Downregulation of p-STAT3 contributes apoptotic effects of SC-1 and SC-43 in breast cancer cells. A, analysis of molecular effects of sorafenib, SC-1 and SC-43 on STAT3-related proteins, PARP-1 and caspase-3. Cells were exposed to sorafenib, SC-1 or SC-43 at doses of 5 μM for MDA-MB-468 cells, and 7.5 μM for MDA-MB-453 and SK-BR3 cells for 36 hours. Cell lysates were prepared and assayed for these molecules by western blotting. Western blot data are representative of three independent experiments. Apoptosis is evidenced by cleavage of PARP-1 or caspase-3. Arrows indicate cleavage forms of caspase-3 or PARP-1. B, protective effect of STAT3 on apoptosis induced by sorafenib, SC-1 or SC-43 in MDA-MB-468 cells. Cells (wild type or ectopic expression of STAT3) were exposed to sorafenib, SC-1 and SC-43 at 5 μM for 36 hours. Apoptotic cells were analyzed by flow cytometry. Columns, mean; bars, SD (n = 3). *P <0.05.