Xenopus GLP-1-inspired discovery of novel GLP-1 receptor agonists as long-acting hypoglycemic and insulinotropic agents with significant therapeutic potential

Recent advances, strategies, and future perspectives of peptide-based drugs in clinical applications

Peptide-based therapies have attracted considerable interest in the treatment of cancer, diabetes, bacterial infections, and neurodegenerative diseases due to their promising therapeutic properties and enhanced safety profiles. This review provides a comprehensive overview of the major trends in peptide drug discovery and development, emphasizing preclinical strategies aimed at improving peptide stability, specificity, and pharmacokinetic properties. It assesses the current applications and challenges of peptide-based drugs in these diseases, illustrating the pharmaceutical areas where peptide-based drugs demonstrate significant potential. Furthermore, this review analyzes the obstacles that must be overcome in the future, aiming to provide valuable insights and references for the continued advancement of peptide-based drugs.

Discovery of novel glucagon-like peptide 1/cholecystokinin 1 receptor dual agonists

The combined use of gastrointestinal hormones for treating metabolic diseases is gaining increasing attention. The potential of developing novel dual agonists targeting both cholecystokinin 1 (CCK-1) receptor and glucagon-like peptide 1 (GLP-1) receptor to improve the treatment of type 2 diabetes and obesity have not been fully explored. In this investigation, we reported a series of novel GLP-1/CCK-1 receptor co-agonists constructed by linking the C-terminus of a GLP-1 receptor agonist (bullfrog GLP-1) to the N-terminus of a CCK-1 receptor selective agonist NN9056. In comprehensive in vitro assays, these co-agonists exhibited complete agonistic potency on GLP-1 and CCK-1 receptor. Remarkably, 1f displayed superior hypoglycemic and insulinotropic effects when compared to NN9056 and semaglutide. Evaluation in Kunming and diet-induced obesity (DIO) mice unveiled significant acute and enduring hypoglycemic effects of 1f. Administration of 1f to DIO mice resulted in substantial weight loss, normalized lipid metabolism, and enhanced glucose regulation. These preclinical observations strongly advocate for the therapeutic potential CCK-1 and GLP-1 pathways could be harnessed in a single fusion peptide, yielding a promising combination therapy strategy for treating metabolic disorders.

Discovery of a potent and long-acting Xenopus GLP-1-based GLP-1/glucagon/Y2 receptor triple agonist

The combination of incretin-based therapies and PYY analogue has shown great potential for the treatment of type 2 diabetes (T2DM) and obesity. In this study we developed the first example of a unimolecular triple agonist peptide to simultaneously target GLP-1, glucagon and Y₂ receptors, aiming for superior weight loss and better glycemic control. The strategy for constructing such a unimolecular triple agonist peptide is the conjugation of the GLP-1R/GCGR dual-agonistic moiety and PYY moiety via maleimide-thiol specific reaction. A novel triple agonist peptide, 3b, was identified via stepwise structure optimization, long-acting modification and in vitro receptor screens. Peptide 3b exhibited potent and balanced GCGR and GLP-1R activities as well as potent and highly selective Y₂R activity. Peptide 3b potently reduced food intake without triggering nausea associated behavior in kaolin consumption and conditioned taste aversion assays. In diet induced obesity (DIO) mice, a lower dose of 3b achieved significantly better effects on lipid metabolism, body weight, and glycemic control than higher dose of GLP-1R mono-agonist, GLP-1R/GCGR dual agonist and GLP-1R/Y₂R dual agonist counterparts. Collectively, these data support the therapeutic potential of our GLP-1R/GCGR/Y₂R triple agonist 3b as a novel anti-obesity and anti-diabetic agent. Targeting GLP-1R, GCGR and Y₂R with unimolecular triple agonist peptide offers a route to develop new obesity and T2DM treatments.

Design of Xenopus GLP-1-Based Long-Acting Dual GLP-1/Y2 Receptor Agonists

GLP-1 receptor (GLP-1R) and neuropeptide Y₂ receptor (Y₂R) dual agonists have shown great potential to treat obesity and type 2 diabetes (T2DM). We developed a multitarget strategy to design monomeric agonists based on Xenopus GLP-1 (xGLP-1) and PYY_3-36 analogues with dual activation activities on GLP-1R and Y₂R. A novel peptide, 6q, was obtained via stepwise structure optimization and in vitro receptor screens. In db/db and diet-induced obesity (DIO) mice, 6q produced greater effects on long-term glycemic control and body weight reduction than GLP-1R and Y₂R monoagonist counterparts. Notably, in high-fat diet-induced nonalcoholic steatohepatitis (NASH) mice, 6q treatment significantly reduced hepatic triglyceride and total cholesterol levels and reversed hepatic steatosis compared with GLP-1R monoagonist (liraglutide) treatment. Collectively, these data support the therapeutic potential of our GLP-1R/Y₂R dual agonist 6q as a novel antidiabetic, antiobesity, and antisteatotic agent.

