IGF-I Variability Over Repeated Measures in Patients With Acromegaly Under Long-Acting Somatostatin Receptor Ligands

IGF-I assay methods and biologic variability: evaluation of acromegaly treatment response

Serum insulin-like growth factor (IGF-I) is the primary biochemical measure of disease activity in patients with acromegaly, and the 2014 Endocrine Society guidelines recommended normal age-adjusted serum IGF-I as the biochemical target of treatment. However, quantification and interpretation of IGF-I levels are subject to limitations that may affect therapeutic decisions. Techniques for measuring IGF-I have evolved greatly over the past 40 years and continue to do so. Results can vary substantially for different assays, procedures, and laboratories. For any assay, the interpretation of IGF-I values requires robust reference ranges. Using currently available large normative databases, the upper limit of normal (ULN) for IGF-I in middle-aged and elderly individuals is lower than historical reference ranges. Thus, the goal of achieving IGF-I < 1× ULN is more demanding than in the past, and some patients with acromegaly who were classified as "normal" (IGF-I < 1× ULN) in previous studies would be reclassified as above the ULN based on newer normative data. In addition, substantial intra-individual, week-to-week variation in serum IGF-I levels (unrelated to assay performance) has been observed. With changes over time in the measurement of IGF-I and the advent of updated reference ranges derived from large normative databases, it is difficult to justify rigid adherence to the goal of maintaining IGF-I below the ULN for all patients with acromegaly. Instead, symptoms, comorbidities, and quality of life should be considered, along with growth hormone and IGF-I levels, when evaluating the need for further treatment.

Treatment of acromegaly with the nonpeptide, highly selective somatostatin receptor type 2 agonist paltusotine

Injectable first-generation somatostatin receptor ligands (fg-SRLs) are the standard of care of medical treatment for acromegaly. While fg-SRLs control acromegaly in up to 50 % of patients, they may lead to bothersome injection pain and site reactions. Paltusotine is an investigational, highly selective somatostatin receptor subtype 2 agonist, which is administered orally once a day. To date, phase 2 and 3 clinical trials suggest paltusotine treatment can achieve biochemical and symptom control in acromegaly, with a safety profile comparable to those of the fg-SRLs. Since paltusotine is a once-daily oral drug, it may represent a future treatment option for addressing patient preference or improving quality of life.

Treatment of acromegaly with oral octreotide

Acromegaly is a rare disease caused by a growth hormone excess, usually due to a secreting pituitary adenoma. Somatostatin receptor ligands (SRL) are the mainstay of medical therapy for patients with acromegaly who fail to achieve biochemical control post-operatively or are not eligible for surgical treatment. SRLs are typically administered as monthly injections and have shown to be effective in maintaining biochemical and radiological control of acromegaly. However, these injections may cause local adverse events and are associated with increased psychological burden in some patients. Oral octreotide provides a new alternative for patients responding to injectable SRLs. This new formulation has shown to have similar safety and efficacy profiles compared to injectable SRLs and may be a preferable option for some patients with acromegaly. The aim of this review is to provide an overview of the role of oral octreotide in the management of acromegaly.

Medical treatment of functional pituitary adenomas, trials and tribulations

CONTEXT

Functioning pituitary adenomas (FPAs) include most frequently prolactinomas, somatotroph or corticotroph adenomas, while thyrotroph and gonadotroph adenomas are very rare. Despite their benign histological nature (aggressive tumors are rare and malignant ones exceptional), FPAs could cause significant morbidity and increased mortality due to complications associated with hormonal excess syndromes and/or mass effect leading to compression of adjacent structures. This mini review will focus on the increasing role of medical therapy in the multimodal treatment, which also includes transsphenoidal surgery (TSS) and radiotherapy.

EVIDENCE SYNTHESIS

Most patients with prolactinomas are treated only with medications, but surgery could be considered for some patients in a specialized pituitary center, if higher chances of cure. Dopamine agonists, especially cabergoline, are efficient in reducing tumor size and normalizing prolactin. TSS is the first-line treatment for all other FPAs, but most patients require complex adjuvant treatment, including a combination of therapeutic approaches. Medical therapy is the cornerstone of treatment in all patients after unsuccessful surgery or when surgery cannot be offered and includes somatostatin receptor ligands and dopamine agonists (almost all FPAs), growth hormone receptor antagonists (acromegaly), adrenal steroidogenesis inhibitors and glucocorticoid receptor blockers (Cushing's disease). Novel medical treatments, especially for acromegaly and Cushing's disease are under research.

CONCLUSIONS

An enlarged panel of effective drugs available with increased knowledge of predictive factors for response and/or adverse effects will enhance the possibility to offer a more individualized treatment. This would not only improve disease control and prognosis, but also quality of life.

Consensus on criteria for acromegaly diagnosis and remission

PURPOSE

The 14th Acromegaly Consensus Conference was convened to consider biochemical criteria for acromegaly diagnosis and evaluation of therapeutic efficacy.

METHODS

Fifty-six acromegaly experts from 16 countries reviewed and discussed current evidence focused on biochemical assays; criteria for diagnosis and the role of imaging, pathology, and clinical assessments; consequences of diagnostic delay; criteria for remission and recommendations for follow up; and the value of assessment and monitoring in defining disease progression, selecting appropriate treatments, and maximizing patient outcomes.

