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JCI Insight. 2018 Aug 23;3(16). pii: 122225. doi: 10.1172/jci.insight.122225. [Epub ahead of print]

Transcriptional targeting of oncogene addiction in medullary thyroid cancer.

Author information

1
Division of Endocrinology, Diabetes, and Metabolism, The Ohio State University Wexner Medical Center and Arthur G. James Comprehensive Cancer Center, Columbus, Ohio, USA.
2
Center for Biostatistics.
3
College of Arts and Sciences.
4
Department of Biomedical Informatics, and.
5
Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, USA.
6
Department of Pathology, University of Michigan, Ann Arbor, Michigan, USA.
7
Department of Endocrine Neoplasia and Hormonal Disorders, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Abstract

Metastatic medullary thyroid cancer (MTC) is incurable and FDA-approved kinase inhibitors that include oncogenic RET as a target do not result in complete responses. Association studies of human MTCs and murine models suggest that the CDK/RB pathway may be an alternative target. The objective of this study was to determine if CDKs represent therapeutic targets for MTC and to define mechanisms of activity. Using human MTC cells that are either sensitive or resistant to vandetanib, we demonstrate that palbociclib (CDK4/6 inhibitor) is not cytotoxic to MTC cells but that they are highly sensitive to dinaciclib (CDK1/2/5/9 inhibitor) accompanied by reduced CDK9 and RET protein and mRNA levels. CDK9 protein was highly expressed in 83 of 83 human MTCs and array-comparative genomic hybridization had copy number gain in 11 of 30 tumors. RNA sequencing demonstrated that RNA polymerase II-dependent transcription was markedly reduced by dinaciclib. The CDK7 inhibitor THZ1 also demonstrated high potency and reduced RET and CDK9 levels. ChIP-sequencing using H3K27Ac antibody identified a superenhancer in intron 1 of RET. Finally, combined inhibition of dinaciclib with a RET kinase inhibitor was synergistic. In summary, we have identified what we believe is a novel mechanism of RET transcription regulation that potentially can be exploited to improve RET therapeutic targeting.

KEYWORDS:

Cancer; Endocrinology; Oncology; Thyroid disease; Transcription

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