Sst2 Agonist Research Articles

Effects of somatostatin, a somatostatin agonist, and an antagonist, on a putative migraine trigger pathway

ObjectiveTo determine whether somatostatin (SST) could be a cortico-brainstem neurotransmitter involved in producing the headache of migraine. BackgroundThere is evidence to support the idea that a cortico-brainstem-trigeminal nucleus neuraxis might be responsible for producing migraine headache; we have suggested that SST may be one of the neurotransmitters involved. MethodsRats were anesthetised and prepared for recording neurons in either the periaqueductal gray matter (PAG) or nucleus raphe magnus (NRM), as well as the trigeminal nucleus caudalis (TNC). The dura mater and facial skin were stimulated electrically or mechanically. SST, the SST agonist L054264 and the SST antagonist CYN54806 were injected intravenously, by microinjection, or by iontophoresis into the PAG or NRM. Cortical neuronal activity was provoked by cortical spreading depression (CSD) or light flash (LF) and was monitored by recording cortical blood flow (CBF). ResultsIntravenous injection of SST: (a) selectively decreased the responses of TNC neurons to stimulation of the dura, but not skin, for up to 5 h; (b) decreased the ongoing discharge rate of TNC neurons while simultaneously increasing the discharge rate of neurons in either brainstem nucleus and; (c) prevented, or reversed, the effect of CSD and LF on brainstem and trigeminal neuron discharge rates. CSD and LF decreased the discharge rate of neurons in both brainstem nuclei and increased the discharge rate of TNC neurons. These effects were reversed by L054264 and mimicked by CYN54806. Injections of L054264 into the PAG or NRM reduced the response of TNC neurons to dural stimulation and skin stimulation differentially, depending on the nucleus injected. Injections of CYN54806 into either brainstem nucleus potentiated the responses of TNC neurons to dural and skin stimulation, but without a marked differential effect. ConclusionsThese results imply that SST could be a neurotransmitter in a pathway responsible for migraine pain.

OR01-01 Oral, Once-daily, Paltusotine (Non-peptide Selective Somatostatin Receptor Subtype 2 Agonist) Therapy In Patients With Acromegaly Is Associated With Long-term Biochemical And Symptom Control And Is Preferred Over Injectable Somatostatin-Receptor Ligands

Abstract Disclosure: M.R. Gadelha: Advisory Board Member; Self; Crinetics Pharmaceuticals, Ipsen, Novo Nordisk, and Recordati Rare Diseases. Research Investigator; Self; Crinetics Pharmaceuticals and Recordati Rare Diseases. Speaker; Self; Crinetics Pharmaceuticals, Ipsen, Novo Nordisk, and Recordati Rare Diseases. H.S. Randeva: None. M.B. Gordon: Consulting Fee; Self; Crinetics Pharmaceuticals, HRA Pharma, Novo Nordisk, and Recordati Rare Diseases. Grant Recipient; Self; Ascendis, Camurus, Chiasma, Corcept, Crinetics, Ipsen, Novartis, Novo Nordisk, Opko, Pfizer, and Strongbridge. M. Doknic: Advisory Board Member; Self; Pfizer in CEE region. Research Investigator; Self; Crinetics Pharmaceuticals, Pfizer, Camurus, Ascendis, Opko, Ipsen, and Teva. Speaker; Self; Pfizer, Novartis, Novo Nordisk, Sandoz, and Merck. E. Mezosi: Research Investigator; Self; Crinetics Pharmaceuticals. M. Toth: Consulting Fee; Self; Ipsen, Novartis, Pfizer, and Recordati Rare Diseases. Research Investigator; Self; Crinetics Pharmaceuticals. C.L. Boguszewski: Consulting Fee; Self; Novo Nordisk. Research Investigator; Self; Crinetics Pharmaceuticals and Recordati Rare Diseases. Speaker; Self; Ipsen and Recordati Rare Diseases. C.T. Ferrara-Cook: Employee; Self; Crinetics Pharmaceuticals. A. Casagrande: Employee; Self; Crinetics Pharmaceuticals. A. Krasner: Employee; Self; Crinetics Pharmaceuticals. Paltusotine is an investigational oral, once-daily, non-peptide, SST2 agonist in development for the treatment of acromegaly and neuroendocrine tumors. Interim analysis results from patients with acromegaly treated with paltusotine for up to 2 years in ACROBAT Advance (NCT04261712), an ongoing, 4-year, single-arm, open-label extension study, are reported here. Patients who completed ACROBAT Edge (NCT03789656) or Evolve (NCT03792555) phase 2 parent studies were eligible to enroll in Advance. In Edge, patients were either sub-optimally controlled on injectable somatostatin-receptor ligand (iSRL; octreotide or lanreotide) therapy alone or in combination with cabergoline; or required combination therapy or pasireotide to achieve normal IGF-I levels at baseline. Evolve enrolled patients who had normal IGF-I levels on iSRL monotherapy at baseline. In Advance, adjunctive medication with cabergoline or pegvisomant was allowed in patients who had not achieved normal IGF-1 levels on maximum dose of paltusotine (40 mg). Serum IGF-I levels were measured using Immunodiagnostic Systems iSYS immunoassay. Symptoms were assessed using the Acromegaly Symptom Diary (ASD; score range, 0-70; higher numbers indicate greater symptom burden), which was developed based on FDA recommendations for patient-reported outcome tools. Patient treatment preference was also evaluated. Forty-three patients were enrolled in Advance (Edge, n=32; Evolve, n=11; 88% of eligible patients). At baseline on iSRL, mean (SD) age was 53.0 (11.6) years, 56% were females, 86% had previous pituitary surgery, and none had radiotherapy. Median (IQR) IGF-I levels remained stable: baseline on iSRL, 1.15x ULN (0.84, 1.46; n=43); in Advance, Week 51 1.08x ULN (0.87, 1.26; n=37), Week 77 1.01x ULN (0.85, 1.28; n=27), and Week 103 1.10x ULN (0.96, 1.45; n=10). Among patients receiving adjunctive medication in Advance, 94% were from the Edge study. Acromegaly symptoms were stably controlled: median (IQR) ASD scores at baseline on iSRL, 8.57 (3.57, 20.14; n=21) and, in Advance at Week 77, 8.0 (5.0, 18.0; n=14). At Week 52, 32 (88.9%) of the 36 respondents preferred once-daily oral paltusotine, 2 (5.6%) preferred previous injections, and 2 (5.6%) had no preference. The most common treatment-emergent adverse events (TEAEs) reported were headache (30.2%), arthralgia (25.6%), and fatigue (18.6%). No serious drug-related TEAEs were reported. Of the 6 patients who discontinued the study, 1 (2.3%) was due to a TEAE (headache). Glycemic control, as measured by HbA1c, was stable during paltusotine treatment. In conclusion, with up to 2 years of follow-up in patients with acromegaly, once-daily oral paltusotine treatment was well-tolerated, associated with stable IGF-I and symptom control relative to that achieved by iSRLs, and was preferred over injected therapy. Support: Crinetics Pharmaceuticals. Presentation: Thursday, June 15, 2023

