Characterization of somatostatin receptors (SSTRs) expression and antiproliferative effect of somatostatin analogues in aggressive thyroid cancers

Background: Certain human carcinomas have demonstrated a distinct expression of somatostatin receptors. Data on somatostatin receptor expression in follicular thyroid cancer and anaplastic thyroid cancer has been limited and conflicting. This study seeks to characterize somatostatin receptor expression in follicular thyroid cancer and anaplastic thyroid cancer and to assess the effects of somatostatin analogues. Methods: Anaplastic thyroid cancer (Hth7 and 8505C) and follicular thyroid cancer (FTC-236) (Sigma-Aldrich, St. Louis, MO) cells were cultured. Capillary immunoblotting and reverse transcription polymerase chain reaction (RT-PCR) were used to determine the basal expression of protein and mRNA of SSTR1-SSTR5. Cells were treated with the somatostatin analogues octreotide, pasireotride (SOM230), and KE-108 for 48h. IC50 was determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and cell proliferation was measured by viable cell count. Presence of SSTR2 was assessed by immunohistochemistry. Results: Immunoblotting analysis demonstrated that most cell lines expressed SSTR1-SSTR3 and SSTR5 in varying degrees. Reverse transcription polymerase chain reaction analysis showed that mRNA expression for SSTR2 and SSTR3 correlated with protein expression. MTT assays showed that KE-108 and SOM230 were able to inhibit cell proliferation. Tissue microarray (TMA) showed that SSTR2 was highly expressed in human tissues of aggressive thyroid carcinomas. Conclusion: Follicular thyroid cancer and anaplastic thyroid cancer express SSTR1-3 and SSTR5 in distinct fashions both at a message and protein level. Our results suggest that somatostatin receptors are still a relevant and promising drug target against non-medullary thyroid cancers. Published by Elsevier Inc.