title: IRES inhibition induces terminal differentiation and synchronized death in triple-negative breast cancer and glioblastoma cells.
abstract: Internal ribosome entry site (IRES)-mediated translation is a specialized mode of protein synthesis which malignant cells depend on to survive adverse microenvironmental conditions. Our lab recently reported the identification of a group of compounds which selectively interfere with IRES-mediated translation, completely blocking de novo IGF1R synthesis, and differentially modulating synthesis of the two c-Myc isoforms. Here, we examine the phenotypic consequences of sustained IRES inhibition in human triple-negative breast carcinoma and glioblastoma cells. A sudden loss of viability affects the entire tumor cell population after ∼72-h continuous exposure to the lead compound. The extraordinarily steep dose-response relationship (Hill-Slope coefficients -15 to -35) and extensive physical connections established between the cells indicate that the cells respond to IRES inhibition collectively as a population rather than as individual cells. Prior to death, the treated cells exhibit prominent features of terminal differentiation, with marked gains in cytoskeletal organization, planar polarity, and formation of tight junctions or neuronal processes. In addition to IGF1R and Myc, specific changes in connexin 43, BiP, CHOP, p21, and p27 also correlate with phenotypic outcome. This unusual mode of tumor cell death is absolutely dependent on exceeding a critical threshold in cell density, suggesting that a quorum-sensing mechanism may be operative. Death of putative tumor stem cells visualized in situ helps to explain the inability of tumor cells to recover and repopulate once the compound is removed. Together, these findings support the concept that IRES-mediated translation is of fundamental importance to maintenance of the undifferentiated phenotype and survival of undifferentiated malignant cells.
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Medicine, Division of Hematology/Oncology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Christos
authors.initials: C
authors.lastname: Vaklavas
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Grizzle
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Medicine, Division of Hematology/Oncology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Pediatrics, Seoul National University Bundang Hospital, Gyeonggi-do, 463-707, South Korea.
authors.forename: Hyoungsoo
authors.initials: H
authors.lastname: Choi
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Bevill Biomedical Research Bldg Room 765, 845 19th Street S, Birmingham, AL, 35294, USA.|Analytical Development Division, Novavax Inc., Rockville, MD, 20850, USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Meng
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Radiology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Kurt R
authors.initials: KR
authors.lastname: Zinn
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.|Department of Medicine, Division of Hematology/Oncology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Kedar
authors.initials: K
authors.lastname: Shrestha
authors.affiliation: Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, 35294, USA. scblume704@gmail.com.|Department of Medicine, Division of Hematology/Oncology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA. scblume704@gmail.com.|Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Bevill Biomedical Research Bldg Room 765, 845 19th Street S, Birmingham, AL, 35294, USA. scblume704@gmail.com.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Blume
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics; D015415:Biomarkers; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D005260:Female; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D000067556:Internal Ribosome Entry Sites / Q000235:genetics*; D014411:Neoplastic Stem Cells / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects; D019108:Tight Junctions / Q000378:metabolism; D064726:Triple Negative Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014404:Tubulin / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D015415:Biomarkers; D000067556:Internal Ribosome Entry Sites; D014404:Tubulin
keywords: Glioblastoma; Hill slope coefficient; Quorum-sensing; Terminal differentiation; Triple-negative breast cancer