title: Mechanisms underlying the cytotoxic effects of Tachpyr--a novel metal chelator.
abstract: Tachpyr (N,N'N"-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane), a novel metal chelator, was previously shown to deplete intracellular iron and exert a cytotoxic effect on cultured bladder cancer cells. Tachpyr binds Fe(II) and readily reduces Fe(III). The iron(II)-Tachpyr chelate undergoes intramolecular oxidative dehydrogenation resulting in mono- and diimino Fe(II) complexes. The present study investigates the redox-activity of the Tachpyr-iron complex to better define the mechanism of Tachpyr's cytotoxicity. Tachpyr's mechanism of cytotoxicity was studied using cell-free solutions, isolated DNA, and cultured mammalian cells by employing UV-VIS spectrophotometry, oximetry, spin-trapping technique, and electron paramagnetic resonance (EPR) spectrometry. The results show that: (1) Tachpyr by itself after 24 h of incubation had a cytotoxic effect on cultured cells; (2) fully oxidized Tachpyr had no cytotoxic effects on cultured cells even after 24 h of incubation; (3) Tachpyr protected isolated DNA against H(2)O(2)-induced damage, but not against HX/XO-induced damage; and (4) Tachpyr-Fe(II) chelate slows down but does not block oxidation of Fe(II), allows O*(-)(2)-induced or Tachpyr-induced reduction of Fe(III), and consequently promotes production of *OH through the Haber-Weiss reaction cycle. The results indicate that Tachpyr can protect cells against short-term, metal-mediated damage. However, upon prolonged incubation, Tachpyr exerts cytotoxic effects. Therefore, in addition to iron depletion, low-level oxidative stress, which in part occurs because of redox cycling of the coordinated iron ion, may contribute to the cytotoxic effects of Tachpyr.
authors.affiliation: Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892-1002, USA.
authors.forename: Ayelet M
authors.initials: AM
authors.lastname: Samuni
authors.forename: Murali C
authors.initials: MC
authors.lastname: Krishna
authors.forename: William
authors.initials: W
authors.lastname: DeGraff
authors.forename: Angelo
authors.initials: A
authors.lastname: Russo
authors.forename: Roy P
authors.initials: RP
authors.lastname: Planalp
authors.forename: Martin W
authors.initials: MW
authors.lastname: Brechbiel
authors.forename: James B
authors.initials: JB
authors.lastname: Mitchell
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D002277:Carcinoma / Q000188:drug therapy* / Q000473:pathology; D002374:Catalase / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002474:Cell-Free System; D002614:Chelating Agents / Q000494:pharmacology*; D003514:Cyclohexylamines / Q000633:toxicity*; D004247:DNA / Q000737:chemistry / Q000187:drug effects; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007501:Iron / Q000737:chemistry; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D046911:Macromolecular Substances; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000737:chemistry; D010101:Oxygen Consumption / Q000187:drug effects; D010957:Plasmids / Q000235:genetics; D011725:Pyridines / Q000633:toxicity*; D013482:Superoxide Dismutase / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: D000970:Antineoplastic Agents; D002614:Chelating Agents; D003514:Cyclohexylamines; D004277:DNA, Single-Stranded; D046911:Macromolecular Substances; D011725:Pyridines; C114047:tachpyr; D004247:DNA; D007501:Iron; D002374:Catalase; D013482:Superoxide Dismutase; D010100:Oxygen