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

SSTR2 expression in neoplastic and normal anterior pituitary is impacted by age, sex, and hormonal status

Pituitary neuroendocrine tumors (PitNETs) are among the most common tumors encountered in neurooncology. While the majority of PitNETs demonstrate indolent behavior, a subset of tumors demonstrates aggressive behavior, including invasion into surrounding structures. As traditional imaging has limited capacity to distinguish tumor from post-operative changes, better methods of tumor delineation are needed to guide management. Somatotroph adenomas are known to express high levels of SSTR2, and SSTR2-targeting PET imaging has shown clinical utility in the management of neuroendocrine tumors and meningiomas. In this retrospective study of archival PitNETs (n = 271) and autopsy controls (AC) (n = 20), we show that although significant differences in SSTR2 immunostaining are appreciable between adenoma subtypes and ACs, high-staining cases are encountered in all subtypes. In ACs, females demonstrated significantly stronger SSTR2 staining than males. Weak age-related trends towards increasing labelling in females and decreasing labelling in males were noted but these did not reach statistical significance. Decreasing age-related trends were seen in gonadotrophs in both sexes; this was statistically significant in females. Our findings suggest that SSTR2-targeting imaging modalities may assist clinical management of a subset of PitNETs and that these results may need to be interpreted with consideration of patient age and sex.

Somatostatin receptors in pituitary somatotroph adenomas as predictors of response to somatostatin receptor ligands: A pathologist's perspective

There are five subtypes of somatostatin receptors (SST1-5), which are expressed in several types of solid neoplasms, neuroendocrine tumors, and pituitary adenomas. Most commonly, SST2 and SST5, are of interest regarding diagnostic, treatment, and prognostic purposes. In this article the basic biological characteristics of SST are briefly reviewed, and focus given to the immunohistochemical evaluation of SST2 and SST5 in growth hormone (GH)-secreting pituitary tumors, and their quantification as predictors of response to treatment with somatostatin receptor ligands (SRL), the mainstay of the pharmacological therapy available for these tumors. Although many different scoring systems for SST2 immunohistochemistry showing correlation with SRL response have been reported, among which the immunoreactivity score (IRS) has been the most consistently used, a universally validated immunohistochemical technique and scoring scheme is lacking. Efforts should be made on collaborative multicenter studies aiming at validating homogeneous immunostaining protocols and a scoring system for SST2 and SST5 expression, to help clinicians to define the optimal therapeutic strategy for the patients with somatotroph tumors.

Predicting Response to Medical Treatment in Acromegaly via Granulation Pattern, Expression of Somatostatin Receptors Type 2 and 5 and E-Cadherin

Resistance to first-generation somatostatin receptor ligand (fgSRL) treatment in acromegaly is common, making the identification of biomarkers that predict fgSRL response a desired goal. We conducted a retrospective analysis on 21 patients with acromegaly who underwent surgery and subsequent pharmacological treatment. Through immunohistochemistry (IHC), we assessed the expression of the somatostatin receptor subtypes SSTR2 and SSTR5, E-Cadherin, and cytokeratin granulation pattern (sparsely or densely). Patients were divided into responders and non-responders based on their biochemical response to fgSRL and/or the newer agent, Pasireotide, or the GH-blocker, Pegvisomant. Patients resistant to fgSRL (n = 12) exhibited lower SSTR2 and E-Cadherin expressions. Sparsely granulated tumors were more frequent in the non-responder group. SSTR2 (p = 0.024, r = 0.49) and E-Cadherin (p = 0.009, r = 0.64) positively correlated with the Insulin-like Growth Factor 1 (IGF-1) decrease after fgSRL, while SSTR5 (p = 0.107, r = -0.37) showed a trend towards negative correlation. SSTR5 positivity seemed to be associated with Pasireotide response, albeit the number of treated patients was too low (n = 4). No IHC markers correlated with Pegvisomant response. Our findings suggest that densely granulated tumors, with positive SSTR2 and E-Cadherin seem to be associated with favorable fgSRL responses. The strongest predictive value of the studied markers was found for E-Cadherin, which seems to surpass even SSTR2.

