Treatment escape reduces the effectiveness of cabergoline during long-term treatment of acromegaly in monotherapy or in association with first-generation somatostatin receptor ligands

Predictors of biochemical and structural response to medical therapy in patients with active acromegaly following surgery: a real-world perspective

BACKGROUND

Somatostatin receptor analogs (SRAs) and dopamine agonists (DAs) are the main medical treatments for patients with acromegaly who fail to achieve remission after surgery. We aimed to explore the potential role of select clinical, biochemical, and radiological factors in predicting biochemical and structural responses to medical therapy in a real-world setting.

METHODS

This retrospective cohort study included 58 patients with active acromegaly following surgery treated with Octreotide long-acting release (LAR) (± Cabergoline). Biochemical outcomes were defined as the tight biochemical response (TBR; normal insulin-like growth factor-1(IGF-1)) and biochemical control (BC; IGF-1 ≤ 1.2 upper limit of normal (ULN)). The structural response was defined as > 25% reduction in one dimension of the tumor at the last visit. Univariate and multivariate analyses assessed the predictors of biochemical and structural response.

RESULTS

The mean age of the participants was 41.5 ± 11.7 years. They were followed for a median of 27.6 (19.2-43.2) months. At the last visit, TBR and BC were achieved in 48.3% and 51.7% of the patients. Moreover, 51.4% of the patients showed a structural response. Applying the age-sex adjusted model, post-operative IGF-1 was inversely associated with TBR [OR 0.34, P = 0.006] and BC [OR 0.30, P = 0.004]. Moreover, Knosp grading < 3 compared to ≥ 3, and T2-hypointensity compared to the non-T2-hypointensity were associated with higher odds of TBR [OR 3.98, P = 0.04], [OR 27.63, P = 0.01], and BC [OR 5.80, P = 0.01], [OR 35.15, P = 0.01], respectively.

CONCLUSIONS

Post-operative IGF-1, Knosp grading, and T2-hypointensity could be considered for an individualized treatment plan in acromegaly. Accordingly, we propose an individual multidisciplinary treatment approach for patients not achieving remission after surgery.

Real-world value of cabergoline in the treatment of acromegaly

Cabergoline is an ergot derivative long-acting dopamine receptor 2 (DR2) selective agonist administered orally and widely used for the treatment of prolactin-secreting adenomas and Parkinson's disease. DR2 is expressed in most somatotroph adenomas. In acromegaly, cabergoline is used off-label and its role is limited by the relatively modest efficacy for achieving hormonal remission and thus, it is largely indicated in patients with mild elevation of GH/IGF-I postoperatively. It can be given as monotherapy, usually at a higher weekly dose than usually required to treat prolactinomas, but also as an add-on treatment in patients partially responding to the somatostatin receptor ligands octreotide or lanreotide. IGF-1 normalization with cabergoline can be achieved in about a third of the patients. Low baseline IGF-1 level (below 1.5 x ULN) before cabergoline initiation is a good predictor for remission. Combination treatment with the GH receptor antagonist pegvisomant can also be beneficial. The inexpensive, well-tolerated and convenient oral administration of cabergoline makes it an attractive medical therapy for active 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.

Dissecting the in vitro efficacy of octreotide and cabergoline in GH- and GH/PRL-secreting pituitary tumors

CONTEXT

Cabergoline (CAB) is an off-label medical therapy for acromegaly, overshadowed by first-generation somatostatin receptor ligands, e.g. octreotide (OCT).

OBJECTIVE

Head-to-head comparison between OCT and CAB in inhibiting growth hormone (GH) secretion in primary cultures of GH- and GH/PRL-secreting tumors. To investigate the role of somatostatin (SST) and dopamine type 2 (D2R) receptor expression.

DESIGN

To evaluate the antisecretory effect of OCT and CAB, together with receptor mRNA expression, in 23 tumor cultures.

SETTING AND PATIENTS

Acromegaly patients referred to the Erasmus Medical Center (Rotterdam, The Netherlands).

INTERVENTIONS

72-hour OCT and CAB treatment (10 nM).

MAIN OUTCOME MEASURES

GH concentrations in cell culture media.

