title: Evaluation of copper-64-labeled somatostatin agonists and antagonist in SSTr2-transfected cell lines that are positive and negative for p53: implications for cancer therapy.
abstract: OBJECTIVE
  Radiolabeled somatostatin analogs have become important agents for molecular imaging and targeted radiotherapy of somatostatin receptor-positive tumors. Here we determine the effect of the tumor suppressor protein, p53, on trafficking (64)Cu to tumor cell nuclei from DOTA vs. CB-TE2A-conjugated agonist Y3-TATE and the antagonist (64)Cu-CB-TE2A-sst2-ANT in cell lines that are positive or negative for p53.
  
  
  METHODS
  Receptor binding, internalization, cyclic adenosine monophosphate (cAMP) and nuclear localization studies were performed with the somatostatin receptor subtype 2 (SSTr2) agonists, (64)Cu-CB-TE2A-Y3-TATE and (64)Cu-DOTA-Y3-TATE vs. antagonist, (64)Cu-CB-TE2A-sst2-ANT, in SSTr2-transfected p53 +/+ and -/- HCT116 colorectal carcinoma cells.
  
  
  RESULTS
  The antagonist, (64)Cu-CB-TE2A-sst2-ANT, bound 8-9-fold more SSTr2 binding sites than did the (64)Cu-labeled agonists. (64)Cu-CB-TE2A-Y3-TATE was more efficiently internalized than (64)Cu-DOTA-Y3-TATE, while (64)Cu-CB-TE2A-sst2-ANT showed lower yet significant levels of internalization. CB-TE2A-Y3-TATE acted as a full agonist, inhibiting cAMP production, whereas CB-TE2A-sst2-ANT showed no inhibition of cAMP production. The (64)Cu from agonists (64)Cu-DOTA-Y3-TATE and (64)Cu-CB-TE2A-Y3-TATE showed greater nuclear localization at 24 h in p53 +/+ vs. -/- cells; however, there was no difference in the levels of (64)Cu from the antagonist based on p53 status. Surprisingly, the DOTA and CB-TE2A-conjugated agonists showed similar nuclear localization in the p53 +/+ and -/- cells, suggesting no difference in (64)Cu release from these chelators in the HCT116 cell lines.
  
  
  CONCLUSIONS
  Based on these in vitro data, the agonist (64)Cu-CB-TE2A-Y3-TATE demonstrates the most promise as an agent for targeted radiotherapy in p53 positive, SSTr2-positive tumors.
authors: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO 63110, USA.
authors: Kim
authors: K
authors: Nguyen
authors: Jesse J
authors: JJ
authors: Parry
authors: Buck E
authors: BE
authors: Rogers
authors: Carolyn J
authors: CJ
authors: Anderson
mesh_terms: D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D056831:Coordination Complexes / Q000493:pharmacokinetics; D003301:Copper Radioisotopes / Q000493:pharmacokinetics*; D006801:Humans; D010455:Peptides / Q000493:pharmacokinetics; D017481:Receptors, Somatostatin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects* / Q000235:genetics
chemical_list: C573097:64Cu-CB-TE2A-Y3-TATE; C573098:64Cu-CB-TE2A-sst2-ANT; C573096:64Cu-DOTA-Y3-TATE; D056831:Coordination Complexes; D003301:Copper Radioisotopes; D010455:Peptides; D017481:Receptors, Somatostatin; D016159:Tumor Suppressor Protein p53; C093733:somatostatin receptor 2