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