum and toxicity. ‘Pharmacokinetic’ monitoring was performed to evaluate the effect of an intra‐individual dose escalation of PEG‐ASP from 500 to 1000 U/m2 intravenously in successive doses. Serum asparaginase activity was targeted at ≥100 U/l for 1 week and ≥50 U/l for 10 d. The second course of PEG‐ASP was administered to 23 patients. Due to hypersensitivity reactions in five patients, only 18 patients were evaluable for pharmacokinetic monitoring. With respect to the PEG‐ASP activity, an effective depletion of asparagine could be postulated in the majority of patients during 10 d after the first administration. The effect of an intraindividual dose escalation form 500 to 1000 U/m2 was evaluable in 17 of 22 patients. An increment in peak PEG‐ASP activity >70% was observed in 65% of the patients. PEG‐ASP was well tolerated. Despite the long half‐life of PEG‐ASP, neither pancreatic nor central nervous toxicities occurred among the 26 adult patients treated in this pilot study.

A population pharmacokinetic model for pegylated‐asparaginase in children

We analysed 1221 serum activity measurements in 168 children from the Berlin‐Frankfürt‐Münster acute lymphoblastic leukaemia studies, ALL‐BFM (Berlin‐Frankfürt‐Münster) 95 and ALL‐BFM REZ, in order to develop a pharmacokinetic model describing the activity‐time course of pegylated (PEG)‐asparaginase for all dose levels. Patients received 500, 750, 1000 or 2500 U/m2 PEG‐asparaginase on up to nine occasions. Serum samples were analysed for asparaginase activity and data analysis was done using nonlinear mixed effects modelling (NONMEM Vers. VI, Globomax, Hanouet, MD, USA). Different linear and nonlinear models were tested. The best model applicable to all dosing groups was a one‐compartmental model with clearance (Cl) increasing with time according to the formula: Cl=Cli *e(0·0793 *t) where Cli = initial clearance and t = time after dose. The parameters found were: volume of distribution (V) 1·02 ± 26% l/m2, Cli 59·9 ± 59% ml/d per m2 (mean ± interindividual variability). Interoccasion variability was substantial with 0·183 l/m2 for V and 44·7 ml/d per m2 for Cl, respectively. A subgroup of the patients showed a high clearance, probably due to the development of inactivating antibodies. This is the first model able to predict the activity‐time course of PEG‐asparaginase at different dosing levels and can therefore be used for developing new dosing regimens.