Preparation and imaging studies of 99Tcm–EDDA/HYNIC-Lys0-TOCA

The new somatostatin analogue 99Tcm-EDDA/HYNIC-Lys0-TOCA was designed and synthesized. The biological studies were carried out in normal and tumor-bearing nude mice in order to evaluate its potential application as an imaging agent for somatostatin receptor positive tumor. The labelling efficiency of 99Tcm-EDDA/HYNIC-Lys0-TOCA was approximately 96% under the optimized conditions, and more than 99% could be reached after Sep-pak column purification. The radiolabelled complex showed satisfactory stability in vitro. 99Tcm-EDDA/HYNIC-Lys0-TOCA displayed a rapid blood clearance ( about 20min of half-life) and the predominant excretion via the kidney and urinary system in normal mice. Meanwhile, the substantial uptakes of radioactivity in stomach, lung and adrenal were observed. The biodistribution in tumor-bearing nude mice of 99Tcm-EDDA/HYNIC-Lys0-TOCA suggested that there was high radioactivity uptake in tumor and rapid blood clearance, and thus high T/NT ratios of tumor to blood and muscle were obtained 1h post injection. The radio-tracer remained almost stable in urine as assayed by HPLC. Planar gamma imaging allowed contrasting visualisation of tumours at 1h and 2h post injection. All these results indicated that 99Tcm-EDDA/HYNIC-Lys0-TOCA is a novel promising candidate for somatostatin receptor -positive tumor imaging.