Purity >99% by HPLC. Selective Heat Shock Protein 90 (Hsp90) inhibitor. Displays binding to the ATP site (KD = 1.2 μM) of Hsp90. Inhibits activities of oncogenic kinases (e.g. src, Raf), p53 and steroid receptors. Because Hsp90 client proteins play important roles in the regulation of the cell cycle, cell growth, cell survival, apoptosis and oncogenesis, it obstructs the proliferation of cancer cells and shows anti-cancer activity in experimental animals.