A Case Study for Critical Reagent Qualification for Ligand Binding Assays Using Equivalence Test Methodology

Qualifying critical reagents in ligand binding assays by parallel testing of current and candidate reagent lots is recommended by regulatory agencies and industry groups, but specific guidance on the format of reagent qualification experiments is limited. Equivalence testing is a statistically sound approach that is consistent with the objective of critical reagent qualification. We present power analysis for equivalence regions ranging from 1.25- to 1.5-fold multiples of the GM ratio (centered on 1) of current and candidate lots, over a range of assay variability from 5 to 30% coefficient of variation (CV). A 1.25-fold equivalence region can be tested using 6 to 12 plates per lot for assays with up to 15% CV but is not practical for more variable assays. For these assays, wider equivalence regions are justified so long as care is taken to avoid assay drift and the assay remains suitable for the intended use. The equivalence test method is illustrated using historical data from passing and failing reagent qualification experiments. Simulation analysis was performed to support the design of qualification experiments using 6, 12, or 18 plates per lot over a broad range of assay variability. A challenge in implementing the equivalence test approach is selecting an appropriate equivalence region. Equivalence regions providing 90% power using 12 plates/lot were consistent with 1.5σ bounds, which are recommended for equivalence testing of critical quality attributes of biosimilars.

Critical reagent inventory management system and web portal specifically optimized for supporting external clients

High-quality critical reagents are essential for the establishment of robust ligand binding assays to support regulated bioanalysis. To ensure consistency in assay performance over the lifetime of a project, a well-defined set of processes is needed for critical reagent life cycle management. Moreover, contract research organizations must support reagent life cycle management for diverse global clients. To address these needs, the authors designed and implemented a customized inventory management system, known as LCM+. This software solution provides external clients with efficient, secure access via a web portal to their critical reagent information, pertinent documentation and inventory tracking. Hence, the authors believe that LCM+ can serve as a useful prototype to aid the design of future inventory management systems for optimal management of critical reagents.

Simple method to determine the concentration and incorporation ratio of ruthenium-labeled antibodies

Aim: Ruthenium-labeled antibodies are commonly used detection reagents in bioanalysis assays and must be characterized to ensure quality. The aim of this work was to develop a method to determine the concentration and incorporation ratio (the degree of labeling [DOL]) of ruthenium-labeled antibodies by UV/VIS spectroscopy. Materials & methods: Free SULFO-TAG compound was scanned using UV/VIS and showed an absorbance peak at 292 nm. In contrast, antibodies demonstrate UV absorbance at 280 nm. After experimentally determining the extinction coefficients at 280 and 292 nm of free ruthenium and antibody, we generated a formula based on the Beer-Lambert law that calculates both concentration and DOL of these ruthenium-labeled antibodies. Conclusion: The concentration and DOL values determined by our method were comparable to those determined from bicinchoninic acid and LC/MS for the same reagents. This method creates a faster and more accessible reagent characterization process that uses far less reagent than the more traditional alternatives.

Lot-to-lot reproducibility, stability and life cycle management of antibody reagents for flow cytometry

The increasing number of biopharmaceuticals, gene and cell therapies in development has seen a growing use of flow cytometry to measure biomarkers, generate pharmacokinetic data, assess immunogenicity and investigate target engagement. The importance of these data types and their inclusion in regulatory submissions mean that flow cytometry analyses are now expected to demonstrate robust performance and comply with both regulatory and scientific recommendations during their validation and subsequent use in sample analysis. The control of the 'critical reagents' commonly used in flow cytometry presents some specific challenges, particularly when an assay is required for use over a long period of time across different phases of a drug development program, or where it is deployed in complex, multisite clinical studies. This paper highlights some key challenges in flow cytometry reagent management with some of the strategies employed to control and monitor flow cytometry critical reagents.

The impact of ligand binding based assays critical reagent characterization and storage

Biological critical reagents are the foundation of many bioanalytical methods and often chemically modified or conjugated with various chemical tags. As such, the quality and performance of these methods are inherently tied to the quality and stability of critical reagents. This article will outline recommendations for conjugated critical reagent development and characterization. Examples of the impact of regent quality will be discussed for the two common bioanalytical assays in support of drug development for biotherapeutics. Finally, a brief discussion of conjugated reagent stability and recommendations for storage and testing will be presented.

Critical reagent generation, characterization, handling and storage workflows: impact on ligand binding assays

The foundation of pharmacokinetics and antidrug antibodies assay robustness relies on the use of high-quality reagents. Over the past decade, there has been increasing interest within the pharmaceutical industry, as well as regulators, on defining best practices and scientific approaches for generation, characterization and handling of critical reagents. In this review, we will discuss current knowledge and practices on critical reagent workflows and state-of-the-art approaches for characterization, generation, stability and storage and how each of these steps can impact ligand-binding assay robustness.

