Wogonin, an active compound in Scutellaria baicalensis, induces apoptosis and reduces telomerase activity in the HL-60 leukemia cells

Crude extract of Scutellaria baicalensis (S. baicalensis) has cytotoxic effect on human myelogenous leukemia cells (HL-60). We invesigated which compound from the crude extract is responsible for the cytotoxic effect on HL-60 cells. We identified 29 compounds from the crude extract using high performance liquid chromatography mass spectrometry (HPLC/MS). Two of the compounds, baicalin and wogonoside, are converted to baicalein and wogonin, respectively, after treatment with beta-glucuronidase. We observed a dose-dependent reduction in cell viability when cells with either wogonin or aqueous extract of S. baicalensis. Several of the apoptotic features including deoxyribonucleic acid (DNA) fragmentation and increased caspase-3 activity were found in cells treated with wogonin and aqueous extract. The changes were associated with down-regulation of Bcl-2, and not Bax. Furthermore, treatment of HL-60 cells with wogonin or S. baicalensis led to the inhibition of human telomerase reverse transcriptase (hTERT), human telomerase-associated protein 1 (hTP1) and c-myc messenger ribonucleic acid (m-RNA) expression. Wogonin and S. baicaleisis down-regulated the telomerase activity. Our findings suggest that wogonin may be the major compound in S. baicalensis responsible for HL-60 growth inhibition in vitro. The inhibition of HL-60 cell growth is mediated partly through the induction of Bax/Bcl-2 apoptosis and by telomerase inhibition through suppression of c-myc, which is a promoter of hTERT.