Rational Design of PEGylated Nanogels: Optimization of Degree of PEGylation and Development of a Novel Enzyme-Responsive Grafted Layer

Since its ideation in the late 1960s, PEGylation, or the covalent linking of polyethylene glycol (PEG) to biological molecules, has emerged as a prominent strategy for overcoming numerous barriers encountered in the biological milieu. PEG conjugation can increase circulation time, reduce both protein adsorption and phagocytic clearance, and increase stability. While many of these PEGylated nanotherapeutics have seen widespread usage and market success, others fail to reach the public due to a lack of efficacy and unintended immunogenicity. These highly differential outcomes highlight the need to apply rational design to the development of PEGylated nanotherapeutics. In this work, we first examined the relationships between the degree of PEGylation and cellular uptake. To this end, we synthesized non-PEGylated, PEG-mushroom, and PEG-brush configured P(DEAEMA-co-CHMA)-g-PEGMA nanoparticles (NPs) and studied their uptake in vitro. Lower PEG-ligand surface density caused increased hydrophobicity and surface charge, enhancing uptake through favorable interactions with the plasma membrane. Furthermore, the PEG-brush configuration was associated with improved particle stealth, and we subsequently assessed the primary pathways of nanoparticle (NP) endocytosis in human ovarian adenocarcinoma (OVCAR-3) cells and murine macrophages (RAW 264.7). Finally, our group developed a novel responsive stealth coating of PEG-tetrapeptide conjugates and studied its efficacy in vitro. When entirely coated with PEG-tetrapeptides, NPs were ignored by phagocytes. Shedding the PEG-tetrapeptide grafts appeared to promote uptake in our ovarian adenocarcinoma model. These data highlight the importance of optimizing PEG surface composition and configuration to achieve desired delivery kinetics. Through careful design, a balance can be struck between increased circulation and cellular uptake without hindering drug release.