Mono-PEGylated dimeric exendin-4 as high receptor binding and long-acting conjugates for type 2 anti-diabetes therapeutics

Customizable Click Biochemistry Strategy for the Design and Preparation of Glucagon-like Peptide-1 Conjugates and Coagonists

The development of oligomeric glucagon-like peptide-1 (GLP-1) and GLP-1-containing coagonists holds promise for enhancing the therapeutic potential of the GLP-1-based drugs for treating type 2 diabetes mellitus (T2DM). Here, we report a facile, efficient, and customizable strategy based on genetically encoded SpyCatcher-SpyTag chemistry and an inducible, cleavable self-aggregating tag (icSAT) scheme. icSAT-tagged SpyTag-fused GLP-1 and the dimeric or trimeric SpyCatcher scaffold were designed for dimeric or trimeric GLP-1, while icSAT-tagged SpyCatcher-fused GLP-1 and the icSAT-tagged SpyTag-fused GIP were designed for dual GLP-1/GIP (glucose-dependent insulinotropic polypeptide) receptor agonist. These SpyCatcher- and SpyTag-fused protein pairs were spontaneously ligated directly from the cell lysates. The subsequent icSAT scheme, coupled with a two-step standard column purification, resulted in target proteins with authentic N-termini, with yields ranging from 35 to 65 mg/L and purities exceeding 99%. In vitro assays revealed 3.0- to 4.1-fold increased activities for dimeric and trimeric GLP-1 compared to mono-GLP-1. The dual GLP-1/GIP receptor agonist exhibited balanced activity toward the GLP-1 receptor or the GIP receptor. All the proteins exhibited 1.8- to 3.0-fold prolonged half-lives in human serum compared to mono-GLP-1 or GIP. This study provides a generally applicable click biochemistry strategy for developing oligomeric or dual peptide/protein-based drug candidates.

The construction of long-acting exendin-4 analog and its hypoglycemic effect in diabetic mice

Exendin-4 is a glucagon-like polypeptide-1 (GLP-1) analog derived from lizard venom, but its short half-life affects drug administration compliance. An anti-HSA nanobody with a smaller size to guide the peptide coupling to Human Serum Albumin(HSA) in vivo may be a feasible strategy for constructing inexpensive, long-acting exendin-4 analogs. For this purpose, a fusion protein (exendin-4-(G4S)3-sdAbHSA), in which a humanized anti-HSA nanobody to the C-terminal of exendin-4 through the (Gly4Ser)3 flexible joint, was constructed. The target gene was designed according to the preferred codons and cloned into expression vector pET21b of Escherichia coli. The fusion protein could be efficiently expressed as a soluble protein, and purified to a purity over 98% by two steps of chromatography columns. In the streptozotocin-induced mouse diabetes model, the purified product had similar hypoglycemic activity as exendin-4, but dropped to the lowest value from 1 to 2 h to more than 8-10 h. The results show that this construction form does not interfere with the binding of exendin-4 to GLP-1 receptor, and can significantly prolong its half-life in vivo. This study has important reference value for constructing long-acting exendin-4 analogs and establishing efficient and green production process.

A review of recent research and development on GLP-1 receptor agonists-sustained-release microspheres

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly used in treating type 2 diabetes (T2D). However, owing to their limited oral bioavailability, most commercially available GLP-1 RAs are administered through frequent subcutaneous injections, which may result in poor patient compliance during clinical treatment. To improve patients' compliance, sustained-release GLP-1 RA-loaded microspheres have been explored. This review is an overview of recent progress and research in GLP-1 RA-loaded microspheres. First, the fabrication methods of GLP-1 RA-loaded microspheres including the coacervation method, emulsion-solvent evaporation method based on agitation, premix membrane emulsification technology, spray drying, microfluidic droplet technology, and supercritical fluid technology are summarized. Next, the strategies for maintaining GLP-1 RAs' stability and activity in microspheres by adding additives and PEGylation are reviewed. Finally, the effect of particle size, drug distribution, the internal structure of microspheres, and the hydrogel/microsphere composite strategy on improved release behavior is summarized.

Myeloid cell modulation by a GLP-1 receptor agonist regulates retinal angiogenesis in ischemic retinopathy

Ischemic retinopathies including diabetic retinopathy are major causes of blindness. Although neurons and Müller glia are recognized as important regulators of reparative and pathologic angiogenesis, the role of mononuclear phagocytes (MPs) — particularly microglia, the resident retinal immune cells — is unclear. Here, we found MP activation in human diabetic retinopathy, especially in neovessels from human neovascular membranes in proliferative retinopathy, including TNF-α expression. There was similar activation in the mouse oxygen-induced retinopathy (OIR) model of ischemia-induced neovascularization. Glucagon-like peptide-1 receptor (GLP-1R) agonists are in clinical use for glycemic control in diabetes and are also known to modulate microglia. Herein, we investigated the effect of a long-acting GLP-1R agonist, NLY01. Following intravitreal administration, NLY01 selectively localized to MPs in retina with OIR. NLY01 modulated MPs but not retinal endothelial cell viability, apoptosis, and tube formation in vitro. In OIR, NLY01 treatment inhibited MP infiltration and activation, including MP expression of cytokines in vivo. NLY01 significantly suppressed global induction of retinal inflammatory cytokines, promoted reparative angiogenesis, and suppressed pathologic retinal neovascularization. Collectively, these findings indicate the important role of mononuclear phagocytes in regulation of retinal vascularization in ischemia and suggest modulation of MPs as a potentially new treatment strategy for ischemic retinopathies.

