Radiolabeling of annexin A5 with 99mTc: comparison of HYNIC-Tc vs. iminothiolane-Tc-tricarbonyl conjugates

In the perspective of expanding the use of annexin A5 (anx A5) as radioactive tracer of cell death in vivo, we recently described its radiolabeling with 99mTc-tricarbonyl [99mTc(H2O)3(CO)3]+ via the mercaptobutyrimidyl group (anx A5-SH). The aim of the present article was to compare this new method with the HYNIC strategy (anx A5-HYNIC), recognized at present as the reference for the radiolabeling of proteins with 99mTc. Similar radiolabeling yields and better chemical stability were obtained with the [anx A5-SH-99mTc-tricarbonyl] complex. Since the [anx A5-HYNIC-99mTc(tricine)2] conjugate shows isomeric forms which can affect the biological properties whereas [anx A5-SH-99mTc-tricarbonyl] is less or not prone to such drawback, the latter seems superior to the former. Furthermore, (anx A5-SH) is readily obtained via commercial sources of Traut's reagent whereas (anx A5-HYNIC) is not. The results provide encouraging evidence in the development of anx A5-labeled reagent for apoptose imaging.