Glycosylation: impact, control and improvement during therapeutic protein production

Direct Glycan Analysis of Biological Samples and Intact Glycoproteins by Integrating Machine Learning-Driven Surface-Enhanced Raman Scattering and Boronic Acid Arrays

Frequent monitoring of glycan patterns is a critical step in studying glycan-mediated cellular processes. However, the current glycan analysis tools are resource-intensive and less suitable for routine use in standard laboratories. We developed a novel glycan detection platform by integrating surface-enhanced Raman spectroscopy (SERS), boronic acid (BA) receptors, and machine learning tools. This sensor monitors the molecular fingerprint spectra of BA binding to cis-diol-containing glycans. Different types of BA receptors could yield different stereoselective reactions toward different glycans and exhibit unique vibrational spectra. By integration of the Raman spectra collected from different BA receptors, the structural information can be enriched, eventually improving the accuracy of glycan classification and quantification. Here, we established a SERS-based sensor incorporating multiple different BA receptors. This sensing platform could directly analyze the biological samples, including whole milk and intact glycoproteins (fetuin and asialofetuin), without tedious glycan release and purification steps. The results demonstrate the platform's ability to classify milk oligosaccharides with remarkable classification accuracy, despite the presence of other non-glycan constituents in the background. This sensor could also directly quantify sialylation levels of a fetuin/asialofetuin mixture without glycan release procedures. Moreover, by selecting appropriate BA receptors, the sensor exhibits an excellent performance of differentiating between α2,3 and α2,6 linkages of sialic acids. This low-cost, rapid, and highly accessible sensor will provide the scientific community with an invaluable tool for routine glycan screening in standard laboratories.

Comparison of the efficiency of the Sec and Tat secretory pathways in the secretion of recombinant neurturin protein using de novo designed signal peptides

Since cytoplasmic expression of heterologous proteins with disulfide bonds leads to the formation of inclusion bodies in E. coli, periplasmic production is preferable. The N-terminal signal peptide attached to the secreted protein determines the type of secretory pathway through which the target protein is secreted; Sec, Tat, or SRP. The aim of this study was to design and compare two novel signal peptides for the secretion of recombinant neurturin (as a model) via the Sec and Tat pathways. For this purpose, we aligned the natural signal peptides from E. coli and Bacillus subtilis to identify the conserved amino acids and those with the highest repetition. The SignalP4.1 and TatP1.0 software were used to determine the secretion efficiency of the new signal peptides. The efficiency of new signal peptides was then evaluated and compared experimentally with two naturally used signal peptides. Quantitative analysis of Western blot bands showed that approximately 80% of the expressed neurturin was secreted into the periplasmic space by new signal peptides. Circular dichroism spectroscopy also confirmed the correct secondary structure of the secreted neurturin. In conclusion, these novel signal peptides can be used to secrete any other recombinant proteins to the periplasmic space of E. coli efficiently.

Genotype-dependent N-glycosylation and newly exposed O-glycosylation affect plasmin-induced cleavage of histidine-rich glycoprotein (HRG)

Histidine-rich glycoprotein (HRG) is an abundant plasma protein harboring at least three N-glycosylation sites. HRG integrates many biological processes, such as coagulation, antiangiogenic activity, and pathogen clearance. Importantly, HRG is known to exhibit five genetic variants with minor allele frequencies of more than 10%. Among them, Pro204Ser can induce a fourth N-glycosylation site (Asn202). Considerable efforts have been made to reveal the biological function of HRG, whereas data on HRG glycosylation are scarcer. To close this knowledge gap, we used C18-based LC-MS/MS to study the glycosylation characteristics of six HRG samples from different sources. We used endogenous HRG purified from human plasma and compared its glycosylation to that of the recombinant HRG produced in Chinese hamster ovary cells or human embryonic kidney 293 cells, targeting distinct genotypic isoforms. In endogenous plasma HRG, every N-glycosylation site was occupied predominantly with a sialylated diantennary complex-type glycan. In contrast, in the recombinant HRGs, all glycans showed different antennarities, sialylation, and core fucosylation, as well as the presence of oligomannose glycans, LacdiNAcs, and antennary fucosylation. Furthermore, we observed two previously unreported O-glycosylation sites in HRG on residues Thr273 and Thr274. These sites together showed more than 90% glycan occupancy in all HRG samples studied. To investigate the potential relevance of HRG glycosylation, we assessed the plasmin-induced cleavage of HRG under various conditions. These analyses revealed that the sialylation of the N- and O-glycans as well as the genotype-dependent N-glycosylation significantly influenced the kinetics and specificity of plasmin-induced cleavage of HRG.

Opportunities and challenges of RiPP-based therapeutics

Covering: up to 2024Ribosomally synthesised and post-translationally modified peptides (RiPPs) comprise a substantial group of peptide natural products exhibiting noteworthy bioactivities ranging from antiinfective to anticancer and analgesic effects. Furthermore, RiPP biosynthetic pathways represent promising production routes for complex peptide drugs, and the RiPP technology is well-suited for peptide engineering to produce derivatives with specific functions. Thus, RiPP natural products possess features that render them potentially ideal candidates for drug discovery and development. Nonetheless, only a small number of RiPP-derived compounds have successfully reached the market thus far. This review initially outlines the therapeutic opportunities that RiPP-based compounds can offer, whilst subsequently discussing the limitations that require resolution in order to fully exploit the potential of RiPPs towards the development of innovative drugs.

Effect of Modification Strategies on the Biological Activity of Peptides/Proteins

Covalent attachment of biologically active peptides/proteins with functional moieties is an effective strategy to control their biodistribution, pharmacokinetics, enzymatic digestion, and toxicity. This review focuses on the characteristics of different modification strategies and their effects on the biological activity of peptides/proteins and illustrates their relevant applications and potential.

