Measurement of in Vivo Drug Load Distribution of Cysteine-Linked Antibody–Drug Conjugates Using Microscale Liquid Chromatography Mass Spectrometry

Site-Specific Stability Evaluation of Antibody-Drug Conjugate in Serum Using a Validated Liquid Chromatography-Mass Spectrometry Method

Antibody-drug conjugate (ADC) consists of engineered antibodies and cytotoxic drugs linked via a chemical linker, and the stability of ADC plays a crucial role in ensuring its safety and efficacy. The stability of ADC is closely related to the conjugation site; however, no method has been developed to assess the stability of different conjugation sites due to the low response of conjugated peptides. In this study, an integrated strategy was developed and validated to assess the stability of different conjugation sites on ADC in serum. Initial identification of the conjugated peptides of the model drug ado-trastuzumab emtansine (T-DM1) was achieved by the proteomic method. Subsequently, a semiquantitative method for conjugated peptides was established in liquid chromatography-hybrid linear ion trap triple quadrupole mass spectrometry (LC-QTRAP-MS/MS) based on the qualitative information. The pretreatment method of the serum sample was optimized to reduce matrix interference. The method was then validated and applied to evaluate the stability of the conjugation sites on T-DM1. The results highlighted differences in stability among the different conjugation sites on T-DM1. This is the first study to assess the stability of different conjugation sites on the ADC in serum, which will be helpful for the design and screening of ADCs in the early stages of development.

Desalting strategies for native mass spectrometry

In native mass spectrometry (MS) salts are indispensable for preserving the native structures of biomolecules, but detrimental to mass sensitivity, resolution, and accuracy. Such a conflict makes desalting in native MS more challenging, distinctive, and sample-dependent than in peptide-centric MS. This review first briefly introduces the charged residue mechanism whereby native-like gaseous protein ions are released from electrospray droplets, revealing a higher degree of salt adduction than denatured proteins. Subsequently, this review summarizes and explores the existing strategies, underlying mechanisms and future perspectives of desalting in native MS. These strategies mainly focus on buffer exchange into volatile salts (offline and online approaches), addition of solution additives (e.g., anion, supercharging reagent, solution phase chelator and amino acid), use of submicron electrospray emitters (down to 60 nm), and other potential approaches (e.g., induced and electrophoretic nanoelectrospray ionization). The strategies of online buffer exchange and using nanoscale electrospray emitters are highlighted. This review would not only be a valuable addition to the field of sample preparation in MS, but would also serve as a beginner's guide to desalting in native MS.

A modelling approach to compare ADC deconjugation and systemic elimination rates of individual drug-load species using native ADC LC-MS data from human plasma

Native liquid chromatography mass spectrometry (LC-MS) is a commonly used approach for intact analysis of inter-chain cysteine conjugated antibody-drug conjugates (ADCs). Coupling native LC-MS with affinity capture provides a platform for intact ADC analysis from in vivo samples and characterisation of individual drug load species, specifically the impact of drug linker deconjugation, hydrolysis, and differential clearance in a biological system.This manuscript describes data generated from native LC-MS analysis of ADCs from human plasma, both in vitro incubations and clinical samples. It also details the pharmacokinetic (PK) model built to specifically characterise the disposition of individual drug load species from MMAE and MMAF interchain cysteine conjugated ADCs.In vitro deconjugation and hydrolysis rates were similar across both ADCs. Differential clearance of higher loaded species in vivo was pronounced for the MMAE conjugated ADC, while systemic elimination after accounting for deconjugation was similar across drug loads for the MMAF conjugated ADC. This is the first report of affinity capture native LC-MS analysis, and subsequent modelling of deconjugation, hydrolysis and clearance rates of individual drug load species using clinical data from cysteine conjugated ADCs.

Automated high-throughput buffer exchange platform enhances rapid flow analysis of antibody drug conjugates by high resolution mass spectrometry

Antibody drug conjugates (ADCs) are an increasingly important therapeutic class of molecules for the treatment of cancer. Average drug-to-antibody ratio (DAR) and drug-load distribution are critical quality attributes of ADCs with the potential to impact efficacy and toxicity of the molecule and need to be analytically characterized and understood. Several platform methods including hydrophobic interaction chromatography (HIC) and native size-exclusion chromatography-mass spectrometry (nSEC-MS) have been developed for that purpose; however, each presents some limitations. In this work, we assessed a new sample preparation and buffer exchange platform coupled with high-resolution mass spectrometry for characterizing the drug-load and distribution of several cysteine-linked ADCs conjugated with a variety of chemotypes. Several criteria were evaluated during the optimization of the buffer exchange-mass spectrometry system performance and the data generated with the system were compared with results from nSEC-MS and HIC. The results indicated that the platform enables automated and high throughput quantitative DAR characterization for antibody-drug conjugates with high reproducibility and offers several key advantages over existing approaches that are used for chemotype-agnostic ADC characterization.

