title: Quercetin selectively inhibits bioreduction and enhances apoptosis in melanoma cells that overexpress tyrosinase.
abstract: Tyrosinase is expressed in melanoma cells and catalyzes the formation of 3,3',4',5,7-pentahydroxyflavone (quercetin) into reactive quinone species and subsequent glutathionyl adducts. Therefore, we examined the effect of quercetin metabolism on the glutathione (GSH) bioreduction pathway and cell viability in DB-1 melanoma cells that express varying levels of tyrosinase (Tyr+). In a cell-free system, GSH was significantly decreased by quercetin, which coincided with the formation of glutathionyl adducts. In Tyr+ clones, quercetin decreased bioreduction capacity and increased reactive oxygen species (ROS) to a greater degree compared to control cells. The antioxidant/electrophile response element-induced enzymes, glutathione-S-transferase (GST), and nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 were expressed at high levels in Tyr+ cells and contributed to pro-oxidant quercetin metabolism. The basal level of ROS and apoptosis was higher in Tyr+ cells and were selectively increased after exposure to quercetin. The increase in apoptosis following quercetin exposure was p53/Bax mediated and correlated with a decrease in GST-driven bioreduction capacity and an increase in ROS. In conclusion, quercetin can selectively sensitize Tyr+ expressing melanoma cells to apoptosis and may serve as an adjuvant to chemotherapy by enhancing cell death and interfering with GST-mediated drug resistance.
authors.affiliation: Department of Nutritional Sciences, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Thilakavathy
authors.initials: T
authors.lastname: Thangasamy
authors.forename: Sivanandane
authors.initials: S
authors.lastname: Sittadjody
authors.forename: Susan
authors.initials: S
authors.lastname: Lanza-Jacoby
authors.forename: Phyllis R
authors.initials: PR
authors.lastname: Wachsberger
authors.forename: Kirsten H
authors.initials: KH
authors.lastname: Limesand
authors.forename: Randy
authors.initials: R
authors.lastname: Burd
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008544:Melanocytes / Q000187:drug effects / Q000201:enzymology; D008545:Melanoma / Q000201:enzymology*; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D011794:Quercetin / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D011794:Quercetin; D014442:Monophenol Monooxygenase; D005978:Glutathione