Development and Validation of an ADA-Tolerant Assay for Quantification of an Exatecan-Based ADC in Monkey Plasma

BACKGROUND

The development of an anti-drug antibody (ADA)-tolerant pharmacokinetic (PK) assay is important when the drug exposure is irrelevant to toxicity in the presence of ADA. We aimed to develop and validate an ADA-tolerant assay for an exatecan-based antibody-drug conjugate (ADC) in monkey plasma.

RESULTS

The assay tolerated 5.00 µg/mL of ADA at 12 µg/mL of ADC. Its accuracy and precision results satisfied the acceptance criteria. Furthermore, the assay was free from hook and matrix effects and exhibited good dilutional linearity. Additionally, the ADC in plasma samples was stable under different storage conditions.

METHOD

An ADA-tolerant ADC assay was configured with an anti-payload antibody for capture, and a drug-target protein combined with a horseradish peroxidase (HRP)-labeled antibody against a drug-target-protein tag for detection. Samples were firstly acidified to dissociate drug and ADA complexes, and to convert the carboxylate form to the lactone form of exatecan molecules; then, the ADAs in the samples were removed with a naked antibody-coated microplate. The treated samples were further incubated with coated anti-payload antibody and captured ADC molecules were quantified by the detection reagent. The developed assay was optimized and validated against regulatory guidelines.

CONCLUSIONS

The assay met both methodological and sample-related ADA tolerance requirements, and was applicable to a nonclinical study in cynomolgus monkeys.

An overview of site-specific methods for achieving antibody drug conjugates with homogenous drug to antibody ratio

INTRODUCTION

Antibody drug conjugates (ADCs) have emerged as a potent tool in cancer treatment, where cytotoxic drugs are linked to antibodies targeting specific antigens. While conventional ADC synthesis methods have seen success as commercials therapeutics, there is a growing interest in next-generation ADCs, looking at homogeneity of the drug-to-antibody ratio.

AREAS COVERED

The article provides a high-level overview for achieving said homogeneity by site-directed conjugations via encompassing engineered amino acids, enzyme-mediated strategies, peptide sequences, affinity peptides, and beyond. As the field rapidly evolves with multiple ADCs in clinical trials and the advent of biosimilars, the article explores the benefits and challenges in both conventional and non-platform ADC technologies.

EXPERT OPINION

The choice of site selection approach must be based on multiple criteria as discussed in this report. Two ADCs made from conjugation to engineered cysteines have been approved by regulatory agencies which have contributed to the excitement in this space. For the others, though successful as proof-of-concept, the true test of merit will be determined as these technologies advance into the clinic. The promise of improving the therapeutics index and decreasing toxicities will continue to drive progress in this area.

Pharmacokinetics and toxicity considerations for antibody-drug conjugates: an overview

Antibody-drug conjugates (ADCs) is one of the fastest-growing drug-delivery systems. It involves a monoclonal antibody conjugated with payload via a ligand that directly targets the expressive protein of diseased cell. Hence, it reduces systemic exposure and provides site-specific delivery along with reduced toxicity. Because of this advantage, researchers have gained interest in this novel system. ADCs have displayed great promise in drug delivery and biomedical applications. However, a lack of understanding exists on their mechanisms of biodistribution, metabolism and side effects. To gain a better understanding of the therapeutics, careful consideration of the pharmacokinetics and toxicity needs to be undertaken. In this review, different pharmacokinetics parameters including distribution, bioanalysis and heterogeneity are discussed for developing novel therapeutics.

Hybrid liquid chromatography high resolution and accuracy mass spectrometry approach for quantification of antibody-drug conjugates at the intact protein level in biological samples

Preclinical in vivo and in vitro characterization of Antibody-Drug Conjugates (ADCs) involves the development of several bioanalytical methods to address many drug exposure questions. The current pharma industry approach requires at least three different assays that must be run, i.e., total antibody (mAb), conjugated payload or conjugated mAb, and free payload assays. Herein we present analytical performances of a quantitative hybrid Ligand Binding/Liquid Chromatography High Resolution and Accuracy Mass Spectrometry (LB/LCHRAM) method that can condense much of the necessary bioanalytical information in one method. The method includes an immuno-capture step, and it detects whole ADC molecules. It was applied to plasma mouse samples and showed reliable bioanalytical performance according to full method validation standards. Quantitation using extracted ion chromatograms and deconvoluted mass peaks was evaluated. The limit of quantitation resulted in 0.5ng of protein on column with a linear dynamic range spanning from 0.5 to 10μg/mL. Moreover, lower drug-to-antibody ratio (DAR) ADC species can be simultaneously detected, also enabling qualitative characterization of in vivo ADC conjugation.

