AT-7687, a novel GIPR peptide antagonist, combined with a GLP-1 agonist, leads to enhanced weight loss and metabolic improvements in cynomolgus monkeys.

OBJECTIVES: Obesity represents a global health crisis with significant patient burdens and healthcare costs. Despite the advances with glucagon-like peptide-1 (GLP-1) receptor agonists in treating obesity, unmet needs remain. This study characterizes a novel glucose-dependent insulinotropic polypeptide receptor (GIPR) peptide antagonist, AT-7687, evaluating its potential to enhance obesity treatment. METHODS: We assessed the in vitro potency and pharmacokinetics of AT-7687, alongside its therapeutic effects when administered subcutaneously (SC) alone and in combination with liraglutide to high-fat-diet-fed obese non-human primates (NHP). The study spanned a 42-day treatment period and a 15-day washout period. RESULTS: AT-7687 demonstrated a subnanomolar cAMP antagonistic potency (pKB of 9.5) in HEK-293 cells and a 27.4 h half-life in NHPs. It effectively maintained weight stability in obese monkeys, whereas placebo recipients had an 8.6% weight increase by day 42 (P = 0.01). Monotherapy with liraglutide resulted in a 12.4% weight reduction compared to placebo (P = 0.03) and combining AT-7687 with liraglutide led to a 16.3% weight reduction (P = 0.0002). The combination therapy significantly improved metabolic markers, reducing insulin levels by 52% (P = 0.008), glucose by 30% (P = 0.02), triglycerides by 39% (P = 0.05), total cholesterol by 29% (P = 0.03), and LDL cholesterol by 48% (P = 0.003) compared to placebo. AT-7687 treatment was well tolerated and not associated with any side effects. CONCLUSIONS: This study underscores the potential of AT-7687 as a promising addition to current obesity treatments.

GIP receptor antagonism eliminates paradoxical growth hormone secretion in some patients with acromegaly.

CONTEXT: About 30% of patients with active acromegaly experience paradoxically increased growth hormone (GH) secretion during the diagnostic oral glucose tolerance test (OGTT). Endogenous glucose-dependent insulinotropic polypeptide (GIP) is implicated in this paradoxical secretion. OBJECTIVE: We used the GIP receptor (GIPR) antagonist GIP(3-30)NH2 to test the hypothesis that GIP mediates this paradoxical response when GIPR is abundantly expressed in somatotropinomas. DESIGN, PATIENTS, SETTING, INTERVENTIONS: 25 treatment-naïve patients with acromegaly were enrolled. Each patient underwent one OGTT during simultaneous placebo infusion and one OGTT during a GIP(3-30)NH2 infusion. Blood samples were drawn at baseline and regularly after infusions to measure GH. We assessed pituitary adenoma size by magnetic resonance imaging and GIPR expression by immunohistochemistry on resected somatotropinomas. For mechanistic confirmation, we applied in vitro and ex vivo approaches. MAIN OUTCOME MEASURE: The effect of GIP(3-30)NH2 on paradoxical GH secretion during OGTT as a measure of GIP involvement. RESULTS: In four of seven patients with paradoxical GH secretion, GIP(3-30)NH2 infusion completely abolished the paradoxical response (P = 0.0003). Somatotrophs were available from three of four of these patients, all showing abundant GIPR expression. Adenoma size did not differ between patients with and without paradoxical GH secretion. CONCLUSIONS: Of 25 patients with acromegaly, seven had paradoxical GH secretion during OGTT, and pharmaceutical GIPR blockade abolished this secretion in four. Corresponding somatotroph adenomas abundantly expressed GIPR, suggesting a therapeutic target in this subpopulation of patients. In vitro and ex vivo analyses confirmed the role of GIP and the effects of the antagonist.

The Annexin-A1 mimetic RTP-026 promotes acute cardioprotection through modulation of immune cell activation.

AIMS: The cardio-protective and immuno-regulatory properties of RTP-026, a synthetic peptide that spans the Annexin-A1 (AnxA1) N-terminal region, were tested in rat acute myocardial infarction. METHODS AND RESULTS: In vitro, selective activation of formyl-peptide receptor type 2 (FPR2) by RTP-026 occurred with apparent EC50 in the 10-30 nM range. With human primary cells, RTP-026 counteracted extension of neutrophil life-span and augmented phagocytosis of fluorescent E.coli by blood myeloid cells. An in vivo model of rat acute infarction was used to quantify tissue injury and phenotype immune cells in myocardium and blood. The rat left anterior descending coronary artery was occluded and then reopened for 2-hour or 24-hour reperfusion. For the 2-hour reperfusion protocol, RTP-026 (25-500 µg/kg; given i.v. at the start of reperfusion) significantly reduced infarct size by ∼50 %, with maximal efficacy at 50 µg/kg. Analyses of cardiac immune cells showed that RTP-026 reduced neutrophil and classical monocyte recruitment to the damaged heart. In the blood, RTP-026 (50 µg/kg) attenuated activation of neutrophils and monocytes monitored through CD62L and CD54 expression. Modulation of vascular inflammation by RTP-026 was demonstrated by reduction in plasma levels of mediators like TNF-α, IL-1ß, KC, PGE2 and PGF2α⊡ For the 24-hour reperfusion protocol, RTP-026 (30 µg/kg given i.v. at 0, 3 and 6 h reperfusion) reduced necrotic myocardium by ∼40 %. CONCLUSIONS: RTP-026 modulate immune cell responses and decreases infarct size of the heart in preclinical settings. Tempering over-exuberant immune cell activation by RTP-026 is a suitable approach to translate the biology of AnxA1 for therapeutic purposes.

