Growth hormone receptor antagonists: discovery, development, and use in patients with acromegaly

Autocrine human GH promotes radioresistance in mammary and endometrial carcinoma cells

Although recent advances in breast cancer treatment regimes have improved patient prognosis, resistance to breast cancer therapies, such as radiotherapy, is still a major clinical challenge. In the current study, we have investigated the role of autocrine human GH (hGH) in resistance to ionising radiation (IR)-based therapy. Cell viability and total cell number assays demonstrated that autocrine hGH promoted cell regrowth in the mammary carcinoma cell lines, MDA-MB-435S and T47D, and the endometrial carcinoma cell line, RL95-2, following treatment with IR. In addition, autocrine hGH enhanced MDA-MB-435S and T47D cell clonogenic survival following radiation exposure. The enhanced clonogenic survival afforded by autocrine hGH was mediated by JAK2 and Src kinases. Investigation into the DNA repair capacity demonstrated that autocrine hGH reduced IR-induced DNA damage in MDA-MB-435S and T47D cells. Functional antagonism of hGH increased RL95-2 sensitivity to IR in cell viability and total cell number assays, reduced clonogenic survival and enhanced the induction of DNA damage. Thus, autocrine hGH reduced sensitivity to treatment with IR in mammary and endometrial carcinoma cell lines in vitro, while functional antagonism of hGH sensitised endometrial carcinoma cells to IR. Functional antagonism of hGH, used in conjunction with radiotherapy, may therefore enhance treatment efficacy and improve the prognosis of patients with breast and endometrial cancer.

A botulinum toxin-derived targeted secretion inhibitor downregulates the GH/IGF1 axis

Botulinum neurotoxins (BoNTs) are zinc endopeptidases that block release of the neurotransmitter acetylcholine in neuromuscular synapses through cleavage of soluble N-ethylmaleimide-sensitive fusion (NSF) attachment protein receptor (SNARE) proteins, which promote fusion of synaptic vesicles to the plasma membrane. We designed and tested a BoNT-derived targeted secretion inhibitor (TSI) targeting pituitary somatotroph cells to suppress growth hormone (GH) secretion and treat acromegaly. This recombinant protein, called SXN101742, contains a modified GH-releasing hormone (GHRH) domain and the endopeptidase domain of botulinum toxin serotype D (GHRH-LHN/D, where HN/D indicates endopeptidase and translocation domain type D). In vitro, SXN101742 targeted the GHRH receptor and depleted a SNARE protein involved in GH exocytosis, vesicle-associated membrane protein 2 (VAMP2). In vivo, administering SXN101742 to growing rats produced a dose-dependent inhibition of GH synthesis, storage, and secretion. Consequently, hepatic IGF1 production and resultant circulating IGF1 levels were reduced. Accordingly, body weight, body length, organ weight, and bone mass acquisition were all decreased, reflecting the biological impact of SXN101742 on the GH/IGF1 axis. An inactivating 2-amino acid substitution within the zinc coordination site of the endopeptidase domain completely abolished SXN101742 inhibitory actions on GH and IGF1. Thus, genetically reengineered BoNTs can be targeted to nonneural cells to selectively inhibit hormone secretion, representing a new approach to treating hormonal excess.

[Treatment of acromegaly: a critical analysis of the last ten years]

The ten previous years in terms of acromegaly treatment were essentially characterized by the experience accumulated with new formulations of somatostatin analogues or new drugs such GH-receptor antagonists recently available. Surgery remains the first-line treatment and its results did not change despite the generalization of endoscopy, which mainly seems to decrease local side-effects. The setting of radiotherapy was essentially modified by the increasing use of gamma-knife or stereotactic radiotherapy; however, their results are essentially the same as the classic fractionated, conventional radiotherapy and nobody knows if it will decrease the side-effects of this therapeutic modality. Nevertheless, thanks to a multistep therapeutic strategy, combining the different therapeutic modalities, it has become very rare for acromegaly not to be controlled in a patient.

Improvement of cardiac parameters in patients with acromegaly treated with medical therapies

In acromegaly, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) excess results in a specific cardiomyopathy characterized by concentric cardiac hypertrophy primarily associated with diastolic dysfunction that can lead to impaired systolic function and eventually heart failure. This review of the literature evaluates the effect of therapeutic intervention on cardiac parameters. Clinical studies investigating the impact of treatments for acromegaly on cardiac function published between January 1980 and January 2009 were identified through electronic searches of Medline. Suppression of GH and IGF-1 following surgery or medical treatment with somatostatin analogue therapy is effective in decreasing left ventricular (LV) hypertrophy, with subsequent improvement in cardiac function. First-line treatment with somatostatin analogues resulted in improved cardiac outcome compared with first-line surgery, possibly due to somatostatin analogues acting directly through somatostatin receptors on cardiac cells. Additional cardiac improvement has been reported when somatostatin analogue treatment was combined with surgery. In patients where complete biochemical control was not achieved, an improved cardiac performance following treatment with somatostatin analogues has been reported. Treatment with pegvisomant has been demonstrated to reduce LV hypertrophy and improve diastolic and systolic performance. In contrast, reports have suggested that treatment with the dopamine agonist cabergoline increased the incidence of valvular heart disease. Although surgery and somatostatin analogues are effective in improving cardiomyopathy, a greater beneficial effect is observed with somatostatin analogue treatment. Selected patients with acromegaly should consider first-line therapy or pre-treatment with somatostatin analogues prior to surgery to achieve biochemical control and improve cardiac dysfunction.

Glycometabolic control in acromegalic patients with diabetes: a study of the effects of different treatments for growth hormone excess and for hyperglycemia

BACKGROUND

Diabetes mellitus is frequently observed in patients with acromegaly. Current therapies for acromegaly may impact glucose regulation, influencing insulin sensitivity and secretion. The question whether these therapies modify control and progression of diabetes once present is still open.

AIM

Aim of our study is to analyze glucose control in acromegalic patients with diabetes, evaluating the relation with treatments for GH excess and for diabetes.

METHODS

Seventy patients with acromegaly and diabetes were studied. Duration and treatments of acromegaly and diabetes were recorded, together with clinical and metabolic parameters.

RESULTS

Most patients (92.8%) were treated with somatostatin analogs (SSA), either alone or in combination with dopamine-agonists (20%) or pegvisomant (15.7%); 7.1% of patients had been treated by surgery alone. Metformin (65.7%), alone or in combination with other hypoglycemic drugs, was the most frequent treatment for diabetes, followed by insulin (21.5%). Only 15.7% were treated with diet alone. The whole cohort showed a very good control of diabetes and acromegaly. Median glycated hemoglobin was 6.4% (5.9-7). IGF-I was within normal range for age in most patients. No relation was observed between duration of acromegaly or diabetes and metabolic control. SSA had a negative effect on insulin secretion, but these effects did not influence glucose control. Finally, we observed a low prevalence of nephropathy (6%) and retinopathy (20%).

CONCLUSIONS

Our study shows that a good control of hyperglycemia can be obtained with success in the majority of acromegalic patients with diabetes, independently of the type of treatment for GH excess.

Mutual regulation of growth hormone and bone morphogenetic protein system in steroidogenesis by rat granulosa cells

GH induces preantral follicle growth and differentiation with oocyte maturation. However, the effects of GH on ovarian steroidogenesis and the mechanisms underlying its effects have yet to be elucidated. In this study, we investigated the actions of GH on steroidogenesis by rat granulosa cells isolated from early antral follicles by focusing on the ovarian bone morphogenetic protein (BMP) system. We found that GH suppressed FSH-induced estradiol production with reduction in aromatase expression and, in contrast, GH increased FSH-induced progesterone level with induction of steroidogenic acute regulatory protein, side chain cleavage cytochrome P450, and 3β-hydroxysteroid dehydrogenase. The effects of GH on steroidogenesis by granulosa cells were enhanced in the presence of the BMP antagonist noggin. Coculture of GH with oocytes did not alter GH regulation of steroidogenesis. Steroid production induced by cAMP donors was not affected by GH treatment and the GH effects on FSH-induced steroid production were not accompanied by changes in cAMP synthesis, suggesting that GH actions were not directly mediated by the cAMP-protein kinase A pathway. GH exerted synergistic effects on MAPK activation elicited by FSH, which regulated FSH-induced steroidogenesis. In addition, GH-induced signal transducer and activator of transcription phosphorylation was involved in the induction of IGF-I expression. GH increased IGF-I, IGF-I receptor, and FSH receptor expression in granulosa cells, and inhibition of IGF-I signaling restored GH stimulation of FSH-induced progesterone production, suggesting that endogenous IGF-I is functionally involved in GH effects on progesterone induction. BMP inhibited IGF-I effects that increased FSH-induced estradiol production with suppression of expression of the GH/IGF-I system, whereas GH/IGF-I actions impaired BMP-Sma and Mad related protein 1/5/8 signaling through down-regulation of the expression of BMP receptors. Thus, GH acts to modulate estrogen and progesterone production differentially through endogenous IGF-I activity in granulosa cells, in which GH-IGF-I interaction leads to antagonization of BMP actions including suppression of FSH-induced progesterone production. Mutual balance between GH/IGF-I and BMP signal intensities may be a key for regulating gonadotropin-induced steroidogenesis in growing follicles.

