Rational Design of Cationic Nanogels with Serum Tolerance for Efficient siRNA Delivery and Antitumor Therapy

Cationic polymers have been applied widely for siRNA delivery, yet most of the conventional linear or branched polymers make RNA polyplexes with poor serum stability and low delivery efficacy. We here propose cationic nanogels as a better alternative and demonstrate their advantages for siRNA delivery. Using a recently developed electrostatic-templated polymerization method, we synthesized a series of cationic nanogels with precisely controlled chemical composition, size, and cross-linking degree, enabling the systematic exploration of structure-performance relationships for nanogel-mediated siRNA delivery. We show that the nanogels, with their stable 3D structure, offer both surface and interior sites for siRNA loading depending on the N/P ratio. At high N/P ratios, siRNA binds primarily to the interior sites of the nanogels, which provide enhanced protection against competing serum proteins and facilitate efficient cellular uptake. Furthermore, the chemical composition, size, and degree of cross-linking of the nanogels cooperatively influence siRNA loading and cellular uptake. The optimal formulation, poly(vinylbenzyl trimethylammonium chloride) (PVBTMA) nanogel, incorporates a strong charge group and a hydrophobic phenyl spacer that facilitate siRNA loading and cellular uptake, respectively. With an optimal size of 107 nm and 5% cross-linking, PVBTMA nanogel achieves superior siRNA internalization compared to widely used transfection agents like Lipofectamine 3000 and branched PEI_25k. Finally, when loaded with tumor-specific gene silencer siPLK1, the PVBTMA nanogel facilitates superior gene silencing in vitro and effectively inhibits tumor growth in vivo. Our findings clarify the distinct advantages of cationic nanogels as carriers for siRNA delivery and highlight their promising potential for therapeutic applications.