2.3. SRB assay

Viable prostate cancer cells were measured by using the SRB (Sulphorhodamine B, Sigma‐Aldrich) assay, as previously described. 32 Briefly, the cells were treated with variable concentrations of CUDC‐907 for 72 hours. Cells were fixed with cold 10% (wt/vol) trichloroacetic acid for 3 hours and stained with SRB for 30 minutes, after which the excess dye was removed by washing with 1% (vol/vol) acetic acid. The cell‐bound SRB dye was dissolved in 10 mmol/L Tris base solution and plates were read at 515 nm using a microplate reader. IC₅₀ values were calculated as drug concentrations necessary to inhibit 50% of cell growth compared to vehicle control‐treated cells using the GraphPad Prism 5.0 software. The IC₅₀ values for the cell lines are presented as means of triplicates ± standard errors from at least three independent experiments.