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

• Published in: PloS one Vol. 11; no. 10; p. e0165107
• Main Authors: Sufit, Alexandra, Lee-Sherick, Alisa B., DeRyckere, Deborah, Rupji, Manali, Dwivedi, Bhakti, Varella-Garcia, Marileila, Pierce, Angela M., Kowalski, Jeanne, Wang, Xiaodong, Frye, Stephen V., Earp, H. Shelton, Keating, Amy K., Graham, Douglas K.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 26.10.2016; Public Library of Science (PLoS)
• Subjects: Adenine - analogs & derivatives; Adenine - pharmacology; Analysis; Anticancer properties; Antineoplastic Agents - pharmacology; Antitumor agents; Apoptosis; Biochemistry; Biology; Biology and Life Sciences; Biotechnology; Blood diseases; Brain cancer; c-Mer Tyrosine Kinase; Cancer therapies; Cell cycle; Cell death; Cell Death - drug effects; Cell Line, Tumor; Cell number; Cell Proliferation - drug effects; Cellular Senescence - drug effects; Chemical compounds; Chemistry; Drug dosages; Enzyme Activation - drug effects; Enzyme inhibitors; Flow cytometry; Galactosidase; Gene expression; Gene Expression Regulation, Neoplastic - drug effects; Glioblastoma; Glioblastoma - pathology; Glioblastoma multiforme; Glioblastomas; Health aspects; Humans; Inhibition; Inhibitors; Intercellular Signaling Peptides and Proteins - metabolism; Iodides; Kinases; Lung cancer; Medical prognosis; Medicine; Medicine and Health Sciences; Metaphase; Neural Stem Cells - drug effects; Neural Stem Cells - pathology; Pediatrics; Pharmaceutical sciences; Pharmacology; Pharmacy; Piperazines - pharmacology; Polyploidy; Prognosis; Propidium iodide; Protein Kinase Inhibitors - pharmacology; Protein-tyrosine kinase receptors; Proteins; Proto-Oncogene Proteins - antagonists & inhibitors; Receptor Protein-Tyrosine Kinases - antagonists & inhibitors; Research and Analysis Methods; Ribonucleic acid; RNA; RNA-mediated interference; Senescence; Signaling; Staining; Therapeutic applications; Tumor cell lines; Tumorigenesis; Tumorigenicity; Tumors; Tyrosine; Viability; β-Galactosidase; Atlanta Georgia; United States > US; Colorado
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0165107

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 MERTK-selective small molecule tyrosine kinase inhibitor, UNC2025, has similar anti-tumor effects in GBM cell lines. 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. 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 anti-tumor activity in GBM by multiple mechanisms. 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.