Fab antibody fragments: some applications in clinical toxicology

[Severe intoxication after yew (Taxus) ingestion-case report and literature review]

BACKGROUND

Severe yew (Taxus) intoxication is a rare condition that can lead to life-threatening cardiac arrhythmia. The survival of patients requires highly specialized emergency and intensive care treatment.

OBJECTIVES

Systematic overview of the clinical picture and important treatment options.

METHODS

Case report of severe yew intoxication with subsequent literature review of comparable case reports. Analysis of 33 case reports with a total of 37 critically intoxicated patients from the years 2000-2024 from Europe and North America.

RESULTS

Severe yew intoxications were almost exclusively the result of suicidal intent. Patients average age was 33 (± 14.5) years. The use of antiarrhythmic drugs and electrical stimulation of the heart often proved to be ineffective or deteriorating in its effect over time. The use of lipid emulsion and/or digoxin-specific Fab fragments has little evidence. The average duration of a clinically relevant arrhythmogenic effect was 22±11.7 h.

CONCLUSIONS

The management of yew intoxication is primarily limited to symptomatic treatment. The availability of venoarterial extracorporeal membrane oxygenation (VA-ECMO) in a "bridge-to-recovery" concept appears to be of utmost importance.

PET imaging of Aspergillus infection using Zirconium-89 labeled anti-β-glucan antibody fragments

PURPOSE

Invasive fungal diseases, such as pulmonary aspergillosis, are common life-threatening infections in immunocompromised patients and effective treatment is often hampered by delays in timely and specific diagnosis. Fungal-specific molecular imaging ligands can provide non-invasive readouts of deep-seated fungal pathologies. In this study, the utility of antibodies and antibody fragments (Fab) targeting β-glucans in the fungal cell wall to detect Aspergillus infections was evaluated both in vitro and in preclinical mouse models.

METHODS

The binding characteristics of two commercially available β-glucan antibody clones and their respective antigen-binding Fabs were tested using biolayer interferometry (BLI) assays and immunofluorescence staining. In vivo binding of the Zirconium-89 labeled antibodies/Fabs to fungal pathogens was then evaluated using PET/CT imaging in mouse models of fungal infection, bacterial infection and sterile inflammation.

RESULTS

One of the evaluated antibodies (HA-βG-Ab) and its Fab (HA-βG-Fab) bound to β-glucans with high affinity (KD = 0.056 & 21.5 nM respectively). Binding to the fungal cell wall was validated by immunofluorescence staining and in vitro binding assays. ImmunoPET imaging with intact antibodies however showed slow clearance and high background signal as well as nonspecific accumulation in sites of infection/inflammation. Conversely, specific binding of [89Zr]Zr-DFO-HA-βG-Fab to sites of fungal infection was observed when compared to the isotype control Fab and was significantly higher in fungal infection than in bacterial infection or sterile inflammation.

CONCLUSIONS

[89Zr]Zr-DFO-HA-βG-Fab can be used to detect fungal infections in vivo. Targeting distinct components of the fungal cell wall is a viable approach to developing fungal-specific PET tracers.

Generalized biomolecular modeling and design with RoseTTAFold All-Atom

Deep-learning methods have revolutionized protein structure prediction and design but are presently limited to protein-only systems. We describe RoseTTAFold All-Atom (RFAA), which combines a residue-based representation of amino acids and DNA bases with an atomic representation of all other groups to model assemblies that contain proteins, nucleic acids, small molecules, metals, and covalent modifications, given their sequences and chemical structures. By fine-tuning on denoising tasks, we developed RFdiffusion All-Atom (RFdiffusionAA), which builds protein structures around small molecules. Starting from random distributions of amino acid residues surrounding target small molecules, we designed and experimentally validated, through crystallography and binding measurements, proteins that bind the cardiac disease therapeutic digoxigenin, the enzymatic cofactor heme, and the light-harvesting molecule bilin.

Unleashing the power of antibodies: Engineering for tomorrow's therapy

Antibodies play a crucial role in host defense against various diseases. Antibody engineering is a multidisciplinary field that seeks to improve the quality of life of humans. In the context of disease, antibodies are highly specialized proteins that form a critical line of defense against pathogens and the disease caused by them. These infections trigger the innate arm of immunity by presenting on antigen-presenting cells such as dendritic cells. This ultimately links to the adaptive arm, where antibody production and maturation occur against that particular antigen. Upon binding with their specific antigens, antibodies trigger various immune responses to eliminate pathogens in a process called complement-dependent cytotoxicity and phagocytosis of invading microorganisms by immune cells or induce antibody-dependent cellular cytotoxicity is done by antibodies. These engineered antibodies are being used for various purposes, such as therapeutics, diagnostics, and biotechnology research. Cutting-edge techniques that include hybridoma technology, transgenic mice, display techniques like phage, yeast and ribosome displays, and next-generation sequencing are ways to engineer antibodies and mass production for the use of humankind. Considering the importance of antibodies in protecting from a diverse array of pathogens, investing in research holds great promise to develop future therapeutic targets to combat various diseases.

Digoxin-specific antibodies: a novel dosing strategy

Digoxin-specific antibodies (digoxin-Fabs) are of value in the treatment of a strongly suspected or a known, potentially life-threatening digoxin toxicity. These antibodies are not registered for use in Europe; therefore Dutch hospital pharmacies are not allowed to keep them in stock. In the Netherlands, digoxin-Fabs are stored in a national calamity stock of emergency medicines at the National Institute for Public Health and the Environment. In the case of a medical emergency, digoxin-Fabs are available after contact with the Dutch Poisons Information Centre. Recent studies have shown that the dose of digoxin-Fabs required to effectively treat digoxin toxicity is lower than previously thought. In this article, we present the adjusted digoxin-Fab dosing strategy currently recommended by the Dutch Poisons Information Centre ( www.vergiftigingen.info ). This new dose titration strategy is safe and effective and has a cost-saving side-effect.

Development and characterization of anti-IL-5 monoclonal antibody Fab fragment for blocking IL-5/IL-5Rα binding

Interleukin-5 (IL-5) is a homodimeric cytokine that is a crucial regulator of the proliferation, activation, and maturation of eosinophils. Anti-IL-5 monoclonal antibodies, which block the binding of IL-5 to the IL-5 receptor subunit alpha (IL-5Rα), have been successfully used to treat eosinophilic (EOS) asthma. The currently marketed monoclonal antibody drugs require repeated injections for administration, which seriously affect patient compliance and high systemic exposure for injectable drug delivery. Here we successfully screened and developed the Fab (fragment of antigen binding), which is 1/3rd the molecular weight of IgG, favoring inhalation-mediated delivery to the lungs, making it more effective for asthma treatment. The 20A12-Fab-H12L3 can bind to IL-5 with a binding constant of 1.236E-09 M while significantly inhibiting the IL-5/IL-5Rα complex formation. We found that the light chain amino acids (S46 and F71) significantly affected the antibody expression during humanization. The 20A12-Fab-H12L3 significantly inhibited the proliferation of TF-1 cells and blocked the IL-5 binding to the IL-5Rα-overexpressing human embryonic kidney (HEK)-293 cells in vitro. Therefore, based on the mutant IL-5 binding with Fab, we explained why antibodies blocked IL-5 binding to IL-5Rα. Thus, this study provided a candidate pharmaceutical antibody for inhalation drug delivery.

