In this study, we developed coordinative amphiphiles for use as novel siRNA transporters. As a modification of a conventional cationic lipid structure, we replaced the cationic head with zinc(II)-dipicolylamine complex (Zn/DPA) as a phosphate-directing group, and used various membrane-directing groups in the place of the hydrophobic tails. These simple amphiphiles are readily synthesized and easy to modify. The Zn/DPA head groups bind to the phosphate backbones of siRNAs, and to our surprise, they prevented the enzymatic degradation of siRNAs by RNase A. Interestingly, the Zn/DPA head itself exhibited moderate transfection efficiency, and its combination with a membrane-directing group-oleoyl (CA1), pyrenebutyryl (CA2), or biotin (CA3)-enhanced the delivery efficiency without imparting significant cytotoxicity. Notably, the uptake pathway was tunable depending on the nature of the membrane-directing group. CA1 delivered siRNAs mainly through caveolae-mediated endocytosis, and CA2 through clathrin- and caveolin-independent endocytosis; CA3 recruited siRNAs specifically into biotin receptor-positive HepG2 cells through receptor-mediated endocytosis. Thus, it appears possible to develop tunable siRNA transporters simply by changing the membrane-directing parts. These are the first examples of amphiphilic siRNA transporters accompanying coordinative interactions between the amphiphiles and siRNAs.
Curved biodegradable microneedles for application to the outer surface of blood vessels are produced to enhance drug delivery to vascular tissues suffering from hyperplasia or atherosclerosis. Spatially discrete thermal drawing and post-annealing processes are employed to fabricate microneedles on a curved surface. Insertion of microneedles into arteries in vivo and ex vivo is demonstrated, and their mechanical properties and drug-delivery function are studied.
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