7-Nitro-4-(phenylthio)benzofurazan is a potent generator of superoxide and hydrogen peroxide.
Here, we report on 7-nitro-4-(phenylthio)benzofurazan (NBF-SPh), the most potent derivative among a set of patented anticancer 7-nitrobenzofurazans (NBFs), which have been suggested to function by perturbing protein-protein interactions. We demonstrate that NBF-SPh participates in toxic redox-cycling, rapidly generating reactive oxygen species (ROS) in the presence of molecular oxygen, and this is the first report to detail ROS production for any of the anticancer NBFs. Oxygraph studies showed that NBF-SPh consumes molecular oxygen at a substantial rate, rivaling even plumbagin, menadione, and juglone. Biochemical and enzymatic assays identified superoxide and hydrogen peroxide as products of its redox-cycling activity, and the rapid rate of ROS production appears to be sufficient to account for some of the toxicity of NBF-SPh (LC(50) = 12.1 μM), possibly explaining why tumor cells exhibit a sharp threshold for tolerating the compound. In cell cultures, lipid peroxidation was enhanced after treatment with NBF-SPh, as measured by 2-thiobarbituric acid-reactive substances, indicating a significant accumulation of ROS. Thioglycerol rescued cell death and increased survival by 15-fold to 20-fold, but pyruvate and uric acid were ineffective protectants. We also observed that the redox-cycling activity of NBF-SPh became exhausted after an average of approximately 19 cycles per NBF-SPh molecule. Electrochemical and computational analyses suggest that partial reduction of NBF-SPh enhances electrophilicity, which appears to encourage scavenging activity and contribute to electrophilic toxicity.
Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA. eric.patridge@gmail.com
Eric V
EV
Patridge
Emma S E
ES
Eriksson
Philip G
PG
Penketh
Raymond P
RP
Baumann
Rui
R
Zhu
Krishnamurthy
K
Shyam
Leif A
LA
Eriksson
Alan C
AC
Sartorelli
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D006861:Hydrogen Peroxide / Q000378:metabolism; D007928:Lethal Dose 50; D015227:Lipid Peroxidation / Q000187:drug effects; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism; D051379:Mice; D010069:Oxadiazoles / Q000008:administration & dosage / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
C578083:7-nitro-4-(phenylthio)benzofurazan; D000970:Antineoplastic Agents; D010069:Oxadiazoles; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; D013481:Superoxides; D006861:Hydrogen Peroxide; D010100:Oxygen