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 temozolomideinduced 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. Mol Cancer Ther; 13(10); 2399-411. Ó2014 AACR.

Temozolomide competes for P-glycoprotein and contributes to chemoresistance in glioblastoma cells

“…CD133+ GBM cells were also shown to have increased levels of miRNA-9, upregulated expression of MDR1 and chemoresistant [13]. Knockdown of MDR1 in GBM cells resulted in enhanced TMZ-mediated cell death supporting a role for the MDR1 gene in TMZ resistance [12][13][14].…”

Mesenchymal Stem Cell–Derived Exosomes Stimulate Cycling Quiescence and Early Breast Cancer Dormancy in Bone Marrow

“…Exosomes from these MSCs were transferred to fresh BCCs for assessment of total and active P-glycoprotein (P-gp). Using specific antibodies (34), flow cytometry analyses (Fig. 5E) indicated an increase in total P-gp Cell-cycle analyses of BCCs treated with na€ ve and primed exosomes.…”

Epigenetic targeting of glioma stem cells: Short-term and long-term treatments with valproic acid modulate DNA methylation and differentiation behavior, but not temozolomide sensitivity

“…These data clearly indicate that the DNA methylation status of the MGMT promoter and its epigenetic switch induced by VPA are not the only determinant factors to predict and induce TMZ chemosensitivity of GSCs. A complex and extensive chemo-resistance landscape characterizes these cancer cells and other molecular mechanisms, such as the overexpression of p-glycoprotein (54), are involved in TMZ resistance (55)(56)(57)(58).…”