A platform for qualitative and quantitative characterization of α-Gal and NeuGc at the oligosaccharide level

Glycosylation modification serves as a pivotal quality attribute in glycoprotein-based therapeutics, emphasizing its role in drug safety and efficacy. Prior studies have underscored the potential immunogenic risks posed by the presence of galactose-α-1,3-galactose (α-Gal) and N-glycolylneuraminic acid (NeuGc) in glycoprotein formulations. This accentuates the imperative for developing robust qualitative and quantitative analytical methods to monitor these immunogenic epitopes, thereby ensuring drug safety. In the present investigation, α-Gal and NeuGc were accurately quantified using UPLC-FLR-MS/MS at the oligosaccharide level. Remarkably, α-Gal could be identified when the ion intensity ratio or the mass-to-charge ratio (m/z) of 528.19 to 366.14 exceeded 1. Concurrently, NeuGc and N-acetylneuraminic acid (NeuAc) could be unambiguously identified through their respective fragment ions at m/z 673.23 and m/z 657.23. Furthermore, relative quantification of α-Gal and NeuGc was achieved using fluorescence signals. This study introduces a sensitive and reliable analytical approach for the qualitative and quantitative assessment of α-Gal and NeuGc in glycoprotein pharmaceuticals. The methodology offers significant potential for application in process control and optimization of glycoprotein production, aimed at minimizing immunogenicity and enhancing product quality.

Agents for the Treatment of Gout: Current Advances and Future Perspectives

Gout is characterized by hyperuricemia and the deposition of monosodium urate (MSU) crystals around joints. Despite the availability of several drugs on the market, its treatment remains challenging owing to the notable side effects, such as hepatorenal toxicity and cardiovascular complications, that are associated with most existing agents. This perspective aims to summarize the current research progress in the development of antigout agents, particularly focusing on xanthine oxidase (XO) and urate anion transporter 1 (URAT1) inhibitors from a medicinal chemistry viewpoint and their preliminary structure-activity relationships (SARs). This perspective provides valuable insights and theoretical guidance to medicinal chemists for the discovery of antigout agents with novel chemical structures, better efficiency, and lower toxicity.

Enzyme Engineering Strategies for the Bioenhancement of L-Asparaginase Used as a Biopharmaceutical

Over the past few years, there has been a surge in the industrial production of recombinant enzymes from microorganisms due to their catalytic characteristics being highly efficient, selective, and biocompatible. L-asparaginase (L-ASNase) is an enzyme belonging to the class of amidohydrolases that catalyzes the hydrolysis of L-asparagine into L-aspartic acid and ammonia. It has been widely investigated as a biologic agent for its antineoplastic properties in treating acute lymphoblastic leukemia. The demand for L-ASNase is mainly met by the production of recombinant type II L-ASNase from Escherichia coli and Erwinia chrysanthemi. However, the presence of immunogenic proteins in L-ASNase sourced from prokaryotes has been known to result in adverse reactions in patients undergoing treatment. As a result, efforts are being made to explore strategies that can help mitigate the immunogenicity of the drug. This review gives an overview of recent biotechnological breakthroughs in enzyme engineering techniques and technologies used to improve anti-leukemic L-ASNase, taking into account the pharmacological importance of L-ASNase.

Modulating antibody effector functions by Fc glycoengineering

Antibody based drugs, including IgG monoclonal antibodies, are an expanding class of therapeutics widely employed to treat cancer, autoimmune and infectious diseases. IgG antibodies have a conserved N-glycosylation site at Asn297 that bears complex type N-glycans which, along with other less conserved N- and O-glycosylation sites, fine-tune effector functions, complement activation, and half-life of antibodies. Fucosylation, galactosylation, sialylation, bisection and mannosylation all generate glycoforms that interact in a specific manner with different cellular antibody receptors and are linked to a distinct functional profile. Antibodies, including those employed in clinical settings, are generated with a mixture of glycoforms attached to them, which has an impact on their efficacy, stability and effector functions. It is therefore of great interest to produce antibodies containing only tailored glycoforms with specific effects associated with them. To this end, several antibody engineering strategies have been developed, including the usage of engineered mammalian cell lines, in vitro and in vivo glycoengineering.

Peptides Targeting HER2-Positive Breast Cancer Cells and Applications in Tumor Imaging and Delivery of Chemotherapeutics

Breast cancer represents the most common cancer type and one of the major leading causes of death in the female worldwide population. Overexpression of HER2, a transmembrane glycoprotein related to the epidermal growth factor receptor, results in a biologically and clinically aggressive breast cancer subtype. It is also the primary driver for tumor detection and progression and, in addition to being an important prognostic factor in women diagnosed with breast cancer, HER2 is a widely known therapeutic target for drug development. The aim of this review is to provide an updated overview of the main approaches for the diagnosis and treatment of HER2-positive breast cancer proposed in the literature over the past decade. We focused on the different targeting strategies involving antibodies and peptides that have been explored with their relative outcomes and current limitations that need to be improved. The review also encompasses a discussion on targeted peptides acting as probes for molecular imaging. By using different types of HER2-targeting strategies, nanotechnology promises to overcome some of the current clinical challenges by developing novel HER2-guided nanosystems suitable as powerful tools in breast cancer imaging, targeting, and therapy.

Strategic Approaches to Improvise Peptide Drugs as Next Generation Therapeutics

In recent years, the occurrence of a wide variety of drug-resistant diseases has led to an increase in interest in alternate therapies. Peptide-based drugs as an alternate therapy hold researchers' attention in various therapeutic fields such as neurology, dermatology, oncology, metabolic diseases, etc. Previously, they had been overlooked by pharmaceutical companies due to certain limitations such as proteolytic degradation, poor membrane permeability, low oral bioavailability, shorter half-life, and poor target specificity. Over the last two decades, these limitations have been countered by introducing various modification strategies such as backbone and side-chain modifications, amino acid substitution, etc. which improve their functionality. This has led to a substantial interest of researchers and pharmaceutical companies, moving the next generation of these therapeutics from fundamental research to the market. Various chemical and computational approaches are aiding the production of more stable and long-lasting peptides guiding the formulation of novel and advanced therapeutic agents. However, there is not a single article that talks about various peptide design approaches i.e., in-silico and in-vitro along with their applications and strategies to improve their efficacy. In this review, we try to bring different aspects of peptide-based therapeutics under one article with a clear focus to cover the missing links in the literature. This review draws emphasis on various in-silico approaches and modification-based peptide design strategies. It also highlights the recent progress made in peptide delivery methods important for their enhanced clinical efficacy. The article would provide a bird's-eye view to researchers aiming to develop peptides with therapeutic applications.

