Functional comparison of annexin V analogues labeled indirectly and directly with iodine-124

We are interested in imaging cell death in vivo using annexin V radiolabeled with 124I. In this study, [124I]4IB-annexin V and [124I]4IB-ovalbumin were made using [124I]N-hydroxysuccinimidyl-4-iodobenzoate prepared by iododestannylation of N-hydroxysuccinimidyl-4-(tributylstannyl)benzoate. [124I]4IB-annexin V binds to phosphatidylserine-coated microtiter plates and apoptotic Jurkat cells and accumulates in hepatic apoptotic lesions in mice treated with anti-Fas antibody, while [124I]4IB-ovalbumin does not. In comparison with 124I-annexin V, [124I]4IB-annexin V has a higher rate of binding to phosphatidylserine in vitro, a higher kidney and urine uptake, a lower thyroid and stomach content uptake, greater plasma stability and a lower rate of plasma clearance. Binding of radioactivity to apoptotic cells relative to normal cells in vitro and in vivo appears to be lower for [124I]4IB-annexin V than for 124I-annexin V.