Oligomerization of a Glucagon-like Peptide 1 Analog: Bridging Experiment and Simulations

Tuning the double lipidation of salmon calcitonin to introduce a pore-like membrane translocation mechanism

A widespread strategy to increase the transport of therapeutic peptides across cellular membranes has been to attach lipid moieties to the peptide backbone (lipidation) to enhance their intrinsic membrane interaction. Efforts in vitro and in vivo investigating the correlation between lipidation characteristics and peptide membrane translocation efficiency have traditionally relied on end-point read-out assays and trial-and-error-based optimization strategies. Consequently, the molecular details of how therapeutic peptide lipidation affects it's membrane permeation and translocation mechanisms remain unresolved. Here we employed salmon calcitonin as a model therapeutic peptide and synthesized nine double lipidated analogs with varying lipid chain lengths. We used single giant unilamellar vesicle (GUV) calcein influx time-lapse fluorescence microscopy to determine how tuning the lipidation length can lead to an All-or-None GUV filling mechanism, indicative of a peptide mediated pore formation. Finally, we used a GUVs-containing-inner-GUVs assay to demonstrate that only peptide analogs capable of inducing pore formation show efficient membrane translocation. Our data provided the first mechanistic details on how therapeutic peptide lipidation affects their membrane perturbation mechanism and demonstrated that fine-tuning lipidation parameters could induce an intrinsic pore-forming capability. These insights and the microscopy based workflow introduced for investigating structure-function relations could be pivotal for optimizing future peptide design strategies.

Fatty acid conjugated EPI-X4 derivatives with increased activity and in vivo stability

Dysregulation of the CXCL12/CXCR4 axis is implicated in autoimmune, inflammatory, and oncogenic diseases, positioning CXCR4 as a pivotal therapeutic target. We evaluated optimized variants of the specific endogenous CXCR4 antagonist, EPI-X4, addressing existing challenges in stability and potency. Our structure-activity relationship study investigates the conjugation of EPI-X4 derivatives with long-chain fatty acids, enhancing serum albumin interaction and receptor affinity. Molecular dynamic simulations revealed that the lipid moieties stabilize the peptide-receptor interaction through hydrophobic contacts at the receptor's N-terminus, anchoring the lipopeptide within the CXCR4 binding pocket and maintaining essential receptor interactions. Accordingly, lipidation resulted in increased receptor affinities and antagonistic activities. Additionally, by interacting with human serum albumin lipidated EPI-X4 derivatives displayed sustained stability in human plasma and extended circulation times in vivo. Selected candidates showed significant therapeutic potential in human retinoblastoma cells in vitro and in ovo, with our lead derivative exhibiting higher efficacies compared to its non-lipidated counterpart. This study not only elucidates the optimization trajectory for EPI-X4 derivatives but also underscores the intricate interplay between stability and efficacy, crucial for delineating their translational potential in clinical applications.

Structure-Based Computational Scanning of Chemical Modification Sites in Biologics

To address the challenges of short half-life, immunogenicity, and nonspecific distribution, chemical modifications of peptide and protein-based drugs have emerged as a versatile strategy for improving their therapeutic efficacy. One such modification involves the derivatization of peptides and proteins with fatty acids, which can protract their half-life, modify their biodistribution, and potentially enable targeted delivery to specific tissues or disease sites of interest. However, the present strategies for the synthesis of such synthetically modified biologics require numerous rounds of experimental testing and often yield unstable, inactive, or heterogeneous products. To address the inefficiencies in designing modified biologics, we developed a hybrid computational workflow that integrates RosettaMatch from the Rosetta suite of protein modeling tools with molecular dynamics (MD) simulations. This approach not only reduces the number of amino acid positions that need to be experimentally tested by targeting only the most promising candidates for modification but also expedites the design of chemically modified biologics with the desired properties, ensuring a rapid and cost-effective development cycle. Although we demonstrate the utility of our method on a peptide therapeutic, GLP-1, with different fatty acid derivatizations, this straightforward approach has the potential to streamline the design process of a diverse range of chemically modified therapeutics, enabling tailored enhancements to their pharmacokinetic properties.

Prediction of subcutaneous drug absorption - Development of novel simulated interstitial fluid media for predictive subcutaneous in vitro assays

Media that mimic physiological fluids at the site of administration have proven to be valuable in vitro tools for predicting in vivo drug release, particularly for routes of administration where animal studies cannot accurately predict human performance. The objective of the present study was to develop simulated interstitial fluids (SISFs) that mimic the major components and physicochemical properties of subcutaneous interstitial fluids (ISFs) from preclinical species and humans, but that can be easily prepared in the laboratory and used in in vitro experiments to estimate in vivo drug release and absorption of subcutaneously administered formulations. Based on data from a previous characterization study of ISFs from different species, two media were developed: a simulated mouse-rat ISF and a simulated human-monkey ISF. The novel SISFs were used in initial in vitro diffusion studies with a commercial injectable preparation of liraglutide. Although the in vitro model used for this purpose still requires significant refinement, these two new media will undoubtedly contribute to a better understanding of the in vivo performance of subcutaneous injectables in different species and will help to reduce the number of unnecessary in vivo experiments in preclinical species by implementation in predictive in vitro models.

