Comparative Evaluation of Anti-HER2 Affibody Molecules Labeled with (64)Cu Using NOTA and NODAGA

Imaging using affibody molecules enables discrimination between breast cancer metastases with high and low expression of HER2, making appropriate therapy selection possible. This study aimed to evaluate if the longer half-life of (64)Cu (T(1/2) = 12.7 h) would make (64)Cu a superior nuclide compared to (68)Ga for PET imaging of HER2 expression using affibody molecules. The synthetic ZHER2:S1 affibody molecule was conjugated with the chelators NOTA or NODAGA and labeled with (64)Cu. The tumor-targeting properties of (64)Cu-NOTA-ZHER2:S1 and (64)Cu-NODAGA-ZHER2:S1 were evaluated and compared with the targeting properties of (68)Ga-NODAGA-ZHER2:S1 in mice. Both (64)Cu-NOTA-ZHER2:S1 and (64)Cu-NODAGA-ZHER2:S1 demonstrated specific targeting of HER2-expressing xenografts. At 2 h after injection of (64)Cu-NOTA-ZHER2:S1, (64)Cu-NODAGA-ZHER2:S1, and (68)Ga-NODAGA-ZHER2:S1, tumor uptakes did not differ significantly. Renal uptake of (64)Cu-labeled conjugates was dramatically reduced at 6 and 24 h after injection. Notably, radioactivity uptake concomitantly increased in blood, lung, liver, spleen, and intestines, which resulted in decreased tumor-to-organ ratios compared to 2 h postinjection. Organ uptake was lower for (64)Cu-NODAGA-ZHER2:S1. The most probable explanation for this biodistribution pattern was the release and redistribution of renal radiometabolites. In conclusion, monoamide derivatives of NOTA and NODAGA may be suboptimal chelators for radiocopper labeling of anti-HER2 affibody molecules and, possibly, other scaffold proteins with high renal uptake.