Cryptotanshinone inhibits breast cancer cell growth by suppressing estrogen receptor signaling.

Estrogen receptor (ER) is a major therapeutic target for the treatment of breast cancer, because of the crucial role of estrogen signaling deregulation in the development and progression of breast cancer. In this study, we report the identification of a novel ER binding compound, cryptotanshinone (CPT), by screening the CADD database. We also show that CPT effectively inhibits estrogen-induced ER transactivation and gene expression of ER target genes. Furthermore, we showed that CPT suppressed breast cancer cell growth mainly in an ER dependent manner. Finally, we confirmed the potential therapeutic efficiency of CPT using xenograft experiments in vivo. Taken together, our results describe a novel mechanism for the anticancer activity of CPT and provide supporting evidence for its use as a potential therapeutic agent to treat patients with ER positive breast cancer.