Discovery of once-weekly, peptide-based selective GLP-1 and cholecystokinin 2 receptors co-agonizts

A group of long-acting, peptide-based, and selective GLP-1R/CCK-2R dual agonizts were identified by rational design. Guided by sequence analysis, structural elements of the CCK-2R agonist moiety were engineered into the GLP-1R agonist Xenopus GLP-1, resulting in hybrid peptides with potent GLP-1R/CCK-2R dual activity. Further modifications with fatty acids resulted in novel metabolically stable peptides, among which 3d and 3 h showed potent GLP-1R and CCK-2R activation potencies and comparable stability to semaglutide. In food intake tests, 3d and 3 h also showed a potent reduction in food intake, superior to that of semaglutide. Moreover, the acute hypoglycemic and insulinotropic activities of 3d and 3 h were better than that of semaglutide and ZP3022. Importantly, the limited pica response following 3d and 3 h administration in SD rats preliminarily indicated that the food intake reduction effects of 3d and 3 h are independent of nausea/vomiting. In a 35-day study in db/db mice, every two days administration of 3d and 3 h increased islet areas and numbers, insulin contents, β-cell area, β-cell proliferation, as well as improved glucose tolerance, and decreased HbA1c, to a greater extent than ZP3022 and semaglutide. In a 21-day study in DIO mice, once-weekly administration of 3d and 3 h significantly induced body weight loss, improved glucose tolerance, and normalized lipid metabolism, to a greater extent than semaglutide. The current study showed the antidiabetic and antiobesity potentials of GLP-1R/CCK-2R dual agonizts that warrant further investigation.

A GLP-1/glucagon/CCK-2 receptors tri-agonist provides new therapy for obesity and diabetes

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 receptor (GLP-1R) and glucagon receptor (GCGR) dual agonists have exerted promising therapeutic effects for the treatment of obesity and diabetes in clinical development. Moreover, GLP-1R and cholecystokinin 2 receptor (CCK-2R) dual agonists have been shown to restore pancreas function and improve glycemic control in many preclinical studies. In the present study, we describe for the first time that the beneficial effects of GLP-1R/GCGR and GLP-1R/CCK-2R dual agonists can be integrated into one peptide, resulting in significant anti-diabetes and anti-obesity effectiveness.

EXPERIMENTAL APPROACH

The in vitro potency of a novel GLP-1R/GCGR/CCK-2R tri-agonist (xGLP/GCG/gastrin) against GLP-1R, GCGR, CCK-1R and CCK-2R was determined on cells expressing the corresponding receptors by cAMP accumulation or ERK1/2 phosphorylation assays. The in vivo anti-diabetes and anti-obesity effects of xGLP/GCG/gastrin were studied in both db/db and diet induced obesity (DIO) mice.

KEY RESULTS

xGLP/GCG/gastrin was a potent and selective GLP-1R, GCGR, and CCK-2R tri-agonist. In DIO mice, the metabolic benefits of xGLP-1/GCG/gastrin such as reduction of body weight and hepatic lipid contents were significantly better than those of ZP3022 (GLP-1R/CCK-2R dual agonist) and liraglutide. In the short term study in db/db mice, xGLP/GCG/gastrin treatment exerted considerable effects on increasing islet numbers, islet areas, and insulin content. In the long-term treatment study in db/db mice, xGLP-1/GCG/gastrin displayed a significantly sustained improvement in glucose tolerance and glucose control compared with those of liraglutide, ZP3022, cotadutide (GLP-1R/GCGR dual agonist), and xGLP/GCG-15.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate the therapeutic promise of xGLP-1/GCG/gastrin for obesity and diabetes.

Stapled, Long-Acting Xenopus GLP-1-Based Dual GLP-1/Glucagon Receptor Agonists with Potent Therapeutic Efficacy for Metabolic Disease

