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

Biomarkers of response to treatment in acromegaly

INTRODUCTION

Medical treatment of acromegaly is based in a `trial and error` approach. First-generation somatostatin receptor ligands (fg-SRL) are prescribed as first-line medical therapy to the vast majority of patients, despite lack of disease control in approximately 60% of patients. However, other drugs used in acromegaly treatment are available (cabergoline, pasireotide and pegvisomant).

AREAS COVERED

In this article, we review and discuss the biomarkers of response to medical treatment in acromegaly.

EXPERT OPINION

Biomarkers for fg-SRL that can already be applied in clinical practice are: gender, age, pretreatment GH and IGF-I levels, cytokeratin granulation pattern, and the expression of somatostatin receptor type 2. Using biomarkers of response could guide treatment towards precision medicine with greater efficacy and lower costs.

Growth hormone receptor agonists and antagonists: From protein expression and purification to long-acting formulations

Recombinant human growth hormone (rhGH) and GH receptor antagonists (GHAs) are used clinically to treat a range of disorders associated with GH deficiency or hypersecretion, respectively. However, these biotherapeutics can be difficult and expensive to manufacture with multiple challenges from recombinant protein generation through to the development of long-acting formulations required to improve the circulating half-life of the drug. In this review, we summarize methodologies and approaches used for making and purifying recombinant GH and GHA proteins, and strategies to improve pharmacokinetic and pharmacodynamic properties, including PEGylation and fusion proteins. Therapeutics that are in clinical use or are currently under development are also discussed.

Structure and function of a dual antagonist of the human growth hormone and prolactin receptors with site-specific PEG conjugates

Human growth hormone (hGH) is a pituitary-derived endocrine protein that regulates several critical postnatal physiologic processes including growth, organ development, and metabolism. Following adulthood, GH is also a regulator of multiple pathologies like fibrosis, cancer, and diabetes. Therefore, there is a significant pharmaceutical interest in developing antagonists of hGH action. Currently, there is a single FDA-approved antagonist of the hGH receptor (hGHR) prescribed for treating patients with acromegaly and discovered in our laboratory almost 3 decades ago. Here, we present the first data on the structure and function of a new set of protein antagonists with the full range of hGH actions-dual antagonists of hGH binding to the GHR as well as that of hGH binding to the prolactin receptor. We describe the site-specific PEG conjugation, purification, and subsequent characterization using MALDI-TOF, size-exclusion chromatography, thermostability, and biochemical activity in terms of ELISA-based binding affinities with GHR and prolactin receptor. Moreover, these novel hGHR antagonists display distinct antagonism of GH-induced GHR intracellular signaling in vitro and marked reduction in hepatic insulin-like growth factor 1 output in vivo. Lastly, we observed potent anticancer biological efficacies of these novel hGHR antagonists against human cancer cell lines. In conclusion, we propose that these new GHR antagonists have potential for development towards multiple clinical applications related to GH-associated pathologies.

Exosomal RNAs in the development and treatment of pituitary adenomas

Exosomes are small extracellular vesicles that carry various bioactive molecules including various RNAs that modulate the activities of recipient cells. It has drawn considerable attention as means of cell communication and drug delivery. Exosome plays important role in various tumors, but it is rarely summarized in pituitary adenoma (PA). PA is the second most common primary central nervous system tumor, and its recurrence and persistent postoperative hormone hypersecretion lead to compromised quality of life. How exactly exosomes impact tumor development and hormone secretion is important for the development of this tumor diagnosis and treatment. In this review, we discuss how exosomal RNAs impact PAs and their potential as future clinical therapies. In our literature review, first, we found that exosomal microRNA hsa-miR-1180-3p is a potential early biomarker for NFPAs. Since NFPAs are typically difficult to diagnose, this is an especially important finding. Second, exosomal protein transcripts are potential invasive biomarker, such as MMP1, N-cadherin, CDK6, RHOU, INSM1, and RASSF10. Third, exosomal contents such as hsa-miR-21-5p promote distant bone formation of GHPA patients. Fourth, tumor suppressors in the exosome constitute novel therapeutic application of exosome, including long noncoding RNA (lncRNA) H19, miR-149-5p, miR-99a-3p, and miR-423-5p. This review discusses the possible mechanisms of exosome and their contents in PA and promotes the use of exosomes in both clinical diagnosis and treatment of this tumor.

The Clinical Application of Growth Hormone and Its Biological and Molecular Mechanisms in Assisted Reproduction

Growth hormone (GH) has been used as a co-gonadotrophin in assisted reproduction, particularly in poor ovarian responders. The application of GH has been alleged to activate primordial follicles and improve oocyte quality, embryo quality, and steroidogenesis. However, the effects of GH on the live birth rate among women is controversial. Additionally, although the basic biological mechanisms that lead to the above clinical differences have been investigated, they are not yet well understood. The actions of GH are mediated by GH receptors (GHRs) or insulin-like growth factors (IGFs). GH regulates the vital signal transduction pathways that are involved in primordial follicular activation, steroidogenesis, and oocyte maturation. However, the therapeutic windows and duration of GH administration during assisted reproductive technology require further investigation. The review aimed to clarify the role of GH in human fertility from a molecular and biological point of view to provide evidence for proper GH administration.

Growth hormone modulates Trypanosoma cruzi infection in vitro

OBJECTIVE

Chagas disease (CD) is caused by the protozoan parasite, Trypanosoma cruzi. It affects 7 to 8 million people worldwide and leads to approximately 50,000 deaths per year. In vitro and in vivo studies had demonstrated that Trypanosoma cruziinfection causes an imbalance in the hypothalamic-pituitary-adrenal (HPA) axis that is accompanied by a progressive decrease in growth hormone (GH) and prolactin (PRL) production. In humans, inactivating mutations in the GH receptor gene cause Laron Syndrome (LS), an autosomal recessive disorder. Affected subjects are short, have increased adiposity, decreased insulin-like growth factor-I (IGFI), increased serum GH levels, are highly resistant to diabetes and cancer, and display slow cognitive decline. In addition, CD incidence in these individuals is diminished despite living in highly endemic areas. Consequently, we decided to investigate the in vitro effect of GH/IGF-I on T. cruzi infection.

DESIGN

We first treated the parasite and/or host cells with different peptide hormones including GH, IGFI, and PRL. Then, we treated cells using different combinations of GH/IGF-I attempting to mimic the GH/IGF-I serum levels observed in LS subjects.

RESULTS

We found that exogenous GH confers protection against T. cruzi infection. Moreover, this effect is mediated by GH and not IGFI. The combination of relatively high GH (50 ng/ml) and low IGF-I (20 ng/ml), mimicking the hormonal pattern seen in LS individuals, consistently decreased T. cruzi infection in vitro.

CONCLUSIONS

The combination of relatively high GH and low IGF-I serum levels in LS individuals may be an underlying condition providing partial protection against T. cruzi infection.

The biochemical diagnosis of acromegaly: revising the role of measurement of IGF-I and GH after glucose load in 5 questions

INTRODUCTION

Acromegaly is a rare disorder characterized by the excessive secretion of growth hormone (GH), mostly caused by pituitary adenomas. While in full-blown cases the diagnosis is easy to establish, milder cases are more challenging. Additionally, establishing whether full cure after surgery is reached may be difficult.

AREAS COVERED

In this article, we will review the challenges posed by the variability in measurements of GH and its main effector insulin-like growth factor I (IGF-I) due to both biological changes, co-morbidities, and assays variability.

EXPERT OPINION

Interpretation of GH and IGF-I assays is important in establishing an early diagnosis of acromegaly, in avoiding misdiagnosis, and in establishing if cure is achieved by surgery. Physicians should be familiar with the variables that affect measurements of these 2 hormones, and with the performance of the assays available in their practice.

