Figure 1. The RONS critical threshold. The accumulation of RONS above a critical threshold level leads to cancer cell death.

RONS = Reactive Oxygen Nitrogen Species

Reactive oxygen species or ROS refers to chemically reactive molecules containing oxygen such as the superoxide anion (O2•), hydroxyl radical (•HO), peroxyl radical (HOO•) as well as non-radical derivatives such as hydrogen peroxides (H2O2) and singlet oxygen. Reactive nitrogen species or RNS refers to nitric oxide (NO) and its derivatives such as peroxynitrite (ONOO−), a highly reactive radical which is the product of the reaction between NO and superoxide anion. These two species, ROS and RNS, are collectively known as RONS. RONS have effects on multiple targets and pathways, including effects on p53 and on epigenetic mediators that are important in antitumor activity.



Figure 2. Vulnerability to RONS is an Achilles’ Heel for cancer.

Figure 2. Vulnerability to RONS is an Achilles’ Heel for cancer.

One of the hallmarks of cancer cells is a high level of free radicals. In contrast, normal tissue effectively controls oxidative stress and free radical levels are close to zero. This oxidative pressure in tumor cells is an Achilles’ Heel, rendering them selectively vulnerable and sensitive to an exogenous increase in reactive oxygen and nitrogen species (RONS); in contrast, the low steady state levels of RONS in normal tissue differentially protect it from acute spikes in oxidative stress—this discrepancy, known as a differential stress response (DSR), is the biological basis for the exquisite selectivity and lack of systemic toxicity of RRx-001—a major advantage over other small molecule histone deacetylase inhibitors (HDACis) and DNA Methyltransferase inhibitors (DNMTis) that manifest non-mechanistic or off-target toxicities. The epigenetic enzymes, DNA methyltransferases and histone deacetylases, have conserved critical cysteine residues located within their active sites that are amenable to RRx-001-induced oxidation, resulting in a loss of enzymatic activity only in the tumor, not in differentially protected normal tissue, which is at the heart of epigenetic resensitizationor ‘episensitization’ to failed chemotherapies.



Figure 3. EpicentRx compounds act as a small molecule “alarm clock” to awaken the immune system put to sleep by cancer.

Immunostimulation with Tumor Associated Macrophages

Tumors essentially put the immune system to sleep. Paradoxically macrophages, which should destroy cancer cells, can actually act in reverse to promote tumor growth and inhibit antitumoral T cell responses. In this way, these so-called M2 tumor associated macrophages aid and abet the tumor. Through RONS, EpicentRx compounds such as RRx-001 act to “wake up” the immune system by redirecting macrophage differentiation from an M2 angiogenic, immunosuppressive, and tumor-promoting state to an M1 phenotype that enables cytotoxic T cells to infiltrate tumors and kill cancer cells, rendering immunotherapy successful.