GSK2374697, a novel albumin-binding domain antibody (AlbudAb), extends systemic exposure of exendin-4: first study in humans--PK/PD and safety

Augmented antitumor immune responses of HER2-targeted pyroptotic induction by long-lasting recombinant immunopyroptotins

Pyroptosis is a well-documented form of programmed cell death caused by the gasdermin-driven perforation of cell membranes. Selective induction of pyroptosis in tumor cells represents a promising antitumor strategy to enhance the efficacy of immunotherapy. In this study, we established a recombinant protein-based immunopyroptotin strategy that led to the intratumoral induction of pyroptosis for HER2-directed therapy. Long-lasting immunopyroptotins were constructed by sequentially fusing the humanized anti-HER2 single-chain antibody P1h3, albumin-binding peptide (ABD035 or dAb7h8), cathepsin B-cleavable peptide B2, endosome-disruptive peptide E5C3, and active pyroptotic effector gasdermin D-N fragment (GN). After purification, we evaluated the cytotoxicity and antitumor immune responses primarily induced by the immunopyroptotins in HER2-overexpressing breast cancer cells. The resulting ABD035-immunoGN and dAb7h8-immunoGN showed improved in vitro cytotoxicity in HER2-overexpressing cancer cells compared with that in the immunotBid that we previously generated to induce tumor cell apoptosis. The binding of long-lasting immunopyroptotins to albumin increased the half-life by approximately 7-fold in nude mice. The enhanced antitumor efficacy of long-lasting immunopyroptotins was confirmed in both N87 tumor-bearing T cell-deficient mice and 4T1-hHER2 bilateral tumor-bearing immunocompetent mice. Immunopyroptotin treatment elicited systemic antitumor immune responses involving CD8+ T cells and mature dendritic cells and upregulated the expression of proinflammatory cytokines, leading to sustained remission of non-injected distant tumors. This study extends the repertoire of antibody-based therapeutics through the tumor-targeted delivery of a constitutively active pore-forming gasdermin-N fragment, which shows great potential for pyroptosis-based antitumor therapy.

Impact of tissue penetration and albumin binding on design of T cell targeted bispecific agents

Bispecific agents are a rapidly growing class of cancer therapeutics, and immune targeted bispecific agents have the potential to expand functionality well beyond monoclonal antibody agents. Humabodies⁎ are fully human single domain antibodies that can be linked in a modular fashion to form multispecific therapeutics. However, the effect of heterogeneous delivery on the efficacy of crosslinking bispecific agents is currently unclear. In this work, we utilize a PSMA-CD137 Humabody with an albumin binding half-life extension (HLE) domain to determine the impact of tissue penetration on T cell activating bispecific agents. Using heterotypic spheroids, we demonstrate that increased tissue penetration results in higher T cell activation at sub-saturating concentrations. Next, we tested the effect of two different albumin binding moieties on tissue distribution using albumin-specific HLE domains with varying affinities for albumin and a non-specific lipophilic dye. The results show that a specific binding mechanism to albumin does not influence tissue penetration, but a non-specific mechanism reduced both spheroid uptake and distribution in the presence of albumin. These results highlight the potential importance of tissue penetration on bispecific agent efficacy and describe how the design parameters including albumin-binding domains can be selected to maximize the efficacy of bispecific agents.

A pan-SARS-CoV-2-specific soluble angiotensin-converting enzyme 2-albumin fusion engineered for enhanced plasma half-life and needle-free mucosal delivery

Immunocompromised patients often fail to raise protective vaccine-induced immunity against the global emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Although monoclonal antibodies have been authorized for clinical use, most have lost their ability to potently neutralize the evolving Omicron subvariants. Thus, there is an urgent need for treatment strategies that can provide protection against these and emerging SARS-CoV-2 variants to prevent the development of severe coronavirus disease 2019. Here, we report on the design and characterization of a long-acting viral entry-blocking angiotensin-converting enzyme 2 (ACE2) dimeric fusion molecule. Specifically, a soluble truncated human dimeric ACE2 variant, engineered for improved binding to the receptor-binding domain of SARS-CoV-2, was fused with human albumin tailored for favorable engagement of the neonatal fragment crystallizable receptor (FcRn), which resulted in enhanced plasma half-life and allowed for needle-free transmucosal delivery upon nasal administration in human FcRn-expressing transgenic mice. Importantly, the dimeric ACE2-fused albumin demonstrated potent neutralization of SARS-CoV-2 immune escape variants.