Molecular design of peptide therapeutics via N-terminal modification

Glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, and glucagon are three naturally occurring peptide hormones that mediate glucoregulation. Several agonists representing appropriately modified native ligands have been developed to maximize metabolic benefits with reduced side-effects and many have entered the clinic as type 2 diabetes and obesity therapeutics. In this work, we describe strategies for improving the stability of the peptide ligands by making them refractory to dipeptidyl peptidase-4 catalyzed hydrolysis and inactivation. We describe a series of alkylations with variations in size, shape, charge, polarity, and stereochemistry that are able to engender full activity at the receptor(s) while simultaneously resisting enzyme-mediated degradation. Utilizing this strategy, we offer a novel method of modulating receptor activity and fine-tuning pharmacology without a change in peptide sequence.

A Robust Platform for the Molecular Design of Potent, Protease-Stable, Long-Acting GIP Analogues

Glucose-dependent insulinotropic peptide (GIP) is a 42-amino acid peptide hormone that regulates postprandial glucose levels. GIP binds to its cognate receptor, GIPR, and mediates metabolic physiology by improved insulin sensitivity, β-cell proliferation, increased energy consumption, and stimulated glucagon secretion. Dipeptidyl peptidase-4 (DPP4) catalyzes the rapid inactivation of GIP within 6 min in vivo. Here, we report a molecular platform for the design of GIP analogues that are refractory to DPP4 action and exhibit differential activation of the receptor, thus offering potentially hundreds of GIP-based compounds to fine-tune pharmacology. The lead compound from our studies, which harbored a combination of N-terminal alkylation and side-chain lipidation, was equipotent and retained full efficacy at GIPR as the native peptide, while being completely refractory toward DPP4, and was resistant to trypsin. The GIP analogue identified from these studies was further evaluated in vivo and is one of the longest-acting GIPR agonists to date.

Sequence-based prediction of the intrinsic solubility of peptides containing non-natural amino acids

Non-natural amino acids are increasingly used as building blocks in the development of peptide-based drugs as they expand the available chemical space to tailor function, half-life and other key properties. However, while the chemical space of modified amino acids (mAAs) such as residues containing post-translational modifications (PTMs) is potentially vast, experimental methods for measuring the developability properties of mAA-containing peptides are expensive and time consuming. To facilitate developability programs through computational methods, we present CamSol-PTM, a method that enables the fast and reliable sequence-based prediction of the intrinsic solubility of mAA-containing peptides in aqueous solution at room temperature. From a computational screening of 50,000 mAA-containing variants of three peptides, we selected five different small-size mAAs for a total number of 37 peptide variants for experimental validation. We demonstrate the accuracy of the predictions by comparing the calculated and experimental solubility values. Our results indicate that the computational screening of mAA-containing peptides can extend by over four orders of magnitude the ability to explore the solubility chemical space of peptides and confirm that our method can accurately assess the solubility of peptides containing mAAs. This method is available as a web server at https://www-cohsoftware.ch.cam.ac.uk/index.php/camsolptm .

A Spectroscopic and Molecular Dynamics Study on the Aggregation Properties of a Lipopeptide Analogue of Liraglutide, a Therapeutic Peptide against Diabetes Type 2

The pharmacokinetics of peptide drugs are strongly affected by their aggregation properties and the morphology of the nanostructures they form in their native state as well as in their therapeutic formulation. In this contribution, we analyze the aggregation properties of a Liraglutide analogue (LG18), a leading drug against diabetes type 2. LG18 is a lipopeptide characterized by the functionalization of a lysine residue (K26) with an 18C lipid chain. To this end, spectroscopic experiments, dynamic light scattering measurements, and molecular dynamics simulations were carried out, following the evolution of the aggregation process from the small LG18 clusters formed at sub-micromolar concentrations to the mesoscopic aggregates formed by aged micromolar solutions. The critical aggregation concentration of LG18 in water (pH = 8) was found to amount to 4.3 μM, as assessed by the pyrene fluorescence assay. MD simulations showed that the LG18 nanostructures are formed by tetramer building blocks that, at longer times, self-assemble to form micrometric supramolecular architectures.