Cloning and characterization of the porcine gastrin/cholecystokinin type 2 receptor.

The gastrointestinal hormone cholecystokinin (CCK) regulates digestive processes and satiety in addition to centrally mediated effects on nociception and anxiety. CCK signals through two seven-trans-membrane receptors named the CCK-1 receptor and the CCK-2 receptor. The expression pattern and biological effects mediated by the CCK-1 and CCK-2 receptors are highly divergent. The pig is a widely used preclinical animal model in medical research, but up until recently, the porcine CCK-2 receptor was described as a pseudogene in the publicly available genomic sequence databases. Thus, it was challenging to interpret data from this animal model in studies of CCK biology and pharmacology. Here we describe an in silico prediction of the porcine CCK-2 receptor and the subsequent cloning, expression, and in vitro pharmacological characterization. We find a high degree of sequence homology with the human orthologue as well as CCK-2 receptors of other major species used in pre-clinical research. We also show that the endogenous ligands CCK-8 and Gastrin-17 bind and activate the porcine CCK-2 receptor with similar affinities and potencies as seen for the human CCK-2 receptor. We conclude that the pig has a functional CCK-2 receptor which is highly comparable to the human orthologue and therefore the pig qualifies as a valid preclinical model for the study of human CCK biology and pharmacology.

[Sar1, Ile4, Ile8]-angiotensin II Potentiates Insulin Receptor Signalling and Glycogen Synthesis in Hepatocytes.

The angiotensin II type I receptor (AT1R) is involved in the regulation of cardiovascular function. Excessive activation of AT1R by angiotensin II (Ang II) leads to cardiovascular disease and may be involved in the development of insulin resistance and diabetes. Functionally selective Ang II analogues, such as the [Sar1, Ile4, Ile8]-angiotensin II (SII Ang II) analogue, that only activate a subset of signalling networks have been demonstrated to have beneficial effects on cardiovascular function in certain settings, including lowering blood pressure and increasing cardiac performance. Here, we studied the effect of SII Ang II on insulin receptor (IR) signalling and glucose metabolism in primary rat hepatocytes. We show that long-term pre-treatment of hepatocytes with SII Ang II increased insulin-stimulated glycogen synthesis, while Ang II and the AT1R antagonist losartan had no effect. Insulin-stimulated suppression of hepatic glucose output was not affected by Ang II or SII Ang II. It is well known that insulin regulates glycogen synthesis and glucose output through Akt-mediated phosphorylation of glycogen synthase kinase α/ß (GSK3α/ß) and forkhead box protein O1 (FOXO1), respectively. In line with this, we show that SII Ang II potentiated insulin-stimulated phosphorylation of Akt and GSK3α/ß, but not FOXO1. Furthermore, we demonstrate that the effect of SII Ang II on insulin-stimulated signalling and glycogen synthesis was dependent on Src and Gαq, as inhibitors of these proteins abolished the potentiating effect of SII Ang II. Thus, our results demonstrate that SII Ang II may have a positive effect on IR signalling and glucose metabolism in hepatocytes.

A bioluminescence resonance energy transfer 2 (BRET2) assay for monitoring seven transmembrane receptor and insulin receptor crosstalk.

The angiotensin AT1 receptor is a seven transmembrane (7TM) receptor, which mediates the regulation of blood pressure. Activation of angiotensin AT1 receptor may lead to impaired insulin signaling indicating crosstalk between angiotensin AT1 receptor and insulin receptor signaling pathways. To elucidate the molecular mechanisms behind this crosstalk, we applied the BRET2 technique to monitor the effect of angiotensin II on the interaction between Rluc8 tagged insulin receptor and GFP2 tagged insulin receptor substrates 1, 4, 5 (IRS1, IRS4, IRS5) and Src homology 2 domain-containing protein (Shc). We demonstrate that angiotensin II reduces the interaction between insulin receptor and IRS1 and IRS4, respectively, while the interaction with Shc is unaffected, and this effect is dependent on Gαq activation. Activation of other Gαq-coupled 7TM receptors led to a similar reduction in insulin receptor and IRS4 interactions whereas Gαs- and Gαi-coupled 7TM receptors had no effect. Furthermore, we used a panel of kinase inhibitors to show that angiotensin II engages different pathways when regulating insulin receptor interactions with IRS1 and IRS4. Angiotensin II inhibited the interaction between insulin receptor and IRS1 through activation of ERK1/2, while the interaction between insulin receptor and IRS4 was partially inhibited through protein kinase C dependent mechanisms. We conclude that the crosstalk between angiotensin AT1 receptor and insulin receptor signaling shows a high degree of specificity, and involves Gαq protein, and activation of distinct kinases. Thus, the BRET2 technique can be used as a platform for studying molecular mechanisms of crosstalk between insulin receptor and 7TM receptors.

