Quantitative Mass Spectrometry Imaging by Targeted-DESI-MSI in MRM Mode Provides Higher Sensitivity and Specificity...

Quantitative mass spectrometry imaging (QMSI) is being applied for spatial quantification of drugs and metabolites using mass spectrometry imaging (MSI) tools. DESI-MSI is ideally suited to QMSI as a soft and ambient ionization technique. However, some challenging issues of QMSI include extraction efficiency, matrix effect, sensitivity, and specificity, which need to be addressed. Here, we applied targeted DESI-MSI in multiple reaction monitoring (MRM) mode for QMSI of chloroquine, an antimalarial drug, as a model in mice kidneys and carefully addressed those challenging issues. A triple quadrupole mass spectrometer coupled with a DESI source was used to quantify the chloroquine (transition m/z 320.2 → 247.1) drug. A deuterated internal standard chloroquine-d₅ (transition m/z 325.2 → 147.1), was used to normalize the data from pixel to pixel. A mimetic in-tissue model was employed to constract a calibration curve demonstrating good linearity (y = 0.0041x, R² = 0.9953) and precision (RSD < 15%). The calibration curve was validated by back-calculation, with results falling within acceptable ranges (accuracy error< ±15%). Finally, the dosed (30 mg/kg) chloroquine was quantified in three spatial regions (cortex, medulla, and pelvis) in the mice kidneys. The highest concentrations of chloroquine in the pelvis (399.85 and 436.28 ng/mg of kidney tissue at 30 and 60 min intervals) region is consistent with the previous report that a portion of the drug is eliminated from the kidney as unchanged forms. This study provides valuable insights into using DESI-MSI in MRM mode for the QMSI of drugs in biological tissues and will have implications for future research on pharmacology and toxicology.