Inhibitory Effect Of Octreotide Research Articles

TGF-β1/Smad2/3 signaling pathway modulates octreotide antisecretory and antiproliferative effects in pituitary somatotroph tumor cells.

Octreotide (OCT) is used to inhibit hormone secretion and growth in somatotroph tumors, although a significant percentage of patients are resistant. It has also been tested in nonfunctioning (NF) tumors but with poor results, with these outcomes having been associated with SSTR2 levels and impaired signaling. We investigated whether OCT inhibitory effects can be improved by TGF-β1 in functioning and nonfunctioning somatotroph tumor cells. OCT effects on hormone secretion and proliferation were analyzed in the presence of TGF-β1 in WT and SSTR2-overexpressing secreting GH3 and silent somatotroph tumor cells. The mechanism underlying these effects was assessed by studying SSTR and TGFβR signaling pathways mediators. In addition, we analyzed the effects of OCT/TGF-β1 treatment on tumor growth and cell proliferation in vivo. The inhibitory effects of OCT on GH- and PRL-secretion and proliferation were improved in the presence of TGF-β1, as well as by SSTR2 overexpression. The OCT/TGF-β1 treatment induced downregulation of pERK1/2 and pAkt, upregulation of pSmad3, and inhibition of cyclin D1. In vivo experiments showed that OCT in the presence of TGF-β1 blocked tumor volume growth, decreased cell proliferation, and increased tumor necrosis. These results indicate that SSTR2 levels and the stimulation of TGF-β1/TGFβR/Smad2/3 pathway are important for strengthening the antiproliferative and antisecretory effects of OCT.

Inhibitory effects of octreotide on the progression of hepatic fibrosis via the regulation of Bcl-2/Bax and PI3K/AKT signaling pathways

In a previous study, we showed that octreotide alleviate hepatic fibrosis. However, its underlying molecular mechanisms are still poorly understood. In the current study, rats with CCl4-induced liver injury and Hepatic Stellate Cells (HSCs) were employed for in vitro and in vivo studies to observe the effects of octreotide on progression of liver fibrosis. The results in rats indicated that octreotide remarkably alleviated hepatic injury. The treated rats showed improved pathological manifestations and reduced liver indicators, e.g., liver weight, liver index and liver hydroxyproline (Hyp) content. Additionally, activities of serum total bilirubin (TBIL), aspartate transaminase (AST) and alanine transaminase (ALT), and serum levels of hyaluronic acid (HA), laminin (LN), type IV collagen (IV-C) and procollagen III peptide (PIIIP) also decreased. Furthermore, releasing inflammatory factors and proliferation of activated HSCs under different treatments were detected in which levels of IL-1β, IL-6, TNF-α decreased and hepatocytes proliferative capacity reduced through Bcl-2/Bax-dependent apoptosis. Finally, our results demonstrated that octreotide was able to exert an inhibitory effect on the activation of HSCs regulating the PI3K/AKT signaling pathway. In summary, our study corroborated that octreotide could prevent liver fibrosis probably via modulating Bcl-2/Bax and PI3K/AKT signaling pathway.

Anti-inflammatory Effect of Somatostatin Analogue Octreotide on Rheumatoid Arthritis Synoviocytes.

Somatostatin and its analogues are known to have modulatory effects on immune response and their anti-proliferative, anti-angiogenic, and analgesic properties make them attractive candidates for a therapeutic use in immune-mediated diseases, such as rheumatoid arthritis. Here, we demonstrate the ability of the somatostatin analogue octreotide to inhibit interleukin-15 and to increase interleukin-10 production by rheumatoid arthritis fibroblast-like synovial cells maintained in a chronic inflammatory state. We also prove that the inhibitory effect of octreotide on interleukin-15 and tumor necrosis factor-α production depended on the increase in interleukin-10, since neutralizing anti-interleukin-10 antibody was able to partially reverse this inhibition. In addition, our observations suggest an octreotide control on purinergic signaling, with an inhibitory effect on purinergic P2X and P2Y receptors activation. This would have great implications, considering the roles of P2 receptors in the onset of inflammation. Data here reported extend knowledge on the biological action of octreotide and underline its multiple effects on immune response, which could make octreotide an attractive and valid support for the therapy of diseases where several inflammatory mediators are involved, such as rheumatoid arthritis, and in which the simultaneous action on different aspects can be a successful strategy.

