Direct transfer of multicellular tumor spheroids grown in agarose microarrays for high-throughput mass spectrometry imaging analysis.

Abstract

Multicellular tumor spheroids (MCTSs) play an important role in biological studies and cancer research. There is an emerging research interest in molecular profiling and drug distribution of MCTSs by leveraging the superior sensitivity and molecular specificity of mass spectrometry imaging (MSI). Current methods for sample preparation of MCTSs can suffer from low throughput, as MCTSs are typically individually transferred from cell culture into an MSI embedding media and sectioned individually, or sometimes, a few spheroids are placed in a small block of embedding media in preparation for MSI. Here, we developed a method to minimize the sample preparation steps needed to create high-throughput MCTS frozen sections for MSI. Agarose-based microarrays created from Microtissues^® molds were used during MCTS culturing, after which the entire MCTS agarose microarray was taken out of the cell culture well and then directly embedded in 5% gelatin, without the need for a transfer step for each individual MCTS into the embedding media. This method enables rapid profiling of up to 81 MCTSs for larger MCTSs (500-800 µm) or up to 256 MCTSs for smaller MCTSs (200-300 µm) in a single section, remarkably improving the throughput possible for MSI MCTS workflows. Notably, sectioning MCTSs together in the agarose microarray also improves MCTS visualization during sectioning, such that staining each MCTS section to ensure the presence of the MCTSs within the embedding media is not necessary during the sectioning process. The method described here provides a more direct, convenient strategy to achieve high-throughput sections. MSI MCTS sectioning throughput is an important advancement for both pharmaceutical testing of MCTS; the direct transfer 3D cell cultures grown within cell culture-compatible polymer scaffolding are also critical for expanding MSI for the characterization of microfluidic and complex in vitro models, where agarose is readily utilized as a non-adhesive 3D cell culture scaffold.