RESULTS

OCT showed a slightly higher efficacy compared with CAB (GH decrease -39.5% vs. -32.5%, p = 0.079). The effect of the two drugs was superimposable in GH/PRL co-secreting tumors (-42.1% vs. -44.8%), where SST1 and D2R had a higher expression compared to the pure GH-secreting ones (p = 0.020 and p = 0.026). OCT was more effective than CAB in 8/23 cultures, while CAB was more effective than OCT in 3/23 (CAB + group). In CAB + tumors, SST1 expression was higher compared to the other groups (p = 0.034). At ROC curve analysis, SST1 and D2R discriminated between GH and GH/PRL co-secretion (AUC 0.856, p = 0.013; AUC 0.822, p = 0.024). SST1 was the best predictor of CAB response (≥50% GH reduction, AUC 0.913, p = 0.006; 80% sensitivity, 94% specificity).

CONCLUSIONS

OCT is 5-10% more effective than CAB in vitro. SST1 mRNA expression can represent a reliable marker of GH/PRL co-secreting tumors showing a preferential response to CAB treatment.

Efficacy of cabergoline add-on therapy in patients with acromegaly resistance to somatostatin analogs treatment and the review of literature

Objective

It is reported that adding cabergoline to somatostatin analog (SSA) normalizes IGF-1 levels approximately in one-third of patients with acromegaly. We investigated the effect of combination therapy and potential predictors of response in patients with acromegaly who do not respond to SSA therapy alone.

Methods

Fifty acromegaly patients (M/F 23/27, mean age 50.88 ± 12.34 years) were divided into two groups as the active and control groups in this connection. Before and after treatment, we not only evaluated serum GH and IGF-1 levels and tumor size but also analyzed the factors relevant to the effect of the combined therapy.

Results

Adding cabergoline to SSA treatment led to IGF-1 normalization in 42% (21/50) of patients. Mean GH levels decreased from 2.64 ± 1.79 to 1.34 ± 0.99 ng/mL (p < .0001) and IGF-1 levels decreased from 432.92 ± 155.61 to 292.52 ± 126.15 ng/mL (p < .0001). GH and IGF-1 reduction in percent (%) were significantly higher in the controlled group (63% to 40%, p = 0.023 and 45% to 19%, p = 0.0001). Moreover, tumor size decrease was significantly higher in controlled group (-3.6 cm to -1.66 cm, p = 0.005).

Conclusion

According to the results of our study, the addition of cabergoline to SSA normalized IGF-1 levels in a considerable amount of acromegaly patients with a moderately elevated IGF-1 level, regardless of serum PRL levels. Besides, cabergoline treatment was also influential in patients with higher IGF-1 levels despite a lower remission rate.

The Future of Somatostatin Receptor Ligands in Acromegaly

Currently, the first-generation somatostatin receptor ligands (fg-SRLs), octreotide LAR and lanreotide autogel, are the mainstays of acromegaly treatment and achieve biochemical control in approximately 40% of patients and tumor shrinkage in over 60% of patients. Pasireotide, a second-generation SRL, shows higher efficacy with respect to both biochemical control and tumor shrinkage but has a worse safety profile. In this review, we discuss the future perspectives of currently available SRLs, focusing on the use of biomarkers of response and precision medicine, new formulations of these SRLs and new drugs, which are under development. Precision medicine, which is based on biomarkers of response to treatment, will help guide the decision-making process by allowing physicians to choose the appropriate drug for each patient and improving response rates. New formulations of available SRLs, such as oral, subcutaneous depot, and nasal octreotide, may improve patients' adherence to treatment and quality of life since there will be more options available that better suit each patient. Finally, new drugs, such as paltusotine, somatropin, ONO-5788, and ONO-ST-468, may improve treatment adherence and present higher efficacy than currently available drugs.

