Spheroid-Based Approach to Assess Tissue Relevance of Analysis of Dispersed-Settled Tissue Cells by Cytometry of Reaction Rate Constant

File main pdf file (CRRC of dispersed-settled spheroidal cells.pdf) describes experimental results and their interpretation for a study of tissue relevance of analyses of dispersed-settled tissues cells by Cytometry of Reaction Rate Constant (CRRC). CRRC uses time-lapse fluorescence microscopy to measure a rate constant of a catalytic reaction in individual cells and, thus, facilitate accurate size determination for cell subpopulations with distinct efficiencies of this reaction. Practical CRRC requires that a tissue sample be disintegrated into a suspension of dispersed cells and these cells settle on the support surface before being analyzed by CRRC. We call such cells “dispersed-settled” to distinguish them from cells cultured as a monolayer. Studies of the dispersed-settled cells can be tissue-relevant only if the cells maintain their 3D tissue state during the multi-hour CRRC procedure. Here we propose an approach for assessing tissue relevance of the CRRC-based analysis of the dispersed-settled cells. Our approach utilizes cultured multicellular spheroids as a 3D cell model and cultured cell monolayers as a 2D cell model. The CRRC results of the dispersed-settled cells derived from spheroids are compared to those of spheroids and monolayers in order to find if the dispersed-settled cells are representative of the spheroids. To demonstrate its practical use, we applied this approach to a cellular reaction of multi-drug-resistance (MRD) transport which was followed by extrusion of a fluorescent substrate from the cells. The approach proved to be reliable and revealed long-term maintenance of MDR transport in the dispersed-settled cells obtained from cultured ovarian cancer spheroids. Accordingly, CRRC can be used to determine accurately the size of a cell subpopulation with an elevated level of MDR transport in tumor samples, which makes CRRC a suitable method for the development of MDR-based predictors of chemoresistance. The proposed spheroid-based approach for validation of CRRC is applicable to other types of cellular reactions, and, thus, will be an indispensable tool for transforming CRRC from an experimental technique into practical analytical tool.