title: Copper-64 radiolabeling and biological evaluation of bifunctional chelators for radiopharmaceutical development.
abstract: BACKGROUND
  The development of novel bifunctional chelates for attaching copper-64 to biomolecules has been an active area of research for several years. However, many of these (64)Cu-chelates have poor in vivo stability or harsh radiolabeling conditions.
  
  
  METHODS
  In this study, two triazacyclononane analogs; C-NE3TA (4-carboxymethyl-7-[2-(carboxymethyl-amino)-3-(4-nitro-phenyl)-propyl]-[1,4,7]triazo-nan-1-yl-acetic acid) and N-NE3TA (4-carboxymethyl-7-[2-[carboxymethyl-(4-nitro-benzyl)-amino]-ethyl]-[1,4,7]triazonan-1-yl-acetic acid) were evaluated for their labeling efficiency with (64)Cu at room temperature and evaluated in vitro and in vivo. In vitro studies included complexation kinetics with Cu(II) using a spectrophotometric method and rat serum stability, while the in vivo biodistribution was evaluated using SCID mice.
  
  
  RESULTS
  C-NE3TA and N-NE3TA were labeled at >95% efficiency up to ~3.4Ci/μmol. Both C-NE3TA and N-NE3TA formed complexes with Cu(II) almost immediately, with the Cu(II) complexation by C-NE3TA being faster than the formation of Cu(II)-N-NE3TA. Both (64)Cu-N-NE3TA and (64)Cu-C-NE3TA were 96.1% and 90.5% intact after 48h incubation in rat serum, respectively. This is compared to (64)Cu complexes of the control chelators, p-NH(2)-Bn-DOTA and p-NH(2)-Bn-NOTA, with 93.9% and 97.9% retention of (64)Cu in the complex, respectively. In vivo evaluation of (64)Cu-N-NE3TA and (64)Cu-C-NE3TA demonstrates good clearance from normal tissues except for the liver, where 59% and 51% of the radioactivity is retained at 24h compared to 1h for (64)Cu-N-NE3TA and (64)Cu-C-NE3TA, respectively. This compares to 78% and 3% retention for (64)Cu-p-NH(2)-Bn-DOTA and (64)Cu-p-NH(2)-Bn-NOTA.
  
  
  CONCLUSIONS
  These studies demonstrate that while N-NE3TA and C-NE3TA appear to be superior chelators for (64)Cu than p-NH(2)-Bn-DOTA, they are not better than p-NH(2)-Bn-NOTA. Nevertheless, it may still be interesting to evaluate these chelators after conjugation to biomolecules.
authors: Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors: Ravindra A
authors: RA
authors: De Silva
authors: Sandeep
authors: S
authors: Jain
authors: Kimberly A
authors: KA
authors: Lears
authors: Hyun-Soon
authors: HS
authors: Chong
authors: Chi Soo
authors: CS
authors: Kang
authors: Xiang
authors: X
authors: Sun
authors: Buck E
authors: BE
authors: Rogers
mesh_terms: D000818:Animals; D002614:Chelating Agents / Q000737:chemistry* / Q000493:pharmacokinetics*; D003301:Copper Radioisotopes / Q000737:chemistry*; D055808:Drug Discovery; D004355:Drug Stability; D005260:Female; D006571:Heterocyclic Compounds / Q000097:blood / Q000737:chemistry* / Q000493:pharmacokinetics*; D007553:Isotope Labeling; D007700:Kinetics; D051379:Mice; D019275:Radiopharmaceuticals / Q000097:blood / Q000737:chemistry* / Q000493:pharmacokinetics*; D051381:Rats; D013696:Temperature
chemical_list: D002614:Chelating Agents; D003301:Copper Radioisotopes; D006571:Heterocyclic Compounds; D019275:Radiopharmaceuticals