Pharmacokinetics and Pharmacodynamics in Mice of a Pegylated Recombinant Erwinia Chrysanthemi-Derived L-Asparaginase.

L-asparaginase is a standard and well-established component of the treatment of children with acute lymphoblastic leukemia (ALL). Commercially available preparations present several limitations: 1) they are strongly immunogenic, prompting immediate cessation of treatment when signs of hypersensitivity occur, 2) they are extracted from bacterial sources (Escherichia coli or Erwinia chrysantemi), using non optimal production processes, and 3) native forms have short half-lives, necessitating to be administrated several times a week. Using recombinant and state-of-the-art PEGylation technologies, Asparec®, a new Erwinia chrysanthemi-derived L-asparaginase (crisantaspase), has been designed with the objective of developing a compound with improved pharmacokinetic (PK) and pharmacodynamic (PD) properties and reduced immunogenicity as compared to the native enzyme. This new compound is intended to be administered as second line therapy when hypersensitivity has developed to the Escherichia coli L-asparaginase.

A recombinant crisantaspase (r-crisantaspase) has been engineered and further modified by covalent conjugation to methoxy-polyethylene glycol (PEG) molecules of 2, 5 or 10 kDa using a stable PEG-protein linkage, yielding PEG conjugates of high specific activity (range: 483 to 543 U/mg). In order to characterize the PK/PD profile of PEG conjugates and select a candidate for further development, groups of 2 to 4 mice received in 3 consecutive experiments a single intravenous administration of PEG-r-crisantaspase conjugates or Erwinase®, the commercially available crisantaspase. Groups of animals treated with Oncaspar®, the commercially available PEGylated Escherichia coli asparaginase, were included in the last 2 experiments for further comparison. Plasma L-asparagine level and residual enzymatic activity were measured for up to 10 days post-injection for PD and PK evaluation, respectively.

Administration of 5, 25, 125, and 250 U/kg of PEG-r-crisantaspase conjugates induced a depletion of plasma L-asparagine level for at least 48 hours (hrs) while comparable results were achieved when Erwinase® was injected at 250 U/kg but not at lower doses. The 5 kDa PEG-r-crisantaspase conjugate displayed the longest duration of action with depletion of L-asparagine levels sustained for 96 hrs at 5 U/kg as compared to 48 hrs for the 2 and 10 kDa PEG-r-crisantaspase conjugates at the same dose. Effect was dose-related, as 25 and 50 U/kg of the 2 kDa PEG-r-crisantaspase conjugate depleted plasma L-asparagine for 6 and 10 days, respectively, and depletion lasted for at least 10 days for the 5 kDa PEG-r-crisantaspase conjugate at the same doses. Enzymatic activity results obtained over 8 days were in line with the L-asparagine data. In particular, the half-life of the 5 kDa PEG-r-crisantaspase conjugate was higher (38 hrs) as compared to the 2 kDa (13 hrs) and 10 kDa (26 hrs) PEG-r-crisantaspase conjugates, and Erwinase® (6 hrs). Finally, 5 U/kg of 5 kDa PEG-r-crisantaspase conjugate and 1 U/kg of Oncaspar®, equivalent with regards to protein content (10 μg/kg), displayed comparable PD data, whereas the PEG-r-crisantaspase conjugate showed a longer half-life (38 versus 28 hrs).

Results indicate that 5 U/kg of PEG-r-crisantaspase conjugates were at least as potent as 250 U/kg of Erwinase® at depleting L-asparaginase levels and showed a longer half-life, indicating that PEGylation significantly improved potency and duration of action of r-crisantaspase. Taken together, data also support the development of the 5 kDa PEG-r-crisantaspase conjugate as a promising second line treatment for ALL.

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