Field-Flow Fractionation in Molecular Biology and Biotechnology

Field-flow fractionation (FFF) is a family of single-phase separative techniques exploited to gently separate and characterize nano- and microsystems in suspension. These techniques cover an extremely wide dynamic range and are able to separate analytes in an interval between a few nm to 100 µm size-wise (over 15 orders of magnitude mass-wise). They are flexible in terms of mobile phase and can separate the analytes in native conditions, preserving their original structures/properties as much as possible. Molecular biology is the branch of biology that studies the molecular basis of biological activity, while biotechnology deals with the technological applications of biology. The areas where biotechnologies are required include industrial, agri-food, environmental, and pharmaceutical. Many species of biological interest belong to the operational range of FFF techniques, and their application to the analysis of such samples has steadily grown in the last 30 years. This work aims to summarize the main features, milestones, and results provided by the application of FFF in the field of molecular biology and biotechnology, with a focus on the years from 2000 to 2022. After a theoretical background overview of FFF and its methodologies, the results are reported based on the nature of the samples analyzed.

Direct Assessment of Oligomerization of Chemically Modified Peptides and Proteins in Formulations using DLS and DOSY-NMR

PURPOSE

Protein higher order structure (HOS) including the oligomer distribution can be critical for efficacy, safety and stability of drug products (DP). Oligomerization is particularly relevant to chemically modified protein therapeutics that have an extended pharmacokinetics profile. Therefore, the direct assessment of protein oligomerization in drug formulation is desired for quality assurance and control.

METHODS

Here, two non-invasive methods, dynamic light scattering (DLS) and diffusion ordered spectroscopy (DOSY) NMR, were applied to measure translational diffusion coefficients (Ddls and Dnmr) of proteins in formulated drug products. The hydrodynamic molecular weights (MWhd), similar to hydrodynamic size, of protein therapeutics were derived based on a log(Ddls) vs log(MWhd) correlation model established using protein standards.

RESULTS

An exponent value of -0.40 ± 0.01 was established for DLS measured log(D) vs. log(MWhd) using protein standards and a theoretical exponent value of -0.6 was used for unstructured polyethylene glycol (PEG) chains. The analysis of DLS derived MWhd of the primary species showed the fatty acid linked glucagon-like peptide 1 (GLP-1) was in different oligomer states, but the fatty acid linked insulin and PEG linked proteins were in monomer states. Nevertheless, equilibrium and exchange between oligomers in formulations were universal and clearly evidenced from DOSY-NMR for all drugs except peginterferon alfa-2a.

CONCLUSION

The correlation models of log(D) vs. log(MWhd) could be a quick and efficient way to predict MWhd of protein, which directly informs on the state of protein folding and oligomerization in formulation.

In Vivo Mechanism of Action of Sodium Caprate for Improving the Intestinal Absorption of a GLP1/GIP Coagonist Peptide

Sodium caprate (C10) has been widely evaluated as an intestinal permeation enhancer for the oral delivery of macromolecules. However, the effect of C10 on the intestinal absorption of peptides with different physicochemical properties and its permeation-enhancing effect in vivo remains to be understood. Here, we evaluated the effects of C10 on intestinal absorption in rats with a glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GIP-GLP1) dual agonist peptide (LY) and semaglutide with different enzymatic stabilities and self-association behaviors as well as the oral exposure of the LY peptide in minipigs. Furthermore, we investigated the mechanism of action (MoA) of C10 for improving the intestinal absorption of the LY peptide in vivo via live imaging of the rat intestinal epithelium and tissue distribution of the LY peptide in minipigs. The LY peptide showed higher proteolytic stability in pancreatin and was a monomer in solution compared to that in semaglutide. C10 increased in vitro permeability in the minipig intestinal organoid monolayer to a greater extent for the LY peptide than for semaglutide. In the rat jejunal closed-loop model, C10 increased the absorption of LY peptide better than that of semaglutide, which might be attributed to higher in vitro proteolytic stability and permeability of the LY peptide. Using confocal live imaging, we observed that C10 enabled the rapid oral absorption of a model macromolecule (FD4) in the rat intestine. In the duodenum tissues of minipigs, C10 was found to qualitatively reduce the tight junction protein level and allow peptide uptake to the intestinal cells. C10 decreased the transition temperature of the artificial lipid membrane, indicating an increase in membrane fluidity, which is consistent with the above in vivo imaging results. These data indicated that the LY's favorable physicochemical properties combined with the effects of C10 on the intestinal mucosa resulted in an ∼2% relative bioavailability in minipigs.

Intestinal epithelium penetration of liraglutide via cholic acid pre-complexation and zein/rhamnolipids nanocomposite delivery

BACKGROUND

Oral administration offered a painless way and improved compliance for diabetics. However, the emerging GLP-1 analog peptide drugs for diabetes primarily rely on the injection route, and the development of oral dosage forms was hampered by the low oral bioavailability due to the structural vulnerability to digestive enzymes and molecule impermeability in the gastrointestinal tract.

