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

Lessons learned from studies with the growth hormone receptor

Findings related to GH's biological activities have continued to be a fascinating topic over the past decade. Below, I will review several items related to the actions of GH including the GH/GHR interaction, pegvisomant (a GH receptor antagonist), GHR gene disruptions in mice, and clinical consequences of human GHR gene mutations.

Growth hormone is permissive for neoplastic colon growth

Growth hormone (GH) excess in acromegaly is associated with increased precancerous colon polyps and soft tissue adenomas, whereas short-stature humans harboring an inactivating GH receptor mutation do not develop cancer. We show that locally expressed colon GH is abundant in conditions predisposing to colon cancer and in colon adenocarcinoma-associated stromal fibroblasts. Administration of a GH receptor (GHR) blocker in acromegaly patients induced colon p53 and adenomatous polyposis coli (APC), reversing progrowth GH signals. p53 was also induced in skin fibroblasts derived from short-statured humans with mutant GHR. GH-deficient prophet of pituitary-specific positive transcription factor 1 (Prop1)(-/-) mice exhibited induced colon p53 levels, and cross-breeding them with Apc(min+/-) mice that normally develop intestinal and colon tumors resulted in GH-deficient double mutants with markedly decreased tumor number and size. We also demonstrate that GH suppresses p53 and reduces apoptosis in human colon cell lines as well as in induced human pluripotent stem cell-derived intestinal organoids, and confirm in vivo that GH suppresses colon mucosal p53/p21. GH excess leads to decreased colon cell phosphatase and tensin homolog deleted on chromosome 10 (PTEN), increased cell survival with down-regulated APC, nuclear β-catenin accumulation, and increased epithelial-mesenchymal transition factors and colon cell motility. We propose that GH is a molecular component of the "field change" milieu permissive for neoplastic colon growth.

Safety of long-term treatment with Pegvisomant: analysis of Spanish patients included in global ACROSTUDY

PURPOSE

To evaluate the long-term safety of Pegvisomant (PEG) in the Spanish cohort of ACROSTUDY.

METHODS

As of July 2013, 199 Spanish patients were included in ACROSTUDY, a global non interventional safety PEG surveillance study. Patients were observed for safety, biochemical outcome and magnetic resonance imaging evaluations.

RESULTS

PEG was administered during an average period of 6.7 ± 2.1 years and a mean daily dose of 15.5 ± 7.5 mg. 48.2% of patients received PEG monotherapy. 90.9% of patients had received other medical treatment before PEG start. 195 adverse events (AEs) were reported in 88 patients (44.2%), and serious AEs were described in 31 patients (15.6%). There were no cases of liver tests >10 ULN, or permanent liver damage. Tumor size changes were locally reported in 61 cases (33.5%), with increases observed in 11 patients (6%). In acromegalic patients with diabetes mellitus a decrease in fasting serum glucose value was reported, reaching statistical significance after 1 and 4 years of treatment (-24.6 and -25.9 mg/dl, p = 0.04). After 60 months, normal or lower limit of normal (LLN) IGF-I levels were found in 67.9% of patients. 85.5% of patients showed an IGF-I normal or <LLN at any time after PEG start. Most patients with uncontrolled IGF-I levels were on submaximal PEG doses.

CONCLUSIONS

ACROSTUDY carried out with the Spanish cohort confirmed that PEG has a favorable safety and efficacy profile. The percentage of patients considered under control was similar to data reported globally and in other local ACROSTUDY results.

Long-term treatment with pegvisomant for acromegaly: a 10-year experience

BACKGROUND

Efficacy of the GH-receptor antagonist pegvisomant (PEG) has differed between preclinical and observational studies mainly due to dose adjustment and IGF-I normalization criteria. An escape phenomenon has also been described, but its definition and underlying causes have not been fully established.

OBJECTIVE

To re-evaluate the outcomes of long-term PEG in a series of previously published patients and analyse the escape phenomenon.

METHODS

We reviewed all patients with acromegaly resistant to SSA in whom PEG was started as monotherapy, who had been included in a previous publication. We prospectively evaluated 64 (56·3% women) from six tertiary care referral hospitals in Spain, for whom data as of June 2014 were available. Escape to PEG was defined as confirmed loss of biochemical control (IGF-I >1·2xULN), after at least 6 months of previous control with a stable dose of PEG.

RESULTS

Patients were followed up for 13·0 (5·9-34·8) years since diagnosis, and 9·0 (4·1-10·4) years since the first administration of PEG. Fifty-one (89·5%) patients had an adequate IGF-I control at the last follow-up visit, 9 of them without treatment. Tumour growth was reported in 6 of 64 cases (9·4%), none of whom had received prior radiotherapy (P = 0·011). Seven patients died during follow-up. We found 16 escapes in 10 patients (15·6%). We identified potential underlying causes in 9 cases (tumour regrowth, previous treatment modifications, concomitant menopause and change in testosterone administration). The reason was unknown in 7 escapes, which occurred in 6 patients (9·4%). All patients, except one, achieved subsequent biochemical control after treatment adjustment.

CONCLUSIONS

We reassure the efficacy and safety of long-term PEG. An escape phenomenon may occur, but it can be overcome by adjusting therapy.

Genetic Predictors of Response to Different Medical Therapies in Acromegaly

In the era of predictive medicine, management of diseases is evolving into a more personal and individualized approach, as more data are available regarding clinical, biochemical, radiological, molecular, histopathological, and genetic aspects. In the particular setting of acromegaly, which is a rare, chronic, debilitating, and disfiguring disease, an optimized approach deems even more necessary, especially because of an associated increased morbidity and mortality, the impact on patients' quality of life, and the increased cost of frequently necessary life-long treatments. In this paper, we review the available studies that address potential genetic influences on acromegaly, their role in the outcome, and response to treatments, as well as their contribution to the risk of developing side effects. We focus mainly on pharmacogenetic factors involved during treatment with dopamine agonists, somatostatin analogs, and pegvisomant. Specifically, mutations in dopamine receptors, somatostatin receptors, growth hormone receptors, and metabolic pathways involved in growth hormone action; polymorphisms in the insulin-like growth factor and the insulin-like growth factor binding proteins; and polymorphisms in other genes that may determine differences in the frequency of developing adverse events.

