Novel chimeric somatostatin analogs: facts and perspectives

Role of Somatostatin Signalling in Neuroendocrine Tumours

Somatostatin (SST) is a small peptide that exerts inhibitory effects on a wide range of neuroendocrine cells. Due to the fact that somatostatin regulates cell growth and hormone secretion, somatostatin receptors (SSTRs) have become valuable targets for the treatment of different types of neuroendocrine tumours (NETs). NETs are a heterogeneous group of tumours that can develop in various parts of the body, including the digestive system, lungs, and pituitary. NETs are usually slow growing, but they are often diagnosed in advanced stages and can display aggressive behaviour. The mortality rate of NETs is not outstandingly increased compared to other malignant tumours, even in the metastatic setting. One of the intrinsic properties of NETs is the expression of SSTRs that serve as drug targets for SST analogues (SSAs), which can delay tumour progression and downregulate hormone overproduction. Additionally, in many NETs, it has been demonstrated that the SSTR expression level provides a prognostic value in predicting a therapeutic response. Furthermore, higher a SSTR expression correlates with a better survival rate in NET patients. In recent studies, other epigenetic regulators affecting SST signalling or SSA–mTOR inhibitor combination therapy in NETs have been considered as novel strategies for tumour control. In conclusion, SST signalling is a relevant regulator of NET functionality. Alongside classical SSA treatment regimens, future advanced therapies and treatment modalities are expected to improve the disease outcomes and overall health of NET patients.

Somatostatin receptor expression and patients' response to targeted medical treatment in pituitary tumors: evidences and controversies

BACKGROUND

Somatostatin receptors (SSTs) are widely co-expressed in pituitary tumors. SST₂ and SST₅ are the most represented SST subtypes. First-generation somatostatin receptor ligands (SRLs) mainly target SST₂, while pasireotide, a multi-receptor ligand, shows high binding affinity for both SST₅ and SST₂. Therefore, SRLs are routinely used as medical treatment for GH-, TSH-, and ACTH-secreting pituitary tumors.

METHODS

Critical revision of literature data correlating SST expression with patients' response to SRLs.

RESULTS

SST₂ expression in somatroph tumors directly correlates with GH and IGF-1 decrease after first-generation SRL treatment. SST₂ immunohistochemistry represents a valuable tool to predict biochemical response to first-generation SRLs in acromegalic patients. Pasireotide seems to exert its biological effects via SST₂ in unselected patients. However, in those subjects resistant to first-generation SRLs, harbouring tumors with negligible SST₂ expression, pasireotide can act throughout SST₅. More than somatotroph tumors, TSH-omas represent the paradigm of tumors showing a satisfactory response to SRLs. This is probably due to the high SST₂ expression observed in nearly 100% of cases, as well as to the balanced amount of SST₅. In corticotroph tumors, pasireotide mainly act via SST₅, although there is a need for translational studies correlating its efficacy with SST expression in this peculiar tumor histotype.

CONCLUSIONS

The assumption "more target receptor, more drug efficacy" is not straightforward for SRLs. The complex pathophysiology of SSTs, and the technical challenges faced to translate research findings into clinical practice, still need our full commitment to make receptor evaluation a worthwhile procedure for individualizing treatment decisions.

The role of combination medical therapy in the treatment of acromegaly

PURPOSE

Uncontrolled acromegaly results in approximately 2-fold excess mortality. Pituitary surgery is first-line therapy, and medical treatment is indicated for persistent disease. While cabergoline and pegvisomant are used in select patients, somatostatin receptor ligands (SRLs) remain the cornerstone of medical treatment. Management of patients poorly responsive to SRLs is therefore, challenging. The purpose of this review is to highlight the options for combination medical therapy in the treatment of acromegaly, with an emphasis on efficacy and safety.

METHODS

All original articles/abstracts detailing combination medical therapy in acromegaly were identified from a PubMed search.

