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Abstract Context Paltusotine is a nonpeptide selective somatostatin receptor 2 agonist in development as once-daily oral treatment for acromegaly. Objective To evaluate the efficacy and safety of paltusotine in the treatment of patients with acromegaly previously controlled with injected somatostatin receptor ligands (SRLs). Methods This phase 3, randomized, double-blind, placebo-controlled trial enrolled adults with acromegaly who had IGF-I ≤1.0 times the upper limit of normal (×ULN) while receiving a stable dose of depot octreotide or lanreotide. Patients were switched from injected SRLs and randomized to receive paltusotine or placebo orally for 36 weeks. The primary endpoint was proportion of patients maintaining IGF-I ≤1.0× ULN. Secondary endpoints were change in IGF-I level, change in Acromegaly Symptom Diary score, and maintenance of mean 5-sample GH <1.0 ng/mL. Results The primary endpoint was met: 83.3% (25/30) of patients receiving paltusotine and 3.6% (1/28) receiving placebo maintained IGF-I ≤1.0× ULN (odds ratio, 126.53; 95% CI, 13.73->999.99; P < .0001). Paltusotine was also superior to placebo for all secondary endpoints: mean (± SE) change in IGF-I of 0.04 ± 0.09× ULN vs 0.83 ± 0.1× ULN (P < .0001); mean (± SE) change in Acromegaly Symptom Diary score of −0.6 ± 1.5 vs 4.6 ± 1.6 (P = .02); mean GH maintained at <1.0 ng/mL in 20/23 (87.0%) vs 5/18 (27.8%) patients (odds ratio, 16.61; 95% CI, 2.86-181.36; P = .0003). The most common adverse events were acromegaly symptoms and gastrointestinal effects characteristic of SRLs. Conclusion Replacement of injected SRLs by once-daily oral paltusotine was effective in maintaining both biochemical and symptom control in patients with acromegaly and was well tolerated.

Glioblastoma remains an incurable tumour (median survival: ~ 15 months) and little clinical progress has been made over the past decades. Therefore, identification of novel biomarkers and therapeutic targets is imperative. Targeting the somatostatin/cortistatin-system is considered a successful avenue for treating different tumour pathologies. Thus, we comprehensively characterized (clinically and molecularly) the expression of the somatostatin/cortistatin-system components [ligands and receptors (SSTRs)] using five cohorts of patients and tested the in-vitro therapeutic response of different SSTR-agonists and somatostatin analogs (SSAs) in primary patient-derived glioblastoma cells. A clear downregulation of the whole somatostatin/cortistatin-system (except for SSTR5) in glioblastoma vs . non-tumour brain samples was demonstrated, with high discriminatory capacity. Moreover, poor overall-survival and critical aggressiveness-parameters ( i.e., recurrence, IDH1 -wildtype and G-CIMP status, classical and mesenchymal GBM-subtypes, EGFR -amplification) were robustly associated with SSTR1/SSTR2 downregulation. Notably, octreotide, pasireotide, and SSTR1/2/5-agonists treatments significantly reduced cell-proliferation in primary patient-derived GBM-cells. Molecularly, antitumour effects of octreotide/pasireotide were exerted through key signalling-factors related to glioblastoma-aggressiveness ( i.e., CDKN1A-B/JAK-STAT/NF-κB/TGF-β-pathways). Altogether, this study demonstrated that somatostatin/cortistatin-system is drastically altered in GBM representing a useful prognostic tool, and that SSTR-modulators might represent a potential therapeutic strategy to treat specific subsets of patients with GBM.

Somatostatin analogs, such as octreotide, lanreotide, and pasireotide, which function as somatostatin receptor ligands (SRLs), are the main drugs used for the treatment of acromegaly. These ligands are also used as important molecules for radiation therapy and imaging of neuroendocrine tumors. Somatostatin receptors (SSTRs) are canonical G protein-coupled proteins that play a role in metabolism, growth, and pathological conditions such as hormone disorders, neurological diseases, and cancers. Cryogenic electron microscopy combined with the protein structure prediction platform AlphaFold has been used to determine the 3-dimensional structures of many proteins. Recently, several groups published a series of papers illustrating the 3-dimensional structure of SSTR2, including that of the inactive/activated SSTR2-G protein complex bound to different ligands. The results revealed the residues that contribute to the ligand binding pocket and demonstrated that Trp8-Lys9 (the W-K motif) in somatostatin analogs is the key motif in stabilizing the bottom part of the binding pocket. In this review, we discuss the recent findings related to the structural analysis of SSTRs and SRLs, the relationships between the structural data and clinical findings, and the future development of novel structure-based therapies.