Inhibitory GH receptor extracellular domain monoclonal antibodies: three-dimensional epitope mapping

GH receptor (GHR) mediates the anabolic and metabolic effects of GH. We previously characterized a monoclonal antibody (anti-GHR(ext-mAb)) that reacts with subdomain 2 of the rabbit GHR extracellular domain (ECD) and is a conformation-specific inhibitor of GH signaling in cells bearing rabbit or human GHR. Notably, this antibody has little effect on GH binding and also inhibits inducible metalloproteolysis of the GHR that occurs in the perimembranous ECD stem region. In the current study, we demonstrate that anti-GHR(ext-mAb) inhibits GH-dependent cellular proliferation and also inhibits hepatic GH signaling in vivo in mice that adenovirally express rabbit GHR, as assessed with our noninvasive bioluminescence hepatic signaling assay. A separate monoclonal antibody (anti-GHR(mAb 18.24)) is a sister clone of anti-GHR(ext-mAb). Here, we demonstrate that anti-GHR(mAb 18.24) also inhibits rabbit and human GHR signaling and inducible receptor proteolysis. Further, we use a random PCR-generated mutagenic expression system to map the three-dimensional epitopes in the rabbit GHR ECD for both anti-GHR(ext-mAb) and anti-GHR(mAb 18.24). We find that each of the two antibodies has similar, but nonidentical, discontinuous epitopes that include regions of subdomain 2 encompassing the dimerization interface. These results have fundamental implications for understanding the role of the dimerization interface and subdomain 2 in GHR activation and regulated GHR metalloproteolysis and may inform development of therapeutics that target GHR.

Signaling cross talk between growth hormone (GH) and insulin-like growth factor-I (IGF-I) in pancreatic islet β-cells

Dysfunction and destruction of pancreatic islet β-cells is a hallmark of diabetes. Better understanding of cell signals regulating β-cell growth and antiapoptosis will allow development of therapeutic strategies for diabetes by preservation and expansion of β-cell mass. GH and IGF-I share a complicated physiological relationship and have both been implicated in β-cell function. GH and IGF-I exert their biological effects through binding to respective receptors (GHR and IGF-IR) and subsequently engaging downstream signaling pathways. However, their collaborative roles in modulation of β-cell mass and the underlying molecular mechanisms remain poorly understood. In this study, we demonstrate that cultured β-cells are appealing systems for investigating potential GH-IGF-I signaling cross talk. We uncover that GH specifically promotes formation of a protein complex containing GHR, Janus kinase 2 (a nonreceptor kinase coupled to GH/GHR signaling), and IGF-IR. More importantly, GH and IGF-I synergistically activate both signal transducer and activator of transcription 5 and Akt pathways. Concomitantly, β-cells proliferate more robustly and are better protected from serum deprivation-induced apoptosis when exposed to GH and IGF-I in combination vs. GH or IGF-I alone. The augmented proliferative effects by GH and IGF-I are confirmed in isolated islets. Taken together, our findings strongly suggest that there exists a novel signaling relationship between GH/GHR and IGF-I/IGF-IR systems in β-cells, i.e. IGF-IR may serve as a proximal component of GH/GHR signaling, contributing to enhancement of β-cell mass and function. In support of this, IGF-IR knockdown in β-cells resulted in the desensitization of acute GH-induced signal transducer and activator of transcription 5 activation.

Cotreatment with pegvisomant and a somatostatin analog (SA) in SA-responsive acromegalic patients

CONTEXT

Cotreatment of acromegaly with pegvisomant and a somatostatin analog (SA) has proven feasible. Previous studies in the field have focused on patients with an insufficient response to SA monotherapy in whom pegvisomant was added without changing the SA dose.

OBJECTIVE

The objective of the study was to study whether patients sufficiently controlled on SA monotherapy can be transferred to combination therapy with low-dose pegvisomant and a reduced SA dose.

DESIGN

Eighteen acromegalic patients well controlled on SA monotherapy, mean ± se aged 54 ± 3 yr, were randomized in a parallel study over 24 wk to unchanged SA monotherapy or cotreatment with pegvisomant (15-30 mg twice a week) and SA (half the usual dosage).

SETTING

This was an investigator-initiated study in a single tertiary referral center.

MAIN OUTCOME MEASURES

Glucose tolerance, substrate metabolism, insulin sensitivity, body composition, and quality of life were measured.

RESULTS

Median pegvisomant dose was 52.5 mg/wk (range 30-60). IGF-I (micrograms per liter) was comparable both at baseline (P = 0.88) and after 24 wk of treatment (P = 0.48). The change in IGF-I between baseline and wk 24 also did not differ between groups (P = 0.15). Apart from increased peak insulin levels during the oral glucose tolerance test in the cotreatment group, no substantial differences between the two groups were detected. Moderately elevated liver enzymes were found in 17% of the patients on pegvisomant therapy.

CONCLUSION

Acromegalic patients well controlled on SA monotherapy can maintain safe IGF-I levels during 24 wk of cotreatment with low-dose pegvisomant and a 50% reduced SA dose. This treatment modality, however, does not seem to provide significant benefits for the patients.

Combination treatment with somatostatin analogues and pegvisomant in acromegaly

Mono-therapy using long-acting somatostatin analogues and surgery cannot provide optimal biochemical control in a large proportion of patients with acromegaly. This results in increased mortality, poor control of signs and symptoms of disease and decreased quality of life. Combined treatment with somatostatin analogues and pegvisomant (a growth-hormone-receptor antagonist) seems to be an attractive option. Combination treatment is highly effective at normalising the level of insulin-like growth factor 1 in over 90% of patients and has a favourable effect on quality of life in those with biochemically controlled acromegaly. Moreover, combination therapy with somatostatin analogues results in a clinically relevant decrease in tumour size in about 20% of patients, whereas pegvisomant (PEG-V) mono-therapy does not decrease pituitary tumour size. Transient elevations in the levels of transaminases are the main adverse effects of combination treatment, which occur in about 11-15% of patients.

[Growth hormone receptor antagonist in the treatment of acromegaly]

Exploration of construction, function and interaction of human growth hormone and growth hormone receptor in details resulted in the innovation of the new growth hormone receptor antagonist, pegvisomant. Pegvisomant with different mechanism of action extended the tools of medical management of acromegaly. Importance of the novel treatment modality is high. In one hand the necessity of the strict control of growth hormone/insulin-like growth factor-I axis has been proven regarding the mortality of the disease. On the other hand, despite the use of all current modes of treatment (surgery, radiotherapy, dopamine agonists, somatostatin analogs), a significant cohort of patients with acromegaly remains inadequately controlled. Pegvisomant has been registered in 2004. Since 2006, it has been used in Hungary for the treatment of acromegaly in patients who have had an inadequate response to surgery and/or radiation therapy and/or other medical therapies, or for whom these therapies are not appropriate. Clinical use of pegvisomant in the treatment of acromegaly is effective, well tolerated, and safe, based on international Acrostudy database. In order to improve the efficacy of therapy clinical trials started with pegvisomant and somatostatin analog combination treatment. Evidence of several further effects of the growth hormone/insulin-like growth factor-I axis suggests other potential uses of growth hormone receptor antagonists.

Serum proteome changes in acromegalic patients following transsphenoidal surgery: novel biomarkers of disease activity

CONTEXT

Transsphenoidal adenomectomy is the primary treatment for acromegaly. However, assessment of the therapeutical outcome remains problematic since the existing biomarkers of disease activity frequently show discordant results.

OBJECTIVE

To discover novel serum biomarkers of disease activity in acromegalic patients before and after surgery.

