Bioassay-guided isolation, characterization, and mechanistic study of the bioactive components from Scutellaria barbata for the anti-proliferative effect on human hepatoma cells in vitro and in vivo.

摘要

Motivated by the severe health hazards worldwide caused by liver cancer, and the pronounced side effects of some recent anti-hepatoma agents in clinical treatment, we have initiated a research project in screening safe and effective agents from Traditional Chinese Medicine (TCM) for the treatment of hepatoma. The main objective of this research is to define the in vitro and in vivo anti-proliferative activities and to identify the action mechanisms of a TCM, the aerial part of Scutellaria barbata , in human hepatoma cells (HepG2 and Hep3B cells).;Pa exhibited anti-proliferative effects on HepG2 and Hep3B cells, through cell-cycle arrest and apoptosis, with IC50 values being 12.5 and 25.7 muM respectively. However, Pa produced insignificant cytotoxic effect on WRL-68 cells, a normal hepatic cell line. Pa also caused cell death in R-HepG2 cells, a multi-drug resistant (MDR) cell line developed from HepG2 cells. Microarray analysis indicated that a hypothetical protein FLJ10803 was found to be down-regulated upon the treatment of Pa on HepG2 cells. The sub-cellular localization of FLJ10803 was demonstrated by over-expression of the GFP fusion protein in HepG2 cells.;The anti-tumor effects of Pa could be enhanced by photodynamic therapy (PDT) approach, presumably due to the rapid generation of reactive oxygen species in the drug-binding site. Pa-PDT showed potent cytotoxicity on hepatoma cell lines, HepG2 and Hep3B, with IC50 values being 0.4 and 1.5 muM, respectively. The antitumor effects were confirmed by studies using animal model, where Pa treatment (300mug/kg/day, s.c.) could significantly inhibit the growth of Hep3B cells in nude mice after PDT treatment in vivo. Fluorescent imaging showed that Pa was located at the mitochondria, and the induction of cell death was found to be initiated by the mitochondrial dependent apoptotic pathway. Results of 2D-gel analysis suggested that Pa-PDT activated an immune-marker expression pathway that results in an over expression of HLA class I proteinsin Pa-PDT treated HepG2 cells.;Both mRNA and protein expression levels of P-glycoprotein, one of the major factors involved in drug resistance, was decreased in Pa-treated R-HepG2 cells. The chemo-sensitivity of these MDR cells towards doxorubicin would be enhanced by pretreatment of Pa.;In the study, 35 TCMs with historical background in treating liver diseases were screened. S. barbata was chosen for intensive studies based on its significant anti-hepatoma activity. Using bioassay-guided purification approach, an active component, pheophorbide a (Pa) - a chlorophyll derivative, was isolated from Scutellaria barbata.;To conclude, Pa may be a candidate for further development into an anti-hepatomic agent for clinical application.