Graphical Abstract

Highly-sensitive label-free deep profiling of N-glycans released from biomedically-relevant samples

Alterations of protein glycosylation can serve as sensitive and specific disease biomarkers. Labeling procedures for improved separation and detectability of oligosaccharides have several drawbacks, including incomplete derivatization, side-products, noticeable desialylation/defucosylation, sample loss, and interference with downstream analyses. Here, we develop a label-free workflow based on high sensitivity capillary zone electrophoresis-mass spectrometry (CZE-MS) for profiling of native underivatized released N-glycans. Our workflow provides a >45-fold increase in signal intensity compared to the conventional CZE-MS approaches used for N-glycan analysis. Qualitative and quantitative N-glycan profiling of purified human serum IgG, bovine serum fetuin, bovine pancreas ribonuclease B, blood-derived extracellular vesicle isolates, and total plasma results in the detection of >250, >400, >150, >310, and >520 N-glycans, respectively, using injected amounts equivalent to <25 ng of model protein and nL-levels of plasma-derived samples. Compared to reported results for biological samples of similar amounts and complexity, the number of identified N-glycans is increased up to ~15-fold, enabling highly sensitive analysis of sample amounts as low as sub-0.2 nL of plasma volume equivalents. Furthermore, highly sialylated N-glycans are identified and structurally characterized, and untreated sialic acid-linkage isomers are resolved in a single CZE-MS analysis.

Non-classical C-saccharide linkage of dehydroalanine: synthesis of C-glycoamino acids and C-glycopeptides

Herein, a non-classical C-saccharide linkage is reported via a C5 radical of pentose or C6 radical of hexose addition to Michael acceptors. C(sp³)-S cleaved glycosyl thianthrenium salts are developed as the glycosyl radical agents. The reaction provides an efficient toolkit to synthesize β-glycosyl substituted unnatural amino acids as well as for the late-stage C-saccharide modification of peptides.

Development and validation of a method for analyzing the sialylated glycopeptides of recombinant erythropoietin in urine using LC-HRMS

Erythropoietin (EPO) is a glycoprotein hormone that stimulates red blood cell production. It is produced naturally in the body and is used to treat patients with anemia. Recombinant EPO (rEPO) is used illicitly in sports to improve performance by increasing the blood's capacity to carry oxygen. The World Anti-Doping Agency has therefore prohibited the use of rEPO. In this study, we developed a bottom-up mass spectrometric method for profiling the site-specific N-glycosylation of rEPO. We revealed that intact glycopeptides have a site-specific tetra-sialic glycan structure. Using this structure as an exogenous marker, we developed a method for use in doping studies. The profiling of rEPO N-glycopeptides revealed the presence of tri- and tetra-sialylated N-glycopeptides. By selecting a peptide with a tetra-sialic acid structure as the target, its limit of detection (LOD) was estimated to be < 500 pg/mL. Furthermore, we confirmed the detection of the target rEPO glycopeptide using three other rEPO products. We additionally validated the linearity, carryover, selectivity, matrix effect, LOD, and intraday precision of this method. To the best of our knowledge, this is the first report of a doping analysis using liquid chromatography/mass spectrometry-based detection of the rEPO glycopeptide with a tetra-sialic acid structure in human urine samples.

Emulating nonribosomal peptides with ribosomal biosynthetic strategies

Peptide natural products are important lead structures for human drugs and many nonribosomal peptides possess antibiotic activity. This makes them interesting targets for engineering approaches to generate peptide analogues with, for example, increased bioactivities. Nonribosomal peptides are produced by huge mega-enzyme complexes in an assembly-line like manner, and hence, these biosynthetic pathways are challenging to engineer. In the past decade, more and more structural features thought to be unique to nonribosomal peptides were found in ribosomally synthesised and posttranslationally modified peptides as well. These streamlined ribosomal pathways with modifying enzymes that are often promiscuous and with gene-encoded precursor proteins that can be modified easily, offer several advantages to produce designer peptides. This review aims to provide an overview of recent progress in this emerging research area by comparing structural features common to both nonribosomal and ribosomally synthesised and posttranslationally modified peptides in the first part and highlighting synthetic biology strategies for emulating nonribosomal peptides by ribosomal pathway engineering in the second part.

Glycosyl Radical-Based Synthesis of C-Glycoamino Acids and C-Glycopeptides

Radical-based reactions usually exhibit excellent functional-group compatibilities due to their mild initiation conditions. Glycosyl radical involved C-glycosylation modifications are important strategies to achieve highly regio- and chemoselective constructions of C-glycosidic bonds or C-glycoside linkages of peptides and proteins. In this Concept, we cover recent developments in glycosyl radical-based synthesis of unnatural amino acids and late-stage modification of peptides and proteins, and provide a preliminary outlook on the possible development of this direction in the future.

Liquid chromatography and capillary electrophoresis in glycomic and glycoproteomic analysis

Glycosylation is one of the most significant and abundant post-translational modifications in cells. Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycomic and glycoproteomic analysis is highly challenging because of the large diversity of structures, low abundance, site-specific heterogeneity, and poor ionization efficiency of glycans and glycopeptides in mass spectrometry (MS). MS is a key tool for characterization of glycans and glycopeptides. However, MS alone does not always provide full structural and quantitative information for many reasons, and thus MS is combined with some separation technique. This review focuses on the role of separation techniques used in glycomic and glycoproteomic analyses, liquid chromatography and capillary electrophoresis. The most important separation conditions and results are presented and discussed.

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Monitoring multiple quality attributes of a complex Fc-fusion protein during cell culture production processes by mD-LC-MS peptide mapping

Fc-fusion proteins represent a successful class of biopharmaceutical products. They are considered highly heterogeneous products due to the common degradation of amino acids that occurs during their production in upstream and downstream processes (e.g., oxidation and deamidation) and, above all, their complex glycosylation profile. Multi-dimensional liquid chromatography-mass spectrometry (mD-LC-MS) has recently gained much interest for process analytical technology, enabling the integration of this analytical technology in production and purification environments. In this study, an online mD-LC-MS/MS peptide mapping method was developed for monitoring multiple quality attributes, including the N-glycosylation state of a complex Fc-fusion protein, which is made by combining two heavily glycosylated cytokines with an Fc domain. This fully automated workflow includes sample purification, reduction, digestion, peptide mapping, and subsequent mass spectrometric analysis. Two immobilized enzyme cartridges based on trypsin and Lys-C protease were employed to generate a detailed glycosylation mapping, as trypsin allowed the identification of only one of four glycosylation sites, while Lys-C was more informative for two other sites. Site-specific glycosylation information such as antennarity, sialyation, and core fucosylation state was also determined. In addition to glycans, other post-translational modifications could be monitored simultaneously during the cell culture production processes by the mD-LC-MS/MS approach. In summary, the generated data demonstrate the applicability of mD-LC-MS for the monitoring and trending of multiple attributes for complex antibody formats over production processes in an automated and fast manner, compared to the complex and time-consuming traditional offline assays.