Human serum albumin binders: A piggyback ride for long-acting therapeutics

Human serum albumin (HSA) is the most abundant protein in the blood and has desirable properties as a drug carrier. One of the most promising ways to exploit HSA as a carrier is to append an albumin-binding moiety (ABM) to a drug for in situ HSA binding upon administration. Nature- and library-derived ABMs vary in size, affinity, and epitope, differentially improving the pharmacokinetics of an appended drug. In this review, we evaluate the current state of knowledge regarding various aspects of ABMs and the unique advantages of ABM-mediated drug delivery. Furthermore, we discuss how ABMs can be specifically modulated to maximize potential benefits in clinical development.

Derivatization with fatty acids in peptide and protein drug discovery

Peptides and proteins are widely used to treat a range of medical conditions; however, they often have to be injected and their effects are short-lived. These shortcomings of the native structure can be addressed by molecular engineering, but this is a complex undertaking. A molecular engineering technology initially applied to insulin - and which has now been successfully applied to several biopharmaceuticals - entails the derivatization of peptides and proteins with fatty acids. Various protraction mechanisms are enabled by the specific characteristics and positions of the attached fatty acid. Furthermore, the technology can ensure a long half-life following oral administration of peptide drugs, can alter the distribution of peptides and may hold potential for tissue targeting. Due to the inherent safety and well-defined chemical nature of the fatty acids, this technology provides a versatile approach to peptide and protein drug discovery.

Generation of novel long-acting GLP-1R agonists using DARPins as a scaffold

Glucagon-like peptide-1 (GLP-1) has been considered to be a promising peptide for treatment of type 2 diabetes mellitus (T2DM). However, the extremely short half-life (minutes) of native GLP-1 limits its clinical application potential. Here, we designed two GLP-1 analogues by genetic fusion of GLP-1 to one or two tandem human serum albumin-binding designed ankyrin repeat proteins (DARPins), denoted as GLP-DARPin or GLP-2DARPin. The two DARPin-fusion GLP-1 proteins were expressed in E. coli and purified, followed by measurements of their bioactivities and half-lives in mice. The results revealed that the half-life of GLP-2DARPin, binding two HSA molecules, was approximately 3-fold longer than GLP-DARPin (52.3 h versus 18.0 h). In contrast, the bioactivity results demonstrated that the blood glucose-lowering effect of GLP-DARPin was more potent than that of GLP-2DARPin. The oral glucose tolerance tests indicated that blood glucose levels were significantly reduced for at least 48 h by GLP-DARPin, but were reduced for only 24 h by GLP-2DARPin. Injected once every two days, GLP-DARPin substantially reduced blood glucose levels in streptozotocin (STZ)-induced diabetic mice to the same levels as normal mice. During the treatment course, GLP-DARPin significantly reduced the food intake and body weight of diabetic mice up to approximately 17% compared with the control group. A histological analysis revealed that GLP-DARPin alleviated islet loss in diabetic mice. These findings suggest that long-acting GLP-DARPin holds great potential for further development into drugs for the treatment of T2DM and obesity. Meanwhile, our data indicate that albumin-binding DARPins can be used as a universal scaffold to improve the pharmacokinetic profiles and pharmacological activities of therapeutic peptides and proteins.

Challenges and advancements in the pharmacokinetic enhancement of therapeutic proteins

Nowadays, proteins are frequently administered as therapeutic agents in human diseases. However, the main challenge regarding the clinical application of therapeutic proteins is short circulating plasma half-life that leads to more frequent injections for maintaining therapeutic plasma levels, increased therapy costs, immunogenic reactions, and low patient compliance. So, the development of novel strategies to enhance the pharmacokinetic profile of therapeutic proteins has attracted great attention in pharmaceuticals. So far, several techniques, each with their pros and cons, have been developed including chemical bonding to polymers, hyper glycosylation, Fc fusion, human serum albumin fusion, and recombinant PEG mimetics. These techniques mainly classify into three strategies; (i) the endosomal recycling of neonatal Fc receptor which is observed for immunoglobulins and albumin, (ii) decrease in receptor-mediated clearance, and (iii) increase in hydrodynamic radius through chemical and genetic modifications. Recently, novel PEG mimetic peptides like proline/alanine/serine repeat sequences are designed to overcome pitfalls associated with the previous technologies. Biodegradability, lack of or low immunogenicity, product homogeneity, and a simple production process, currently make these polypeptides as the preferred technology for plasma half-life extension of therapeutic proteins. In this review, challenges and pitfalls in the pharmacokinetic enhancement of therapeutic proteins using PEG-mimetic peptides will be discussed in detail.

