Background: Limited studies have indicated that indocyanine green (ICG) dye can enhance cancer cell death when irradiated with laser light at 805 nm wavelength. However, the mechanism for cell damage in ICG irradiated medium is still unclear. The objective of this work was to elucidate the factors that govern cell death in ICG mediated laser damage.

Methods: 9L-SF glioma cells were divided into two groups. The first group of cells (Group 1) were incubated with ICG for 5 minutes and suspended in bovine calf serum or PBS without ICG. The second group of cells (Group 2) received no incubation with ICG and was suspended in bovine calf serum or PBS with ICG. Both groups were exposed to diode laser emitting 805 nm wavelength and varying energy densities. Samples were then evaluated with a survival assay using fluorescein diacetate (FDA) and propidium iodide (PI). The temperature changes during laser irradiation were measured with infrared thermometry and calculated with mathematical simulations. Survival curves were derived for different laser parameters and medium temperatures.

Results: In Group 1, survival curves indicate no increase in cell death. In Group 2, a 2-log decrease in cell survival is seen in BCS compared to PBS. In addition, doubling the laser energy density from 12.5 J/cm² to 25 J/cm² or doubling the ICG concentration from 20 μg/ml to 40 μg/ml yields a 2-log decrease in cell survival. These results correlate with increased medium temperature measured via infrared thermometry and mathematical modeling.

Conclusions: Indocyanine Green enhances the cell death when treated with laser light at 805 nm wavelength. This effect occurs by a predominantly thermal mechanism, in vitro. In vivo experiments are being design to test ICG enhanced photothermal ablation of superficial tumors.