Abstract 5044: Antitumor activity comparison of two somatostatin receptor ligands radiolabeled with Lutetium-177 (SSO110 and DOTA-TATE) alone or combined with chemotherapy in mice bearing AR42J SST2-positive tumors

Abstract Only a limited number of studies have compared the therapeutic effects of repetitive cycles of radiolabeled somatostatin (SST) analogues or assessed potential synergy of these analogues with chemotherapy agents. Hence, a comparison was conducted in an in vivo AR42J tumor model with an SST2 antagonist, [177Lu]Lu-satoreotide tetraxetan ([177Lu]LuSSO110), and a SST2 agonist, [177Lu]Lu-DOTA-TATE. The efficacy of treatment combining [177Lu]Lu-satoreotide tetraxetan with capecitabine plus temozolomide was also assessed. Swiss Nude mice were xenografted with AR42J tumor cells. For the evaluation of the tumor response to radiation therapy, animals received one weekly dose of [177Lu]LuSSO110 or [177Lu]Lu-DOTA-TATE for four consecutive weeks. For combined treatments, animals received one weekly dose of [177Lu]LuSSO110 at 20 MBq for four consecutive weeks in association with daily doses of capecitabine and temozolomide (CAPTEM). Weekly treatment for four consecutive weeks with [177Lu]LuSSO110 at 15 MBq revealed a significantly reduced tumor growth, with 68 days to reach a tumor volume of 850 mm3, compared to [177Lu]Lu-DOTA-TATE at 15 MBq or 30 MBq, with, respectively, 43 days and 48 days. This was associated with a 3.5 fold higher tumor uptake of [177Lu]LuSSO110 (15 MBq) compared to [177Lu]Lu-DOTA-TATE, with no or mild effects on body weight, hematological toxicity, or renal toxicity. In AR42J tumor-bearing mice treated once a week for four consecutive weeks, [177Lu]LuSSO110 (15 MBq) associated with CAPTEM regimen did not significantly increase the median time to reach a tumor volume of 1000 mm3 as compared to treatment with [177Lu]Lu-satoreotide alone: 50.7 vs 42.2 days, respectively. The association of the two treatments only led to mild weight losses. Repeated administrations of [177Lu]LuSSO110 were able to potentiate peptide receptor radionuclide therapy with a higher tumor uptake and longer median survival compared to [177Lu]Lu-DOTA-TATE. The The combination of [177Lu]Lu-satoreotide with capecitabine and temozolomide did not show any synergy, but no antagonism was observed either. Citation Format: Olivier Raguin, Marcel Krüger, Peggy Provent, Funda Cay, Elodie Marie dit chatel, Marie Lux, Stéphane Lezmi, Florence Meyer-Losic, Pascale Plas, Ben Pais, Cyril Berthet. Antitumor activity comparison of two somatostatin receptor ligands radiolabeled with Lutetium-177 (SSO110 and DOTA-TATE) alone or combined with chemotherapy in mice bearing AR42J SST2-positive tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5044.

Small Molecule SST2 Agonist as a Potential Therapeutic for Acromegaly and Neuroendocrine Tumors

Small Molecule SST2 Agonist as a Potential Therapeutic for Acromegaly and Neuroendocrine Tumors

Discovery of Paltusotine (CRN00808), a Potent, Selective, and Orally Bioavailable Non-peptide SST2 Agonist.

