In vitro activity: The Kd for AT13387 binding is 0.7 nM. This compares to a Kd of 6.7 nM for the binding of the ansamycin 17-AAG to the same site. The mean stoichio metry of binding for AT13387 is 1.03. The inhibition of a number of isolated kinases by AT13387 is also investigated including CDK 1, CDK 2, CDK4, FGFR3, PKB-b, JAK2, VEGFR2, PDGFRβ and Aurora B. None of the tested kinases are significantly inhibited at concentrations below 30 μM. AT13387 is a potent inhibitor of the proliferat ion and survival of many different cell lines (such as MES-SA cell line) from a variety of different tumor types. Across a panel of 30 tumor cell lines, AT13387 potently inhibits cell proliferation with GI50 values in the range 13-260 nM. AT13387 inhibits proliferation of the non-tumorigenic human prostate epithelial cell line PNT2 with a GI50 value of 480 NM.

Kinase Assay: Kd values for AT13387 binding to HSP90 are determined with a competition Isothermal Calorimetry (ITC) format. ITC experiments are performed on a Micro Cal VP-ITC at 25 °C in a buffer comprising 25 mM Tris, 100 mM NaCl, 1 mM MgCl2 and 1 mM Tris(2-carboxy- ethyl)phosphine at pH 7.4 in order to maintain the higher affinity.

Cell Assay: The human cell lines including A375, 22RV1, T474, DU1 45, LNCa P, MCF-7, DA-MB-468 are seeded into 96-well plates before the addition of AT13387 in 0.1% (v/v) DMSO. GI50 are determined using a 10-point dose response curve for three cell doubling times. After AT13387 incubation 10% (v/v), Alamar blueis added, and cells are incubated for a further 4 hours. Fluorescence is read.