Background and objective: Laser-induced hyperthermia, laserthermia, is a promising new method for treating neoplasms. The response of different cell types to conventional hyperthermia varies [Bhuyan, Cancer Res 1979; 39:2277-2284; Raaphorst et al., Cancer Res 1979; 39:396-401]. We investigated the possible relationship between sensitivity to laser treatment and tumorigenic potential of three closely related cell types. Non-tumorigenic cells PYS-2 and differentiated F9S1 were compared to tumorigenic cells F9S1.
Study design/materials and methods: The contact Nd:YAG laser was used in a continuous-wave mode with a power setting of 6W, exposure times were 2 and 4 min [Castrén-Persons et al., Lasers Surg Med 1991; 11:595-600; Castrén-Persons, unpublished data]. The frosted-end probe was placed in the middle of the well and a thermocouple was attached 5 mm from the tip of the probe. The total amount of energy was measured for each well. A 4 min, 44 degrees C water bath treatment was used as comparison. Untreated wells served as controls. May-Grünwald-Giemsa staining and 3H-thymidine labeling were used for the analysis.
Results: Laserthermia killed all three cell types significantly more effectively than the water bath. PYS-2 cells were the most sensitive to the laser treatment. At the same temperature, PYS-2 cells were only slightly affected by water bath induced heating; the differentiated F9 cells were the most sensitive to this treatment. During the laser treatments, the energy required for holding the temperature seemed to depend not only on the cell type but also on the amount of cells treated: the more cells in the well, the more energy was needed.
Conclusion: Our results suggest that laser sensitivity is a cell-type specific feature which is not directly related to the proliferation rate or benign or malignant behavior of the cells.