Size Exclusion Chromatography Strategies and MASH Explorer for Large Proteoform Characterization

Top-down mass spectrometry (MS)-based analysis of larger proteoforms (>50 kDa) is typically challenging due to an exponential decay in the signal-to-noise ratio with increasing protein molecular weight (MW) and coelution with low-MW proteoforms. Size exclusion chromatography (SEC) fractionates proteins based on their size, separating larger proteoforms from those of smaller size in the proteome. In this protocol, we initially describe the use of SEC to fractionate high-MW proteoforms from low-MW proteoforms. Subsequently, the SEC fractions containing the proteoforms of interest are subjected to reverse-phase liquid chromatography (RPLC) coupled online with high-resolution MS. Finally, proteoforms are characterized using MASH Explorer, a user-friendly software environment for in-depth proteoform characterization.

Comparative Analysis of Antibodies and Heavily Glycosylated Macromolecular Immune Complexes by Size-Exclusion Chromatography Multi-Angle Light Scattering, Native Charge Detection Mass Spectrometry, and Mass Photometry

Qualitative and quantitative mass analysis of antibodies and related macromolecular immune complexes is a prerequisite for determining their identity, binding partners, stoichiometries, and affinities. A plethora of bioanalytical technologies exist to determine such characteristics, typically based on size, interaction with functionalized surfaces, light scattering, or direct mass measurements. While these methods are highly complementary, they also exhibit unique strengths and weaknesses. Here, we benchmark mass photometry (MP), a recently introduced technology for mass measurement, against native mass spectrometry (MS) and size exclusion chromatography multi-angle light scattering (SEC-MALS). We examine samples of variable complexity, namely, IgG4Δhinge dimerizing half-bodies, IgG-RGY hexamers, heterogeneously glycosylated IgG:sEGFR antibody-antigen complexes, and finally megadalton assemblies involved in complement activation. We thereby assess the ability to determine (1) binding affinities and stoichiometries, (2) accurate masses, for extensively glycosylated species, and (3) assembly pathways of large heterogeneous immune complexes. We find that MP provides a sensitive approach for characterizing antibodies and stable assemblies, with dissociation correction enabling us to expand the measurable affinity range. In terms of mass resolution and accuracy, native MS performs the best but is occasionally hampered by artifacts induced by electrospray ionization, and its resolving power diminishes when analyzing extensively glycosylated proteins. In the latter cases, MP performs well, but single-particle charge detection MS can also be useful in this respect, measuring masses of heterogeneous assemblies even more accurately. Both methods perform well compared to SEC-MALS, still being the most established method in biopharma. Together, our data highlight the complementarity of these approaches, each having its unique strengths and weaknesses.

Simultaneous monitoring of multiple attributes of pyrrolobenzodiazepine antibody-drug conjugates by size exclusion chromatography - high resolution mass spectrometry

Antibody-drug conjugates (ADCs) are an emerging class of oncology treatments combining the unique specificity of monoclonal antibodies with the highly cytotoxic properties of small molecule compounds. Pyrrolobenzodiazepines (PBDs) are highly potent agents capable of inhibiting cellular DNA replication which leads to apoptosis. To ensure efficacy and patient safety upon administration of such toxic and heterogeneous molecules, their structure and quality attributes must be closely monitored. Size exclusion chromatography (SEC) is a powerful, fast and robust tool for the separation of compounds varying in molecular weight. When using volatile components in the chromatographic mobile phase, SEC has also been shown to be amenable for interfacing to mass spectrometry, providing potential for reliable identification of protein isoforms across the size variants present. Here, we present a SEC-MS method developed for the characterisation of PBD-based ADCs on the intact molecular level. We demonstrate that information on ADC monomers such as the glycoform distribution and the average drug-antibody ratio (DAR) can be obtained in 15 minutes of analysis time. Qualitative and quantitative information on low and high molecular weight impurities such as aggregates and fragments, fundamental for critical quality attribute analysis of biopharmaceuticals, can be generated simultaneously. SEC-MS enables the characterisation of multiple product quality attributes of complex biotherapeutics at the same time.