Epigenetic reprogramming using 5-azacytidine promotes an anti-cancer response in pancreatic adenocarcinoma cells

Curative management of pancreatic adenocarcinoma is limited because this malignancy remains resistant to most chemotherapeutic drugs. Strategies that reverse epigenetic alterations offer a unique opportunity for cancer cell reprogramming, which is valuable for development of new treatments. The aim of this work was to reprogram pancreatic ductal adenocarcinoma (PDAC) cells toward a less aggressive and drug-responsive phenotype. The process applied is called “epigenetic reprogramming”. To evaluate the efficiency of PDAC epigenetic reprogramming, we assessed tumor growth and drug response in PANC-1 cells after exposure to non-cytotoxic doses of the demethylating agent 5-azacytidine (5-AZA). Here, we showed that an epigenetic regimen using 5-AZA promoted an anti-cancer response by inhibiting PDAC tumor growth in vivo after the engraftment of treated cells. Remarkably, the subsequent addition of gemcitabine (GEM) to the 5-AZA-mediated reprogramming resulted in a marked growth inhibition effect in GEM-resistant pancreatic cancer cells. We observed that various characteristic peptides expressed in the pancreas, which included the antiproliferative hormone somatostatin (SST) and the SST receptor 2 (SSTR2), were significantly upregulated in the epigenetically reprogrammed PDAC cells. The inhibitory effect of octreotide (OCT), an SST analog, was tested on PDAC cells and found to be improved after cell reprogramming. Furthermore, we found that SST gene expression restoration following 5-AZA treatment or following knockdown of the DNA methyltransferase (DNMT) 1 enzyme was associated with the reversion of SST epigenetic silencing through regional CpG demethylation. Lastly, we confirmed the efficacy of 5-AZA-based epigenetic reprogramming in vivo using a PDAC tumor growth model. In conclusion, this study demonstrates that epigenetic reprogramming using the demethylating compound 5-AZA shows anti-cancer effects in PANC-1 cells and is potentially attractive for the treatment of solid tumors.

Locally produced insulin-like growth factor-1 by orbital fibroblasts as implicative pathogenic factor rather than systemically circulated IGF-1 for patients with thyroid-associated ophthalmopathy

To determine the correlation between clinical activity scores (CAS) of thyroid-associated ophthalmology (TAO) patients and their locally produced and/or systemically circulating insulin-like growth factor-1 (IGF-1), and to assess the possible pathogenic role of IGF-1 in TAO. Eighteen patients with TAO, and 16 age- and gender-matched controls were included in the present study. Among them, orbital tissue surgically collected from five TAO patients and five healthy controls was used for orbital fibroblasts (OFs) culture and in vitro study. Total and free IGF-1 in serum levels were determined by an ELISA kit for all the participants in this study. The IGF-1 concentration in culture media of OFs was determined using a noncompetitive time-resolved radioimmunoassay kit. The effect of octreotide (OCT), a somatostatin analog, on proliferation of OFs was assessed using the MTT assay. IGF-1 mRNA levels were measured by real-time polymerase chain reaction (PCR). Cultured OFs from both TAO patients and normal donors secreted IGF-1, and the secretion continued over a 72 hour period in vitro. IGF-1 secretion by OFs was elevated in the TAO group. Both the elevated secretion of IGF-1 and proliferation of OFs from TAO patients could be inhibited by OCT. Result of quantitative PCR showed that IGF-1 mRNA expression by OFs in TAO patients was up-regulated more than 2-fold compared with normal controls (P < 0.05), and this up-regulation was prevented by OCT treatment. Total and free serum IGF-1 levels in TAO patients were similar to those of normal controls. However, the IGF-1 level in cultured medium of OFs from TAO patients, but not serum levels of IGF-1, was positively correlated with CAS (r = 0.97, P = 0.017). Local production of IGF-1 by cultured OFs may be positively correlated with CAS, whereas systemically circulating IGF-1 may remain unchanged in TAO patients. Thus, locally produced IGF-1 may develop a role in the pathogenesis of TAO in an autocrine or paracrine fashion. The inhibitory effect of OCT on proliferating and IGF-1 mRNA levels of cultured OFs from TAO patients may be used as the mechanistic explanation for somatostatin analog as a valuable option in the treatment of TAO.

