The Use of IGF-I to Monitor Long-Acting Growth Hormone Therapy-Timing is an Art…

Utilizing Somapacitan, a Long-acting Growth Hormone Formulation, for the Treatment of Adult Growth Hormone Deficiency: A Guide for Clinicians

OBJECTIVE

Somapacitan is the first approved and currently the only long-acting growth hormone (GH) formulation in the United States for treatment of adults with growth hormone deficiency (GHD). The aim of this review was to provide a practical approach for clinicians on how to utilize somapacitan in the treatment of adults with GHD.

METHODS

Literature search was performed on PubMed using key words, including adult GHD, long-acting growth hormone, somapacitan, treatment, and management. The discussion of treatment aspects utilizing somapacitan was based on evidence from previous clinical studies and personal experience.

RESULTS

Clinical trial data demonstrated that somapacitan, a once-weekly reversible albumin-binding GH derivative, decreased truncal fat, improved visceral fat and lean body mass, increased insulin-like growth factor-I standard deviation score and exerted neutral effects on glucose metabolism. Overall, somapacitan was well-tolerated, adverse event rates were comparable with daily GH, antisomapacitan or anti-GH antibodies were not detected, and treatment satisfaction was in favor of somapacitan vs daily GH.

CONCLUSION

Somapacitan is an efficacious, safe, convenient and well-tolerated once-weekly long-acting GH formulation that reduces the treatment burden of once-daily GH injections for adults with GHD. This article provides a review of the pharmacology of somapacitan and offers practical recommendations based on previous clinical trial data on how to initiate, dose titration, monitoring and dose adjustments whilst on therapy in adults with GHD. Timing of measurement of serum insulin-like growth factor-I levels, information on administration, recommendations on missed doses, and clinical recommendations on dosing in certain sub-population of patients are also discussed.

Childhood growth hormone treatment: challenges, opportunities, and considerations

With long standing demand and popularity, growth hormone treatments continue to be a topic of interest for paediatric endocrinologists and general paediatricians due to ongoing issues regarding their long-term effects, the safety of childhood treatment, and the introduction of long-acting growth hormone preparations in the past decade. Moreover, uncertainty regarding how to approach individual patients and their treatment indications remains, particularly concerning tailored treatment goals and objectives; this uncertainty is further complicated by the multitude of approved indications that surpass substitution therapy. The paediatric endocrinologist thus grapples with pertinent questions, such as what defines reasonable treatment goals for each individual given their indications, and when (and how) to initiate the necessary discussions about risks and benefits with patients and their families. The aim of this Review is to offer advanced physiological concepts of growth hormone function, map out approved paediatric indications for treatment along with evidence on their effects and safety, highlight controversies and complexities surrounding childhood growth hormone treatment, and discuss the potential of long-acting growth hormone and future directions in the realm of childhood growth hormone treatment.

Hypopituitarism

Partial or complete deficiency of anterior or posterior pituitary hormone production leads to central hypoadrenalism, central hypothyroidism, hypogonadotropic hypogonadism, growth hormone deficiency, or arginine vasopressin deficiency depending on the hormones affected. Hypopituitarism is rare and likely to be underdiagnosed, with an unknown but rising incidence and prevalence. The most common cause is compressive growth or ablation of a pituitary or hypothalamic mass. Less common causes include genetic mutations, hypophysitis (especially in the context of cancer immunotherapy), infiltrative and infectious disease, and traumatic brain injury. Clinical features vary with timing of onset, cause, and number of pituitary axes disrupted. Diagnosis requires measurement of basal circulating hormone concentrations and confirmatory hormone stimulation testing as needed. Treatment is aimed at replacement of deficient hormones. Increased mortality might persist despite treatment, particularly in younger patients, females, and those with arginine vasopressin deficiency. Patients with complex diagnoses, pregnant patients, and adolescent pituitary-deficient patients transitioning to adulthood should ideally be managed at a pituitary tumour centre of excellence.

