Controlling Endosomal Escape Using pH-Responsive Nanoparticles with Tunable Disassembly

Endosomal escape is a bottleneck in the efficient delivery of therapeutics using nanoparticles; therefore understanding how this property can be optimized is important for achieving better therapeutic outcomes. It has been demonstrated that pH-responsive nanoparticles (pHlexi nanoparticles) have potential to achieve effective escape from the endosomal compartments of the cell. In this paper a library of five pHlexi particles with tunable disassembly pH were synthesized by combining poly(ethylene glycol)-b-poly(2-(diethylamino)ethyl methacrylate) (PEG-b-PDEAEMA) with random copolymers of 2-(diethylamino)ethyl methacrylate and 2-(diisopropylamino)ethyl methacrylate. A series of cellular studies were conducted to investigate the effect of particle composition on in vitro behavior. Endosomal escape was probed using a calcein escape assay in NIH/3T3 fibroblast cells, demonstrating endosomal escape increased with increasing particle concentration. Interestingly, it was shown that endosomal escape was most efficient with particles that disassemble at high (pH 7.2) or low (pH 4.9) pH, with particles that disassemble between pH 5.8 and 6.6 inducing decreased levels of endosomal escape. This change in endosomal escape behavior suggests particles can induce escape by different pathways. The results show that tuning the core component of pHlexi particles can improve the effectiveness of endosomal escape capabilities and thus their ability to act as effective delivery systems.