IC50 measurement

Growth inhibition after SP141 treatment (IC₅₀) was determined using the sulforhodamine B (SRB) assay. Cells were seeded in 96-well plates (5000 cells per well) in complete medium for assays in triplicates. Twenty-four hours later, serial dilutions of the indicated compounds were added to the cells. After 48 hours, cells were fixed by adding a trichloroacetic acid solution (10% final concentration) and stained with a 0.4% SRB solution in 1% acetic acid. Fixed SRB was dissolved in 10 mM tris-HCl solution, and absorbance at 560 nm was read using an MRX spectrophotometer.