Figure 3. DPI does not significantly affect cell viability, even after 5 days of treatment. Cell viability was determined by employing the Sulphorhodamine B (SRB) assay, to measure total protein content. Note that after 5 days of incubation, DPI shows little or no toxicity in MCF7 cells, at a concentration as high as 33 nM. However, some toxicity was observed at 100 nM. Similarly, normal fibroblasts (hTERT-BJ1) showed little or no toxic effects at up to 100 nM, after 5 days of incubation.