title: Endoplasmic reticulum stress-inducing drugs sensitize glioma cells to temozolomide through downregulation of MGMT, MPG, and Rad51.
abstract: Endoplasmic reticulum (ER) stress results from protein misfolding imbalance and has been postulated as a therapeutic strategy. ER stress activates the unfolded protein response which leads to a complex cellular response, including the upregulation of aberrant protein degradation in the ER, with the goal of resolving that stress. O(6)-methylguanine DNA methyltransferase (MGMT), N-methylpurine DNA glycosylase (MPG), and Rad51 are DNA damage repair proteins that mediate resistance to temozolomide in glioblastoma. In this work we sought to evaluate whether ER stress-inducing drugs were able to downmodulate DNA damage repair proteins and become candidates to combine with temozolomide.
  
  
  
  MTT assays were performed to evaluate the cytotoxicity of the treatments. The expression of proteins was evaluated using western blot and immunofluorescence. In vivo studies were performed using 2 orthotopic glioblastoma models in nude mice to evaluate the efficacy of the treatments. All statistical tests were 2-sided.
  
  
  
  Treatment of glioblastoma cells with ER stress-inducing drugs leads to downregulation of MGMT, MPG, and Rad51. Inhibition of ER stress through pharmacological treatment resulted in rescue of MGMT, MPG, and Rad51 protein levels. Moreover, treatment of glioblastoma cells with salinomycin, an ER stress-inducing drug, and temozolomide resulted in enhanced DNA damage and a synergistic antitumor effect in vitro. Of importance, treatment with salinomycin/temozolomide resulted in a significant antiglioma effect in 2 aggressive orthotopic intracranial brain tumor models.
  
  
  
  These findings provide a strong rationale for combining temozolomide with ER stress-inducing drugs as an alternative therapeutic strategy for glioblastoma.
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Enric
authors.initials: E
authors.lastname: Xipell
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Tomás
authors.initials: T
authors.lastname: Aragón
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Naiara
authors.initials: N
authors.lastname: Martínez-Velez
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Beatriz
authors.initials: B
authors.lastname: Vera
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Idoate
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Martínez-Irujo
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Antonia García
authors.initials: AG
authors.lastname: Garzón
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Marisol
authors.initials: M
authors.lastname: Gonzalez-Huarriz
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Arlet M
authors.initials: AM
authors.lastname: Acanda
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Chris
authors.initials: C
authors.lastname: Jones
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Frederick F
authors.initials: FF
authors.lastname: Lang
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Juan
authors.initials: J
authors.lastname: Fueyo
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Candelaria
authors.initials: C
authors.lastname: Gomez-Manzano
authors.affiliation: Department of Medical Oncology, University Hospital of Navarra, Pamplona, Navarra, Spain (E.X., N.M.-V, B.V., M.G.-H, A.M.A, M.M.A); Department of Hepatology, Foundation for Applied Medical Research, Pamplona, Navarra, Spain (T.A.); Department of Pathology, University Hospital of Navarra, Pamplona, Navarra, Spain (M.A.I); Department of Biochemistry, University of Navarra, Pamplona, Navarra, Spain (J.J.M.-I, A.G.G); Divisions of Molecular Pathology and Cancer Therapeutics, The Institute of Cancer Research, London, UK (C.J.); Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas (F.F.L, C.G.-M., J.F.).
authors.forename: Marta M
authors.initials: MM
authors.lastname: Alonso
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000008:administration & dosage* / Q000494:pharmacology; D001932:Brain Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects; D045647:DNA Glycosylases / Q000378:metabolism; D015254:DNA Modification Methylases / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000378:metabolism; D003606:Dacarbazine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D015536:Down-Regulation; D059865:Endoplasmic Reticulum Stress; D005909:Glioblastoma / Q000378:metabolism*; D006801:Humans; D051379:Mice; D011714:Pyrans / Q000008:administration & dosage* / Q000494:pharmacology; D051135:Rad51 Recombinase / Q000378:metabolism; D016019:Survival Analysis; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000095662:Polyether Polyketides
chemical_list: D018906:Antineoplastic Agents, Alkylating; D045647:DNA Glycosylases; D015254:DNA Modification Methylases; D045643:DNA Repair Enzymes; D003606:Dacarbazine; D011714:Pyrans; D051135:Rad51 Recombinase; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins; C010327:salinomycin; D000095662:Polyether Polyketides; C515491:MGMT protein, human; C076131:DNA-3-methyladenine glycosidase II
keywords: DNA damage; ER stress; glioblastoma; salinomycin; temozolomide