Characterizing Antibody-Drug Conjugates and Assigning Drug Conjugation Sites

Significance of the topic

Antibody drug conjugates ADCs are an emerging class of biopharmaceuticals that link monoclonal antibodies with cytotoxic drugs for targeted therapy and enhanced efficacy. The structural heterogeneity and complexity of ADCs require high resolution and high peak capacity analytical methods to accurately characterize drug to antibody ratio DAR and conjugation sites indicating safety and efficacy.

Objectives and study overview

This application note demonstrates how comprehensive two dimensional RPLCxRPLC coupled with high resolution quadrupole time of flight MS can be used to map and assign drug conjugation sites on ADCs such as ado trastuzumab emtansine and brentuximab vedotin. The study provides an elegant workflow to detect and identify conjugated peptides in both lysine and cysteine conjugated ADCs.

Methodology and instrumentation

Sample preparation
Reducing and alkylation of ADCs was followed by tryptic digestion using rapigest and trypsin. Detailed conditions include DTT reduction temperature and time and IAA alkylation prior to overnight digestion.
RPLCxRPLC parameters
First dimension was performed on ZORBAX Bonus RP column at pH 8.2 with methanol ACN second dimension on ZORBAX Eclipse Plus C18 at high flow and acidic mobile phases with gradient shifting modulation to enhance orthogonality and peak capacity.
MS and MSMS conditions
An Agilent 6530 QTOF was operated in positive mode with all ions MSMS at 20 and 40 eV to generate diagnostic fragments specific to DM1 and MMAE payloads identified by high resolution extracted ion chromatograms.
Instrumentation

• Agilent 1290 Infinity II 2D LC Solution with high speed pumps multisampler multicolumn thermostat and valve drive
• Agilent 2 position 4 port valve with loops for modulation
• Agilent 6530 Accurate Mass QTOF LC MS system

Major results and discussion

The RPLCxRPLC UV peptide maps at 214 and 252 nm highlighted additional spots for ADC compared to naked antibody. MS MS maps extracted at the characteristic ion m z 547 for DM1 and m z 718 for MMAE confirmed the identity of conjugated peptides. Sites on heavy and light chains were assigned including lysine conjugates and inter and intrachain cysteine conjugates. Trace intrachain modifications in brentuximab samples were detected demonstrating high method sensitivity.

Benefits and practical applications

• Enhanced chromatographic peak capacity and orthogonality improves separation of complex ADC digests
• All ions MS MS detection enables selective recognition of payload fragments without precursor selection
• Site specific identification supports DAR determination batch to batch consistency and QA QC workflows

Future trends and potential uses

The combination of 2D LC and high resolution MS is expected to expand to other ADC formats and designer bioconjugates. Adoption in regulated quality control environments can support rapid characterization and release testing. Further integration with alternative stationary phases and ion mobility may increase robustness and throughput.

Conclusion

Comprehensive RPLCxRPLC combined with QTOF MS provides an elegant and sensitive platform for mapping ADC conjugation sites and determining DAR. Its robustness and high peak capacity make it suitable for detailed biopharmaceutical characterization and potential routine QC implementation.

References

1. Sandra K Vandenheede I Sandra P Modern chromatographic and mass spectrometric techniques for protein biopharmaceutical characterization Journal of Chromatography A 2014 1335 81 103
2. Fekete S et al Chromatographic electrophoretic and mass spectrometric methods for the analytical characterization of protein biopharmaceuticals Analytical Chemistry 2016 88 480 507
3. Panowski S et al Site specific antibody drug conjugates for cancer therapy mAbs 2014 6 34 45
4. Wakankar A et al Analytical methods for physicochemical characterization of antibody drug conjugates mAbs 2011 3 161 172
5. Beck A Reichert JM Antibody drug conjugates mAbs 2014 6 15 17
6. Sandra K Sandra P The opportunities of 2D LC in the analysis of monoclonal antibodies Bioanalysis 2015 7 2843 2847
7. Sandra K et al Multiple heart cutting and comprehensive two dimensional liquid chromatography hyphenated to mass spectrometry for the characterization of the antibody drug conjugate ado trastuzumab emtansine Journal of Chromatography B 2016 1032 119 130
8. Vanhoenacker G et al Comprehensive two dimensional liquid chromatography of therapeutic monoclonal antibody digests Analytical Bioanalytical Chemistry 2015 407 355 366
9. Vanhoenacker G et al Analysis of monoclonal antibody digests with the Agilent 1290 Infinity 2D LC Solution Agilent Application Note 2013
10. Sandra K et al Identifying monoclonal antibody mutation sites using the Agilent 1290 Infinity II 2D LC solution combined with Q TOF LC MS Agilent Application Note 2016