Pasireotide in Acromegaly: An Overview of Current Mechanistic and Clinical Data

Differences in somatostatin receptor subtype expression in patients with acromegaly: new directions for targeted therapy?

PURPOSE

To analyze the expression of somatostatin receptor (SSTR)2a and 5 by immunohistochemistry (IHC) in surgically resected somatotrophic pituitary adenomas and to associate expression rates with tumor size and clinical, biochemical, and histological parameters and response to somatostatin analog (SA) therapy.

METHODS

Forty-three microsurgically treated patients with histopathologically proven growth hormone (GH)-producing pituitary adenoma were included (WHO 2017). SSTR subtype expression was analyzed in adenoma tissues using monoclonal antibodies (Abcam, SSTR2a-UMB1, SSTR5-UMB4). Expression rates were classified as low (≤ 20% staining positivity), moderate (21-50%), and high (> 50%). Furthermore, biochemical parameters such as human growth hormone (hGH) and insulin-like growth factor-1 (IGF-1) levels were measured and clinical, biochemical, radiological, and histological data were evaluated.

RESULTS

Of the 43 patients included in this study, 28 were female and 15 were male. The median age was 52 years (range 17-72 years). The median tumor size was 1.2 cm (range: 0.13-3.93 cm). All resected tumors showed positivity for somatotrophic hormone (STH). In all tissue samples, SSTR2a signal expression was detectable in immunohistochemistry, while only 39 samples were positive for SSTR5. Thirty-six samples had a high expression of SSTR2a, while three had a moderate and four a low SSTR2a signal. In comparison, SSTR5 signal was high in 26 out of 43 samples, while seven adenomas showed a moderate and six cases a low expression rate of SSTR5. The median IGF-1 was 714.2 µg/l and the median GH 19.6 mU/l (= 6.53 µg/l). The present study indicates that there is no significant relationship between the expression rates of receptor subtypes and the parameters we analyzed. However, our study revealed that smaller adenomas have a lower baseline GH level (p = 0.015), CONCLUSION: IHC with monoclonal antibodies appears to be a suitable method to determine the expression rates of SSTR2a and 5 at protein levels, as it is not possible to draw conclusions regarding receptor subtypes solely on the basis of the parameters analyzed.

Surgical-pharmacological interactions in the treatment of acromegaly

INTRODUCTION

Acromegaly requires a multimodal treatment approach that includes surgery by an expert pituitary neurosurgeon, pharmacological treatment with one or more of the available drugs and radiation therapy. These treatment alternatives are not mutually exclusive but rather complement each other when properly indicated in the individual patient. In this review, we summarize and analyze the available data concerning the choice of the surgical approach (microscopy vs. endoscopy) and the interactions between medical treatment with somatostatin analogs and pituitary surgery.

AREAS COVERED

Technical aspects, complications and outcome of transsphenoidal surgery (TSS); Advantages and disadvantages of the microscopic and endoscopic approaches; Safety and efficacy of somatostatin analogs (SSA); Primary pharmacological therapy versus primary TSS; Benefits of the preoperative treatment with SSA; and the effect of surgical tumor debulking in the therapeutic response to SSA.

EXPERT COMMENTARY

Continuing efforts at improving surgical techniques and at generating more efficacious pharmacological therapies for acromegaly are likely to improve the outcome of these patients. However, an integral approach of the patient aimed not only at achieving biochemical criteria of cure but also at treating the individual comorbidities is mandatory to improve the quality of life of these patients and to reduce their mortality rate.

Cost-effectiveness of somatostatin analogues in the treatment of acromegaly

INTRODUCTION

Somatostatin analogues (SSAs) are the largest contributor to the direct medical cost of acromegaly management worldwide. The aim of this review was to identify and report available evidence on the cost-effectiveness of SSAs in the treatment of acromegaly.

AREAS COVERED

A literature search on relevant papers published up to April 2018 was performed. A total of 22 eligible studies (10 full-text articles and 12 conference abstracts) conducted in 14 countries were included in the analysis. In majority of studies, modelling technique was the principal research method.

EXPERT COMMENTARY

The results of cost-effectiveness analyses: 1) support published recommendations where SSAs are indicated as first-line medical treatment for patients with persistent disease after surgery or who are not eligible for surgery; 2) suggest that preoperative medical therapy with SSAs may be highly cost-effective in acromegalic patients with macroadenoma, in centres without optimal surgical results 3) indicate that in some countries pasireotide and pegvisomant appeared to be cost-effective or even dominant strategies in comparison to first-generation SSAs. The main limitation of economic evaluations was the lack of high-quality studies designed to directly compare various treatment strategies in acromegaly.