Live long and active: Polypeptide-mediated assembly of antibody variable fragments

Antibodies possess multiple biologically relevant features that have been engineered into new therapeutic formats. Two examples include the adaptable specificity of their variable (Fv) region and the extension of plasma circulation times through their crystallizable (Fc) region. Since the invention of the single chain variable fragment (scFv) in 1988, antibody variable regions have been re-engineered into a wide variety of multifunctional nanostructures. Among these strategies, peptide-mediated self-assembly of variable regions through heterologous expression has become a powerful method to produce homogenous, functional biomaterials. This manuscript reviews recent reports of antibody fragments assembled through fusion with peptides and proteins, including elastin-like polypeptides (ELPs), collagen-like polypeptides (CLPs), albumin, transmembrane proteins, leucine zippers, silk protein, and viruses. This review further discusses the current clinical status of engineered antibody fragments and challenges to overcome.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Apelin peptides linked to anti-serum albumin domain antibodies retain affinity in vitro and are efficacious receptor agonists in vivo

The apelin receptor is a potential target in the treatment of heart failure and pulmonary arterial hypertension where levels of endogenous apelin peptides are reduced but significant receptor levels remain. Our aim was to characterise the pharmacology of a modified peptide agonist, MM202, designed to have high affinity for the apelin receptor and resistance to peptidase degradation and linked to an anti-serum albumin domain antibody (AlbudAb) to extend half-life in the blood. In competition, binding experiments in human heart MM202-AlbudAb (pKi  = 9.39 ± 0.09) bound with similar high affinity as the endogenous peptides [Pyr1 ]apelin-13 (pKi  = 8.83 ± 0.06) and apelin-17 (pKi  = 9.57 ± 0.08). [Pyr1 ]apelin-13 was tenfold more potent in the cAMP (pD2  = 9.52 ± 0.05) compared to the β-arrestin (pD2  = 8.53 ± 0.03) assay, whereas apelin-17 (pD2  = 10.31 ± 0.28; pD2  = 10.15 ± 0.13, respectively) and MM202-AlbudAb (pD2  = 9.15 ± 0.12; pD2  = 9.26 ± 0.03, respectively) were equipotent in both assays, with MM202-AlbudAb tenfold less potent than apelin-17. MM202-AlbudAb bound to immobilised human serum albumin with high affinity (pKD  = 9.02). In anaesthetised, male Sprague Dawley rats, MM202-AlbudAb (5 nmol, n = 15) significantly reduced left ventricular systolic pressure by 6.61 ± 1.46 mm Hg and systolic arterial pressure by 14.12 ± 3.35 mm Hg and significantly increased cardiac contractility by 533 ± 170 mm Hg/s, cardiac output by 1277 ± 190 RVU/min, stroke volume by 3.09 ± 0.47 RVU and heart rate by 4.64 ± 2.24 bpm. This study demonstrates that conjugating an apelin mimetic peptide to the AlbudAb structure retains receptor and in vivo activity and may be a new strategy for development of apelin peptides as therapeutic agents.

Exendin-4 analogs in insulinoma theranostics

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

Advances in therapeutic peptides targeting G protein-coupled receptors

Dysregulation of peptide-activated pathways causes a range of diseases, fostering the discovery and clinical development of peptide drugs. Many endogenous peptides activate G protein-coupled receptors (GPCRs) - nearly 50 GPCR peptide drugs have been approved to date, most of them for metabolic disease or oncology, and more than 10 potentially first-in-class peptide therapeutics are in the pipeline. The majority of existing peptide therapeutics are agonists, which reflects the currently dominant strategy of modifying the endogenous peptide sequence of ligands for peptide-binding GPCRs. Increasingly, novel strategies are being employed to develop both agonists and antagonists, to both introduce chemical novelty and improve drug-like properties. Pharmacodynamic improvements are evolving to allow biasing ligands to activate specific downstream signalling pathways, in order to optimize efficacy and reduce side effects. In pharmacokinetics, modifications that increase plasma half-life have been revolutionary. Here, we discuss the current status of the peptide drugs targeting GPCRs, with a focus on evolving strategies to improve pharmacokinetic and pharmacodynamic properties.

Recent Advances in Half-life Extension Strategies for Therapeutic Peptides and Proteins

Peptides and proteins are two classes of molecules with attractive possibilities for therapeutic applications. However, the bottleneck for the therapeutic application of many peptides and proteins is their short halflives in vivo, typically just a few minutes to hours. Half-life extension strategies have been extensively studied and many of them have been proven to be effective in the generation of long-acting therapeutics with improved pharmacokinetic and pharmacodynamic properties. In this review, we summarize the recent advances in half-life extension strategies, illustrate their potential applications and give some examples, highlighting the strategies that have been used in approved drugs and for drugs in clinical trials. Meanwhile, several novel strategies that are still in the process of discovery or at a preclinical stage are also introduced. In these strategies, the two most frequently used half-life extension methods are the reduction in the rate of renal clearance or the exploitation of the recycling mechanism of FcRn by binding to the albumin or IgG-Fc. Here, we discuss half-life extension strategies of recombinant therapeutic protein via genetic fusion, rather than chemical conjugation such as PEGylation. With the rapid development of genetic engineering and protein engineering, novel strategies for half-life extension have been emerged consistently. Some of these will be evaluated in clinical trials and may become viable alternatives to current strategies for making next-generation biodrugs.

