The combination of MALDI-2 and timsTOF fleX brings targeted drug imaging to the next level

Importance of the Topic

The development of advanced imaging techniques for drug metabolism and pharmacokinetics (DMPK) is essential to accelerate drug discovery and optimize therapeutic strategies. Matrix-assisted laser desorption/ionization (MALDI) imaging enables spatially resolved, label-free analysis of drug distribution in tissues. However, conventional MALDI often suffers from limited sensitivity and ion suppression effects, restricting its applicability to low-abundance compounds and metabolites. The integration of laser-induced post-ionization (MALDI-2) with the timsTOF fleX platform addresses these challenges by dramatically enhancing ion yields and expanding the detectable chemical space, offering a powerful tool for targeted drug imaging in preclinical studies.

Study Objectives and Overview

This study aimed to quantify the practical benefits of MALDI-2 for targeted drug imaging in tissue sections. Key objectives included:

• Establishing the sensitivity enhancement of MALDI-2 for a set of standard drug compounds using a dilution series on control liver tissue.
• Demonstrating the translation of this sensitivity gain to dosed biological samples (rat liver and kidney) for two drugs: chloroquine and a novel compound referred to as BI-YYY.
• Assessing the ability of MALDI-2 to reveal metabolites that are undetectable by traditional MALDI imaging.

Methodology

Drug standards (caffeine, chloroquine, rosuvastatin, BI-YYY, reserpine) were prepared in dilution series (1–100 µM) and spotted onto 10 µm fresh-frozen rat liver sections. For in vivo experiments, rats were dosed orally with chloroquine (100 mg/kg) or BI-YYY (120 mg/kg) and sacrificed 24 h or 2 h post-dose, respectively. Liver and kidney tissues were cryosectioned (10 µm), mounted, coated with a DHAP matrix (20 layers via TM-sprayer), and scanned for reference imaging. MALDI Imaging data were acquired in positive ion mode (m/z 100–2000) with 50 µm pixel size, 1 kHz laser repetition, and 30 laser shots per pixel. Comparative imaging was performed by toggling the MALDI-2 laser on and off.

Instrumentation

• timsTOF fleX mass spectrometer with dual ESI/MALDI and MALDI-2 capability
• Bruker TissueScout slide scanner
• HTX TM-sprayer for matrix application
• SCiLS Lab software for image visualization and data extraction
• BioTransformer for in silico metabolism prediction
• Metaboscape 2021 (preliminary) for metabolite annotation workflows

Main Findings and Discussion

The MALDI-2 approach yielded a substantial sensitivity boost across all tested compounds in the standard dilution series. Fold increases in mean peak intensity were observed as follows: caffeine (11×), chloroquine (200×), rosuvastatin (40×), BI-YYY (300×), and reserpine (37×).

In tissue imaging of dosed rats:

• Chloroquine showed a 6-fold higher signal in kidney and 5-fold higher in liver under MALDI-2 relative to MALDI.
• BI-YYY exhibited an 8.5-fold signal increase in kidney and 6-fold in liver with MALDI-2.

Moreover, several chloroquine metabolites that were undetectable or barely visible by conventional MALDI were clearly localized and quantified with MALDI-2, providing new insights into drug biotransformation and distribution.

Benefits and Practical Applications

• Enhanced detection limits enable visualization of low-abundance drugs and metabolites, critical for early-stage DMPK investigations.
• Reduced ion suppression and broader chemical coverage allow imaging of analytes such as sterols, hormones, vitamins, and glycans.
• Improved spatial resolution of drug distribution supports better physiological context and mechanistic understanding.
• Label-free targeted imaging streamlines workflow without the need for isotopic or fluorescent tagging.

Future Trends and Potential Applications

Ongoing developments may include quantitative MALDI-2 protocols, integration with ion mobility separation for enhanced specificity, and expanded use in spatial omics workflows that combine lipidomics, metabolomics, and proteomics. Advances in data analysis, including machine learning–driven annotation and real-time imaging, will further improve throughput and interpretability. The translation of MALDI-2 to clinical diagnostics and high-throughput screening platforms represents an exciting avenue for personalized medicine and biomarker discovery.

Conclusion

The coupling of MALDI-2 with timsTOF fleX significantly elevates the sensitivity and scope of targeted drug imaging. This enhanced performance facilitates detailed mapping of parent drugs and their metabolites in tissue, addressing critical needs in DMPK research and paving the way for innovative applications in pharmaceutical development and translational science.

References

• Soltwisch J et al. Mass spectrometry imaging with laser-induced postionization. Science. 2015;348:211–215.
• Barré FPY et al. Enhanced Sensitivity Using MALDI Imaging Coupled with Laser Postionization (MALDI-2) for Pharmaceutical Research. Anal Chem. 2019;91:10840–10848.
• Djoumbou-Feunang Y et al. BioTransformer: a comprehensive computational tool for small molecule metabolism prediction and metabolite identification. J Cheminform. 2019;11(1):2.