Increasing robustness, reliability and storage stability of critical reagents by freeze-drying

Aim: Stabilization of critical reagents by freeze-drying would facilitate storage and transportation at ambient temperatures, and simultaneously enable constant reagent performance for long-term bioanalytical support throughout drug development. Freeze-drying as a generic process for stable performance and storage of critical reagents was investigated by establishing an universal formulation buffer and lyophilization process. Results: Using a storage-labile model protein, formulation buffers were evaluated to preserve reagent integrity during the freeze-drying process, and to retain functional performance after temperature stress. Application to critical reagents used in pharmacokinetics and anti-drug antibodies assays demonstrated stable functional performance of the reagents after 11 month at +40°C. Conclusion: Stabilization and storage of critical assay reagents by freeze-drying is an attractive alternative to traditional deep freezing.

Critical reagent characterization and re-evaluation to ensure long-term stability: two case studies

Characterization of critical reagents can mitigate adverse impact to ligand-binding assay performance. We investigated the conjugation conditions of a bispecific protein to SULFO-TAG NHS-Ester™ ruthenium to resolve a steady increase in ligand-binding assay background signal. Functional and biophysical attributes in stability samples revealed low pH (4.0) conjugation and formulation buffers were key to decrease aggregate formation. We also identified pH-specific (3.0) purification conditions to reduce aggregate levels from 37% to <5% of a mouse IgG3 reagent antibody. These case studies support the utility of biophysical and functional characterization of critical reagents as a proactive approach to maintain long-term stability and provide the basis for our recommendations a risk-based approach to establish re-evaluation intervals for traditional and novel reagents.

Using multiple platforms for critical reagents selection process to support pharmacokinetic ligand-binding assay development

We have evaluated the utility of epitope binning on biolayer interferometry (BLI) as a strategy to funnel the selection of candidate pairs suitable for pharmacokinetic assay development. Totally, 8 anti-Idiotypic monoclonal antibodies in 64 possible combinations were tested by BLI, ELISA and Gyrolab^®. Two epitope binning approaches were utilized, in-tandem and classic sandwich. Both formats identified four mutually exclusive bins providing 31 and 25 possible antibody pair combinations, respectively. In contrast, the ELISA and Gyrolab yielded 18 and 9 positive pairs, respectively, with only a partial correlation to the BLI results. Several positive pairs by ELISA and Gyrolab, screened negative by BLI. Just over half of the pairs predicted by BLI were positive on ELISA and less than a quarter were positive on Gyrolab. This evaluation showed, in our case, that BLI was limited in its ability to predict candidate pairs that would be successful in pharmacokinetic method development.

The importance of quality critical reagents for the entire developmental lifecycle of a biopharmaceutical: a pharmacokinetic case study

Background: High-quality critical reagents are essential to the successful support of biotherapeutic drug development regardless of the analytical platform used for support. The lack of such a reagent, early in the development lifecycle of a biotherapeutic can have detrimental impact on resource and translation of data across development phases. Results: Here, a pharmacokinetic assay case study is shared that illustrates what can occur when there is a lack of a reproducible and sustainable critical reagent early in the development lifecycle of a biotherapeutic. Various assay formats and critical reagents, as well as reagents generation programs, were initiated to find a reagent and assay format which was fit for purpose. Conclusions: Identification of appropriate critical reagents early in the development lifecycle of a biotherapeutic as advantageous.

Considerations in the development and validation of real-time quantitative polymerase chain reaction and its application in regulated bioanalysis to characterize the cellular kinetics of CAR-T products in clinical studies

Real-time quantitative polymerase chain reaction (qPCR) has become the standard method for monitoring cellular kinetics of CAR-T therapies with measurement of the CAR transgene copy numbers in peripheral blood mononuclear cells isolated from patients receiving the treatment. Unlike other biophysical and immunological methodologies for bioanalytical characterization of conventional small molecule drugs or protein biologics, there is no relevant regulatory guidance to date on the method development and validation for quantitative qPCR assays employed during clinical development of CAR-T products. This paper will provide an overview and considerations in the development and validation of a qPCR assay from sample extraction to assay parameters and its implementation in regulated bioanalysis for CAR-T or other types of cell therapies.

Automated, Generic Reagent and Ultratargeted 2D-LC-MS/MS Enabling Quantification of Biotherapeutics and Soluble Targets down to pg/mL Range in Serum

Mass spectrometry has recently emerged as a powerful analytical tool for the assessment of pharmacokinetics and biomarkers in drug development. Compared with ligand binding assays, a major advantage of mass spectrometry-based assays is that they are less dependent on high quality binding reagents, while a key limitation is the relatively lower sensitivity. To address the sensitivity issue, we have developed a generic reagent, ultratargeted two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) method which combines commercially available protein A affinity capture, targeted analyte isolation by 2D-LC, and targeted detection by multiple reaction monitoring (MRM). A targeted-2D-with-dilution configuration was designed to automate 2D-LC-MS/MS. This method was systematically evaluated using an anti-CD22 monoclonal antibody spiked into monkey and human serum, where lower limits of quantification (LLOQ) of 0.78 and 1.56 ng/mL were achieved, respectively. This represents an over 100-fold improvement in assay sensitivity compared to the conventional LC-MS/MS method. The performance of the method was further confirmed by analyzing another monoclonal antibody, bevacizumab, as well as a soluble antigen, circulating PD-L1. The results indicate that our method enables quantification of antibody therapeutics and antigen biomarkers in both clinical and nonclinical samples in the pg/mL to low ng/mL range. Protein A affinity capture was employed as a universal sample preparation procedure applicable to both full-length antibody therapeutics and antibody-antigen complexes. This novel method is also fully automated and proven to be highly robust for routine bioanalysis in drug development.

