title: Radiolabeled small-molecule ligands for prostate-specific membrane antigen: in vivo imaging in experimental models of prostate cancer.
abstract: OBJECTIVE
  Prostate-specific membrane antigen (PSMA) is a cell surface protein that is overexpressed in prostate cancer, including hormone-refractory and metastatic disease. Our goal in this study was to develop a series of PSMA-based imaging agents for clinical use.
  
  
  METHODS
  We have synthesized and evaluated the in vivo biodistribution of two radiolabeled urea derivatives that have high affinity for PSMA in severe combined immunodeficient mice harboring MCF-7 (breast, PSMA-negative), PC-3 (prostate, PSMA-negative), and LNCaP (prostate, PSMA-positive) xenografts. Radiopharmaceutical binding selectivity and tumor uptake were also evaluated in vivo using dedicated small animal positron emission tomography, single photon emission computed tomography, and gamma scintigraphic imaging devices. N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-S-[(11)C]methyl-L-cysteine ([(11)C]DCMC K(i), 3.1 nmol/L) and N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-S-3-[(125)I]iodo-L-tyrosine ([(125)C]DCIT K(i), 1.5 nmol/L) were synthesized using [(11)C]CH(3)I and with [(125)I]NaI/Iodogen, respectively.
  
  
  RESULTS
  At 30 minutes postinjection, [(11)C]DCMC and [(125)I]DCIT showed tumor/muscle ratios of 10.8 and 4.7, respectively, with clear delineation of LNCaP-derived tumors on imaging. MCF-7- and PC-3-derived tumors showed significantly less uptake of [(11)C]DCMC or [(125)I]DCIT.
  
  
  CONCLUSIONS
  These results show the feasibility of imaging PSMA-positive prostate cancer using low molecular weight agents.
authors.affiliation: Johns Hopkins University, Baltimore, Maryland 21287-2182, USA.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Foss
authors.forename: Ronnie C
authors.initials: RC
authors.lastname: Mease
authors.forename: Hong
authors.initials: H
authors.lastname: Fan
authors.forename: Yuchuan
authors.initials: Y
authors.lastname: Wang
authors.forename: Hayden T
authors.initials: HT
authors.lastname: Ravert
authors.forename: Robert F
authors.initials: RF
authors.lastname: Dannals
authors.forename: Rafal T
authors.initials: RT
authors.lastname: Olszewski
authors.forename: Warren D
authors.initials: WD
authors.lastname: Heston
authors.forename: Alan P
authors.initials: AP
authors.lastname: Kozikowski
authors.forename: Martin G
authors.initials: MG
authors.lastname: Pomper
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D001667:Binding, Competitive; D002250:Carbon Radioisotopes; D045744:Cell Line, Tumor; D005260:Female; D043425:Glutamate Carboxypeptidase II / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D008024:Ligands; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D049268:Positron-Emission Tomography / Q000379:methods*; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000628:therapy; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000378:metabolism / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D000954:Antigens, Surface; D002250:Carbon Radioisotopes; D007457:Iodine Radioisotopes; D008024:Ligands; D019275:Radiopharmaceuticals; C473848:FOLH1 protein, human; D043425:Glutamate Carboxypeptidase II