Effects Of Elemene On Topoisomerase â…  Andâ…±of Human Hepatocarcinoma HepG-2 Cells

ObjectiveHepatocarcinoma is one of the cancers non-sensitive to chemotherapy, and up to now its response to the chemotherapy is less than 20% . Clinical trials of efficacy of targeted anti-neoplasm drugs on hepatocarcinoma are underway of clinical observation and report of the efficacy is not satisfactory.The efficient drugs against hepatocarcinoma are always clinically expected.Elemene (1-methyl-1-vinyl-2,4-diisopropenyl-cyclohexane), a non-cytotoxic antitumor agent isolated from the traditional chinese medicinal herb Rhizoma zedoariae, has been approved by the Chinese Food and Drug Administration for tumors therapy. As a non-cytotoxic drug with high anti-tumor efficacy and less cellular toxicity to normal celles ,ELE has been commonly used in chinese clininal practice and has exhibited a broad spectrum of anti-tumor activity, and what's more, ELE demonstrates efficacy in tumors non-sensitive to chemotherapy, such as hepatocarcinoma. Howerver, its mechanism is still unknown. DNA TOPO I and TOPOⅡare the key enzymes regulating the topology structure of the nucleic acid, and are presently the important targets of anti-tumor drugs,but the relationship between ELE and TOPO I , TOPOⅡhas not been documented.The purpose of this study was to investigate the effects of elemene(ELE) on the proliferation, apoptosis and TOPO I and TOPOⅡof human hepatocarcinoma HepG-2 cells.MethodsAfter interfered by ELE, hepatocarcinoma HepG-2 cells were observed under inverted microscope. Cell proliferation was assessed by MTT assay. Cell cycles were shown via FCM.Apoptosis was detected by Annexin V/PI. mRNA expression of TOPOⅠand TOPOⅡwere analyzed by RT-PCR. Protein expression of TOPOⅠand TOPOⅡwere analyzed by Western-Blot. The activity of TOPOⅠwas measured by a TOPOⅠmediated super coiled PBR322 relaxation. The activity of TOPOⅡwas evaluated by TOPOⅡmediated kDNA decatenation.The super coiled PBR322 and kDNA was also used to determine the direct DNA breakage.ResultsELE significantly inhibited HepG-2 cell proliferation. After 72 h cultured, The control group cells were adherent spindle, tightly packed. For the treated group ,with ELE concentration increasing, cell volume reduced progressively, the membrane folded, the nuclear cytoplasm ratio reduced, nuclear margination with fragmentation, the adhesion strength of original group of HepG-2-piled cells down into individual floating loose, scattered, more cell disintegration debris can be seen in perspective .ELE significantly inhibited HepG-2 cell proliferation ,induced tumor cells apoptosis and induced tumor cells arrested at the S-phase in dose- and time-dependent ways, IC 50 of 24 h, 48 h and 72 h, IC 50 were 96.13μg / ml, 80.84μg / ml and 60.95μg / ml respectively. After interference of ELE, both mRNA and protein expressions of TOPOⅠand TOPOⅡwere down-regulated in a dose-dependent way,in addition,ELE inhibited both the TOPOⅠmediated DNA relaxations,and the TOPOⅡmediated DNA decatenation, but can not directly induce DNA breakage at any concentrations.ConclusionELE could inhibit the proliferation of human hepatocellular carcinoma HepG-2 cells,induce tumor cells apoptosis. The down-regulation of TOPOⅠand TOPOⅡexpression and the interference of TOPOⅠand TOPOⅡactivity might be one of the mechanisms of ELE contribution to HepG-2 cells proliferation inhibition .