SSTR1 and SSTR5 subtypes are the dominant forms of somatostatin receptor in neuroendocrine tumors.

Abstract

The effectiveness of the long acting somatostatin analogues like octreotide and lanreotide depends on the expression of specific somatostatin receptors on the target cells. The immunohistochemical method performed on surgically removed tumors searches the expression of receptors at the level of receptor protein and gives us insight into receptor's cellular localization. The aim of study was to assess the presence of all the 5 subtypes of SSTR 1-5 (including 2A and 2B SSTR isoforms) in surgically treated human neuroendocrine tumors (NETs) to establish which receptor subtype is the dominant form of somatostatin receptor in particular tumor and thus to be able to predict which somatostatin analog will be effective in NETs treatment. 18 samples of neuroendocrine tumors (surgically excised tumors or biopsies) were immunostained with specific antibodies. Expression of SSTR was scored semiquantitatively. Only strong or moderate immunostaining was considered as positive reaction. The summarized expression pattern of SSTR in the investigated neuroendocrine tumors in our material was: SSTR 1> SSTR 5> SSTR 3> SSTR 2A> SSTR 2B. The receptors were distributed mainly in the area of cells cytoplasm with a few specimens showing only membranous or mixed: membranous--cytoplasmic localization. The observed pattern suggests that apart from octreotide and lanreotide, newly synthesized multiligand analogs such as SOM 230, KE 108 or SSTR 1 and SSTR 5 selective analogs could be effective in NETs treatment.