The Placental Variant of Human Growth Hormone Reduces Maternal Insulin Sensitivity in a Dose-Dependent Manner in C57BL/6J Mice

The human placental GH variant (GH-V) is secreted continuously from the syncytiotrophoblast layer of the placenta during pregnancy and is thought to play a key role in the maternal adaptation to pregnancy. Maternal GH-V concentrations are closely related to fetal growth in humans. GH-V has also been proposed as a potential candidate to mediate insulin resistance observed later in pregnancy. To determine the effect of maternal GH-V administration on maternal and fetal growth and metabolic outcomes during pregnancy, we examined the dose-response relationship for GH-V administration in a mouse model of normal pregnancy. Pregnant C57BL/6J mice were randomized to receive vehicle or GH-V (0.25, 1, 2, or 5 mg/kg · d) by osmotic pump from gestational days 12.5 to 18.5. Fetal linear growth was slightly reduced in the 5 mg/kg dose compared with vehicle and the 0.25 mg/kg groups, respectively, whereas placental weight was not affected. GH-V treatment did not affect maternal body weights or food intake. However, treatment with 5 mg/kg · d significantly increased maternal fasting plasma insulin concentrations with impaired insulin sensitivity observed at day 18.5 as assessed by homeostasis model assessment. At 5 mg/kg · d, there was also an increase in maternal hepatic GH receptor/binding protein (Ghr/Ghbp) and IGF binding protein 3 (Igfbp3) mRNA levels, but GH-V did not alter maternal plasma IGF-1 concentrations or hepatic Igf-1 mRNA expression. Our findings suggest that at higher doses, GH-V treatment can cause hyperinsulinemia and is a likely mediator of the insulin resistance associated with late pregnancy.

Pegvisomant Treatment in Acromegaly

Historically, medical treatment of acromegaly has mainly been used as an adjuvant therapy after surgery. In the last decades, an increased range of medical therapy options has been available. Somatostatin analogues have become the cornerstones of medical treatment in acromegaly and are even seen as a primary treatment in a selected group of acromegaly patients. The most recent medical treatment available for acromegaly patients is pegvisomant, a growth hormone receptor antagonist. To date, it is the most effective medical treatment, but it is costly. Pegvisomant is used as monotherapy and combined with somatostatin analogues. In this article, we review clinical studies and cohorts that have documented the efficacy of pegvisomant monotherapy and combined therapy and give a concise overview of associated side effects.

Glucose and Fat Metabolism in Acromegaly: From Mice Models to Patient Care

Patients with active acromegaly are frequently insulin resistant, glucose intolerant, and at risk for developing overt type 2 diabetes. At the same time, these patients have a relatively lean phenotype associated with mobilization and oxidation of free fatty acids. These features are reversed by curative surgical removal of the growth hormone (GH)-producing adenoma. Mouse models of acromegaly share many of these characteristics, including a lean phenotype and proneness to type 2 diabetes. There are, however, also species differences with respect to oxidation rates of glucose and fat as well as the specific mechanisms underlying GH-induced insulin resistance. The impact of acromegaly treatment on insulin sensitivity and glucose tolerance depends on the treatment modality (e.g. somatostatin analogs also suppress insulin secretion, whereas the GH antagonist restores insulin sensitivity). The interplay between animal research and clinical studies has proven useful in the field of acromegaly and should be continued in order to understand the metabolic actions of GH.

Medical Treatment of Acromegaly with Dopamine Agonists or Somatostatin Analogs

Treatment of acromegaly aims to correct (or prevent) tumor compression of surrounding tissues by excising the disease-causing lesion and reduce growth hormone (GH) and IGF-1 levels to normal values. When surgery (the usual first-line treatment) fails to correct GH/IGF-1 hypersecretion, medical treatment with dopamine agonists (DAs; particularly cabergoline) or somatostatin analogs (SAs) can be used. The GH receptor antagonist pegvisomant is helpful in patients who are totally or partially resistant to SAs and can be given in association with both SAs and/or DAs. Thanks to this multistep therapeutic strategy, adequate hormonal disease control is achieved in most patients, giving them normal life expectancy. Comorbidities associated with acromegaly generally improve after treatment, but persistent sequelae may nonetheless impair quality of life.

60 YEARS OF NEUROENDOCRINOLOGY: The hypothalamo-GH axis: the past 60 years

At the time of the publication of Geoffrey Harris's monograph on 'Neural control of the pituitary gland' 60 years ago, the pituitary was recognised to produce a growth factor, and extracts administered to children with hypopituitarism could accelerate growth. Since then our understanding of the neuroendocrinology of the GH axis has included identification of the key central components of the GH axis: GH-releasing hormone and somatostatin (SST) in the 1970s and 1980s and ghrelin in the 1990s. Characterisation of the physiological control of the axis was significantly advanced by frequent blood sampling studies in the 1980s and 1990s; the pulsatile pattern of GH secretion and the factors that influenced the frequency and amplitude of the pulses have been defined. Over the same time, spontaneously occurring and targeted mutations in the GH axis in rodents combined with the recognition of genetic causes of familial hypopituitarism demonstrated the key factors controlling pituitary development. As the understanding of the control of GH secretion advanced, developments of treatments for GH axis disorders have evolved. Administration of pituitary-derived human GH was followed by the introduction of recombinant human GH in the 1980s, and, more recently, by long-acting GH preparations. For GH excess disorders, dopamine agonists were used first followed by SST analogues, and in 2005 the GH receptor blocker pegvisomant was introduced. This review will cover the evolution of these discoveries and build a picture of our current understanding of the hypothalamo-GH axis.

Interventions to Slow Aging in Humans: Are We Ready?

