Bioanalytical methods for therapeutic monoclonal antibodies and antibody–drug conjugates: A review of recent advances and future perspectives

Ligand-binding assays validated for quantitative bioanalysis of a novel antibody-drug conjugate in monkey serum and related application in a nonclinical study

BACKGROUND

Antibody-drug conjugates (ADCs) are an emerging class of targeted therapeutics and are receiving growing attention in the pharmaceutical field. Here we aimed to validate two ligand binding assays for the quantitation of GQ1001, an ADC made of Trastuzumab site-specifically conjugated with DM1, in cynomolgus monkey serum, and then apply the validated assays to a nonclinical study.

METHODS

The quantitative methods for conjugated GQ1001 and total GQ1001 were validated against regulatory guidance documents on bioanalytical method validation under a Good Laboratory Practice (GLP)-compliant environment. The validated assays were applied to a single-dose pharmacokinetic (PK) study of GQ1001 conducted in cynomolgus monkeys.

RESULTS

Both intra- and inter-assay precision and accuracy met the priori-defined acceptance criteria. Neither matrix effect nor hemolysis effect were observed, and the impact of specific interferents on the assays was evaluated. Dilution linearity was good with the expected dilution factors and no hook effect till up to 20.2 mg/mL of GQ1001 was noted. Besides, the stability of the ADC in monkey serum was found to be sufficient to cover the time required for sample storage and analysis. Furthermore, the assays demonstrated good parallelism determined with a study sample and good reproducibility acquired by incurred sample reanalysis (ISR). Using the validated assays, we obtained serum concentrations for the conjugated GQ1001 and the total GQ1001 in the single-dose PK study, and thereafter, evaluated their exposures over the dosing period.

CONCLUSIONS

All tested performance parameters of the assays met the validation acceptance criteria, which supported the application of the two assays in the nonclinical PK study and allowed the evaluation of the related PK parameters for GQ1001.

Quantification of serum daratumumab in multiple myeloma patients by LC-MS/MS, comparison with ELISA

Daratumumab is a fully human immunoglobulin G1 monoclonal antibody employed for treating relapsed/refractory multiple myeloma and light-chain amyloidosis. Quantifying monoclonal antibodies in serum presents challenges due to interference from biological matrices. This research aimed to develop and verify an liquid chromatography tandem-mass spectrometry (LC-MS/MS) approach for quantifying serum daratumumab, employing immunoglobulin G purification without alkylation, and to assess its applicability in patients with multiple myeloma receiving intravenous daratumumab. The chromatographic peaks of the daratumumab-derived peptides and internal standard were well-delineated from the serum digests, with an overall run time of 14 min. The calibration curves for serum daratumumab were linear across over 1-1000 μg/mL. The inter- and intra-day accuracy varied between 92.4 % and 108.4 %, with a coefficient-of-variation below 10 %. In patients receiving intravenous daratumumab, serum concentrations ranged from 181.8 to 975.3 µg/mL. Bland-Altman analysis revealed no significant bias, and Passing-Bablok regression demonstrated a good agreement between the LC-MS/MS method and enzyme-linked immunosorbent assay.

Monitoring small-scale bioreactor studies for media development using polarized total synchronous fluorescence spectroscopy (pTSFS) and synchronous light scattering (SyLS)

Biopharmaceutical process development often involves the use of small-scale bioreactors (SSBR) for optimizing media formulations and process conditions during scale up to commercial scale production. Two key process parameters (CPP) used in SSBR studies are protein titre and viable cell density (VCD). Here, we explore the efficacy of parallel polarized total synchronous fluorescence spectroscopy (TSFS||) and Synchronous Light Scattering (SyLS||) to qualitatively monitor these CPPs and quantitatively predict titre and VCD for a large-scale cell culture media optimization SSBR study. The study involved 71 different media formulations (50+ components each), and the bioprocess was run for 13 days or more. Samples were extracted at set times (Day 0, 3, 9, and 13) and clarified by centrifugation. TSFS|| spectra showed significant emission changes along with increased light scatter over the course of the bioprocess. SyLS|| measurements strongly correlated with particle size data obtained from Dynamic Light Scattering but did not correlate well with VCD probably because of the centrifugation-based sample preparation. Statistical and principal component analysis (PCA) of the pTSFS data showed that spectral variation was greater between media formulations than due to the evolving bioprocess. This prevented the development of accurate global prediction models for media performance (e.g., predicting product titre at day 9 from media spectra measured at day 0). However, classification methods were successfully used to select media subsets with better quantitative prediction accuracy based on spectral similarities. A practical binary (high/low performance) classification model based on Support Vector Machines was generated for media formulation screening. Combining emission and scatter measurements with multivariate data analysis provides a more holistic, multi-attribute bioprocess monitoring method that minimizes the need to use different offline analytical methods. This methodology can be used to monitor process trajectories and deviations, and ultimately be used to predict bioprocess CPPs when implemented on production scale processes where there is much less compositional variation in the media. We believe this SSBR-pTSFS/SyLS approach will provide a valuable resource to develop the design/parameter space for in-process monitoring at production scale from early-stage process/media development studies.