DESIGN

Serum samples of eight newly diagnosed acromegaly patients before and after transsphenoidal surgery were analyzed for proteomic changes by two-dimensional gel electrophoresis. Protein spots displaying statistically significant changes, pre- versus post-surgery, were identified by mass spectrometry (MS), tandem MS (MS/MS), and western blot analysis.

RESULTS

Six protein spots displaying decreased intensities after surgery were identified as transthyretin (two isoforms), haptoglobin α2, β-hemoglobin, and apolipoprotein A-1 (two isoforms). One protein spot, identified as complement C4B precursor, was increased after the surgery.

CONCLUSIONS

Seven serum protein spots were differentially expressed following surgery in acromegalic patients. The identified proteins represent potential novel biomarkers to assess the effectiveness of surgical treatment in acromegalic individuals. Future studies will validate the use of the identified proteins as biomarkers of disease activity after medical treatment of acromegaly.

Acromegaly: a review of current medical therapy and new drugs on the horizon

Acromegaly is a disease that results from a growth hormone (GH)–secreting pituitary tumor. Clinically, the disease is characterized by excessive skeletal growth, soft tissue enlargement with disfigurement, and increased risk of cardiovascular death. The goals of treatment are the removal or reduction of the tumor mass via surgery and normalization of GH secretion. Another treatment goal is the preservation of normal pituitary function if possible. Transsphenoidal surgery by an experienced neurosurgeon is usually the first line of therapy, especially for small tumors. Surgeon expertise is crucial for outcome, with dedicated pituitary surgeons having better results. However, overall cure rates remain low because patients with these tumors usually present at an incurable stage. Therefore, medical therapy to control excess GH secretion plays a significant role in a large proportion of patients with acromegaly who are not cured by surgery or other forms of therapy, such as radiotherapy, and/or are awaiting the effects of radiotherapy. If surgery is not curative, lifelong monitoring and the control of excess GH is usually necessary by a care team experienced in handling this chronic disease. In the past decade major progress has occurred in the development of highly specific and selective pharmacological agents that have greatly facilitated more aggressive management of active acromegaly. Treatment approach should be individualized and take into consideration a patient's tumor size and location, symptoms, comorbid conditions, and preferences. Because a surgical cure can be difficult to achieve, all patients, even those with what seems to be a clinically and biochemically inactive disease, should undergo long-term biochemical testing and pituitary MR imaging.

Development and characterization of high affinity leptins and leptin antagonists

Leptin is a pleiotropic hormone acting both centrally and peripherally. It participates in a variety of biological processes, including energy metabolism, reproduction, and modulation of the immune response. So far, structural elements affecting leptin binding to its receptor remain unknown. We employed random mutagenesis of leptin, followed by selection of high affinity mutants by yeast surface display and discovered that replacing residue Asp-23 with a non-negatively charged amino acid leads to dramatically enhanced affinity of leptin for its soluble receptor. Rational mutagenesis of Asp-23 revealed the D23L substitution to be most effective. Coupling the Asp-23 mutation with alanine mutagenesis of three amino acids (L39A/D40A/F41A) previously reported to convert leptin into antagonist resulted in potent antagonistic activity. These novel superactive mouse and human leptin antagonists (D23L/L39A/D40A/F41A), termed SMLA and SHLA, respectively, exhibited over 60-fold increased binding to leptin receptor and 14-fold higher antagonistic activity in vitro relative to the L39A/D40A/F41A mutants. To prolong and enhance in vivo activity, SMLA and SHLA were monopegylated mainly at the N terminus. Administration of the pegylated SMLA to mice resulted in a remarkably rapid, significant, and reversible 27-fold more potent increase in body weight (as compared with pegylated mouse leptin antagonist), because of increased food consumption. Thus, recognition and mutagenesis of Asp-23 enabled construction of novel compounds that induce potent and reversible central and peripheral leptin deficiency. In addition to enhancing our understanding of leptin interactions with its receptor, these antagonists enable in vivo study of the role of leptin in metabolic and immune processes and hold potential for future therapeutic use in disease pathologies involving leptin.

Influence of pegvisomant on serum ghrelin and leptin levels in acromegalic patients

INTRODUCTION

Pegvisomant (peg) is a GH receptor antagonist. In de novo acromegalic patients with high GH levels, ghrelin and leptin levels are reduced, suggesting a direct GH-mediated effect. The aim of our study was to evaluate whether peg treatment in acromegalic patients may abolish the GH impact on ghrelin and leptin levels.

METHODS

Ghrelin, leptin and endogenous GH were measured in ten peg-treated acromegalic patients (three females/seven males, 47 years (28-57)), ten patients with active (act) and ten patients with inactive disease (inact) as well as in ten gender-, age- and body mass index (BMI)-matched healthy volunteers (controls). Endogenous GH was measured using a special in-house assay without interference by peg; total ghrelin and leptin were determined using a commercial RIA and an immunofluorometric in-house assay respectively.

RESULTS

Age and BMI did not differ significantly between groups. Endogenous GH was significantly higher in peg (6.3 μg/l (1.5-41)) and act (9.3 μg/l (1.7-70)) compared with controls (0.1 μg/l (0.1-3.1)) and inact (0.35 μg/l (0.1-2.0), P<0.001). Ghrelin was significantly higher in peg (232  ng/l (96-351)) compared with act (102 ng/l (33-232), P<0.01), whereas ghrelin was not significantly different between the other groups. Leptin was highest in controls (19 μg/l (4-57)) and lowest in act (6 μg/l (2-21)), but this difference did not reach significance.

CONCLUSION

Treatment with peg seems to disrupt the feedback loop of ghrelin and GH, leading to elevated ghrelin levels. Furthermore, peg therapy appears not to have a strong impact on leptin levels, as acromegalic patients with and without peg treatment showed similar leptin levels.

The acute effect of a single application of cabergoline on endogenous GH levels in patients with acromegaly on pegvisomant treatment

OBJECTIVE

Treatment with pegvisomant, an antagonist of growth hormone (GH) receptors, increases GH levels in a dose dependent manner. Cabergoline can suppress GH secretion in approximately 40% of acromegalic patients. However, the acute effects of cabergoline have not been studied in patients treated with pegvisomant. We performed this cross-sectional study to evaluate endogenous GH after an additional single cabergoline administration.

DESIGN

9 acromegalic patients on pegvisomant therapy were included. A 6h GH profile after pegvisomant alone (P) and a 9h profile in combination with oral cabergoline 0.5mg (PC) were performed. After 3 or 6h, all patients received a standardized light mixed meal. Endogenous serum GH and pegvisomant levels were measured by special in-house assays. The GH assay showed no interference with pegvisomant.

RESULTS

Endogenous GH levels at baseline did not differ significantly between the profiles (P: 16.5 μg/l (range 3.2-36.6 μg/l), PC: 8.0 μg/l (1.6-48 μg/l), p>0.05). In both profiles, GH fluctuated before meal. GH decreased more pronounced in PC but this decrease was not statistically significant. After meal, a significant decline in endogenous GH levels from 16.4 μg/l (0.4-27.1 μg/l, 100%) to 8.1 μg/l (0.2-24.7 μg/l, 66%) appeared in P at 300 min (p<0.01). Also in PC a decline from 7.8 μg/l (1.1-29.6 μg/l, 100%) to 5.2 μg/l (0.4-23.9 μg/l, 75%) at 300 min was observed but it was not significant.

CONCLUSION

Endogenous GH is not significantly decreased after a single oral cabergoline application during pegvisomant treatment in acromegaly.

STAT3alpha is oncogenic for endometrial carcinoma cells and mediates the oncogenic effects of autocrine human growth hormone

We herein demonstrate an oncogenic role for signal transducer and activator of transcription (STAT)-3alpha (the full length STAT3 isoform), which also mediates autocrine human GH (hGH)-stimulated oncogenicity, in human endometrial carcinoma (EC) cells. Autocrine hGH stimulated Y705 phosphorylation of STAT3 and STAT3-mediated transcriptional activity in a SRC and Janus-2 Kinase dependent manner in human EC cell lines. Forced expression of a constitutively active variant of STAT3alpha increased proliferation, anchorage-independent, three-dimensional (3D) Matrigel, and xenograft growth and promoted epithelial-mesenchymal transition, migration, and invasion of EC cells. Conversely, the oncogenic capacity of EC cells was significantly impaired by treatment with JSI-124, an inhibitor of STAT3 phosphorylation and activity, small interfering RNA-mediated depletion of STAT3alpha, or a dominant-negative variant of STAT3alpha. Furthermore, the enhanced EC cell oncogenicity stimulated by autocrine hGH, was also abrogated by functional inhibition or small interfering RNA-mediated depletion of STAT3alpha. STAT3alpha may therefore be a common mediator of oncogenic signaling pathways stimulating progression of EC.