METTL3-mediated RNA m6A Hypermethylation Promotes Tumorigenesis and GH Secretion of Pituitary Somatotroph Adenomas

INTRODUCTION

Pituitary growth hormone-secreting (GH) pituitary adenomas (PAs) cause mass effects and dysregulated hypersecretion of GH. However, somatic mutation burden is low in PAs. While progress has been made in identifying the epigenetic changes involved in GH-PA initiation, the precise details of its tumorigenesis in GH-PA patients remains to be elucidated. As N6-methyladenosine (m6A) has been shown to often play a critical role in various tumors, it represents a possible initiation point for the tumorigenesis of pituitary adenomas. However, the role of RNA methylation in GH adenomas remains unclear.

METHODS

Protein expression of m6A regulators was measured by immunohistochemistry. Global levels and distribution of m6A methylation were separately analyzed by m6A enzyme-linked immunosorbent assay and m6A sequencing (m6A-seq). RNA interference and lentivirus knockdown system were used to investigate the role of methyltransferase-like 3 (METTL3) and its m6A- dependent regulatory mechanism in tumor progression and GH secretion.

RESULTS

We show that both METTL3 messenger RNA and protein expression are elevated in GH-PA samples when compared with both normal pituitary tissue specimens and nonsecreting pituitary adenomas. Levels of m6A modification increased in GH-PAs, and hypermethylated RNAs are involved in hormone secretion and cell development. Knockdown of METTL3 in GH3 cell line resulted in decreased cell growth and GH secretion. Importantly, we found that GNAS and GADD45γ act as the downstream targets in this process.

CONCLUSION

Our findings strongly suggest that m6A methyltransferase METTL3 promotes tumor growth and hormone secretion by increasing expression of GNAS and GADD45γ in a m6A-dependent manner. Thus, METTL3 and the methylated RNAs constitute suitable targets for clinical treatment of GH-PAs.

Small molecules to regulate the GH/IGF1 axis by inhibiting the growth hormone receptor synthesis

Growth hormone (GH) and insulin-like growth factor-1 (IGF1) play an important role in mammalian development, cell proliferation and lifespan. Especially in cases of tumor growth there is an urgent need to control the GH/IGF1 axis. In this study we screened a 38,480-compound library, and in two consecutive rounds of analogues selection, we identified active lead compounds based on the following criteria: inhibition the GH receptor (GHR) activity and its downstream effectors Jak2 and STAT5, and inhibition of growth of breast and colon cancer cells. The most active small molecule (BM001) inhibited both the GH/IGF1 axis and cell proliferation with an IC50 of 10-30 nM of human cancer cells. BM001 depleted GHR in human lymphoblasts. In preclinical xenografted experiments, BM001 showed a strong decrease in tumor volume in mice transplanted with MDA-MB-231 breast cancer cells. Mechanistically, the drug acts on the synthesis of the GHR. Our findings open the possibility to inhibit the GH/IGF1 axis with a small molecule.

Reversible insulin resistance in muscle and fat unrelated to the metabolic syndrome in patients with acromegaly

BACKGROUND

Patients with active acromegaly exhibit insulin resistance despite a lean phenotype whereas controlled disease improves insulin sensitivity and increases fat mass. The mechanisms underlying this paradox remain elusive, but growth hormone (GH)-induced lipolysis plays a central role. The aim of the study was to investigative the molecular mechanisms of insulin resistance dissociated from obesity in patients with acromegaly.

METHODS

In a prospective study, twenty-one patients with newly diagnosed acromegaly were studied at diagnosis and after disease control obtained by either surgery alone (n=10) or somatostatin analogue (SA) treatment (n=11) with assessment of body composition (DXA scan), whole body and tissue-specific insulin sensitivity and GH and insulin signalling in adipose tissue and skeletal muscle.

FINDINGS

Disease control of acromegaly significantly reduced lean body mass (p<0.001) and increased fat mass (p<0.001). At diagnosis, GH signalling (pSTAT5) was constitutively activated in fat and enhanced expression of GH-regulated genes (CISH and IGF-I) were detected in muscle and fat. Insulin sensitivity in skeletal muscle, liver and adipose tissue increased after disease control regardless of treatment modality. This was associated with enhanced insulin signalling in both muscle and fat including downregulation of phosphatase and tensin homolog (PTEN) together with reduced signalling of GH and lipolytic activators in fat.

INTERPRETATION

In conclusion, the study support that uncontrolled lipolysis is a major feature of insulin resistance in active acromegaly, and is characterized by upregulation of PTEN and suppression of insulin signalling in both muscle and fat.

FUNDING

This work was supported by a grant from the Independent Research Fund, Denmark (7016-00303A) and from the Alfred Benzon Foundation, Denmark.

Growth hormone directly favors hepatic ketogenesis in persons with prediabetes or type 2 diabetes mellitus treated with empagliflozin

PURPOSE

Sodium-glucose cotransporter 2 inhibitors increase glucagon secretion by pancreatic alpha cells and the susceptibility to ketoacidosis. On the other hand, growth hormone (GH) stimulates peripheral lipolysis and provides free fatty acids (FFA) for ketogenesis; however, it remains unresolved whether GH directly impacts hepatic ketogenesis. We aimed to investigate the role of physiologic GH levels in promoting ketogenesis in prediabetic or type 2 diabetic patients under empagliflozin treatment.

METHODS

Sixteen patients (11 women, 5 men) with prediabetes or type 2 diabetes mellitus, aged 55.6 ± 4.7 years and with a mean BMI of 30.7 ± 4.8 kg/m² and HbA1c 7.1 ± 1.6% (means ± SD), participated in this study. All of them were submitted to three mixed-meal tests: they received placebo at -60 min (test 1), and empagliflozin 25 mg (test 2, 21st day) and empagliflozin 25 mg plus pegvisomant 30 mg were administered subcutaneously 36 h before (test 3, 28th day). After test 1, all patients were instructed to take empagliflozin 25 mg daily.

RESULTS

The empagliflozin treatment decreased the plasma concentrations of glucose by 14% (P < 0.01), FFA by 23% (P < 0.01), and the insulin/glucagon ratio by 26% (P < 0.01), and it increased β-hydroxybutyrate by 44% (P < 0.05). The GH receptor block by pegvisomant restored the plasma β-hydroxybutyrate to baseline levels.

CONCLUSIONS

We conclude that GH has a direct effect on promoting the ketogenesis environment in patients treated with empagliflozin.

Pegvisomant treatment in acromegaly in clinical practice: Final results of the French ACROSTUDY (312 patients)

OBJECTIVE

We report the final analysis of the French ACROSTUDY, using data revised and enriched since the 2013 interim analysis. Our objective was to validate the use of pegvisomant (PEGV) in the treatment of acromegaly and to determine efficacy and safety.

PATIENTS AND METHODS

Patients with acromegaly treated with PEGV and followed up for at least 5 years were included. Eighty-eight investigators from 62 clinical centers in France included patients from April 2007 to April 2014. PEGV dose and administration frequency were determined by the physicians, based on their clinical evaluation and local habits. No additional examinations beyond those performed in normal follow-up were required. Minimum recommended follow-up included check-ups at treatment initiation, 6 months, 12 months and then annually.

