μPET imaging of EphA2 and EphB4 receptors in ovarian cancer xenografts using 64Cu-labeled YSA-TNYL heterodimer

Objectives The co-overexpression of both EphA2 and EphB4 receptors in various tumor types suggests that Epherin receptors are attractive targets for cancer imaging and therapy (Pasquale. Nat Rev Cancer. 2010;10:165). We recently reported 64Cu-labeled peptide with high binding affinity to EphB4, 64Cu-DOTA-TNYL-RAW, for EphB4 imaging in human prostate PC-3M and colon cancer CT-26 xenografts (Xiong et al., J Nucl. Med., in press). The purpose of this study is to investigate the synergistic effect of a heterodimer peptide recognizing both EphA2 and EphB4 receptors for PET imaging of tumors.

Methods A YSA-TNYL heterodimer was synthesized from YSA and TNYL-RAW peptides through an oligomeric ethylene oxide linker and then labeled with 64Cu via 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (DOTA). The receptor-binding characteristics and tumor-targeting efficacy of heterodimer was evaluated in vitro with SPR and in vivo using µPET imaging.

Results DOTA-YSA-TNYL peptide had comparable binding affinity to EphB4 compared with TNYL-RAW peptide and higher binding affinity to EphA2 compared with YSA peptide. In human ovarian tumor HEY xenografts, 64Cu-DOTA-YSA-TNYL peptide showed significantly higher tumor uptake value compared with monomeric 64Cu-DOTA-TNYL-RAW and monomeric 64Cu-DOTA-YSA peptide tracer analogs at all time points examined. The HEY tumor uptake of 64Cu-DOTA-YSA-TNYL was inhibited partially in the presence of an excess amount of unlabeled TNYL-RAW, YSA, or both TNYL-RAW and YSA peptides. Compared with 64Cu-DOTA-TNYL-RAW and 64Cu-DOTA-YSA, the heterodimer 64Cu-DOTA-YSA-TNYL also showed improved pharmacokinetics, resulting in a significantly higher target-to-background ratio.

Conclusions Heterodimer 64Cu-DOTA-YSA-TNYL showed significantly improved tumor-targeting efficacy and improved imaging property. This class of radiotracers directed at both EphA2 and EphB4 should be useful imaging probes for early tumor detection and noninvasive characterization of Ephrin receptor expression in a variety of solid tumors.

Research Support John S. Dunn Foundatio