title: New uses for old drugs: pharmacophore-based screening for the discovery of P-glycoprotein inhibitors.
abstract: P-glycoprotein (P-gp) is one of the best characterized transporters responsible for the multidrug resistance phenotype exhibited by cancer cells. Therefore, there is widespread interest in elucidating whether existing drugs are candidate P-gp substrates or inhibitors. With this aim, a pharmacophore model was created based on known P-gp inhibitors and it was used to screen a database of existing drugs. The P-gp modulatory activity of the best hits was evaluated by several methods such as the rhodamine-123 accumulation assay using K562Dox cell line, and a P-gp ATPase activity assay. The ability of these compounds to enhance the cytotoxicity of doxorubicin was assessed with the sulphorhodamine-B assay. Of the 21 hit compounds selected in silico, 12 were found to significantly increase the intracellular accumulation of Rhodamine-123, a P-gp substrate. In addition, amoxapine and loxapine, two tetracyclic antidepressant drugs, were discovered to be potent non-competitive inhibitors of P-gp, causing a 3.5-fold decrease in the doxorubicin GI(50) in K562Dox cell line. The overall results provide important clues for the non-label use of known drugs as inhibitors of P-gp. Potent inhibitors with a dibenzoxazepine scaffold emerged from this study and they will be further investigated in order to develop new P-gp inhibitors.
authors.affiliation: Laboratório de Química Orgânica e Farmacêutica, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal Cunha 164, Porto, Portugal.
authors.forename: Andreia
authors.initials: A
authors.lastname: Palmeira
authors.forename: Freddy
authors.initials: F
authors.lastname: Rodrigues
authors.forename: Emília
authors.initials: E
authors.lastname: Sousa
authors.forename: Madalena
authors.initials: M
authors.lastname: Pinto
authors.forename: M Helena
authors.initials: MH
authors.lastname: Vasconcelos
authors.forename: Miguel X
authors.initials: MX
authors.lastname: Fernandes
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D003628:Database Management Systems; D004317:Doxorubicin / Q000494:pharmacology; D055808:Drug Discovery; D005434:Flow Cytometry; D006801:Humans; D020014:K562 Cells; D025341:Principal Component Analysis
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D004317:Doxorubicin; D000251:Adenosine Triphosphatases