Therapeutic siRNA silencing in inflammatory monocytes

Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Nature Biotechnology (Impact Factor: 41.51). 11/2011; 29(11):1005-10. DOI: 10.1038/nbt.1989
Source: PubMed


Excessive and prolonged activity of inflammatory monocytes is a hallmark of many diseases with an inflammatory component. In such conditions, precise targeting of these cells could be therapeutically beneficial while sparing many essential functions of the innate immune system, thus limiting unwanted effects. Inflammatory monocytes-but not the noninflammatory subset-depend on the chemokine receptor CCR2 for localization to injured tissue. Here we present an optimized lipid nanoparticle and a CCR2-silencing short interfering RNA that, when administered systemically in mice, show rapid blood clearance, accumulate in spleen and bone marrow, and localize to monocytes. Efficient degradation of CCR2 mRNA in monocytes prevents their accumulation in sites of inflammation. Specifically, the treatment attenuates their number in atherosclerotic plaques, reduces infarct size after coronary artery occlusion, prolongs normoglycemia in diabetic mice after pancreatic islet transplantation, and results in reduced tumor volumes and lower numbers of tumor-associated macrophages.

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    • "Inflammatory monocytes (Ly6Chigh monocytes), but not the non-inflammatory subset (Ly6Clow monocytes), depend on the chemokine receptor CCR2 to accumulate in injured tissue. More recently, Leuschner et al. first demonstrated that monocyte-targeting siRNA nano-materials could silence CCR2 mRNA in the Ly6Chigh monocyte subset and thus reduce regional recruitment of these cells in atherosclerotic plaques, which consequently reduced the infarct size after coronary artery occlusion [25]. In addition, it has recently been showed that the splenic monocyte population may represent a potential therapeutic target for any anti-inflammatory strategy focusing on inflammatory monocytes. "
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    • "Leuschner et al. developed a lipid nanoparticle that encapsulated a short interfering RNA (siRNA) that targets Ccr2 mRNA (termed siCCR2) [25]. In the ischemia-reperfusion injury model, administration of siCCR2 resulted in reduced monocyte/macrophage accumulation in the heart and reduced the infarct size. "
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    • "Numerous other targets including, inter alia, Egr-1 for Alzheimer's disease [36], hepcidin for anaemia of chronic disease [37] and WEE1 for myeloid and lymphoid leukaemia [38] have been suggested following studies on THP-1 cells and effective and non-perturbing delivery agents to such cells are therefore highly sought after. While a large number of non-viral siRNA delivery systems have been developed and are widely used to mediate delivery to adherent cell lines, fewer options are available for those working with suspension cell lines where typically either lipid based transfection agents, such as Lipofectamine 2000™, or electroporation are used [34] and, while an optimised lipid nanoparticle has been successfully deployed to mediate silencing of CCR2 in an inflammatory monocyte mouse model [35], there remains a need to develop non-toxic agents that can routinely, robustly and specifically effect gene silencing in monocytes both in vitro and in vivo. "
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    ABSTRACT: Cationic amphipathic pH responsive peptides possess high in vitro and in vivo nucleic acid delivery capabilities and function by forming a non-covalent complex with cargo, protecting it from nucleases, facilitating uptake via endocytosis and responding to endosomal acidification by being released from the complex and inserting into and disordering endosomal membranes. We have designed and synthesised peptides to show how Coulombic interactions between ionizable 2,3-diaminopropionic acid (Dap) side chains can be manipulated to tune the functional pH response of the peptides to afford optimal nucleic acid transfer and have modified the hydrogen binding capabilities of the Dap side chains in order to reduce cytotoxicity. When compared with benchmark delivery compounds, the peptides are shown to have low toxicity and are highly effective at mediating gene silencing in adherent MCF-7 and A549 cell lines, primary human umbilical vein endothelial cells and both differentiated macrophage-like and suspension monocyte-like THP-1 cells.
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