(De)Activation (Ir)Reversibly or Degradation: Dynamics of Post-Translational Protein Modifications in Plants

The increasing dynamic functions of post-translational modifications (PTMs) within protein molecules present outstanding challenges for plant biology even at this present day. Protein PTMs are among the first and fastest plant responses to changes in the environment, indicating that the mechanisms and dynamics of PTMs are an essential area of plant biology. Besides being key players in signaling, PTMs play vital roles in gene expression, gene, and protein localization, protein stability and interactions, as well as enzyme kinetics. In this review, we take a broader but concise approach to capture the current state of events in the field of plant PTMs. We discuss protein modifications including citrullination, glycosylation, phosphorylation, oxidation and disulfide bridges, N-terminal, SUMOylation, and ubiquitination. Further, we outline the complexity of studying PTMs in relation to compartmentalization and function. We conclude by challenging the proteomics community to engage in holistic approaches towards identification and characterizing multiple PTMs on the same protein, their interaction, and mechanism of regulation to bring a deeper understanding of protein function and regulation in plants.

Insights into ultra-low affinity lipase-antibody noncovalent complex binding mechanisms

Detection of host cell protein (HCP) impurities is critical to ensuring that recombinant drug products, including monoclonal antibodies (mAbs), are safe. Mechanistic characterization as to how HCPs persist in drug products is important to refining downstream processing. It has been hypothesized that weak lipase-mAb interactions enable HCP lipases to evade drug purification processes. Here, we apply state-of-the-art methods to establish lipase-mAb binding mechanisms. First, the mass spectrometry (MS) approach of fast photochemical oxidation of proteins was used to elucidate putative binding regions. The CH1 domain was identified as a conserved interaction site for IgG1 and IgG4 mAbs against the HCPs phospholipase B-like protein (PLBL2) and lysosomal phospholipase A2 (LPLA2). Rationally designed mutations in the CH1 domain of the IgG4 mAb caused a 3- to 70-fold K_D reduction against PLBL2 by surface plasmon resonance (SPR). LPLA2-IgG4 mutant complexes, undetected by SPR and studied using native MS collisional dissociation experiments, also showed significant complex disruption, from 16% to 100%. Native MS and ion mobility (IM) determined complex stoichiometries for four lipase-IgG4 complexes and directly interrogated the enrichment of specific lipase glycoforms. Confirmed with time-course and exoglycosidase experiments, deglycosylated lipases prevented binding, and low-molecular-weight glycoforms promoted binding, to mAbs. This work demonstrates the value of integrated biophysical approaches to characterize micromolar affinity complexes. It is the first in-depth structural report of lipase-mAb binding, finding roles for the CH1 domain and lipase glycosylation in mediating binding. The structural insights gained offer new approaches for the bioengineering of cells or mAbs to reduce HCP impurity levels.Abbreviations: CAN, Acetonitrile; AMAC, Ammonium acetate; BFGS, Broyden-Fletcher-Goldfarb-Shanno; CHO, Chinese Hamster Ovary; K_D, Dissociation constant; DTT, Dithiothreitol; ELISA, Enzyme-linked immunosorbent assay; FPOP, Fast photochemical oxidation of proteins; FA, Formic acid; F(ab'), Fragment antibodies; HCP, Host cell protein; IgG, Immunoglobulin; IM, Ion mobility; LOD, Lower limit of detection; LPLA2, Lysosomal phospholipase A2; Man, Mannose; MS, Mass spectrometry; MeOH, Methanol; MST, Microscale thermophoresis; mAbs, Monoclonal antibodies; PPT1, Palmitoyl protein thioesterase; ppm, Parts per million; PLBL2, Phospholipase B-like protein; PLD3, Phospholipase D3; PS-20, Polysorbate-20; SP, Sphingomyelin phosphodiesterase; SPR, Surface plasmon resonance; TFA, Trifluoroacetic acid.

Genetically engineered birds; pre-CRISPR and CRISPR era

Generating biopharmaceuticals in genetically engineered bioreactors continues to reign supreme. Hence, genetically engineered birds have attracted considerable attention from the biopharmaceutical industry. Fairly recent genome engineering methods have made genome manipulation an easy and affordable task. In this review, we first provide a broad overview of the approaches and main impediments ahead of generating efficient and reliable genetically engineered birds, and various factors that affect the fate of a transgene. This section provides an essential background for the rest of the review, in which we discuss and compare different genome manipulation methods in the pre-CRISPR and CRISPR era in the field of avian genome engineering.

2-Dimensional ultra-high performance liquid chromatography and DMT-MM derivatization paired with tandem mass spectrometry for comprehensive serum N-glycome characterization

Glycosylation is a prominent co- and post-translational modification which contributes to a variety of important biological functions. Protein glycosylation characteristics, particularly N-glycosylation, are influenced by changes in one's pathological state, such as through the presence of disease, and as such, there is great interest in N-glycans as potential disease biomarkers. Human serum is an attractive source for N-glycan based biomarker studies as circulatory proteins are representative of one's physiology, with many serum proteins containing N-glycosylation. The difficulty in comprehensively characterizing the serum N-glycome arises from the absence of a biosynthetic template resulting in great structural heterogeneity and complexity. To help overcome these challenges we developed a 2-dimensional liquid chromatography platform which utilizes offline weak anion exchange (WAX) chromatography in the first dimension and hydrophilic interaction liquid chromatography (HILIC) in the second dimension to separate N-glycans by charge, corresponding to degree of sialylation, and size, respectively. Performing these separations offline enables subsequent derivatization with 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) for sialic acid linkage determination and the identification of sialic acid linkage isomers. Subsequent tandem mass spectrometry analysis revealed the identification of 212 complete and partial N-glycan structures including low abundant N-glycans containing acetyl and sulphate modifications. The identifications obtained through this platform were then applied to N-glycans released from a set of stage 3 gastric cancer serum samples obtained from patients before (pre-op) and after (post-op) tumour resection to investigate how the serum N-glycome can facilitate differentiation between the two pathological states.

