Transcriptional Antagonism by CDK8 Inhibition Improves Therapeutic Efficacy of MEK Inhibitors

ABSTRACT: Aberrant RAS/MAPK signaling, a common driver of oncogenesis, can be therapeutically targeted with clinically approved MEK inhibitors. Single agent therapy ultimately results in tumor outgrowth in most settings and combination therapies are required to achieve significant clinical benefit in most advanced cancers. Here we focus on identifying MEK inhibitor-based combination therapies in RAS-mutant neuroblastoma. Mutations that activate the RAS/MAPK signaling pathway, while rare at diagnosis, are more frequent in relapsed neuroblastoma. More than 50% of children with high-risk neuroblastoma ultimately relapse and treatment options for relapsed neuroblastoma are limited so most children with relapsed disease do not survive. Here we use a genome-scale CRISPR-Cas9 functional genomic screen to identify genes that, when lost, sensitize RAS-mutant neuroblastoma to MEK inhibition. We discover that loss of either CCNC or CDK8, two members of the mediator kinase module, sensitizes neuroblastoma to MEK inhibition. Furthermore, we demonstrate that small molecule kinase inhibitors of CDK8 improve response to MEK inhibitors in vitro and in vivo in RAS-mutant neuroblastoma and other adult solid tumors, suggesting that the addition of CDK8 inhibitors could improve clinical outcome. Using transcriptional profiling, we unexpectedly find that loss of CDK8 or CCNC antagonizes the transcriptional signature induced by MEK inhibition. When combined, loss of CDK8 or CCNC prevents the compensatory upregulation of pro-growth gene expression induced by MEK inhibition. These findings propose a new therapeutic combination for RAS-mutant neuroblastoma and may have clinical relevance for other RAS-driven malignancies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE190178 | GEO | 2023/02/22

REPOSITORIES: GEO