title: P-glycoprotein induction in Caco-2 cells by newly synthetized thioxanthones prevents paraquat cytotoxicity.
abstract: The induction of P-glycoprotein (P-gp), an ATP-dependent efflux pump, has been proposed as a strategy against the toxicity induced by P-gp substrates such as the herbicide paraquat (PQ). The aim of this study was to screen five newly synthetized thioxanthonic derivatives, a group known to interact with P-gp, as potential inducers of the pump's expression and/or activity and to evaluate whether they would afford protection against PQ-induced toxicity in Caco-2 cells. All five thioxanthones (20 µM) caused a significant increase in both P-gp expression and activity as evaluated by flow cytometry using the UIC2 antibody and rhodamine 123, respectively. Additionally, it was demonstrated that the tested compounds, when present only during the efflux of rhodamine 123, rapidly induced an activation of P-gp. The tested compounds also increased P-gp ATPase activity in MDR1-Sf9 membrane vesicles, indicating that all derivatives acted as P-gp substrates. PQ cytotoxicity was significantly reduced in the presence of four thioxanthone derivatives, and this protective effect was reversed upon incubation with a specific P-gp inhibitor. In silico studies showed that all the tested thioxanthones fitted onto a previously described three-feature P-gp induction pharmacophore. Moreover, in silico interactions between thioxanthones and P-gp in the presence of PQ suggested that a co-transport mechanism may be operating. Based on the in vitro activation results, a pharmacophore model for P-gp activation was built, which will be of further use in the screening for new P-gp activators. In conclusion, the study demonstrated the potential of the tested thioxanthonic compounds in protecting against toxic effects induced by P-gp substrates through P-gp induction and activation.
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. rsilva@ff.up.pt.
authors.forename: Renata
authors.initials: R
authors.lastname: Silva
authors.affiliation: Laboratório de Química Orgânica e Farmacêutica, Departamento de Ciências Químicas, Faculdade de Farmácia, Centro de Química Medicinal (CEQUIMED-UP), Universidade do Porto, Rua Jorge Viterbo Ferreira 228, 4050-313, Porto, Portugal. apalmeira@ff.up.pt.
authors.forename: Andreia
authors.initials: A
authors.lastname: Palmeira
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. helenacarmo@ff.up.pt.
authors.forename: Helena
authors.initials: H
authors.lastname: Carmo
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. daniel.barbosa@ff.up.pt.
authors.forename: Daniel José
authors.initials: DJ
authors.lastname: Barbosa
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. mariline.gameiro@gmail.com.
authors.forename: Mariline
authors.initials: M
authors.lastname: Gameiro
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. anagomex1989@gmail.com.
authors.forename: Ana
authors.initials: A
authors.lastname: Gomes
authors.affiliation: Laboratório de Química Orgânica e Farmacêutica, Departamento de Ciências Químicas, Faculdade de Farmácia, Centro de Química Medicinal (CEQUIMED-UP), Universidade do Porto, Rua Jorge Viterbo Ferreira 228, 4050-313, Porto, Portugal. gpaiva.mafalda@gmail.com.
authors.forename: Ana Mafalda
authors.initials: AM
authors.lastname: Paiva
authors.affiliation: Laboratório de Química Orgânica e Farmacêutica, Departamento de Ciências Químicas, Faculdade de Farmácia, Centro de Química Medicinal (CEQUIMED-UP), Universidade do Porto, Rua Jorge Viterbo Ferreira 228, 4050-313, Porto, Portugal. esousa@ff.up.pt.
authors.forename: Emília
authors.initials: E
authors.lastname: Sousa
authors.affiliation: Laboratório de Química Orgânica e Farmacêutica, Departamento de Ciências Químicas, Faculdade de Farmácia, Centro de Química Medicinal (CEQUIMED-UP), Universidade do Porto, Rua Jorge Viterbo Ferreira 228, 4050-313, Porto, Portugal. madalena@ff.up.pt.
authors.forename: Madalena
authors.initials: M
authors.lastname: Pinto
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. mlbastos@ff.up.pt.
authors.forename: Maria de Lourdes
authors.initials: Mde L
authors.lastname: Bastos
authors.affiliation: REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal. remiao@ff.up.pt.
authors.forename: Fernando
authors.initials: F
authors.lastname: Remião
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis*; D001692:Biological Transport; D018938:Caco-2 Cells; D003198:Computer Simulation; D005434:Flow Cytometry; D006540:Herbicides / Q000633:toxicity*; D006801:Humans; D010269:Paraquat / Q000633:toxicity*; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D013892:Thioxanthenes / Q000737:chemistry / Q000494:pharmacology; D044004:Xanthones / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D006540:Herbicides; D013892:Thioxanthenes; D044004:Xanthones; D020112:Rhodamine 123; C484911:thioxanthone; D010269:Paraquat
keywords: Activation; Caco-2 cells; Induction; P-glycoprotein; Thioxanthones