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Assessing the carcinogenic potential of novel therapeutics
Abstracts / Toxicology Letters 258S (2016) S62–S324
(7,12-dimethylbenz[␣]anthracene), a well-known CYP1B1 inducer also enhanced uPAR expression. However, CYP1B1 siRNA and TMS (tetramethoxystilbene), a specific CYP1B1 inhibitor prevented uPAR mRNA induction. CYP1B1 overexpression or DMBA also activated PAI-1 expression which was suppressed by TMS. We also found that CYP1B1 induction caused an increased integrin 1 and ␣5 expression. uPAR promoter activity was also strongly decreased in CYP1B1 siRNA-treated cells. Interestingly, CYP1B1 siRNA did not cause a significant decrease of integrins mRNA level although integrin ␣5 protein level was strongly suppressed, indicating protein degradation may play an important role in regulating integrin protein level. Surprisingly, CYP1B1 down-regulated p53 expression through MDM2 activation which may cause uPAR induction. Taken together, our data suggest that CYP1B1 promotes cancer cell progression and metastasis via activating uPAR pathway which is one of the target of p53 signaling. http://dx.doi.org/10.1016/j.toxlet.2016.06.1412 P03-012 Phase II metabolism of the chlorzoxazone: Identification of O- and N-glucuronides produced by distinct UDP-glucuronosyltransferases in human hepatocytes N. Quesnot 1,∗ , S. Valenca 2 , M. Robin 1 , P. Loyer 1 1
INSERM, UMR991, Liver, Metabolisms and Cancer, CHU Pontchaillou, F-35033 Rennes, France 2 Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brazil
The cytochrome P4502E1 (CYP2E1) is an enzyme of significant importance in Human Health. Indeed, the CYP2E1 is induced in various physiopathological conditions such as diabetes and obesity and contribute to the tumorigenesis via its involvement in the activation of pro-carcinogens and ROS production. Chlorzoxazone, through its transformation into 6-hydroxychlorzoxazone is used to measure CYP2E1 activity in vitro and currently remains the only pharmacologic probe for CYP2E1 in human. Using chlorzoxazone, our objective was to compare the CYP2E1 activities in primary human hepatocytes, hepatocyte-like HepaRG cells and HepG2 wild type or overexpressing CYP2E1. Ours results evidenced the major impact of the phase II metabolism on the transformation of the 6-OHCXZ in a downstream metabolite, specially in the metabolically competent models of human hepatocytes and HepaRG cells. We postulated that the HepG2 cells lacking the expression of major UDP-glucuronosyl transferases would accumulate the 6-OHCXZ while primary hepatocytes and HepaRG would produce an O-glucuronide from the 6-OHCXZ. Chromatograms obtained with hepatocytes and HepaRG confirmed the presence of an O-glucuronide and indicated the presence of an additional peak that did not disappear with the treatment with glucuronidase. For the first time in vitro, we identified a N-glucuronide derived from CXZ independently from the CYP2E1 activity. In addition, we showed the N-glucuronide resistance to glucuronidase hydrolysis and the consequence on the CYP2E1 phenotyping in humans. To identify the phase II enzymes implicated, we selected UGTs candidates and confirmed their involvement in the production of the differents glucuronides using recombinant microsomes and cells expressing specific UGTs. http://dx.doi.org/10.1016/j.toxlet.2016.06.1413
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P03-013 Effect of arsenic exposure on Nrf2-Keap1 pathway and epigenetic modification B. Janasik 1,∗ , E. Reszka 2 , M. Stanislawska 1 , E. Jablonska 2 , R. Kuras 1 , E. Wieczorek 2 , B. Malachowska 3 , W. Fendler 3 , W. Wasowicz 1 1 Department of Environmental and Biological Monitoring, Nofer Institute of Occupational Medicine, Lodz, Poland 2 Department of Toxicology and Carcinogenesis, Nofer Institute of Occupational Medicine, Lodz, Poland 3 Department of Biostatistics and Translational Medicine, Medical University of Lodz, Poland
Arsenic is a known toxic element and carcinogen that is present in industrial settings and in the environment. There has been increasing evidence of the correlation between the generation of reactive oxygen species (ROS), DNA damage, tumor promotion, and arsenic exposure. Transcription factor nuclear factor-erythroid 2related factor 2 (NRF2) controls cellular adaptation to oxidants and electrophiles by inducing antioxidant and detoxification genes in response to redox stress. To explore associations between As level and NRF2-regulated cytoprotective genes expression, an observational study was conducted in a population of 61 occupationally exposed men aged 42–54 years and in a control group of 52 men aged 32–51 years without occupational exposure. NRF2, KEAP1, GSTP1, HMOX1, NQO1, PRDX1, TXNRD1 genes expression in peripheral blood leukocytes was determined by means of quantitative real-time PCR. The mean urine As level in the exposed and control group was found to be: 44.8 ± 67.3 mcg/L (range 2.8–511.6 