The workshop entitled ‘Interventions to Slow Aging in Humans: Are We Ready?’ was held in Erice, Italy, on October 8–13, 2013, to bring together leading experts in the biology and genetics of aging and obtain a consensus related to the discovery and development of safe interventions to slow aging and increase healthy lifespan in humans. There was consensus that there is sufficient evidence that aging interventions will delay and prevent disease onset for many chronic conditions of adult and old age. Essential pathways have been identified, and behavioral, dietary, and pharmacologic approaches have emerged. Although many gene targets and drugs were discussed and there was not complete consensus about all interventions, the participants selected a subset of the most promising strategies that could be tested in humans for their effects on healthspan. These were: (i) dietary interventions mimicking chronic dietary restriction (periodic fasting mimicking diets, protein restriction, etc.); (ii) drugs that inhibit the growth hormone/IGF-I axis; (iii) drugs that inhibit the mTOR–S6K pathway; or (iv) drugs that activate AMPK or specific sirtuins. These choices were based in part on consistent evidence for the pro-longevity effects and ability of these interventions to prevent or delay multiple age-related diseases and improve healthspan in simple model organisms and rodents and their potential to be safe and effective in extending human healthspan. The authors of this manuscript were speakers and discussants invited to the workshop. The following summary highlights the major points addressed and the conclusions of the meeting.

The prolactin receptor as a therapeutic target in human diseases: browsing new potential indications

INTRODUCTION

Prolactin (PRL) signaling has emerged as a relevant target in breast and prostate cancers. This has encouraged various laboratories to develop compounds targeting the PRL receptor (PRLR). As the latter is widely distributed, it is timely to address whether other conditions could also benefit from such inhibitors.

AREAS COVERED

The authors briefly overview the two classes of PRLR blockers, which involve: i) PRL-core based analogs that have been validated as competitive antagonists in various preclinical models, and ii) anti-PRLR neutralizing antibodies that are currently in clinical Phase I for advanced breast and prostate cancers. The main purpose of this review is to discuss the multiple organs/diseases that may be considered as potential targets/indications for such inhibitors. This is done in light of reports suggesting that PRLR expression/signaling is increased in disease, and/or that systemic or locally elevated PRL levels correlate with (or promote) organ pathogenesis.

EXPERT OPINION

The two immediate challenges in the field are i) to provide the scientific community with potent anti-prolactin receptor antibodies to map prolactin receptor expression in target organs, and ii) to take advantage of the availability of functionally validated PRLR blockers to establish the relevance of these potential indications in humans.

Autocrine human growth hormone stimulates the tumor initiating capacity and metastasis of estrogen receptor-negative mammary carcinoma cells

The oncogenic effects of autocrine human growth hormone (hGH) have been intensively investigated in estrogen receptor-positive mammary carcinoma (ER + MC) cells. We demonstrated herein that autocrine hGH promoted cancer stem cell (CSC)-like properties of estrogen receptor-negative mammary carcinoma (ER-MC) cells in vitro. In xenograft studies, autocrine hGH increased the tumor initiating capacity of ER-MC cells. We also observed that autocrine hGH promoted migration and invasion of ER-MC cells in vitro, and metastasis in vivo. Thus, inhibition of hGH is a potential therapeutic strategy to prevent tumor initiation and metastasis of ER-MC.

Development and characterization of a novel GHR antibody antagonist, GF185

Here, we describe the development of a panel of monoclonal antibodies targeting the growth hormone receptor (GHR). Of these monoclonal antibodies (Mabs), GF185 was selected for further characterization due to its activities. Competitive receptor-binding assays and Western blotting analyses were used to demonstrate that GF185's epitopes are localized within subdomain 1 of the growth hormone receptor extracellular domain (GHR-ECD). Subsequently, we evaluated GF185's antagonistic activities in vivo and in vitro and showed that GF185 was able to neutralize growth hormone (GH) signalling and inhibit GH-induced Ba/F3-GHR proliferation. Our findings suggest that GF185 may serve as an attractive tool for GHR-related research and has a potential future application for the treatment of GH-dependent disease.

The discovery of medicines for rare diseases

There is a pressing need for new medicines (new molecular entities; NMEs) for rare diseases as few of the 6800 rare diseases (according to the NIH) have approved treatments. Drug discovery strategies for the 102 orphan NMEs approved by the US FDA between 1999 and 2012 were analyzed to learn from past success: 46 NMEs were first in class; 51 were followers; and five were imaging agents. First-in-class medicines were discovered with phenotypic assays (15), target-based approaches (12) and biologic strategies (18). Identification of genetic causes in areas with more basic and translational research such as cancer and in-born errors in metabolism contributed to success regardless of discovery strategy. In conclusion, greater knowledge increases the chance of success and empirical solutions can be effective when knowledge is incomplete.

STAT3 upregulation in pituitary somatotroph adenomas induces growth hormone hypersecretion

Pituitary somatotroph adenomas result in dysregulated growth hormone (GH) hypersecretion and acromegaly; however, regulatory mechanisms that promote GH hypersecretion remain elusive. Here, we provide evidence that STAT3 directly induces somatotroph tumor cell GH. Evaluation of pituitary tumors revealed that STAT3 expression was enhanced in human GH-secreting adenomas compared with that in nonsecreting pituitary tumors. Moreover, STAT3 and GH expression were concordant in a somatotroph adenoma tissue array. Promoter and expression analysis in a GH-secreting rat cell line (GH3) revealed that STAT3 specifically binds the Gh promoter and induces transcription. Stable expression of STAT3 in GH3 cells induced expression of endogenous GH, and expression of a constitutively active STAT3 further enhanced GH production. Conversely, expression of dominant-negative STAT3 abrogated GH expression. In primary human somatotroph adenoma-derived cell cultures, STAT3 suppression with the specific inhibitor S3I-201 attenuated GH transcription and reduced GH secretion in the majority of derivative cultures. In addition, S3I-201 attenuated somatotroph tumor growth and GH secretion in a rat xenograft model. GH induced STAT3 phosphorylation and nuclear translocation, indicating a positive feedback loop between STAT3 and GH in somatotroph tumor cells. Together, these results indicate that adenoma GH hypersecretion is the result of STAT3-dependent GH induction, which in turn promotes STAT3 expression, and suggest STAT3 as a potential therapeutic target for pituitary somatotroph adenomas.