New formulations and approaches in the medical treatment of acromegaly

PURPOSE OF REVIEW

To discuss novel drug formulations being developed for the medical treatment of acromegaly and to highlight recent data from studies reporting more effective therapeutic strategies using existing drugs.

RECENT FINDINGS

Despite advances in the management of acromegaly a significant number of patients remain uncontrolled. Primary medical treatment is being increasingly considered, but use of somatostatin analogues, the current mainstay of medical therapy, achieves control in only around 60% of patients, whilst 10-20% may be controlled with dopamine agonists. Consequently, improvements in drug efficacy and convenience are needed. Newer longer-acting somatostatin analogues are in development and combination regimes with the growth hormone receptor antagonist, pegvisomant, given at more cost-effective weekly doses show promising results. Somatostatin analogue-resistant tumours may respond to ligands with higher affinities to other receptors, such as pasireotide (SOM 230). Further, the combined dopamine/somatostatin receptor analogue BIM-23A760 has increased affinity to somatostatin receptors 2 and 5 and to the dopamine 2 receptor, and phase 2 clinical studies are underway.

SUMMARY

These novel drugs, formulations and treatment regimes should potentially add to the armamentarium of treatment options for patients with acromegaly.

A pegylated growth hormone receptor antagonist, pegvisomant, does not enter the brain in humans

BACKGROUND

GH receptors exist in the hippocampus, cerebral cortex, and hypothalamus, possibly influencing mood, cortical blood flow, and neuronal growth and mediating negative feedback.

RATIONALE

Pegvisomant is a recombinant mutated GH molecule with high affinity, but little or no activating capability, for the GH receptor. It is used clinically as a GH antagonist.

HYPOTHESIS

Systemic pegvisomant enters brain interstitial fluid via putative choroid-plexus GH receptors, thereby allowing for antagonism of central actions of GH. SUBJECTS AND LOCATION: Six adults requiring a cerebrospinal fluid (CSF) examination for nonneoplastic and noninflammatory syndromes participated at a tertiary medical center.

METHODS

Direct assays were conducted of serum and CSF pegvisomant concentrations 18-24 h after sc injection of pegvisomant (20 mg).

OUTCOMES

Median (range) concentrations of pegvisomant in serum were 215 (74-539) microg/liter and in CSF 0.035 (0.010-0.28) microg/liter (P=0.016). CSF drug levels were indistinguishable from assay threshold. Corresponding GH values were 0.29 (0.010-1.3) in serum and 0.075 microg/liter (0.01-0.13) in CSF. The geometric mean ratios of serum/CSF pegvisomant and GH concentrations were 5116:1 and 3.5:1, respectively, thus defining a more than 1400-fold difference between mutated and natural GH.

CONCLUSIONS

Based upon CSF measurements, a pegylated GH-receptor antagonist does not cross the human blood-brain barrier, thereby sparing inhibition of central nervous system GH actions. Thus, the capability of this antagonist to stimulate GH secretion predominantly reflects its actions outside the blood-brain barrier, such as via the median eminence and/or via suppression of IGF-I concentrations.

Prostate cancer and acromegaly

Acromegalic patients have an increased prevalence of prostatic disorders compared to age-matched healthy subjects. Increased size of the whole prostate or the transitional zone, together with an elevated incidence of other structural changes, such as nodules, cysts, and calcifications, have been reported. Prostate enlargement in young acromegalic patients with low testosterone levels due to central hypogonadism supports the hypothesis that chronic GH and IGF-I excess cause prostate hyperplasia. The relationship between prostatic carcinoma and acromegaly is, until now, only circumstantial. Long-term follow-up of these patients is necessary since epidemiologic studies showed association between serum IGF-I levels in the upper normal limit and prostate cancer in the general population. This review approaches prostate diseases in patients with acromegaly.

Crystal structure of an affinity-matured prolactin complexed to its dimerized receptor reveals the topology of hormone binding site 2

We report the first crystal structure of a 1:2 hormone.receptor complex that involves prolactin (PRL) as the ligand, at 3.8-A resolution. Stable ternary complexes were obtained by generating affinity-matured PRL variants harboring an N-terminal tail from ovine placental lactogen, a closely related PRL receptor (PRLR) ligand. This structure allows one to draw up an exhaustive inventory of the residues involved at the PRL.PRLR site 2 interface, consistent with all previously reported site-directed mutagenesis data. We propose, with this description, an interaction model involving three structural components of PRL site 2 ("three-pin plug"): the conserved glycine 129 of helix alpha3, the hydrogen bond network involving surrounding residues (glycine cavity), and the N terminus. The model provides a molecular basis for the properties of the different PRL analogs designed to date, including PRLR antagonists. Finally, comparison of our 1:2 PRL.PRLR(2) structure with those of free PRL and its 1:1 complex indicates that the structure of PRL undergoes significant changes when binding the first, but not the second receptor. This suggests that the second PRLR moiety adapts to the 1:1 complex rather than the opposite. In conclusion, this structure will be a useful guiding tool for further investigations of the molecular mechanisms involved in PRLR dimerization and activation, as well as for the optimization of PRLR antagonists, an emerging class of compounds with high therapeutic potential against breast and prostate cancer.

Octreotide LAR: safety and tolerability issues

BACKGROUND

Somatostatin analogues are the cornerstone in therapy of acromegaly and functioning neuroendocrine tumors. Long-acting retard formulations have improved patient survival and contributed considerably to quality of life. The first such compound was octreotide LAR ('long-acting release'), characterized by high affinity to somatostatin receptor subtypes 2 and 5, which has to be injected intramuscularly every 4 weeks.

OBJECTIVE

The aim was to screen all octreotide LAR-related literature and assess the compound's profile for safety and tolerability.

METHODS

An extensive literature search has been performed using the MEDLINE database to retrieve data from clinical studies evaluating the efficacy and tolerability of octreotide LAR.

RESULTS/CONCLUSION

Octreotide LAR is well tolerated; however, diarrhea and gallstone formation were identified as the main adverse events. Impairment of glucose homeostasis was a regular phenomenon, but its occurrence was unpredictable. General side effects such as headache, abdominal discomfort or fatigue were also reported. According to incidental case reports, administration during pregnancy appears to be safe for both mother and child; however, definitive evidence is missing. In addition, octreotide LAR has been evaluated for further indications including treatment of solid tumor entities, due to its antiproliferative effect. Currently, several compounds (lanreotide, SOM230) with a broader receptor spectrum are under evaluation and may improve treatment efficacy and lower incidence of side effects.

Pegvisomant: current and potential novel therapeutic applications

BACKGROUND

Pegvisomant is a genetically engineered molecule, which exhibits specific growth hormone (GH) antagonism by directly interacting with the GH receptor. It is currently licensed for the treatment of acromegaly where surgery and medical therapy with somatostatin analogues have failed.

OBJECTIVE

To delineate the role of pegvisomant in the treatment of acromegaly and its novel application in other areas of clinical medicine where suppression of GH action may be of therapeutic benefit.

METHODS

A literature review from PubMed- and EMBASE-listed publications and the web-sites of licensing organisations for medicinal products.

CONCLUSION

Pegvisomant is currently used as a second line therapy in the management of acromegaly. It is highly effective in suppressing the metabolic effects of elevated GH levels when used alone or in combination with somatostatin analogues. However, its long term efficacy and safety for this indication has yet to be established. Preliminary data indicate that pegvisomant may have a role in management of type 1 diabetes with beneficial effects on insulin sensitivity and in preventing the progression of microvascular complications. Additional roles as an adjunct to cancer chemotherapy regimens and for the diagnosis of GH deficiency have been proposed, but have yet to be confirmed.

Comparison of pegvisomant and long-acting octreotide in patients with acromegaly naïve to radiation and medical therapy

BACKGROUND

Normalization of IGF-I in patients with acromegaly is associated with a decrease in mortality. Pegvisomant may be more effective in lowering IGF-I than octreotide.

