Synthetic octreotide. Its identification, labeling and preliminary animal experiments

Tumor-receptor imaging in nude mice bearing pancreatic tumor was studied by using radiolabeled somatostatin analog 131I-Tyr3-octreotide synthesized by the authors. Octreotide was synthesized by the combined solid-liquid phase method. After purification with HPLC and identification, it was labeled with 131I by Chloramine T method. The 131I-Tyr3-octreotide, purified through Sephadex G-10, was injected into the tail vein of pancreatic tumor-bearing nude mice. Static images were acquired with gamma camera at 1 hr, 2 hr, 3 hr, 4 hr, 5 hr, 6 hr, respectively. Biodistribution was investigated at 3 hr after reinjection of the labeled compound and T/NT value was calculated. The pure octreotide prepared in the laboratory was identified by HPLC, AAA and FAB-MS(M + 1= 1135). Accumulation at tumor site could be demonstrated at one hour after injection. A clear visualization of tumor was acquired at two hours after injection. T/B value at 2 hr was as high as 5.31. The scintigraphy at 6 hours after injection showed little specific accumulation in tumor site. T/NT ratio for muscle at 3 hr was 3.43. The 131I-Tyr3-octreotide prepared by the authors could be used for receptor imaging of somatostatin receptor-positive tumors