The Effect of Varying Doses of UVC Radiation on the Viability of Human Cancer Cells

Abstract

UVC radiation has the ability to damage DNA in cells. This causes the cell to either arrest division or undergo apoptosis. In this study we observed the effects of increasing doses of UVC radiation on the division rates and viability of cells from the human cancer cell line MCF7. We hypothesized that at a certain dose the cells would no longer be able to repair DNA and apoptosis would be induced. Furthermore, we hypothesized that the division rate would decrease as the dose of UVC increased. Cells were irradiated at either, 0 mJ/cm2 (negative control), 0.31 mJ/cm2, 1.55 mJ/cm2, 4.65 mJ/cm2, 9.3 mJ/cm2, 18.6 mJ/cm2, 37.2 mJ/cm2, or 74.4 mJ/cm2. 48 hours after irradiation, a Trypan Blue viability assay was performed to determine the percentage of dead cells at each dose. To compare division rates, the total number of cells in each treatment was taken as a percentage of the total number of non- treated cells. The IC50 for apoptosis was found to be 21.25 mJ/cm2. Our results showed that the total number of cells decreased significantly between 0 mJ/cm2, and 4.65 mJ/cm2. At concentrations above 4.65 mJ/cm2, the total number of cells remained constant. Suggesting that this is the point in which cells may have stopped growing. In contrast, the percentage of dead cells did not differ between the nontreated cells and those treated with UVC doses up to 9.3 mJ/cm2, but was significantly higher at doses above 18.6 mJ/cm2. The point at which the percentage of dead cells begins to increase significantly and where division rates plateau is relatively close, thus, we infer that this the point in which cells stopped trying to repair their DNA and instead began to undergo apoptosis. As we hypothesized, at a high enough dose, the DNA in cells would become irreparable and the cells would die. Because all cells above this dose show significant death, the observation is consistent with our hypothesis.

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