Anti-HER2 Affibody-Conjugated Photosensitizer for\nTumor Targeting Photodynamic Therapy

Abstract

Antibody-coupled photosensitive molecules can achieve an ideal\ntumor-specific photodynamic therapy (PDT) and show strong clinical\napplication potential. However, some inherent disadvantages, such\nas long circulation half-life, poor permeation into solid tumors,\nand difficulty in obtaining uniform coupling products, present potential\nproblems to clinical applications. In this study, we propose a novel\ndesign of targeting photosensitizers, based on a very small targeting\nprotein (an affibody molecule) coupled with photosensitive compounds,\nto address these problems. In the synthesis, photosensitive pyropheophorbide-a\n(Pyro) is modified with a PEG linker (molecular weight of 727 Da)\nand then site specifically coupled to the anti-HER2 Z_HER2:2891 affibody protein to provide a homogeneous protein-coupled photosensitizer\nvia a convenient process. In vitro and in vivo experiments show that\nthis molecule has an ideal selectivity for binding and photocytotoxicity\nagainst HER2-positive cells (more than 50-fold selectivity between\nHER2-high expression and HER2-low expression cells) and highly specific\ntumor accumulation; at a relatively low dose, it effectively eliminated\nHER2-high expression NCI–N87 tumors in a mouse model. It is\nworth noting that Pyro only has a moderate photodynamic activity;\nhowever, the affibody-coupled Pyro molecule (Pyro-Linker-Z_HER2) still shows excellent tumor therapeutic function. The more ideal\ntumor permeability of small ligands may be helpful to enhance the\ndrug concentration in the tumor site and the ability to penetrate\ndeeply inside the tumor. Coupling photosensitive compounds with affibody\nproteins may provide a new way for targeting PDT of tumors.