NVP-AUY922 / VER-52296: A novel 3,4 diarylisoxazole Hsp90 chaperone inhibitor discovered via structure-based drug design

B281

Hsp90 is a molecular chaperone currently the focus of significant research interest as a target for small molecule anti-cancer therapeutic agents. First-in-class inhibitors based on the natural product geldanamycin (including 17-AAG, 17-DMAG and IPI-504) have entered Phase I/II clinical trials. These agents confer their inhibitory effect by competitive binding to an ATP binding site on the N-terminal domain of the protein. We have previously described the elaboration of the diarylpyrazole screening hit CCT018159 via structure-based design which led to the identification of the potent pyrazole inhibitor VER-49009 (FP IC₅₀ = 25 nM; GI₅₀ in HCT116 human colon cancer cells = 260 nM). Further structure-driven medicinal chemistry optimization of VER-49009 identified a novel 3,4 diarylisoxazole class of inhibitors which had significantly improved potency in growth inhibition assays (in various human cancer cell lines) compared to VER-49009. The isoxazole series of compounds exhibited tighter binding (as exemplified by a 10-fold slower off rate) compared to the equivalent pyrazole and most likely accounts for their increased cellular potency. The binding mode of these new ligands was established and shown to be consistent with the pyrazole series, making similar key direct and water-mediated interactions with the protein. From a series of highly potent isoxazole analogues, NVP-AUY922 (VER-52296) was selected for further development due to its high potency for Hsp90, in vitro cellular activity and pharmacokinetic parameters as determined by cassette dosing. In particular NVP-AUY922 demonstrated high tumor uptake and retention compared to plasma when dosed i.p or i.v. and exhibited high potency against the Hsp90 ATPase site with a Ki of 9nM in an FP assay and significant in vitro growth inhibition (in the range 2-25nM) against a panel of human cancer cell lines. Its cellular mode of action, as determined by the depletion of Hsp90 client proteins and induction of Hsp72 was clearly consistent with Hsp90 inhibition. In addition, NVP-AUY922 showed excellent efficacy in a range of subcutaneous and orthotopic xenograft models covering major cancer types (including HCT116 colon, U87MG glioblastoma, PC3 prostate, BT474 breast and WM266 melanoma) with diverse oncogenic profiles. Analysis of in vivo pharmocodynamic markers was consistent with an Hsp90 mode of action. NVP-AUY922 has recently entered phase I clinical trials.