title: 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.affiliation: Department of Radiation Oncology, University of Iowa, Iowa City, IA 52242, United States.
authors.forename: William M
authors.initials: WM
authors.lastname: Rockey
authors.forename: Ling
authors.initials: L
authors.lastname: Huang
authors.forename: Kyle C
authors.initials: KC
authors.lastname: Kloepping
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Baumhover
authors.forename: Paloma H
authors.initials: PH
authors.lastname: Giangrande
authors.forename: Michael K
authors.initials: MK
authors.lastname: Schultz
mesh_terms: D000818:Animals; D052157:Aptamers, Nucleotide / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry*; D003301:Copper Radioisotopes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D017430:Prostate-Specific Antigen / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry; D013696:Temperature
chemical_list: D052157:Aptamers, Nucleotide; D002614:Chelating Agents; D003301:Copper Radioisotopes; D019275:Radiopharmaceuticals; D017430:Prostate-Specific Antigen