Identification of the DEAD box RNA helicase DDX3 as a therapeutic target in colorectal cancer
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Marise R. Heerma van Voss1,2, Farhad Vesuna1, Kari Trumpi3, Justin Brilliant1, Cynthia Berlinicke4, Wendy de Leng2, Onno Kranenburg3, Johan G. Offerhaus2, Horst Bürger5, Elsken van der Wall6, Paul J. van Diest2, Venu Raman1,2,7
1Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
2Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands
3Department of Surgery, University Medical Center Utrecht, Utrecht, The Netherlands
4Wilmer Eye Institute, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
5Institute of Pathology, Paderborn, Germany
6Department of Internal Medicine, University Medical Center Utrecht, Utrecht, The Netherlands
7Department of Oncology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
Venu Raman, e-mail: [email protected]
Keywords: colorectal cancer, DEAD-box RNA helicases, Wnt signaling, small molecule inhibitors, β-catenin
Received: May 01, 2015 Accepted: July 09, 2015 Published: August 01, 2015
Identifying druggable targets in the Wnt-signaling pathway can optimize colorectal cancer treatment. Recent studies have identified a member of the RNA helicase family DDX3 (DDX3X) as a multilevel activator of Wnt signaling in cells without activating mutations in the Wnt-signaling pathway. In this study, we evaluated whether DDX3 plays a role in the constitutively active Wnt pathway that drives colorectal cancer.
We determined DDX3 expression levels in 303 colorectal cancers by immunohistochemistry. 39% of tumors overexpressed DDX3. High cytoplasmic DDX3 expression correlated with nuclear β-catenin expression, a marker of activated Wnt signaling. Functionally, we validated this finding in vitro and found that inhibition of DDX3 with siRNA resulted in reduced TCF4-reporter activity and lowered the mRNA expression levels of downstream TCF4-regulated genes. In addition, DDX3 knockdown in colorectal cancer cell lines reduced proliferation and caused a G1 arrest, supporting a potential oncogenic role of DDX3 in colorectal cancer.
RK-33 is a small molecule inhibitor designed to bind to the ATP-binding site of DDX3. Treatment of colorectal cancer cell lines and patient-derived 3D cultures with RK-33 inhibited growth and promoted cell death with IC50 values ranging from 2.5 to 8 μM. The highest RK-33 sensitivity was observed in tumors with wild-type APC-status and a mutation in CTNNB1.
Based on these results, we conclude that DDX3 has an oncogenic role in colorectal cancer. Inhibition of DDX3 with the small molecule inhibitor RK-33 causes inhibition of Wnt signaling and may therefore be a promising future treatment strategy for a subset of colorectal cancers.
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