Need for a risk-based control strategy for managing glycosylation profile for biosimilar products

INTRODUCTION

Monoclonal antibodies, though a popular class of therapeutics, are complex molecules that are manufactured using complex processes, making it nontrivial to maintain high level of batch-to-batch consistency in product quality. Glycosylation is a posttranslation modification that is widely considered a critical quality attribute (CQA) as its variations are known to impact the Fc effector functions of mAbs. With continuing rise of biosimilars, comparability of these products to the reference product with respect to glycosylation is a topic of immense interest.

AREAS COVERED

In this article, we focus on the various aspects related to this topic including criticality of the various glycosylated forms, as well as comparability of biosimilars with respect to glycosylation.

EXPERT OPINION

We propose that manufacturers should focus on those glycoforms that are present in larger amounts and are known to be critical with respect to the biotherapeutic's safety and efficacy. Such risk-based evaluation of glycoforms and their control would offer an optimal route to biosimilar manufacturers for a cost-effective approach toward product development without compromising on the safety and efficacy characteristics of the therapeutic. For mAbs lacking Fc effector function, devising stringent glycosylation control strategies can be bypassed, thereby simplifying process and product development.

Building better biobetters: From fundamentals to industrial application

Biological drugs or biopharmaceuticals off patent open a large market for biosimilars and biobetters, follow-on biologics. Biobetters, in particular, are new drugs designed from existing ones with improved properties such as higher selectivity, stability, half-life and/or lower toxicity/immunogenicity. Glycosylation is one of the most used strategies to improve biological drugs, nonetheless bioconjugation is an additional alternative and refers to the covalent attachment of polymers to biological drugs. Extensive research on novel polymers is underway, nonetheless PEGylation is still the best alternative with the longest clinical track record. Innovative trends based on genetic engineering techniques such as fusion proteins and PASylation are also promising. In this review, all these alternatives wereexplored as well as current market trends, legislation and future perspectives.

Creation of monoclonal antibody expressing CHO cell lines grown with sodium butyrate and characterization of resulting antibody glycosylation

Chinese hamster ovary (CHO) cells are the primary mammalian cell lines utilized to produce monoclonal antibodies (mAbs). The upsurge in biosimilar development and the proven health benefits of mAb treatments reinforces the need for innovative methods to generate robust CHO clones and enhance production, while maintaining desired product quality attributes. Among various product titer-enhancing approaches, the use of histone deacetylase inhibitors (HDACis) such as sodium butyrate (NaBu) has yielded promising results. The titer-enhancing effect of HDACi treatment has generally been observed in lower producer cell lines but those studies are typically done on individual clones. Here, we describe a cell line development (CLD) platform approach for creating clones with varying productivities. We then describe a method for selecting an optimal NaBu concentration to evaluate potential titer-enhancing capabilities in a fed-batch study. Finally, a method for purifying the mAb using protein A chromatography, followed by glycosylation analysis using mass spectrometry, is described. The proposed workflow can be applied for a robust CLD process optimization to generate robust clones, enhance product expression, and improve product quality attributes.

Predicted N-terminal N-linked glycosylation sites may underlie membrane protein expression patterns in Saccharomyces cerevisiae

N-linked glycosylation is one type of posttranslational modification that proteins undergo during expression. The following describes the effects of N-linked glycosylation on high-level membrane protein expression in yeast with an emphasis on Saccharomyces cerevisiae. N-linked glycosylation is highlighted here as an important consideration when preparing membrane protein gene constructs for expression in S. cerevisiae, which continues to be used as a workhorse in both research and industrial applications. Non-native N-linked glycosylation commonly occurs during the heterologous expression of mammalian proteins in many yeast species which can have important immunological consequences when used in the production of biotherapeutic proteins or peptides. Further, non-native N-linked glycosylation can lead to improper protein folding and premature degradation, which can impede high-level expression yields and hinder downstream analysis. Multiple strategies are presented in this article, which suggest different methods that can be implemented to circumvent the unwanted consequences of N-linked glycosylation during the expression process. These considerations may have long-term benefits for high-level protein production in S. cerevisiae across a broad spectrum of expression targets with special emphasis placed on G-protein coupled receptors, one of the largest families of membrane proteins.

An Integrated Strategy Reveals Complex Glycosylation of Erythropoietin Using Mass Spectrometry

The characterization of therapeutic glycoproteins is challenging due to the structural heterogeneity of the therapeutic protein glycosylation. This study presents an in-depth analytical strategy for glycosylation of first-generation erythropoietin (epoetin beta), including a developed mass spectrometric workflow for N-glycan analysis, bottom-up mass spectrometric methods for site-specific N-glycosylation, and a LC-MS approach for O-glycan identification. Permethylated N-glycans, peptides, and enriched glycopeptides of erythropoietin were analyzed by nanoLC-MS/MS, and de-N-glycosylated erythropoietin was measured by LC-MS, enabling the qualitative and quantitative analysis of glycosylation and different glycan modifications (e.g., phosphorylation and O-acetylation). The newly developed Python scripts enabled the identification of 140 N-glycan compositions (237 N-glycan structures) from erythropoietin, especially including 8 phosphorylated N-glycan species. The site-specificity of N-glycans was revealed at the glycopeptide level by pGlyco software using different proteases. In total, 114 N-glycan compositions were identified from glycopeptide analysis. Moreover, LC-MS analysis of de-N-glycosylated erythropoietin species identified two O-glycan compositions based on the mass shifts between non-O-glycosylated and O-glycosylated species. Finally, this integrated strategy was proved to realize the in-depth glycosylation analysis of a therapeutic glycoprotein to understand its pharmacological properties and improving the manufacturing processes.

Longitudinal monitoring of cell metabolism in biopharmaceutical production using label-free fluorescence lifetime imaging microscopy

Chinese hamster ovary (CHO) cells are routinely used in the biopharmaceutical industry for production of therapeutic monoclonal antibodies (mAbs). Although multiple offline and time-consuming measurements of spent media composition and cell viability assays are used to monitor the status of culture in biopharmaceutical manufacturing, the day-to-day changes in the cellular microenvironment need further in-depth characterization. In this study, two-photon fluorescence lifetime imaging microscopy (2P-FLIM) was used as a tool to directly probe into the health of CHO cells from a bioreactor, exploiting the autofluorescence of intracellular nicotinamide adenine dinucleotide phosphate (NAD(P)H), an enzymatic cofactor that determines the redox state of the cells. A custom-built multimodal microscope with two-photon FLIM capability was utilized to monitor changes in NAD(P)H fluorescence for longitudinal characterization of a changing environment during cell culture processes. Three different cell lines were cultured in 0.5 L shake flasks and 3 L bioreactors. The resulting FLIM data revealed differences in the fluorescence lifetime parameters, which were an indicator of alterations in metabolic activity. In addition, a simple principal component analysis (PCA) of these optical parameters was able to identify differences in metabolic progression of two cell lines cultured in bioreactors. Improved understanding of cell health during antibody production processes can result in better streamlining of process development, thereby improving product titer and verification of scale-up. To our knowledge, this is the first study to use FLIM as a label-free measure of cellular metabolism in a biopharmaceutically relevant and clinically important CHO cell line.

