Photodynamic therapy targeting VCAM-1-expressing human umbilical vein endothelial cells using a PpIX–VCAM-1 binding peptide–quantum dot conjugate

Abstract

With increasing knowledge of the relevance of vascular cell adhesion molecule 1 (VCAM-1) for tumor growth, metastasis, angiogenesis, and related processes, it has become an attractive anti-tumor strategy to target VCAM-1 expression on the tumor vasculature. We designed a new targeted nanodrug, denoted PVQ, based on a photosensitizer (for the photodynamic effect), VCAM-1 target and quantum dot (QD) carrier, using conjugated water-dispersible colloidal CdSe–CdS/ZnS QDs, protoporphyrin IX (PpIX) photosensitizers, and VCAM-1 binding peptides. Its targeting ability and photodynamic therapy (PDT) efficiency against VCAM-1 expression in human umbilical vein endothelial cells (HUVECs) were then investigated. Conjugates of QD–VCAM-1 binding peptide (VQ), PpIX–VCAM-1 binding peptide (PV), and PVQ prepared using amide coupling were verified by agarose gel electrophoresis, Fourier transform infrared spectroscopy, and fluorescence spectrometry. VCAM-1 expression in HUVECs was induced by TNF-α treatment. PVQ conjugates were co-cultured with VCAM-1 expressing (VCAM-1(+)) and non-expressing (VCAM-1(−)) HUVECs, and target imaging, ROS generation, cell death, and apoptosis were analyzed using confocal fluorescence microscopy. VCAM-1 target imaging could not distinguish between VCAM-1(+) and VCAM-1(−) HUVECs after only 6 h of incubation; however it could distinguish between the cells after incubation for 24 h. After incubation for ca. 30 min, PVQ generated a significantly higher yield of ROS (3.6 fold) in VCAM-1(+) HUVECs compared with VCAM-1(−) cells, during 10 min of irradiation at a wavelength of 405 nm, and this was followed by a second rise in ROS at 30 min after irradiation. Moreover, cell destruction was observed clearly in VCAM-1(+) cells treated with PVQ and almost all cells became round after 30 min of irradiation at 405 nm. PVQ-induced PDT effects caused a significant apoptosis (onset and late apoptosis) in VCAM-1(+) HUVECs at 6 h after PDT treatment. In conclusion, PVQ shows a great potential for targeted PDT in cancer therapy.