IntroductionA common drawback of many anticancer therapies is non-specificity in action of killing. We investigated the potential of ultra-low intensity and frequency pulsed electromagnetic fields (PEMFs) to kill breast cancer cells. Our criteria to accept this technology as a potentially valid therapeutic approach were: 1) cytotoxicity to breast cancer cells and; 2) that the designed fields proved innocuous to healthy cell classes that would be exposed to the PEMFs during clinical treatment.MethodsMCF7 breast cancer cells and their normal counterparts, MCF10 cells, were exposed to PEMFs and cytotoxic indices measured in order to design PEMF paradigms that best kill breast cancer cells. The PEMF parameters tested were: 1) frequencies ranging from 20 to 50 Hz; 2) intensities ranging from 2 mT to 5 mT and; 3) exposure durations ranging from 30 to 90 minutes per day for up to three days to determine the optimum parameters for selective cancer cell killing.ResultsWe observed a discrete window of vulnerability of MCF7 cells to PEMFs of 20 Hz frequency, 3 mT magnitude and exposure duration of 60 minutes per day. The cell damage accrued in response to PEMFs increased with time and gained significance after three days of consecutive daily exposure. By contrast, the PEMFs parameters determined to be most cytotoxic to breast cancer MCF-7 cells were not damaging to normal MCF-10 cells.ConclusionBased on our data it appears that PEMF-based anticancer strategies may represent a new therapeutic approach to treat breast cancer without affecting normal tissues in a manner that is non-invasive and can be potentially combined with existing anti-cancer treatments.

Single cell analysis is an important tool to gain deeper insights into microbial physiology for the characterization and optimization of bioprocesses. In this study a novel single cell analysis technique was applied for estimating viability and membrane potential (MP) of Bacillus megaterium cells cultured in minimal medium. Its measurement principle is based on the analysis of the electrical cell properties and is called impedance flow cytometry (IFC). Comparatively, state-of-the-art fluorescence-based flow cytometry (FCM) was used to verify the results obtained by IFC. Viability and MP analyses were performed with cells at different well-defined growth stages, focusing mainly on exponential and stationary phase cells, as well as on dead cells. This was done by PI and DiOC(2)(3) staining assays in FCM and by impedance measurements at 0.5 and 10 MHz in IFC. In addition, transition growth stages of long-term cultures and agar plate colonies were characterized with both methods. FCM and IFC analyses of all experiments gave comparable results, quantitatively and qualitatively, indicating that IFC is an equivalent technique to FCM for the study of physiological cell states of bacteria.

The determination of cell viability is essential to many areas of life sciences and biotechnology. Typically, cell viability measurements are based on the optical analysis of stained cells, which requires additional labeling steps and is hard to implement on-line. Frequency-dependent impedance flow cytometry (IFC) provides a label-free, fast and reliable alternative to determine cell viability at the single-cell level based on the Coulter principle. Here, we describe the application of IFC to eukaryotic cell cultures and compare the results to commonly used staining methods. Yeast cell parameters were assessed in normal and heatinactivated cells as well as in alcoholic fermentation and long-term batch cultures providing a precise and fast determination of the cell viability and further quantitative measures of the cell culture status. As an important new application we have investigated recombinant protein production in the widely used baculovirus insect cell expression system. The IFC analysis revealed the presence of a subpopulation of cells, which correlates with the protein expression yield, but is not detectable with conventional optical cell counters. We tentatively identify this subpopulation as cells in the late phase of infection. Their detection can serve as a predictor for the optimal time point of harvest. The IFC technique should be generally applicable to many eukaryotic cell cultures in suspension, possibly also implemented on-line. We thank Alexandra Meng for valuable suggestions on the manuscript and Doppelleu Boxer AG for providing yeast samples from their large-scale production tank. Notes Author contributions Christian Opitz, Grit Schade, Marcel Ottiger and Stephan Grzesiek designed the study. Christian Opitz, Grit Schade and Silvan Kaufmann carried out data acquisition, analysis and interpretation

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