Automated Electrorotation to Reveal Dielectric Variations Related to HER-2/neu Overexpression in MCF-7 Sublines 1 Massimo Cristofanilli, 2 Giovanni De Gasperis, Lisha Zhang, Mien–Chie Hung, Peter R. C. Gascoyne, and Gabriel N. Hortobagyi Departments of Breast Medical Oncology [M. C., G. N. H.], Experimental Pathology [G. D. G., P. R. C. G.], and Tumor Biology [L. Z., M. C. H.], The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 ABSTRACT Purpose: Electrorotation (ROT) is a technique that al- lows for determination of the dielectric properties of living cells when exposed to a rotating electric field. We evaluated the ROT behavior of MCF/neo and p185 neu transfectancts MCF/HER2–11 and MCF/HER2–18 to investigate whether differences in HER-2/neu expression were associated with differences in dielectric properties in these cells. Experimental Design: P185 neu was measured by West- ern blotting in MCF/neo cells and HER-2/neu transfectants MCF/HER2–11 and MCF/HER2–18. ROT spectra and cell membrane-specific capacitance were obtained for each cell line. Results: The mean cell membrane-specific capacitance values for MCF/neo, MCF/HER2–11, and MCF/HER2–18 were 2.09, 1.70, and 2.56 F/cm 2 , respectively. The mean specific capacitance for MCF/neo was significantly different from that for MCF/HER2–11 (P  0.006) and that for MCF/HER2–18 (P  0.007). Conclusions: ROT is sufficiently sensitive to detect vari- ations in dielectric properties in breast cancer cell lines overexpressing p185 neu . These differences may be related to the morphological alterations determined by HER-2/neu overexpression. INTRODUCTION Cell separation techniques are fundamental in cell biology and have application to molecular diagnostics and therapeutics. The ability to effectively isolate and characterize single cells from a heterogeneous population (1– 4) represents the most limiting factor to the widespread utilization of many current sorting technologies (5– 8). Improvements in cell-sorting meth- ods depend on the use of novel cellular properties able to discriminate among cell types and manipulate selective cells. One such property, dielectric affinity, can be exploited for cell separation (3, 9). A cell suspended in a medium with different dielectric properties becomes electrically polarized when subjected to an electric field. Interaction between this induced polarization and the field produces various electrokinetic effects (9 –12), e.g., a spatially inhomogeneous field will exert a lateral dielectro- phoretic force on an uncharged particle, directing it away from regions of high electric field strength. A rotating field, in con- trast, will induce the particle to spin, a phenomenon called ROT. 3 Cellular ROT involves using a rotating electric field gen- erated by a four-electrode arrangement to induce isolated single cells to rotate (13, 14). The direction and rate of the spin strongly depend on the frequency and spatial configuration of the field and on the dielectric properties of the suspending medium and the cells. This noninvasive technique can be used to characterize the dielectric properties of individual living cells. Because it can discriminate between single cells, ROT can be used to characterize the dielectric properties of cell subpopula- tions that can be differentiated within a cell mixture through size, morphology, staining susceptibility, and other biological criteria (15–18). For this reason, ROT is an ideal tool for defining the operating parameters for dielectrophoretic cell- sorting devices, in which cell types with different properties are physically separated and purified according to their dielectric properties. An example is the successful separation of human breast cancer cells and leukemia cells from diluted human blood after ROT characterization of the different cell types (3, 19). Significantly, cells separated this way do not seem to be dam- aged by the field exposure, as demonstrated by their ability to reestablish growth with minimal loss afterward (20, 21). The relationship between dielectric characteristics and hu- man HER-2/neu (c-erbB-2) gene expression is of interest to us because HER-2/neu is amplified in many adenocarcinomas, overexpressed in 30% of primary breast carcinomas, and considered an important prognostic factor (22). In vitro and in vivo experiments have demonstrated that overexpression of the normal HER-2/neu gene product, p185 neu , results in changes in cell morphology and manifestation of the tumorigenic pheno- type in various cell lines (23, 24). We evaluated the ROT behavior of MCF/neo and p185 neu transfectancts MCF/HER2–11 and MCF/HER2–18 to investi- gate whether differences in HER-2/neu expression were associ- ated with differences in dielectric properties in these cells. Received 1/31/01; revised 11/27/01; accepted 11/29/01. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported in part by the Nellie B. Connely Breast Cancer Research Fund. 2 To whom requests for reprints should be addressed, at Department of Breast Medical Oncology, Box 424, The University of Texas, M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030. Phone: (713) 792-2817; Fax: (713) 794-4385; E-mail: mcristof@ mdanderson.org. 3 The abbreviations used are: ROT, electrorotation; C spec , cell mem- brane-specific capacitance. 615 Vol. 8, 615– 619, February 2002 Clinical Cancer Research Research. on April 21, 2021. © 2002 American Association for Cancer clincancerres.aacrjournals.org Downloaded from