Synthesis and validation of clickable multimeric mannose ligands for dendritic cell targeting

Abstract

The efficacy of therapeutics can be enhanced with their off-target effects being minimized through targeted delivery. In vaccination and cancer immunotherapy, targeting dendritic cells (DCs) and macrophages (Mφs) is crucial for the activation of the immune system. To this end, we have developed a set of carbohydrate-based ligands targeting C-type lectins (CTLs) present on the surface of DCs for receptor-mediated uptake. Branched structures functionalized with up to four mannose units were synthesized through CuI-catalysed click chemistry, and the products were further functionalized with the DBCO group to facilitate their conjugation with cargos of interest via Cu-free click chemistry. Thus, the ligands were conjugated with fluorescein azide, and the fluorescent conjugates were assessed for their internalization in CTL expressing immature DCs. The results showed that high-mannose branched structures were efficiently internalized through the endocytic pathway, with a positive qualitative correlation between branching degree of sugar-based ligands and internalization. As evidence for payload delivery, conjugating with a mannotriose ligand quantitatively increased the uptake of a fluorescently labeled oligonucleotide by immature DCs. Our work supports the use of click chemistry to synthesize and conjugate promising ligands for efficient delivery of nucleic acid-based drugs.