Gábor Transform-Based Antibody Quantitation in Serum: An Interlaboratory Liquid Chromatography/High-Resolution Mass Spectrometry Investigation

Therapeutic monoclonal antibodies (t-mAbs) are crucial for treating various conditions, including cancers and autoimmune disorders. Accurate quantitation and pharmacokinetic monitoring of t-mAbs in serum are essential, but current methods like ligand binding assays (LBAs) and bottom-up peptide liquid chromatography-tandem mass spectrometry (LC-MS/MS) can lack the sensitivity and specificity needed to meet clinical demands. Emerging techniques using high-resolution mass spectrometry (HRMS) in top-down and middle-up approaches offer improved ability to accurately quantify mAb proteoforms apart from degradation products by keeping the sample proteins intact or minimizing digestion. This study describes the first use of Gábor transform (GT)-based iFAMS Quant+ software to quantify a t-mAb (vedolizumab) from ∼400 samples using an Agilent 6545XT AdvanceBio Q-TOF at the University of Oregon. These results are compared to a previously validated laboratory-developed test (LDT) from Mayo Clinic utilizing a Thermo Q Exactive Plus Orbitrap. The Mayo method used conventional extracted ion chromatograms (XICs) of select charge states for quantitation, while the iFAMS Quant+ method utilized GT-based charge state deconvolution, background subtraction, and signal integration. Calibration and quality control (QC) analyses and Passing-Bablok regression of 351 subject samples demonstrated excellent agreement between the two methods. The iFAMS Quant+ workflow exhibited unique advantages for characterizing interferents and analyte signal anomalies due to its deconvolution-based approach.

The potential for therapeutic drug monitoring of belatacept and other biologicals in solid organ transplantation

In solid organ transplantation (SOT), biologicals such as recombinant therapeutic proteins, monoclonal antibodies, fusion proteins and conjugates are increasingly used for immunosuppression, desensitization, ABO (blood group) incompatibility, antibody-mediated rejections and atypical haemolytic uremic syndrome. In this paper, we review the medical evidence available for biologicals used in SOT and the potential for improvement by the application of therapeutic drug monitoring (TDM) and model-informed precision dosing. Biologicals are used for off-label indications within the field of SOT, building on the experience from their use on labelled indications. Dosing is currently mostly standard, and experience vs. effect and toxicity is limited. Pharmacokinetic characteristics of these large, partly also immunogenic molecules differ from those of traditional small molecules. Individualization by concentration measurements and modelling has mostly been proof-of-concept or feasibility studies that lack the power to provide evidence for improvement in clinical outcome. For some drugs such as alemtuzumab, eculizumab, rituximab, tocilizumab and belatacept, studies have demonstrated significant interindividual variability in pharmacokinetics. Variability in absorption from subcutaneous administration may increase interindividual variability. There is also an economic aspect of appropriate dosing that needs to be pursued. Available assays and models to refine interpretation are in place, but trials of adequate size to document the usefulness of TDM and MIPD are scarce. Collaboration within the TDM community seems mandatory to establish studies of sufficient strength to provide evidence for the use of biologicals that are currently used off-label in SOT and furthermore to identify the settings where TDM may be beneficial.

A fully validated LC‑MS/MS method for quantifying bevacizumab in plasma samples from patients with NSCLC and its implications in therapeutic drug monitoring

Given the increasing use of bevacizumab in combinatorial drug therapy for a multitude of different cancer types, there is a need for therapeutic drug monitoring to analyze the possible correlation between drug trough concentration, and therapeutic effect and adverse reactions. An ultra-performance liquid chromatography tandem-mass spectrometry method was then developed and validated to determine bevacizumab levels in human plasma samples. Chromatographic separation was achieved on a Shimadzu InertSustainBio C18 HP column, whereas subsequent mass spectrometric analysis was performed using a Shimadzu 8050CL triple quadrupole mass spectrometer equipped with an electro-spray ionization source in the positive ion mode. In total, three multiple reaction monitoring transitions of each of the surrogate peptides were chosen with 'FTFSLDTSK' applied as the quantification peptide whereas 'VLIYFTSSLHSGVPSR' and 'STAYLQMNSLR' were designated as the verification peptides using the Skyline software. This analytical method was then fully validated, with specificity, linearity, lower limit of quantitation, accuracy, precision, stability, matrix effect and recovery calculated. The linearity of this method was developed to be within the concentration range 5-400 µg/ml for bevacizumab in human plasma. Subsequently, eight patients with non-small cell lung cancer (NSCLC) were recruited and injected with bevacizumab over three periods of treatment to analyze their steady-state trough concentration and differences. To conclude, the results of the present study suggest that bevacizumab can be monitored in a therapeutic setting in patients with NSCLC.