Non-covalent albumin-binding ligands for extending the circulating half-life of small biotherapeutics

Peptides and small protein scaffolds are gaining increasing interest as therapeutics. Similarly to full-length antibodies, they can bind a target with a high binding affinity and specificity while remaining small enough to diffuse into tissues. However, despite their numerous advantages, small biotherapeutics often suffer from a relatively short circulating half-life, thus requiring frequent applications that ultimately restrict their ease of use and user compliance. To overcome this limitation, a large variety of half-life extension strategies have been developed in the last decades. Linkage to ligands that non-covalently bind to albumin, the most abundant serum protein with a circulating half-life of ∼19 days in humans, represents one of the most successful approaches for the generation of long-lasting biotherapeutics with improved pharmacokinetic properties and superior efficacy in the clinic.

The biodistribution and clearance of AlbudAb, a novel biopharmaceutical medicine platform, assessed via PET imaging in humans

Abstract

Conjugation or fusion to AlbudAbs™ (albumin-binding domain antibodies) is a novel approach to extend the half-life and alter the tissue distribution of biological and small molecule therapeutics. To understand extravasation kinetics and extravascular organ concentrations of AlbudAbs in humans, we studied tissue distribution and elimination of a non-conjugated ⁸⁹Zr-labeled AlbudAb in healthy volunteers using positron emission tomography/computed tomography (PET/CT).

Methods

A non-conjugated AlbudAb (GSK3128349) was radiolabeled with ⁸⁹Zr and a single 1 mg (~ 15 MBq) dose intravenously administered to eight healthy males. ⁸⁹Zr-AlbudAb tissue distribution was followed for up to 7 days with four whole-body PET/CT scans. ⁸⁹Zr-AlbudAb tissue concentrations were quantified in organs of therapeutic significance, measuring standardized uptake value and tissue/plasma ratios. Plasma pharmacokinetics were assessed by gamma counting and LC-MS/MS of blood samples.

Results

⁸⁹Zr-AlbudAb administration and PET/CT procedures were well tolerated, with no drug-related immunogenicity or adverse events. ⁸⁹Zr-AlbudAb rapidly distributed throughout the vasculature, with tissue/plasma ratios in the liver, lungs, and heart relatively stable over 7 days post-dose, ranging between 0.1 and 0.5. The brain tissue/plasma ratio of 0.025 suggested minimal AlbudAb blood-brain barrier penetration. Slowly increasing ratios in muscle, testis, pancreas, and spleen reflected either slow AlbudAb penetration and/or ⁸⁹Zr residualization in these organs. Across all tissues evaluated, the kidney tissue/plasma ratio was highest (0.5–1.5 range) with highest concentration in the renal cortex. The terminal half-life of the ⁸⁹Zr-AlbudAb was 18 days.

Conclusion

Evaluating the biodistribution of ⁸⁹Zr-AlbudAb in healthy volunteers using a low radioactivity dose was successful (total subject exposure ~ 10 mSv). Results indicated rapid formation of reversible, but stable, complexes between AlbudAb and albumin upon dosing. ⁸⁹Zr-AlbudAb demonstrated albumin-like pharmacokinetics, including limited renal elimination. This novel organ-specific distribution data for AlbudAbs in humans will facilitate a better selection of drug targets to prosecute using the AlbudAb platform and significantly contribute to modeling work optimizing dosing of therapeutic AlbudAbs in the clinic.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0514-9) contains supplementary material, which is available to authorized users.