The discovery of a novel 4-(4-aminopiperidinyl)-3,6-diarylquinoline series of potent SST2 agonists is described. This class of molecules exhibit excellent selectivity over SST1, SST3, SST4, and SST5 receptors. The compound 3-[4-(4-aminopiperidin-1-yl)-3-(3,5-difluorophenyl)quinolin-6-yl]-2-hydroxybenzonitrile (22, paltusotine, formerly known as CRN00808) showed no direct inhibition of major cytochrome P450 enzymes or the hERG ion channel and had sufficient exposure in rats and excellent exposure in dogs upon oral dosing. In pharmacodynamic studies, compound 22 dose-dependently suppressed growth hormone (GH) secretion induced by an exogenous growth-hormone-releasing hormone (GHRH) challenge in both male and female rats following a single oral dose and suppressed IGF-1 levels with repeated oral administration in both rats and dogs. To the best of our knowledge, compound 22 is the first non-peptide SST2 agonist to advance to human clinical trials and is currently in Phase 3 trials in acromegaly patients and a Phase 2 trial in neuroendocrine tumor patients suffering from carcinoid syndrome.

Somatostatin, as a Bridge Between the GH-Axis and the Gth-Axis

Somatostatin (SST) is a 14-amino acid peptide produced in the hypothalamus of vertebrates, including fish. It regulates many physiological processes such as growth development and metabolic processes in the animal’s body. Negative control of growth hormone in vivo and in vitro was characterized in several fish species such as salmon, goldfish, rainbow trout and tilapia. Although very important, the SST/SST-R system in Nile tilapia (Oreochromis niloticus) was not deeply characterized. The somatostatin system in tilapia possess two ligands (Somatostatin1b and Somatostatin 2), and five receptors (SST-R 1-5). Unlike mammals, in fish, FSH and LH are secreted from different cell populations in the pituitary. By performing cell specific transcriptome analysis of double-labelled transgenic tilapia expressing GFP and RFP in LH or FSH cells, respectively, we identified genes specifically enriched in each cell type. Analysis of the RNA-seq discovered 4 types of SST-Rs: sstr2, sstr3, sstr5 and sstr5x3. The specific localization of each SST-R was identified by In Situ hybridization with specific probes for each of the SST-Rs. SST-R2 and SST-R5x3 were expressed on LH and FSH cells, while SST-R5 was exclusively expressed on LH cells. Interestingly, SST-R3, which was expressed on GH secreting cells, was also expressed on both gonadotropin-secreting cells. Transactivation assays, using COS7 cell line transfected with tilapia SST-Rs together with the reporter plasmid CRE-luc, demonstrated an effect through the cAMP/PKA pathway. Signal transduction analysis demonstrated that SST agonist (Octreotide; IC50 = 0.8-60nM) decreased the cAMP/PKA pathway, while an opposite effect was found when SST antagonist (Cyclosomatostatin; EC50 = 0.1 - 188 nM) was used. To understand the physiological effects of somatostatin on gonadotropins and GH release, we examined the effect of ip injection (100 μg/kg BW) of somatostatin agonist and antagonist on plasma FSH, LH and GH levels. SST agonist decreased plasma GH and FSH levels, as fast as two hours post injection and their levels remained low until the end of the experiment. On the other hand, SST antagonist increased LH and FSH levels two hours post injection, but while FSH levels remained high during the entire experiment, LH levels went back to basal levels afterwards. Our results show - for the first time in fish - a direct effect of SST on gonadotropin release, that could serve as a bridge between the GH-axis and the GTH-axis. The research was funded by the Israel Science Foundation (ISF) no. 1540/17.

Characterization of Neurons Expressing the Novel Analgesic Drug Target Somatostatin Receptor 4 in Mouse and Human Brains.

Somatostatin is an important mood and pain-regulating neuropeptide, which exerts analgesic, anti-inflammatory, and antidepressant effects via its Gi protein-coupled receptor subtype 4 (SST4) without endocrine actions. SST4 is suggested to be a unique novel drug target for chronic neuropathic pain, and depression, as a common comorbidity. However, its neuronal expression and cellular mechanism are poorly understood. Therefore, our goals were (i) to elucidate the expression pattern of Sstr4/SSTR4 mRNA, (ii) to characterize neurochemically, and (iii) electrophysiologically the Sstr4/SSTR4-expressing neuronal populations in the mouse and human brains. Here, we describe SST4 expression pattern in the nuclei of the mouse nociceptive and anti-nociceptive pathways as well as in human brain regions, and provide neurochemical and electrophysiological characterization of the SST4-expressing neurons. Intense or moderate SST4 expression was demonstrated predominantly in glutamatergic neurons in the major components of the pain matrix mostly also involved in mood regulation. The SST4 agonist J-2156 significantly decreased the firing rate of layer V pyramidal neurons by augmenting the depolarization-activated, non-inactivating K+ current (M-current) leading to remarkable inhibition. These are the first translational results explaining the mechanisms of action of SST4 agonists as novel analgesic and antidepressant candidates.

