MCF cells were transfected with NC or miR-20a, cultured in normal medium or EBSS for 24 h. Cells suspension was mixed with low melting agarose (AB0015, Life Technologies, Carlsbad, CA, USA) and plated onto comet slide to perform single-cell gel electrophoresis.54 Comet images were captured using a fluorescence microscope (Leica, Wetzlar, Germany); DNA damage was quantified by measuring the Tail Moment (TM) using CASP software (http://casplab.com).