Novel peptidic glucagon receptor (GCGR) and glucagon-like peptide 1 receptor (GLP-1R) dual agonists are reported to have increased efficacy over GLP-1R monoagonists for the treatment of diabetes and obesity. We identified a novel Xenopus GLP-1-based dual GLP-1R/GCGR agonist (xGLP/GCG-13) designed with a proper activity ratio favoring the GLP-1R versus the GCGR. However, the clinical utility of xGLP/GCG-13 is limited by its short in vivo half-life. Starting from xGLP/GCG-13, dual Cys mutation was performed, followed by covalent side-chain stapling and serum albumin binder incorporation, resulting in a stabilized secondary structure, enhanced agonist potency at GLP-1R and GCGR, and improved stability. The lead peptide 2c (stapled xGLP/GCG-13 analogue with a palmitic acid albumin binder) exhibits balanced GLP-1R and GCGR activations and potent, long-lasting effects on in vivo glucose control. 2c was further explored pharmacologically in diet-induced obesity and db/db rodent models. Chronic administration of 2c potently induced body weight loss and hypoglycemic effects, improved glucose tolerance, increased energy expenditure, and normalized lipid metabolism and adiposity in relevant animal models. These results indicated that 2c has potential for development as a novel antidiabetic and/or antiobesity drug. Furthermore, we propose that the incorporation of a proper serum protein-binding motif into a di-Cys staple is an effective method for improving the stabilities and bioactivities of peptides. This approach is likely applicable to other therapeutic peptides, such as glucose-dependent insulin-tropic peptide receptor (GIPR) and GLP-1R dual agonists or GLP-1R/GCGR/GIPR triagonists.

Design of novel Xenopus GLP-1-based dual glucagon-like peptide 1 (GLP-1)/glucagon receptor agonists

Dual activation of the glucagon receptor (GCGR) and glucagon-like peptide 1 receptor (GLP-1R) has the potential to lead to an effective therapy for the treatment of diabetes and obesity. Here, we report the discovery of a series of peptides with dual activity on GLP-1R and GCGR that were discovered by rational design. Structural elements of oxyntomodulin (OXM), glucagon or exendin-4 were engineered into the selective GLP-1R agonist Xenopus GLP-1 (xGLP-1) on the basis of sequence analysis, resulting in hybrid peptides with potent dual activity at GLP-1R and GCGR. Further modifications with fatty acid resulted in a novel metabolically stable peptide (xGLP/GCG-15) with enhanced and balanced GLP-1R and GCGR activations. This lead peptide was further explored pharmacologically in both db/db and diet-induced obesity (DIO) rodent models. Chronic administration of xGLP/GCG-15 significantly induced hypoglycemic effects and body weight loss, improved glucose tolerance, and normalized lipid metabolism, adiposity, and liver steatosis in relevant rodent models. These preclinical studies suggest that xGLP/GCG-15 has potential for development as a novel anti-obesity and/or anti-diabetic candidate. Considering the equal effects of xGLP/GCG-15 and the clinical candidate MEDI0382 on reverse hepatic steatosis, it may also be explored as a new therapy for nonalcoholic steatohepatitis (NASH) in the future.

Stapled and Xenopus Glucagon-Like Peptide 1 (GLP-1)-Based Dual GLP-1/Gastrin Receptor Agonists with Improved Metabolic Benefits in Rodent Models of Obesity and Diabetes

Diabetes is characterized by pancreas dysfunction and is commonly associated with obesity. Hypoglycemic agents capable of improving β-cell function and reducing body weight therefore are gaining increasing interest. Though glucagon-like peptide 1 receptor (GLP-1R)/cholecystokinin 2 receptor (CCK-2R) dual agonist ZP3022 potently increases β-cell mass and improves glycemic control in diabetic db/db mice, the in vivo half-life (t_1/2) is short, and its body weight reducing activity is limited. Here, we report the discovery of a series of novel GLP-1R/CCK-2R dual agonists. Starting from Xenopus GLP-1, dual cysteine mutation was conducted followed by covalent side chain stapling and albumin binder incorporation, resulting in a stabilized secondary structure, increased agonist potency, and improved stability. Further C-terminal conjugation of gastrin-6 generated GLP-1R/CCK-2R dual agonists, among which 6a and 6b showed higher stability and hypoglycemic activity than liraglutide and ZP3022. Desirably, 6a and 6b exhibited prominent metabolic benefits in diet-induced obesity mice without causing nausea responses and exerted considerable effects on β-cell restoration in db/db mice. These preclinical studies suggest the potential role of GLP-1R/CCK-2R dual agonists as effective agents for treating diabetes and related metabolic disorders.

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.

