title: Chaperone-targeting cytotoxin and endoplasmic reticulum stress-inducing drug synergize to kill cancer cells.
abstract: Diverse physiological and therapeutic insults that increase the amount of unfolded or misfolded proteins in the endoplasmic reticulum (ER) induce the unfolded protein response, an evolutionarily conserved protective mechanism that manages ER stress. Glucose-regulated protein 78/immunoglobulin heavy-chain binding protein (GRP78/BiP) is an ER-resident protein that plays a central role in the ER stress response and is the only known substrate of the proteolytic A subunit (SubA) of a novel bacterial AB(5) toxin. Here, we report that an engineered fusion protein, epidermal growth factor (EGF)-SubA, combining EGF and SubA, is highly toxic to growing and confluent epidermal growth factor receptor-expressing cancer cells, and its cytotoxicity is mediated by a remarkably rapid cleavage of GRP78/BiP. Systemic delivery of EGF-SubA results in a significant inhibition of human breast and prostate tumor xenografts in mouse models. Furthermore, EGF-SubA dramatically increases the sensitivity of cancer cells to the ER stress-inducing drug thapsigargin, and vice versa, demonstrating the first example of mechanism-based synergism in the action of a cytotoxin and an ER-targeting drug.
authors.affiliation: SibTech, Inc, Brookfield, CT 06804, USA. mbacker@sibtech.com
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Backer
authors.forename: Arcadius V
authors.initials: AV
authors.lastname: Krivoshein
authors.forename: Carl V
authors.initials: CV
authors.lastname: Hamby
authors.forename: John
authors.initials: J
authors.lastname: Pizzonia
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Gilbert
authors.forename: Yonaton S
authors.initials: YS
authors.lastname: Ray
authors.forename: Harrison
authors.initials: H
authors.lastname: Brand
authors.forename: Adrienne W
authors.initials: AW
authors.lastname: Paton
authors.forename: James C
authors.initials: JC
authors.lastname: Paton
authors.forename: Marina V
authors.initials: MV
authors.lastname: Backer
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy; D004357:Drug Synergism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000473:pathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005260:Female; D006360:Heat-Shock Proteins / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D009374:Neoplasms, Experimental / Q000188:drug therapy*; D011471:Prostatic Neoplasms / Q000188:drug therapy; D017510:Protein Folding / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D001427:Bacterial Toxins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D011993:Recombinant Fusion Proteins; D004815:Epidermal Growth Factor