RESULTS

In this study, the non-covalent interaction between cholic acid (CA) and liraglutide (LIRA) was found and theoretically explained by molecular docking simulation. Formation of this physical complex of liraglutide and cholic acid (LIRA/CA Complex) reduced the self-aggregation of LIRA and accelerated intestinal epithelium penetration. By the anti-solvent method, LIRA/CA Complex was loaded into zein/rhamnolipids nanoparticles (LIRA/CA@Zein/RLs) with a loading efficiency of 76.8%. LIRA was protected from fast enzymatic degradation by the hydrophobic zein component. Meanwhile, Rhamnolipids, a glycolipid with surface activity, promoted endocytosis while also stabilizing the nanoparticles. The two components worked synergistically to ensure the delivery of LIRA/CA Complex to intestinal villi and improved oral absorption without disrupting tight junctions. LIRA/CA@Zein/RLs demonstrated a considerable intestinal epithelium absorption in mouse gastrointestinal section and a retention in vivo over 24 h, resulting in a significant and long-lasting hypoglycemic effect in Type 2 diabetes mice.

CONCLUSION

This study provided a promising oral delivery approach for LIRA and exhibited the potential for further translation into clinical application.

GLP-1R Signaling and Functional Molecules in Incretin Therapy

Glucagon-like peptide-1 receptor (GLP-1R) is a critical therapeutic target for type 2 diabetes mellitus (T2DM). The GLP-1R cellular signaling mechanism relevant to insulin secretion and blood glucose regulation has been extensively studied. Numerous drugs targeting GLP-1R have entered clinical treatment. However, novel functional molecules with reduced side effects and enhanced therapeutic efficacy are still in high demand. In this review, we summarize the basis of GLP-1R cellular signaling, and how it is involved in the treatment of T2DM. We review the functional molecules of incretin therapy in various stages of clinical trials. We also outline the current strategies and emerging techniques that are furthering the development of novel therapeutic drugs for T2DM and other metabolic diseases.

Considerations in the developability of peptides for oral administration when formulated together with transient permeation enhancers

This paper reviews many of the properties of a peptide that need to be considered prior to development as an oral dosage form when co-formulated with a permeation enhancer to improve oral bioavailability, including the importance and implications of peptide half-life on variability in pharmacokinetic profiles. Clinical considerations in terms of food and drug-drug interactions are also discussed. The paper further gives a brief overview how permeation enhancers overcome barriers that limit oral absorption of peptides and thereby improve their oral bioavailability, albeit bioavailabilities are still low single digit and variability is high.

Identification of a Multi-Component Formulation for Intestinal Delivery of a GLP-1/Glucagon Co-agonist Peptide

PURPOSE

Oral delivery of therapeutic peptides has been challenging due to multiple physiological factors and physicochemical properties of peptides. We report a systematic approach to identify formulation compositions combining a permeation enhancer and a peptidase inhibitor that minimize proteolytic degradation and increase absorption of a peptide across the small intestine.

METHODS

An acylated glucagon-like peptide-1/glucagon co-agonist peptide (4.5 kDa) was selected as a model peptide. Proteolytic stability of the peptide was investigated in rat and pig SIF. Effective PEs and multiple component formulations were identified in rats. Relative bioavailability of the peptide was determined in minipigs via intraduodenal administration (ID) of enteric capsules.

RESULTS

The peptide degraded rapidly in the rat and pig SIF. Citric acid, SBTI, and SBTCI inhibited the enzymatic degradation. The peptide self-associated into trimers in solution, however, addition of PEs monomerized the peptide. C10 was the most effective PE among tested PEs (DPC, LC, rhamnolipid, C12-maltosides, and SNAC) to improve intestinal absorption of the peptide in the rat IJ-closed loop model. A combination of C10 and SBTI or SBTCI increased the peptide exposure 5-tenfold compared to the exposure with the PE alone in the rat IJ-cannulated model, and achieved 1.06 ± 0.76% bioavailability in minipigs relative to subcutaneous via ID administration using enteric capsules.

CONCLUSION

We identified SBTI and C10 as an effective peptidase inhibitor and PE for intestinal absorption of the peptide. The combination of SBTI and C10 addressed the peptide physiochemical properties and provides a formulation strategy to achieve intestinal delivery of this peptide.

