beta-hydroxyisovalerylshikonin inhibits the cell growth of various cancer cell lines and induces apoptosis in leukemia HL-60 cells through a mechanism different from those of Fas and etoposide

beta-Hydroxyisovalerylshikonin (beta-HIVS), which was isolated from the pla nt, Lithospermium radix, inhibited the growth of various lines of cancer ce lls derived from human solid tumors at low concentrations between 10(-8) an d 10(-6) M. When HL-60 cells were treated with 10(-6) M beta-HIVS for 3 h, characteristic features of apoptosis, such as DNA fragmentation, nuclear fr agmentation, and activation of caspase-3-like activity, were observed. The most characteristic features of the effect of beta-HIVS were the remarkable morphological changes induced upon treatment of HL-60 cells with beta-HIVS , as visualized on the staining of actin filaments with phalloidin labeled with tetramethylrhodamine B isothiocyanate. Moreover, activation of MAP kin ases, such as ERK2, JNK and p38, was detected after treatment with 10(-6) M beta-HIVS preceding the appearance of the characteristics of apoptosis, an d the features of the activation of these MAP kinases were quite different from those of Fas and anticancer drug-induced apoptosis. The activation of JNK by beta-HIVS was not inhibited by inhibitors of caspases, suggesting th at JNK is located either upstream or independent of the caspase signaling p athway. beta-HIVS did not inhibit the activity of topoisomerase II. These r esults indicate that beta-HIVS induces apoptosis in HL-60 cells through a m echanism unlike those reported for anti-Fas antibodies and etoposide.