Optimizing Conjugation Chemistry, Antibody Conjugation Site, and Surface Density in Antibody-Nanogel Conjugates (ANCs) for Cell-Specific Drug Delivery

Targeted delivery of therapeutics using antibody-nanogel conjugates (ANCs) with a high drug-to-antibody ratio has the potential to overcome some of the inherent limitations of antibody-drug conjugates (ADCs). ANC platforms with simple preparation methods and precise tunability to evaluate structure-activity relationships will greatly contribute to translating this promise into clinical reality. In this work, using trastuzumab as a model antibody, we demonstrate a block copolymer-based ANC platform that allows highly efficient antibody conjugation and formulation. In addition to showcasing the advantages of using an inverse electron-demand Diels-Alder (iEDDA)-based antibody conjugation, we evaluate the influence of antibody surface density and conjugation site on the nanogels upon the targeting capability of ANCs. We show that compared to traditional strain-promoted alkyne-azide cycloadditions, the preparation of ANCs using iEDDA provides significantly higher efficiency, which results in a shortened reaction time, simplified purification process, and enhanced targeting toward cancer cells. We also find that a site-specific disulfide-rebridging method in antibodies offers similar targeting abilities as the more indiscriminate lysine-based conjugation method. The more efficient bioconjugation using iEDDA allows us to optimize the avidity by fine-tuning the surface density of antibodies on the nanogel. Finally, with trastuzumab-mertansine (DM1) antibody-drug combination, our ANC demonstrates superior activities in vitro compared to the corresponding ADC, further highlighting the potential of ANCs in future clinical translation.

Implementation of Systematic Bioanalysis of Antibody–Drug Conjugates for Preclinical Pharmacokinetic Study of Ado-Trastuzumab Emtansine (T-DM1) in Rats

Antibody–drug conjugates (ADCs) are composed of monoclonal antibodies covalently bound to cytotoxic drugs by a linker. They are designed to selectively bind target antigens and present a promising cancer treatment without the debilitating side effects of conventional chemotherapies. Ado-trastuzumab emtansine (T-DM1) is an ADC that received US FDA approval for the treatment of HER2-positive breast cancer. The purpose of this study was to optimize methods for the quantification of T-DM1 in rats. We optimized four analytical methods: (1) an enzyme-linked immunosorbent assay (ELISA) to quantify the total trastuzumab levels in all drug-to-antibody ratios (DARs), including DAR 0; (2) an ELISA to quantify the conjugated trastuzumab levels in all DARs except DAR 0; (3) an LC–MS/MS analysis to quantify the levels of released DM1; and (4) a bridging ELISA to quantify the level of anti-drug antibodies (ADAs) of T-DM1. We analyzed serum and plasma samples from rats injected intravenously with T-DM1 (20 mg/kg, single dose) using these optimized methods. Based on these applied analytical methods, we evaluated the quantification, pharmacokinetics, and immunogenicity of T-DM1. This study establishes the systematic bioanalysis of ADCs with validated assays, including drug stability in matrix and ADA assay, for future investigation on the efficacy and safety of ADC development.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

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.

ADME and DMPK considerations for the discovery and development of antibody drug conjugates (ADCs)

 The therapeutic concept of antibody drug conjugates (ADCs) is to selectively target tumour cells with small molecule cytotoxic drugs to maximise cell kill benefit and minimise healthy tissue toxicity.An ADC generally consists of an antibody that targets a protein on the surface of tumour cells chemically linked to a warhead small molecule cytotoxic drug.To deliver the warhead to the tumour cell, the antibody must bind to the target protein and in general be internalised into the cell. Following internalisation, the cytotoxic agent can be released in the endosomal or lysosomal compartment (via different mechanisms). Diffusion or transport out of the endosome or lysosome allows the cytotoxic drug to express its cell-killing pharmacology. Alternatively, some ADCs (e.g. EDB-ADCs) rely on extracellular cleavage releasing membrane permeable warheads.One potentially important aspect of the ADC mechanism is the 'bystander effect' whereby the cytotoxic drug released in the targeted cell can diffuse out of that cell and into other (non-target expressing) tumour cells to exert its cytotoxic effect. This is important as solid tumours tend to be heterogeneous and not all cells in a tumour will express the targeted protein.The combination of large and small molecule aspects in an ADC poses significant challenges to the disposition scientist in describing the ADME properties of the entire molecule.This article will review the ADC landscape and the ADME properties of successful ADCs, with the aim of outlining best practice and providing a perspective of how the field can further facilitate the discovery and development of these important therapeutic modalities.

