Anja Richter

Abstract 4460: Targeting the redox-protective protein MTH1 for cancer therapy: A novel way to exploit the unique redox status of cancer cells

Cancer cells are characterized by an increase in the rate of reactive oxygen species (ROS) production and an altered redox environment compared to normal cells. The role of ROS in tumorigenesis is two-fold. On the one hand, ROS play a causal role in tumor development and progression by inducing genomic instability and aberrant, pro-tumorigenic signalling. On the other hand, high levels of ROS can also be toxic to cancer cells, oxidizing and damaging both DNA and free nucleotides (dNTPs), which can lead to cell death. MutT Homolog 1 (MTH1) is a redox-protective phosphatase that converts ROS-oxidized nucleotides (8-oxo-dGTP) into their corresponding monophosphates, thus preventing their incorporation into genomic DNA and the resultant DNA damage and cell death. Recent studies have shown that MTH1 is up-regulated in various cancers and its activity is required for cancer cell survival and proliferation. Genetic knockdown of MTH1 and MTH1 small molecule inhibition led to DNA damage and cancer-specific cell death in vitro and in vivo, while having little effect on normal cells with a lower rate of ROS production. Hence, the unique redox status of cancer cells makes them reliant on redox-protective proteins like MTH1, which opens a novel therapeutic window to selectively induce cancer cell death via oxidative stress, while sparing normal cells. In order to validate MTH1 as a potential cancer therapeutic target, a wide range of cancer cells (lung, bone, colon, skin, and breast) were treated with a selective MTH1 inhibitor (TH588) or MTH1 shRNAs, and analysed for proliferation, cell survival, ROS levels and DNA damage. We found that MTH1 inhibition impaired cancer cell proliferation as well as anchorage-independent growth. Furthermore, TH588 induced cancer cell damage, as assessed by DNA damage markers and cancer cell death. Various normal, non-transformed cells (normal bronchial epithelial cells, normal lung fibroblasts and normal human epidermal melanocytes) were not affected by MTH1 inhibition. Antioxidants, which eliminate ROS, reversed the effects on cancer cells, indicating that ROS is the driver of cancer cell death and growth impairment upon MTH1 inhibition. Consequently, combination approaches using the MTH1 inhibitor together with pro-oxidants, further increased cancer cell susceptibility to oxidative stress. Based on our data, a MTH1 inhibitor may have clinical potential as a single agent or in combination with ROS inducers for the treatment of patients with various forms of cancer. Citation Format: Andrea Glasauer, Horst Irlbacher, Anja Richter, Luisella Toschi, Michael Steckel, Andrea Haegebarth. Targeting the redox-protective protein MTH1 for cancer therapy: A novel way to exploit the unique redox status of cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4460. doi:10.1158/1538-7445.AM2015-4460

Abstract 1049: Pharmacological characterization of a novel potent nicotinamide phosphoribosyltransferase (NAMPT) inhibitor with robust in vivo efficacy and increased therapeutic index with niacin supplementation

Nicotinamide adenine dinucleotide (NAD+) is an important metabolite and cofactor for a number of cellular processes including genomic stability and epigenetic regulation. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate limiting enzyme in NAD+ salvaging from nicotinamide. Many tumor cells have an increased need for NAD+ and are therefore highly sensitive to NAMPT inhibition. We have developed a selective and potent small molecule inhibitor, Cmpd1, which inhibits the NAMPT enzyme with sub-nanomolar potency. In cells, Cmpd1 treatment leads to an almost complete reduction of both NAD- and ATP-levels, followed by the induction of cell death. In order to identify sensitive cancer subtypes and associated biomarkers, we analyzed cell sensitivity to NAMPT inhibition in a panel of 240 cell lines. Small cell lung cancer and hematological malignancies were particularly sensitive to NAMPT inhibition. Overall, expression levels of NAMPT and NAD+ consuming enzymes correlated well with sensitivity to NAMPT inhibition. In order to investigate the effect of niacin on the antiproliferative effect of NAMPT inhibition across the cell panel, we further analyzed the cell sensitivity in the presence of niacin. Cells with a functional Preiss-Handler pathway can generate NAD+ from niacin, independent of NAMPT. We found that the antiproliferative effect of Cmpd1 was neutralized by niacin in 60% of the analyzed cells. The mRNA levels of nicotinate phosphoribosyltransferase 1 (NAPRT1), a central enzyme of the Preiss-Haendler pathway, predicted well the niacin rescue status of the cells. In vivo, niacin supplementation led to an at least 10-fold increase in the maximum tolerated dose of Cmpd1 in mice. Antitumor efficacy of Cmpd1 was abolished by niacin supplementation in xenografts derived from NAPRT1 expressing cells, but not in NAPRT1-deficient models. These data demonstrate that the therapeutic index of NAMPT inhibitors may be increased in NAPRT1-deficient tumors by niacin supplementation. Citation Format: Maria Quanz, Claudia Merz, Andreas Bernthaler, Stefan Kaulfuss, Anja Richter, Marcus Bauser, Andrea Haegebarth. Pharmacological characterization of a novel potent nicotinamide phosphoribosyltransferase (NAMPT) inhibitor with robust in vivo efficacy and increased therapeutic index with niacin supplementation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1049.