SI-2 is an inhibitor of steroid receptor coactivator 3 (SRC-3). It has been shown to selectively reduce the transcriptional activities and the protein concentrations of SRC-3 in cells through direct physical interactions with SRC-3.1 SI-2 induces death in various breast cancer cells with IC50 values of 3-20 nM without affecting normal cell viability.[1] At 2 mg/kg, SI-2 can also inhibit primary tumor growth and reduce SRC-3 protein levels in an MDA-MB-468 breast cancer mouse model.[1]