Inhibition of endothelial proliferation by the somatostatin analogue SOM230

Demystifying "Steroid Withdrawal" During Remission in Cushing's Disease: Is Mineralocorticoid Replacement the Answer?

OBJECTIVE

To study renin-angiotensin-aldosterone axis status (RAAS) in patients of Cushing's disease (CD) at baseline and 6 weeks after curative trans-sphenoidal surgery and evaluate the role of mineralocorticoid replacement in the resolution of "steroid withdrawal syndrome" (SWS). Postoperative RAAS status had not been evaluated in previous studies, although aldosterone levels have been shown to be suppressed during medical therapy with pasireotide and cabergoline.

MATERIALS AND METHODS

This was a prospective, single-center study. Patients with CD, aged between 15-75 years, undergoing curative pituitary surgery were recruited. An 8 am and 11 pm cortisol and adrenocorticotropic hormone (ACTH) were measured at baseline. An 8 am cortisol was measured 6 weeks after surgery to demonstrate remission. Plasma-renin activity and plasma-aldosterone concentration were measured at baseline and 6 weeks after curative surgery.

RESULTS

A total of 14 patients (11 female, 3 male) were recruited initially, of these 8 patients completed the study. The plasma-renin activity was not suppressed at baseline and did not rise significantly after surgery (P = 0.717). However, plasma-aldosterone concentration was in the low-normal range at baseline and had risen significantly 6 weeks after surgery (P = 0.013). No difference was noted in subgroups with or without hypertension.

CONCLUSION

Curative pituitary surgery leads to normalization of plasma-aldosterone concentration in patients with CD just 6 weeks after surgery. Hence, mineralocorticoid replacement may not prove beneficial in alleviating the "SWS" in postsurgical CD patients who have achieved remission.

Role of the tumor microenvironment in digestive neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a group of heterogeneous tumors whose incidence increased over the past few years. Around half of patients already present with metastatic disease at the initial diagnosis. Despite extensive efforts, cytotoxic and targeted therapies have provided only limited efficacy for patients with metastatic GEP-NETs, mainly due to the development of a certain state of resistance. One factor contributing to both the failure of systemic therapies and the emergence of an aggressive tumor phenotype may be the tumor microenvironment (TME), comprising dynamic and adaptative assortment of extracellular matrix components and non-neoplastic cells, which surround the tumor niche. Accumulating evidence shows that the TME can simultaneously support both tumor growth and metastasis and contribute to a certain state of resistance to treatment. In this review, we summarize the current knowledge of the TME of GEP-NETs and discuss the current therapeutic agents that target GEP-NETs and those that could be of interest in the (near) future.

Pasireotide is more effective than octreotide, alone or combined with everolimus on human meningioma in vitro

Pasireotide is a somatostatin analog (SSA) that targets somatostatin receptor subtype 1 (SST1), SST2, SST3, and SST5 with a high affinity. Pasireotide has a better antisecretory effect in acromegaly, Cushing's disease, and neuroendocrine tumors than octreotide. In this study, we compared the effects of pasireotide to those of octreotide in vitro on meningioma primary cell cultures, both alone and in combination with the mTOR inhibitor everolimus. Significant mRNA expression levels of SST1, SST2, and SST5 were observed in 40.5%, 100%, and 35% of meningioma samples, respectively. Pasireotide had a significantly stronger inhibitory effect on cell proliferation than octreotide. The effect of pasireotide, but not of octreotide, was significantly stronger in the group expressing the highest level of SST1 mRNA. Combined treatment with pasireotide and everolimus induced a higher reduction in cell viability than that with octreotide plus everolimus. Moreover, pasireotide decreased Akt phosphorylation and reversed everolimus-induced Akt hyperphosphorylation to a higher degree than octreotide. Using 4E-BP1 siRNA (si4E-BP), we demonstrated that 4E-BP1 protein silencing significantly reversed the response to everolimus, both alone and in combination with SSAs. Moreover, si4E-BP completely reversed the inhibition of cyclin D1 expression level and the increase in p27kip1 induced by SSAs, both alone and in combination with everolimus. Our results strongly support the need for further studies on the combination of pasireotide and everolimus in medical therapy for meningiomas.

