Gene Summary

Gene:SSTR3; somatostatin receptor 3
Aliases: SS3R, SS3-R, SS-3-R, SSR-28
Summary:This gene encodes a member of the somatostatin receptor protein family. Somatostatins are peptide hormones that regulate diverse cellular functions such as neurotransmission, cell proliferation, and endocrine signaling as well as inhibiting the release of many hormones and other secretory proteins. Somatostatin has two active forms of 14 and 28 amino acids. The biological effects of somatostatins are mediated by a family of G-protein coupled somatostatin receptors that are expressed in a tissue-specific manner. Somatostatin receptors form homodimers and heterodimers with other members of the superfamily as well as with other G-protein coupled receptors and receptor tyrosine kinases. This protein is functionally coupled to adenylyl cyclase. Alternate splicing results in multiple transcript variants. [provided by RefSeq, Jul 2013]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:somatostatin receptor type 3
Source:NCBIAccessed: 21 August, 2015


What does this gene/protein do?
Show (17)
Pathways:What pathways are this gene/protein implicaed in?
Show (1)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 21 August 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Cancer RNA
  • Tumor Burden
  • Carcinoid Tumours
  • Apoptosis
  • Antineoplastic Agents, Hormonal
  • Pituitary Tumors
  • Sex Factors
  • beta Catenin
  • Protein Isoforms
  • Gene Expression
  • Tumor Markers
  • Chromosome 22
  • Lung Cancer
  • Helicobacter Infections
  • Adenoma
  • Thyroid Cancer
  • Polymerase Chain Reaction
  • Receptors, Somatostatin
  • Base Sequence
  • Stomach Cancer
  • Cancer Gene Expression Regulation
  • Pituitary Gland
  • Neuroendocrine Tumors
  • Case-Control Studies
  • Messenger RNA
  • Octreotide
  • Somatostatin
  • Young Adult
  • Molecular Sequence Data
  • Up-Regulation
  • Pancreatic Cancer
  • Dyspepsia
  • Adolescents
  • Indium Radioisotopes
  • Tumor Suppressor Proteins
  • RT-PCR
  • Radiopharmaceuticals
  • Immunohistochemistry
  • Cell Proliferation
Tag cloud generated 21 August, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (7)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: SSTR3 (cancer-related)

Yang LX, Li BL, Liu XH, et al.
RNA-seq reveals determinants of sensitivity to chemotherapy drugs in esophageal carcinoma cells.
Int J Clin Exp Pathol. 2014; 7(4):1524-33 [PubMed] Free Access to Full Article Related Publications
Chemotherapy remains the mainstay of treatment for patients with incurable disease of esophageal carcinoma. Most patients respond poorly to chemotherapy, it is necessary to figure out biomarkers for chemotherapy sensitivity or resistance to perform the individualized therapy. In present work, the sensitivities of two ESCC cell lines to 9 chemotherapy drugs were identified and the transcriptome of these two cell lines were investigated by RNA-seq, the correlation between the sensitivity to drugs and expression of some genes was attempted to construct. Eca-1 was more resistant to most of the chemotherapy drugs than Eca-109 cell line. RNA-seq results showed that there is dramatic difference in the basal expression between these two ESCC cell lines. Pathway analysis demonstrated that these differentially expressed genes were mainly enriched in Gαi signaling, calcium signaling, cAMP-mediated signaling, G-protein coupled receptor signaling and actin cytoskeleton signaling pathways. The molecules in Gαi signaling (ADCY1 and SSTR3) and actin cytoskeleton signaling (MYH6 and MYH7) were highly expressed in multidrug-resistant Eca-1 cells, which were validated by quantitative PCR. Activation of these two pathways results in the upregulation of downstream signaling, PKA signaling and Src-STAT3, and downregulation of RAF-ERK signaling, which was validated by immunoblotting experiments. Our work proposed that activation of Gαi signaling or actin cytoskeleton signaling may confer ESCC cells resistance to most chemotherapy drugs. Our work might provide potential biomarkers and therapeutic targets for treatment of EC patients.

Wang S, Bao Z, Liang QM, et al.
Octreotide stimulates somatostatin receptor-induced apoptosis of SW480 colon cancer cells by activation of glycogen synthase kinase-3β, A Wnt/β-catenin pathway modulator.
Hepatogastroenterology. 2013; 60(127):1639-46 [PubMed] Related Publications
BACKGROUND/AIMS: Peptide hormone somatostatin and its receptors (SSTRs) have a wide range of physiological functions and play a role in the treatment of numerous human diseases, including colorectal cancer. Octreotide, a somatostatin-analog peptide, inhibits growth of colonic cancer SW480 cells through Wnt/β-catenin pathway modulation. However, the specific octreotide-stimulating SSTR subtypes and the signal-transduction mechanism responsible for the negative regulation of Wnt/β-catenin pathway by octreotide have not been fully elucidated.
METHODOLOGY: Octreotide-induced apoptosis in SW480 colon cancer cells mediated by SSTR2,SSTR5-dependent regulation of the Wnt/β-catenin pathway components GSK-3β and β-catenin was investigated. Cell apoptosis of SW480 cells was measured by apoptosis-DNA ladder assay. SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 mRNA expression levels were confirmed by RT-PCR; β-catenin, TCF-4, cyclin D1, c-Myc, and GSK-3β protein levels were examined by Western blot. The distribution of β-catenin in the cell was analyzed with immunocytochemistry.
RESULTS: Octreotide treatment increased SSTR2,SSTR5-induced apoptosis of SW480 colon cancer cells, promoted the plasma membrane accumulation of β-catenin, inactivated T-cell factor-dependent transcription, and downregulated Wnt target genes cyclin D1 and c-Myc. Further, octreotide treatment mediated the activation of GSK-3.
CONCLUSIONS: These preliminary findings showed the negative regulation of the Wnt/β-catenin pathway by peptide hormone G protein-coupled receptors SSTRs.

Ruscica M, Magni P, Steffani L, et al.
Characterization and sub-cellular localization of SS1R, SS2R, and SS5R in human late-stage prostate cancer cells: effect of mono- and bi-specific somatostatin analogs on cell growth.
Mol Cell Endocrinol. 2014; 382(2):860-70 [PubMed] Related Publications
Somatostatin (SST) and SST receptors (SS1R, SS2R, SS3R, SS4R and SS5R) appear to play a significant role in the progression of human prostate cancer (PCa), which is associated with heterogeneity of SSRs expression and specific cell localization as we already demonstrated in the LNCaP cell line, an in vitro model of human androgen-dependent PCa. In this study, PC-3 and DU-145 human castration-resistant PCa cells were found to express all SSRs, while LNCaP expressed all but SS4R. A 48-h treatment with BIM-23244 (SS2R/SS5R) or BIM-23926 (SS1R) SST analogs was more effective in inhibiting cell proliferation, compared to BIM-23120 (SS2R), BIM-23206 (SS5R) and BIM-23704 (SS1R/SS2R). BIM-23926 (SS1R) treatment increased the amount of p21 and decreased phosphorylated (p) ERK1/2. BIM-23244 (SS2R/SS5R) led to p21 increment only in PC-3 cells, and to pERK1/2 reduction in both cell lines. SS1R/SS2R and SS2R/SS5R receptor dimers were natively present on cell membrane and their amount was increased by BIM-23704 (SS1R/SS2R) or BIM-23244 (SS2R/SS5R) treatment, respectively. SS1R, SS2R and SS5R were differently distributed among nuclear, lysosomal and microsomal compartment, according to their different recycling dynamics. These results show that, in PC-3, DU-145 and LNCaP cells, activation of SS1R and SS2R/SS5R leads to relevant antiproliferative effects.