Safety and IGF-1 levels with once daily oral sst2 agonist paltusotine (CRN00808) in acromegaly patients previously treated with peptide long-acting somatostatin receptor ligands: Initial data from the open label ACROBAT Edge phase 2 study

Safety and IGF-1 levels with once daily oral sst2 agonist paltusotine (CRN00808) in acromegaly patients previously treated with peptide long-acting somatostatin receptor ligands: Initial data from the open label ACROBAT Edge phase 2 study

Discovery of substituted 3H-pyrido[2,3-d]pyrimidin-4-ones as potent, biased, and orally bioavailable sst2 agonist

The discovery of a novel 3H-pyrido[2,3-d]pyrimidin-4-one series as potent and biased sst2 agonists is described. This class of molecules exhibits excellent sst2 potency and selectivity against sst1, sst3, and sst5 receptors, and they are significantly more potent at inhibiting cAMP production than inducing internalization. The orally bioavailable 6-(3-chloro-5-methylphenyl)-3-(3-fluoro-5-hydroxyphenyl)-5-({methyl[(2S)-pyrrolidin-2-ylmethyl]amino}methyl)-3H,4H-pyrido[2,3-d]pyrimidin-4-one (36) also suppresses GH secretion in GHRH-challenged rats in a dose-dependent manner.

Discovery of nonpeptide 3,4-dihydroquinazoline-4-carboxamides as potent and selective sst2 agonists

Nonpeptide sst2 agonists can provide a new treatment option for patients with acromegaly, carcinoid tumors, and neuroendocrine tumors. Our medicinal chemistry efforts have led to the discovery of novel 3,4-dihydroquinazoline-4-carboxamides as sst2 agonists. This class of molecules exhibits excellent human sst2 potency and selectivity against sst1, sst3, sst4 and sst5 receptors. Leading compound 3-(3-chloro-5-methylphenyl)-6-(3-fluoro-2-hydroxyphenyl)-N,7-dimethyl-N-{[(2S)-pyrrolidin-2-yl]methyl}-3,4-dihydroquinazoline-4-carboxamide (28) showed no inhibition of major CYP450 enzymes (2C9, 2C19, 2D6 and 3A4) and weak inhibition of the hERG channel.

TBR-760, a Dopamine-Somatostatin Compound, Arrests Growth of Aggressive Nonfunctioning Pituitary Adenomas in Mice.

TBR-760 (formerly BIM-23A760) is a chimeric dopamine (DA)-somatostatin (SST) compound with potent agonist activity at both DA type 2 (D2R) and SST type 2 (SSTR2) receptors. Studies have shown that chimeric DA-SST compounds are more efficacious than individual DA and/or SST analogues, either alone or combined, in inhibiting secretion from primary cultures of human somatotroph and lactotroph tumor cells. Nonfunctioning pituitary adenomas (NFPAs) express both D2R and SSTR2 and, consequently, may respond to TBR-760. We used a mouse model with the pro-opiomelanocortin (POMC) gene knocked out that spontaneously develops aggressive NFPAs. Genomic microarray and DA and SST receptor messenger RNA expression analysis indicate that POMC KO mouse tumors and human NFPAs have similar expression profiles, despite arising from different cell lineages, establishing POMC KO mice as a model for study of NFPAs. Treatment with TBR-760 for 8 weeks resulted in nearly complete inhibition of established tumor growth, whereas tumors from vehicle-treated mice increased in size by 890 ± 0.7%. Comparing TBR-760 with its individual DA and SST components, TBR-760 arrested tumor growth. Treatment with equimolar or 10×-higher doses of the individual SST or DA agonists, either alone or in combination, had no significant effect. One exception was the lower dose of DA agonist that induced modest suppression of tumor growth. Only the chimeric compound TBR-760 arrested tumor growth in this mouse model of NFPA. Further, significant tumor shrinkage was observed in 20% of the mice treated with TBR-760. These results support the development of TBR-760 as a therapy for patients with NFPA.

SUN-118 Somatostatin Agonist Conjugated to the Evans Blue Moiety Is a Superior Analog in the Diagnosis and Treatment of Tumors Characterized by High Somatostatin Receptor Expression

