Figure 7.

¹³¹I treatment significantly reduced the survival rate of RA-treated MCF-7 cells. Cells were treated with or without 1 μM tRA for 48 h, and then incubated with HBSS containing 0, 10, or 100 μCi/ml Na ¹³¹I and 0, 1, or 10 μM NaI, respectively for 7 h. Cells were harvested and applied to clonogenic assay as described (33). (a) Uptake of ¹³¹I^- by MCF-7 cells. After the incubation with ¹³¹I, β-ray activity of the trapped ¹³¹I was counted by a Geiger Mueller counter. The count was normalized to the cell number. (b) The survival rate of MCF-7 cells after the ¹³¹I treatment. The rate was calculated as a percentage of cell colonies treated with ¹³¹I^- compared with those treated with only HBSS. Solid columns, RA-treated MCF-7 cells; open columns, unstimulated MCF-7 cells. Values are means ± SD (n = 6). *, P < 0.0001, when compared with the group of unstimulated MCF-7 cells.