Linkers: An Assurance for Controlled Delivery of Antibody-Drug Conjugate

As one of the major therapeutic options for cancer treatment, chemotherapy has limited selectivity against cancer cells. Consequently, this therapeutic strategy offers a small therapeutic window with potentially high toxicity and thus limited efficacy of doses that can be tolerated by patients. Antibody-drug conjugates (ADCs) are an emerging class of anti-cancer therapeutic drugs that can deliver highly cytotoxic molecules directly to cancer cells. To date, twelve ADCs have received market approval, with several others in clinical stages. ADCs have become a powerful class of therapeutic agents in oncology and hematology. ADCs consist of recombinant monoclonal antibodies that are covalently bound to cytotoxic chemicals via synthetic linkers. The linker has a key role in ADC outcomes because its characteristics substantially impact the therapeutic index efficacy and pharmacokinetics of these drugs. Stable linkers and ADCs can maintain antibody concentration in blood circulation, and they do not release the cytotoxic drug before it reaches its target, thus resulting in minimum off-target effects. The linkers used in ADC development can be classified as cleavable and non-cleavable. The former, in turn, can be grouped into three types: hydrazone, disulfide, or peptide linkers. In this review, we highlight the various linkers used in ADC development and their design strategy, release mechanisms, and future perspectives.

Enzyme-linked immunosorbent assays for quantification of MMAE-Conjugated ADCs and total antibodies in cynomolgus monkey sera

Antibody-drug conjugates (ADCs) are commonly heterogeneous and require extensive assessment of exposure-efficacy and exposure-safety relationships in preclinical and clinical studies. In this study, we report the generation of a monoclonal antibody against monomethyl auristatin E (MMAE) and the development, validation, and application of sensitive and high-throughput enzyme-linked immunosorbent assays (ELISA) to measure the concentrations of MMAE-conjugated ADCs and total antibodies (tAb, antibodies in ADC plus unconjugated antibodies) in cynomolgus monkey sera. These assays were successfully applied to in vitro plasma stability and pharmacokinetic (PK) studies of SMADC001, an MMAE-conjugated ADC against trophoblast cell surface antigen 2 (TROP-2). The plasma stability of SMADC001 was better than that of similar ADCs coupled with PEG4-Val-Cit, Lys (m-dPEG24)-Cit, and Val-Cit linkers. The developed ELISA methods for the calibration standards of ADC and tAb revealed a correlation between serum concentrations and the OD₄₅₀ values, with R² at 1.000, and the dynamic range was 0.3–35.0 ng/mL and 0.2–22.0 ng/mL, respectively; the intra- and inter-assay accuracy bias% ranged from −12.2% to −5.2%, precision ranged from −12.4% to −1.4%, and the relative standard deviation (RSD) was less than 6.6% and 8.7%, respectively. The total error was less than 20.4%. The development and validation steps of these two assays met the acceptance criteria for all addressed validation parameters, which suggested that these can be applied to quantify MMAE-conjugated ADCs, as well as in PK studies. Furthermore, these assays can be easily adopted for development of other similar immunoassays.

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A specific monoclonal antibody against MMAE was generated via hybridoma technology.

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ELISA was used to quantify MMAE-ADCs with a calibration range of 0.5–35 ng/mL.

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ELISA was used to quantify total antibodies with a calibration range of 0.6–22 ng/mL.

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Pharmacokinetic profiles of SMADC001 in cynomolgus monkeys were investigated.

Overcoming challenges associated with the bioanalysis of cysteine-conjugated metabolites in the presence of antibody-drug conjugates

Aim: Investigations have shown that for the antibody-drug conjugate (ADC) belantamab mafodotin, concentrations of the cysteine-conjugated metabolite, Cys-mcMMAF, were overestimated in the presence of the ADC during sample processing when utilizing a historical SPE method. Results: A new assay was developed utilizing an acidic protein precipitation to remove the ADC early in the extraction process, thus eliminating the risk of overestimating Cys-mcMMAF in the presence of belantamab mafodotin. In vitro experiments demonstrated a linear relationship between the concentration of belantamab mafodotin and the release of Cys-mcMMAF. Extensive stability assessments were performed to cover storage of study samples. Conclusion: This work emphasized the critical importance of understanding the performance of a bioanalytical method for free toxic payload in the presence of the ADC.

cIRCR201-dPBD, a Novel Pyrrolobenzodiazepine Dimer-Containing Site-Specific Antibody-Drug Conjugate Targeting c-Met Overexpression Tumors

c-Met, as a receptor expressed on the cell membrane, contributes to the growth and metastasis of tumors, as well as angiogenesis, mainly through the hepatocyte growth factor (HGF)/c-Met axis during tumor progression. Although several c-Met inhibitors, including small molecules and monoclonal antibody inhibitors, are currently being investigated, their clinical outcomes have not been promising. Development of an antibody-drug conjugate (ADC) against c-Met could be an attractive therapeutic strategy that would provide superior antitumor efficacy with broad-spectrum c-Met expression levels. In the present study, site-specific drug-conjugate technology was applied to develop an ADC using the human-mouse cross-reactive c-Met antibody and a prodrug pyrrolobenzodiazepine (PBD). The toxin payload was uniformly conjugated to the light-chain C-terminus of the native cIRCR201 antibody (drug-to-antibody ratio = 2), as confirmed using LC-MS. Using a high-throughput screening system, we found that cIRCR201-dPBD exhibited varying sensitivities depending on the expression levels of c-Met, and it induced receptor-mediated endocytosis and toxin-mediated apoptosis in 47 different cancer cell lines. cIRCR201-dPBD also showed significant antitumor activity on the MET-amplified cancer cells using in vivo xenograft models. Therefore, cIRCR201-dPBD could be a promising therapeutic strategy for tumors with c-Met expression.