Vieria Neto L, Wildemberg LE, Colli LM, et al.
ZAC1 and SSTR2 are downregulated in non-functioning pituitary adenomas but not in somatotropinomas.
PLoS One. 2013; 8(10):e77406 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: There are few data regarding ZAC1 expression in clinically non-functioning pituitary adenomas (NFPA). Because somatotropinomas and NFPA behave differently with respect to tumor shrinkage during somatostatin analogs (SA) therapy, we sought to compare the ZAC1 and somatostatin receptor (sstr) types 1, 2, 3 and 5 mRNA expression in these two pituitary adenoma subtypes and in normal human pituitaries.
METHODS: ZAC1 and SSTR mRNA expression levels were evaluated using real-time RT-PCR (TaqMan) in 20 NFPA and compared with the expression levels in 23 somatotropinomas and five normal pituitaries. The NFPA invasiveness was evaluated using magnetic resonance imaging with Hardy's modified criteria. Ki-67 and p53 were evaluated using immunohistochemistry.
RESULTS: A total of 20 patients with NFPA [6 males, median age 56 years (range: 30-78)], 23 with acromegaly [12 males, median age 43 years (range: 24-57)] and five normal pituitaries [4 males, median age 48 years (range: 36-54)] were included. Four of the patients (20%) had Hardy's grade 2 tumors; all of the others had Hardy's grade 3 tumors. The Ki-67 median expression was 2.35 (range: 0.2-9.23), and only four of the tumors (20%) were positive for p53. The ZAC1 mRNA expression was significantly lower in NFPA than in somatotropinomas and in normal pituitaries (p<0.001 for both), as well as the SSTR2 (p=0.001 and 0.01, respectively). The SSTR3 expression was higher in the NFPA than in the somatotropinomas and in the normal pituitaries (p=0.03 and 0.02, respectively). No correlation was found between the ZAC1 mRNA expression and the tumor invasiveness, Ki-67 and p53.
CONCLUSION: ZAC1 and SSTR2 are underexpressed and SSTR3 is overexpressed in NFPA compared to those in somatotropinomas and in normal pituitaries, which might explain the lack of tumor shrinkage that is observed in response to commercially available SA therapy in patients with NFPA.

Arne G, Nilsson B, Dalmo J, et al.
Gastrointestinal stromal tumors (GISTs) express somatostatin receptors and bind radiolabeled somatostatin analogs.
Acta Oncol. 2013; 52(4):783-92 [PubMed] Related Publications
BACKGROUND: Gastrointestinal stromal tumors (GISTs) can be effectively treated with tyrosine kinase inhibitors (TKIs). However, some patients with GIST develop drug resistance, and alternative treatment strategies are therefore needed. The aim of this study was to analyze the expression of somatostatin receptors (SSTR) in GIST as a target for peptide receptor-mediated radiotherapy (PRRT).
MATERIAL AND METHODS: Expression profiling of SSTR1-5 was performed on biopsies from 34 GISTs (16 gastric tumors, 15 small intestinal tumors, and three rectal tumors). SSTR scintigraphy ((111)In-octreotide) and measurement of (111)In activity in tumor specimens was performed in seven patients. Uptake and internalization of (177)Lu- octreotate was studied in primary cell cultures from two patients.
RESULTS: Quantitative PCR analysis showed expression of SSTR1 and SSTR2 in the majority of tumors, while SSTR3-5 were expressed at low levels. Immunohistochemical analysis confirmed the presence of SSTR1 and SSTR2 proteins in all GISTs, and SSTR3-5 in a subset of tumors. Diagnostic imaging by SSTR scintigraphy, using (111)In-octreotide, demonstrated tumor uptake of (111)In in three of six GIST patients. Measurement of (111)In activity in excised tumor specimens from five patients gave tumor-to-blood (T/B) activity ratios of between eight and 96. Tumor cells in primary culture (gastric and small intestinal GIST) specifically bound and internalized (177)Lu when incubated with the therapeutic compound (177)Lu-octreotate for 4-48 hours (p < 0.05).
CONCLUSION: Peptide receptor-mediated radiotherapy via SSTR may provide a novel treatment strategy in carefully selected GIST patients with TKI-resistant tumors.

Ramírez C, Cheng S, Vargas G, et al.
Expression of Ki-67, PTTG1, FGFR4, and SSTR 2, 3, and 5 in nonfunctioning pituitary adenomas: a high throughput TMA, immunohistochemical study.
J Clin Endocrinol Metab. 2012; 97(5):1745-51 [PubMed] Related Publications
CONTEXT: Nonfunctioning pituitary adenomas (NFPA) are the most common pituitary neoplasms. There is no clinical, biochemical, or histopathological marker that would accurately predict recurrence of NFPA.
OBJECTIVE: The aim of this study was to evaluate a large group of NFPA for the presence of potential markers of biological behavior.
DESIGN AND SETTING: A cross-sectional study using a high throughput tissue microarray technology was conducted at tertiary care centers.
MATERIALS AND METHODS: Seventy-four gonadotroph and null cell adenomas were included in the tissue microarray. Using highly specific antibodies and appropriate controls, we determined the expression of Ki-67, pituitary tumor transforming gene 1, the N-terminally truncated pituitary tumor-derived fibroblast growth factor receptor-4 (FGFR4), as well as somatostatin receptor subtypes 2, 3, and 5 (SSTR2, -3, and -5), in an attempt to establish correlations and/or associations with clinical characteristics of the patients.
RESULTS: Median Ki-67 index was 1.49 (interquartile range, 0.62-2.49). Pituitary tumor transforming gene 1 nuclear immunoreactivity was found in all but one tumor (median percentage of positive nuclei, 11.44); immunopositivity for FGFR4 was found in the majority of the tumors, with variable levels of expression. The immunostaining score for SSTR2 was significantly higher than that for SSTR3 or SSTR5. FGFR4 expression correlated positively with SSTR2 and SSTR5 immunostaining scores (r = 0.59; P < 0.001; and r = 0.46; P < 0.001, respectively). Multivariate analysis revealed that the Ki-67 index was significantly associated with a tumor size greater than 3 cm (odds ratio, 2.32; 95% confidence interval, 1.17-4.58) as well as with tumor recurrence (odds ratio, 1.4; 95% confidence interval, 1.03-1.89).
CONCLUSIONS: Ki-67 is the most consistent marker of biological behavior in NFPA. The finding of significant amounts of SSTR2 and SSTR5 may have therapeutic implications regarding the use of somatostatin analogs in preventing tumor recurrence.

