Abstract 4337: Novel potent and selective orally available CDK8/19 kinase inhibitors

CDK8 and its paralog CDK19 are cyclin-dependent kinases and together with CDK7 and CDK9 belongs to the group of C-terminal domain (CTD) kinases that phosphorylate the CTD of RNA polymerase II, thus regulating transcription. CDK8 together with its partner Cyclin C, MED12 and MED13 are components of multi-protein Mediator complex which couples action of transcription factors with the molecular machinery that carries out transcription, e.g. CDK8 couple basal transcriptional machinery to sequence-specific transcription factors such as Notch, p53, β-catenin, and also repress the transcription of other genes. As Mediator independent roles, CDK8 has been shown to act as part of a separate complex behaving as a histone kinase. Moreover, CDK8 has been identified as a major kinase in the response to IFN signaling mediated STAT1-S727 phosphorylation. Several studies indicated that high overexpression and activity of CDK8 could be a driver of malignant progression in colorectal cancer being a marker of poor prognosis. Moreover, in gastric cancer CDK8 expression and the delocalization of β-catenin expression showed a significant positive correlation with carcinogenesis and tumor progression, especially lymph node metastasis. Recently, gene amplification of CDK8, CDK19, CCNC and MED13 in breast cancers has been related with poor response to adjuvant therapy. These results suggest that CDK8 inhibitors may become a unique class of anticancer drugs that could increase the efficacy of cancer therapy by blocking chemotherapy-induced production of tumor-promoting secreted factors. We have carried out a medium throughput screening campaign which led to the discovery of several low nanomolar hits belonging to 3 different chemical series. Later on, we have performed a Hit Generation phase, designing novel inhibitors within a patentable chemical space. Here, we have taken into account information from the chemical structures of the screening hits, X-ray structure of CDK8 protein co-crystalized with sorafenib, docking studies, chemical feasibility and intellectual property. We have identified a novel chemical series of CDK8/19 inhibitors. After a HtL exploration we have reached lead compounds with potency in the picomolar range and high selectivity versus a panel of 468 protein kinases. The leads display cellular activity by blocking β−catenin reporter activity and STAT1 phoshorylation in the low nanomolar range. Lead compounds have been screened in a panel of tumoral cell lines, showing a defined profile in terms of sensitivity with GI50s which range from nanomolar to low micromolar values. These inhibitors induce cell death in a dose response manner. The novel chemical series show a drug-like profile in terms of solubility, permeability, CYP450 inhibition and hERG. The identified lead compounds are orally bioavailable, with good clearance, volume of distribution and exposure levels. A selected lead compound has been used in in vivo PK-PD studies showing positive results. Citation Format: Carmen Blanco Aparicio, Oliver Renner, Elena Gomez-Casero, Maria Isabel Albarran, Antonio Cebria, Borja Barrera, Enara Aguirre, Maria del Carmen Rodriguez de Miguel, Manuel Urbano, Ana Isabel Hernandez, Cristina Gomez de la Oliva, Virginia Rivero, Rosario Concepcion Riesco, Sonia Martinez Gonzalez, Joaquin Pastor. Novel potent and selective orally available CDK8/19 kinase inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4337.