Application of Af4-Multidetection to Liraglutide in Its Formulation: Preserving and Representing Native Aggregation

Aggregation is among the most critical parameters affecting the pharmacological and safety profile of peptide Active Pharmaceutical Ingredients (APIs). For this reason, it is of utmost importance to define the exact aggregation state of peptide drugs, particularly when the API is marketed as a ready-to-use solution. Consequently, appropriate non-destructive techniques able to replicate the peptide environment must be employed. In our work, we exploited Asymmetrical Flow Field-Flow Fractionation (AF4), connected to UV, dRI, fluorescence, and MALS detectors, to fully characterize the aggregation state of Liraglutide, a peptide API used for the treatment of diabetes type 2 and chronic obesity. In previous studies, Liraglutide was hypothesized to assemble into hexa-octamers in phosphate buffer, but no information on its behavior in the formulation medium was provided up to now. The method used allowed researchers to work using formulation as the mobile phase with excellent recoveries and LoQ/LoD, discerning between stable and degraded samples, and detecting, when present, aggregates up to 108 Da. The native state of Liraglutide was assessed and found to be an association into pentamers, with a non-spherical conformation. Combined to benchmark analyses, the sameness study was complete and descriptive, also giving insight on the aggregation process and covalent/non-covalent aggregate types.

Characterization and impact of peptide physicochemical properties on oral and subcutaneous delivery

Peptides, an emerging modality within the biopharmaceutical industry, are often delivered subcutaneously with evolving prospects on oral delivery. Barrier biology within the subcutis or gastrointestinal tract is a significant challenge in limiting absorption or otherwise disrupting peptide disposition. Aspects of peptide pharmacokinetic performance and ADME can be mitigated with careful molecular design that tailors for properties such as effective size, hydrophobicity, net charge, proteolytic stability, and albumin binding. In this review, we endeavor to highlight effective techniques in qualifying physicochemical properties of peptides and discuss advancements of in vitro models of subcutaneous and oral delivery. Additionally, we will delineate empirical findings around the relationship of these physicochemical properties and in vivo (animal or human) impact. We conclude that robust peptide characterization methods and in vitro techniques with demonstrated correlations to in vivo data are key routines to incorporate in the drug discovery and development to improve the probability of technical and commercial success of peptide therapeutics.

Design and Development of a New Glucagon-Like Peptide-1 Receptor Agonist to Obtain High Oral Bioavailability

PURPOSE

Semaglutide is the only oral GLP-1 RA in the market, but oral bioavailability is generally limited in range of 0.4-1%. In this study, a new GLP-1RA named SHR-2042 was developed to gain higher oral bioavailability than semaglutide.

METHOD

Self-association of SHR-2042, semaglutide and liraglutide were assessed using SEC-MALS. The intestinal perfusion test in SD rats was used to select permeation enhancers (PEs) including SNAC, C10 and LCC. ITC, CD and DLS were used to explore the interaction between SHR-2042 and SNAC. Gastric administrated test in SD rats was used to screen SHR-2042 granules with different SHR-2042/SNAC ratios. The oral bioavailability of SHR-2042 was studied in rats and monkeys.

RESULT

The designed GLP-1RA, SHR-2042, gives a better solubility and lipophilicity than semaglutide. While it forms a similar oligomer with that of semaglutide. During the selection of PEs, SNAC shows better exposure than the other competing PEs including C10 and LCC. SHR-2042 and SNAC bind quickly and exhibit hydrophobic interaction. SNAC could promote monomerization of SHR-2042 and form micelles to trap the monomerized SHR-2042. The oral bioavailability of SHR-2042 paired with SNAC is 0.041% (1:0, w/w), 0.083% (1:10, w/w), 0.32% (1:30, w/w) and 2.83% (1:60, w/w) in rats. And the oral bioavailability of SHR-2042 matched with SNAC is 3.39% (1:30, w/w) in monkeys, which is over 10 times higher than that of semaglutide.

CONCLUSION

We believe that the design and development of oral SHR-2042 will provide a new way to design more and more GLP-1RAs with high oral bioavailability in the future.

In-silico study of the interactions between acylated glucagon like-peptide-1 analogues and the native receptor

We have performed a series of multiple molecular dynamics (MD) simulations of glucagon-like peptide-1 (GLP-1) and acylated GLP-1 analogues in complex with the endogenous receptor (GLP-1R) to obtain a molecular understanding of how fatty acid (FA) chain structure, acylation position on the peptide, and presence of a linker affect the binding. MD simulations were analysed to extract heatmaps of receptor-peptide interaction patterns and to determine the free energy of binding using the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) approach. The extracted free energies from MM-PBSA calculations are in qualitative agreement with experimentally determined potencies. Furthermore, the interaction patterns seen in the receptor-GLP-1 complex simulations resemble previously reported binding interactions validating the simulations. Analysing the receptor-GLP-1 analogue complex simulations, we found that the major differences between the systems stem from FA interactions and positioning of acylation in the peptide. Hydrophobic interactions between the FA chain and a hydrophobic patch on the extracellular domain contribute significantly to the binding affinity. Acylation on Lys26 resulted in noticeably more interactions between the FA chain and the extracellular domain hydrophobic patch than found for acylation on Lys34 and Lys38, respectively. The presence of a charged linker between the peptide and FA chain can potentially stabilise the complex by forming hydrogen bonds to arginine residues in the linker region between the extracellular domain and the transmembrane domain. A molecular understanding of the fatty acid structure and its effect on binding provides important insights into designing acylated agonists for GLP-1R.Communicated by Ramaswamy H. Sarma.

