An electrochemiluminescence assay for quantification of Denileukin Diftitox and its anti-drug antibodies in rat serum

Denileukin Diftitox (DD), comprising fragments of diphtheria toxin (DT) and interleukin-2 (IL2), was developed for the treatment of lymphoma and has been approved for marketing in Japan. Toxicological evaluation including pharmacokinetics and immunogenicity in preclinical animals is important for drug development and thus the assays of DD and anti-drug antibody (ADA) were developed by electrochemiluminescence (ECL) detection. For the DD assay, ruthenium-labeled anti-DT Ab and biotinylated anti-IL2 Ab were mixed with serum samples and the mixture was captured by streptavidin-coated wells for ECL detection. For the ADA assay, signals of immuno-complex of biotinylated DD, ruthenium-labeled DD, and ADA, bound to streptavidin plate were determined. DD was quantifiable from 10 ng/mL. Accuracy and precision of quality control samples were within ±20% and 20%, respectively, and stability of DD in rat serum was successfully assessed. Precision of positive control samples of ADA was within the acceptance criteria and cut point values for ADA detection in the screening and confirmatory assay were determined by statistical analysis. Drug-induced ADA was detected by screening assay followed by confirmatory assay. The developed method was successfully applied to assess pharmacokinetics and immunogenicity to support toxicity studies in rats.

CD86 occupancy in belatacept-treated kidney transplant patients is not associated with clinical and infectious outcomes

The CD86 occupancy assay has been developed to measure the number of CD86 molecules unbound to belatacept, but its association with clinical outcomes has not been assessed yet. All kidney transplant patients switched to belatacept in our center between 2016 and 2018 were included. Blood samples were collected before each infusion for 1 year to assess CD86 occupancy by CD86 antibody cytometry staining on the surface of CD14⁺ monocytes. Results were expressed as the median fluorescence intensity (MFI) value of CD86 staining. At each infusion, the MFI_{Day of infusion} /MFI_{Day 0} ratio was calculated. Forty-one patients were consecutively included. After every 2-week infusion period, CD86 MFI ratio dropped from 1.00 to 0.73 [0.57-0.98], p = .07. However, this ratio progressively increased to 0.78 [0.53-1.13] at 1 year, which was not statistically different from pre-switch ratio, p = .4. Over the first year, the MFI ratio coefficient of variation was 31.58% [23.75-38.31]. MFI ratio was not different between patients with or without opportunistic infections: 0.73 [0.60-0.88] versus 0.80 [0.71-1.00], p = .2, or between patients with or without EBV DNAemia, p = .2. Despite previous in vitro results, the CD86 occupancy assay suffers from a high intra-individual variability and does not appear to be relevant to clinical outcomes.

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.

Effects of Adjuvants on the Immunogenicity and Efficacy of a Zika Virus Envelope Domain III Subunit Vaccine

Zika virus (ZIKV), a mosquito-borne flavivirus, has attracted global attention due to its close association with congenital Zika syndrome and neurological diseases, and transmission through additional routes, such as sexual contact. Currently there are no vaccines approved for ZIKV, and thus, there is an urgent need to develop an effective and safe ZIKV vaccine. Domain III (DIII) of the ZIKV envelope (E) protein is an important vaccine target, and a vaccine developed using a mutant DIII of E (EDIII) protein protects adult and pregnant mice, and unborn offspring, against ZIKV infection. Here, we have used immunocompetent BALB/c mice treated with anti-interferon-α/β receptor 1 (Ifnar1) antibodies to investigate whether three adjuvants (aluminum (Alum), monophosphoryl lipid A (MPL), and MF59), either alone or in combination, could improve the efficacy of this EDIII subunit vaccine. Our data show that, although vaccine formulated with a single adjuvant induced a specific antibody and cellular immune response, and reduced viral load in mice challenged with ZIKV, the combination of Alum and MPL adjuvants led to a more robust and balanced immune response, stronger neutralizing activity against three recent ZIKV human strains, and greater protection against a high-dose ZIKV challenge. Particularly, the combination of Alum with MPL significantly reduced viral titers and viral RNA copy numbers in sera and tissues, including the male reproductive organs. Overall, this study has identified the combination of Alum and MPL as the most effective adjuvant for ZIKV EDIII subunit vaccines, and it has important implications for subunit vaccines against other enveloped viruses, including non-ZIKV flaviviruses.

Characterization of labeled reagents in ligand-binding assays by a surface plasmon resonance biosensor

Aim: Ligand-binding assay (LBA) reagent labeling may change the binding characteristics of the reagent to its target and degrade its performance in LBAs. Results: A surface plasmon resonance (SPR) biosensor was used to evaluate the impact of the biotin labeling process on reagent-binding kinetics and affinity for a specific target. The SPR results demonstrate that the biotin molar challenge ratio affects both association and dissociation rates for the labeled reagent binding to its target. The SPR results also predict the labeled reagent performance in LBAs. Conclusion: The methodology used in this study provides an example of using an SPR biosensor as an efficient way to analytically and functionally characterize critical reagents and to understand their performance postmodification in LBAs.

