Effect of Gd-DTPA on cell proliferation. Approximately, 1000 MCF-7 cells are incubated in 0, 1, 10, 25, 50, 75, 100, and 125 mM Gd-DTPA. Cell proliferation is measured by MTT assay at 3, 24, 48, and 72 hours. The viable cells are (a) quantified by a standard curve (for n=3 analyzed by standard error) and (b) control normalized percent viability using Gd-DTPA free medium (0 mM) using SEM and a two-way ANOVA with Bonferroni posttests to evaluate the relative differences in viability for each concentration of Gd-DTPA. A p < 0.05 is considered to be statistically significant. As the Gd-DTPA concentration increases, cell proliferation is reduced. However, at 24 hours, the effects of Gd-DTPA to cell viability are similar to that of Gd-DTPA free medium. Significant decreases in cell viability are observed for MCF-7 cells in 25 mM and above Gd-DTPA at 48 and 72 hours. Therefore, exposure to Gd-DTPA should be limited to a maximum of 24 hours in order to limit harmful effects of Gd-DTPA on cell proliferation.