Abstract Context Combination therapy with somatostatin receptor ligand (SRL) plus pegvisomant for patients with acromegaly is recommended after a maximizing dose on monotherapy. Lower-dose combination regimens are not well studied. Objective To compare cost-effectiveness and efficacy of 3 lower-dose combination regimens in controlled and uncontrolled acromegaly Design and Setting Prospective, randomized, open-label, parallel arm study at a tertiary referral pituitary center. Patients Adults with acromegaly regardless of response to prior SRL and biochemical control status at baseline, stratified by an SRL dose required for insulin-like growth factor (IGF)-I normalization during any 3-month period within 12 months preceding enrollment. Intervention Combination therapy for 24 to 32 weeks on arm A, high-dose SRL (lanreotide 120 mg/octreotide long-acting release [LAR] 30 mg) plus weekly pegvisomant (40-160 mg/week); arm B, low-dose SRL (lanreotide 60 mg/octreotide LAR 10 mg) plus weekly pegvisomant; or arm C, low-dose SRL plus daily pegvisomant (15-60 mg/day) Main Outcome Measure Monthly treatment cost in each arm in participants completing ≥ 24 weeks of therapy. Results Sixty patients were enrolled and 52 were evaluable. Fifty of 52 (96%) demonstrated IGF-I control regardless of prior SRL responsiveness (arm A, 14/15 [93.3%]; arm B, 22/23 [95.7%]; arm C, 14/14 [100%]). Arm B was least costly (mean, $9837 ± 1375 per month), arm C was most expensive (mean, $22543 ± 11158 per month), and arm A had an intermediate cost (mean, $14261 ± 1645 per month). Approximately 30% of patients required pegvisomant dose uptitration. Rates of adverse events were all < 10%. Conclusions Low-dose SRL plus weekly pegvisomant represents a novel dosing option for achieving cost-effective, optimal biochemical control in patients with uncontrolled acromegaly requiring combination therapy.

The somatostatin-secreting δ-cells comprise ~5% of the cells of the pancreatic islets. The δ-cells have complex morphology and might interact with many more islet cells than suggested by their low numbers. δ-Cells contain ATP-sensitive potassium channels, which open at low levels of glucose but close when glucose is elevated. This closure initiates membrane depolarization and electrical activity and increased somatostatin secretion. Factors released by neighbouring α-cells or β-cells amplify the glucose-induced effects on somatostatin secretion from δ-cells, which act locally within the islets as paracrine or autocrine inhibitors of insulin, glucagon and somatostatin secretion. The effects of somatostatin are mediated by activation of somatostatin receptors coupled to the inhibitory G protein, which culminates in suppression of the electrical activity and exocytosis in α-cells and β-cells. Somatostatin secretion is perturbed in animal models of diabetes mellitus, which might explain the loss of appropriate hypoglycaemia-induced glucagon secretion, a defect that could be mitigated by somatostatin receptor 2 antagonists. Somatostatin antagonists or agents that suppress somatostatin secretion have been proposed as an adjunct to insulin therapy. In this Review, we summarize the cell physiology of somatostatin secretion, what might go wrong in diabetes mellitus and the therapeutic potential of agents targeting somatostatin secretion or action.

