title: Differences in sensitivity to UVC, UVB and UVA radiation of a multidrug-resistant cell line overexpressing P-glycoprotein.
abstract: Multidrug resistance (MDR) is the phenomenon in which cultured tumor cells, selected for resistance to one chemotherapeutic agent, simultaneously acquire resistance to several apparently unrelated drugs. The MDR phenotype is multifactorial. The best-studied mechanism involves the expression of a membrane protein that acts as an energy-dependent efflux pump, known as P-glycoprotein (Pgp), capable of extruding toxic materials from the cell. In this work, resistance to UVA radiation, but not to UVC nor UVB, was observed in an MDR leukemia cell line. This cell line overexpresses Pgp. To study the role of Pgp in the resistance to UVA radiation, two MDR modulators or reversing agents (verapamil and cyclosporin A) capable of blocking Pgp activity were used. Cell viability was assessed and the techniques of flow cytometry and fluorescence microscopy were employed to measure the extrusion of rhodamine 123 by the efflux pump. The results show that MDR modulators did not modify the resistance to UVA radiation. Furthermore, although cell viability was not significantly altered, Pgp function was impaired after UVA treatment, suggesting that this glycoprotein may be a physical target for oxidative damage, and that other factors may be responsible for the UVA resistance. In agreement with this, it was found that the resistant cell line presented a higher catalase activity than the parental (non-MDR) cell line.
authors.affiliation: Instituto de Biofísica Carlos Chagas Filho, Rio de Janeiro, Brazil.
authors.forename: G S
authors.initials: GS
authors.lastname: Trindade
authors.forename: M A
authors.initials: MA
authors.lastname: Capella
authors.forename: L S
authors.initials: LS
authors.lastname: Capella
authors.forename: O R
authors.initials: OR
authors.lastname: Affonso-Mitidieri
authors.forename: V M
authors.initials: VM
authors.lastname: Rumjanek
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D018432:Drug Resistance, Multiple / Q000502:physiology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020014:K562 Cells; D010084:Oxidation-Reduction; D011836:Radiation Tolerance / Q000502:physiology*; D014466:Ultraviolet Rays
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D006861:Hydrogen Peroxide; D002374:Catalase