Sensitive LC-MS/MS Bioanalytical Quantitation of Antisense Oligonucleotides

Importance of the Topic

Antisense oligonucleotides represent a rapidly expanding class of therapeutic agents and research tools. Their precise quantitation in biological matrices is critical for pharmacokinetic evaluation, safety assessments, and therapeutic monitoring. Analytical challenges such as low endogenous concentrations, strong nonspecific binding, and complex sample matrices require highly sensitive and robust methods.

Objectives and Study Overview

This application note details a bioanalytical method for both quantitative and qualitative measurement of antisense oligonucleotides in human plasma. The primary goals were to establish low limits of quantification (LLOQs), broad linear dynamic range, and reliable recovery rates using a tandem quadrupole mass spectrometer coupled with advanced UPLC technology.

Methodology and Instrumentation

Sample preparation involved liquid–liquid extraction from human plasma using phenol:chloroform:isoamyl alcohol followed by chloroform, drying, and reconstitution in EDTA solution. Chromatographic separation was performed on a Waters ACQUITY Premier UPLC System equipped with a Premier Oligonucleotide C18 column (1.7 μm, 2.1 × 50 mm). Mobile phases comprised 100 mM hexafluoroisopropanol and 15 mM DIPEA in water (A) and in 80% acetonitrile (B), delivered at 0.5 mL/min with a 5-minute gradient (5–80% B). The Xevo TQ Absolute mass spectrometer operated in negative-ion electrospray mode using multiple reaction monitoring. Key instrument parameters included a 2.5 kV capillary voltage, 600 °C desolvation temperature, and collision gas flow of 0.15 mL/min.

Main Results and Discussion

High-performance surfaces (MaxPeak HPS) in both the UPLC system and column minimized nonspecific binding to metal surfaces, improving analyte recovery and sensitivity. Representative spectra demonstrated clear charge-state clusters and fragment ions for a 25-mer phosphorothioated antisense (GEM91). The method achieved an LLOQ of 0.1 ng/mL and a linear dynamic range from 0.1 to 10,000 ng/mL (r2 > 0.99, 1/x2 weighting). Quality control samples showed mean accuracies of 90–114% and coefficients of variation below 10.5%. Multiple MRM transitions provided flexibility to select the most selective and sensitive ion pairs in complex plasma backgrounds.

Benefits and Practical Applications

• Demonstrated sub-ng/mL quantitation of antisense oligonucleotides in human plasma
• Broad five-order linear dynamic range for pharmacokinetic studies
• Robust recovery and minimized adsorption through HPS technology
• Flexibility to choose optimal MRM transitions for selectivity in different matrices

Future Trends and Potential Applications

Further improvements in ion source design and surface coatings are expected to lower detection limits and simplify sample preparation. The workflow may be extended to other nucleic acid modalities such as siRNA, microRNA, and modified oligonucleotides. High-throughput automation and integration with data-rich informatics will streamline preclinical and clinical bioanalysis.

Conclusion

The combination of the Waters Xevo TQ Absolute mass spectrometer and ACQUITY Premier UPLC with MaxPeak HPS surfaces delivers a highly sensitive, robust, and flexible platform for bioanalytical quantitation of antisense oligonucleotides in human plasma. This approach meets the stringent requirements for routine pharmacokinetic and bioavailability studies.

References

1. Guilherme J. Guimaraes et al Impact of nonspecific adsorption to metal surfaces in ion pair-RP LC-MS impurity analysis of oligonucleotides Journal of Pharmaceutical and Biomedical Analysis 2022 208 114439
2. Jennifer M. Nguyen et al Assessing the impact of nonspecific binding on oligonucleotide bioanalysis Future Science Bioanalysis 2021 13(16)
3. Kathryn Brennan Mary Trudeau Paul D. Rainville Utilization of the ACQUITY Premier System and Column for improved oligonucleotide bioanalytical chromatographic performance Waters Application Note 720007119 January 2021