Abstract 1420: RRx-001 inhibits glucose erythrocyte and tumor glucose 6-phosphate dehydrogenase

Abstract

Abstract Cancer cells are characterized by an excess of reactive oxygen species (ROS) levels, which are balanced by high levels of glutathione (GSH) to protect against ROS-induced cytotoxicity. Glucose 6-phosphate dehydrogenase (G6PD), the first key enzyme of the pentose phosphate pathway (PPP), ensures NADPH supply for reduced glutathione regeneration. RRx-001, a novel redox active anticancer agent, derived from the aerospace industry, which has successfully completed a Phase 1 clinical trial and is scheduled to begin multiple Phase 2 studies, induces cell cycle-specific apoptosis through increase in intracellular ROS leading to free thiol depletion. The purpose of the present study was to evaluate whether the mechanism by which RRx-001 targets the antioxidant capacity of tumor cells is related to G6PD inhibition. Since red blood cells (RBC) are particularly dependent on G6PD synthesis, we initially explored the effects of RRx-001 on the erythrocytic PPP. Glucose consumption was higher for human RBC (hRBC) treated with RRx-001 (10 μM) compared to untreated cells. PPP was inhibited in RRx-001 treated hRBC. Methylene blue, which normally stimulates PPP flux, did not increase glucose utilization of treated cells. Analysis of PPP flux revealed that RRx-001 inhibits G6PD preventing conversion of glucose-6-phosphate to 6-phosphogluconolactone and reduction of NADP(+). Compared to G6PD inhibitors dehydroepiandrosterone and aminonicotinamide, RRx-001 was 10 fold more potent. Given the critical importance of G6PD and NADPH to fuel both the proliferation of tumor cells and to detoxify ROS, we secondarily investigated whether RRx-001 has anti-proliferative and viability effects on hepatocellular carcinoma (Hep G2) and colorectal adenocarcinoma (Caco-2 and HT-29) cell lines. Through tetrazolium and bromodeoxyuridine incorporation assays, performed as indicators of cellular proliferation, RRx-001 inhibited cell growth in a dose dependent (1 - 20 μM) manner. The suppression of growth of the RRx-001 incubated cells was correlated with inhibition of G6PD (r=0.81, n=9, P<0.05). RRx-001 also reduced viability of all carcinoma cell lines. Given the key roles of the PPP in GSH metabolism, and the observation that cell lines overexpressing G6PD are associated with the formation of tumors in mice, inhibition of G6PD by RRx-001 is an attractive target, particularly in combination with standard of care radiotherapy or cytotoxic drugs that also generate ROS or free radical intermediates either directly or indirectly. Citation Format: Pedro Cabrales, Bryan Oronsky, Jan Scicinski. RRx-001 inhibits glucose erythrocyte and tumor glucose 6-phosphate dehydrogenase. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1420. doi:10.1158/1538-7445.AM2014-1420