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

Paul A Clarke ,Will Court,Melanie Valenti,Aurélie Mallinger,Maria-Jesus Ortiz-Ruiz,Paul Workman,Robert Tepoele,Stefan Hecht,Sharon Gowan,Dirk Wienke,Alexis De Haven Brandon,Kai Schiemann,Gary Box,Felix Rohdich,Toby Roe,Wolfgang Kaufmann,Olajumoke Adeniji-Popoola,Richard Schneider,Stefan Weigt,Klaus Urbahns,Stephanie Simon,Samer El Bawab,Christina Esdar,Julian Blagg,Andree Blaukat,Kenneth Ewan ,Trevor Dale ,Steve Hobbs ,Phllip Hewitt ,Stefanie Czasch ,Florence I Raynaud ,Suzanne A Eccles

doi:10.7554/elife.20722

Paul A Clarke , Will Court + Show 30 more

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https://doi.org/10.7554/elife.20722

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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 impact on 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 modest, though significant, efficacy against human tumor lines and patient-derived xenografts. Altered gene expression was consistent with CDK8/19 inhibition, including profiles associated with super-enhancers, immune and inflammatory responses and stem cell function. In a mouse model expressing oncogenic beta-catenin, treatment shifted cells within hyperplastic intestinal crypts from a stem cell to a transit amplifying phenotype. In two species, neither probe 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 clinical development of CDK8/19 inhibitors.

Highlights

The Mediator complex is a multi-subunit regulator of transcription in eukaryotes that transfers signals from DNA-bound transcription factors to the RNA polymerase II pre-initiation complex (Allen and Taatjes, 2015; Yin and Wang, 2014; Poss et al, 2013)
We tested selected compounds from a further three chemical series that we identified from the literature and again could not detect any substantial selectivity for cyclin-dependent kinase 8 (CDK8) versus CDK19 (Figure 1—source data 1)
CDK8 may reportedly act both as an oncogene and as a tumor suppressor, but until recently, the absence of a potent and selective inhibitor of CDK8 has restricted many functional studies to genetic inhibition using shRNA or siRNA (Mitra et al, 2006; Chattopadhyay et al, 2010; Gu et al, 2013; Firestein et al, 2008, 2010; Seo et al, 2010; Adler et al, 2012; Starr et al, 2009)

Summary

Introduction

The Mediator complex is a multi-subunit regulator of transcription in eukaryotes that transfers signals from DNA-bound transcription factors to the RNA polymerase II pre-initiation complex (Allen and Taatjes, 2015; Yin and Wang, 2014; Poss et al, 2013). It has a role in transcription elongation and pausing, and can influence chromatin structure, where it facilitates the formation of enhancer-promoter gene loops and is enriched at ‘super-enhancer’ regions (Allen and Taatjes, 2015; Poss et al, 2013; Whyte, 2013). As a kinase that reversibly associates with the Mediator, CDK8 is thought to regulate gene expression through phosphorylation of transcription factors and Mediator subunits (Rzymski et al, 2015)

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