Muscarella LA, D'Alessandro V, la Torre A, et al.
Gene expression of somatostatin receptor subtypes SSTR2a, SSTR3 and SSTR5 in peripheral blood of neuroendocrine lung cancer affected patients.
Cell Oncol (Dordr). 2011; 34(5):435-41 [PubMed] Related Publications
BACKGROUND: Somatostatin (SS) acts as a universal endocrine off-switch, and also inhibits the growth of neuroendocrine tumours through its specific receptors (SSTRs). Somatostatin receptors are G-protein-coupled receptors, which are encoded by five separate genes (SSTR1-5). Short peptide analogues demonstrate specific binding only for the subgroup consisting of SSTR2a, SSTR3 and SSTR5. Moreover, previous studies reported that expression of mRNA for SSTR2a correlated with therapeutic outcome in patients with carcinoid tumours treated with somatostatin analogs.
PURPOSE: To develop and apply a Real Time Quantitative PCR technique (RT-qPCR) to compare and contrast the mRNA levels of SSTR2a, SSTR3 and SSTR5 in Neuroendocrine Lung Cancer affected patients.
METHODS: Peripheral blood samples from 21 neuroendocrine lung cancer affected patients (14 SCLC, 6 LC and 1 LCNEC) subjected to scintigraphy with (111)In-DTPA-D-Phe(1)-octreotide (OctreoScan) and 24 healthy blood donors were investigated by RT-qPCR. mRNA levels for SSTR2a, SSTR3 and SSTR5 were measured in peripheral blood samples with a relative quantification method using plasmid dilutions as calibration curves and GAPDH as reference gene.
RESULTS: A statistically significant increase in target genes/GAPDH copy number ratio was found for SSTR2a (median 38; IQR 22-141) and SSTR5 (median 51; IQR 19-499) in neuroendocrine lung cancer affected patients as compared with samples from healthy blood donors (P ≤ 0.0003 and P ≤ 0.0005). Since low levels of expression were detected in the control group for all three genes, optimal cut-off values were assessed using ROC curve analyses and were equal to 9.05 for SSTR2a and 16.97 for SSTR5. These cut off values resulted in a sensitivity of 86% (95%IC 65-95) for both markers and a specificity of 83% (95%IC 64-93%) and 79% (95%IC 60-91%) for SSTR2a and SSTR5 respectively. Comparison between OctreoScan results and RT-qPCR analysis demonstrated agreement in 76% of the cases.
CONCLUSIONS: Our results suggest that SSTR2a and SSTR5 mRNAs are detectable in peripheral blood of neuroendocrine lung cancer affected patients using real-time quantitative PCR, with a good agreement with OctreoScan. The high sensitivity of this non-invasive molecular technique suggests that this method could represent a useful tool in the clinical management of neuroendocrine lung cancers.

Taboada GF, Neto LV, Luque RM, et al.
Impact of gsp oncogene on the mRNA content for somatostatin and dopamine receptors in human somatotropinomas.
Neuroendocrinology. 2011; 93(1):40-7 [PubMed] Related Publications
INTRODUCTION: It has been reported in some series that gsp+ somatotropinomas are more sensitive to somatostatin analogues (SA) and dopamine's actions which may be related to their somatostatin receptor (SSTR) and dopamine receptor (DR) profile. No previous studies have been undertaken to evaluate the SSTR and DR profile related with the gsp status in somatotropinomas.
OBJECTIVES: To determine if (1) gsp status is correlated with response to octreotide LAR (LAR) and tumor expression patterns of SSTR1-5 and DR1-5 and (2) cAMP level can directly modulate SSTR and DR mRNA levels.
METHODS: Response to SA was evaluated by GH and IGF-I percent reduction after 3 and 6 months of treatment with LAR. Conventional PCR and sequencing were used to identify gsp+ tumors. Quantitative real-time PCR was used to determine SSTR and DR tumor expression. Primary pituitary cell cultures of primates were used to study whether SSTR and DR expression is regulated by forskolin.
RESULTS: The response to LAR did not significantly differ between patients with gsp+ and gsp- tumors; however, gsp+ tumors expressed higher levels of SSTR1, SSTR2, DR2 and a lower level of SSTR3. Forskolin increased SSTR1, SSTR2, DR1 and DR2 expression in cell cultures.
CONCLUSION: Elevated SSTR1, SSTR2, and DR2 tumor expression may help improve responsiveness to SA and DA therapy; however, this study may not have been appropriately powered to observe significant effects in the clinical response. Elevated cAMP levels could be directly responsible for the upregulation in SSTR1, SSTR2 and DR2 mRNA levels observed in gsp+ patients.

Nishioka H, Tamura K, Iida H, et al.
Co-expression of somatostatin receptor subtypes and estrogen receptor-α mRNAs by non-functioning pituitary adenomas in young patients.
Mol Cell Endocrinol. 2011; 331(1):73-8 [PubMed] Related Publications
The expression by non-functioning adenomas (NFoma) of somatostatin receptor (SSTR) subtypes and estrogen receptor (ERα) is poorly understood. Consequently, the mRNAs of SSTR subtypes (SSTR) 1, 2, 3, and 5, dopamine receptor (D2R), and ERα were measured by real-time quantitative RT-PCR in 59 NFomas and 50 functioning adenomas; the latter included 30 GH-secreting adenomas (GHomas) and 20 prolactinomas (PRLomas). NFomas expressed higher levels of SSTR3 than functioning adenomas but had lower levels of SSTR2, SSTR5 and D2R mRNAs than GHomas. Their ERα levels were higher than those of GHomas. The SSTR subtype mRNA levels in NFomas correlated significantly with each other; there was also a good correlation between the SSTR subtypes and ERα in NFomas. These correlations were largely only observed in younger patients (<50 years). The present study describes the differential expression of SSTR subtypes in the largest number of NFoma patients studied thus far, and further proposes possible involvements of SSTR3 and estrogen in the pathophysiology of NFomas.

Nakayama Y, Wada R, Yajima N, et al.
Profiling of somatostatin receptor subtype expression by quantitative PCR and correlation with clinicopathological features in pancreatic endocrine tumors.
Pancreas. 2010; 39(8):1147-54 [PubMed] Related Publications
OBJECTIVES: Pancreatic endocrine tumor (PET) presents variable clinical features. Five subtypes of somatostatin receptor (SSTR) are involved in hormone secretion and cell proliferation. In this paper, we explore the correlation between the SSTR subtype messenger RNA (mRNA) expression and clinicopathological features of PET.
METHODS: Twenty-one cases of PET and 5 cases of pancreatic adenocarcinomas (AC) were studied. Using total RNA extracted from paraffin sections and fresh tissues, SSTR subtype mRNA was quantified by real-time polymerase chain reaction. The hormones and MIB1 index were examined using immunohistochemical techniques.
RESULTS: The mRNA levels of SSTR1, SSTR2, SSTR3, and SSTR5 were high in PET compared with AC, whereas the expression of SSTR4 was low in PET and AC. Levels of each subtype did not vary with histological grades. Somatostatin receptor 2 levels in functioning tumors were slightly low compared with nonfunctioning tumors. Four distinct groups of PET were identified by hierarchical cluster analysis, and two of these groups showed reduced SSTR5 with elevation of MIB1 index.
CONCLUSIONS: The study showed a heterogeneous expression profile of SSTR subtype mRNA and the association of reduction in SSTR5 with high proliferative activity. Such profiling of SSTR subtypes may provide useful information on tumor biology and treatment of PET.

