title: Steroid treatment, accumulation, and antagonism of P-glycoprotein in multidrug-resistant cells.
abstract: According to multiple reports, progesterone is not transported by P-glycoprotein (Pgp), which mediates multidrug resistance through active drug efflux. However, progesterone has been shown to block Pgp- mediated efflux of other drugs. To extend these observations and to examine the effect of modulating Pgp phosphorylation, the accumulation of progesterone and 14 other steroids in untreated and calphostin C-treated multidrug-resistant human colon carcinoma SW620 Ad300 cells was compared to the accumulation in parental SW620 cells. However, the accumlation of more hydrophilic steroids was reduced by as much as 50%. Progesterone and progesterone-like compounds, however were potent inhibitors of Pgp-mediated vinblastine efflux; increased antagonism correlated with increased steroid hydrophobicity. Treatment with calphostin C, a PKC inhibitor which decreases Pgp phosphorylation, increased progesterone efflux, modulated Pgp antagonism by steroids, and inhibited photoaffinity labeling of Pgp by progesterone. These results extend previous observations that Pgp can mediate the transport of, and be antagonized by, a variety of steroids and that these properties vary with both steroid's hydrophobicity and the phosphorylated state of Pgp.
authors.affiliation: Developmental Endocrinology Branch, NICHD, NIH, Bethesda, Maryland 20892, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Barnes
authors.forename: B
authors.initials: B
authors.lastname: Dickstein
authors.forename: G B
authors.initials: GB
authors.lastname: Cutler
authors.forename: T
authors.initials: T
authors.lastname: Fojo
authors.forename: S E
authors.initials: SE
authors.lastname: Bates
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000345:Affinity Labels; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D009281:Naphthalenes / Q000494:pharmacology; D010766:Phosphorylation; D011374:Progesterone / Q000378:metabolism* / Q000494:pharmacology; D013256:Steroids / Q000378:metabolism* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D000903:Antibiotics, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D009281:Naphthalenes; D013256:Steroids; D011374:Progesterone; D014747:Vinblastine; D014700:Verapamil; C058819:calphostin C