mcg/L) and 16.3 ± 27.8 mcg/L (range 1.2–124.2 mcg/L) respectively. NRF2 mRNA level was positively correlated with expression of investigated NRF2-target genes in both groups (p < 0.0001). The multivariate linear regression adjusting for inorganic arsenic concentration showed that urine As level was significantly associated with genes expression of TXNRD1, GSTP1, HMOX1, PRDX1. The global DNA methylation was significantly higher in occupationally exposed workers than in controls (p < 0.0001). The results of this study indicate that arsenic occupational exposure is positively associated with global DNA methylation. The findings provide evidence showing Nrf2-Keap1 pathway to play a role in adaptive response against arsenic. http://dx.doi.org/10.1016/j.toxlet.2016.06.1414 P03-014 Assessing the carcinogenic potential of novel therapeutics P. Bentley 1,∗ , T. MacLachlan 2 , H. Martus 3 , J. Moggs 3 1
Toxicodynamix International LLC, Hendersonville, NC, USA Novatis Institutes of Biomedical Research, Cambridge, MA, USA 3 Novartis Institutes of Biomedical Research, Basel, Switzerland 2
Assessing the carcinogenic potential of pharmaceutical agents during drug development is challenging, particularly for innovative therapeutics of diverse modalities and target biology. The standard life-time rodent studies when applied to the more classical small molecular weight drug candidates indicate carcinogenic potential of about 50% of the tested compounds, and extensive mechanistic studies are often required to determine the human relevance of these findings. These rodent assays are generally not applicable to
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Abstracts / Toxicology Letters 258S (2016) S62–S324
bio-therapeutics or cell and gene therapies, however, these latter modalities, which may involve intrinsic modification of the host genome, require distinct cancer hazard identification approaches. For all these agents a weight of evidence approach to cancer risk assessment is required based on the mode of action, the target biology and the balance of data from a variety of preclinical cancer identification models. The potential association between target modulation and tumorigenic phenotypes should be systematically assessed based on preclinical genetic models and human cancer genome databases. Recent advances in molecular carcinogenesis should be taken into consideration, for example the ability of a therapeutic agent to induce sustained cell proliferation, prevent cell death, enhance cell de-differentiation or induce specific epigenetic changes. As well as information from appropriate human derived cellular systems, either in vitro or in an animal host and available clinical data. A pragmatic weight of evidence risk assessment should also include waivers of rodent bioassays in situations where they are unlikely to add value to the drug product label or enhance clinical risk management. http://dx.doi.org/10.1016/j.toxlet.2016.06.1415 P03-015 Treatment with a mixture of aristolochic acid I and II influences their genotoxicity and expression of biotransformation enzymes in rats in vivo M. Stiborova 1 , F. Barta 1 , H. Dracinska 1,∗ , A. Hudecova 1 , P. Hodek 1 , M. Balogova 1 , J. Mraz 2 , S. Duskova 2 , H.H. Schmeiser 3 , V.M. Arlt 4 1 Department of Biochemistry, Faculty of Science, Charles University in Prague, 128 43 Prague 2, Czech Republic 2 Centre of Occupational Health, National Institute of Public Health, 100 42 Prague 10, Czech Republic 3 German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany 4 Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King’s College London, London SE1 9NH, UK
Aristolochic acids (AA), a natural mixture of plant alkaloids AAI and AAII, cause aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN) associated with urothelial malignancy. AAI is either reductively activated to species forming AAI-DNA adducts by NAD(P)H:quinone oxidoreductase 1 (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 or oxidatively detoxified to 8-hydroxyaristolochic acid (AAIa) by CYP1A and 2C. The impact of exposure to either AAI or AAII alone or in combination on genotoxicity of AA and expression and activities of enzymes dictating AA metabolism was investigated in rats in vivo. The AA-DNA adducts were formed in liver, kidney and lung of rats treated with AAI, AAII and both compounds in combination. The higher levels of AAII- than AAI-derived DNA adducts were formed. Compared to rats treated with AAI or AAII alone, the sum of total levels of AA-DNA adducts was higher in liver and kidney of rats treated with both AA in combination. Exposure of rats to AA led to strong induction of NOQ1 activity in liver, mainly by exposure to the combination of both compounds. In addition, marker activities of CYP1A1, 1A2 and 2C6 were increased in livers of all exposed animals. Enhanced activities of CYP1A1/2 and 2C6 correlated with an increase in oxidation of AAI to its detoxification metabolite AAIa.
