MALDI-FTICR Imaging Mass Spectrometry of Drugs and Metabolites in Tissue

Abstract

A new approach is described for imaging mass spectrometry analysis of drugs and metabolites in tissue using matrix-assisted laser desorption ionization-Fourier transform ion cyclotron resonance (MALDI-FTICR). The technique utilizes the high resolving power to produce images from thousands of ions measured during a single mass spectrometry (MS)-mode experiment. Accurate mass measurement provides molecular specificity for the ion images on the basis of elemental composition. Final structural confirmation of the targeted compound is made from accurate mass fragment ions generated in an external quadrupole-collision cell. The ability to image many small molecules in a single measurement with high specificity is a significant improvement over existing MS/MS based technologies. Example images are shown for olanzapine in kidney and liver and imatinib in glioma.An important phase of drug discovery is determining how a potentially therapeutic compound is distributed and metabolized within the body. Traditional imaging techniques like positron emission tomography, magnetic resonance imaging, and whole-body radiography share a key advantage in their compatibility with living systems but have limited spatial resolution and require molecular or radioisotope tags that do not distinguish molecular forms having the tag. The wide applicability of imaging mass spectrometry (IMS) has been demonstrated in recent studies investigating molecular classes that include peptides, 1-4 proteins, 5-8 and phospholipids. 9-11 IMS also permits the analysis of drugs and metabolites direct from tissue without target specific labels or reagents. [12][13][14][15][16][17] IMS analyses of pharmaceutical compounds present unique analytical challenges. The lowm/z region of a matrix-assisted laser desorption ionization (MALDI) spectrum (less than m/z 1000) contains a large population of ions from compounds endogenous to the tissue sample as well as matrix-related adduct clusters and fragments. Given such a high density of ions, it is inevitable that other species will share the same nominal mass as the target compound and often, as in the case of matrix ions, at substantially different intensities. The mass analyzer must therefore be capable of distinguishing target compounds of interest from this large chemical background. The traditional strategy for MALDI IMS analyses of pharmaceutical compounds is to perform the imaging experiment in MS/MS mode. Essentially, all ions in the range of the targeted precursor are fragmented and the abundance of the target compound is determined from the measured intensity of one or more of its structurally EXPERIMENTAL SECTIONOlanzapine and imatinib tablets were obtained from the Vanderbilt University Hospital Pharmacy. All animal studies were approved by the Institutional Animal Care and Use Committee at Vanderbilt University. Olanzapine Animal ModelOLZ was administered (p.o.) at pharmacologically relevant doses (8 mg/kg) to 10 week-old male Fischer 344 rats. Animals were euthanized at 2 h postdose by isofl...

MALDI In-Source Decay, from Sequencing to Imaging

“…For small molecules analysis, two main classes may be distinguished -exogenous drugs and endogenous metabolites. Exogenous drugs have been studied in MALDI-MSI far later than proteins (since 2004) for different targets such as olanzapine (antipsychotic) [85][86][87], imatinib [87], vinblastine [88], and banoxantrone [89] (cancer drugs). Among endogenous metabolites, lipids such as glycerophospholipids and glycosphingolipids or simple lipids like cholesterol, diacylglycerols, or triacylglycerols have been extensively investigated [90].…”

Vacuum compatible sample positioning device for matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry imaging

“…Moreover, the flexibility of scheduling the stage movement allows for introduction of internal calibrants, 28, 29 thus utilizing both high resolving power and mass accuracy of FT-ICR MS for MSI experiments. 30,31 Reported spatial resolution, although substantially improved, was by no means limited by the device positional accuracy. Reduction of the raster size in oversampling experiments (Figs.…”

Advanced Mass Calibration and Visualization for FT-ICR Mass Spectrometry Imaging

“…MALDI MS imaging platforms are now commercially available, along with a suite of commercial and open-source software tools for image generation. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) [3] offers the highest mass resolving power and mass accuracy for MS imaging experiments and has been used to spatially map neuro-peptides [4], lipids [5][6][7], and small molecules [8,9] from biological tissue sections. Further, orbital trapping FT-MS (i.e., the Orbitrap mass analyzer from Thermo Fisher Scientific) [10] is also seeing increased use for MS imaging of lipids [11][12][13], drugs [14], and peptides [15][16][17].…”

“…In this context, mass calibration is essential for the ultimate chemical specificity of mass spectral images. Cornett et al have employed internal calibration (with respect to matrix related ions) for MALDI imaging of pharmaceuticals (and their metabolites) that resulted in under 1 part-per-million (ppm) standard deviation for olanzapine in rat liver [8]. Similarly, a lock mass calibration has been used for low ppm error Orbitrap FT-MS imaging of lipids [12] and peptides [16].…”