Albumin-binding tag derived Exendin-4 analogue for treating hyperglycemia and diabetic complications

Current study was conducted to design and screen a long-lasting Exendin-4 analog for treating type 2 diabetes via the novel strategy of albumin binding combined with thrombin enzymolysis. First, a series of fusion peptides, containing different albumin-binding tags, a determinate thrombin-cleavable linker and a native Exendin-4, were prepared via chemosynthesis for in vitro and in vivo characterization. Surface plasmon resonance assay, thrombin cleavage assay and plasma stability test were performed for screening the optimal HEX peptide with enhanced albumin-binding affinity, controlled-release as well as plasma stability. The in vivo anti-diabetic efficacies of the selected candidate were further assessed via both acute and chronic pharmacodynamic evaluation in diabetic model animals. HEX15 exhibited either the highest affinity for human serum albumin or the superior in vitro stability and controlled release of Exendin-4 among 21 HEX peptides. Glucose tolerance test and hypoglycemic duration assay both revealed the notably improved the glucose tolerance and prolonged normoglycemic duration, respectively, of diabetic mice after single treatment of HEX15. Furthermore, chronic dosing of HEX15 significantly ameliorated the manifestations of diabetes in the db/db mice, including body weight, food intake, glycometabolism as well as hyperlipemia. Interestingly, combination therapy of HEX15 and long non-coding RNA-ENST00000411554 notably accelerated the wound healing and improved foot ulcer symptoms in model rats with diabetic foot ulcers. In summary, based on the strategy of linking the heptapeptide tag and thrombin-based sustained release, a long-acting Exendin-4 analog, HEX15, holds potential to be developed as a drug for ameliorating T2D as well as diabetic complications.

Design and evaluation of GLP-1 receptor G-protein biased agonist with prolonged efficacy on diabetes

AIM

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have emerged as potent drug development target for treating diabetes and obesity. Here, we designed and evaluated novel long-acting GLP-1R G protein biased agonist with potent clinical application.

MAIN METHODS

GLP-1R G-protein biased sequences were screened via a high-throughput autocrine-based strategy and then fused to Exendin (9-39). These fusion peptides were further performed with site-specific modification. Surface plasmon resonance (SPR) measurements, GLP-1R activation potencies and plasma stability tests were applied to screen optimal candidate. Acute and chronic hypoglycemic and insulinotropic activities of selected agent were evaluated in diabetic and obese rodent animals.

MAIN FINDINGS

AX09 exert highest binding affinities for GLP-1R extracellular domain (GLP-1R ECD). Further in vitro plasma stability and GLP-1R activation assays demonstrated better potency of AX18. Acute pharmacodynamic evaluation of AX18 demonstrated the promising insulinotropic and hypoglycemic activities which were exhibited in a dose-dependent manner. Prolonged hypoglycemic efficacies of AX18 were also observed in both hypoglycemic duration test and multiple oral glucose tolerance tests (OGTTs) in the diabetic mice. Further pharmacokinetic test in cynomolgus monkeys exhibited that the half-life of AX18 was more than 6 days. Once weekly treatment of AX18 in diabetic mice for 8-week achieved significantly improved %HbA1C, insulin resistance, glucose tolerance, β-cells and diabetic retinal injury. Chronic treatment of AX18 in diet-induced obese (DIO) mice also exhibited beneficial efficacies on %HbA1C, inflammation-related factors lowering, and weight gains.

CONCLUSION

AX18, as a novel GLP-1R G protein biased agonist, exhibited potency for treating diabetes mellitus and its complications.

Role of lipid nanocarriers for enhancing oral absorption and bioavailability of insulin and GLP-1 receptor agonists

Growing demand for insulin and glucagon-like peptide-1 receptor agonists (GLP-1 RA) is observed, considering the progressive nature of diabetes and the potential therapeutic role of peptides in its treatment. However, chronic parenteral administration is responsible for pain and rashes at the site of injection. Oral delivery of insulin and GLP-1 RA promises better patient compliance owing to their ease of administration and reduction in chances of peripheral hypoglycaemia and weight gain. The review article discusses the potential of lipid carriers in combination with different strategies such as absorption enhancers, PEGylation, lipidisation, etc. The lipid nanocarriers improve the membrane permeability and oral bioavailability of high molecular weight peptides. Additionally, the clinical status of different nanocarriers for anti-diabetic peptides is discussed. Previous research on nanocarriers showed significant hypoglycaemic activity and safety in animal studies; however, extrapolation of the same in human subjects is not validated. With the rising global burden of diabetes, the lipid nanocarriers show the potential to revolutionise treatment with oral delivery of insulin and GLP-1 RA.

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.

GLP-1R agonists for the treatment of obesity: a patent review (2015-present)

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) is an endogenous peptide which is secreted by enteroendocrine L cells, GLP-1 receptor agonists (GLP-1 RAs) can exhibit glucoregulation by stimulating insulin release, promote satiety, delay gastric emptying, and reduce energy intake. Liraglutide is the only GLP-1 RA approved for the treatment of obesity. The phase III clinical study of semaglutide has completed and the result showed significant weight loss effect. GLP-1 RAs have been proven to be safe and effective in clinical trials, they are considered to be promising anti-obesity drugs.

