Sulforhodamine B Proliferation (SRB) Assay

Cells were seeded into 96 well plates (500 cells/well). After 24 h of incubation, cells were irradiated and then fixed up to 120 h post-treatment by adding 50 μl 25% trichloracetic acid (Sigma-Aldrich, UK) at 4°C for 1 h. Wells were washed in dH₂O and dried. Fifty microliter SRB dye [0.4% SRB dissolved in 1% glacial acetic acid (VWR International)] was added to the wells and the cells were incubated for 30 min. The cells were then washed 4 times in 1% glacial acetic acid and incubated for 60 min after the addition of 150 μl 10 mM Tris-NaOH buffer (pH 10.5). A Biohit BP800 spectrophotometer (Biohit Ltd, UK) and Wallac 1,420 Manager program (PerkinElmer, UK) were used to analyze optical density at 540 nm.