Background: Cancer with over 11 million deaths every year is the second leading cause of death.The search for new anti-cancer drugs is one of the most prominent research areas of natural products.Wide ranges of anticancer drugs (over of 60%) applied in cancer chemotherapy have been derived from natural source such as vincristine, irinotecan and etoposide.Since the ancient times, some of European local plants have been used to treat all kinds of diseases including cance, however, now the medical value of these plants are gradually neglected.In this study we screened anticancer active extracts from European local medicinal plants and further investigate the mechanisms of one of them which show specifically effect on leukemia cell line.Methods: 1.Anticancer activity assay.The leaves, stems, flowers and roots of 11 flowering plants as well as 5 ferns were extracted with water or alcohol.Cytotoxicity of 30 extracts obtained were evaluated on 5 cancer cell lines: HepG2 (liver carcinoma cell line), MCF7 (breast cancer cell lines), Lovo (colon cancer cell line), U87 (glioblastoma cell line), Jurkat (T cell leukemia cell line), as well as on normal, control cell lines by following three ways.(1) MTT assay.Complete dose-response curves were generated and IC(50) values were calculated for these extracts.(2) Two-color fluorescence cell viability assay.The assay produced an uniform green fluorescence in live cells and a bright red fluorescence in dead cells, which was detected by confocal microscopy.(3) High throughput screening technology.An automated high throughput live cell imaging system (Chipman Technologies) was used.This system combines long term incubation conditions with phase contrast imaging and machine vision technology to automatically analyze and quantify basic and dynamic parameters of cell populations, as well as cell morphological features.2.Inducing Apoptosis effect of one extract (No 8) on jurkat cell line.Of all these extracts, one extract (No 8) appears specific effect on leukemia cell lines (Jurkat, Molt-4, RS4;1 l).So inducing Apoptosis effect of the extract on jurkat cell line was further explored.Apoptotic rates were detected using FITCAnnexin V/Propidium Iodide (PI) stainings by Flow cytometry.Expressions of apoptotic associated proteins Bcl-2,Bax, caspase-3, 9 were determined by western blot and flurometric immunosorbent enzyme assay.The change of membrane potential ofmitochondria was observed using Rhodamine123 fluorescence staining.The releasing level of cytochrome C was examined by western blot.Results: 5 extracts exhibited substantial cytotoxic effects on five cell lines, inhibiting at least 80% of tumor cell proliferation at high concentrations.The results indicated IC50 values ranging from 50 to 100 μg/mL and their activity showed dose-effect relationship.Picture made by confocal microscopy and movie made by live cell imaging system showed the Morphological change.One extract (No8) appears particularly interesting as it exhibits high cytotoxicity only for the leukemia cell lines (IC50 values lower than 5 μg/mL), while all other cancer cell lines tested were either considerably less or not at all affected.It also had no effect on the control normal cell line and leucocyte.No work on an anti-leukemia cell activity of this plant extract has been reported so far in the literature.A closer study of its activities is in progress.Flow cytometry showed the extract could induce apoptosis of Jurkat cells and exhibit dose-effect and time-effect relationship.During extract-induced apoptosis, expressions of Bax were significantly upregulated P<0.05, expressions of Bcl-2 were downregulated P<0.05, caspase3, 9 were activated.Membrane potential of mitochondria decreased, releasing level of apoptosis factor cytochrome C from mitochondria increased.(data no show).Conclusion: 5 extracts from European local plants demonstrated anticancer effects.One extract specifically shows specific effect on leukemia cell lines.The extract significant induced apoptosis ofjurkat cells, its mechanism is related to activate mitochondrial signal transduction pathway.Perspectives: We expect that the specific effect on leukemia cells is caused by single individual components that can be purified and identified using standard methods.Then the compound obtained has a potential for becoming anticancer drug.