Aqueous extracts of Salvia miltiorrhizae Bunge have been extensively used in the treatment of cardiovascular disorders and
cancer in Asia. Recently, a compound, 5-(3-hydroxypropyl)-7-methoxy-2-(3'-methoxy-4'-hydroxyphenyl)-3-benzo[b]furancarbaldehyde (
salvinal), isolated from this plant showed inhibitory activity against
tumor cell growth and induced apoptosis in human
cancer cells. In the present study, we investigated the cytotoxic effect and mechanisms of action of
salvinal in human
cancer cell lines.
Salvinal caused inhibition of cell growth (IC50 range, 4-17 microM) in a variety of human
cancer cell lines. Flow cytometry analysis showed that
salvinal treatment resulted in a concentration-dependent accumulation of cells in the G(2)/M phase. We observed, using
Hoechst 33258 dye staining, that
salvinal blocked the cell cycle in mitosis. In vitro and in vivo examinations showed that
salvinal inhibited
tubulin polymerization in a concentration-dependent manner. Immunocytochemical studies demonstrated that
salvinal treatment caused the changes of cellular microtubule network, similar to the effect of
colchicine. In addition,
salvinal treatment resulted in upregulation of
cyclin B1 levels, activation of Cdc2
kinase, and Cdc25c phosphorylation. Furthermore, elevation of levels of MPM-2 phosphoepitopes in
salvinal-treated cells in a concentration-dependent manner was also observed. Similar to the effect of other antitubulin agent, hyperphosphorylation of Bcl-2, induction of DNA fragmentation and activation of
caspase-3 activity occurred in
salvinal-treated cells. In particular,
salvinal exhibited similar inhibitory activity against parental KB,
P-glycoprotein-overexpressing KB vin10 and KB taxol-50 cells, and
multidrug resistance-associated protein (MRP)-expressing
etoposide-resistant KB 7D cells. Taken together, our data demonstrate that
salvinal inhibits
tubulin polymerization, arrests cell cycle at mitosis, and induces apoptosis. Notably,
Salvinal is a poor substrate for transport by
P-glycoprotein and MRP.
Salvinal may be useful in the treatment of human
cancers, particularly in patients with drug resistance.