Somatostatin Analogs and Glucose Metabolism in Acromegaly: A Meta-analysis of Prospective Interventional Studies

INTRODUCTION

Somatostatin analogs (SSAs) effectivelycontrol growth hormone secretion in first and second line treatmentof acromegaly. Their effect onglucose metabolism is still debated.

AIM

to address the following questions: 1) Do SSAs affect fasting plasma glucose (FPG), fasting plasma insulin (FPI), glycosylated hemoglobin (HbA1c), glucose load (2h-OGTT), HOMA-I, HOMA-β, triglycerides (TGD), weight (W) or body mass index (BMI)? 2) Do lanreotide (LAN) and octreotide LAR (OCT) affect metabolism differently? 3)Does their effect depend on disease control?

METHODS

We performed a meta-analysis of prospective interventional trialstreating acromegaly with SSAs. Inclusion criteria: all studies reporting glyco-metabolic outcomes before and after SSAs with a minimum 6-month follow-up.

RESULTS

The inclusion criteria were met by 47 studies treating 1297 subjects (631 F). SSA treatment effectively lowered FPI (effect size [ES] -6.67 mU/L, 95%CI: -8.38 to -4.95mU/L; p<0.001), HOMA-I (ES -1.57, CI: -2.42 to -0.72; p<0.001), HOMA-β (ES -47.45, CI: -73.15 to -21.76; p<0.001) and TGD (ES -0.37 mmol/L, CI: -0.47 to -0.27 mmol/L; p<0.001). SSAs worsened 2h-OGTT (ES 0.59 mmol/L, CI: 0.05 to 1.13 mmol/L; p=0.032), but not FPG. A mild but significant increase in HbA1c (ES 0.12%, CI: 0.00to 0.25%; p=0.044) was found in OCT treated subjects.

CONCLUSIONS

SSA treatment in acromegaly patients-while improving disease control- reduces insulin levels, increases after load glucose and, ultimately, increases HbA1c levels without affecting FPG. The findings suggest that clinicians treating acromegaly with SSAs should consider targeting post-prandial glucose.

Effect of AP102, a subtype 2 and 5 specific somatostatin analog, on glucose metabolism in rats

PURPOSE

Somatostatin analogs are widely used to treat conditions associated with hormonal hypersecretion such as acromegaly and metastatic neuroendocrine tumors. First generation somatostatin analogs, such as octreotide and lanreotide, have high affinity for somatostatin receptor subtype 2 (SSTR2), but have incomplete efficacy in many patients. Pasireotide targets multiple SSTRs, having the highest affinity for SSTR5, but causes hyperglycemia and diabetes mellitus in preclinical and clinical studies. AP102 is a new somatostatin analogs with high affinity at both SSTR2 and SSTR5. We aimed to characterize the effects of AP102 vs. pasireotide on random and dynamic glucose levels, glucoregulatory hormone concentrations and growth axis measures in healthy Sprague-Dawley rats.

METHODS

Three doses of each compound were evaluated under acute conditions (1, 10, and 30 µg/kg s.c.), and two doses during a chronic (4-week) infusion (3 and 10 µg/kg/h s.c.).

RESULTS

Neither acute nor chronic AP102 administration altered blood glucose concentrations or dynamic responses following an intraperitoneal glucose tolerance test. In contrast, acute and chronic pasireotide dosing increased random and post-intraperitoneal glucose tolerance test blood glucose measures, compared to vehicle-treated controls. Both AP102 and pasireotide acutely suppressed growth hormone levels, although insulin-like growth factor-1 and somatic growth was suppressed to a greater extent with pasireotide.

CONCLUSIONS

AP102 is a new dual SSTR2/SSTR5-specific somatostatin analog that acutely reduces growth hormone but does not cause hyperglycemia during acute or chronic administration in a healthy rat model. Further studies in diabetic animals and in humans are necessary to determine the potential utility of AP102 in the clinical setting.