Predictors of biochemical response to somatostatin receptor ligands in acromegaly

Although predictors of response to first-generation somatostatin receptor ligands (fg-SRLs), and to a lesser extent to pasireotide, have been studied in acromegaly for many years, their use is still not recommended in clinical guidelines. Is there insufficient evidence to use them? Numerous biomarkers including various clinical, functional, radiological and molecular markers have been identified. The first ones are applicable pre-surgery, while the molecular predictors are utilized for patients not cured after surgery. In this regard, factors predicting a good response to fg-SRLs are specifically: low basal GH, a low GH nadir in the acute octreotide test, T2 MRI hypointensity, a densely granulated pattern, high immunohistochemistry staining for somatostatin receptor 2 (SSTR2), and E-cadherin. However, there is still a lack of consensus regarding which of these biomarkers is more useful or how to integrate them into clinical practice. With classical statistical methods, it is complex to define reliable and generalizable cut-off values for a single biomarker. The potential solution to the limitations of traditional methods involves combining systems biology with artificial intelligence, which is currently providing answers to such long-standing questions that may eventually be finally included into the clinical guidelines and make personalized medicine a reality. The aim of this review is to describe the current knowledge of the main fg-SRLs and pasireotide response predictors, discuss their current usefulness, and point to future directions in the research of this field.

A novel somatostatin receptor ligand for human ACTH - and GH -secreting pituitary adenomas

OBJECTIVE

Somatostatin receptor ligands have come to play a pivotal role in the treatment of both ACTH- and GH-secreting pituitary adenomas. Clinical efficacy averages 30-50%, thus a considerable number of patients with Cushing's disease or acromegaly remain unresponsive to this therapeutic approach. HTL0030310 is a new somatostatin receptor ligand selective for subtype 5 over subtype 2, thus with a different receptor profile compared to clinical somatostatin receptor ligands.

DESIGN

Assessment of the effect of HTL0030310 on hormone secretion in human ACTH- and GH-secreting pituitary adenomas in vitro.

METHODS

Primary cultures from 3 ACTH-secreting and 5 GH-secreting pituitary adenomas were treated with 1, 10 and 100 nM HTL0030310 alone or with 10 nM CRH or GHRH, respectively. Parallel incubations with 10 nM pasireotide were also carried out. ACTH and GH secretion were assessed after 4 and 24 hour incubation; SSTR2, SSTR3, SSTR5, GH and POMC expression were evaluated after 24 hours.

RESULTS

HTL0030310 reduced unchallenged ACTH and POMC levels up to 50% in 2 ACTH-secreting adenomas and blunted CRH-stimulated ACTH/POMC by 20-70% in all 3 specimens. A reduction in spontaneous GH secretion was observed in 4 GH-secreting adenomas and in 2 specimens during GHRH co-incubation. SSTRs expression was detected in all specimens.

CONCLUSIONS

This first study on a novel somatostatin receptor 5-preferring ligand indicates that HTL0030310 can inhibit hormonal secretion in human ACTH- and GH-secreting pituitary adenomas. These findings suggest a potential new avenue for somatostatin ligands in the treatment of Cushing's disease and acromegaly.

Acromegaly among a Moroccan population

Acromegaly is defined as an acquired dysmorphytic syndrome due to excessive secretion of growth hormone (GH) and consequently of insulin-like growth factor-1 (IGF-1). This is a retrospective study of patients who were hospitalized in the Endocrinology Department of the Mohammed V Military Academic Hospital in Rabat over a period of 14 years (2008 to 2022), reporting on their clinical, paraclinical and evolutionary profiles and comparing the results with the data in the literature. Nineteen patients were included in our study. The mean age was 42.7 ± 11.6 years, with a male predominance. The clinical manifestations were dominated by a dysmorphic syndrome present in 97.4% of cases, followed by complications related to acromegaly in 88.9% of cases. The diagnosis was made when GH and IGF-1 values were elevated in 88.9% and 93.8% of cases, respectively; with a mean GH value of 25.1 μg/L. Magnetic resonance imaging (MRI) was used to diagnose the location of pituitary adenoma in all cases, 78.9% of which were macroadenomas and 21.1% microadenomas. The majority of patients (78.9%) had recourse to transsphenoidal surgery. Medical treatment was carried out in 89.5% of cases. Postoperative radiotherapy was performed in 33% of cases. Disease control was achieved in 30.1% of cases. This study shows the complex management of acromegaly. Disease control is a necessary condition in order to avoid complications, but is often difficult to obtain.

