Mass spectrometry imaging of proteins and drugs

Laser light irradiation can ionize huge molecules with molecular weight exceeding tens of thousands without their destruction. Such ionized molecules can be detected using mass spectrometry, allowing for the analysis of proteins and drugs that are extremely important in the field of medicine.
     With the employment of an imaging technique combined with mass spectrometry, i.e., mass spectrometry imaging (MSI), the sample’s molecules are separated based on their mass-to-charge ratio (m/z), and their spatial distribution is measured simultaneously. The figure below shows the MSI results of cancer cells administrated with a photosensitizer for photodynamic therapy (PDT), protoporphyrin IX (PpIX), and an anticancer drug, docetaxel. These results suggest the efficacy of PDT using PpIX for docetaxel-resistant cancer cells because of the accumulated amount of PpIX in the cancer cells compared to docetaxel. We are also developing a MSI system that enables observation at the cellular level, which is not possible with commercially available systems.
     Due to the mixture of various substances in a biological sample, liquid chromatography is needed to separate them before performing mass spectrometry. However, a conventional laser ionization is conducted in a vacuum. Thus there is a difficulty in combining that with liquid chromatography. Therefore, we are also developing high-performance devices to ionize samples by laser irradiation in the atmosphere and subsequently analyze them using mass spectrometry.

Hiroki Kannen, Shusei Nomura, Hisanao Hazama, Yasufumi Kaneda, Tatsuya Fujino, Kunio Awazu: "Enhancement of Ionization Efficiency Using Zeolite in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Multiple Drugs in Cancer Cells (Mass Spectrometry of Multiple Drugs in Cells Using Zeolite)," Mass Spectrometry 9(1):A0091 (2020).