Octreotide inhibits capsaicin-induced activation of C and Aδ afferent fibres in rat hairy skin in vivo

1. The present study investigated whether the somatostatin receptor (SSTR) agonist, octreotide, could inhibit the activation of dorsal skin afferent fibres induced by local injection of capsaicin in the rat. 2. Single unit activity from Aδ mechano-heat sensitive (AMH; n = 41) and C mechano-heat sensitive (CMH; n = 30) afferents was recorded after their isolation in thin filaments from the dorsal cutaneous nerve branches. The effect of subcutaneous octreotide injection on the change in discharge rate and mechanical threshold induced by capsaicin was determined. 3. Capsaicin (0.05%) injection into the edge of the receptive field of both AMH and CMH units increased their discharge rate and decreased their mechanical threshold. Pre-injection of octreotide inhibited these responses, and co-application of SSTR antagonist, cyclosomatostatin, reversed the inhibitory effect of octreotide. 4. The present study provides electrophysiological evidence that the signal evoked by the somatostatin receptor inhibits the activation and mechanical sensitization evoked by capsaicin in the terminals in small-diameter sensory neurons.

Effects of Bone Morphogenetic Protein (BMP) on Adrenocorticotropin Production by Pituitary Corticotrope Cells: Involvement of Up-Regulation of BMP Receptor Signaling by Somatostatin Analogs

The mechanism by which somatostatin analogs suppress ACTH production by corticotropinomas has yet to be fully elucidated. We here studied the effects of somatostatin analogs on ACTH secretion using mouse corticotrope AtT20 cells focusing on the biological activity of bone morphogenetic proteins (BMPs). BMP ligands, receptors and Smads, and somatostatin receptors (SSTRs)-2, -3, and -5 were expressed in AtT20 cells. BMP-2, -4, -6, and -7 decreased basal ACTH production with BMP-4 effects being the most prominent. BMP-4 also inhibited CRH-induced ACTH production and proopiomelanocortin (POMC) transcription. However, the decrease in CRH-induced cAMP accumulation caused by BMP-4 was not sufficient to completely account for BMP-4 actions, indicating that ACTH suppression by BMPs was not directly linked to cAMP inhibition. CRH-activated ERK1/ERK2, p38-MAPK, stress-activated protein kinase/c-Jun NH(2)-terminal kinase, protein kinase C, and Akt pathways and CRH-induced ACTH synthesis was significantly decreased in the presence of U0126 or SB203580. Because BMPs attenuated CRH-induced ERK and p38 phosphorylation, it was suggested that BMP-4 suppresses ACTH production by inhibiting CRH-induced ERK and p38 phosphorylation. Somatostatin analogs octreotide and pasireotide (SOM230) significantly suppressed CRH-induced ACTH and cAMP production in AtT20 cells and reduced ERK and p38 phosphorylation. Notably, CRH-induced ACTH production was enhanced in the presence of noggin, a BMP-binding protein. The inhibitory effects of octreotide and SOM230 on CRH-induced ACTH production were also attenuated by noggin, implying that the endogenous BMP system plays a key role in inhibiting CRH-induced ACTH production by AtT20 cells. The findings that OCT and SOM230 up-regulated BMP-Smad1/Smad5/Smad8 signaling and ALK-3 and BMPRII and down-regulated inhibitory Smad6/7 establish that the activation of endogenous BMP system is functionally involved in the mechanism by which somatostatin analogs suppress CRH-induced ACTH production.

The multi-ligand somatostatin analogue SOM230 inhibits ACTH secretion by cultured human corticotroph adenomas via somatostatin receptor type 5

