Pegvisomant in combination with long-acting somatostatin analogues in acromegaly: the role of the GH receptor deletion of exon 3

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.

A systematic literature review to evaluate extended dosing intervals in the pharmacological management of acromegaly

PURPOSE

This systematic literature review investigated whether extended dosing intervals (EDIs) of pharmacological acromegaly treatments reduce patient burden and costs compared with standard dosing, while maintaining effectiveness.

METHODS

MEDLINE/Embase/the Cochrane Library (2001-June 2021) and key congresses (2018-2021) were searched and identified systematic literature review bibliographies reviewed. Included publications reported on efficacy/effectiveness, safety and tolerability, health-related quality of life (HRQoL), and patient-reported and economic outcomes in longitudinal/cross-sectional studies in adults with acromegaly. Interventions included EDIs of pegvisomant, cabergoline, and somatostatin receptor ligands (SRLs): lanreotide autogel/depot (LAN), octreotide long-acting release (OCT), pasireotide long-acting release (PAS), and oral octreotide; no comparator was required.

RESULTS

In total, 35 publications reported on 27 studies: 3 pegvisomant monotherapy, 11 pegvisomant combination therapy with SRLs, 9 LAN, and 4 OCT; no studies reported on cabergoline, PAS, or oral octreotide at EDIs. Maintenance of normal insulin-like growth factor I (IGF-I) was observed in ≥ 70% of patients with LAN (1 study), OCT (1 study), and pegvisomant monotherapy (1 study). Achievement of normal IGF-I was observed in ≥ 70% of patients with LAN (3 studies) and pegvisomant in combination with SRLs (4 studies). Safety profiles were similar across EDI and standard regimens. Patients preferred and were satisfied with EDIs. HRQoL was maintained and cost savings were provided with EDIs versus standard regimens.

CONCLUSIONS

Clinical efficacy/effectiveness, safety, and HRQoL outcomes in adults with acromegaly were similar and costs lower with EDIs versus standard regimens. Physicians may consider acromegaly treatment at EDIs, especially for patients with good disease control.

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.

MECHANISMS IN ENDOCRINOLOGY: Clinical and pharmacogenetic aspects of the growth hormone receptor polymorphism

Pharmacogenetics aims to maximize the beneficial effects of a medical therapy by identifying genetic finger prints from responders and non-responders and, thereby improving safety and efficacy profile of the drug. Most subjects who are deficient in growth hormone (GHD) are candidates for recombinant human GH (rhGH) therapy. To date, it is well established that even after adjustments for several clinical variables, such as age, gender, body composition and the age at onset of the GHD, response to rhGH treatment is highly variable among individuals, part of which is believed to be due to genetic factors within the GH system. As the first genetic variant to potentially influence the individual response to rhGH therapy in children with growth disorders, polymorphism in the GH receptor (GHR) has attracted a great interest as a target for pharmacogenetics. Studies have been conducted to compare the functional and molecular effects of the full-length GHR (fl-GHR) isoform with the exon 3 deleted (d3-GHR) isoform in children and adults treated with rhGH therapy. Additionally, the impact of the GHR polymorphism has been investigated in relation to the clinical status and response to medical treatment in acromegaly, especially to the GHR antagonist drug pegvisomant. We have performed a narrative review of the studies performed to date on the association of GHR polymorphism with rhGH response in children and adults, and its potential influence in the medical management of acromegaly. In addition, data from studies on the general population and in other chronic diseases examining a role of this genetic variant in the regulation of growth and metabolism are summarized.

The exon3-deleted growth hormone receptor gene polymorphism (d3-GHR) is associated with insulin and spontaneous growth in short SGA children (NESGAS)

OBJECTIVE

The effect of a common polymorphism in the Growth Hormone (GH) receptor (d3-GHR) gene on growth, metabolism and body composition was examined in short children born small for gestational age (SGA) on GH treatment.

DESIGN

In 96 prepubertal, short SGA children treated with high-dose GH (67μg/kg/day) in the NESGAS study, insulin sensitivity (IS), insulin secretion and disposition index (DI) were determined during the first year of treatment. Body composition was analysed by DXA. The d3-GHR locus was determined by simple multiplex PCR.

RESULTS

At baseline, children in the d3-GHR group (d3/fl (n=37), d3/d3 (n=7)) had significantly lower IS (median (25-75 percentile)) (223.3% (154.4-304.8)) vs. (269.7% (185.1-356.7)) (p=0.03) and higher concentrations of glucose (mean (SD)) (4.4mmol/L (0.6) vs. 4.2mmol/L (0.7)) (p=0.03), C-peptide (232.1pmol/L (168.8-304.1) vs. 185.1pmol/L (137.7-253.9)) (p=0.04) and insulin (19.2pmol/L (11.8-32.2)) vs. (13.7pmol/L (9.3-20.8)) (p=0.04) compared to children homozygous for the full length allele (fl/fl-GHR (n=52)). There were no differences in DI or insulin secretion. Postnatal, spontaneous growth was significantly greater in the d3-GHR group compared to the fl/fl-GHR group (p=0.02). There were no significant differences in growth response, body composition or metabolism after one year of GH therapy.

