Clustered versus Uniform Display of GALA-Peptides on Carrier Nanoparticles: Enhancing the Permeation of Noncharged Fluid Lipid Membranes.

GALA-peptide is a random coil in neutral pH; in acidic pH, it becomes an amphipathic α-helix that aggregates in solution, possibly via its hydrophobic facet that runs along the helix's long axis. In the presence of fluid lipid membranes, the GALA-helix exhibits membrane-active properties that originate from the same hydrophobic facet; these properties make GALA a candidate for inclusion in drug delivery systems requiring permeation of the endosomal membrane to enable drug escape into the cytoplasm. Previous work has shown that the uniform functionalization of carrier nanoparticles with GALA-peptides improved their membrane activity and enhanced the endosomal escape of delivered therapeutics. The present study aims to evaluate the potential role of altering membrane activity via cluster-displayed GALA-peptides (for higher local valency) on the surface of carrier nanoparticles. The presentation of GALA-peptides on carrier nanoparticles was also designed to be pH-dependent. The peptide display on the surface of the carrier nanoparticles was uniform in neutral pH; in the acidic endosomal pH, the surface of nanocarriers formed domains (patches) with high local densities of GALA-peptides. The interactions between GALA-functionalized carrier nanoparticles and target lipid vesicles, utilized as endosome membrane surrogates that were used to primarily capture the fluid nature of these membranes, were studied as a function of pH. At endosomal pH values, ranging from 5.5 to 5.0, the greatest permeability of target membranes was induced by nanocarriers with clustered rather than uniformly displayed GALA. This enhancing effect had an optimum; at even more acidic pH values, too close an approximation of GALA-peptides residing within the same patches resulted in preferential intrapatch peptide interactions rather than interactions with the apposing target lipid membranes. This behavior could have the same physicochemical origin as the aforementioned GALA-peptide aggregation, observed in solution with decreasing pH at increasing peptide concentrations. The findings of this study support the potential of utilizing the clustered display of GALA-peptides on carrier nanoparticles to increase the permeation of fluid membranes used herein to capture this critical physical property of endosomal membranes and therefore to ultimately improve the endosomal escape of delivered therapeutics, enhancing therapeutic efficacy.