Molecular Evolution of Antiparathion Nanobody with Enhanced Sensitivity and Specificity Based on Structural Analysis

Nanobody (Nb) has gained significant attention in immunoassays owing to its numerous advantages, particularly its ease of molecular evolution. However, the limited understanding of how high sensitivity and specificity attained for antihapten Nbs hamper the development of high-performance Nbs. Herein, the antiparathion Nb (Nb9) we prepared previously was chosen as the model, and an approach based on X-ray crystallography, molecular docking, and rational site-directed saturation mutation for constructing a rapid and effective platform for nanobody evolution was described. Based on the structural analysis, two mutants, namely Nb-D5 (IC50 = 2.4 ± 0.2 ng/mL) and Nb-D12 (IC50 = 2.7 ± 0.1 ng/mL), were selected out from a six-sites directed saturation mutation library, 3.5-fold and 3.1-fold sensitivity enhancement over Nb9 to parathion, respectively. Besides, Nb-D12 exhibited improved sensitivity for quinalphos, triazophos, and coumaphos (5.4-35.4 ng/mL), indicating its broader detection potential. Overall, our study advances an effective strategy for the future rational evolution of Nbs with desirable performance.

Structural Insights into the Stability and Recognition Mechanism of the Antiquinalphos Nanobody for the Detection of Quinalphos in Foods

Nanobodies (Nbs) have great potential in immunoassays due to their exceptional physicochemical properties. With the immortal nature of Nbs and the ability to manipulate their structures using protein engineering, it will become increasingly valuable to understand what structural features of Nbs drive high stability, affinity, and selectivity. Here, we employed an anti-quinalphos Nb as a model to illustrate the structural basis of Nbs' distinctive physicochemical properties and the recognition mechanism. The results indicated that the Nb-11A-ligand complexes exhibit a "tunnel" binding mode formed by CDR1, CDR2, and FR3. The orientation and hydrophobicity of small ligands are the primary determinants of their diverse affinities to Nb-11A. In addition, the primary factors contributing to Nb-11A's limited stability at high temperatures and in organic solvents are the rearrangement of the hydrogen bonding network and the enlargement of the binding cavity. Importantly, Ala 97 and Ala 34 at the active cavity's bottom and Arg 29 and Leu 73 at its entrance play vital roles in hapten recognition, which were further confirmed by mutant Nb-F3. Thus, our findings contribute to a deeper understanding of the recognition and stability mechanisms of anti-hapten Nbs and shed new light on the rational design of novel haptens and directed evolution to produce high-performance antibodies.

In vivo Neutralization of Colchicine Toxicity by a PASylated Anticalin in a Rat Model

We have investigated the pharmacokinetics (PK) and in vivo activity of an Anticalin exhibiting picomolar affinity towards colchicine, a plant toxin with low tolerable dose in humans. PK analysis of the 20-kDa "Colchicalin" protein in male Sprague Dawley rats (n=3) revealed a very short plasma half-life (3.5min), which was prolonged 21-fold via genetic fusion with a 200-residue Pro/Ala sequence (PASylation). The scavenging activity of the PASylated Colchicalin was investigated over 3.5h via stoichiometric application following a sub-toxic i.v. dose of colchicine on anesthetized rats (n=2) leading to a rapid rise in total plasma colchicine concentration. We then established a 14-day intoxication model in rats (n=3) at a 30mg/kg p.o. colchicine dose which was characterized by severe weight loss, elevated neutrophil-to-lymphocyte ratio and shortened survival. Colchicalin administration at 4.2% of the neutralizing dose (125mg/kg/day daily for 12 consecutive days) resulted in faster relief of the symptoms in 2/3 of animals (n=6) compared to the control group without Colchicalin treatment (n=5). Nevertheless, 1/3 of the rats died suddenly after the first Colchicalin injection, probably due to a steep rise in the total colchicine plasma concentration, which suggests further improvement of the dosing scheme prior to potential application in acute human colchicine poisoning.

Adeno-associated virus-vectored delivery of HIV biologics: the promise of a "single-shot" functional cure for HIV infection

The ability of immunoglobulin-based HIV biologics (Ig-HIV), including broadly neutralizing antibodies, to suppress viral replication in pre-clinical and clinical studies illustrates how these molecules can serve as alternatives or adjuncts to antiretroviral therapy for treating HIV infection. However, the current paradigm for delivering Ig-HIVs requires repeated passive infusions, which faces both logistical and economic challenges to broad-scale implementation. One promising way to overcome these obstacles and achieve sustained expression of Ig-HIVs in vivo involves the transfer of Ig-HIV genes to host cells utilizing adeno-associated virus (AAV) vectors. Because AAV vectors are non-pathogenic and their genomes persist in the cell nucleus as episomes, transgene expression can last for as long as the AAV-transduced cell lives. Given the long lifespan of myocytes, skeletal muscle is a preferred tissue for AAV-based immunotherapies aimed at achieving persistent delivery of Ig-HIVs. Consistent with this idea, recent studies suggest that lifelong immunity against HIV can be achieved from a one-time intramuscular dose of AAV/Ig-HIV vectors. However, realizing the promise of this approach faces significant hurdles, including the potential of AAV-delivered Ig-HIVs to induce anti-drug antibodies and the high AAV seroprevalence in the human population. Here we describe how these host immune responses can hinder AAV/Ig-HIV therapies and review current strategies for overcoming these barriers. Given the potential of AAV/Ig-HIV therapy to maintain ART-free virologic suppression and prevent HIV reinfection in people living with HIV, optimizing this strategy should become a greater priority in HIV/AIDS research.

Significant Improvement in Digoxin Immunoassays Over Four Decades: Newer Assays are Less Affected by Interferences

BACKGROUND

Digitalis glycosides derived from foxglove plants have been used for medicinal purposes since the 16th century. Currently, digoxin derived from foxgloves is used clinically. Owing to the narrow therapeutic range, therapeutic drug monitoring is essential; however, digoxin immunoassays suffer from interference.

METHODS

The issue of interference was reviewed for both older polyclonal antibody-based digoxin assays and newer monoclonal antibody-based digoxin assays. A literature search was conducted using PubMed, ScienceDirect, Scopus, Web of Science, and ResearchGate for studies on digoxin immunoassays published in the English language from 1969 to the present.