Discovery of lixisenatide analogues as long-acting hypoglycemic agents using novel peptide half-life extension technology based on mycophenolic acid

Noncovalent binding of peptides to human serum albumin protects against renal clearance and enzymatic degradation. Herein, we investigated the effect of mycophenolic acid (MPA) albumin binders for improving the stability of peptides. For proof-of-principle, the short acting glucagon-like peptide-1 (GLP-1) receptor agonist lixisenatide was selected and functionalized with different MPA albumin binders. In vitro, all lixisenatide analogues showed well preserved GLP-1 receptor activation potency. High performance affinity chromatography (HPAC) and ultrafiltration analyses indicated that DiMPA was able to confer high albumin affinity to lixisenatide and revealed that affinity is increased for DiMPA modified lixisenatide analogues containing OEG spacers. In db/db mice, the selected peptide 2c showed comparable efficacies to lixisenatide with respect to glucose-lowering and insulinotropic activities. Furthermore, the duration of action of glucose homeostasis of 2c was comparable to semaglutide in db/db mice. Importantly, DiMPA albumin binder did not bring significant toxicity of lixisenatide, as reflected by the comparable toxicity indexes in 2c and semaglutide groups after 2 weeks dosing in normal Kunming mice. Short-term study (21 days) conducted on db/db mice showed the better therapeutic efficacies of 2c than semaglutide on pancreas islets protection. Importantly, in chronic studies (84 days) on db/db mice, 2c exhibited a sustained improvement in glycaemic control, to a greater extent than that of semaglutide. Thus, we propose DiMPA modification as a novel and general method for development of long-acting GLP-1 receptor agonists for type 2 diabetes treatments, and 2c as a promising antidiabetic candidate.

DiMPA albumin binders were effectively applied to lixisenatide to make 2c as a long-acting antidiabetic agent.

Novel mono-lipidated dimeric glucagon-like peptide-1 receptor agonist with improved long-acting and hypoglycemic activity

Dimerization is a useful tool to boost ligand–receptor interaction. Both lipidation and dimerization effectively prolong the short half-life (t_1/2) of peptides by facilitating binding with serum albumin and increasing hydrodynamic size. Here, we described two novel GLP-1 conjugates with high glucagon-like peptide-1 (GLP-1) receptor activation potencies, dimerized GLP-1 (Di-GLP-1) and lipidated Di-GLP-1 (Lip-Di-GLP-1). Di-GLP-1 and Lip-Di-GLP-1 were prepared through cysteine–maleimide specific coupling reactions using Gly₈-Cys₃₁-GLP-1, bis-maleimide amine, and activated palmitic acid. The receptor activation potencies of Di-GLP-1 and Lip-Di-GLP-1 were 13.6-fold and 9.5-fold higher than GLP-1, respectively. The in vivo hypoglycemic and insulinotropic activities of Di-GLP-1 and Lip-Di-GLP-1 were also better than GLP-1 in db/db mice. Furthermore, Lip-Di-GLP-1 was found to have greater circulating t_1/2 than synthesized liraglutide by 1.8-fold. Accordingly, the improved pharmacokinetic profiles of Lip-Di-GLP-1 resulted in protracted antidiabetic effects as confirmed by hypoglycemic duration test. Moreover, Lip-Di-GLP-1 administered in mice potently inhibits gastric emptying and reduce food intake. Chronic Lip-Di-GLP-1 treatment in db/db mice resulted in significant improvements in food intake, body weight, pancreatic function and corrected hyperglycemia, which was more effective than synthesized liraglutide. Our research indicated that combined dimerization and lipidation were effectively applied to GLP-1, and the preclinical results suggested the potential usage of Lip-Di-GLP-1 as a long-acting antidiabetic agent.

Dimerization and lipidation were effectively applied to GLP-1 to make Lip-Di-GLP-1 as a long-acting antidiabetic agent.

Synthesis and pharmaceutical characterization of site specific mycophenolic acid-modified Xenopus glucagon-like peptide-1 analogs

To develop novel long-acting antidiabetic agents, mycophenolic acid (MPA) was used to modify Xenopus glucagon-like peptide-1 analog (GLP-1) (1) at three Lys residues through a γ-glutamyl linker. Similarly, 6-aminocaproic acid and 12-aminolauric acid with different lengths of fatty chain were used as MPA derivatives which were then conjugated with 1. By using proper protection and deprotection strategies, the synthetic process was completed directly on the resin to minimize the side reactions, and nine MPA-modified 1 derivatives (2a-2i) were obtained. Compounds 2b and 2c, which showed high GLP-1 receptor activation potencies and glucose lowering activities, were selected for further C-terminal modification to improve their stabilities and bioactivities, giving compounds 3a-3d. The receptor activation potencies and hypoglycemic activities of 3a-3d were comparable to that of liraglutide. Physicochemical and in vitro stability tests revealed that MPA conjugation led to enhanced albumin binding abilities as reflected by the improved stabilities of 3a-3d. In particular, at a dose of 25 nmol kg^-1, the in vivo antidiabetic and insulinotropic activities of 3d were comparable to those of semaglutide. Finally, long-term administration of 3d achieved beneficial effects on glucose tolerance normalization and glycated hemoglobin (HbA1c) lowering, and no hepatotoxicity was observed. In conclusion, this research demonstrated that MPA derivatization was a practical way to develop long-acting antidiabetic peptides.