title: Targeting the unfolded protein response in cancer therapy.
abstract: Rapid growth of tumor cells coupled with inadequate vascularization leads to shortage of oxygen and nutrients. The unfolded protein response (UPR), a defense cellular mechanism activated during such stress conditions, is a complex process that includes upregulation of the endoplasmic reticulum chaperones, such as glucose-regulated protein 78 (GRP78). Due to its central role in UPR, GRP78 is overexpressed in many cancers; it is implicated in cancer cell survival through supporting of drug- and radioresistance as well as metastatic dissemination, and is generally associated with poor outcome. This is the reason why selective destruction of GRP78 could become a novel anticancer strategy. GRP78 is the only known substrate of the proteolytic A subunit (SubA) of a bacterial AB(5) toxin, and the selective SubA-induced cleavage of GRP78 leads to massive cell death. Targeted delivery of SubA into cancer cells via specific receptor-mediated endocytosis could be a suitable strategy for assaulting tumor cells. We fused SubA to epidermal growth factor (EGF), whose receptor (EGFR) is frequently overexpressed in tumor cells, and demonstrated that the resulting EGF-SubA immunotoxin is an effective killer of EGFR-positive tumor cells. Furthermore, because of its unique mechanism of action, EGF-SubA synergizes with UPR-inducing drugs, which opens a possibility for the development of mechanism-based combination regimens for effective anticancer therapy. In this chapter, we provide experimental protocols for the assessment of the effects of EGF-SubA on EGFR-positive cancer cells, either alone or in combination with UPR-inducing drugs.
authors.affiliation: Sibtech, Inc., Brookfield, Connecticut, USA.
authors.forename: Marina V
authors.initials: MV
authors.lastname: Backer
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Backer
authors.forename: Prakash
authors.initials: P
authors.lastname: Chinnaiyan
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000494:pharmacology* / Q000627:therapeutic use; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D002460:Cell Line; D004354:Drug Screening Assays, Antitumor / Q000379:methods*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy*; D019284:Thapsigargin / Q000494:pharmacology / Q000627:therapeutic use; D056811:Unfolded Protein Response
chemical_list: D000970:Antineoplastic Agents; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D004815:Epidermal Growth Factor; D019284:Thapsigargin; D002392:Catechin; C045651:epigallocatechin gallate; D066246:ErbB Receptors