RNAi-mediated gene-targeting through systemic application of polyethylenimine (PEI)-complexed siRNA in vivo

Abstract

RNA interference (RNAi) represents a powerful, naturally occurring biological strategy for inhibition of gene expression. It is mediated through small interfering RNAs (siRNAs), which trigger specific mRNA degradation. In mammalian systems, however, the application of siRNAs is severely limited by the instability and poor delivery of unmodified siRNA molecules into the cells in vivo. In this study, we show that the noncovalent complexation of synthetic siRNAs with low molecular weight polyethylenimine (PEI) efficiently stabilizes siRNAs and delivers siRNAs into cells where they display full bioactivity at completely nontoxic concentrations. More importantly, in a subcutaneous mouse tumor model, the systemic (intraperitoneal, i.p.) administration of complexed, but not of naked siRNAs, leads to the delivery of the intact siRNAs into the tumors. The i.p. injection of PEI-complexed, but not of naked siRNAs targeting the c-erbB2/neu (HER-2) receptor results in a marked reduction of tumor growth through siRNA-mediated HER-2 downregulation. Hence, we establish a novel and simple system for the systemic in vivo application of siRNAs through PEI complexation as a powerful tool for future therapeutic use.

RNAi-mediated gene silencing in tumour tissue using replication-competent retroviral vectors

“…Silencing of stable, endogenously expressed (reporter) genes represents a more relevant model of RNAi application than transfection of reporter plasmids. 36 Moreover evaluation of sustained RNAi delivery necessitates sustained reporter gene expression. Several studies have tested RNAi delivery vehicles on cell lines stably expressing firefly luciferase and have reached similar knockdown efficiencies as we describe here.…”

“…Several studies have tested RNAi delivery vehicles on cell lines stably expressing firefly luciferase and have reached similar knockdown efficiencies as we describe here. 36,37 However, the knockdown was only transient in these studies although high amounts of siRNA/shRNA were applied. Our system, in contrast, mediates a dose-independent, sustained RNAi effect.…”

Intravenous injection of siRNA directed against hypoxia-inducible factors prolongs survival in a Lewis lung carcinoma cancer model

“…Toxic effects of PEI in lung have been described. 1 Therefore, we also tested intratracheal administration of siRNA complexed with lipofectamine. In this case, mice survived, however, siRNA uptake was observed almost exclusively in macrophages, as determined by flow cytometry of cells from bronchoalveolar lavages.…”

“…In comparison, the intraperitoneal injection of siRNA in a complex with PEI for gene inhibition in subcutaneous tumor models has been described. 1 Intraperitoneal administration was included in this study as a reference technique. However, it appeared unsuitable for targeting of the lung tumor tissue.…”

“…Successful transfection of subcutaneous tumor models has been described for synthetic siRNAs complexed with polyethylenimine (PEI) that were administered intraperitoneally. 1 The feasibility of this and other routes of administration for targeting lung tumors by siRNA has not been investigated.…”