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Energetics and Efficiency of Photoinactivation of Murine Tumor Cells Containing Hematoporphyrin¹

New York State Department of Health, Roswell Park Memorial Institute, Buffalo, New York 14263

² To whom requests for reprints should be addressed.

Hematoporphyrin derivative at an intracellular concentration in TA-3 mouse mammary carcinoma cells of 0.6 or 0.9 mM required input of 3.0 to 3.6 x 10⁹ quanta/cell of red light (620 nm) to achieve a 90% kill. At an intracellular concentration of 1.2 mM, this light requirement drops to 1.5 x 10⁹ quanta/cell. The energy for this photodynamic process is about 100 times higher than that required for ionizing radiation to achieve the same level of kill for these cells. The quantum yield for singlet oxygen formation (the cytotoxic agent in most photodynamic processes) from hematoporphyrin derivative is 0.75 ± 0.07 in ethanol but only 0.16 ± 0.07 within TA-3 cells, indicating possible intracellular complexing and quenching

¹ This investigation was supported by Grant CA 16717 awarded by the National Cancer Institute, Department of Health, Education and Welfare. This is Paper 4 of the series, "Photoradiation Therapy".

Received 12/15/75. Accepted 3/26/76.