Info: An Hsp90 inhibitor (IC50 = 16.1 nM in a fluorescence polarization assay); induces HER2 degradation via disrupting Hsp90-HER2 interactions and decreases growth in SK-BR-3 breast cancer cells (IC50 = 50 nM for both); decreases viability of MM.1S and dexamethasone-resistant MM.1R cells at 1 µM; It induces cell cycle arrest at the G1/S phase in MM.1R cells at 100 nM; decreases tumor volume in MDA-MB-231 and HCC1806 breast cancer xenograft mouse models at 75 mg/kg every other day