Antibody-Drug Conjugate (ADC) Analysis with the Agilent ProteoAnalyzer System

Significance of the topic

Capillary electrophoresis with sodium dodecyl sulfate (CE-SDS) is a high-resolution analytical platform for characterizing antibody-drug conjugates (ADCs). ADC critical quality attributes (CQAs) such as heterogeneity, fragment composition, monomeric purity, and drug-to-antibody ratio (DAR) directly affect safety and efficacy. Reliable CE-SDS workflows accelerate ADC development, support lot release and stability testing, and complement orthogonal methods (for example hydrophobic interaction chromatography and mass spectrometry) to deliver a comprehensive molecular picture.

Objectives and overview of the study

This application note evaluates the Agilent ProteoAnalyzer system for CE-SDS analysis of both cysteine- and lysine-conjugated ADCs. Goals were to demonstrate the system’s resolving power, sizing and quantification precision, and ability to report characteristic fragment patterns under reduced and nonreduced conditions. Representative commercial materials (SigmaMab standard and ADC mimic, Trastuzumab and two Trastuzumab-based ADCs) were analyzed to illustrate method performance and interpretive strategies for ADC CQAs.

Methodology

• Samples: SiLu SigmaMab Universal Antibody Standard, SigmaMab ADC Mimic, Trastuzumab, Trastuzumab deruxtecan (cysteine-linked), and Trastuzumab emtansine (T-DM1, lysine-linked).
• Sample preparation: Reconstituted to 10 mg/mL and diluted to 1.5 mg/mL; protein concentration confirmed by NanoDrop (Protein A280; extinction coefficient 14.3).
• CE-SDS conditions: Analyses performed under both reducing and nonreduced conditions following Agilent Protein Broad Range P240 kit procedures. Samples were covalently labeled and incubated at 70 °C for 10 minutes. For nonreduced runs, injection parameters were adjusted (7 kV, 6 s) for optimal separation. The ProteoAnalyzer Broad Range kit lower marker (LM) only method was used for acquisitions.
• Size calibration: NIST mAb was used as an external ladder for sizing nonreduced species to correct migration shifts due to secondary structure.

Used instrumentation

• Agilent ProteoAnalyzer system (parallel capillary CE-SDS platform).
• Agilent Protein Broad Range P240 kit (p/n 5191-6640).
• NIST monoclonal antibody standard used as size ladder.
• NanoDrop spectrophotometer for protein concentration verification.

Key results and discussion

• Resolution and precision: The ProteoAnalyzer resolved closely related ADC fragments and delivered high reproducibility. Reported sizing precision for triplicate runs was better than 2.5% CV and quantification precision below 10% CV across tested samples.
• Cysteine-conjugated ADCs (reduced): Reduced CE-SDS showed expected LC and HC peaks and, in some cases, partial separation of unconjugated light chain (L0) and singly loaded light chain (L1). The degree of separation depended on payload properties and antibody conformation.
• Cysteine-conjugated ADCs (nonreduced): Nonreduced electropherograms revealed fragment patterns characteristic of positional isomers—L, H, HL, HH, HHL and intact HHLL species. These fragments reflect dissociation patterns in SDS caused by blocked interchain disulfides where drugs occupy cysteine sites. Use of the NIST mAb ladder enabled assignment of apparent molecular weights (for example an intact mAb ~150 kDa; L ~25–35 kDa; HH ~100 kDa; HHL ~125–131 kDa depending on sample).
• Lysine-conjugated ADCs (T-DM1): Under nonreduced CE-SDS, lysine-linked ADCs typically retain disulfide connectivity and produce electropherograms resembling unconjugated mAbs, enabling robust monomeric purity assessment. Reduced analysis of T-DM1 revealed additional higher-molecular-weight species (approximately 75, 100, and 125 kDa) consistent with nondisulfide covalent crosslinks formed during conjugation/manufacturing. The reported DAR distribution for T-DM1 is heterogeneous (0–8) with an average around 3.5, which can influence dye-binding efficiency and detection sensitivity.
• Analytical caveats: High DAR for lysine conjugates can reduce available dye-reactive lysines and thus diminish CE-SDS signal if labeling chemistry targets lysine residues. CE-SDS alone may not fully resolve DAR positional isomers; combining CE-SDS with HIC and mass spectrometry enables comprehensive DAR and payload location characterization.

Benefits and practical applications of the method

• Fast, high-resolution separation of ADC species enables monitoring of manufacturing-induced heterogeneity and process-related impurities.
• Quantitative sizing and relative concentration data support lot release, stability testing, and formulation comparability studies.
• Compatibility with standard protein ladders (NIST mAb) allows size calibration across nonreduced separations where secondary structure affects migration.
• Parallel-capillary operation increases throughput for development and QC laboratories handling multiple ADC samples.

Future trends and potential applications

• Integration with mass spectrometry (CE‑MS) to directly link fragment masses and payload identities for definitive DAR and positional isomer mapping.
• Improved fluorescent labeling chemistries that are less dependent on lysine availability to maintain sensitivity for high-DAR lysine-linked ADCs.
• Higher-throughput microfluidic CE-SDS formats and further automation to support biomanufacturing scale-up and routine QC testing.
• Advanced data analysis, including machine-learning algorithms to deconvolute complex electropherograms and predict positional isomer distributions from fragment patterns.
• Expanded application to novel conjugation chemistries (site-specific enzymatic linkers, engineered cysteine or non-natural amino acid sites) requiring tailored calibration and interpretation approaches.

Conclusions

The Agilent ProteoAnalyzer system provides robust CE-SDS workflows for ADC characterization, delivering high resolution and reproducible sizing and quantification for both cysteine- and lysine-conjugated ADCs. Reduced and nonreduced analyses yield complementary information: reduced runs facilitate LC/HC and payloaded-light-chain discrimination, while nonreduced runs reveal interchain fragment distributions and positional isomers. CE-SDS is an effective component of an orthogonal analytical toolbox for ADC development and QC when used alongside HIC and mass spectrometry.

References

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