Structure and selective cytotoxicity of CLV, MAD-28, and MAD-44. (A) Structures of CLV, MAD-28, and MAD-44. The chemical synthesis of MAD-28 and MAD-44 is described in SI Appendix, Fig. S1B. (B) Effect of MAD-28, CLV, and MAD-44 on cell survival of control noncancerous human breast cells MCF-10A (Left) or human epithelial breast cancer cells MDA-MB-231 (Right). Alamar blue cell viability measurements were performed on cells at 2, 3, and 6 d following application of 1.25 μM MAD-28, CLV, or MAD-44. The results show that the three different compounds had no significant effect on the viability of control cells and that MDA-28 had a potent and selective killing effect on cancer cells. Percentage of cell survival was determined based on cells treated with DMSO. Error bars represent SD obtained from three individual experiments. **P < 0.01; ***P < 0.001.