LC-MS/MS method for the simultaneous determination of Lys-MCC-DM1, MCC-DM1 and DM1 as potential intracellular catabolites of the antibody-drug conjugate trastuzumab emtansine (T-DM1)

Quantifying payloads of antibody‒drug conjugates using a postcolumn infused-internal standard strategy with LC‒MS

BACKGROUND

Antibody‒drug conjugates (ADCs) are innovative biopharmaceutics consisting of a monoclonal antibody, linkers, and cytotoxic payloads. Monitoring circulating payload concentrations has the potential to identify ADC toxicity; however, accurate quantification faces challenges, including low plasma concentrations, severe matrix effects, and the absence of stable isotope-labeled internal standards (SIL-IS) for payloads and their derivatives. Previous studies used structural analogs as internal standards, but different retention times between structural analogs and target analytes may hinder effective matrix correction. Therefore, a more flexible approach is required for precise payload quantification.

RESULTS

We developed an LC‒MS/MS method incorporating a postcolumn-infused internal standard (PCI-IS) strategy for quantifying payloads and their derivatives of trastuzumab emtansine, trastuzumab deruxtecan, and sacituzumab govitecan, including DM1, MCC-DM1, DXd, SN-38, and SN-38G. Structural analogs (maytansine, Lys-MCC-DM1, and exatecan) were selected as PCI-IS candidates, and their accuracy performance was evaluated based on the percentage of samples within 80%-120% quantification accuracy. Compared to the approach without PCI-IS correction, exatecan enhanced the accuracy performance from 30-40%-100% for SN-38 and DXd, while maytansine and Lys-MCC-DM1 showed comparable accuracy for DM1 and MCC-DM1. This validated PCI-IS analytical method showed superior normalization of matrix effect in all analytes compared to the conventional internal standard approach. The clinical application of this approach showed pronounced differences in DXd and SN-38 concentrations before and after PCI-IS correction. Moreover, only DXd concentrations after PCI-IS correction were significantly higher in patients with thrombocytopenia (p = 0.037).

SIGNIFICANCE

This approach effectively addressed the issue of unavailability of SIL-IS for novel ADC payloads and provided more accurate quantification, potentially yielding more robust statistical outcomes for understanding the exposure-toxicity relationship in ADCs. It is anticipated that this PCI-IS strategy may be extrapolated to quantify payloads and derivatives in diverse ADCs, thereby providing invaluable insights into drug toxicity and fortifying patient safety in ADC usage.

Mono-amino acid linkers enable highly potent small molecule-drug conjugates by conditional release

The endosome cleavable linkers have been widely employed by antibody-drug conjugates and small molecule-drug conjugates (SMDCs) to control the accurate release of payloads. An effective linker should provide stability in systemic circulation but efficient payload release at its targeted tumor sites. This conflicting requirement always leads to linker design with increasing structural complexity. Balance of the effectiveness and structural complexity presents a linker design challenge. Here, we explored the possibility of mono-amino acid as so far the simplest cleavable linker (X-linker) for SMDC-based auristatin delivery. Within a diverse set of X-linkers, the SMDCs differed widely in bioactivity, with one (Asn-linker) having significantly improved potency (IC50 = 0.1 nM) and fast response to endosomal cathepsin B cleavage. Notably, this SMDC, once grafted with effector protein fragment crystallizable (Fc), demonstrated a profound in vivo therapeutic effect in aspects of targetability, circulation half-life (t1/2 = 73 h), stability, and anti-tumor efficacy. On the basis of these results, we believe that this mono-amino acid linker, together with the new SMDC-Fc scaffold, has significant potential in targeted delivery application.

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

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

HER2-Selective and Reversible Tyrosine Kinase Inhibitor Tucatinib Potentiates the Activity of T-DM1 in Preclinical Models of HER2-positive Breast Cancer

