Transferrin-Appended Nanocaplet for Transcellular siRNA Delivery into Deep Tissues.

Transferrin (Tf) is known to induce transcytosis, which is a consecutive endocytosis/exocytosis event. We developed a Tf-appended nanocaplet (NC⊃siRNA) for the purpose of realizing siRNA delivery into deep tissues and RNA interference (RNAi) subsequently. For obtaining NC⊃siRNA, a macromonomer (Gu) bearing multiple guanidinium (Gu) ion units, azide (N) groups, and trityl (Trt)-protected thiol groups in the main chain, side chains, and termini, respectively, was newly designed. Because of a multivalent Gu-phosphate salt-bridge interaction, Gu can adhere to siRNA along its strand. When I was added to a preincubated mixture of Gu and siRNA, oxidative polymerization of Gu took place along the siRNA strand, affording NC⊃siRNA, the smallest siRNA-containing reactive nanocaplet so far reported. This conjugate was converted into NC⊃siRNA by the click reaction with a Gu-appended bioadhesive dendron (Glue) followed by a benzophenone derivative (BP). Then, Tf was covalently immobilized onto NC⊃siRNA by Gu-mediated adhesion followed by photochemical reaction with BP. With the help of Tf-induced transcytosis, NC⊃siRNA permeated deeply into a cancer spheroid, a 3D tissue model, at a depth of up to nearly 70 μm, unprecedentedly.