Currently, there is no effective medical treatment for patients with pituitary-dependent Cushing's disease. A novel somatostatin (SS) analogue, named SOM230, with high binding affinity to SS receptor subtypes sst(1), sst(2), sst(3) and sst(5) was recently introduced. We compared the in vitro effects of the sst(2)-preferring SS analogue octreotide (OCT) and the multi-ligand SOM230 on ACTH release by human and mouse corticotroph tumour cells. By quantitative RT-PCR the sst subtype expression level was determined in human corticotroph adenomas. In vitro, the inhibitory effect of OCT and SOM230 on ACTH release by dispersed human corticotroph adenoma cells and mouse AtT20 corticotroph adenoma cells was determined. In addition, the influence of dexamethasone on the responsiveness to OCT and SOM230 was studied. Corticotroph adenomas expressed predominantly sst(5) mRNA (six out of six adenomas), whereas sst(2) mRNA expression was detected at significantly lower levels. In a 72 h incubation with 10 nmol/l SOM230, ACTH release was inhibited in three out of five cultures (range -30 to -40%). Ten nmol/l OCT slightly inhibited ACTH release in only one of five cultures (- 28%). In AtT20 cells, expressing sst(2), sst(3) and sst(5), SOM230 inhibited ACTH secretion with high potency (IC(50) 0.2 nmol/l). Dexamethasone (10 nmol/l) pre-treatment did not influence the sensitivity of the cells to the inhibitory effect of SOM230, suggesting that sst(5) is relatively resistant to negative control by glucocorticoids. The selective expression of sst(5) receptors in corticotroph adenomas and the preferential inhibition of ACTH release by human corticotroph adenoma cells by SOM230 in vitro, suggest that SOM230 may have potential in the treatment of patients with pituitary-dependent Cushing's disease.

Inhibitory effect of octreotide on gastric cancer growth via MAPK pathway.

Somatostatin and its analogues may suppress the growth of various tumor cells. However, the effect of octreotide on growth of gastric adenocarcinoma is still largely unknown. This study was to explore if octreotide could inhibit the growth of gastric adenocarcinoma and its probable mechanisms. Proliferation of gastric cancer cell line affected by octreotide was determined by (3)H-thymidine incorporation. After xenografts of human gastric cancer were implanted orthotopically in stomach, nude mice were administrated octreotide for 8 weeks. The mRNA of somatostatin receptor in the SGC-7901 cells was detected by reverse transcription polymerase chain reaction technique. Extracellular signal-regulated protein kinase and c-Fos in gastric cancer tissues were measured by immunohistochemistry and Western blot. Activator protein-1 binding activity was examined by electrophoretic mobility sift assay. (3)H-thymidine incorporation into SGC-7901 cells was significantly decreased by octreotide in a concentration dependent manner. Either size or weight of tumors treated with octreotide was significantly reduced in vivo. The inhibition rate for tumor was 62.3 % in octreotide group. The genes of somatostatin receptors 2 and 3 were expressed in SGC-7901 gastric cancer cell lines. Extracellular signal-regulated protein kinase and c-Fos protein level were decreased in gastric adenocarcinoma treated with octreotide. Moreover, fetal calf serum stimulated activator protein-1 binding activity could be suppressed by octreotide potentially. Inhibition of sequential molecular events in MAPK pathway may interpret the mechanisms underlying the effect of octreotide on the growth of gastric adenocarcinoma.

Treatment of metastatic carcinoid tumours with octreotide

It was previously reported that treatment of metastatic carcinoid tumours with octreotide resulted in complete histological regression of such tumours in women.1 Previous cases of octreotide-related regression in carcinoid tumour masses were also reported.2-4 Our recent observation of a patient with hepatic metastases and carcinoid syndrome revealed that even though no discernible regression in tumour mass was found, octreotide treatment led to rapid improvement in hepatic function. A 79-year-old man was admitted to our hospital in November 2000, with a one-month history of facial flushing, headache and pressure in his ears. These attacks lasted 1–2 minutes and occurred several times a day. On examination, a purplish-red facial appearance, conjunctival hyperaemia and an enlarged liver were noted. Cardiac auscultation was within normal limits. Laboratory tests indicated hepatocellular damage and hepatic dysfunction (Table 1). He had no history of heavy alcohol consumption. Serological tests were negative for hepatitis A, B and C viruses. MRI of the abdomen revealed multiple metastases in the liver and multiple lymph nodes up to 2 cm in diameter in the para-aortic area. A liver biopsy was not attempted because of the prolonged partial thromboplastin time. His urinary 5-hydroxyindoleacetic acid level was elevated at 1326 μmol/24 h (normal range: 10.4–31.2). Imaging studies with CT and MR showed no evidence of a primary tumour. Because of the severity of the carcinoid symptoms and signs indicating hepatic dysfunction, we decided to treat this patient with a somatostatin analogue. Octreotide 50 μg three times daily was begun. During a two-week follow-up, the carcinoid symptoms markedly improved. In addition, hepatic function tests noticeably improved. A repeat MRI three weeks after the start of treatment showed no evidence of mass regression. This patient is on follow-up and octreotide treatment is continuing at the same dose for 12 months. The urinary 5-hydroxyindoleacetic acid level decreased to 271 μmol/24 h at month 4 of treatment. Abdominal MRI at 6 and 12 months of treatment showed no evidence of regression in hepatic and intra-abdominal lymph node metastases. He remains well and is still free of symptoms. Serial biochemical evaluation showed no evidence of deterioration in liver function. It is well known that somatostatin analogues have antiproliferative and antimitotic actions. The effect on liver function tests in our patient may not be explained by the decrease in tumour bulk, although we cannot exclude radiographically undetectable tumour regression. Somatostatin and analogues may have direct and indirect effects on hepatocytes and non-parenchymal liver cells.5, 6 Growth factors are able to modify hepatocyte proliferation in vivo, i.e. transforming growth factor β-1 produced by non-parenchymal liver cells is able to inhibit hepatocyte proliferation.7 Inhibitory effects of octreotide on the release of paracrine/growth factors from tumour cells might explain the recovery of liver function in the short term. Whatever the cause, octreotide led to symptomatic and functional recovery of metastatic carcinoid syndrome in our patient.