Aggregation Behavior of Structurally Similar Therapeutic Peptides Investigated by 1H NMR and All-Atom Molecular Dynamics Simulations

Understanding of peptide aggregation propensity is an important aspect in pharmaceutical development of peptide drugs. In this work, methodologies based on all-atom molecular dynamics (AA-MD) simulations and 1H NMR (in neat H2O) were evaluated as tools for identification and investigation of peptide aggregation. A series of structurally similar, pharmaceutically relevant peptides with known differences in aggregation behavior (D-Phe6-GnRH, ozarelix, cetrorelix, and degarelix) were investigated. The 1H NMR methodology was used to systematically investigate variations in aggregation with peptide concentration and time. Results show that 1H NMR can be used to detect the presence of coexisting classes of aggregates and the inclusion or exclusion of counterions in peptide aggregates. Interestingly, results suggest that the acetate counterions are included in aggregates of ozarelix and cetrorelix but not in aggregates of degarelix. The peptides investigated in AA-MD simulations (D-Phe6-GnRH, ozarelix, and cetrorelix) showed the same rank order of aggregation propensity as in the NMR experiments. The AA-MD simulations also provided molecular-level insights into aggregation dynamics, aggregation pathways, and the influence of different structural elements on peptide aggregation propensity and intermolecular interactions within the aggregates. Taken together, the findings from this study illustrate that 1H NMR and AA-MD simulations can be useful, complementary tools in early evaluation of aggregation propensity and formulation development for peptide drugs.

The incretin/glucagon system as a target for pharmacotherapy of obesity

Obesity is a chronic, multifactorial, relapsing disease. Despite multicomponent lifestyle interventions, including pharmacotherapy, maintaining bodyweight loss is challenging for many people. The pathophysiology of obesity is complex, and currently approved pharmacotherapies only target a few of the many pathways involved; thus, single-targeting agents have limited efficacy. Proglucagon-derived peptides, glucagon, and the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), represent attractive targets for managing obesity and metabolic disorders because they may have direct roles in multiple mechanisms including satiety, energy homeostasis, and lipolytic activity. Unimolecular dual and triple agonists targeting glucagon and incretin hormone receptors have been shown to promote bodyweight loss, lower glucose levels, and reduce food intake in animal models of obesity. Multiple dual receptor agonists are in clinical development for the treatment of obesity, including GLP-1/GIP and GLP-1/glucagon receptor agonists. The extent to which glucagon contributes to treatment effects remains to be understood, but it may promote bodyweight loss by reducing food intake, while concomitant GLP-1 receptor agonism ensures normal glucose control. Further research is required to fully understand the molecular mechanisms of action and metabolic effects of both dual and triple receptor agonists.

Amyloidogenicity of peptides targeting diabetes and obesity

Since the discovery of insulin, a century ago, the repertoire of therapeutic polypeptides targeting diabetes - and now also obesity - have increased substantially. The focus on quality has shifted from impure and unstable preparations of animal insulin to highly pure, homologous recombinant insulin, along with other peptide-based hormones and analogs such as amylin analogs (pramlintide, davalintide, cagrilintide), glucagon and glucagon-like peptide-1 receptor agonists (GLP-1, liraglutide, exenatide, semaglutide). Proper formulation, storage, manipulation and usage by professionals and patients are required in order to avoid agglomeration into high molecular weight products (HMWP), either amorphous or amyloid, which could result in potential loss of biological activity and short- or long-term immune reaction and silent inactivation. In this narrative review, we present perspective of the aggregation of therapeutic polypeptides used in diabetes and other metabolic diseases, covering the nature and mechanisms, analytical techniques, physical and chemical stability, strategies aimed to hamper the formation of HMWP, and perspectives on future biopharmaceutical developments.

Small-angle X-ray scattering for the proteomics community: current overview and future potential

Introduction: Proteins are biological nanoparticles. For structural proteomics and hybrid structural biology, complementary methods are required that allow both high throughput and accurate automated data analysis. Small-angle X-ray scattering (SAXS) is a method for observing the size and shape of particles, such as proteins and complexes, in solution. SAXS data can be used to model both the structure, oligomeric state, conformational changes, and flexibility of biomolecular samples.Areas covered: The key principles of SAXS, its sample requirements, and its current and future applications for structural proteomics are briefly reviewed. Recent technical developments in SAXS experiments are discussed, and future potential of the method in structural proteomics is evaluated.Expert opinion: SAXS is a method suitable for several aspects of integrative structural proteomics, with current technical developments allowing for higher throughput and time-resolved studies, as well as the analysis of complex samples, such as membrane proteins. Increasing automation and streamlined data analysis are expected to equip SAXS for structure-based screening workflows. Originally, structural genomics had a heavy focus on folded, crystallizable proteins and complexes - SAXS is a method allowing an expansion of this focus to flexible and disordered systems.

