Induction of apoptosis and cell cycle arrest by bortezomib. (A) Effect of different concentrations of bortezomib on cell cycle progression of H460 and SW1573 cells upon 24 or 48 hours of exposure. Mean of at least three independent experiments, SD. Ut: untreated. (B) Time and concentration course Western blot analysis of total cell extracts of H460 and SW1573 cells showing the effect of treatment with bortezomib on the expression level of Mcl-1.