Classical somatostatin analogues (SST-A), such as octreotide and lanreotide, bind mainly SSTR2 whilst the multiligand pasireotide binds with the highest affinity SSTR5. The selective immunodetection of ligand binding domain (LBD) of SSTR subtypes with specific monoclonal antibodies may be useful to explain the potential efficacy of different SSTA on pituitary tumours growth and/or secretory activity.
Patients and Methods: We applied new monoclonal antibodies (Y-SSTR MoAbs, Ypsilon biotechnology, Naples, Italy) recognizing the second extracellular loop of SSTR2 and SSTR5 for the immunohistochemical screening of SST-LBD expression in an archival series of 110 pituitary tumours: 43 PRL-secreting, 45 ACTH-secreting, 22 non secreting. We used formalin fixed/paraffine embedded tissue sections from pituitary adenomas and, as control, sections from normal tissue areas surrounding the same tumor. A standard streptavidin-biotin-labeled peroxidase immunostaining was performed. Negative controls were performed with non immune serum. The degree of immunopositivity was evaluated semi-quantitatively according to an arbitrary scale.
Results: A specific immunostaining reaction for SSTR2 was detectable in 90% of PRL-secreting tumors with medium-high intensity and in 80% of ACTH-secreting tumors with low-medium intensity. Immunostaining for SSTR5 was found in all but 2 of PRL-secreting adenomas with variable intensity from low-medium to high and in 100% of ACTH secreting adenomas with intensity from medium to high. No immunostaining for SSTR2 and SSTR5 was observed in non-secreting adenomas.
Conclusions: Y-SSTR2 and 5 MoAbs can be used to detect the presence of SST-LBD on the membrane of pituitary cells in classical paraffin embedded histological sections. The presence of SSTR LBD on adenomatous cells may address the choise of either classical or panligand SST analogues for the medical treatment of pituitary adenomas, when surgery is not indicated or fails.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
05 - 09 May 2012
European Society of Endocrinology