Concentration- and pH-Dependent Oligomerization of the Thrombin-Derived C-Terminal Peptide TCP-25

Peptide oligomerization dynamics affects peptide structure, activity, and pharmacodynamic properties. The thrombin C-terminal peptide, TCP-25 (GKYGFYTHVFRLKKWIQKVIDQFGE), is currently in preclinical development for improved wound healing and infection prevention. It exhibits turbidity when formulated at pH 7.4, particularly at concentrations of 0.3 mM or more. We used biochemical and biophysical approaches to explore whether the peptide self-associates and forms oligomers. The peptide showed a dose-dependent increase in turbidity as well as α-helical structure at pH 7.4, a phenomenon not observed at pH 5.0. By analyzing the intrinsic tryptophan fluorescence, we demonstrate that TCP-25 is more stable at high concentrations (0.3 mM) when exposed to high temperatures or a high concentration of denaturant agents, which is compatible with oligomer formation. The denaturation process was reversible above 100 µM of peptide. Dynamic light scattering demonstrated that TCP-25 oligomerization is sensitive to changes in pH, time, and temperature. Computational modeling with an active 18-mer region of TCP-25 showed that the peptide can form pH-dependent higher-order end-to-end oligomers and micelle-like structures, which is in agreement with the experimental data. Thus, TCP-25 exhibits pH- and temperature-dependent dynamic changes involving helical induction and reversible oligomerization, which explains the observed turbidity of the pharmacologically developed formulation.

The Glucagon-Like Peptide 2 Analog Teduglutide Reversibly Associates to Form Pentamers

Glucagon-like peptide 1 and 2 and their analog peptide therapeutics are known to reversibly associate to form oligomers. Here we report the association properties of the glucagon-like peptide 2 analog teduglutide at concentrations up to ∼15 mg/mL. Both sedimentation equilibrium (SE-AUC) and sedimentation velocity (SV-AUC) show that teduglutide dissociates completely to monomers below 0.1 mg/mL. SE-AUC shows that the apparent weight-average molar mass increases substantially between 0.1 and 1 mg/mL, reaching a maximum of ∼14.5 kDa (∼3.9-mer) near 2 mg/mL, and then falling at higher concentrations because of strong solution nonideality effects (highly positive second virial coefficient). Circular dichroism spectra over the range from 0.1 to 2 mg/mL show that self-association is accompanied by significant increases in alpha-helix content, and that the associated state has a distinct tertiary structure. The SV-AUC data up to 2.2 mg/mL are fitted fairly well by an ideal rapidly reversible monomer-pentamer association. The SE-AUC modeling included thermodynamic nonideality effects. SE-AUC data up to ∼15 mg/mL imply a monomer-pentamer association at lower concentrations, but the pentamers also appear to weakly associate to form decamers. These results illustrate the importance of directly modeling the solution nonideality effects, which if neglected would lead to an incorrect preferred stoichiometry.

Solution structures of long-acting insulin analogues and their complexes with albumin

The lipidation of peptide drugs is one strategy to obtain extended half-lives, enabling once-daily or even less frequent injections for patients. The half-life extension results from a combination of self-association and association with human serum albumin (albumin). The self-association and association with albumin of two insulin analogues, insulin detemir and insulin degludec, were investigated by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) in phenolic buffers. Detemir shows concentration-dependent self-association, with an equilibrium between hexamer, dihexamer, trihexamer and larger species, while degludec appears as a dihexamer independent of concentration. The solution structure of the detemir trihexamer has a bent shape. The stoichiometry of the association with albumin was studied using DLS. For albumin-detemir the molar stoichiometry was determined to be 1:6 (albumin:detemir ratio) and for albumin-degludec it was between 1:6 and 1:12 (albumin:degludec ratio). Batch SAXS measurements of a 1:6 albumin:detemir concentration series revealed a concentration dependence of complex formation. The data allowed the modelling of a complex between albumin and a detemir hexamer and a complex consisting of two albumins binding to opposite ends of a detemir dihexamer. Measurements of size-exclusion chromatography coupled to SAXS revealed a complex between a degludec dihexamer and albumin. Based on the results, equilibria for the albumin-detemir and albumin-degludec mixtures are proposed.

