title: Reversal of P-glycoprotein (P-gp) mediated multidrug resistance in colon cancer cells by cryptotanshinone and dihydrotanshinone of Salvia miltiorrhiza.
abstract: OBJECTIVE
  Multidrug resistance (MDR) of cancer cells to a broad spectrum of anticancer drugs is an obstacle to successful chemotherapy. Overexpression of P-glycoprotein (P-gp), an ATP-binding cassette (ABC) membrane transporter, can mediate the efflux of cytotoxic drugs out of cancer cells, leading to MDR and chemotherapy failure. Thus, development of safe and effective P-gp inhibitors plays an important role in circumvention of MDR. This study investigated the reversal of P-gp mediated multidrug resistance in colon cancer cells by five tanshinones including tanshinone I, tanshinone IIA, cryptotanshinone, dihydrotanshinone and miltirone isolated from Salvia miltiorrhiza (Danshen), known to be safe in traditional Chinese medicine.
  
  
  METHODS
  The inhibitory effects of tanshinones on P-gp function were compared using digoxin bi-directional transport assay in Caco-2 cells. The potentiation of cytotoxicity of anticancer drugs by effective tanshinones were evaluated by MTT assay. Doxorubicin efflux assay by flow cytometry, P-gp protein expression by western blot analysis, immunofluorescence for P-gp by confocal microscopy, quantitative real-time PCR and P-gp ATPase activity assay were used to study the possible underlying mechanisms of action of effective tanshinones.
  
  
  RESULTS
  Bi-directional transport assay showed that only cryptotanshinone and dihydrotanshinone decreased digoxin efflux ratio in a concentration-dependent manner, indicating their inhibitory effects on P-gp function; whereas, tanshinone I, tanshinone IIA and miltirone had no inhibitory effects. Moreover, both cryptotanshinone and dihydrotanshinone could potentiate the cytotoxicity of doxorubicin and irinotecan in P-gp overexpressing SW620 Ad300 colon cancer cells. Results from mechanistic studies revealed that these two tanshinones increased intracellular accumulation of the P-gp substrate anticancer drugs, presumably by down-regulating P-gp mRNA and protein levels, and inhibiting P-gp ATPase activity.
  
  
  CONCLUSIONS
  Taken together, these findings suggest that cryptotanshinone and dihydrotanshinone could be further developed for sensitizing resistant cancer cells and used as an adjuvant therapy together with anticancer drugs to improve their therapeutic efficacies for colon cancer.
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Hu
authors.affiliation: School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Kenneth K W
authors.initials: KK
authors.lastname: To
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Lan
authors.initials: L
authors.lastname: Lu
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Shen
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Ruby L Y
authors.initials: RL
authors.lastname: Chan
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Mingxing
authors.initials: M
authors.lastname: Li
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: John H K
authors.initials: JH
authors.lastname: Yeung
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China. Electronic address: chcho@chuk.edu.hk.
authors.forename: Chi Hin
authors.initials: CH
authors.lastname: Cho
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000378:metabolism; D045784:Abietanes / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D018938:Caco-2 Cells; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D004077:Digoxin / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D004365:Drugs, Chinese Herbal / Q000494:pharmacology; D005663:Furans; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000077146:Irinotecan; D010616:Phenanthrenes / Q000494:pharmacology*; D011809:Quinones; D027561:Salvia miltiorrhiza / Q000737:chemistry
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D045784:Abietanes; D000972:Antineoplastic Agents, Phytogenic; D004365:Drugs, Chinese Herbal; D005663:Furans; D010616:Phenanthrenes; D011809:Quinones; C021751:tanshinone; C000713095:dihydrotanshinone I; C037886:cryptotanshinone; D004077:Digoxin; D000077146:Irinotecan; D004317:Doxorubicin; D002166:Camptothecin
keywords: Cryptotanshinone; Dihydrotanshinone; Multidrug resistance; P-glycoprotein; Salvia miltiorrhiza