High-Throughput Multi-attribute Analysis of Antibody-Drug Conjugates Enabled by Trapped Ion Mobility Spectrometry and Top-Down Mass Spectrometry

Antibody-drug conjugates (ADCs) are one of the fastest growing classes of anticancer therapies. Combining the high targeting specificity of monoclonal antibodies (mAbs) with cytotoxic small molecule drugs, ADCs are complex molecular entities that are intrinsically heterogeneous. Primary sequence variants, varied drug-to-antibody ratio (DAR) species, and conformational changes in the starting mAb structure upon drug conjugation must be monitored to ensure the safety and efficacy of ADCs. Herein, we have developed a high-throughput method for the analysis of cysteine-linked ADCs using trapped ion mobility spectrometry (TIMS) combined with top-down mass spectrometry (MS) on a Bruker timsTOF Pro. This method can analyze ADCs (∼150 kDa) by TIMS followed by a three-tiered top-down MS characterization strategy for multi-attribute analysis. First, the charge state distribution and DAR value of the ADC are monitored (MS1). Second, the intact mass of subunits dissociated from the ADC by low-energy collision-induced dissociation (CID) is determined (MS2). Third, the primary sequence for the dissociated subunits is characterized by CID fragmentation using elevated collisional energies (MS3). We further automate this workflow by directly injecting the ADC and using MS segmentation to obtain all three tiers of MS information in a single 3-min run. Overall, this work highlights a multi-attribute top-down MS characterization method that possesses unparalleled speed for high-throughput characterization of ADCs.

State-of-the-Art Native Mass Spectrometry and Ion Mobility Methods to Monitor Homogeneous Site-Specific Antibody-Drug Conjugates Synthesis

Antibody-drug conjugates (ADCs) are biotherapeutics consisting of a tumor-targeting monoclonal antibody (mAb) linked covalently to a cytotoxic drug. Early generation ADCs were predominantly obtained through non-selective conjugation methods based on lysine and cysteine residues, resulting in heterogeneous populations with varying drug-to-antibody ratios (DAR). Site-specific conjugation is one of the current challenges in ADC development, allowing for controlled conjugation and production of homogeneous ADCs. We report here the characterization of a site-specific DAR2 ADC generated with the GlyCLICK three-step process, which involves glycan-based enzymatic remodeling and click chemistry, using state-of-the-art native mass spectrometry (nMS) methods. The conjugation process was monitored with size exclusion chromatography coupled to nMS (SEC-nMS), which offered a straightforward identification and quantification of all reaction products, providing a direct snapshot of the ADC homogeneity. Benefits of SEC-nMS were further demonstrated for forced degradation studies, for which fragments generated upon thermal stress were clearly identified, with no deconjugation of the drug linker observed for the T-GlyGLICK-DM1 ADC. Lastly, innovative ion mobility-based collision-induced unfolding (CIU) approaches were used to assess the gas-phase behavior of compounds along the conjugation process, highlighting an increased resistance of the mAb against gas-phase unfolding upon drug conjugation. Altogether, these state-of-the-art nMS methods represent innovative approaches to investigate drug loading and distribution of last generation ADCs, their evolution during the bioconjugation process and their impact on gas-phase stabilities. We envision nMS and CIU methods to improve the conformational characterization of next generation-empowered mAb-derived products such as engineered nanobodies, bispecific ADCs or immunocytokines.

Native size-exclusion chromatography-mass spectrometry: suitability for antibody-drug conjugate drug-to-antibody ratio quantitation across a range of chemotypes and drug-loading levels

Native size-exclusion chromatography-mass spectrometry (nSEC-MS) is an analytical methodology that is appropriate for accurately quantitating the drug-to-antibody ratio (DAR) on a wide variety of interchain cysteine-linked antibody-drug conjugates (ADCs), irrespective of chemotype. In the current preclinical environment, novel ADCs conjugated with unique drug-linkers need to progress toward the clinic as quickly as possible. Platform analytical approaches can reduce time-to-clinic because key process development and optimization activities can be decoupled from the development of bespoke, molecule-specific analytical methods. In this work, we assessed the potential of nSEC-MS as a platformable, quantitative DAR method. The nSEC-MS method was evaluated according to performance characteristics and parameters described in the ICH guideline Validation of Analytical Procedures: Text and Methodology Q2(R1). In order to comprehensively assess the accuracy and bias of nSEC-MS DAR quantitation, ADCs were generated using three different drug-linker chemotypes with DARs ranging from 2 to 8. These molecules were tested by hydrophobic interaction chromatography (HIC) and nSEC-MS, and DARs obtained from both methods were compared to assess the degree to which nSEC-MS quantitation aligned with the HIC release assay. Our results indicated that there is no bias introduced by nSEC-MS quantitation of DAR and that SEC-MS data can be bridged to HIC data without the need for a correction factor or offset. nSEC-MS was also found to be suitable for unbiased DAR quantitation in the other ADC chemotypes that were evaluated. Based on the totality of our work, we conclude that, used as intended, nSEC-MS is well suited for quantitating DAR on a variety of interchain cysteine-linked ADCs in an accurate, unbiased manner.