SUBJECTS AND METHODS

The efficacy and safety of pegvisomant and octreotide long-acting release (LAR) were compared in 118 patients with acromegaly in this 52-week, multicenter, open-label, randomized study. The primary endpoint was IGF-I normalization at week 52. Secondary endpoints included mean changes from baseline in IGF-I, IGF binding protein 3, acromegaly signs and symptom scores, ring size, acromegaly quality of life questionnaire scores, and safety.

RESULTS

Fifty-six patients received pegvisomant and 57 received octreotide LAR. IGF-I normalized in 51% of pegvisomant patients and 34% treated with octreotide LAR (p=0.09, ns). Patients with baseline IGF-I > or = 2x upper limit of normal had a higher rate of IGF-I normalization with pegvisomant vs octreotide LAR (p=0.05). Among the patients who did not achieve a normalized IGF-I, pegvisomant-treated patients were more likely to be receiving < 30 mg of study drug (71% vs 16%). Treatment-related adverse events were mild-to-moderate in both groups. Mean fasting glucose decreased in diabetic and non-diabetic patients on pegvisomant whereas octreotide LAR was associated with an increase at week 52 (p=0.005 and p=0.003 between groups, respectively). Mean change in tumor volume during treatment was similar between groups.

CONCLUSIONS

Pegvisomant and octreotide LAR were equally effective in normalizing IGF-I in the overall population, and pegvisomant was more effective in patients with higher baseline IGF-I levels. Pegvisomant had a more favorable effect on parameters of glycemic control.

Impact of growth hormone receptor blockade on substrate metabolism during fasting in healthy subjects

CONTEXT

Experimental studies in GH-deficient patients and in healthy subjects receiving somatostatin-infusion suggest that GH is an important regulator of substrate metabolism during fasting. These models may not adequately reflect the selective effects of GH, and GH receptor (GHR) blockade offers a new model to define the metabolic role of GH.

OBJECTIVE

The aim of this study was to investigate the impact of GHR blockade on substrate metabolism and insulin sensitivity during fasting.

DESIGN

We conducted a randomized, placebo-controlled, crossover study in 10 healthy young men.

INTERVENTION

After 36 h of fasting with saline or pegvisomant (GHR blockade), the subjects were studied during a 4-h basal period and 2.5-h hyperinsulinemic euglycemic clamp.

MAIN OUTCOME

We measured whole-body and forearm glucose, lipid, and protein metabolism, peripheral insulin sensitivity, and acyl and desacyl ghrelin.

RESULTS

GHR blockade significantly suppressed circulating free fatty acids (1226 +/- 83 vs. 1074 +/- 65 micromol/liter; P = 0.03) and ketone bodies (3080 +/- 271 vs. 2015 +/- 235 micromol/liter; P <or= 0.01), as well as forearm uptake of free fatty acids (0.341 +/- 0.150 vs. 0.004 +/- 0.119 micromol/100 ml x min; P < 0.01) and lipid oxidation (1.3 +/- 0.1 vs. 1.2 +/- 0.1 mg/kg x min; P = 0.03) in the basal period. By contrast, IGF-I levels in either serum or peripheral tissues were not impacted by GHR blockade, and protein metabolism was also unaffected. Basal glucose levels were elevated by GHR blockade, but insulin sensitivity was similar; this was associated with an increased acyl/desacyl ghrelin ratio.

CONCLUSION

GHR blockade, without changes in circulating or tissue IGF-I levels, selectively suppresses lipid mobilization and oxidation after short-term fasting. This supports the notion that stimulation of lipolysis is a primary and important effect of GH.

Pituitary tumours: acromegaly

Excessive production of the growth hormone (GH) is responsible for acromegaly. It is related to a pituitary GH-secreting adenoma in most cases. Prevalence is estimated 40-130 per million inhabitants. It is characterised by slowly progressive acquired somatic disfigurement (mainly involving the face and extremities) and systemic manifestations. The rheumatologic, cardiovascular, respiratory and metabolic consequences determine its prognosis. The diagnosis is confirmed by an increased serum GH concentration, unsuppressible by an oral glucose load and by detection of increased levels of insulin-like growth factor-I (IGF-I). Treatment is aimed at correcting (or preventing) tumour compression by excising the disease-causing lesion, and at reducing GH and IGF-I levels to normal values. When surgery, the usual first-line treatment, fails to correct GH/IGF-I hypersecretion, medical treatment with somatostatin analogues and/or radiotherapy can be used. The GH-receptor antagonist (pegvisomant) is helpful in patients who are resistant to somatostatin analogues. Thanks to this multistep therapeutic strategy, adequate hormonal disease control is achieved in most cases, allowing a normal life expectancy.

A randomized, controlled, multicentre trial comparing pegvisomant alone with combination therapy of pegvisomant and long-acting octreotide in patients with acromegaly

OBJECTIVE

For patients with acromegaly who are suboptimally controlled on long-acting octreotide (LAR), treatment options are to switch to pegvisomant monotherapy (PM) or add pegvisomant to LAR (P-LAR). Our objective was to evaluate if the safety and efficacy of these regimens differ.

DESIGN

This was an open-label, multicentre, randomized, 40-week outpatient study. The control arm consisted of patients controlled on LAR (n = 28).

PATIENTS

A total of 27 patients with suboptimally controlled acromegaly [as indicated by a serum IGF-I level > or = 1.3 x upper limit of normal (ULN) of the age-related reference range] were randomized to PM (10 mg once daily initially, then adjusted in 5-mg increments every 8 weeks based on IGF-I levels) and 29 to P-LAR (LAR dosing remained fixed).

MEASUREMENTS

The primary end-point was adverse events (AEs). The secondary end-point was biochemical IGF-I-based efficacy. The RIA for IGF-I was discontinued by the manufacturer during the study and a chemiluminescent assay was subsequently used. Previously obtained IGF-I levels were re-analysed.

RESULTS

PM and P-LAR were well tolerated and there were no differences in the number of AEs. Patients receiving P-LAR tended to be more likely to have clinically significant increases in hepatic transaminase levels, especially those receiving high-dose LAR. Normalization of IGF-I was similar with both regimens (56% and 62% of patients for PM and P-LAR respectively). The change in IGF-I assay resulted in lower rates of IGF-I normalization than expected. Reductions in fasting glucose levels were greater with PM than with P-LAR (-0.8 mmol/l; 95% confidence interval -1.16, -0.53 mmol/l).

CONCLUSIONS

In patients suboptimally controlled on LAR, PM and P-LAR were equally well tolerated and effective in normalizing IGF-I, and overall clinical improvement was observed with both regimens. Thus, pegvisomant monotherapy and adjunctive therapy are equally viable options for the treatment of LAR-resistant acromegaly.

Somatostatin analog and pegvisomant combination therapy for acromegaly

Optimal biochemical control cannot be attained by long-acting somatostatin analog monotherapy in a large proportion of patients with acromegaly. Such therapy might result in increased mortality, poor control of signs and symptoms of disease and decreased quality of life. Combination treatment with somatostatin analogs and pegvisomant (a growth-hormone-receptor antagonist) is, however, highly effective at normalizing the level of insulin-like growth factor I in over 90% of patients and might also have a favorable effect on quality of life in those with biochemically controlled acromegaly. Moreover, whereas pegvisomant monotherapy does not lead to a decrease in the size of the pituitary tumor, combination therapy with somatostatin analogs results in a clinically relevant decrease in tumor size in about 20% of patients. The main adverse effects of combination treatment are transient elevations in the levels of transaminases, which occur in about 15% of patients, especially in those with diabetes mellitus. In this Review, we discuss the available data on the long-term efficacy and safety of somatostatin analog-pegvisomant combination treatment and its potential use in patients with acromegaly.

