Taspoglutide, an analog of human glucagon-like Peptide-1 with enhanced stability and in vivo potency

Deciphering the conformational landscape of few selected aromatic noncoded amino acids (NCAAs) for applications in rational design of peptide therapeutics

Amino acids are the essential building blocks of both synthetic and natural peptides, which are crucial for biological functions and also important as biological probes for mapping the complex protein-protein interactions (PPIs) in both prokaryotic and eukaryotic systems. Mapping the PPIs through the chemical biology approach provides pharmacologically relevant peptides, which can have agonistic or antagonistic effects on the targeted biological systems. It is evidenced that ≥ 60 peptide-based drugs have been approved by the US-FDA so far, and the number will improve further in the foreseeable future, as ≥ 140 peptides are currently in clinical trials. However, natural peptides often require fine-tuning of their pharmacological properties by strategically replacing the α_L-amino acids of the peptides with non-coded amino acids (NCAA), for which codons are absent in the genetic code for biosynthesis of proteins, prior to their applications as therapeutics. Considering the diverse repertoire of the NCAAs, the conformational space of many NCAAs is yet to be explored systematically in the context of the rational design of therapeutic peptides. The current study deciphers the conformational landscape of a few such Cα-substituted aromatic NCAAs (Ing: 2-indanyl-L-Glycine; Bpa: 4-benzoyl-L-phenylalanine; Aic: 2-aminoindane-2-carboxylic acid) both in the context of tripeptides and model synthetic peptide sequences, using alanine (Ala) and proline (Pro) as the reference. The combined data obtained from the computational and biophysical studies indicate the general success of this approach, which can be exploited further to rationally design optimized peptide sequences of unusual architecture with potent antimicrobial, antiviral, gluco-regulatory, immunomodulatory, and anti-inflammatory activities.

Prevention of diabetes-associated fibrosis: Strategies in FcRn-targeted nanosystems for oral drug delivery

Diabetes mellitus is a chronic disease with an elevated risk of micro- and macrovascular complications, such as fibrosis. To prevent diabetes-associated fibrosis, the symptomatology of diabetes must be controlled, which is commonly done by subcutaneous injection of antidiabetic peptides. To minimize the pain and distress associated with such injections, there is an urgent need for non-invasive oral transmucosal drug delivery strategies. However, orally administered peptide-based drugs are exposed to harsh conditions in the gastrointestinal tract and poorly cross the selective intestinal epithelium. Thus, targeting of drugs to receptors expressed in epithelial cells, such as the neonatal Fc receptor (FcRn), may therefore enhance uptake and transport through mucosal barriers. This review compiles how in-depth studies of FcRn biology and engineering of receptor-binding molecules may pave the way for design of new classes of FcRn-targeted nanosystems. Tailored strategies may open new avenues for oral drug delivery and provide better treatment options for diabetes and, consequently, fibrosis prevention.

Structure and dynamics of semaglutide- and taspoglutide-bound GLP-1R-Gs complexes

The glucagon-like peptide-1 receptor (GLP-1R) regulates insulin secretion, carbohydrate metabolism, and appetite and is an important target for treatment of type 2 diabetes and obesity. Multiple GLP-1R agonists have entered into clinical trials, with some, such as semaglutide, progressing to approval. Others, including taspoglutide, failed due to the high incidence of side effects or insufficient efficacy. GLP-1R agonists have a broad spectrum of signaling profiles, but molecular understanding is limited by a lack of structural information on how different agonists engage with the GLP-1R. Here, we report cryoelectron microscopy (cryo-EM) structures and cryo-EM 3D variability analysis of semaglutide- and taspoglutide-bound GLP-1R-Gs protein complexes. These reveal similar peptide interactions to GLP-1 but different motions within the receptor and bound peptides, providing insights into the molecular determinants of GLP-1R peptide engagement.

A Non-Perturbative Molecular Grafting Strategy for Stable and Potent Therapeutic Peptide Ligands

The gut-derived incretin hormone, glucagon-like peptide-1 (GLP1), plays an important physiological role in attenuating post-prandial blood glucose excursions in part by amplifying pancreatic insulin secretion. Native GLP1 is rapidly degraded by the serine protease, dipeptidyl peptidase-4 (DPP4); however, enzyme-resistant analogues of this 30-amino-acid peptide provide an effective therapy for type 2 diabetes (T2D) and can curb obesity via complementary functions in the brain. In addition to its medical relevance, the incretin system provides a fertile arena for exploring how to better separate agonist function at cognate receptors versus susceptibility of peptides to DPP4-induced degradation. We have discovered that novel chemical decorations can make GLP1 and its analogues completely DPP4 resistant while fully preserving GLP1 receptor activity. This strategy is also applicable to other therapeutic ligands, namely, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-2 (GLP2), targeting the secretin family of receptors. The versatility of the approach offers hundreds of active compounds based on any template that target these receptors. These observations should allow for rapid optimization of pharmacological properties and because the appendages are in a position crucial to receptor stimulation, they proffer the possibility of conferring "biased" signaling and in turn minimizing side effects.

Impact of non-proteinogenic amino acids in the discovery and development of peptide therapeutics

With the development of modern chemistry and biology, non-proteinogenic amino acids (NPAAs) have become a powerful tool for developing peptide-based drug candidates. Drug-like properties of peptidic medicines, due to the smaller size and simpler structure compared to large proteins, can be changed fundamentally by introducing NPAAs in its sequence. While peptides composed of natural amino acids can be used as drug candidates, the majority have shown to be less stable in biological conditions. The impact of NPAA incorporation can be extremely beneficial in improving the stability, potency, permeability, and bioavailability of peptide-based therapies. Conversely, undesired effects such as toxicity or immunogenicity should also be considered. The impact of NPAAs in the development of peptide-based therapeutics is reviewed in this article. Further, numerous examples of peptides containing NPAAs are presented to highlight the ongoing development in peptide-based therapeutics.

Hydrocarbon-Stitched Peptide Agonists of Glucagon-Like Peptide-1 Receptor

Glucagon-like peptide 1 (GLP-1) is a natural peptide agonist of the GLP-1 receptor (GLP-1R) found on pancreatic β-cells. Engagement of the receptor stimulates insulin release in a glucose-dependent fashion and increases β-cell mass, two ideal features for pharmacologic management of type 2 diabetes. Thus, intensive efforts have focused on developing GLP-1-based peptide agonists of GLP-1R for therapeutic application. A primary challenge has been the naturally short half-life of GLP-1 due to its rapid proteolytic degradation in vivo. Whereas mutagenesis and lipidation strategies have yielded clinical agents, we developed an alternative approach to preserving the structure and function of GLP-1 by all-hydrocarbon i, i + 7 stitching. This particular "stitch" is especially well-suited for reinforcing and protecting the structural fidelity of GLP-1. Lead constructs demonstrate striking proteolytic stability and potent biological activity in vivo. Thus, we report a facile approach to generating alternative GLP-1R agonists for glycemic control.

