Effect of GBT on cell cycle progression in A431 cells. (A) Analysis of cell cycle progression. (B) Expression of cell cycle regulatory proteins in GBT-treated cells for 24 h. Band intensity compared to untreated cells was calculated using ImageJ after normalization to β-actin expression. The data represent two independent experiments. (C) The inhibition of cell growth by GBT for 3 days at concentrations without cell death by GBT. Growth inhibition was assessed by counting trypan blue-excluding cells. The data represent the mean of two independent triplicate experiments; the error bars show the standard deviation.