Therapeutic siRNA silencing in inflammatory monocytes in mice

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Abstract
In vivo silencing in specific cell types remains the main obstacle for therapeutic applications of siRNAs. Leuschner et al. now show that an optimized lipid nanoparticle delivers siRNA to inflammatory monocytes in mice and, when transporting CCR2 siRNA, has therapeutic effects in cardiovascular disease, cancer and transplant rejection. 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.