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L-asparaginase is an effective drug for treatment of children with acute lymphoblastic leukemia (ALL). The effectiveness is thought to result from depletion of asparagine in serum and cells. We investigated the clinical response in vivo of 1000 IU/m2 pegylated (PEG)-asparaginase and its pharmacokinetic, pharmacodynamic and intracellular effects in children with newly diagnosed ALL before start of combination chemotherapy. The in vivo window response was significantly related to immunophenotype and genotype: 26/38 common/pre B-ALL cases, especially those with hyperdiploidy and TELAML1 rearrangement, demonstrated a good clinical response compared to 8/17 T-ALL (P=0.01) and BCRABL-positive ALL (P=0.04). A poor in vivo clinical window response was related to in vitro resistance to L-asparaginase (P=0.02) and both were prognostic factors for long-term event-free survival (hazard ratio 6.4, P=0.004; hazard ratio 3.7, P=0.01). After administration of one in vivo dose of PEG-asparaginase no changes in apoptotic parameters or in intracellular levels of twenty amino acids in leukemic cells could be measured, in contradiction to the changes found after in vitro exposure. This may be explained by the rapid removal of apoptotic cells from the circulation in vivo. One additional dose of PEG-asparaginase upfront ALL treatment did not lead to other severe toxicities.Leukemia (2008) 22, 1665–1679; doi:10.1038/leu.2008.165; published online 26 June 2008 [ABSTRACT FROM AUTHOR]

Discusses the role of asparaginase (ASP) in treatment of children with acute lymphoblastic leukemia. Revelation that different preparations and ways of administration of ASP results in different plasma activities; Description of functioning of ASP; Information that pharmacokinetics and pharmacodynamics of polyethylene glycol-ASP are not well characterized in the cerebrospinal fluid (CSF); Explanation for the lack of depletion of asparagine depletion in CSF.