RESULTS

Radioimmunoassays for digoxin in the 1970s and, later, first-generation nonradioimmunoassay methods were liable to several interferences, including digoxin-like immunoreactive substances, spironolactone, potassium canrenoate, and various digoxin metabolites. However, for the last 10-15 years, next next-generation digoxin immunoassays have been virtually free from such interferences. Nevertheless, certain herbal supplements, as well as both Digibind and DigiFab, interfere with serum digoxin measurement, even with the more recently developed digoxin assays.

CONCLUSIONS

More recently introduced monoclonal antibody-based digoxin assays are superior to the older polyclonal antibody-based digoxin assays.

Relationship among surface electric double layer of cardiomyocyte membrane and toxicology of digoxin and opening of ion channels

We applied a new idea that the potential effect can change the ion adsorption structure on the cell surface to explore the mechanism of digoxin poisoning and the regulation of ion channels. The effects of digoxin on the electrophoretic mobility and behaviors (non-contraction or contraction or autorhythmicity) of cardiomyocytes were observed by single-cell electrophoresis technique (imitate the opening method of in vivo channel) and the method of decomposing surface potential components on the cells. As well as affect the association with electrical activity. The results suggested that the increase of cardiomyocytes transmembrane potential and the Na⁺-K⁺ exchange on the cell surface of the action potential phase 4 caused by the poisoning dose of digoxin, leading to the oscillation of adsorbed ions on the cell surface and the incomplete channel structure, which were the mechanism of cardiac ectopic beats. The results revealed that the opening of ion channels is regulated by the surface electric double layer of the cell membrane.

Generation of a recombinant antibody for sensitive detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a major pathogen that causes nosocomial infections and often exhibits antibiotic resistance. Therefore, the development of an accurate method for detecting P. aeruginosa is required to control P. aeruginosa-related outbreaks. In this study, we established an enzyme-linked immunosorbent assay method for the sensitive detection of three P. aeruginosa strains, UCBPP PA14, ATCC 27853, and multidrug-resistant ATCC BAA-2108. We produced a recombinant antibody (rAb) against P. aeruginosa V‐antigen (PcrV), which is a needle tip protein of the type III secretion system of P. aeruginosa using mammalian cells with high yield and purity, and confirmed its P. aeruginosa binding efficiency. The rAb was paired with commercial anti-P. aeruginosa Ab for a sandwich ELISA, resulting in an antigen-concentration-dependent response with a limit of detection value of 230 CFU/mL. These results suggest that the rAb produced herein can be used for the sensitive detection of P. aeruginosa with a wide range of applications in clinical diagnosis and point-of-care testing.

Developing a computational pharmacokinetic model of systemic snakebite envenomation and antivenom treatment

Snakebite envenomation is responsible for over 100,000 deaths and 400,000 cases of disability annually, most of which are preventable through access to safe and effective antivenoms. Snake venom toxins span a wide molecular weight range, influencing their absorption, distribution, and elimination within the body. In recent years, a range of scaffolds have been applied to antivenom development. These scaffolds similarly span a wide molecular weight range and subsequently display diverse pharmacokinetic behaviours. Computational simulations represent a powerful tool to explore the interplay between these varied antivenom scaffolds and venoms, to assess whether a pharmacokinetically optimal antivenom exists. The purpose of this study was to establish a computational model of systemic snakebite envenomation and treatment, for the quantitative assessment and comparison of conventional and next-generation antivenoms. A two-compartment mathematical model of envenomation and treatment was defined and the system was parameterised using existing data from rabbits. Elimination and biodistribution parameters were regressed against molecular weight to predict the dynamics of IgG, F(ab')₂, Fab, scFv, and nanobody antivenoms, spanning a size range of 15-150 kDa. As a case study, intramuscular envenomation by Naja sumatrana (equatorial spitting cobra) and its treatment using Fab, F(ab')₂, and IgG antivenoms was simulated. Variable venom dose tests were applied to visualise effective antivenom dose levels. Comparisons to existing antivenoms and experimental rescue studies highlight the large dose reductions that could result from recombinant antivenom use. This study represents the first comparative in silico model of snakebite envenomation and treatment.

Improved Characteristics of RANKL Immuno-PET Imaging Using Radiolabeled Antibody Fab Fragments

Purpose: RANKL expression in the tumor microenvironment has been identified as a biomarker of immune suppression, negating the effect of some cancer immunotherapies. Previously we had developed a radiotracer based on the FDA-approved RANKL-specific antibody denosumab, [⁸⁹Zr]Zr-DFO-denosumab, enabling successful immuno-PET imaging. Radiolabeled denosumab, however, showed long blood circulation and delayed tumor uptake, potentially limiting its applications. Here we aimed to develop a smaller radiolabeled denosumab fragment, [⁶⁴Cu]Cu-NOTA-denos-Fab, that would ideally show faster tumor accumulation and better diffusion into the tumor for the visualization of RANKL. Experimental design: Fab fragments were prepared from denosumab using papain and conjugated to a NOTA chelator for radiolabeling with ⁶⁴Cu. The bioconjugates were characterized in vitro using SDS-PAGE analysis, and the binding affinity was assessed using a radiotracer cell binding assay. Small animal PET imaging evaluated tumor targeting and biodistribution in transduced RANKL-ME-180 xenografts. Results: The radiolabeling yield of [⁶⁴Cu]Cu-NOTA-denos-Fab was 58 ± 9.2%, with a specific activity of 0.79 ± 0.11 MBq/µg (n = 3). A radiotracer binding assay proved specific targeting of RANKL in vitro. PET imaging showed fast blood clearance and high tumor accumulation as early as 1 h p.i. (2.14 ± 0.21% ID/mL), which peaked at 5 h p.i. (2.72 ± 0.61% ID/mL). In contrast, [⁶⁴Cu]Cu-NOTA-denosumab reached its highest tumor uptake at 24 h p.i. (6.88 ± 1.12% ID/mL). [⁶⁴Cu]Cu-NOTA-denos-Fab specifically targeted human RANKL in transduced ME-180 xenografts compared with the blocking group and negative ME-180 xenograft model. Histological analysis confirmed RANKL expression in RANKL-ME-180 xenografts. Conclusions: Here, we report on a novel RANKL PET imaging agent, [⁶⁴Cu]Cu-NOTA-denos-Fab, that allows for fast tumor imaging with improved imaging contrast when compared with its antibody counterpart, showing promise as a potential PET RANKL imaging tool for future clinical applications.

