Interactions of the major metabolite of the cancer chemopreventive drug oltipraz with cytochrome c: a novel pathway for cancer chemoprevention.
The major metabolite of the cancer chemopreventive agent oltipraz, a pyrrolopyrazine thione (PPD), has been shown to be a phase 2 enzyme inducer, an activity thought to be key to the cancer chemopreventive action of the parent compound. In cells, mitochondria are the major source of reactive oxygen species (ROS) and cytochrome c (cyt c) is known to participate in mitochondrial electron transport and confer antioxidant and peroxidase activities. To understand possible mechanisms by which PPD acts as a phase 2 enzyme inducer, a study of its interaction with cyt c was undertaken. UV-visible spectroscopic results demonstrate that PPD is capable of reducing oxidized cyt c. The reduced cyt c is stable for a long period of time in the absence of an oxidizing agent. In the presence of ferricyanide, the reduced cyt c is rapidly oxidized back to its oxidized form. Further, UV-visible spectroscopic studies show that during the reduction process the coordination environment and redox state of iron in cyt c are changed. Low-temperature EPR studies show that during the reduction process, the heme iron changes from a low-spin state of s = 1/2 to a low-spin state of s = 0. Room-temperature EPR studies demonstrate that PPD inhibits the peroxidase activity of cyt c. EPR spin trapping experiments using DMPO show that PPD inhibits the superoxide radical scavenging activity of oxidized cyt c. From these results, we propose that PPD interacts with cyt c, binding to and then reducing the heme, and this may enhance ROS levels in mitochondria. This in turn could contribute to the mechanism by which the parent compound, oltipraz, might trigger the cancer chemopreventive increase in transcription of phase 2 enzymes. The modifications of cyt c function by the oltipraz metabolite may have implications for the regulation of apoptotic cell death.
Velayutham
Murugesan
M
Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute, and Division of Cardiovascular Medicine, Department of Internal Medicine, Ohio State University College of Medicine, Columbus, OH 43210, USA.
Muthukumaran
Rajendra B
RB
Sostaric
Joe Z
JZ
McCraken
John
J
Fishbein
James C
JC
Zweier
Jay L
JL
D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000378:metabolism*; D018890:Chemoprevention; D045304:Cytochromes c / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D006321:Heart / Q000502:physiology; D006736:Horses; D013058:Mass Spectrometry; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009369:Neoplasms / Q000378:metabolism / Q000517:prevention & control; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology*; D017382:Reactive Oxygen Species; D013056:Spectrophotometry, Ultraviolet; D013871:Thiones; D013876:Thiophenes
D016588:Anticarcinogenic Agents; D000975:Antioxidants; D011719:Pyrazines; D017382:Reactive Oxygen Species; D013871:Thiones; D013876:Thiophenes; C026209:oltipraz; D045304:Cytochromes c; D009195:Peroxidase