Successful Medical Treatment of Adult Nesidioblastosis With Pasireotide over 3 Years: A Case Report

Nesidioblastosis is a rare cause of endogenous hyperinsulinemic hypoglycemia in adults. Diagnosis is often challenging and therapeutic options are scarce.In 2009, a 46-year-old female patient presented with recurrent severe hypoglycemia and immediate recovery after glucose ingestion. Although 72-h-fasting test was positive, various imaging technologies (sonography, computed tomography, somatostatin receptor scintigraphy, dopamine receptor positron emission tomography [DOPA-PET]) were negative. Endoscopic ultrasound revealed a lesion in the pancreatic corpus, whereas selective arterial calcium stimulation test, portal venous sampling and GLP-1-receptor scintigraphy were indicative of a lesion in the pancreatic tail, which was surgically removed. The histopathologic examination revealed beta cell hyperplasia and microadenomas expressing glucagon. After surgery, the patient was free of symptoms for 6 months, after which hypoglycemic episodes recurred. After unsuccessful treatment with corticosteroids and somatostatin analogs, treatment with pasireotide, a novel somatostatin analog with high affinity to somatostatin receptor 5 and a possible side effect of hyperglycemia, was initiated (0.6 mg BID). To date, our patient has been free of severe hypoglycemic episodes ever since. Yearly repeated imaging procedures have shown no abnormities over the last 3 years.We report for the first time that pasireotide was successfully used in the treatment of adult nesidioblastosis.

Pasireotide for the Medical Management of Feline Hypersomatotropism

Background

Feline hypersomatotropism (HST) is a cause of diabetes mellitus in cats. Pasireotide is a novel multireceptor ligand somatostatin analog that improves biochemical control of humans with HST.

Hypothesis/Objectives

Pasireotide improves biochemical control of HST and diabetes mellitus in cats.

Animals

Hypersomatotropism was diagnosed in diabetic cats with serum insulin‐like growth factor‐1 (IGF‐1) concentration >1,000 ng/mL by radioimmunoassay and pituitary enlargement.

Methods

Insulin‐like growth factor 1 was measured and glycemic control assessed using a 12‐hour blood glucose curve on days 1 and 5. On days 2, 3, and 4, cats received 0.03 mg/kg pasireotide SC q12h. IGF‐1, insulin dose, and estimated insulin sensitivity (product of the area under the blood glucose curve [BGC] and insulin dose) were compared pre‐ and post treatment. Paired t‐tests or Wilcoxon signed rank tests were employed for comparison where appropriate; a linear mixed model was created to compare BGC results.

Results

Insulin‐like growth factor 1 decreased in all 12 cats that completed the study (median [range] day 1: 2,000 ng/mL [1,051–2,000] and day 5: 1,105 ng/mL [380–1,727], P = .002, Wilcoxon signed rank test). Insulin dose was lower on day 5 than on day 1 (mean reduction 1.3 [0–2.7] units/kg/injection, P = .003, paired t‐test). The product of insulin dose and area under the BGC was lower on day 5 than day 1 (difference of means: 1,912; SD, 1523; u × mg/dL × hours, P = .001; paired t‐test). No clinically relevant adverse effects were encountered.

Conclusions

Short‐acting pasireotide rapidly decreased IGF‐1 in cats with HST and insulin‐dependent diabetes. The decrease in IGF‐1 was associated with increased insulin sensitivity.

Pasireotide in Acromegaly: An Overview of Current Mechanistic and Clinical Data

BACKGROUND

Acromegaly is an insidious neuroendocrine disorder caused by hypersecretion of growth hormone (GH) by a somatotroph adenoma. Somatostatin receptor ligands (SRLs) are recommended as first-line medical therapy in patients for whom surgery has failed or is contraindicated. There are 5 known somatostatin receptor subtypes (SSTRs), 2 of which, i.e. SSTR2 and SSTR5, are expressed by a majority of somatotroph adenomas. The currently available SRLs, i.e. octreotide and lanreotide, primarily bind to SSTR2. Pasireotide (SOM230) is a new multireceptor-targeted SRL which has a broader binding profile and an increased affinity for SSTR1, 2, 3, and 5.

METHODS

PubMed searches were performed to identify all of the available published English language data on pasireotide with regard to the mechanism of action, in vitro effects, and clinical data.

