Authors:
 Halena R. VanDeusen1*, Johnny R. Ramroop2*, Katherine L. Morel3, Song Yi Bae1, Anjali V. Sheahan3, Zoi Sychev1, Nathan A. Lau4, Larry C. Cheng5, Victor M. Tan5, Zhen Li6, Ashley Petersen7, John K. Lee4,14, Jung Wook Park8, 9, Rendong Yang10, Justin H. Hwang11, 12, Ilsa Coleman4, Owen N. Witte9, Colm Morrissey13, Eva Corey13, Peter S. Nelson4,14, Leigh Ellis3,12, Justin M. Drake1,15,16
 
 
 Affiliations:
 1Department of Pharmacology, University of Minnesota-Twin Cities, Minneapolis, MN. 2Departments of Cancer Biology and Genetics, Comprehensive Cancer Center, The Ohio State University, Columbus, OH. 3Department of Oncologic Pathology, Dana-Farber Cancer Institute, Boston, MA. 4Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, WA. 5Graduate Program in Quantitative Biomedicine, School of Graduate Studies, Rutgers University, New Brunswick, NJ. 6Cancer Metabolism and Growth Program, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ. 7Division of Biostatistics, School of Public Health, University of Minnesota-Twin Cities, Minneapolis, MN. 8Department of Pathology, Duke School of Medicine, Duke University, Durham, NC. 9Department of Microbiology, Immunology, and Molecular Genetics, University of California–Los Angeles, Los Angeles, CA. 10The Hormel Institute, University of Minnesota, Austin, MN. 11Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts. 12Broad Institute of Harvard and MIT, Cambridge, Massachusetts. 13Department of Urology, University of Washington, Seattle, WA. 14Department of Medicine, University of Washington, Seattle, WA. 15Department of Urology, University of Minnesota-Twin Cities, Minneapolis, MN. 16Masonic Cancer Center, University of Minnesota-Twin Cities, Minneapolis, MN
 
 
 Abstract Body:
 Increased treatment of metastatic castration resistant prostate cancer (mCRPC) with second-generation anti-androgen therapies (ADT) has coincided with a greater incidence of lethal, aggressive variant of prostate cancer (AVPC) tumors that have lost androgen receptor (AR) signaling. AVPC tumors may also express neuroendocrine markers, termed neuroendocrine prostate cancer (NEPC). Recent evidence suggests kinase signaling may be an important driver of NEPC. While kinases such as AURKA have been identified as important for NEPC growth, targeting these kinases for treatment has not dramatically improved patient survival and there remains a need to improve NEPC treatment options. To identify targetable kinases in NEPC, we performed global phosphoproteomics comparing AR-negative to AR-positive prostate cancer cell lines and identified multiple altered signaling pathways, including enrichment of RET kinase activity in the AR-negative cell lines. We also analyzed multiple clinical and patient derived xenografts transcript datasets to look for RET kinase expression and enrichment in subsets of patient populations. Finally, we utilized genetic and pharmacological approaches to reduce RET kinase activity in multiple models of NEPC to determine if RET kinase is necessary for NEPC cell growth and proliferation. We found that RET kinase was highly upregulated and enriched in the NEPC patient samples relative to AdCa or double negative tumor samples. Additionally, we found that knockown of RET kinase reduced cell proliferation by 80% in NCI-H660 cells and 50% in PC3 cells. Additionally, pharmacological inhibition with multiple RET inhibitors, including AD80 and two FDA approved RET targeted agents (BLU-6667 and LOXO-292), dramatically reduced downstream signaling of ERK1/2 and reduced growth and viability in multiple mouse and human NEPC models. Overall, identification of aberrantly expressed RET kinase as a driver of tumor growth in multiple models of NEPC provides a significant rationale for testing the clinical application of RET inhibitors in patients with NEPC and future work will investigate the relationship between RET activity and response to RET inhibitors in our models prior to clinical evaluation.
 
 
 Funding Acknowledgments:
 Prostate Cancer Foundation Young Investigator Award, Department of Defense
 
 
 Corresponding Author Email:
 jdrake@umn.edu
 
 
 Conflict of Interest:
 Nothing to Disclose

Targeting RET Kinase in Neuroendocrine Prostate Cancer