Antiproliferative Effect Of Somatostatin Research Articles

Differential Expression of Somatostatin Receptor Subtype 1–5 Proteins in Numerous Human Normal Tissues

5 Human somatostatin receptor subtypes (sst1-5) mediate the antisecretory and antiproliferative effects of somatostatin. We examined somatostatin receptor protein expression in 28 human normal tissues. Immunostaining was performed with specific polyclonal antibodies for sst1-5. Staining pattern and distribution of ssts were evaluated. Anterior pituitary was positively stained for all 5 ssts. Pancreatic islets exhibited a positive staining for sst1-3 and sst5. Adrenal cortex expressed all 5 receptor subtypes, while the medulla was positive for sst3 and sst5 only. The thyroid expressed sst5 only, limited to single interfollicular cells. All 5 ssts were detected in the ovary, limited to luteinized granulosa cells of the corpus luteum. In the testis, sst2A was detected in the basal parts of the tubules, while sst5 was positively stained in the luminal parts. Sst1 was found in Leydig cells only. Stomach was positively stained for all 5 ssts. Investigation of the kidney revealed differential expression, with sst2A being found in the glomerules. The tubules expressed all 5 ssts. In the bone marrow cells of the granulocytopoiesis expressed sst2A only. The cerebellum expressed sst5 in a certain cell type, representing presumably Purkinje cells, while sst2A was stained in intercellular fibers. The expression of somatostatin receptor subtypes in a variety of human normal tissues may indicate a physiological role in these organs. Somatostatin analogues may offer new diagnostic and therapeutic implications for tumours related to these tissues. However, treatment of defined tumours with somatostatin analogues may also alter other normal tissues.

Successful Treatment of Idiopathic Intracranial Hypertension (IIH) with Octreotide (P03.229)

Objective: To document a case of successful treatment of Ideopathic Intracranial Hypertension(IIH) with octreotide. Background Growth hormone mediated hyper secretion of CSF is the most accepted mechanism for IIH. Data from 57,968 children in the Pfizer International Growth Study database showed that IIH was one of the major side effects (80%) of GH. Octreotide, a somatostatin analogue, inhibits pituitary growth hormone(GH)secretion, and antagonizes GH and insulin like growth factor (IGF) action by blocking GH receptors. Design/Methods: A 39 year-old, obese female presented with headaches, intermittent visual blurring, and floaters for two years. Her examination was unremarkable except for papilloedema on fundoscopic exam. Computerized perimetry revealed marked impairment in the bilateral nasal fields. Brain MRI was normal, MR venogram showed hypoplastic left transverse venous sinus. The cerebrospinal fluid pressure was 30 cm of water, with a pulsatile CSF column. After initial use of diuretics being ineffective, lumbar punctures were recommended, but patient was not compliant to it. Results: Treatment with subcutaneous octreotide resulted in significant improvement of headaches, and normalization of visual fields and papilloedema. She tolerated the treatment well, except for formation of gallstones, for which treatment was stopped at around 9 months. However she continues to have persistent normalization of the vision and normal computerized perimetry after one and half year in follow up. Conclusions: Somatostatin receptors (SSTR I-5) are found in the choroid plexus, arachnoid granulations, and retina, which mediate the antisecretory and antiproliferative effects of somatostatin, which could be responsible for decreasing the intracranial pressure in IIH. Panagopoulos et al. treated 26 IIH patients with Octreotide for 6-8 months. Majority showed improvement of headache, visual symptoms, papilloedema and significant reduction of CSF pressure, which was persistent in follow up for three years. Further studies are warranted for its potential use in the treatment of IIH. Disclosure: Dr. Vyas has nothing to disclose. Dr. Phadke has received personal compensation for activities with Teva Neurosciences, Berlex and Glaxo Smith Kline as a speaker.

Tumoral Prostate Shows Different Expression Pattern of Somatostatin Receptor 2 (SSTR2) and Phosphotyrosine Phosphatase SHP-1 (PTPN6) According to Tumor Progression

Prostate proliferation is dependent of androgens and many peptide hormones. Recent reports suggest that SSTR2 and SHP-1 were two fundamental components on antiproliferative effect of somatostatin. Many studies on SHP-1 revealed that the expression of this protein was diminished or abolished in several of the cancer cell lines and tissues examined. However, it is necessary to confront the cell lines data with real situation in cancer cases. Our studies have shown that epithelial expressions of both proteins, SHP-1 and SSTR2, in normal and benign hyperplasia are localized in the luminal side of duct and acinar cells. Also, SSTR2 is expressed in stromal cells. In malignant prostate tissue, SHP-1 was diminished in 28/45 cases or absent in 12/45 cases, whereas SSTR2 epithelial was diminished in 38/45 cases or lost in only 2/45 cases. The intensity of immunostained was highly negative correlated with Gleason grade for two proteins.