Therapeutic Antibodies: An Overview

Polyclonal immunoglobulin (Ig) preparations have been used for several decades for treatment of primary and secondary immunodeficiencies and for treatment of some infections and intoxications. This has demonstrated the importance of Igs, also called antibodies (Abs) for prevention and elimination of infections. Moreover, elucidation of the structure and functions of Abs has suggested that they might be useful for targeted treatment of several diseases, including cancers and autoimmune diseases. The development of technologies for production of specific monoclonal Abs (MAbs) in large amounts has led to the production of highly effective therapeutic antibodies (TAbs), a collective term for MAbs (MAbs) with demonstrated clinical efficacy in one or more diseases. The number of approved TAbs is currently around hundred, and an even larger number is under development, including several engineered and modified Ab formats. The use of TAbs has provided new treatment options for many severe diseases, but prediction of clinical effect is difficult, and many patients eventually lose effect, possibly due to development of Abs to the TAbs or to other reasons. The therapeutic efficacy of TAbs can be ascribed to one or more effects, including binding and neutralization of targets, direct cytotoxicity, Ab-dependent complement-dependent cytotoxicity, Ab-dependent cellular cytotoxicity or others. The therapeutic options for TAbs have been expanded by development of several new formats of TAbs, including bispecific Abs, single domain Abs, TAb-drug conjugates, and the use of TAbs for targeted activation of immune cells. Most promisingly, current research and development can be expected to increase the number of clinical conditions, which may benefit from TAbs.

Virus neutralisation by intracellular antibodies

For decades antibodies were largely thought to provide protection in extracellular spaces alone, mediating their effector functions by mechanisms such as entry-blocking, complement activation and phagocyte recruitment. However, a wealth of research has shown that antibodies are also capable of neutralising numerous viruses inside cells. Efficacy has now been demonstrated at virtually all intracellular stages of the viral life cycle. Antibodies can neutralise viruses in endosomes by blocking uncoating, fusion mechanisms, or new particle egress. Neutralisation can also occur in the cytosol via recruitment of the intracellular antibody receptor TRIM21. In addition to these direct neutralisation effects, recent research has shown that antibodies can mediate virus control indirectly by promoting MHC class I presentation and thereby increasing the CD8 T cell response. This provides valuable new insight into how non-neutralising antibodies can mediate potent protection in vivo. Overall, the importance of understanding the mechanisms of intracellular neutralisation by antibodies is highlighted by the ongoing need to develop new methods to control viruses. Using or inducing antibodies to block virus replication inside cells is now an innovative approach used by several vaccination and therapeutic strategies.

Extending the in vivo Half-Life of Adalimumab Fab via Sortase A-Mediated Conjugation of Adalimumab Fab with Modified Fatty Acids

Adalimumab, a full-length monoclonal antibody, is widely used as an anti-tumor necrosis factor-α (anti-TNF-α) agent. In this article, we aimed to prolong the in vivo half-life of adalimumab antigen-binding fragment (Fab) through Sortase A (SrtA)-mediated conjugation of its Fab with fatty acid (FA). In our study, adalimumab Fab analog was prepared by adding an SrtA recognition sequence (LPETGG) and His6 tag to the heavy chain C-terminal of the Fab via (G4S)3 linker. Four FA motifs with different linkers were designed and synthesized by solid-phase methodology, then conjugated with the Fab analog using SrtA to produce Fab bioconjugates. The successful generation of four Fab bioconjugates (Fab–FA1, Fab–FA2, Fab–FA3, and Fab–FA4) was confirmed by SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) and mass spectrometry. Then, the bioactivities and half-life of these Fab bioconjugates were examined using TNF-α-/human serum albumin (HSA)-binding enzyme-linked immunosorbent assay, cytotoxicity assay, and pharmacokinetic study, respectively. All Fab bioconjugates exhibited similar TNF-α-neutralizing activities when compared with the Fab analog, even in the presence of albumin, indicating that there were no apparent influences on the functional site of Fab after FA modification. However, different degrees of affinity for HSA were observed among these Fab–FA bioconjugates, with Fab–FA3 exhibiting the maximal affinity. An in vivo study in mice further revealed remarkably improved pharmacokinetics of Fab– FA3 with a 15.2-fold longer plasma half-life (19.86 hours) compared with that of the Fab analog (1.31 hours). In summary, we have developed a novel long-acting adalimumab Fab bioconjugate, Fab–FA3, with more sustained in vivo activity, which can be used for drug development targeting TNF-α-mediated inflammatory diseases.

Adaptor CAR Platforms-Next Generation of T Cell-Based Cancer Immunotherapy

The success of conventional chimeric antigen receptor (CAR) therapy in the treatment of refractory hematologic malignancies has triggered the development of novel exciting experimental CAR technologies. Among them, adaptor CAR platforms have received much attention. They combine the flexibility and controllability of recombinant antibodies with the power of CARs. Due to their modular design, adaptor CAR systems propose answers to the central problems of conventional CAR therapy, such as safety and antigen escape. This review provides an overview on the different adaptor CAR platforms available, discusses the possibilities and challenges of adaptor CAR therapy, and summarizes the first clinical experiences.

Loop Grafting between Similar Local Environments for Fc-Silent Antibodies

Reduction of the affinity of the fragment crystallizable (Fc) region with immune receptors by substitution of one or a few amino acids, known as Fc-silencing, is an established approach to reduce the immune effector functions of monoclonal antibody therapeutics. This approach to Fc-silencing, however, is problematic as it can lead to instability and immunogenicity of the developed antibodies. We evaluated loop grafting as a novel approach to Fc-silencing in which the Fc loops responsible for immune receptor binding were replaced by loops of up to 20 amino acids from similar local environments in other human and mouse antibodies. Molecular dynamics simulations of the designed variants of an Fc region in a complex with the immune receptor FcγIIIa confirmed that loop grafting potentially leads to a significant reduction in the binding of the antibody variants to the receptor, while retaining their stability. In comparison, standard variants with less than eight substituted amino acids showed possible instability and a lower degree of Fc-silencing due to the occurrence of compensatory interactions. The presented approach to Fc-silencing is general and could be used to modulate undesirable side effects of other antibody therapeutics without affecting their stability or increasing their immunogenicity.

Passive Monoclonal and Polyclonal Antibody Therapies

Passive antibody therapies have a long history of use. In the 19th century, antibodies from xenographic sources of polyclonal antibodies were used to treat infections (diphtheria). They were used often as protection from infectious agents and toxins. Complications related to their use involved development of immune complexes and severe allergic reactions. As a result, human source plasma for polyclonal antibodies became the preferential source for antibodies. They are used to treat infection, remove toxins, prevent hemolytic disease of the newborn, modify inflammatory reactions, and control autoimmune diseases. Continued improvements in processing decreased the transfusion/infusion transmission of infections. In the late 20th century (∼1986), monoclonal antibodies were developed. The first monoclonal antibodies were of xenographic source and were wrought with problems of immunogenicity. These forms of antibodies did not gain favor until chimerization took pace in the mid-1990s and in 1998 two monoclonal antibodies were approved one to treat respiratory syncytial virus and the other for breast cancers. Further development of humanized and then fully human monoclonal antibodies has led to an evolution of therapies with these agents. Monoclonal antibodies are being researched or approved to treat a multitude of diseases to include oncologic, inflammatory, autoimmune, cardiovascular, respiratory, neurologic, allergic, benign hematologic, infections, orthopedic, coagulopathy, metabolic and to decrease morbidity of disease (diminution of pain), modify disease progression, and potentially anatomic development. In this chapter, we will review the history of use of these passive antibody therapies, their mechanism of action, pharmacologic-therapeutic classification, particular medical indication, adverse reactions, and potential future use of these medications.

