Summary
Visible light irradiation of suspensions of ascites tumor cells vitally stained with acridine orange resulted in the inability of the treated cells to produce tumors. The appropriate controls (irradiated unstained and stained unirradiated cells) were uninhibited in their growth. Ehrlich, Krebs-2, and Sarcoma 180 ascites tumor cells were similarly affected by this type of oxidative radiation injury.
A wide range of intracellular concentrations of the sensitizer was effective in producing the radiation damage. The irradiated stained cells lost their ability to produce solid and ascites tumors and were unable to exist as free cells in the peritoneum. Untreated Sarcoma 180 ascites tumor cells were also found to lose their individuality immediately after inoculation into Swiss-Webster mice. However, these cells were able to regain their free-growing state after 19 hours in the host mice, whereas the stained irradiated cells could not. Cells damaged by the photo-oxidative mechanism were found to be incapable of initiating an immune response from the host.
The microscopic test of cellular viability which utilizes acridine orange as the differential stain was unable to detect the photosensitized inactivation.
The author was aided by an Alfred P. Sloan Foundation predoctoral fellowship, and this work was supported in part by research grant C-1345 from the National Cancer Institutes of Health, Public Health Service, and by grants from the Damon Runyon Memorial Fund, the Elsa U. Pardee Foundation, and the Rippel Foundation.
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