title: (64)Cu-labeled peptide for PET of breast carcinomas expressing the Thomsen-Friedenreich carbohydrate antigen.
abstract: Thomsen-Friedenreich (TF) antigen is a disaccharide, galactose β1-3 N-acetylgalactosamine (Galβ1-3GalNAc), expressed on the cell surfaces of most human carcinomas including breast. In this study, we synthesized and evaluated the in vitro and in vivo properties of a (64)Cu-radiolabeled TF antigen-specific peptide derived from bacteriophage display for the purpose of breast tumor targeting and PET of human breast tumors in xenografted mice.
  
  
  METHODS
  The TF antigen-specific peptide IVWHRWYAWSPASRI was synthesized with the chelator 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) at the amino terminus, followed by a Gly-Ser-Gly (GSG) spacer. Amino acids Asp and Arg were introduced at both ends to enhance its solubility. Purified NO2A-GSG-DRD-IVWHRWYAWSPASRI-DRD (NO2A-TFpep) was radiolabeled with (64)Cu and evaluated for binding to human MDA-MB-435 breast cancer cells, 50% inhibitory concentration (IC(50)), and serum stability. In vivo pharmacokinetic and small-animal PET studies were performed using SCID mice bearing MDA-MB-435 tumor xenografts.
  
  
  RESULTS
  (64)Cu-NO2A-TFpep bound to human MDA-MB-435 breast carcinoma cells, whereas almost no binding was observed to normal human breast 184A1 cells. The peptide exhibited an apparent IC(50) value of 70 ± 8.0 nM. In vivo biodistribution studies indicated radiolabeled peptide accumulation in tumors of MDA-MB-435 xenografted SCID mice of approximately 1.10 ± 0.20 percentage injected dose per gram (%ID/g) and 0.90 ± 0.12 %ID/g, at 0.5 and 1 h, respectively. Accumulation of radioactivity was low in other organs, with the exception of liver (1.52 ± 0.12 %ID/g) and kidneys (15.4 ± 1.73 %ID/g) at 1 h. Live imaging studies with (64)Cu-NO2A-TFpep (15 MBq) demonstrated good tumor uptake at 1 h after injection, whereas no tumor uptake was observed with a scrambled radiolabeled peptide (64)Cu-NO2A-GSG-DRD-RWSWWAVHRIPYSAI-DRD.
  
  
  CONCLUSIONS
  (64)Cu-NO2A-TFpep may function as a noninvasive in vivo tumor imaging agent of human breast and other carcinomas expressing the TF carbohydrate antigen. This is the first such TF antigen-targeting peptide used in tumor imaging.
authors: Department of Biochemistry, University of Missouri-Columbia School of Medicine, Columbia, Missouri, USA.
authors: Senthil R
authors: SR
authors: Kumar
authors: Fabio A
authors: FA
authors: Gallazzi
authors: Thomas P
authors: TP
authors: Quinn
authors: Susan L
authors: SL
authors: Deutscher
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015295:Antigens, Tumor-Associated, Carbohydrate / Q000737:chemistry / Q000378:metabolism*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D003301:Copper Radioisotopes; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007553:Isotope Labeling; D051379:Mice; D008969:Molecular Sequence Data; D064847:Multimodal Imaging; D010446:Peptide Fragments / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography / Q000379:methods*; D055550:Protein Stability; D014057:Tomography, X-Ray Computed
chemical_list: D015295:Antigens, Tumor-Associated, Carbohydrate; D003301:Copper Radioisotopes; D010446:Peptide Fragments; C016467:Thomsen-Friedenreich antigen