Targeting Protumoral Tumor-Associated Macrophages with Nanobody-Functionalized Nanogels through Strain Promoted Azide Alkyne Cycloaddition Ligation

Tumor-associated macrophages (TAMs) with high expression levels of the Macrophage Mannose Receptor (MMR, CD206) exhibit a strong angiogenic and immune suppressive activity. Thus, they are a highly attractive target in cancer immunotherapy, with the aim to modulate their protumoral behavior. Here, we introduce polymer nanogels as potential drug nanocarriers which were site-specifically decorated with a Nanobody (Nb) specific for the MMR. Using azide-functionalized RAFT chain transfer agents, they provide access to amphiphilic reactive ester block copolymers that self-assemble into micelles and are afterwards core-cross-linked toward fully hydrophilic nanogels with terminal azide groups on their surface. MMR-targeting Nb can site-selectively be functionalized with one single cyclooctyne moiety by maleimide-cysteine chemistry under mildly reducing conditions which enables successful chemoorthogonal conjugation to the nanogels. The resulting Nb-functionalized nanogels were highly efficient in targeting MMR-expressing cells and TAMs both in vitro and in vivo. We believe that these findings pave the road for targeted eradication or modulation of pro-tumoral MMR high TAMs.