AREAS COVERED

This review provides an overview of recently published patents describing modified GLP-1 RAs, multi-agonists in the treatment or prevention of obesity from January 2015 to April 2020. Moreover, small molecule GLP-1 RAs, recombinant fusion proteins, combination of GLP-1 RAs with other drugs and the preparation of GLP-1 RAs are also covered.

EXPERT OPINION

Currently, research on anti-obesity effect of modified GLP-1 RAs has grown significantly, liraglutide accounts for approximately 56% of the global obesity drug market. Long-acting analogues and multifunctional peptides showed good weight loss activity. As more and more clinical trials are carried out, we believe that GLP-1 RAs will occupy an important position in the market of obesity treatment.

Novel mono-PEGylated dimeric GLP-1 conjugate with enhanced receptor activation and prolonged anti-diabetes efficacies

AIMS

To design and evaluate novel mono-PEGylated dimeric GLP-1 conjugate with enhanced GLP-1 receptor activation and prolonged anti-diabetes efficacies.

MAIN METHODS

All these novel GLP-1 conjugates were produced by using solid-phase synthesis method and further specific cysteine-maleimide modification. In vitro GLP-1R activation assay was performed in CHO cells stably expressing human GLP-1 receptor. The binding affinity for human serum albumin (HSA) in vitro was also conducted using surface plasmon resonance measurement. Subsequently, selected GLP-1 conjugate was subjected to evaluate the acute and chronic efficacies in vivo.

KEY FINDINGS

Four novel glucagon-like peptide-1 (GLP-1) conjugates, termed DIG-1 to DIG-4, were designed and prepared with high purity. Moreover, DIG-1(PEG-5 kDa) and DIG-2 (PEG-10 kDa) exerted ~3-fold and ~2-fold higher potencies of GLP-1R activation than native GLP-1, respectively, and both obviously higher than the DIG-3 (PEG-10 kDa) and DIG-4 (PEG-30 kDa). Then DIG-2 exhibited better in vivo glucose-stabilizing and insulinotropic efficacies than DIG-1 by using multiple oral glucose tests (OGTTs) in SD rats. Furthermore, prolonged glucose-lowering ability of DIG-2 exhibited in hypoglycemic duration test and multiple OGTTs in diabetic db/db mice. Pharmacokinetic data of DIG-2 in cynomolgus monkeys revealed a half-life of ~97.2 h and ~120.4 h after a single subcutaneous (s.c.) administration at doses of 100 and 150 nmol/kg, respectively. Chronic treatment of DIG-2 in db/db mice for consecutive 8-week significantly ameliorate the diabetic symptoms including deteriorative % hemoglobin A1C (HbA1C), glucose tolerance and pancreatic function.

SIGNIFICANCE

DIG-2, as a novel mono-PEGylated dimeric GLP-1 conjugate, holds enhanced receptor activation and prolonged anti-diabetes efficacies.

Engineering a protease-based and site-specific PEGylation-based strategy for the controlled release of exenatide

Using the commercially available antidiabetic drug exenatide (exendin-4) as a model peptide, we designed a novel exenatide derivative, termed LEX-1, comprising a 12-mer albumin-binding peptide, a protease-sensitive linker and a native exenatide. In addition, site-specific PEGylation was performed using LEX-1 as a lead sequence to generate four exenatide derivatives (LEX-2 to LEX-5). Moreover, we determined the optimal molecular weight of maleimide-derivatized PEG for the site-specific PEGylation of LEX-1 by an in vitro stability assay and an in vivo hypoglycemic efficacy test. As a result, LEX-3 (PEG10 kDa) exerted enhanced proteolytic stability, rational release rate of free exenatide and the best glucose-stabilizing capability compared with others. In addition, the prolonged hypoglycemic effects of LEX-1 and LEX-3 were demonstrated in type 2 diabetic mice by multiple OGTTs and a hypoglycemic duration test. Furthermore, a pharmacokinetic test was conducted using Sprague Dawley (SD) rats; LEX-3 (PEG10 kDa) showed the best circulating t _1/2 of ∼119.7 h for exenatide release from LEX-3, suggesting that LEX-3 has the potential to be developed into a once-weekly antidiabetic agent. The consecutive 8 week treatment of both LEX-1 and LEX-3 exhibited enhanced beneficial efficacies on body weight gain, cumulative food intake, % fat and hemoglobin A1c (HbA1c) reduction compared with exenatide treatment. Meanwhile, the chronic administration of LEX-1 and LEX-3 also effectively improved the blood biochemical indexes. Our results indicate the enhanced antidiabetic effects of LEX-1 and LEX-3, and our strategy of PEGylation and albumin conjugation can be applied to other bioactive agents.

Exendin-4 analogs in insulinoma theranostics

Insulinomas, neuroendocrine tumors arising from pancreatic beta cells, often show overexpression of the glucagon‐like peptide‐1 receptor. Therefore, imaging with glucagon‐like peptide analog exendin‐4 can be used for diagnosis and preoperative localization. This review presents an overview of the development and clinical implementation of exendin‐based tracers for nuclear imaging, and the potential use of exendin‐4 based tracers for optical imaging and therapeutic applications such as peptide receptor radionuclide therapy or targeted photodynamic therapy.

