Evaluation of necrosis avidity of radioiodinated 5-hydroxytryptophan and its potential applications in myocardial infarction imaging

Abstract

This study aimed to seek necrosis avid agents with high safety from DNA binding agents. The interaction of 5-hydroxytryptophan (5-HTP) with DNA was investigated by a series of spectroscopic studies. Then, 5-HTP was labeled with iodine-131 ([131I]5-HTP) and the necrosis avidity of [131I]5-HTP was evaluated by in vitro cell binding assays, in vivo biodistribution experiments and blocking experiment. Finally, the potential of [131I]5-HTP to image necrotic myocardium was explored in rat models with myocardial infarction by SPECT/CT imaging. Results showed that 5-HTP bound to DNA in groove binding mode and the binding constant was 1.69×104 L/mol. [131I]5-HTP showed specific affinity to necrotic A549 cells, which might be related to cell nucleus. Biodistribution and autoradiography results showed preferential accumulation of [131I]5-HTP in necrotic muscle (necrotic/viable muscle ratio: 6.95±0.68 at 3h post-injection (p.i.)), which could be blocked by 5-HTP with 66.7% decline, indicating that [131I]5-HTP might share the same necrotic targets with 5-HTP. On SPECT/CT images, a hotspot was clearly observed at 3h p.i. in the necrotic myocardium while not in the control myocardium. In conclusion, [131I]5-HTP is a novel necrosis avid agent and can rapidly visualize necrotic myocardium at 3h p.i. The necrosis avidity mechanism of [131I]5-HTP may be attributed to its interactions with exposed DNA in the necrotic tissues.