Rapid pharmacokinetic analysis of small drugs by mass spectrometry imaging combined with product ion analysis

Importance of the Topic

Mass spectrometry imaging (MSI) enables label-free localization of drugs and their metabolites directly in tissue sections. Rapid pharmacokinetic profiling in organs like kidney, brain and liver is critical for understanding drug distribution, efficacy, toxicity and off-target effects.

Objectives and Study Overview

This study applied a new MALDI-MSI platform (iMScope QT) combined with product-ion (MS/MS) analysis to map the small drugs imipramine and chloroquine and their major metabolites in mouse tissues two hours after intraperitoneal administration. Key aims were to optimize matrix application and instrument parameters for high sensitivity, spatial resolution and throughput.

Methodology and Instrumentation

Sample Preparation and Acquisition:

• C57BL/6 male mice dosed with imipramine and chloroquine (30 mg/kg IP); organs harvested after 2 h.
• 10 µm sagittal sections of kidney, brain and liver mounted on ITO slides.
• Matrix: Î-CHCA applied as a 0.7 µm film via iMLayer under vacuum.
• MSI: iMScope QT with AP-MALDI source and Q-TOF analyser; positive mode, m/z 150–450; pixel size 50×50 µm; laser diameter 25 µm; 70% power; 100 shots at 1 kHz; detector voltage 2.4 kV; DL temperature 300 °C.
• Data rate: 9–10 spectra/s. MS/MS used for confirmatory identification.

Major Results and Discussion

Detection of Parent Drugs and Metabolites:

• Imipramine metabolites (desdimethyl-, desipramine, 2-hydroxy) detected in kidney, brain and liver; glucuronide conjugate mainly in kidney pelvis.
• Chloroquine and derivatives (desethyl, bis-desethyl, M-(-N(C₂H₅)₂), di-N-oxide) localized with tissue specificity.

Organ Distribution Patterns:

• Kidney: Imipramine and desipramine enriched in cortex and upper medulla; glucuronide in inner medulla and pelvis. Chloroquine and desethylchloroquine in pelvis/medulla; M-(-)2 variant in cortex and outer medulla.
• Brain: Imipramine and metabolites abundant in hindbrain, midbrain, thalamus, hypothalamus and septum. Chloroquine species focused in lateral ventricles, fourth ventricle and fornix.
• Liver: Both drugs and most metabolites present; chloroquine series showed higher hepatic accumulation.

Practical Benefits and Applications

Rapid MSI with iMScope QT allows high-resolution pharmacokinetic mapping without labels. The approach accelerates drug biodistribution studies, aids toxicology assessment and guides dose optimization in preclinical research.

Future Trends and Opportunities

• Extending time-course and dose-response studies for comprehensive PK profiling.
• Integration with quantitative MS imaging to measure absolute concentration gradients.
• Application to other therapeutic compounds, including biologics and drug-carrier systems.
• Advanced MS/MS workflows for untargeted metabolite discovery.

Conclusion

This work demonstrates the capability of a novel MALDI-MSI platform to rapidly and sensitively visualize small drugs and their metabolites across multiple organs. The detailed spatial maps obtained inform on drug metabolism and distribution, supporting safer and more effective therapeutic development.

Used Instrumentation

• iMScope QT (Shimadzu) with atmospheric-pressure MALDI source
• Quadrupole time-of-flight mass spectrometer
• iMLayerTM matrix deposition system