Effects of selective somatostatin analogs and cortistatin on cell viability in cultured human non-functioning pituitary adenomas

Clinically "non-functioning" human pituitary adenomas (NFPA) constitute about 35% of pituitary adenomas. Somatostatin receptors (SSTR) expression in these adenomas has previously been described both in vitro and in vivo, without evidence for a correlation with tumor volume or the therapeutic efficacy of somatostatin analogs. This study was performed on 13 surgically removed pituitary macroadenomas, diagnosed before surgery as "non-functioning". In addition, 3 growth hormone (GH)-secreting adenomas served as controls. A specimen from each tumor was dispersed and digested to isolate and culture the tumor cells, and the in vitro effects of SSTR2 and SSTR5 selective analogs and Cortistatin (CST) (100nM) on cell viability were studied. The quantity of viable cells was estimated using the XTT method. RNA purification of tumor samples and subsequent RT-PCR studies for SSTR2 and SSTR5 expression were performed. Somatostatin analog with high affinity for SSTR2 reduced cell viability by 20-80% in 8 of 13 NFPAs studied, all expressing the SSTR2. The inhibitory effect on cell viability of SSTR5-selective analog was 15-80% in 10 of 13 NFPAs studied, all but three expressing the SSTR5. CST, however, effectively reduced cell viability in only 6 NFPAs. Cell viability was inhibited by all peptides studied in 2 out of 3 GH-secreting adenomas, expressing both receptors. The third adenoma responded to SSTR2 analog and expressed only SSTR2. These results suggest the involvement of SSTR2 and SSTR5 in the anti-proliferative effects of somatostatin; however, CST is less potent in reducing cell viability in these tumors.

Somatostatin/somatostatin receptor signalling: Phosphotyrosine phosphatases

Activation of phosphotyrosine phosphatases (PTPs) by somatostatin receptor (SSTR) represents one of the main intracellular mechanisms involved in the antiproliferative effect of somatostatin (SST) and analogues. Since their molecular cloning, the role of PTPs is emerging as a major regulator of different cell functions including cell proliferation, differentiation, cell to cell interactions, cell matrix adhesion and cell migration. It was demonstrated that PTPs possess high substrate specificity and their activity is tightly regulated. Importantly, different G protein-coupled receptors transduce their biological activities through PTPs. PTPs were identified as down-stream effectors of SSTRs to transduce antiproliferative signals, and so far, three family members (SHP-1, SHP-2 and DEP-1/PTPeta) have been identified as selective SSTR intracellular effectors. Here, the molecular mechanisms leading SSTRs to regulate PTP activity are discussed, focusing on recent data showing a close interplay between PTPs and tyrosine kinases to transduce tumoral cell growth arrest following SST analogs administration.

The activation of the phosphotyrosine phosphatase eta (r-PTP eta) is responsible for the somatostatin inhibition of PC Cl3 thyroid cell proliferation.

The aim of this study was the characterization of the intracellular effectors of the antiproliferative activity of somatostatin in PC Cl3 thyroid cells. Somatostatin inhibited PC Cl3 cell proliferation through the activation of a membrane phosphotyrosine phosphatase. Conversely, PC Cl3 cells stably expressing the v-mos oncogene (PC mos) were completely insensitive to the somatostatin antiproliferative effects since somatostatin was unable to stimulate a phosphotyrosine phosphatase activity. In PC mos cells basal phosphotyrosine phosphatase activity was also reduced, suggesting that the expression of a specific phosphotyrosine phosphatase was impaired in these transformed cells. We suggested that this phosphotyrosine phosphatase could be r-PTP eta whose expression was abolished in the PC mos cells. To directly prove the involvement of r-PTP eta in somatostatin's effect, we stably transfected this phosphatase in PC mos cells. This new cell line (PC mos/PTP eta) recovered somatostatin's ability to inhibit cell proliferation, showing dose-dependence and time course similar to those observed in PC Cl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTP eta did not restore the antiproliferative effects of somatostatin. PC mos/PTP eta cells showed a high basal phosphotyrosine phosphatase activity which, similarly to PC Cl3 cells, was further increased after somatostatin treatment. The specificity of the role of r-PTP eta in somatostatin receptor signal transduction was demonstrated by measuring its specific activity after somatostatin treatment in an immunocomplex assay. Somatostatin highly increased r-PTP eta activity in PCCl3 and PC mos/PTP eta (+300%, P < 0.01) but not in PCmos cells. Conversely, no differences in somatostatin-stimulated SHP-2 activity, (approximately +50%, P < 0.05), were observed among all the cell lines. The activation of r-PTP eta by somatostatin caused, acting downstream of MAPK kinase, an inhibition of insulin-induced ERK1/2 activation with the subsequent blockade of the phosphorylation, ubiquitination, and proteasome degradation of the cyclin-dependent kinase inhibitor p27(kip1). Ultimately, high levels of p27(kip1) lead to cell proliferation arrest. In conclusion, somatostatin inhibition of PC Cl3 cell proliferation requires the activation of r-PTP eta which, through the inhibition of MAPK activity, causes the stabilization of the cell cycle inhibitor p27(kip1).

