Abstract 4432: Discovery of novel Pin1 inhibitors by structure-guided fragment evolution that downregulate cyclin D1 expression in PC-3 prostate cancer cells

Abstract

Abstract Pin1 is a peptidyl-prolyl isomerase (PPIase) that is specialized for catalysing isomerization around pSer/Thr-Pro bonds. As isomerisation around such bonds can promote major conformational changes within proteins, Pin1 is able to influence signaling dynamics and outcomes within pathways regulated by proline-directed kinases such as: MAP kinases, cyclin-dependent kinases and GSK-3β. Pin1 overexpression is only weakly oncogenic in itself, but enhances transformation by ErbB2 or activated Ras alleles. Remarkably however, cells from Pin1 deficient mice are resistant to transformation by Ras and ErbB2. As Pin1-deficient mice have a mild phenotype, there are considerable grounds for hope that Pin1 inhibitors will have value for the therapy of cancer and also inflammatory disorders. Here we report the discovery of our second series of cell active Pin1 inhibitors. Screening of a 700 member fragment library at high concentrations in a PPIase assay revealed 37 potential novel hits. Only two of these hits could be verified to bind Pin1 by 2D NMR, and we were able to obtain a crystal structure of just one of the novel hits bound to Pin1, a pyridyl pyrazole acid. After examining a number of 6-5 unfused ring system acids, we selected a phenyl-imidazole acid as a start point. A program of structure-guided medicinal chemistry led to the discovery of a series of ligands that occupied a novel combination of surfaces within the Pin1 active site, distinct from that occupied by our previously published amino acid-derived inhibitors. This effort culminated in VER-158197, a sub-micromolar (∼750 nM) inhibitor of Pin1 that exhibits high permeability in a CaCo-2 permeability assays and inhibits the growth of Pin1-dependent PC-3 prostate cancer cells (GI50 ∼ 13 uM). Mode of action studies indicated that VER-158197 downregulated cyclin D1 expression and prevented the phosphorylation of p70 S6 Kinase on Thr389 that is normally observed in repsonse to insulin stimulation. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4432.