In-Depth Structure and Function Characterization of Heterogeneous Interchain Cysteine-Conjugated Antibody-Drug Conjugates

Kinetic Modeling of the Antibody Disulfide Bond Reduction Reaction With Integrated Prediction of the Drug Load Profile for Cysteine-Conjugated ADCs

Antibody-drug conjugates (ADC) constitute a groundbreaking advancement in the field of targeted therapy. In the widely utilized cysteine conjugation, the cytotoxic payload is attached to reduced interchain disulfides which involves a reduction of the native monoclonal antibody (mAb). This reaction needs to be thoroughly understood and controlled as it influences the critical quality attributes (CQAs) of the final ADC product, such as the drug-to-antibody ratio (DAR) and the drug load distribution (DLD). However, existing methodologies lack a mechanistic description of the relationship between process parameters and CQAs. In this context, kinetic modeling provides comprehensive reaction understanding, facilitating the model-based optimization of reduction reaction parameters and potentially reduces the experimental effort needed to develop a robust process. With this study, we introduce an integrated modeling framework consisting of a reduction kinetic model for the species formed during the mAb reduction reaction in combination with a regression model to quantify the number of conjugated drugs by DAR and DLD. The species formed during reduction will be measured by analytical capillary gel electrophoresis (CGE), and the DAR and DLD will be derived from reversed-phase (RP) chromatography. First, we present the development of a reduction kinetic model to describe the impact of reducing agent excess and reaction temperature on the kinetic, by careful investigation of different reaction networks and sets of kinetic rates. Second, we introduce a cross-analytical approach based on multiple linear regression (MLR), wherein CGE data is converted into the RP-derived DAR/DLD. By coupling this with the newly developed reduction kinetic model, an integrated model encompassing the two consecutive reaction steps, reduction and conjugation, is created to predict the final DAR/DLD from initial reduction reaction conditions. The integrated model is finally utilized for an in silico screening to analyze the effect of the reduction conditions, TCEP excess, temperature and reaction time, directly on the final ADC product.

Imaged capillary isoelectric focusing method development for charge variants of high DAR ADCs

BACKGROUND

Charge heterogeneity is a critical quality attribute for therapeutic biologics including antibody-drug conjugates (ADCs). Developing an ion exchange chromatography (IEX) or an imaged capillary isoelectric focusing (icIEF) method for ADCs with high drug-to-antibody ratio (DAR) is challenging because of the increased hydrophobicity from the payload-linker, DAR heterogeneity, and payload-linker instability. A sub-optimal method can be poorly stability-indicating due to the inability to discern contributions from charge and size variants conjugated with different number of drugs/payloads. Systematic strategy and guidance on charge variant method development is highly desired for high DAR ADCs with various complex structures.

RESULTS

This work encompasses the development and optimization of icIEF methods for high DAR ADCs of various DAR values (4-8) and payload linker chemistry. Method optimization focuses on improving resolution and stability indicating capabilities and differentiating contributions from the protein and payload-linker. Types, proportion, and combination of solubilizers and carrier ampholytes, as well as focusing parameters were interrogated. Our findings show that the structural units of the linker, the DAR, and the payload chemistry prescribe the selection of buffer, solubilizer, and ampholyte. We demonstrate that a stronger denaturant or solubilizer is needed for high DAR ADCs with polyethylene glycol (PEG)-containing linker structure compared to peptide linker. For unstable payload-linker, buffer system enhances sample stability which is vital to method robustness. In addition, a longer isoelectric focusing time is necessary for an ADC than its corresponding antibody to reach optimal focusing.

SIGNIFICANCE

To the best of our knowledge, this is the first comprehensive study on icIEF method development for charge variant determination of high DAR ADCs with unique physicochemical properties.

Recent Technological and Intellectual Property Trends in Antibody-Drug Conjugate Research

Antibody-drug conjugate (ADC) therapy, an advanced therapeutic technology comprising antibodies, chemical linkers, and cytotoxic payloads, addresses the limitations of traditional chemotherapy. This study explores key elements of ADC therapy, focusing on antibody development, linker design, and cytotoxic payload delivery. The global rise in cancer incidence has driven increased investment in anticancer agents, resulting in significant growth in the ADC therapy market. Over the past two decades, notable progress has been made, with approvals for 14 ADC treatments targeting various cancers by 2022. Diverse ADC therapies for hematologic malignancies and solid tumors have emerged, with numerous candidates currently undergoing clinical trials. Recent years have seen a noteworthy increase in ADC therapy clinical trials, marked by the initiation of numerous new therapies in 2022. Research and development, coupled with patent applications, have intensified, notably from major companies like Pfizer Inc. (New York, NY, USA), AbbVie Pharmaceuticals Inc. (USA), Regeneron Pharmaceuticals Inc. (Tarrytown, NY, USA), and Seagen Inc. (Bothell, WA, USA). While ADC therapy holds great promise in anticancer treatment, challenges persist, including premature payload release and immune-related side effects. Ongoing research and innovation are crucial for advancing ADC therapy. Future developments may include novel conjugation methods, stable linker designs, efficient payload delivery technologies, and integration with nanotechnology, driving the evolution of ADC therapy in anticancer treatment.