Analysis of an Antibody-Drug Conjugate on a Novel Benchtop MALDI-TOF/TOF Platform

Importance of the Topic

Antibody–drug conjugates (ADCs) are a rapidly growing class of targeted cancer therapeutics combining monoclonal antibodies with potent cytotoxic payloads. Precise determination of the drug-to-antibody ratio (DAR) and drug distribution among antibody subunits is crucial for quality control, efficacy, and safety during ADC development and manufacturing.

Study Objectives and Overview

This study evaluates three sample preparation workflows for Ado-trastuzumab emtansine (KADCYLA®) prior to MALDI-TOF/TOF analysis to identify the most reliable method for DAR determination:

• Workflow 1 (W1): Reduction only
• Workflow 2 (W2): Deglycosylation followed by reduction
• Workflow 3 (W3): Deglycosylation, IdeS digestion, then reduction

The goal is to achieve well-resolved mass spectra of light and heavy chain subunits, enabling accurate calculation of DAR via peak area ratios.

Methodology and Instrumentation

Samples were processed using a 30 kDa MWCO ultracentrifugation filter and the following reagents:

• Deglycosylation: IgGZERO (Genovis; 1 U/µg protein, 37 °C, 30 min)
• Digestion: FabRICATOR (IdeS, Genovis; 1 U/µg protein, 37 °C, 30 min)
• Reduction: 50 mM TCEP, 50 °C, 1 hr
• Sample cleanup: C4 ZipTips; elution with 30% ACN/0.1% TFA; matrix: 2,5-DHAP
• Mass spectrometer: Bruker neofleX MALDI-TOF/TOF in positive linear mode

Main Results and Discussion

Workflow 1 produced incompletely resolved glycosylated heavy chain peaks, yielding a low DAR (3.61) and poor reproducibility. Workflow 3 improved mass accuracy by splitting the heavy chain into Fc/2′ and Fd′ fragments, but overlap between high-DAR light chain species and low-DAR Fd′ fragments hindered precise quantification. Workflow 2 delivered well-resolved, reproducible peaks for both chains, with an average DARdegly = 3.90 (replicates 3.88 and 3.92), consistent with reported values for trastuzumab-emtansine.

Benefits and Practical Applications

The optimized W2 method offers:

• Rapid acquisition of subunit mass spectra by MALDI-TOF/TOF
• Accurate and reproducible DAR determination aligned with theoretical expectations
• A simplified sample preparation workflow suitable for routine QC of ADC batches

Future Trends and Opportunities

Advancements may include automation of deglycosylation and reduction steps, integration with high-throughput MALDI platforms, and extension to diverse ADC formats and payload chemistries. Combining MALDI-TOF/TOF with ion mobility or top-down MS may further enhance subunit resolution and structural characterization.

Conclusion

Deglycosylation followed by reduction (Workflow 2) on a benchtop MALDI-TOF/TOF platform provides the most robust approach for rapid, accurate DAR analysis of trastuzumab-emtansine. This streamlined workflow supports quality control and process development in ADC research and production.