Transcellular stomach absorption of a derivatized glucagon-like peptide-1 receptor agonist

Oral administration of therapeutic peptides is hindered by poor absorption across the gastrointestinal barrier and extensive degradation by proteolytic enzymes. Here, we investigated the absorption of orally delivered semaglutide, a glucagon-like peptide-1 analog, coformulated with the absorption enhancer sodiumN-[8-(2-hydroxybenzoyl) aminocaprylate] (SNAC) in a tablet. In contrast to intestinal absorption usually seen with small molecules, clinical and preclinical dog studies revealed that absorption of semaglutide takes place in the stomach, is confined to an area in close proximity to the tablet surface, and requires coformulation with SNAC. SNAC protects against enzymatic degradation via local buffering actions and only transiently enhances absorption. The mechanism of absorption is shown to be compound specific, transcellular, and without any evidence of effect on tight junctions. These data have implications for understanding how highly efficacious and specific therapeutic peptides could be transformed from injectable to tablet-based oral therapies.

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.

Glycation of human serum albumin impairs binding to the glucagon-like peptide-1 analogue liraglutide

The long-acting glucagon-like peptide-1 analogue liraglutide has proven efficiency in the management of type 2 diabetes and also has beneficial effects on cardiovascular diseases. Liraglutide's protracted action highly depends on its capacity to bind to albumin via its palmitic acid part. However, in diabetes, albumin can undergo glycation, resulting in impaired drug binding. Our objective in this study was to assess the impact of human serum albumin (HSA) glycation on liraglutide affinity. Using fluorine labeling of the drug and ¹⁹F NMR, we determined HSA affinity for liraglutide in two glycated albumin models. We either glycated HSA in vitro by incubation with glucose (G25- or G100-HSA) or methylglyoxal (MGO-HSA) or purified in vivo glycated HSA from the plasma of diabetic patients with poor glycemic control. Nonglycated commercial HSA (G0-HSA) and HSA purified from plasma of healthy individuals served as controls. We found that glycation decreases affinity for liraglutide by 7-fold for G100-HSA and by 5-fold for MGO-HSA compared with G0-HSA. A similarly reduced affinity was observed for HSA purified from diabetic individuals compared with HSA from healthy individuals. Our results reveal that glycation significantly impairs HSA affinity to liraglutide and confirm that glycation contributes to liraglutide's variable therapeutic efficiency, depending on diabetes stage. Because diabetes is a progressive disease, the effect of glycated albumin on liraglutide affinity found here is important to consider when diabetes is managed with this drug.

Glucagon-like Peptide 1 Conjugated to Recombinant Human Serum Albumin Variants with Modified Neonatal Fc Receptor Binding Properties. Impact on Molecular Structure and Half-Life

Glucagon-like peptide 1 (GLP-1) is a small incretin hormone stimulated by food intake, resulting in an amplification of the insulin response. Though GLP-1 is interesting as a drug candidate for the treatment of type 2 diabetes mellitus, its short plasma half-life of <3 min limits its clinical use. A strategy for extending the half-life of GLP-1 utilizes the long half-life of human serum albumin (HSA) by combining the two via chemical conjugation or genetic fusion. HSA has a plasma half-life of around 21 days because of its interaction with the neonatal Fc receptor (FcRn) expressed in endothelial cells of blood vessels, which rescues circulating HSA from lysosomal degradation. We have conjugated GLP-1 to C34 of native sequence recombinant HSA (rHSA) and two rHSA variants, one with increased and one with decreased binding affinity for human FcRn. We have investigated the impact of conjugation on FcRn binding affinities, GLP-1 potency, and pharmacokinetics, combined with the solution structure of the rHSA variants and GLP-1-albumin conjugates. The solution structures, determined by small-angle X-ray scattering, show the GLP-1 pointing away from the surface of rHSA. Combining the solution structures with the available structural information about the FcRn and GLP-1 receptor obtained from X-ray crystallography, we can explain the observed in vitro and in vivo behavior. We conclude that the conjugation of GLP-1 to rHSA does not affect the interaction between rHSA and FcRn, while the observed decrease in the potency of GLP-1 can be explained by a steric hindrance of binding of GLP-1 to its receptor.

Peptide hormones and lipopeptides: from self-assembly to therapeutic applications

This review describes the properties and activities of lipopeptides and peptide hormones and how the lipidation of peptide hormones could potentially produce therapeutic agents combating some of the most prevalent diseases and conditions. The self‐assembly of these types of molecules is outlined, and how this can impact on bioactivity. Peptide hormones specific to the uptake of food and produced in the gastrointestinal tract are discussed in detail. The advantages of lipidated peptide hormones over natural peptide hormones are summarised, in terms of stability and renal clearance, with potential application as therapeutic agents. © 2017 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.