First, A549 and PC9 cells were seeded in several 96-well plates with about 4000 cells per well. After the cells adhered to the wall, one of the 96-well plates was fixed with trichloroacetic acid and one plate was treated every 12 or 24 hours until the cells were all overgrown. Then all 96-well plates were washed with trichloroacetic acid, dried and stained with Sulforhodamine B sodium salt (SRB) (Sigma, USA). After the SRB was washed with acetic acid and dried, 150 µL of 10 mmol/L Tris was added to the 96-well plates, and the absorbance was measured with the microplate reader (Thermo Fisher, USA) at 562 nm. The method above is based on previous report.26 (link)