RESULTS

Preclinical studies have demonstrated that pasireotide has a broader range of functional activity than octreotide. Recently, the efficacy of pasireotide in attenuating GH and insulin-like growth factor 1 (IGF-1) levels in patients with acromegaly has been evaluated in phase III clinical trials. Pasireotide demonstrated superiority over octreotide in achieving biochemical control (i.e. GH ≤2.5 µg/l and age- and sex-matched IGF-1 normalization) in patients with acromegaly, as well as significant efficacy in treating patients who were previously inadequately controlled on the maximum allowed doses of octreotide and lanreotide. Pasireotide-induced hyperglycemia was the most concerning adverse event but was reversible upon discontinuation of pasireotide.

CONCLUSION

The clinical data support pasireotide as a promising new therapy for the treatment of acromegaly, and the long-acting formulation was recently approved in the US and Europe for the treatment of acromegaly.

Cushing's disease and hypertension: in vivo and in vitro study of the role of the renin-angiotensin-aldosterone system and effects of medical therapy

OBJECTIVE/METHODS

Cushing's disease (CD) is often accompanied by hypertension. CD can be treated surgically and, given the expression of somatostatin subtype 5 and dopamine 2 receptors by corticotroph pituitary adenomas, pharmacologically. Indeed, we recently observed that stepwise medical combination therapy with the somatostatin-analog pasireotide, the dopamine-agonist cabergoline, and ketoconazole (which directly suppresses steroidogenesis) biochemically controlled CD patients and lowered their blood pressure after 80 days. Glucocorticoids (GC) modulate the renin-angiotensin-aldosterone system (RAAS) among others by increasing hepatic angiotensinogen expression and stimulating mineralocorticoid receptors (MR). This study therefore evaluated plasma RAAS components in CD patients before and after drug therapy. In addition, we studied whether cabergoline/pasireotide have direct relaxant effects in angiotensin II (Ang II)-constricted iliac arteries of spontaneously hypertensive rats, with and without concomitant GR/MR stimulation with dexamethasone or hydrocortisone.

RESULTS

Baseline concentrations of angiotensinogen were elevated, while renin and aldosterone were low and suppressed, respectively, even in patients treated with RAAS-blockers. This pattern did not change after 80 days of treatment, despite blood pressure normalization, nor after 4 years of remission. In the presence of dexamethasone, pasireotide inhibited Ang II-mediated vasoconstriction.

CONCLUSIONS

The low plasma renin concentrations, even under RAAS blockade, in CD may be the consequence of increased GC-mediated MR stimulation and/or the elevated angiotensinogen levels in such patients. The lack of change in RAAS-parameters despite blood pressure and cortisol normalization suggests persisting consequences of long-term exposure to cortisol excess. Finally, pasireotide may have a direct vasodilating effect contributing to blood pressure lowering.

Pasireotide is more effective than octreotide in reducing hepatorenal cystogenesis in rodents with polycystic kidney and liver diseases

In polycystic liver (PLD) and kidney (PKD) diseases, increased cyclic adenosine monophosphate (cAMP) levels trigger hepatorenal cystogenesis. A reduction of the elevated cAMP by targeting somatostatin receptors (SSTRs) with octreotide (OCT; a somatostatin analog that preferentially binds to SSTR2) inhibits cyst growth. Here we compare the effects of OCT to pasireotide (PAS; a more potent somatostatin analog with broader receptor specificity) on: (1) cAMP levels, cell cycle, proliferation, and cyst expansion in vitro using cholangiocytes derived from control and PCK rats (a model of autosomal recessive PKD [ARPKD]), healthy human beings, and patients with autosomal dominant PKD (ADPKD); and (2) hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice (a model of ADPKD). Expression of SSTRs was assessed in control and cystic cholangiocytes of rodents and human beings. Concentrations of insulin-like growth factor 1 (IGF1) and vascular endothelial growth factor (VEGF) (both involved in indirect action of somatostatin analogs), and expression and localization of SSTRs after treatment were evaluated. We found that PAS was more potent (by 30%-45%) than OCT in reducing cAMP and cell proliferation, affecting cell cycle distribution, decreasing growth of cultured cysts in vitro, and inhibiting hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice. The levels of IGF1 (but not VEGF) were reduced only in response to PAS. Expression of SSTR1 and SSTR2 (but not SSTR3 and SSTR5) was decreased in cystic cholangiocytes compared to control. Although both OCT and PAS increased the immunoreactivity of SSTR2, only PAS up-regulated SSTR1; neither drug affected cellular localization of SSTRs.

