GUB06-046, a novel secretin/glucagon-like peptide 1 co-agonist, decreases food intake, improves glycemic control, and preserves beta cell mass in diabetic mice

Advances in obesity pharmacotherapy; learning from metabolic surgery and beyond

Currently, metabolic surgery (MS) constitutes the most effective means for durable weight loss of clinically meaningful magnitude, type 2 diabetes remission and resolution of non-alcoholic steatohepatitis, as well as other obesity-related comorbidities. Accumulating evidence on the mechanisms through which MS exerts its actions has highlighted the altered secretion of hormonally active peptides of intestinal origin with biological actions crucial to energy metabolism as key drivers of MS clinical effects. The initial success of glucagon-like peptide-1 (GLP-1) receptor agonists regarding weight loss and metabolic amelioration have been followed by the development of unimolecular dual and triple polyagonists, additionally exploiting the effects of glucagon and/or glucose-dependent insulinotropic polypeptide (GIP) which achieves a magnitude of weight loss approximating that of common MS operations. Through the implementation of such therapies, the feasibility of a "medical bypass", namely the replication of the clinical effects of MS through non-surgical interventions may be foreseeable in the near future. Apart from weight loss, this approach ought to be put to the test also regarding other clinical outcomes, such as liver steatosis and steatohepatitis, cardiovascular disease, and overall prognosis, on which MS has a robustly demonstrated impact. Besides, a medical bypass as an alternative, salvage, or combination strategy to MS may promote precision medicine in obesity therapeutics.

Novel Noninvasive Approaches to the Treatment of Obesity: From Pharmacotherapy to Gene Therapy

Recent insights into the pathophysiologic underlying mechanisms of obesity have led to the discovery of several promising drug targets and novel therapeutic strategies to address the global obesity epidemic and its comorbidities. Current pharmacologic options for obesity management are largely limited in number and of modest efficacy/safety profile. Therefore, the need for safe and more efficacious new agents is urgent. Drugs that are currently under investigation modulate targets across a broad range of systems and tissues, including the central nervous system, gastrointestinal hormones, adipose tissue, kidney, liver, and skeletal muscle. Beyond pharmacotherapeutics, other potential antiobesity strategies are being explored, including novel drug delivery systems, vaccines, modulation of the gut microbiome, and gene therapy. The present review summarizes the pathophysiology of energy homeostasis and highlights pathways being explored in the effort to develop novel antiobesity medications and interventions but does not cover devices and bariatric methods. Emerging pharmacologic agents and alternative approaches targeting these pathways and relevant research in both animals and humans are presented in detail. Special emphasis is given to treatment options at the end of the development pipeline and closer to the clinic (ie, compounds that have a higher chance to be added to our therapeutic armamentarium in the near future). Ultimately, advancements in our understanding of the pathophysiology and interindividual variation of obesity may lead to multimodal and personalized approaches to obesity treatment that will result in safe, effective, and sustainable weight loss until the root causes of the problem are identified and addressed.

Secretin as a Satiation Whisperer With the Potential to Turn into an Obesity-curbing Knight

The obesity pandemic requires effective preventative and therapeutic intervention strategies. Successful and sustained obesity treatment is currently limited to bariatric surgery. Modulating the release of gut hormones is considered promising to mimic bariatric surgery with its beneficial effects on food intake, body weight, and blood glucose levels. The gut peptide secretin was the first molecule to be termed a hormone; nevertheless, only recently has it been established as a legitimate anorexigenic peptide. In contrast to gut hormones that crosstalk with the brain either directly or by afferent neuronal projections, secretin mediates meal-associated brown fat thermogenesis to induce meal termination, thereby qualifying this physiological mechanism as an attractive, peripheral target for the treatment of obesity. In this perspective, it is of pivotal interest to deepen our as yet superficial knowledge on the physiological roles of secretin as well as meal-associated thermogenesis in energy balance and body weight regulation. Of note, the emerging differences between meal-associated thermogenesis and cold-induced thermogenesis must be taken into account. In fact, there is no correlation between these 2 entities. In addition, the investigation of potential effects of secretin in hedonic-driven food intake, bariatric surgery and chronic treatment using suitable application strategies to overcome pharmacokinetic limitations will provide further insight into its potential to influence energy balance. The aim of this article is to review the facts on secretin's metabolic effects, address prevailing gaps in our knowledge, and provide an overview on the opportunities and challenges of the therapeutic potential of secretin in body weight control.