RESULTS

Studies reviewed included retrospective and open-label prospective studies. While the combination of SRL and cabergoline was generally well tolerated, a lower baseline insulin-like growth factor-1 (IGF-1) level was the best predictor of efficacy; this combination may be most effective in patients with mildly elevated IGF-1. SRL-pegvisomant combination normalized IGF-1 in the majority of patients; continued efficacy despite individual drug dosing reduction was also reported. The risk of significant liver enzyme elevation was, however, higher than that reported with SRL monotherapy; close monitoring is recommended. Data on pegvisomant-cabergoline combination is limited, but this may be an option in the setting of SRL intolerance. Reports on temozolomide used in combination with other medical therapies in patients with aggressive GH-secreting tumors are also summarized.

CONCLUSION

While more prospective, randomized controlled trials on long-term efficacy and safety are needed, combination medical therapy remains a treatment strategy that should be considered for acromegaly patients poorly responsive to SRLs.

Somatostatin and dopamine receptor regulation of pituitary somatotroph adenomas

Somatostatin and dopamine receptors are expressed in normal and tumoral somatotroph cells. Upon receptor stimulation, somatostatin and the somatostatin receptor ligands octreotide, lanreotide, and pasireotide, and to a lesser extent, dopamine and the dopamine analogs bromocriptine and cabergoline, suppress growth hormone (GH) secretion from a GH-secreting pituitary somatotroph adenoma. Somatostatin and dopamine receptors are G_αi-protein coupled that inhibit adenylate cyclase activity and cAMP production and reduce intracellular calcium concentration and calcium flux oscillations. Although their main action on somatotroph cells is acute inhibition of GH secretion, they also may inhibit GH production and possibly somatotroph proliferation. These receptors have been reported to create complexes that exhibit functions distinct from that of receptor monomers. Somatostatin suppression of GH is mediated mainly by somatostatin receptor subtype 2 and to a lesser extent by SST5. Human somatostatin receptor subtype 5 has also been shown to harbor mutations associated with GH levels, somatotroph tumor behavior, and somatostatin receptor ligand (SRL) responsiveness. Reviewing current knowledge of somatostatin and dopamine receptor expression and signaling in normal and tumoral somatotroph cells offers insights into mechanisms underlying SRL and dopamine agonist effectiveness in patients with acromegaly.

Molecular basis of pharmacological therapy in Cushing's disease

Cushing's disease (CD) is a severe endocrine condition caused by an adrenocorticotropin (ACTH)-producing pituitary adenoma that chronically stimulates adrenocortical cortisol production and with potentially serious complications if not or inadequately treated. Active CD may produce a fourfold increase in mortality and is associated with significant morbidities. Moreover, excess mortality risk may persist even after CD treatment. Although predictors of risk in treated CD are not fully understood, the importance of early recognition and adequate treatment is well established. Surgery with resection of a pituitary adenoma is still the first line therapy, being successful in about 60-70 % of patients; however, recurrence within 2-4 years may often occur. When surgery fails, medical treatment can reduce cortisol production and ameliorate clinical manifestations while more definitive therapy becomes effective. Compounds that target hypothalamic-pituitary axis, glucocorticoid synthesis or adrenocortical function are currently used to control the deleterious effects of chronic glucocorticoid excess. In this review we describe and analyze the molecular basis of the drugs targeting the disease at central level, suppressing ACTH secretion, as well as at peripheral level, acting as adrenal inhibitors, or glucocorticoid receptor antagonists. Understanding of the underlying molecular mechanisms in CD and of glucocorticoid biology should promote the development of new targeted and more successful therapies in the future. Indeed, most of the drugs discussed have been tested in limited clinical trials, but there is potential therapeutic benefit in compounds with better specificity for the class of receptors expressed by ACTH-secreting tumors. However, long-term follow-up with management of persistent comorbidities is needed even after successful treatment of CD.

Fine-tuning somatostatin receptor signalling by agonist-selective phosphorylation and dephosphorylation: IUPHAR Review 5

The biological actions of somatostatin are mediated by a family of five GPCRs, named sst1 to sst5 . Somatostatin receptors exhibit equally high-binding affinities to their natural ligand somatostatin-14 and largely overlapping distributions. The overexpression of somatostatin receptors in human tumours is the molecular basis for diagnostic and therapeutic application of the stable somatostatin analogues octreotide, lanreotide and pasireotide. The efficiency of somatostatin receptor signalling is tightly regulated and ultimately limited by the coordinated phosphorylation and dephosphorylation of intracellular carboxyl-terminal serine and threonine residues. Here, we review and discuss recent progress in the generation and application of phosphosite-specific antibodies for human sst2 and sst5 receptors. These phosphosite-specific antibodies are unique tools to monitor the spatial and temporal dynamics of receptors phosphorylation and dephosphorylation. Using a combined approach of phosphosite-specific antibodies and siRNA knock-down screening, relevant kinases and phosphatases were identified. Emerging evidence suggests distinct mechanisms of agonist-selective fine-tuning for individual somatostatin receptors. The recently uncovered differences in phosphorylation and dephosphorylation of these receptors may hence be of physiological significance in mediating responses to acute, persistent or repeated stimuli in a variety of target tissues.