RESULTS

In total, 312 patients were enrolled. Mean age was 46.1±14.3 years at introduction of PEGV. Median PEGV treatment duration was 6.3 years and median follow-up was 5.6 years. Median dose at initiation was 10mg/day. The percentages of patients with IGF-1 ≤ ULN (upper limit of normal) were 10% (n=300) at baseline, 54% at 6 months (n=278), and 61.7% (n=253) at 2 years, then stabilizing at 64.4% (n=180) at 5 years. Mean PEGV dose was 17.4±11.7mg in patients with controlled disease versus 21.1±17.3mg in those without control at 5 years. At 5 years, 21.8% of patients (54/248) were receiving >30mg PEGV per day. In patients with at least one pituitary imaging procedure during the 5-year follow-up (n=292), the most recent image showed stable tumor volume in 212 subjects (72.6%), increased volume in 13 (4.5%), and decreased volume in 30 (10.3%). No PEGV treatments were permanently discontinued due to transaminase elevation. There were no cases of liver failure.

CONCLUSION

The French ACROSTUDY showed normalization of IGF-1 levels in 64.4% of a real-life cohort of patients, mostly with uncontrolled disease despite multiple prior therapies. Long-term follow-up showed a sustained effectiveness and good long-term safety.

A novel peptide antagonist of the human growth hormone receptor

Excess circulating human growth hormone (hGH) in vivo is linked to metabolic and growth disorders such as cancer, diabetes, and acromegaly. Consequently, there is considerable interest in developing antagonists of hGH action. Here, we present the design, synthesis, and characterization of a 16-residue peptide (site 1-binding helix [S1H]) that inhibits hGH-mediated STAT5 phosphorylation in cultured cells. S1H was designed as a direct sequence mimetic of the site 1 mini-helix (residues 36-51) of wild-type hGH and acts by inhibiting the interaction of hGH with the human growth hormone receptor (hGHR). In vitro studies indicated that S1H is stable in human serum and can adopt an α-helix in solution. Our results also show that S1H mitigates phosphorylation of STAT5 in cells co-treated with hGH, reducing intracellular STAT5 phosphorylation levels to those observed in untreated controls. Furthermore, S1H was found to attenuate the activity of the hGHR and the human prolactin receptor, suggesting that this peptide acts as an antagonist of both lactogenic and somatotrophic hGH actions. Finally, we used alanine scanning to determine how discrete amino acids within the S1H sequence contribute to its structural organization and biological activity. We observed a strong correlation between helical propensity and inhibitory effect, indicating that S1H-mediated antagonism of the hGHR is largely dependent on the ability for S1H to adopt an α-helix. Taken together, these results show that S1H not only acts as a novel peptide-based antagonist of the hGHR but can also be applied as a chemical tool to study the molecular nature of hGH-hGHR interactions.

Body Composition Changes with Long-term Pegvisomant Therapy of Acromegaly

Context

In active acromegaly, the lipolytic and insulin antagonistic effects of growth hormone (GH) excess alter adipose tissue (AT) deposition, reduce body fat, and increase insulin resistance. This pattern reverses with surgical therapy. Pegvisomant treats acromegaly by blocking GH receptor (GHR) signal transduction and lowering insulin-like growth factor 1 (IGF-1) levels. The long-term effects of GHR antagonist treatment of acromegaly on body composition have not been studied.

Methods

We prospectively studied 21 patients with active acromegaly who were starting pegvisomant. Body composition was examined by whole body magnetic resonance imaging, proton magnetic resonance spectroscopy of liver and muscle and dual-energy x-ray absorptiometry, and endocrine and metabolic markers were measured before and serially during 1.0 to 13.4 years of pegvisomant therapy. The data of patients with acromegaly were compared with predicted and to matched controls.

Results

Mass of visceral AT (VAT) increased to a peak of 187% (1.56-229%) (P < .001) and subcutaneous AT (SAT) to 109% (–17% to 57%) (P = .04) of baseline. These remained persistently and stably increased, but did not differ from predicted during long-term pegvisomant therapy. Intrahepatic lipid rose from 1.75% to 3.04 % (P = .04). Although lean tissue mass decreased significantly, skeletal muscle (SM) did not change. IGF-1 levels normalized, and homeostasis model assessment insulin resistance and HbA1C were lowered.

Conclusion

Long-term pegvisomant therapy is accompanied by increases in VAT and SAT mass that do not differ from predicted, stable SM mass and improvements in glucose metabolism. Long-term pegvisomant therapy does not produce a GH deficiency-like pattern of body composition change.

Enhanced Bioactivity of a Human GHR Antagonist Generated by Solid-Phase Site-Specific PEGylation

Growth hormone (GH) has been implicated in cancer progression andis a potential target for anticancer therapy. Currently, pegvisomant is the only GH receptor (GHR) antagonist approved for clinical use. Pegvisomant is a mutated GH molecule (B2036) which is PEGylated on amine groups to extend serum half-life. However, PEGylation significantly reduces the bioactivity of the antagonist in mice. To improve bioactivity, we generated a series of B2036 conjugates with the site-specific attachment of 20, 30, or 40 kDa methoxyPEG maleimide (mPEG maleimide) by introduction of a cysteine residue at amino acid 144 (S144C). Recombinant B2036-S144C was expressed in Escherichia coli, purified, and then PEGylated using cysteine-specific conjugation chemistry. To avoid issues with dimerization due to the introduced cysteine, B2036-S144C was PEGylated while immobilized on an Ni-nitrilotriacetic (Ni-NTA) acid column, which effectively reduced disulfide-mediated dimer formation and allowed efficient conjugation to mPEG maleimide. Following PEGylation, the IC₅₀ values for the 20, 30, and 40 kDa mPEG maleimide B2036-S144C conjugates were 66.2 ± 3.8, 106.1 ± 7.1, and 127.4 ± 3.6 nM, respectively. The circulating half-life of the 40 kDa mPEG conjugate was 58.3 h in mice. Subcutaneous administration of the 40 kDa mPEG conjugate (10 mg/kg/day) reduced serum insulin-like growth factor I (IGF-I) concentrations by 50.6%. This in vivo reduction in serum IGF-I was at a considerably lower dose compared to the higher doses required to observe comparable activity in studies with pegvisomant. In conclusion, we have generated a novel PEGylated GHR antagonist by the solid-phase site-specific attachment of mPEG maleimide at an introduced cysteine residue, which effectively reduces serum IGF-I in vivo.

Classical and novel GH receptor signaling pathways

In this review, I summarize historical and recent features of the classical pathways activated by growth hormone (GH) through the cell surface GH receptor (GHR). GHR is a cytokine receptor superfamily member that signals by activating the non-receptor tyrosine kinase, JAK2, and members of the Src family kinases. Activation of the GHR engages STATs, PI3K, and ERK pathways, among others, and details of these now-classical pathways are presented. Modulating elements, including the SOCS proteins, phosphatases, and regulated GHR metalloproteolysis, are discussed. In addition, a novel physical and functional interaction of GHR with IGF-1R is summarized and discussed in terms of its mechanisms, consequences, and physiological and therapeutic implications.

Genetic Code Expansion Enables Site-Specific PEGylation of a Human Growth Hormone Receptor Antagonist through Click Chemistry

Regulation of human growth hormone (GH) signaling has important applications in the remediation of several diseases including acromegaly and cancer. Growth hormone receptor (GHR) antagonists currently provide the most effective means for suppression of GH signaling. However, these small 22 kDa recombinantly engineered GH analogues exhibit short plasma circulation times. To improve clinical viability, between four and six molecules of 5 kDa poly(ethylene glycol) (PEG) are nonspecifically conjugated to the nine amines of the GHR antagonist designated as B2036 in the FDA-approved therapeutic pegvisomant. PEGylation increases the molecular weight of B2036 and considerably extends its circulation time, but also dramatically reduces its bioactivity, contributing to high dosing requirements and increased cost. As an alternative to nonspecific PEGylation, we report the use of genetic code expansion technology to site-specifically incorporate the unnatural amino acid propargyl tyrosine (pglY) into B2036 with the goal of producing site-specific protein-polymer conjugates. Substitution of tyrosine 35 with pglY yielded a B2036 variant containing an alkyne functional group without compromising bioactivity, as verified by a cellular assay. Subsequent conjugation of 5, 10, and 20 kDa azide-containing PEGs via the copper-catalyzed click reaction yielded high purity, site-specific conjugates with >89% conjugation efficiencies. Site-specific attachment of PEG to B2036 is associated with substantially improved in vitro bioactivity values compared to pegvisomant, with an inverse relationship between polymer size and activity observed. Notably, the B2036-20 kDa PEG conjugate has a molecular weight comparable to pegvisomant, while exhibiting a 12.5 fold improvement in half-maximal inhibitory concentration in GHR-expressing Ba/F3 cells (103.3 nM vs 1289 nM). We expect that this straightforward route to achieve site-specific GHR antagonists will be useful for GH signal regulation.