Ishii A, Imanishi Y, Kobayashi K, et al.
The levels of somatostatin receptors in causative tumors of oncogenic osteomalacia are insufficient for their agonist to normalize serum phosphate levels.
Calcif Tissue Int. 2010; 86(6):455-62 [PubMed] Related Publications
Oncogenic osteomalacia (OOM) is a rare disease characterized by renal phosphate wasting and osteomalacia and is caused by the secretion of fibroblast growth factor 23 (FGF-23) from causative tumors. Scintigraphy with octreotide, which binds to somatostatin receptors (SSTRs), is a useful way to locate causative tumors in OOM patients. However, the therapeutic effects of octreotide acetate are still controversial. Two OOM patients were administered octreotide acetate intramuscularly. Ten causative OOM tumors, including two resected from the patients participating in the octreotide administration study, were examined for expression of genes encoding SSTRs by quantitative real-time RT-PCR and immunohistochemistry. Octreotide therapy did not improve hypophosphatemia in either case, despite temporal decreases in FGF-23 levels in one patient. The mean expression levels of SSTR1, SSTR3, and SSTR5 were similar in the OOM and non-OOM tumors. Expression of SSTR2 was significantly higher in the OOM tumors than in the non-OOM tumors. Immunohistochemical examinations revealed the presence of SSTR2A, SSTR2B, and SSTR5 in both the OOM and non-OOM tumors. The expression of SSTR genes in OOM tumors contributes to positive imaging using octreotide scintigraphy. However, the levels of SSTRs seem to be insufficient for the octreotide therapy to improve hypophosphatemia. Further studies are needed to clarify the mechanisms by which FGF-23 secretion from OOM tumors is suppressed by octreotide acetate.

Slaby O, Sachlova M, Bednarikova M, et al.
Gene expression of somatostatin receptor 4 predicts clinical outcome of patients with metastatic neuroendocrine tumors treated with somatostatin analogs.
Cancer Biother Radiopharm. 2010; 25(2):237-43 [PubMed] Related Publications
Somatostatin analogs (SSA) are the standard diagnostic and treatment tools in the clinical management of patients with neuroendocrine tumors (NETs) expressing somatostatin receptors (SSTRs). Although symptomatic and biochemical control is obtained with SSA in the majority of functional NETs, antineoplastic effects of SSA are partial and of limited duration. The aim of this study was to quantify expression levels of five SSTR subtypes (SSTR1-SSTR5) and correlate them with the clinical outcomes of patients with NETs who underwent SSA therapy. The expression levels were analyzed using real-time polymerase chain reaction in a series of 22 metastatic NETs with a median time of 10 months on the SSA therapy (range 2-82 months). The median duration of disease stabilization in patients who developed progression (n = 14) was 9 months (range 3-92 months). The median survival period for all patients was 44 months (range 3-175 months). According to RECIST criteria, one (5%) partial objective tumor response was obtained, disease stabilization was achieved in 10 (45%) patients, and progressive disease was observed in 11 (50%). Analysis of mRNA expression of the SSTR subtypes showed that SSTR2 and SSTR5 were expressed in all of the studied NETs; SSTR1 and SSTR4 in all but 3 tumors (86%); and SSTR3 in only 10 NETs (49%). Interestingly, our preliminary data suggest that only the levels of SSTR4, though it has the lowest affinity for SSA of all SSTR subtypes, were significantly associated with the stabilization of disease during SSA therapy (p = 0.0357). These levels correlated with time to progression (p = 0.0015) and overall survival (p = 0.0017) in NET patients.

Martinez-Alonso M, Llecha N, Mayorga ME, et al.
Expression of somatostatin receptors in human melanoma cell lines: effect of two different somatostatin analogues, octreotide and SOM230, on cell proliferation.
J Int Med Res. 2009 Nov-Dec; 37(6):1813-22 [PubMed] Related Publications
Somatostatin analogues (SAs) are potential anticancer agents. This study was designed to investigate the expression of somatostatin receptors (SSTRs) in melanoma cells and the effect of two SAs on cell proliferation and viability. Eighteen primary and metastatic human cutaneous melanoma cell lines were treated with octreotide and SOM230. Expression of SSTR1, SSTR2, SSTR3 and SSTR5 was assessed by real-time polymerase chain reaction. Proliferation, viability and cell death were assessed using standard assays. Inhibition was modelled by mixed-effect regression. Melanoma cells expressed one or more SSTR. Both SAs inhibited proliferation of most melanoma cell lines, but inhibition was < 50%. Neither SA affected cell viability or induced cell death. The results suggest that melanoma cell lines express SSTRs. The SAs investigated, under the conditions used in this study, did not, however, significantly inhibit melanoma growth or induce cell death. Novel SAs, combination therapy with SAs and their anti-angiogenic properties should be further investigated.

Klagge A, Krause K, Schierle K, et al.
Somatostatin receptor subtype expression in human thyroid tumours.
Horm Metab Res. 2010; 42(4):237-40 [PubMed] Related Publications
Somatostatin receptors (SSTR) are expressed in various endocrine tumours. The expression of SSTR at the tumour cell surface confers the possibility for diagnostic imaging and therapy of tumours using radiolabeled somatostatin analogues. The majority of currently available somatostatin analogues show a higher binding affinity for the SSTR2 subtype. To date, the precise expression pattern of the SSTR subtypes 1-5 in thyroid epithelial tumours remains to be determined. We investigated the mRNA expression of SSTR1-5 in benign and malignant epithelial thyroid tumours [20 cold thyroid nodules (CTNs), 20 toxic thyroid nodules (TTNs), 20 papillary, 20 follicular, and 5 anaplastic carcinomas (PTCs, FTCs, ATCs, respectively)] and compared them to normal surrounding thyroid tissues. Four out of five SSTR subtypes were detected in malignant thyroid tumours, benign neoplasia, and normal surrounding tissue with a predominant expression of SSTR2 and SSTR5, and a weak expression of SSTR1 and SSTR3. Weak SSTR4 mRNA expression was detected in some PTCs. Compared to normal thyroid tissue, SSTR2 was significantly upregulated in PTC and ATC. In addition significant upregulation of SSTR3 was found in PTC. SSTR5 mRNA expression was increased in PTC and FTC and significantly decreased in CTN and TTN compared to normal thyroid tissue. SSTR2 is the predominant subtype in thyroid epithelial tumours with a high expression pattern, in particular, in PTC . Perspectively, the expression of distinct SSTR in thyroid epithelial tumours might represent a promising avenue for diagnostics and therapy of advanced thyroid cancer with somatostatin analogues.

Taboada GF, Luque RM, Neto LV, et al.
Quantitative analysis of somatostatin receptor subtypes (1-5) gene expression levels in somatotropinomas and correlation to in vivo hormonal and tumor volume responses to treatment with octreotide LAR.
Eur J Endocrinol. 2008; 158(3):295-303 [PubMed] Related Publications
OBJECTIVE: To determine whether the somatostatin receptor subtype (SSTR) expression profile correlates with hormonal and tumor volume responses to postsurgical octreotide long acting repeatable (OCT LAR) treatment.
DESIGN AND METHODS: Quantitative real-time RT-PCR was used to evaluate the absolute mRNA copy numbers for all five SSTR subtypes in 22 somatotropinomas. Response to OCT LAR was studied by hormone levels (GH and IGF-I) and tumor volume (sella turcica magnetic resonance imaging).
RESULTS: SSTR5 was present at the highest level followed by SSTR2, SSTR3, SSTR1, and SSTR4 (2327 (1046-5555), 2098 (194-23 954), 97 (0-460), 14 (0-29 480), and 0 (0-652) copies respectively). Positive correlations were found between SSTR2 levels and the percentage decrease of GH and IGF-I after 3 (r=0.49, P<0.027 and r=0.49, P<0.029 respectively) and 6 (r=0.59, P<0.006 and r=0.58, P<0.008 respectively) months of OCT LAR. A negative correlation was found between SSTR5 mRNA levels and the percentage decrease of GH after 3 months of OCT LAR (r=-0.52, P=0.016, n=21). A higher SSTR2/SSTR5 ratio was observed among patients who obtained hormonal control with OCT LAR, when compared with those uncontrolled (2.4 (0.7-10) vs 0.3 (0.1-7.7), P=0.001). A ROC curve analysis showed a SSTR2/SSTR5 ratio of 1.3 as the best predictor of disease control, with a sensitivity of 88% and a specificity of 92% - area under curve, 0.9. A positive correlation was also found between SSTR2 mRNA levels and the percentage decrease in tumor volume after 6 months of OCT LAR (r=0.79, P=0.002, n=12).
CONCLUSIONS: Somatostatin receptor subtype 2 mRNA expression levels in somatotropinomas correlate positively with in vivo hormonal and tumor volume responses to OCT LAR.

