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The Antitumor Agent Imexon Activates Antioxidant Gene Expression: Evidence for an Oxidative Stress Response

Authors' Affiliations: ¹ University of Arizona Cancer Center, Tucson, Arizona and ² Department of Experimental Therapeutics and Center for Targeted Therapy, M. D. Anderson Cancer Center, Houston, Texas

Requests for reprints: Amanda F. Baker, Arizona Cancer Center, Room 3977, 1515 North Campbell Avenue, Tucson, AZ 85724. Phone: 520-626-0301/6704; Fax: 520-626-6704; E-mail: abaker{at}azcc.arizona.edu.

Purpose: The aim of this study was to identify biomarkers that may be predictive for the clinical activity of the redox-active antitumor agent imexon.

Experimental Design: cDNA microarray and quantitative real-time PCR were used to identify global changes in gene expression in peripheral blood mononuclear cells (PBMC) collected from patients treated with imexon during a phase I trial. Electrophoretic mobility shift assays and Western blot analysis were done using the RPMI8226 myeloma cell line grown in vitro and PBMCs treated ex vivo to investigate the molecular mechanism responsible for these gene changes.

Results: Both cDNA microarray and quantitative real-time PCR showed the up-regulation of many antioxidant genes, including thioredoxin reductase-1, glutaredoxin-2, and peroxiredoxin-3 in PBMCs collected from patients treated with imexon. Studies in PBMCs treated ex vivo and RPMI8226 myeloma cells showed that imexon increased binding to the activator protein-1 consensus sequence measured by electrophoretic mobility shift assay. Supershift analysis showed that the majority of the activator protein-1 DNA binding activity was c-Jun, with minor contribution of Jun-D. Nuclear translocation of the nuclear factor (erythroid-derived 1)-like 2 transcription factor and its binding to the antioxidant response element was also increased after imexon treatment, which correlated with an increase in the message levels for nuclear factor (erythroid-derived 1)-like 2/antioxidant response element–regulated antioxidant genes.

Conclusions: Together, these results show that a predominant biological effect of imexon is a change in redox state that can be detected in surrogate normal tissues as increased redox-sensitive transcription factor binding and increased antioxidant gene expression.