Developments in the Management of Growth Hormone Deficiency: Clinical Utility of Somapacitan

Growth hormone (GH) replacement therapy for growth hormone deficiency (GHD) in children and adults has for over 25 years, until recently, been administered as daily injections. This daily treatment regimen often incurs a burden to patients and caregivers, leading to high rates of non-adherence and, consequently, decreased treatment efficacy outcomes. To address this shortcoming, long-acting growth hormones (LAGHs) have been developed with the aim of reducing the burden of daily injections, thereby potentially improving treatment adherence and outcomes. Somapacitan (Sogroya®) (Novo Nordisk, Bagsværd, Denmark) is a LAGH currently approved for the treatment of adult and childhood GHD (AGHD and CGHD, respectively) in several countries. Other LAGHs, such as somatrogon (Ngenla®) (Pfizer, New York, United States) and lonapegsomatropin/TransCon GH (Skytrofa®) (Ascendis Pharma, Copenhagen, Denmark), are also currently approved and available for the treatment of CGHD in several countries. In this review, we will consider the method of protraction, pharmacokinetics (PK) and pharmacodynamics (PD), efficacy, and safety results of somapacitan in adult and pediatric trials and how these characteristics differ from those of the other aforementioned LAGHs. Additionally, the administration of somapacitan and timing of measurement of serum insulin-like growth factor-I (IGF-I) levels are summarized. Information on administration, advice on missed doses, and clinical guidelines are discussed, as well as identifying which patients are suitable for somapacitan therapy, and how to monitor and adjust dosing whilst on therapy.

Somatrogon injection for the treatment of pediatric growth hormone deficiency with comparison to other LAGH products

INTRODUCTION

Somatrogon (NGENLA™) is a long-acting GH (LAGH) formulation that was approved in Canada in October 2021 for the treatment of pediatric growth hormone deficiency (GHD). Somatrogon has also received approval in Australia, Japan, the European Union, the USA, and the UK. Somatrogon is a glycoprotein that utilizes three copies of the C-terminal peptide of human chorionic gonadotropin to delay its clearance allowing for once-weekly administration.

AREAS COVERED

The purpose of this article is to describe the development of somatrogon for treatment of individuals with GHD. Trials of somatrogon demonstrated positive efficacy results in adults (Phase 2) and children (Phase 2 and 3) with GHD including non-inferiority of height velocity compared to daily GH, with no concerning side effects. Growth responses, pharmacodynamics and safety data are compared to other LAGH products, lonapegsomatropin and somapacitan, in Phase 3 trials in pediatric GHD.

EXPERT OPINION

New LAGH products, including somatrogon, have the potential to increase patient adherence as well as improve quality of life and clinical outcomes. Clinicians will need to identify the best candidates for LAGH therapy and understand how to safely monitor and adjust therapy. Long-term surveillance studies are necessary to demonstrate adherence, efficacy, cost-effectiveness, and safety of LAGH preparations.

Model-Based Analysis of IGF-I Response, Dosing, and Monitoring for Once-Weekly Somapacitan in Children With GH Deficiency

Context

Growth hormone (GH) replacement therapy improves longitudinal growth and adult height in children with GH deficiency (GHD). GH stimulates insulin-like growth factor (IGF)-I release, the biomarker used for monitoring GH activity during treatment.

Objective

This study aims to provide model-based insights into the dose-IGF-I responses of once-weekly somapacitan, a novel long-acting GH, compared with daily GH in children with GHD.

Methods

Analyses included dosing information and 1473 pharmacokinetic samples from 210 somapacitan-treated pediatric patients with GHD across 3 trials, including phase 1 (NCT01973244), phase 2 (NCT02616562; REAL 3), and phase 3 (NCT03811535; REAL 4), as well as 1381 IGF-I samples from 186 patients with GHD treated with somapacitan in REAL 3 and REAL 4. Pharmacokinetic/pharmacodynamic modeling to characterize somapacitan dose-IGF-I response and predict the response to dosing day changes.

Results

Relationships were established between somapacitan dose, exposure, change from baseline IGF-I SD score (SDS), and height velocity (HV). A linear model permitted the development of a tool to calculate estimated average weekly IGF-I exposure from a single IGF-I sample obtained at any time within the somapacitan dosing interval at steady state. In practice, the use of this tool requires knowledge of somapacitan injection timing relative to IGF-I sample collection timing. IGF-I SDS simulations support flexible dosing day changes while maintaining at least 4 days between doses.

Conclusion

We characterized the dose-IGF-I response of somapacitan in children with GHD. To support physicians in IGF-I monitoring, we present a practical guide about expected weekly average IGF-I concentrations in these patients and provide insights on dosing day flexibility.

What do we do now that the long-acting growth hormone is here?