Personalized Medical Treatment in Patients with Acromegaly: A Review

Acromegaly is associated with significant morbidity and mortality if not appropriately treated. In addition to insulin-like growth factor 1 (IGF-1) and growth hormone (GH) normalization, and tumor shrinkage, treatment goals include symptom relief, managing complications and improving quality of life. Surgical resection is a first-line treatment in most patients, with few being pretreated pre-operatively with medications. Somatostatin receptor ligands (SRLs), injectable and more recently oral capsules, have been the cornerstone of first-line medical therapy for persistent disease. However, several factors, including sparsely granulated adenomas, absent/low somatostatin receptor (SSTR2) status, imaging T2-hyperintensity, young age and aryl hydrocarbon receptor interacting protein mutations could predict first-generation SRL resistance. Patients with these characteristics may be better candidates for the GH receptor antagonist, pegvisomant, or in cases of large tumors the second-generation SRL, pasireotide. Combination therapy should be further pursued in patients who remain biochemically uncontrolled or have high remnant tumor after monotherapy. An efficacious and cost-effective pegvisomant dose-sparing effect of SRLs when used in combination has been demonstrated. With such a wide array of medical treatment options, it is increasingly important to tailor treatment to patients' unique characteristics as well as preferences, with a goal of personalizing management to achieve high quality outcomes.

Prolactin Response to Metformin in Cabergoline-Resistant Prolactinomas: A Pilot Study

INTRODUCTION

Cabergoline is the treatment of choice for prolactinomas. However, 10-20% of prolactinomas are resistant to cabergoline. Metformin, a biguanide widely used in the treatment of diabetes mellitus, has been shown to reduce prolactin secretion in various pituitary tumor-cell lineages both in vitro and in vivo and in human pituitary adenomas in vitro. The aim of this study is to test the effects of metformin addition to cabergoline treatment on prolactin levels in patients with resistant prolactinomas.

SUBJECTS AND METHODS

This is a prospective study performed in an outpatient clinic in a reference center. Ten adult patients (26-61 years) with prolactinomas (7 M), persistent hyperprolactinemia (38-386 ng/mL) under cabergoline treatment (2-7 mg/week) for at least 6 months (6-108 months), features of metabolic syndrome, and not taking metformin were included. Metformin (1.0-2.5 g v.o./day) was given according to patients' tolerance. Cabergoline doses were kept unchanged. Serum prolactin levels were measured before and after short- (30-60 days) and long-term (120-180 days) metformin treatment.

RESULTS

Mean prolactin levels did not show any significant changes (148 ± 39 vs. 138 ± 42 vs. 133 ± 39 ng/mL, before, at 30-60 days, and at 120-180 days, respectively, p = 0.196) after metformin (mean dose: 1.25 g/day; range: 1.0-2.0 g/day). No patient reached a normal prolactin level during metformin treatment. Two patients were considered partial responders for exhibiting prolactin decreases ≥50% at a single time point during metformin.

CONCLUSION

Metformin addition to ongoing high-dose cabergoline treatment in patients with cabergoline-resistant prolactinomas failed to show a consistent inhibitory effect in serum prolactin levels.

New and emerging pharmacological treatment options for acromegaly

Introduction: Transsphenoidal surgery is the first-line treatment for acromegaly, but even in referral centers, approximately 50% of patients are not cured, and adjuvant pharmacological treatment is necessary. Widely used therapies encompass different drug classes, such as injectable somatostatin receptor ligands (SRLs), oral dopamine agonists and injectable growth hormone receptor antagonists, but approximately 40% of patients still have disease activity in real-life practice. Therefore, there is a need for new medical therapies to allow disease control in a larger proportion of patients, increase quality of life, reduce morbidity and mortality and improve treatment adherence in acromegaly.Areas covered: In this review, the authors cover new and emerging drugs under development or drugs recently approved for the treatment of acromegaly.Expert opinion: Disease control is essential to reduce morbidity and mortality in acromegaly but is still not achieved in a significant proportion of patients or takes a long time to be achieved with currently available options and treatment algorithms. Therefore, the development of new drugs as well as the establishment of biomarkers of disease control to allow precision medicine will improve treatment and outcomes in acromegaly.

