Mtt labeling agent

To assess cell proliferation, a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT)-based protocol was used. Directly after electroporation, cells were seeded at a density of 2500 (HUH6 and HepT1) or 5000 (HepG2) cells per well in a 96-well format (Nunc, Wiesbaden, Germany) in 100 μL RPMI medium. Ten microliters of MTT labeling agent (5 mg/mL, Sigma) was added to each well and incubated at 37 °C for 4 h. One hundred microliters of a SDS-HCl solution was added to each well and mixed thoroughly. Microplate was incubated overnight at 37 °C in a humidified chamber. The absorbance of this colorimetric reaction was quantified on the GENios reader (Tecan, Männedorf, Switzerland) by measuring at a wavelength of 595 nm.

Cellular viability was assayed by measuring intracellular reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) to formazan. The MTT labeling agent (Sigma-Aldrich) was added to the cells at a final concentration of 0.5 mg/ml. The converted dye was solubilized in 10% SDS in 0.01 M HCl and measured at 550 nm with a plate reader (TriStar LB941, Berthold Technologies).
The CytoTox-Glo™ Cytotoxicity Assay kit (Promega) was used according to the manufacturer’s instructions. Aliquots of cell culture medium were collected for analysis of lactate dehydrogenase (LDH) activity as described previously [17 (link)].