Design and characterization of novel oxyntomodulin derivatives with potent dual GLP-1/glucagon receptor activation and prolonged antidiabetic effects

AIMS

To investigate the combination of dimerization and PEGylation to enhance the receptor activation and in vivo stability of Oxyntomodulin (OXM).

MAIN METHODS

All LDM peptides were produced by using standard method of solid phase synthesis. The in vitro effects of LDM peptides were assessed by glucagon-like peptide-1 receptor (GLP-1R) and glucagon receptor (GcgR) binding test and Proteolytic stability test. Subsequently, saline, Liraglutide and three doses of LDM-3 treated groups were subjected to the evaluation of aute and long-term efficacy.

KEY FINDINGS

Five long-acting OXM conjugates, termed LDM-1 to LDM-5, were designed using cysteine (Cys)-specific modification reaction including the activated PEG, bisMal-NH₂, and OXM-Cys, and all prepared with high purity. LDM-3 exhibited greater GLP-1R and GcgR activation and ameliorative serum stability. In addition, LDM-3 was identified with enhanced insulinotropic and glycemic abilities in the gene knockout mice. The prolonged glucose-lowering effects of the LDM-3 were proved by hypoglycemic duration test and multiple oral glucose tolerance tests (OGTTs) in the diet-induced obesity (DIO) mice. Furthermore, the pharmacokinetic tests in Sprague Dawley (SD) rat and cynomolgus monkey exhibited the lifespans of LDM-3 at 90 nmol·kg^-1 were 101.5 h and 119.4 h, respectively. Nevertheless, consecutive 8-week administration of LDM-3 improved the cumulative body weight gain, food intake, % HbA1c, glucose tolerance and the pancreatic of the obese mice.

SIGNIFICANCE

LDM-3, as a dual GLP-1R and GcgR agonist, holds potential to be developed as a promising therapeutic candidate for both diabetes and obesity.

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.

Mono-PEGylates of exenatide in branched and dimeric structures can improve in vivo stability and hypoglycemic bioactivity

Exenatide, a synthetic version of exendin-4, is a glucagon-like peptide-1 receptor agonist (GLP-1RA) used for treating diabetes, but its relatively short half-life is a major disadvantage. In this study, we attempted residue-specific mono-PEGylation to the middle of the amino acid backbone to extend its in vivo half-life. Exenatide was point-mutated from Lys to Cys at the 12th residue to yield a variant (K12C), and PEG-maleimide of varying molecular weights (MW) (5, 10, 20, 40 kD) was site-specifically conjugated to yield a mono-PEGylate with branched T-shape molecular structure. In another approach, we conjugated a bis-maleimide PEG (10 kD) to the middle of two K12Cs to yield an H-shape homodimer PEGylate In vitro bioactivity assays indicated that: (1) PEGylates conjugated with higher MW PEG lead to stronger receptor binding, (2) the branched form was superior to the linear configuration in the binding, and (3) both T-shape and H-shape mono-PEGylates demonstrated better potency than the native exenatide, evidenced by lower EC₅₀. Db/db mouse experiments to evaluate in vivo hypoglycemic activity indicated that: (1) all mono-PEGylates resulted in improved glucose tolerance compared to the native exenatide, (2) the homodimer PEGylate demonstrated much stronger hypoglycemic activity, especially during the initial period, and (3) the H-shape and T-shape mono-PEGylates (40 kD) maintained hypoglycemia for up to ca. 168 and 140 h, representing approximately 12- and 14-fold increase, respectively, compared with the native exenatide. Our findings suggest that the exenatide mono-PEGylates in unclassical molecular structures can improve in vivo pharmacokinetics properties.

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.

Squalene-PEG-Exendin as High-Affinity Constructs for Pancreatic Beta-Cells

Novel drug delivery systems targeting native, transplanted, or cancerous beta-cells are of utmost importance. Herein, we present new exendin-4 derivatives with modified unnatural amino acids at strategic positions within the polypeptide sequence. The modified peptides allowed modular orthogonal chemical modifications to attach imaging agents and amphiphilic squalene-PEG groups. The resulting conjugates, SQ-PEG-ExC₁-Cy5 and SQ-PEG-ExC₄₀-Cy5 fluorescence probes, display low nanomolar affinity to GLP-1R in fluorescence-based binding assays with EC₅₀ at 1.1 ± 0.2 and 0.8 ± 0.2 nM, respectively. Naturally expressing GLP-1R MIN6 cells and recombinantly transfected CHL-GLP-1R positive cells were specifically targeted by all of the new beta-cell probes in vitro. Specific islet targeting was observed after i.v. injection of SQ-PEG-ExC₁-Cy5 with SQ-PEG in normoglycemic mice ex vivo. Semiquantitative biodistribution analysis by epifluorescence indicated prolonged blood half-life (3.8 h) for the amphiphilic Ex conjugate. Liver and pancreas were identified as main biodistribution organs for SQ-PEG-ExC₁-Cy5.

