In vitro activity: The 50% inhibitory concentrations (IC50) for Ganetespib against malignant mast cell lines are 10-50 times lower than that for 17-AAG, indicating that triazolone class of HSP90 inhibitors likely exhibits greater potency than geldanamycin based inhibitors. Ganetespib inhibits MG63 cell lines with IC50 of 43 NM. Ganetespib binds to the ATP-binding domain at the N-terminus of Hsp90 and serves as a potent Hsp90 inhibitor by causing degradation of multiple oncogenic Hsp90 client proteins including HER2/neu, mutated EGFR, Akt, c-Kit, IGF-1R, PDGFRα, Jak1, Jak2, STAT3, STAT5, HIF-1α, CDC2 and c-Met as well as Wilms' tumor 1. Ganetespib, at low nanomolar concentrations, potently arrests cell proliferation and induces apoptosis in a wide variety of human cancer cell lines, including many receptor tyrosine kinase inhibitor- and tanespimycin-resistant cell lines. Ganetespib exhibits potent cytotoxicity in a range of solid and hematologic tumor cell lines, including those that express mutated kinases that confer resistance to small-molecule tyrosine kinase inhibitors. Ganetespib treatment rapidly caused the degradation of known Hsp90 client proteins, exhibits superior potency to the ansamycin inhibitor 17-AAG, and shows sustained activity even with short exposure times. In anohter study, Ganetespib induces apoptosis of malignant canine mast cell lines. Ganetespib is active at significantly lower concentrations for C2 and BR canine malignant mast cells with IC50 of 19 and 4 nM, respectively, while 17-AAG inhibits C2 and BR canine malignant mast cells with IC50 of 958 and 44 nM, respectively. Both the expression of WT and mutant Kit are downregulated by 100 nM Ganetespib after 24 hours in all lines treated including C2 and BMCMCs cells. However, no effects on PI3K or HSP90 expression are observed following treatment with Ganetespib.

Kinase Assay: Exponentially growing cells are processed in lysis buffer (20 mM HEPES, pH 7.4, 1 mM EDTA, 5 mM MgCl2, 100 mM KCl) and incubated with increasing concentrations of 17-AAG or ganetespib for 30 min at 4°C, and incubated with biotin-GM linked to Dynabeads MyOne Streptavidin T1 magnetic beads for 1 h at 4°C. Beads are washed three times in lysis buffer and heated for 5 min at 95°C in SDS-PAGE sample buffer. Samples are resolved on 4-12% Bis-Tris gradient gel and Western blots are performed using an anti-HSP90 antibody.

Cell Assay: A total of 1.5 × 103 OSA cells are seeded in 96-well plates in 10% serum-containing complete medium and incubated overnight to determine the 50% inhibitory concentrations. Plates are, harvested at day 5 following 0.001, 0.005, 0.01, 0.05, 0.1, 0.5 and 1 μM Ganetespib, treatment and analyzed. Fluorescence measurements are made using a plate reader with excitation at 485 nm and emission detection at 530 nm. Relative cell number is calculated as a percentage of the control wells: absorbance of sample/absorbance of DMSO treated cells × 100.