Glucagon-Like Peptide-1 Receptor Agonists and Strategies To Improve Their Efficiency

Type 2 diabetes mellitus (T2DM) is increasing in global prevalence and is associated with serious health problems (e.g., cardiovascular disease). Various treatment options are available for T2DM, including the incretin hormone glucagon-like peptide-1 (GLP-1). GLP-1 is a therapeutic peptide secreted from the intestines following food intake, which stimulates the secretion of insulin from the pancreas. The native GLP-1 has a very short plasma half-life, owning to renal clearance and degradation by the enzyme dipeptidyl peptidase-4. To overcome this issue, various GLP-1 agonists with increased resistance to proteolytic degradation and reduced renal clearance have been developed, with several currently marketed. Strategies, such as controlled release delivery systems, methods to reduce renal clearance (e.g., PEGylation and conjugation to antibodies), and methods to improve proteolytic stability (e.g., stapling, cyclization, and glycosylation) provide means to further improve the ability of GLP-1 analogs. These will be discussed in this literature review.

GLP-1RAs in type 2 diabetes: mechanisms that underlie cardiovascular effects and overview of cardiovascular outcome data

Patients with type 2 diabetes (T2DM) have a substantial risk of developing cardiovascular disease. The strong connection between the severity of hyperglycaemia, metabolic changes secondary to T2DM and vascular damage increases the risk of macrovascular complications. There is a challenging demand for the development of drugs that control hyperglycaemia and influence other metabolic risk factors to improve cardiovascular outcomes such as cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, hospitalization for unstable angina and heart failure (major adverse cardiovascular events). In recent years, introduction of the new drug class of glucagon-like peptide-1 receptor agonists (GLP-1RAs) has changed the treatment landscape as GLP-1RAs have become well-established therapies in T2DM. The benefits of GLP-1RAs are derived from their pleiotropic effects, which include appetite control, glucose-dependent secretion of insulin and inhibition of glucagon secretion. Importantly, their beneficial effects extend to the cardiovascular system. Large clinical trials have evaluated the cardiovascular effects of GLP-1RAs in patients with T2DM and elevated risk of cardiovascular disease and the results are very promising. However, important aspects still require elucidation, such as the specific mechanisms involved in the cardioprotective effects of these drugs. Careful interpretation is necessary because of the heterogeneity across the trials concerning the definition of cardiovascular risk or cardiovascular disease, baseline characteristics, routine care and event rates. The aim of this review is to describe the main clinical aspects of the GLP-1RAs, compare them using data from both the mechanistic and randomized controlled trials and discuss potential reasons for improved cardiovascular outcomes observed in these trials. This review may help clinicians to decide which treatment is most appropriate in reducing cardiovascular risk in patients with T2DM.

Battle of GLP-1 delivery technologies

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) belong to an important therapeutic class for treatment of type 2 diabetes. Six GLP-1 RAs, each utilizing a unique drug delivery strategy, are now approved by the Food and Drug Administration (FDA) and additional, novel GLP-1 RAs are still under development, making for a crowded marketplace and fierce competition among the manufacturers of these products. As rapid elimination is a major challenge for clinical application of GLP-1 RAs, various half-life extension strategies have been successfully employed including sequential modification, attachment of fatty-acid to peptide, fusion with human serum albumin, fusion with the fragment crystallizable (Fc) region of a monoclonal antibody, sustained drug delivery systems, and PEGylation. In this review, we discuss the scientific rationale of the various half-life extension strategies used for GLP-1 RA development. By analyzing and comparing different approved GLP-1 RAs and those in development, we focus on assessing how half-life extending strategies impact the pharmacokinetics, pharmacodynamics, safety, patient usability and ultimately, the commercial success of GLP-1 RA products. We also anticipate future GLP-1 RA development trends. Since similar drug delivery strategies are also applied for developing other therapeutic peptides, we expect this case study of GLP-1 RAs will provide generalizable concepts for the rational design of therapeutic peptides products with extended duration of action.

Recent Advances in GLP-1 Receptor Agonists for Use in Diabetes Mellitus

Preclinical Research Mimetics of Glucagon-like peptide 1 (GLP-1) represent a useful alternative or complementary treatment choice to insulin in the treatment of diabetes mellitus. The lack of hypoglycemia as a side effect when GLP-1 receptor agonists are used along with the tendency of these therapeutic agents to prevent or even reduce weight gain makes them valuable targets in therapy development. However, native GLP-1 and many of its early analogues have very short half-lives, requiring repeated treatment to maintain therapeutic levels. As all current treatments are injected subcutaneously, a large focus has been made on trying to extend the half-lives of GLP-1 analogues while retaining bioactivity. Most success in this regard has been achieved with the use of peptide-protein fusions, which are not as well suited for oral administration. However, recent work focused on the development of non-fusion peptides with increased half-lives that may be more appropriate for oral administration. This minireview discusses the structural characteristics of past and present analogues as well as the recent work conducted toward developing novel GLP-1 receptor agonists. Drug Dev Res 78 : 292-299, 2017. © 2017 Wiley Periodicals, Inc.

Gold nanoparticles as an efficient drug delivery system for GLP-1 peptides

In this work, the potential application of gold nanoparticles for GLP-1 analogues delivery was studied. For this purpose, the original sequence of the incretin GLP-1 was slightly modified in the C-terminal region by adding a cysteine residue to facilitate conjugation to the gold surface. The interaction between peptides and gold nanoparticles and also the colloid stability of the conjugates were studied by UV-vis spectrophotometry, TEM, IR and XPS spectroscopy. Moreover, the permeability of these conjugates was assayed using a Caco-2/goblet monolayer model. On the basis of the stability and permeability results, one of the conjugates was chosen to be administered intraperitoneally to normoglycemic rats. The intraperitoneal delivery of the GLP-1 analogue using gold nanoparticles led to decrease levels of blood glucose in the same way as native GLP-1, thereby demonstrating that the formulation of the analogue is stable in physiological conditions and maintains the activity of this incretin.

Effect of varying degrees of renal impairment on the pharmacokinetics and tolerability of taspoglutide

AIM

To evaluate single-dose pharmacokinetics and tolerability of taspoglutide in people with varying degrees of renal impairment and matched healthy participants.