Quantification of an Antibody-Conjugated Drug in Fat Plasma by an Affinity Capture LC-MS/MS Method for a Novel Prenyl Transferase-Mediated Site-Specific Antibody-Drug Conjugate

The novel prenyl transferase-mediated, site-specific, antibody-drug conjugate LCB14-0110 is comprised of a proprietary beta-glucuronide linker and a payload (Monomethyl auristatin F, MMAF, an inhibitor for tubulin polymerization) attached to human epidermal growth factor receptor 2 (HER2)-targeting trastuzumab. A LC-MS/MS method was developed to quantify the antibody-conjugated drug (acDrug) for in vitro linker stability and preclinical pharmacokinetic studies. The method consisted of affinity capture, enzymatic cleavage of acDrug, and LC-MS/MS analysis in the positive ion mode. A quadratic regression (weighted 1/concentration2), with the equation y = ax2 + bx + c, was used to fit calibration curves over the concentration range of 19.17~958.67 ng/mL for acDrug. The qualification run met the acceptance criteria of ±25% accuracy and precision values for quality control (QC) samples. The overall recovery was 42.61%. The dilution integrity was for a series of 5-fold dilutions with accuracy and precision values ranging within ±25%. The stability results indicated that acDrug was stable at all stability test conditions (short-term: 1 day, long-term: 10 months, Freeze/Thaw (F/T): 3 cycles). This qualified method was successfully applied to in vitro linker stability and pharmacokinetic case studies of acDrug in rats.

Determination of ADC Concentration by Ligand-Binding Assays

Total antibody, conjugated antibody or antibody-conjugated drug, and free drug are key analytes required to establish exposure-response relationships for ADCs. Therefore, bioanalytical strategies for ADCs include ligand-binding assays (LBA) and LC-MS/MS methods. Here we describe detailed methodology to develop a solid-phase-based enzyme-linked immunosorbent assay (ELISA), which is the most widely used LBA to quantify large-molecule components of ADC in biological matrices such as plasma, serum, tumor, or tissue homogenates. The approach presented here is designed to quantify total antibody concentrations in ADC containing samples, and can be easily adapted to quantify conjugated antibody concentrations.

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.

Bioanalytical workflow for novel scaffold protein–drug conjugates: quantitation of total Centyrin protein, conjugated Centyrin and free payload for Centyrin–drug conjugate in plasma and tissue samples using liquid chromatography–tandem mass spectrometry

Aim: Alternative scaffold proteins have emerged as novel platforms for development of therapeutic applications. One such application is in protein–drug conjugates (PDCs), which are analogous to antibody–drug conjugates. Methodology: Liquid chromatography–mass spectrometry methods for quantitation of total protein, conjugate and free payload for a PDC based on Centyrin scaffold were developed. Tryptic peptides generated from a region of the Centyrin that does not contain a conjugation site, and another that has the conjugation site with the linker-payload attached were used as surrogates of the total and conjugated Centyrin, respectively. Conclusion: The methods were successfully applied to analysis of samples from mice to quantify the plasma and tissue concentrations. This same workflow can potentially be applied to other PDCs and site-specific antibody–drug conjugates.

A single liquid chromatography-quadrupole time-of-flight mass spectrometric method for the quantification of total antibody, antibody-conjugated drug and free payload of antibody-drug conjugates

A single hybrid affinity-captured-LC-TOF-MS/MS method was developed and applied for the quantification of total antibody, antibody conjugated drug and free payload of antibody drug conjugate (ADC). Adcetris®, a valine-citrulline monomethyl auristatin E conjugated ADC, was used as a model ADC compound. A quadratic regression (weighted 1/concentration) was used to fit calibration curves over the concentration range 30.65-613.00 ng/mL with an equation y = ax²  + bx + c for the antibody-conjugated drug of Adcetris®. The qualification run met the acceptance criteria of ±25% accuracy and precision values for quality control samples. For the analysis of total antibody, a signature peptide (TTPPVLDSDGSFFLYSK, molecular weight 1874) was used after affinity capture using magnetic beads and on-bead trypsin digestion. A quadratic regression (weighted 1/concentration) was used to fit calibration curves over the concentration range 5.00-100.00 μg/mL with an equation y = ax²  + bx + c for total antibody. For free payload analysis of monomethyl auristatin E, a protein precipitation method followed by LC-TOF-MS/MS analysis was used. A quadratic regression (weighted 1/concentration) was used to fit calibration curves over the concentration range 1.01-2200 ng/mL with an equation y = ax²  + bx + c for free payload. Pharmacokinetic study samples and in vitro stability samples in rat were successfully analyzed by this a hybrid affinity-captured-LC-TOF-MS/MS method. This single platform method is a useful complementary method for the pharmacokinetics study of ADC with valine-citrulline linker at the early drug discovery stage.