Mechanisms Influencing the Pharmacokinetics and Disposition of Monoclonal Antibodies and Peptides

Monoclonal antibodies (mAbs) and peptides are an important class of therapeutic modalities that have brought improved health outcomes in areas with limited therapeutic optionality. Presently, there more than 90 mAb and peptide therapeutics on the United States market, with over 600 more in various clinical stages of development in a broad array of therapeutic areas, including diabetes, autoimmune disorders, oncology, neuroscience, and cardiovascular and infectious diseases. Notwithstanding this potential, there is high clinical rate of attrition, with approximately 10% reaching patients. A major contributor to the failure of the molecules is often times an incomplete or poor understanding of the pharmacokinetics (PK) and disposition profiles leading to limited or diminished efficacy. Increased and thorough characterization efforts directed at disseminating mechanisms influencing the PK and disposition of mAbs and peptides can aid in improving the design for their intended pharmacological activity, and thereby their clinical success. The PK and disposition factors for mAbs and peptides are broadly influenced by target-mediated drug disposition and nontarget-related clearance mechanisms related to the interplay between the relationship of the structure and physiochemical properties of mAbs and peptides with physiologic processes. This review focuses on nontarget-related factors influencing the disposition and PK of mAbs and peptides. Contemporary considerations around the increasing in silico approaches to identify nontarget-related molecule limitations and enhancing the druggability of mAbs and peptides, including parenteral and nonparenteral delivery strategies that are geared toward improving patient experience and compliance, are also discussed.

David vs. Goliath: The Structure, Function, and Clinical Prospects of Antibody Fragments

Since the licensing of the first monoclonal antibody therapy in 1986, monoclonal antibodies have become the largest class of biopharmaceuticals with over 80 antibodies currently approved for a variety of disease indications. The development of smaller, antigen binding antibody fragments, derived from conventional antibodies or produced recombinantly, has been growing at a fast pace. Antibody fragments can be used on their own or linked to other molecules to generate numerous possibilities for bispecific, multi-specific, multimeric, or multifunctional molecules, and to achieve a variety of biological effects. They offer several advantages over full-length monoclonal antibodies, particularly a lower cost of goods, and because of their small size they can penetrate tissues, access challenging epitopes, and have potentially reduced immunogenicity. In this review, we will discuss the structure, production, and mechanism of action of EMA/FDA-approved fragments and of those in clinical and pre-clinical development. We will also discuss current topics of interest surrounding the potential use of antibody fragments for intracellular targeting and blood-brain barrier (BBB) penetration.

Strategies for modifying drug residence time and ocular bioavailability to decrease treatment frequency for back of the eye diseases

INTRODUCTION

Treating posterior eye diseases has become a major area of focus for pharmaceutical and biotechnology companies. Current standard of care for treating posterior eye diseases relies on administration via intravitreal injection. Although effective, this is not without complications and there is great incentive to develop longer-acting therapeutics and/or sustained release delivery systems. Here, we present an overview of emerging technologies for delivery of biologics to the back of the eye.

AREAS COVERED

Posterior eye diseases, intravitreal injection, age-related macular degeneration, anti-VEGF, ocular pharmacokinetics, novel technologies to extend half-life, in vivo models, translation to the clinic, and hurdles to effective patient care.

EXPERT OPINION

Posterior eye diseases are a worldwide public health issue. Although anti-VEGF molecules represent a major advance for treating diseases involving choroidal neovascularization, frequent injection can be burdensome for patients and clinicians. There is a need for effective and patient-friendly treatments for posterior eye diseases. Many technologies that enable long-acting delivery to the back of the eye are being evaluated. However, successful development of novel therapies and delivery technologies is hampered by a multitude of factors, including patient education, translatability of in vitro/in vivo preclinical data to the clinic, and regulatory challenges associated with novel technologies.

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

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

Overview of Antibody Drug Delivery

Monoclonal antibodies (mAbs) are one of the most important classes of therapeutic proteins, which are used to treat a wide number of diseases (e.g., oncology, inflammation and autoimmune diseases). Monoclonal antibody technologies are continuing to evolve to develop medicines with increasingly improved safety profiles, with the identification of new drug targets being one key barrier for new antibody development. There are many opportunities for developing antibody formulations for better patient compliance, cost savings and lifecycle management, e.g., subcutaneous formulations. However, mAb-based medicines also have limitations that impact their clinical use; the most prominent challenges are their short pharmacokinetic properties and stability issues during manufacturing, transport and storage that can lead to aggregation and protein denaturation. The development of long acting protein formulations must maintain protein stability and be able to deliver a large enough dose over a prolonged period. Many strategies are being pursued to improve the formulation and dosage forms of antibodies to improve efficacy and to increase the range of applications for the clinical use of mAbs.