Monitoring mAb proteoforms in mouse plasma using an automated immunocapture combined with top-down and middle-down mass spectrometry

Monoclonal antibodies (mAbs) have established themselves as the leading biopharmaceutical therapeutic modality. Once the developability of a mAb drug candidate has been assessed, an important step is to check its in vivo stability through pharmacokinetics (PK) studies. The gold standard is ligand-binding assay (LBA) and liquid chromatography-mass spectrometry (LC-MS) performed at the peptide level (bottom-up approach). However, these analytical techniques do not allow to address the different mAb proteoforms that can arise from biotransformation. In recent years, top-down and middle-down mass spectrometry approaches have gained popularity to characterize proteins at the proteoform level but are not yet widely used for PK studies. We propose here a workflow based on an automated immunocapture followed by top-down and middle-down liquid chromatography-tandem mass spectrometry (LC-MS/MS) approaches to characterize mAb proteoforms spiked in mouse plasma. We demonstrate the applicability of our workflow on a large concentration range using pembrolizumab as a model. We also compare the performance of two state-of-the-art Orbitrap platforms (Tribrid Eclipse and Exploris 480) for these studies. The added value of our workflow for an accurate and sensitive characterization of mAb proteoforms in mouse plasma is highlighted.

M-protein detection by mass spectrometry for minimal residual disease in multiple myeloma

Multiple myeloma (MM) is characterized by excessive production of monoclonal immunoglobulins (M proteins). Routine screening methods for M proteins to assess prognosis are unable to detect low levels of M proteins produced by residual tumor cells, ie, minimal residual disease (MRD). Assessment of MRD can be conducted by examining residual tumor cells in bone marrow or circulating M proteins. Advances in mass spectrometry have enabled reliable and highly sensitive detection of low abundance serum biomarkers making it a viable and significantly less invasive approach. Mass spectrometry can achieve dynamic monitoring of MRD and identify therapeutic monoclonal antibodies as well as oligoclonal proteins. In this review we summarize mass spectrometry methods in M protein detection and their applications of MRD detection in MM.

Development of a liquid chromatography-based versatile bioanalysis for bevacizumab based on pretreatment combining aptamer affinity purification and centrifugal ultrafiltration concentration

We report on the development of a versatile and accurate bioanalytical method for bevacizumab using a pretreatment method combining affinity purification with anti-idiotypic DNA aptamers and centrifugal ultrafiltration concentration, followed by liquid chromatography (LC)-fluorescence analysis. An affinity purification method using Sepharose beads as an affinity support removed immunoglobulin G and a large amount of coexisting substances in the serum sample. Purified bevacizumab was separated as a single peak by conventional LC and detected fluorometrically, showing good linearity (R2 = 0.999) in the range of 5-200 μg/mL, sufficient to analyze bevacizumab concentrations in the blood of bevacizumab-treated patients. By combining this purification method with a concentration method using a centrifugal filtration device that inhibits non-specific adsorption of bevacizumab, the quantitative range was reduced by a factor of 10 while showing good linearity (R2 = 0.999) in the 0.5-20 μg/mL range. The developed analytical method is expected to be used not only for general bioanalysis of therapeutic mAbs in clinical settings, but also for next-generation antibody drugs that show drug efficacy at low concentrations and for analysis of trace samples.

Bioanalytical Assays for Pharmacokinetic and Biodistribution Study of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are produced by the chemical linkage of cytotoxic agents and monoclonal antibodies. The complexity and heterogeneity of ADCs and the low concentration of cytotoxic agent released in vivo poses big challenges to their bioanalysis. Understanding the pharmacokinetic behavior, exposure-safety, and exposure-efficacy relationships of ADCs is needed for their successful development. Accurate analytical methods are required to evaluate intact ADCs, total antibody, released small molecule cytotoxins, and related metabolites. The selection of appropriate bioanalysis methods for comprehensive analysis of ADCs is mainly dependent on the properties of cytotoxic agents, the chemical linker, and the attachment sites. The quality of the information about the whole pharmacokinetic profile of ADCs has been improved due to the development and improvement of analytical strategies for detection of ADCs, such as ligand-binding assays and mass spectrometry-related techniques. In this article, we will focus on the bioanalytical assays that have been used in the pharmacokinetic study of ADCs and discuss their advantages, current limitations, and potential challenges. SIGNIFICANCE STATEMENT: This article describes bioanalysis methods which have been used in pharmacokinetic study of ADCs and discusses the advantages, disadvantages and potential challenges of these assays. This review is useful and helpful and will provide insights and reference for bioanalysis and development of ADCs.