Identification of a modified coagulation factor X with enhanced activation properties as potential hemostatic agent

Hemophilia A and hemophilia B are X-linked inherited bleeding disorders caused by a deficiency of coagulation factor VIII and IX, respectively. Standard of care is prophylactic factor replacement therapy; however, the development of neutralizing antibodies against these factors represents serious complications underlining the need for alternative treatment approaches. Human coagulation factor X has a central role within the blood coagulation system making it an attractive target for the development of alternative treatment strategies for patients with hemophilia. This study focuses on a modified variant of the human coagulation factor X with enhanced hemostatic bypass activity due to insertion of a factor IX derived activation sequence. This molecule design leads to the direct activation of the modified factor X protein by factor XIa allowing it to bypass the need for coagulation factor VIIIa/factor IXa. The modified variant was able to correct in-vitro activated partial prothrombin time of human and murine factor VIII/factor IX deficient plasma. Furthermore, reduced blood loss in factor VIII knock-out mice was observed after intravenous application of the modified factor X variant. In conclusion, these data suggest that the factor X variant described here could potentially serve as a bypassing agent independent of the inhibitor status of hemophilia patients. However, more research is needed to further investigate the potential of this molecule.

Comparative Analysis of Different N-glycan Preparation Approaches and Development of Optimized Solid-Phase Permethylation Using Mass Spectrometry

Protein N-glycosylation characterization is challenging due to structural micro- and macro-heterogeneity. Although various N-glycan preparation strategies, including purification and derivatization, have been previously developed prior to mass spectrometric analysis, systematic evaluation still needs to be performed. This study compared the different N-glycan purification strategies, including filter-aided sample preparation, de-N-glycosylated protein precipitation, and trypsin digestion followed by reversed phase-based solid-phase extraction, and derivatization approaches, such as solid-phase permethylation, reductive amination, and reduction. With the comparative analysis, an optimized solid-phase permethylation (OSPP) workflow was developed for mass spectrometric N-glycomics, showing simplified analysis for N-glycan compositions and high yields using etanercept. The N-glycan samples released from trastuzumab and adalimumab were utilized to test OSPP to obtain their N-glycan profiles using mass spectrometry. Based on different standard procedures across laboratories, this study provides the reference for analysts to select an appropriate N-glycan preparation method with their research purposes.

7-Fluorosialyl Glycosides Are Hydrolysis Resistant but Readily Assembled by Sialyltransferases Providing Easy Access to More Metabolically Stable Glycoproteins

The maintenance of therapeutic glycoproteins within the circulatory system is associated, in large part, with the integrity of sialic acids as terminal sugars on the glycans. Glycoprotein desialylation, either by spontaneous cleavage or through host sialidases, leads to protein clearance, mainly through the liver. Thus, the installation of minimally modified sialic acids that are hydrolysis-resistant yet biologically equivalent should lead to increased circulatory half-lives and improved pharmacokinetic profiles. Here we describe the chemoenzymatic synthesis of CMP-sialic acid sugar donors bearing fluorine atoms at the 7-position, starting from the corresponding 4-deoxy-4-fluoro-N-acetylhexosamine precursors. For the derivative with natural stereochemistry we observe efficient glycosyl transfer by sialyltransferases, along with improved stability of the resultant 7-fluorosialosides toward spontaneous hydrolysis (3- to 5-fold) and toward cleavage by GH33 sialidases (40- to 250-fold). Taking advantage of the rapid transfer of 7-fluorosialic acid by sialyltransferases, we engineered the O-glycan of Interferon α-2b and the N-glycans of the therapeutic glycoprotein α1-antitrypsin. Studies of the uptake of the glyco-engineered α1-antitrypsin by HepG2 liver cells demonstrated the bioequivalence of 7-fluorosialic acid to sialic acid in suppressing interaction with liver cell lectins. In vivo pharmacokinetic studies reveal enhanced half-life of the protein decorated with 7-fluorosialic acid relative to unmodified sialic acid in the murine circulatory system. 7-Fluorosialylation therefore offers considerable promise as a means of prolonging circulatory half-lives of glycoproteins and may pave the way toward biobetters for therapeutic use.

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.

Pharmacokinetics Versus In Vitro Antiproliferative Potency to Design a Novel Hyperglycosylated hIFN-α2 Biobetter

PURPOSE

IFN4N is a glycoengineered version of recombinant human interferon alpha 2 (rhIFN-α2) that was modified to exhibit four N-glycosylation sites. It shows reduced in vitro specific biological activity (SBA) mainly due to R23 mutation by N23. However, it has improved pharmacokinetics and led to a high in vivo antitumor activity in mice. In order to prepare a new IFN-based biobetter, this work compares the influence of glycosylation (affecting pharmacokinetics) with the in vitro antiproliferative SBA on the in vivo efficacy.

METHODS

Based on IFN4N, three groups of muteins were designed, produced, and characterized. Group A: variants with the same glycosylation degree (4N) but higher in vitro antiproliferative SBA (R23 restored); group B: muteins with higher glycosylation degree (5N) but similar in vitro antiproliferative activity; and group C: variants with improved glycosylation (5N and 6N) and in vitro antiproliferative bioactivity.

RESULTS

Glycoengineering was successful for improving pharmacokinetics, and R23 restoration considerably increased in vitro antiproliferative activity of new muteins compared to IFN4N. Hyperglycosylation was able to improve the in vivo efficacy similarly to or even better than R23 restoration. Additionally, the highest glycosylated mutein exhibited the lowest immunogenicity.

CONCLUSIONS

Hyperglycosylation constitutes a successful strategy to prepare a novel IFN biobetter.