Recombinant immunotoxins with albumin-binding domains have long half-lives and high antitumor activity

Recombinant immunotoxins (RITs) are chimeric proteins consisting of a Fv that binds to a cancer cell and a portion of a protein toxin. One of these, Moxetumomab pasudotox, was shown to be effective in treating patients with some leukemias, where the cells are readily accessible to the RIT. However, their short half-life limits their efficacy in solid tumors, because penetration into the tumors is slow. Albumin and agents bound to albumin have a long half-life in the circulation. To increase the time tumor cells are exposed to RITs, we have produced and evaluated variants that contain either an albumin-binding domain (ABD) from Streptococcus or single-domain antibodies from Llama. We have inserted these ABDs into RITs targeting mesothelin, between the Fv and the furin cleavage site. We find that these proteins can be produced in large amounts, are very cytotoxic to mesothelin-expressing cancer cell lines, and have a high affinity for human or mouse serum albumin. In mice, the RIT containing an ABD from Streptococcus has a longer half-life and higher antitumor activity than the other two. Its half-life in the circulation of mice ranges from 113 to 194 min compared with 13 min for an RIT with no ABD. Cell uptake studies show the RIT enters the target cell bound to serum albumin. We conclude that RITs with improved half-lives and antitumor activity should be evaluated for the treatment of cancer in humans.

Half-life extension using serum albumin-binding DARPin® domains

A long systemic half-life is key for therapeutic proteins. To that end we have generated serum albumin-binding designed ankyrin repeat domains. These domains bind serum albumin of different species with nanomolar affinities, and have significantly improved pharmacokinetic properties both in mouse and cynomolgus monkey compared to non-serum albumin-binding DARPin® domains. In addition, they exhibit high thermal stability and long storage stability, which is an essential feature for their use in drug development. Covalently linking a serum albumin-binding DARPin® domain to domains with other target specificities results in improvements of multiple orders of magnitude in exposure and terminal half-life, both in mouse and cynomolgus monkey. Pharmacokinetic assessment of such constructs revealed terminal half-life values ranging from 27 h to 80 h in mouse, and from 2.6 days to 20 days in cynomolgus monkey. Extrapolation by allometric scaling on these findings suggests terminal half-life values of 5-50 days in human, indicating that pharmacokinetic properties in the range of monoclonal antibodies can be achieved with DARPin® drug candidates. Such serum albumin-binding DARPin® domains are thus valuable tools for the generation of multi-functional drugs with an extended in vivo half-life.

A Hydrogel-Microsphere Drug Delivery System That Supports Once-Monthly Administration of a GLP-1 Receptor Agonist

We have developed a chemically controlled very long-acting delivery system to support once-monthly administration of a peptidic GLP-1R agonist. Initially, the prototypical GLP-1R agonist exenatide was covalently attached to hydrogel microspheres by a self-cleaving β-eliminative linker; after subcutaneous injection in rats, the peptide was slowly released into the systemic circulation. However, the short serum exenatide half-life suggested its degradation in the subcutaneous depot. We found that exenatide undergoes deamidation at Asn²⁸ with an in vitro and in vivo half-life of approximately 2 weeks. The [Gln²⁸]exenatide variant and exenatide showed indistinguishable GLP-1R agonist activities as well as pharmacokinetic and pharmacodynamic effects in rodents; however, unlike exenatide, [Gln²⁸]exenatide is stable for long periods. Two different hydrogel-[Gln²⁸]exenatide conjugates were prepared using β-eliminative linkers with different cleavage rates. After subcutaneous injection in rodents, the serum half-lives for the released [Gln²⁸]exenatide from the two conjugates were about 2 weeks and one month. Two monthly injections of the latter in the Zucker diabetic fatty rat showed pharmacodynamic effects indistinguishable from two months of continuously infused exenatide. Pharmacokinetic simulations indicate that the delivery system should serve well as a once-monthly GLP-1R agonist for treatment of type 2 diabetes in humans.

The Current State of Peptide Drug Discovery: Back to the Future?

Over the past decade, peptide drug discovery has experienced a revival of interest and scientific momentum, as the pharmaceutical industry has come to appreciate the role that peptide therapeutics can play in addressing unmet medical needs and how this class of compounds can be an excellent complement or even preferable alternative to small molecule and biological therapeutics. In this Perspective, we give a concise description of the recent progress in peptide drug discovery in a holistic manner, highlighting enabling technological advances affecting nearly every aspect of this field: from lead discovery, to synthesis and optimization, to peptide drug delivery. An emphasis is placed on describing research efforts to overcome the inherent weaknesses of peptide drugs, in particular their poor pharmacokinetic properties, and how these efforts have been critical to the discovery, design, and subsequent development of novel therapeutics.

CCL20 neutralization by a monoclonal antibody in healthy subjects selectively inhibits recruitment of CCR6+ cells in an experimental suction blister

AIMS

GSK3050002, a humanized IgG1κ antibody with high binding affinity to human CCL20, was administered in a first-in-human study to evaluate safety, pharmacokinetics (PK) and pharmacodynamics (PD). An experimental skin suction blister model was employed to assess target engagement and the ability of the compound to inhibit recruitment of inflammatory CCR6 expressing cells.

