A Comparison of [ 99m Tc]Duramycin and [ 99m Tc]Annexin V in SPECT/CT Imaging Atherosclerotic Plaques.

PURPOSE: Apoptosis is a key factor in unstable plaques. The aim of this study is to evaluate the utility of visualizing atherosclerotic plaques with radiolabeled duramycin and Annexin V.

PROCEDURES: ApoE-/- mice were fed with a high-fat diet to develop atherosclerosis, C57 mice as a control. Using a routine conjugation protocol, highly pure [99m Tc]duramycin and [99m Tc]Annexin V were obtained, which were applied for in vitro cell assays of apoptosis and in vivo imaging of atherosclerotic plaques in the animal model. Oil Red O staining, TUNEL, hematoxylin-eosin (HE), and CD68 immunostaining were used to evaluate the deposition of lipids and presence of apoptotic macrophages in the lesions where focal intensity positively correlated with the uptake of both tracers.

RESULTS: [99m Tc]duramycin and [99m Tc]Annexin V with a high radiochemical purity (97.13 ± 1.52 and 94.94 ± 0.65 %, respectively) and a well stability at room temperature were used. Apoptotic cells binding activity to [99m Tc]duramycin (Kd, 6.92 nM and Bmax, 56.04 mol/1019 cells) was significantly greater than [99m Tc]Annexin V (Kd, 12.63 nM and Bmax, 31.55 mol/1019 cells). Compared with [99m Tc]Annexin V, [99m Tc]duramycin bound avidly to atherosclerotic lesions with a higher plaque-to-background ratio (P/B was 8.23 ± 0.91 and 5.45 ± 0.48 at 20 weeks, 15.02 ± 0.23 and 12.14 ± 0.22 at 30 weeks). No plaques were found in C57 control mice. Furthermore, Oil Red O staining showed lipid deposition areas were significantly increased in ApoE-/- mice at 20 and 30 weeks, and TUNEL and CD68 staining confirmed that the focal uptake of both tracers contained abundant apoptotic macrophages.

CONCLUSIONS: This stable, fast clearing, and highly specific [99m Tc]duramycin, therefore, can be useful for the quantification of vulnerable atherosclerotic plaques.