Priority Research Papers:

Epigenetic effects of RRx-001: a possible unifying mechanism of anticancer activity

Hongjuan Zhao, Shoucheng Ning, Jan Scicinski, Bryan Oronsky, Susan J. Knox and Donna M. Peehl _

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Oncotarget. 2015; 6:43172-43181. https://doi.org/10.18632/oncotarget.6526

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Hongjuan Zhao1, Shoucheng Ning2, Jan Scicinski3, Bryan Oronsky3, Susan J. Knox2 and Donna M. Peehl1

1 Department of Urology, Stanford University School of Medicine, Stanford, CA, USA

2 Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA

3 EpicentRx, Inc., Mountain View, CA, USA

Correspondence to:

Donna M. Peehl, email:

Keywords: RRx-001, epigenetics, cancer, DNA methylation, acetylation

Received: November 09, 2015 Accepted: November 27, 2015 Published: December 09, 2015


RRx-001 is a novel aerospace-derived compound currently under investigation in several ongoing Phase II studies. In a Phase I trial, it demonstrated anti-cancer activity and evidence of resensitization to formerly effective therapies in heavily pre-treated patients with relapsed/refractory solid tumors. RRx-001 generates reactive oxygen and nitrogen species (ROS and RNS) and nitric oxide (NO), elicits changes in intracellular redox status, modulates tumor blood flow, hypoxia and vascular function and triggers apoptosis in cancer cells. We investigated the effect of RRx-001 on the epigenome of SCC VII cancer cells. RRx-001 at 0.5 and 2 μM significantly decreased global DNA methylation, i.e., 5-methylcytosine levels, in SCC VII cells. Consistently, 0.5-5 μM RRx-001 significantly decreased Dnmt1 and Dnmt3a protein expression in a dose- and time-dependent manner. In addition, global methylation profiling identified differentially methylated genes in SCC VII cells treated with 0.5, 2, and 5 μM RRx-001 compared to control cells. Twenty-three target sites were hypomethylated and 22 hypermethylated by >10% in the presence of at least two different concentrations of RRx-001. Moreover, RRx-001 at 2 μM significantly increased global acetylated histone H3 and H4 levels in SCC VII cells after 24 hour treatment, suggesting that RRx-001 regulates global acetylation in cancer cells. These results demonstrate that, in contrast to the traditional “one drug one target” paradigm, RRx-001 has multi(epi)target features, which contribute to its anti-cancer activity and may rationalize the resensitization to previously effective therapies observed in clinical trials and serve as a unifying mechanism for its anticancer activity.

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