Inhibitory effects of octreotide on luminal cholecystokinin-releasing factor, plasma cholecystokinin, and pancreatic secretion in conscious rats.

Luminal cholecystokinin-releasing factor (LCRF), purified from rat intestinal secretions, is an intraluminal regulator of cholecystokinin (CCK) secretion during bile and pancreatic juice diversion. Because the LCRF content was not influenced by intravenous administration of atropine or somatostatin, the inhibitory effect of a potent somatostatin analog octreotide on LCRF content, the plasma CCK level, and pancreatic secretion was examined. Rats were prepared with bile and pancreatic cannulae and two duodenal cannulae and with an external jugular vein cannula. After 1.5-hour basal collection, bile and pancreatic juice was diverted for 2 hours, during which octreotide was infused intravenously or into the duodenal lumen. The changes in pancreatic secretion were recorded for 2 hours, and the plasma CCK level and LCRF content 2 hours after the treatment were measured. Bile and pancreatic juice diversion significantly increased pancreatic secretion and plasma CCK and LCRF levels. Intravenous infusion of octreotide (0.2 and 0.5 nmol/kg/hour) inhibited all parameters. Intraduodenal infusion of a lower dose of octreotide (33 nmol/kg/hour) inhibited pancreatic secretion, but did not inhibit CCK release or LCRF content. The higher doses (100 and 300 nmol/kg/hour) inhibited all parameters. Intravenous and intraduodenal administrations of octreotide inhibited CCK release and LCRF content and pancreatic secretion induced by bile and pancreatic juice diversion.

The inhibitory effect of octreotide on experimental colorectal carcinogenesis.

This study was conducted to investigate the effect of octreotide on colorectal carcinogenesis by administering octreotide either alone or combined with polyglactin, which is a well-known suture material, on chemically induced colorectal cancer development in rats. A total of 72 rats were divided into six groups. Two groups were subjected to a colotomy and repair using polyglactin. Another two groups underwent a sham procedure. The fifth group received octreotide alone and the sixth group served as a control. Both groups of rats in the polyglactin and sham groups received octreotide additionally. Methylnitrosourea was administered rectally to all the animals at a dose of 4 mg/kg per week for 20 weeks to induce carcinogenesis. Octreotide was injected twice a day at a total daily dose of 100 microg/kg. The thymidine labeling index was used to assess the synthesis phase fraction in order to measure the cell proliferation rate. The mean number of tumors per rat was significantly higher in the polyglactin group than in both the sham and control groups. It was significantly lower in the octreotide and polyglactin + octreotide groups than in the control and polyglactin groups, respectively. All the animals in the octreotide group had one tumor, while 66.6% of the control group had multiple tumors. The number of multiple tumors was significantly lower in the polyglactin + octreotide and sham + octreotide groups than in the polyglactin and sham groups, respectively. The mean tumor size in the octreotide group was significantly smaller than in the control group, whereas it was larger in the polyglactin group in comparison with the sham and control groups. It was also reduced in the polyglactin + octreotide group in comparison with the polyglactin group. The thymidine labeling index was significantly higher in the polyglactin group compared with both the sham and control groups, whereas it was lower in the octreotide group in comparison with the control group. The addition of octreotide administration to the polyglactin usage and the sham procedure significantly decreased the thymidine labeling indexes. These results indicate that octreotide reduces the frequency of tumor occurrence and has an inhibitory effect on its development in chemically induced experimental colorectal cancer. Octreotide can also reduce the enhancing effect of polyglactin on colorectal carcinogenesis when it is combined with polyglactin.

