Synthesis and radiolabeling of chelator-RNA aptamer bioconjugates with copper-64 for targeted molecular imaging.

Abstract

Ribonucleic acid (RNA) aptamers with high affinity and specificity for cancer-specific cell-surface antigens are promising reagents for targeted molecular imaging of cancer using positron emission tomography (PET). For this application, aptamers must be conjugated to chelators capable of coordinating PET-radionuclides (e.g., copper-64, (64)Cu) to enable radiolabeling for in vivo imaging of tumors. This study investigates the choice of chelator and radiolabeling parameters such as pH and temperature for the development of (64)Cu-labeled RNA-based targeted agents for PET imaging. The characterization and optimization of labeling conditions are described for four chelator-aptamer complexes. Three commercially available bifunctional macrocyclic chelators (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid mono N-hydroxysuccinimide [DOTA-NHS]; S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid [p-SCN-Bn-NOTA]; and p-SCN-Bn-3,6,9,15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid [p-SCN-Bn-PCTA]), as well as the polyamino-macrocyclic diAmSar (3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane-1,8-diamine) were conjugated to A10-3.2, a RNA aptamer which has been shown to bind specifically to a prostate cancer-specific cell-surface antigen (PSMA). Although a commercial bifunctional version of diAmSar was not available, RNA conjugation with this chelator was achieved in a two-step reaction by the addition of a disuccinimidyl suberate linker. Radiolabeling parameters (e.g., pH, temperature, and time) for each chelator-RNA conjugate were assessed in order to optimize specific activity and RNA stability. Furthermore, the radiolabeled chelator-coupled RNA aptamers were evaluated for binding specificity to their target antigen. In summary, key parameters were established for optimal radiolabeling of RNA aptamers for eventual PET imaging with (64)Cu.

• Authors: William M Rockey, Ling Huang, Kyle C Kloepping, Nicholas J Baumhover, Paloma H Giangrande, Michael K Schultz
• Journal: Bioorganic & medicinal chemistry (Bioorg Med Chem) Vol. 19 Issue 13 Pg. 4080-90 (Jul 01 2011) ISSN: 1464-3391 [Electronic] England
• PMID: 21658962 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2011 Elsevier Ltd. All rights reserved.

Chemical References

• Aptamers, Nucleotide
• Chelating Agents
• Copper Radioisotopes
• Radiopharmaceuticals
• Prostate-Specific Antigen

Topics

• Animals
• Aptamers, Nucleotide (chemistry)
• Chelating Agents (chemistry)
• Copper Radioisotopes (chemistry)
• Hydrogen-Ion Concentration
• Isotope Labeling
• Male
• Mice
• Positron-Emission Tomography
• Prostate-Specific Antigen (chemistry)
• Prostatic Neoplasms (diagnostic imaging)
• Radiopharmaceuticals (chemical synthesis, chemistry)
• Temperature