Somatostatin receptor expression and clinical outcome of multilineage pituitary tumours expressing PIT1 and SF1

The application of transcription factor immunohistochemistry to pituitary neuroendocrine tumour (PitNET) assessment has allowed identification of tumours that do not conform to a single lineage. Multilineage pituitary transcription factor 1 (PIT1) and steroidogenic factor 1 (SF1) PitNETs are a rare and relatively newly described tumour subtype. These tumours express both transcription factors and may also express combinations of hormones corresponding to both lineages. Histological and clinical characteristics can vary, and overall clinical behaviour and prognosis is not known. We describe the clinical outcomes and somatostatin receptor status (SSTR) of a series of nine cases identified from our cohort of pituitary tumours at Westmead Hospital. Eight PitNETs (88.9%) expressed growth hormone and caused acromegaly at presentation. Of the seven macrotumours that caused acromegaly, one had cavernous sinus invasion. The Ki-67 labeling index score ranged from 0.6% to 3.6%. About 88% of tumours that secreted excess growth hormone exhibited strong immunostaining for SSTR 2 and all tumours displayed weak immunoreactivity for SSTR5. In 62.5% of patients with acromegaly, cure was achieved after surgical resection. Somatostatin receptor ligands resulted in clinical remission in cases where medical treatment was initiated. There was no new tumour recurrence or regrowth over an overall mean follow-up period of 62.5 months.

Approach of Acromegaly during Pregnancy

Acromegaly-related sub/infertility, tidily related to suboptimal disease control (1/2 of cases), correlates with hyperprolactinemia (1/3 of patients), hypogonadotropic hypogonadism—mostly affecting the pituitary axis in hypopituitarism (10−80%), and negative effects of glucose profile (GP) anomalies (10−70%); thus, pregnancy is an exceptional event. Placental GH (Growth Hormone) increases from weeks 5−15 with a peak at week 37, stimulating liver IGF1 and inhibiting pituitary GH secreted by normal hypophysis, not by somatotropinoma. However, estrogens induce a GH resistance status, protecting the fetus form GH excess; thus a full-term, healthy pregnancy may be possible. This is a narrative review of acromegaly that approaches cardio-metabolic features (CMFs), somatotropinoma expansion (STE), management adjustment (MNA) and maternal-fetal outcomes (MFOs) during pregnancy. Based on our method (original, in extenso, English—published articles on PubMed, between January 2012 and September 2022), we identified 24 original papers—13 studies (3 to 141 acromegalic pregnancies per study), and 11 single cases reports (a total of 344 pregnancies and an additional prior unpublished report). With respect to maternal acromegaly, pregnancies are spontaneous or due to therapy for infertility (clomiphene, gonadotropins or GnRH) and, lately, assisted reproduction techniques (ARTs); there are no consistent data on pregnancies with paternal acromegaly. CMFs are the most important complications (7.7−50%), especially concerning worsening of HBP (including pre/eclampsia) and GP anomalies, including gestational diabetes mellitus (DM); the best predictor is the level of disease control at conception (IGF1), and, probably, family history of 2DM, and body mass index. STE occurs rarely (a rate of 0 to 9%); some of it symptoms are headache and visual field anomalies; it is treated with somatostatin analogues (SSAs) or alternatively dopamine agonists (DAs); lately, second trimester selective hypophysectomy has been used less, since pharmaco-therapy (PT) has proven safe. MNA: PT that, theoretically, needs to be stopped before conception—continued if there was STE or an inoperable tumor (no clear period of exposure, preferably, only first trimester). Most data are on octreotide > lanreotide, followed by DAs and pegvisomant, and there are none on pasireotide. Further follow-up is required: a prompt postpartum re-assessment of the mother’s disease; we only have a few data confirming the safety of SSAs during lactation and long-term normal growth and developmental of the newborn (a maximum of 15 years). MFO seem similar between PT + ve and PT − ve, regardless of PT duration; the additional risk is actually due to CMF. One study showed a 2-year median between hypophysectomy and pregnancy. Conclusion: Close surveillance of disease burden is required, particularly, concerning CMF; a personalized approach is useful; the level of statistical evidence is expected to expand due to recent progress in MNA and ART.