RESULTS

In a patient with typical acromegaly features, insulin-like growth factor (IGF)-I > 1.3 times the upper limit of normal for age confirms the diagnosis. Random growth hormone (GH) measured after overnight fasting may be useful for informing prognosis, but is not required for diagnosis. For patients with equivocal results, IGF-I measurements using the same validated assay can be repeated, and oral glucose tolerance testing might also be useful. Although biochemical remission is the primary assessment of treatment outcome, biochemical findings should be interpreted within the clinical context of acromegaly. Follow up assessments should consider biochemical evaluation of treatment effectiveness, imaging studies evaluating residual/recurrent adenoma mass, and clinical signs and symptoms of acromegaly, its complications, and comorbidities. Referral to a multidisciplinary pituitary center should be considered for patients with equivocal biochemical, pathology, or imaging findings at diagnosis, and for patients insufficiently responsive to standard treatment approaches.

CONCLUSION

Consensus recommendations highlight new understandings of disordered GH and IGF-I in patients with acromegaly and the importance of expert management for this rare disease.

MPOWERED Trial Open-Label Extension: Long-term Efficacy and Safety Data for Oral Octreotide Capsules in Acromegaly

CONTEXT

The MPOWERED core trial (NCT02685709) and open-label extension (OLE) phase investigated long-term efficacy and safety of oral octreotide capsules (OOC) in patients with acromegaly. Core trial primary endpoint data demonstrated noninferiority to injectable somatostatin receptor ligands (iSRLs). Core trial completers were invited to participate in the OLE phase.

OBJECTIVE

To assess long-term efficacy and safety of OOC in patients with acromegaly who previously responded to and tolerated both OOC and injectable octreotide/lanreotide and completed the core phase.

METHODS

The unique study design of transitioning between OOC and iSRLs allowed within-patient evaluations. The proportion of biochemical responders (insulin-like growth factor I < 1.3 × upper limit of normal) at end of each extension year who entered that year as responders was the main outcome measure.

RESULTS

At year 1 extension end, 52/58 patients from both the monotherapy and the combination therapy groups were responders (89.7%; 95% CI 78.8-96.1), 36/41 (87.8%; 95% CI 73.8-95.9) in year 2, and 29/31 (93.5%; 95% CI 78.6-99.2) in year 3. No new or unexpected safety signals were detected; 1 patient withdrew owing to treatment failure. Patients who transitioned from iSRLs in the core trial to OOC in the OLE phase reported improved treatment convenience/satisfaction and symptom control.

CONCLUSION

Patient-reported outcome data support for the first time that transitioning patients randomized to iSRL (who previously responded to both OOC and iSRLs) back to OOC had a significant effect on patients' symptoms score in a prospective cohort. The MPOWERED OLE showed long-term maintenance of response and sustained safety with OOC.

ACROBAT Edge: Safety and efficacy of switching injected SRLs to oral paltusotine in patients with acromegaly

CONTEXT

Paltusotine is a once-daily, oral, non-peptide small-molecule somatostatin receptor type 2 (SST2) agonist in clinical development for treatment of acromegaly.

OBJECTIVE

To evaluate change in IGF-I levels in patients switched from octreotide LAR or lanreotide depot monotherapy to paltusotine.

DESIGN

Phase 2, open-label, prospective, multicenter, multinational, non-randomized, single-arm exploratory study in which dosage up-titrations were performed in a double-blinded manner.

SETTING

26 global sites.

PARTICIPANTS

Patients with acromegaly switched to paltusotine from injected SRL-based therapy.

INTERVENTIONS

Patients received 13-week treatment with once-daily oral paltusotine (10-40 mg/day).

MAIN OUTCOME MEASURES

Primary endpoint was change from baseline to week 13 in IGF-I for patients who switched from long-acting octreotide or lanreotide monotherapy to paltusotine (Group 1). All patients underwent a 4-week paltusotine washout at end of treatment period (weeks 13-17). IGF-I, GH, patient reported outcome, and safety data were collected.

RESULTS

Forty-seven patients enrolled. In Group 1 (n = 25), IGF-I and GH showed no significant change between SRL baseline and end of paltusotine treatment at week 13 (median change in IGF-I = -0.03×upper limit of normal [ULN], P = 0.6285; GH = -0.05 ng/mL, P = 0.6285). IGF-I and GH rose significantly in the 4 weeks after withdrawing paltusotine (median change in IGF-I = 0.55×ULN, P < 0.0001 [median increase 39%]; GH = 0.72 ng/mL, P < 0.0001 [109.1% increase]). No patients discontinued due to adverse events; no treatment-related serious adverse events were reported.

CONCLUSIONS

These results suggest once daily, oral paltusotine is effective in maintaining IGF-I values in patients with acromegaly who switched from injected SRLs. Paltusotine was well tolerated with a safety profile consistent with other SRLs.

Acromegaly: pathogenesis, diagnosis, and management

Growth hormone-secreting pituitary adenomas that cause acromegaly arise as monoclonal expansions of differentiated somatotroph cells and are usually sporadic. They are almost invariably benign, yet they can be locally invasive and show progressive growth despite treatment. Persistent excess of both growth hormone and its target hormone insulin-like growth factor 1 (IGF-1) results in a wide array of cardiovascular, respiratory, metabolic, musculoskeletal, neurological, and neoplastic comorbidities that might not be reversible with disease control. Normalisation of IGF-1 and growth hormone are the primary therapeutic aims; additional treatment goals include tumour shrinkage, relieving symptoms, managing complications, reducing excess morbidity, and improving quality of life. A multimodal approach with surgery, medical therapy, and (more rarely) radiation therapy is required to achieve these goals. In this Review, we examine the epidemiology, pathogenesis, diagnosis, complications, and treatment of acromegaly, with an emphasis on the importance of tailoring management strategies to each patient to optimise outcomes.