An Hsp90 inhibitor; binds to Hspα and Hspβ (IC50s = 100 and 103 nM, respectively) and Hsp90 isolated from erlotinib-resistant NSCLC cells (IC50 = 70 nM); inhibits proliferation of 40 human cancer cell lines (IC50s = 0.04-0.9 μM); dose-dependently reduces tumor growth in a U87MG glioblastoma mouse xenograft model at 40-160 mg/kg; prolongs survival in a U87MG mouse orthotopic model at 160 mg/kg