Improving spatially resolved analysis of tissue sections for DMPK and toxicity studies

Small molecule focused applications of MSI range from drug metabolism and pharmacokinetic (DMPK) studies in drug discovery, tissue classification in molecular histopathology, to determination of pesticides on plant material. Tissue classification in assisted histology based on differences in molecular composition of the tissue types analysed often does not require analyte identification. Annotation of the features causing the differences in statistical models based on the accurate mass is often sufficient. DMPK and toxicity studies, which have the aim to map the distribution of single compounds such as pharmaceuticals or biomarkers require confirmation of identity for the observed feature.

The most commonly used MSI techniques are secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and desorption electrospray ionization - mass spectrometry (DESI-MS). The main difference between these techniques is the ionization process. In SIMS primary ions or ion clusters are directed onto the sample surface resulting in ablation of the surface and formation of secondary analyte ions. MALDI requires a matrix to be applied to the sample surface that absorbs light emitted by the laser at a wavelength in the UV range. The absorption of the UV light results in rapid evaporation and emission of matrix and analyte ions from the surface of the sample. DESI uses a sprayer to form primarily charged droplets. High voltage is applied to a solvent and nebulized using a gas-flow. Charged droplets colliding with the sample surface dissolve compounds and lead to formation of secondary droplets carrying the compounds to the mass spectrometer inlet.

The aim of the project is to improve existing and develop new methods for identification, validation and quantification of compounds within tissue sections to improve spatially resolved tissue analysis. The refined and newly developed methods will be validated against established methods such as LC-MS analysis, laser dissection micro capturing or coating with isotopically labelled compounds.