Background: Radiolabeled somatostatin (SST) analogs have been proven to be effective in the diagnosis and treatment of neuroendocrine tumors (NETs), which are characterized by high somatostatin receptor (SSTR2) expression. At present, there are several SST analogs available that differ from each other in the affinity for SSTR2 and tumor retention time. To date, only a single SST agonist -DOTA-TATE- has been approved by the FDA for imaging and treatment of NETs. Recent studies have shown that addition of Evans blue (EB) moiety to an SST agonist results in superior uptake and increased retention time within the tumors. The goal of our study was to compare the diagnostic and therapeutic efficacy of three different radiolabeled SST analogs in a tumor mice model: EB-TATE - a novel modified agonist; DOTA-TATE - an agonist and JR11 - an antagonist. Methods: A rat pancreatic cell line (AR42J), characterized by high SSTR2 expression, was used to create a subcutaneous xenograft mice model. The AR42J cells formed sizable tumors within two weeks post-injection. The 86Y-EB-TATE, 68Ga-DOTA-TATE, and 68Ga-DOTA-JR11 were used to determine standard uptake values by positron emission tomography (PET) imaging. For treatment purposes, the SST analogs were labeled with 177Lu to generate 177Lu-EB-TATE, 177Lu-DOTA-TATE and 177Lu-DOTA-JR11. The mice were assigned to treatment groups based on comparable tumor volume at baseline and received two doses (0.5mCi) of the 177Lu-labeled analogs one week apart. Tumor measurements were performed twice per week and the mice were euthanized if their tumor burden exceeded 2 cm at any point in the study or after 6 weeks - landmark of the end of the study. Results: Among the three analogs tested, the novel SST analog 86Y-EB-TATE was characterized by 4.3- and 3.7- fold higher tumor uptake in comparison to 68Ga-DOTA-TATE (p<0.001) and 68Ga-DOTA-JR11 (p<0.001), respectively. There was no significant difference between the uptake of 68Ga-DOTA-TATE and 68Ga-DOTA-JR11 (p=0.9). Consistently with higher tumor uptake on imaging, 177Lu-EB-TATE-treated mice responded to the treatment with an overall 86.5±13.2% reduction in the tumor volume after two weeks post-therapy. On the contrary, despite therapy with 177Lu-DOTA-TATE and 177Lu-DOTA-JR11, the mice treated with these agents presented with tumor progression exceeding 2 cm and were euthanized. Consequently, the progression-free survival (PFS) was significantly longer in 177Lu-EB-TATE group (24±0 days) compared with 177Lu-DOTA-TATE (7.7±2.6 days, p<0.001) and 177Lu-DOTA-JR11 (6.3±3 days, p<0.001). There was no difference in PFS between 177Lu-DOTA-TATE and 177Lu-DOTA-JR11-treated mice (p=0.3). Conclusion: EB-TATE is characterized by superior diagnostic and therapeutic efficacy in comparison to DOTA-TATE and DOTA-JR11. EB-TATE might be used as imaging and therapeutic agent in tumors characterized by high SSTR2 expression.

OR23-05 Human Absorption, Metabolism, Excretion, and Absolute Oral Bioavailability of 14C-CRN00808, an Orally Bioavailable, Nonpeptide, Selective, Somatostatin Receptor 2 (sST2) Biased Agonist for the Treatment of Acromegaly

Injected depot formulations of somatostatin peptide analogs are routinely used to treat acromegaly and neuroendocrine tumors (NETs). CRN00808, a small molecule nonpeptide selective somatostatin receptor 2 (sst2) agonist, is being evaluated for efficacy and safety in patients with acromegaly. The current Phase 1 study was conducted in two Parts: In Part A, the absorption, metabolism, excretion, and mass balance of a single oral dose of 20 mg [14C]-CRN00808 (3.0 MBq) oral solution was characterized in six healthy male subjects. Plasma, blood, urine, and feces were collected for up to 432 hours, and were analyzed for total radioactivity and CRN00808 concentrations (plasma only). Metabolite profiling was conducted on the plasma, urine, and feces samples. In Part B, the absolute bioavailability of CRN00808 was determined by administering a single oral dose of 20 mg CRN00808 compared with a single micro-tracer intravenous (IV) bolus injection of 50 µg [14C]-CRN00808 (0.0185 MBq) in five healthy male subjects. The IV dose was administered approximately 90 minutes after the oral dose. Plasma samples were collected for up to 144 hours and were analyzed for total radioactivity and CRN00808 concentrations (plasma only).Key data from Part A and Part B will be presented. Available data from Part A of the study show that >90% of radioactivity was recovered within 7 days of dosing. The primary route of excretion was the feces (>90%) with minimal excretion in the urine (<10%). Absorption of total [14C]-CRN00808-derived radioactivity in plasma was rapid (median Tmax=1 hour), and the mean Cmax, AUC0-∞, and t1/2 were determined to be 194 ng-equivalents/mL, 3340 ng-equivalents.hr/mL, and 31 hours, respectively. The pharmacokinetic parameters of unchanged CRN00808 in plasma were similar, suggesting that majority of the circulating drug-derived radioactivity is accounted for by unchanged CRN00808 and there are no abundant circulating metabolites. Treatment emergent adverse events associated with CRN00808 were generally mild and transient, and consistent with those reported with other somatostatin agonists. In conclusion, results from this clinical trial in healthy volunteers confirm that CRN00808 has excellent drug-like properties for chronic once-daily oral treatment of patients with acromegaly.

