Nanobody-photosensitizer conjugates for targeted photodynamic therapy

Photodynamic therapy (PDT) induces cell death through light activation of a photosensitizer (PS). Targeted delivery of PS via
monoclonal antibodies has improved tumor selectivity. However, these conjugates have long half-lives, leading to relatively long
photosensitivity in patients. In an attempt to target PS specifically to tumors and to accelerate PS clearance, we have developed new
conjugates consisting of nanobodies (NB) targeting the epidermal growth factor receptor (EGFR) and a traceable PS (IRDye700DX). These
fluorescent conjugates allow the distinction of cell lines with different expression levels of EGFR. Results show that these conjugates
specifically induce cell death of EGFR overexpressing cells in low nanomolar concentrations, while PS alone or the NB–PS conjugates in the
absence of light induce no toxicity. Delivery of PS using internalizing biparatopic NB–PS conjugates results in even more pronounced
phototoxicities. Altogether, EGFR-targeted NB–PS conjugates are specific and potent, enabling the combination of molecular imaging with
cancer therapy.