Integrating Thiolated Mass Tags with Immuno-Mass Spectrometry Imaging to Map the Spatial Signatures of Functional Proteins in Cancer Tissues

Cancer cells are marked by metabolic reprogramming. Mapping metabolites and their related functional proteins contributes to a comprehensive understanding of metabolic regulation during cancer progression. Mass spectrometry imaging enables the visualization of metabolites in heterogeneous cancer tissues. However, direct mass spectrometry analysis of functional proteins is challenging due to their high molecular weight and low ionization efficiency. Herein, we developed three mass probes for matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) analysis of Ki67, glutaminase, and arginase on biological samples. Mass probes were created by assembling thiolated mass tags (MTs) and specific antibodies on gold nanoparticles (AuNPs). The probes were able to target Ki67, glutaminase, and arginase for MALDI-MSI analysis. Thiolated MTs were dissociated online during MALDI-MSI. This empowered the conversion of Ki67, glutaminase, and arginase signals to MT ions, realizing functional protein analysis by MALDI-MSI. Additionally, MALDI-MSI was able to detect related metabolites directly in adjacent tissue sections, providing complementary data on metabolites and their related functional proteins. This helped to deepen our understanding of cancer metabolism from multiple perspectives.