title: Effects of steroids and verapamil on P-glycoprotein ATPase activity: progesterone, desoxycorticosterone, corticosterone and verapamil are mutually non-exclusive modulators.
abstract: P-glycoprotein (P-gp) is a membranous ATPase responsible for the multidrug resistance (MDR) phenotype. Using membrane vesicles prepared from the highly resistant cell line DC-3F/ADX we studied the influence of P-gp ATPase activity of four progesterone derivatives which specifically bind to P-gp and reverse MDR. Progesterone and desoxycorticosterone stimulate P-gp ATPase activity with, respectively, apparent concentrations giving half-maximal activation of 20-25 microM and 40-50 microM, and activation factors of 2.3 (at 100 microM progesterone) and 1.8 (at 170 microM desoxycorticosterone). Hydrocortisone above 100 microM stimulates P-gp ATPase activity while corticosterone has no apparent stimulating effect. Our data are consistent with the location of the binding sites for the progesterone derivatives on the P-gp membranous domain. The effects of these steroids on verapamil-stimulated P-gp ATPase activity support a non-competitive mechanism, i.e. the binding sites for verapamil and steroids are mutually non-exclusive for P-gp ATPase modulation. A similar non-competitive inhibition of progesterone-stimulated P-gp ATPase activity by desoxycorticosterone or by corticosterone leads to the conclusion that these steroids, although sharing related structures, have distinct modulating sites on P-gp. As expected from their mutually non-exclusive interactions on P-gp, progesterone and verapamil when mixed induce a synergistic modulation of P-gp ATPase activity. Since drug transport by P-gp is believed to be coupled to its ATPase activity, a corresponding synergistic effect of these two modulators for the inhibition of P-gp-mediated drug resistance can be expected.
authors.affiliation: Section de Biophysique des Protéines et des Membranes, DBCM, CEA, Gif/Yvette, France.
authors.forename: S
authors.initials: S
authors.lastname: Orlowski
authors.forename: L M
authors.initials: LM
authors.lastname: Mir
authors.forename: J
authors.initials: J
authors.lastname: Belehradek
authors.forename: M
authors.initials: M
authors.lastname: Garrigos
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects* / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000187:drug effects* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003345:Corticosterone / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D003900:Desoxycorticosterone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018432:Drug Resistance, Multiple / Q000502:physiology*; D004357:Drug Synergism; D006868:Hydrolysis; D011374:Progesterone / Q000031:analogs & derivatives / Q000494:pharmacology; D013256:Steroids / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D013256:Steroids; D003900:Desoxycorticosterone; D011374:Progesterone; D000255:Adenosine Triphosphate; D014700:Verapamil; D000251:Adenosine Triphosphatases; D003345:Corticosterone