ACROSTUDY: the Italian experience

ACROSTUDY is a world-wide non-interventional, post marketing surveillance study performed to monitor the safety and outcomes of pegvisomant (PEG) in clinical practice. We report data from acromegaly patients who have been included in the Italian ACROSTUDY registry. The data of 341 acromegaly patients (171 males) were available for analysis using data freeze (12/9/2012). Patients were enrolled in 25 Italian endocrine centres. Before and during PEG treatment IGF-I, liver enzymes, metabolic parameters, and pituitary MRI were assessed. Before PEG, 54.3% patients had been treated with medical therapy and surgery, 22.9% medical therapy only, and 15.8% medical plus radiation and surgical therapy. 199 adverse events were reported in 98 patients (28.7%). Serious adverse events were documented in 29 patients (8.5%). 71.1% of patients had no significant change in tumor volume. Central MRI reading was performed in 34 patients; in 7 patients, an increase in tumor volume was found. Hormonal efficacy progressively increased since the start of PEG. After 6 years, normal IGF-I levels were found in 70.9% of patients (mean daily dose 18.1 mg). 87.1% of patients were treated with daily PEG although in 8.8% of patients, it was administered 2-6 times per week and in 3.8% with weekly injections. 74.8% received a PEG dose 10-15 mg/daily. PEG is a drug with a favorable safety profile which is efficacious also considering that in Italy it is currently available as third-line therapy.

Validation of serum IGF-I as a biomarker to monitor the bioactivity of exogenous growth hormone agonists and antagonists in rabbits

The development of new growth hormone (GH) agonists and growth hormone antagonists (GHAs) requires animal models for pre-clinical testing. Ideally, the effects of treatment are monitored using the same pharmacodynamic marker that is later used in clinical practice. However, intact rodents are of limited value for this purpose because serum IGF-I, the most sensitive pharmacodynamic marker for the action of GH in humans, shows no response to treatment with recombinant human GH and there is little evidence for the effects of GHAs, except when administered at very high doses or when overexpressed. As an alternative, more suitable model, we explored pharmacodynamic markers of GH action in intact rabbits. We performed the first validation of an IGF-I assay for the analysis of rabbit serum and tested precision, sensitivity, linearity and recovery using an automated human IGF-I assay (IDS-iSYS). Furthermore, IGF-I was measured in rabbits of different strains, age groups and sexes, and we monitored IGF-I response to treatment with recombinant human GH or the GHA Pegvisomant. For a subset of samples, we used LC-MS/MS to measure IGF-I, and quantitative western ligand blot to analyze IGF-binding proteins (IGFBPs). Although recovery of recombinant rabbit IGF-I was only 50% in the human IGF-I assay, our results show that the sensitivity, precision (1.7–3.3% coefficient of variation) and linearity (90.4–105.6%) were excellent in rabbit samples. As expected, sex, age and genetic background were major determinants of IGF-I concentration in rabbits. IGF-I and IGFBP-2 levels increased after single and multiple injections of recombinant human GH (IGF-I: 286±22 versus 434±26 ng/ml; P<0.01) and were highly correlated (P<0.0001). Treatment with the GHA lowered IGF-I levels from the fourth injection onwards (P<0.01). In summary, we demonstrated that the IDS-iSYS IGF-I immunoassay can be used in rabbits. Similar to rodents, rabbits display variations in IGF-I depending on sex, age and genetic background. Unlike in rodents, the IGF-I response to treatment with recombinant human GH or a GHA closely mimics the pharmacodynamics seen in humans, suggesting that rabbits are a suitable new model to test human GH agonists and antagonists.

Dynamic analysis of GH receptor conformational changes by split luciferase complementation

The transmembrane GH receptor (GHR) exists at least in part as a preformed homodimer on the cell surface. Structural and biochemical studies suggest that GH binds GHR in a 1:2 stoichiometry to effect acute GHR conformational changes that trigger the activation of the receptor-associated tyrosine kinase, Janus kinase 2 (JAK2), and downstream signaling. Despite information about GHR-GHR association derived from elegant fluorescence resonance energy transfer/bioluminescence resonance energy transfer studies, an assessment of the dynamics of GH-induced GHR conformational changes has been lacking. To this end, we used a split luciferase complementation assay that allowed detection in living cells of specific ligand-independent GHR-GHR interaction. Furthermore, GH treatment acutely augmented complementation of enzyme activity between GHRs fused, respectively, to N- and C-terminal fragments of firefly luciferase. Analysis of the temporal pattern of GH-induced complementation changes, pharmacological manipulation, genetic alteration of JAK2 levels, and truncation of the GHR intracellular domain (ICD) tail suggested that GH acutely enhances proximity of the GHR homodimer partners independent of the presence of JAK2, phosphorylation of GHR-luciferase chimeras, or an intact ICD. However, subsequent reduction of complementation requires JAK2 kinase activity and the ICD tail. This conclusion is in contrast to existing models of the GHR activation process.

Aggressive pituitary adenomas--diagnosis and emerging treatments

The WHO categorizes pituitary tumours as typical adenomas, atypical adenomas and pituitary carcinomas, with typical adenomas constituting the major class. However, the WHO classification does not provide an accurate correlation between histopathological findings and clinical behaviour. Tumours lacking typical histological features are classified as atypical, but not all are clinically atypical or exhibit aggressive behaviour. Pituitary carcinomas, by definition, have craniospinal or systemic metastases, although not all display classical cytological features of malignancy. Aggressive pituitary adenomas, defined from a clinical perspective, have earlier and more frequent recurrences and can be resistant to conventional treatments. Specific biomarkers have not yet been identified that can distinguish between clinically aggressive and nonaggressive pituitary adenomas, although the antigen Ki-67 proliferation index might be of value. This Review highlights the need to develop new biomarkers to facilitate the early detection of clinically aggressive pituitary adenomas and discusses emerging markers that hold promise for their identification. Defining aggressiveness is of crucial importance for improving the management of patients by enhancing prognostic predictions and effectiveness of treatment. New drugs, such as temozolomide, have potential use in the management of these patients; anti-VEGF therapy, mTOR and tyrosine kinase inhibitors are also potentially useful in managing selected patients.

