We previously found that multiple intraperitoneal administration of
magnolol from Magnolia obovata inhibited
tumor metastasis and growth in vivo, and that the anti-metastatic effect of
magnolol was due to the inhibition of the
tumor cell invasion. The purpose of this study was to clarify the inhibitory mechanism of
magnolol on the growth of
tumor cells, and we expect that
magnolol may have the ability to induce apoptosis in
tumor cells. In an in vitro proliferation assay, 100 microM of
magnolol inhibited the proliferation of B16-BL6, THP-1, BAE and HT-1080 cells, but 30 microM of
magnolol did not affected cells proliferation. In addition, 100 microM of
magnolol induced apoptotic cell death within 24 h in three tumor cell lines, B16-BL6, THP-1 and HT-1080, not BAE cells, and then up-regulated the activity of
caspase-3 and
caspase-8. The up-regulation of
caspases activity by 100 microM of
magnolol was suppressed by the inhibitor of all
caspases,
z-VAD-fmk. These data suggest that
magnolol possesses ability to inhibit
tumor growth, and the ability is due to the induction of apoptosis with the activation of
caspases.