Somatostatin Receptor Subtypes in Human Thymoma and Inhibition of Cell Proliferation by Octreotide in Vitro

Abstract

Somatostatin (SS) and SS receptor (SSR) subtypes, code-named sst1–5, are heterogeneously expressed in the normal human thymus. This suggests their involvement in controlling the immune and/or neuroendocrine functions in this organ. Moreover, recently a high in vivo uptake of[ 111In-DTPA-d-Phe1]octreotide has been reported in patients bearing thymoma. The present study characterizes in vivo and in vitro, functional SS-binding sites in a human thymoma. A high uptake of[ 111In-DTPA-d-Phe1]octreotide was observed in the chest of a patient with myasthenia gravis due to a cortical thymoma. Specific binding of[ 125I-Tyr11]SS-14 was found on a membrane preparation of the surgically removed thymoma. Scatchard analysis showed high affinity binding sites (Kd, 47.5 ± 2.5 pmol/L) with low maximum binding capacity (23.5 ± 2.5 fmol/mg membrane protein). RT-PCR analysis showed the presence of sst1, sst2A, and a predominant sst3 messenger RNA (mRNA) expression in the tumor tissue. Primary cultured tumor cells expressed ss...