title: Gomisin A alters substrate interaction and reverses P-glycoprotein-mediated multidrug resistance in HepG2-DR cells.
abstract: Through an extensive herbal drug screening program, we found that gomisin A, a dibenzocyclooctadiene compound isolated from Schisandra chinensis, reversed multidrug resistance (MDR) in Pgp-overexpressing HepG2-DR cells. Gomisin A was relatively non-toxic but without altering Pgp expression, it restored the cytotoxic actions of anticancer drugs such as vinblastine and doxorubicin that are Pgp substrates but may act by different mechanisms. Several lines of evidence suggest that gomisin A alters Pgp-substrate interaction but itself is neither a Pgp substrate nor competitive inhibitor. (1) First unlike Pgp substrates gomisin A inhibited the basal Pgp-associated ATPase (Pgp-ATPase) activity. (2) The cytotoxicity of gomisin A was not affected by Pgp competitive inhibitors such as verapamil. (3) Gomisin A acted as an uncompetitive inhibitor for Pgp-ATPase activity stimulated by the transport substrates verapamil and progesterone. (4) On the inhibition of rhodamine-123 efflux the effects of gomisin A and the competitive inhibitor verapamil were additive, so were the effects of gomisin A and the ATPase inhibitor vanadate. (5) Binding of transport substrates with Pgp would result in a Pgp conformational change favoring UIC-2 antibody reactivity but gomisin A impeded UIC-2 binding. (6) Photocrosslinking of Pgp with its transport substrate [125I]iodoarylazidoprazosin was inhibited by gomisin A in a concentration-dependent manner. Taken together our results suggest that gomisin A may bind to Pgp simultaneously with substrates and alters Pgp-substrate interaction.
authors.affiliation: Bioactive Products Research Group, Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong S A R, China.
authors.forename: Chi-Keung
authors.initials: CK
authors.lastname: Wan
authors.forename: Guo-Yuan
authors.initials: GY
authors.lastname: Zhu
authors.forename: Xiao-Ling
authors.initials: XL
authors.lastname: Shen
authors.forename: Apurba
authors.initials: A
authors.lastname: Chattopadhyay
authors.forename: Saibal
authors.initials: S
authors.lastname: Dey
authors.forename: Wang-Fun
authors.initials: WF
authors.lastname: Fong
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D016588:Anticarcinogenic Agents / Q000737:chemistry / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D015153:Blotting, Western / Q000379:methods; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D034242:Cyclooctanes / Q000737:chemistry / Q000494:pharmacology*; D004149:Dioxoles / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D017705:Lignans / Q000737:chemistry / Q000494:pharmacology*; D011224:Prazosin / Q000031:analogs & derivatives / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D020112:Rhodamine 123 / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D016588:Anticarcinogenic Agents; D001386:Azides; D034242:Cyclooctanes; D004149:Dioxoles; D017705:Lignans; D012333:RNA, Messenger; D020112:Rhodamine 123; D014638:Vanadates; C033585:schizandrol B; D014747:Vinblastine; D000255:Adenosine Triphosphate; C041552:azidoprazosin; D014700:Verapamil; D000251:Adenosine Triphosphatases; D011224:Prazosin