Evaluation of growth hormone (GH) action in mice: discovery of GH receptor antagonists and clinical indications

The discovery of a growth hormone receptor antagonist (GHA) was initially established via expression of mutated GH genes in transgenic mice. Following this discovery, development of the compound resulted in a drug termed pegvisomant, which has been approved for use in patients with acromegaly. Pegvisomant treatment in a dose dependent manner results in normalization of IGF-1 levels in most patients. Thus, it is a very efficacious and safe drug. Since the GH/IGF-1 axis has been implicated in the progression of several types of cancers, many have suggested the use of pegvisomant as an anti-cancer therapeutic. In this manuscript, we will review the use of mouse strains that possess elevated or depressed levels of GH action for unraveling many of GH actions. Additionally, we will describe experiments in which the GHA was discovered, review results of pegvisomant's preclinical and clinical trials, and provide data suggesting pegvisomant's therapeutic value in selected types of cancer.

Role of UGT1A1 and ADH gene polymorphisms in pegvisomant-induced liver toxicity in acromegalic patients

CONTEXT

Hepatotoxicity is one of the most serious adverse effects in acromegalic patients treated with pegvisomant (PEG-V). Recent studies have found an association between this adverse event and the UGT1A1 allele 28 polymorphism associated with Gilbert's syndrome.

OBJECTIVE

To determine whether UGT1A1*28 and alcohol dehydrogenase (ADH) polymorphisms influence liver toxicity during PEG-V treatment.

DESIGN AND SETTING

Multicenter observational retrospective study conducted in 13 tertiary care endocrinology units in Italy.

PATIENTS

A total of 112 patients with active disease resistant to somatostatin analogs (SSTa) and 108 controls were enrolled.

INTERVENTIONS

Clinical and biochemical data were recorded by electronic clinical reporting forms. Blood or DNA samples were sent to the coordinating center for genotyping.

RESULTS

No differences in genotypes between patients and controls were found. During PEG-V therapy liver function tests (LFT), abnormalities and overt hepatotoxicity developed in 17 and 4.5% of patients respectively. Logistic and linear regression analyses showed an association between LFT abnormalities during the follow-up visit and prior events of LFT abnormalities in medical history (odds ratio=1.25; P=0.04) and the number of concomitant medications, other than SSTa (B=3.9; P=0.03). No correlation between LFT alterations and UGT1A1 allele 28 as well as ADH1C and B polymorphisms was found.

CONCLUSIONS

UGT1A1 allele 28 and ADH1C and B polymorphisms do not predict increased risk of hepatotoxicity during PEG-V therapy. Conversely, patients with multi-therapies and with previous episodes of liver disease should be carefully managed, due to the observed association between these conditions and LFT abnormalities during PEG-V therapy.

Short-term administration of pegvisomant improves hepatic insulin sensitivity and reduces soleus muscle intramyocellular lipid content in young adults with type 1 diabetes

CONTEXT

Data on the metabolic effects of GH derived from studies using GH suppression by pharmacological agents may not reflect selective actions.

OBJECTIVE

The purpose of this study was to evaluate the effects of GH antagonism on glucose and lipid metabolism using pegvisomant, a selective GH receptor antagonist in patients with type 1 diabetes (T1D).

DESIGN AND PARTICIPANTS

In a randomized, placebo-controlled, crossover study, 10 young adults with T1D were evaluated at baseline and after 4 weeks of treatment with either 10 mg of pegvisomant or placebo. The assessments included an overnight euglycemic steady state followed by a hyperinsulinemic euglycemic clamp and used glucose and glycerol cold stable isotopes.

OUTCOME MEASURES

Hepatic and peripheral insulin sensitivity (IS), lipid turnover, and intramyocellular lipid (IMCL) were measured.

RESULTS

Compared with placebo, pegvisomant treatment resulted in lower IGF-I levels (P < .001). During the overnight steady state, insulin requirements for euglycemia (P = .019), insulin levels (P = .008), and glucose production rates (Ra) (P = .033) were reduced. During the clamp study, glucose infusion rates (P = .031) increased and glucose Ra (P = .015) decreased whereas glucose disposal rates were unchanged. Free fatty acid levels were similar during the steady state but were lower during the clamp (P = .040) after pegvisomant. Soleus muscle IMCL decreased after treatment (P = .024); however, no change in tibialis anterior muscle was observed.

CONCLUSIONS

The study demonstrates that GH antagonism in T1D results in improved hepatic insulin sensitivity. Lack of consistent changes in free fatty acid levels may suggest a direct effect of GH on IS. Unchanged peripheral IS despite reductions in IMCL indicate that GH-induced alterations in IMCL may not be causally linked to glucose metabolism.

Rapid decline in bone turnover markers but not bone mineral density in acromegalic patients after transsphenoidal surgery

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) play important roles in maintaining bone metabolism and bone mineral density (BMD) in adulthood, in addition to stimulating longitudinal bone growth in childhood. However, information on the effect of GH excess on bone metabolism and BMD is incomplete and requires further analysis. The aim of this study is to clarify the effect of rapid decline in GH levels after transsphenoidal surgery (TSS) on bone metabolism in acromegalic patients. In this prospective study, 22 patients (11 males and 11 females) with active acromegaly underwent TSS. Bone formation marker (serum bone alkaline phosphatase: BAP), bone resorption marker (urinary type I collagen cross-linked N-telopeptide: urinary NTx) and BMD were measured before and at 3 and 12 months after TSS. BAP was significantly decreased at 12 months after TSS, but not at 3 months. Urinary NTx was significantly decreased at 3 and 12 months after TSS. BMD did not change after TSS. In conclusion, the rapid fall in GH level after TSS had no effect on BMD for up to 12 months after TSS despite the decrease in markers of bone formation and resorption.

