title: Temozolomide induces the production of epidermal growth factor to regulate MDR1 expression in glioblastoma cells.
abstract: Glioblastoma multiforme (GBM) commonly resists the frontline chemotherapy treatment temozolomide. The multidrug resistance gene (MDR1) and its protein, P-glycoprotein (P-gp), are associated with chemoresistance. This study investigated the mechanisms underlying MDR1-mediated resistance by GBM to temozolomide. P-gp trafficking was studied by flow cytometry and Western blot analysis. MDR1 expression was analyzed by real-time PCR and reporter gene assays. AP-1 interaction with MDR1 was studied by chromatin immunoprecipitation assay. EGF production was analyzed by ELISA, EGFR signaling was determined by Western blot analysis, and in vivo response to erlotinib and/or temozolomide was studied in nude mice. During the early phase of temozolomide treatment, intracellular P-gp was trafficked to the cell membrane, followed by conformational change into active P-gp. At the later phase, gene transcription of MDR1 was induced by temozolomide-mediated production of EGF. EGF activated ERK1/2-JNK-AP-1 cofactors (c-jun and c-fos). An inhibitor of EGFR kinase (erlotinib) given to nude mice with GBM prevented temozolomide-induced resistance. The results identified an essential role for activated EGFR in the resistance of GBM to temozolomide. Temozolomide resistance occurred through a biphasic response; first, by a conformational change in P-gp into the active form and, second, by releasing EGF, which caused autocrine stimulation of GBM cells to induce MDR1. Pharmacologic inhibition of EGFR kinase blunted the ability of GBM cells to resist temozolomide. These findings may explain reports on the common occurrence of mutant EGFR (EGFRvIII) and EGFR expansion in the resistance of GBM cells.
authors: New Jersey Medical School, Rutgers University, Newark, New Jersey.
authors: Jessian L
authors: JL
authors: Munoz
authors: Department of Chemistry, University of Puerto Rico-Cayey, Cayey, Puerto Rico.
authors: Vivian
authors: V
authors: Rodriguez-Cruz
authors: New Jersey Medical School, Rutgers University, Newark, New Jersey.
authors: Steven J
authors: SJ
authors: Greco
authors: New Jersey Medical School, Rutgers University, Newark, New Jersey.
authors: Vipul
authors: V
authors: Nagula
authors: Robert Wood Johnson Medical School, Cancer Institute of New Jersey, Rutgers University, New Brunswick, New Jersey.
authors: Kathleen W
authors: KW
authors: Scotto
authors: New Jersey Medical School, Rutgers University, Newark, New Jersey. rameshwa@njms.rutgers.edu.
authors: Pranela
authors: P
authors: Rameshwar
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D066246:ErbB Receptors; D005260:Female; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D015398:Signal Transduction; D000077204:Temozolomide; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D018906:Antineoplastic Agents, Alkylating; C410723:epidermal growth factor receptor VIII; D003606:Dacarbazine; D066246:ErbB Receptors; D000077204:Temozolomide