Block of A1 astrocyte conversion by microglia is neuroprotective in models of Parkinson's disease

Activation of microglia by classical inflammatory mediators can convert astrocytes to a neurotoxic A1 phenotype in a variety of neurological diseases^1,2. Development of agents that could inhibit the formation of A1 reactive astrocytes could be used to treat these diseases for which there are no disease modifying therapies. Glucagon-like peptide-1 receptor (GLP-1R) agonists have been touted as potential neuroprotective agents for neurologic disorders such as Alzheimer’s disease (AD) and Parkinson’s disease (PD)^3-13. The mechanisms by which GLP-1R agonists are neuroprotective are not known. Here we show that a potent, brain penetrant long acting GLP-1R agonist NLY01 protects against the loss of dopamine neurons and behavioral deficits in the α-synuclein preformed fibril (α-syn PFF) model of sporadic PD^14,15. NLY01 also prolongs the life and reduces the behavioral deficits and neuropathological abnormalities in the human A53T α-synuclein (hA53T) transgenic (Tg) model of α-synucleinopathy induced neurodegeneration¹⁶. We found that NLY01 is a potent GLP-1R agonist with favorable properties that is neuroprotective via the direct prevention of microglial mediated conversion of astrocytes to an A1 neurotoxic phenotype. In light of NLY01 favorable properties it should be evaluated in the treatment of PD and related neurologic disorders characterized by microglial activation.

Improving long-term subcutaneous drug delivery by regulating material-bioenvironment interaction

Subcutaneous long-acting release (LAR) formulations have been extensively developed in the clinic to increase patient compliance and reduce treatment cost. Despite preliminary success for some LAR systems, a major obstacle limiting the therapeutic effect remains on their interaction with surrounding tissues. In this review, we summarize how living bodies respond to injected or implanted materials, and highlight some typical strategies based on smart material design, which may significantly improve long-term subcutaneous drug delivery. Moreover, possible strategies to achieve ultra-long (months, years) subcutaneous drug delivery systems are proposed. Based on these discussions, we believe the well-designed subcutaneous long-acting formulations will hold great promise to improve patient quality of life in the clinic.

Xenopus-derived glucagon-like peptide-1 and polyethylene-glycosylated glucagon-like peptide-1 receptor agonists: long-acting hypoglycaemic and insulinotropic activities with potential therapeutic utilities

BACKGROUND AND PURPOSE

Incretin-based therapies based on glucagon-like peptide-1 (GLP-1) receptor agonists are effective treatments of type 2 diabetes. Abundant research has focused on the development of long-acting GLP-1 receptor agonists. However, all GLP-1 receptor agonists in clinical use or development are based on human or Gila GLP-1. We have identified a potent GLP-1 receptor agonist, xGLP-1B, based on Xenopus GLP-1.

EXPERIMENTAL APPROACH

To further modify the structure of xGLP-1B, alanine scanning was performed to study the structure -activity relationship of xGLP-1B. Two strategies were then employed to improve bioactivity. First, the C-terminal tail of lixisenatide was appended to cysteine-altered xGLP-1B analogues. Second, polyethylene glycol (PEG) chains with different molecular weights were conjugated with the peptides, giving a series of PEGylated conjugates. Comprehensive bioactivity studies of these conjugates were performed in vitro and in vivo.

RESULTS

From the in vitro receptor activation potency and in vivo acute hypoglycaemic activities of conjugates 25 -36, 33 was identified as the best candidate for further biological assessments. Conjugate 33 exhibited prominent hypoglycaemic and insulinotropic activities, as well as improved pharmacokinetic profiles in vivo. The prolonged antidiabetic duration of 33 was further confirmed by pre-oral glucose tolerance tests (OGTT) and multiple OGTT. Furthermore, chronic treatment of db/db mice with 33 ameliorated non-fasting blood glucose and insulin levels, reduced HbA1c values and normalized their impaired glucose tolerance. Importantly, no in vivo toxicity was observed in mice treated with 33.

CONCLUSIONS AND IMPLICATIONS

Peptide 33 is a promising long-acting type 2 diabetes therapeutic deserving further investigation.

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.

Quantitative Impact of Plasma Clearance and Down-regulation on GLP-1 Receptor Molecular Imaging

PURPOSE

Quantitative molecular imaging of beta cell mass (BCM) would enable early detection and treatment monitoring of type 1 diabetes. The glucagon-like peptide-1 (GLP-1) receptor is an attractive target due to its beta cell specificity and cell surface location. We quantitatively investigated the impact of plasma clearance and receptor internalization on targeting efficiency in healthy B6 mice.

PROCEDURES

Four exenatide-based probes were synthesized that varied in molecular weight, binding affinity, and plasma clearance. The GLP-1 receptor internalization rate and in vivo receptor expression were quantified.

RESULTS

Receptor internalization (54,000 receptors/cell in vivo) decreased significantly within minutes, reducing the benefit of a slower-clearing agent. The multimers and albumin binding probes had higher kidney and liver uptake, respectively.

CONCLUSIONS

Slow plasma clearance is beneficial for GLP-1 receptor peptide therapeutics. However, for exendin-based imaging of islets, down-regulation of the GLP-1 receptor and non-specific background uptake result in a higher target-to-background ratio for fast-clearing agents.

