Preparation and Biological Evaluation of ^99mTc Labeled Somatostatin Analogue ^99mTc-HYNIC-KE108

Most tumor cells overexpress somatostatin receptors. It is well known that somatostatin and its analogues can bind to somatostatin receptors specifically. Therefore, radionuclide-labeled somatostitin and its analogues may be used for the early diagnosis of somatostatin receptor positive tumours. In order to explore the feasibility of somatostatin analogues HYNIC-KE108 for somatostatin receptor positive tumor imaging, the new somatostatin analogue ^99mTc-HYNIC-KE108 was designed and synthesized. The lipid water partition coefficient and in vitro stability of the markers were determined. The biological studies were carried out in normal mice and also in tumor-bearing nude mice. The labelling yield of ^99mTc-HYNIC-KE108 was approximately 90% under the optimized conditions, and the radiochemical purity was more than 98% after Waters Oasis HLB colunm purification. The lipid-water partition coefficient of the marker LogP was 0.43±0.02 (n=3). The labelled complex showed satisfactory stability in vitro. ^99mTc-HYNIC-KE108 displayed a rapid blood and metabolized by kidneys. Meanwhile, the substantial uptakes of radioactivity in stomach, lung and liver were observed. The biodistribution of the labeled compound in tumor-bearing mice was 1.14±0.91(%ID•g^-1) at 4 h after injection. There was high radioactivity uptake in tumor and rapid blood clearance, and thus high ratios of tumor to blood and muscle were obtained at 4 h post injection. The tumor-to-normal tissue ratio (T/NT) for blood, muscle and heart were 1.78, 8.14 and 3.35, respectively. All these results indicate that ^99mTc-HYNIC-KE108 is a novel promising candidate for somatostatin receptor positive tumor imaging.