Therapeutic advances in neuroendocrine neoplasms with hepatic metastases

Although neuroendocrine neoplasms are characterized by slow progression and indolent biology, most patients develop early hepatic metastasis. Surgical resection is currently the only way to cure. One- or two-step procedures may be undertaken to remove the primary tumor and hepatic metastasis as thoroughly as possible. Liver transplantation is difficult to be widely applied due to resource scarcity. Other drawbacks include strict criteria for patient selection and high recurrence rate. Liver-directed therapies, mainly referring to TAE/TACE and RFA, are widely used in NET G1/G2 patients. Pharmacological therapies include somatostatin analogues, targeted therapy and systemic chemotherapy. Some clinical trials have demonstrated longer OS and PFS in experimental groups compared with placebo groups. Currently, a combined-modality approach including surgery, liver-targeted therapy and medication is the trend in treatment of NEN hepatic metastases. How to determine the most suitable strategy in specific clinical circumstances? Which subpopulation of patients will benefit most from a specific therapy? We expect more clinical evidence of high quality to answer these questions.

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.

Balance between somatostatin and D2 receptor expression drives TSH-secreting adenoma response to somatostatin analogues and dopastatins

CONTEXT

First-line therapy for thyrotropin-secreting pituitary adenomas (TSHomas) is neurosurgery, while medical treatment rests mainly on somatostatin analogues. Clinically available sst(2) -preferring analogues, octreotide and lanreotide, induce normalization of hormone levels in approximately 90% of patients and tumour shrinkage in 45%.

OBJECTIVE

We evaluated somatostatin 1, 2, 3 and 5 and dopamine D2 receptor expression in tumour samples from three TSHomas, and the relationships between receptor expression, in vitro antiproliferative response and clinical data, including octreotide test and three months of therapy with octreotide long-acting repeatable (LAR). TSHoma cell proliferation was tested in vitro using octreotide, cabergoline and two chimeric compounds, BIM-23A760 and BIM-23A387.

RESULTS

All patients showed significant TSH lowering to acute octreotide test, but a hormonal response to long-term treatment was observed in only two patients, showing a high sst(5) /sst(2) ratio. Patient 2, characterized by high expression of sst(2) and sst(1) and a relative lower expression of sst(5) , experienced tachyphylaxis after prolonged octreotide treatment. In vitro, the somatostatin/dopamine receptor agonist BIM-23A760 caused the highest antiproliferative effect among those tested. Combined treatment with octreotide and cabergoline displayed an additive effect of magnitude comparable to that of the other chimeric compound (BIM-23A387). Octreotide resistance was confirmed in cells isolated from the nonresponder patient, although it could be overcome by treatment with the chimeric compounds.

CONCLUSIONS

  A high sst(5) /sst(2) ratio might be predictive of a positive outcome to long-term treatment with somatostatin analogues in TSHomas. Moreover, combined somatostatin and D(2) receptor targeting might be considered as a potential tool to improve the response rate in octreotide-resistant tumours.

Differential expression of genes related to drug responsiveness between sparsely and densely granulated somatotroph adenomas

