title: Tumor-Specific Binding of Radiolabeled PEGylated GIRLRG Peptide: A Novel Agent for Targeting Cancers.
abstract: Cancer-specific targeting sparing normal tissues would significantly enhance cancer therapy outcomes and reduce cancer-related mortality. One approach is to target receptors or molecules that are specifically expressed on cancer cells. Peptides as cancer-specific targeting agents offer advantages such as ease of synthesis, low antigenicity, and enhanced diffusion into tissues. Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum stress chaperone that regulates the unfolded protein response and is overexpressed in various cancers. In this study, we evaluated GIRLRG peptide that specifically targets GRP78 for cancer-specific binding (in vitro) and noninvasive tumor imaging (in vivo).
  
  
  METHODS
  GIRLRG peptide was modeled into the GRP78 ATPase domain using computational modeling. Surface plasmon resonance studies were performed to determine the affinity of GIRLRG peptide to GRP78 protein. GIRLRG was conjugated with PEG to prolong its circulation in mice. Tumor binding efficacy of PEG-GIRLRG peptide was evaluated in nude mice bearing heterotopic cervical (HT3), esophageal (OE33), pancreatic (BXPC3), lung (A549), and glioma (D54) tumors. Nano-SPECT/CT imaging of the mice was performed 48 and 72 h after injection with111In-labeled PEG-GIRLRG or PEG-control peptide. Post-SPECT biodistribution studies were performed 96 h after injection of the radiolabeled peptides.
  
  
  RESULTS
  Using molecular modeling and surface plasmon resonance, we identified that GIRLRG was binding with an affinity constant of 2.16 × 10-3M in the ATPase domain of GRP78. GIRLRG peptide specifically bound to cervical, lung, esophageal, and glioma cells. SPECT imaging revealed that111In-PEG-GIRLRG specifically bound to cervical, esophageal, pancreatic, lung, and brain tumors. Post-SPECT biodistribution data also validated the SPECT imaging results.
  
  
  CONCLUSIONS
  GIRLRG peptide specifically binds to the ATPase domain of GRP78. Radiolabeled PEG-GIRLRG could be used to target various cancers. Further studies would be required to translate PEG-GIRLRG peptide into the clinic.
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Vaishali
authors.initials: V
authors.lastname: Kapoor
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.|Medical Scientist Training Program, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: David Y A
authors.initials: DY
authors.lastname: Dadey
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.|Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Kim
authors.initials: K
authors.lastname: Nguyen
authors.affiliation: Carbone Cancer Center, University of Wisconsin, Madison, Wisconsin.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Wildman
authors.affiliation: Medical Guidance Systems, St. Louis, Missouri; and.
authors.forename: Kelly
authors.initials: K
authors.lastname: Hoye
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Arpine
authors.initials: A
authors.lastname: Khudanyan
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.|Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Nilantha
authors.initials: N
authors.lastname: Bandara
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.|Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Buck E
authors.initials: BE
authors.lastname: Rogers
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri dhallahan@radonc.wustl.edu dthotala@radonc.wustl.edu.|Siteman Cancer Center, School of Medicine, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Thotala
authors.affiliation: Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri dhallahan@radonc.wustl.edu dthotala@radonc.wustl.edu.|Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, Missouri.|Siteman Cancer Center, School of Medicine, Washington University in St. Louis, St. Louis, Missouri.
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Hallahan
mesh_terms: D000072283:A549 Cells; D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011485:Protein Binding; D000072417:Protein Domains; D013379:Substrate Specificity
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D009842:Oligopeptides; D011092:Polyethylene Glycols; D000251:Adenosine Triphosphatases
keywords: GIRLRG peptide; GRP78; SPECT; molecular imaging