Pegaspargase Other names: L-asparagine amidohydrolase Putative L-asparaginase precursor

Pegaspargase is a covalent conjugate of Escherichia coli-derived L-asparaginase with monomethoxypolyethylene glycol.

The mechanism of action of L-asparaginase is the enzymatic cleavage of the amino acid L-asparagine into aspartic acid and ammonia. Depletion of L-asparagine in blood results in inhibition of protein-synthesis, DNA-synthesis and RNA-synthesis, especially in leukaemic blasts which are not able to synthesise L-asparagine, thus undergoing apoptosis.

Normal cells, in contrast, are capable of synthesising L-asparagine and are less affected by its rapid depletion during treatment with the enzyme L-asparaginase. The PEGylation does not change the enzymatic properties of L-asparaginase, but it influences the pharmacokinetics and immunogenicity of the enzyme.

Pharmacodynamic effects

Anti-leukaemic effect of L-asparaginase is related to a sustained L-asparagine depletion in blood and cerebrospinal fluid (CSF). The pharmacodynamic (PD) effect of pegaspargase was assessed after IM (Study CCG-1962) and IV administration (AALL07P4).

In Study CCG-1962, PD effect of pegaspargase was assessed through serial measurements of asparagine in serum (n=57) and CSF (n=50) of newly diagnosed paediatric patients with standard-risk ALL who received three intramuscular doses of pegaspargase (2,500 Units/m² BSA), one each during induction and two during delayed intensification treatment phases. A reduction in serum asparagine concentration was evident by the 4th day after the first Induction dose and reached an apparent nadir by the 10th day after the dose. Serum asparagine concentrations of approximately 1 μM persisted for approximately 3 weeks. Asparagine concentration fell to <3 μM when asparaginase activity was >0.1 U/mL. CSF asparagine of 2.3 μM pre-treatment fell to 1.1 μM on Day 7 and 0.6 μM on Day 28 of Induction.

In Study AALL07P4, the PD effect of pegaspargase was assessed in 47 evaluable subjects with high risk B-precursor ALL who received IV doses of pegaspargase 2,500 U/m² BSA during the Induction and Consolidation phases. Plasma L-asparagine concentrations were depleted to below the assay limit of quantification within 24 hours following the Induction and first Consolidation dose of pegaspargase and depletion was sustained for approximately two weeks. CSF asparagine concentrations were reduced by the 4th day following the Induction dose, and remained largely undetectable by the 18^th day after dosing.

Based on results from these two studies, a 2,500 U/m² BSA dose of pegaspargase administered IM (CCG-1962) and IV (AALL07P4) provides maintenance of L-asparagine depletion for approximately two weeks following dosing.

Pegaspargase pharmacokinetic properties were based on asparaginase activity measured by an enzymatic assay after IM (CCG-1962) and IV (AALL07P4, DFCI 11-001) administration.

In Study CCG-1962, mean asparaginase activity reached peak value of 1 U/mL on Day 5 after the injection. The mean half-life after absorption from the injection site was 1.7 days and the elimination half-life was 5.5 days. The volume of distribution at steady-state and clearance were estimated at 1.86 L/m² and 0.169 L/m² per day, respectively.

In Study AALL07P4, PK parameters after a single 2,500 U/m² IV dose during Induction were calculated by noncompartmental PK analysis from sequential plasma samples and are depicted in the table below. The C_max and AUC of pegaspargase trended lower in males, subjects with larger BMI, and subjects >10 years. During Induction, following a single IV dose of pegaspargase 2,500 U/m², asparaginase activity ≥0.1 U/mL was sustained for up to 18 days post-dose in 95.3% of subjects.

Pharmacokinetic Parameters After a Single IV Dose of pegaspargase 2,500 U/m² BSA During Induction (N=47; Study AALL07P4):

In Study DFCI 11-001, assessments of asparaginase activity were performed following a single IV dose of pegaspargase 2,500 U/m² BSA during Induction, and every two weeks during post-Induction. During Induction, plasma asparaginase activity ≥0.1 U/mL was sustained in 93.5% of subjects 18 days after administration. During the post-Induction phase, a nadir (trough) asparaginase activity above 0.4 U/mL was sustained in 100% of subjects from Week 7 up until Week 25. These results indicate that, when pegaspargase 2,500 U/m² BSA is administered as single and repeated doses every two weeks, clinically relevant asparaginase activity is sustained over the entire dosing interval (i.e., two weeks).

