The presence of
somatostatin receptors has been demonstrated in various endocrine
tumors as well as in normal tissues. We recently have cloned five human
somatostatin receptor subtypes (SSTR1-SSTR5). These mRNAs are expressed in a tissue-specific manner. In this study, we have determined the
somatostatin receptor subtypes expressed in various endocrine
tumors using a
reverse transcriptase polymerase chain reaction method. In two cases of
glucagonoma and its metastatic lymph nodes in one case, all the SSTR subtype mRNAs except SSTR5
mRNA were expressed. In four cases of
insulinoma,
SSTR1 and SSTR4 mRNAs were detected, but SSTR2
mRNA was not detected in one case and SSTR3
mRNA was not detected in two cases, indicating a heterogeneous expression of SSTR subtypes in
insulinomas. Interestingly, SSTR3
mRNA, which is highly expressed in rat pancreatic islets, is not expressed in normal human pancreatic islets, while
SSTR1, SSTR2, and SSTR4 mRNAs are expressed. In three cases of
pheochromocytoma,
SSTR1 and SSTR2 mRNAs were detected, showing an expression pattern identical to that of normal adrenal gland. In a
carcinoid,
SSTR1 and SSTR4 mRNAs were detected. We have also found that human SSTR2 shows a high affinity for
SMS 201-995, which has been used clinically for the treatment of endocrine
tumors. Since
SMS 201-995 was effective in the treatment of a patient with
glucagonoma in which SSTR2
mRNA was present, but had no effect in a patient with
carcinoid in which SSTR2
mRNA was not detected, this study suggests that the efficacy of
SMS 201-995 may depend, at least in part, on the expression of SSTR2 in
tumors.