Automation of Immunoglobulin Glycosylation Analysis

The development of reliable, affordable, high-resolution glycomics technologies that can be used for many samples in a high-throughput manner are essential for both the optimization of glycosylation in the biopharmaceutical industry as well as for the advancement of clinical diagnostics based on glycosylation biomarkers. We will use this chapter to review the sample preparation processes that have been used on liquid-handling robots to obtain high-quality glycomics data for both biopharmaceutical and clinical antibody samples. This will focus on glycoprotein purification, followed by glycan or glycopeptide generation, derivatization and enrichment. The use of liquid-handling robots for glycomics studies on other sample types beyond antibodies will not be discussed here. We will summarize our thoughts on the current status of the field and explore the benefits and challenges associated with developing and using automated platforms for sample preparation. Finally, the future outlook for the automation of glycomics will be discussed along with a projected impact on the field in general.

Comparison of Three Glycoproteomic Methods for the Analysis of the Secretome of CHO Cells Treated with 1,3,4-O-Bu3ManNAc

Comprehensive analysis of the glycoproteome is critical due to the importance of glycosylation to many aspects of protein function. The tremendous complexity of this post-translational modification, however, makes it difficult to adequately characterize the glycoproteome using any single method. To overcome this pitfall, in this report we compared three glycoproteomic analysis methods; first the recently developed N-linked glycans and glycosite-containing peptides (NGAG) chemoenzymatic method, second, solid-phase extraction of N-linked glycoproteins (SPEG), and third, hydrophilic interaction liquid chromatography (HILIC) by characterizing N-linked glycosites in the secretome of Chinese hamster ovary (CHO) cells. Interestingly, the glycosites identified by SPEG and HILIC overlapped considerably whereas NGAG identified many glycosites not observed in the other two methods. Further, utilizing enhanced intact glycopeptide identification afforded by the NGAG workflow, we found that the sugar analog 1,3,4-O-Bu₃ManNAc, a "high flux" metabolic precursor for sialic acid biosynthesis, increased sialylation of secreted proteins including recombinant human erythropoietin (rhEPO).

Increased yield of enzymatic synthesis by chromatographic selection of different N-glycoforms of yeast invertase

Invertases are glycosidases applied for synthesis of alkyl glycosides that are important and effective surfactants. Stability of invertases in the environment with increased content of organic solvent is crucial for increase of productivity of glycosidases. Their stability is significantly influenced by N-glycosylation. However, yeast N-glycosylation pathways may synthesize plethora of N-glycan structures. A total natural crude mixture of invertase glycoforms (EINV) extracted from Saccharomyces cerevisiae was subfractionated by anion-exchange chromatography on industrial monolithic supports to obtain different glycoforms (EINV1-EINV3). Separated glycoforms exhibited different stabilities in water-alcohol solutions that are in direct correlation with the amount of phosphate bound to N-glycans. Observed differences in stability of different invertase glycoforms were used to improve productivity of methyl β-d-fructofuranoside (MF) synthesis. The efficiency and yield of MF synthesis were improved more than 50% when the most stabile glycoform bearing the lowest amount of phosphorylated N-glycans is selected and utilized. These data underline the importance of analysis of glycan structures attached to glycoproteins, demonstrate different impact of N-glycans on the surface charge and enzyme stability in regard to particular reaction environment, and provide a platform for improvement of yield of industrial enzymatic synthesis by chromatographic selection of glycoforms on monolithic supports.

Therapeutic Fc-fusion proteins: Current analytical strategies

Fc-Fusion proteins represent a successful class of biopharmaceutical products, with already 13 drugs approved in the European Union and United States as well as three biosimilar versions of etanercept. Fc-Fusion products combine tailored pharmacological properties of biological ligands, together with multiple functions of the fragment crystallizable domain of immunoglobulins. There is a great diversity in terms of possible biological ligands, including the extracellular domains of natural receptors, functionally active peptides, recombinant enzymes, and genetically engineered binding constructs acting as cytokine traps. Due to their highly diverse structures, the analytical characterization of Fc-Fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product-specific methods over conventional generic/platform methods. This can be explained, for example, by the presence of numerous sialic acids, leading to high diversity in terms of isoelectric points and complex glycosylation profiles including multiple N- and O-linked glycosylation sites. In this review, we highlight the wide range of analytical strategies used to fully characterize Fc-fusion proteins. We also present case studies on the structural assessment of all commercially available Fc-fusion proteins, based on the features and critical quality attributes of their ligand-binding domains.

Clustering and curation of electropherograms: an efficient method for analyzing large cohorts of capillary electrophoresis glycomic profiles for bioprocessing operations

The accurate assessment of antibody glycosylation during bioprocessing requires the high-throughput generation of large amounts of glycomics data. This allows bioprocess engineers to identify critical process parameters that control the glycosylation critical quality attributes. The advances made in protocols for capillary electrophoresis-laser-induced fluorescence (CE-LIF) measurements of antibody N-glycans have increased the potential for generating large datasets of N-glycosylation values for assessment. With large cohorts of CE-LIF data, peak picking and peak area calculations still remain a problem for fast and accurate quantitation, despite the presence of internal and external standards to reduce misalignment for the qualitative analysis. The peak picking and area calculation problems are often due to fluctuations introduced by varying process conditions resulting in heterogeneous peak shapes. Additionally, peaks with co-eluting glycans can produce peaks of a non-Gaussian nature in some process conditions and not in others. Here, we describe an approach to quantitatively and qualitatively curate large cohort CE-LIF glycomics data. For glycan identification, a previously reported method based on internal triple standards is used. For determining the glycan relative quantities our method uses a clustering algorithm to ‘divide and conquer’ highly heterogeneous electropherograms into similar groups, making it easier to define peaks manually. Open-source software is then used to determine peak areas of the manually defined peaks. We successfully applied this semi-automated method to a dataset (containing 391 glycoprofiles) of monoclonal antibody biosimilars from a bioreactor optimization study. The key advantage of this computational approach is that all runs can be analyzed simultaneously with high accuracy in glycan identification and quantitation and there is no theoretical limit to the scale of this method.

More comprehensive standards for monitoring glycosylation

Biologics manufacturers must continually monitor the attachment of carbohydrates, called glycans, to their products, because any variability can impact safety and efficacy. To help the industry meet this challenge, the United States Pharmacopeial Convention (USP) offers glycan reference standards and validated methods for glycoprofiling using high-performance liquid chromatography (HPLC). The industry has recently adopted more advanced technologies for glycan analysis, including ultra-high performance liquid chromatography (UHPLC) and mass spectrometry. In this study, we confirm that USP's glycan reference standards are compatible with UHPLC by demonstrating comparable peak separation and glycan identification to HPLC methods. The improved resolving power and shorter run-times of UHPLC also allowed us to identify many of the minor glycan components present in USP's glycan reference standards. These more comprehensively characterized glycan reference standards will enable manufacturers to assess the micro-heterogeneity that can negatively impact the safety and efficacy of biological products.

