Abstract

Deamination of asparagine (Asn) and glutamine (Gln) by asparaginase (ASNase) induces apoptosis of ALL lymphoblasts, which lack ability to synthesize Asn de-novo. Early treatment intensification after Induction, including PEG-ASNase instead of native E.Coli-ASNase, in addition to more vincristine and intravenous methotrexate, improves outcome in pediatric ALL patients presenting with unfavorable features, who show rapid early response to Induction chemotherapy (

Seibel NL, et al.,
Blood
,
2003
;
102
:
224a
). Erwinase was used for patients with overt clinical allergy to E.Coli-ASNase. We evaluated the population pharmacokinetics and pharmacodynamics (PK-PD) of the three ASNase formulations employed on CCG-1961. The PK-PD parameters of native and PEG-ASNase in this group of HR ALL patients were similar to those reported from SR ALL patients from CCG-1962 (
Avramis VI, et al.,
Blood
,
2002
;
99
:
1986
–1994
). Population PK (NONMEM) showed the expected half-lives of native E.Coli-ASNase (6000 IU/m2): 1.3 days; PEG-ASNase (2500 IU/m2): 6.5 days; and Erwinase (6000 IU/m2): 0.8 days. Repeated doses resulted in an accumulation of activity with moderate prolongation of elimination half-lives for all formulations. PEG-ASNase provided > 0.3 IU/ml activity for > 21 days for most patients in Delayed Intensification. We measured simultaneous amino acid levels in 430 sera samples obtained from various phases of CCG-1961 from these 187 fully evaluable patients with detectable post-treatment ASNase activity. The averages of pre-treatment control serum levels for Asn and Gln were 44.8 ± 3.0 μM (mean ± SE) and 363.8 ± 23.9 μM, respectively. There were no statistical differences between the PD effects of ASNase formulations on serum Asn deamination, although the lowest Asn levels averaging 2.6 ± 0.4 μM were obtained on 11–14 days post-PEG-ASNase samples (n=14). Glutamine deamination enhanced Asn depletion, and deamination correlated with ASNase activity. At levels >0.4 IU/ml, PEG-ASNase and native ASNase provided 95 ± 8% and 85 ± 26% Gln deamination, respectively (p=0.04). Eleven to 14 days after PEG-ASNase, Gln levels averaged 13 ± 5 μM (n=14). In general, Erwinase provided greater Gln deamination (94 ± 5%, n=19) 2–3 days post administration, than either native or PEG-ASNases at comparable activity levels, which were 70–80% (p<0.001). Greater Gln deamination yielded lower Asn levels after Erwinase. These PD results provide insight into the benefit of PEG-ASNase intensification and possibly Erwinase substitution in the treatment of patients with high risk ALL treated with augmented BFM therapy and need to be further explored.

Author notes

Corresponding author