Proglucagon-Derived Peptides as Therapeutics

Initially discovered as an impurity in insulin preparations, our understanding of the hyperglycaemic hormone glucagon has evolved markedly over subsequent decades. With description of the precursor proglucagon, we now appreciate that glucagon was just the first proglucagon-derived peptide (PGDP) to be characterised. Other bioactive members of the PGDP family include glucagon-like peptides -1 and -2 (GLP-1 and GLP-2), oxyntomodulin (OXM), glicentin and glicentin-related pancreatic peptide (GRPP), with these being produced via tissue-specific processing of proglucagon by the prohormone convertase (PC) enzymes, PC1/3 and PC2. PGDP peptides exert unique physiological effects that influence metabolism and energy regulation, which has witnessed several of them exploited in the form of long-acting, enzymatically resistant analogues for treatment of various pathologies. As such, intramuscular glucagon is well established in rescue of hypoglycaemia, while GLP-2 analogues are indicated in the management of short bowel syndrome. Furthermore, since approval of the first GLP-1 mimetic for the management of Type 2 diabetes mellitus (T2DM) in 2005, GLP-1 therapeutics have become a mainstay of T2DM management due to multifaceted and sustainable improvements in glycaemia, appetite control and weight loss. More recently, longer-acting PGDP therapeutics have been developed, while newfound benefits on cardioprotection, bone health, renal and liver function and cognition have been uncovered. In the present article, we discuss the physiology of PGDP peptides and their therapeutic applications, with a focus on successful design of analogues including dual and triple PGDP receptor agonists currently in clinical development.

Discovery of small molecule positive allosteric modulators of the secretin receptor

The secretin receptor (SCTR) is a prototypic Class B1 G protein-coupled receptor (GPCR) that represents a key target for the development of therapeutics for the treatment of cardiovascular, gastrointestinal, and metabolic disorders. However, no non-peptidic molecules targeting this receptor have yet been disclosed. Using a high-throughput screening campaign directed at SCTR to identify small molecule modulators, we have identified three structurally related scaffolds positively modulating SCTRs. Here we outline a comprehensive study comprising a structure-activity series based on commercially available analogs of the three hit scaffold sets A (2-sulfonyl pyrimidines), B (2-mercapto pyrimidines) and C (2-amino pyrimidines), which revealed determinants of activity, cooperativity and specificity. Structural optimization of original hits resulted in analog B2, which substantially enhances signaling of truncated secretin peptides and prolongs residence time of labeled secretin up to 13-fold in a dose-dependent manner. Furthermore, we found that investigated compounds display structural similarity to positive allosteric modulators (PAMs) active at the glucagon-like peptide-1 receptor (GLP-1R), and we were able to confirm cross-recognition of that receptor by a subset of analogs. Studies using SCTR and GLP-1R mutants revealed that scaffold A, but not B and C, likely acts via two distinct mechanisms, one of which constitutes covalent modification of Cys-347^GLP-1R known from GLP-1R-selective modulators. The scaffolds identified in this study might not only serve as novel pharmacologic tools to decipher SCTR- or GLP-1R-specific signaling pathways, but also as structural leads to elucidate allosteric binding sites facilitating the future development of orally available therapeutic approaches targeting these receptors.

Development of a Testing Funnel for Identification of Small-Molecule Modulators Targeting Secretin Receptors

The secretin receptor (SCTR), a prototypical class B G protein-coupled receptor (GPCR), exerts its effects mainly by activating Gαs proteins upon binding of its endogenous peptide ligand secretin. SCTRs can be found in a variety of tissues and organs across species, including the pancreas, stomach, liver, heart, lung, colon, kidney, and brain. Beyond that, modulation of SCTR-mediated signaling has therapeutic potential for the treatment of multiple diseases, such as heart failure, obesity, and diabetes. However, no ligands other than secretin and its peptide analogs have been described to regulate SCTRs, probably due to inherent challenges in family B GPCR drug discovery. Here we report creation of a testing funnel that allowed targeted detection of SCTR small-molecule activators. Pursuing the strategy to identify positive allosteric modulators (PAMs), we established a unique primary screening assay employing a mixture of three orthosteric stimulators that was compared in a screening campaign testing 12,000 small-molecule compounds. Beyond that, we developed a comprehensive set of secondary assays, such as a radiolabel-free target engagement assay and a NanoBiT (NanoLuc Binary Technology)-based approach to detect β-arrestin-2 recruitment, all feasible in a high-throughput environment as well as capable of profiling ligands and hits regarding their effect on binding and receptor function. This combination of methods enabled the discovery of five promising scaffolds, four of which have been validated and further characterized with respect to their allosteric activities. We propose that our results may serve as starting points for developing the first in vivo active small molecules targeting SCTRs.