Pasireotide in the Personalized Treatment of Acromegaly

The delay in controlling the disease in patients who do not respond to first-line treatment with first generation somatostatin receptor ligands (first-generation SRLs) can be quantified in years, as every modification in the medical therapy requires some months to be fully evaluated. Considering this, acromegaly treatment should benefit from personalized medicine therapeutic approach by using biomarkers identifying drug response. Pasireotide has been positioned mostly as a compound to be used in first-generation SRLs resistant patients and after surgical failure, but sufficient data are now available to indicate it is a first line therapy for patients with certain characteristics. Pasireotide has been proved to be useful in patients in which hyperintensity T2 MRI signal is shown and in those depicting low SST2 and high expression of SST5, low or mutated AIP condition and sparsely granulated immunohistochemical pattern. This combination of clinical and pathological characteristics is unique for certain patients and seems to cluster in the same cases, strongly suggesting an etiopathogenic link. Thus, in this paper we propose to include this clinico-pathologic phenotype in the therapeutic algorithm, which would allow us to use as first line medical treatment those compounds with the highest potential for achieving the fastest control of GH hypersecretion as well as a positive effect upon tumor shrinkage, therefore accelerating the implementation of precision medicine for acromegaly. Moreover, we suggest the development, validation and clinical use of a pasireotide acute test, able to identify patients responsive to pasireotide LAR as the acute octreotide test is able to do for SRLs.

Resistance to Dopamine Agonists in Pituitary Tumors: Molecular Mechanisms

Pituitary neuroendocrine tumors (PitNET) are commonly benign tumors accounting for 10-25% of intracranial tumors. Prolactin-secreting adenomas represent the most predominant type of all PitNET and for this subtype of tumors, the medical therapy relies on the use of dopamine agonists (DAs). DAs yield an excellent therapeutic response in reducing tumor size and hormonal secretion targeting the dopamine receptor type 2 (D2DR) whose higher expression in prolactin-secreting adenomas compared to other PitNET is now well established. Moreover, although DAs therapy does not represent the first-line therapy for other PitNET, off-label use of DAs is considered in PitNET expressing D2DR. Nevertheless, DAs primary or secondary resistance, occurring in a subset of patients, may involve several molecular mechanisms, presently not fully elucidated. Dopamine receptors (DRs) expression is a prerequisite for a proper DA function in PitNET and several molecular events may negatively modify DR membrane expression, through the DRs down-regulation and intracellular trafficking, and DR signal transduction pathway. The current mini-review will summarise the presently known molecular events that underpin the unsuccessful therapy with DAs.

Surgical and Pharmacological Outcomes in Acromegaly: Real-Life Data From the Mexican Acromegaly Registry

CONTEXT

Acromegaly registries constitute a valuable source of therapeutic outcome information in real-life.

OBJECTIVE

The objective of this work is to analyze surgical and pharmacological outcomes in the Mexican Acromegaly Registry (MAR).

DESIGN AND METHODS

Data were extracted from the MAR informatic platform. Surgical remission was defined by a postoperative postglucose (GH) of less than 1 ng/mL and an insulin-like growth factor 1 (IGF-1) of less than 1.2 × upper limit of normal (ULN). Pharmacological remission was defined by a basal GH of less than 1 ng/mL and an IGF-1 of less than 1.2 × ULN.

RESULTS

A total of 650 surgical outcomes were analyzed (94.6% transsphenoidal). Surgical remission was achieved in 40.15%, whereas 44.15% remained biochemically active. Persistently active disease after surgery was significantly associated with harboring an invasive macroadenoma, a basal GH of greater than 10 ng/mL, and/or an IGF-1 of greater than 2 × ULN at diagnosis on bivariate and multivariate analysis. The outcome of monotherapy with first-generation somatostatin analogs (SSAs) was evaluated in 267 patients (adjunctive in 65%), of whom 28.4% achieved remission. Persistently active disease was significantly associated with harboring an invasive macroadenoma as well as with pretreatment basal GH and IGF-1 levels of greater than 10 ng/mL and greater than 2 × ULN, respectively, on bivariate and multivariate analysis. Combined therapy with SSA and cabergoline was analyzed in 100 patients, of whom 19% achieved remission and 44% remained active; in this subset of patients, only a pretreatment IGF-1 of greater than 2 × ULN was significantly associated with persistent disease activity.

CONCLUSION

Surgical and pharmacological outcomes in acromegaly are highly dependent on tumor size/invasiveness as well as on the degree of hypersomatotropinemia.

