Enhancement of in vivo targeting properties of ErbB2 aptamer by chemical modification

Aptamers have great potential for diagnostics and therapeutics due to high specificity to target molecules. However, studies have shown that aptamers are rapidly distributed and excreted from blood circulation due to nuclease degradation. To overcome this issue and to improve in vivo pharmacokinetic properties, inverted deoxythymidine (idT) incorporation at the end of aptamer has been developed. The goal of this study was to evaluate the biological characterization of 3'-idT modified ErbB2 aptamer and compare with that of unmodified aptamer via nuclear imaging. ErbB2-idT aptamer was labeled with radioisotope F-18 by base-pair hybridization using complementary oligonucleotide platform. The hyErbB2-idT aptamer demonstrated specific binding to targets in a ErbB2 expressing SK-BR-3 and KPL4 cells in vitro. Ex vivo biodistribution and in vivo imaging was studied in KPL4 xenograft bearing Balb/c nu/nu mice. F-18-hyErbB2-idT aptamer had significantly higher retention in the tumor (1.36 +/- 0.17%ID/g) than unmodified F-18-hyErbB2 (0.98 +/- 0.19%ID/g) or scrambled aptamer (0.79 +/- 0.26% ID/g) at 1 h post-injection. F-18-hyErbB2-idT aptamer exhibited relatively slow blood clearance and delayed excretion by the renal and hepatobiliary system than F-18-hyErbB2 aptamer. In vivo PET imaging study showed that F-18-hyErbB2-idT aptamer had more stronger PET signals on KPL4 tumor than F-18-hyErbB2 aptamer. The results of this study demonstrate that attachment of idT at 3'-end of aptamer have a substantial influence on biological stability and extended blood circulation led to enhanced tumor uptake of aptamer.