title: Intracellular reduction/activation of a disulfide switch in thiosemicarbazone iron chelators.
abstract: Iron scavengers (chelators) offer therapeutic opportunities in anticancer drug design by targeting the increased demand for iron in cancer cells as compared to normal cells. Prochelation approaches are expected to avoid systemic iron depletion as chelators are liberated under specific intracellular conditions. In the strategy described herein, a disulfide linkage is employed as a redox-directed switch within the binding unit of an antiproliferative thiosemicarbazone prochelator, which is activated for iron coordination following reduction to the thiolate chelator. In glutathione redox buffer, this reduction event occurs at physiological concentrations and half-cell potentials. Consistent with concurrent reduction and activation, higher intracellular thiol concentrations increase cell susceptibility to prochelator toxicity in cultured cancer cells. The reduction of the disulfide switch and intracellular iron chelation are confirmed in cell-based assays using calcein as a fluorescent probe for paramagnetic ions. The resulting low-spin Fe(III) complex is identified in intact Jurkat cells by EPR spectroscopy measurements, which also document a decreased concentration of active ribonucleotide reductase following exposure to the prochelator. Cell viability and fluorescence-based assays show that the iron complex presents low cytotoxicity and does not participate in intracellular redox chemistry, indicating that this antiproliferative chelation strategy does not rely on the generation of reactive oxygen species.
authors.affiliation: University of Arizona, Department of Chemistry and Biochemistry, 1306 E. University Blvd., Tucson, AZ 85721-0041, USA. tomat@email.arizona.edu.
authors.forename: Eman A
authors.initials: EA
authors.lastname: Akam
authors.forename: Tsuhen M
authors.initials: TM
authors.lastname: Chang
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Astashkin
authors.forename: Elisa
authors.initials: E
authors.lastname: Tomat
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004220:Disulfides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D007501:Iron / Q000378:metabolism; D007502:Iron Chelating Agents / Q000737:chemistry* / Q000494:pharmacology*; D019169:Jurkat Cells; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D013882:Thiosemicarbazones / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D004220:Disulfides; D007502:Iron Chelating Agents; D017382:Reactive Oxygen Species; D013882:Thiosemicarbazones; D007501:Iron
references.citation: Biochim Biophys Acta. 2012 Mar;1820(3):291-317
references.pmid: 21851850
references.citation: Free Radic Biol Med. 2012 Jun 1-15;52(11-12):2254-65
references.pmid: 22561702
references.citation: Chem Rev. 2009 Oct;109(10):4885-910
references.pmid: 19637926
references.citation: Free Radic Biol Med. 2005 Aug 1;39(3):403-11
references.pmid: 15993339
references.citation: Curr Cancer Drug Targets. 2006 Aug;6(5):409-31
references.pmid: 16918309
references.citation: Biochim Biophys Acta. 2013 May;1830(5):3139-42
references.pmid: 23127894
references.citation: Mini Rev Med Chem. 2012 May;12(5):364-70
references.pmid: 22303968
references.citation: J Inorg Biochem. 2011 Nov;105(11):1422-31
references.pmid: 21955844
references.citation: J Am Chem Soc. 2014 Mar 5;136(9):3579-88
references.pmid: 24524232
references.citation: Mol Pharmacol. 2011 Jun;79(6):921-31
references.pmid: 21389104
references.citation: Sci Transl Med. 2010 Aug 4;2(43):43ra56
references.pmid: 20686179
references.citation: Biomarkers. 2012 Dec;17(8):671-91
references.pmid: 22900535
references.citation: Free Radic Biol Med. 2001 Jun 1;30(11):1191-212
references.pmid: 11368918
references.citation: J Biol Chem. 2012 Oct 12;287(42):35768-35778
references.pmid: 22915594
references.citation: Blood. 2009 Oct 1;114(14):3064-73
references.pmid: 19589922
references.citation: Metallomics. 2012 Aug;4(9):899-909
references.pmid: 22700084
references.citation: Dalton Trans. 2010 Mar 7;39(9):2177-87
references.pmid: 20162187
references.citation: Bioconjug Chem. 2010 May 19;21(5):979-87
references.pmid: 20429547
references.citation: Biochim Biophys Acta. 2009 Jul;1790(7):702-17
references.pmid: 18485918
references.citation: Pharmacol Rev. 2005 Dec;57(4):547-83
references.pmid: 16382108
references.citation: Nat Rev Cancer. 2013 May;13(5):342-55
references.pmid: 23594855
references.citation: ACS Chem Biol. 2010 Jun 18;5(6):603-10
references.pmid: 20455574
references.citation: Anal Biochem. 1997 May 15;248(1):31-40
references.pmid: 9177722
references.citation: J Biol Chem. 2012 Feb 10;287(7):4397-402
references.pmid: 22147695
references.citation: Chem Rev. 2013 Jul 10;113(7):5071-109
references.pmid: 23577659
references.citation: J Biol Chem. 1996 Aug 23;271(34):20291-9
references.pmid: 8702762
references.citation: Breast Cancer Res Treat. 2011 Feb;126(1):63-71
references.pmid: 20390345
references.citation: J Med Chem. 2009 Sep 10;52(17):5271-94
references.pmid: 19601577
references.citation: Inorg Chem. 2006 Jul 10;45(14):5607-16
references.pmid: 16813425
references.citation: Inorg Chem. 2001 Mar 26;40(7):1646-53
references.pmid: 11261975
references.citation: Cancer Res. 2011 Sep 1;71(17):5871-80
references.pmid: 21750178
references.citation: Biochem J. 2010 May 13;428(2):183-90
references.pmid: 20331437
references.citation: J Am Chem Soc. 2012 Aug 1;134(30):12668-74
references.pmid: 22642558
references.citation: Free Radic Biol Med. 2013 Dec;65:1174-1194
references.pmid: 24036104
references.citation: J Immunol. 2000 Dec 15;165(12):6771-5
references.pmid: 11120797
references.citation: J Med Chem. 2007 Nov 29;50(24):6212-25
references.pmid: 17963372
references.citation: Chembiochem. 2010 Jan 4;11(1):59-62
references.pmid: 19937900
references.citation: Nat Chem Biol. 2013 Feb;9(2):119-25
references.pmid: 23242256
references.citation: Crit Rev Oncol Hematol. 2014 Jan;89(1):1-15
references.pmid: 24275533
references.citation: Cancer Res. 2011 Nov 1;71(21):6728-37
references.pmid: 21875943
references.citation: Dalton Trans. 2007 Aug 14;(30):3214-20
references.pmid: 17893764
references.citation: Dalton Trans. 2013 Jun 14;42(22):7846-9
references.pmid: 23591852
references.citation: Chem Commun (Camb). 2011 Mar 28;47(12):3550-2
references.pmid: 21327187
references.citation: J Med Chem. 2006 Nov 2;49(22):6510-21
references.pmid: 17064069
references.citation: Cell Biochem Funct. 2006 Nov-Dec;24(6):555-9
references.pmid: 16142688
references.citation: Free Radic Biol Med. 2012 Jan 1;52(1):1-6
references.pmid: 22027063