The interaction between the natural metalloendopeptidase inhibitor BJ46a and its target toxin jararhagin analyzed by structural mass spectrometry and molecular modeling

Snakebite envenoming affects millions of people worldwide, being officially considered a neglected tropical disease by the World Health Organization. The antivenom is effective in neutralizing the systemic effects of envenomation, but local effects are poorly neutralized, often leading to permanent disability. The natural resistance of the South American pit viper Bothrops jararaca to its venom is partly attributed to BJ46a, a natural snake venom metalloendopeptidase inhibitor. Upon complex formation, BJ46a binds non-covalently to the metalloendopeptidase, rendering it unable to exert its proteolytic activity. However, the structural features that govern this interaction are largely unknown. In this work, we applied structural mass spectrometry techniques (cross-linking-MS and hydrogen-deuterium exchange MS) and in silico analyses (molecular modeling, docking, and dynamics simulations) to understand the interaction between BJ46a and jararhagin, a metalloendopeptidase from B. jararaca venom. We explored the distance restraints generated from XL-MS experiments to guide the modeling of BJ46a and jararhagin, as well as the protein-protein docking simulations. HDX-MS data pinpointed regions of protection/deprotection at the interface of the BJ46a-jararhagin complex which, in addition to the molecular dynamics simulation data, reinforced our proposed interaction model. Ultimately, the structural understanding of snake venom metalloendopeptidases inhibition by BJ46a could lead to the rational design of drugs to improve anti-snake venom therapeutics, alleviating the high morbidity rates currently observed.

Perspectives for Glyco-Engineering of Recombinant Biopharmaceuticals from Microalgae

Microalgae exhibit great potential for recombinant therapeutic protein production, due to lower production costs, immunity to human pathogens, and advanced genetic toolkits. However, a fundamental aspect to consider for recombinant biopharmaceutical production is the presence of correct post-translational modifications. Multiple recent studies focusing on glycosylation in microalgae have revealed unique species-specific patterns absent in humans. Glycosylation is particularly important for protein function and is directly responsible for recombinant biopharmaceutical immunogenicity. Therefore, it is necessary to fully characterise this key feature in microalgae before these organisms can be established as industrially relevant microbial biofactories. Here, we review the work done to date on production of recombinant biopharmaceuticals in microalgae, experimental and computational evidence for N- and O-glycosylation in diverse microalgal groups, established approaches for glyco-engineering, and perspectives for their application in microalgal systems. The insights from this review may be applied to future glyco-engineering attempts to humanize recombinant therapeutic proteins and to potentially obtain cheaper, fully functional biopharmaceuticals from microalgae.

mRNA Transfection into CHO-Cells Reveals Production Bottlenecks

Obtaining highly productive Chinese hamster ovary (CHO)-cell clones for the production of therapeutic proteins relies on multiple time-consuming selection steps. Several CHO-cell strains with high degrees of genomic and epigenetic variation are available. Each harbor potential advantages and disadvantages for any given product, particularly those considered difficult to express. A simple test system to quickly assess compatibility of cell line and product may therefore prove useful. Transient plasmid transfection falls short of the specific productivities of stable producer cells, making it unsuitable for the elucidation of high specific productivity bottlenecks. The aim of the study is to reach specific productivities approaching those of industrial production cell lines by transfection of in vitro transcribed mRNA. The system is characterized with respect to transfection efficacy (by quantitative PCR) and protein production (by flow cytometry and biolayer interferometry). Fluorescence of intracellular eGFP saturates at higher amounts of mRNA per cell, while the amount of secreted and intracellular EPO-Fc remain linearly correlated to the amount of mRNA taken up. Nevertheless, MS shows a severe reduction in N-glycosylation quality. This method allows for rapid elucidation of bottlenecks that would otherwise remain undetected until later during cell line development, giving insight into suitable strategies for preemptive targeted metabolic engineering and host cell line optimization.

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.

Innovation in Cell Banking, Expansion, and Production Culture

Cell culture-based production processes enable the development and commercial supply of recombinant protein products. Such processes consist of the following elements: thaw and initiation of culture, seed expansion, and production culture. A robust cell source storage system in the form of a cell bank is developed and cells are thawed to initiate the cell culture process. Seed culture expansion generates sufficient cell mass to initiate the production culture. The production culture provides an environment where the cells can synthesize the product and is optimized to deliver the highest possible product concentration with acceptable product quality. This chapter describes the significant innovations made in these process elements and the resulting improvements in the overall efficiency, robustness, and safety of the processes and products.

Current strategies in extending half-lives of therapeutic proteins

Macromolecular protein and peptide therapeutics have been proven to be effective in treating critical human diseases precisely. Thanks to biotechnological advancement, a huge number of proteins and peptide therapeutics were made their way to pharmaceutical market in past few decades. However, one of the biggest challenges to be addressed for protein therapeutics during clinical application is their fast degradation in serum and quick elimination owing to enzymatic degradation, renal clearance, liver metabolism and immunogenicity, attributing to the short half-lives. Size and hydrophobicity of protein molecules make them prone to kidney filtration and liver metabolism. On the other hand, proteasomes responsible for protein destruction possess the capability of specifically recognizing almost all kinds of foreign proteins while avoiding any unwanted destruction of cellular components. At present almost all protein-based drug formulations available in market are administered intravenously (IV) or subcutaneously (SC) with high dosing at frequent interval, eventually creating dose-fluctuation-related complications and reducing patient compliance vastly. Therefore, artificially increasing the therapeutic half-life of a protein by attaching to it a molecule that increases the overall size (eg, PEG) or helps with receptor mediated recycling (eg, albumin), or manipulating amino acid chain in a way that makes it more prone towards aggregate formation, are some of the revolutionary approaches to avoid the fast degradation in vivo. Half-life extension technologies that are capable of dramatically enhancing half-lives of proteins in circulation (2-100 folds) and thus improving their overall pharmacokinetic (PK) parameters have been successfully applied on a wide range of protein therapeutics from hormones and enzymes, growth factor, clotting factor to interferon. The focus of the review is to assess the technological advancements made so far in enhancing circulatory half-lives and improving therapeutic potency of proteins.