Orally delivered siRNA targeting macrophage Map4k4 suppresses systemic inflammation

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Abstract
The therapeutic potential of gene silencing with siRNAs (short interfering RNAs) is great — in theory. In practice many obstacles will need to be overcome before it becomes a practical proposition, and one of those is the safe delivery of the siRNA to its target tissue. A new delivery system described in this issue may prove to be a significant step towards that end. siRNAs designed to silence expression of the enzyme MAP4k4 in macrophages were encapsulated in micrometre-sized β1,3-D-glucan particles and administered orally to mice. The encapsulated siRNA increased survival rates in mice with lipopolysaccharide-induced inflammation — a common model for inflammatory diseases — and suppressed systemic inflammation. The method is up to 250 times more potent in vivo than previously reported forms of systemic siRNA delivery. Encapsulated small interfering RNA nanoparticles are shown to silence a kinase mediator of inflammatory responses in mice in vitro and in vivo. Gene silencing by double-stranded RNA, denoted RNA interference, represents a new paradigm for rational drug design1. However, the transformative therapeutic potential of short interfering RNA (siRNA) has been stymied by a key obstacle—safe delivery to specified target cells in vivo2. Macrophages are particularly attractive targets for RNA interference therapy because they promote pathogenic inflammatory responses in diseases such as rheumatoid arthritis, atherosclerosis, inflammatory bowel disease and diabetes3. Here we report the engineering of β1,3-d-glucan-encapsulated siRNA particles (GeRPs) as efficient oral delivery vehicles that potently silence genes in mouse macrophages in vitro and in vivo. Oral gavage of mice with GeRPs containing as little as 20 μg kg-1 siRNA directed against tumour necrosis factor α (Tnf-α) depleted its messenger RNA in macrophages recovered from the peritoneum, spleen, liver and lung, and lowered serum Tnf-α levels. Screening with GeRPs for inflammation genes revealed that the mitogen-activated protein kinase kinase kinase kinase 4 (Map4k4) is a previously unknown mediator of cytokine expression. Importantly, silencing Map4k4 in macrophages in vivo protected mice from lipopolysaccharide-induced lethality by inhibiting Tnf-α and interleukin-1β production. This technology defines a new strategy for oral delivery of siRNA to attenuate inflammatory responses in human disease.