Site-specific fatty chain-modified exenatide analogs with balanced glucoregulatory activity and prolonged in vivo activity

The therapeutic utility of exenatide (Ex-4) is limited due to short plasma half-life of 2.4h and thus numerous approaches have been used to obtain a longer action time. However, such strategies often attend to one thing and lose another. The study aimed to identify a candidate with balanced glucoregulatory activity and prolonged in vivo activity. A series of fatty chain conjugates of Ex-4 were designed and synthesized. First, thirteen cysteine modified peptides (1-13) were prepared. Peptides 1, 10, and 13 showed improved glucagon-like peptide-1 (GLP-1) receptor activate potency and were thus selected for second step modifications to yield conjugates I-1-I-9. All conjugates retained significant GLP-1 receptor activate potency and more importantly exerted enhanced albumin-binding properties and in vitro plasma stability. The protracted antidiabetic effects of the most stable I-3 were further confirmed by both multiple intraperitoneal glucose tolerance test and hypoglycemic efficacies test in vivo. Furthermore, once daily injection of I-3 to streptozotocin (STZ) induced diabetic mice achieved long-term beneficial effects on hemoglobin A1C (HbA1C) lowering and glucose tolerance. Once daily injection of I-3 to diet induced obesity (DIO) mice also achieved favorable effects on food intake, body weight, and blood chemistry. Our results suggested that I-3 was a promising agent deserving further investigation to treat obesity patients with diabetes.

Phenylbutazone, a New Long-Acting Agent that can Improve the Peptide Pharmacokinetic Based on Serum Albumin as a Drug Carrier

As a NPY-2 receptor agonist, PYY24-36- Leu31 is reported to suppress appetite and has a potential in obesity treatment, but its short half-life limits the clinical application. The use of chemical modification to improve interactions with human serum albumin (HSA) is an effective strategy for prolonging the half-lives of peptide analogues. So based on the characteristics that phenylbutazone has a good combination with HSA, we selected a proper linker to link with PYY24-36 -Leu31 to create long-acting and highly biologically active PYY24-36 -Leu31 conjugates, and successfully find a novel, long-acting PYY24-36 -Leu31 conjugate 8 that, when dosed every other day in diet induce obese (DIO) mice for 2 weeks, results in a significant reduction in food intake and body weight and improvement in blood parameter and hepatic steatosis.

Chemical Conjugation of Evans Blue Derivative: A Strategy to Develop Long-Acting Therapeutics through Albumin Binding

The efficacy of therapeutic drugs is highly dependent on their optimal in vivo pharmacokinetics. Albumin conjugation is considered to be one of the most effective means of protracting the short lifespan of peptides and proteins. In this study, we proposed a novel platform for developing long lasting therapeutics by conjugating a small molecular albumin binding moiety, truncated Evans blue, to either peptides or proteins. Using the anti-diabetic peptide drug Exendin-4 as a model peptide, we synthesized a new long-acting Exendin-4 derivative (denoted as Abextide). Through complexation with albumin in situ, the biological half-life of Abextide was significantly extended. The hypoglycemic effect of Abextide was also improved remarkably over Exendin-4. Thus, Abextide has considerable potential to treat type 2 diabetes. This strategy as a general technology platform can be applied to other small molecules and biologics for the development of long-acting therapeutic drugs.

Synthetic covalently linked dimeric form of H2 relaxin retains native RXFP1 activity and has improved in vitro serum stability

Human (H2) relaxin is a two-chain peptide member of the insulin superfamily and possesses potent pleiotropic roles including regulation of connective tissue remodeling and systemic and renal vasodilation. These effects are mediated through interaction with its cognate G-protein-coupled receptor, RXFP1. H2 relaxin recently passed Phase III clinical trials for the treatment of congestive heart failure. However, its in vivo half-life is short due to its susceptibility to proteolytic degradation and renal clearance. To increase its residence time, a covalent dimer of H2 relaxin was designed and assembled through solid phase synthesis of the two chains, including a judiciously monoalkyne sited B-chain, followed by their combination through regioselective disulfide bond formation. Use of a bisazido PEG7 linker and "click" chemistry afforded a dimeric H2 relaxin with its active site structurally unhindered. The resulting peptide possessed a similar secondary structure to the native monomeric H2 relaxin and bound to and activated RXFP1 equally well. It had fewer propensities to activate RXFP2, the receptor for the related insulin-like peptide 3. In human serum, the dimer had a modestly increased half-life compared to the monomeric H2 relaxin suggesting that additional oligomerization may be a viable strategy for producing longer acting variants of H2 relaxin.

Glucagon-like peptide-1 (GLP-1) analogs: recent advances, new possibilities, and therapeutic implications

Glucagon-like peptide-1 (GLP-1) is an incretin that plays important physiological roles in glucose homeostasis. Produced from intestine upon food intake, it stimulates insulin secretion and keeps pancreatic β-cells healthy and proliferating. Because of these beneficial effects, it has attracted a great deal of attention in the past decade, and an entirely new line of diabetic therapeutics has emerged based on the peptide. In addition to the therapeutic applications, GLP-1 analogs have demonstrated a potential in molecular imaging of pancreatic β-cells; this may be useful in early detection of the disease and evaluation of therapeutic interventions, including islet transplantation. In this Perspective, we focus on GLP-1 analogs for their studies on improvement of biological activities, enhancement of metabolic stability, investigation of receptor interaction, and visualization of the pancreatic islets.

Novel coumarin modified GLP-1 derivatives with enhanced plasma stability and prolonged in vivo glucose-lowering ability

BACKGROUND AND PURPOSE

The short biological half-life limits the therapeutic use of glucagon-like peptide-1 (GLP-1) and chemical modification to improve the interaction of peptides with serum albumin represents an effective strategy to develop long-acting peptide analogues. Coumarin, a natural product, is known to bind tightly to plasma proteins and possesses many biological activities. Therefore, we designed and synthesized a series of coumarin-modified GLP-1 derivatives, hypothesizing that conjugation with coumarin would retain the therapeutic effects and prolong the biological half-life of the conjugates.

