Potent antitumor activity of novel iron chelators derived from di-2-pyridylketone isonicotinoyl hydrazone involves fenton-derived free radical generation.
OBJECTIVE
The development of novel and potent iron chelators as clinically useful antitumor agents is an area of active interest. Antiproliferative activity of chelators often relates to iron deprivation or stimulation of iron-dependent free radical damage. Recently, we showed that novel iron chelators of the di-2-pyridylketone isonicotinoyl hydrazone (PKIH) class have potent and selective antineoplastic activity (E. Becker, et al., Br. J. Pharmacol., 138: 819-30, 2003). In this study, we assessed the effects of the PKIH analogues on the redox activity of iron in terms of understanding their antitumor activity.


METHODS
We tested the PKIH analogues for their ability to promote iron-mediated ascorbate oxidation, benzoate hydroxylation, and plasmid degradation. Subsequent experiments assessed their ability to bind DNA, inhibit topoisomerase I, and cause DNA damage. To measure intracellular reactive oxygen species, we used the redox-sensitive probe, 2',7'-dichloro-fluorescein-diacetate, to measure intracellular PKIH-dependent redox activity.


RESULTS
The PKIH analogues had relatively little effect on ascorbate oxidation in the presence of Fe(III) but stimulated benzoate hydroxylation and plasmid DNA degradation in the presence of Fe(II) and H2O2. These ligands could not inhibit DNA topoisomerase I or cause DNA damage in intact cells. PKIH markedly increased the intracellular generation of reactive oxygen species, and this was inhibited by catalase. This enzyme also decreased the antiproliferative effect of PKIH, indicating H2O2 played a role in its cytotoxic activity.


CONCLUSIONS
Our results suggest that the antiproliferative effects of these chelators relates to intracellular iron chelation, followed by the stimulation of iron-mediated free radical generation via the so-formed iron complex.
Chaston
Timothy B
TB
Children's Cancer Institute Australia for Medical Research, Iron Metabolism and Chelation Program, Sydney, New South Wales, Australia.
Watts
Ralph N
RN
Yuan
Jun
J
Richardson
Des R
DR
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000378:metabolism; D001393:Azoles / Q000494:pharmacology; D002374:Catalase / Q000378:metabolism; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000494:pharmacology*; D004396:Coloring Agents / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005609:Free Radicals; D006801:Humans; D006835:Hydrazones / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology*; D054833:Isoindoles; D008024:Ligands; D008956:Models, Chemical; D016566:Organoselenium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
D000970:Antineoplastic Agents; D001393:Azoles; D002614:Chelating Agents; D004396:Coloring Agents; C045076:Fenton's reagent; D005609:Free Radicals; D006835:Hydrazones; D054833:Isoindoles; D008024:Ligands; D016566:Organoselenium Compounds; D011725:Pyridines; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D013844:Thiazoles; C042986:ebselen; D004247:DNA; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase; D013482:Superoxide Dismutase; D004264:DNA Topoisomerases, Type I; C022616:thiazolyl blue; D001205:Ascorbic Acid; D010100:Oxygen