Apoptosis-inducing effects of two anthraquinones from Hedyotis diffusa WILLD.

Two anthraquinones which inhibit activity of the Src tyrosine kinase were isolated from a water extract of Hedyotis diffusa WILLD. and identified as 2-hydroxy-3-methylanthraquinone (compound 1) and 1-methoxy-2-hydroxyanthraquinone (compound 2). Both compounds showed inhibitory activity against protein tyrosine kinases v-src and pp60src and arrested the growth of SPC-1-A, Bcap37 and HepG2 cancer cells. Observation of mitochondrial membrane potential collapse and caspase-3 activation following treatment with the compounds indicates that their apoptotic induction activity may act via the mitochondrial apoptotic pathway. Compared with compound 2, compound 1 is more active as an antagonist of Src kinase, which might account for its higher potency to induce growth arrest and apoptosis. These results provide a deeper insight into the functions of these two simple anthraquinones and the anti-tumour pathway of Hedyotis diffusa WILLD.