EXPERIMENTAL APPROACH

Four cysteine-modified GLP-1 analogues (1-4) were prepared using Gly8 -GLP-1(7-36)-NH2 peptide as a starting point. These analogues were conjugated with two coumarin maleimides to yield eight compounds (conjugates 6-13) for testing. Activation of human GLP-1 receptors, stability to enzymic inactivation in plasma and binding to human albumin were assessed in vitro. In vivo, effects on oral glucose tolerance tests (OGTT) in rats and on blood glucose levels in db/db mice were studied.

KEY RESULTS

Most conjugates showed well preserved receptor activation efficacy, enhanced albumin-binding properties and improved in vitro plasma stability and conjugate 7 was selected to undergo further assessment. In rats, conjugate 7 had a longer circulating t1/2 than exendin-4 or liraglutide. A prolonged antidiabetic effect of conjugate 7 was observed after OGTT in rats and a prolonged hypoglycaemic effect in db/db mice.

CONCLUSIONS AND IMPLICATIONS

Cysteine-specific coumarin conjugation with GLP-1 offers a useful approach to the development of long-acting incretin-based antidiabetic agents. Conjugate 7 is a promising long-lasting GLP-1 derivative deserving further investigation.

Biological activity studies of the novel glucagon-like peptide-1 derivative HJ07

AIM

To identify the glucose lowering ability and chronic treatment effects of a novel coumarin-glucagon-like peptide-1 (GLP-1) conjugate HJ07.

METHOD

A receptor activation experiment was performed in HEK 293 cells and the glucose lowering ability was evaluated with hypoglycemic duration and glucose stabilizing tests. Chronic treatment was performed by daily injection of exendin-4, saline, and HJ07. Body weight and HbA1c were measured every week, and an intraperitoneal glucose tolerance test was performed before treatment and after treatment.

RESULTS

HJ07 showed well-preserved receptor activation efficacy. The hypoglycemic duration test showed that HJ07 possessed a long-acting, glucose-lowering effect and the glucose stabilizing test showed that the antihyperglycemic activity of HJ07 was still evident at a predetermined time (12 h) prior to the glucose challenge (0 h). The long time glucose-lowering effect of HJ07 was better than native GLP-1 and exendin-4. Furthermore, once daily injection of HJ07 to db/db mice achieved long-term beneficial effects on HbA1c lowering and glucose tolerance.

CONCLUSION

The biological activity results of HJ07 suggest that HJ07 is a potential long-acting agent for the treatment of type 2 diabetes.

(64)Cu labeled sarcophagine exendin-4 for microPET imaging of glucagon like peptide-1 receptor expression

The Glucagon-like peptide 1 receptor (GLP-1R) has become an important target for imaging due to its elevated expression profile in pancreatic islets, insulinoma, and the cardiovascular system. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), several studies have conjugated different chelators to a more stable analog of GLP-1 (such as exendin-4) as PET or SPECT imaging agents with various advantages and disadvantages. Based on the recently developed Sarcophagin chelator, here, we describe the construction of GLP-1R targeted PET probes containing monomeric and dimeric exendin-4 subunit. The in vitro binding affinity of BarMalSar-exendin-4 and Mal2Sar-(exendin-4)2 was evaluated in INS-1 cells, which over-express GLP-1R. Mal2Sar-(exendin-4)2 demonstrated around 3 times higher binding affinity compared with BaMalSar-exendin-4. After (64)Cu labeling, microPET imaging of (64)Cu-BaMalSar-exendin-4 and (64)Cu-Mal2Sar-(exendin-4)2 were performed on subcutaneous INS-1 tumors, which were clearly visualized with both probes. The tumor uptake of (64)Cu-Mal2Sar-(exendin-4)2 was significantly higher than that of (64)Cu-BaMaSarl-exendin-4, which could be caused by polyvalency effect. The receptor specificity of these probes was confirmed by effective blocking of the uptake in both tumor and normal positive organs with 20-fold excess of unlabeled exendin-4. In conclusion, sarcophagine cage conjugated exendin-4 demonstrated persistent and specific uptake in INS-1 insulinoma model. Dimerization of exendin-4 could successfully lead to increased tumor uptake in vivo. Both (64)Cu-BaMalSar-exendin-4 and (64)Cu-Mal2Sar-(exendin-4)2 hold a great potential for GLP-1R targeted imaging.

GLP-1R-targeting magnetic nanoparticles for pancreatic islet imaging

Noninvasive assessment of pancreatic β-cell mass would tremendously aid in managing type 1 diabetes (T1D). Toward this goal, we synthesized an exendin-4 conjugated magnetic iron oxide-based nanoparticle probe targeting glucagon-like peptide 1 receptor (GLP-1R), which is highly expressed on the surface of pancreatic β-cells. In vitro studies in βTC-6, the β-cell line, showed specific accumulation of the targeted probe (termed MN-Ex10-Cy5.5) compared with nontargeted (termed MN-Cy5.5). In vivo magnetic resonance imaging showed a significant transverse relaxation time (T2) shortening in the pancreata of mice injected with the MN-Ex10-Cy5.5 probe compared with control animals injected with the nontargeted probe at 7.5 and 24 h after injection. Furthermore, ΔT2 of the pancreata of prediabetic NOD mice was significantly higher than that of diabetic NOD mice after the injection of MN-Ex10-Cy5.5, indicating the decrease of probe accumulation in these animals due to β-cell loss. Of note, ΔT2 of prediabetic and diabetic NOD mice injected with MN-Cy5.5 was not significantly changed, reflecting the nonspecific mode of accumulation of nontargeted probe. We believe our results point to the potential for using this agent for monitoring the disease development and response of T1D to therapy.