Pasireotide in an insulin-requiring diabetic acromegalic patient without worsening of hyperglycemia

Long-acting pasireotide is an effective treatment option for acromegaly, but it is associated with hyperglycemia, which could impact its use in patients with diabetes. We present a case of a 53-year-old man with acromegaly and type 2 diabetes mellitus (glycated hemoglobin (HbA_1c): 7.5%), who refused surgery to remove a pituitary macroadenoma and enrolled in a Phase 3 clinical trial comparing long-acting pasireotide and long-acting octreotide in acromegalic patients. The patient initially received octreotide, but insulin-like growth factor 1 (IGF-1) levels remained elevated after 12 months (383.9 ng/mL; 193.0 ng/mL; reference range: 86.5–223.8 ng/mL), indicating uncontrolled acromegaly. He switched to pasireotide 40 mg and subsequently increased to 60 mg. Within 6 months, IGF-1 levels normalized (193.0 ng/mL), and they were mostly normal for the next 62 months of treatment with pasireotide (median IGF-1: 190.7 ng/mL). Additionally, HbA_1c levels remained similar to or lower than baseline levels (range, 6.7% to 7.8%) during treatment with pasireotide despite major changes to the patient’s antidiabetic regimen, which included insulin and metformin. Uncontrolled acromegaly can result in hyperglycemia due to an increase in insulin resistance. Despite having insulin-requiring type 2 diabetes, the patient presented here did not experience a long-term increase in HbA_1c levels upon initiating pasireotide, likely because long-term control of acromegaly resulted in increased insulin sensitivity. This case highlights the utility of long-acting pasireotide to treat acromegaly in patients whose levels were uncontrolled after long-acting octreotide and who manage diabetes with insulin.

Octreotide and pasireotide (dis)similarly inhibit pituitary tumor cells in vitro

Somatostatin analogs (SSA) are the mainstay of pharmacological treatment for pituitary adenomas. However, some patients escape from therapy with octreotide, a somatostatin receptor 2 (sst2)-preferring SSA, and pasireotide, a novel multi-sst-preferring SSA, may help to overcome this problem. It has been proposed that correspondence between sst1-sst5 expression pattern and SSA-binding profile could predict patient's response. To explore the cellular/molecular features associated with octreotide/pasireotide response, we performed a parallel comparison of their in vitro effects, evaluating sst1-sst5 expression, intracellular Ca²⁺ signaling ([Ca²⁺]_i), hormone secretion and cell viability, in a series of 85 pituitary samples. Somatotropinomas expressed sst5>sst2, yet octreotide reduced [Ca²⁺]_i more efficiently than pasireotide, while both SSA similarly decreased growth hormone release/expression and viability. Corticotropinomas predominantly expressed sst5, but displayed limited response to pasireotide, while octreotide reduced functional endpoints. Non-functioning adenomas preferentially expressed sst3 but, surprisingly, both SSA increased cell viability. Prolactinomas mainly expressed sst1 but were virtually unresponsive to SSA. Finally, both SSA decreased [Ca²⁺]_i in normal pituitaries. In conclusion, both SSA act in vitro on pituitary adenomas exerting both similar and distinct effects; however, no evident correspondence was found with the sst1-sst5 profile. Thus, it seems plausible that additional factors, besides the simple abundance of a given sst, critically influence the SSA response.

Therapeutic innovations in endocrine diseases - Part 4 : Pasireotide: Long-acting release somatostatin analogue

Pasireotide, the latest long-acting release somatostatin analogue, is distributed more widely to the various somatostatin receptors, which theoretically increases its strength and broadens its scope. Does this reflect genuine therapeutic progress? Or rather does its reduced specificity cause too many adverse reactions to make it a significant therapeutic achievement?

The Impact of Adipose Tissue on Insulin Resistance in Acromegaly

Adipose tissue (AT) is recognized as key contributor to the systemic insulin resistance and overt diabetes seen in metabolic syndrome. Acromegaly is a disease characterized by excessive secretion of growth hormone (GH) and insulin-like growth factor I (IGF-I). GH is known both for its action on AT and for its detrimental effect on glucose metabolism and insulin signaling. In active acromegaly, while body fat deports are diminished, insulin resistance is increased. Early studies have demonstrated defects in insulin action, both at the hepatic and extrahepatic (i.e., muscle and fat) levels, in active disease. This review discusses recent data suggesting that AT inflammation, altered AT distribution, and impaired adipogenesis are potential mechanisms contributing to systemic insulin resistance in acromegaly.