METHODS

Participants in the present study were people with mild renal impairment (n = 10), moderate impairment (n = 10), severe impairment (n = 9), and a matched healthy control group (n = 10). Participants received a single subcutaneous injection of taspoglutide (10 mg) on day 1. Plasma and urine drug concentration, antibody formation, vital signs, ECGs and routine laboratory variables were measured frequently and adverse events (AEs) were monitored for 9 weeks.

RESULTS

Taspoglutide exposure was higher among participants with moderate and severe renal impairment compared with participants with normal renal function. Mean AUC_last was 13% and 38% higher in participants with moderate and severe renal impairment, respectively compared with participants with normal renal function. Likewise, mean peak plasma concentration (C_max ) was 57% and 93% higher in participants with moderate and severe renal function impairment, respectively, compared with participants with normal renal function. Linear regression analyses showed a statistically significant inverse relationship between taspoglutide exposure parameters (AUC and C_max ) and creatinine clearance. Higher incidences of gastrointestinal (GI) AEs were reported in participants with severe renal impairment.

CONCLUSION

Renal impairment altered the pharmacokinetics of taspoglutide. The degree of renal impairment was associated with an increased exposure to taspoglutide and an increased risk of GI AEs.

Review of head-to-head comparisons of glucagon-like peptide-1 receptor agonists

Currently, six glucagon-like peptide-1 receptor agonists (GLP-1RAs) are approved for treating type 2 diabetes. These fall into two classes based on their receptor activation: short-acting exenatide twice daily and lixisenatide once daily; and longer-acting liraglutide once daily, exenatide once weekly, albiglutide once weekly and dulaglutide once weekly. The phase III trial of a seventh GLP-1RA, taspoglutide once weekly, was stopped because of unacceptable adverse events (AEs). Nine phase III head-to-head trials and one large phase II study have compared the efficacy and safety of these seven GLP-1RAs. All trials were associated with notable reductions in glycated haemoglobin (HbA1c) levels, although liraglutide led to greater decreases than exenatide formulations and albiglutide, and HbA1c reductions did not differ between liraglutide and dulaglutide. As the short-acting GLP-1RAs delay gastric emptying, they have greater effects on postprandial glucose levels than the longer-acting agents, whereas the longer-acting compounds reduced plasma glucose throughout the 24-h period studied. Liraglutide was associated with weight reductions similar to those with exenatide twice daily but greater than those with exenatide once weekly, albiglutide and dulaglutide. The most frequently observed AEs with GLP-1RAs were gastrointestinal disorders, particularly nausea, vomiting and diarrhoea. Nauseaoccurred less frequently, however, with exenatide once weekly and albiglutide than exenatide twice daily and liraglutide. Both exenatide formulations and albiglutide may be associated with higher incidences of injection-site reactions than liraglutide and dulaglutide. GLP-1RA use in clinical practice should be customized for individual patients, based on clinical profile and patient preference. Ongoing assessments of novel GLP-1RAs and delivery methods may further expand future treatment options.

Controlled release of biologics for the treatment of type 2 diabetes

Type 2 diabetes is a rapidly growing disease that poses a significant burden to the United States healthcare system. Despite the many available treatments for the disease, close to half of diagnosed type 2 diabetes cases are not properly managed, largely due to inadequate patient adherence to prescribed treatment regimens. Methods for improving delivery - and thereby easing administration - of type 2 drugs have the potential to greatly improve patient health. This review focuses on two peptide drugs - insulin and glucagon-like peptide 1 (GLP-1) - for treatment of type 2 diabetes. Peptide drugs offer the benefits of high potency and specificity but pose a significant delivery challenge due to their inherent instability and short half-life. The development of insulin and GLP-1 analogs highlights the broad spectrum of drug delivery strategies that have been used to solve these problems. Numerous structural modifications and formulations have been introduced to optimize absorption, residence time, stability, route of delivery and frequency of administration. Continual improvements in delivery methods for insulin and GLP-1 receptor agonists are paving the way towards better patient compliance and improved disease management, and thereby enhanced patient quality of life.

Incretin-like effects of small molecule trace amine-associated receptor 1 agonists

Objective

Type 2 diabetes and obesity are emerging pandemics in the 21st century creating worldwide urgency for the development of novel and safe therapies. We investigated trace amine-associated receptor 1 (TAAR1) as a novel target contributing to the control of glucose homeostasis and body weight.

Methods

We investigated the peripheral human tissue distribution of TAAR1 by immunohistochemistry and tested the effect of a small molecule TAAR1 agonist on insulin secretion in vitro using INS1E cells and human islets and on glucose tolerance in C57Bl6, and db/db mice. Body weight effects were investigated in obese DIO mice.

Results

TAAR1 activation by a selective small molecule agonist increased glucose-dependent insulin secretion in INS1E cells and human islets and elevated plasma PYY and GLP-1 levels in mice. In diabetic db/db mice, the TAAR1 agonist normalized glucose excursion during an oral glucose tolerance test. Sub-chronic treatment of diet-induced obese (DIO) mice with the TAAR1 agonist resulted in reduced food intake and body weight. Furthermore insulin sensitivity was improved and plasma triglyceride levels and liver triglyceride content were lower than in controls.

Conclusions

We have identified TAAR1 as a novel integrator of metabolic control, which acts on gastrointestinal and pancreatic islet hormone secretion. Thus TAAR1 qualifies as a novel and promising target for the treatment of type 2 diabetes and obesity.

•

TAAR1 is a novel key player in metabolic control.

•

TAAR1 is expressed in β-cells and intestinal enteroendocrine cells in mice and humans.

•

TAAR1 agonist improved glucose tolerance and reduced body weight in mouse disease models.

Utilization of model-based meta-analysis to delineate the net efficacy of taspoglutide from the response of placebo in clinical trials

The objective of this study was to develop quantitative models to delineate the net efficacy of taspoglutide on fasting plasma glucose (FPG) and glycosylated hemoglobin (HbA1c) from the response of placebo in type 2 diabetes patients, and further find pharmacodynamic potency of taspoglutide and FPG for half of maximum reduction responses of FPG and HbA1c, respectively. Several PD data about taspoglutide treatments for type 2 diabetes patients were digitalized from the published papers related with the clinical development of taspoglutide. The model based meta-analysis (MBMA) studies for FPG and HbA1c were performed with Monolix 4.2 software. The MBMA successfully described the effects of placebo and taspoglutide on pharmacological indexes of FPG and HbA1c through mono and multiple combination therapies in clinical trials. The pharmacodynamic potency (25.3 pmol/l) produced 50% of maximum responses of FPG (−2.39 mmol/l) from the responses of placebo for FPG (−0.371 mmol/l); the response change of FPG (−1.81 mmol/l) affected 50% of maximum response change (−1.74%) for HbA1c from the response of placebo (−0.253%). The leveraging prior knowledge from the longitudinal MBMA will be utilized to guide clinical development of taspoglutide and further support study designs including optimization of dose and duration of therapy.