MON-089 Discovery and Identification of Late Stage Selective Nonpeptide Somatostatin Subtype 5 (sst5) Agonists for the Treatment of Hyperinsulinemic Hypoglycemia

Congenital hyperinsulinism (CHI) results from mutations within the insulin secretion pathway and is characterized by excessive and/or inappropriate insulin secretion by pancreatic islet β-cells. CHI is the most common cause of persistent hypoglycemia in newborns and infants and is estimated to affect 1:2500 to 1:50,000 live births. Prompt recognition and treatment are vital to prevent coma, long-term neurological complications, and even death. If medical control of CHI is unsuccessful, a near-total pancreatectomy may be required, but hypoglycemia often persists. The neuropeptide somatostatin is an important modulator of pancreatic hormonal signaling and activity at different somatostatin receptor (sst) subtypes dictates the suppression of insulin and/or glucagon. The injectable peptide drugs octreotide and lanreotide are potent sst2 agonists used to treat CHI, but in addition to suppressing insulin, the sst2 activity of these peptides may also inhibit glucagon secretion, potentially reducing effectiveness and compromising a key defense against hypoglycemia. Glucagon secretion from α-cells is inhibited through activation of sst2 receptors, while insulin secretion from β-cells is inhibited through activation of sst2 and sst5. We therefore hypothesize that agonists selectively targeting sst5 and lacking sst2 activity will offer an improved efficacy/safety profile for patients with hyperinsulinemic hypoglycemia.Using iterative medicinal chemistry and pharmacology, Crinetics has discovered several classes of highly potent, orally bioavailable, small molecule sst-subtype selective agonists with drug-like pharmaceutical properties. Our discovery efforts aimed at finding a compound to treat CHI have yielded potent and selective nonpeptide sst5 agonists with sub-nanomolar EC50s in cell-based assays of receptor activation. Insulin secretion from isolated human and rat islets was suppressed upon exposure to sst5 agonists. Potent and selective sst5 agonists were then evaluated in a number acute and repeat dose in vivo models (e.g., oGTT, fed/fasted conditions, sulfonylurea-induced hypoglycemia) to assess physiological effects and to gain mechanistic insights. As predicted by the in vitro pharmacology, selective nonpeptide sst5 agonists suppressed insulin secretion and raised blood glucose levels in each model, while having minimal effects on glucagon secretion. Leading sst5 agonists were also evaluated for drug like characteristics, including stability in liver microsomes, lack of inhibition of cytochromes P450 and the hERG ion channel, and were shown to exhibit good exposure upon oral dosing in both rats and dogs. The culmination of these studies has led to a subset of candidate molecules that are being evaluated in genotoxicity, safety pharmacology, and general toxicity studies to determine the molecule most suitable for evaluation in human clinical trials.

OR06-02 TBR-760, a Chimeric Somatostatin-Dopamine Compound, Arrests Aggressive Non-Functioning Pituitary Adenoma Growth In Vivo

TBR-760 is a chimeric dopamine (DA)-somatostatin (SST) compound with potent agonist activity at both DA type 2 (D2R; EC50 0.064nM) and SST type 2 (SSTR2; EC50 1.2nM) receptors. Prior studies have demonstrated that the chimeric DA-SST compounds are more potent and effective than either individual or combinations of individual DA and/or SST analogs in inhibiting secretion from pituitary adenomas. Non-functioning pituitary adenomas (NFPA) express high levels of D2R as well as lower levels of SSTRs, including the type 2 receptor (1), and thus have an appropriate receptor profile to respond to TBR-760. The present study examines the ability of TBR-760 to inhibit tumor growth in a mouse model of aggressive NFPA. Heterozygous and null mutant mice lacking one or both copies, respectively, of the pro-opiomelanocortin (POMC) gene (POMC-KO mice)(2) spontaneously develop aggressive, non-secreting pituitary adenomas (3). The POMC-KO mouse tumors have been shown to express D2R and SSTR2 at a similar level as human NFPAs (4). In addition, merging of microarray data (Affymetrix, U133 plus_2.0 and Mouse Genome 430 2.0 arrays), reveals 154 common gene signatures between human NFPAs and the POMC-KO mouse tumors. In an initial study, heterozygous POMC-KO mice with an established pituitary tumor of approx. 10mm3 (mean volume 8.9±0.3), as determined by MRI, were treated with a range of TBR-760 doses (0.125 to 12.5mg/kg, sc, QD) for 60 days. During that time, tumors in vehicle-treated mice increased in size by 890±0.7%, whereas all doses of TBR-760 tested resulted in a nearly complete inhibition of tumor growth from treatment initiation. We then compared the effect of the TBR-760 chimera with that of its individual SST agonist (SSTA) and DA agonist (DAA) components on tumor growth in the POMC-KO mice. As in the earlier study, TBR-760 treatment (1mg/kg, sc, QD), initiated when the mice had an established tumor of approx. 10mm3, completely arrested tumor growth during the 8 weeks of treatment (final mean tumor volume of 8.5±1.3mm3 vs. 54.61±10.6mm3 in vehicle-treated mice). Treatment with equimolar or 10x-higher doses of the individual SSTA or DAA, either alone or in combination, had no significant effect on tumor growth, except in the lower dose DAA group where a modest suppression of tumor growth was observed. These data demonstrate that only the dual DA-SST chimeric compound, TBR-760, completely arrested tumor growth in the POMC-KO mouse model of NFPA. Further, despite the highly aggressive nature of the POMC-KO tumors, significant tumor shrinkage was observed in 20% of the mice treated with TBR-760. These results support the development of TBR-760 as a medical therapy to prevent or arrest the growth of NFPAs and, potentially, to induce NFPA shrinkage.

