Androgen receptor antagonist 12 (Compound EF2) is an orally active Androgen receptor (AR) antagonist (IC 50 : 0.30 μM). Androgen receptor antagonist 12 inhibits transcriptional activity of variant AR mutants and and the proliferation of AR-positive PCa cell lines. Androgen receptor antagonist 12 blocks AR nuclear translocation. Androgen receptor antagonist 12 inhibits tumor growth in a C4-2B xenograft mouse model. Androgen receptor antagonist 12 can be used for prostate cancer (PCa) research.