Versatile, Sensitive, and Robust Native LC-MS Platform for Intact Mass Analysis of Protein Drugs

Over the past several years, hyphenation of native (nondenaturing) liquid chromatography (nLC) methods, such as size exclusion chromatography (SEC), ion exchange chromatography (IEX), and hydrophobic interaction chromatography (HIC) with mass spectrometry (MS) have become increasingly popular to study the size, charge, and structural heterogeneity of protein drug products. Despite the availability of a wide variety of nLC-MS methods, an integrated platform that can accommodate different applications is still lacking. In this study, we described the development of a versatile, sensitive, and robust nLC-MS platform that can support various nLC-MS applications. In particular, the developed platform can tolerate a wide range of LC flow rates and high salt concentrations, which are critical for accommodating different nLC methods. In addition, a dopant-modified desolvation gas can be readily applied on this platform to achieve online charge-reduction native MS, which improves the characterization of both heterogeneous and labile biomolecules. Finally, we demonstrated that this nLC-MS platform is highly sensitive and robust and can be routinely applied in protein drug characterization.

Investigating the Impact of Sample Preparation on Mass Spectrometry-Based Drug-To-Antibody Ratio Determination for Cysteine- and Lysine-Linked Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are heterogeneous biotherapeutics and differ vastly in their physicochemical properties depending on their design. The number of small drug molecules covalently attached to each antibody molecule is commonly referred to as the drug-to-antibody ratio (DAR). Established analytical protocols for mass spectrometry (MS)-investigation of antibodies and ADCs often require sample treatment such as desalting or interchain disulfide bond reduction prior to analysis. Herein, the impact of the desalting and reduction steps-as well as the sample concentration and elapsed time between synthesis and analysis of DAR-values (as acquired by reversed phase liquid chromatography MS (RPLC-MS))-was investigated. It was found that the apparent DAR-values could fluctuate by up to 0.6 DAR units due to changes in the sample preparation workflow. For methods involving disulfide reduction by means of dithiothreitol (DTT), an acidic quench is recommended in order to increase DAR reliability. Furthermore, the addition of a desalting step was shown to benefit the ionization efficiencies in RPLC-MS. Finally, in the case of delayed analyses, samples can be stored at four degrees Celsius for up to one week but are better stored at -20 °C for longer periods of time. In conclusion, the results demonstrate that commonly used sample preparation procedures and storage conditions themselves may impact MS-derived DAR-values, which should be taken into account when evaluating analytical procedures.

Analysis of ADCs by Native Mass Spectrometry

Mass spectrometry performed in nondenaturing conditions (native MS) has proven its utility for the quantitative and qualitative analysis of antibody-drug conjugates (ADCs), especially when ADCs' subunits involve noncovalent interactions (i.e., cysteine-conjugated ADCs). Its hyphenation to ion mobility spectrometry (IM-MS) allows differentiation of gas-phase ions based on their rotationally averaged collision cross section providing an additional dimension of conformational characterization of ADCs. More recently, size exclusion chromatography (SEC) appeared as an interesting technique to perform online buffer exchange in an automated way prior to native MS/IM-MS analysis. Online SEC-native MS/IM-MS allows the global structural characterization of ADCs and the assessment of some critical quality attributes (CQAs) required for ADC release on the market, such as drug load distribution (DLD), drug-to-antibody ratio (DAR), the average DAR (DARav), and the relative amount of unconjugated mAb.

Quantitative collision-induced unfolding differentiates model antibody-drug conjugates

Antibody-drug conjugates (ADCs) are antibody-based therapeutics that have proven to be highly effective cancer treatment platforms. They are composed of monoclonal antibodies conjugated with highly potent drugs via chemical linkers. Compared to cysteine-targeted chemistries, conjugation at native lysine residues can lead to a higher degree of structural heterogeneity, and thus it is important to evaluate the impact of conjugation on antibody conformation. Here, we present a workflow involving native ion mobility (IM)-MS and gas-phase unfolding for the structural characterization of lysine-linked monoclonal antibody (mAb)-biotin conjugates. Following the determination of conjugation states via denaturing Liquid Chromatography-Mass Spectrometry (LC-MS) measurements, we performed both size exclusion chromatography (SEC) and native IM-MS measurements in order to compare the structures of biotinylated and unmodified IgG1 molecules. Hydrodynamic radii (Rh) and collision cross-sectional (CCS) values were insufficient to distinguish the conformational changes in these antibody-biotin conjugates owing to their flexible structures and limited instrument resolution. In contrast, collision induced unfolding (CIU) analyses were able to detect subtle structural and stability differences in the mAb upon biotin conjugation, exhibiting a sensitivity to mAb conjugation that exceeds native MS analysis alone. Destabilization of mAb-biotin conjugates was detected by both CIU and differential scanning calorimetry (DSC) data, suggesting a previously unknown correlation between the two measurement tools. We conclude by discussing the impact of IM-MS and CIU technologies on the future of ADC development pipelines.

