A methanolic extract of the fruits ofOroxylum 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 thein 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 25–30mM. The inhibition of proliferation of
HL-60 cells due to 36–48 h exposure to 10 or 20mM 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, andOroxylum indicumextract could be used in supplementary cancer therapy.