CONCLUSION

Short SGA children carrying the d3-GHR polymorphism had increased spontaneous growth, lower IS and a compensatory increase in glucose, C-peptide and insulin before GH therapy compared to children homozygous for the full-length allele.

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.

A multivariable prediction model for pegvisomant dosing: monotherapy and in combination with long-acting somatostatin analogues

BACKGROUND

Effective treatment of acromegaly with pegvisomant (PEGV), a growth hormone receptor antagonist, requires an appropriate dose titration. PEGV doses vary widely among individual patients, and various covariates may affect its dosing and pharmacokinetics.

OBJECTIVE

To identify predictors of the PEGV dose required to normalize insulin-like growth factor I (IGF-I) levels during PEGV monotherapy and in combination with long-acting somatostatin analogues (LA-SSAs).

DESIGN

Two retrospective cohorts (Rotterdam + Liège Acromegaly Survey (LAS), total n = 188) were meta-analyzed as a form of external replication to study the predictors of PEGV dosing in addition to LA-SSA, the LAS (n = 83) was used to study the predictors of PEGV monotherapy dosing. Multivariable regression models were used to identify predictors of the PEGV dose required to normalize IGF-I levels.

RESULTS

For PEGV dosing in combination with LA-SSA, IGF-I levels, weight, height and age, were associated with the PEGV normalization dosage (P ≤ 0.001, P ≤ 0.001, P = 0.028 and P = 0.047 respectively). Taken together, these characteristics predicted the PEGV normalization dose correctly in 63.3% of all patients within a range of ±60 mg/week (21.3% within a range of ±20 mg/week). For monotherapy, only weight was associated with the PEGV normalization dose (P ≤ 0.001) and predicted this dosage correctly in 77.1% of all patients within a range of ±60 mg/week (31.3% within a range of ±20 mg/week).

CONCLUSION

In this study, we show that IGF-I levels, weight, height and age can contribute to define the optimal PEGV dose to normalize IGF-I levels in addition to LA-SSA. For PEGV monotherapy, only the patient's weight was associated with the IGF-I normalization PEGV dosage.

The role of combination medical therapy in the treatment of acromegaly

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Experience with pegvisomant treatment in acromegaly in a single Brazilian tertiary reference center: efficacy, safety and predictors of response

Objective

To describe the safety and efficacy of pegvisomant therapy and the predictors of treatment response in acromegaly patients at a single tertiary reference center in Brazil.

Materials and methods

We retrospectively reviewed the clinical, hormonal and radiological data of acromegaly patients treated with pegvisomant in our center. We also evaluated the presence of the d3 isoform of the growth hormone receptor (d3GHR).

Results

Twenty-seven patients were included (17 women). Pegvisomant was used in combination with octreotide LAR in 20 patients (74%), in combination with cabergoline in one (4%) and as monotherapy in six (22%). IGF-I normalization was achieved in 23 patients (85%). Mild and transitory elevation of liver enzymes was observed in two patients (7.4%), tumor growth in one (3.4%) and lipodystrophy in two (7.4%). One patient stopped the drug due to headaches. The GHR isoforms were evaluated in 14 patients, and the presence of at least one d3GHR allele was observed in 43% of them, but it was not a predictor of treatment response. Only pre-treatment IGF-I level was a predictor of treatment response.

Conclusion

Pegvisomant treatment was highly effective and safe in our series of Brazilian patients. A better chance of disease control can be expected in those with lower pre-pegvisomant IGF-I levels.

Growth hormone receptor exon 3 isoforms may have no importance in the clinical setting of multiethnic Brazilian acromegaly patients

BACKGROUND

Acromegaly is associated with significant morbidity and increased mortality, but has a variable severity phenotype. The presence of the exon 3-deleted isoform of the growth hormone receptor (d3-GHR) may influence the disease phenotype and treatment outcomes, including the frequency of biochemical discordance after medical treatment.

AIMS

The objective of this study was to analyze the influence of the d3-GHR isoform on clinical and biochemical characteristics and in the treatment outcomes of Brazilian multiethnic acromegaly patients.

METHODS

We retrospectively analyzed our acromegaly outpatient clinic databank and collected demographic, clinical, biochemical and treatment outcome data from those patients who agreed to participate in the study. A blood sample was collected from all patients, the DNA was extracted and the GHR isoforms were evaluated by PCR, with the full length (fl)-GHR represented by a 935-bp fragment and the d3-GHR represented by a 532-bp fragment.

RESULTS

A total of 121 patients were included. Fifty-six patients (46.3 %) were full-length homozygous (fl/fl), 48 (39.7 %) were heterozygous (fl/d3) and 17 (14.0 %) were d3-GHR homozygous (d3/d3). There was no difference between patients homozygous for the fl isoform and those harboring at least one d3-GHR allele in the demographic, clinical and biochemical data or in the treatment outcomes, including somatostatin receptor ligands (SRL) monotherapy, combination therapy with SRL and cabergoline and pegvisomant treatment. There was also no difference between the groups for the frequency of GH and IGF-I discordance after medical treatment.

CONCLUSION

GHR exon 3 genotyping appears to have no clinical significance, at least in Brazilian acromegaly patients.