Effects of polyethylene glycol attachment on physicochemical and biological stability of E. coli L-asparaginase.

L-asparaginase obtained from E. coli strains is an important enzyme widely used in leukemia treatment. However, hypersensitivity reactions must be considered a relevant adverse effect of asparaginase therapy. One approach to reduce the hypersensitivity reactions caused by this enzyme is to change its physicochemical and biological properties by means of polyethylene glycol (PEG) conjugation, resulting in a less immunogenic enzyme with much longer half-time of plasmatic life. This work investigated the factors that could interfere in PEG-enzyme's stability. The complexation did not affect the range of pH activity and stability was improved in acid medium remaining stable during 1 h at pH 3.5. The PEG-enzyme exhibited activity restoration capacity (32% after 60 min) when subjected to temperatures of 65 degrees C in physiological solution. The PEG-enzyme in vitro assays showed a very high stability in a human serum sample, keeping its activity practically unchanged during 40 min (strength to non-specific antibodies or proteases in serum). An increase of PEG-enzyme catalytic activity during the lyophilization was observed. The process of modification of L-asparaginase with PEG improved both physicochemical and biological stability.