Copper-64 radiolabeling and biological evaluation of bifunctional chelators for radiopharmaceutical development

Ravindra A. De Silva, Sandeep Jain, Kimberly A. Lears, Hyun Soon Chong, Chi Soo Kang, Xiang Sun, Buck E. Rogers

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Introduction: 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 64Cu-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 64Cu 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 64Cu-N-NE3TA and 64Cu-C-NE3TA were 96.1% and 90.5% intact after 48h incubation in rat serum, respectively. This is compared to 64Cu complexes of the control chelators, p-NH2-Bn-DOTA and p-NH2-Bn-NOTA, with 93.9% and 97.9% retention of 64Cu in the complex, respectively. In vivo evaluation of 64Cu-N-NE3TA and 64Cu-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 64Cu-N-NE3TA and 64Cu-C-NE3TA, respectively. This compares to 78% and 3% retention for 64Cu-p-NH2-Bn-DOTA and 64Cu-p-NH2-Bn-NOTA. Conclusions: These studies demonstrate that while N-NE3TA and C-NE3TA appear to be superior chelators for 64Cu than p-NH2-Bn-DOTA, they are not better than p-NH2-Bn-NOTA. Nevertheless, it may still be interesting to evaluate these chelators after conjugation to biomolecules.

Original languageEnglish
Pages (from-to)1099-1104
Number of pages6
JournalNuclear Medicine and Biology
Volume39
Issue number8
DOIs
StatePublished - Nov 1 2012

Keywords

  • Bifunctional chelators
  • Biodistribution
  • Copper-64
  • Serum stability

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