Somatostatin receptor subtype 4 protects against indomethacin-induced gastrointestinal mucosal injury in mouse

Abstract Despite recent advancements in the pharmacologic and endoscopic management of gastrointestinal ulceration, it is still associated with high mortality. Therefore, it is important to understand mucosal protective mechanisms. Somatostatin, present in the endocrine cells &amp; sensory nerves, and its analogues reduce mucosal blood flow, pepsin and gastric acid secretion. Its receptor subtype 4 (sst4) mediates anti-inflammatory &amp; analgesic actions, as discovered by our group. Therefore, our aim was to investigate its role in gastrointestinal injury. We treated sst4 gene-deleted (sst4−/−) and wildtype mice with indomethacine (IDM; 35 mg/kg) or vehicle s.c.. Gastric &amp; small intestine lesions were evaluated after 4 &amp; 48 h macroscopically &amp; microscopically. Plasma protein extravasation &amp; myeloperoxidase (MPO) activity were assessed by ex vivo imaging, TNFα, IL-1, COX2, sst4 &amp; somatostatin mRNA levels by qPCR. Gastric (4h) and small intestinal macroscopic (24 h) lesions, MPO activity (24, 48 h), and plasma extravasation (30 min) were significantly greater in IDM-treated sst4−/− mice, while histopathological scores &amp; small intestinal length did not show strain difference. TNFα, IL-1, COX2 significantly upregulated after 4h in the stomach of sst4−/− mice, and the same pattern was observable in wildtype mice at later timepoint (48 h). These results provide evidence for the protective role of the sst4 receptor against IDM-induced gastrointestinal mucosal injury. This suggests the safety of sst4 agonist drug candidates in the gastrointestinal tract, and even their potential use for gastroprotective indication. Supported by: GINOP-2.3.2-15-2016-00050 – PEPSYS, GINOP-2.3.2 STAY ALIVE, EFOP-3.6.2-16-2017-00008, ÚNKP-19-3-III-PTE-211

Expression and Protective Functions of the sst4 Somatostatin Receptor in the Indomethacin‐Induced Gastrointestinal Mucosal Injury Model of the Mouse

IntroductionGastrointestinal ulceration is associated with high mortality despite advanced management, therefore, understanding of the mucosal protective mechanisms is important. Somatostatin is present in the endocrine cells and sensory nerves, and its analogues were shown to reduce mucosal blood flow, pepsin and gastric acid secretion. Our group discovered that its anti‐inflammatory and analgesic actions are exerted via the somatostatin receptor subtype 4 (sst4). Therefore, we investigated its expression and role in gastrointestinal injury.MethodsSst4 gene‐deleted (sst4−/−) and wildtype mice were treated s.c. with indomethacine (IDM; 35 mg/kg) or vehicle. RNA scope in situ hybridization was performed to localize, qPCR to quantify sst4 and somatostatin mRNA. Macroscopic and microscopic lesions in the stomach and small intestine were evaluated after 4 and 48 h. Plasma protein extravasation was measured by fluorescent, neutrophil myeloperoxidase (MPO) activity bioluminescent ex vivo imaging, TNFα, IL‐1 and COX2 mRNA by qPCR.ResultsSomatostatin mRNA is present in the neuroendocrine D‐cells and significantly upregulated 48 h after IDM. Sst4 mRNA in located in the myenteric plexus neurons, it’s expression did not change in response to mucosal injury.IDM‐induced gastric and small intestinal macroscopic lesions (4, 24 h), gastric MPO activity (24, 48 h) and plasma extravasation (30 min) were significantly greater in sst4−/− mice. TNFα, IL‐1, COX2 expressions significantly increased after 4 h in the stomach of sst4−/− mice, but in wild‐types the same pattern was observed only later, at the 48 h time‐point. IDM‐evoked histopathological alterations and small intestinal length reduction were not altered by the sst4 deletion.ConclusionThis is the first evidence for sst4 expression in myenteric plexus neurons and its protective roles against chemically‐induced gastrointestinal mucosal damage and inflammation. This suggests the safety of sst4 agonist drug candidates in the gastrointestinal tract, and even their potential use for gastroprotective indication.Support or Funding InformationSupported by: GINOP‐2.3.2‐15‐2016‐00050 – PEPSYS, GINOP‐2.3.2 STAY ALIVE, EFOP‐3.6.2‐16‐2017‐00008, ÚNKP‐19‐3‐III‐PTE‐211

Central somatostatin signaling and regulation of food intake.

The discovery of somatostatin (SST) in the hypothalamus implicated the peptide in the inhibition of growth hormone release. However, as observed for numerous neuropeptides, SST was neither restricted to this one brain site nor to this one function. Subsequent studies established a widespread but specific expression of SST in the central nervous system of rodents and humans along with the expression patterns of five receptors (sst1-5 ). Among biological actions, the activation of central SST signaling induced a robust stimulation of food and water intake, which is mediated by the sst2 as assessed using selective sst agonists. The past years have witnessed the identification of brain SST circuitries involved using chemogenetic and optogenetic approaches and further established a physiological orexigenic role of brain SST signaling. The present review will discuss these recent findings.