CONCLUSION

PAS is more effective than OCT in reducing hepatorenal cystogenesis in rodent models; therefore, it might be more beneficial for the treatment of PKD and PLD.

Pasireotide (SOM230) shows efficacy and tolerability in the treatment of patients with advanced neuroendocrine tumors refractory or resistant to octreotide LAR: results from a phase II study

Pasireotide (SOM230) is a novel multireceptor-targeted somatostatin (sst) analog with high binding affinity for sst receptor subtype 1, 2, 3 (sst(1,2,3)) and sst(5). Because of this binding profile, pasireotide may offer symptom control in patients with neuroendocrine tumors (NETs) and carcinoid syndrome no longer responsive to octreotide LAR. This was a phase II, open-label, multicenter study of pasireotide in patients with advanced NET whose symptoms of carcinoid syndrome (diarrhea/flushing) were inadequately controlled by octreotide LAR. Patients received s.c. pasireotide 150 μg twice daily (bid), escalated to a maximum dose of 1200 μg bid until a clinical response was achieved. Forty-four patients were evaluated for efficacy and 45 for tolerability. Pasireotide 600-900 μg s.c. bid effectively controlled the symptoms of diarrhea and flushing in 27% of patients. Evaluation of tumor response in 23 patients showed 13 with stable disease and ten with progressive disease at study end. The most common drug-related adverse events were nausea (27%), abdominal pain (20%), weight loss (20%), and hyperglycemia (16%) and most were of mild or moderate severity. Pasireotide 600-900 μg s.c. bid was effective and generally well tolerated in controlling the symptoms of carcinoid syndrome in 27% of patients with advanced NET refractory or resistant to octreotide LAR therapy.

Pasireotide (SOM230) protects the retina in animal models of ischemia induced retinopathies

The neuropeptide somatostatin and selective analogs for the sst(2/5) receptor subtypes provided neuroprotection against retinal chemical ischemia ex vivo and AMPA [(RS)-α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide] induced retinal toxicity in vivo, when employed in micromolar concentrations (Mastrodimou et al., 2005; Kiagiadaki and Thermos, 2008). The aim of the present study was to investigate the neuroprotective properties of a new metabolically stable agent pasireotide (SOM230) in the above mentioned retinal models of ischemia. Adult Sprague Dawley (250-350 g) rats were employed. For the ex vivo experiments, retinal eye cups were incubated with PBS or the chemical ischemia mixture [iodoacetic acid (5 mM)/sodium cyanide (25 mM)] in the absence or presence of SOM230 (10(-7)-10(-5) M) alone or in the presence of the sst(2) antagonist CYN-154806 (10(-7) or 10(-5) M). In the in vivo model, the animals received intravitreally: PBS (50 mM), AMPA (42 nmol/eye) or AMPA (42 nmol) in combination with SOM230 (10(-7)-10(-5) M). Immunohistochemistry studies using antisera against bNOS, a marker for brain/neuronal NOS containing amacrine cells, protein kinase C (PKC) a marker for rod bipolar cells, and TUNEL studies in conjunction with FACS analysis were employed to examine retinal cell loss and protection. Chemical ischemia led to a loss of bNOS and PKC immunoreactivity which was reversed by SOM230. Partial and full protection of bNOS and PKC immunoreactive neurons, respectively, was observed even at the low concentration of 10(-7) M. The neuroprotective actions of SOM230 (10(-7) or 10(-5) M) were reversed by CYN-154806 (10(-7) or 10(-5) M, respectively). Similarly, SOM230 (10(-7), 10(-6), 10(-5) M) provided neuroprotection in the in vivo model. The dose of 10(-7) M prevented the loss of the bNOS cells and provided almost full protection. These data were substantiated by TUNEL staining and fluorescence-activated cell sorting (FACS) analysis. SOM230 appears very efficacious in its neuroprotective properties in both models of retinal ischemia affording neuroprotection at the concentration or dose of 100 nM. These data suggest that SOM230 might represent a useful pharmacological compound for the treatment of retinal disease.