Targeting neuroendocrine tumors expressing somatostatin receptor subtypes (sst) with radiolabeled somatostatin agonists is an established diagnostic and therapeutic approach in oncology. While agonists readily internalize into tumor cells, permitting accumulation of radioactivity, radiolabeled antagonists do not, and they have not been considered for tumor targeting. The macrocyclic chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was coupled to two potent somatostatin receptor-selective peptide antagonists [NH₂-CO-c(DCys-Phe-Tyr-DAgI⁸(Me,2-naphthoyl)-Lys-ThrPhe-Cys)-OH (sst₃-ODN-8) and a sst₂-selective antagonist (sst₂-ANT)], for labeling with$^{1ll/nat}ln$.$^{111/nat}ln-DOTA-sst_{3}-ODN-8$and$^{111/nat}lnDOTA-[4-NO_{2}-Phe-c(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH_{2}] (^{1ll/nat}lnDOTA-sst_{2}-ANT)$showed high sst₃- and sst₂-binding affinity, respectively. They did not trigger sst₃ or sst₂ internalization but prevented agonist-stimulated internalization.$^{111}ln-DOTA-sst_{3}ODN-8$and$^{111}1n-DOTA-sst_{2}-ANT$were injected intravenously into mice bearing sst₃- and sst₂-expressing tumors, and their biodistribution was monitored. In the sst₃-expressing tumors, strong accumulation of$^{111}ln-DOTA-sst_{3}-ODN-8$was observed, peaking at 1 h with 60% injected radioactivity per gram of tissue and remaining at a high level for >72 h. Excess of sst₃-ODN-8 blocked uptake. As a control, the potent agonist$^{111}1n-DOTA-[1-Nal^{3}]-octreotide$, with strong sst₃-binding and internalization properties showed a much lower and shorter-lasting uptake in sst3-expressing tumors. Similarly,$^{111}1n-DOTA-sst_{2}-ANT$was injected into mice bearing sst₂expressing tumors. Tumor uptake was considerably higher than with the highly potent sst₂-selective agonist$^{111}1n-diethylenetriaminepentaacetic$acid-[Tyr⁳,Thr⁸]-octreotide ($^{111}1n-DTPA-TATE$). Scatchard plots showed that antagonists labeled many more sites than agonists. Somatostatin antagonist radiotracers therefore are preferable over agonists for the in vivo targeting of sst₃- or sst₂-expressing tumors. Antagonist radioligands for other peptide receptors need to be evaluated in nuclear oncology as a result of this paradigm shift.

Progenitors of intraepithelial T cells (IELps) migrate from the thymus to the intestines after birth where they develop into unconventional TCRγδ and TCRαβ lymphocytes in a process of extrathymic lymphopoiesis within cryptopatches. Mechanisms of IELp migration have remained unclear. Here we show that thymic IELps express the somatostatin receptor SSTR2, which contributes to their homing to the gut. IELp homing is Sstr2 dependent and correlates with neonatal induction of Sst encoding somatostatin in neuroendocrine and lamina propria stromal cells. The SSTR2 ligands somatostatin and cortistatin attract IELps in chemotaxis assays and somatostatin triggers IELp binding to the mucosal vascular addressin MAdCAM1. T cell transduction with Sstr2 confers homing to the neonatal colon. Human fetal thymic IELp-like cells express SSTR2 and intestinal stromal cells express SST at the time of initial T cell population, suggesting conserved mechanisms of progenitor seeding of the developing intestines. These results reveal an unexpected role for the SSTR2–somatostatin axis in early immune system development and describe a new role for a small peptide hormone G-protein-coupled receptor in developmental lymphocyte trafficking. Progenitors of intraepithelial T cells (IELps) migrate from the thymus to the intestines after birth where they can develop into unconventional intraepithelial lymphocytes. Here Ocon et al. find that the neuroendocrine peptide hormone somatostatin controls the migration of committed SSTR2-expressing IELps from the thymus to the immature gut.