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.

Eight weeks of treatment with long-acting GLP-1 analog taspoglutide improves postprandial insulin secretion and sensitivity in metformin-treated patients with type 2 diabetes

OBJECTIVE

Loss of pancreatic function is pivotal to the deterioration of fasting and postprandial glycemic control in type 2 diabetes (T2D). We evaluated the effects of a long-acting, human glucagon-like peptide-1 analog, taspoglutide, added to metformin, on pancreatic function and peripheral insulin sensitivity.

MATERIALS/METHODS

We studied 80 T2D patients inadequately controlled [glycosylated hemoglobin (HbA1c), 7.0%-9.5%] receiving stable metformin for ≥12weeks. They were a subset of participants to a phase 2 trial that received also a 240-min mixed-meal tolerance test (MTT) at baseline and study end. Patients received once weekly (QW) sc injection of taspoglutide 5, 10, or 20mg (n=21, 19, or 19), or placebo (n=21), plus metformin, for 8weeks. We measured postprandial plasma glucose (PPG) and insulin profiles, insulin secretion rate (ISR), oral glucose insulin sensitivity (OGIS) index; β-cell glucose sensitivity, glucagon/glucose and insulin/glucagon ratios, and insulin sensitivity-to-insulin resistance (or disposition) index.

RESULTS

After 8 weeks of treatment, taspoglutide 5, 10, and 20mg QW doses vs. placebo improved mean PPG0-240 min (relative change from baseline: -22.1%, -25.9%, and -22.9% vs. -8.1%; P<0.005) and mean postprandial ISR0-240 min (+14%, +18%, and +23% vs. +1%; P<0.005 vs dose). Taspoglutide at 20mg QW dose also resulted in improvements from baseline in OGIS, β-cell glucose sensitivity, glucagon/glucose and insulin/glucagon ratios and the disposition index during the MTT.

CONCLUSION

Taspoglutide QW significantly improved pancreatic function in patients with T2D treated with metformin.

Effect of GLP1R agonists taspoglutide and liraglutide on primary thyroid C-cells from rodent and man

Glucagon-like peptide 1 (GLP1) analogs have been associated with an increased incidence of thyroid C-cell hyperplasia and tumors in rodents. This effect may be due to a GLP1 receptor (GLP1R)-dependent mechanism. As the expression of GLP1R is much lower in primates than in rodents, the described C-cell proliferative lesions may not be relevant to man. Here, we aimed to establish primary thyroid cell cultures of rat and human to evaluate the expression and function of GLP1R in C-cells. In our experiments, GLP1R expression was observed in primary rat C-cells (in situ hybridization) but was not detected in primary human C-cells (mRNA and protein levels). The functional response of the cultures to the stimulation with GLP1R agonists is an indirect measure of the presence of functional receptor. Liraglutide and taspoglutide elicited a modest increase in calcitonin release and in calcitonin expression in rat primary thyroid cultures. Contrarily, no functional response to GLP1R agonists was observed in human thyroid cultures, despite the presence of few calcitonin-positive C-cells. Thus, the lack of functional response of the human cultures adds to the weight of evidence indicating that healthy human C-cells have very low levels or completely lack GLP1R. In summary, our results support the hypothesis that the GLP1R agonist-induced C-cell responses in rodents may not be relevant to primates. In addition, the established cell culture method represents a useful tool to study the physiological and/or pathological roles of GLP1 and GLP1R agonists on normal, non-transformed primary C-cells from rats and man.

Role of plasma kallikrein in diabetes and metabolism

Plasma kallikrein (PK) is a serine protease generated from plasma prekallikrein, an abundant circulating zymogen expressed by the Klkb1 gene. The physiological actions of PK have been primarily attributed to its production of bradykinin and activation of coagulation factor XII, which promotes inflammation and the intrinsic coagulation pathway. Recent genetic, molecular, and pharmacological studies of PK have provided further insight into its role in physiology and disease. Genetic analyses have revealed common Klkb1 variants that are association with blood metabolite levels, hypertension, and coagulation. Characterisation of animal models with Klkb1 deficiency and PK inhibition have demonstrated effects on inflammation, vascular function, blood pressure regulation, thrombosis, haemostasis, and metabolism. These reports have also identified a host of PK substrates and interactions, which suggest an expanded physiological role for this protease beyond the bradykinin system and coagulation. The review summarises the mechanisms that contribute to PK activation and its emerging role in diabetes and metabolism.

Incretin-based therapy for type 2 diabetes mellitus: pancreatic and extrapancreatic effects

The prevalence of type 2 diabetes mellitus has increased at an alarming rate in recent years. Recent estimations project that 366 million people could have diabetes by 2030. The incretin system emerges as a new target for type 2 diabetes therapy, and new molecules are being approved for its use in humans since the year 2005. These agents could be divided into 2 main groups, glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 inhibitors. Endogenous GLP-1 is an incretin hormone composed by a 30-amino acid peptide and is secreted from L-cells in distal small intestine in response to calorie intake, causing a glucose-dependent β-cell response resulting in a restoration of the first-phase insulin response. Additionally, GLP-1 regulates glucagon production, which leads to inhibition of glucogenolysis and gluconeogenesis in the liver. Synthetic molecules such as exenatide and liraglutide have been developed to bind GLP-1 receptor and mimic GLP-1 effects in pancreatic cells and other target organs.

The fate of taspoglutide, a weekly GLP-1 receptor agonist, versus twice-daily exenatide for type 2 diabetes: the T-emerge 2 trial

OBJECTIVE

Taspoglutide is a long-acting glucagon-like peptide 1 receptor agonist developed for treatment of type 2 diabetes. The efficacy and safety of once-weekly taspoglutide was compared with twice-daily exenatide.

RESEARCH DESIGN AND METHODS

Overweight adults with inadequately controlled type 2 diabetes on metformin ± a thiazolidinedione were randomized to subcutaneous taspoglutide 10 mg weekly (n = 399), taspoglutide 20 mg weekly (n = 398), or exenatide 10 µg twice daily (n = 392) in an open-label, multicenter trial. The primary end point was change in HbA(1c) after 24 weeks.