Site-Specific Antibody Conjugation for ADC and Beyond

Antibody-drug conjugates (ADCs) have become a promising class of antitumor agents with four conjugates being approved by regulatory agencies for treating cancer patients. To improve the conventional conjugations that are currently applied to generate these heterogeneous products, various site-specific approaches have been developed. These methods couple cytotoxins or chemotherapeutic drugs to specifically defined sites in antibody molecules including cysteine, glutamine, unnatural amino acids, short peptide tags, and glycans. The ADCs produced showed high homogeneity, increased therapeutic index, and strong antitumor activities in vitro and in vivo. Moreover, there are recent trends in using these next generation technologies beyond the cytotoxin-conjugated ADC. These site-specific conjugations have been applied for the generation of many different immunoconjugates including bispecific Fab or small molecule–antibody conjugates, immunosuppressive antibodies, and antibody–antibiotic conjugates. Thus, it is likely that additional technologies and related site-specific conjugates will emerge in the near future, with various chemicals or small molecular weight proteins in addition to cytotoxin for better treatment of many challenging diseases.

Calculated conjugated payload from immunoassay and LC–MS intact protein analysis measurements of antibody-drug conjugate

Aim: Complex nature of bioconjugates require multiple bioanalytical approaches to support PK and absorption, distribution, metabolism and excretion characterization. For antibody-drug conjugate (ADC) bioanalysis both LC–MS and ligand-binding assays (LBAs) are employed. Results: A method consisting of immunocapture extraction of ADC from biomatrices followed by LC–MS analysis of light and heavy chain is described. Drug antibody ratio (DAR) profiles of ADC Tras-mcVC-PF06380101 dosed at 0.3, 1 and 3 mg/kg in Sprague Dawley rats were obtained. Combined with total antibody (monoclonal antibody) measurement by LBA, conjugated payload concentration was calculated. Conclusion: PK profiles from LBA, ADC and calculated conjugated payload (DAR × monoclonal antibody) were in good agreement. We present a new tool for PK assessment of ADCs while also exploring ADC metabolism and DAR sensitivity of LBA ADC assay.

Antibody-drug conjugate characterization by chromatographic and electrophoretic techniques

Due to the inherent structure complexity and component heterogeneity of antibody drug conjugates (ADCs), separation technologies play a critical role in their characterization. In this review, we focus on chromatographic and electrophoretic approaches used to characterize ADCs with respect to drug-to-antibody ratio, drug distribution and conjugation sites, free small molecule drugs, charge variants, aggregates and fragments, etc. Chromatographic techniques including reversed-phase, ion exchange, size exclusion, hydrophobic interaction, two-dimensional liquid chromatography, and gas chromatography as well as capillary electrophoretic techniques including capillary electrophoresis sodium dodecyl sulfate, capillary zone electrophoresis and capillary isoelectric focusing are reviewed for their applications in the characterization of ADCs.

Antibody–drug conjugate bioanalysis using LB-LC–MS/MS hybrid assays: strategies, methodology and correlation to ligand-binding assays

Background: Antibody–drug conjugates (ADCs) are complex drug constructs with multiple species in the heterogeneous mixture that contribute to their efficacy and toxicity. The bioanalysis of ADCs involves multiple assays and analytical platforms. Methods: A series of ligand binding and LC–MS/MS (LB-LC–MS/MS) hybrid assays, through different combinations of anti-idiotype (anti-Id), anti-payload, or generic capture reagents, and cathepsin-B or trypsin enzyme digestion, were developed and evaluated for the analysis of conjugated-payload as well as for species traditionally measured by ligand-binding assays, total-antibody and conjugated-antibody. Results & conclusion: Hybrid assays are complementary or viable alternatives to ligand-binding assay for ADC bioanalysis and PK/PD modeling. The fit-for-purpose choice of analytes, assays and platforms and an integrated strategy from Discovery to Development for ADC PK and bioanalysis are recommended.

Characterization of therapeutic antibodies and related products by two-dimensional liquid chromatography coupled with UV absorbance and mass spectrometric detection