Effect of somatostatin on cholecystokinin-induced amylase release in rat pancreatic acini.

The effect of somatostatin on cholecystokinin-induced amylase release was investigated in isolated rat pancreatic acini. Acini were isolated by enzymatic digestion and incubated in a HEPES buffered Ringer's solution with testing reagents for 30 minutes at 37 degrees C. The activity of released amylase, cAMP, and inositol phosphate formation were measured. Intracellular calcium concentration ([Ca2+]i) was also checked. Somatostatin 14 and octreotide, a somatostatin analog, inhibited CCK-stimulated amylase release in a concentration-dependent manner. The inhibitory effect of octreotide on CCK-induced amylase release was not shown when the acini were treated with 8-Br-cAMP, irrespective of the presence of IBMX. Forskolin potentiated CCK-induced amylase release and this effect was blocked by octreotide treatment; although CCK-8 (3 x 10(-11) M) failed to stimulate cAMP formation, octreotide significantly inhibited basal cAMP formation in the acini. The increase of [Ca2+]i in response to CCK was inhibited by octreotide. However, CCK-induced inositol phosphate formation was not changed by 10(-9) M octreotide. Octreotide had no effect on CCK-stimulated tyrosine phosphorylation, and tyrosine phosphatase inhibitors (NaF and Na2WO4) did not influence the effect of octreotide on CCK-induced amylase release. From these results, we conclude that octreotide inhibits CCK-induced amylase release by inhibiting basal cAMP formation and decreasing the [Ca2+]i stimulated by CCK.

Central suppressive effect of octreotide on the hyperglycemic response to 2-deoxy- d-glucose injection or cold-swim stress in awake rats: possible mediation role of hypothalamic noradrenergic drive

Somatostatin (SRIH) and its analog have been reported to act within the central nervous system to suppress the hyperglycemic response to a variety of neural stimuli. On the other hand, the hyperglycemic response to 2-deoxy- d-glucose (2-DG) injection or cold-swim stress is well demonstrated to be closely associated with an increase in hypothalamic noradrenergic neuronal activity (NNA). To evaluate whether the suppression of the hypothalamic NNA response could be involved in the central mechanism whereby a SRIH analog inhibits the hyperglycemic response, octreotide, a clinically used long-acting octapeptide SRIH analog, was administered into the third cerebral ventricle of awake rats prior to the intraperitoneal injection of 2-DG or cold-swim stress. Hypothalamic noradrenaline (NA) and its neuronal metabolite, 3,4-dihydroxyphenylethyleneglycol (DHPG), were analyzed, and the ratio of DHPG to NA was used as an index of NNA. Intracerebroventricular (i.c.v.) pretreatment with octreotide suppressed the 2-DG-induced increase in hypothalamic NNA, accompanied by the inhibition of the serum glucose, NA and adrenaline responses. This suppressive effect of octreotide was dose-dependent. Similarly, i.c.v. pretreatment with octreotide prevented the hypothalamic NNA response to cold-swim stress, accompanied by a blockade of the increases in serum glucose, NA and adrenaline. A close relationship between hypothalamic NNA and serum glucose emerged from these studies. Intraperitoneal pretreatment with octreotide had no significant effect on the hyperglycemic or hypothalamic NNA response to 2-DG injection. These findings suggest that the inhibitory effect of octreotide on the hypothalamic NNA response to 2-DG injection or cold-swim stress is associated with the simultaneous suppression of the hyperglycemic response. Supporting the concept that hypothalamic NNA contributes to the modulation of blood glucose in stressful conditions, it is suggested that the suppression of the hypothalamic NNA response is, at least in part, involved in the central mechanism by which octreotide inhibits the hyperglycemic response to 2-DG injection or cold-swim stress.