Octreotide long-acting repeatable for acromegaly

Acromegaly remains a therapeutic challenge for the endocrinologist. Among the available therapeutic options, octreotide long-acting repeatable (Sandostatin(®) LAR(®), Novartis) plays a chief role, both as a primary therapy and as an adjuvant treatment after unsuccessful surgery. A plethora of papers and a meta-analysis have demonstrated its efficacy in: control of clinical picture; achievement of safe growth hormone and normal age-matched IGF-I levels (both factors associated with restoration of normal life expectancy) in 60-70% of patients; control of tumor volume (with real shrinkage in over half of cases); and halt or reversal of most acromegaly-associated comorbidities. Treatment is well tolerated in most patients and can be safely prolonged for many years if required.

Somatostatin receptors in non-neuroendocrine malignancies: the potential role of somatostatin analogs in solid tumors

Somatostatin receptors (sstrs) are G-protein-coupled receptors that mediate various physiological effects when activated by the neuropeptide somatostatin or its synthetic analogs. In addition to the well-documented antisecretory effects of sstr2-preferential somatostatin analogs octreotide and lanreotide, ligand binding to sstr initiates an inhibitory action on tumor growth. This effect may result from both indirect actions (suppression of growth factors and growth-promoting hormones [e.g., GH/IGF-1 axis] and inhibition of angiogenesis) and direct actions (activation of antigrowth activities [e.g., apoptosis]). As solid tumor cells express multiple sstrs, there is a rationale to evaluate the potential antitumor effects of pasireotide (SOM230), a multireceptor-targeted somatostatin analog with high binding affinity for sstr1–3 and sstr5. Pasireotide reduces systemic IGF-1 levels more potently than currently available somatostatin analogs and has been well tolerated in clinical trials.

[Role of somatostatin receptor ligands in the treatment of acromegaly--literature review]

Acromegaly is a rare disease with typical clinical manifestations. Untreated acromegaly carries a 2-4-fold increase in mortality in long-term outcome. The goal of treatment is double, including biochemical control of the disease (normalization of serum IGF1 levels compared to age and gender matched controls, GH levels below 1 ng/ml after oral glucose load, or random GH below 2.5 ng/ml) and control of the tumor mass. The therapeutic modalities currently available for the treatment of acromegaly are: surgery, medical therapy, radiation therapy and their combinations. The cornerstones of medical therapy in acromegaly are the somatostatin receptor ligands due to their effectiveness in controlling GH excess in 60-70 % of patients and their beneficial effects on tumor volume. Somatostatin analogues have an established role as adjuvant therapy after non-curative surgery, and evidence suggests their use as primary treatment for selected patients. The long-term use of somatostatin receptor ligands is safe and they are well tolerated. Future medical therapy consists of pasireotide, a novel, universal somatostatin receptor agonist, and a new class of drugs named dopastatins. The latter so-called chimeric molecules have strong affinity for somatostatin receptors and dopamine-2 receptors, resulting in a more effective blocking of GH secretion, according to preliminary data. The authors of this paper review the current medical therapy of acromegaly, focusing on the role of somatostatin receptor ligands.

Expression of somatostatin receptors in human melanoma cell lines: effect of two different somatostatin analogues, octreotide and SOM230, on cell proliferation

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.

Somatostatin and somatostatin receptors: implications for neoplastic growth and cancer biology

Somatostatin agonists (SM-As) are capable of achieving durable symptomatic relief and significant clinical responses in certain tumours. Herein, we review the diverse direct and indirect mechanisms of antineoplastic activity elicited by SM-As as well as the hurdles that complicate their use as monotherapies in a broader range of malignancies. Emphasis is placed on recent clinical attempts to neutralise the IGF-mediated survival factor effects in the bone metastasis microenvironment in advanced prostate cancer. The first clinical trials of this 'anti-survival factor manipulation' strategy utilised the ability of SM-As to suppress the growth hormone-dependent liver-derived IGF-I bioavailability in combination with other drugs, such as dexamethasone, zolendronate and oestrogens, acting systemically and at the bone metastasis microenvironment. These regimens restored androgen ablation responsiveness in stage D3 prostate cancer patients and successfully produced objective clinical responses while only mild toxicities were observed. Furthermore, we focus on the preclinical experimental data of a targeted SM-A coupled to the super-potent doxorubicin derivative AN-201. The resulting conjugate (AN-238) has shown increased antitumour potency with a favourable toxicity profile. The potential use of novel SM-As as anticancer drugs is discussed in relation to data suggesting other direct and indirect treatment approaches pertaining to the somatostatin system.