Seidl C, Port M, Gilbertz KP, et al.
213Bi-induced death of HSC45-M2 gastric cancer cells is characterized by G2 arrest and up-regulation of genes known to prevent apoptosis but induce necrosis and mitotic catastrophe.
Mol Cancer Ther. 2007; 6(8):2346-59 [PubMed] Related Publications
Tumor cells are efficiently killed after incubation with alpha-emitter immunoconjugates targeting tumor-specific antigens. Therefore, application of alpha-emitter immunoconjugates is a promising therapeutic option for treatment of carcinomas that are characterized by dissemination of single tumor cells in the peritoneum like ovarian cancer or gastric cancer. In diffuse-type gastric cancer, 10% of patients express mutant d9-E-cadherin on the surface of tumor cells that is targeted by the monoclonal antibody d9MAb. Coupling of the alpha-emitter (213)Bi to d9MAb provides an efficient tool to eliminate HSC45-M2 gastric cancer cells expressing d9-E-cadherin in vitro and in vivo. Elucidation of the molecular mechanisms triggered by alpha-emitters in tumor cells could help to improve strategies of alpha-emitter radioimmunotherapy. For that purpose, gene expression of (213)Bi-treated tumor cells was quantified using a real time quantitative-PCR low-density array covering 380 genes in combination with analysis of cell proliferation and the mode of cell death. We could show that (213)Bi-induced cell death was initiated by G(2) arrest; up-regulation of tumor necrosis factor (TNF), SPHK1, STAT5A, p21, MYT1, and SSTR3; and down-regulation of SPP1, CDC25 phosphatases, and of genes involved in chromosome segregation. Together with morphologic changes, these results suggest that (213)Bi activates death cascades different from apoptosis. Furthermore, (213)Bi-triggered up-regulation of SSTR3 could be exploited for improvement of the therapeutic regimen.

Stec-Michalska K, Peczek L, Krakowiak A, et al.
Expression of somatostatin receptor subtype 3 in the gastric mucosa of dyspeptic patients in relation to Helicobacter pylori infection and a family history of gastric cancer.
J Gastroenterol Hepatol. 2008; 23(3):424-9 [PubMed] Related Publications
BACKGROUND AND AIM: The cytotoxic activity of Helicobacter pylori contributes significantly to the pathogenesis of gastric carcinoma. A preliminary study suggested that somatostatin receptor subtype 3 (SSTR3) might play a role in cell apoptosis and the growth of gastric cancer. The aim of the present study was to determine the influence of H. pylori infection and a family history of gastric cancer on the expression of SSTR3 in the gastric mucosa of non-cancer patients with dyspepsia.
METHODS: The expression of the SSTR3 gene in the gastric mucosa of the stomach antrum and corpus of 53 patients was determined by the use of quantitative reverse transcription-polymerase chain reaction.
RESULTS: The SSTR3 mRNA level was lower in the H. pylori-infected patients, as compared to the non-infected patients, independently of a family history of gastric cancer and stomach topography. The greatest decrease of approximately 40% and 35% (P < 0.05) was observed for the antrum of the H. pylori-positive patients without and with a family history of gastric cancer, respectively. In the corpus, these differences were much smaller, regardless of a family history of gastric cancer. Interestingly, for H. pylori-negative patients, the density (at the mRNA level) of the SSTR3 receptor in the antrum was higher than in the corpus mucosa.
CONCLUSIONS: A decrease in the density of SSTR3 (especially in the antrum) in individuals with H. pylori infection and particularly with a family history of gastric cancer may point to an environmental and inherited predisposition in the development of distal gastric cancer.

Horiguchi K, Yamada M, Umezawa R, et al.
Somatostatin receptor subtypes mRNA in TSH-secreting pituitary adenomas: a case showing a dramatic reduction in tumor size during short octreotide treatment.
Endocr J. 2007; 54(3):371-8 [PubMed] Related Publications
TSH-secreting adenoma is a rare pituitary adenoma, and the expression levels of the specific subtypes of somatostatin receptors (sstr) mRNAs have remained obscure. To determine the quantitative expression of the sstr1-5 mRNAs in TSH-secreting adenomas that may be related to the efficacy of treatment with a somatostatin analogue, expression of the sstr1-5 mRNAs was examined and compared in TSH-secreting adenomas and other pituitary adenomas. The pituitary adenomas were obtained at transsphenoidal surgery from 4 cases of TSH-secreting adenoma, including 1 patient showing a significant shrinkage of the tumor size after only 10 days of octreotide treatment, 2 patients without tumor size reduction and 1 patient without treatment, and 5 GH-secreting adenomas, 6 prolactinomas, 5 nonfunctioning adenomas, 4 ACTH-secreting adenomas and normal pituitaries at autopsy from 4 normal subjects. In comparison to the normal pituitary, sstr2A>sstr1>sstr5>sstr3 mRNAs were expressed in the TSH-secreting adenomas examined. No expression of sstr2B or sstr4 mRNA was observed. The expression level of sstr2 mRNA was significantly higher than those in normal pituitary, prolactinomas, ACTH-secreting and nonfunctioning pituitary adenomas. The patient with marked shrinkage of the tumor showed the highest expression of both sstr2 and sstr5 mRNAs among all the cases of pituitary adenoma. A TSH-secreting tumor without shrinkage showed a similar expression level of sstr2 mRNA. These findings demonstrated that TSH-secreting adenomas express sstr1, 2A, 3 and 5 mRNAs, predominantly sstr2A, and in addition to the expression of sstr2 mRNA, the expression level of sstr5 mRNA may be a factor affecting the tumor shrinkage by somatostatin analogues against TSH-secreting adenomas.