There are two main subtypes of GH-producing pituitary adenoma: densely granulated (DG-type) and sparsely granulated (SG-type). Despite the difference in drug responsiveness between the two subtypes, their molecular mechanisms remain unknown. The aim of this study is to evaluate the differential expression of genes related to drug responsiveness between the two subtypes of somatotroph adenoma, and their relationship to the clinical characteristics. Eighty-two acromegaly patients (44 DG-type, 38 SG-type) were studied retrospectively. Clinical characteristics were compared between the two subtypes. Among them, 36 tumor tissue specimens (19 DG-type, 17 SG-type) were available for investigation of the expression of SSTR2, SSTR5 and D2R that are reported to be involved in drug responsiveness by realtime RT-PCR. Protein level was evaluated by immunohistochemical study. Patients with SG-type adenomas were younger in age and showed greater GH suppression by octreotide, but not by bromocriptin, and bigger in size and more invasiveness than DG-type adenomas. The mRNA expression of SSTR2 in DG-type adenomas were greater than those in SG-type adenomas and showed significantly positive correlation with GH suppression by octreotide. There was positive correlation between mRNA and protein levels of SSTR2. These data suggested that the differences of responsiveness to octreotide between DG- and SG-type adenomas are based on the expression levels of SSTR2.

The role of somatostatin and dopamine D2 receptors in endocrine tumors

Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D(2) receptor (D(2)) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D(2) as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D(2) pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.

Reflections on the theory of "silver bullet" octreotide tracers: implications for ligand-receptor interactions in the age of peptides, heterodimers, receptor mosaics, truncated receptors, and multifractal analysis

The classical attitude of Nuclear Medicine practitioners on matters of peptide-receptor interactions has maintained an intrinsic monogamic character since many years. New advances in the field of biochemistry and even in clinical Nuclear Medicine have challenged this type of thinking, which prompted me to work on this review. The central issue of this paper will be the use of somatostatin analogs, i.e., octreotide, in clinical imaging procedures as well as in relation to neuroendocirne tumors. Newly described characteristics of G-protein coupled receptors such as the formation of receptor mosaics will be discussed. A small section will enumerate the regulatory processes found in the cell membrane. Possible new interpretations, other than tumor detection, based on imaging procedures with somatostatin analogs will be presented. The readers will be taken to situations such as inflammation, nociception, mechanosensing, chemosensing, fibrosis, taste, and vascularity where somatostatin is involved. Thyroid-associated orbitopathy will be used as a model for the development of multi-agent therapeutics. The final graphical summary depicts the multifactorial properties of ligand binding.

In vivo and in vitro response to octreotide LAR in a TSH-secreting adenoma: characterization of somatostatin receptor expression and role of subtype 5

Thyrotropin-secreting pituitary adenomas (TSHomas) are a rare cause of hyperthyroidism and account for less than 2% of pituitary adenomas. Medical therapy with somatostatin analogues (SSAs) effectively reduces TSH secretion in approximately 80% of patients and induces shrinkage in about 45% of tumors. According with previous data, resistance to SSA treatment might be due to heterogeneity in somatostatin receptors (SSTRs) expression. We report the case of TSHoma in a 41-year-old man treated with octreotide LAR that caused a dramatic decrease of TSH and thyroid hormones and tumor shrinkage already after 3 months of pre-surgical therapy. In search of potential molecular determinants of octreotide effectiveness, we measured, in primary cultures from this tumor, SSTR and dopamine D2 receptor (D2R) expression, and octreotide and/or cabergoline effects on TSH secretion and cell proliferation. SSTR5 and D2R expression was higher than SSTR2. Octreotide significantly inhibited TSH secretion more effectively than cabergoline (P<0.001), whereas the combined treatment was comparable with cabergoline alone. Similarly, octreotide resulted more effective than cabergoline on cell proliferation, while the combination did not show any additive or synergistic effects. In conclusion, the significant antisecretive and antiproliferative effect of octreotide in this patient might be related to the high expression of SSTR5, in the presence of SSTR2. After reviewing the literature, indeed, in line with previous observations, we hypothesize that SSTR5/SSTR2 ratio in TSHomas may represent a useful marker in predicting the outcome of therapy with SSAs. The role of D2R should be further explored considering that the presence of D2R can influence SSTRs functionality.