Impact of Octreotide and SOM-230 on liver metastasis and hepatic lipidperoxidation in ductal pancreatic adenocarcinoma in Syrian Hamster

Octreotide is a somatostatin analogue binding on two receptor subtypes. In previous trials Octreotide showed inhibitory effects on tumour growth and liver metastasis in experimental pancreatic cancer. Thus we evaluated whether the new somatostatin analogue SOM-230 binding on 4 receptor subtypes has superior effects on carcinogenesis in pancreatic carcinoma. About 120 Syrian hamsters were randomised into six groups (n = 20): Gr.1: Aqua/Aqua, Gr.2: BOP/Aqua, Gr.3: Aqua/Octreotide, Gr.4: BOP/Octreotide, Gr.5: Aqua/SOM-230, Gr.6: BOP/SOM-230. Tumour groups 2,4,6 subcutaneously received 10 mg/kg body weight N-nitrosobis-2-oxopropylamin (BOP) weekly for 10 weeks, healthy control Gr.1,3,5 were given aqua. In the 17th week therapy started with Octreotide and SOM-230 for 16 weeks, after 32 weeks animals were sacrificed. Pancreas and liver were histopathologically analysed. Hepatic lipidperoxidation was determined by activities of antioxidative enzymes gluthation-peroxidase (GSH-Px) and superoxiddismutase (SOD) as well as concentration of thiobarbituric-acid reactive substances (TBARS). Incidence of liver metastases was 88.2% in Gr.2 (BOP/Aqua), it was decreased in Gr.4 (BOP/Octreo: 40%) and Gr.6 (BOP/SOM-230: 50%) (P < 0.05). Mean number/animal and mean-2-dimensional size of liver metastases did not differ between tumour groups. Comparing GSH-Px-activity in intrametastatic and extrametastatic hepatic tissue revealed a significant increase extrametastatically in Gr.2 (BOP/Aqua) and Gr.6 (BOP/SOM-230). SOD-activity in liver metastases was decreased in Gr.2 (1,801) (P < 0.05) versus Gr.4 (8,304) and Gr.6 (7,038). Intrametastatic TBARS concentration was increased in Gr.2 compared to Gr.4 (BOP/Octreotid) and Gr.6 (BOP/SOM-230) (P < 0.05). Octreotide and SOM-230 equally reduced liver metastasis in ductal pancreatic adenocarcinoma probably by a reduction of lipidperoxidation.

Pasireotide (SOM230): development, mechanism of action and potential applications

Pasireotide (SOM230) is a multi-receptor ligand somatostatin analogue with high binding affinity for somatostatin receptor subtypes sst(1,2,3) and sst(5). Pasireotide potently suppresses GH, IGF-I and ACTH secretion, indicating potential efficacy in acromegaly and Cushing's disease. The prolonged inhibition of hormone secretion by pasireotide in animal models and expression of multiple sst receptors in carcinoid tumors suggests that pasireotide may have clinical advantages over octreotide in patients with carcinoid tumors. Direct and indirect antitumor activity has been observed in vitro with pasireotide, including sst receptor-mediated apoptosis and antiangiogenesis, suggesting a possible role for pasireotide in antineoplastic therapy. In summary, preclinical evidence, as well as preliminary results from clinical studies suggests that pasireotide is a promising new treatment for patients with symptoms of metastatic carcinoid tumors refractory or resistant to octreotide, de novo or persistent acromegaly, and that pasireotide has the potential to be the first directed medical therapy for Cushing's disease.

