Photodynamic inhibition of WiDr colorectal cancer cells by formation of gold nanoparticles

Gold (III) chloride trihydrate (Au (III)) typically acts as an oxidizing agent in a redox reaction. This study investigates the effect of photolysis of Au (III) on the repression of WiDr colorectal cancer cells and formation of gold nanoparticles (GNPs) when exposed to endogenous intracellular photosensitizers by violet light irradiation (VLI). A surface plasmon resonance (SPR) peak at 540 nm and the GNPs were detected when Au (III)-treated WiDr cells subjected to VLI at 2.0 mW/cm
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for 1.5 h underwent an electron transfer procedure, on account of the photolysis of endogenous photosensitizers. No notable variation was observed in the inhibition rates of WiDr cells treated with 0.4 mM Au (III) in darkness compared to those exposed to green or red light. However, under VLI, the photochemical impact of Au (III) on WiDr cell suppression increased with higher Au (III) concentrations. Specifically, when WiDr cells were exposed to VLI at 2.0 mW/cm
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for 1.5 h with Au (III) concentrations of 0.2, 0.4, and 0.6 mM, the inhibition rates reached 22.7%, 60.3%, and 85.2%, respectively. Propidium iodide (PI), a non-membrane-permeable fluorescent dye, binds to DNA and serves as a tool to assess cell viability by detecting cell death through apoptosis or necrosis. During the VLI treatment, around 90-95% PI-positive nuclei were expressed in the presence of 0.6 mM Au (III)-treated WiDr cells. Gold (III) ions in an Au (III)-treated WiDr cell system behave as an oxidizing agent by enhancing the level of electron transfer from the endogenous photosensitizers after exposure to VLI and increasing the formation of reactive oxygen species (ROS). Therefore, Au(III) photolysis under VLI has potential applications in photodynamic therapy (PDT).