ADME Considerations and Bioanalytical Strategies for Pharmacokinetic Assessments of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are a unique class of biotherapeutics of inherent heterogeneity and correspondingly complex absorption, distribution, metabolism, and excretion (ADME) properties. Herein, we consider the contribution of various components of ADCs such as various classes of warheads, linkers, and conjugation strategies on ADME of ADCs. Understanding the metabolism and disposition of ADCs and interpreting exposure-efficacy and exposure-safety relationships of ADCs in the context of their various catabolites is critical for design and subsequent development of a clinically successful ADCs. Sophisticated bioanalytical assays are required for the assessments of intact ADC, total antibody, released warhead and relevant metabolites. Both ligand-binding assays (LBA) and hybrid LBA-liquid chromatography coupled with tandem mass spectrometry (LBA-LC-MS/MS) methods have been employed to assess pharmacokinetics (PK) of ADCs. Future advances in bioanalytical techniques will need to address the rising complexity of this biotherapeutic modality as more innovative conjugation strategies, antibody scaffolds and novel classes of warheads are employed for the next generation of ADCs. This review reflects our considerations on ADME of ADCs and provides a perspective on the current bioanalytical strategies for pharmacokinetic assessments of ADCs.

Review of approaches and examples for monitoring biotransformation in protein and peptide therapeutics by MS

Biotherapeutic drugs have emerged in quantity in pharmaceutical pipelines, and increasingly diverse biomolecules are progressed through preclinical and clinical development. As purification, separation, mass spectrometer detection and data processing capabilities improve, there is opportunity to monitor drug concentration by traditional ligand-binding assay or MS measurement and to monitor metabolism, catabolism or other biomolecular mass variants present in circulation. This review highlights approaches and examples of monitoring biotransformation of biotherapeutics by MS as these techniques are poised to add value to drug development in years to come. The increased use of such approaches, and the successful quantitation of biotherapeutic structural modifications, will provide insightful data for the benefit of both researchers and patients.

Unraveling the mysteries of modern size exclusion chromatography - the way to achieve confident characterization of therapeutic proteins

Modern size exclusion chromatography (SEC) can be defined by the use of relatively small columns (e.g., 150 × 4.6 mm) packed with sub-3 μm particles, allowing a 3- to 5-fold increase in method throughput compared to that of conventional SEC. The quick success of the first sub-2 μm SEC column introduced in 2010 led to the development of numerous ultra-high performance (UHP)-SEC columns for the analysis of therapeutic monoclonal antibody (mAb)-based products. Aggregates also known as high-molecular-weight species (HMWS) are indeed one of the most important critical quality attributes (CQAs) of mAbs, as HMWS may decrease the product efficacy or cause immunogenicity effects. Therefore, the confident characterization of mAbs requires strong knowledge of not only modern SEC performance (i.e., selectivity and efficiency) but also the inherent limitations caused by non-specific interactions more likely to occur with complex antibody drug conjugates (ADCs) and some commercial mAb products. This review discusses the importance of liquid chromatographic (LC) instrumentation in order to exploit the full potential of modern SEC columns and current trends to hyphenate SEC to mass spectrometry (MS). Recent applications for antibody-based products (i.e., mAbs, ADCs, Fc-Fusion proteins and bispecific antibodies) are presented. Finally, tips and tricks are provided to further optimize SEC separations and maintaining their performance over time with better understanding of unexpected SEC results.

Qualitative analysis of antibody–drug conjugates (ADCs): an experimental comparison of analytical techniques of cysteine-linked ADCs

Four different cysteine linked antibody-drug conjugates (ADCs) consisting of Trastuzumab-vc-MMAE were analysed with four common analytical techniques with respect to drug-to-antibody ratio (DAR) and molecular weight.

Analytical techniques for the characterization of Antibody Drug Conjugates: Challenges and prospects

Antibody drug conjugates are increasingly being researched for the treatment of cancer. Accurate and reliable characterization of ADCs is inevitable for their development as potential therapeutic agent. Different analytical techniques have been used in order to decipher heterogeneous nature of antibody drug conjugates, enabling successful characterization. This review will summarize specially three major analytical tools i.e. UV-Vis spectroscopy, liquid chromatography, and mass spectrometry used in characterization of antibody drug conjugates. In this review, major challenges during analysis due to the inherent features of analytical techniques and antibody drug conjugates are summarized along with the modifications intended to address each challenge.