Ultrahigh-Throughput Intact Protein Analysis with Acoustic Ejection Mass Spectrometry

The need for high-throughput intact protein analysis has been rising as drug discovery increasingly requires the analysis of large sets of covalent modifiers and protein therapeutics. Liquid chromatography-mass spectrometry (LC-MS) is the primary analytical tool used to date to characterize proteins within the biopharmaceutical industry. However, the speed of LC-MS prevents the analysis of large-scale sample sets (>1000 within a day). Acoustic ejection mass spectrometry (AEMS) has recently been established as an electrospray ionization (ESI)-MS based platform with both fast analytical throughput and high data quality. Since its introduction, this technology has been applied in numerous fields with a primary focus on small-molecule analysis in high-throughput drug discovery and development. Here we explore the application of AEMS to high-throughput intact protein analysis for proteins ranging in molecular weight from 17 to 150 kDa on a prototype high-resolution quadrupole time-of-flight (HR QTOF) based AEMS system. Data quality obtained on this platform is comparable to LC-MS, while the analysis speed is significantly improved to one-second-per-sample. This ultrahigh-throughput intact protein analysis platform has the potential to be used broadly in drug discovery.

Characterization of high-molecular weight by-products in the production of a trivalent bispecific 2+1 heterodimeric antibody

The development of increasingly complex antibody formats, such as bispecifics, can lead to the formation of increasingly complex high- and low-molecular-weight by-products. Here, we focus on the characterization of high molecular weight species (HMWs) representing the highest complexity of size variants. Standard methods used for product release, such as size exclusion chromatography (SEC), can separate HMW by-products from the main product, but cannot distinguish smaller changes in mass. Here, for the identification of the diverse and complex HMW variants of a trivalent bispecific CrossMAb antibody, offline fractionation, as well as production of HMW by-products combined with comprehensive analytical testing, was applied. Furthermore, HMW variants were analyzed regarding their chemical binding nature and tested in functional assays regarding changes in potency of the variants. Changes in potency were explained by detailed characterization using mass photometry, SDS-PAGE analysis, native mass spectrometry (MS) coupled to SEC and bottom-up proteomics. We identified a major portion of the HMW by-products to be non-covalently linked, leading to dissociation and changes in activity. We also identified and localized high heterogeneity of a by-product of concern and applied a CD3 affinity column coupled to native MS to annotate unexpected by-products. We present here a multi-method approach for the characterization of complex HMW by-products. A better understanding of these by-products is beneficial to guide analytical method development and proper specification setting for therapeutic bispecific antibodies to ensure constant efficacy and patient safety of the product through the assessment of by-products.

A Novel Class of On-Treatment Cancer Immunotherapy Biomarker: Trough Levels of Antibody Therapeutics in Peripheral Blood

While immune checkpoint blockade has revolutionized cancer treatment, unfortunately most patients do not benefit from this treatment. Many pharmacodynamic (PD) studies have revealed essential requirements for successful cancer immunotherapy that may provide insight into how we can improve these agents. Despite enormous efforts focused on interrogating the immune system using different biospecimens (e.g. blood, primary tumor, metastatic tumor, microbiome samples), a variety of technologies (e.g. flow cytometry, bulk and single-cell RNA-sequencing, immunohistochemistry), and wide-ranging disciplines (e.g. pathology, genomics, bioinformatics, immunology, cancer biology, metabolomics, bacteriology), discovery of consistent biomarkers of response have remained elusive. Pharmacokinetics (PK) studies, however, not only provide critical information regarding safe dosing but may also reveal useful biomarkers. For example, recent studies found that trough levels of therapeutic monoclonal antibodies (mAbs) or clearance (CL) of them were associated with clinical outcome, which suggests that trough levels of mAbs may represent a new class of on-treatment cancer immunotherapy biomarker. In this review, we summarize the potential utility of trough levels of mAbs, the mechanism of varying PK, consideration for therapeutic drug monitoring, and assay attributes that will facilitate wider utilization of PK information in conjunction with PD assessments.

