Geldanamycin (Item No. 13355) is a potent inhibitor of Hsp90 that exhibits severe hepatotoxicity when used in vivo.1 17-AAG is an analog of geldanamycin which has potent in vivo activity and reduced toxicity.1,2,3 Like other Hsp90 inhibitors, 17-AAG has diverse anti-tumor actions and has potential in treating certain types of cancer.1,2,3 17-AAG inhibits the growth of prostate cancer cell lines (IC50 = 25-45 nM).4 17-AAG promotes the degradation of HER2 and induces growth arrest and apoptosis in breast cancer cells overexpressing HER2 (IC50 = 4-72 nM).5