Mass Spectrometry Specific Imaging of Biomolecules – BIOSPIM

Mass spectrometry has become an unavoidable tool for biomolecules characterization allowing complex mixture analyses, in a short time, with high sensitivity and structural characterization. Thus, in the era of proteomic and high throughput analyses, it plays a key role in biological research. However, improving strategies or methodologies are still very desirable. Development of direct tissue analysis and imaging by Mass Spectrometry is an excellent alternative to classical techniques. Direct analysis of tissues gives access to the identification of hundreds of biomolecules while maintaining tissue integrity and molecular localization. By automation of this approach, molecular images of the distributions of these biomolecules can be obtained by one step analysis. Recent applications demonstrate the potential of such a technology, in particular in the case of pathological studies. It is a well-designed tool for biomarker research, for better understanding of molecular mechanisms implicated in diseases, and for tracking drugs within tissues. In MALDI, molecular data on a wide range of compounds can be retrieved (peptides, proteins, lipids, sugars ...) with localization at the cellular level. To add a dimension of specificity to current developments in mass Spectrometry Imaging (MSI), so that it becomes applicable to compounds that are normally not accessible because of difficulties in their analysis by mass spectrometry (e.g. oligonucleotides) or because of their low level of abundance in comparison to highly abundant species (e.g., minority proteins), we recently proposed a novel concept of specific imaging, which we called the Tag-mass concept. This concept, based on a technique for indirect detection of molecules, will allow the generation of MALDI images of the distributions of a wide range of biomolecules, ranging from peptides and proteins to mRNA and a variety of drugs. This technique will make possible the co-localization of related but distinct classes of molecules, such as mRNAs and their corresponding proteins, or drugs and their target, significantly enhancing our knowledge of the evolution of pathologies following treatment. In this project, specific images in mass spectrometry will be performed by biomolecules targeting using labeled probes showing an affinity for the targets that can be analyzed in MALDI or SIMS mass spectrometry. In this frame, labeled probes will be designed for tag releasing in the ion source of the instrument. Thus, the probe will be indirectly detected by the measurement of the characteristic peak corresponding to the known tag. Depending on the probe used (oligonucleotide, antibody) different methodologies and strategies are proposed. Using MALDI, tag released can be induced either by photodissociation under irradiation by the laser or by fast fragmentation occurring at early stages of the desorption/ionization process. In this context, several probe types will be developed, including in this project oligonucleotides for mRNA targeting, antibodies for peptides or proteins and aptamers for peptides, proteins or drugs. Thus, depending on the probe, methodology will involve either In Situ Hybridization (ISH) technique or immunocytochemistry ones. Finally, for each probe type and each mass spectrometer instrument, one strategy and one approach will be drawn. ...