Targeting of Immune Cells with Trimannosylated Liposomes

Abstract

Dendritic cells (DCs) are a compelling target in cancer immunotherapy as they initialize strong antigen‐specific immune responses. Drug delivery systems (DDSs) such as liposomes provide the opportunity to deliver antigens and immunostimulatory molecules to DCs, which in turn initiate an antigen‐specific immune response. To address predominantly DCs, DDSs need to be equipped with targeting moieties. This study evaluates liposomes, bearing the oligosaccharide trimannose on their surface, for their ability to address DCs in vitro and in vivo. Trimannose as a saccharidic structure is known to be recognized by receptors on the surface of DCs. To obtain trimannosylated liposomes, azide‐bearing trimannose is coupled to alkyne‐functionalized hyperbranched polyglycerol (hbPG) with a bis(hexadecyl)glycerol (BisHD) anchor in a Cu(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC). To enable tracking of the liposomes in vivo, the trimannosylated BisHD‐hbPG lipids are radiolabeled with 18F in a CuAAC. Subsequently, liposomes are produced via the thin‐film hydration method followed by extrusion. The behavior of the trimannosylated liposomes is evaluated in in vitro cell binding assays and in vivo µPET and ex vivo biodistribution studies in healthy C57BL/6 mice and the results are compared to similar liposomes not bearing trimannose on their surface.

Stability of Alkyl Chain-Mediated Lipid Anchoring in Liposomal Membranes

“…An alkyne-group enables the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with functional groups, e.g., dyes like atto 488 azide or other azide-bearing molecules [ 25 ]. This reaction is known from literature and was adapted for the synthesized amphiphilic polyethers [ 31 , 32 ]. For this purpose, the terminal hydroxyl group of PEG was deprotonated using sodium hydride (NaH) (see supplement scheme S1 ).…”

Novel Opportunities for Cathepsin S Inhibitors in Cancer Immunotherapy by Nanocarrier-Mediated Delivery

“…The latter is currently considered to be more effective in terms of cheap recombinant production and precise chemical modification compared to full antibodies or antibody-drug conjugates. More recently, also peptide-based targeting strategies [111,112] or multivalent mannose derivatives [113] have been exploited to guide nanoparticle delivery toward TAM. Interestingly, mannose targeting has also been directly applied to small molecule cathepsin inhibitors by generating glycoconjugates of monomannose, trimannose, and heptamannose with the pan-cathepsin inhibitor DCG-04 [114].…”

Multivalency Beats Complexity: A Study on the Cell Uptake of Carbohydrate Functionalized Nanocarriers to Dendritic Cells

“…A key study by Holla and Skerra revealed that simple mannose-units, and especially branched oligomannosidic structures, in particular a trimannose structure (3,6-di-(α-d-mannopyranosyl)-α-d-mannopyranose) as well as fucose-containing saccharides, in particular a disaccharide (3-(β-l-fucopyranosyl)-2-acetamido-2-deoxy-β-d-glucopyranose), are recognized by DC-SIGN [25]. Based on these observations, we selected four different potential ligands for DC-SIGN that carry a poly(ethylene glycol) (PEG)-based, azide-terminated linker to enable covalent binding through azide-alkyne click reactions to nanocarriers as the target structures for total synthesis (Figure 1) A simple d-mannose monosaccharide 1 and the mentioned trimannose structure 2, which were available from earlier studies [4,26,27], as well as a fucose containing disaccharide 3 and a mannose-terminated glycodendron 4, were chosen as potential ligands. The synthesis of the fucose disaccharide 3 started from N-acetylglucosamine (5), which was deprotonated at the most acidic 1-OH position and then was β-selectively alkylated with progargyl bromide in 52% yield (Scheme 1, top) [29].…”

“…Therefore, they can serve as important mediators in nanomedicine to deliver antigens upon targeting and cell uptake of antigen-loaded nanocarriers [3]. The targeting of DCs is possible through their surface receptor dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), which is known to bind carbohydrate recognition structures through a C-terminal carbohydrate recognition domain (CRD) [4][5][6]. The DC-SIGN receptor is a tetramer that carries four of these CRD domains and can therefore theoretically bind up to four ligands simultaneously [7].…”