RESULTS

Mean baseline HbA(1c) was 8.1%. Both doses of taspoglutide reduced HbA(1c) significantly more than exenatide (taspoglutide 10 mg: -1.24% [SE 0.09], difference -0.26, 95% CI -0.37 to -0.15, P < 0.0001; taspoglutide 20 mg: -1.31% [0.08], difference -0.33, -0.44 to -0.22, P < 0.0001; exenatide: -0.98% [0.08]). Both taspoglutide doses reduced fasting plasma glucose significantly more than exenatide. Taspoglutide reduced body weight (taspoglutide 10 mg, -1.6 kg; taspoglutide 20 mg, -2.3 kg) as did exenatide (-2.3 kg), which was greater than with taspoglutide 10 mg (P < 0.05). HbA(1c) and weight effects were maintained after 52 weeks. More adverse events with taspoglutide 10 and 20 mg than exenatide developed over time (nausea in 53, 59, and 35% and vomiting in 33, 37, and 16%, respectively). Allergic and injection-site reactions were more common with taspoglutide. Discontinuations were greater with taspoglutide. Antitaspoglutide antibodies were detected in 49% of patients.

CONCLUSIONS

Once-weekly taspoglutide demonstrated greater glycemic control than twice-daily exenatide with comparable weight loss, but with unacceptable levels of nausea/vomiting, injection-site reactions, and systemic allergic reactions.

Effects of taspoglutide on glycemic control and body weight in obese patients with type 2 diabetes (T-emerge 7 study)

OBJECTIVE

Therapies that lower blood glucose and provide weight loss may provide meaningful benefits for obese patients with type 2 diabetes mellitus (T2DM). This study assessed the efficacy of taspoglutide compared with placebo on glycemic control and weight in obese patients with T2DM inadequately controlled with metformin monotherapy.

DESIGN AND METHODS

In a 24-week, randomized, double-blind, placebo-controlled, multicenter trial, obese adults with T2DM were randomized (1:1) to weekly subcutaneous taspoglutide 20 mg (10 mg for first 4 weeks) (n = 154) or placebo (n = 151) for 24 weeks. Efficacy measures included hemoglobin A1c (HbA1c) levels, body weight, percentage of patients achieving HbA1c ≤6.5 and ≤7.0%, and fasting plasma glucose (FPG). Adverse events (AEs) were assessed.

RESULTS

Mean baseline HbA1c was 7.55% and mean baseline BMI was 36.7 kg/m(2) . HbA1c reductions from baseline were significantly greater with taspoglutide than placebo (least square mean [LSMean], -0.81% vs. -0.09%; P < 0.0001). Weight loss at week 24 was significantly greater with taspoglutide than placebo (LSMean, -3.16 vs. -1.85 kg; P < 0.01). In the taspoglutide and placebo groups, target HbA1c levels (≤6.5%) were achieved by 49 and 16% of patients, respectively, while 72 and 36% achieved HbA1c levels ≤7%. Decreases in FPG were significantly greater with taspoglutide than placebo (-23.59 vs. 0.09 mg/dl; P < 0.0001). Nausea and vomiting were the most common AEs associated with taspoglutide, but tended to be transient and generally mild or moderate.

CONCLUSIONS

In obese patients with T2DM, once-weekly taspoglutide provided the combined benefits of glycemic control and weight loss.

GLP-1 receptor activation indirectly reduces hepatic lipid accumulation but does not attenuate development of atherosclerosis in diabetic male ApoE(-/-) mice

Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce lipid accumulation in peripheral tissues, attenuating atherosclerosis and hepatic steatosis in preclinical studies. We examined whether GLP-1R activation decreases atherosclerosis progression in high-fat diet-fed male ApoE(-/-) mice after administration of streptozotocin and treatment with the long-acting GLP-1R agonist taspoglutide administered once monthly vs. metformin in the drinking water for 12 wk. Taspoglutide did not reduce plaque area or lipid content in the aortic arch or abdominal aorta, and no significant change in aortic macrophage accumulation was detected after taspoglutide or metformin. In contrast, hepatic triglyceride levels were significantly reduced in livers from taspoglutide-treated mice. Both peripheral and intracerebroventricular administration of exendin-4 rapidly decreased plasma triglyceride levels in fasted mice, and taspoglutide therapy in ApoE(-/-) mice modulated the expression of hepatic genes controlling fatty acid uptake and oxidation. We were unable to detect expression of the entire Glp1r coding sequence in macrophages isolated from ApoE(-/-), C57BL/6, and IL10(-/-) mice. Similarly, Glp1r mRNA transcripts were not detected in RNA from isolated murine hepatocytes. Using Western blotting and tissue extracts from Glp1r(+/+) and Glp1r(-/-) mice, and cells transfected with a tagged murine GLP-1R cDNA, we could not validate the sensitivity and specificity of three different GLP-1R antisera commonly used for the detection of GLP-1R protein. Taken together, these findings illustrate divergent actions of GLP-1R agonists on atherosclerosis progression and accumulation of ectopic lipid in ApoE(-/-) mice and highlight the importance of indirect GLP-1R actions for the control of hepatic lipid accumulation.

Taspoglutide, a once-weekly glucagon-like peptide 1 analogue, vs. insulin glargine titrated to target in patients with Type 2 diabetes: an open-label randomized trial

AIMS

To compare the efficacy and safety of once-weekly taspoglutide with insulin glargine in patients with advanced Type 2 diabetes failing metformin and sulphonylurea combination therapy.

METHODS

This open-label, parallel-group, multi-centre trial randomized 1049 patients continuing metformin 1:1:1 to taspoglutide 10 mg once weekly, taspoglutide 20 mg once weekly or insulin glargine once daily with forced titration to fasting plasma glucose ≤ 6.1 mmol/l. Sulphonylureas were discontinued before randomization. The primary endpoint was change in HbA(1c) after 24 weeks.

RESULTS

After 24 weeks, least-square mean changes from baseline in HbA(1c) in patients receiving taspoglutide 10 mg [-8 mmol/mol (se 1)] [-0.77% (se 0.05)] or taspoglutide 20 mg [-11 mmol/mol (se 1)] [-0.98% (se 0.05)] were non-inferior to insulin glargine [-9 mmol/mol (se 1)] [-0.84% (se 0.05)]; treatment difference of 0.07% (95% CI -0.06 to 0.21) and -0.14% (95% CI -0.28 to -0.01), for taspoglutide 10 and 20 mg, respectively, vs. insulin glargine. Taspoglutide was associated with more adverse events (mainly gastrointestinal) and significantly less hypoglycaemia than insulin glargine.

CONCLUSIONS

Compared with insulin glargine, taspoglutide provided non-inferior HbA(1c) reductions associated with less hypoglycaemia, but more gastrointestinal adverse events.

Red carpeting the newer antidiabetics

The rapidly increasing prevalence of diabetes on a global scale beseeches an urgent need for newer and better treatment options. Our better understanding of the pathophysiology of diabetes has enabled a continual churn out of newer antidiabetic agents with varying modes of action. Sodium-Glucose Transport Proteins-2 inhibitors, dipeptidyl peptidase IV inhibitors, glucagon-like peptide analogues, glucokinase activators, dual peroxisome proliferator-activated receptor agonists, monoclonal antibodies, and dopamine-2 receptor agonists either as monotherapy or combination therapy with the existing oral hypoglycemic agents compound our fight against diabetes. A review of the newer drugs targeting various aspects in the management of diabetes is presented.

