In Vivo siRNA Delivery to Immunosuppressive Liver Macrophages by α-Mannosyl-Functionalized Cationic Nanohydrogel Particles

Leonard Kaps,Nadine Leber,Adrian Klefenz,Niklas Choteschovsky,Lutz Nuhn,Rudolf Zentel,Detlef Schuppan

doi:10.3390/cells9081905

Abstract

Macrophages are the front soldiers of the innate immune system and are vital for immune defense, tumor surveillance, and tissue homeostasis. In chronic diseases, including cancer and liver fibrosis, macrophages can be forced into an immunosuppressive and profibrotic M2 phenotype. M2-type macrophages overexpress the mannose receptor CD206. Targeting these cells via CD206 and macrophage repolarization towards an immune stimulating and antifibrotic M1 phenotype through RNA interference represents an appealing therapeutic approach. We designed nanohydrogel particles equipped with mannose residues on the surface (ManNP) that delivered siRNA more efficiently to M2 polarized macrophages compared to their untargeted counterparts (NonNP) in vitro. The ManNP were then assessed for their in vivo targeting potential in mice with experimental liver fibrosis that is characterized by increased profibrotic (and immunosuppressive) M2-type macrophages. Double-labelled siRNA-loaded ManNP carrying two different near infrared labels for siRNA and ManNP showed good biocompatibility and robust uptake in fibrotic livers as assessed by in vivo near infrared imaging. siRNA–ManNP were highly colocalized with CD206+ M2-type macrophages on a cellular level, while untargeted NP (NonNP) showed little colocalization and were non-specifically taken up by other liver cells. ManNP did not induce hepatic inflammation or kidney dysfunction, as demonstrated by serological analysis. In conclusion, α-mannosyl-functionalized ManNP direct NP towards M2-type macrophages in diseased livers and prevent unspecific uptake in non-target cells. ManNP are promising vehicles for siRNA and other drugs for immunomodulatory treatment of liver fibrosis and liver cancer.

Highlights

Immune therapy represents a novel type of treatment, which boosts the body’s immune system to recognize and eliminate pathogens or abnormal cells, as in cancers, and establish a defense memory
Α-chain end mannose-functionalized amphiphilic block copolymers were obtained by controlled RAFT polymerization, using an α-mannosyl-functionalized chain transfer agent (Man CTA)
In this study α-mannosylated small interfering RNA (siRNA) nanohydrogel carriers were evaluated for specific targeting of profibrotic M2 polarized macrophages through the overexpressed mannose receptor CD206 in liver fibrotic mice

Summary

Introduction

Immune therapy represents a novel type of treatment, which boosts the body’s immune system to recognize and eliminate pathogens or abnormal cells, as in cancers, and establish a defense memory. Tumor cells acquire three major features to evade immune recognition in order to grow and progress: the ability to 1. The (advanced) tumor microenvironment consists of subsets of immunosuppressive cells, and macrophages often play a central in cancer immune suppression. Macrophages are the first line of defense against of the innate immune system to fight pathogens and to clearance foreign, aged, and damaged cells [2]. Especially cancer and fibrosis, macrophages are usually polarized towards an immunosuppressive, alternative (M2-type) macrophage phenotype. It is mainly the cancer cells and the tumor associated stroma that promote macrophage repolarization towards the M2-type, i.e., tumor-associated macrophages (TAM). TAM are the source of various pro-angiogenic, pro-fibrotic, and T cell suppressive cytokines, e.g., vascular endothelial growth factor (VEGF) or transforming growth factor beta 1 (TGFβ1) [2]

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