Laser Desorption Postionization Mass Spectrometry Imaging of Folic Acid Molecules in Tumor Tissue

Mass spectrometry imaging (MSI) is an innovative and powerful tool in biomedical research. It is well-known that folic acid (FA) has a high affinity for folic acid receptor (FR), which is overexpressing in epithelial cancer. Herein, we propose a novel method to diagnose cancer through direct mapping of the label-free FA spatial distribution in tissue sections by state-of-the-art laser desorption postionization-mass spectrometry imaging (LDPI-MSI). Compared with other tumor imaging methods, such as fluorescence imaging, photoacoustic imaging (PAI), magnetic resonance imaging (MRI), and micro-SPECT/CT, complicated synthesis and labeling processes are not required. The LDPI-MSI was performed on 30 μm thick sections from a murine model of breast cancer (inoculation of 4T1 cells) that were predosed with 20 mg/kg of FA. The image obtained from the characteristic mass spectrometric signature of FA at m/z 265 illustrated that FA was concentrated primarily in tumor tissue and displayed somewhat lower retention in adjacent normal controls. The results suggest that the proposed method could be used potentially in cancer diagnosis.