The development of analytical tools for the characterization of large biomolecules is an emerging and rapidly evolving area. This development activity is motivated largely by the current trend involving the increase in development and use of large biomolecules for therapeutic uses. Given the inherent complexity of these biomolecules, which arises from their sheer size and possibilities for chemical modification as well as changes over time (e.g., through modification in solution, aggregation), two-dimensional liquid chromatography (2D-LC) has attracted considerable interest as an analytical tool to address the challenges faced in characterizing these materials. The immediate potential benefits of 2D-LC over conventional one-dimensional liquid chromatography in this context include: (1) higher overall resolving power; (2) complementary information gained from two dimensions of separation in a single analysis; and (3) enabling indirect coupling of separation modes that are inherently incompatible with mass spectrometric (MS) detection (e.g., ion-exchange, because of high-salt eluents) to MS through a more compatible second dimension separation such as reversed-phase LC. In this review we summarize the work in this area, most of which has occurred in the past five years. Although the future is bright for further development in this area, some challenges have already been addressed through new 2D-LC methods. These include: (1) deep characterization of monoclonal antibodies to understand charge heterogeneity, glycosylation patterns, and other modifications; (2) characterization of antibody-drug conjugates to understand the extent and localization of small molecule conjugation; (3) detailed study of excipients in protein drug formulations; and (4) detection of host-cell proteins on biotherapeutic molecule preparations. We fully expect that in the near future we will see this list expanded, and that continued development will lead to methods with further improved performance metrics.

A sensitive multidimensional method for the detection, characterization, and quantification of trace free drug species in antibody-drug conjugate samples using mass spectral detection

Conjugation processes and stability studies associated with the production and shelf life of antibody-drug conjugates (ADCs) can result in free (non-conjugated) drug species. These free drug species can increase the risk to patients and reduce the efficacy of the ADC. Despite stringent purification steps, trace levels of free drug species may be present in formulated ADCs, reducing the therapeutic window. The reduction of sample preparation steps through the incorporation of multidimensional techniques has afforded analysts more efficient methods to assess trace drug species. Multidimensional methods coupling size-exclusion and reversed phase liquid chromatography with ultra-violet detection (SEC-RPLC/UV) have been reported, but offer limited sensitivity and can limit method optimization. The current study addresses these challenges with a multidimensional method that is specific, sensitive, and enables method control in both dimensions via coupling of an on-line solid phase extraction column to RPLC with mass spectral detection (SPE-RPLC/MS). The proposed method was evaluated using an antibody-fluorophore conjugate (AFC) as an ADC surrogate to brentuximab vedotin and its associated parent maleimide-val-cit-DSEA payload and the derived N-acetylcysteine adduct formed during the conjugation process. Assay sensitivity was found to be 2 orders more sensitive using MS detection in comparison to UV-based detection with a nominal limit of quantitation of 0.30 ng/mL (1.5 pg on-column). Free-drug species were present in an unadulterated ADC surrogate sample at concentrations below 7 ng/mL, levels not detectable by UV alone. The proposed SPE-RPLC/MS method provides a high degree of specificity and sensitivity in the assessment of trace free drug species and offers improved control over each dimension, enabling straightforward integration into existing or novel workflows.

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.

Antibody–drug conjugates nonclinical support: from early to late nonclinical bioanalysis using ligand-binding assays

Seema Kumar is a Principal Scientist at Pfizer. She leads a group that provides regulated bioanalytical support including assay development, validation and sample analysis for the PK and immunogenicity assessment for preclinical and clinical development of Pfizer's biotherapeutics portfolio. She is also responsible for scientific oversight of regulated studies outsourced at CROs. Prior to Pfizer, Dr Kumar held a similar role as Director of CLIA certified Clinical Bioanalytical Laboratory at XBiotech USA, Inc. She holds a PhD in Biophysical Chemistry from Johns Hopkins University, and has published several publications in peer-reviewed journals, and contributed to book chapters.

The objective of antibody–drug conjugate (ADC) bioanalysis at different stages of drug development may vary and so are the associated bioanalytical challenges. While at early drug discovery stage involving candidate selection, optimization and preliminary nonclinical assessments, the goal of ADC bioanalysis is to provide PK, toxicity and efficacy data that assists in the design and selection of potential drug candidates, the late nonclinical and clinical drug development stage typically involves regulated ADC bioanalysis that delivers TK data to define and understand pharmacological and toxicological properties of the lead ADC candidate. Bioanalytical strategies and considerations involved in developing successful ligand binding assays for ADC characterization from early discovery to late nonclinical stages of drug development are presented here.

Antibody-Drug Conjugates: Design, Formulation and Physicochemical Stability

The convergence of advanced understanding of biology with chemistry has led to a resurgence in the development of antibody-drug conjugates (ADCs), especially with two recent product approvals. Design and development of ADCs requires the synergistic combination of the monoclonal antibody, the linker and the payload. Advances in antibody science has enabled identification and generation of high affinity, highly selective, humanized or human antibodies for a given target. Novel linker technologies have been synthesized and highly potent cytotoxic drug payloads have been created. As the first generation of ADCs utilizing lysine and cysteine chemistries moves through the clinic and into commercialization, second generation ADCs involving site specific conjugation technologies are being evaluated and tested. The latter aim to be better characterized and controlled, with wider therapeutic indices as well as improved pharmacokinetic-pharmacodynamic (PK-PD) profiles. ADCs offer some interesting physicochemical properties, due to conjugation itself, and to the (often) hydrophobic payloads that must be considered during their CMC development. New analytical methodologies are required for the ADCs, supplementing those used for the antibody itself. Regulatory filings will be a combination of small molecule and biologics. The regulators have put forth some broad principles but this landscape is still evolving.