Combined therapy of somatostatin analogues with pegvisomant for the treatment of acromegaly: a meta-analysis of prospective studies

BACKGROUND

Acromegaly is a rare, chronic and severe disease. Drug therapy including somatostatin analogues (SAs), dopamine receptor agonists and growth hormone receptor antagonists (pegvisomant, PEG) are commonly used to treat patients who do not respond to surgery. The use of combination therapy with PEG and SAs has become more common over the last decade. We performed this study to accurately evaluate the effect of combination therapy of SAs with PEG on acromegalic patients.

METHODS

PubMed, EMBASE, The Cochrane Library, ClinicalTrials.gov, Scopus, Web of Science, Chinese Biomedical Literature Database and Trip database were searched for relevant studies. Prospective clinical trials treating acromegaly with the co-administration of SAs and PEG were included. We performed a meta-analysis by using Stata 12.1. Sensitivity analysis was conducted to explore heterogeneity.

RESULTS

Nine studies were included in this meta-analysis. The overall rate of serum insulin-like growth factor 1 (IGF-1) normalization was 66% (95% CI: 52-78%; I² = 62.59%). The combination therapy did not significantly change patients' fasting plasma glucose (ES: 0.011 mmol*L^- 1; 95% CI: - 0.374 to 0.397 mmol*L^- 1; P = 0.954) or glycosylated haemoglobin (ES: - 0.074%; 95% CI: - 0.166 to 0.315%; P = 0.544) while decreasing the fasting plasma insulin (ES: - 21.487 pmol*L^-1; 95% CI: - 35.713 to - 7.260 pmol*L^-1; P = 0.003). Elevation of liver enzyme levels was found in 14% (95% CI: 8 to 21%) of the patients. There was no significant difference for serious adverse events and treatment discontinuation due to adverse event between SAs monotherapy group and combination therapy group.

CONCLUSIONS

Combined therapy of SAs and PEG effectively normalized IGF-1 levels in most of the patients whose IGF-1 level was greater than the upper limit of normal after high dose SAs monotherapy. The therapy also decreased significantly FPI levels with a neutral effect on glucose parameters in acromegaly patients. Moreover, elevated liver enzyme levels were observed in a small number of patients, which suggests a need for liver function monitoring.

TRIAL REGISTRATION

We have our protocol registered in PROSPERO. (Registration number: CRD42019115549 ).

Long-Acting Human Growth Hormone Receptor Antagonists Produced in E. coli and Conjugated with Polyethylene Glycol

Growth hormone (GH) is a peptide hormone that mediates actions through binding to a cell surface GH receptor (GHR). The GHR antagonist, B2036, combines an amino acid substitution at 120 that confers GHR antagonist activity, with eight additional amino acid substitutions. Conjugation to polyethylene glycol (PEG) increases the serum half-life of these proteins due to reduced renal clearance. Recombinant forms of GH and its antagonists are mainly produced in prokaryotic expression systems, such as E. coli. However, efficient production in E. coli is problematic, as these proteins form aggregates as inclusion bodies resulting in poor solubility. In the present study, we demonstrate that N-terminal fusion to a thioredoxin (Trx) fusion partner improves soluble expression of codon-optimized B2036 in E. coli when expressed at 18 °C. Expression, purification and PEGylation protocols were established for three GHR antagonists: B2036, B20, and G120Rv. Following purification, these antagonists inhibited the proliferation of Ba/F3-GHR cells in a concentration-dependent manner. PEGylation with amine-reactive 5 kDa methoxy PEG succinimidyl propionate yielded a heterogeneous mixture of conjugates containing four to seven PEG moieties. PEGylation significantly reduced in vitro bioactivity of the conjugates. However, substitution of lysine to arginine at amino acid residue 120 in B2036 improved the in vitro activity of the PEGylated protein when compared to unmodified PEGylated B2036. Pharmacokinetic analysis demonstrated that the circulating half-life of PEGylated B20 was 15.2 h in mice. Taken together, we describe an effective strategy to produce biologically active PEGylated human GHR antagonists.

Italian Association of Clinical Endocrinologists (AME) and Italian AACE Chapter Position Statement for Clinical Practice: Acromegaly - Part 2: Therapeutic Issues

Any newly diagnosed patient should be referred to a multidisciplinary team experienced in the treatment of pituitary adenomas. The therapeutic management of acromegaly always requires a personalized strategy. Normal age-matched IGF-I values are the treatment goal. Transsphenoidal surgery by an expert neurosurgeon is the primary treatment modality for most patients, especially if there are neurological complications. In patients with poor clinical conditions or who refuse surgery, primary medical treatment should be offered, firstly with somatostatin analogs (SSAs). In patients who do not reach hormonal targets with first-generation depot SSAs, a second pharmacological option with pasireotide LAR or pegvisomant (alone or combined with SSA) should be offered. Irradiation could be proposed to patients with surgical remnants who would like to be free from long-term medical therapies or those with persistent disease activity or tumor growth despite surgery or medical therapy. Since the therapeutic tools available enable therapeutic targets to be achieved in most cases, the challenge is to focus more on the quality of life.

Growth hormone-releasing hormone (GHRH) deficiency promotes inflammation-associated carcinogenesis

The somatotropic axis, in addition to its well-known metabolic and endocrine effects, plays a pivotal role in modulation of inflammation. Moreover, growth hormone (GH)-releasing hormone (GHRH) has been involved in the development of various human tumors. In this work we aimed to investigate the consequences of GHRH deficiency on the development of inflammation-associated colon carcinogenesis in a mouse model of isolated GH deficiency due to generalized ablation of the GHRH gene [GHRH knock out (GHRHKO)]. Homozygous GHRHKO (-/-) male mice and wild type (C57/BL6, +/+) male mice as control group, were used. After azoxymetane (AOM)/dextran sodium sulfate (DSS) treatment -/- mice displayed higher Disease Activity Index (DAI) score, and more marked weight loss compared to +/+ animals. Additionally, -/- mice showed a significant increase in total tumors, in particular of large size predominantly localized in distal colon. In colonic tissue of AOM/DSS-treated -/- mice we found the presence of invasive adenocarcinomas, dysplasia and colitis with mucosal ulceration. Conversely, AOM/DSS-treated +/+ mice showed only presence of adenomas, without invasion of sub-mucosa. Treatment with AOM/DSS significantly increased prostaglandin (PG)E₂ and 8-iso-PGF_2α levels along with cyclooxygenase-2 (COX-2), tumor necrosis factor (TNF)-α, nuclear factor kappa B (NF-kB) and inducible nitric oxide synthase (iNOS) gene expression, in colon specimens. The degree of increase of all these parameters was more markedly in -/- than +/+ mice. In conclusion, generalized GHRH ablation increases colon carcinogenesis responsiveness in male mice. Whether this results from lack of GH or GHRH remains to be established.

