Purpose: Green fluorescent protein (GFP) encoding adenovirus (ADV) was surface modified with polyethylene glycol (PEG) for microencapsulation within poly(lactic-co-glycolic acid) (PLGA) microspheres with the aim of improving stability and gene transfection activity.
Methods: A series of PEGylated ADV (PEG-ADV) with different PEG seeding densities on the viral surface was prepared and the GFP expression efficiency of each PEG-ADV in the series determined. The physical stabilities of naked ADV and PEG-ADV were comparatively evaluated by exerting a high shear homogenization process or by exposure to low pH. Naked ADV or PEG-ADV was microencapsulated within PLGA microspheres using a water-in-oil-in-water (W/O/W) double emulsion and solvent evaporation method. In vitro cumulative ADV and PEG-ADV release profiles from PLGA microspheres were determined over a 10-day period. GFP transfection efficiencies into HeLa cells were quantified, and the relative extent of the immune response for ADV and PEG-ADV encapsulated within PLGA microspheres was analyzed using macrophage cells.
Results: The physical stability of PEGylated ADV was greatly enhanced relative to that of naked ADV under the simulated W/O/W formulation conditions, such as exposure to an aqueous/organic interface during high shear-stressed homogenization. PEG-ADV was also more stable than ADV at low pH. ADV and PEG-AD were both released from PLGA microspheres similarly in a sustained fashion. However, when the ADV and PEG-ADV encapsulated microspheres transfected into HeLa cells, PEG-ADV microspheres demonstrated a higher GFP gene transfection efficiency than ADV microspheres. The PEG-ADV microspheres also exhibited a reduced extent of innate immune response for macrophage cells.
Conclusions: PEGylated ADV could be more safely microencapsulated within PLGA microspheres than naked ADV due to their enhanced physical stability under the harsh formulation conditions and acidic microenvironmental conditions of the microsphere, thereby increasing gene transfection efficiency.