Combined EGFR and Autophagy Modulation Impairs Cell Migration and Enhances Radiosensitivity in Human Glioblastoma Cells

Abstract

Glioblastoma (GBM) remains the most aggressive and lethal brain tumor due to its molecular heterogeneity and high motility and invasion capabilities of its cells, resulting in high resistance to current standard treatments (surgery, followed by ionizing radiation combined with Temozolomide chemotherapy administration). Locus amplification, gene overexpression, and genetic mutations of epidermal growth factor receptor (EGFR) are hallmarks of GBM that can ectopically activate downstream signaling oncogenic cascades such as PI3K/Akt/mTOR pathway. Importantly, alteration of this pathway, involved also in the regulation of autophagy process, can improve radioresistance in GBM cells, thus promoting the aggressive phenotype of this tumor. In this work, the endogenous EGFR expression profile and autophagy were modulated to increase radiosensitivity behavior of human T98G and U373MG GBM cells. Our results primarily indicated that EGFR interfering induced radiosensitivity according to a decrease of the clonogenic capability of the investigated cells, and an effective reduction of the in vitro migratory features. Moreover, EGFR interfering resulted in an increase of Temozolomide (TMZ) cytotoxicity in T98G TMZ-resistant cells. In order to elucidate the involvement of the autophagy process as pro-death or pro-survival role in cells subjected to EGFR interfering, the key autophagic gene ATG7 was silenced, thereby producing a transient block of the autophagy process. This autophagy inhibition rescued clonogenic capability of irradiated and EGFR-silenced T98G cells, suggesting a pro-death autophagy contribution. To further confirm the functional interplay between EGFR and autophagy pathways, Rapamycin-mediated autophagy induction during EGFR modulation promoted further impairment of irradiated cells, in terms of clonogenic and migration capabilities. Taken together, these results might suggest a novel combined EGFR-autophagy modulation strategy, to overcome intrinsic GBM radioresistance, thus improving the efficacy of standard treatments. J. Cell. Physiol. 229: 1863-1873, 2014. © 2014 Wiley Periodicals, Inc.

Peiminine Inhibits Glioblastoma in Vitro and in Vivo Through Cell Cycle Arrest and Autophagic Flux Blocking

“…Autophagy is a double-edged sword in tumour progression and treatment: it can either facilitate cancer survival under metabolic stress or induce autophagic tumour cell death [35,36]. Mounting evidence accumulated in recent years suggests that inhibition of autophagy can reduce the treatment resistance of chemotherapy and radiotherapy in various types of cancers [37,38], which is also the case in GBM treatment [39,40]. To clarify the role of autophagy in peiminine therapy for GBM, LN229 and U251 cells were observed under TEM after peiminine treatment (Fig.…”

Glioblastoma, hypoxia and autophagy: a survival-prone ‘ménage-à-trois’

“…Indeed, autophagy can positively or negatively regulate both GBM invasion and resistance to therapy, the two hallmarks of GBM aggressiveness. 85 Concerning invasion and cell motility, whereas Catalano et al 86 reported an impairment of migration and invasion of GBM cells after autophagy induction, Palumbo et al 87 noticed this impairment after autophagy inhibition, especially when EGFR was coinhibited, thus highlighting the importance of growth factor signaling.…”

Autophagic flux response and glioblastoma sensitivity to radiation

“…A study by Lomonaco et al 33 provided evidence that inhibition of autophagy enhanced CD133+ glioblastoma stem cell sensitivity to ionizing radiation after bafilomycin treatment or Atg5 silencing. Notably, Palumbo et al 30 found that Atg7 silencing resulted in reduced T98 cell sensitivity to radiation and to a combination of radiation with anti-EGFR therapy 34 , indicating a complex role of different Atgs in radiation response. …”