Brazilian multicenter study on pegvisomant treatment in acromegaly

OBJECTIVE

Investigate the therapeutic response of acromegaly patients to pegvisomant (PEGV) in a real-life, Brazilian multicenter study.

SUBJECTS AND METHODS

Characteristics of acromegaly patients treated with PEGV were reviewed at diagnosis, just before and during treatment. All patients with at least two IGF-I measurements on PEGV were included. Efficacy was defined as any normal IGF-I measurement during treatment. Safety data were reviewed. Predictors of response were determined by comparing controlled versus uncontrolled patients.

RESULTS

109 patients [61 women; median age at diagnosis 34 years; 95.3% macroadenomas] from 10 Brazilian centers were studied. Previous treatment included surgery (89%), radiotherapy (34%), somatostatin receptor ligands (99%), and cabergoline (67%). Before PEGV, median levels of GH, IGF-I and IGF-I % of upper limit of normal were 4.3 µg/L, 613 ng/mL, and 209%, respectively. Pre-diabetes/diabetes was present in 48.6% and tumor remnant in 71% of patients. Initial dose was 10 mg/day in all except 4 cases, maximum dose was 30 mg/day, and median exposure time was 30.5 months. PEGV was used as monotherapy in 11% of cases. Normal IGF-I levels was obtained in 74.1% of patients. Glycemic control improved in 56.6% of patients with pre-diabetes/diabetes. Exposure time, pre-treatment GH and IGF-I levels were predictors of response. Tumor enlargement occurred in 6.5% and elevation of liver enzymes in 9.2%. PEGV was discontinued in 6 patients and 3 deaths unrelated to the drug were reported.

CONCLUSIONS

In a real-life scenario, PEGV is a highly effective and safe treatment for acromegaly patients not controlled with other therapies.

Endocytosis and Degradation of Pegvisomant and a Potential New Mechanism That Inhibits the Nuclear Translocation of GHR

CONTEXT

Pegvisomant, a growth hormone receptor (GHR) antagonist, is a well-known drug that was designed to treat acromegaly. However, recent studies have indicated that the GHR is a "moonlighting" protein that may exhibit dual functions based on its localization in the plasma membrane and nucleus. In light of this finding, we explored whether pegvisomant is a potential "moonlighting" GHR antagonist. In addition, the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant are not fully understood.

OBJECTIVE

This study investigated whether pegvisomant is a "moonlighting" antagonist and explored the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

METHODS

Indirect immunofluorescence and Western blot coupled with pharmacological inhibitors and gene silencing (small interfering RNA) were used to explore the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant. Western blot, immunohistochemistry, and indirect immunofluorescence coupled with subcellular fractionation analysis were used to determine the effect of pegvisomant on GHR's nuclear localization in vitro and in vivo.

RESULTS

Here, we show that the endocytosis of pegvisomant is mainly mediated though the clathrin pathway. Further study of the postendocytic sorting of pegvisomant shows that pegvisomant enters into different types of endosomes under GHR mediation. In addition, GHR is slightly downregulated by pegvisomant; further study indicates that proteasomes and lysosomes may cooperate to regulate pegvisomant/GHR degradation. Most importantly, we show that pegvisomant inhibits the nuclear localization of GHR.

CONCLUSION

Our study showed that pegvisomant is a "moonlighting" antagonist. In addition, we revealed the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

Targeting growth hormone function: strategies and therapeutic applications

Human growth hormone (GH) is a classical pituitary endocrine hormone that is essential for normal postnatal growth and has pleiotropic effects across multiple physiological systems. GH is also expressed in extrapituitary tissues and has localized autocrine/paracrine effects at these sites. In adults, hypersecretion of GH causes acromegaly, and strategies that block the release of GH or that inhibit GH receptor (GHR) activation are the primary forms of medical therapy for this disease. Overproduction of GH has also been linked to cancer and the microvascular complications that are associated with diabetes. However, studies to investigate the therapeutic potential of GHR antagonism in these diseases have been limited, most likely due to difficulty in accessing therapeutic tools to study the pharmacology of the receptor in vivo. This review will discuss current and emerging strategies for antagonizing GH function and the potential disease indications.

Emerging therapies are offering an expanded toolkit for combatting the effects of human growth hormone overproduction. Human growth hormone (GH) is a major driver of postnatal growth; however, systemic or localized overproduction is implicated in the aberrant growth disease acromegaly, cancer, and diabetes. In this review, researchers led by Jo Perry, from the University of Auckland, New Zealand, discuss strategies that either inhibit GH production, block its systemic receptor, or interrupt its downstream signaling pathways. The only licensed GH receptor blocker is pegvisomant, but therapies are in development that include long-acting protein and antibody-based blockers, and nucleotide complexes that degrade GHR production have also shown promise. Studies investigating GHR antagonism are limited, partly due to difficulty in accessing therapeutic tools which block GHR function, but overcoming these obstacles may yield advances in alleviating chronic disease.

Excess growth hormone suppresses DNA damage repair in epithelial cells

Growth hormone (GH) decreases with age, and GH therapy has been advocated by some to sustain lean muscle mass and vigor in aging patients and advocated by athletes to enhance performance. Environmental insults and aging lead to DNA damage, which - if unrepaired - results in chromosomal instability and tumorigenesis. We show that GH suppresses epithelial DNA damage repair and blocks ataxia telangiectasia mutated (ATM) kinase autophosphorylation with decreased activity. Decreased phosphorylation of ATM target proteins p53, checkpoint kinase 2 (Chk2), and histone 2A variant led to decreased DNA repair by nonhomologous end-joining. In vivo, prolonged high GH levels resulted in a 60% increase in unrepaired colon epithelial DNA damage. GH suppression of ATM was mediated by induced tripartite motif containing protein 29 (TRIM29) and attenuated tat interacting protein 60 kDa (Tip60). By contrast, DNA repair was increased in human nontumorous colon cells (hNCC) where GH receptor (GHR) was stably suppressed and in colon tissue derived from GHR-/- mice. hNCC treated with etoposide and GH showed enhanced transformation, as evidenced by increased growth in soft agar. In mice bearing human colon GH-secreting xenografts, metastatic lesions were increased. The results elucidate a mechanism underlying GH-activated epithelial cell transformation and highlight an adverse risk for inappropriate adult GH treatment.

Site-selective protein conjugation at histidine

Site-selective conjugation generally requires both (i) molecular engineering of the protein of interest to introduce a conjugation site at a defined location and (ii) a site-specific conjugation technology. Three N-terminal interferon α2-a (IFN) variants with truncated histidine tags were prepared and conjugation was examined using a bis-alkylation reagent, PEG(10kDa)-mono-sulfone 3. A histidine tag comprised of two histidines separated by a glycine (His2-tag) underwent PEGylation. Two more IFN variants were then prepared with the His2-tag engineered at different locations in IFN. Another IFN variant was prepared with the His-tag introduced in an α-helix, and required three contiguous histidines to ensure that two histidine residues in the correct conformation would be available for conjugation. Since histidine is a natural amino acid, routine methods of site-directed mutagenesis were used to generate the IFN variants from E. coli in soluble form at titres comparable to native IFN. PEGylation conversions ranged from 28-39%. A single step purification process gave essentially the pure PEG-IFN variant (>97% by RP-HPLC) in high recovery with isolated yields ranging from 21-33%. The level of retained bioactivity was strongly dependent on the site of PEG conjugation. The highest biological activity of 74% was retained for the PEG10-106(HGHG)-IFN variant which is unprecedented for a PEGylated IFN. The His2-tag at 106(HGHG)-IFN is engineered at the flexible loop most distant from IFN interaction with its dimeric receptor. The biological activity for the PEG10-5(HGH)-IFN variant was determined to be 17% which is comparable to other PEGylated IFN conjugates achieved at or near the N-terminus that have been previously described. The lowest retained activity (10%) was reported for PEG10-120(HHH)-IFN which was prepared as a negative control targeting a IFN site thought to be involved in receptor binding. The presence of two histidines as a His2-tag to generate a site-selective target for bis-alkylating PEGylation is a feasible approach for achieving site-selective PEGylation. The use of a His2-tag to strategically engineer a conjugation site in a protein location can result in maximising the retention of the biological activity following protein modification.