The Implication of Gut Hormones in the Regulation of Energy Homeostasis and Their Role in the Pathophysiology of Obesity

PURPOSE OF REVIEW

This review provides an update on the role of gut hormones and their interactions in the regulation of energy homeostasis, describes gut hormone adaptations in obesity and in response to weight loss, and summarizes the current evidence on the role of gut hormone-based therapies for obesity treatment.

RECENT FINDINGS

Gut hormones play a key role in regulating eating behaviour, energy and glucose homeostasis. Dysregulated gut hormone responses have been proposed to be pathogenetically involved in the development and perpetuation of obesity. Summarizing the major gut hormone changes in obesity, obese individuals are characterized by blunted postprandial ghrelin suppression, loss of premeal ghrelin peaks, impaired diurnal ghrelin variability and reduced fasting and postprandial levels of anorexigenic peptides. Adaptive alterations of gut hormone levels are implicated in weight regain, thus complicating hypocaloric dietary interventions, and can further explain the profound weight loss and metabolic improvement following bariatric surgery. A plethora of compounds mimicking gut hormone changes after bariatric surgery are currently under investigation, introducing a new era in the pharmacotherapy of obesity. The current trend is to combine different gut hormone receptor agonists and target multiple systems simultaneously, in order to replicate as closely as possible the gut hormone milieu after bariatric surgery and circumvent the counter-regulatory adaptive changes associated with dietary energy restriction. An increasing number of preclinical and early-phase clinical trials reveal the additive benefits obtained with dual or triple gut peptide receptor agonists in reducing body weight and improving glycaemia. Gut hormones act as potent regulators of energy and glucose homeostasis. Therapeutic strategies targeting their levels or receptors emerge as a promising approach to treat patients with obesity and hyperglycaemia.

The Fight Against Obesity Escalates: New Drugs on the Horizon and Metabolic Implications

PURPOSE OF REVIEW

There is currently a steep rise in the global prevalence of obesity. Pharmaceutical therapy is a valuable component of conservative obesity therapy. Herein, medications currently in the phase of preclinical or clinical testing are reviewed, along with an overview of the mechanisms that regulate energy intake and expenditure. In addition, the current and potential future directions of obesity drug therapy are discussed.

RECENT FINDINGS

Although the current arsenal of obesity pharmacotherapy is limited, a considerable number of agents that exert their actions through a variety of pharmacodynamic targets and mechanisms are in the pipeline. This expansion shapes a potential near future of obesity conservative management, characterized by tailored combined therapeutic regimens, targeting not only weight loss but also improved overall health outcomes. The progress regarding the elucidation of the mechanisms which regulate the bodily energy equilibrium has led to medications which mimic hormonal adaptations that follow bariatric surgery, in the quest for a "Medical bypass." These, combined with agents which could increase energy expenditure, point to a brilliant future in the conservative treatment of obesity.

The gut hormone secretin triggers a gut-brown fat-brain axis in the control of food intake

NEW FINDINGS

What is the topic of this review? Brown fat's role in meal-associated thermogenesis and the related consequences for energy balance regulation with a focus on the gut hormone secretin, which has been identified as the endocrine molecular mediator of meal-associated brown fat thermogenesis. What advances does it highlight? The finding of the secretin-induced gut-brown fat-brain axis creates new opportunities to manipulate brown fat and thereby energy balance in a natural way while living in a thermoneutral environment. The role of brown fat as a mere catabolic heater organ needs to be revised and more attention should be directed towards the regulatory role of brown fat beyond energy expenditure.

