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Assessing the mechanism and therapeutic potential of modulators of the human Mediator complex-associated protein kinases

ABSTRACT: Mediator-associated kinases CDK8/19 are context-dependent drivers or suppressors of tumorigenesis. Their inhibition is predicted to have pleiotropic effects, but it is unclear whether this will limit the clinical utility of CDK8/19 inhibitors. We discovered two series of potent chemical probes with high selectivity for CDK8/19. Despite pharmacodynamic evidence for robust on-target activity, the compounds exhibited only modest efficacy against human tumor cell line or patient-derived xenografts. Expression profiling detected altered gene expression consistent with CDK8/19 inhibition, including profiles associated with superenhancer–regulated gene expression. In a mouse model expressing oncogenic beta-catenin, treatment shifted cells within hyperplastic intestinal crypts from a stem cell to a transit amplifying phenotype. Finally, in two species, neither test compound was tolerated at therapeutically-relevant exposures. The complex nature of the toxicity observed with two structurally-differentiated chemical series is consistent with on-target effects posing significant challenges to the further clinical development of CDK8/19 inhibitors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE80470 | GEO | 2016/12/01

SECONDARY ACCESSION(S): PRJNA319020

REPOSITORIES: GEO

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Project description:There is an unmet need for chemical tools to explore the role of the Mediator complex in human pathologies ranging from cancer to cardiovascular disease. Here we determine that CCT251545 a WNT-pathway inhibitor discovered by cell-based screening is a potent and selective chemical probe for the Mediator complex-associated protein kinases CDK8 and CDK19. CCT251545 is an ATP competitive inhibitor with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand binding site. In contrast to Type II inhibitors of CDK8/19 CCT251545 displays potent cell-based activity. We show that CCT251545 and close analogues not only alter WNT-pathway regulated gene expression but also other CDK8/19 targets including STAT1-regulated gene expression. Consistent with this we find that phospho-STAT1SER727 is a biomarker of CDK8 kinase activity in vitro and in vivo. Finally we demonstrate in vivo activity of CCT251545 in WNT-dependent tumours. Compound 1,2, 6 and 9 are close analogues of a 3,4,5-trisubstituted pyridine series identified from a high-throughput cell-based reporter assay of WNT signalling. They were shown to be potent and selective inhibitors of the Mediator complex-associated protein kinases CDK8 and CDK19. They are ATP competitive inhibitors with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand-binding site. A 3D culture model of murine intestinal-derived organoids expressing a transgenic doxycycline-inducible mutant beta-catenin expression following removal of doxycycline results in reduced WNT signalling and was compared to treatment for 24 hours with coumpound 2, 6 and 9. Compound 2 (n=3), compound 6 (n=4), compound 9 (n=3), doxycycline removal (n=4), doxycycline treatment (n=7). Samples were hybridized agianst mouse reference. Compounds 2, 6 and 9 are close analogues of a 3,4,5-trisubstituted pyridine series identified from a high-throughput cell-based reporter assay of WNT signalling. They were shown to be potent and selective inhibitors of the Mediator complex-associated protein kinases CDK8 and CDK19. They are ATP competitive inhibitors with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand-binding site.

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Assessing the mechanism and therapeutic potential of modulators of the human Mediator complex-associated protein kinases

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