O-Glycosylated 24 kDa human growth hormone has a mucin-like biantennary disialylated tetrasaccharide attached at Thr-60

MS was used to characterize the 24 kDa human growth hormone (hGH) glycoprotein isoform and determine the locus of O-linked oligosaccharide attachment, the oligosaccharide branching topology, and the monosaccharide sequence. MALDI-TOF/MS and ESI-MS/MS analyses of glycosylated 24 kDa hGH tryptic peptides showed that this hGH isoform is a product of the hGH normal gene. Analysis of the glycoprotein hydrolysate by high-performance anion-exchange chromatography with pulsed amperometric detection and HPLC with fluorescent detection for N-acetyl neuraminic acid (NeuAc) yielded the oligosaccharide composition (NeuAc(2), N-acetyl galactosamine(1), Gal(1)). After beta-elimination to release the oligosaccharide from glycosylated 24 kDa hGH, collision-induced dissociation of tryptic glycopeptide T6 indicated that there had been an O-linked oligosaccharide attached to Thr-60. The sequence and branching structure of the oligosaccharide were determined by ESI-MS/MS analysis of tryptic glycopeptide T6. The mucin-like O-oligosaccharide sequence linked to Thr-60 begins with N-acetyl galactosamine and branches in a bifurcated topology with one appendage consisting of galactose followed by NeuAc and the other consisting of a single NeuAc. The oligosaccharide moiety lies in the high-affinity binding site 1 structural epitope of hGH that interfaces with both the growth hormone and the prolactin receptors and is predicted to sterically affect receptor interactions and alter the biological actions of hGH.

Growth hormone receptor antagonist treatment reduces exercise performance in young males

CONTEXT

The effects of GH on exercise performance remain unclear.

OBJECTIVE

The aim of the study was to examine the effects of GH receptor (GHR) antagonist treatment on exercise performance.

DESIGN

Subjects were treated with the GHR antagonist pegvisomant or placebo for 16 d. After the treatment period, they exercised to determine exercise performance and hormonal and metabolic responses.

PARTICIPANTS

Twenty healthy males participated in the study.

INTERVENTION

Subjects were treated with the GHR antagonist (n = 10; 10 mg/d) or placebo (n = 10). After the treatment period, they performed a maximal oxygen uptake (VO(2 max)) test and a prolonged exercise test, consisting of 60 min of submaximal cycling followed by exercise to fatigue at 90% of VO(2 max).

MAIN OUTCOME MEASURES

VO(2 max) was measured before and after the treatment period. Hormonal and metabolic responses and time to exhaustion during prolonged exercise were determined.

RESULTS

Resting serum IGF-I concentration decreased by 20% in the GHR antagonist-treated group (P < 0.05), whereas no change was observed in the placebo group. Conversely, resting serum GH concentration was significantly higher in the treatment group compared with the placebo group (P < 0.01). VO(2 max) did not change significantly in either group after the treatment period. Time to exhaustion at 90% of VO(2 max) was significantly shorter in the treatment group (P < 0.05). No significant differences were observed between the groups in terms of changes in serum free fatty acids, glycerol, VO(2), or relative fat oxidation.

CONCLUSION

GH might be an important determinant of exercise capacity during prolonged exercise, but GHR antagonist did not alter fat metabolism during exercise.

Emerging role of insulin-like growth factor receptor inhibitors in oncology: early clinical trial results and future directions

Preclinical evidence that targeting the insulin-like growth factor receptor (IGF-IR) is effective in cancer treatment has been accumulating for almost two decades. Efforts to develop drugs began in the late 1990s, and initial data from clinical trials were reported in 2006. The biological rationale for IGF-IR targeting has potential relevance to many tumor types, and early results have justified expanded programs to evaluate IGF-IR-targeting agents in many areas of clinical need. More than two dozen drug candidates have been developed and clinical trials are underway for at least 12 of these. Early clinical trials reveal an acceptable safety profile together with pharmacodynamic evidence that the receptor can be successfully targeted. It is premature to draw conclusions regarding efficacy, but well-documented instances of single-agent activity were noted during phase I evaluations, and recent evidence from a phase II study suggests that co-administration of an anti-IGF-IR antibody with chemotherapy for non-small-cell lung cancer improves objective response rate and progression-free survival. With more than 70 trials involving a variety of drug candidates underway, the IGF-IR is becoming one of the most intensively investigated molecular targets in oncology. Early results justify the continuation of ongoing research across a broad range of cancer indications.

The effect of acute application of pegvisomant alone and in combination with octreotide on endogenous GH levels during a 6-h test in patients with acromegaly on constant pegvisomant treatment

OBJECTIVE

Co-treatment with somatostatin analogues and growth hormone receptor antagonists in acromegaly might be a new treatment option abolishing the negative effects of monotherapy. Nevertheless, little is known about the acute effect of the combined treatment on endogenous GH and pegvisomant levels.

DESIGN

Ten acromegalic patients on constant pegvisomant therapy were included. Two 6-h GH secretion profiles were performed once after pegvisomant alone (P), the other after an additional 100 microg octreotide sc injection (PO). After 180 min, all patients received a standardized light mixed meal. Endogenous serum GH and pegvisomant levels were measured by special in-house assays. In addition, insulin and glucose were measured.

RESULTS

In the combined profile PO, a significant decrease of median endogenous GH was seen (p<0.01, median percentage decline 75.2%, range 23.7-88.2), which was not seen in profile P. Seven of 10 patients had a decline >70% and might be seen as responders. After meal, endogenous GH significantly decreased only in profile P (p<0.01). Pegvisomant levels did not differ significantly between profiles and did not change significantly during the tests. After meal, glucose levels rose higher and later and insulin levels lower and later in profile PO than in profile P.

CONCLUSION

During pegvisomant treatment, endogenous GH can be reduced significantly by acute application of a somatostatin analogue. Therefore, in acromegalic patients on pegvisomant therapy GH regulation due to somatostatin analogues seems to be preserved.

Effects of somatostatin analogs on glucose homeostasis: a metaanalysis of acromegaly studies

BACKGROUND

Somatostatin analogs (SSA) may influence glucose metabolism, but the clinical relevance of this effect is uncertain because trials performed so far are limited in terms of number of patients and heterogeneity for length and type of follow-up.

PURPOSE

The purpose of the study was to assess, via the metaanalysis of acromegaly studies, the clinical impact of SSA on glucose metabolism. The outcomes analyzed were fasting plasma glucose, fasting plasma insulin, hemoglobin A(1c), and plasma glucose concentrations during oral glucose tolerance test.

STUDY SELECTION

Eligibility criteria were: 1) duration of SSA treatment of at least 3 wk; 2) available numerical data for at least one of the four biochemical outcomes investigated; 3) measurement of the outcomes before and after SSA treatment; and 4) no selection of acromegalic patients for their responsivity to SSA. After revision, only 31 studies fulfilled eligibility criteria and were therefore selected for data extraction and analysis.

DATA SYNTHESIS

SSA treatment was found to induce statistically significant decrease in fasting plasma insulin [effect size -0.45, 95% confidence interval (CI) from -0.58 to -0.32, P < 0.001], without any significant change of fasting plasma glucose (effect size +0.04, 95% CI from -0.07 to +0.15, P = 0.52) and hemoglobin A(1c) (effect size +0.11, 95% CI from -0.02 to +0.23, P = 0.09). Serum glucose values during the oral glucose tolerance test were shown to significantly change during SSA treatment (effect size +0.31, 95% CI from +0.17 to +0.45, P < 0.001), although with high inconsistency among trials.

CONCLUSIONS

Our data suggest that modifications of glucose homeostasis induced by SSA may have an overall minor clinical impact in acromegaly.

Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects

In evolutionary terms, GH and intracellular STAT 5 signaling is a very old regulatory system. Whereas insulin dominates periprandially, GH may be viewed as the primary anabolic hormone during stress and fasting. GH exerts anabolic effects directly and through stimulation of IGF-I, insulin, and free fatty acids (FFA). When subjects are well nourished, the GH-induced stimulation of IGF-I and insulin is important for anabolic storage and growth of lean body mass (LBM), adipose tissue, and glycogen reserves. During fasting and other catabolic states, GH predominantly stimulates the release and oxidation of FFA, which leads to decreased glucose and protein oxidation and preservation of LBM and glycogen stores. The most prominent metabolic effect of GH is a marked increase in lipolysis and FFA levels. In the basal state, the effects of GH on protein metabolism are modest and include increased protein synthesis and decreased breakdown at the whole body level and in muscle together with decreased amino acid degradation/oxidation and decreased hepatic urea formation. During fasting and stress, the effects of GH on protein metabolism become more pronounced; lack of GH during fasting increases protein loss and urea production rates by approximately 50%, with a similar increase in muscle protein breakdown. GH is a counterregulatory hormone that antagonizes the hepatic and peripheral effects of insulin on glucose metabolism via mechanisms involving the concomitant increase in FFA flux and uptake. This ability of GH to induce insulin resistance is significant for the defense against hypoglycemia, for the development of "stress" diabetes during fasting and inflammatory illness, and perhaps for the "Dawn" phenomenon (the increase in insulin requirements in the early morning hours). Adult patients with GH deficiency are insulin resistant-probably related to increased adiposity, reduced LBM, and impaired physical performance-which temporarily worsens when GH treatment is initiated. Conversely, despite increased LBM and decreased fat mass, patients with acromegaly are consistently insulin resistant and become more sensitive after appropriate treatment.