Multidisciplinary management of acromegaly: A consensus

The 13th Acromegaly Consensus Conference was held in November 2019 in Fort Lauderdale, Florida, and comprised acromegaly experts including endocrinologists and neurosurgeons who considered optimal approaches for multidisciplinary acromegaly management. Focused discussions reviewed techniques, results, and side effects of surgery, radiotherapy, and medical therapy, and how advances in technology and novel techniques have changed the way these modalities are used alone or in combination. Effects of treatment on patient outcomes were considered, along with strategies for optimizing and personalizing therapeutic approaches. Expert consensus recommendations emphasize how best to implement available treatment options as part of a multidisciplinary approach at Pituitary Tumor Centers of Excellence.

Novel therapies for acromegaly

Acromegaly is a systemic disease associated with increased morbidity and mortality. Most of these comorbidities can be prevented or delayed with adequate disease treatment. Although three modalities of treatment (surgery, medical treatment, and radiotherapy) are available and new drugs were approved in the last decades, there are still some patients that maintain disease activity despite treatment. Therefore, there is a need for novel therapies for acromegaly and for that purpose new formulations of currently used drugs and also new drugs are currently under study. In this review, we summarize the novel therapies for acromegaly.

The Role of Dopamine Agonists in Pituitary Adenomas

Dopamine agonist therapy is the primary therapy for prolactin-secreting adenomas and usually results in normoprolactinemia, eugonadism, and tumor reduction. Cabergoline is superior to bromocriptine with regard to efficacy and tolerance. Withdrawal of cabergoline can be attempted in patients with normal prolactin levels on low doses of medication and evidence of radiographic tumor involution. Dopamine agonists have been used off label in patients with acromegaly, Cushing disease, and nonfunctioning adenomas. A trial of cabergoline monotherapy can be effective in patients with biochemically mild acromegaly. Cabergoline combination with somatostatin receptor ligands or pegvisomant improves insulin-like growth factor level 1 in majority of patients.

Associations of Ki-67 Labeling Index with Clinical and Paraclinical Features of Growth Hormone-Secreting Pituitary Adenomas: A Single Center Report from Iran

BACKGROUND

Acromegaly is a rare disorder resulting from benign growth hormone (GH)-secreting pituitary adenomas in 90% of the cases. In recent years, many researchers have studied the Ki-67 index level of pituitary tumors and its relationship with demographics, biochemical parameters, clinical behavior, and recurrence rate.

OBJECTIVES

This study aimed to evaluate the correlation of Ki-67 index level with clinicoradiological and endocrinological parameters in confirmed GH-secreting pituitary adenomas, as well as with the surgical response and medical treatment after surgery.

METHODS

We collected the medical and pathologic records of 49 patients with GH-secreting pituitary adenoma who underwent surgeries from 2008 to 2017 in Shariati hospital affiliated to Tehran University of Medical Sciences.

RESULTS

According to MRI reports, 94% of the tumors were macroadenomas. The MRI findings also revealed the median maximal adenoma diameter of 18.5 mm. About 40% of the patients achieved remission three months after the surgery. Younger patients had a significantly higher Ki-67 index level (P = 0.036). We did not observe any significant difference in the Ki-67 index level regarding gender, tumor type, maximal tumor diameter, tumor invasiveness, tumor secretory type, and remission. Interestingly, the Ki-67 index level was negatively correlated with the insulin-like growth factor-1 (IGF-1) level at the last follow-up (P = 0.02). In logistic regression analysis, patients with higher preoperative GH serum levels had a better outcome.

CONCLUSIONS

Our results indicated a negative correlation between age and Ki-67 index level. However, there was no association between the Ki-67 index level and some tumor behaviors, as well as short- and long-term remission.

Systemic Complications of Acromegaly and the Impact of the Current Treatment Landscape: An Update

Acromegaly is a chronic systemic disease with many complications and is associated with increased mortality when not adequately treated. Substantial advances in acromegaly treatment, as well as in the treatment of many of its complications, mainly diabetes mellitus, heart failure, and arterial hypertension, were achieved in the last decades. These developments allowed change in both prevalence and severity of some acromegaly complications and furthermore resulted in a reduction of mortality. Currently, mortality seems to be similar to the general population in adequately treated patients with acromegaly. In this review, we update the knowledge in complications of acromegaly and detail the effects of different acromegaly treatment options on these complications. Incidence of mortality, its correlation with GH (cumulative exposure vs last value), and IGF-I levels and the shift in the main cause of mortality in patients with acromegaly are also addressed.