Taboada GF, Luque RM, Bastos W, et al.
Quantitative analysis of somatostatin receptor subtype (SSTR1-5) gene expression levels in somatotropinomas and non-functioning pituitary adenomas.
Eur J Endocrinol. 2007; 156(1):65-74 [PubMed] Related Publications
OBJECTIVE: It is believed that the variable effectiveness of somatostatin analogs in post-surgical management of somatotropinomas and non-functioning pituitary adenomas (NFPA) may be due in part to variable expression of somatostatin receptor isoforms (SSTR1-5), within and between pituitary tumor types.
DESIGN AND METHODS: Quantitative real-time RT-PCR was used to compare absolute mRNA copy numbers for all five SSTR isoforms in 23 somatotropinomas and 19 NFPA.
RESULTS: Somatostatin receptor subtype 5 mRNA was present at the highest level in somatotropinomas, followed by SSTR2>SSTR3>SSTR1>SSTR4. In contrast, SSTR3 mRNA was present at the highest level in NFPA, followed by SSTR2, while SSTR1, SSTR4, and SSTR5 transcripts were only detectable in select tumors. Among somatotropinomas, a positive correlation was found between SSTR2 mRNA levels and the percent decrease of GH (%GH) after 3 and 6 months of therapy with octreotide long acting repeatable (LAR) (r=0.51 and r=0.66; P=0.05 and P=0.008). Also the percent decrease of IGF-I (%IGF-I) after 3 months of octreotide LAR was negatively correlated with SSTR5 and %IGF-I after 6 months of octreotide LAR was positively correlated with SSTR2.
CONCLUSIONS: The present report is a large series examining SSTR mRNA levels in somatotropinomas and NFPA. These initial findings suggest that detailed knowledge of the SSTR mRNA expression profile in somatotropinomas can help to predict the hormonal response to therapy with LAR. Also, it appears that SSTR3 in NFPA may be a potential target for SSTR3 preferential or universal ligands such as pasireotide.

Yoshihara A, Isozaki O, Hizuka N, et al.
Expression of type 5 somatostatin receptor in TSH-secreting pituitary adenomas: a possible marker for predicting long-term response to octreotide therapy.
Endocr J. 2007; 54(1):133-8 [PubMed] Related Publications
In TSH-secreting pituitary adenomas (TSHoma), octreotide (OCT) therapy reduces tumor size and TSH secretion in some cases but not in others. As OCT acts through various types of somatostatin receptors (SSTRs), the different responses of TSHoma to OCT might be explained by the differences of SSTR expression. We therefore studied the expression of subtype-specific SSTR mRNA transcripts in tumor tissues by RT-PCR. Type 2 (SSTR2) mRNA transcripts were detected in all 8 tumors but those of SSTR3 and SSTR5 were demonstrated only in 5 of them. Serum TSH levels were decreased by OCT administration test in all patients but OCT therapy was effective in two patients out of three. SSTR5 mRNA was detected in two tumors from the responder, but not in one tumor that was resistant to OCT. These observations suggest that the temporal decrease of TSH by OCT may be mediated by SSTR2, and that the long term response to OCT therapy may be related with the expression of SSTR5. Therefore, the expression of SSTR5 in TSHoma may be a useful marker for predicting the outcome of the therapy, but further studies with larger numbers of patients are necessary.

Casarini AP, Pinto EM, Jallad RS, et al.
Dissociation between tumor shrinkage and hormonal response during somatostatin analog treatment in an acromegalic patient: preferential expression of somatostatin receptor subtype 3.
J Endocrinol Invest. 2006; 29(9):826-30 [PubMed] Related Publications
INTRODUCTION: About a third of acromegalic patients is resistant to available SS analogs (SA), octreotide (OCT) and lanreotide (LAN). Such resistance is related to reduction of SS receptor (SSTR) density or to a different expression of SSTR subtypes. There are 5 known SSTR subtypes. SSTR2 and SSTR5 are usually expressed in GH-secreting pituitary tumors, and both SA bind preferentially to SSTR2 and, to a lesser extent, to SSTR5. We herein describe an acromegalic patient who presented impressive tumor shrinkage without hormonal normalization during primary therapy with SA.
MATERIAL AND METHODS: This 23-yr-old male acromegalic patient was treated with slow-release LAN (LAN-SR), 30 mg every 10 days for six months, followed by OCT-LAR, 30 mg every 28 days for an additional six months with a 75% tumor volume reduction but without GH and IGF-I normalization. Subsequently, he underwent pituitary surgery and expression of SSTR in the removed tumor was performed by real time RT-PCR by the 2-deltaCt method, using GAPDH as internal control. All PCR products were confirmed by automated sequencing.
RESULTS: SSTR expression revealed an unusual profile, with almost exclusively expression of SSTR3.
CONCLUSIONS: These unusual clinical and receptor subtypes profile suggest an important role of SSTR3 on tumor shrinkage. The low affinity of LAN and OCT for this SSTR subtype could be compensated by its high expression in this GH-secreting pituitary macroadenoma.

Jaquet P, Gunz G, Saveanu A, et al.
BIM-23A760, a chimeric molecule directed towards somatostatin and dopamine receptors, vs universal somatostatin receptors ligands in GH-secreting pituitary adenomas partial responders to octreotide.
J Endocrinol Invest. 2005; 28(11 Suppl International):21-7 [PubMed] Related Publications
We report the comparative efficacy of a somatostatin receptor 1 and 5 subtypes (SSTR2 and SSTR5), and dopamine D2 (DAD2) compound, BIM-23A760, in suppressing GH secretion, in cell culture from human GH-secreting tumors, from patients partially responsive to long-term treatments with octreotide or lanreotide. In 18 tumors tested, the SSTR2, SSTR5, and DAD2 mRNAs were coexpressed. The SSTR2-selective analog, BIM-23197, the SSTR5-selective analog, BIM-23268, and the dopamine (DA) analog, BIM-53097, produced a mean maximal suppression of GH secretion (24 +/- 3, 20 +/- 3, and 20 +/- 3%, respectively) that was similar to that obtained with octreotide (23 +/- 3%). Nevertheless, based on individual responses, 60% of the tumors were mostly sensitive to the SSTR2 analog while 19 and 21% of the tumors were mainly responsive to the SSTR5 analog and to the DA analog, respectively. Among a series of new chimeric compounds that bind the SSTR2, SSTR5, and DAD2 receptors with variable affinities, BIM-23A760 produced greater maximal suppression of GH secretion than octreotide (38 +/- 2 vs 24 +/- 2%; p<0.03). The EC50 for BIM-23A760 was 2 pmol/l. In the presence of sulpride, the dose response inhibition of GH secretion by the trihybrid molecule, BIM-23A760, was partially reversed. The trihybrid produced also a maximal suppression of PRL greater than octreotide (74 +/- 5 vs 46 +/- 11%). When SSTRs pan inhibitors such as BIM-23A779 (binding affinity for SSTR1, SSTR2, SSTR3, SSTR5, respectively: 2.5, 0.3, 0.6, 0.6 nmol/l) or SOM230 were tested for their suppressive effects on GH secretion, they were less potent than the previous dopastatin hybrid molecule. After a brief exposure to a SSTR2-selective analog, BIM-23197, or to a DA analog, BIM-53097, the maximal GH suppression was achieved during 12 h. Under exposure to BIM-23A760, in the same conditions, maximal suppression of GH secretion lasted for 24 h. Such a longer biological effect, yet not explained, probably participates in the higher efficacy of BIM-23A760. The higher efficacy of BIM-23A760 is, at least partially, linked to its high affinity for the SSTR2 receptor subtype (IC50: 3 pmol/l). As compared to the dopastatin compound, the lower efficacy of the universal somatostatin ligands in the inhibition of GH secretion of GH-secreting tumors argues for the use of drugs targeted, according to specific receptors expression and functionality which may vary among the various classes of tumors.

