Assessment of PEG-Asparaginase and Erwinia Asparaginase Activity Under Variable Storage Conditions.

Background: PEG-Asparaginase and Erwinia asparaginase are enzyme-based anticancer therapies used in the treatment of acute lymphoblastic leukaemia (ALL) and lymphoblastic lymphoma (LBL), where adequate plasma enzyme activity is required for therapeutic efficacy. In many study groups, therapeutic drug monitoring is routinely applied due to pharmacokinetic variability and the risk of hypersensitivity reactions followed by increased clearance and insufficient treatment. In clinical practice, samples may be exposed to prolonged transport and variable pre-analytical conditions. Knowledge on pre-analytical stability is important for correct interpretation of PEG-Asparaginase and Erwinia asparaginase activity in plasma. This study aimed to evaluate the in vitro stability of PEG-Asparaginase and Erwinia asparaginase under pre-analytical conditions. Methods: Three experimental stability studies were conducted at two activity levels. Enzyme stability in plasma was assessed during storage at 4 °C and 20 °C for up to 14 days and following three freeze-thaw cycles. Stability in whole blood prior to centrifugation was evaluated over 24 h. Enzyme activity was measured using a validated spectrophotometric assay, and stability was defined as a deviation within ±15% of baseline activity. Results: Both enzymes remained stable in plasma for up to 14 days at 4 °C and 20 °C, and no clinically relevant reduction in enzyme activity of freeze-thaw cycling was observed. In whole blood, Erwinia asparaginase and high-activity PEG-Asparaginase remained stable for 24 h at 20 °C, whereas low-activity PEG-Asparaginase showed a reduction in activity of approximately 22%, mainly within the first two hours. Conclusions: PEG-Asparaginase and Erwinia asparaginase are stable in plasma for up to 14 days at room temperature, enabling shipment of plasma samples by mail. However, prompt centrifugation is recommended for samples with low PEG-Asparaginase activity to ensure accurate therapeutic drug monitoring.