Evaluation of long-term stability of L-asparaginase encapsulated PLL-g-PEG nanoparticles in solution to aid in therapeutic delivery

L-asparaginase (L-ASNase) is a therapeutic enzyme that is widely used for the treatment of hematopoietic diseases such as acute lymphoblastic leukemia and lymphomas. L-ASNase destroys asparagine dependent tumors by degrading circulating L-asparagine and thereby destroying malignant cells. As a protein drug, L-ASNase carries a few inherent drawbacks including short circulating half-life, low stability, and low catalytic activity under physiological conditions. Moreover, due to the bacterial origin of L-ASNase used in treatments, there have been reports with high frequency of hypersensitivity reactions in patients. The use of this drug in adult cancer populations has largely been hindered not only due to its immunological side effects but also due to non-immunogenic toxicities such as pancreatitis, liver toxicities, coagulopathy, and neurotoxicity. Therefore, it is vital to find new methods to decrease its immunogenic/toxicity profile while increasing the stability and half-life. The purpose of this study is to achieve a new L-ASNase polymer nanocarrier to improve stability of the enzyme while masking it from the immune system of the host. We designed and characterized a nanoparticle (NP) where a poly-L-lysine-grafted-poly(ethylene) glycol co-polymer was used to encapsulate L-ASNase. The primary focus of the study was to evaluate the stability and encapsulation efficiency of this NP construct over time. There was no aggregation of NPs observed during the study period of 6 months in solution and NPs had a 0.436 mV surface charge. L-ASNase NPs showed a percent asparaginase activity of 31% compared to free L-ASNase. Under physiological conditions NPs were found to be intact and retained the encapsulated proteins for up to 6 months in solution. Together, these results demonstrate that L-ASNase loaded PLL-g-PEG NPs may serve as a fundamental platform to design nanocarriers to prolong stability in solution.