METHODS

This study was a randomized, double-blind (sponsor open), placebo-controlled, single-centre, single ascending intravenous dose escalation trial in 48 healthy male volunteers.

RESULTS

GSK3050002 (0.1-20 mg kg^-1 ) was well tolerated and no safety concerns were identified. The PK was linear over the dose range, with a half-life of approximately 2 weeks. Complex of GSK3050002/CCL20 increased in serum and blister fluid with increasing doses of GSK3050002. There were dose-dependent decreases in CCR6⁺ cell recruitment to skin blisters with maximal effects at doses of 5 mg kg^-1 and higher, doses at which GSK3050002/CCL20 complex in serum and blister fluid also appeared to reach maximum levels.

CONCLUSIONS

These results indicate a relationship between PK, target engagement and PD, suggesting a selective inhibition of recruitment of CCR6⁺ cells by GSK3050002 and support further development of GSK3050002 in autoimmune and inflammatory diseases.

Fusion of Ssm6a with a protein scaffold retains selectivity on NaV 1.7 and improves its therapeutic potential against chronic pain

Voltage-gated sodium channel Na_V 1.7 serves as an attractive target for chronic pain treatment. Several venom peptides were found to selectively inhibit Na_V 1.7 but with intrinsic problems. Among them, Ssm6a, a recently discovered centipede venom peptide, shows the greatest selectivity against Na_V 1.7, but dissociates from the target too fast and loses bioactivity in synthetic forms. As a disulfide-rich venom peptide, it is difficult to optimize Ssm6a by artificial mutagenesis and produce the peptide with common industrial manufacturing methods. Here, we developed a novel protein scaffold fusion strategy to address these concerns. Instead of directly mutating Ssm6a, we genetically fused Ssm6a with a protein scaffold engineered from human muscle fatty acid-binding protein. The resultant fusion protein, SP-TOX, maintained the selectivity and potency of Ssm6a upon Na_V 1.7 but dissociated from target at least 10 times more slowly. SP-TOX dramatically reduced inflammatory pain in a rat model through DRG-targeted delivery. Importantly, SP-TOX can be expressed cytosolically in Escherichia coli and purified in a cost-effective way. In summary, our study provided the first example of cytosolically expressed fusion protein with high potency and selectivity on Na_V 1.7. Our protein scaffold fusion approach may have its broad application in optimizing disulfide-rich venom peptides for therapeutic usage.

Fab-dsFv: A bispecific antibody format with extended serum half-life through albumin binding

An antibody format, termed Fab-dsFv, has been designed for clinical indications that require monovalent target binding in the absence of direct Fc receptor (FcR) binding while retaining substantial serum presence. The variable fragment (Fv) domain of a humanized albumin-binding antibody was fused to the C-termini of Fab constant domains, such that the VL and VH domains were individually connected to the Cκ and CH1 domains by peptide linkers, respectively. The anti-albumin Fv was selected for properties thought to be desirable to ensure a durable serum half-life mediated via FcRn. The Fv domain was further stabilized by an inter-domain disulfide bond. The bispecific format was shown to be thermodynamically and biophysically stable, and retained good affinity and efficacy to both antigens simultaneously. In in vivo studies, the serum half-life of Fab-dsFv, 2.6 d in mice and 7.9 d in cynomolgus monkeys, was equivalent to Fab'-PEG.

Extending the half-life of a fab fragment through generation of a humanized anti-human serum albumin Fv domain: An investigation into the correlation between affinity and serum half-life

We generated an anti-albumin antibody, CA645, to link its Fv domain to an antigen-binding fragment (Fab), thereby extending the serum half-life of the Fab. CA645 was demonstrated to bind human, cynomolgus, and mouse serum albumin with similar affinity (1–7 nM), and to bind human serum albumin (HSA) when it is in complex with common known ligands. Importantly for half-life extension, CA645 binds HSA with similar affinity within the physiologically relevant range of pH 5.0 – pH 7.4, and does not have a deleterious effect on the binding of HSA to neonatal Fc receptor (FcRn). A crystal structure of humanized CA645 Fab in complex with HSA was solved and showed that CA645 Fab binds to domain II of HSA. Superimposition with the crystal structure of FcRn bound to HSA confirmed that CA645 does not block HSA binding to FcRn. In mice, the serum half-life of humanized CA645 Fab is 84.2 h. This is a significant extension in comparison with < 1 h for a non-HSA binding CA645 Fab variant. The Fab-HSA structure was used to design a series of mutants with reduced affinity to investigate the correlation between the affinity for albumin and serum half-life. Reduction in the affinity for MSA by 144-fold from 2.2 nM to 316 nM had no effect on serum half-life. Strikingly, despite a reduction in affinity to 62 µM, an extension in serum half-life of 26.4 h was still obtained. CA645 Fab and the CA645 Fab-HSA complex have been deposited in the Protein Data Bank (PDB) with accession codes, 5FUZ and 5FUO, respectively.