The results demonstrate that induction of CYP enzymes by treatment of rats with AAI combined with AAII decreases the toxic effect of AAI, but induction of NQO1 potentiates its genotoxicity. Supported by GACR (14-18344S) and UNCE (204025/2012). http://dx.doi.org/10.1016/j.toxlet.2016.06.1416 P03-016 NADH:cytochrome b5 reductase and cytochrome b5 act as sole electron donors to human cytochrome P450 1A1-catalyzed oxidation and DNA adduct formation by benzo[a]pyrene M. Stiborova 1 , I. Radek 1 , M. Moserova 1,∗ , E. Frei 2 , K. Kopka 2 , D.H. Phillips 3 , V.M. Arlt 3 1 Department of Biochemistry, Faculty of Science, Charles University in Prague, 128 43 Prague 2, Czech Republic 2 Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany 3 Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King’s College London, London SE1 9NH, UK
Benzo[a]pyrene (BaP) is a human carcinogen that covalently binds to DNA after activation by cytochrome P450 (CYP). We investigated whether NADH:cytochrome b5 reductase (CBR) in the presence of cytochrome b5 can act as sole electron donor to human CYP1A1 during BaP oxidation and replace the canonical NADPH:cytochrome P450 reductase (POR) system. Two systems containing human CYP1A1 were utilized: human recombinant CYP1A1 expressed with POR, CBR, epoxide hydrolase and cytochrome b5 in SupersomesTM and human recombinant CYP1A1 reconstituted with POR and/or with CBR and cytochrome b5 in liposomes. BaP-9,10-dihydrodiol, BaP-7,8-dihydrodiol, BaP-1,6dione, BaP-3,6-dione, BaP-9-ol, BaP-3-ol, a metabolite of unknown structure, and two BaP-DNA adducts were generated by the CYP1A1-SupersomesTM system, both in the presence of NADPH and NADH. The major BaP-DNA adduct detected by 32P-postlabeling was characterized as 10-(deoxyguanosin-N2-yl)-7,8,9-trihydroxy7,8,9,10-tetrahydro-BaP (assigned adduct 1), while the minor adduct is probably a guanine adduct derived from 9-hydroxy-BaP4,5-epoxide (assigned adduct 2). BaP-3-ol as the major metabolite, BaP-9-ol, BaP-1,6-dione, BaP-3,6-dione, an unknown metabolite, and adduct 2 were observed in the system using CYP1A1 reconstituted with POR plus NADPH. When CYP1A1 was reconstituted with CBR, and cytochrome b5 plus NADH, BaP-3-ol was the predominant metabolite, too, and an additional BaP-DNA adduct (assigned adduct X) with unknown structure was observed. Our results demonstrate that the NADH/cytochrome b5/CBR system acts as the sole electron donor both for the first and second reduction of CYP1A1 during the oxidation of BaP in vitro. They suggest that NADH-dependent CBR can replace NADPH-dependent POR in the CYP1A1-catalyzed metabolism of BaP. Supported by GACR (14-18344S). http://dx.doi.org/10.1016/j.toxlet.2016.06.1417
(7,12-dimethylbenz[␣]anthracene), a well-known CYP1B1 inducer also enhanced uPAR expression. However, CYP1B1 siRNA and TMS (tetramethoxystilbene), a specific CYP1B1 inhibitor prevented uPAR mRNA induction. CYP1B1 overexpression or DMBA also activated PAI-1 expression which was suppressed by TMS. We also found that CYP1B1 induction caused an increased integrin 1 and ␣5 expression. uPAR promoter activity was also strongly decreased in CYP1B1 siRNA-treated cells. Interestingly, CYP1B1 siRNA did not cause a significant decrease of integrins mRNA level although integrin ␣5 protein level was strongly suppressed, indicating protein degradation may play an important role in regulating integrin protein level. Surprisingly, CYP1B1 down-regulated p53 expression through MDM2 activation which may cause uPAR induction. Taken together, our data suggest that CYP1B1 promotes cancer cell progression and metastasis via activating uPAR pathway which is one of the target of p53 signaling. http://dx.doi.org/10.1016/j.toxlet.2016.06.1412 P03-012 Phase II metabolism of the chlorzoxazone: Identification of O- and N-glucuronides produced by distinct UDP-glucuronosyltransferases in human hepatocytes N. Quesnot 1,∗ , S. Valenca 2 , M. Robin 1 , P. Loyer 1 1
INSERM, UMR991, Liver, Metabolisms and Cancer, CHU Pontchaillou, F-35033 Rennes, France 2 Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brazil
