title: Combined xanthorrhizol-curcumin exhibits synergistic growth inhibitory activity via apoptosis induction in human breast cancer cells MDA-MB-231.
abstract: BACKGROUND
  It has been suggested that combined effect of natural products may improve the treatment effectiveness in combating proliferation of cancer cells. The present study was undertaken to evaluate the possibility that the combination of xanthorrhizol and curcumin might show synergistic growth inhibitory effect towards MDA-MB-231 human breast cancer cells via apoptosis induction. The effective dose that produced 50% growth inhibition (GI50) was calculated from the log dose-response curve of fixed-combinations of xanthorrhizol and curcumin generated from the sulforhodamine B (SRB) assay. The experimental GI50 value was used to determine the synergistic activity of the combination treatment by isobolographic analysis and combination-index method. Further investigation of mode of cell death induced by the combination treatment was conducted in the present study.
  
  
  RESULTS
  Isobole analysis revealed that substances interaction was synergistic when xanthorrhizol and curcumin were added concurrently to the cultures but merely additive when they were added sequentially. The synergistic combination treatment was then applied to the cultures to investigate the mode of cell death induced by the treatment. Immunofluorescence staining using antibody MitoCapturetrade mark revealed the possibility of altered mitochondrial transmembrane potential, which is one of the hallmark of apoptosis. Hoechst 33258 nuclear staining assay showed the rate of apoptosis of MDA-MB-231 cells to increase in response to the treatment. Apoptotic cell death was further confirmed by DNA fragmentation assay, where internucleosomal excision of DNA was induced upon treatment with xanthorrhizol-curcumin.
  
  
  CONCLUSIONS
  This is the first time the combined cytotoxic effect of xanthorrhizol and curcumin on MDA-MB-231 cells has been documented and our findings provide experimental support to the hypothesis that combined xanthorrhizol-curcumin showed synergistic growth inhibitory activity on MDA-MB-231 cells via apoptosis induction.
authors.affiliation: Bioassay Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.|School of Biosciences and Biotechnology, Faculty of Science and Technology, National University of Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
authors.forename: Yew Hoong
authors.initials: YH
authors.lastname: Cheah
authors.affiliation: Bioassay Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.|School of Biosciences and Biotechnology, Faculty of Science and Technology, National University of Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
authors.forename: Fariza Juliana
authors.initials: FJ
authors.lastname: Nordin
authors.affiliation: Bioassay Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.
authors.forename: Rozie
authors.initials: R
authors.lastname: Sarip
authors.affiliation: School of Biosciences and Biotechnology, Faculty of Science and Technology, National University of Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
authors.forename: Thiam Tsui
authors.initials: TT
authors.lastname: Tee
authors.affiliation: School of Biosciences and Biotechnology, Faculty of Science and Technology, National University of Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
authors.forename: Hawariah Lope Pihie
authors.initials: HLP
authors.lastname: Azimahtol
authors.affiliation: Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 80310 Skudai, Johor, Malaysia.
authors.forename: Hasnah M
authors.initials: HM
authors.lastname: Sirat
authors.affiliation: Phytochemistry Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.
authors.forename: Badrul Amini Abd
authors.initials: BAA
authors.lastname: Rashid
authors.affiliation: Bioassay Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.
authors.forename: Noor Rain
authors.initials: NR
authors.lastname: Abdullah
authors.affiliation: Bioassay Unit, Herbal Medicine Research Center, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia.
authors.forename: Zakiah
authors.initials: Z
authors.lastname: Ismail