Somatostatin receptor gene expression and inhibitory effects of octreotide on primary cultures of orbital fibroblasts from Graves' ophthalmopathy

To explore the mechanism underlying the effects of the somatostatin (SST) analogue octreotide in Graves' ophthalmopathy (GO), we investigated the expression of SST and of SST receptor (sst(1-5)) genes in primary cultures of fibroblasts established from retroorbital tissue of GO patients and of control subjects. We determined also SST specific binding sites by competitive binding of [(125)ITyr(11)]SST-14 and the effect of octreotide on cell growth, cAMP accumulation, Bcl-2 intracellular levels and apoptosis in GO fibroblast primary cultures. All primary cultures expressed the SST gene transcript and one or more ssts that have a high affinity for the two analogues (class 1 sst. The sst(2) transcript was found in nine, sst(3) in five and sst(5) in eight out of ten GO cell cultures. Sst(2) was detected in all six, and sst(3) in four out of the six control cell cultures. Sst(4) was absent from all samples, and sst(1) was found only in six out of the ten GO samples. SST-14 and octreotide inhibited the binding of [(125)I-Tyr(11)]SST-14 with a half-maximal inhibition of binding (IC(50)) of 0.80+/-0.37 and 33. 7+/- 33.1 nmol/l respectively in GO cell cultures, and with an IC(50) of 0.9 and 1.5 nmol/l in control cultures. Octreotide (10(-6) and 10(-7) M) significantly decreased (P<0.001) forskolin-induced but not basal cAMP accumulation; at both doses for 72 h it inhibited cell growth (20 and 55% respectively), and induced apoptosis (20 and 40%), and abolished Bcl-2 protein in cell lysates. In conclusion, SST and sst transcripts are expressed and functional in cultured retroorbital fibroblasts. The presence of class 1 sst in GO tissue and the inhibition exerted by octreotide on retroorbital cell growth and activity in vitro may account for the effects of SST analogue administration in vivo in GO.

Effects of octreotide and erythromycin on gastric myoelectrical and motor activities in patients with gastroparesis.

Simultaneous recordings of gastric manometry and myoelectrical activity were made in 10 patients with gastroparesis. Intravenous erythromycin (100 mg) was administered in the fasting state for a period of 30 min. Subcutaneous injection of octreotide (100 microg) was administered before one of the four identical test meals. It was found that octreotide significantly decreased the antral motility index (30-min fasting: 4.51+/-1.04 vs 1.75+/-0.97, P < 0.02; 60-min fed: 5.16+/-1.44 vs 3.4+/-1.41, P < 0.05) and the dominant power of the EGG (fasting power: 35.19+/-1.54 vs 30.84+/-1.57 dB, P < 0.004; postprandial power increase: 5.52+/-1.06 vs -0.27+/-0.87, P < 0.001). Erythromycin significantly increased the antral motility index (3.16+/-0.96 vs 9.5+/-0.61, P < 0.001) and the dominant power of the EGG (28.86+/-1.57 dB vs 33.55+/-1.59 dB, P < 0.005) in the fasting state. An improvement in the regularity of the gastric slow wave was also noted with erythromycin. It was concluded that: (1) the inhibitory effect of octreotide on postprandial gastric motility and myoelectrical activity suggests that caution should be exercised when octreotide is used in patients with gastroparesis; and (2) the stimulatory effect of erythromycin on gastric myoelectrical activity may enhance gastric motility and gastric emptying in patients with gastroparesis.

Potentiation of the anti-proliferative effects of anti-cancer drugs by octreotide in vitro and in vivo.

The somatostatin analogue octreotide (SMS 201-995) exerts potent anti-proliferative effects in a number of experimental cancer models. Here we report on the inhibitory effect of octreotide in combination with the chemotherapeutic agents mitomycin C, doxorubicin, 5-fluorouracil, or taxol on the growth of AR42J pancreatic cancer cells in vitro. The dose-dependent anti-proliferative effects of mitomycin C, doxorubicin and taxol were synergistically enhanced by octreotide. Combinations of octreotide and 5-fluorouracil resulted either in additive or, at high concentrations of the chemotherapeutic agent, in synergistic interactions. Combined treatment with doxorubicin and octreotide was also studied for time dependency and potential efficacy in tumour-bearing animals. Pretreatment (24 h) with doxorubicin resulted in clear synergy. However, pretreatment with octreotide 24 h prior to addition of doxorubicin resulted only in an additive interaction. It was shown in AR42J-tumour-bearing nude mice that the combination of doxorubicin and octreotide was well tolerated. Tumour growth was inhibited to 9% of controls, compared with 44% in the doxorubicin alone arm (day 14 of treatment). Our in vitro and in vivo interaction studies suggest that octreotide potentiates the effect of various chemotherapeutic agents in a synergistic or additive manner.

