Pharmacoanalytical assays of Erwinia asparaginase (erwinase) and pharmacokinetic results in high-risk acute lymphoblastic leukemia (HR ALL) patients: simulations of erwinase population PK-PD models.

BACKGROUND: Asparaginases are the cornerstone therapy of many successful combination regimens for the treatment of acute lymphoblastic leukemia (ALL), the most common malignancy in children and adolescents. Currently, two asparaginase formulations are available in the US, native Escherichia coli asparaginase (ASNase) and pegaspargase. A third formulation native Erwinia asparaginase (Erwinase, ERW) has recently been made available under a licensing exception for personal use. We report here the development and validation process of ERW pharmacoanalytical assays and the results in a few patients.
MATERIALS AND METHODS: We developed and systematically validated the ERW enzyme activity and ERW concentration, anti-ERW antibody and related assays. Pharmacokinetic and pharmacodynamic (PK-PD) studies were performed in a limited number of patients who received 6,000 IU/m2 x 3 per week x 2 courses, and 4 patients who received 25,000 IU/m2 x 3 per week x 2 courses of ERW.
RESULTS: The linearity and range of the Erwinase calibration lines for the pharmacoanalytical assays were excellent. The accuracy and precision were better than the FDA limit allows for oncology biological products (<30%) coefficient of variation (%CV) and related parameters in the quantification of ERW concentration. The validation of these parameters was equal to or better than during the assay development. PK-PD analyses of ERW in a few patients yielded an average half-life of elimination of 15.8+/-1.64 hours. There was an excellent PD response post ERW administration resulting in an ERW concentration-dependent asparagine (ASN, <0.5 microM) and glutamine (GLN, <50 microM) deamination. Pharmacodynamic correlations demonstrated that 0.1 to 0.2 IU/ml of ERW in serum were sufficient for 90% GLN and/or ASN deamination for up to 2 weeks. No anti-ERW antibody [Ab(+)] was seen among those few patients. None of the other 5 patients had an adverse event. Based on these post hoc results, simulations on various doses and schedules of this drug have been made.
CONCLUSION: The pharmacoanalytical assays were excellent tools to evaluate the PK and PD data of ERW in pediatric patients with HR ALL. However, this initial PK-PD evidence needs further validation in future clinical trials. Insights into the PD contributions of ERW in anti-E. coli ASNase Ab(+) patients will guide us in optimal design and use of ERW as part of combination chemotherapy regimens in future clinical trials.