Pharmacologic neuroimaging of the ontogeny of dopamine receptor function

Characterization of the ontogeny of the cerebral dopaminergic system is crucial for gaining a greater understanding of normal brain development and its alterations in response to drugs of abuse or conditions such as attention-deficit hyperactivity disorder. Pharmacological MRI (phMRI) was used to determine the response to dopamine transporter (DAT) blockers cocaine and methylphenidate (MPH), the dopamine releaser D-amphetamine (AMPH), the selective D1 agonist dihydrexidine, and the D2/D3 agonist quinpirole in young (<30 days old) and adult (>60 days old) rats. In adult rats, cocaine (0.5 mg/kg i.v.) or MPH (2 mg/kg) induced primarily positive cerebral blood volume (rCBV) changes in the dopaminergic circuitry, but negative rCBV changes in the young animals. Microdialysis measurements in the striatum showed that young rats have a smaller increase in extracellular dopamine in response to cocaine than adults. The young rats showed little rCBV response to the selective D1 agonist dihydrexidine in contrast to robust rCBV increases observed in the adults, whereas there was a similar negative rCBV response in the young and adult rats to the D2 agonist quinpirole. We also performed a meta-analysis of literature data on the development of D1 and D2 receptors and the DAT. These data suggest a predominance of D2-like over D1-like function between 20 and 30 days of age. These combined results suggested that the dopamine D1 receptor is functionally inhibited at young age.

Somatostatin analogues in the treatment of gastroenteropancreatic neuroendocrine tumours, current aspects and new perspectives

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) are rare tumours that present many clinical features.They secrete peptides and neuroamines that cause distinct clinical syndromes, including carcinoid syndrome. However, many are clinically silent until late presentation with mass effects.In 2000 the WHO developed a new classification which gives a better description of the characteristics and biological behaviour of the tumour.Surgical resection is the treatment of first choice for a patient with a GEP NET. In metastatic disease multiple therapeutic approaches are possible. In these cases the goal is to improve quality of life and to extent survival.GEP NETs express somatostatin receptors (SSTRs), which are bound by somatostatin (SST) or its synthetic analogues, although the subtypes and number of SSTRs expressed is very variable.Somatostatin analogues are used frequently to control hormone-related symptoms while their anti-neoplastic activity, even if it has not been widely studied and the regarding data are discordant, seems to result prevalently in tumour stabilisation.A few patients who fail to respond or cease to respond to standard SST analogues treatment seem to have a response to higher doses of these drugs.The use of higher doses of somatostatin analogues or the development of new subtype selective agonists and chimaeric somatostatin analogues, or pan-somatostatin will probably improve the clinical management of these patients.This review provides an update on the use of somatostatin analogues in the management of GEP NETs and discusses novel clinical strategies based on SSTR 2 gene transfer therapy.

Clinical aspects and therapeutic outcome in thyrotropin-secreting pituitary adenomas: a single center experience

BACKGROUND AND AIM

The management of pituitary adenomas secreting TSH has evolved considerably over the last decades.We report the clinical features, management, and outcome of a large monocentric series.

MATERIAL AND METHODS

A monocentric retrospective cohort of 26 patients admitted to our Department of Endocrinology between 1983 and 2007, followed for a period up to 204 months. The diagnosis of TSH-secreting adenoma was based on clinical and biochemical findings of central hyperthyroidism. Evaluation of basal and dynamic pituitary function, magnetic resonance imaging or computerized tomography scan were performed in all patients. Twenty-two patients, of whom 15 pre-treated by somatostatin analogs (SSA), underwent trans-sphenoidal surgery and were regularly re-evaluated.

RESULTS

The number of cases increased over the years. Age at diagnosis, micro- to macroadenoma ratio, and mean estimated latency between first symptoms and diagnosis did not appreciably change over time. Latency was significantly shorter in macroadenomas. Following surgery, 55% of patients obtained remission (success rate of 40 and 67% in macro- and microadenomas, respectively). SSA pre-treatment led to an apparent although not statistically- significant increase in success rate in micro- but not in macroadenomas.

CONCLUSIONS

In a monocentric group of 26 TSH-secreting adenomas the high ratio between micro- and macroadenomas remained stable over time with a significantly shorter diagnosis latency in macroadenomas. A more precocious recognition of the tumors and possibly the use of presurgical SSA allowed a high remission rate. A varied combination of neurosurgery, SSA, radiotherapy, and thyroid ablation led to the control of the disease in all the patients studied.

Expression analysis of dopamine receptor subtypes in normal human pituitaries, nonfunctioning pituitary adenomas and somatotropinomas, and the association between dopamine and somatostatin receptors with clinical response to octreotide-LAR in acromegaly

CONTEXT

Dopamine receptor (DR) and somatostatin receptor subtype expression in pituitary adenomas may predict the response to postsurgical therapies.