The cytochrome P4502E1 (CYP2E1) is an enzyme of significant importance in Human Health. Indeed, the CYP2E1 is induced in various physiopathological conditions such as diabetes and obesity and contribute to the tumorigenesis via its involvement in the activation of pro-carcinogens and ROS production. Chlorzoxazone, through its transformation into 6-hydroxychlorzoxazone is used to measure CYP2E1 activity in vitro and currently remains the only pharmacologic probe for CYP2E1 in human. Using chlorzoxazone, our objective was to compare the CYP2E1 activities in primary human hepatocytes, hepatocyte-like HepaRG cells and HepG2 wild type or overexpressing CYP2E1. Ours results evidenced the major impact of the phase II metabolism on the transformation of the 6-OHCXZ in a downstream metabolite, specially in the metabolically competent models of human hepatocytes and HepaRG cells. We postulated that the HepG2 cells lacking the expression of major UDP-glucuronosyl transferases would accumulate the 6-OHCXZ while primary hepatocytes and HepaRG would produce an O-glucuronide from the 6-OHCXZ. Chromatograms obtained with hepatocytes and HepaRG confirmed the presence of an O-glucuronide and indicated the presence of an additional peak that did not disappear with the treatment with glucuronidase. For the first time in vitro, we identified a N-glucuronide derived from CXZ independently from the CYP2E1 activity. In addition, we showed the N-glucuronide resistance to glucuronidase hydrolysis and the consequence on the CYP2E1 phenotyping in humans. To identify the phase II enzymes implicated, we selected UGTs candidates and confirmed their involvement in the production of the differents glucuronides using recombinant microsomes and cells expressing specific UGTs. http://dx.doi.org/10.1016/j.toxlet.2016.06.1413
S95
P03-013 Effect of arsenic exposure on Nrf2-Keap1 pathway and epigenetic modification B. Janasik 1,∗ , E. Reszka 2 , M. Stanislawska 1 , E. Jablonska 2 , R. Kuras 1 , E. Wieczorek 2 , B. Malachowska 3 , W. Fendler 3 , W. Wasowicz 1 1 Department of Environmental and Biological Monitoring, Nofer Institute of Occupational Medicine, Lodz, Poland 2 Department of Toxicology and Carcinogenesis, Nofer Institute of Occupational Medicine, Lodz, Poland 3 Department of Biostatistics and Translational Medicine, Medical University of Lodz, Poland
Arsenic is a known toxic element and carcinogen that is present in industrial settings and in the environment. There has been increasing evidence of the correlation between the generation of reactive oxygen species (ROS), DNA damage, tumor promotion, and arsenic exposure. Transcription factor nuclear factor-erythroid 2related factor 2 (NRF2) controls cellular adaptation to oxidants and electrophiles by inducing antioxidant and detoxification genes in response to redox stress. To explore associations between As level and NRF2-regulated cytoprotective genes expression, an observational study was conducted in a population of 61 occupationally exposed men aged 42–54 years and in a control group of 52 men aged 32–51 years without occupational exposure. NRF2, KEAP1, GSTP1, HMOX1, NQO1, PRDX1, TXNRD1 genes expression in peripheral blood leukocytes was determined by means of quantitative real-time PCR. The mean urine As level in the exposed and control group was found to be: 44.8 ± 67.3 mcg/L (range 2.8–511.6 mcg/L) and 16.3 ± 27.8 mcg/L (range 1.2–124.2 mcg/L) respectively. NRF2 mRNA level was positively correlated with expression of investigated NRF2-target genes in both groups (p < 0.0001). The multivariate linear regression adjusting for inorganic arsenic concentration showed that urine As level was significantly associated with genes expression of TXNRD1, GSTP1, HMOX1, PRDX1. The global DNA methylation was significantly higher in occupationally exposed workers than in controls (p < 0.0001). The results of this study indicate that arsenic occupational exposure is positively associated with global DNA methylation. The findings provide evidence showing Nrf2-Keap1 pathway to play a role in adaptive response against arsenic. http://dx.doi.org/10.1016/j.toxlet.2016.06.1414 P03-014 Assessing the carcinogenic potential of novel therapeutics P. Bentley 1,∗ , T. MacLachlan 2 , H. Martus 3 , J. Moggs 3 1
