MERTK Inhibition Induces Polyploidy and Promotes Cell Death and Cellular Senescence in Glioblastoma Multiforme

• Type of Material: Article
• Authors: Alexandra Sufit, University of Colorado; Alisa B. Lee-Sherick, University of Colorado; Deborah DeRyckere, Emory University; Manali Rupji, Emory University; Bhakti Dwivedi, Emory University; Marileila Varella-Garcia, University of Colorado; Angela M. Pierce, University of Colorado; Jeanne Kowalski, Emory University; Xiaodong Wang, University of North Carolina at Chapel Hill; Stephen V. Frye, University of North Carolina at Chapel Hill; H. Shelton Earp, University of North Carolina at Chapel Hill; Amy K. Keating, University of Colorado; Douglas Graham, Emory University
• Language: English
• Date: 2016-10-26
• Publisher: Public Library of Science
• Publication Version: Final Published Version
• Copyright Statement: © 2016 Sufit et al.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1371/journal.pone.0165107
• Title of Journal or Parent Work: PLoS ONE
• ISSN: 1932-6203
• Volume: 11
• Issue: 10
• Start Page: e0165107
• End Page: e0165107
• Grant/Funding Information: This study was supported by NIH R01 1CA137078 to DKG, K12 68372 to AKK, TL1 TR001080 to AS; and the St. Baldrick’s Foundation Scholar Award AKK.; St. Baldrick's Foundation to Amy K. Keating.; National Cancer Institute TL1 TR001080 to Alexandra Sufit.; National Cancer Institute K12 68372 to Amy K. Keating.; National Cancer Institute 1CA137078 to .
• Keywords: APOPTOSIS; SUPPRESSION; AXL; LINES; Science & Technology; RECEPTOR TYROSINE KINASE; Science & Technology - Other Topics; CENTRAL-NERVOUS-SYSTEM; Multidisciplinary Sciences; LUNG-CANCER; INTERFERENCE; INCREASES CHEMOSENSITIVITY
• Research Categories: Chemistry, Biochemistry; Health Sciences, Oncology

Abstract

Background: MER receptor tyrosine kinase (MERTK) is expressed in a variety of malignancies, including glioblastoma multiforme (GBM). Our previous work demonstrated that inhibition of MERTK using RNA interference induced cell death and chemosensitivity in GBM cells, implicating MERTK as a potential therapeutic target. Here we investigate whether a novel MERTKselective small molecule tyrosine kinase inhibitor, UNC2025, has similar anti-tumor effects in GBM cell lines. Methods: Correlations between expression of GAS6, a MERTK ligand, and prognosis were determined using data from the TCGA database. GBM cell lines (A172, SF188, U251) were treated in vitro with increasing doses of UNC2025 (50-400nM). Cell count and viability were determined by trypan blue exclusion. Cell cycle profiles and induction of apoptosis were assessed by flow cytometric analysis after BrdU or Po-Pro-1/propidium iodide staining, respectively. Polyploidy was detected by propidium iodide staining and metaphase spread. Cellular senescence was determined by β-galactosidase staining and senescence-associated secretory cytokine analysis. Results: Decreased overall survival significantly correlated with high levels of GAS6 expression in GBM, highlighting the importance of TAM kinase signaling in GBM tumorigenesis and/or therapy resistance and providing strong rationale for targeting these pathways in the clinic. All three GBM cell lines exhibited dose dependent reductions in cell number and colony formation (>90% at 200nM) after treatment with UNC2025. Cell cycle analysis demonstrated accumulation of cells in the G2/M phase and development of polyploidy. After extended exposure, 60-80% of cells underwent apoptosis. The majority of surviving cells (65-95%) were senescent and did not recover after drug removal. Thus, UNC2025 mediates antitumor activity in GBM by multiple mechanisms. Conclusions: The findings described here provide further evidence of oncogenic roles for MERTK in GBM, demonstrate the importance of kinase activity for MERTK tumorigenicity and validate UNC2025, a novel MERTK inhibitor, as a potential therapeutic agent for treatment of GBM.