Current Development of Monoclonal Antibodies in Cancer Therapy

Exploiting the unique specificity of monoclonal antibodies has revolutionized the treatment and diagnosis of haematological and solid organ malignancies; bringing benefit to millions of patients over the past decades. Recent achievements include conjugating antibodies with toxic payloads resulting in superior efficacy and/or reduced toxicity, development of molecular imaging techniques targeting specific antigens for use as predictive and prognostic biomarkers, the development of novel bi- and tri-specific antibodies to enhance therapeutic benefit and abrogate resistance and the success of immunotherapy agents. In this chapter, we review an overview of antibody structure and function relevant to cancer therapy and provide an overview of pivotal clinical trials which have led to regulatory approval of monoclonal antibodies in cancer treatment. We further discuss resistance mechanisms and the unique side effects of each class of antibody and provide an overview of emerging therapeutic agents.

Switchable control over in vivo CAR T expansion, B cell depletion, and induction of memory

Chimeric antigen receptor (CAR) T cell therapy represents a powerful strategy in immuno-oncology. Nevertheless, associated life-threatening toxicities and chronic B cell aplasia have underscored the need to control engineered T cells in the patient. To address these challenges, we have previously developed a switchable CAR (sCAR) T cell platform that allows dose-titratable control over CAR T cell activity by using antibody-based switches. Here, we demonstrate in a syngeneic murine model that the switchable platform can impart antitumor efficacy while dissociating long-term persistence from chronic B cell aplasia. Further, the functional reversibility of the switchable platform can be leveraged to incorporate “rest” phases through cyclical dosing of the switch to enable the induction of a robust central memory population for in vivo, on-demand expansion of sCAR T cells.

Chimeric antigen receptor (CAR) T cells with a long-lived memory phenotype are correlated with durable, complete remissions in patients with leukemia. However, not all CAR T cell products form robust memory populations, and those that do can induce chronic B cell aplasia in patients. To address these challenges, we previously developed a switchable CAR (sCAR) T cell system that allows fully tunable, on/off control over engineered cellular activity. To further evaluate the platform, we generated and assessed different murine sCAR constructs to determine the factors that afford efficacy, persistence, and expansion of sCAR T cells in a competent immune system. We find that sCAR T cells undergo significant in vivo expansion, which is correlated with potent antitumor efficacy. Most importantly, we show that the switch dosing regimen not only allows control over B cell populations through iterative depletion and repopulation, but that the “rest” period between dosing cycles is the key for induction of memory and expansion of sCAR T cells. These findings introduce rest as a paradigm in enhancing memory and improving the efficacy and persistence of engineered T cell products.

Physiologically based pharmacokinetic modelling of acute digoxin toxicity and the effect of digoxin-specific antibody fragments

CONTEXT

Recommended doses of digoxin-specific antibody fragments (digoxin-Fab) for treatment of acute digoxin poisoning are pharmacokinetically unsubstantiated and theoretically excessive. Physiologically based pharmacokinetic (PBPK) modelling creates clinical simulations which are closely related to physiological and pharmacokinetic behaviour. This paper details the formulation of a PBPK model of digoxin and explores its use as a simulation tool for acute digoxin toxicity and its management.

MATERIALS AND METHODS

A PBPK model of digoxin was constructed and validated for acute digoxin poisoning management by comparing simulations with observed individual acute overdose patients. These simulations were compared with standard two-compartment PK model simulations.

RESULTS

PBPK model simulations showed good agreement with post-absorption plasma concentrations of digoxin measured in 6 acute overdose patients. PBPK predictions were accurate to 1.5-fold or less of observed clinical values, proving to be more accurate than two-compartment simulations of the same patients which produced up to a 4.9-fold change.

CONCLUSIONS

Compared to conventional two-compartment modelling, PBPK modelling is superior in generating realistic simulations of acute digoxin toxicity and the response to digoxin-Fab. Simulation capacity provides realistic, continuous data which has the potential to substantiate alternative, less expensive, and safer digoxin-Fab dosing strategies for the treatment of acute digoxin toxicity.

Patient awareness, knowledge and use of colchicine: an exploratory qualitative study in the Counties Manukau region, Auckland, New Zealand

INTRODUCTION Treatment of gout, specifically with colchicine, varies globally. Colchicine can be fatal due to its narrow therapeutic index and potential for interactions. In New Zealand, cases of intentional and unintentional colchicine overdose have been documented. AIMS To explore patients' knowledge on the use of gout medicines, and in particular their awareness of the maximum dose of colchicine, the dangers of colchicine overdose, and their opinions on restricting colchicine dispensing. The study also investigates where patients receive gout information. METHODS Thirty people with gout presenting to their regular gout clinic in Auckland currently or previously taking colchicine were invited to participate in a 30-min semi-structured interview. Data were analysed using a general inductive thematic approach. FINDINGS Overall, participants had a lack of knowledge regarding colchicine and used variable doses during an acute gout attack. Participants were unsure of the maximum dose of colchicine and several took more than prescribed. The prophylactic use of colchicine and allopurinol varied from 3 weeks to 15 years. Mixed views were reported on restricting colchicine supply. Most participants received gout information from their general practitioner (GP). CONCLUSION Poor understanding of colchicine contributed to inappropriate use and highlights the need for targeted patient education. Considerable inter-patient variability exists in the use of colchicine for acute gout, suggesting the efficacy of low dose regimens be explored. The length of adjunctive colchicine use, as part of a prophylaxis regimen, needs to be regularly reviewed and tailored to each patient. Further research is required on limiting the amount of colchicine dispensed.

