2.9. Sulforhodamine B (SRB) Assay

To assess the cell viability, we used the sulforhodamine B (SRB) assay, as previously described [41]. Briefly, 2 × 10⁵ cells/well were seeded in 48-well plates and cultured overnight to allow the cells to attach. Then, cells were treated with mevalonate or cholesterol in the presence or absence of 4-OH tamoxifen or doxorubicin, for 48 h. At the end of the treatment, cell monolayers were fixed with chilled 10% (wt/vol) trichloroacetic acid for 15 min at 4 °C. Plates were then washed with PBS and allowed to dry. Next, cells were stained with 0.04% (wt/vol) SRB for 30 min, after which the excess dye was removed by washing repeatedly with 1% (vol/vol) acetic acid. The protein-bound dye was dissolved in 10 mM Tris base solution for OD determination at 510 nm using a Varioskan^TM LUX microplate reader (ThermoFisher).