title: Differential interactions of cytochalasins with P-glycoprotein.
abstract: Cytochalasins are a family of structurally related natural product cytotoxins that selectively depolymerize microfilaments. In this study, the interaction between several cytochalasins and the drug transporter P-glycoprotein was investigated. Dihydrocytochalasin B and cytochalasin E consistently sensitized P-glycoprotein-overexpressing human breast carcinoma cells (MCF-7/ADR) to daunomycin, vinblastine, and actinomycin D without affecting the cytotoxicity of cisplatin. These compounds did not affect the sensitivities of the parental MCF-7 cells to anticancer drugs, indicating that their effects are due to P-glycoprotein inhibition. Effects of dihydrocytochalasin B and cytochalasin E were observed at concentrations as low as 2.5 and 5 microM, respectively. In contrast, cytochalasins A, B, C, D, H, and J did not sensitize MCF-7/ADR cells to any of the drugs. The accumulation of [3H]-vinblastine by MCF-7/ADR cells and by drug-resistant human ovarian carcinoma cells (SKVLB1) was increased to the greatest extent by verapamil, followed by dihydrocytochalasin B > cytochalasin E > cytochalasin B, whereas cytochalasins A, C, D, H, and J did not alter intracellular accumulation of the drug. Similarly to verapamil, dihydrocytochalasin B significantly stimulated the ATPase activity of P-glycoprotein, while other cytochalasins were ineffective. These results demonstrate that very closely related compounds can differentially interact with P-glycoprotein. For example, the only difference between cytochalasin B and dihydrocytochalasin B is the saturation of a carbon-carbon double bond in dihydrocytochalasin B. These structural differences may provide important insight into chemical determinants for drug interaction with P-glycoprotein.
authors.affiliation: Department of Pharmacology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Zilfou
authors.forename: C D
authors.initials: CD
authors.lastname: Smith
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects* / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002945:Cisplatin / Q000633:toxicity; D003572:Cytochalasins / Q000737:chemistry / Q000633:toxicity*; D003609:Dactinomycin / Q000633:toxicity; D018432:Drug Resistance, Multiple; D006801:Humans; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000633:toxicity; D014747:Vinblastine / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003572:Cytochalasins; D003609:Dactinomycin; D014747:Vinblastine; D014700:Verapamil; D000251:Adenosine Triphosphatases; D002945:Cisplatin