Endocrine Abstracts (2010) 22 P661

SSTR5 ligand binding domain immunohistological detection in pituitary adenomas using Y-SSTR5 a new mouse monoclonal antibody

Valentina Rossi1, Stefania Staibano2, Laura Del Basso De Caro2, Giuseppe Bellastella1, Gennaro Ilardi2, Luigi Cavallo4, Annamaria Colao3 & Antonio Agostino Sinisi1

1Department of Clinical and Experimental Medicine and Surgery, Second University of Napoli, Napoli, Italy; 2Department of Biomorphological Science, Federico II University, Napoli, Italy; 3Department of Molecular and Clinical Endocrinology and Oncology, Federico II University, Napoli, Italy; 4Department of Neurological Science, Federico II University, Napoli, Italy.

Polyclonal antibodies against somatostatin receptors (SSTRs) available up to now recognizing intracellular sites of receptors and their recycling products do not detect bioactive ligand binding domains (LBDs) and are of limited performance in paraffin-embedded tissues. Aim of this study was to evaluate by immunohistochemistry the expression of SSTR5 on an archival series of pituitary tumors using a new MoAbs against the SST-binding domain (Y-SSTR5).

Methods: We used paraffined tissue sections from 20 non-secreting pituitary tumors (NS) and 14 PRL-secreting (PRL) adenomas and, as control, sections from normal tissue 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: Immunostaining for SSTR5 was found in 90% of NS (low-medium 55%, high 35%) and in 100% of PRLS adenomas (low-medium 14%, high 86%).

Conclusion: SSTR5 was found in the majority of pituitary tumors examined. PRLS adenomas showed a tendency to higher expression of receptor protein. Y SSTR5 MoAb can be used to detect SSTR5 on the membrane of pituitary cells in classical paraffin embedded histological sections. The specific detection of LBD SSTR5 by MoAb can support a potential choice of panligand or SST analogues targeting SSTR5 in resistant/recurrent pituitary tumors.

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