Shikonin treatment selectively induces apoptosis in prostate cancer cells. (A) Shikonin treatment inhibits prostate cancer cell viability without affecting normal prostate epithelial cells. DU-145, PC-3 and PrEC cells were treated with various doses (0.5, 1, 2.5, 5 and 10 μM) of Shikonin for 24 h and CCK-8 assay was used for the measurement of cell viability. (B) Shikonin treatment induces DNA fragmentation in prostate cancer cells. Cells were treated with various doses (0.5,1,2.5, 5 and 10 μM) of Shikonin for 24 h and TUNEL assay was done using flow cytometry and the % TUNEL positive cells were measured. (C) Shikonin treatment induces PARP activation. Cells were treated with 2.5 μM of Shikonin for 24 h and the cell lysates were analyzed by western blotting for the detection of cleaved PARP, a marker for PARP activation. (D) Shikonin treatment induces caspase-3 activation. Cells were treated with various doses of Shikonin (0.5, 1, 2.5, 5 and 10 μM) for 48 h and measurement of caspase-3 activity was done using the CASPASE-3 Colorimetric Activity Assay kit. Data is expressed in means ± SEM and represents the results of three independent experiments (p < 0.05).