Expression of somatostatin receptors in human pancreatic tumor

Somatostatin (SST) and its analogues are candidates for use as endocrine agents in the treatment of pancreatic neoplasm. To determine whether the status of SST receptors in the human pancreatic tumors differs from that in the tumor-free pancreata of the human and whether pancreatic adenocarcinoma expresses the same subgroup of SST receptors as found in gastrinomas, this study visualized and characterized SST receptors in human control pancreata (n = 10) as well as pancreatic cancers (n = 12) and gastrinomas (n = 8) with storage phosphor autoradiography. Both pancreatic adenocarcinoma and gastrinoma expressed specific SST receptors. The binding capacity (Bmax, 35.4 +/- 7.6 fmol/mg protein) and the affinity (Kd, 0.32 +/- 0.27 nM) of SST receptors in gastrinomas were significantly higher than in pancreatic cancers (Bmax, 15 +/- 2.5 fmol/mg protein; Kd, 2.16 +/- 0.4 nM). No specific SST receptors were detected in the human control pancreata. Octreotide showed similarly high potencies of inhibition of 125I-SST-28 binding as SST-28 in gastrinomas. Unlike gastrinomas, little competitive binding of 125I-SST-28 was found with octreotide in pancreatic cancers. In conclusion, compared with the control pancreas, an up-regulation of SST receptors was present in both pancreatic cancer and gastrinoma. The subgroup of SST receptors in pancreatic cancers differs from that in gastrinomas.