Hydrophilic Surface Modification of Cationic Unimolecular Bottlebrush Vectors Moderate pDNA and RNP Bottleplex Stability and Delivery Efficacy

A cationic unimolecular bottlebrush polymer with chemically modified end-groups was synthesized to understand the impact of hydrophilicity on colloidal stability, nucleic acid delivery performance, and toxicity. The bottlebrush polymer template was synthesized using grafting-through techniques and was therefore composed of a polynorbornene backbone with poly(2-(dimethylamino)ethyl methacrylate) side chains with dodecyl trithiocarbonate end-groups. Postpolymerization modification was performed to fully remove the end-groups or install hydroxy and methoxy poly(ethylene glycol) functional groups on the bottlebrush exterior. The bottlebrush family was preformulated with biological payloads of pDNA and CRISPR-Cas9 RNP in both water and PBS to understand binding, aggregation kinetics, cytotoxicity, and delivery efficacy. Increasing end-group hydrophilicity and preformulation of bottleplexes in PBS increased colloidal stability and cellular viability; however, this did not always result in increased transfection efficiency. The bottlebrush family exemplifies how formulation conditions, polymer loading, and end-group functionality of bottlebrushes can be tuned to balance expression with cytotoxicity ratios and result in enhanced overall performance.