Qualitative and quantitative characterization of protein biotherapeutics with liquid chromatography mass spectrometry

In the last decade, the advancement of liquid chromatography mass spectrometry (LC/MS) techniques has enabled their broad application in protein characterization, both quantitatively and qualitatively. Owing to certain important merits of LC/MS techniques (e.g., high selectivity, flexibility, and rapid method development), LC/MS assays are often deemed as preferable alternatives to conventional methods (e.g., ligand-binding assays) for the analysis of protein biotherapeutics. At the discovery and development stages, LC/MS is generally employed for two purposes absolute quantification of protein biotherapeutics in biological samples and qualitative characterization of proteins. For absolute quantification of a target protein in bio-matrices, recent work has led to improvements in the efficiency of LC/MS method development, sample treatment, enrichment and digestion, and high-performance low-flow-LC separation. These advances have enhanced analytical sensitivity, specificity, and robustness. As to qualitative analysis, a range of techniques have been developed to characterize intramolecular disulfide bonds, glycosylation, charge variants, primary sequence heterogeneity, and the drug-to-antibody ratio of antibody drug conjugate (ADC), which has enabled a refined ability to assess product quality. In this review, we will focus on the discussion of technical challenges and strategies of LC/MS-based quantification and characterization of biotherapeutics, with the emphasis on the analysis of antibody-based biotherapeutics such as monoclonal antibodies (mAbs) and ADCs. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 36:734-754, 2017.

Novel strategy using tryptic peptide immunoaffinity-based LC–MS/MS to quantify denosumab in monkey serum

Aim: Denosumab is a recombinant fully human IgG2 that has a high affinity and specificity for human RANKL. Commercially available RANKL labeled with an Fc fragment cannot be used to establish an indirect ELISA. To characterize denosumab pharmacokinetic a robust and accuracy method should be developed urgently. Results: In this study, an immunoaffinity enrichment method coupled with LC–MS/MS was established. The LC–MS/MS method acquired a linear range from 0.1 to 30 μg/ml. The intra- and inter-run precision (CV%) was within 11.5 and 10.5%, respectively. More importantly, the LC–MS/MS pharmacokinetic data were consistent with ELISA. Conclusion: This approach accelerated the quantification, reduced the costs and provided an alternative in case of lacking the special antigen to denosumab or a RANKL-biotinylated reagent.

ELISA reagent coverage evaluation by affinity purification tandem mass spectrometry

Host cell proteins (HCPs) must be adequately removed from recombinant therapeutics by downstream processing to ensure patient safety, product quality, and regulatory compliance. HCP process clearance is typically monitored by enzyme-linked immunosorbent assay (ELISA) using a polyclonal reagent. Recently, mass spectrometry (MS) has been used to identify specific HCP process impurities and monitor their clearance. Despite this capability, ELISA remains the preferred analytical approach due to its simplicity and throughput. There are, however, inherent difficulties reconciling the protein-centric results of MS characterization with ELISA, or providing assurance that ELISA has acceptable coverage against all process-specific HCP impurities that could pose safety or efficacy risks. Here, we describe efficient determination of ELISA reagent coverage by proteomic analysis following affinity purification with a polyclonal anti-HCP reagent (AP-MS). The resulting HCP identifications can be compared with the actual downstream process impurities for a given process to enable a highly focused assessment of ELISA reagent suitability. We illustrate the utility of this approach by performing coverage evaluation of an anti-HCP polyclonal against both an HCP immunogen and the downstream HCP impurities identified in a therapeutic monoclonal antibody after Protein A purification. The overall goal is to strategically implement affinity-based mass spectrometry as part of a holistic framework for evaluating HCP process clearance, ELISA reagent coverage, and process clearance risks. We envision coverage analysis by AP-MS will further enable a framework for HCP impurity analysis driven by characterization of actual product-specific process impurities, complimenting analytical methods centered on consideration of the total host cell proteome.

Non-clinical Safety Evaluation of Biotherapeutics - Challenges, Opportunities and new Insights

New challenges and opportunities in nonclinical safety testing of biotherapeutics were presented and discussed at the 5th European BioSafe Annual General Membership meeting in November 2015 in Ludwigshafen. This article summarizes the presentations and discussions from both the main and the breakout sessions. The following topics were covered in six main sessions: The following questions were discussed across 4 breakout sessions (i-iv) and a case-study based general discussion (v).

Unconjugated payload quantification and DAR characterization of antibody–drug conjugates using high-resolution MS

Aim: The application of high-resolution MS to antibody–drug conjugate (ADC) drug development may provide insight into their safety and efficacy. Quantification of unconjugated cytotoxic drug (payload) and characterization of drug-to-antibody ratio distribution were determined in plasma using orthogonal acceleration quadrupole-time-of-flight MS. Results: Unconjugated payload quantification determined by quadrupole-time-of-flight-based MRMhighresolution and triple quadrupole-based multiple reaction monitoring were comparable and achieved detection limits of 0.030 and 0.015 ng/ml, respectively. As determined by immunocapture and TOF-MS, drug-to-antibody ratio remained unchanged up to 3-weeks postdose for an ADC containing engineered glutamine linkers, but declined from four to three over 2 weeks in an ADC containing engineered cysteine linkers. Conclusion: The use of high-resolution MS in ADC drug discovery confirms its utility within the bioanalytical discipline.

