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 (Tf NC⊃siRNA) for the purpose of realizing siRNA delivery into deep tissues and RNA interference (RNAi) subsequently. For obtaining Tf NC⊃siRNA, a macromonomer (Az Gu) bearing multiple guanidinium ion (Gu+ ) units, azide (N3 ) 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, Az Gu can adhere to siRNA along its strand. When I2 was added to a preincubated mixture of Az Gu and siRNA, oxidative polymerization of Az Gu took place along the siRNA strand, affording Az NC⊃siRNA, the smallest siRNA-containing reactive nanocaplet so far reported. This conjugate was converted into Glue/BP NC⊃siRNA by the click reaction with a Gu+ -appended bio-adhesive dendron (Glue) followed by a benzophenone derivative (BP). Then, Tf was covalently immobilized onto Glue/BP NC⊃siRNA by Gu+ -mediated adhesion followed by photochemical reaction with BP. With the help of Tf-induced transcytosis, Tf NC⊃siRNA permeated deeply into a cancer spheroid, a 3D-tissue model, at depth of up to nearly 70 µm, unprecedentedly.