In standard 52-week phase III clinical trials, once weekly lonapegsomatropin, somatrogon and somapacitan have been found to yield non-inferior height velocities and similar safety profiles to daily GH (DGH) in children with pediatric growth hormone deficiency (PGHD). Lonapegsomatropin, a long-acting GH therapy (LAGH), was approved by the United States Food and Drug Administration (FDA) in August 2021 for the treatment of PGHD and has also been approved in other regions of the world. Somatrogon was approved for the treatment of PGHD beginning in some regions beginning in late 2021. Somapacitan was approved by the FDA for the treatment of Adult GHD in August 2020. The phase III clinical trial of somapacitan for the treatment of PGHD has been completed and demonstrated non-inferiority of somapacitan to DGH. New LAGH products may improve patient adherence, quality of life and clinical outcomes, particularly in patients with poor adherence to daily GH injections in the future. With the availability of new LAGH products, clinicians will need to identify the best candidates for LAGH therapy and understand how to monitor and adjust therapy. Long-term surveillance studies are needed to demonstrate adherence, efficacy, cost-effectiveness and safety of LAGH preparations and to understand how the non-physiological pharmacokinetic and pharmacodynamic profiles following administration of each LAGH product relate to short- and long-term safety and efficacy of LAGH therapy.

Spotlight on Lonapegsomatropin Once-Weekly Injection and Its Potential in the Treatment of Growth Hormone Deficiency in Pediatric Patients

Lonapegsomatropin, a long-acting GH therapy (LAGH), was approved by the United States Food and Drug Administration in August 2021 for the treatment of pediatric growth hormone deficiency (GHD). Lonapegsomatropin is a prodrug consisting of unmodified GH transiently conjugated to methoxypolyethylene glycol which enables time-release of GH with a half-life of ~25 hours allowing for once-weekly administration. Clinical trials of lonapegsomatropin have demonstrated positive efficacy results in children (phase 2 and 3) and adults (phase 2) with GHD. The phase 3 trial in children with GHD established non-inferiority and statistical superiority of height velocity with lonapegsomatropin (11.2 cm/yr) compared to daily GH (10.3 cm/yr), with no concerning side effects with lonapegsomatropin. Similar growth responses have been reported in other LAGH products in phase 2 (somapacitan) and phase 3 (somatrogon) trials. Lonapegsomatropin is distributed in temperature-stable, prefilled cartridges at 9 different doses that can be prescribed based upon specific weight brackets designed to deliver approximately 0.24 mg/kg/wk. An electronic delivery device is required to combine the powdered medication with the diluent and deliver the medication subcutaneously through a small gauge needle to the recipient. The pharmacodynamic data from the clinical trials of lonapegsomatropin has been used to develop models to estimate an average IGF-1 value drawn at any time during the weekly injection interval. This average IGF-1 value may be used to for safety monitoring and/or to guide dose adjustment. New LAGH products, including lonapegsomatropin, may potentially improve patient adherence, quality of life and clinical outcomes, particularly in patients with poor adherence to daily GH injections in the future. With the availability of new LAGH products, clinicians will need to identify the best candidates for LAGH therapy and understand how to monitor and adjust therapy. Long-term surveillance studies are needed to demonstrate adherence, efficacy, cost-effectiveness and safety of LAGH preparations.

Efficacy and Safety of Weekly Somatrogon vs Daily Somatropin in Children With Growth Hormone Deficiency: A Phase 3 Study

CONTEXT

Somatrogon is a long-acting recombinant human growth hormone (rhGH) in development for once-weekly treatment of children with growth hormone deficiency (GHD).

OBJECTIVE

We aimed to compare the efficacy and safety of once-weekly somatrogon with once-daily somatropin in prepubertal children with GHD.

METHODS

In this 12-month, open-label, randomized, active-controlled, parallel-group, phase 3 study, participants were randomized 1:1 to receive once-weekly somatrogon (0.66 mg/kg/week) or once-daily somatropin (0.24 mg/kg/week) for 12 months. A total of 228 prepubertal children (boys aged 3-11 years, girls aged 3-10 years) with GHD, impaired height and height velocity (HV), and no prior rhGH treatment were randomized and 224 received ≥1 dose of study treatment (somatrogon: 109; somatropin: 115). The primary endpoint was annualized HV at month 12.