Using albumin to improve the therapeutic properties of diabetes treatments

Achieving tight glycaemic control remains an unmet need for many patients with type 2 diabetes, despite improved treatments. To meet glycaemic targets, attempts have been made to improve existing drugs and to develop new classes of drugs. Recent advances include insulin analogues that more closely mimic physiologic insulin levels, and incretin-based therapies, which capitalize on the glucoregulatory properties of native glucagon-like peptide-1 (GLP-1). Although promising, these agents are associated with limitations, including hypoglycaemia with insulin, gastrointestinal adverse events with GLP-1 receptor agonists and frequent dosing with both classes. Albumin is an abundant natural drug carrier that has been used to improve the half-life, tolerability and efficacy of a number of bioactive agents. Here, we review the physiologic roles of albumin and how albumin technologies are being used to prolong duration of action of therapies for diabetes, including insulin and incretin-based therapies.

Clinical Efficacy and Safety of Once-Weekly Glucagon-Like Peptide-1 Agonists in Development for Treatment of Type 2 Diabetes Mellitus in Adults

OBJECTIVE:

To review pharmacologic, pharmacokinetic, efficacy, and safety data of once-weekly glucagon-like peptide-1 (GLP-1) agonists exenatide long-acting release (LAR), albiglutide, and taspoglutide in treatment of type 2 diabetes mellitus (T2DM).

DATA SOURCES:

A MEDLINE search (1966-August 2011) was conducted using the following key words: type 2 diabetes mellitus, glucagon-like peptide-1 agonists once weekly, glucagon-like peptide-1 agonists, exenatide LAR, albiglutide, and taspoglutide.

STUDY SELECTION AND DATA EXTRACTION:

All articles published in English identified from the data sources were evaluated, prioritizing randomized controlled trials with human data. The references of published articles identified were examined for additional studies appropriate for the review.

DATA SYNTHESIS:

Native GLP-1 increases glucose-dependent insulin secretion, decreases glucagon secretion, and slows gastric emptying in healthy individuals, but these effects may be blunted in patients with T2DM. Because native GLP-1 is rapidly degraded by dipeptidyl peptidase-IV, it is not a practical treatment option. Currently, 2 GLP-1 receptor agonists have been approved by the Food and Drug Administration: exenatide twice daily and liraglutide once daily. Several additional GLP-1 agonists, including exenatide LAR, albiglutide, and taspoglutide, are in various stages of clinical trials and have been modified to increase their half-lives. These agents have shown significant improvements in hemoglobin A1c, fasting plasma glucose, and postprandial plasma glucose, as well as improvements in body weight, blood pressure, and lipid parameters. These agents allow for less-frequent dosing schedules, improved glycemic control throughout the day, and improved treatment satisfaction compared to some available agents. GLP-1 agonists have been well tolerated, with the most common adverse effects being gastrointestinal related, which occurred early in therapy but typically resolved after 4-8 weeks. The incidence of hypoglycemia was infrequent and mild during therapy.

CONCLUSIONS:

Once-weekly GLP-1 agonists provide similar glycemic control with weight reduction, as well as overall higher treatment satisfaction for patients because of their ease of use and need for less-frequent dosing compared to some available agents.

PET of insulinoma using ¹⁸F-FBEM-EM3106B, a new GLP-1 analogue

Derived from endocrine pancreatic beta cells, insulinomas express glucagon-like peptide-1 (GLP-1) receptor with high density and incidence. In this study, we labeled a novel GLP-1 analogue, EM3106B, with (18)F and performed PET imaging to visualize insulinoma tumors in an animal model. A GLP-1 analogue that contains multiple lactam bridges, EM3106B, was labeled with (18)F through a maleimide-based prosthetic group, N-2-(4-(18)F-fluorobenzamido)ethylmaleimide ((18)F-FBEM). The newly developed radiotracer was characterized by cell based receptor-binding assay, cell uptake and efflux assay. The stability in serum was evaluated by radio-HPLC analysis. In vivo PET imaging was performed in nude mice bearing subcutaneous INS-1 insulinoma tumors and MDA-MB-435 tumors of melanoma origin. Ex vivo biodistribution study was performed to confirm the PET imaging data. EM3106B showed high binding affinity (IC(50) = 1.38 nM) and high cell uptake (5.25 ± 0.61% after 120 min incubation). (18)F-FBEM conjugation of EM3106B resulted in high labeling yield (24.9 ± 2.4%) and high specific activity (>75 GBq/μmol at the end of bombardment). EM3106B specifically bound and was internalized by GLP-1R positive INS-1 cells. After intravenous injection of 3.7 MBq (100 μCi) of (18)F-FBEM-EM3106B, the INS-1 tumors were clearly visible with high contrast in relation to the contralateral background on PET images, and tumor uptake of (18)F-FBEM-EM3106B was determined to be 28.5 ± 4.7 and 25.4 ± 4.1% ID/g at 60 and 120 min, respectively. (18)F-FBEM-EM3106B showed low uptake in MB-MDA-435 tumors with low level of GLP-1R expression. Direct tissue sampling biodistribution experiment confirmed high tracer uptake in INS-1 tumors and receptor specificity in both INS-1 tumor and pancreas. In conclusion, (18)F-FBEM-EM3106B exhibited GLP-1R-receptor-specific targeting properties in insulinomas. The favorable characteristics of (18)F-FBEM-EM3106B, such as high specific activity and high tumor uptake, and high tumor to nontarget uptake, demonstrate that it is a promising tracer for clinical insulinoma imaging.

Obesity - an indication for GLP-1 treatment? Obesity pathophysiology and GLP-1 treatment potential

Obesity is common and associated with a high rate of morbidity and mortality; therefore, treatment is of great interest. At present, bariatric surgery is the only truly successful treatment of severe obesity. Mimicking one of the effects of bariatric surgery, namely the increased secretion of glucagon-like peptide (GLP)-1, by artificially increasing the levels of GLP-1 might prove successful as obesity treatment. Recent studies have shown that GLP-1 is a physiological regulator of appetite and food intake. The effect on food intake and satiety is preserved in obese subjects and GLP-1 may therefore have a therapeutic potential. The GLP-1 analogues result in a moderate average weight loss, which is clinically relevant in relation to reducing the risk of type 2 diabetes and cardiovascular disease. Inspired by the hormone profile after gastric bypass, a future strategy in obesity drug development could be to combine several hormones, and thereby produce a superior appetite suppressing hormone profile that may result in a weight loss exceeding that seen in single-agent trials. In conclusion, with the GLP-1 analogues combining a moderate weight loss with beneficial effects on metabolic and cardiovascular risk factors, it seems that we are on the right track for future treatment of obesity.