Expression of somatostatin and somatostatin receptor subtypes 1-5 in human normal and diseased kidney

Somatostatin mediates inhibitory functions through five G protein-coupled somatostatin receptors (sst1-5). We used immunohistochemistry, immunofluorescence, and RT-PCR to determine the presence of somatostatin receptors sst1, sst2A, sst2B, sst3, sst4, and sst5 in normal and IgA nephropathy human kidney. All somatostatin receptors were detected in the thin tubules (distal convoluted tubules and loops of Henle) and thick tubules (proximal convoluted tubules) in the tissue sections from nephrectomy and biopsy samples. Immunopositive sst1 and sst4 staining was more condensed in the cytoplasm of tubular epithelial cells. In normal kidney tissue sections, podocytes and mesangial cells in the glomeruli stained for sst1, sst2B, sst4 and sst5, and stained weakly for sst3. In IgA kidney tissue, the expression of somatostatin receptors was significantly increased with particular immmunopositive staining for sst1, sst2B, sst4, and sst5 within glomeruli. In the epithelial cells, the staining for sst2B and sst4 in proximal tubules and sst1, sst2B, and sst5 in distal tubules was increased. The mRNA expression of sst1-5 was also detected by RT-PCR. Somatostatin and all five receptor subtypes were ubiquitously distributed in normal kidney and IgA nephropathy. The increased expression of somatostatin receptors in IgA nephropathy kidney might be the potential pathogenesis of inflammatory renal disease.

In vitro antiangiogenic activity of selective somatostatin subtype-1 receptor agonists

BACKGROUND

Endothelial cells of human blood vessels (arteries and veins) show high levels of somatostatin subtype-1 receptor (sst(1)). The aim of the present study is to investigate the inhibitory effects of novel somatostatin analogs, highly selective for human sst(1), on in vitro angiogenesis and their modulation of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor-2 (VEGFR-2) expression.

MATERIALS AND METHODS

Somatostatin analogs BIM-23745 and BIM-23926 were tested for their ability to prevent proliferation and migration of human endothelial HMEC-1 cells, to modulate VEGF and VEGFR-2 expression and to inhibit sprouting of microvessels from cultured human placental vessel explants in fibrin matrix for 28 days.

RESULTS

The somatostatin sst(1 )receptor-selective agonists, BIM-23745 and BIM-23926 showed a suppression of endothelial proliferation (e.g. 10(-6) M BIM-23475, 40.0 +/- 2.1% vs. 100% of controls; 10(-7) M BIM-23926, 55.3 +/- 3.3% vs. 100% of controls), migration (e.g. 10(-7) M BIM-23475, 35.0 +/- 1.56% vs. 100% of controls; 10(-7) M BIM-23926, 53.7 +/- 1.77% vs. 100% of controls) and microvessel sprouting (e.g. 10(-8) M BIM-23475, 42.8 +/- 5.6% vs. 100% of controls; 10(-7) M BIM-23926, 17.2 +/- 11.8% vs. 100% of controls). A small but significant percentage of cells exposed to BIM-23745 and BIM-23926 for 24 h and for 72 h presented typical apoptotic morphology. Moreover, both the analogs significantly inhibit VEGF and VEGFR-2 gene expression in endothelial cells grown for 144 h in a fibrin matrix and the VEGF secretion in conditioned media.

CONCLUSIONS

The inhibition of endothelial activities suggests potential therapeutic utility for administration of somatostatin sst(1 )receptor-selective agonists in the proliferative diseases involving angiogenesis.

Medical treatment of diabetic retinopathy with somatostatin analogues

Traditional management strategies for retinal neovascularisation accompanying proliferative diabetic retinopathy include photocoagulation laser therapy. The development of preventative pharmacological treatments aimed at replacing or delaying this acute intervention has been an active research area and somatostatin analogues have shown promise in reducing the progression of retinal vascular pathologies. This review summarises the present knowledge on the molecular and cellular mechanisms of neovascularisation, and the rationale for the therapeutic use of somatostatin analogues as well as the results of two key recent clinical trials using octreotide. The potential use of octreotide and other somatostatin analogues in reducing the risk of severe visual impairment in proliferative diabetic retinopathy is discussed and pharmacological treatment regimens are proposed as an additional strategy or a less invasive alternative to laser therapy.

