Integrin-Mediated Targeting of Liposomally Bound siRNAs to Tumor Vasculatures

Abstract

The discovery of RNA interference (RNAi) technique gave birth to a promising new therapeutic modality for silencing disease-causing genes. Small interfering RNAs (siRNAs), double stranded RNAs containing ~21–23 nucleotides, are being increasingly exploited in designing potential anticancer therapeutics due to the ease of their syntheses and high target specificities. So far, cationic liposomes mediated siRNA delivery systems appear to be one of the most promising candidates for systemic applications. However, the lack of tumor-specific delivery often poses a major threat to clinical success. To this end, we have developed effective liposomal delivery systems for delivering siRNA selectively via integrin receptors (αβ heterodimeric transmembrane glycoprotein receptors) which are highly upregulated on the endothelial cells of tumor vasculature compared to their expression levels in other quiescent vessels in normal tissues. With a view to exploit RNAi for tumor-specific systemic applications, the present report focuses on the use CDC20siRNAs (cell division cycle homologue 20), a key cell cycle regulator for the completion of mitosis in organisms from yeast to human and overexpressed in several carcinomas. Herein we report on the details of protocols for preparing the α5β1 integrin receptor selective and tumor-vasculature targeting liposomal formulation of pegylated RGDK-lipopeptide that can efficiently and stably encapsulate siRNAs. We show that intravenous administration of the liposomal formulation can lead to significant melanoma (B16F10) tumor growth inhibition in C57BL/6J mice via apoptosis of tumor endothelial cells.