Photosensitizer-Conjugated Gold Nanorods for Enzyme-Activatable Fluorescence Imaging and Photodynamic Therapy

We report on the development of photosensitizer-conjugated gold nanorods (MMP2P-GNR) in which photosensitizers were conjugated onto the surface of gold nanorods (GNR) via a protease-cleavable peptide linker. We hypothesized that fluorescence and phototoxicity of the conjugated photosensitizers would be suppressed in their native state, becoming activated only after cleavage by the target protease matrix metalloprotease-2 (MMP2). Quantitative analysis of the fluorescence and singlet oxygen generation (SOG) demonstrated that the MMP2P-GNR conjugate emitted fluorescence intensity corresponding to 0.4% ± 0.01% and an SOG efficiency of 0.89% ± 1.04% compared to free pyropheophorbide-a. From the in vitro cell studies using HT1080 cells that overexpress MMP2 and BT20 cells that lack MMP2, we observed that fluorescence and SOG was mediated by the presence or absence of MMP2 in these cell lines. This novel activatable photosensitizing system may be useful for protease-mediated fluorescence imaging and subsequent photodynamic therapy for various cancers.