Workshop report: Crystal City V--quantitative bioanalytical method validation and implementation: the 2013 revised FDA guidance

In September 2013, the FDA released a draft revision of the Bioanalytical Method Validation (BMV) Guidance, which included a number of changes to the expectations for bioanalysis, most notably the inclusion of biomarker assays and data. To provide a forum for an open, inclusive discussion of the revised draft BMV Guidance, the AAPS and FDA once again collaborated to convene a two-and-a-half day workshop during early December 2013 in Baltimore, MD, USA. The resulting format embodied extensive open discussion and each thematic session included only brief, concise descriptions by Agency and industry representatives prior to opening the floor discussion. The Workshop was built around four thematic sessions (Common Topics, Chromatographic, Ligand-Binding Assays, and Biomarkers) and a final session with international regulators, concluding with a review of the outcomes and recommendations from the thematic sessions. This Workshop report summarizes the outcomes and includes topics of agreement, those where the FDA will consider the Industry's perspective, and those where the workshop provided a first open dialogue. This article will be available to the bioanalytical community at http://www.aaps.org/BMV13 .

Resolution of matrix interference: quantitative and quasi-quantitative ligand-binding assays case studies

Background: Matrix effects pose a constant challenge in developing robust ligand-binding assays to be validated for use in nonclinical and clinical study support. When notable matrix effects of any kind are present, it can render an otherwise sound method ineffective. We present two case studies detailing the mitigation of observed matrix effects. Method: A dimeric protein was removed from unknown samples in an anti-therapeutic antibody assay through protein extraction. Nonspecific matrix effects in a quantitative ligand-binding assays were mitigated through development of a specialized buffer. Results: The protein extraction method reproducibly reduced the artificially high responses of naïve samples, enabling the accurate detection of anti-therapeutic antibodies. Design of experiments was used to evaluate and select the optimal components and associated concentrations in order to reduce the observed matrix effect to acceptable limits. Conclusion: Our results suggest there are multiple techniques available for the bioanalytical scientist to mitigate both matrix effects in ligand-binding assays.

Bioanalysis of antibody-drug conjugates: American Association of Pharmaceutical Scientists Antibody-Drug Conjugate Working Group position paper

Antibody-drug conjugates (ADCs) typically consist of a cytotoxic drug covalently bound to an antibody by a linker. These conjugates have the potential to substantially improve efficacy and reduce toxicity compared with cytotoxic small-molecule drugs. Since ADCs are generally complex heterogeneous mixtures of multiple species, these novel therapeutic products present unique bioanalytical challenges. The growing number of ADCs being developed across the industry suggests the need for alignment of the bioanalytical methods or approaches used to assess the multiple species and facilitate consistent interpretation of the bioanalytical data. With limited clinical data, the current strategies that can be used to provide insight into the relationship between the multiple species and the observed clinical safety and efficacy are still evolving. Considerations of the bioanalytical strategies for ADCs based on the current industry practices that take into account the complexity and heterogeneity of ADCs are discussed.

PK of immunoconjugate anticancer agent CMD-193 in rats: ligand-binding assay approach to determine in vivo immunoconjugate stability

Background: Antibody–drug conjugates (ADCs) are a new generation of anticancer therapeutics. The objective of this manuscript is to propose a methodology that can be used to assess the stability of the ADCs by using the PK data obtained by ligand-binding assays that measure various components of ADCs. Results: The ligand-binding assays format of different components of ADCs provided unique valuable PK information. The mathematical manipulation of the bioanalytical data provided an insight into the in vivo integrity, indicating that the loading of the calicheamicin on the G193 antibody declines in an apparent slow first-order process. Conclusion: This report demonstrates the value of analyzing various components of the ADC and their PK profiles to better understand the disposition and in vivo stability of ADCs.

Considerations for the nonclinical safety evaluation of antibody drug conjugates for oncology

Antibody drug conjugates (ADCs) include monoclonal antibodies that are linked to cytotoxic small molecules. A number of these agents are currently being developed as anti-cancer agents designed to improve the therapeutic index of the cytotoxin (i.e., cytotoxic small molecule or cytotoxic agent) by specifically delivering it to tumor cells. This paper presents primary considerations for the nonclinical safety evaluation of ADCs and includes strategies for the evaluation of the entire ADC or the various individual components (i.e., antibody, linker or the cytotoxin). Considerations are presented on how to design a nonclinical safety assessment program to identify the on- and off-target toxicities to enable first-in-human (FIH) studies. Specific discussions are also included that provide details as to the need and how to conduct the studies for evaluating ADCs in genetic toxicology, tissue cross-reactivity, safety pharmacology, carcinogenicity, developmental and reproductive toxicology, biotransformation, toxicokinetic monitoring, bioanalytical assays, immunogenicity testing, test article stability and the selection of the FIH dose. Given the complexity of these molecules and our evolving understanding of their properties, there is no single all-encompassing nonclinical strategy. Instead, each ADC should be evaluated on a case-by-case scientifically-based approach that is consistent with ICH and animal research guidelines.