Long-term treatment of acromegalic patients resistant to somatostatin analogues with the GH receptor antagonist pegvisomant: its efficacy in relation to gender and previous radiotherapy

CONTEXT

Pegvisomant is an effective treatment for somatostatin analogue-resistant acromegaly, but the determinants defining the response to this treatment are largely unknown.

OBJECTIVE

To investigate the efficacy of pegvisomant treatment in resistant acromegalic patients (e.g. serum IGF1 at least 1.25 x upper normal limit) in a clinical setting and the factors conditioning this response.

DESIGN AND SETTING

A retrospective cross-sectional study performed in six Spanish University hospitals from 2004 to 2007. Patients Forty-four acromegalic patients (61.4% female, mean age: 49+/-14), 95% of whom had undergone pituitary surgery and 61% having received pituitary radiotherapy. The mean follow-up was 22.7+/-11.2 months. Main outcome measures IGF1 levels reflected treatment efficacy, and the influence of gender, age, weight, previous radiotherapy and duration of treatment was assessed.

RESULTS

IGF1 normalisation was achieved in 84% of the patients. Male gender (P<0.05), previous irradiation (P<0.05) and the treatment duration (r=0.364, P<0.02) were associated with a better response to pegvisomant therapy. There was a significant decrease in HbA1c (P<0.001) and in the mean insulin dose (P<0.01) in acromegalic diabetic patients. Although 25% of patients experienced mild adverse events, pegvisomant was only withdrawn in four patients due to side effects (two cases of tumour growth, one liver dysfunction and one headache).

CONCLUSIONS

Long-term pegvisomant is a very effective therapy in resistant acromegaly. Male gender and prior radiotherapy influence the therapeutic response rate.

Current therapy and drug pipeline for the treatment of patients with acromegaly

INTRODUCTION

Acromegaly is a multisystem disease resulting from chronic exposure to supraphysiological levels of growth hormone (GH), and is associated with significant morbidity and excess mortality. The etiology is almost exclusively an underlying pituitary adenoma. Current therapeutic interventions include surgery, radiotherapy, and medical therapy.

RESULTS

Despite surgery, around 50% of patients fail to achieve the biochemical targets shown to correlate with normalization of mortality rates. Radiotherapy is efficacious in controlling tumor growth and GH secretion; still, achievement of biochemical targets may take up to a decade and a number of safety issues have been raised with this treatment modality. Medical therapy, therefore, has an important role as adjuvant therapy in patients who fail to achieve control with surgery, or while awaiting the effects of radiotherapy to be realized. Furthermore, medical therapy is increasingly being used as primary therapy. Current medical therapies include dopaminergic agonists, somatostatin analogs, and GH receptor (GHR) antagonists. Dopaminergic agonists achieve biochemical targets in up to 30% of patients, and somatostatin analogs in around 60%. The currently available GHR antagonist pegvisomant effectively controls insulin-like growth factor-I levels in over 90% of patients; however, it has no effect on the tumor itself and has considerable financial implications. Research into optimizing the somatostatin and dopaminergic systems has led to promising advances in agonist development. Moieties with selectivity for various combinations of somatostatin receptor subtype receptors have been examined, along with molecules that additionally show high affinity for the dopaminergic D2 receptor. Of the molecules studied in vitro, only pasireotide (SOM230) and BIM-23A760 are currently undergoing further development. Other innovations to improve convenience of currently available drugs are also being investigated.

CONCLUSION

Significant advances in under standing of the somatostatin and dopaminergic system have aided drug development. This may lead to new clinically available therapies enabling control of acromegaly in a larger proportion of patients, and at an earlier stage in their disease management.

Autocrine human growth hormone promotes tumor angiogenesis in mammary carcinoma

Accumulating literature implicates pathological angiogenesis and lymphangiogenesis as playing key roles in tumor progression. Autocrine human growth hormone (hGH) is a wild-type orthotopically expressed oncogene for the human mammary epithelial cell. Herein we demonstrate that autocrine hGH expression in the human mammary carcinoma cell line MCF-7 stimulated the survival, proliferation, migration, and invasion of a human microvascular endothelial cell line (HMEC-1). Autocrine/paracrine hGH secreted from mammary carcinoma cells also promoted HMEC-1 in vitro tube formation as a consequence of increased vascular endothelial growth factor-A (VEGF-A) expression. Semiquantitative RT-PCR analysis demonstrated that HMEC-1 cells express both hGH and the hGH receptor (hGHR). Functional antagonism of HMEC-1-derived hGH reduced HMEC-1 survival, proliferation, migration/invasion, and tube formation in vitro. Autocrine/paracrine hGH secreted by mammary carcinoma cells increased tumor blood and lymphatic microvessel density in a xenograft model of human mammary carcinoma. Autocrine hGH is therefore a potential master regulator of tumor neovascularization, coordinating two critical processes in mammary neoplastic progression, angiogenesis and lymphangiogenesis. Consideration of hGH antagonism to inhibit angiogenic processes in mammary carcinoma is therefore warranted.

Growth hormone receptor polymorphism and the effects of pegvisomant in acromegaly

BACKGROUND

Sensitivity to pegvisomant therapy is highly variable in patients with acromegaly but determinants of this variability are still unknown. Lack of exon 3 (d3-) of the growth hormone (GH) receptor (GHR) has been associated with increased biological activity of GH.

OBJECTIVE

To assess whether the presence of d3-GHR haplotype may have a role in predicting dose regimen and response to pegvisomant in acromegaly.

DESIGN

Case series. Setting Institutional referral center at a tertiary care hospital. Patients Nineteen acromegalic patients with active disease after unsuccessful neurosurgery and somatostatin analog therapy.

MEASUREMENTS

Before and 1, 3, 6 and 12 months after treatment with pegvisomant, IGF-I; GH receptor genotype, determined from peripheral blood by polymerase chain reaction. All patients started treatment with pegvisomant at 10 mg/daily and then increased the dose, according to a fixed schedule, during a 12-month follow-up until normalization of IGF-I levels.

RESULTS

d3-GHR patients required a significant lower dose of pegvisomant and shorter treatment time to normalize IGF-I.

CONCLUSION

The GHR genotype could be useful in predicting dose and individual response to pegvisomant in acromegaly.

Insulin and insulin-like growth factor signalling in neoplasia

Insulin and insulin-like growth factors (IGFs) are well known as key regulators of energy metabolism and growth. There is now considerable evidence that these hormones and the signal transduction networks they regulate have important roles in neoplasia. Epidermiological, clinical and laboratory research methods are being used to investigate novel cancer prevention and treatment strategies related to insulin and IGF signalling. Pharmacological strategies under study include the use of novel receptor-specific antibodies, receptor kinase inhibitors and AMP-activated protein kinase activators such as metformin. There is evidence that insulin and IGF signalling may also be relevant to dietary and lifestyle factors that influence cancer risk and cancer prognosis. Recent results are encouraging and have justified the expansion of many translational research programmes.

The impact of PEGylation on biological therapies

The term PEGylation describes the modification of biological molecules by covalent conjugation with polyethylene glycol (PEG), a non-toxic, non-immunogenic polymer, and is used as a strategy to overcome disadvantages associated with some biopharmaceuticals. PEGylation changes the physical and chemical properties of the biomedical molecule, such as its conformation, electrostatic binding, and hydrophobicity, and results in an improvement in the pharmacokinetic behavior of the drug. In general, PEGylation improves drug solubility and decreases immunogenicity. PEGylation also increases drug stability and the retention time of the conjugates in blood, and reduces proteolysis and renal excretion, thereby allowing a reduced dosing frequency. In order to benefit from these favorable pharmacokinetic consequences, a variety of therapeutic proteins, peptides, and antibody fragments, as well as small molecule drugs, have been PEGylated. This paper reviews the chemical procedures and the conditions that have been used thus far to achieve PEGylation of biomedical molecules. It also discusses the importance of structure and size of PEGs, as well as the behavior of linear and branched PEGs. A number of properties of the PEG polymer--e.g. mass, number of linking chains, the molecular site of PEG attachment--have been shown to affect the biological activity and bioavailability of the PEGylated product. Releasable PEGs have been designed to slowly release the native protein from the conjugates into the blood, aiming at avoiding any loss of efficacy that may occur with stable covalent PEGylation. Since the first PEGylated drug was developed in the 1970s, PEGylation of therapeutic proteins has significantly improved the treatment of several chronic diseases, including hepatitis C, leukemia, severe combined immunodeficiency disease, rheumatoid arthritis, and Crohn disease. The most important PEGylated drugs, including pegademase bovine, pegaspargase, pegfilgrastim, interferons, pegvisomant, pegaptanib, certolizumab pegol, and some of the PEGylated products presently in an advanced stage of development, such as PEG-uricase and PEGylated hemoglobin, are reviewed. The adaptations and applications of PEGylation will undoubtedly prove useful for the treatment of many previously difficult-to-treat conditions.

