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J Nucl Med. 2008; 49 (Supplement 1):94P
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Radiopharmaceutical Chemistry: Radiopharmacy

Radiopharmacy II

Labelling of 2nd-generation cys2-annexin-A5 with Tc99m-HYNIC, Tc99m-tricarbonyl and Ga68 and biological evaluation

Dirk Rattat1, Marijke de Saint-Hubert2, Ellen Devos2, Humphrey Fonge1, Kristof Prinsen1, Sigrid Stroobants2, Luc Mortelmans2, Chris Reutelingsperger3 and Alfons Verbruggen1

1 Radiopharmacy, KUL, Leuven, Belgium; 2 Nuclear Medicine, UZ GHB, Leuven, Belgium; 3 Biochemistry, University, Maastricht, Netherlands

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Objectives: Evaluation of "second generation" cys2-annexin-A5 derivatives, radiolabelled with Tc99m or Ga68, as tracer agents for in vivo visualization of apoptosis.

Methods: Cys2-annexin-A5 is a new generation annexin-A5, bearing a single cysteine residue for site-specific conjugation of suitable chelators via thiol-chemistry. HYNIC-cys2-annexin (1) and DTPA-cys2-annexin (2) were prepared using maleimide derivatives. 1 was labelled with Tc99m via a reported method and 2 was labelled with Tc99m(CO)3 using Isolink kit and with Ga68. Biodistribution of the radiolabelled complexes was studied in normal NMRI mice at 1 and 4 h p.i. In vivo specificity for apoptosis was tested in a Fas-mediated hepatic apoptosis model in mice for Tc99m-1 and Tc99m(CO)3-2 using SPECT-imaging, ex vivo biodistribution and autoradiography. H&E staining was performed to confirm apoptosis.

Results: Radiolabelling yields were 85% for Tc99m-1 and 50-70% for Ga68-2 and Tc99m(CO)3-2. Biodistribution of the purified tracers in normal mice was similar to that of 1st-generation Tc99m-HYNIC-annexin-A5 for Tc99m-1, but different for Tc99m(CO)3-2 and especially Ga68-2, the latter showing persistent high blood retention. In the Fas-mediated hepatic apoptosis model uptake of Tc99m-1 and Tc99m(CO)3-2 in apoptotic tissue was significantly higher than in controls for both tracers, also visible on SPECT imaging at 1h p.i.

Conclusions: Biodistribution of Tc99m-1 and Tc99m(CO)3-2 in normal mice was different depending on the way of labelling, while the specificity of the novel radiolabelled annexin derivatives for apoptosis was retained.

Research Support: Euregional PACT project 4-BMG-II-2=70





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