Analysis of pituitary adenoma expression patterns suggests a potential role for the NeuroD1 transcription factor in neuroendocrine tumor-targeting therapies

NeuroD1’s roles in the pathogenesis of pituitary adenomas and in the biology of the normal adult pituitary gland have been insufficiently researched. Much of the work investigating its expression patterns has yielded contradictory results. Objective: morphological study of NeuroD1 transcription factor expression in different types of pituitary adenomas and in normal adult human pituitary glands. Materials and methods: This study analyzed 48 pituitary adenomas and nine normal pituitary glands. In all cases, immunohistochemical study was performed with antibodies to NeuroD1, 6 hormones of adenohypophysis, Ki-67, and CK7. We used confocal laser scanning microscopy, electron microscopy and electron immunocytochemistry. Results: NeuroD1 expression was detected in all cases of plurihormonal adenomas, mammosomatotropinomas, corticotropinomas, prolactinomas, gonadotropinomas, null-cell pituitary adenomas, and in normal pituitary glands. The average numbers of NeuroD1 expressing cells in normal adenohypophysis specimens were significantly lower than in the adenomas overall (p=0.006). NeuroD1 expression was confirmed by several methods (in prolactinomas, by double stain immunohistochemistry; in mammosomatotropinomas, by double stain immunohistochemistry, confocal laser scanning microscopy, and electron immunocytochemistry; and in somatotropinomas, by electron immunocytochemistry). Conclusion: Immunohistochemistry, confocal microscopy, and double label electron immunocytochemistry confirmed NeuroD1’s key role in the pathogenesis of pituitary tumors, regardless of their hormonal state. Its expression level in pituitary adenomas is significantly higher than in the normal pituitary gland and has no reliable correlation with any studied hormones or Ki-67. These findings suggest that NeuroD1 should be investigated further as a potential molecular target in tumor-targeting therapies.

Long-term treatment with pegvisomant: observations from 2090 acromegaly patients in ACROSTUDY

Objectives ACROSTUDY is an international, non-interventional study of acromegaly patients treated with pegvisomant (PEGV), a growth hormone receptor antagonist and has been conducted since 2004 in 15 countries to study the long-term safety and efficacy of PEGV. This report comprises the second interim analysis of 2090 patients as of May 12, 2016. Methods Descriptive analyses of safety, pituitary imaging and outcomes on PEGV treatment up to 12 years were performed. Results Prior to starting PEGV, 96% of patients had reported surgery, radiation, medical therapy or any combinations of those. At start of PEGV, 89% of patients had IGFI levels above the upper limit of normal (ULN). The percentage of patients with normal IGFI levels increased from 53% at year 1 to 73% at year 10, and the average daily dose of PEGV increased from 12.8 mg (year 1) to 18.9 mg (year 10). A total of 4832 adverse events (AEs) were reported in 1137 patients (54.4%), of which 570 were considered treatment related in 337 patients (16.1%). Serious AEs were reported in 22% of patients, of which 2.3% were considered treatment related. Locally reported MRIs showed most patients (72.2%) had no change in tumor size relative to the prior scan; 16.8% had a decrease, 6.8% an increase and 4.3% both. In patients with normal liver tests at PEGV start, an ALT or AST elevation of >3× ULN at any time point during their follow-up was reported in 3%. Conclusions This second interim analysis confirms that long-term use of PEGV is an effective and safe treatment in patients with acromegaly.

Growth hormone: isoforms, clinical aspects and assays interference

The measurement of circulating concentrations of growth hormone (GH) is an indispensable tool in the diagnosis of both GH deficiency and GH excess. GH is a heterogeneous protein composed of several molecular isoforms, but the physiological role of these different isoforms has not yet been fully understood. The 22KD GH (22 K-GH) is the main isoform in circulation, followed by 20KD GH (20 K-GH) and other rare isoforms. Studies have been performed to better understand the biological actions of the different isoforms as well as their importance in pathological conditions. Generally, the non-22 K- and 20 K-GH isoforms are secreted in parallel to 22 K-GH, and only very moderate changes in the ratio between isoforms have been described in some pituitary tumors or during exercise. Therefore, in a diagnostic approach, concentrations of 22 K-GH accurately reflect total GH secretion. On the other hand, the differential recognition of GH isoforms by different GH immunoassays used in clinical routine contributes to the known discrepancy in results from different GH assays. This makes the application of uniform decision limits problematic. Therefore, the worldwide efforts to standardize GH assays include the recommendation to use 22 K-GH specific GH assays calibrated against the pure 22 K-GH reference preparation 98/574. Adoption of this recommendation might lead to improvement in diagnosis and follow-up of pathological conditions, and facilitate the comparison of results from different laboratories.

Pituitary Diseases and Bone

Neuroendocrinology of bone is a new area of research based on the evidence that pituitary hormones may directly modulate bone remodeling and metabolism. Skeletal fragility associated with high risk of fractures is a common complication of several pituitary diseases such as hypopituitarism, Cushing disease, acromegaly, and hyperprolactinemia. As in other forms of secondary osteoporosis, pituitary diseases generally affect bone quality more than bone quantity, and fractures may occur even in the presence of normal or low-normal bone mineral density as measured by dual-energy X-ray absorptiometry, making difficult the prediction of fractures in these clinical settings. Treatment of pituitary hormone excess and deficiency generally improves skeletal health, although some patients remain at high risk of fractures, and treatment with bone-active drugs may become mandatory. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary diseases.

MANAGEMENT OF ENDOCRINE DISEASE: Personalized medicine in the treatment of acromegaly

Acromegaly is associated with high morbidity and elevated mortality when not adequately treated. Surgery is the first-line treatment for most patients as it is the only one that can lead to immediate cure. In patients who are not cured by surgery, treatment is currently based on a trial-and-error approach. First-generation somatostatin receptor ligands (fg-SRL) are initiated for most patients, although approximately 25% of patients present resistance to this drug class. Some biomarkers of treatment outcome are described in the literature, with the aim of categorizing patients into different groups to individualize their treatments using a personalized approach. In this review, we will discuss the current status of precision medicine for the treatment of acromegaly and future perspectives on the use of personalized medicine for this purpose.

Diabetes Secondary to Acromegaly: Physiopathology, Clinical Features and Effects of Treatment

Acromegaly is a rare disease due to chronic GH excess and to the consequent increase in IGF-1 levels. Both GH and IGF-1 play a role in intermediate metabolism affecting glucose homeostasis. Indeed, chronic GH excess impairs insulin sensitivity, increases gluconeogenesis, reduces the glucose uptake in adipose tissue and muscle and alters pancreatic β cells function. As a consequence, glucose metabolism alterations are a very frequent complication in acromegaly patients, further contributing to the increased cardiovascular risk and mortality. Treatment modalities of acromegaly differently impact on glucose tolerance. Successful surgical treatment of acromegaly ameliorates glucose metabolism abnormalities. Drugs used to treat acromegaly patients may per se affect glucose homeostasis, therefore influencing patients' management. Indeed pegvisomant has been shown to positively impact on glucose metabolism, while somatostatin analogs, especially pasireotide, can cause hyperglycaemia. On the other hand, robust data on the effect of dopamine agonists on glycaemic profile are still lacking. This review summarizes the available data on diabetes mellitus in acromegaly patients, with a focus on the potential effects of the medical treatment of the disease on glucose homeostasis, providing an overview of the current state of the art.