EBF recommendation on practical management of critical reagents for antidrug antibody ligand-binding assays

Immunogenicity assays are required to measure antidrug antibodies that are generated against biotherapeutic modalities. As for any ligand-binding assays, critical reagents (CR) play a crucial role in immunogenicity assays, as the robustness and reliability of an assay are defined by the quality and long-term availability of these reagents. The current regulatory guidelines do not provide clear directions on how to implement and verify lot-to-lot changes of CR during an assay life cycle, or the acceptance criteria that should be used when implementing new lots of CR. These aspects were extensively discussed within the European Bioanalysis Forum community. In this paper, CR for immunogenicity assays are identified and the minimum requirements for introducing new lots of CR in immunogenicity assays are described.

EBF recommendation on practical management of critical reagents for PK ligand-binding assays

Critical reagents play a crucial role in ligand-binding assays; the robustness and reliability of an assay is defined by the quality and long-term availability of these reagents. However, neither regulatory guidelines nor relevant scientific papers provide clear directions for set-up, life cycle management and, more importantly, the acceptance criteria required for the testing of the critical reagents for pharmacokinetic, biomarker and immunogenicity assays. The ambiguity from current guidelines can be a challenge for the bioanalytical community. Members of the European Bioanalysis Forum community undertook a more pragmatic approach on how to assess the impact of critical reagents. In this paper, a review and corresponding gap analysis of the current guidelines and relevant papers will be provided as well as decision trees proposed for lot-to-lot changes of critical reagents for pharmacokinetic assays.

Surface plasmon resonance as a tool for ligand-binding assay reagent characterization in bioanalysis of biotherapeutics

Ligand-binding assay (LBA) performance depends on quality reagents. Strategic reagent screening and characterization is critical to LBA development, optimization and validation. Application of advanced technologies expedites the reagent screening and assay development process. By evaluating surface plasmon resonance technology that offers high-throughput kinetic information, this article aims to provide perspectives on applying the surface plasmon resonance technology to strategic LBA critical reagent screening and characterization supported by a number of case studies from multiple biotherapeutic programs.

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.

2015 White Paper on recent issues in bioanalysis: focus on new technologies and biomarkers (Part 3 – LBA, biomarkers and immunogenicity)

The 2015 9th Workshop on Recent Issues in Bioanalysis (9th WRIB) took place in Miami, Florida with participation of 600 professionals from pharmaceutical and biopharmaceutical companies, biotechnology companies, contract research organizations and regulatory agencies worldwide. WRIB was once again a 5 day, week-long event – A Full Immersion Bioanalytical Week – specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest in bioanalysis. The topics covered included both small and large molecules, and involved LCMS, hybrid LBA/LCMS and LBA approaches, including the focus on biomarkers and immunogenicity. This 2015 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2015 edition of this comprehensive White Paper has been divided into three parts. Part 3 discusses the recommendations for large molecule bioanalysis using LBA, biomarkers and immunogenicity. Part 1 (small molecule bioanalysis using LCMS) and Part 2 (hybrid LBA/LCMS and regulatory inputs from major global health authorities) have been published in volume 7, issues 22 and 23 of Bioanalysis, respectively.

Recommendations and best practices for reference standards and reagents used in bioanalytical method validation

The continued globalization of pharmaceutics has increased the demand for companies to know and understand the regulations that exist across the globe. One hurdle facing pharmaceutical and biotechnology companies developing new drug candidates is interpreting the current regulatory guidance documents and industry publications associated with bioanalytical method validation (BMV) from each of the different agencies throughout the world. The objective of this commentary is to provide our opinions on the best practices for reference standards and key reagents, such as metabolites and internal standards used in the support of regulated bioanalysis based on a review of current regulatory guidance documents and industry white papers for BMV.

Free analyte QC concept: a novel approach to prove correct quantification of free therapeutic protein drug/biomarker concentrations

Quantification of free drug concentrations is highly challenging due to the dynamic drug–ligand equilibrium, which may result in incorrect results. Current QC concepts do not adequately cover all of the important influencing factors: the assay itself (format and procedure); the calibration concept; the sample preparation; and the sample storage. Here, we propose a ‘free analyte QC concept’ that enables quantitative testing of these four factors and, thus, provides best possible proof of correct free drug quantification. The principle of the free analyte QC concept and an example of its application for a free drug assay is described. A comparison of this novel approach with current approaches and how the new concept fits (or does not fit) with current regulatory guidelines is discussed.