Colon cancer cell growth inhibition by bortezomib. HCT116 colon cancer cells with p53 wild type (p53+/+) and p53 null (HCT116p53-/-) were treated with bortezomib at different concentrations for 48 hours. Cell growth was determined by MTT assay (A) or by direct cell counting (B). The resultant data were plotted in histogram by setting no bortezomib treatment controls as OD values at 1 (A) or as cell numbers at 100. Each bar represents the mean ± SD derived from three independent determinations.