[Acromegaly]

Acromegaly is a rare disease usually caused by growth hormone (GH) hypersecretion, due to a pituitary adenoma; in very rare cases, acromegaly is due to ectopic secretion of GHRH, responsible for pituitary hyperplasia. Owing to its insidious onset, acromegaly is often diagnosed late (4 to > 10 years after onset), at an average age of about 40 years, in front of an acquired, slowly progressing disfigurement mainly involving the face and extremities. Acromegaly has also rheumatologic, cardiovascular, respiratory and metabolic consequences which determine its prognosis. The diagnosis is based on an increased serum GH concentration unsuppressed following an oral glucose load (oral glucose tolerance test -OGTT-) and an increased insulin-like growth factor-I (IGF-I); according to a 2000 Consensus statement, if the basal serum GH is above 0,4microg/L (1.2mIU/L) and/or if the IGF-I is elevated, an OGTT must be performed. If the lowest GH value (nadir) during OGTT remains above 1microg/L (3mIU/L), acromegaly is confirmed. With the generalized use of very sensitive assays nowadays, it has recently been considered that this cutoff should be decreased to 0,3microg/L (0.9mIU/L). Treatment is aimed at correcting (or preventing) tumor compression by excising the culprit lesion, and at reducing GH and IGF-I levels to normal values (or at least to a "safe" GH level of < 2microg/L or < 6mIU/L). A stepwise therapeutic strategy is used: transsphenoidal surgery is often the first-line treatment; when surgery fails to correct GH/IGF-I hypersecretion, medical treatment with somatostatin analogs and/or radiotherapy can be used, somatostatin analogs being generally preferred; the GH antagonist (pegvisomant) is used in patients that are resistant or intolerant to somatostatin analogs. Prognosis of acromegaly has improved in the recent years: adequate hormonal disease control is achieved in most cases, allowing life expectancy similar to that of the general population.

Autocrine human growth hormone stimulates oncogenicity of endometrial carcinoma cells

Recent published data have demonstrated elevated levels of human GH (hGH) in endometriosis and endometrial adenocarcinoma. Herein, we demonstrate that autocrine production of hGH can enhance the in vitro and in vivo oncogenic potential of endometrial carcinoma cells. Forced expression of hGH in endometrial carcinoma cell lines RL95-2 and AN3 resulted in an increased total cell number through enhanced cell cycle progression and decreased apoptotic cell death. In addition, autocrine hGH expression in endometrial carcinoma cells promoted anchorage-independent growth and increased cell migration/invasion in vitro. In a xenograft model of human endometrial carcinoma, autocrine hGH enhanced tumor size and progression. Changes in endometrial carcinoma cell gene expression stimulated by autocrine hGH was consistent with the altered in vitro and in vivo behavior. Functional antagonism of hGH in wild-type RL95-2 cells significantly reduced cell proliferation, cell survival, and anchorage-independent cell growth. These studies demonstrate a functional role for autocrine hGH in the development and progression of endometrial carcinoma and indicate potential therapeutic relevance of hGH antagonism in the treatment of endometrial carcinoma.

Growth hormone excess and the development of growth hormone receptor antagonists

In 1990, a single amino acid substitution in the growth hormone (GH) gene at position 119 was found to transform the consequent protein from an agonist to an antagonist at the growth hormone receptor (GHR). Further amino acid substitutions plus prolongation of the half-life of the protein by pegylation resulted in the first clinically effective GHR antagonist, pegvisomant. Following extensive clinical trials, this medication has emerged as the most efficacious therapy for treatment-resistant acromegaly. Subsequent advances in our understanding of GH-GHR interactions and downstream GH signalling pathways suggest that pegvisomant binds to preformed GHR dimers and prevents rotational changes within the receptor-GH complex necessary for intracellular signalling to occur. This article reviews the discovery of pegvisomant, from initial experimental data to successful licensing of the drug for treatment-resistant acromegaly, and discusses its other potential therapeutic uses in diseases with abnormalities in the GH-IGF-I axis.

Growth hormone signaling in vivo in human muscle and adipose tissue: impact of insulin, substrate background, and growth hormone receptor blockade

CONTEXT

GH induces insulin resistance in muscle and fat, and in vitro data indicate that this may involve cross-talk between the signaling pathways of the two hormones.

OBJECTIVE

Our objective was to investigate GH and insulin signaling in vivo in human muscle and fat tissue in response to GH, GH receptor blockade, and insulin stimulation.

DESIGN

We conducted two randomized crossover studies.

PARTICIPANTS

Sixteen healthy males participated.

INTERVENTION

GH was administered as a bolus (n = 8) and constant infusion (n = 8). The bolus study included three arms: 1) control (saline), 2) GH (0.5 mg iv), and 3) GH blockade (pegvisomant 30 mg sc), each combined with a hyperinsulinemic glucose clamp. The infusion study included two arms: 1) GH infusion (45 ng/.kg.min, 5.5 h) and 2) saline infusion (5.5 h) combined with a hyperinsulinemic glucose clamp during the final 2.5 h.

MAIN OUTCOME MEASURES

Muscle and fat biopsies were subjected to Western blotting for expression of Stat5/p-Stat5, Akt/p-Akt, and ERK1/2/p-ERK1/2 and to real-time RT-PCR for expression of SOCS1-3 and IGF-I mRNA.

RESULTS

GH significantly reduced insulin sensitivity. The GH bolus as well as GH infusion induced phosphorylation of Stat5 in muscle and fat, and SOCS3 and IGF-I mRNA expression increased after GH infusion. Hyperinsulinemia induced Akt phosphorylation in both tissues, irrespective of GH status. In muscle, ERK1/2 phosphorylation was increased by insulin, but insulin per se did not induce phosphorylation of Stat5.

CONCLUSIONS

GH exposure associated with insulin resistance acutely translates into GH receptor signaling in human muscle and fat without evidence of cross-talk with insulin signaling pathways. The molecular mechanisms subserving GH-induced insulin resistance in humans remain unclarified.

Ghrelin in pathological conditions

The recently identified gastric hormone ghrelin was initially described as a natural Growth Hormone Secretagogue Receptor ligand. Apart from ghrelin's first discovered action, which was the stimulation of Growth Hormone release, implications for many other functions have been reported. It seems that ghrelin exhibits an important role in conditions related to processes regulating nutrition, body composition and growth, as well as heart, liver, thyroid or kidney dysfunction. In this review, current available knowledge about ghrelin's role in various pathological conditions is presented.

Growth hormone promotes lymphangiogenesis

The lymphatic system plays an important role in inflammation and cancer progression, although the molecular mechanisms involved are poorly understood. As determined using comparative transcriptional profiling studies of cultured lymphatic endothelial cells versus blood vascular endothelial cells, growth hormone receptor was expressed at much higher levels in lymphatic endothelial cells than in blood vascular endothelial cells. These findings were confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction and Western blot analyses. Growth hormone induced in vitro proliferation, sprouting, tube formation, and migration of lymphatic endothelial cells, and the mitogenic effect was independent of vascular endothelial growth factor receptor-2 or -3 activation. Growth hormone also inhibited serum starvation-induced lymphatic endothelial cell apoptosis. No major alterations of lymphatic vessels were detected in the normal skin of bovine growth hormone-transgenic mice. However, transgenic delivery of growth hormone accelerated lymphatic vessel ingrowth into the granulation tissue of full-thickness skin wounds, and intradermal delivery of growth hormone resulted in enlargement and enhanced proliferation of cutaneous lymphatic vessels in wild-type mice. These results identify growth hormone as a novel lymphangiogenic factor.