title: Reversal of drug resistance mediated by multidrug resistance protein (MRP) 1 by dual effects of agosterol A on MRP1 function.
abstract: We previously isolated agosterol A (AG-A) from a marine Spongia sp. and found that it completely reversed colchicine resistance in P-glycoprotein (Pgp)-over-expressing KB-C2 cells and vincristine resistance in multidrug-resistance protein (MRP)1-over-expressing CV60 cells. However, a tri-deacetylated derivative of AG-A (IAG-A) showed almost no activity in reversing Pgp- or MRP1-mediated drug resistance. In this study, we examined the mechanisms by which AG-A reverses MRP1-mediated drug resistance by investigating the interaction between agosterols and MRP1 in MRP1-over-expressing human KB carcinoma (KB/MRP) cells. [3H]-Leukotriene C4 (LTC4), [3H]-2,4-dinitrophenyl-S-glutathione uptake into membrane vesicles prepared from KB/MRP cells and intracellular [3H]-vincristine accumulation and efflux in KB/MRP cells were measured with or without AG-A and/or inactive IAG-A. AG-A reduced MRP1-mediated [3H]-LTC4 transport in a dose-dependent manner, but IAG-A did not. Inhibition by AG-A was competitive, with a K(i) value of 31 microM. AG-A at 10 microM enhanced the accumulation of [3H]-vincristine in KB/MRP cells to the level of that in control cells in the absence of the agent. Likewise, ATP-dependent efflux of [3H]-vincristine from KB/MRP cells was enhanced compared with KB-3-1 cells and inhibited by AG-A. In addition, AG-A reduced intracellular levels of glutathione, a compound required for MRP1-mediated transport of some anti-cancer drugs. These findings suggest that AG-A reverses MRP1-mediated drug resistance by directly inhibiting the capacity of MRP1 to transport drugs. In addition, the capacity of AG-A to reduce cellular glutathione levels may contribute to the modulating activity of MRP1.
authors.affiliation: Department of Cancer Chemotherapy, Institute for Cancer Research, Faculty of Medicine, Kagoshima University, Kagoshima, Japan.
authors.forename: Z S
authors.initials: ZS
authors.lastname: Chen
authors.forename: S
authors.initials: S
authors.lastname: Aoki
authors.forename: M
authors.initials: M
authors.lastname: Komatsu
authors.forename: K
authors.initials: K
authors.lastname: Ueda
authors.forename: T
authors.initials: T
authors.lastname: Sumizawa
authors.forename: T
authors.initials: T
authors.lastname: Furukawa
authors.forename: H
authors.initials: H
authors.lastname: Okumura
authors.forename: X Q
authors.initials: XQ
authors.lastname: Ren
authors.forename: M G
authors.initials: MG
authors.lastname: Belinsky
authors.forename: K
authors.initials: K
authors.lastname: Lee
authors.forename: G D
authors.initials: GD
authors.lastname: Kruh
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: S
authors.initials: S
authors.lastname: Akiyama
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000970:Antineoplastic Agents / Q000633:toxicity*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003078:Colchicine / Q000494:pharmacology*; D004317:Doxorubicin / Q000633:toxicity; D018432:Drug Resistance, Multiple; D005047:Etoposide / Q000633:toxicity; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007624:KB Cells; D008387:Marine Toxins / Q000633:toxicity*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D013261:Sterols / Q000633:toxicity*; D014750:Vincristine / Q000493:pharmacokinetics / Q000633:toxicity
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D008387:Marine Toxins; D011994:Recombinant Proteins; D013261:Sterols; C429345:agosterol A; D014750:Vincristine; D005047:Etoposide; D004317:Doxorubicin; D000255:Adenosine Triphosphate; D003078:Colchicine