Regulation of pancreatic islet beta-cell mass by growth factor and hormone signaling

Dysfunction and destruction of pancreatic islet beta cells is a hallmark of diabetes. Better understanding of cellular signals in beta cells will allow development of therapeutic strategies for diabetes, such as preservation and expansion of beta-cell mass and improvement of beta-cell function. During the past several decades, the number of studies analyzing the molecular mechanisms, including growth factor/hormone signaling pathways that impact islet beta-cell mass and function, has increased exponentially. Notably, somatolactogenic hormones including growth hormone (GH), prolactin (PRL), and insulin-like growth factor-1 (IGF-1) and their receptors (GHR, PRLR, and IGF-1R) are critically involved in beta-cell growth, survival, differentiation, and insulin secretion. In this chapter, we focus more narrowly on GH, PRL, and IGF-1 signaling, and GH-IGF-1 cross talk. We also discuss how these signaling aspects contribute to the regulation of beta-cell proliferation and apoptosis. In particular, our novel findings of GH-induced formation of GHR-JAK2-IGF-1R protein complex and synergistic effects of GH and IGF-1 on beta-cell signaling, proliferation, and antiapoptosis lead to a new concept that IGF-1R may serve as a proximal component of GH/GHR signaling.

"Bio"-macromolecules: polymer-protein conjugates as emerging scaffolds for therapeutics

Polymer-protein conjugates are biohybrid macromolecules derived from covalently connecting synthetic polymers with polypeptides. The resulting materials combine the properties of both worlds: chemists can engineer polymers to stabilize proteins, to add functionality, or to enhance activity; whereas biochemists can exploit the specificity and complexity that Nature has bestowed upon its macromolecules. This has led to a wealth of applications, particularly within the realm of biomedicine. Polymer-protein conjugation has expanded to include scaffolds for drug delivery, tissue engineering, and microbial inhibitors. This feature article reflects upon recent developments in the field and discusses the applications of these hybrids from a biomaterials standpoint.

Comparative inhibition of the GH/IGF-I axis obtained with either the targeted secretion inhibitor SXN101959 or the somatostatin analog octreotide in growing male rats

Abnormally high GH/IGF-I levels, most often caused by adenomas arising from pituitary somatotrophs, generate deleterious effects. We recently described a targeted secretion inhibitor (SXN101742) comprising a GHRH domain and the endopeptidase domain of botulinum toxin serotype D (GHRH-light chain endopeptidase type D domain [LC/D] associated to a heavy chain translocation domain [HN]) able to down-regulate the GH/IGF-I axis. In the present study, we compared the effect of a single iv bolus of a related molecule developed for clinical studies (SXN101959, 1 mg/kg) with a sc infusion of the somatostatin analog octreotide (SMS201-995, 10 μg/kg · h) to lower GH/IGF-I activity in growing male rats. Ten days after administration of SXN101959 or initiation of the octreotide infusion, body and pituitary weights, body length, GH peaks, and IGF-I production were reduced by both treatments but to a greater extent with SXN101959. In contrast to unaltered GH gene expression and increased GH storage in pituitaries from octreotide-treated rats, the inhibition of GH secretion was associated with a collapse of both GH mRNA and protein level in pituitaries from SXN101959-treated rats, in line with a specific decrease in hypothalamic GHRH production, not observed with octreotide. SXN101959 did not induce major apoptotic events in anterior pituitary and exhibited a reversible mode of action with full recovery of somatotroph cell functionality 30 days after treatment. Octreotide infusion permanently decreased ghrelin levels, whereas SXN101959 only transiently attenuated ghrelinemia. Both treatments limited bone mass acquisition and altered specifically tissues development. In conclusion, SXN101959 exerts a powerful and reversible inhibitory action on the somatotropic axis. Specific features of SXN101959, including long duration of action coupled to a strong inhibition of pituitary GH synthesis, represent advantages when treating overproduction of GH.

Pathology, pathophysiology, and treatment strategies of endocrine disorders and their cardiac complications

The cardiovascular system is affected by a multitude of endocrine disorders, including dysfunction of the thyroid, calcium, glucocorticoids, insulin/glucose, and growth hormone axes. Since most of these changes in the cardiovascular system are reversible when treated, early diagnosis is important, as if left untreated, they may become fatal. This review focuses on the pathophysiology, clinical presentation, pathology, and treatment of patients with these endocrine diseases who present with a variety of cardiovascular manifestations. Neuroendocrine tumors presenting with the carcinoid syndrome and their cardiovascular manifestations are also discussed.

[Drug therapy for acromegaly]

Prolonged overproduction of growth hormone, like insulin-like growth factor-1 hypersecretion leads to acromegaly in adults. This is associated with several co-morbidities and increased mortality. Despite typical clinical features and modern diagnostic tools, it often takes years to diagnose from the onset of the disease. The aims of the treatment are to reduce or control tumour growth, inhibit growth hormone hypersecretion, normalize insulin-like growth factor-1 levels, treat co-morbidities and, therefore, reduce mortality. There are three approaches for therapy: surgery, medical management (dopamine agonists, somatostatin analogues and growth hormone receptor antagonist), and radiotherapy. Efficient therapy of the disease is based on the appropriate multidisciplinary team management. The review provides a summary of medical treatment for acromegaly.

Pegvisomant bioavailability of single 30 mg/mL subcutaneous injection compared to two 15 mg/mL subcutaneous injections: a pharmacokinetic, safety and tolerability study

OBJECTIVE

The study was conducted to evaluate the pharmacokinetics (PK), relative bioavailability (relBA), safety and tolerability of two single-dose pegvisomant subcutaneous (SC) administrations: one injection of 30 mg/mL (1 × 30 mg/mL) versus two injections of two 15 mg/mL (2 × 15 mg/mL).

DESIGN

This was a 2-period, single-dose, crossover study in 14 healthy male and female subjects. All subjects received both administrations during the two treatment periods separated by a two-week washout. Serum samples were collected intensively up to 360 h post injection and were assayed by a validated enzyme linked immunosorbent assay (ELISA) for pegvisomant. PK parameters including AUC and Cmax were derived by noncompartmental analyses. Mixed effects model was used to obtain bioavailability estimates. Safety and tolerability were assessed by clinical monitoring, including adverse events, laboratory assessments and injection site reactions.

RESULTS

All subjects completed the study. The relBA of 1 × 30 mg/mL relative to 2 × 15 mg/mL was 123.89% with a 90% CI (112.91-135.93%). Adjusted for the difference in actual pegvisomant amounts in both formulations the dose-adjusted relBA reduced to 112.97% with a 90% CI (103.09-123.80%). Single injection with a higher drug concentration in injection solution might have a role in this 13% higher bioavailability for 1 × 30 mg/mL administration. Other PK parameters for the two administrations were comparable. No laboratory abnormalities, vital signs, ECG, or injection site reactions of clinical concern were observed in either treatment.