Current Analytical Strategies for Antibody-Drug Conjugates in Biomatrices

Antibody-drug conjugates (ADCs) are a new class of biotherapeutics, consisting of a cytotoxic payload covalently bound to an antibody by a linker. Ligand-binding assay (LBA) and liquid chromatography-mass spectrometry (LC-MS) are the favored techniques for the analysis of ADCs in biomatrices. The goal of our review is to provide current strategies related to a series of bioanalytical assays for pharmacokinetics (PK) and anti-drug antibody (ADA) assessments. Furthermore, the strengths and limitations of LBA and LC-MS platforms are compared. Finally, potential factors that affect the performance of the developed assays are also provided. It is hoped that the review can provide valuable insights to bioanalytical scientists on the use of an integrated analytical strategy involving LBA and LC-MS for the bioanalysis of ADCs and related immunogenicity evaluation.

Research Progress on Quantification Methods of Drug Concentration of Monoclonal Antibodies

Background:

With the development of monoclonal antibodies (mAbs) from the first generation of mice to the fourth generation of human origin, the efficacy and safety in the treatment of many diseases have been continuously improved. MAbs have been widely used in the treatment of cancer, chronic inflammatory diseases, and so on. However, the treatment response of mAbs varies greatly among individuals, and drug exposure may be affected by a variety of physiological and pathological factors, such as combined use of drugs and progression of disease. Therefore, studies tend to recommend therapeutic drug monitoring and individualized treatment strategies.

Objective:

In this paper, the commonly used methods of quantification of monoclonal antibodies were reviewed, especially liquid chromatography- mass spectrometry (LC-MS/MS) and enzyme-linked immunosorbent assay (ELISA), to provide technical support for therapeutic drug detection and individualize dosing for patients.

Conclusion:

For patients achieving mAbs treatment, it is necessary to carry out therapeutic drug monitoring and take it as a routine monitoring index. We recommend that for pharmaceutical laboratories in hospitals, establishing an appropriate assay formats, such as ELISA and LC-MS/MS is critical to determine drug concentration and antidrug antibody (ADA) for mAbs.

Antibody-Drug Conjugate Targets, Drugs and Linkers

Antibody-drug conjugates offer the possibility of directing powerful cytotoxic agents to a malignant tumor while sparing normal tissue. The challenge is to select an antibody target expressed exclusively or at highly elevated levels on the surface of tumor cells and either not all or at low levels on normal cells. The current review explores 78 targets that have been explored as antibody-drug conjugate targets. Some of these targets have been abandoned, 9 or more are the targets of FDA-approved drugs, and most remain active clinical interest. Antibody-drug conjugates require potent cytotoxic drug payloads, several of these small molecules are discussed, as are the linkers between the protein component and small molecule components of the conjugates. Finally, conclusions regarding the elements for the successful antibody-drug conjugate are discussed.

A rapid and universal liquid chromatograph-mass spectrometry-based platform, refmAb-Q nSMOL, for monitoring monoclonal antibody therapeutics

Accurate multiplexed quantitation of unique signature peptides derived from monoclonal antibody therapeutics with a universal reference antibody refmAb-Q using Fab-selective proteolysis nSMOL coupled with LC-MS/MS.

Drug-to-Antibody Ratio Estimation via Proteoform Peak Integration in the Analysis of Antibody-Oligonucleotide Conjugates with Orbitrap Fourier Transform Mass Spectrometry

The therapeutic efficacy and pharmacokinetics of antibody-drug conjugates (ADCs) in general, and antibody-oligonucleotide conjugates (AOCs) in particular, depend on the drug-to-antibody ratio (DAR) distribution and average value. The DAR is considered a critical quality attribute, and information pertaining to it needs to be gathered during ADC/AOC development, production, and storage. However, because of the high structural complexity of ADC/AOC samples, particularly in the initial drug-development stages, the application of the current state-of-the-art mass spectrometric approaches can be limited for DAR analysis. Here, we demonstrate a novel approach for the analysis of complex ADC/AOC samples, following native size-exclusion chromatography Orbitrap Fourier transform mass spectrometry (FTMS). The approach is based on the integration of the proteoform-level mass spectral peaks in order to provide an estimate of the DAR distribution and its average value with less than 10% error. The peak integration is performed via a truncation of the Orbitrap's unreduced time-domain ion signals (transients) before mass spectra generation via FT processing. Transient recording and processing are undertaken using an external data acquisition system, FTMS Booster X2, coupled to a Q Exactive HF Orbitrap FTMS instrument. This approach has been applied to the analysis of whole and subunit-level trastuzumab conjugates with oligonucleotides. The obtained results indicate that ADC/AOC sample purification or simplification procedures, for example, deglycosylation, could be omitted or minimized prior to the DAR analysis, streamlining the drug-development process.