Stabilized helical peptides: overview of the technologies and therapeutic promises

INTRODUCTION

Helical structures in proteins and naturally occurring peptides play a major role in a variety of biological processes by mediating interactions with proteins and other macromolecules such as nucleic acids and lipid membranes. The use of short synthetic peptides encompassing helical segments to modulate or disrupt such interactions, when associated with human diseases, represents great pharmacological interest.

AREAS COVERED

Multiple chemical approaches have been developed to increase the conformational and metabolic stabilities of helical peptides and to improve their biomedical potential. After a brief overview of these technologies and the most recent developments, this review will focus on the main therapeutic areas and targets and will discuss their promise.

EXPERT OPINION

Potential benefits associated with increased helix stability extend beyond simple affinity enhancement. Some peptidomimetic helices are being endowed with features desirable for cellular activity such as increased resistance to proteolysis and/or cell permeability. Recent advances in the field of peptide and related peptidomimetic helices are not just conceptual, but are likely to be of practical utility in the process of optimizing peptides as clinical candidates, and developing medium-size therapeutics.

An overview of once-weekly glucagon-like peptide-1 receptor agonists--available efficacy and safety data and perspectives for the future

Incretin-based therapies, such as the injectable glucagon-like peptide-1 (GLP-1) receptor agonists and orally administered dipeptidyl peptidase-4 (DPP-4) inhibitors, have recently been introduced into clinical practice. At present, the GLP-1 receptor agonists need to be administered once or twice daily. Several once-weekly GLP-1 receptor agonists are in phase 3 development. This review examines the efficacy, safety and perspective for the future of the once-weekly GLP-1 receptor agonists: exenatide once weekly, taspoglutide, albiglutide, LY2189265 and CJC-1134-PC, and compared them to the currently available agonists, exenatide BID and liraglutide QD. A greater reduction in haemoglobin A1c (HbA1c) and fasting plasma glucose was found with the once-weekly GLP-1 receptor agonists compared with exenatide BID, while the effect on postprandial hyperglycaemia was modest with the once-weekly GLP-1 receptor agonist. The reduction in HbA1c was in most studies greater compared to oral antidiabetic drugs and insulin glargine. The reduction in weight did not differ between the short- and long-acting agonists. The gastrointestinal side effects were less with the once-weekly agonists compared with exenatide BID, except for taspoglutide. Antibodies seem to be most frequent with exenatide once weekly, while hypersensitivity has been described in few patients treated with taspoglutide. Injection site reactions differ among the long-acting GLP-1 receptor agonists and are observed more frequently than with exenatide BID and liraglutide. In humans, no signal has been found indicating an association between the once-weekly agonists and C-cell cancer. The cardiovascular safety, durability of glucose control and effect on weight will emerge from several ongoing major long-term trials. The once-weekly GLP-1 receptor analogues are promising candidates for the treatment of type 2 diabetes, although their efficacy may not be superior to once-daily analogue liraglutide.

Taspoglutide, a novel human once-weekly GLP-1 analogue, protects pancreatic β-cells in vitro and preserves islet structure and function in the Zucker diabetic fatty rat in vivo

AIM

Glucagon-like peptide-1 (GLP-1) has protective effects on pancreatic β-cells. We evaluated the effects of a novel, long-acting human GLP-1 analogue, taspoglutide, on β-cells in vitro and in vivo.

METHODS

Proliferation of murine pancreatic β (MIN6B1) cells and rat islets in culture was assessed by imaging of 5-ethynyl-2'-deoxyuridine-positive cells after culture with taspoglutide. Apoptosis was evaluated with the transferase-mediated 2'-deoxyuridine 5'-triphosphate nick-end labelling assay in rat insulinoma (INS-1E) cells and isolated human islets exposed to cytokines (recombinant interleukin-1β, interferon-γ, tumour necrosis factor-α) or lipotoxicity (palmitate) in the presence or absence of taspoglutide. Islet morphology and survival and glucose-stimulated insulin secretion in perfused pancreata were assessed 3-4 weeks after a single application of taspoglutide to prediabetic 6-week-old male Zucker diabetic fatty (ZDF) rats.

RESULTS

Proliferation was increased in a concentration-dependent manner up to fourfold by taspoglutide in MIN6B1 cells and was significantly stimulated in isolated rat islets. Taspoglutide almost completely prevented cytokine- or lipotoxicity-induced apoptosis in INS-1E cells (control 0.5%, cytokines alone 2.2%, taspoglutide + cytokines 0.6%, p < 0.001; palmitate alone 8.1%, taspoglutide + palmitate 0.5%, p < 0.001) and reduced apoptosis in isolated human islets. Treatment of ZDF rats with taspoglutide significantly prevented β-cell apoptosis and preserved healthy islet architecture and insulin staining intensity as shown in pancreatic islet cross sections. Basal and glucose-stimulated insulin secretion of in situ perfused ZDF rat pancreata was normalized after taspoglutide treatment.

CONCLUSIONS

Taspoglutide promoted β-cell proliferation, prevented apoptosis in vitro and exerted multiple β-cell protective effects on islet architecture and function in vivo in ZDF rats.

Incretin receptors in non-neoplastic and neoplastic thyroid C cells in rodents and humans: relevance for incretin-based diabetes therapy

While incretins are of great interest for the therapy of diabetes 2, the focus has recently been brought to the thyroid, since rodents treated with glucagon-like peptide-1 (GLP-1) analogs were found to occasionally develop medullary thyroid carcinomas. Incretin receptors for GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) were therefore measured in various rodent and human thyroid conditions. In vitro GLP-1 and GIP receptor autoradiography were performed in normal thyroids, C-cell hyperplasia and medullary thyroid carcinomas in rodents. Receptor incidence and density were assessed and compared with the receptor expression in human thyroids, medullary thyroid carcinomas, and TT cells. GLP-1 receptors are expressed in C cells of normal rat and mice thyroids. Their density is markedly increased in rat C-cell hyperplasia and medullary thyroid carcinomas, where their incidence amounts to 100%. GIP receptors are neither detected in normal rodent thyroids nor in C-cell hyperplasia, but are present in all rat medullary thyroid carcinomas. No GLP-1 or GIP receptors are detected in normal human thyroids. Whereas only 27% of all human medullary thyroid carcinomas express GLP-1 receptors, up to 89% express GIP receptors in a high density. TT cells lack GLP-1 receptors but express GIP receptors. GLP-1 receptors are frequently expressed in non-neoplastic and neoplastic C cells in rodents while they are rarely detected in human C-cell neoplasia, suggesting species differences. Conversely, GIP receptors appear to be massively overexpressed in neoplastic C cells in both species. The presence of incretin receptors in thyroid C cell lesions suggests that this organ should be monitored before and during incretin-based therapy of diabetes.

