Assessment of effect of photosensitizers on cytotoxicity of photodynamic therapy in human breast cancer cell cultures

Background: Photodynamic therapy (PDT) might be of clinical value for patients with breast cancer with local recurrences or metastasis. However, there is a need for improved photosensitizers that are effective in combination with laser light and have few, if any, side-effects. We evaluated in vitro the effectiveness of a second generation photosensitizer by testing the influence of laser light on cell cultures of a human breast carcinoma cell line, incubated with meta-tetrahydroxy-phenylchlorin (m-THPC) (=Temoporfin®).Experimental design: Five thousand MCF-7 cells were plated in 96-well plates. Forty-eight hours before laser treatment, the cells were plated to achieve a monolayer configuration. Twenty-four hours after plating, they were incubated with m-THPC. On day 6 after treatment with m-THPC we lysed the cells to extract the intracellular ATP that correlates with the number of living cells. The ATP-CVA was used to assess the cytotoxicity of the tested photosensitizer m-THPC at various concentrations and the relevant laser light alone prior to their combination after six days of culture.Results: We found a dose-response for m-THPC alone ranging from 2 to 16 μg/ml. The calculated inhibition concentration to produce 50% cell kill (IC50) was 4.55 μg/ml. We also observed a very low cytotoxicity for laser irradiation alone but a very strong cell kill for the combination of m-THPC together with laser light.Conclusions: PDT gave almost total cell kill at m-THPC concentrations that are not toxic in vitro.