Galactose-modified zinc phthalocyanines for colon cancer photodynamic therapy

In a previous research, galactose groups were introduced into the structure of zinc phthalocyanine (ZnPc) to enhance water solubility and tumor-targeting ability for in vivo fluorescence imaging. Galactose-modified ZnPcs (T1-4) showed great potential as near-infrared optical probes in the diagnose of cancer. However, it had not yet been determined whether they could also serve as antitumor candidates for photodynamic therapy (PDT). In this study, the cellular uptake, photodynamic activity and anti-tumor mechanisms of T1-4 against colon cancer in vitro were investigated. The results showed that the cellular uptake of T1-4 in colon cancer and fibroblast cell lines was both concentration- and time-dependent, and ZnPc with one galactose group (T1) exhibited the optimal cellular uptake. Under 650 nm laser irradiation for 20 min (6 J/cm²), T1-3 (1.25-40 µM) displayed significant cytotoxicity against colon cancer cells. T1 mainly localized in lysosomes of CT-26, and T1-PDT destroyed the membrane structure of cells. The anti-tumor mechanism of T1-PDT in CT-26 cells was mainly related to the induction of autophagy, which was accompanied by upregulation of the autophagy biomarkers beclin-1 and LC3-II, and meanwhile downregulation of the autophagy-related protein P62. These findings reinforced the potential of galactose-modified ZnPcs (T1-4) as photosensitive agents for colon cancer PDT and their anti-tumor mechanism was related to the activation of autophagy in colon cancer cells.