In vitro activity: PU-H71 (1 μM) potently suppresses the growth of triple-negative breast cancers (TNBC) cell lines MDA-MB-468, MDA-MB-231, and HCC-1806 with IC50 of 65, 140 and 87 nM, respectively. PU-H71 (1 μM) kills 80%, 65%, and 80% of the initial population of MDA-MB-468, MDA-MB-231, and HCC-1806 cells, respectively. PU-H71 (0.25-1 μM) induces a dose-dependent degradation or inactivation of tumor driving molecules, including EGFR, IGF1R, HER3, c-Kit, Raf-1and Akt. Treatment for 24 h with 1 μM PU-H71, augments the percent of cells in G2-M phase of MDA-MB-468 to 69%, mediated by reduction in CDK1 and Chk1 expression. PU-H71 induces apoptosis in TNBC in part by inactivation and downregulation of Akt and Bcl-xL. PU-H71 leads to a proteasome-mediated reduction in IRAK-1 and TBK1 levels, resulting in approximately 84% and 90% reduction in NF-κB activity in MDA-MB-231 cells treated with 0.5 and 1μM PU-H71, respectively. PU-H71 markedly contains MDA-MB-231 cell invasion, with 90% suppression at 1 μM. PU-H71 (2.5 μM) generates endoplasmic reticulum (ER) stress and activated the Unfolded Protein Response (UPR) as evidenced by XBP1 mRNA splicing (2.3-fold) and up-regulation of Grp94 (3.7-fold), Grp78 (4.9-fold), and CHOP (48-fold) protein expression and ATF4 (1.8-fold) mRNA expression. PU-H71 (1 μM) induces the mitochondrial pathway of apoptosis in HeLa cells, mediated by caspase but not calpain activation. In response to PU-H71-induced ER stress, apoptosis is triggered in melanoma, cervix, colon, liver and lung cancer cells, but not in normal human fibroblasts. PU-H71 is able to induce apoptosis overcoming the resistance conferred by Bcl-2.

Kinase Assay: Measurements are performed in black 96-well microtiter plates. Cell lysates are prepared by rupturing cellular membranes by freezing at -70℃ and dissolving the cellular extract in HFB [20 mM Hepes (K), pH 7.3, 50 mM KCl, 5 mM MgCl2, 20 mM Na2MoO4, 0.01% Nonidet P-40] with added protease and phosphatase inhibitors. Saturation curves are recorded in which fluorescently labeled geldanamycin (Cy3B-GM) (3 nM) is treated with increasing amounts of cellular lysates. The amount of lysate that results in polarization (mP) readings corresponding to 90%-99% bound ligand is chosen for the competition study. Here, each 96-well plate contains 3 nM Cy3B-GM, cellular lysate (amounts as determined and normalized to total Hsp90 as determined by Western blot analysis using Hsp90 purified from HeLa cells as standard) and tested Hsp90 inhibitor in a final volume of 100 μL. The plate is left for 24 h on a shaker at 4 ℃, and the fluorescence polarization (FP) values in mP are recorded. EC50 values are determined as the competitor concentrations at which 50% of the Cy3B-GM is displaced. FP measurements are performed on an Analyst GT microplate reader.

Cell Assay: Exponentially growing MDA-MB-231 cells are seeded into black 96-well microtiter plates and incubated in medium containing either vehicle control (DMSO) or compounds for the indicated time at 37 ℃. Plates containing 3 replicate wells per assay condition are seeded at a density of 8×103 cells for each cell line in 100μL medium. After exposure of cells to the Hsp90 inhibitors, plates are equilibrated to room temperature (20-25 ℃) for approximately 30 min, and 100 μL CellTiter-Glo reagent are added to each well. Plates are mixed for 2 min on an orbital shaker and then incubated for 15 min to 2 h at room temperature. The luminescence signal in each well is measured in an Analyst GT microplate reader.

Proc Natl Acad Sci U S A. 2009 May 19;106(20):8368-73; Biochim Biophys Acta. 2013 Jun;1833(6):1356-66.