Dual agonist occupancy of AT1-R-α2C-AR heterodimers results in atypical Gs-PKA signaling.

Hypersecretion of norepinephrine (NE) and angiotensin II (AngII) is a hallmark of major prevalent cardiovascular diseases that contribute to cardiac pathophysiology and morbidity. Herein, we explore whether heterodimerization of presynaptic AngII AT1 receptor (AT1-R) and NE α2C-adrenergic receptor (α2C-AR) could underlie their functional cross-talk to control NE secretion. Multiple bioluminescence resonance energy transfer and protein complementation assays allowed us to accurately probe the structures and functions of the α2C-AR-AT1-R dimer promoted by ligand binding to individual protomers. We found that dual agonist occupancy resulted in a conformation of the heterodimer different from that induced by active individual protomers and triggered atypical Gs-cAMP-PKA signaling. This specific pharmacological signaling unit was identified in vivo to promote not only NE hypersecretion in sympathetic neurons but also sympathetic hyperactivity in mice. Thus, we uncovered a new process by which GPCR heterodimerization creates an original functional pharmacological entity and that could constitute a promising new target in cardiovascular therapeutics.

A BRET assay for monitoring insulin receptor interactions and ligand pharmacology.

The insulin receptor (IR) belongs to the receptor tyrosine kinase super family and plays an important role in glucose homeostasis. The receptor interacts with several large docking proteins that mediate signaling from the receptor, including the insulin receptor substrate (IRS) family and Src homology-2-containing proteins (Src). Here, we applied the bioluminescence resonance energy transfer 2 (BRET2) technique to study the IR signaling pathways. The interaction between the IR and the substrates IRS1, IRS4 and Shc was examined in response to ligands with different signaling properties. The association between IR and the interacting partners could successfully be monitored when co-expressing green fluorescent protein 2 (GFP2) tagged substrates with Renilla reniformis luciferase 8 (Rluc8) tagged IR. Through additional optimization steps, we developed a stable and flexible BRET2 assay for monitoring the interactions between the IR and its substrates. Furthermore, the insulin analogue X10 was characterized in the BRET2 assay and was found to be 10 times more potent with respect to IRS1, IRS4 and Shc recruitment compared to human insulin. This study demonstrates that the BRET2 technique can be applied to study IR signaling pathways, and that this assay can be used as a platform for screening and characterization of IR ligands.

Biased signaling of the angiotensin II type 1 receptor can be mediated through distinct mechanisms.

BACKGROUND: Seven transmembrane receptors (7TMRs) can adopt different active conformations facilitating a selective activation of either G protein or ß-arrestin-dependent signaling pathways. This represents an opportunity for development of novel therapeutics targeting selective biological effects of a given receptor. Several studies on pathway separation have been performed, many of these on the Angiotensin II type 1 receptor (AT1R). It has been shown that certain ligands or mutations facilitate internalization and/or recruitment of ß-arrestins without activation of G proteins. However, the underlying molecular mechanisms remain largely unresolved. For instance, it is unclear whether such selective G protein-uncoupling is caused by a lack of ability to interact with G proteins or rather by an increased ability of the receptor to recruit ß-arrestins. Since uncoupling of G proteins by increased ability to recruit ß-arrestins could lead to different cellular or in vivo outcomes than lack of ability to interact with G proteins, it is essential to distinguish between these two mechanisms. METHODOLOGY/PRINCIPAL FINDINGS: We studied five AT1R mutants previously published to display pathway separation: D74N, DRY/AAY, Y292F, N298A, and Y302F (Ballesteros-Weinstein numbering: 2.50, 3.49-3.51, 7.43, 7.49, and 7.53). We find that D74N, DRY/AAY, and N298A mutants are more prone to ß-arrestin recruitment than WT. In contrast, receptor mutants Y292F and Y302F showed impaired ability to recruit ß-arrestin in response to Sar1-Ile4-Ile8 (SII) Ang II, a ligand solely activating the ß-arrestin pathway. CONCLUSIONS/SIGNIFICANCE: Our analysis reveals that the underlying conformations induced by these AT1R mutants most likely represent principally different mechanisms of uncoupling the G protein, which for some mutants may be due to their increased ability to recruit ß-arrestin2. Hereby, these findings have important implications for drug discovery and 7TMR biology and illustrate the necessity of uncovering the exact molecular determinants for G protein-coupling and ß-arrestin recruitment, respectively.