title: Reversal of multidrug resistance by Marsdenia tenacissima and its main active ingredients polyoxypregnanes.
abstract: BACKGROUND
  Multidrug resistance (MDR) of cancer is often associated with the overexpression of ATP-binding cassette (ABC) transporters, such as P-glycoprotein (P-gp), multidrug resistance-associated protein-1 (MRP-1) and breast cancer resistance protein (BCRP or ABCG2), in cancer cells, which facilitates the active efflux of a wide variety of chemotherapeutic drugs out of the cells. Marsdenia tenacissima is a traditional Chinese medicinal herb that has long been clinically used for treatment of cancers, particularly in combinational use with anticancer drugs. Polyoxypregnanes (POPs) are identified as main constituents of this herb, and three of them have been reported to exhibit P-gp modulatory effect and thus reverse MDR. Therefore, it is of great necessity to investigate more POPs that have potential to reverse transporters-mediated MDR.
  
  
  OBJECTIVE
  We aimed to identify POPs as the chemical basis responsible for circumventing ABC transporters-mediated MDR by M. tenacissima.
  
  
  METHODS
  The MDR reversal effects of M. tenacissima crude extract together with a series of isolated POPs were evaluated on several MDR cancer cell lines that overexpress P-gp, MRP1 or ABCG2. The activities of P-gp, MRP1 and ABCG2 were determined by the flow cytometry-based substrate efflux assay. Molecular docking of POPs to a three-dimensional human P-gp homology structure was also performed.
  
  
  RESULTS
  The crude extract of M. tenacissima was firstly found to circumvent P-gp-mediated MDR. Then, 11 polyoxypregnane compounds (POPs) isolated from this herb were found to overcome P-gp-, MRP1- and/or ABCG2-mediated MDR. Further mechanistic study delineated that the reversal of MDR by these POPs was due to significant increase in the intracellular concentrations of the substrate anticancer drugs via their inhibition of different ABC transporter-mediated efflux activities. Furthermore, molecular docking revealed that POPs with P-gp modulatory effect bound to P-gp and fitted well into the cavity between the alpha and beta subunit of P-gp via forming hydrogen bonds. In addition, several key structural determinants for inhibition of P-gp, MRP1 or ABCG2 by POPs were illustrated.
  
  
  CONCLUSIONS
  Our findings advocated the rational use of M. tenacissima to enhance efficacies of conventional anticancer drugs in tumors with ABC drug transporters-mediated MDR. Furthermore, 11 POPs were found to contribute to MDR reversal effect of M. tenacissima via inhibition of different ABC efflux transporters.
authors.affiliation: School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China.
authors.forename: Kenneth K W
authors.initials: KKW
authors.lastname: To
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China.
authors.forename: Xu
authors.initials: X
authors.lastname: Wu
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China.
authors.forename: Chun
authors.initials: C
authors.lastname: Yin
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China.
authors.forename: Stella
authors.initials: S
authors.lastname: Chai
authors.affiliation: Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China; State Key Laboratory of Drug Research and Natural Products Chemistry Department, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, PR China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Yao
authors.affiliation: Department of Pharmaceutical Biology, Johannes Gutenberg University, Mainz, Germany.
authors.forename: Onat
authors.initials: O
authors.lastname: Kadioglu
authors.affiliation: Department of Pharmaceutical Biology, Johannes Gutenberg University, Mainz, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Efferth
authors.affiliation: Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China; State Key Laboratory of Drug Research and Natural Products Chemistry Department, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, PR China. Electronic address: yye@mail.shcnc.ac.cn.
authors.forename: Yang
authors.initials: Y
authors.lastname: Ye
authors.affiliation: School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region; Joint Research Laboratory of Promoting Globalization of Traditional Chinese Medicines between The Chinese University of Hong Kong and Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China. Electronic address: linge@cuhk.edu.hk.
authors.forename: Ge
authors.initials: G
authors.lastname: Lin
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2 / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D018432:Drug Resistance, Multiple / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D031101:Marsdenia / Q000737:chemistry*; D062105:Molecular Docking Simulation; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy; D010936:Plant Extracts / Q000494:pharmacology*; D011278:Pregnanes / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D000970:Antineoplastic Agents; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D010936:Plant Extracts; D011278:Pregnanes; C116614:ABCG2 protein, human; C421109:multidrug resistance-associated protein 1
keywords: ABCG2; Calcein AM (PubChem CID390986); Doxorubicin (PubChem CID31703); Fumitremorgin C (PubChem CID403923); MK571(PubChem CID16760569); MRP1; Marsdenia tenacissima; Mitoxantrone (PubChem CID4212); Multidrug resistance; P-glycoprotein; Pheophorbide A (PubChem CID5323510); Polyoxypregnane compounds; Rhodamine 123 (PubChem CID65217); Sulforhodamine B (PubChem CID65191); Valspodar (PubChem CID5281884); Verapamil (PubChem CID2520)