Covalent Cell Surface Conjugation of Nanoparticles by a Combination of Metabolic Labeling and Click Chemistry

Conjugation of nanoparticles (NP) to the surface of living cells is of interest in the context of exploiting the tissue homing properties of ex vivo engineered T cells for tumor-targeted delivery of drugs loaded into NP. Cell surface conjugation requires either a covalent or non-covalent reaction. Non-covalent conjugation with ligand-decorated NP (LNP) is challenging and involves a dynamic equilibrium between the bound and unbound state. Covalent NP conjugation results in a permanently bound state of NP, but the current routes for cell surface conjugation face slow reaction kinetics and random conjugation to proteins in the glycocalyx. To address the unmet need for alternative bioorthogonal strategies that allow for efficient covalent cell surface conjugation, we developed a 2-step click conjugation sequence in which cells are first metabolically labeled with azides followed by reaction with sulfo-6-methyl-tetrazine-dibenzyl cyclooctyne (Tz-DBCO) by SPAAC, and subsequent IEDDA with trans-cyclooctene (TCO) functionalized NP. In contrast to using only metabolic azide labeling and subsequent conjugation of DBCO-NP, our 2-step method yields a highly specific cell surface conjugation of LNP, with very low non-specific background binding.