CONCLUSIONS

Comparable BA, safety and tolerability of the new 30 mg/mL strength to the currently marketed 15 mg/mL strength were established in this study.

Long-term treatment of somatostatin analog-refractory growth hormone-secreting pituitary tumors with pegvisomant alone or combined with long-acting somatostatin analogs: a retrospective analysis of clinical practice and outcomes

Background

Pegvisomant (PEGV) is widely used, alone or with somatostatin analogs (SSA), for GH-secreting pituitary tumors poorly controlled by SSAs alone. No information is available on specific indications for or relative efficacies of PEGV?+?SSA versus PEGV monotherapy. Aim of our study was to characterize real-life clinical use of PEGV vs. PEGV?+?SSA for SSA-resistant acromegaly (patient selection, long-term outcomes, adverse event rates, doses required to achieve control).

Methods

A retrospective analysis of data collected in 2005–2010 in five hospital-based endocrinology centers in Rome was performed. Sixty-two adult acromegaly patients treated ≥6 months with PEGV (Group 1, n?=?35) or PEGV?+?SSA (Group 2, n?=?27) after unsuccessful maximal-dose SSA monotherapy (≥12 months) were enroled. Groups were compared in terms of clinical/biochemical characteristics at diagnosis and before PEGV or PEGV?+?SSA was started (baseline) and end-of-follow-up outcomes (IGF-I levels, adverse event rates, final PEGV doses).

Results

Group 2 showed higher IGF-I and GH levels and sleep apnea rates, higher rates residual tumor tissue at baseline, more substantial responses to SSA monotherapy and worse outcomes (IGF-I normalization rates, final IGF-I levels). Tumor growth and hepatotoxicity events were rare in both groups. Final daily PEGV doses were similar and significantly increased with treatment duration in both groups.

Conclusions

PEGV and PEGV?+?SSA are safe, effective solutions for managing SSA-refractory acromegaly. PEGV?+?SSA tends to be used for more aggressive disease associated with detectable tumor tissue. With both regimens, ongoing monitoring of responses is important since PEGV doses needed to maintain IGF-I control are likely to increase over time.

A dwarf mouse model with decreased GH/IGF-1 activity that does not experience life-span extension: potential impact of increased adiposity, leptin, and insulin with advancing age

Reduced growth hormone (GH) action is associated with extended longevity in many vertebrate species. GH receptor (GHR) null (GHR(-)(/-)) mice, which have a disruption in the GHR gene, are a well-studied example of mice that are insulin sensitive and long lived yet obese. However, unlike other mouse lines with reduced GH action, GH receptor antagonist (GHA) transgenic mice have reduced GH action yet exhibit a normal, not extended, life span. Understanding why GHA mice do not have extended life span though they share many physiological attributes with GHR(-)(/-) mice will help provide clues about how GH influences aging. For this study, we examined age- and sex-related changes in body composition, glucose homeostasis, circulating adipokines, and tissue weights in GHA mice and littermate controls. Compared with previous studies with GHR(-)(/-) mice, GHA mice had more significant increases in fat mass with advancing age. The increased obesity resulted in significant adipokine changes. Euglycemia was maintained in GHA mice; however, hyperinsulinemia developed in older male GHA mice. Overall, GHA mice experience a more substantial, generalized obesity accompanied by altered adipokine levels and glucose homeostasis than GHR(-)(/-) mice, which becomes more exaggerated with advancing age and which likely contributes to the lack of life-span extension in these mice.

The place of medical treatment of acromegaly: current status and perspectives

INTRODUCTION

Acromegaly is characterized by elevated growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels and by progressive somatic disfigurement and systemic manifestations, which lead to a mortality rate higher than the general population. Therefore, diagnosis and properly treatment should be performed as soon as possible.

AREAS COVERED

This article focuses on the state of the art of acromegaly medical treatment. Somatostatin analogs, dopamine agonists and GH receptor antagonist were reviewed. Somatostatin analogs, the first-choice pharmacotherapy, can be used as primary or pre-operative treatment or as secondary therapy after failed surgery. Dopamine agonists have been used in patients with slightly elevated hormone levels and/or mixed GH/prolactin adenomas. Pegvisomant is indicated for resistant to somatostatin analogs/dopamine agonists. Combined treatment is also an option for resistant cases. Other non-conventional therapies and perspectives of treatment were also been discussed.

EXPERT OPINION

The control of disease activity in acromegaly is of paramount importance. Medical treatment is an important option for cases in which surgery was unsuccessful or not indicated. Despite the achievements in medical treatment, somatotropic tumor aggressiveness and/or resistance to the drugs currently available remain a concern. Therefore, novel therapy targets based on molecular pathogenesis of GH-secreting tumors are currently in development, aiming at fulfilling this important gap.

Pegvisomant and cabergoline combination therapy in acromegaly

Combination with cabergoline may offer additional benefits to acromegalic patients on pegvisomant monotherapy. We evaluated the safety and efficacy profile of this combination and investigated the determinants of response. An observational, retrospective, cross-sectional study. Fourteen acromegalic patients (9 females), who were partially resistant to somatostatin analogs and on pegvisomant monotherapy. Cabergoline was added because of the presence of persistent mildly increased IGF-I. The mean follow-up time was 18.3 ± 10.4 months. The efficacy and safety profile was assessed. The influence of clinical and biochemical characteristics on treatment efficacy was studied. IGF-I levels returned to normal in 4 patients (28%) at the end of the study. In addition, some decline in IGF-I levels was observed in a further 5 patients. The % IGF-I decreased from 158 ± 64% to 124 ± 44% (p = 0.001). The average change in IGF-I was -18 ± 27% (range -67 to +24%). Lower baseline IGF-I (p = 0.007), female gender (p = 0.013), lower body weight (p = 0.031), and higher prolactin (PRL) levels (p = 0.007) were associated with a better response to combination therapy. There were no significant severe adverse events. Significant tumour shrinkage was observed in 1 patient. Combination therapy with pegvisomant and cabergoline could provide better control of IGF-I in some patients with acromegaly. Baseline IGF-I levels, female gender, body weight, and PRL levels affect the response to this combination therapy.

