Purpose: Based on a unique phase alignment that occurs during formulation, we postulated that PEG-ylation of the cargo enzyme would enhance its encapsulation within diblock copolymer nanocarriers and thus resistance to proteases.
Methods: A freeze-thaw modified double emulsion technique was utilized to encapsulate either the catalytically active enzyme catalase (MW approximately 250 kDa) or PEG-catalase in PEG-PLA polymer nanocarriers (PNC). Spectrophotometer measurement of substrate depletion was utilized to monitor enzyme activity. Isotope labeling of the enzyme was used in conjunction with activity measurements to determine PNC loading efficiency and PNC-enzyme resistance to proteases. This labeling also enabled blood clearance measurements of PNC-loaded and non-loaded enzymes in mice.
Results: Non-loaded PEG-catalase exhibited longer circulation times than catalase, but was equally susceptible to proteolysis. Modulation of the ratio of relatively hydrophilic to hydrophobic domains in the diblock PEG-PLA copolymer provided either filamentous or spherical PNC loaded with PEG-catalase. For both PNC geometries, encapsulation and resistance to proteases of the resultant PNC-loaded enzyme were more effective for PEG-catalase than catalase. Isotope tracing showed similar blood levels of PNC-loaded and free PEG-catalase in mice.
Conclusions: PEGylation enhances active catalase loading within PNC and resistance to protease degradation, relative to unloaded PEG-catalase.