The oncogenic receptor HER2 is overexpressed in many cancers, including up to 20% of breast cancers. Despite the availability of HER2-targeted treatments, patients’ disease often progresses during therapy, underscoring the need for novel treatment strategies. The addition of tucatinib, a reversible, highly selective HER2 tyrosine kinase inhibitor (TKI), to treatment with trastuzumab and capecitabine significantly improved survival outcomes of patients with HER2-positive metastatic breast cancer, including those with active brain metastases. We rationalized that combining tucatinib with other HER2-targeting agents with complementary mechanisms of action would further increase efficacy against tumors. We characterized the activity of tucatinib with the antibody–drug conjugate T-DM1 in preclinical models of breast cancer, including HER2-positive breast cancer cells and patient-derived xenograft (PDX) models. Mechanistic details on tucatinib activity were obtained in internalization and catabolism studies. In combination, tucatinib and T-DM1 showed an enhanced, often synergistic, cytotoxic response and demonstrated improved antitumor activity in vivo, including in PDX models refractory to T-DM1 single-agent activity. Mechanistically, tucatinib mediated an increase in inactive HER2 molecules at the cell surface through inhibition of HER2 ubiquitination, resulting in increased internalization and catabolism of T-DM1. The combination was correlated with enhanced HER2 pathway inhibition, decreased proliferation, and increased apoptosis. In a xenograft model of brain metastasis, tucatinib penetrated intracranial tumor tissues, inhibiting tumor growth and improving survival. These results suggest that tucatinib may be the optimal TKI partner for HER2-targeted therapies and support clinical studies of its combination with T-DM1, including in patients with brain metastases.

SIGNIFICANCE

The preclinical findings in breast cancer models presented here demonstrate that combining tucatinib with T-DM1 enhances the antitumor activity of either agent alone, supporting clinical studies of the combination in HER2-positive breast cancer, including in patients with brain metastases, which remains an important unmet medical need.

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.

Sensitive LC-MS/MS quantification of unconjugated maytansinoid DM4 and its metabolite S-methyl-DM4 in human plasma

Aim: To report the development and validation of an LC-MS/MS method for the simultaneous determination of unconjugated payload DM4 and its metabolite S-methyl-DM4 in human plasma. Methodology: A workflow of protein precipitation followed by reduction and solid phase extraction was employed to remove antibody-maytansinoid conjugates from plasma matrix, release DM4 from endogenous conjugates, and generate a clean sample extract for analysis, respectively. Sodium adduct species of both analytes were selected for multiple reaction monitoring to meet the assay sensitivity requirement in liquid chromatography with tandem mass spectrometry. Conclusion: The method was fully validated for a dynamic range of 0.100-50.0 ng/ml for both analytes along with desired stability and acceptable incurred sample reanalysis.

Target-responsive subcellular catabolism analysis for early-stage antibody-drug conjugates screening and assessment

Events including antibody‒antigen affinity, internalization, trafficking and lysosomal proteolysis combinatorially determine the efficiency of antibody-drug conjugate (ADC) catabolism and hence the toxicity. Nevertheless, an approach that conveniently identifies proteins requisite for payload release and the ensuing toxicity for mechanistic studies and quality assessment is lacking. Considering the plethora of ADC candidates under development, we developed a target-responsive subcellular catabolism (TARSC) approach that examines ADC catabolism and probes changes in response to targeted interferences of proteins of interest. We firstly applied TARSC to study the commercial T-DM1 and the biosimilar. We recorded unequivocal catabolic behaviors regardless of the absence and presence of the targeted interferences. Their negligible differences in TARSC profiles agreed with their undifferentiated anti-tumoral efficacy according to further in vitro viability and in vivo tumor growth assays, highlighting TARSC analysis as a useful tool for biosimilarity assessment and functional dissection of proteins requisite for ADC catabolism. Additionally, we employed TARSC to investigate the catabolic behavior of a new trastuzumab-toxin conjugate. Collectively, TARSC can not only characterize ADC catabolism at (sub)cellular level but also comprehensively determine which protein targets affect payload release and therapeutic outcomes. Future use of TARSC is thus anticipated in early-stage screening, quality assessment and mechanistic investigations of ADCs.

Current LC-MS-based strategies for characterization and quantification of antibody-drug conjugates

The past few years have witnessed enormous progresses in the development of antibody-drug conjugates (ADCs). Consequently, comprehensive analysis of ADCs in biological systems is critical in supporting discovery, development and evaluation of these agents. Liquid chromatography-mass spectrometry (LC-MS) has emerged as a promising and versatile tool for ADC analysis across a wide range of scenarios, owing to its multiplexing ability, rapid method development, as well as the capability of analyzing a variety of targets ranging from small-molecule payloads to the intact protein with a high, molecular resolution. However, despite this tremendous potential, challenges persist due to the high complexity in both the ADC molecules and the related biological systems. This review summarizes the up-to-date LC-MS-based strategies in ADC analysis and discusses the challenges and opportunities in this rapidly-evolving field.

