NOVEL TARGETED DESI MRM TQ SYSTEM PROVIDING INCREASED SENSITIVITY AND ACQUISITION SPEED FOR MASS SPECTROMETRY IMAGING

Significance of the Topic

The ability to detect low-abundance drugs and metabolites directly in tissue is crucial for understanding biodistribution, pharmacokinetics, and biomarker discovery in pharmaceutical and clinical research. DESI-MRM on a tandem quadrupole system combines high specificity with rapid acquisition, enabling targeted mass spectrometry imaging (MSI) with enhanced sensitivity.

Objectives and Study Overview

This work aimed to evaluate a novel DESI source coupled to a triple quadrupole mass spectrometer operating in multiple reaction monitoring (MRM) mode for:

• Determining limits of detection (LODs) for a set of pharmaceutical compounds on tissue
• Imaging the distribution of gefitinib and its metabolites in dosed mouse liver sections

Methodology and Instrumentation

Several pharmaceuticals (chloroquine, propranolol, olanzapine, erlotinib, moxifloxacin, terfenadine, irinotecan) were spotted in tenfold dilution series on porcine liver sections. Gefitinib was administered intravenously to mice (10 mg/kg), with livers harvested at 0.5, 1, 3, 8, and 24 hours post-dose. Tissue sections (18 μm) were analyzed using a DESI XS source with a High-Performance sprayer on a triple quadrupole mass spectrometer in positive ion mode. Acquisition parameters included flow rate 2 μL/min (95:5 MeOH:water), nebulizing gas pressure 10–15 psi, capillary voltage 0.55–0.8 kV, pixel sizes 15–75 μm, and scan rates 5–50 Hz. MRM transitions were optimized using standards and transferred from UHPLC-MS/MS studies. Data were processed with MassLynx, HDI software, and MetaboAnalyst for ROI intensity analysis.

Main Results and Discussion

• Targeted DESI-MRM imaging achieved sub-1 μM LODs for all tested compounds, with terfenadine reaching 0.022 μM.
• Chloroquine was detected at 0.3 μM with S/N>14 at both 10 Hz and 50 Hz, demonstrating high-speed acquisition had minimal impact on sensitivity.
• In mouse liver, gefitinib exhibited S/N~2,500 and was 15–20 times more intense than its most abundant metabolite (M11). Ten out of 16 known metabolites were detected and spatially resolved across the post-dose timepoints, with intensity trends reflecting pharmacokinetic profiles.

Benefits and Practical Applications

• High sensitivity and specificity of MRM enable detection of low-level analytes in complex tissues without extensive sample preparation.
• Rapid acquisition (up to 50 Hz) supports high-throughput imaging workflows.
• Direct translation of traditional DMPK transitions to imaging facilitates integrated pharmacokinetic and spatial distribution studies.

Future Trends and Opportunities

Emerging developments may include:

• Integration of multiplexed MRM methods for broader panels of biomarkers and drugs.
• Automation of data processing pipelines for real-time imaging and quantitative analysis.
• Combining DESI-MRM with ion mobility for additional separation and specificity.
• Application to clinical tissue biopsies for personalized medicine and diagnostics.

Conclusion

This study demonstrates that DESI-MRM on a triple quadrupole platform provides a powerful approach for sensitive and rapid mass spectrometry imaging of drugs and metabolites in tissues. The method achieves low micromolar detection limits, supports high-throughput acquisition, and effectively translates targeted DMPK assays to spatially resolved analyses.

References

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