Targeting the unfolded protein response in glioblastoma cells with the fusion protein EGF-SubA

PLoS One. 2012;7(12):e52265. doi: 10.1371/journal.pone.0052265. Epub 2012 Dec 20.

Abstract

Rapidly growing tumors require efficient means to allow them to adapt to fluctuating microenvironments consisting of hypoxia, nutrient deprivation, and acidosis. The unfolded protein response (UPR) represents a defense mechanism allowing cells to respond to these adverse conditions. The chaperone protein GRP78 serves as a master UPR regulator that is aberrantly expressed in a variety of cancers, including glioma. Therefore, cancer cells may be particularly reliant upon the adaptive mechanisms offered by the UPR and targeting GRP78 may represent a unique therapeutic strategy. Here we report that diffuse expression of GRP78 protein is present in Grade III-IV, but not Grade I-II glioma. To determine the role GRP78 plays in glioblastoma tumorigenesis, we explored the anti-tumor activity of the novel fusion protein EGF-SubA, which combines EGF with the cytotoxin SubA that has been recently shown to selectively cleave GRP78. EGF-SubA demonstrated potent tumor-specific proteolytic activity and cytotoxicity in glioblastoma lines and potentiated the anti-tumor activity of both temozolomide and ionizing radiation. To determine if the tumor microenvironment influences EGF-SubA activity, we maintained cells in acidic conditions that led to both UPR activation and increased EGF-SubA induced cytotoxicity. EGF-SubA was well tolerated in mice and led to a significant tumor growth delay in a glioma xenograft mouse model. The UPR is emerging as an important adaptive pathway contributing to glioma tumorigenesis. Targeting its primary mediator, the chaperone protein GRP78, through specific, proteolytic cleavage with the immunotoxin EGF-SubA represents a novel and promising multi-targeted approach to cancer therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Endoplasmic Reticulum Chaperone BiP
  • Epidermal Growth Factor / genetics
  • Epidermal Growth Factor / metabolism
  • Epidermal Growth Factor / pharmacology*
  • Glioblastoma / genetics
  • Glioblastoma / metabolism*
  • Heat-Shock Proteins / genetics
  • Heat-Shock Proteins / metabolism
  • Humans
  • Immunoblotting
  • Mice
  • Reverse Transcriptase Polymerase Chain Reaction
  • Subtilisins / genetics
  • Subtilisins / metabolism*
  • Subtilisins / pharmacology*
  • Tissue Array Analysis
  • Unfolded Protein Response / drug effects*
  • Unfolded Protein Response / genetics

Substances

  • Endoplasmic Reticulum Chaperone BiP
  • HSPA5 protein, human
  • Heat-Shock Proteins
  • Hspa5 protein, mouse
  • Epidermal Growth Factor
  • Subtilisins

Grants and funding

PC is currently funded by The Ben and Catherine Ivy Foundation and The American Cancer Society (RSG-11-029-01-CSM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.