title: Bortezomib overcomes MGMT-related resistance of glioblastoma cell lines to temozolomide in a schedule-dependent manner.
abstract: Development of drug resistance after standard chemotherapy for glioblastoma multiforme (GBM) with temozolomide (TMZ) is associated with poor prognosis of GBM patients and is at least partially mediated by a direct DNA repair pathway involving O6-methylguanine methyltransferase (MGMT). This enzyme is under post-translational control by a multisubunit proteolytic cellular machinery, the 26S proteasome. Inhibition of the proteasome by bortezomib (BZ), a boronic acid dipeptide already in clinical use for the treatment of myeloma, has been demonstrated to induce growth arrest and apoptosis in GBM cells. In this study we investigated the effect of sequential treatment with BZ and TMZ on cell proliferation-viability and apoptosis of the human T98G and U87 GBM cell lines. We also tested for an effect of treatment on MGMT expression and important upstream regulators of the latter, including nuclear factor kappa B (NFκB), p44/42 mitogen-activated protein kinase (MAPK), p53, signal transducer and activator of transcription 3 (STAT3) and hypoxia-inducible factor 1α (HIF-1α). The sequence of drug administration for maximal cytotoxicity favored BZ prior to TMZ in T98G cells while the opposite was the case for U87 cells. Maximal efficacy was associated with downregulation of MGMT, reduced IκBα-mediated proteasome-dependent nuclear accumulation of NFκB, attenuation of p44/42 MAPK, AKT and STAT3 activation, and stabilization of p53 and inactive HIF-1α. Collectively, these results suggest that proteasome inhibition by BZ overcomes MGMT-mediated GBM chemoresistance, with scheduling of administration being critical for obtaining the maximal tumoricidal effect of combination with TMZ.
authors: Department of Medical Oncology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece, pvlacho@med.uth.gr.
authors: Panagiotis J
authors: PJ
authors: Vlachostergios
authors: Eleana
authors: E
authors: Hatzidaki
authors: Christina D
authors: CD
authors: Befani
authors: Panagiotis
authors: P
authors: Liakos
authors: Christos N
authors: CN
authors: Papandreou
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage*; D001897:Boronic Acids / Q000008:administration & dosage*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011719:Pyrazines / Q000008:administration & dosage*; D050796:STAT3 Transcription Factor / Q000378:metabolism; D000077204:Temozolomide; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D011719:Pyrazines; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D016159:Tumor Suppressor Protein p53; D000069286:Bortezomib; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D000077204:Temozolomide
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