RESUMO
PURPOSE: Mammalian tumor cells differ in their response to ionizing radiation to a degree that some patients are readily curable with conventional doses of radiation, while others are rarely controlled. In experimental systems, it is possible to demonstrate differences between cell lines both in intrinsic radiosensitivity and in the apparent capacity to repair damage. Retinoic acid is a substance that has previously been reported to increase radiosensitivity, but at concentrations likely to have cytostatic effects or induce cellular differentiation. We chose several head and neck cancer cell lines to investigate radiation sensitivity and synergism in combination with retinoic acid. Material and Methods: Seventeen head and neck cancer cell lines (MDA886, P1, P13, A-431, PCI-50, UMSCC-10A, UMSCC-10B, UMSCC-11A, UMSCC-11B, UMSCC-17A, UMSCC-17B, UMSCC-19, UMSCC-22B, UMSCC-30, UMSCC-38, 1YA, 1YB) are irradiated with variable dose of radiation (1 Gy, 5 Gy, 9 Gy) for determination of radiosensitivity of each cell lines. The less radiosensitive cell lines are treated with retinoic acid for evaluation of the effects of retinoic acid on cellular X-ray sensitivity and recovery from X ray-induced potentially lethal damage. RESULTS: Lowest growth inhibition rates are seen UMSCC-11A and 1YA cell lines in 1 Gy, so that we treated with retinoic acid such cell lines. We obtained the following RESULTS: 1) two cell lines appear not inhibitory effect on recovery from X-ray induced potentially lethal damage but growth inhibition synergism when irradiated with retinoic acid in 1 Gy of radiation dose. 2) two cell lines were little effect on radiosensitivity and inhibitory effect on recovery from X-ray damage in 0.5 Gy radiation dose. CONCLUSION: We found that direct radiosensitizing effects of retinoic acid on 1 Gy of radiation dose may act synergistically for cell growth inhibition in vitro study(three cell lines: UMSCC-11A, 1YA, UMSCC-11B). Further in vitro and in vivo experiments are now necessary to evaluate retinoic acid as radiosensitizer for head and neck cancer radiation therapy.