Aptamer imaging with Cu-64 labeled AS1411: Preliminary assessment in lung cancer

Abstract Introduction AS1411 is a 26-base guanine-rich oligonucleotide aptamer shown binding to surface nucleolin, a protein over-expressed in multiple cancer cells, thus AS1411 labeled with a PET isotope can be explored as a potential diagnostic imaging agent. Our objective was to perform preliminary biological characterization of64 Cu-labeled AS1411 in vitro and in vivo. Methods Four chelators (DOTA, CB-TE2A, DOTA-Bn and NOTA-Bn) were selected to label AS1411 with Cu-64. 185 kBq (5 μCi) of each tracer was incubated in each well with H460 cells at 37 °C for 1, 3, 6, 12, 24 and 48 h, respectively (n = 4). For microPET/CT imaging, 7.4 MBq (200 μCi) of AS1411 labeled with either64 Cu-DOTA or64 Cu-CB-TE2A was I.V. injected and multiple scans were obtained at 1, 3, 6 and 24 h post injection. Afterward in vivo biodistribution studies were performed. Results Percent uptake of64 Cu-DOTA-AS1411 and64 Cu-CB-TE2A-AS1411 was significantly higher than that of64 Cu-DOTA-Bn-AS1411 and64 Cu-NOTA-Bn-AS1411. About 90% of uptake for64 Cu-DOTA-AS1411 and64 Cu-CB-TE2A-AS1411 was internalized into cells within 3 h and the internalization process was completed before 24 h. Both tracers demonstrated reasonable in vivo stability and high binding affinity to the cells. MicroPET imaging with64 Cu-CB-TE2A-AS1411 showed clear tumor uptake at both legs from 1 to 24 h post injection, whereas both tumors were undetectable for up to 24 h with64 Cu-DOTA-AS1411. In addition,64 Cu-CB-TE2A-AS1411 had faster in vivo pharmacokinetics than64 Cu-DOTA-AS1411 with lower liver uptake and higher tumor to background contrast. Conclusion CB-TE2A is a preferred chelator with higher tumor-to-background ratio, lower liver uptake and faster clearance than DOTA. Aptamer imaging with64 Cu-CB-TE2A-AS1411 may be feasible for detecting lung cancer, if an appropriate chelator can be identified and further validation can be performed with a known control oligonucleotide. It may also be used as a companion diagnostic imaging agent for AS1411 in the treatment of cancer.