Assessment of disulfide and hinge modifications in monoclonal antibodies

During the last years there was a substantial increase in the use of antibodies and related proteins as therapeutics. The emphasis of the pharmaceutical industry is on IgG1, IgG2, and IgG4 antibodies, which are therefore in the focus of this article. In order to ensure appropriate quality control of such biopharmaceuticals, deep understanding of their chemical degradation pathways and the resulting impact on potency, pharmacokinetics, and safety is required. Criticality of modifications may be specific for individual antibodies and has to be assessed for each molecule. However, some modifications of conserved structure elements occur in all or at least most IgGs. In these cases, criticality assessment may be applicable to related molecules or molecule formats. The relatively low dissociation energy of disulfide bonds and the high flexibility of the hinge region frequently lead to modifications and cleavages. Therefore, the hinge region and disulfide bonds require specific consideration during quality assessment of mAbs. In this review, available literature knowledge on underlying chemical reaction pathways of modifications, analytical methods for quantification and criticality are discussed. The hinge region is prone to cleavage and is involved in pathways that lead to thioether bond formation, cysteine racemization, and iso‐Asp (Asp, aspartic acid) formation. Disulfide or sulfhydryl groups were found to be prone to reductive cleavage, trisulfide formation, cysteinylation, glutathionylation, disulfide bridging to further light chains, and disulfide scrambling. With regard to potency, disulfide cleavage, hinge cleavage, disulfide bridging to further light chains, and cysteinylation were found to influence antigen binding and fragment crystallizable (Fc) effector functionalities. Renal clearance of small fragments may be faster, whereas clearance of larger fragments appears to depend on their neonatal Fc receptor (FcRn) functionality, which in turn may be impeded by disulfide bond cleavage. Certain modifications such as disulfide induced aggregation and heterodimers from different antibodies are generally regarded critical with respect to safety. However, the detection of some modifications in endogenous antibodies isolated from human blood and the possibility of in vivo repair mechanisms may reduce some safety concerns.

Antibody to FcεRIα Suppresses Immunoglobulin E Binding to High-Affinity Receptor I in Allergic Inflammation

PURPOSE

High-affinity receptor I (FcεRI) on mast cells and basophils plays a key role in the immunoglobulin E (IgE)-mediated type I hypersensitivity mediated by allergen cross-linking of the specific IgE-FcεRI complex. Thus, prevention of IgE binding to FcεRI on these cells is an effective therapy for allergic disease. We have developed a strategy to disrupt IgE binding to FcεRI using an antibody targeting FcεRIα.

MATERIALS AND METHODS

Fab fragment antibodies, which lack the Fc domain, with high affinity and specificity for FcεRIα and effective inhibitory activity against IgE-FcεRI binding were screened. IgE-induced histamine, β-hexosaminidase and Ca²⁺ release in basophils were determined by ELISA. A B6.Cg-Fcer1a(tm1Knt) Tg(FCER1A)1Bhk/J mouse model of passive cutaneous anaphylaxis (PCA) was used to examine the inhibitory effect of NPB311 on allergic skin inflammation.

RESULTS

NPB311 exhibited high affinity to human FcεRIα (KD=4 nM) and inhibited histamine, β-hexosaminidase and Ca²⁺ release in a concentration-dependent manner in hFcεRI-expressing cells. In hFcεRIα-expressing mice, dye leakage was higher in the PCA group than in controls, but decreased after NPB311 treatment. NPB311 could form a complex with FcεRIα and inhibit the release of inflammation mediators.

CONCLUSION

Our approach for producing anti-FcεRIα Fab fragment antibody NPB311 may enable clinical application to a therapeutic pathway in IgE/FcεRI-mediated diseases.

Plant-derived cardiac glycosides: Role in heart ailments and cancer management

Cardiac glycosides, the cardiotonic steroids such as digitalis have been in use as heart ailment remedy since ages. They manipulate the renin-angiotensin axis to improve cardiac output. However; their safety and efficacy have come under scrutiny in recent times, as poisoning and accidental mortalities have been observed. In order to better understand and exploit them as cardiac ionotropes, studies are being pursued using different cardiac glycosides such as digitoxin, digoxin, ouabain, oleandrin etc. Several cardiac glycosides as peruvoside have shown promise in cancer control, especially ovary cancer and leukemia. Functional variability of these glycosides has revealed that not all cardiac glycosides are alike. Apart from their specific affinity to sodium-potassium ATPase, their therapeutic dosage and behavior in poly-morbidity conditions needs to be considered. This review presents a concise account of the key findings in recent years with adequate elaboration of the mechanisms. This compilation is expected to contribute towards management of cardiac, cancer, even viral ailments.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

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.

Spotlight on idarucizumab and its potential for the reversal of anticoagulant effects of dabigatran

Idarucizumab is the first targeted antidote of dabigatran, a direct oral anticoagulant used for prevention and treatment of venous thromboembolism and prevention of stroke in atrial fibrillation. Idarucizumab is a humanized fragment of a monoclonal antibody, which binds dabigatran reversibly with high affinity and, when administered intravenously, immediately neutralizes its anticoagulant effect. It is rapidly cleared by the kidney with captured dabigatran. In Phase I and II trials, no significant adverse events have been reported. Specifically, idarucizumab has no anticoagulant or procoagulant effect by itself. Idarucizumab is currently being evaluated in an ongoing Phase III trial, in patients treated with dabigatran presenting with severe active bleeding or requiring emergency surgery or an invasive procedure and are at high risk of bleeding. The results of the interim analysis confirm the ability of idarucizumab to neutralize dabigatran instantaneously, without rebound effect, except in rare patients with very high baseline levels of anticoagulant. Although not definitely proving clinical efficacy, due to the noncontrolled design of the trial and the heterogeneity of patient conditions, these promising results on an intermediate criterion with strong rationale have led to the approval of idarucizumab for these indications. However, several questions are unresolved. First, activity measurement of dabigatran in blood, useless in current practice, could be useful to guide the treatment and avoid over- or underutilization of the antidote; but so far, it has not been largely available in real time. Second, the translation of anticoagulant neutralization to an effect on mortality and better outcome is highly dependent on the global management of these patients, especially rapid diagnosis, supportive care, and easy access to antidote administration. Although idarucizumab represents a remarkable achievement in drug design and development, whether it will be an important step toward improved safety of patients treated with dabigatran in the real world will have to be demonstrated in the postmarketing phase.

Intranasal exposure to monoclonal antibody Fab fragments to Japanese cedar pollen Cry j1 suppresses Japanese cedar pollen-induced allergic rhinitis

BACKGROUND AND PURPOSE

Fab fragments (Fabs) of antibodies have the ability to bind to specific allergens but lack the Fc portion that exerts effector functions via binding to receptors including FcεR1 on mast cells. In the present study, we investigated whether intranasal administration of the effector function-lacking Fabs of a monoclonal antibody IgG1 (mAb, P1-8) to the major allergen Cry j1 of Japanese cedar pollen (JCP) suppressed JCP-induced allergic rhinitis in mice.

EXPERIMENTAL APPROACH

Balb/c mice sensitized with JCP on days 0 and 14 were challenged intranasally with the pollen on days 28, 29, 30 and 35. Fabs prepared by the digestion of P1-8 with papain were also administered intranasally 15 min before each JCP challenge.

KEY RESULTS

Intranasal administration of P1-8 Fabs was followed by marked suppression of sneezing and nasal rubbing in mice with JCP-induced allergic rhinitis. The suppression of these allergic symptoms by P1-8 Fabs was associated with decreases in mast cells and eosinophils and decreased hyperplasia of goblet cells in the nasal mucosa.