Toxicodynamix International LLC, Hendersonville, NC, USA Novatis Institutes of Biomedical Research, Cambridge, MA, USA 3 Novartis Institutes of Biomedical Research, Basel, Switzerland 2
Assessing the carcinogenic potential of pharmaceutical agents during drug development is challenging, particularly for innovative therapeutics of diverse modalities and target biology. The standard life-time rodent studies when applied to the more classical small molecular weight drug candidates indicate carcinogenic potential of about 50% of the tested compounds, and extensive mechanistic studies are often required to determine the human relevance of these findings. These rodent assays are generally not applicable to
S96
Abstracts / Toxicology Letters 258S (2016) S62–S324
bio-therapeutics or cell and gene therapies, however, these latter modalities, which may involve intrinsic modification of the host genome, require distinct cancer hazard identification approaches. For all these agents a weight of evidence approach to cancer risk assessment is required based on the mode of action, the target biology and the balance of data from a variety of preclinical cancer identification models. The potential association between target modulation and tumorigenic phenotypes should be systematically assessed based on preclinical genetic models and human cancer genome databases. Recent advances in molecular carcinogenesis should be taken into consideration, for example the ability of a therapeutic agent to induce sustained cell proliferation, prevent cell death, enhance cell de-differentiation or induce specific epigenetic changes. As well as information from appropriate human derived cellular systems, either in vitro or in an animal host and available clinical data. A pragmatic weight of evidence risk assessment should also include waivers of rodent bioassays in situations where they are unlikely to add value to the drug product label or enhance clinical risk management. http://dx.doi.org/10.1016/j.toxlet.2016.06.1415 P03-015 Treatment with a mixture of aristolochic acid I and II influences their genotoxicity and expression of biotransformation enzymes in rats in vivo M. Stiborova 1 , F. Barta 1 , H. Dracinska 1,∗ , A. Hudecova 1 , P. Hodek 1 , M. Balogova 1 , J. Mraz 2 , S. Duskova 2 , H.H. Schmeiser 3 , V.M. Arlt 4 1 Department of Biochemistry, Faculty of Science, Charles University in Prague, 128 43 Prague 2, Czech Republic 2 Centre of Occupational Health, National Institute of Public Health, 100 42 Prague 10, Czech Republic 3 German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany 4 Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King’s College London, London SE1 9NH, UK
Aristolochic acids (AA), a natural mixture of plant alkaloids AAI and AAII, cause aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN) associated with urothelial malignancy. AAI is either reductively activated to species forming AAI-DNA adducts by NAD(P)H:quinone oxidoreductase 1 (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 or oxidatively detoxified to 8-hydroxyaristolochic acid (AAIa) by CYP1A and 2C. The impact of exposure to either AAI or AAII alone or in combination on genotoxicity of AA and expression and activities of enzymes dictating AA metabolism was investigated in rats in vivo. The AA-DNA adducts were formed in liver, kidney and lung of rats treated with AAI, AAII and both compounds in combination. The higher levels of AAII- than AAI-derived DNA adducts were formed. Compared to rats treated with AAI or AAII alone, the sum of total levels of AA-DNA adducts was higher in liver and kidney of rats treated with both AA in combination. Exposure of rats to AA led to strong induction of NOQ1 activity in liver, mainly by exposure to the combination of both compounds. In addition, marker activities of CYP1A1, 1A2 and 2C6 were increased in livers of all exposed animals. Enhanced activities of CYP1A1/2 and 2C6 correlated with an increase in oxidation of AAI to its detoxification metabolite AAIa.