Expression of somatostatin receptor subtypes and growth inhibition in human exocrine pancreatic cancers.

The antiproliferative effects of somatostatin and its analogs on human pancreatic cancers were studied: (1) by evaluating the gene expression of somatostatin receptor (sstr) subtypes in human pancreatic cancer cell lines and cancer tissue specimens, (2) by evaluating the antiproliferative effects of somatostatin analogs, and (3) by evaluating the effect of sstr-2 cDNA transduction. Using a reverse transcriptase polymerase chain reaction (RT-PCR), the gene expression of five sstr subtypes (sstr-1 to -5) was examined in eight cell lines, and in ten pancreatic cancer tissues and in the normal surrounding pancreatic tissues. The antiproliferative effects of somatostatin (SS) -14 and its two analogs (SMS 201-995, RC-160) were examined by means of an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (thiazolyl blue)) assay on three cell lines and Panc-1 transfectants with human sstr (hsstr)-2A cDNA. Sstr-2 was expressed in all samples tested. All examined cell lines simultaneously expressed sstr-2 and -5, while most of the examined pancreatic cancer tissues did not express both of these subtypes simultaneously. Somatostatin analogs inhibited epidermal growth factor (EGF)-stimulated pancreatic cancer cell proliferation. The cell proliferation was further and significantly inhibited by 14% in stable transfectants of Panc-1 cells with hsstr-2A. Based on these findings, it is concluded that somatostatin analogs with their antiproliferative effects mediated by sstr-2 could be potentially useful in the treatment of pancreatic cancers.

Somatostatin receptor type 2 mediated suppression of Helicobacter pylori proliferation in vitro

Backeround & Aims: As is shown in somatostatin action to cell proliferation, somatostatin shows antiproliferative effect on Helicobacter pylori (H. pylori) in vitro from our preliminary data. At least five different types of somatostatin receptor (SSTR-1 to SSTR-5) have been cloned from various tissues. We investigated which type(s) of receptor may be involved in somatostatin action against H. pylori proliferation in vitro. Methods: H. pylori (ATCC43504, 103 CFU/mL) was cultured in 5 mL Brucella broth. Bacterial number was calculated 48 h after incubation by counting the colonies on the blood agar. Chemicals were dissolved in absolute methanol and added into the broth at a final methanol concentration of 1%. Somatostatin analogs (MK-678: high affinity for type 2, BIM-23052: for type 3 & 5, BIM-23268: for type 5 with some affinity for type 1 & 3, and BIM-23295: for type 2, 3 & 4) are gifts from Dr. D. H. Coy (Tulane Univ. Med. Cntr. New Orleans, LO). Exp.1) The effect of somatostatin and somatostatin analogs (10 -n mol/L) on H. pylori proliferation was investigated. Exp. 2) The influence of purified IgG against SSTR-1 peptide [41-52] (SSTR-1-Ab: 1.0 og/mL), IgG against SSTR-2 peptide [31-41] (SSTR-2-Ab: 1.0 pg/mL) produced and characterized in our laboratory (Endocrine Regul. 29:189,1995 & 30:67,1996) or IgG from nonimmune rabbit serum (Control-IgG: 1.0 lag/mL) on somatostatin (10 -n mol/L)-induced antiproliferative effect on H. pylori was tested. Results: 1) Somatostatin at 10 -H mol/L significantly inhibited proliferation of ATCC43504 by 92%. MK-678 and BIM-23295 also dramatically suppressed proliferation by 89% and 79%, respectively (P<0.01). BIM-23268 less potent, but significantly (P<0.05) showed an antiproliferative effect. In contrast, BIM-23052 had no effect. 2) Neither SSTR-1-Ab nor SSTR-2-Ab itself modified H. pylori proliferation. In Control-lgG treated group, somatostatin inhibited H. pylori proliferation by 88%. This antiproliferative effect of somatostatin was partially blocked by SSTR-2-Ab co-incubation by 52% (P<0.05). SSTR-1-Ab had no effect. (Each bar represents the mean _+ SEM of 5 samples. **P<0.01 vs respective vehicle, #P<0.05 vs Control-IgG+Somatostatin)

Somatostatin analogs affect proliferation of human thyroid carcinoma cell lines in vitro.