Patients with newly diagnosed ALL received a single IM injection of pegaspargase (2,500 U/m² BSA) or native asparaginase from E. coli (25,000 U/m² BSA) or from Erwinia (25,000 U/m² BSA). The plasma elimination half-life of pegaspargase was statistically significantly longer (5.7 days) than the plasma elimination half-lives of the native asparaginases from E. coli (1.3 days) and Erwinia (0.65 days). The immediate cell death of leukaemic cells in vivo, measured by rhodamine fluorescence, was the same for all three L-asparaginase preparations.

ALL patients with several relapses were treated either with pegaspargase or with native asparaginase from E. coli as part of an induction therapy. Pegaspargase was given IM in a dose of 2,500 U/m² BSA on days 1 and 15 of induction. The mean plasma half-life of pegaspargase was 8 days in non-hypersensitive patients (AUC 10.35 U/ml/day), and 2.7 days in hypersensitive patients (AUC 3.52 U/ml/day).

Specific populations

The controlled studies were not designed to formally evaluate the pharmacokinetics of pegaspargase in specific populations. A population pharmacokinetic evaluation of pegaspargase based on data obtained from Studies AALL07P4 (IV), DFCI 11-001 (IV), and CCG-1962 (IM) identified that clearance (linear and saturable) increased approximately proportional to BSA and volume of distribution increased slightly more proportional to BSA. No statistically significant differences in PK characteristics between male and female subjects were identified in this analysis.

The impact of renal and hepatic impairment on the PK of pegaspargase has not been evaluated. As pegaspargase is a protein with a high molecular weight, it is not excreted renally, and no change of pharmacokinetic of pegaspargase in patients with renal impairment is foreseen.

Since the proteolytic enzymes responsible for pegaspargase metabolism are ubiquitously distributed in tissues the exact role of the liver is unknown: however any decrease in liver function is not expected to present clinical relevant problems in the use of pegaspargase.

There are no data available for elderly patients.

Acute toxicity

Only very high doses of pegaspargase given to mice intraperitoneally as a single dose (25,000–100,000 U/kg body weight) caused the death of 14% of all treated mice. Mild hepatotoxicity was observed with the same dosages. Adverse reactions were loss of body weight, piloerection and reduced activity. Reduced splenic weight might be a sign of potential immunosuppressant effect of the treatment.

Pegaspargase was well tolerated both in rats and dogs when administered intravenously in single dose up to 500 U/kg body weight.

Repeated dose toxicity

A 4-week study in rats treated with a dose of pegaspargase of 400 U/kg/day intraperitoneal resulted in a fall in food intake and body weight compared to the control group.

A 3-month study in mice with pegaspargase at doses up to 500 U/kg intraperitoneal or intramuscular resulted in slight hepatocellular changes only at the highest intraperitoneal dose.

A temporary suppression in body weight gains and a temporary reduction in total leukocyte counts were observed in dogs which were treated with pegaspargase 1200 U/kg weekly for 2 weeks. Increased serum glutamic pyruvic transaminase activity also occurred in one out of four dogs.

Immunogenicity

No immunogenic response was detected in a 12-week study in mice in which pegaspargase was administered weekly at the dose of 10.5 U/mouse intramuscular or intraperitoneally.

Reproductive toxicity

No studies of reproductive toxicity were conducted with pegaspargase.

Embryotoxicity studies with L-asparaginase have given evidence of teratogenic potential in rats treated from day 6 to 15 of gestation with a No Observed Effect Level (NOEL) for teratogenic effects at 300 U/kg intravenous. In rabbits doses of 50 or 100 U/kg intravenous on days 8 and 9 of gestation induced viable fetuses with congenital malformations: no NOEL has been determined. Multiple malformations and embryolethal effects were observed with doses in the therapeutic range. Investigations of the effect on fertility and peri- and postnatal development were not conducted.

Carcinogenicity, mutagenicity, fertility

Long-term investigations of carcinogenicity or studies of the effect on fertility in animals were not conducted with pegaspargase.

Pegaspargase was not mutagenic in the Ames test using Salmonella typhimurium strains.