DDASSQ: an open-source, multiple peptide sequencing strategy for label free quantification based on an OpenMS pipeline in the KNIME analytics platform

In this study we investigated the performance of a computational pipeline for protein identification and label free quantification (LFQ) of LC–MS/MS data sets from experimental animal tissue samples, as well as the impact of its specific peptide search combinatorial approach. The full pipeline workflow was composed of peptide search engine adapters based on different identification algorithms, in the frame of the open‐source OpenMS software running within the KNIME analytics platform. Two different in silico tryptic digestion, database‐search assisted approaches (X!Tandem and MS‐GF+), de novo peptide sequencing based on Novor and consensus library search (SpectraST), were tested for the processing of LC‐MS/MS raw data files obtained from proteomic LC‐MS experiments done on proteolytic extracts from mouse ex vivo liver samples. The results from proteomic LFQ were compared to those based on the application of the two software tools MaxQuant and Proteome Discoverer for protein inference and label‐free data analysis in shotgun proteomics. Data are available via ProteomeXchange with identifier PXD025097.

Importance and Considerations of Antibody Engineering in Antibody-Drug Conjugates Development from a Clinical Pharmacologist's Perspective

Antibody-drug conjugates (ADCs) appear to be in a developmental boom, with five FDA approvals in the last two years and a projected market value of over $4 billion by 2024. Major advancements in the engineering of these novel cytotoxic drug carriers have provided a few early success stories. Although the use of these immunoconjugate agents are still in their infancy, valuable lessons in the engineering of these agents have been learned from both preclinical and clinical failures. It is essential to appreciate how the various mechanisms used to engineer changes in ADCs can alter the complex pharmacology of these agents and allow the ADCs to navigate the modern-day therapeutic challenges within oncology. This review provides a global overview of ADC characteristics which can be engineered to alter the interaction with the immune system, pharmacokinetic and pharmacodynamic profiles, and therapeutic index of ADCs. In addition, this review will highlight some of the engineering approaches being explored in the creation of the next generation of ADCs.

Potential Role of CD47-Directed Bispecific Antibodies in Cancer Immunotherapy

The prosperity of immunological therapy for cancer has aroused enormous passion for exploiting the novel targets of cancer immunotherapy. After the approval of blinatumomab, a bispecific antibody (bsAb) targeting on CD19 for acute lymphoblastic leukemia, a few of CD47-targeted bsAbs for cancer immunotherapy, are currently in clinical research. In our review of CD47-targeted bsAbs, we described the fundamental of bsAbs. Then, we summarized the information of four undergoing phase I researches, reviewed the main toxicities relevant to CD47-targeted bsAb immunological therapy of on-target cytotoxicity to healthy cells and a remarkable antigen-sink. Finally, we described possible mechanisms of resistance to CD47-targeted bsAb therapy. More clinical researches are supposed to adequately confirm its security and efficacy in clinical practice.

Bioanalysis in the Age of New Drug Modalities

In the absence of regulatory guidelines for the bioanalysis of new drug modalities, many of which contain multiple functional domains, bioanalytical strategies have been carefully designed to characterize the intact drug and each functional domain in terms of quantity, functionality, biotransformation, and immunogenicity. The present review focuses on the bioanalytical challenges and considerations for RNA-based drugs, bispecific antibodies and multi-domain protein therapeutics, prodrugs, gene and cell therapies, and fusion proteins. Methods ranging from the conventional ligand binding assays and liquid chromatography-mass spectrometry assays to quantitative polymerase chain reaction or flow cytometry often used for oligonucleotides and cell and gene therapies are discussed. Best practices for method selection and validation are proposed as well as a future perspective to address the bioanalytical needs of complex modalities.

Characterization of Antibody-Drug Conjugate Pharmacokinetics and in Vivo Biotransformation Using Quantitative Intact LC-HRMS and Surrogate Analyte LC-MRM

