Energetics and efficiency of photoinactivation of murine tumor cells containing hematoporphyrin.

Hematoporphryrin derivative at an intracellular concentration in TA-3 mouse mammary carcinoma cells of 0.6 or 0.9 mM required input of 3.0 X 3.6 X 10(9) 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 10(9)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.