ABSTRACT

Brown fat research concentrates on the energy expenditure function of this heating organ, whereas previous evidence for a role of brown fat in regulating energy intake has been mostly neglected. Ingestion of a single mixed meal activates human brown fat thermogenesis to the same degree as cold. In mice, activation of brown fat thermogenesis with a β₃ -adrenergic receptor agonist inhibits food intake. Pharmacological β-blockade, however, inhibits neither meal-associated thermogenesis nor food intake. We recently identified the gut hormone secretin as a non-adrenergic activator of brown fat. In vivo, secretin treatment acutely increases energy expenditure and inhibits food intake in wild-type, but not in uncoupling protein 1 (UCP1)-knockout (KO) mice, which lack thermogenic brown fat function. Concurrently, secretin alters gene expression of melanocortinergic peptides of hypothalamic neurons in wild-type mice, but not UCP1-KO. Blocking endogenous secretin with a neutralizing antibody attenuates brown fat thermogenesis during refeeding, increases food intake of mice, and alters ad libitum feeding behaviour. Taken together, these findings demonstrate that secretin triggers an endocrine gut-brown adipose tissue-brain axis in the control of satiation. We hypothesize that meal-associated activation of brown adipose tissue thermogenesis induced by secretin results in a rise in brain temperature and increased melanocortinergic signalling. Taken together, brown fat is not a mere heating organ dissipating excess calories but also involved in gut-brain communication in the control of food intake.

Drug discovery approaches targeting the incretin pathway

Incretin pathway plays an important role in the development of diabetes medications. Interventions in DPP-4 and GLP-1 receptor have shown remarkable efficacy in experimental and clinical studies and imperatively become one of the most promising therapeutic approaches in the T2DM drug discovery pipeline. Herein, we analyzed the actionmechanismsof DPP-4 and GLP-1 receptor targeting the incretin pathway in T2DM treatment. We gave an insight into the structural requirements for the potent DPP-4 inhibitors and revealed a classification of DPP-4 inhibitors by stressing on the binding modes of these ligands to the enzyme. We then reviewed the drug discovery strategies for the development of peptide and non-peptide GLP-1 receptor agonists (GLP-1 RAs). Furthermore, the drug design strategies for DPP-4 inhibitors and GLP-1R agonists were detailed accurately. This review might provide an efficient evidence for the highly potent and selective DPP-4 inhibitors and the GLP-1 RAs, as novel medicines for patients suffering from T2DM.

Will medications that mimic gut hormones or target their receptors eventually replace bariatric surgery?

Bariatric surgery is currently the most effective therapeutic modality through which sustained beneficial effects on weight loss and metabolic improvement are achieved. During recent years, indications for bariatric surgery have been expanded to include cases of poorly controlled type 2 (T2DM) diabetes mellitus in lesser extremes of body weight. A spectrum of the beneficial effects of surgery is attributed to robust changes of postprandial gut peptide responses that are observed post operatively. Consolidated knowledge regarding gut peptide physiology as well as emerging new evidence shedding light on the mode of action of previously overlooked gut hormones provide appealing potential obesity and T2DM therapeutic perspectives. The accumulation of evidence from the effect of exogenous administration of native gut peptides alone or in combinations to humans as well as the development of mimetic agents exerting agonistic effects on combinations of gut hormone receptors pave the way for future integrated gut peptide-based treatments, which may mimic the effects of bariatric surgery.

The preprohormone expression profile of enteroendocrine cells following Roux-en-Y gastric bypass in rats

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) leads to rapid remission of type 2 diabetes (T2D) and sustained body weight loss, but the underlying molecular mechanisms are still not fully understood. To further elucidate these mechanisms and identify potentially novel preprohormone encoding genes with anti-diabetic and/or anti-obesity properties, we performed a comprehensive analysis of gene expression changes in enteroendocrine cells after RYGB in diet-induced obese (DIO) rats.

METHODS

The mRNA expression profiles of enteroendocrine cell enriched samples were characterized at 9, 22 and 60 days after RYGB surgery in a DIO rat model. Enteroendocrine cells were identified by chromogranin A immunohistochemistry and isolated by laser capture microdissection (LCM) from five regions covering the full rostro-caudal extension of the gastrointestinal (GI) tract. RNA sequencing and bioinformatic analyses were subsequently applied to identify differentially expressed preprohormone encoding genes.

