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Despite considerable progress in the design of multifunctionalized nanoparticles (NPs) that selectively target specific cell types, their systemic application often results in unwanted liver accumulation. The exact mechanisms for this general observation are still unclear. Here we asked whether the number of cell-targeting antibodies per NP determines the extent of NP liver accumulation and also addressed the mechanisms by which antibody-coated NPs are retained in the liver. We used polysarcosine-based peptobrushes (PBs), which in an unmodified form remain in the circulation for >24 h due to the absence of a protein corona formation and low unspecific cell binding, and conjugated them with specific average numbers (2, 6, and 12) of antibodies specific for the dendritic cell (DC) surface receptor, DEC205. We assessed the time-dependent biodistribution of PB–antibody conjugates by in vivoimaging and flow cytometry. We observed that PB–antibody conjugates were trapped in the liver and that the extent of liver accumulation strongly increased with the number of attached antibodies. PB–antibody conjugates were selectively captured in the liver viaFc receptors (FcR) on liver sinusoidal endothelial cells, since systemic administration of FcR-blocking agents or the use of F(ab′)2fragments prevented liver accumulation. Cumulatively, our study demonstrates that liver endothelial cells play a yet scarcely acknowledged role in liver entrapment of antibody-coated NPs and that low antibody numbers on NPs and the use of F(ab′)2antibody fragments are both sufficient for cell type-specific targeting of secondary lymphoid organs and necessary to minimize unwanted liver accumulation.

The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is a powerful, highly reliable and selective reaction which allows for a rapid synthesis in high yields and under mild conditions (pH, temperature). However, the cytotoxicity of copper requires its complete removal prior to an application in vivo. This is an issue especially when it comes to CuAAC reactions on macromolecular structures or drug delivery systems, as copper might be retained by these systems. Thus, a quantification of the final copper content of these systems is inevitable, which we exemplified for a CuAAC reaction on liposomes using 64Cu-spiked Cu(I). In this respect, a Cu(II) nitrate solution was irradiated at the TRIGA Mark II research reactor Mainz to obtain c.a.[64Cu]Cu(II). The irradiated solution was directly used for a CuAAC on liposomes. After purification, their copper content was calculated utilizing γ-ray spectrometry. Only 0.018% of the added 64Cu-activity was still present in the liposome containing fractions after purification. This refers to a total amount of copper of 0.17 ng. The amount of retained copper is so low, that an in vivoapplication of the liposomes is absolutely reasonable. Besides this particular study, the experimental methodology may be applied to study many other CuAAC reactions, used for the synthesis of radiolabeled or non-radioactive species, which are intended for human applications.

Multifunctional and highly biocompatible polyether structures play a key role in shielding liposomes from degradation in the bloodstream, providing also multiple functional groups for further attachment of targeting moieties. In this work hyperbranched polyglycerol (hbPG) bearing lipids with long alkyl chain anchor are evaluated with respect to steric stabilization of liposomes. The branched polyether lipids possess a hydrophobic bis(hexadecyl)glycerol membrane anchor for the liposomal membrane. hbPG was chosen as a multifunctional alternative to PEG, enabling the eventual linkage of multiple targeting vectors. Different hbPG lipids (Mn= 2900 and 5200 g mol–1) were examined. A linear bis(hexadecyl)glycerol-PEG lipid (Mn= 3000 g mol–1) was investigated as well, comparing hbPG and PEG with respect to shielding properties. Radiolabeling of the polymers was carried out using 1-azido-2-(2-(2-[18F]fluoroethoxy)ethoxy)ethane ([18F]F-TEG-N)3via copper-catalyzed alkyne–azide cycloaddition with excellent radiochemical yields exceeding 95%. Liposomes were prepared by the thin-film hydration method followed by repeated extrusion. Use of a custom automatic extrusion device gave access to reproducible sizes of the liposomes (hydrodynamic radius of 60–94 nm). The in vivo fate of the bis(hexadecyl)glycerol polyethers and their corresponding assembled liposome structures were evaluated via noninvasive small animal positron emission tomography (PET) imaging and biodistribution studies (1 h after injection and 4 h after injection) in mice. Whereas the main uptake of the nonliposomal polyether lipids was observed in the kidneys and in the bladder after 1 h due to rapid renal clearance, in contrast, the corresponding liposomes showed uptake in the blood pool as well as in organs with good blood supply, that is, heart and lung over the whole observation period of 4 h. The in vivo behavior of all three liposomal formulations was comparable, albeit with remarkable differences in splenic uptake. Overall, liposomes shielded by the branched polyglycerol lipids show a favorable biodistribution with greatly prolonged blood circulation times, rendering them promising novel nanovesicles for drug transport and targeting.

Tumor necrosis factor‐alpha (TNF‐α) is a pleiotropic immune stimulatory cytokine and natural endotoxin that can induce necrosis and regression in solid tumors. However, systemic administration of TNF‐α is not feasible due to its short half‐life and acute toxicity, preventing its widespread use in cancer treatment. Dendritic mesoporous silica nanoparticles (DMSN) are used coated with a pH‐responsive block copolymer gate system combining charged hyperbranched polyethylenimine and nonionic hydrophilic polyethylenglycol to encapsulate TNF‐α and deliver it into various cancer cell lines and dendritic cells. Half‐maximal effective concentration (EC50) for loaded TNF‐α is reduced by more than two orders of magnitude. Particle stability and premature cargo release are assessed with enzyme‐linked immunosorbent assay. TNF‐α‐loaded particles are stable for up to 5 d in medium. Tumor cells are grown in vitro as 3D fluorescent ubiquitination‐based cell cycle indicator spheroids that mimic in vivo tumor architecture and microenvironment, allowing real‐time cell cycle imaging. DMSN penetrate these spheroids, release TNF‐α from its pores, preferentially affect cells in S/G2/M phase, and induce cell death in a time‐ and dose‐dependent manner. In conclusion, DMSN encapsulation is demonstrated, which is a promising approach to enhance delivery and efficacy of antitumor drugs, while minimizing adverse side effects. Dendritic mesoporous silica nanoparticlesare used to encapsulate the highly toxic antitumor drug TNF‐α. Efficiency of the employed system is tested in 2D and 3D tumor cell cultures. Encapsulation in mesoporous silica nanoparticles is a promising approach to enhance delivery and efficacy of antitumor drugs is demonstrated, while minimizing adverse side effects.

In article number 1700012, Helmut Jonuleit and co‐workers utilize dendritic mesoporous silica nanoparticles for drug delivery to increase the efficacy of anti‐tumor drug TNF‐α, while decreasing its side‐effects.