Small-molecular Toll-like receptor 7/8 (TLR7/8) agonists hold promise as immune modulators for a variety of immune therapeutic purposes including cancer therapy or vaccination. However, due to their rapid systemic distribution causing difficult-to-control inflammatory off-target effects, their application is still problematic, in particular systemically. To address this problem, we designed and robustly fabricated pH-responsive nanogels serving as versatile immunodrug nanocarriers for safe delivery of TLR7/8-stimulating imidazoquinolines after intravenous administration. To this aim, a primary amine-reactive methacrylamide monomer bearing a pendant squaric ester amide is introduced, which is polymerized under controlled RAFT polymerization conditions. Corresponding PEGderived squaric ester amide block copolymers self-assemble into precursor micelles in polar protic solvents. Their cores are aminereactive and can sequentially be transformed by acid-sensitive cross-linkers, dyes, and imidazoquinolines. Remaining squaric ester amides are hydrophilized affording fully hydrophilic nanogels with profound stability in human plasma but stimuli-responsive degradation upon exposure to endolysosomal pH conditions. The immunomodulatory behavior of the imidazoquinolines alone or conjugated to the nanogels was demonstrated by macrophages in vitro. In vivo, however, we observed a remarkable impact of the nanogel: After intravenous injection, a spatially controlled immunostimulatory activity was evident in the spleen, whereas systemic off-target inflammatory responses triggered by the small-molecular imidazoquinoline analogue were absent. These findings underline the potential of squaric ester-based, pH-degradable nanogels as a promising platform to permit intravenous administration routes of small-molecular TLR7/8 agonists and, thus, the opportunity to explore their adjuvant potency for systemic vaccination or cancer immunotherapy purposes.

Immunosuppressive M2 macrophages govern the immunophathogenic micromilieu in many severe diseases including cancer or fibrosis, thus, their re‐polarization through RNA interference is a promising concept to support combinatorial therapies. For targeted siRNA delivery, however, safe and stable carriers are required that manage cell specific transport to M2 macrophages. Here, siRNA‐loaded cationic nanogels are reported with α‐mannosyl decorated surfaces that target and modify M2 macrophages selectively. Via amphiphilic precursor block copolymers bearing one single α‐mannosyl moiety at their chain end mannosylated cationic nanohydrogel particles (ManNP) were obtained of 20 nm diameter determined by dynamic light scattering and cryogenic electron transmission microscopy. α‐Mannosyl surface modification is confirmed by agglutination with concanavalin A. SiRNA‐loaded ManNP preferentially targets the overexpressed mannose receptor CD206 on M2 macrophages, as shown by in vitro cell uptake studies in M2 polarized primary macrophages. This specificity is confirmed, since ManNP uptake could be reduced by blocking of CD206 with mannan. Effective ManNP‐guided siRNA delivery is confirmed by sequence‐specific gene knockdown of CSF‐1R in M2‐type macrophages exclusively, while the expression levels in M1‐polarized macrophages is not affected. In conclusion, α‐mannosyl‐functionalized ManNPs are promising universal siRNA carriers for targeted immunomodulatory treatment of immunosuppressive macrophages.

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.

Significance Fibrosis is a consequence of most chronic liver diseases, but currently no approved antifibrotic treatment is available. M2-type macrophages drive fibrosis progression and prevent regression, even when effective causal therapies have been employed. M2-type macrophages activate a cascade of fibrogenic effector cells and can prevent removal of excess scar tissue. To switch these profibrogenic M2 to fibrolytic (regenerative) macrophages, we developed a pH-degradable, nanogel-based delivery system which can be covalently functionalized with the macrophage-repolarizing bisphosphonate alendronate. The nanogels efficiently deliver the clinically approved drug into hepatic nonparenchymal cells after intravenous administration. They do not eliminate macrophages but repolarize their phenotype and subsequently block fibrosis progression. This approach establishes a nanotherapeutic delivery platform to treat further M2-type macrophage-driven diseases, including cancer.

Front Cover: Targeting immunosuppressive M2 macrophages for siRNA‐mediated repolarization towards immunoactive M1 macrophages is achieved by α‐mannosylfunctionalized cationic nanohydrogel particles. These particles are prepared from amphiphilic reactive ester block copolymers obtained by RAFT polymerization. A novel α‐mannosyl‐chain‐transfer‐agent guarantees selective α‐chain end group polymer functionalization. Subsequent self‐assembly and cross‐linking affords α‐mannosyl‐functionalized cationic nanohydrogels that complex and deliver siRNA to M2 macrophages. This is reported by Nadine Leber, Leonard Kaps, Aiting Yang, Misbah Aslam, Mariacristina Giardino, Adrian Klefenz, Niklas Choteschovsky, Sebastian Rosigkeit, Asmaa Mostafa, Lutz Nuhn, Detlef Schuppan, and Rudolf Zentel in article 1900162.

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