Kumar U, Grigorakis SI, Watt HL, et al.
Somatostatin receptors in primary human breast cancer: quantitative analysis of mRNA for subtypes 1--5 and correlation with receptor protein expression and tumor pathology.
Breast Cancer Res Treat. 2005; 92(2):175-86 [PubMed] Related Publications
Somatostatin receptors (SSTRs) have been identified in most hormone-producing tumors as well as in breast cancer. In the present study, we determined SSTR1-5 expression in primary ductal NOS breast tumors through semi-quantitative RT-PCR and immunocytochemistry. The results from the analysis of 98 samples were correlated with several key histological markers and receptor expression. All five SSTR subtypes are variably expressed at the mRNA level in breast tumors with 91% of samples showing SSTR1, 98% SSTR2, 96% SSTR3, 76% SSTR4, and 54% SSTR5. SSTR1-5 are localized to both tumor cells and the surrounding peritumoral regions as detected by immunocytochemistry. Levels of SSTR mRNA, when corrected for beta-actin levels, were highest for SSTR3 followed by SSTR1, SSTR2, SSTR5, and SSTR4. Furthermore, there was good correlation between mRNA and protein expression with 84% for SSTR1, 79% for SSTR2, 89% for SSTR3, 68% for SSTR4, 68% for SSTR5, and 78% for all five receptors. SSTR1, 2 and 4 were correlated with ER levels whereas SSTR2 showed an additional correlation with PR levels. These correlations were independent of patient age and histological grade. Moreover, using immunocytochemistry, blood vessels exhibited receptor-specific localization for SSTR2 and SSTR5. Our results indicate significant correlations between mRNA and protein expression along with receptor-specific correlations with histological markers as well as ER and PR levels. Differential distribution of SSTR subtypes in tumors and receptor-specific expression in vascular structures may be considered as a novel diagnosis for breast tumors with receptor subtype agonists.

Bläker M, Schmitz M, Gocht A, et al.
Differential expression of somatostatin receptor subtypes in hepatocellular carcinomas.
J Hepatol. 2004; 41(1):112-8 [PubMed] Related Publications
BACKGROUND/AIMS: Somatostatin analogues inhibit cell proliferation by stimulation of distinct somatostatin receptor (SSTR) subtypes. In recent years, these compounds have been introduced into the therapy of advanced hepatocellular carcinoma (HCC). The efficacy of this treatment is under debate due to the controversial results of clinical trials. Despite the widespread clinical use of somatostatin analogues in HCC, little is known about the expression of each of the five SSTRs in these tumors.
METHODS: We analyzed the expression of SSTR subtypes in 56 HCCs by immunohistochemistry using subtype-specific antibodies. Six of the samples were also investigated by RT-PCR using subtype-specific oligonucleotide primers.
RESULTS: HCCs display differential, individual expression patterns as well as variable expression levels for SSTRs. The overall expression rate of SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 is 46, 41, 64, 0, and 75%, respectively. No significant correlation was observed between SSTR expression and tumor stage, differentiation, histological tumor type, or underlying liver disease.
CONCLUSIONS: Individual patterns and levels of SSTR expression might determine the response to treatment with somatostatin analogues in HCC. Selective treatment of these tumors based on the analysis of SSTR subtype expression might lead to an increase in response rates.

Arena S, Barbieri F, Thellung S, et al.
Expression of somatostatin receptor mRNA in human meningiomas and their implication in in vitro antiproliferative activity.
J Neurooncol. 2004; 66(1-2):155-66 [PubMed] Related Publications
Somatostatin receptors (SSTRs) have been detected in many normal and malignant tissues. This wide expression has been used for diagnostic, prognostic and therapeutic purposes. Five SSTR subtypes (SSTR 1-5) have been identified whose activation is responsible for the signal transduction through many different intracellular pathways. In the present study the expression of SSTR mRNA was determined by reverse-transcriptase (RT)-PCR in 42 meningiomas. About 88% of the tumors analyzed (37/42) were positive for at least one of the five SSTR subtypes displaying a variable pattern of expression of the different SSTR subtypes. SSTRI and SSTR2 were the most frequently mRNA detected (69% and 79% of the sample analyzed, respectively). The other subtypes were found in the 43%, 33% and 33% of cases for SSTR3, SSTR4 and SSTR5, respectively. In 22, out of 42 patients (52%) three or more SSTRs were detected. The expression of the different SSTR subtypes did not correlate with the expression of bcl-2 (apoptosis-associated protein) and MIB-1 (a proliferation marker), assessed by immunohistochemistry in a series of 34 tumor samples, while a correlation between the expression of SSTR3 and p53 was observed (p = 0.08). To evaluate a possible role of SSTR in the control of human meningioma cell proliferation, seven primary cell cultures obtained from fresh meningioma surgical tissues, were analyzed for their proliferative behavior by MTT assay and for their response to SST by [3H]-thymidine incorporation. In four out of six tumors (in one case no SSTR were detected) the treatment with SST caused a significant inhibition of DNA synthesis induced by the tumor-promoter phorbol myristate acetate. The evidence of the expression of SSTRs, mainly of SSTR2, in this series of specimens we analyzed altogether with in vitro antiproliferative effects of SST may open interesting perspectives for the diagnosis and the therapy of meningiomas.

Nielsen S, Mellemkjaer S, Rasmussen LM, et al.
Expression of somatostatin receptors on human pituitary adenomas in vivo and ex vivo.
J Endocrinol Invest. 2001; 24(6):430-7 [PubMed] Related Publications
UNLABELLED: The distribution and biologic activity of somatostatin receptor subtypes (SSTR) in pituitary adenomas is not clarified, especially regarding clinically non-functioning adenomas (NFPA). We therefore characterized SSTR in human pituitary adenomas by combining molecular biology and in vivo scintigraphy. Co-expression of gonadotropin-releasing hormone receptor (GnRH-R) mRNA was also assessed to see whether this feature was associated with adenoma subtype and SSTR status. Pituitary tumor biopsies were obtained during transsphenoidal adenomectomy from 21 patients (11 NFPA, 7 acromegalics, 2 prolactinomas, 1 Cushing's disease). Expression of mRNA encoding the 5 known SSTR subtypes and the GnRH-R was determined by RT-PCR. Twelve patients also underwent a pre-operative somatostatin receptor scintigraphy. Most adenomas (no.=18) expressed mRNA for more than one SSTR. SSTR2 mRNA was expressed in 18 cases, whereas SSTR4 was absent in all but one. SSTR3 was frequently expressed in NFPAs. Somatostatin receptor scintigraphy was positive in most cases, and with a significantly higher uptake index in GH-producing adenomas all of which expressed SSTR2 mRNA. The uptake index appeared to be related to receptor density rather than tumor volume. Expression of GnRH-R mRNA was found in both NFPAs and GH-producing adenomas and was not significantly associated with a particular SSTR subtype population.
IN CONCLUSION: 1) the distribution of SSTR is not significantly different between NFPA and GH-producing adenomas; and 2) somatostatin receptor scintigraphy reveals a higher uptake in GH-producing adenomas which is not significantly related to either SSTR distribution or tumor volume.