2015 White Paper on recent issues in bioanalysis: focus on new technologies and biomarkers (Part 2 – hybrid LBA/LCMS and input from regulatory agencies)

The 2015 9th Workshop on Recent Issues in Bioanalysis (9th WRIB) took place in Miami, Florida with participation of over 600 professionals from pharmaceutical and biopharmaceutical companies, biotechnology companies, contract research organizations and regulatory agencies worldwide. It is once again a 5-day week long event – a full immersion bioanalytical week – specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest in bioanalysis. The topics covered included both small and large molecules, and involved LCMS, hybrid LBA/LCMS, LBA approaches including the focus on biomarkers and immunogenicity. This 2015 White Paper encompasses recommendations that emerged from the extensive discussions held during the workshop, and is aimed at providing the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to advance scientific excellence, improve quality and deliver better regulatory compliance. Due to its length, the 2015 edition of this comprehensive White Paper has been divided into three parts. Part 2 covers the recommendations for hybrid LBA/LCMS and regulatory agencies’ inputs. Part 1 (small molecule bioanalysis using LCMS) and Part 3 (large molecule bioanalysis using LBA, biomarkers and immunogenicity) will be published in volume 7 of Bioanalysis, issues 22 and 24, respectively.

GSK2374697, a long duration glucagon-like peptide-1 (GLP-1) receptor agonist, reduces postprandial circulating endogenous total GLP-1 and peptide YY in healthy subjects

We investigated the effects of a long-duration glucagon-like peptide-1 (GLP-1) receptor agonist, GSK2374697, on postprandial endogenous total GLP-1 and peptide YY (PYY). Two cohorts of healthy subjects, one normal/overweight and one obese, were randomized to receive GSK2374697 2 mg (n = 8 each) or placebo (n = 4 and n = 2) subcutaneously on days 1, 4 and 7. Samples for plasma endogenous GLP-1 and PYY were collected after breakfast on days -1 and 12. Weighted mean area under the curve (0-4 h) of total GLP-1 and PYY in treated subjects was reduced compared with placebo. The least squares mean difference for change from baseline was -1.24 pmol/l [95% confidence interval (CI) -2.33, -0.16] and -4.47 pmol/l (95% CI -8.74, -0.20) for total GLP-1 and PYY, respectively, in normal/overweight subjects (p < 0.05 for both), and -1.56 (95% CI -2.95, -0.16) and -3.02 (95% CI -8.58, 2.55), respectively, in obese subjects (p < 0.05 for GLP-1). In healthy subjects, GSK2374697 reduced postprandial total GLP-1 and PYY levels, suggesting feedback suppression of enteroendocrine L-cell secretion of these peptides.

Fusion Proteins for Half-Life Extension of Biologics as a Strategy to Make Biobetters

The purpose of making a "biobetter" biologic is to improve on the salient characteristics of a known biologic for which there is, minimally, clinical proof of concept or, maximally, marketed product data. There already are several examples in which second-generation or biobetter biologics have been generated by improving the pharmacokinetic properties of an innovative drug, including Neulasta(®) [a PEGylated, longer-half-life version of Neupogen(®) (filgrastim)] and Aranesp(®) [a longer-half-life version of Epogen(®) (epoetin-α)]. This review describes the use of protein fusion technologies such as Fc fusion proteins, fusion to human serum albumin, fusion to carboxy-terminal peptide, and other polypeptide fusion approaches to make biobetter drugs with more desirable pharmacokinetic profiles.

The role of albumin receptors in regulation of albumin homeostasis: Implications for drug delivery

Albumin is the most abundant protein in blood and acts as a molecular taxi for a plethora of small insoluble substances such as nutrients, hormones, metals and toxins. In addition, it binds a range of medical drugs. It has an unusually long serum half-life of almost 3weeks, and although the structure and function of albumin has been studied for decades, a biological explanation for the long half-life has been lacking. Now, recent research has unravelled that albumin-binding cellular receptors play key roles in the homeostatic regulation of albumin. Here, we review our current understanding of albumin homeostasis with a particular focus on the impact of the cellular receptors, namely the neonatal Fc receptor (FcRn) and the cubilin-megalin complex, and we discuss their importance on uses of albumin in drug delivery.