Failure of Asparagine (ASN) Depletion, Not Inadequate Asparaginase (ASNase) Activity, Predicts Relapse in Standard Risk (SR) Childhood Acute Lymphoblastic Leukemia (ALL): A Children’s Oncology Group (COG) Report.
Authors: Avramis Vassilios I. , Holcenberg John S. , Ettinger Alice G. , Stork Linda C. , La Mei , Gaynon Paul S. 
Published: October 2019

Abstract
Introduction: The mechanisms of treatment failure in ALL are poorly understood. Attention has focused on the intrinsic resistance of the leukemic blast. ASNase contributes importantly to response and outcome in ALL. In about 1/3 of 1st relapse patients, we found inadequate ASN depletion, i.e., ASN > 3 mmoles on Day 14 of Induction (11 days following a single dose of pegylated ASNase) and an inferior re-induction rate (Pediatr Blood Cancer2006; 47:141). Patients with relapse have a superior re-induction rate with qwk rather than conventional qow pegylated ASNase (Blood2000; 96:1709). In the present study, we hypothesized that inadequate ASN depletion with standard ASNase dosing leads to relapse in newly diagnosed children with ALL.
Methods: Between 1997 and 1998, 118 children with NCI standard risk ALL were enrolled on Children’s Cancer Group CCG-1962 study after informed consent (Blood2002; 99:1986). By random allocation, patients received either native ASNase 6,000 IU/m2 tiw × 9 in Induction and × 6 in each of 2 Delayed Intensification (DI) phases (n=59, 15 relapses, 1 2nd malignancy) or a single dose of pegylated ASNase 2500 IU/m2 (n=59, 10 relapses) in Induction and each of 2 DI phases. All ASNase was administered intramuscularly and begun on Day 3–5 of Induction and each DI phase. Multiple samples were obtained for each patient and cooled promptly to prevent ex-vivo deamination, which may lead to falsely low, not falsely high ASN values. We examined the incidence of relapse by 8 years in patients ranked by ASN concentration and ASNase activity.
Results: The overall 4-year EFS is 84%. Overall, 17/ 31 patients (55%) in the highest Day 14 ASN tertile relapsed compared to 7/ 75 (9%) in the lower two tertiles (p<0.001). The median Day 14 ASN for relapse and remission patients was 3.8 and 0.1 [native ASNase] and 4.9 and 0.63 mmoles [pegylated ASNase]. Day 7 ASN was less informative. ASNase activity was not predictive of outcome.
Conclusion: In vivo, asparagine (ASN) depletion reflects a balance between ASNase activity and ASN production, which may vary for an individual over time and among individuals. ASN depletion on Induction Day 14, 9–11days after ASNase administration, predicts outcome in children with SR ALL receiving either native or pegylated ASNase. ASNase activity is not predictive. Failure to achieve adequate ASN depletion in Induction may contribute to relapse in childhood ALL.
ASN Concentration Induction Day Pegylated ASNase Native ASNase Day 7 ASN μmoles Relapses/ total μmoles Relapses/ total 1st tertile > 1.14 3/ 16 > 0.99 6/ 16 2nd tertile 0.03–1.12 4/ 16 0.04–0.73 3/17 3rd tertile 0.01 2/ 19 0.01 4/23 DAy 14 ASN 1st tertile > 2.78 9/ 17 > 2.62 8/ 14 2nd tertile 0.18–2.68 0/ 17 0.23–0.27 3/ 15 3rd tertile 0.01–0.07 1/ 17 0.01 3/ 26 ASNase Activity Induction Day Pegylated ASNase Native ASNase Day 7 Activity IU/ml Relapses/ total IU/ml Relapses/ total 1st tertile ≤0.64 3/17 ≤0.23 5/19 2nd tertile 0.65–0.92 2/18 0.24–0.51 3/18 3rd tertile 0.93–1.63 4/17 0.52–1.13 5/19 DAy 14 Activity 1st tertile ≤ 0.31 2/17 ≤ 0.23 5/18 2nd tertile 0.34–0.66 4/18 0.24–0.42 4/19 3rd tertile 0.68–1.25 4/17 0.42–1.24 5/18