Abstract Context Pheochromocytomas and paragangliomas (PPGLs) with pathogenic mutations in the succinate dehydrogenase subunit B (SDHB) are associated with a high metastatic risk. Somatostatin receptor 2 (SSTR2)–dependent imaging is the most sensitive imaging modality for SDHB-related PPGLs, suggesting that SSTR2 expression is a significant cell surface therapeutic biomarker of such tumors. Objective Exploration of the relationship between SSTR2 immunoreactivity and SDHB immunoreactivity, mutational status, and clinical behavior of PPGLs. Evaluation of SSTR-based therapies in metastatic PPGLs. Methods Retrospective analysis of a multicenter cohort of PPGLs at 6 specialized Endocrine Tumor Centers in Germany, The Netherlands, and Switzerland. Patients with PPGLs participating in the ENSAT registry were included. Clinical data were extracted from medical records, and immunohistochemistry (IHC) for SDHB and SSTR2 was performed in patients with available tumor tissue. Immunoreactivity of SSTR2 was investigated using Volante scores. The main outcome measure was the association of SSTR2 IHC positivity with genetic and clinical–pathological features of PPGLs. Results Of 202 patients with PPGLs, 50% were SSTR2 positive. SSTR2 positivity was significantly associated with SDHB- and SDHx-related PPGLs, with the strongest SSTR2 staining intensity in SDHB-related PPGLs (P = .01). Moreover, SSTR2 expression was significantly associated with metastatic disease independent of SDHB/SDHx mutation status (P < .001). In metastatic PPGLs, the disease control rate with first-line SSTR-based radionuclide therapy was 67% (n = 22, n = 11 SDHx), and with first-line “cold” somatostatin analogs 100% (n = 6, n = 3 SDHx). Conclusion SSTR2 expression was independently associated with SDHB/SDHx mutations and metastatic disease. We confirm a high disease control rate of somatostatin receptor–based therapies in metastatic PPGLs.

Abstract Context Medical treatment of acromegaly is currently performed through a trial-and-error approach using first-generation somatostatin receptor ligands (fgSRLs) as first-line drugs, with an effectiveness of about 50%, and subsequent drugs are indicated through clinical judgment. Some biomarkers can predict fgSRLs response. Objective Here we report the results of the ACROFAST study, a clinical trial in which a protocol based on predictive biomarkers of fgSRLs was evaluated. Methods This was a prospective trial (21 university hospitals) comparing the effectiveness and time-to-control of 2 treatment protocols during 12 months: (A) a personalized protocol in which the first options were fgSRLs as monotherapy or in combination with pegvisomant, or pegvisomant as monotherapy depending on the short acute octreotide test (sAOT) results, tumor T2 magnetic resonance (MRI) signal or immunostaining for E-cadherin; and (B) a control group with treatment always started by fgSRLs and the other drugs included after demonstrating inadequate control. Results Eighty-five patients participated; 45 in the personalized and 40 in the control group. More patients in the personalized protocol achieved hormonal control compared to those in the control group (78% vs 53%, P < .05). Survival analysis revealed a hazard ratio for achieving hormonal control adjusted by age and sex of 2.53 (CI, 1.30-4.80). Patients from the personalized arm were controlled in a shorter period of time (P = .01). Conclusion Personalized medicine is feasible using a relatively simple protocol, and it allows a higher number of patients to achieve control in a shorter period of time.

Somatostatin (SS) plays an important role in regulating food intake and following digestive functions of vertebrates mediated via somatostatin receptor (SSTR). However, the feedback regulation by which food intake regulate SS and SSTRs expression, and thereby their functions, remains poorly understood. Here, we cloned somatostatin genes ( pss1, pss2 and pss3 ) and somatostatin receptors genes ( sstr2a, sstr2b, sstr2c, sstr3a, sstr3b, sstr5a and sstr5b ) from tilapia, Oreochromis niloticus and conducted their tissue distribution. Phylogenetic analysis and genomic synteny maps revealed their high homology across the vertebrates and evolution history. Following, synthesized SS-14 and SS-28 were both confirmed to bind to SSTRs and mediated Erk1/2 or Akt phosphorylation in a dose-dependent manner and time-course effect in 293T cell line as well as tilapia primary hepatocytes. It was observed that the expression levels of SS family showed dynamic change during food intake. In the early stages of feeding, pss2 expressed in gastric epithelium was down-regulated by food intake, and the following low pH after feeding reversed to up-regulate the pss2 mRNA level. This down and up dynamic change hinted that the first down pss2 prompted food digesting and the next up pss2 inhibited digestion, but it might need further explore to prove. Compared with it, sstr3a expression levels in submucosa up-regulated after feeding but did not display dynamic change. Our results contribute to the understanding of how somatostatin family respond to food intake during different stages of feeding, which provides basis for subsequent study of their function in gastrointestine of tilapia.