A Versatile Polymer-Based Platform for Intracellular Delivery of Macromolecules

The plasma membrane barrier greatly restricts intracellular delivery of macromolecules. Currently available methods suffer from various limitations, including low delivery efficiency, high cytotoxicity, or incompatibility with a wider range of macromolecules or cell types. To overcome these issues, stimuli-responsive polymers such as the bio-inspired, pH-responsive poly(l-lysine isophthalamide) grafted with l-phenylalanine at a stoichiometric ratio of 50% (PP50) can be used. In mildly acidic environments, the pseudopeptidic polymer can permeabilize the plasma membrane overcoming the problem of payload entrapment in the endosomes and allowing for efficient intracellular delivery. It is demonstrated that PP50 is capable of intracellular delivery by simple co-incubation at pH 6.5 with various macromolecules, including different-sized Dextrans, green fluorescent protein (GFP), and an apoptotic peptide. The delivery process is fast, nontoxic, and compatible with multiple cell types, including adherent and suspension cell lines, primary human mesenchymal stem cells, and cells grown as spheroids. In addition, apoptotic peptide delivery by co-incubation with PP50 is over three times more effective than delivery using other common methods, including poly(ethyleneimine) (PEI), cell penetrating peptides (CPPs), and electroporation. The findings suggest that payload delivery by co-incubation with PP50 is a flexible, controllable method allowing delivery of various payloads to many different cell types in vitro.