MTT assay

Cells were plated in 96-well plates at a density of 1×10³ cells/well. Cell proliferation was determined using the MTT colorimetric assay (R&D Systems, Inc.) over 1 week. Every other day, cell proliferation was determined following incubation with the MTT solution (50 µg/well) for 4 h. Following the MTT incubation, the purple formazan crystals were dissolved using DMSO (Sigma-Aldrich; Merck KGaA) and proliferation was analyzed at a wavelength of 540 nm. All experiments were performed in triplicate.