OBJECTIVES

Our objectives were to assess and compare the mRNA levels of DR1-5 and somatostatin receptors 1-5 in normal pituitaries (NPs), nonfunctioning pituitary adenomas (NFPAs), and somatotropinomas. In addition, we determined whether the level of DR expression correlates with the in vivo response to octreotide-LAR in acromegalic patients.

DESIGN AND PATIENTS

Eight NPs, 30 NFPAs, and 39 somatotropinomas were analyzed for receptor mRNA levels by real-time RT-PCR. The DR2 short variant was estimated as the DR2 long/DR2 total (DR2T). The relationship between DR expression and the postsurgical response to octreotide-LAR was assessed in 19 of the acromegalic patients.

RESULTS

DR3 was not detected. The relationship between expression levels of DR subtypes in NPs and somatotropinomas was DR2T>>>DR4>>DR5>DR1, whereas in NFPAs, DR2T>>>DR4>>DR1>DR5. The DR2 short variant was the predominant DR2 variant in the majority of samples. In acromegalics treated with octreotide-LAR, DR1 was negatively correlated with percent GH reduction (3 months: r = -0.67, P = 0.002; and 6 months: r = -0.58, P = 0.009), and DR5 was positively correlated with percent IGF-I reduction (3 months: r = 0.55, P = 0.01; and 6 months: r = 0.47, P = 0.04).

CONCLUSIONS

DR2 is the predominant DR subtype in NPs, NFPAs, and somatotropinomas. The fact that DR1, DR4, and DR5 are also expressed in many adenomas tested suggests that these receptors might also play a role in the therapeutic impact of postsurgical medical therapies in patients with NFPA and acromegaly. This was supported by the finding that the in vivo response to octreotide-LAR was negatively associated with DR1 and positively associated with DR5.

Therapeutic options in the management of acromegaly: focus on lanreotide Autogel

BACKGROUND

In acromegaly, expert surgery is curative in only about 60% of patients. Postoperative radiation therapy is associated with a high incidence of hypopituitarism and its effect on growth hormone (GH) production is slow, so that adjuvant medical treatment becomes of importance in the management of many patients.

OBJECTIVE

To delineate the role of lanreotide in the treatment of acromegaly.

METHODS

Search of Medline, Embase, and Web of Science databases for clinical studies of lanreotide in acromegaly.

RESULTS

Treatment with lanreotide slow release and lanreotide Autogel((R)) normalized GH and insulin-like growth factor-I (IGF-I) concentrations in about 50% of patients. The efficacy of 120 mg lanreotide Autogel((R)) on GH and IGF-I levels was comparable with that of 20 mg octreotide LAR. There were no differences in improvement of cardiac function, decrease in pancreatic beta-cell function, or occurrence of side effects, including cholelithiasis, between octreotide LAR and lanreotide Autogel(R). When postoperative treatment with somatostatin analogs does not result in normalization of serum IGF-I and GH levels after noncurative surgery, pegvisomant alone or in combination with somatostatin analogs can control these levels in a substantial number of patients.

Guidelines for the treatment of growth hormone excess and growth hormone deficiency in adults

The V Consensus Group Meeting on 'Guidelines for Treatment of GH Excess and GH Deficiency in the Adult' was an international workshop held on February 20-22, 2006 in Santa Monica, California, USA. The principal aim of this meeting was to provide guidelines for the evaluation and treatment of adults with either form of abnormal GH secretion: GH excess or GH deficiency. The workshop included debates as to the choice of primary treatment, discussions of the targets for adequate treatment, and concluded with presentations on open issues germane to adult GH treatment including the role of GH in malignancies, the impact of longterm treatment on bone, and a cost-benefit analysis. The meeting was comprised of 66 delegates representing 13 different countries.

Differential cytotoxicity of novel somatostatin and dopamine chimeric compounds on bronchopulmonary and small intestinal neuroendocrine tumor cell lines

BACKGROUND

Survival rates for gastrointestinal (GI) and bronchopulmonary (BP) neuroendocrine tumors (NETs) have not significantly altered (overall 67%, 5-year survival) in 30 years (1973-2004), whereas the incidence has increased ( approximately 1000%) in the same time frame. No effective or specific antineoplastic agent is available for treatment, although somatostatin analogs inhibit tumor secretion. Given the coexistence of somatostatin and dopamine regulatory receptors on NET cells, the antiproliferative efficacy as well as the signaling and transcriptional targets of their ligands were evaluated.