RESULTS

HV at month 12 was 10.10 cm/year for somatrogon-treated subjects and 9.78 cm/year for somatropin-treated subjects, with a treatment difference (somatrogon-somatropin) of 0.33 (95% CI: -0.24, 0.89). The lower bound of the 2-sided 95% CI was higher than the prespecified noninferiority margin (-1.8 cm/year), demonstrating noninferiority of once-weekly somatrogon vs daily somatropin. HV at month 6 and change in height standard deviation score at months 6 and 12 were similar between both treatment groups. Both treatments were well tolerated, with a similar percentage of subjects experiencing mild to moderate treatment-emergent adverse events in both groups (somatrogon: 78.9%, somatropin: 79.1%).

CONCLUSION

The efficacy of once-weekly somatrogon was noninferior to once-daily somatropin, with similar safety and tolerability profiles. (ClinicalTrials.gov no. NCT02968004).

Effective GH Replacement With Once-weekly Somapacitan vs Daily GH in Children with GHD: 3-year Results From REAL 3

CONTEXT

Current GH therapy requires daily injections, which can be burdensome. Somapacitan is a long-acting GH derivative in development for treatment of GH deficiency (GHD).

OBJECTIVE

Evaluate the efficacy, safety, and tolerability of once-weekly somapacitan after 3 years of treatment.

DESIGN

A multicenter, randomized, controlled, phase 2 study comparing somapacitan and once-daily GH for 156 weeks (NCT02616562).

SETTING

Twenty-nine sites in 11 countries.

PATIENTS

Fifty-nine children with GHD randomized (1:1:1:1) and exposed to treatment. Fifty-three children completed the 3-year period.

INTERVENTIONS

Patients received somapacitan (0.04 [n = 14], 0.08 [n = 15], or 0.16 [n = 14] mg/kg/wk) or daily GH (n = 14) (0.034 mg/kg/d, equivalent to 0.238 mg/kg/wk) subcutaneously during the first year, after which all patients on somapacitan received 0.16 mg/kg/wk.

MAIN OUTCOME MEASURES

Height velocity (HV) at year 3; changes from baseline in height SD score (HSDS), HVSDS, and IGF-I SDS.

RESULTS

The estimated treatment difference (95% CI) in HV for somapacitan 0.16/0.16 mg/kg/wk vs daily GH at year 3 was 0.8 cm/y (-0.4 to 2.1). Change in HVSDS from baseline to year 3 was comparable between somapacitan 0.16/0.16 mg/kg/wk, the pooled somapacitan groups, and daily GH. A gradual increase in HSDS from baseline was observed for all groups. At year 3, mean HSDS was similar for the pooled somapacitan groups and daily GH. Change from baseline to year 3 in mean IGF-I SDS was similar across treatments.

CONCLUSIONS

Once-weekly somapacitan in children with GHD showed sustained efficacy over 3 years in all assessed height-based outcomes with similar safety and tolerability to daily GH. A plain language summary (1) is available for this study.

CLINICAL TRIAL INFORMATION

This study has been registered at ClinicalTrials.gov, number NCT02616562 (REAL 3).

Guidance for the treatment of adult growth hormone deficiency with somapacitan, a long-acting growth hormone preparation

Adult growth hormone deficiency (AGHD) is a rare endocrine disorder characterized by an abnormal body composition, metabolic abnormalities associated with increased cardiovascular diseases, bone loss, and impaired quality of life. Daily subcutaneous injections with recombinant growth hormone (GH) can alleviate the abnormalities associated with AGHD. Several long-acting GH (LAGH) preparations are currently in development that aim to reduce treatment burden for patients receiving daily GH injections. Somapacitan (Sogroya^®; Novo Nordisk, Denmark) is the first LAGH preparation that has been approved for treatment of AGHD in the United States, Europe, and Japan. The recent approval of somapacitan and anticipated approval of other LAGH molecules presents new questions for physicians planning to treat AGHD with LAGH in the future. Differences in the technologies used to prolong the half-life of recombinant GH are expected to result in variations in pharmacokinetic and pharmacodynamic profiles between preparations. Therefore, it is essential that physicians understand and consider such variations when treating patients with these novel GH replacement therapies. Here, we present a set of treatment recommendations that have been created to guide physicians initiating therapy with somapacitan in patients with AGHD who are eligible for GH replacement. Furthermore, we will review the published data that underlie these recommendations to explain the rationale for the treatment and monitoring advice provided.