Effect of ribavirin in combination with SAHA in ESR1-negative breast cancer cells MDA-MB-231 on tamoxifen sensitivity. Western blot analyses of procaspase 8 and 9 are shown after 24 h of treatment with different concentrations of 4-OHTam. They were either pretreated with 900 μM ribavirin in combination with 10 μM SAHA or remained untreated MDA-MB-231 cells. β-Actin was probed as the loading control. The decrease of procaspase levels is an indication of increased apoptosis, which is being caused by pretreatment with ribavirin and SAHA. A representative experiment is shown.