Abstract 18955: VSMC-Targeted Aptamer-siRNA Chimeras as Inhibitors of Intimal Hyperplasia

Abstract

Arterial revascularization by stenting is associated with restenosis due to proliferation of vascular smooth muscle cells (VSMCs) and intimal hyperplasia. Although the use of cell cycle inhibitors in drug eluting stents (DES) has reduced the rate of in-stent restenosis, this approach also inhibits re-endothelialization, thereby requiring prolonged antithrombotic regimens to prevent stent thrombosis. Delivery of nucleic acid aptamers by DES is a potential novel approach due to their high specific binding affinity and potential for modification by medicinal chemistry. The goal of this study was to identify RNA aptamers that (1) internalize into VSMCs and/or (2) specifically inhibit VSMC activation. Using an in vivo compatible RNA aptamer library, VSMC-specific aptamers were selected using a cell-internalization SELEX (systematic evolution of ligands by exponential enrichment) process with iterative rounds of positive selection using VSMCs and negative selection using endothelial cells (ECs). The top candidate aptamers demonstrated 15-20-fold specificity for internalization into cultured VSMCs vs . ECs. Specificity of these aptamers was confirmed by ex vivo studies that demonstrated preferential internalization into denuded, but not endothelium-intact, aortic segments. In addition, several of the VSMC-targeting aptamers exhibited differential effectiveness in inhibiting VSMC migration as measured by Boyden chamber assays. In proof-of-concept delivery studies, we next engineered aptamer-siRNA chimeras using siRNAs targeting Nox1 NADPH oxidase, which has been implicated in intimal hyperplasia. These VSMC-targeting aptamer-siRNA chimeras retain specificity for VSMCs and are being evaluated for efficacy in reducing intimal formation in a murine model of vascular injury. In conclusion, we developed novel VSMC-targeting aptamers that may serve as a platform technology to selectively deliver therapeutics to VSMCs over ECs. The aptamers that inhibited cell migration present an opportunity for dual-action VSMC-targeted therapeutic agents. Future refinement of this panel of VSMC-directed aptamers will enable broader application of targeted therapies for vascular-proliferative diseases.