The analysis of quantitative expression of somatostatin and dopamine receptors in gastro-entero-pancreatic tumours opens new therapeutic strategies

OBJECTIVE

Somatostatin (sst) are present in the majority of gastro-entero-pancreatic (GEP) tumours. Effects of somatostatin receptor (sst) analogues are partial and of limited duration. Cell lines derived from GEP express dopaminergic receptors D(2). New chimeric analogues simultaneously recognising sst(2) and sst(5) or sst(2) and D(2) have additive effects in inhibition of GH and prolactin secretion in pituitary adenomas. Our aim was to quantify the expression of sst and D(2) mRNA in human GEP tumours.

DESIGN AND METHODS

mRNA expression of sst(1), sst(2), sst(3) and sst(5) as well as D(2), was analysed using real-time PCR (TaqMan probe) in a series of 35 patients with GEP tumours (pancreas (n = 19) and intestinal (n = 16)). Levels of expression were compared with a group of 13 somatotroph adenomas.

RESULTS

All GEP tumours express sst(1), sst(2) and D(2). Expression of sst(3) and sst(5) was observed in 89 and 76% of tumours respectively with highly variable levels. sst(2) mRNA expression was higher in nonfunctional tumours (P < 0.009) and sst5 was higher in pancreatic than in intestinal tumours (P < 0.02). Whereas sst(2) levels were similar between GEP and somatotroph tumours, levels of sst(5) and D(2) were higher in the former (394.9 +/- 156.1 x 10(-2) vs 69.7 +/- 19.5 x 10(-2) copy/copy beta-Gus (P < 0.0036) and 519.6 +/- 121.2 x 10(-2) vs 50.0 +/- 21.6 x 10(-2) copy/copy beta-Gus (P < 0.0001) respectively). In small tumours ( < 30 mm), sst(2) density appeared as a crucial parameter in somatostatin receptor scintigraphy results, whereas in big tumours, a consistent bias in SRS results was introduced by the size. In pancreatic GEP, high-level sst(3) expression was found in tumours with more active angiogenesis (higher microvessel density and vascular endothelial growth factor expression (P < 0.03)).

CONCLUSIONS

GEP tumours co-express sst(2) and D(2) in 100% of cases and sst(5) in 89% thus supporting the testing of bi-specific agonists (sst(2)/sst(5) or sst(2)/D(2)) in these tumours.

Rationale for the use of somatostatin analogs as antitumor agents

BACKGROUND

There is a need for novel antitumor agents that demonstrate efficacy in currently refractory tumors without adding to the toxicity of therapy. The somatostatin analogs, which have demonstrated antineoplastic activities in experimental tumor models, and good tolerability and safety profiles are attractive candidates.

MATERIALS AND METHODS

Data from preclinical studies provide evidence for direct and indirect mechanisms by which somatostatin analogs exert antitumor effects.

RESULTS

Direct antitumor activities, mediated through somatostatin receptors (sst(1)-sst(5)) expressed in tumor cells, include blockade of autocrine/paracrine growth-promoting hormone and growth factor production, inhibition of growth factor-mediated mitogenic signals and induction of apoptosis. Indirect antitumor effects include inhibition of growth-promoting hormone and growth factor secretion, and antiangiogenic actions. Many human tumors express more than one somatostatin receptor subtype, with sst(2) being predominant. Somatostatin analogs such as octreotide and lanreotide, which present a high affinity for sst(2), are in current clinical use to alleviate symptoms in patients with endocrine tumors, and radiolabeled somatostatin analogs have been developed for diagnosis and radiotherapy.

CONCLUSIONS

While the rationale exists for the use of somatostatin analogs as antitumor agents, studies are ongoing to identify analogs with activity across the range of receptor subtypes to maximize the potential of such treatment.

Endocrine tumours of the gastrointestinal tract. Somatostatin receptors as tools for diagnosis and therapy: molecular aspects

Somatostatin is a neuropeptide that acts as an endogenous inhibitor of various cellular functions including endocrine and exocrine secretions and the proliferation of normal and tumour cells. Its action is mediated by a family of G-protein-coupled receptors (sst1-sst5) that are widely distributed in normal and tumour cells. Gastroenteropancreatic endocrine tumours express multiple somatostatin receptors, sst2 being clearly predominant. These receptors represent the molecular basis for the clinical use of somatostatin analogues in the treatment of endocrine tumours and their in vivo localisation. This review covers current knowledge in somatostatin receptor biology and signalling.