First Evaluation of Radioiodinated Flavonoids as Necrosis-Avid Agents and Application in the Early Assessment of Tumor Necrosis.

A rapid and accurate identification of necrotic tissues is of great importance to define disease severity, predict prognosis, and monitor responses to therapies. To seek necrosis-avid agents with clinically translational potential, we first evaluated the necrosis avidity of flavonoids in rodent models of muscular, myocardial, and tumoral necrosis. In this study, the necrosis avidity of eight radioiodinated 5,7dihydroxyflavones was tested by ex vivo gamma counting, histochemical staining, and autoradiography in mouse models of ethanol-induced muscular necrosis. The necrosis avidity of a lead tracer, I-131-5, was further assessed in rat models of myocardial infarction and reperfusion. Therapy response was evaluated by I-131-5 single photon emission computed tomography/computed tomography imaging 24 h after combretastatin A-4 disodium phosphate (CA4P) therapy on rats bearing W256 breast carcinomas. The necrosis avidity mechanism for the tracers was studied by in vitro DNA binding experiments of 12 5,7-dihydroxyflavones and in vivo blocking experiments of I-131-5. In the results, all I-131-5,7-dihydroxyflavones showed intense uptake to necrotic muscles, and I-131-5 emerged as the most potential tracer among them. I-131-5 obtained a necrotic-viable myocardium ratio of 5.0 +/- 0.9 in post-mortem biodistribution on reperfused myocardial infarction models and achieved necrosis imaging on CA4P-treated W256 tumors 4 h after tracer injection. DNA binding studies suggested that necrosis avidity was related to DNA binding to a certain extent. The uptake of I-131-5 in necrotic muscle was markedly blocked by excessive ethidium bromide and cold 5 with a 51.95% and 64.29% decline at 1 h after coinjection, respectively. In conclusion, flavonoids are necrosis-avid agents. Furthermore, I-131-5 can serve as a promising necrosis-avid diagnostic tracer for the rapid imaging of necrotic tissues, supporting the further molecular design of radiotracer based on 5.