High-throughput Analysis of DNA-Modifying Enzymes by an Agilent RapidFire System

Importance of the Topic

Epigenetic and DNA repair processes are central to cancer biology and drug discovery pipelines. High-throughput, quantitative assays that monitor these enzymatic modifications directly on native DNA accelerate the identification of novel therapeutic agents and reduce artefacts associated with labels or probes.

Objectives and Study Overview

This work demonstrates the application of the Agilent RapidFire High-throughput Mass Spectrometry System for label-free, multiplexed analysis of DNA-modifying enzymes. Two model systems are explored: the AlkB enzyme responsible for repair of ethenoadenine lesions, and the SssI DNA methyltransferase catalysing cytosine methylation. A small-molecule inhibitor screen is also presented.

Applied Methodology and Instrumentation

The RapidFire platform integrates microfluidic solid-phase extraction with time-of-flight mass spectrometry to deliver sample-to-sample cycle times of approximately 8 seconds, enabling analysis of over ten thousand samples per day directly from 96- or 384-well plates without offline processing.

Applied Instrumentation

• Agilent RapidFire high-throughput MS system
• Microfluidic solid-phase extraction module
• Time-of-flight mass spectrometer
• Standard 96- and 384-well plate formats

Main Results and Discussion

In the AlkB assay, direct MS detection resolved the native substrate, two repair intermediates (epoxide and glycol) and the final adenine product over time, revealing basal intermediate levels and accurate kinetic profiles. In the SssI methylation assay, all nine methylation states of a 24-mer duplex were quantified, with five methylations predominating and differential site kinetics evident. A concentration–response curve for the inhibitor S-adenosylhomocysteine yielded an IC50 of ~14 micromolar. A screen of 384 bioactive compounds identified eight hits, notably substituted quinolones consistent with known MTase inhibitors.

Benefits and Practical Applications

• Label-free detection of native DNA substrates and products
• Multiplex analysis of substrates, intermediates and products in a single run
• Elimination of time-consuming substrate labelling or antibody development
• High throughput (>10 000 samples/day) with minimal sample preparation
• Quantitative normalization using internal standards and percentage conversion metrics

Future Trends and Opportunities

The platform’s throughput and multiplex capacity position it for integration into large-scale screening campaigns. Extensions may include analysis of additional DNA and RNA modifying enzymes, coupling with high-resolution MS or ion mobility, miniaturization to nanoliter volumes and application of machine learning to kinetic data interpretation.

Conclusion

The Agilent RapidFire TOF-MS approach provides a rapid, robust and label-free workflow for comprehensive analysis of DNA-modifying enzymes. It delivers detailed mechanistic insights and supports high-throughput inhibitor discovery without compromise to data quality.

References

1. Kelley MR, Fishel ML. DNA Repair Proteins as Molecular Targets for Cancer Therapeutics. Anticancer Agents Med Chem. 2008;8(4):417–425.
2. Mishra MV et al. DNMT1 as a Molecular Target in a Multimodality-Resistant Phenotype in Tumor Cells. Mol Cancer Res. 2008;6(2):243–249.
3. Koike K et al. Anti-Tumor Effect of AlkB Homolog 3 Knockdown in Hormone-Independent Prostate Cancer Cells. Curr Cancer Drug Targets. 2012;12(7):847–856.
4. Pan Z et al. Impaired Placental Trophoblast Lineage Differentiation in Alkbh1(-/-) Mice. Dev Dyn. 2008;237(2):316–327.
5. Delaney JC et al. AlkB Reverses Etheno DNA Lesions Caused by Lipid Oxidation in vitro and in vivo. Nat Struct Mol Biol. 2005;12(10):855–860.
6. Phiasivongsa P et al. Quinoline Derivatives for Modulating DNA Methylation. Patent Appl 20110256092. 2011.