Photodestruction of mouse epithelial tumors after oral acridine orange and argon laser.

at 9 spectral lines at wavelengths ranging from 514.5 to 454.5 nm. This laser spectrum encompasses the maximum reported to produce chromosomal lesions in salamander lung tissue explants exposed to AO (2). Approximately 60% of the incident nonreflected light of these wavelengths is thought to penetrate the epidermis (6) and should therefore reach dermal tissues in sufficient intensity to activate a phototoxic dye present in a tumor. The maximum permissible skin irradiance level for human exposures to argon laser for up to 8 hr is 200 mihiwatts/sq cm over areas of up to 25 cm (American National Standards Institute, Z-136 1, 1973.) At these irradiance levels, one need not be concerned with the pressure effects and nonlinear effects that may occur with the use of high energy-pulsed laser in cancer therapy (7, 9). There have been reports of the use of photosensitizing agents and conventional light sources in experimental tumor destruction. Jesionek and Tappeiner (10) in 1903 claimed some success in the treatment of skin cancer using the photodynamic action of eosin, but then apparently abandoned the treatment. Recently, Diamond et a!. (5) have used hematoporphyrin, which, like AO, is selectively taken up by tumor cells, with high-intensity light bulbs to induce in complete destruction of gliomata implanted s.c. in the flanks of rats. Treatment with either light or hematoporphyrin alone had no effect. We wanted to determine whether complete tumor necrosis without damage to surrounding tissues would occur if mice were fed AO, followed by argon laser exposure. To ensure that the combination of AO and argon laser irradiation was phototoxic to tumor cells, Ehrlich ascites cells were first studied. A suspension of 2 X 106 washed cells per ml was incubated for 2 hr in the dark with AO in lactated Ringer's solution. After incubation, the cells were washed twice before being resuspended in lactated Ringer's solution. Following irradiation, the number of dead cells was assessed by staining with the nonvital dye, trypan blue. Epithelial tumors were induced in inbred male C3H mice weighing between 25 and 30 g by the twice-weekly application of 100 p1 of 0.66% benzo(a)pyrene in toluene. Six to 8 weeks after the 1st application, acanthomas began to appear, many of which subsequently developed into invasive ulcerating carcinomas. Benign epithelial tumors showing hyperkeratosis, acanthosis, and papillomatosis were defined as acanthomas; malignant epithelial tumors of squamous cell type, with SUMMARY The photosensitizing dye acridine orange …