Dose response experiment using C1 and C2 in human breast cancer MDA-MB-231 cells. MDA-MB-231 cells were treated with either solvent DMSO or C1 and C2 at 5, 10, 20 μM for 24 h. (A) Anti-proliferative effects of C1 and C2. MDA-MB-231 cells were treated with C1 and C2 for 24 h, then medium was removed and cells were treated with MTT solution. (B) The inhibition of CT-like activity in MDA-MB-231 cells treated with C1 and C2. (C) Western blot analysis using antibodies to proteasome target proteins (Bax and IκB-α), XIAP, and PARP. (D) Cellular morphological changes visualized by phase-contrast imaging.