The results demonstrate that induction of CYP enzymes by treatment of rats with AAI combined with AAII decreases the toxic effect of AAI, but induction of NQO1 potentiates its genotoxicity. Supported by GACR (14-18344S) and UNCE (204025/2012). http://dx.doi.org/10.1016/j.toxlet.2016.06.1416 P03-016 NADH:cytochrome b5 reductase and cytochrome b5 act as sole electron donors to human cytochrome P450 1A1-catalyzed oxidation and DNA adduct formation by benzo[a]pyrene M. Stiborova 1 , I. Radek 1 , M. Moserova 1,∗ , E. Frei 2 , K. Kopka 2 , D.H. Phillips 3 , V.M. Arlt 3 1 Department of Biochemistry, Faculty of Science, Charles University in Prague, 128 43 Prague 2, Czech Republic 2 Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany 3 Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King’s College London, London SE1 9NH, UK
Benzo[a]pyrene (BaP) is a human carcinogen that covalently binds to DNA after activation by cytochrome P450 (CYP). We investigated whether NADH:cytochrome b5 reductase (CBR) in the presence of cytochrome b5 can act as sole electron donor to human CYP1A1 during BaP oxidation and replace the canonical NADPH:cytochrome P450 reductase (POR) system. Two systems containing human CYP1A1 were utilized: human recombinant CYP1A1 expressed with POR, CBR, epoxide hydrolase and cytochrome b5 in SupersomesTM and human recombinant CYP1A1 reconstituted with POR and/or with CBR and cytochrome b5 in liposomes. BaP-9,10-dihydrodiol, BaP-7,8-dihydrodiol, BaP-1,6dione, BaP-3,6-dione, BaP-9-ol, BaP-3-ol, a metabolite of unknown structure, and two BaP-DNA adducts were generated by the CYP1A1-SupersomesTM system, both in the presence of NADPH and NADH. The major BaP-DNA adduct detected by 32P-postlabeling was characterized as 10-(deoxyguanosin-N2-yl)-7,8,9-trihydroxy7,8,9,10-tetrahydro-BaP (assigned adduct 1), while the minor adduct is probably a guanine adduct derived from 9-hydroxy-BaP4,5-epoxide (assigned adduct 2). BaP-3-ol as the major metabolite, BaP-9-ol, BaP-1,6-dione, BaP-3,6-dione, an unknown metabolite, and adduct 2 were observed in the system using CYP1A1 reconstituted with POR plus NADPH. When CYP1A1 was reconstituted with CBR, and cytochrome b5 plus NADH, BaP-3-ol was the predominant metabolite, too, and an additional BaP-DNA adduct (assigned adduct X) with unknown structure was observed. Our results demonstrate that the NADH/cytochrome b5/CBR system acts as the sole electron donor both for the first and second reduction of CYP1A1 during the oxidation of BaP in vitro. They suggest that NADH-dependent CBR can replace NADPH-dependent POR in the CYP1A1-catalyzed metabolism of BaP. Supported by GACR (14-18344S). http://dx.doi.org/10.1016/j.toxlet.2016.06.1417