Antibody-drug conjugates (ADCs) pose challenges to bioanalysis because of their inherently intricate structures and potential for very complex catabolism. Common bioanalysis strategy is to measure the concentration of ADCs and Total Antibody (Ab) as well as deconjugated warhead in circulation. The ADCs and the Total Ab can be quantified with ligand binding assays (LBA) or with hybrid immunocapture-liquid chromatography coupled with multiple reaction monitoring mass spectrometry (LBA-LC-MRM). With the LBA-LC-MRM approach, a surrogate analyte, often the signature peptide, and released warhead can be used for the quantification of the Total Ab and ADCs, respectively. Recent advances in analytical instrumentation, especially the development of high resolution mass spectrometers (HRMS), have enabled characterization and quantification of intact macromolecules such as ADCs. The LBA-LC-HRMS approach employs immunocapture, followed by chromatographic separation at the macromolecule level and detection of the intact analyte. We developed an intact quantification method with 1-10 μg/mL linear dynamic range using 25 μL of plasma sample volume. This method was qualified for the measurement of naked monoclonal antibody (mAb), a site-specific cysteine-conjugated ADC with drug to antibody ratio ∼2 (DAR2) and a site-nonspecific cysteine-conjugated ADC (DAR8) in rat plasma. Samples from a rat pharmacokinetic (PK) study were analyzed with both methods. For the naked mAb, the results from both assays matched well. For ADCs, new species were observed from the LBA-HRMS method. The results demonstrated that potential biotransformation of the ADC was unveiled using the intact quantification approach while not being observed with traditional LBA-LC-MRM approach. Our work demonstrated an application of novel intact quantification by supporting animal PK studies. Moreover, our results suggest that the intact quantification method can provide novel perspectives on ADC in vivo characterization and quantification, which can benefit future drug candidate optimization as well as the immunogenicity impact evaluation and safety assessment.

Development of a chromatography-free method for high-throughput MS-based bioanalysis of therapeutic monoclonal antibodies

Aim: Our objective was to test the feasibility of developing an LC-free, MS-based approach for high-throughput bioanalysis of humanized therapeutic monoclonal antibodies. Methodology: A universal tryptic peptide from human IgG1, IgG3 and IgG4 was selected as the surrogate peptide for quantitation. After tryptic digestion, the surrogate peptide was fractionated via solid-phase extraction before being subjected to direct infusion-based MS/MS analysis. A high-resolution, multiplexed (MSX = 2) parallel reaction monitoring method was developed for data acquisition. Results & conclusion: This proof-of-concept study demonstrated the feasibility of achieving high-throughput MS-based bioanalysis of monoclonal antibodies using an LC-free workflow with sensitivity comparable to conventional LC-MS/MS-based methods.

An Automated Multicycle Immunoaffinity Enrichment Approach Developed for Sensitive Mouse IgG1 Antibody Drug Analysis in Mouse Plasma Using LC/MS/MS

In the immuno-oncology field, surrogate mouse monoclonal antibodies are often preferred in establishing proper PK/PD/efficacy correlations as well as supporting anticipated mouse to human translation. Thus, a highly sensitive and specific bioanalytical method is needed in quantifying those surrogate mouse antibodies after dosing in mice. Unfortunately, when specific reagents, such as recombinant target antigen and anti-idiotypic antibody, are not available, measuring mouse surrogate antibody drugs in mice is very challenging for ligand binding assay (LBA) due to the severe cross reactivity potential. Different from LBA, if at least one unique surrogate peptide can be identified from the surrogate antibody sequence, the immunoaffinity enrichment based LC/MS/MS assay may be able to differentiate the analyte response from the high endogenous immunoglobulin background and provide adequate sensitivity. Herein, a new automated multicycle immunoaffinity enrichment method was recently developed to extract a surrogate mouse IgG1 (mIgG1) antibody drug from mouse plasma using a commercially available antimouse IgG1 secondary antibody. In the assay, reuse of the capture antibody up to six times mostly resolved the binding capacity issue caused by the abundant endogenous mIgG1 and made the immunoaffinity enrichment step more cost-effective. Combined with a unique surrogate peptide identified from the antibody, the LC/MS/MS assay achieved a limit of quantitation of 5 ng/mL with satisfactory assay precision, accuracy, and dynamic range. The successful implementation of this novel approach in discovery pharmacokinetic (PK) studies eliminates the dependence on specially generated immunoaffinity capturing reagents.

Mass Spectrometry-Based Methods for Immunoglobulin G N-Glycosylation Analysis

Mass spectrometry and its hyphenated techniques enabled by the improvements in liquid chromatography, capillary electrophoresis, novel ionization, and fragmentation modes are truly a cornerstone of robust and reliable protein glycosylation analysis. Boost in immunoglobulin G (IgG) glycan and glycopeptide profiling demands for both applied biomedical and research applications has brought many new advances in the field in terms of technical innovations, sample preparation, improved throughput, and confidence in glycan structural characterization. This chapter summarizes mass spectrometry basics, focusing on IgG and monoclonal antibody N-glycosylation analysis on several complexity levels. Different approaches, including antibody enrichment, glycan release, labeling, and glycopeptide preparation and purification, are covered and illustrated with recent breakthroughs and examples from the literature omitting excessive theoretical frameworks. Finally, selected highly popular methodologies in IgG glycoanalytics such as liquid chromatography-mass spectrometry and matrix-assisted laser desorption ionization are discussed more thoroughly yet in simple terms making this text a practical starting point either for the beginner in the field or an experienced clinician trying to make sense out of the IgG glycomic or glycoproteomic dataset.

