Aldo-keto reductases (AKRs) oxidize structurally diverse PAH trans-dihydrodiols to yield reactive and redox active o-quinones. This study examined the ability of AKR1C2 and AKR1C4 to oxidize PAH trans-dihydrodiols of the benz[a]anthracene series. The enzymes oxidized 100% of the racemic trans-dihydrodiols and the highest utilization ratios were observed for the more potent proximate carcinogens 7,12-dimethylbenz[a]anthracene-3,4-diol (DMBA-3,4-diol) and 7-methylbenz[a]anthracene-3,4-diol (7-MBA-3,4-diol). Human multiple tissue expression array analysis revealed high expression of AKR1C isoforms in the human lung carcinoma cell line A549. Both Western blot analysis using AKR1C9 antisera and enzymatic assays using 1-acenapthanol as substrate confirmed the presence of active AKR1C enzymes in A549 cells. To determine the importance of AKR1C-mediated trans-dihydrodiol oxidation in A549 cells, DMBA-3,4-diol was incubated with cell lysates in the presence of 2-mercaptoethanol. Liquid chromatography/mass spectrometric analysis identified peaks that corresponded to the synthetically prepared mono- and bis-thioether conjugates of DMBA-3,4-dione confirming the ability of these cells to oxidize DMBA-3,4-diol to the corresponding o-quinone. Together, these studies demonstrate the importance of human AKR1Cs in PAH activation and their possible role in lung cancer.
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