CRISPR-Cas9 screens identify regulators of antibody-drug conjugate toxicity

Antibody-drug conjugates (ADCs) selectively deliver chemotherapeutic agents to target cells and are important cancer therapeutics. However, the mechanisms by which ADCs are internalized and activated remain unclear. Using CRISPR-Cas9 screens, we uncover many known and novel endolysosomal regulators as modulators of ADC toxicity. We identify and characterize C18ORF8/RMC1 as a regulator of ADC toxicity through its role in endosomal maturation. Through comparative analysis of screens with ADCs bearing different linkers, we show that a subset of late endolysosomal regulators selectively influence toxicity of noncleavable linker ADCs. Surprisingly, we find cleavable valine-citrulline linkers can be processed rapidly after internalization without lysosomal delivery. Lastly, we show that sialic acid depletion enhances ADC lysosomal delivery and killing in diverse cancer cell types, including with FDA (US Food and Drug Administration)-approved trastuzumab emtansine (T-DM1) in Her2-positive breast cancer cells. Together, these results reveal new regulators of endolysosomal trafficking, provide important insights for ADC design and identify candidate combination therapy targets.

Conjugation of DM1 to anti-CD30 antibody has potential antitumor activity in CD30-positive hematological malignancies with lower systemic toxicity

An anti-CD30 antibody-drug conjugate incorporating the antimitotic agent DM1 and a stable SMCC linker, anti-CD30-MCC-DM1, was generated as a new antitumor drug candidate for CD30-positive hematological malignancies. Here, the in vitro and in vivo pharmacologic activities of anti-CD30-MCC-DM1 (also known as F0002-ADC) were evaluated and compared with ADCETRIS (brentuximab vedotin). Pharmacokinetics (PK) and the safety profiles in cynomolgus monkeys were assessed. Anti-CD30-MCC-DM1 was effective in in vitro cell death assays using CD30-positive lymphoma cell lines. We studied the properties of anti-CD30-MCC-DM1, including binding, internalization, drug release and actions. Unlike ADCETRIS, anti-CD30-MCC-DM1 did not cause a bystander effect in this study. In vivo, anti-CD30-MCC-DM1 was found to be capable of inducing tumor regression in subcutaneous inoculation of Karpas 299 (anaplastic large cell lymphoma), HH (cutaneous T-cell lymphoma) and L428 (Hodgkin's disease) cell models. The half-lives of 4 mg/kg and 12 mg/kg anti-CD30-MCC-DM1 were about 5 days in cynomolgus monkeys, and the tolerated dose was 30 mg/kg in non-human primates, supporting the tolerance of anti-CD30-MCC-DM1 in humans. These results suggest that anti-CD30-MCC-DM1 presents efficacy, safety and PK profiles that support its use as a valuable treatment for CD30-positive hematological malignancies.

Study on the Heterogeneity of T-DM1 and the Analysis of the Unconjugated Linker Structure under a Stable Conjugation Process

Trastuzumab emtansine (T-DM1) is a target-specific anticancer antibody-drug conjugate (ADC). In the present study, critical quality attributes for different manufactured products, such as the drug to antibody ratio (DAR), conjugation site, and site conjugation ratio, are similar, which is contrary to the traditional view that conjugation at lysine sites is randomly assigned. To investigate this result, a series samples with different DARs were prepared. Site conjugation ratios of the 27 different conjugation sites (corresponding to 54 potential sites) were analyzed. We found that the correlation coefficients of the 26 site conjugation ratio and the DAR were R ² > 0.9, and the remaining one was R ² > 0.7. By comparing three batches of samples with a DAR value of ∼3.3 in a stability study, we found that degradation rates of conjugation sites of the samples incubated at 40 °C were basically the same. These data show that the conjugation ratio and the conjugation stability of each site may remain consistent if the process parameters are stable. LC/MS/MS was used to study the unconjugated linker of the crosslink byproducts produced by a two-step method. We determined four forms of unconjugated linkers: (N-maleimidomethyl) cyclohexane-1-carboxylate (MCC) unconjugated to DM1, hydrolyzed MCC unconjugated to DM1, lys-MCC-lys, and lys-MCC-cys. We believe that the current study can provide an effective guide for the processing of ADCs, control of product quality, and reduction of side reaction products.