Personalized nanomedicine: a rapid, sensitive, and selective UV–vis spectrophotometry method for the quantification of nanostructured PEG-asparaginase activity in children’s plasma

Yong Zhang,1,* Yongren Wang,2,3,* Ru Wang,4 Yan Shen,4 Jing Xu,1 Thomas J Webster,5 Yongjun Fang2,3 1Department of Pharmacy, Children’s Hospital of Nanjing Medical University, Nanjing 210008, China; 2Department of Hematology and Oncology, Children’s Hospital of Nanjing Medical University, Nanjing 210008, China; 3Key Laboratory of Hematology, Nanjing Medical University, Nanjing 210008, China; 4State Key Laboratory of Natural Medicines, Department of Pharmaceutics, China Pharmaceutical University, Nanjing 210009, China; 5Department of Chemical Engineering, Northeastern University, Boston, MA 02115, USA *These authors contributed equally to this work Purpose: PEGylated asparaginase (PEG-ASNase), which hydrolyzes asparagine to ammonia and aspartic acid, is an effective nanostructured antitumor agent for acute lymphoblastic leukemia (ALL). In order to monitor the activity of PEG-ASNase in plasma and design an individualization project, a rapid and sensitive method to determine PEG-ASNase activity in plasma using ultraviolet–visible spectrophotometry was established. Methods: PEG-ASNase is commonly used in acute lymphoblastic leukemia. With Nessler’s reagent as the chromogenic reagent of ammonia, a stable yellow complex was produced. The units of enzyme activity were defined as micromoles of ammonia released per minute. Results: Calibration curves fitted by plotting the OD at 450 nm of the Nessler product vs concentration were linear in the range of 27.8–1,111.0 IU/L with r2=0.999. The lower limit of quantification for PEG-ASNase activity in human plasma was 20 IU/L with good accuracy and precision. The intra- and interday precision (relative standard deviation) values were below 10% and accuracy ranged from 90% to 110% at all quality control levels. Analytical recoveries were determined between 90% and 110% for all quality control samples. Conclusion: This study proved that the Nessler method is well validated and can be successfully applied in the determination of plasma samples in the clinical setting for patients with ALL. It takes personalized nanomedicine to an entirely new level. Keywords: PEG-ASNase, Nessler’s reagent, UV–vis spectrophotometry, enzyme activity, personalized nanomedicine, ALL, Nessler method, plasm