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. Howe ver, 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 photosens itizer by testing the influence of laser light on cell cultures of a h uman breast carcinoma cell line, incubated with meta-tetrahydroxy-phen ylchlorin (m-THPC) (=Temoporfin(R)). Experimental design: Five thousan d MCF-7 cells were plated in 96-well plates. Forty-eight hours before laser treatment, the cells were plated to achieve a monolayer configur ation. Twenty-four hours after plating, they were incubated with m-THP C. 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 photose nsitizer 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 mu g/ml . The calculated inhibition concentration to produce 50% cell kill (IC 50) was 4.55 mu g/ml. We also observed a very low cytotoxicity for las er irradiation alone but a very strong cell kill for the combination o f m-THPC together with laser light. Conclusions: PDT gave almost total cell kill at m-THPC concentrations that are not toxic in vitro.