CONCLUSIONS AND IMPLICATIONS

These results demonstrated that intranasal exposure to P1-8 Fabs was effective in suppressing JCP-induced allergic rhinitis in mice, suggesting that allergen-specific mAb Fabs might be used as a tool to regulate allergic pollinosis.

Switch-mediated activation and retargeting of CAR-T cells for B-cell malignancies

Chimeric antigen receptor T (CAR-T) cell therapy has produced impressive results in clinical trials for B-cell malignancies. However, safety concerns related to the inability to control CAR-T cells once infused into the patient remain a significant challenge. Here we report the engineering of recombinant antibody-based bifunctional switches that consist of a tumor antigen-specific Fab molecule engrafted with a peptide neo-epitope, which is bound exclusively by a peptide-specific switchable CAR-T cell (sCAR-T). The switch redirects the activity of the bio-orthogonal sCAR-T cells through the selective formation of immunological synapses, in which the sCAR-T cell, switch, and target cell interact in a structurally defined and temporally controlled manner. Optimized switches specific for CD19 controlled the activity, tissue-homing, cytokine release, and phenotype of sCAR-T cells in a dose-titratable manner in a Nalm-6 xenograft rodent model of B-cell leukemia. The sCAR-T-cell dosing regimen could be tuned to provide efficacy comparable to the corresponding conventional CART-19, but with lower cytokine levels, thereby offering a method of mitigating cytokine release syndrome in clinical translation. Furthermore, we demonstrate that this methodology is readily adaptable to targeting CD20 on cancer cells using the same sCAR-T cell, suggesting that this approach may be broadly applicable to heterogeneous and resistant tumor populations, as well as other liquid and solid tumor antigens.

High contrast tumor imaging with radio-labeled antibody Fab fragments tailored for optimized pharmacokinetics via PASylation

Although antigen-binding fragments (Fabs) of antibodies constitute established tracers for in vivo radiodiagnostics, their functionality is hampered by a very short circulation half-life. PASylation, the genetic fusion with a long, conformationally disordered amino acid chain comprising Pro, Ala and Ser, provides a convenient way to expand protein size and, consequently, retard renal filtration. Humanized αHER2 and αCD20 Fabs were systematically fused with 100 to 600 PAS residues and produced in E. coli. Cytofluorimetric titration analysis on tumor cell lines confirmed that antigen-binding activities of the parental antibodies were retained. The radio-iodinated PASylated Fabs were studied by positron emission tomography (PET) imaging and biodistribution analysis in mouse tumor xenograft models. While the unmodified αHER2 and αCD20 Fabs showed weak tumor uptake (0.8% and 0.2% ID/g, respectively; 24 h p.i.) tumor-associated radioactivity was boosted with increasing PAS length (up to 9 and 26-fold, respectively), approaching an optimum for Fab-PAS₄₀₀. Remarkably, 6- and 5-fold higher tumor-to-blood ratios compared with the unmodified Fabs were measured in the biodistribution analysis (48 h p.i.) for αHER2 Fab-PAS₁₀₀ and Fab-PAS₂₀₀, respectively. These findings were confirmed by PET studies, showing high imaging contrast in line with tumor-to-blood ratios of 12.2 and 5.7 (24 h p.i.) for αHER2 Fab-PAS₁₀₀ and Fab-PAS₂₀₀. Even stronger tumor signals were obtained with the corresponding αCD20 Fabs, both in PET imaging and biodistribution analysis, with an uptake of 2.8% ID/g for Fab-PAS₁₀₀vs. 0.24% ID/g for the unmodified Fab. Hence, by engineering Fabs via PASylation, plasma half-life can be tailored to significantly improve tracer uptake and tumor contrast, thus optimally matching reagent/target interactions.

Nano-antidotes for drug overdose and poisoning

The number of intoxications from xenobiotics—natural or synthetic foreign chemicals, or substances given in higher doses than typically present in humans—has risen tremendously in the last decade, placing poisoning as the leading external cause of death in the United States. This epidemic has fostered the development of antidotal nanomedicines, which we call “nano-antidotes,” capable of efficiently neutralizing offending compounds in situ. Although prototype nano-antidotes have shown efficacy in proof-of-concept studies, the gap to clinical translation can only be filled if issues such as the clinical relevance of intoxication models and the safety profile of nano-antidotes are properly addressed. As the unmet medical needs in resuscitative care call for better treatments, this Perspective critically reviews the recent progress in antidotal medicine and emerging nanotechnologies.

Fourier transform infrared spectroscopy provides an evidence of papain denaturation and aggregation during cold storage

Papain is a cysteine protease with wide substrate specificity and many applications. Despite its widespread applications, cold stability of papain has never been studied. Here, we used differential spectroscopy to monitor thermal denaturation process. Papain was the most stabile from 45 °C to 60 °C with ΔG°321 of 13.9±0.3 kJ/mol and Tm value of 84±1 °C. After cold storage, papain lost parts of its native secondary structures elements which gave an increase of 40% of intermolecular β-sheet content (band maximum detected at frequency of 1621 cm(-1) in Fourier transform infrared (FT-IR) spectrum) indicating the presence of secondary structures necessary for aggregation. The presence of protein aggregates after cold storage was also proven by analytical size exclusion chromatography. After six freeze-thaw cycles around 75% of starting enzyme activity of papain was lost due to cold denaturation and aggregation of unfolded protein. Autoproteolysis of papain did not cause significant loss of the protein activity. Upon the cold storage, papain underwent structural rearrangements and aggregation that correspond to other cold denatured proteins, rather than autoproteolysis which could have the commercial importance for the growing polypeptide based industry.

Fab fragments of ovine antibody to colchicine enhance its clearance in the rat

CONTEXT

Colchicine is an anti-inflammatory alkaloid used for the treatment of acute gout, but has a narrow therapeutic index. Colchicine overdoses are relatively rare, but have high mortality requiring rapid treatment.

OBJECTIVE

To evaluate the ability of a newly available ovine fragment antigen-binding (Fab) antibody to colchicine (ColchiFab(™)) to protect rats against renal and other injury 24 h after colchicine ingestion.

MATERIALS AND METHODS

Rats were gavaged with colchicine (5 mg/kg), then 2 h later injected intraperitoneally with 5 ml of sterile saline, or Fab anti-colchicine, a newly available ovine antibody to colchicine. Samples of blood were taken at 1, 2, 5 and 24 h after gavage, and urine was collected from 5 to 24 h after gavage. Concentrations of colchicine in tissue, blood and urine were measured by liquid chromatography/mass spectrometry, concentrations of Fab anti-colchicine, urinary neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 or KIM-1 by enzyme-linked immunosorbent assay or ELISA, while concentrations of creatine kinase and creatinine (Cr) were measured enzymatically.

