(127c) Membrane Capacitance: A Biomarker for Tumourgenicity/Stem Cell-like in Human Oral Cancer Cells

Oral cancer is the 6^th most common cancer in the world. Oral Squamous Cell Carcinoma (OSCC) accounts for around 90% of oral cancer. It is an aggressive cancer with very poor survival rate, which is in part due to tumour recurrence after drug treatment. Growing evidence has pointed to another potential contributing factor, which is the cellular “stemness” behaviour within the tumour itself, giving rise to heterogeneity and subpopulations of cancer cells with “stem-like” characteristics. These subpoplulations play a role in increasing tumorgenesis, resist anticancer treatments and permitting tumour recurrence. Despite controversy that surround these stem-like subpopulations, a lot of work has been carried out in this area in order to understand their physiology and their potential mechanisms that may allow better drug targeting and eradication.

Dielectrophoresis (DEP) has been used as a characterization tool for many years, by fitting the Clausius-Mossotti factor as a function of frequency to the data, a DEP spectrum (or “fingerprint”) can be produced and the electrophysiological parameters can be extracted.  These parameters include cytoplasmic conductivity (an indicator of ionic strength within the cytoplasm), effective membrane conductance (Geff)-indicative of how well the ions are conducting across the membrane, and effective membrane capacitance (Ceff)- indicative of membrane morphology (foldings and roughness).

The aim of this work was to use DEP to investigate the electrophysiological properties of OSCC cells with subpopulations of varying tumourgenic tendencies, in order to establish whether a “fingerprint” exists that can identify those subpopulations and provide a potential tool for the non-invasive, label-free and reliable isolations of these putative tumorgenic cells.

Using rapid adherence to collagen IV, subsets of cells with different tumorigenic abilities were isolated from a panel of OSCC and dysplastic cell lines, and their tumourgenicity was assessed using translational methods in mice.  Furthermore, the membrane morphology study was also further supplemented with scanning electron microscopy and subsequent modulation with 4-methylumbelliferone (4-MU).  We used one oral dysplastic and three OSCC-derived cell lines.  Our results showed that the rapid adherent cells (RAC) to collagen IV, enriched for increased tumorigenic ability, had significantly higher effective membrane capacitance than middle (MAC) and late (LAC) adherent cells. SEM results showed a corresponding rough membrane surface that appeared to be very rich in protrusions (filopodia) relative to MAC and LAC. Subsequent treatment with 4-MU significantly reduced the effective membrane capacitance seen and in turn, a reduction of these membrane protrusions. To our knowledge, this is the first study that uses DEP to study OSSC cells with different tumorigenic abilities. It showed that these cells possessed different electrophysiological properties, and demonstrated the potential use of effective membrane capacitance as a biomarker of tumourgenicity and the stem-cell likeness of human oral cancer cells. These results suggest that DEP could potentially be used in the future for reliable, label-free isolation of putative tumorigenic cells.