Nanoplex-Mediated Delivery of siRNA to Inhibit Angiogenesis In Vivo
Dr Raymond Schiffelers, Assistant Professor of Pharmaceutics, Utrecht University, speaks at RNAi Europe 2004.
Date Posted: Friday, January 06, 2006
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Abstract
siRNA offers the prospects of potent, highly specific, (post-)transcriptional gene silencing and promises important biomedical applications. However, like all nucleic acid-based strategies, delivery systems seem essential to help these relatively large, negatively charged molecules to cross the cellular membrane and reach their intracellular site of action. In this presentation we describe the engineering of a peptide-targeted, sterically stabilized and cationic polymer that is able to complex siRNA into nanoplexes. The net positive charge of these particles is shielded and thereby cell interaction can be mediated by the targeting peptide.
In vitro, the nanoplexes demonstrated affinity for angiogenic endothelial cells and are able to silence a variety of transfected or consecutively expressed reporter genes.
In vivo, we tested siRNA-nanoplexes targeted against vascular endothelial growth factor-receptor 2 (mVEGFR2). mVEGFR2 is a receptor that plays a crucial role during neovasculature formation and it is specifically expressed on the surface of angiogenic endothelial cells. Therapeutic effects were investigated in two models of pathological angiogenesis caused by subcutaneous tumor growth or ocular inflammation.
After intravenous administration in tumor-bearing mice, levels of fluorescently labeled 'free' siRNA were undetectable at 1 h after administration in any of the organs investigated. In contrast, after administration of nanoplexes, delivery of siRNA to tumor tissue could be visualized. Injection of siRNA against mVEGFR2 resulted in strong inhibition of tumor growth with concomitant loss of blood vessel organization and reduction in blood vessel density.
In the ocular inflammation model caused by implantation of viral DNA in the murine eye, dose-dependent inhibition of angiogenesis was observed. Based on this lead compound, intravenous administration of siRNA may provide effective treatment for neovascularization diseases.
About the Speaker
Raymond Schiffelers studied bio-pharmaceutical sciences at the Leiden-Amsterdam Center for Drug Research (LACDR). In 1993-1994 he investigated tumor-targeted liposomes at the Dept. of Biopharmaceutics and in the following year he worked at the Dept. of Vascular Biology of SmithKline&Beecham Pharmaceuticals in Welwyn (UK) on murine models for atherosclerosis.
From 1996 to 2000 his research was aimed at liposomal targeting of antimicrobial agents to bacterial infections as part of a project initiated by the Dept. of Medical Microbiology & Infectious Diseases of the Erasmus University Rotterdam and the Dept. of Pharmaceutics of the Utrecht Institute for Pharmaceutical Sciences (UIPS). This research resulted in his Ph.D. degree, obtained in February 2001.
Since August 2000, he is funded by the Dutch Cancer Society on strategies to target the angiogenic tumor endothelium. As part of this project he spend one year at Intradigm Co. (USA) where he studied, in collaboration with several academic groups, strategies for endothelial cell-targeted delivery of siRNA.