Potent Antitumor Activity of Novel Iron Chelators Derived from Di-2-Pyridylketone Isonicotinoyl Hydrazone Involves Fenton-Derived Free Radical Generation

Abstract

Purpose: 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.Experimental Design: 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 redoxsensitive 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 H 2 O 2 . 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 H 2 O 2 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.

The Potent and Novel Thiosemicarbazone Chelators Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone and 2-Benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone Affect Crucial Thiol Systems Required for Ribonucleotide Reductase Activity

“…S1). For example, unlike the inhibitory effect of catalase (1000 U/ml) on the antiproliferative activity of the earlier generation chelator, pyridylketone isonicotinyl hydrazone (PKIH) (Chaston et al, 2004), this enzyme or membrane-permeable, pegylated-catalase (1000 U/ml) did not affect the antiproliferative activity of thiosemicarbazones (Supplemental Fig. S1A; P. Jansson, D. R. Richardson, unpublished results).…”

A class of iron chelators with a wide spectrum of potent antitumor activity that overcomes resistance to chemotherapeutics

“…Furthermore, upon PKIH and DpT ligands forming Fe complexes, these ligands generate cytotoxic ROS (10,(26)(27)(28). The resulting oxidative damage potentiates the antiproliferative activity of PKIH and DpT chelators compared with 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone or DFO, which bind Fe but do not redox cycle (29).…”

The Iron Chelator Dp44mT Causes DNA Damage and Selective Inhibition of Topoisomerase IIα in Breast Cancer Cells

“…Further studies will be needed to ascertain the conversion of Dp44mT in vivo and the activity of the metabolites for better comparison with bisdioxopiperazines (ICRF-187/ICRF-193) activity (40,41). Other iron chelating analogues of di-2-pyridylketone isonicotinoyl hydrazone have been tested for DNA cleavage activity and do not inhibit top1 (42). No reports have provided data on top2 activity for these analogues.…”