A new anti-human Fc method to capture and analyze ADCs for characterization of drug distribution and the drug-to-antibody ratio in serum from pre-clinical species

Antibody-drug conjugates (ADCs) are becoming a major class of oncology therapeutics. They combine monoclonal antibody specificity for over-expressed tumor antigens and the high cytoxicity of small molecular drugs (SMDs) and can therefore selectively kill tumor cells while minimizing toxicity to normal cells. Nevertheless, the premature deconjugation of ADCs in the circulation may trigger off target toxicity in patients. The released free drug level must be low in circulation for an extended period of time as well as the de-conjugation rate to ensure an acceptable therapeutic window. As a result, the assessment of the stability of the linker between payload and mAb in the systemic circulation is of paramount importance before entering in clinical trial. Here we report a new universal method to immunocapture and analyze by LC-MS the stability and distribution of ADCs in sera from relevant preclinical species (mouse, rat and cynomolgus monkey). Furthermore we demonstrated that this workflow can be applied to both ADCs with cleavable and non cleavable linkers. Last but not least, the results obtained in cynomolgus serum using immunoprecipitation and LC-MS analysis were cross validated using an ELISA orthogonal method. As the ligand used for immunoprecipitation is targeting the Fc part of mAb (CaptureSelect™ Human IgG-Fc PK Biotin), this protocol can be applied to analyze the stability of virtually all ADCs in sera for preclinical studies without the need to prepare specific molecular tools.

Where Did the Linker-Payload Go? A Quantitative Investigation on the Destination of the Released Linker-Payload from an Antibody-Drug Conjugate with a Maleimide Linker in Plasma

The reactive thiol of cysteine is often used for coupling maleimide-containing linker-payloads to antibodies resulting in the generation of antibody drug conjugates (ADCs). Currently, a numbers of ADCs in drug development are made by coupling a linker-payload to native or engineered cysteine residues on the antibody. An ADC conjugated via hinge-cysteines to an auristatin payload was used as a model in this study to understand the impact of the maleimide linkers on ADC stability. The payload was conjugated to trastuzumab by a protease-cleavable linker, maleimido-caproyl-valine-citruline-p-amino-benzyloxy carbonyl (mcVC-PABC). In plasma stability assays, when the ADC (Trastuzumab-mcVC-PABC-Auristatin-0101) was incubated with plasma over a 144-h time-course, a discrepancy was observed between the measured released free payload concentration and the measured loss of drug-to-antibody ratio (DAR), as measured by liquid chromatography-mass spectrometry (LC-MS). We found that an enzymatic release of payload from ADC-depleted human plasma at 144 h was able to account for almost 100% of the DAR loss. Intact protein mass analysis showed that at the 144 h time point, the mass of the major protein in ADC-depleted human plasma had an additional 1347 Da over the native albumin extracted from human plasma, exactly matching the mass of the linker-payload. In addition, protein gel electrophoresis showed that there was only one enriched protein in the 144 h ADC-depleted and antipayload immunoprecipitated plasma sample, as compared to the 0 h plasma immunoprecipitated sample, and the mass of this enriched protein was slightly heavier than the mass of serum albumin. Furthermore, the albumin adduct was also identified in 96 h and 168 h postdose in vivo cynomolgus monkey plasma. These results strongly suggest that the majority of the deconjugated mc-VC-PABC-auristatin ultimately is transferred to serum albumin, forming a long-lived albumin-linker-payload adduct. To our knowledge, this is the first report quantitatively characterizing the extent of linker-payload transfer to serum albumin and the first clear example of in vivo formation of an albumin-linker-payload adduct.

Characterization of antibody-drug conjugates by mass spectrometry: advances and future trends

Antibody-drug conjugates (ADCs) are emerging modalities in the pharmaceutical industry. The unique target-specific binding of antibody allows targeted delivery of cytotoxic small molecules to cancer cells, and thus expands the therapeutic window. However, in-depth characterization of ADCs is complex because it involves the characterization of antibody, conjugated molecules and antibody conjugates as a whole. In this review, we describe the practical use of mass spectrometry for ADC characterization including qualitative and quantitative analysis. Technical advances, limitations and future trends will also be discussed.

Use of a charge reducing agent to enable intact mass analysis of cysteine-linked antibody-drug-conjugates by native mass spectrometry

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The use of nESI-MS to examine intact Antibody Drug Conjugates (ADC).

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Use of TEAA as charge reducing agent improves cysteine-linked ADC characterization.

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TEAA preserves the intact mAb and facilitate easy drug load determination by native MS.