Somatostatin inhibits AP-1 function via multiple protein phosphatases

We have reported previously that the widespread inhibitory actions of somatostatin might be mediated by its ability to inhibit the expression of the immediate early genes c-fos and c-jun. The products of these genes form a heterodimeric transcription factor complex [activator protein 1 (AP-1)], which is known to be induced by treatment with phorbol esters. In the present study, we sought to investigate the mechanisms by which somatostatin inhibits immediate early gene expression. For our experiments, we used a rat pituitary adenoma cell line (GH3), which is known to express multiple subclasses of somatostatin receptors. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated both AP-1 binding and transcriptional activity in GH3 cells and the somatostatin analogue octreotide inhibited this response by 40-70%. In the presence of two different phosphatase inhibitors, sodium orthovanadate or okadaic acid, the ability of somatostatin to inhibit AP-1 binding and transcriptional activity was abolished. This effect of octreotide, which appears to be mediated by the SSTR2 and SSTR5 subtypes of somatostatin receptors, was paralleled by its ability to inhibit TPA-stimulated GH3 cell proliferation. Pretreatment of the GH3 cells with pertussis toxin (200 ng/ml) reversed the inhibitory effect of octreotide on both AP-1 function and cellular proliferation. Our observations lead us to conclude that somatostatin not only inhibits immediate early gene expression but also inhibits AP-1 binding and transcriptional activity via the action of several classes of protein phosphatases. This effect, which is pertussis toxin sensitive, might be one mechanism by which somatostatin inhibits cellular proliferation.

Octreotide, the reticuloendothelial system, and experimental liver tumour.

The inhibitory effect of octreotide on the growth of liver tumour is probably mediated (at least in part) by stimulation of the hepatic reticuloendothelial system (RES) activity. This study therefore investigated the effect of octreotide on the hepatic and splenic RES (assessed by the uptake of technetium 99m labelled albumin colloid, 99mTc-AC) in normal and tumour bearing rats and in animals treated with gadolinium chloride. The effects of gadolinium chloride and octreotide alone or in combination on the growth of liver tumour were also studied. Octreotide significantly stimulates both hepatic and splenic uptake of 99mTc-AC in normal rats and tumour bearing rats. In controls, the uptake of 99mTc-AC was significantly reduced by gadolinium chloride and was not changed by octreotide. RES blockade with gadolinium chloride significantly increased (p < 0.001) tumour growth compared with controls (hepatic replacement 42%; 95% confidence intervals (CI), 27.6 to 56.4 v 16.7%, 95% CI, 11.1 to 21.3%) whereas octreotide significantly inhibited (p < 0.001) the percentage hepatic replacement by tumour (0.7%; 95% CI, 0 to 2.3 v 16.7%; 95% CI, 11.1 to 21.3). This study highlights the importance of the RES in the development of liver tumour. Furthermore, octreotide inhibited the growth of liver tumour in rats with RES blockade, albeit to a lesser degree than in normal animals. These findings suggest that octreotide inhibits the growth of hepatic tumour by mechanisms other than stimulation of RES activity.

Effect of Octreotide Acetate on Pancreatic Exocrine and Endocrine Functions after Pancreatoduodenal Resection

In view of forecasting the effect of octreotide acetate (Sandostatin) in preventing fistula formation after pancreatic surgery, 9 patients, who had pancreatoduodenectomy 8-12 days before, underwent a 2-day study. The first day, by means of a catheter located in the jejunal loop separately anastomosed to the pancreatic remnant, basal and after secretin stimulation pancreatic secretion was evaluated. During the 2nd day the possible inhibitory effect of octreotide on basal and stimulated secretion was investigated. Under the experimental conditions of the study Sandostatin showed little effect on the water and bicarbonate increase as stimulated by secretin. A greater hormone inhibitory effect on amylase production and pancreatic endocrine function was seen. On the basis of these results the use of Sandostatin can hardly be seen as useful in preventing fistula formation after pancreatic resection.