title: Melanin as a target for melanoma chemotherapy: pro-oxidant effect of oxygen and metals on melanoma viability.
abstract: Melanoma cells have a poor ability to mediate oxidative stress, which may be attributed to constitutive abnormalities in their melanosomes. We hypothesize that disorganization of the melanosomes will allow chemical targeting of the melanin within. Chemical studies show that under oxidative conditions, synthetic melanins demonstrate increased metal affinity and a susceptibility to redox cycling with oxygen to form reactive oxygen species. The electron paramagnetic resonance (EPR)-active 5,5'-dimethyl-pyrollidine N-oxide spin adduct was used to show that binding of divalent Zn or Cu to melanin induces a pro-oxidant response under oxygen, generating superoxide and hydroxyl radicals. A similar pro-oxidant behaviour is seen in melanoma cell lines under external peroxide stress. Melanoma cultures grown under 95% O2/5% CO2 atmospheres show markedly reduced viability as compared with normal melanocytes. Cu- and Zn-dithiocarbamate complexes, which induce passive uptake of the metal ions into cells, show significant antimelanoma activity. The antimelanoma effect of metal- and oxygen-induced stress appears additive rather than synergistic; both treatments are shown to be significantly less toxic to melanocytes.
authors.affiliation: Department of Chemistry, University of California, Irvine, CA 92697-2025, USA. pfarmer@uci.edu
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Farmer
authors.forename: Shirley
authors.initials: S
authors.lastname: Gidanian
authors.forename: Babbak
authors.initials: B
authors.lastname: Shahandeh
authors.forename: Angel J
authors.initials: AJ
authors.lastname: Di Bilio
authors.forename: Nilou
authors.initials: N
authors.lastname: Tohidian
authors.forename: Frank L
authors.initials: FL
authors.lastname: Meyskens
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival; D002478:Cells, Cultured; D003300:Copper / Q000737:chemistry; D003497:Cyclic N-Oxides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000737:chemistry; D007231:Infant, Newborn; D008297:Male; D008543:Melanins / Q000378:metabolism*; D008545:Melanoma / Q000188:drug therapy* / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D016877:Oxidants / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D017382:Reactive Oxygen Species; D013997:Time Factors; D015032:Zinc / Q000737:chemistry
chemical_list: D003497:Cyclic N-Oxides; D004791:Enzyme Inhibitors; D007211:Indoles; D008543:Melanins; D008670:Metals; D016877:Oxidants; D017382:Reactive Oxygen Species; C069977:2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy; D003300:Copper; D015032:Zinc; D010100:Oxygen; C033871:5,6-dihydroxyindole