Multicellular tumor spheroids (MTS) are a well-established model system for drug development and are a valuable in vitro research tool for use prior to employing animal models. These 3D-cell cultures are thought to display chemical gradients of oxygen and nutrients throughout their structure, giving rise to distinct microenvironments in radial layers, thus mimicking the pathophysiological environment of a tumor. Little is known about the localized distributions of metabolites within these microenvironments. To address this, here we utilize high spectral resolution Fourier-transform ion cyclotron resonance (FT-ICR), MALDI mass spectrometry imaging (MSI) to image the distribution of endogenous metabolites in breast cancer MCF-7 spheroids. We show that known specific metabolite markers (adenosine phosphates and glutathione) indicate that the central region of these cell culture models experiences increased hypoxic and oxidative stress. By using discriminatory analysis, we have identified which m/z values localize towards the outer proliferative or central hypoxic regions of an MTS and have assigned elemental formula with sub-ppm error. Using this information, we have mapped these metabolites back to distinct pathways to improve our understanding of the molecular environment and biochemistry of these tumor models.

Successful matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI) relies on the selection of the most appropriate matrix and optimization of the matrix application parameters. In order to achieve reproducible high spatial-resolution imaging data, several commercially available automated matrix application platforms have become available. However, the high cost of these commercial matrix sprayers is restricting access into this emerging research field. Here, we report an automated platform for matrix deposition, employing a converted commercially available 3D printer ($300) and other parts commonly found in an analytical chemistry lab as a low-cost alternative to commercial sprayers. Using printed fluorescent rhodamine B microarrays and employing experimental design, the matrix deposition parameters were optimized to minimize surface analyte diffusion. Finally, the optimized matrix application method was applied to image three-dimensional MCF-7 cell culture spheroid sections (ca. 500 μm diameter tissue samples) and sections of mouse brain. Using this system, we demonstrate robust and reproducible observations of endogenous metabolite and steroid distributions with a high spatial resolution.

The term electroceutical has been used to describe implanted devices that deliver electrical stimuli to modify biological function. Herein, we describe a new concept in electroceuticals, demonstrating for the first time the electrochemical activation of metal-based prodrugs. This is illustrated by the controlled activation of Pt(iv) prodrugs into their active Pt(ii) forms within a cellular context allowing selectivity and control of where, when and how much active drug is generated.

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