RESULTS

Colchicine equilibrated rapidly throughout the body and increased serum creatine kinase. Fab anti-colchicine also rapidly redistributed to the blood and remained at high concentrations over 24 h. Fab anti-colchicine caused a rapid 7.1-fold increase in serum colchicine level, followed by excretion of both colchicine and Fab anti-colchicine through the urine. This was associated with the accumulation of colchicine in the kidney, a reversal of colchicine-induced diarrhoea, and increasing urinary NGAL level; from 168 ± 48 to 477 ± 255 ng/mmol Cr [mean ± standard deviation or SD].

DISCUSSION

Fab anti-colchicine greatly increased the clearance of colchicine, although increasing NGAL level suggested the presence of mild kidney damage.

CONCLUSION

These data suggest clinical utility for Fab anti-colchicine in the treatment of colchicine overdose.

American Society of Nephrology quiz and questionnaire 2014: acid-base and electrolyte disorders

The Nephrology Quiz and Questionnaire remains an extremely popular session for attendees of the Annual Kidney Week Meeting of the American Society of Nephrology. Once again, in 2014 the conference hall was overflowing with audience members and eager quiz participants. Topics covered by the expert discussants included electrolyte and acid-base disorders, glomerular disease, ESRD/dialysis, and transplantation. Complex cases from each of these categories along with single-best-answer questions were prepared and submitted by the panel of experts. Before the meeting, program directors of United States nephrology training programs and nephrology fellows answered the questions using an Internet-based questionnaire. During the live session, members of the audience tested their knowledge and judgment on a series of case-oriented questions prepared and discussed by the experts. They compared their answers in real time using audience response devices with the answers of the nephrology fellows and training program directors. The correct and incorrect answers were then discussed after the audience responses and the results of the questionnaire were displayed. As always, the audience, lecturers, and moderators enjoyed this educational session. This article recapitulates the acid-base and electrolyte disorders portion of the session and reproduces its educational value for the readers of the Clinical Journal of the American Society of Nephrology. Enjoy the clinical cases and expert discussions.

IgY pharmacokinetics in rabbits: implications for IgY use as antivenoms

This paper presents the first study of chicken IgY pharmacokinetics (PK) in rabbits. We measured IgY blood serum concentrations using a specific high sensitivity ELISA method. The fast initial component observed when studying horse Fab, F(ab')2 or IgG was absent from IgY PK. During the first 80 min of observation there was only a single slow exponential decay, which sped up afterward to the point that IgY became undetectable after 216 h of observation; due to this time course, PK parameters were determined with trapezoidal integration. The most significant IgY pharmacokinetic parameters determined were (all presented as medians and their 95% confidence interval): Area Under the Curve = 183.8 (135.2, 221.5) mg·h·L(-1); Distribution volume of the central compartment·[Body Weight (BW)](-1) = 46.0 (21.7, 70.3) mL·kg(-1); Distribution volume in steady state·BW(-1) = 56.8 (44.4, 68.5) mLkg(-1); Mean Residence Time = 40.1 (33.6, 48.5) h; Total plasma clearance·BW(-1) = 1.44 (1.15, 1.66) mL·h(-1)·kg(-1). Anti IgY IgG titers determined by ELISA increased steadily after 72 h, and reached 2560 (1920, 5760) dilution(-1) at 264 h; anti-chicken IgG concentrations rose up to 3.19 (2.31, 6.17) μg/mL in 264 h. Our results show that IgY PK lacks the fast initial decay observed in other PK studies using horse IgG, F(ab')2 or Fab, remains in the body 39.0 (28.7, 47.2) % much as IgG and is ≈3 times more immunogenic that horse IgG in rabbits.

Intratracheal exposure to Fab fragments of an allergen-specific monoclonal antibody regulates asthmatic responses in mice

Fab fragments (Fabs) maintain the ability to bind to specific antigens but lack effector functions due to the absence of the Fc portion. In the present study, we tested whether Fabs of an allergen-specific monoclonal antibody (mAb) were able to regulate asthmatic responses in mice. Asthmatic responses were induced in BALB/c mice by passive sensitization with anti-ovalbumin (OVA) polyclonal antibodies (pAbs) (day 0) and by active sensitization with OVA (days 0 and 14), followed by intratracheal (i.t.) challenge with OVA on day 1 and days 28, 29, 30 and 35. Fabs prepared by the digestion of an anti-OVA IgG1 (O1-10) mAb with papain were i.t. administered only once 30 min before antigenic challenge on day 1 or day 35. The results showed that i.t. administration of O1-10 Fabs with OVA markedly suppressed the early and/or late phases of asthmatic responses caused by passive and active sensitization. Similar results were obtained when Fabs of anti-OVA IgG2b mAb (O2B-3) were i.t. administered. In contrast, neither i.t. injection of intact 01-10/O2B-3 nor systemic injection of O1-10 Fabs suppressed the asthmatic responses. In vitro studies revealed that the capture of OVA by O1-10 Fabs prevented the subsequent binding of intact anti-OVA pAbs to the captured OVA. These results suggest that asthmatic responses may be down-regulated by the i.t. exposure to Fabs of an allergen-specific mAb via a mechanism involving the capture of allergen by Fabs in the respiratory tract before the interaction of intact antibody and allergen essential for the induction of asthmatic responses.

Feasibility of polyelectrolyte-driven Fab fragment separation

The use of antigen-binding fragments (Fabs) as biotherapeutic agents is gaining interest and thus requires development of adequate purification strategies aimed at separating Fabs from other proteins. Thus, the feasibility of using a copolymer for separation of Fabs from monoclonal antibodies (mAbs) and fragment constant regions (Fcs) was evaluated, employing a blend of purified solutions of these proteins. The use of a copolymer exerting both hydrophobic as well as anionic properties resulted in high precipitation yields for both the mAb and Fc fragment, even at ionic strength of 150 mM NaCl. On the contrary, Fabs exhibited reduced precipitation yields upon copolymer addition. These observations are attributed to differences in protein physicochemical parameters, allowing mAbs and Fcs to be precipitated via conjoint electrostatic and hydrophobic interactions. In contrast, Fabs were mainly precipitated via electrostatic interactions, being reduced at higher ionic strength. This finding was corroborated by hydrophobicity analysis using 2-p-toluidinonaphthalene-6-sulfonate, showing enhanced hydrophobicity of Fcs compared to mAbs alone, while Fabs exhibited the lowest hydrophobicity. Within the context of increasing demand for Fabs as therapeutic proteins, these results may open up a simpler purification strategy for this protein class, potentially also to be implemented within the context of polymer-driven protein purification during fermentation.

Site-specific functionalization of proteins and their applications to therapeutic antibodies

Protein modifications are often required to study structure and function relationships. Instead of the random labeling of lysine residues, methods have been developed to (sequence) specific label proteins. Next to chemical modifications, tools to integrate new chemical groups for bioorthogonal reactions have been applied. Alternatively, proteins can also be selectively modified by enzymes. Herein we review the methods available for site-specific modification of proteins and their applications for therapeutic antibodies.