Visualization of Gefitinib and Related Metabolites in Rat Liver Using DESI-Tandem Quadrupole Mass Spectrometry

Significance of the topic

The spatial mapping of parent drugs and their metabolites in tissue is a critical component of preclinical drug discovery and development. Localized tissue concentrations inform on organ penetration, accumulation, potential off-target effects, and support interpretation of pharmacokinetics and toxicology. Mass spectrometry imaging (MSI) approaches that do not require radiolabeled compounds expand applicability to early discovery studies, reduce additional animal use, and enable simultaneous visualization of drug-related species and endogenous biomarkers.

Objectives and study overview

This application note demonstrates a targeted DESI (desorption electrospray ionization) MSI workflow using tandem quadrupole mass spectrometry in multiple reaction monitoring (MRM) mode to visualize gefitinib and related metabolites in frozen rat liver sections after a single subcutaneous dose. The goals were to show implementation of DESI imaging on a Xevo TQ Absolute XR instrument, to detect drug and metabolite spatial distributions at discovery-relevant doses, and to compare tissue temporal profiles with plasma pharmacokinetics.

Methodology

• In vivo: Male Sprague Dawley rats (175–225 g) dosed subcutaneously with gefitinib 10 mg/kg or vehicle; livers collected at 0, 1, 3, 8 and 24 h post-dose.
• Tissue preparation: Fresh-frozen liver cryosectioned to 10 µm, thaw-mounted on standard glass slides and dessicated prior to analysis.
• DESI-MSI acquisition: Positive ion DESI-ESI on a Xevo TQ Absolute XR tandem quadrupole operating in targeted MRM mode. Imaging parameters included 60 µm pixel size, nominal 30 µm spray diameter, spray impact angle ≈75°, sprayer-to-surface distance 2 mm, acquisition speeds 1 and 10 Hz. Specific MRM transitions were used for gefitinib and multiple putative metabolites.
• Data handling: MassLynx control and targeted imaging processed with High Definition Imaging (HDI) software.

Used instrumentation

• Xevo TQ Absolute XR tandem quadrupole mass spectrometer.
• DESI XS source configured for positive ion DESI-ESI imaging.
• MassLynx software for MS control and HDI software for image visualization.

Main results and discussion

• Detection: Gefitinib and seven drug-related metabolites were detected in liver sections using MRM DESI-MSI. No drug-related signals were observed in vehicle or predose samples.
• Prominent species: The putative N‑oxide metabolite (M594577) produced the strongest signal, followed by the parent drug gefitinib and the morpholino carbonyl metabolite (M605211).
• Temporal profile: Gefitinib and the major metabolites showed a clear time-dependent distribution—highest intensities at 1–3 h post-dose, declining by 8 h and weak or low-level presence at 24 h—consistent with plasma pharmacokinetic data (peak plasma concentration ~6 h, t1/2 ≈6.5 h reported previously).
• Low-abundance metabolites: Several secondary metabolites (e.g., ring-opened, O‑demethylated and dihydroxylated species) were observed at low intensity or only at later time points, suggesting either low hepatic abundance or concentrations below the method’s detection limit in tissue.
• Analytical performance: Targeted MRM acquisition on a triple quadrupole provided enhanced sensitivity and selectivity versus untargeted high-resolution methods in the presence of complex tissue background and low discovery-level doses (1–10 mg/kg). The MS source swap to DESI required minimal instrument downtime (<30 minutes), enabling rapid transition from routine LC-MS workflows to imaging.

Practical benefits and uses of the method

• Non‑radiolabeled spatial mapping: Enables tissue distribution studies without synthesis of radiolabeled drug, accelerating early discovery and aligning with 3Rs principles by avoiding additional dedicated radiolabel studies.
• Workflow integration: Simple implementation on existing triple quadrupole platforms supports a rapid targeted imaging pipeline from discovery metabolite profiling to tissue localization.
• Targeted sensitivity and specificity: MRM imaging allows unambiguous detection of parent drug and known metabolites at pharmacologically relevant concentrations amid endogenous and vehicle-derived background ions.
• Support for ADME and safety: Spatial data complement plasma/tissue quantitative assays to inform on local exposure, potential accumulation sites, and correlations with histopathology or biomarker changes.

Conclusions

DESI-MSI performed in MRM mode on a tandem quadrupole instrument enables sensitive, selective visualization of gefitinib and multiple metabolites in rat liver following a single subcutaneous dose. The approach reproduced a time-dependent tissue distribution consistent with plasma pharmacokinetics, identified major and minor metabolites with differing abundances, and demonstrated that targeted DESI-MRM is a practical tool for tissue localization studies without radiolabeling.

Future trends and potential applications

• Quantitative imaging: Combining targeted MRM imaging with tissue calibration approaches and correlative LC-MS/MS to deliver more quantitative spatial maps.
• Multimodal integration: Correlating DESI-MSI with histology, autoradiography where available, and other imaging modalities (e.g., MALDI-MSI, IMS) for comprehensive tissue pharmacology studies.
• Expanded targeted panels: Development of standardized MRM panels for families of drugs to streamline discovery workflows and inter-study comparability.
• Improved sensitivity and throughput: Hardware and software advances to lower limits of detection and increase imaging speed for larger cohorts and whole-organ studies.
• Data analytics: Automated image alignment, co-registration with histology, and statistical spatial analysis to link local drug/metabolite distributions with efficacy or toxicity endpoints.
• Application space: Use in ADME profiling, safety assessment, biomarker co-localization, and support of translational studies where radiolabeling is impractical.

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