J. Am. Chem. Soc. doi:10.1021/jacs.5b00944

Credit: JACS

Analyses of biological processes at the single-cell level have revealed that cells with identical genotypes can behave quite differently. This means that the average values obtained from measurements of ensembles of cultured cells may not accurately represent the phenotypes of many of the individual cells. This heterogeneity can make it especially difficult to study complex systems like tumors, which usually contain many metabolically dissimilar cell types. Xue et al. have constructed a microfluidic device to help them study cellular heterogeneity, and this 'lab-on-a-chip' can simultaneously analyze metabolites and proteins from a single cell. Each one of these devices (see image) contains 310 1.5-nanoliter-sized chambers, enabling the user to perform ∼100 single-cell assays and the appropriate controls at the same time. A single cell is loaded into each nanochamber; the cell is then lysed, and the elements of the cell lysate are then captured by a miniaturized antigen array patterned into each chamber, where the amounts of seven selected proteins, cAMP, cGMP, glutathione and glucose are determined. The authors used this microfluidic device to study single GBM39 neurosphere tumor cells before and after treatment with erlotinib, an epidermal growth factor receptor (EGFR) inhibitor. The data obtained from the single-cell experiments confirmed what had been observed in bulk solution: that erlotinib inhibits EGFR phosphorylation, glucose uptake and the activity of hexokinase 2. Further analysis of the data indicated that there were two distinct phenotypes of tumor cells: 80% of the cells had high glucose uptake, low cAMP levels and low cGMP levels, whereas the remaining cells had the opposite metabolic phenotype. The authors suggest that it will be relatively straightforward to increase the number of proteins and metabolites that the microfluidic device can measure, and such a device could be used to better understand how cell-to-cell metabolic differences can result in major changes in cellular behavior.