Fluorescent exendin-4 derivatives for pancreatic β-cell analysis

The ability to reliably identify pancreatic β-cells would have far reaching implications for a greater understanding of β-cell biology, measurement of β-cell mass in diabetes, islet transplantation, and drug development. The glucagon-like peptide-1 receptor (GLP1R) is highly expressed on the surface of insulin producing pancreatic β-cells. Using systematic modifications of the GLP1R ligand, exendin-4, we screened over 25 compounds and identified a palette of fluorescent exendin-4 with high GLP1R binding affinity. We show considerable differences in affinity, as well as utility of the top candidates for flow cytometry and microscopy of β-cells. Some of the developed compounds should be particularly useful for basic and translational β-cell research.

A PEGylated analog of the gut hormone oxyntomodulin with long-lasting antihyperglycemic, insulinotropic and anorexigenic activity

Peptide agonists of the glucagon-like peptide 1 (GLP-1) receptor (GLP1R) are rapidly gaining favor as antidiabetic agents, since in addition to increasing glucose-dependent insulin secretion, they also cause weight loss. Oxyntomodulin (OXM), a natural peptide with sequence homology to both glucagon and GLP-1, has glucose-lowering activity in rodents and anorectic activity in rodents and humans, but its clinical utility is limited by a short circulatory half-life due to rapid renal clearance and degradation by dipeptidyl peptidase IV (DPP-IV). Here, we describe the development of a novel DPP-IV-resistant, long-acting GLP1R agonist, based on derivatization of a suitably chosen OXM analog with high molecular weight polyethylene glycol (PEG) ('PEGylation'). PEG-OXM exerts an anti-hyperglycemic effect in diet-induced obese (DIO) mice in a glucose-dependent manner, with a maximally efficacious dose of 0.1mg/kg, and reduces food intake and body weight with a minimally efficacious dose of 1mg/kg. If this pharmacology is recapitulated in patients with type 2 diabetes, these results indicate PEG-OXM as a potential novel once-weekly GLP-1 mimetic with both glucose-lowering activity and weight loss efficacy.

Site-specific PEGylated Exendin-4 modified with a high molecular weight trimeric PEG reduces steric hindrance and increases type 2 antidiabetic therapeutic effects

The purpose of this study was to optimize an Exendin-4 (Ex4-Cys) site-specific PEGylation method with a high-molecular-weight trimeric PEG. Here, we describe the preparation of C-terminal specific PEGylated Ex4-Cys (C40-tPEG-Ex4-Cys), which was performed using cysteine and amine residue specific coupling reactions between Ex4-Cys and activated trimeric PEG. The C40-PEG-Ex4-Cys was obtained at high yields (~83%) and characterized by MALDI-TOF mass spectrometry. The receptor binding affinity of C40-PEG(5K)-Ex4-Cys was 3.5-fold higher than that of N-terminal PEGylated Ex4-Cys (N(ter)-PEG(5K)-Ex4-Cys), and receptor binding by the trimeric PEG (tPEG; 23, 50 kDa) adduct was much higher than that of branched PEG (20 kDa). Furthermore, C40-tPEG(50K)-Ex4-Cys was found to have greater blood circulating t(1/2) and AUC(inf) values than native Ex4-Cys by 7.53- and 45.61-fold, respectively. Accordingly, its hypoglycemic duration was much greater at 59.2 h than that of native Ex4-Cys at 7.3 h, with a dose of 25 nM/kg. The results of this study show that C-terminal specific PEGylation using trimeric PEG is effective when applied to Ex4-Cys and suggest that C40-tPEG(50K)-Ex4-Cys has considerable potential as a type 2 antidiabetic agent.

A site-specific PEGylated analog of exendin-4 with improved pharmacokinetics and pharmacodynamics in vivo

Objectives

Our aim was to improve the in vivo pharmacokinetics and pharmacodynamics of exendin-4 by using site-specific PEGylation.

Methods

We designed the PEGylated peptide based on its structure and activity relationship and prepared the conjugate by two steps of chromatographic purification. After obtained the conjugate we confirmed its glucose-lowering activity in normal mice and determined its half-life in SD rats. Then we evaluated its anti-diabetic activity in a multiple low-dose Streptozocin (STZ)-induced diabetic mice model.

Key findings

With the process established in this study the product conjugate was obtained with a yield of over 60% and purity of above 99%. The conjugate maintained its original conformation after modification. In SD rats its half-life was prolonged to 27.12 ± 5.75 h which was 17.61-fold longer than that of the natural exendin-4 for which the half-life was only 1.54 ± 0.47 h. Its anti-diabetic activity was significantly improved in the diabetic mice.

Conclusions

Compare with native exendin-4, the C-terminal site-specific PEGylated analog of exendin-4 obtained in this study has an improved pharmacokinetics and pharmacodynamics in vivo and could be regarded as a potential candidate for the future development of anti-diabetic drugs.