SAT-260 Selective Nonpeptide Somatostatin Subtype 5 (sst5) Agonists Suppress Induced Insulin Secretion in Pancreatic Islets from both Rats and Healthy Human Donors

Hyperinsulinemia is a heterogeneous condition in which dangerously low blood sugar levels are caused by improperly regulated insulin secretion from pancreatic ß-cells. The most severe form of hyperinsulinemia arises from congenital hyperinsulinism (CHI), a set of genetic disorders in which the underlying pathology is driven by mutations in key genes that regulate insulin secretion. CHI is the most common cause of persistent hypoglycemia in newborns and infants, and prompt recognition and treatment are vital to prevent coma, long-term neurological complications, and even death. The neuropeptide somatostatin is an important modulator of hormonal signaling from the pancreas mediated by different somatostatin receptor (sst) subtypes. Glucagon secretion from α-cells is inhibited through sst2 receptor activation and insulin secretion from β-cells is inhibited through sst2, sst3, and sst5. The injectable peptide drugs octreotide and lanreotide are primarily agonists at sst2 and are often prescribed for these patients in an attempt to reduce insulin secretion, but their efficacy is limited, and they carry the risk of impairing glucagon secretion, an important defense mechanism against hypoglycemia. We hypothesize that an orally available selective sst5 agonist may be a useful new approach to managing hyperinsulinemia. We launched an iterative medicinal chemistry program that led to the discovery of selective sst5 agonists, with multiple nonpeptide series possessing EC50s < 1 nM in cell-based assays of receptor activation (these compounds also routinely possess similar potencies for the rat sst5 receptor). We have shown that these sst5 agonists potently suppress insulin and raise plasma glucose in multiple glycemic studies in rats. To explore the mechanism of selective sst agonism and its translation from rat studies to humans, we undertook a series of studies using pancreatic islets isolated from human donors and from naïve Sprague Dawley rats. Selective sst5 agonists were compared to selective sst2 and selective sst3 agonists as well as somatostatin peptides for their capacity to suppress insulin and/or glucagon from islets under various conditions including increasing glucose concentrations and the presence of a sulfonylurea (the increased insulin secretion mimics many CHI patients). In both human and rat islets, we found that selective sst5 agonists potently suppressed insulin secretion more effectively than selective sst2 or sst3 agonists, while having little effect on glucagon secretion, demonstrating their potential efficacy in the human condition. These studies support our program to identify and develop potent nonpeptide selective sst5 agonists with pharmaceutical and safety characteristics suitable for evaluation in human clinical trials.

MON-464 Non-Clinical Profiling of ONO-5788, a Novel Oral Small Molecule Somatostatin Receptor Type-2 (SST2) Agonist, to Support Studies in Humans

Somatostatin analogues (SSAs) are indicated for use in acromegaly and gastroenteropancreatic neuroendocrine tumors (GEP NETs). However, SSAs are administered as injections which can be a challenge for patients and healthcare providers. ONO-5788 is a novel low molecular weight orally administered molecule with potent and selective agonistic effects at the human SST2 subtype. ONO-5788 could offer the advantages of a more convenient route of administration for patients with acromegaly and other indications and also a preferential safety profile compared to injections. In order to support clinical evaluation of ONO-5788, a series of non-clinical experiments were undertaken. Findings: In vitro, ONO-5788 and its active metabolite, ONO-ST1-641, has a greater agonistic effect on human SST2 compared to other somatostatin receptor subtypes, with EC50 values of 0.11 and 0.016 nmol/L, respectively. There is no difference in mean EC50 values between human SST2 and rat SST2. ONO-5788 and ONO-ST1-641 significantly inhibits growth hormone-releasing hormone (GHRH)-induced GH secretion from primary cultured rat pituitary cells. In vivo studies in rats confirmed that a single oral dose of ONO-5788 resulted in systemic exposure of ONO-5788 and ONO-ST1-641 that increased in a dose dependent manner. Orally administrated ONO-5788 significantly inhibited both GHRH-induced GH secretion and basal GH secretion at all the doses tested (≥0.1 and ≥0.03 mg/kg, respectively). ONO-5788 and ONO-ST1-641 administrated intravenously significantly inhibited GHRH-induced GH secretion with effect on maximum inhibition of GH secretion similar to octreotide (ONO-5788 98.0%, ONO-ST1-641 98.6%, octreotide 98.7%, respectively). Plasma concentrations of ONO-5788 and ONO-ST1-641 required to supress serum GH level to a clinically meaningful degree in acromegaly patients were estimated to be 21.3 and 1.29 ng/mL. In experiments evaluating the effects on insulin and glucagon secretion in anaesthetised rats, ONO-5788, ONO-ST1-641, octreotide and pasireotide significantly inhibited glucagon secretion, but ONO-5788 and ONO-ST1-641 had no significant impact on insulin secretion at doses up to 10-fold higher than the dose required for either of these compounds to almost maximally inhibit GH secretion. In contrast, pasireotide and octreotide showed a significant inhibition of insulin secretion at equivalent doses of both ONO-5788 and ONO-ST1-641. A standard battery of preclinical safety and toxicology studies provided adequate evidence of safety to support commencement of a Phase I study in healthy volunteers to measure the safety, pharmacokinetics, and pharmacodynamics of ONO-5788. Conclusion: Orally administered ONO-5788 demonstrates potency as a SST2 agonist and has the potential to be a new treatment option for patients with acromegaly and NET.