In 2012, the International Agency for Research on Cancer (IARC) classified diesel exhaust as a Group 1 carcinogen due to sufficient evidence that exposure is associated with increased risk for lung cancer in humans. However, only a subset of individuals exposed to diesel exhaust develops cancer, indicating the need to identify the genes involved in metabolic activation of these compounds and their genetic variants. Nitro-polycyclic aromatic hydrocarbons (NO2-PAH) are a major component of diesel exhaust and require metabolic activation to exert their carcinogenic activity. A representative NO2-PAH, 3-nitrobenzanthrone (3-NBA), is metabolically activated to 3-aminobenzanthrone (3-ABA) via a 6-electron nitroreduction catalyzed by NQO1 and POR. The reaction leads to the formation of 3-aminobenzanthrone (3-ABA) derived DNA adducts which promote G to T transversions. Building upon previous data that shows human aldo-keto reductase 1C3 (AKR1C3) contains nitroreductase activity towards chemotherapeutic agents (Guise, C.P., Abbattista, M.R., et al., Cancer Res, 70(4), 2010), we chose to examine the nitroreductase activity of AKR1C1-AKR1C4 towards NO2-PAH. We have demonstrated here for the first time that AKR1C enzymes catalyze the nitroreduction of 3-NBA to 3-ABA. We monitored reactions with reverse phase HPLC coupled to in-line photo-diode-array detection (PDA) and fluorescence detection (FLD) to quantify 3-NBA and 3-ABA levels. Fluorescence and UV spectroscopy were used to validate the identity of the compounds. This method was adapted for discontinuous enzymatic assays to measure steady state kinetic parameters for the nitoreductase activity of AKR1C1-AKR1C4 and NQO1. Results indicate that the NQO1 catalyzed reduction of 3-NBA has a higher specific activity, but the combined specific activities of AKR1C catalyzed reduction may play a more significant role in the overall production of 3-ABA. These results suggest that the relative expression of NQO1 and AKR1C enzymes will determine their respective contribution to 3-NBA reduction, especially since all the aforementioned enzymes are inducible by the Nrf2-Keap1 system. This work is supported by P30E513508 and RO1 CA39504 to TMP.
Citation Format: Jessica R. Murray, Meng Huang, Tianzhu Zang, Volker M. Arlt, Heinz H. Schmeiser, Trevor M. Penning. Metabolic activation of 3-nitrobenzanthrone by human aldo-keto reductases (AKR1C1-AKR1C4). [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 4580A. doi:10.1158/1538-7445.AM2015-4580A