Antiproliferative effects of somatostatin (SRIH) analogs were investigated in human thyroid carcinoma cell lines. Membrane preparations from six human thyroid cell lines, including follicular (RO 87-M-1 and RO 82-W-1), papillary (NPA87), and anaplastic (RO 90-D-1) carcinomas, a follicular adenoma, as well as benign and malignant human thyroid tissues, contained high affinity SRIH-binding sites. Ligand-binding studies ([125I]Tyr11-SRIH) demonstrated mean dissociation constants ranging from 114-224 pmol/L, and 20-154 fmol/mg membrane protein mean receptor sites, in cell lines. Four cell lines were grown for 3 days in monolayers with SRIH analogs (octreotide or MK0678) at concentrations from 0.05-100 nmol/L in serum-free medium to assess changes in cell numbers. At the highest dose, MK0678 produced dose-dependent inhibition of growth in RO 87-M-1 and NPA87, each to about 70% of that in control cells. Octreotide produced dose-dependent stimulation of growth in RO 87-M-1 cells, but caused growth inhibition in NPA87 cells, with loss of effect at the highest dose. RO 82-W-1 did not respond to MK0678, yet caused biphasic inhibition with octreotide (75% and 45% of control cell numbers at 0.05 and 100 nmol/L doses, respectively). Anaplastic cells, RO 90-D-1, did not respond to either analog despite similar ligand binding. Addition of epidermal growth factor (100 micrograms/L) or TSH (200 mU/L) increased the sensitivity of RO 87-M-1 cells to growth inhibition by the lowest dose of MK0678, producing biphasic dose-response curves. In conclusion, the present data demonstrate specific SRIH binding to membranes of thyroid carcinoma cells and tissues as well as discordant growth effects of different SRIH analogs on the same cell lines. This may be a result of differential stimulation and regulation of distinct SRIH receptor subtypes.

Inhibition of DNA synthesis by somatostatin in rat hepatocytes stimulated by hepatocyte growth factor or epidermal growth factor

The antiproliferative effects of somatostatin on hepatocytes stimulated by hepatocyte growth factor (HGF) or epidermal growth factor (EGF) were investigated using primary cultures of adult rat hepatocytes. Somatostatin inhibits HGF-induced (at a dose of 10 ng/mL) or EGF-induced (at a dose of 100 ng/mL) 3H-thymidine incorporation into hepatocytes in a dose-dependent manner (10−10 to 10−8 M). This inhibition was confirmed by autoradiography. The effect of somatostatin was nontoxic as judged by preserved albumin synthesis, a marker for differentiated hepatocyte function. In the presence or absence of somatostatin, neither HGF nor EGF significantly altered intracellular cyclic adenosine monophosphate (cAMP). We conclude that somatostatin is a potent inhibitor of HGF-or EGF-induced deoxyribonucleic acid synthesis in adult rat hepatocytes. The mechanism of this inhibition appears to be independent of cAMP. The significance of somatostatin in liver regeneration has yet to be

Antiproliferative effects of somatostatin and the somatostatin analog SMS 201-995 on three human breast cancer cell lines.

The antiproliferative effect of somatostatin and the somatostatin analog SMS 201-995 on three human breast cancer cell lines (CG5, T 47 D, and ZR 75-1) is reported. Both peptides markedly inhibited CG5 cell growth with a maximal inhibition of about 40% as compared with control cells. The antiproliferative effect of somatostatin on T 47 D and ZR 75-1 cells was much less evident. These results suggest that somatostatin is a peptide inhibitory factor for human breast cancer cells. Possible therapeutic implications of these findings are still to be investigated.

Somatostatin inhibits rapid centrosomal separation and cell proliferation induced by epidermal growth factor.

The role of endogenous growth inhibitors in the regulation of cell proliferation is unclear. Although there are numerous studies on the stimulatory effect of peptide hormones such as insulin, the somatomedins and epidermal growth factor (EGF) on cell proliferation, little is known about the existence of hormones that might exert an antiproliferative effect on cells. Somatostatin (SS), a cyclic tetradecapeptide hormone that is widely distributed in the body, exerts an inhibitory effect on numerous cellular processes. We observed that SS at concentrations of 10(-8) - 10(13M), inhibited EGF-induced centrosomal separation, which recent evidence suggests is necessary for DNA synthesis in response to EGF. This SS effect was associated with inhibition of DNA synthesis and cell replication induced by EGF in gerbil fibroma and HeLa cells. Inhibition of centrosomal separation and the consequent antiproliferative effect of SS may represent a biologically significant action of this ubiquitous hormone.