A dominant-negative FGF1 mutant (the R50E mutant) suppresses tumorigenesis and angiogenesis

Fibroblast growth factor-1 (FGF1) and FGF2 play a critical role in angiogenesis, a formation of new blood vessels from existing blood vessels. Integrins are critically involved in FGF signaling through crosstalk. We previously reported that FGF1 directly binds to integrin αvβ3 and induces FGF receptor-1 (FGFR1)-FGF1-integrin αvβ3 ternary complex. We previously generated an integrin binding defective FGF1 mutant (Arg-50 to Glu, R50E). R50E is defective in inducing ternary complex formation, cell proliferation, and cell migration, and suppresses FGF signaling induced by WT FGF1 (a dominant-negative effect) in vitro. These findings suggest that FGFR and αvβ3 crosstalk through direct integrin binding to FGF, and that R50E acts as an antagonist to FGFR. We studied if R50E suppresses tumorigenesis and angiogenesis. Here we describe that R50E suppressed tumor growth in vivo while WT FGF1 enhanced it using cancer cells that stably express WT FGF1 or R50E. Since R50E did not affect proliferation of cancer cells in vitro, we hypothesized that R50E suppressed tumorigenesis indirectly through suppressing angiogenesis. We thus studied the effect of R50E on angiogenesis in several angiogenesis models. We found that excess R50E suppressed FGF1-induced migration and tube formation of endothelial cells, FGF1-induced angiogenesis in matrigel plug assays, and the outgrowth of cells in aorta ring assays. Excess R50E suppressed FGF1-induced angiogenesis in chick embryo chorioallantoic membrane (CAM) assays. Interestingly, excess R50E suppressed FGF2-induced angiogenesis in CAM assays as well, suggesting that R50E may uniquely suppress signaling from other members of the FGF family. Taken together, our results suggest that R50E suppresses angiogenesis induced by FGF1 or FGF2, and thereby indirectly suppresses tumorigenesis, in addition to its possible direct effect on tumor cell proliferation in vivo. We propose that R50E has potential as an anti-cancer and anti-angiogenesis therapeutic agent (“FGF1 decoy”).

Use of prolactin receptor antagonist to better understand prolactin regulation of pituitary homeostasis

The anterior pituitary is permanently regulated by processes of apoptosis and proliferation in order to maintain tissue homeostasis. Several factors have been implicated in this regulation and lately, prolactin (PRL) has been included into that list. However, since PRL is secreted by anterior pituitary lactotropes, the actual outcome of its autocrine/paracrine actions on pituitary cells has remained difficult to assess. The availability of the pure PRL receptor antagonist Del1-9-G129R-hPRL has been helpful to circumvent this problem. While PRL has been traditionally associated with increased cell proliferation, recent studies revealed that this hormone actually induces apoptosis and decreases proliferation of anterior pituitary cells, by mechanisms involving the PRL receptor. The aim of this short review is to overview our current understanding of the regulation of pituitary homeostasis by PRL. Moreover, studies involving Del1-9-G129R-hPRL have helped anticipate to what extent future treatments involving PRL receptor inhibitors may interfere with processes regulated by PRL at the central level.

Analysis of the landscape of biologically-derived pharmaceuticals in Europe: dominant production systems, molecule types on the rise and approval trends

A thorough sort of the human drugs approved by the European Medicines Agency (EMA) between its establishment in 1995 until June 2012 is presented herein with a focus on biologically-derived pharmaceuticals. Over 200 (33%) of the 640 approved therapeutic drugs are derived from natural sources, produced via recombinant DNA technology, or generated through virus propagation. A breakdown based on production method, type of molecule and therapeutic category is presented. Current EMA approvals demonstrate that mammalian cells are the only choice for glycoprotein drugs, with Chinese hamster ovary cells being the dominant hosts for their production. On the other hand, bacterial cells and specifically Escherichia coli are the dominant hosts for protein-based drugs, followed by the yeast Saccharomyces cerevisiae. The latter is the dominant host for recombinant vaccine production, although egg-based production is still the main platform of vaccine provision. Our findings suggest that the majority of biologically-derived drugs are prescribed for cancer and related conditions, as well as the treatment of diabetes. The approval rate for biologically-derived drugs shows a strong upward trend for monoclonal antibodies and fusion proteins since 2009, while hormones, antibodies and growth factors remain the most populous categories. Despite a clear pathway for the approval of biosimilars set by the EMA and their potential to drive sales growth, we have only found approved biosimilars for three molecules. In 2012 there appears to be a slow-down in approvals, which coincides with a reported decline in the growth rate of biologics sales.

Genetic analysis in a patient presenting with meningioma and familial isolated pituitary adenoma (FIPA) reveals selective involvement of the R81X mutation of the AIP gene in the pathogenesis of the pituitary tumor

Familial isolated pituitary adenoma (FIPA), defined as the occurrence of at least two cases of pituitary adenoma in a family that does not exhibit features of syndromic diseases, such as Carney complex or Multiple Endocrine Neoplasia type 1 or 4, is a rare autosomal dominant disease with low penetrance. About 20 % of the families with FIPA harbor inactivating mutation in aryl hydrocarbon receptor-interacting protein gene (AIP) associated with loss of heterozygosity of the same genetic locus (11q13) in the tumor. Rarely different types of extra-pituitary tumors have been described in the setting of AIP mutation-positive FIPA. We present the case of a patient who was diagnosed with acromegaly due to the AIP mutation c.241C>T (p.R81X) at the age of 34 years, and treated by transsphenoidal surgery. At the age of 43 years she was diagnosed with a meningioma, and at age 46 had recurrence of the somatotropinoma. Genetic studies demonstrated loss of the normal allele (by sequencing and microsatellite analysis) in DNA from the pituitary adenoma but not from the meningioma, suggesting a selective involvement of AIP mutation in the pathogenesis of the pituitary adenoma, and a casual association with the meningioma. Further investigations are required to define the exact role of AIP in non-pituitary tumorigenesis.