Rapid Analysis of Reduced Antibody Drug Conjugate by Online LC-MS/MS with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Antibody drug conjugates (ADCs), which harness the high targeting specificity of monoclonal antibodies (mAb) with the potency of small molecule therapeutics, are one of the fastest growing pharmaceutical classes. Nevertheless, ADC conjugation techniques and processes may introduce intrinsic heterogeneity including primary sequence variants, varied drug-to-antibody ratio (DAR) species, and drug positional isomers, which must be monitored to ensure the safety and efficacy of ADCs. Liquid chromatography coupled to mass spectrometry (LC-MS) is a powerful tool for characterization of ADCs. However, the conventional bottom-up MS analysis workflows require an enzymatic digestion step which can be time consuming and may introduce artifactual modifications. Herein, we develop an online LC-MS/MS method for rapid analysis of reduced ADCs without digestion, enabling determination of DAR, characterization of the primary sequence, and localization of the drug conjugation site of the ADC using high-resolution Fourier transform ion cyclotron resonance (FTICR) MS. Specifically, a model cysteine-linked ADC was reduced to generate six unique subunits: light chain (Lc) without drug (Lc0), Lc with 1 drug (Lc1), heavy chain (Hc) without drug (Hc0), and Hc with 1-3 drugs (Hc1-3, respectively). A concurrent reduction strategy is applied to assess ADC subunits in both the partially reduced (intrachain disulfide bonds remain intact) and fully reduced (all disulfide bonds are cleaved) forms. The entire procedure including the sample preparation and LC-MS/MS takes less than 55 min, enabling rapid multiattribute analysis of ADCs.

Bioanalytical Challenges in Support of Complex Modalities of Antibody-Based Therapeutics

Antibody-based therapeutic classes are evolving from monoclonal antibodies to antibody derivatives with complex structures to achieve advanced therapeutic effect. These antibody derivatives may contain multiple functional domains and are often vulnerable to in vivo biotransformation. Understanding the pharmacokinetics of these antibody derivatives requires a sophisticated bioanalytical approach to carefully characterize the whole drug and each functional domain with respect to quantity, functionality enabled by biotransformation, and corresponding immune responses. Ligand binding assays and liquid chromatography-mass spectrometry assays are predominantly used in bioanalytical support of monoclonal antibodies and are continuously used for antibody derivatives such as antibody drug conjugate and bispecific antibodies. However, they become increasingly cumbersome in coping with increased complexity of drug modality and associated biotransformation. In this mini-review, we examined the current pharmacokinetic assays in the literature for antibody drug conjugate and bispecific antibodies, and presented our view of promising bioanalytical technologies to address the distinct bioanalytical needs of complex modalities.

Bottom-up sample preparation for the LC-MS/MS quantification of anti-cancer monoclonal antibodies in bio matrices

Therapeutic monoclonal antibodies (mAbs) are rapidly taking over the treatment of many malignancies, and an astonishing number of mAbs is in development. This causes a high demand for quantification of mAbs in biomatrices both for measuring therapeutic mAb concentrations and to support pharmacokinetics and pharmacodynamics studies. Conventionally, ligand-binding assays are used for these purposes, but LC-MS is gaining popularity. Although intact (top-down) and subunit (middle-down) mAb quantification is reported, signature peptide (bottom-up) quantification is currently most advantageous. This review provides an overview of the reported bottom-up mAb quantification methods in biomatrices as well as general recommendations regarding signature peptide and internal standard selection, reagent use and optimization of digestion in bottom-up quantification methods.

Integrated hemolysis monitoring for bottom-up protein bioanalysis

Background: Hemolysis can result in analyte suppression or enhancement and it can affect the extraction efficiency and analyte stability. Triskelion developed an LC–MS method to monitor hemolysis. The concept can be integrated into existing and new quantitative protein LC–MS methods and can be validated according to the most appropriate tier. Results/methodology: In this proof of concept study, the tryptic target LLVVYPWTQR was used to quantify hemoglobin. The peptide target has only few variations considering the most common (laboratory) animals and is thus nearly generic. It was shown that LC–MS is a suitable technique for the quantification of hemoglobin in hemolyzed samples and that the signals are not affected by lipemia. Conclusion: LC–MS exhibited the best performance to monitor hemolysis when the results were compared with UV–VIS and visual inspection, especially when samples were lipemic.