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This method is particularly beneficial for users of low resolution mass spectrometers.

Antibody-drug-conjugates (ADC) are a growing class of anticancer biopharmaceuticals. Conjugation of cysteine linked ADCs, requires initial reduction of mAb inter-chain disulfide bonds, as the drugs are attached via thiol chemistry. This results in the active mAb moiety being transformed from a covalently linked tetramer to non-covalently linked complexes, which hinders precise determination of drug load with LC–MS. Here, we show how the addition of the charge reducing agent triethylammonium acetate (TEAA) preserves the intact mAb structure, is well suited to the study of cysteine linked conjugates and facilitates easy drug load determination by direct infusion native MS.

Cutting-edge mass spectrometry methods for the multi-level structural characterization of antibody-drug conjugates

Antibody drug conjugates (ADCs) are highly cytotoxic drugs covalently attached via conditionally stable linkers to monoclonal antibodies (mAbs) and are among the most promising next-generation empowered biologics for cancer treatment. ADCs are more complex than naked mAbs, as the heterogeneity of the conjugates adds to the inherent microvariability of the biomolecules. The development and optimization of ADCs rely on improving their analytical and bioanalytical characterization by assessing several critical quality attributes, namely the distribution and position of the drug, the amount of naked antibody, the average drug to antibody ratio, and the residual drug-linker and related product proportions. Here brentuximab vedotin (Adcetris) and trastuzumab emtansine (Kadcyla), the first and gold-standard hinge-cysteine and lysine drug conjugates, respectively, were chosen to develop new mass spectrometry (MS) methods and to improve multiple-level structural assessment protocols.

Current Approaches for Absorption, Distribution, Metabolism, and Excretion Characterization of Antibody-Drug Conjugates: An Industry White Paper

An antibody-drug conjugate (ADC) is a unique therapeutic modality composed of a highly potent drug molecule conjugated to a monoclonal antibody. As the number of ADCs in various stages of nonclinical and clinical development has been increasing, pharmaceutical companies have been exploring diverse approaches to understanding the disposition of ADCs. To identify the key absorption, distribution, metabolism, and excretion (ADME) issues worth examining when developing an ADC and to find optimal scientifically based approaches to evaluate ADC ADME, the International Consortium for Innovation and Quality in Pharmaceutical Development launched an ADC ADME working group in early 2014. This white paper contains observations from the working group and provides an initial framework on issues and approaches to consider when evaluating the ADME of ADCs.

Antibody-conjugated drug assay for protease-cleavable antibody-drug conjugates

BACKGROUND

Antibody-drug conjugates (ADCs) require multiple assays to characterize their PK. These assays can separately evaluate the ADC by quantifying the antibody or the conjugated drug and may give different answers due to assay measurement differences, heterogeneous nature of ADCs and potential biotransformations that occur in vivo.

RESULTS

We present a new version of the antibody-conjugated drug assay for valine-citrulline-linked monomethylauristatin E (vcMMAE) ADCs. A stable isotope-labeled internal standard, protein A affinity capture and solid-phase cleavage of MMAE using papain was used prior to LC-MS/MS analysis.

CONCLUSION

The assay was used to assess the difference in ex vivo drug-linker stability of native-cysteine versus engineered cysteine ADCs and to determine the number of drugs per antibody of a native-cysteine ADC in vivo.

In vivo biotransformations of antibody–drug conjugates

The selective delivery of potent pharmacologically active compounds to target tissue or cells by antibody–drug conjugates makes this immuno-conjugate a promising modality for the treatment of cancers. A thorough understanding of the structural integrity of the linker, the payload and the conjugation site during biological exposure is critical throughout the process of novel linker-payload design and optimization of PK profile. This understanding is a key aspect of the effort to maximize efficacy while minimizing toxicity in preclinical testing and to ensure the translation to the clinical setting. The complexity of this bioconjugate modality is a source of significant challenge for analytical interrogation and analysis in vivo. Therefore, we report herein a survey of various types of biotransformation events that have been elucidated in recent years.

Challenges and advances in the assessment of the disposition of antibody-drug conjugates

Antibody‐drug conjugates (ADCs) are a rapidly growing therapeutic platform for the treatment of cancer. ADCs consist of a cytotoxic small molecule drug linked to an antibody to provide targeted delivery of the cytotoxic agent to the tumor. Understanding the pharmacokinetics (PK) and pharmacodynamics (PD) of ADCs is crucial in their design to optimize dose and regimen, to maximize efficacy and to minimize toxicity in patients. Significant progress has been made in recent years in this area, however, many fundamental questions still remain. This review discusses factors to consider while assessing the disposition of ADCs, and the unique challenges associated with these therapeutics. Current tools that are available and strategies to enable appropriate assessment are also discussed. © 2015 Genentech Inc. Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.