Apoptosis is a process that leads to programmed cell death and also a therapeutic target of cancer. In this study, potential apoptotic effects of shikonin on human bladder cancer cells (T24) in vitro were evaluated. Apoptosis induction, cell viability and morphological changes were investigated and caspase-3 and -9 activity was determined by flow cytometric assay and reverse transcription-polymerase chain reaction. The results showed marked differences in G0/G1 cell cycle arrest and cell death of the T24 cells between shikonin treated and untreated groups. Within 72 hours of treatment, shikonin influenced the cyclin dependent kinase (CDK) and cyclin activity by increasing p21 and decreasing cyclin E, CDK2 and CDK4 protein levels. A marked increase was found in apoptosis induction when the T24 cells were treated with shikonin compared to the untreated group, also confirmed by flow cytometry assay. Shikonin also promoted caspase-3 activity, which led to the induction of caspase-activated DNase (CAD) and cleavage poly(ADP-ribose)polymerase. Furthermore, the shikonin-induced apoptosis of the T24 cells was markedly blocked by the broad-spectrum caspase inhibitor, z-VAD-fmk. Shikonin may be a potential agent for the treatment of bladder transitional cell carcinoma since it induces apoptosis through the activation of caspase-3 activity in T24 human bladder cancer cells.
