Abstract
Direct-current, low-intensity, electric fields were suggested as a minimally invasive treatment for various cancers. The tumor microenvironment may affect treatment efficacy, albeit it has not generally been considered when evaluating novel anti-cancer treatments. We evaluate the effects of electric treatment on epithelial, breast-cancer cells, co-cultured with non-cancerous fibroblasts, a simplified model for the tumor-microenvironment. We evaluate changes in morphology, cytoskeleton, and focus on dynamic intracellular structure and mechanics. Multiple-particle tracking was used within living cells to quantify time-dependent structural and mechanical changes. Cancer cells suffer severe cell death and exhibit transient rounding and changes in internal structural and mechanics. Interestingly, treating cancer cells in co-culture with fibroblasts delays and reduces their responses to treatment. Our particle-tracking data indicates a mechanism relating the observed changes in intracellular transport to transient changes in the microtubule network and its motors. In contrast, fibroblasts are only minimally affected by treatment, separately or in co-culture. To conclude, intracellular mechanics reveal time-dependent responses after treatment, unavailable by bulk measurements. This time-dependence could provide a window of opportunity for continued treatment. We demonstrate the importance of evaluating anti-cancer treatments within their microenvironment, which can affect response magnitude and time-course.
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Acknowledgments
The authors would like to thank Adi Netzer for her assistance with the cell proliferation measurements. This study was partially funded by the Dr. I. Libling Fund for Cancer Research, and the Eunice Geller Cancer Research Fund.
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12013_2011_9244_MOESM1_ESM.tif
Immunofluorescence staining of cytoskeleton of epithelial breast-cancer cells (MDA-MB-231) at different time points following DC-LIEF treatment. We have stained for F-actin (left column, green in merge), α-tubulin (middle column, red) and cell nuclei (blue), see Materials and methods for protocols. a Before treatment cells are spread out and close to confluence with a small number of naturally rounded cells. F-actin stress fibers are apparent. b Within about 30 min, significant changes in F-actin and α-tubulin distributions are visible. c Two hours after treatment, cells mostly spread out again, and the cytoskeletal structure returns to normal (TIF 9818 kb)
12013_2011_9244_MOESM2_ESM.tif
Immunofluorescence staining of cytoskeleton of epithelial breast-cancer cells (MDA-MB-231) at different time points following DC-LIEF treatment. We have stained for F-actin (left column, green in merge), α-tubulin (middle column, red) and cell nuclei (blue), see Materials and methods for protocols. a Before treatment cells are spread out and close to confluence with a small number of naturally rounded cells. F-actin stress fibers are apparent. b Within about 30 min, significant changes in F-actin and α-tubulin distributions are visible. c Two hours after treatment, cells mostly spread out again, and the cytoskeletal structure returns to normal (TIF 13169 kb)
Time-lapse video of epithelial breast-cancer cells (MDA-MB-231) treated in co-culture with fibroblasts from a breast-tumor-adjacent site. Fibroblasts (larger cells) do not change morphologically. Cancer cells, smaller, more “triangularly” shaped exhibit rounding at about 25 min after treatment and spread out again within an h. Scale bar is 50 μm (AVI 3620 kb)
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Yizraeli, M.L., Weihs, D. Time-Dependent Micromechanical Responses of Breast Cancer Cells and Adjacent Fibroblasts to Electric Treatment. Cell Biochem Biophys 61, 605–618 (2011). https://doi.org/10.1007/s12013-011-9244-y
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DOI: https://doi.org/10.1007/s12013-011-9244-y