Label-Free Selection of Cancer Cells by Dielectrophoresis and Evaluation of Invasive Potential by Single-Cell Protease Secretion Assay

Enzymatic secretion in single tumor cells plays a pivotal role in cancer progression and metastasis. Matrix metalloproteinase 9 (MMP9) acts as a degradation agent for gelatin and collagen within the extracellular matrix and contributes to invasion and metastasis. Despite this established importance, the heterogeneous nature of enzyme secretion within the tumor microenvironment remains elusive at the single-cell level. Herein, we present an approach to investigate the secretion of MMP9 by individual tumor cells. Dielectrophoresis (DEP) is used to selectively capture individual cells at an array of bipolar electrodes (BPEs) each aligned to an overlying microchamber, which serves as a reaction volume for subsequent assay. The MMP9 activity of isolated cells is then assessed through use of a fluorogenic FRET-based substrate, which displays fluorescence upon cleavage of a peptide by MMP9. The reported workflow allows for the quantification of secretion behavior among cells, the acquisition of temporal secretion profiles, and the identification of highly invasive cells, which are critical for evaluating disease progression and treatment. The DEP-BPE platform's ability to isolate live, label-free cells enhances the potential for functional assays of complex cellular behaviors over time, in contrast to previously reported endpoint measurements on lysed cells.