METHODS

The cytotoxic effects of 12 somatostatin/dopamine compounds were evaluated in 3 NET cell lines, and real-time polymerase chain reaction and enzyme-linked immunoadsorbent assay studies were performed to delineate antiproliferative signaling pathways.

RESULTS

The atypical BP-NET, NCI-H720, was most sensitive to the sst(5) analog BIM23206 (half-maximal concentration, 2.4 pM) and demonstrated similar sensitivity to lanreotide and the sst(2) analog BIM23120. The typical BP-NET, NCI-H727, was most sensitive to BIM23120 (0.7 nM) and to the pan-somatostatin receptor analog (BIM23A779). The GI-NET, KRJ-I, was most sensitive to sst(2,5) analogs lanreotide (1 nM) and BIM23244 (7.4 nM). Lanreotide activated extracellular signal regulated kinase-1/2 phosphorylation and p21(WAF1/CIP1) transcription, but inhibited Ki-67 transcription. NCI-H720 was most sensitive to the sst(2,5)- and D(2)-selective compound BIM23A761 (4.2 nM), as was NCI-H727 (5.5 nM). KRJ-I did not respond to any chimeric analog. BIM23A761 activated c-Jun N-terminal kinase signaling and caused inhibition of Ki-67 transcription. P21(WAF1/CIP1) transcription was activated only in NCI-H727 cells.

CONCLUSIONS

The different responses of each individual cell line suggested that NETs from different locations arising from different neuroendocrine cells may require cell-specific antiproliferative agents based on the unique receptor profile of individual lesions.

The role of somatostatin analogues in the treatment of neuroendocrine tumours

Neuroendocrine tumours belong to a heterogeneous family of neoplasms, originating in endocrine glands (such as the pituitary, parathyroid or the neuroendocrine adrenal glands), in endocrine islets (within the thyroid or pancreas) as well as in endocrine cells dispersed between exocrine cells throughout the digestive or respiratory tracts. The clinical behaviour of neuroendocrine tumours is variable; they may be functioning or not functioning, ranging from well-differentiated slow growing neuroendocrine tumours to poorly differentiated neuroendocrine tumours, which are highly aggressive malignant tumours. The development of somatostatin analogues as important diagnostic and treatment tools have revolutionised the clinical management of patients with neuroendocrine tumours. However, although symptomatic relief and stabilisation of tumour growth for various periods of time are observed in many patients treated with somatostatin analogues, tumour regression is rare. Development of new somatostatin analogues and new drug combination therapies should further improve the clinical management of these patients.

Management of acromegaly: is there a role for primary medical therapy?

Acromegaly is a chronic, debilitating disease caused by chronic growth hormone (GH) hypersecretion which results in chronic medical comorbidities, poor quality of life and high mortality rates. Successful treatment can improve clinical signs and symptoms and normalize mortality rates. Over 95% of acromegaly is caused by a somatotroph adenoma of the pituitary, and the first-line treatment is generally transsphenoidal surgery, which can be curative in 50-60% of patients. Nonetheless, high rates of persistent acromegaly following surgery and the limited efficacy of radiation therapy necessitate chronic medical treatment for many patients. Somatostatin analogues have become the preferred first-line medical therapy for many practitioners, as they achieve better biochemical and direct tumor control than the dopamine agonists, and long-acting preparations make once monthly administration possible. Cabergoline, a dopamine agonist, offers a lower-cost option and may be effective in patients with a pituitary tumor that co-secretes GH and prolactin. Pegvisomant is a GH receptor antagonist that produces exceptional biochemical response rates but lacks any direct effects on the tumor, which may limit its effectiveness as life-long monotherapy. Combinations of these three drug classes have not been rigorously studied, and preliminary trials do not suggest improved clinical outcomes. While medical treatment options for acromegaly have significantly improved over the last 30 years, limitations remain, and a multi-specialty team approach is necessary for the effective long-term management of patients with acromegaly.