Baicalein, a flavonoid extracted from a methanolic extract of Oroxylum indicum inhibits proliferation of a cancer cell line in vitro via induction of apoptosis

A methanolic extract of the fruits of Oroxylum indicum, which is widely used in traditional Chinese herbal medicine for its anti-inflammatory, anti-pyretic and anti-hypersensitivity effects, inhibited in vitro proliferation of HL-60 cells. The flavonoid baicalein was found as an active component in the extract. Analysis of freeze-dried fruits of the plant indicated that this component comprised about 4% of the material by dry weight. In this study, we investigated the in vitro effects of baicalein on the viability and induction of apoptosis in the HL-60 cell line. The cell viability after treating with baicalein for 24 h was quantified by counting viable cells using trypan blue staining. The results showed that baicalein caused a 50% inhibition of HL-60 cells at concentrations of 25-30 mu M. The inhibition of proliferation of HL-60 cells due to 36-48 h exposure to 10 or 20 mu M baicalein was associated with the accumulation of cells at S or G2M phases. However, proliferation inhibition at a higher dose may be associated with induction by apoptosis, as evidenced by the typical nuclear fragmentation using DNA fragmentation assay and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). The results indicate that baicalein has anti-tumor effects on human cancer cells, and Oroxylum indicum extract could be used in supplementary cancer therapy.