Discovery and characterization of taspoglutide, a novel analogue of human glucagon-like peptide-1, engineered for sustained therapeutic activity in type 2 diabetes

AIM

Glucagon-like peptide-1 (GLP-1) receptor agonists for the treatment of type 2 diabetes are administered by daily injection because of short plasma half-lives, which result partly from the biochemical instability of these peptides. There is a medical need for GLP-1 analogues that can be administered less frequently for patient convenience.

METHODS

We synthesized a series of human GLP-1 (hGLP-1(7-36)NH(2) ) derivatives containing α-aminoisobutyric acid (Aib) substitutions, analysed their enzymatic stabilities and evaluated their secondary structures using circular dichroism (CD) and nuclear magnetic resonance (NMR).

RESULTS

Plasma stability experiments showed that only the analogue containing Aib substitutions in both the N-terminus (position 8) and the C-terminus (position 35), [Aib⁸(,)³⁵]hGLP-1(7-36)NH₂ (BIM-51077), was fully resistant to enzymatic cleavage. Incubation with human plasma kallikrein or plasmin confirmed that the Aib substitution at position 35 prevented protease cleavage around this residue, which contributes to the significantly enhanced plasma stability and increased plasma half-life. CD revealed increased C-terminal α-helicity in Aib³⁵-substituted analogues compared with both hGLP-1(7-36)NH₂ and analogues containing only Aib⁸ substitutions. Based on NMR studies, the secondary structure of BIM-51077 is similar to hGLP-1(7-36)NH₂ with a slight increase in α-helicity in the C-terminus. Compared with hGLP-1(7-36)NH₂, BIM-51077 had similar binding affinity for the human GLP-1 receptor and activated this receptor with similar potency.

CONCLUSIONS

We have discovered an Aib⁸(,)³⁵-substituted analogue of native hGLP-1(7-36)NH₂ (BIM-51077) that retains the structure of the native peptide, and has similar activity and enhanced stability. A sustained-release formulation of this molecule (taspoglutide) is in phase-3 clinical development.

Treatment of diabetes with glucagon-like peptide-1 gene therapy

IMPORTANCE OF THE FIELD

Glucagon-like peptide (GLP)-1 receptor agonists are in widespread clinical use for the treatment of diabetes. While effective, these peptides require frequent injections to maintain efficacy. Therefore, alternative delivery methods including gene therapy are currently being evaluated.

AREAS COVERED IN THIS REVIEW

Here, we review the biology of GLP-1, evidence supporting the clinical use of the native peptide as well as synthetic GLP-1 receptor agonists, and the rationale for their delivery by gene therapy. We then review progress made in the field of GLP-1 gene therapy for both type 1 and type 2 diabetes.

WHAT THE READER WILL GAIN

Efforts to improve the biological half-life of GLP-1 receptor agonists are discussed. We focus on the development of both viral and non-viral gene delivery methods, highlighting vector designs and the strengths and weaknesses of these approaches. We also discuss the utility of targeting regulated GLP-1 production to tissues including the liver, muscle, islet and gut.

TAKE HOME MESSAGE

GLP-1 is a natural peptide possessing several actions that effectively combat diabetes. Current delivery methods for GLP-1-based drugs are cumbersome and do not recapitulate the normal secretion pattern of the native hormone. Gene therapy offers a useful method for directing long-term production and secretion of the native peptide. Targeted production of GLP-1 using tissue-specific promoters and delivery methods may improve therapeutic efficacy, while also eliminating the burden of frequent injections.

Development of potent glucagon-like peptide-1 agonists with high enzyme stability via introduction of multiple lactam bridges

Glucagon-like peptide-1 (GLP-1) has the ability to lower the blood glucose level, and its regulatory functions make it an attractive therapeutic agent for the treatment of type 2 diabetes. However, its rapid degradation by enzymes like dipeptidyl peptidase-IV (DPP-IV) and neutral endopeptidase (NEP) 24.11 severely compromises its effective clinical use. Whereas specific DPP-IV inhibitors have been developed, NEP 24.11 targets multiple sites in the GLP-1 sequence, which makes it difficult to block. To address this drawback, we have designed and synthesized conformationally constrained GLP-1 analogues by introducing multiple lactam bridges that stabilized both alpha-helices in the N- and C-terminal regions simultaneously. In addition to improving the receptor activation capability (up to 5-fold) by fixing the alpha-helical conformations required for optimal receptor interaction, the introduced lactam bridges provided outstanding shielding over NEP 24.11 (half-life of >96 h). These highly constrained peptides are the first examples of NEP 24.11-resistant GLP-1 analogues.

Safety and tolerability of high doses of taspoglutide, a once-weekly human GLP-1 analogue, in diabetic patients treated with metformin: a randomized double-blind placebo-controlled study

AIMS

The study objective was to investigate the safety and tolerability of up-titration to high doses of taspoglutide, a once-weekly human glucagon-like peptide-1 analogue, in subjects with Type 2 diabetes inadequately controlled on metformin alone.

METHODS

In this double-blind phase II trial, subjects were randomized to placebo or taspoglutide (20 mg; three separate groups) administered once weekly by subcutaneous injection for 4 weeks. This was followed by dose maintenance at 20 mg, or titration to 30 mg (20/30) or 40 mg (20/40) once weekly with matched placebo for an additional 4 weeks. Subjects were monitored for adverse events (AEs) throughout the study and 4-week follow-up.

RESULTS

One hundred and twenty-nine subjects were randomized and treated [mean age 57 years, mean baseline glycated haemoglobin (HbA(1c)), 7.9%]. The most frequently reported AEs were nausea and vomiting. The number of patients reporting gastrointestinal AEs did not increase following titration to higher doses of taspoglutide or when continuing the initial 20 mg regimen. Three subjects were withdrawn from the study as a result of gastrointestinal AEs (one before and two after titration to higher doses). Although not designed to investigate efficacy, improvement in glycaemic control was observed in all active arms of the study. The proportion of subjects achieving HbA(1c) < 7.0% after 8 weeks of treatment was 72, 53 and 70% in the 20/20-, 20/30- and 20/40-mg arms, respectively, vs. 19% for placebo.

CONCLUSIONS

Taspoglutide was safe, well tolerated at high doses and efficacious for lowering HbA(1c). Up-titration of dose was not associated with a worsening AE profile.