MALDI Imaging and Spatial SILAC Proteomics of Three-Dimensional Multicellular Spheroids Dynamically Dosed with Doxorubicin-Encapsulating Liposomes

Microphysiological systems, such as multicellular spheroids, hold great promise for drug screening experiments. Spheroids may be dosed statically, where the drug is introduced to the growing chamber at one time point, or dynamically, where the drug is introduced via a fluidic component. Dynamic dosing can generate pharmacokinetic curves that more closely represent those seen in vivo than static dosing. In this work, we demonstrate the dynamic dosing of colorectal cancer spheroids in a 3D printed fluidic device with liposomal doxorubicin. Spheroids are valuable models to evaluate dynamic dosing, as they recapitulate the nutrient, oxygen, and pH gradients of solid tumors. Spheroids feature distinct cellular populations with a necrotic core, quiescent middle layer, and proliferative outer layer. Drug and liposome penetration are tracked with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) and fluorescence imaging, showing that liposomal doxorubicin is stable to fluidic dosing and penetrates spheroids after 48 h. To provide a comprehensive pharmacodynamic profile of the distinct cellular regions within spheroids, we employ spatially stable isotopic labeling by amino acids in cell culture (spatial SILAC) proteomics to isotopically label the core and outer layers. Proteomic analysis reveals 714 upregulated proteins in the core upon treatment and 30 in the outer layers, as well as 103 downregulated proteins in the core and 1276 in the outer layers. Spatial SILAC uncovers the differential regulation of proteins associated with glycolysis, the TCA cycle, and lipid synthesis upon drug treatment between the spheroid core and outer layers. Using MALDI MSI and spatial SILAC proteomics, we interrogate the effects of dynamic dosing with liposomal doxorubicin on spheroid regions that would be overlooked by bulk analysis.