RESULTS

From the analysis of enteroendocrine cell mRNA expression profiles, a total of 54 preprohormones encoding genes were found to be differentially regulated at one or more time-points following RYGB. These included well-known RYGB associated preprohormone genes (e.g. Gcg, Cck, Gip, Pyy and Sct) and less characterized genes with putative metabolic effects (e.g. Nmu, Guca2a, Guca2b, Npw and Adm), but also 16 predicted novel preprohormone genes. Among the list of gene transcripts, Npw, Apln and Fam3d were further validated using in situ mRNA hybridization and corresponding peptides were characterized for acute effects on food intake and glucose tolerance in mice.

CONCLUSION

We present a comprehensive mRNA expression profile of chromogranin A positive enteroendocrine cells following RYGB in rats. The data provides a region-specific characterization of all regulated preprohormone encoding genes in the rat GI tract including 16 not hitherto known. The comprehensive catalogue of preprohormone expression changes may support our understanding of hormone mediated effects of RYGB on diabetes remission and body weight reduction.

Emerging hormonal-based combination pharmacotherapies for the treatment of metabolic diseases

Obesity and its comorbidities, such as type 2 diabetes mellitus and cardiovascular disease, constitute growing challenges for public health and economies globally. The available treatment options for these metabolic disorders cannot reverse the disease in most individuals and have not substantially reduced disease prevalence, which underscores the unmet need for more efficacious interventions. Neurobiological resilience to energy homeostatic perturbations, combined with the heterogeneous pathophysiology of human metabolic disorders, has limited the sustainability and efficacy of current pharmacological options. Emerging insights into the molecular origins of eating behaviour, energy expenditure, dyslipidaemia and insulin resistance suggest that coordinated targeting of multiple signalling pathways is probably necessary for sizeable improvements to reverse the progression of these diseases. Accordingly, a broad set of combinatorial approaches targeting feeding circuits, energy expenditure and glucose metabolism in concert are currently being explored and developed. Notably, several classes of peptide-based multi-agonists and peptide-small molecule conjugates with superior preclinical efficacy have emerged and are currently undergoing clinical evaluation. Here, we summarize advances over the past decade in combination pharmacotherapy for the management of obesity and type 2 diabetes mellitus, exclusively focusing on large-molecule formats (notably enteroendocrine peptides and proteins) and discuss the associated therapeutic opportunities and challenges.

Novel GLP-1/GLP-2 co-agonists display marked effects on gut volume and improves glycemic control in mice

AIM

Analogues of several gastrointestinal peptide hormones have been developed into effective medicines for treatment of diseases such as type 2 diabetes mellitus (T2DM), obesity and short bowel syndrome (SBS). In this study, we aimed to explore whether the combination of glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) into a potent co-agonist could provide additional benefits compared to existing monotherapies.

METHODS

A short-acting (GUB09-123) and a half-life extended (GUB09-145) GLP-1/GLP-2 co-agonist were generated using solid-phase peptide synthesis and tested for effects on food intake, body weight, glucose homeostasis, and gut proliferation in lean mice and in diabetic db/db mice.

RESULTS

Sub-chronic administration of GUB09-123 to lean mice significantly reduced food intake, improved glucose tolerance, and increased gut volume, superior to monotherapy with the GLP-2 analogue teduglutide. Chronic administration of GUB09-123 to diabetic mice significantly improved glycemic control and showed persistent effects on gastric emptying, superior to monotherapy with the GLP-1 analogue liraglutide. Due to the short-acting nature of the molecule, no effects on body weight were observed, whereas a marked and robust intestinotrophic effect on mainly the small intestine volume and surface area was obtained. In contrast to GUB09-123, sub-chronic administration of a half-life extended GUB09-145 to lean mice caused marked dose-dependent effects on body weight while maintaining its potent intestinotrophic effect.

CONCLUSION

Our data demonstrate that the GLP-1/GLP-2 co-agonists have effects on gut morphometry, showing a marked increase in intestinal volume and mucosal surface area. Furthermore, effects on glucose tolerance and long-term glycemic control are evident. Effects on body weight and gastric emptying are also observed depending on the pharmacokinetic properties of the molecule. We suggest that this novel co-agonistic approach could exemplify a novel concept for treatment of T2DM or SBS.