An integrated multiplatform bioanalytical strategy for antibody–drug conjugates: a novel case study

Background: The bioanalytical strategy for antibody–drug conjugates (ADC) includes numerous measurements integrally designed to provide comprehensive characterization of PK, PD and immunogenicity. This manuscript describes the utilization of reagents specifically tailored to an ADC with a microtubule polymerization inhibitor payload and cathepsin B cleavable linker. Methods: The PK strategy includes the evaluation of physiological levels of total antibody, active ADC, total ADC, antibody-conjugated payload and unconjugated payload. These data are evaluated in the context of target and antidrug antibody levels to elucidate bioactive ADC. Results & conclusion: Herein, we discuss how this strategy has been applied and present our preliminary observations. Continuously evolving to meet pipeline demands, the integrated bioanalytical data will provide critical insights into the exposure–response relationship.

Pharmacokinetics, pharmacodynamics, and immunogenicity of belatacept in adult kidney transplant recipients

BACKGROUND AND OBJECTIVES

Belatacept is a first-in-class, selective co-stimulation blocker recently approved for the prophylaxis of organ rejection in adult kidney transplant recipients. The objective of this study was to report the pharmacokinetics, pharmacodynamics, and immunogenicity of belatacept.

METHODS

The pharmacokinetics, pharmacodynamics (CD86 receptor occupancy), and immunogenicity of belatacept were studied in de novo adult kidney transplant recipients in phase II and III clinical studies.

RESULTS

Following multiple doses of 5 or 10 mg/kg, the geometric mean (percentage coefficient of variation) maximum serum concentration and area under the serum concentration-time curve over one dosing interval of belatacept were 136 (20%) and 238 (27%) μg/mL, and 13,587 (27%) and 21,241 (35%) μg·h/mL, respectively. The median belatacept elimination half-life was 8-9 days. Belatacept exhibited concentration-dependent binding to CD86 receptors. The pre-dose CD86 receptor occupancy by belatacept decreased from 94 to 65% between day 5 and 1 year post-transplant, with corresponding pre-dose trough serum concentrations of belatacept decreasing from ~35 to 4 μg/mL during this period. The cumulative incidence of developing anti-belatacept antibodies was 5.3% up to 3 years post-transplant and had no impact on belatacept exposure.

CONCLUSIONS

Belatacept in adult kidney transplant demonstrated linear pharmacokinetics with low variability, concentration-dependent pharmacodynamics, and a low incidence of anti-drug antibodies.

Parallelism: considerations for the development, validation and implementation of PK and biomarker ligand-binding assays

The goal of this article is to discuss the fundamental key questions around parallelism assessments: why to do it, when to do it and how to do it, with consideration for different molecule types and the scientific rationale that drives different approaches. Current practices for both PK and biomarker assays regarding which samples to pick, whether to pool or not pool samples, as well as generally accepted acceptance criteria are discussed, while also highlighting the many outstanding questions that remain. In order to reach the long-term goal of understanding and developing best practices for implementation of parallelism testing for both PK and biomarker assays, industry and regulators will need to keep the conversations going, and commit to generating and reviewing data for the purposes of our own education. Means to easily share data in open forums to facilitate and build common understandings should continue and will be necessary to expedite resolution of many of these questions.

Conjugated critical reagent characterization for ligand-binding assays: using MALDI-TOF-MS as an orthogonal tool to assess assay performance

Large-molecule biotherapeutics are forming an increasingly large percentage of emerging pharmaceutical pipelines. These molecules present specific challenges to the bioanalysts charged with measuring in vivo concentrations of the biotherapeutic. The challenges are typically met using ligand-binding assays in support of pharmacokinetic, pharmacodynamic and immunogenicity assays. Ligand-binding assays employ complex biological molecules that specifically recognize the biotherapeutic for quantitation. Generally, a minimum of one of these critical reagents must be chemically modified to generate a signal that is measured in the assay. Once chemically modified it is necessary to characterize the reagent prior to use in an assay. The concentration, purity and molar incorporation ratio of chemical modification are key characteristics. This article presents mass spectral techniques for determining the molar incorporation ratio. Case studies are provided to demonstrate the time and cost savings that can be realized with timely and detailed characterization of critical reagents for ligand-binding assays.

Ligand binding assay critical reagents and their stability: recommendations and best practices from the Global Bioanalysis Consortium Harmonization Team

The L4 Global Harmonization Team on reagents and their stability focused on the management of critical reagents for pharmacokinetic, immunogenicity, and biomarker ligand binding assays. Regulatory guidance recognizes that reagents are important for ligand binding assays but do not address numerous aspects of critical reagent life cycle management. Reagents can be obtained from external vendors or developed internally, but regardless of their source, there are numerous considerations for their reliable long-term use. The authors have identified current best practices and provided recommendations for critical reagent lot changes, stability management, and documentation.

Large molecule specific assay operation: recommendation for best practices and harmonization from the global bioanalysis consortium harmonization team

The L2 Global Harmonization Team on large molecule specific assay operation for protein bioanalysis in support of pharmacokinetics focused on the following topics: setting up a balanced validation design, specificity testing, selectivity testing, dilutional linearity, hook effect, parallelism, and testing of robustness and ruggedness. The team additionally considered the impact of lipemia, hemolysis, and the presence of endogenous analyte on selectivity assessments as well as the occurrence of hook effect in study samples when no hook effect had been observed during pre-study validation.