Expression of a hindlimb-determining factor Pitx1 in the forelimb of the lizard Pogona vitticeps during morphogenesis

With over 9000 species, squamates, which include lizards and snakes, are the largest group of reptiles and second-largest order of vertebrates, spanning a vast array of appendicular skeletal morphology. As such, they provide a promising system for examining developmental and molecular processes underlying limb morphology. Using the central bearded dragon (Pogona vitticeps) as the primary study model, we examined limb morphometry throughout embryonic development and characterized the expression of three known developmental genes (GHR, Pitx1 and Shh) from early embryonic stage through to hatchling stage via reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC). In this study, all genes were found to be transcribed in both the forelimbs and hindlimbs of P. vitticeps. While the highest level of GHR expression occurred at the hatchling stage, Pitx1 and Shh expression was greatest earlier during embryogenesis, which coincides with the onset of the differentiation between forelimb and hindlimb length. We compared our finding of Pitx1 expression—a hindlimb-determining gene—in the forelimbs of P. vitticeps to that in a closely related Australian agamid lizard, Ctenophorus pictus, where we found Pitx1 expression to be more highly expressed in the hindlimb compared with the forelimb during early and late morphogenesis—a result consistent with that found across other tetrapods. Expression of Pitx1 in forelimbs has only rarely been documented, including via in situ hybridization in a chicken and a frog. Our findings from both RT-qPCR and IHC indicate that further research across a wider range of tetrapods is needed to more fully understand evolutionary variation in molecular processes underlying limb morphology.

Does eating less make you live longer and better? An update on calorie restriction

The complexity of aging is hard to be captured. However, apart from its tissue-specific features, a structural and functional progressive decline of the whole organism that leads to death, often preceded by a phase of chronic morbidity, characterizes the common process of aging. Therefore, the research goal of scientists in the field moved from the search for strategies able to extend longevity to those ensuring healthy aging associated with a longer lifespan referred to as “healthspan”. The aging process is plastic and can be tuned by multiple mechanisms including dietary and genetic interventions. To date, the most robust approach, efficient in warding off the cellular markers of aging, is calorie restriction (CR). Here, after a preliminary presentation of the major debate originated by CR, we concisely overviewed the recent results of CR treatment on humans. We also provided an update on the molecular mechanisms involved by CR and the effects on some of the age-associated cellular markers. We finally reviewed a number of tested CR mimetics and concluded with an evaluation of future applications of such dietary approach.

Interventions to slow cardiovascular aging: Dietary restriction, drugs and novel molecules

Cardiovascular aging is a highly dynamic process. Despite the fact that cardiovascular function and structure change with age, they can still be modulated even in aged humans. The most prominent approaches to improve age-dependent vascular changes include dietary restriction and pharmacologic agents interacting with signaling pathways implicated in this context. These include inhibition of TOR, glycolysis, and GH/IGF-1, activation of sirtuins, and AMPK, as well as modulators of inflammation, epigenetic pathways, and telomeres. Promising nutritional approaches include Mediterranean diet and novel dietary bioactives including flavanols, anthocyanins, and lignins. Many plant bioactives improve cardiovascular parameters implied in vascular healthy aging including endothelial function, arterial stiffness, blood pressure, cholesterol, and glycemic control. However, the mechanism of action of most bioactives is not established and it remains to be elucidated whether they act as dietary restriction mimetics or via other modes of action. Even more importantly, whether these interventions can slow or even reverses components of cardiovascular aging itself and can increase healthspan or longevity in humans needs to be determined.

Pegvisomant in acromegaly: an update

BACKGROUND

In 2007, we published an opinion document to review the role of pegvisomant (PEG) in the treatment of acromegaly. Since then, new evidence emerged on the biochemical and clinical effects of PEG and on its long-term efficacy and safety.

AIM

We here reviewed the emerging aspects of the use of PEG in clinical practice in the light of the most recent literature.

RESULTS

The clinical use of PEG is still suboptimal, considering that it remains the most powerful tool to control IGF-I in acromegaly allowing to obtain, with a pharmacological treatment, the most important clinical effects in terms of signs and symptoms, quality of life and comorbidities. The number of patients with acromegaly exposed to PEG worldwide has become quite elevated and the prolonged follow-up allows now to deal quite satisfactorily with many clinical issues including major safety issues, such as the concerns about possible tumour (re)growth under PEG. The positive or neutral impact of PEG on glucose metabolism has been highlighted, and the clinical experience, although limited, with sleep apnoea and pregnancy has been reviewed. Finally, the current concept of somatostatin receptor ligands (SRL) resistance has been addressed, in order to better define the acromegaly patients to whom the PEG option may be offered.

CONCLUSIONS

PEG increasingly appears to be an effective and safe medical option for many patients not controlled by SRL but its use still needs to be optimized.

Metabolic Alterations at the Crossroad of Aging and Oncogenesis

Aging represents the major risk factor for cancer. Cancer and aging are characterized by a similar dysregulated metabolism consisting in upregulation of glycolysis and downmodulation of oxidative phosphorylation. In this respect, metabolic interventions can be viewed as promising strategies to promote longevity and to prevent or delay age-related disorders including cancer. In this review, we discuss the most promising metabolic approaches including chronic calorie restriction, periodic fasting/fasting-mimicking diets, and pharmacological interventions mimicking calorie restriction. Metabolic interventions can also be viewed as adjuvant anticancer strategies to be combined to standard cancer therapy (chemotherapeutic agents, ionizing radiation, and drugs with specific molecular target), whose major limiting factors are represented by toxicity against healthy cells but also limited efficacy easily circumvented by tumor cells. In fact, conventional cancer therapy is unable to distinguish normal and cancerous cells and thus causes toxic side effects including secondary malignancies, cardiovascular and respiratory complications, endocrinopathies, and other chronic conditions, that resemble and, in some cases, accelerate the age-related disorders and profoundly affect the quality of life. In this scenario, geroscience contributes to the understanding of the mechanisms of protection of normal cells against a cytotoxic agent and finding strategies focused on the preserving healthy cells while enhancing the efficacy of the treatment against malignant cells.

Crosstalk between insulin-like growth factor (IGF) receptor and integrins through direct integrin binding to IGF1

It has been generally accepted that integrin cell adhesion receptors are involved in growth factor signaling (integrin-growth factor crosstalk), since antagonists to integrins often suppress growth factor signaling. Partly because integrins have been originally identified as cell adhesion receptors to extracellular matrix (ECM) proteins, current models of the crosstalk between IGF1 and integrins propose that ECM ligands (e.g., vitronectin) bind to integrins and IGF1 binds to IGF receptor type 1 (IGF1R), and two separate signals merge inside the cells. Our research proves otherwise. We discovered that IGF1 interacts directly with integrins, and induces integrin-IGF-IGF1R complex formation on the cell surface. IGF1 signaling can be detected in the absence of ECM (anchorage-independent conditions). Integrin antagonists block both ECM-integrin interaction and IGF-integrin interaction, and do not distinguish the two. This is one possible reason why integrin-IGF1 interaction has not been detected. With these new discoveries, we believe that the direct IGF-integrin interaction should be incorporated into models of IGF1 signaling. The integrin-binding defective mutant of IGF1 is defective in inducing IGF signaling, although the mutant still binds to IGF1R. Notably, the IGF1 mutant is dominant-negative and suppresses cell proliferation induced by wt IGF1, and suppresses tumorigenesis in vivo, and thus the IGF1 mutant has potential as a therapeutic.

Pegvisomant: a growth hormone receptor antagonist used in the treatment of acromegaly

PURPOSE

To review published data on pegvisomant and its therapeutic role in acromegaly.

