Polycation Architecture and Assembly Direct Successful Gene Delivery: Micelleplexes Outperform Polyplexes via Optimal DNA Packaging

Cellular delivery of biomacromolecules is vital to medical research and therapeutic development. Cationic polymers are promising and affordable candidate vehicles for these precious payloads. However, the impact of polycation architecture and solution assembly on the biological mechanisms and efficacy of these vehicles has not been clearly defined. In this study, four polymers containing the same cationic poly(2-(dimethylamino)ethyl methacrylate) (D) block but placed in different architectures have been synthesized, characterized, and compared for cargo binding and biological performance. The D homopolymer and its diblock copolymer poly(ethylene glycol)-block-poly(2-(dimethylamino) ethyl methacrylate) (OD) readily encapsulate pDNA to form polyplexes. Two amphiphilic block polymer variants, poly(2-(dimethylamino)ethyl methacrylate)-block-poly(n-butyl methacrylate) (DB) and poly(ethylene glycol)-block-poly(2-(dimethylamino)ethyl methacrylate)-block-poly(n-butyl methacrylate) (ODB), self-assemble into micelles, which template pDNA winding around the cationic corona to form micelleplexes. Micelleplexes were found to have superior delivery efficiency compared to polyplexes and detailed physicochemical and biological characterizations were performed to pinpoint the mechanisms by testing hypotheses related to cellular internalization, intracellular trafficking, and pDNA unpackaging. For the first time, we find that the higher concentration of amines housed in micelleplexes stimulates both cellular internalization and potential endosomal escape, and the physical motif of pDNA winding into micelleplexes, reminiscent of DNA compaction by histones in chromatin, preserves the pDNA secondary structure in its native B form. This likely allows greater payload accessibility for protein expression with micelleplexes compared to polyplexes, which tightly condense pDNA and significantly distort its helicity. This work provides important guidance for the design of successful biomolecular delivery systems via optimizing the physicochemical properties.