Immunogenicity testing strategy and bioanalytical assays for antibody–drug conjugates

Background: Immunogenicity testing is an important component of clinical development for large-molecule biotherapeutics. New complex types of large molecules, such as antibody–drug conjugates (ADCs), require careful evaluation of the testing strategy and bioanalytical assays used to monitor the development of antitherapeutic antibodies. Results: An electrochemiluminescence-based immunoassay for the detection and epitope characterization of anti-ADC antibodies was validated. Using this assay format, antibodies directed against the monoclonal antibody and linker–drug components of the ADC were successfully detected in a multiple-dose rat toxicity study. Conclusion: Immunogenicity assays incorporating epitope determination may provide additional information about the characteristics of induced antitherapeutic antibodies, including the magnitude and timing of the various types of antibody responses.

In vivo testing of drug-linker stability

Antibody-drug conjugates (ADCs) are promising biotherapeutics designed to selectively deliver highly cytotoxic drugs to tumor cells while sparing normal tissues. They can be viewed as prodrugs, stable in the bloodstream in order to minimize drug release in circulation and efficiently converted into active drugs in the tumor tissues. Designing the right combination of monoclonal antibody (mAb), linker and drug, requires monitoring and understanding the behavior of all three components in the bloodstream and tumor. In particular, linkers have been shown to influence efficacy and safety profiles of ADCs, and monitoring in vivo "drug-linker stability" is therefore critical to help the linker choice and is performed by identifying the pharmacokinetics (PK) profiles. PK properties of ADCs are measured by following the profiles of three entities: (a) the conjugate (mAb entity carrying at least one drug), (b) the total antibody (mAb entity regardless of drug load), as well as (c) the free drugs and metabolites entities. This chapter focuses on the key analytical methods (ELISA immunoassays, TFC-MS/MS, and HRMS) used to support the PK profiles assessment of the three entities, allowing the characterization of ADC "drug-linker stability".

Bioanalytical assay strategies for the development of antibody–drug conjugate biotherapeutics

Antibody–drug conjugates (ADCs) are monoclonal antibodies with covalently bound cytotoxic drugs. They are designed to target tumor antigens selectively and offer the hope of cancer treatment without the debilitating side-effects of conventional therapies. The concept of ADCs is not new; however, development of these therapeutics is challenging and only recently are promising clinical data emerging. These challenges include ADC bioanalysis, such as quantifying in serum/plasma for PK studies and strategies for assessing immunogenicity. ADCs have complex molecular structures incorporating large- and small-molecule characteristics and require diverse analytical methods, including ligand-binding assays and MS-based methods. ADCs are typically mixtures with a range of drug-to-antibody ratios. Biotransformations in vivo can lead to additional changes in drug-to-antibody ratios resulting in dynamically changing mixtures. Thus, a standard calibration curve consisting of the reference standard may not be appropriate for quantification of analytes in vivo and represents a unique challenge. This paper will share our perspective on why ADC bioanalysis is so complex and describe the strategies and rationale that we have used for ADCs, with highlights of original data from a variety of nonclinical and clinical case studies. Our strategy has involved novel protein structural characterization tools to help understand ADC biotransformations in vivo and use of the analyte knowledge gained to guide the development of quantitative bioanalytical assays.

Risks and untoward toxicities of antibody-based immunoconjugates

Antibody-based immunoconjugates are specifically targeted monoclonal antibodies that deliver a cytotoxic payload to their target. The cytotoxic agents can be highly potent drugs, radionuclides or toxins. Such molecules, referred to as antibody-drug conjugates, radioimmunoconjugates and immunotoxins, respectively, represent a promising approach for enhancing the efficacy of unconjugated (naked) antibodies for improved therapeutic results. Though tremendous progress has been achieved over the last few decades, the safety of these molecules still remains a matter of concern and a careful design is required for achieving a relatively safe toxicity profile along with therapeutic effectiveness. This review focuses on the toxicities arising from the use of these potent agents.

Challenges in the development and manufacturing of antibody-drug conjugates

Advances in antibody-drug conjugates (ADCs) will permit sensitive discrimination between healthy and cancer cells. Promising clinical results generated much hope that this targeted prodrug therapy will offer more effective treatment options to patients. Manufacturing such highly potent biopharmaceuticals presents a series of unique challenges. Some specific skills required for the process development and production of ADCs are discussed. In addition to the accuracy and reliability needed to handle these potent and costly materials, coworker safety and equipment cleaning are of particular importance. The ideas and concepts shared in this article are based on the experience that Lonza has gained in the ADC field since 2004.