Lamszus K, Meyerhof W, Westphal M
Somatostatin and somatostatin receptors in the diagnosis and treatment of gliomas.
J Neurooncol. 1997; 35(3):353-64 [PubMed] Related Publications
Somatostatin analogues are in clinical use for the diagnosis and treatment of several oncological indications, namely pituitary adenomas and endocrine gastrointestinal tumors. In addition for a variety of malignancies their potential value is being studied. It has been speculated that somatostatin plays a role in the homeostasis of gliomas, and that gliomas could be susceptible to antiproliferative effects of somatostatin analogues. These assumptions were tested in 20 human cell lines derived from malignant gliomas and 4 glioblastoma tissue specimens, which were analyzed for their expression of the five known somatostatin receptor genes (SSTR1-5) and for the receptor function. Using semiquantitative PCR techniques, SSTR2 transcripts were found in all 20 cell lines and 4 glioblastomas, SSTR1 transcripts were detected in 9 cell lines and 4 glioblastomas, and SSTR3 transcripts were noted in 7 cell lines and 1 glioblastoma. SSTR4 and SSTR5 transcripts were only rarely detected. Gene expression profiles in glioblastoma tissue specimens resembled those of the cell lines in quality as well as quantity, with average transcript levels being highest for the SSTR2, followed by SSTR1 and SSTR3. However, when compared to GH3 anterior pituitary tumor cells, the relative amounts of PCR amplified DNA fragments were found to be at least 120 fold lower in glioblastoma cell lines and tumor specimens. Binding studies indicated that glioblastoma derived cells contained only minute amounts of SSTRs. No inhibition of proliferation was observed when 10 selected cell lines were incubated with somatostatin-14 (SST-14) or octreotide (SMS 201-995) at concentrations ranging from 10(-9) M to 10(-6) M, however, the proliferation of two cell lines was weakly stimulated after 6 days of incubation with 10(-6) M octreotide. The activity of adenylate cyclase, stimulated by forskolin, was inhibited by maximally 25% at 10(-6) M SST-14 or octreotide in one of 5 selected glioblastoma cell lines. Somatostatin peptides do not seem to exert anti-proliferative effects on glioblastoma cells and therefore appear to be of no obvious value for glioblastoma therapy. Most likely the amount of cell surface SSTRs is not sufficient to mediate antiproliferative effects. Since it has been described that SSTRs are detectable on most differentiated gliomas as well as astrocytes, it may be speculated that SSTRs may be relevant only in the context of well differentiated cellular programs but lose their significance with progressive dedifferentiation.

Jaïs P, Terris B, Ruszniewski P, et al.
Somatostatin receptor subtype gene expression in human endocrine gastroentero-pancreatic tumours.
Eur J Clin Invest. 1997; 27(8):639-44 [PubMed] Related Publications
Somatostatin and its analogues are now of current use in the management of endocrine gastroentero-pancreatic (GEP) tumours for the purpose of inhibiting hormone hypersecretion, carrying scintigraphy imaging and attempting to slow down tumour growth. Recent molecular studies have revealed the existence of up to five membrane somatostatin receptor subtypes termed SSTR1-5. However, whether or not scintigraphy imaging and tumour characteristics are correlated with specific subtype(s) remains unclear. SSTR1-5 messenger RNA (mRNA) transcripts were investigated in 38 endocrine GEP tumours (32 islet cell tumours, six carcinoid) using reverse transcriptase polymerase chain reaction (RT-PCR), and their distribution was analysed with respect to tumour characteristics and scintigraphy imaging. SSTR2, SSTR5 and SSTR4 were detected in most cases of endocrine GEP tumours (92%, 84%, and 82% respectively), but SSTR1 and SSTR3 were less frequently observed (66% and 50% respectively). No clear-cut correlation was found between tumour characteristics and subtype mRNA distribution. Moreover, no differences in mRNA subtype distribution were found between the 17 tumours detected by scintigraphy and the four tumours not detected by this method. Somatostatin receptor mRNA subtypes are widely expressed in endocrine GEP tumours, but their distribution is not correlated with tumour characteristics or scintigraphy positivity.

Sinisi AA, Bellastella A, Prezioso D, et al.
Different expression patterns of somatostatin receptor subtypes in cultured epithelial cells from human normal prostate and prostate cancer.
J Clin Endocrinol Metab. 1997; 82(8):2566-9 [PubMed] Related Publications
The transcripts of five SRIH receptor subtypes (SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5) were investigated by RT-PCR in epithelial cells (EC) and stromal cells (SC) from primary cultures of five normal human prostates and six prostate cancers. Primary cultures of prostate EC were established in serum-free keratynocyte medium with 5% FCS, epidermal growth factor, and bovine pituitary extract; SC were cultured in MEM with 10% FCS. Total RNA was extracted from EC and SC using a modified guanidine thiocyanate method. RT-PCR was performed after deoxyribonuclease treatment, using SSTR1-, SSTR2-, SSTR3-, SSTR4-, and SSTR5-specific-primers and adding glyceraldehyde-3-phosphate dehydrogenase-specific primers as internal control. A PCR product of the expected size of 334 bp, corresponding to SSTR1, was expressed only in EC from prostate cancer, whereas the expected 461-bp product of SSTR2 was found only in EC from normal prostate. SSTR3 messenger RNA was undetectable in normal and cancer EC, whereas SSTR4 and SSTR5 were present in both cell types. SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 messenger RNAs were not expressed in SC from both normal and cancer prostates. The RT-PCR method clearly demonstrated SSTRs' expression in the human prostate EC in vitro with differences between normal and tumoral samples. Our results may explain the ineffectiveness of some SSTR2 selective SRIH analogues in the treatment of prostate cancer and suggest that the absence of SSTR2 could represent a growth advantage in prostate cancer.

Hofland LJ, Lamberts SW
Somatostatin receptors and disease: role of receptor subtypes.
Baillieres Clin Endocrinol Metab. 1996; 10(1):163-76 [PubMed] Related Publications
A variety of human neuroendocrine tumours express SSTR. The five recently cloned human SSTR subtypes have a distinct chromosomal localization and pharmacological profile, and a tissue-specific expression pattern which suggests a differential function of SSTR subtypes in different organ systems. Most tumours carrying SSTR may express multiple SSTR subtypes, while the SSTR2 subtype is most predominantly expressed. The somatostatin analogue, octreotide, binds with high affinity to the SSTR2 and SSTR5 subtype and with a low affinity to the SSTR3 subtype. This analogue does not bind to the SSTR1 and SSTR4 subtypes. No major differences in the binding characteristics have been found between octreotide and two other clinically used octapeptide SST-analogues, BIM-23014 and RC-160. Our preliminary data indicate that an absent hormonal response to octreotide in vitro also implies an absent response to BIM-23014 and RC-160. The expression of the SSTR2 subtype in human tumours is proposed to be related to a clinical beneficial effect of octreotide treatment, while the functional significance of the other SSTR subtypes is not clear at present. In addition it is unclear which subtype(s) is involved in the antimitotic actions of SST(-analogues). Further developments with regard to the oncological application of SST analogues await the identification of the SSTR subtype(s) mediating anti-proliferative effects, as well as the development of analogues which selectively activate this subtype(s). A good correlation has been found between the presence of SSTR2 subtype mRNA and binding of [125I-Tyr3]octreotide in human primary tumours. Therefore, SSTR scintigraphy of human primary tumours and their metastases presumably visualizes SSTR2-expressing tumours, although it is reasonable to assume that SSTR5, and to a lesser extent SSTR3, when expressed simultaneously with SSTR2, also contribute to the visualization of tumours.

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