Suppression of Cytosolic NADPH Pool by Thionicotinamide Increases Oxidative Stress and Synergizes with Chemotherapy

Abstract

NAD 1 kinase (NADK) is the only known cytosolic enzyme that converts NAD 1 to NADP 1 , which is subsequently reduced to NADPH. The demand for NADPH in cancer cells is elevated as reducing equivalents are required for the high levels of nucleotide, protein, and fatty acid synthesis found in proliferating cells as well as for neutralizing high levels of reactive oxygen species (ROS). We determined whether inhibition of NADK activity is a valid anticancer strategy alone and in combination with chemotherapeutic drugs known to induce ROS. In vitro and in vivo inhibition of NADK with either small-hairpin RNA or thionicotinamide inhibited proliferation. Thionicotinamide enhanced the ROS produced by several chemotherapeutic drugs and produced synergistic cell kill. NADK inhibitors alone or in combination with drugs that increase ROS-mediated stress may represent an efficacious antitumor combination and should be explored further.

Genome-Wide CRISPR Screen for Essential Cell Growth Mediators in Mutant KRAS Colorectal Cancers

“…NADK has previously been proposed as a possible therapeutic target in cancer, since NADPH is essential to support enhanced biosynthesis and to control redox status (17) (Figure 2D). Consistent with this, administration of thionicotinamide (thioNa), a small molecule inhibitor of NADK (18), showed significant inhibition of the growth of HCT116 MUT xenografts but not of HCT116 WT xenografts (Figures 2E and 2F). KHK has also recently been described as a possible therapeutic target for hepatocellular carcinoma (19,20).…”

NAD- and NADPH-Contributing Enzymes as Therapeutic Targets in Cancer: An Overview

“…NADK generates NADPH that is important to scavenge ROS, and promote cell longevity [97,98]. Thus, targeting NADK in cancer has been recognized as another potential anti-cancer target [10].…”

“…NADK is inhibited by thionicotinamide adenine dinucleotide (NADS) and thionicotinamide adenine dinucleotide phosphate (NADPS) [10,11,86]. The prodrug thionicotinamide, (TN) is converted into NADS and NADPS intracellularly and acts as dual inhibitor of NADK and glucose-6-phosphate dehydrogenase (G6PD) that catalyzes NADPH production.…”

“…The prodrug thionicotinamide, (TN) is converted into NADS and NADPS intracellularly and acts as dual inhibitor of NADK and glucose-6-phosphate dehydrogenase (G6PD) that catalyzes NADPH production. Reducing intracellular NADPH results in an increase in ROS [10,11]. Reduction of NADP + by dehydrogenases produces NADPH the substrate for glutathione reductase and mediates the production 5-phosphoribosyl-1-pyrophosphate (PRPP), the substrate for the synthesis of purine and pyrimidine.…”

“…TN successfully delayed tumor growth in xenograft mouse models of colon cancer and diffuse large B cell lymphoma (DLBCL) and in vitro synergized with other ROS-inducing chemotherapeutic agents [10]. As mutant IDH requires NADPH to produce D-2HG, thus, a NADK inhibitor might be a novel therapeutic approach for treating mutant IDH cancer cells to decrease the NADPH pool which may not be sufficient to facilitate the production of the D-2HG oncometabolite.…”