METHODS

Electronic searches of the published literature were conducted using the keywords: acromegaly, growth hormone (GH) receptor (antagonist), pegvisomant, therapy. Relevant articles (n = 141) were retrieved and considered for inclusion in this manuscript.

RESULTS

Pegvisomant is a genetically engineered, recombinant growth hormone receptor antagonist, which is effective in normalizing serum insulin-like growth factor 1 (IGF-1) levels in the majority of patients with acromegaly and ameliorating symptoms and signs associated with GH excess. Pegvisomant does not have direct antiproliferative effects on the underlying somatotroph pituitary adenoma, which is the etiology of GH excess in the vast majority of patients with acromegaly. Therefore, patients receiving pegvisomant monotherapy require regular pituitary imaging in order to monitor for possible increase in tumor size. Adverse events in patients on pegvisomant therapy include skin rashes, lipohypertrophy at injection sites, and idiosyncratic liver toxicity (generally asymptomatic transaminitis that is reversible upon drug discontinuation), thus necessitating regular patient monitoring.

CONCLUSIONS

Pegvisomant is an effective therapeutic agent in patients with acromegaly who are not in remission after undergoing pituitary surgery. It mitigates excess GH action, as demonstrated by IGF-1 normalization, but has no direct effects on pituitary tumors causing acromegaly. Regular surveillance for possible tumor growth and adverse effects (hepatotoxicity, skin manifestations) is warranted.

The Effect of the Exon-3-Deleted Growth Hormone Receptor on Pegvisomant-Treated Acromegaly: A Systematic Review and Meta-Analysis

BACKGROUND

The common exon 3 deletion polymorphism of the growth hormone receptor (d3-GHR) is associated with disease severity in acromegaly patients. The GHR antagonist pegvisomant (PEGV) is highly effective in treating severe acromegaly. Response to PEGV treatment seems to be influenced by d3-GHR and appears to be more responsive to PEGV, although available results remain conflicting.

OBJECTIVE

To assess the influence of d3-GHR on the responsiveness of acromegaly patients to PEGV by compiling the evidence derived from the largest available studies.

DESIGN

A systematic review of the literature identified three published studies and one conference abstract. Acromegaly patients (n = 324, 49.7% d3-GHR carriers) were treated with either PEGV monotherapy or PEGV combined with long-acting somatostatin analogues and/or cabergoline. A meta-analysis of raw data from these studies was performed.

RESULTS

No significant effect of the d3-GHR was observed while bringing insulin-like growth factor I (IGF-I) levels below the upper limit of normal with PEGV, which was defined as the lowest IGF-I level during PEGV treatment (mean difference: -2.3%; 95% CI: -6.5 to 1.8, p = 0.270). The PEGV dose required to achieve the lowest IGF-I levels was also not significantly influenced by individuals carrying d3-GHR (mean difference: 4.1 mg weekly; 95% CI: -5.1 to 13.2, p = 0.385). For both outcomes, separate analysis of PEGV monotherapy and combination treatment gave similar results.

CONCLUSION

Our findings suggest that the d3-GHR polymorphism has no effect on biochemical disease control in acromegaly, as it is not of added value for either the prediction of PEGV responsiveness or the determination of the required PEGV dose.

Anti-aging pharmacology: Promises and pitfalls

Life expectancy has grown dramatically in modern times. This increase, however, is not accompanied by the same increase in healthspan. Efforts to extend healthspan through pharmacological agents targeting aging-related pathological changes are now in the spotlight of geroscience, the main idea of which is that delaying of aging is far more effective than preventing the particular chronic disorders. Currently, anti-aging pharmacology is a rapidly developing discipline. It is a preventive field of health care, as opposed to conventional medicine which focuses on treating symptoms rather than root causes of illness. A number of pharmacological agents targeting basic aging pathways (i.e., calorie restriction mimetics, autophagy inducers, senolytics etc.) are now under investigation. This review summarizes the literature related to advances, perspectives and challenges in the field of anti-aging pharmacology.

New medical therapies of acromegaly

Acromegaly is a rare disease associated with significant morbidity and increased mortality. Treatment of acromegaly aims at controlling growth hormone hypersecretion, improving patients' symptoms and comorbidities and normalizing mortality. The therapeutic options for acromegaly include surgery, medical therapies and radiotherapy. However, despite all these treatment options, approximately one-half of patients are not adequately controlled. Progress in molecular research has made possible to develop new therapeutic strategies to improve control of acromegaly. This article will review the new medical approaches to acromegaly which consist in evolution of traditional therapeutic protocols and development of new molecules with different profiles of activity.

Advancing Treatment of Pituitary Adenomas through Targeted Molecular Therapies: The Acromegaly and Cushing Disease Paradigms

The current treatment of pituitary adenomas requires a balance of conservative management, surgical resection, and in select tumor types, molecular therapy. Acromegaly treatment is an evolving field where our understanding of molecular targets and drug therapies has improved treatment options for patients with excess growth hormone levels. We highlight the use of molecular therapies in this disease process and advances in this field, which may represent a paradigm shift for the future of pituitary adenoma treatment.

In vitro impact of pegvisomant on growth hormone-secreting pituitary adenoma cells

Pegvisomant (PEG), an antagonist of growth hormone (GH)-receptor (GHR), normalizes insulin-like growth factor 1 (IGF1) oversecretion in most acromegalic patients unresponsive to somatostatin analogs (SSAs) and/or uncontrolled by transsphenoidal surgery. The residual GH-secreting tumor is therefore exposed to the action of circulating PEG. However, the biological effect of PEG at the pituitary level remains unknown. To assess the impact of PEG in vitro on the hormonal secretion (GH and prolactin (PRL)), proliferation and cellular viability of eight human GH-secreting tumors in primary cultures and of the rat somatolactotroph cell line GH4C1. We found that the mRNA expression levels of GHR were characterized in 31 human GH-secreting adenomas (0.086 copy/copy β-Gus) and the GHR was identified by immunocytochemistry staining. In 5/8 adenomas, a dose-dependent inhibition of GH secretion was observed under PEG with a maximum of 38.2±17% at 1μg/mL (P<0.0001 vs control). A dose-dependent inhibition of PRL secretion occurred in three mixed GH/PRL adenomas under PEG with a maximum of 52.8±11.5% at 10μg/mL (P<0.0001 vs control). No impact on proliferation of either human primary tumors or GH4C1 cell line was observed. We conclude that PEG inhibits the secretion of GH and PRL in primary cultures of human GH(/PRL)-secreting pituitary adenomas without effect on cell viability or cell proliferation.

Current and future medical treatments for patients with acromegaly

INTRODUCTION

Acromegaly is a relatively rare condition of growth hormone (GH) excess associated with significant morbidity and, when left untreated, high mortality. Therapy for acromegaly is targeted at decreasing GH and insulin-like growth hormone 1 levels, ameliorating patients' symptoms and decreasing any local compressive effects of the pituitary adenoma. The therapeutic options for acromegaly include surgery, medical therapies (such as dopamine agonists, somatostatin receptor ligands and the GH receptor antagonist pegvisomant) and radiotherapy. However, despite all these treatments option, approximately 50% of patients are not adequately controlled.

AREAS COVERED

In this paper, the authors discuss: 1) efficacy and safety of current medical therapy 2) the efficacy and safety of the new multireceptor-targeted somatostatin ligand pasireotide 3) medical treatments currently under clinical investigation (oral octreotide, ITF2984, ATL1103), and 4) preliminary data on the use of new injectable and transdermal/transmucosal formulations of octreotide.

EXPERT OPINION

This expert opinion supports the need for new therapeutic agents and modalities for patients with acromegaly.