Abstract
Differences of radiosensitivity between two mouse squamous cell carcinoma lines (SCCVII and NR-S1) measured by colony formation assay has been shown to reflect their in vivo radiation sensitivity differences measured by tumor growth delay assay in the body of transplanted animals. This study was carried out to characterize in vitro chronological behavior of the two cell lines after ionizing radiation exposure.
Logarithmic growth phase culture of the two cell lines were exposed to 0 Gy (non-irradiation), 4 Gy and 8 Gy of X ray, respectively. Immediately after irradiation, the cells were harvested, counted and appropriate number of the cells was plated onto new culture dishes. They were incubated at 37 oC in a humidified 5% CO2 incubator for 24 hours, then transferred onto an incubation chamber equipped inside a timelapse microscopy. A phase-contrast image of individual cells was captured at every 5 min during 48 hours observation period, resulting in a total of 576 images. Chronological behavior of two cell lines on captured images was then compared.
SCCVII showed mostly the non-synchronized proliferation among cells at non-irradiation condition. Cell fusions were rarely observed in this cell line. By 4 Gy and 8 Gy irradiations, most of cells showed remarkable growth retardation and enlargement. Even at this situation, cells proliferated individually and did not fuse with each other. On contrary, cells of NR-S1 showed the synchronized proliferation with neighboring cells at non-irradiation condition. The synchronized cells seemed to be fused with each other during mitosis then divided into multiple daughter cells. This feature was also observed in the cells exposed to 4 Gy and 8 Gy X ray. Growth retardation or enlargement of cells was not observed as in the cells of SCCVII. We are planning to investigate correlation of these behavioral features and radiation sensitivity.
