Mutagenic activation of IQ, PhIP, and MeIQx by hepatic microsomes from rat, monkey and man: low mutagenic activation of MeIQx in cynomolgus monkeys in vitro reflects low DNA adduct levels in vivo

Cooked meat, poultry and fish contain a number of mutagenicand carcinogenic heterocyclic amines, including 2-amino-3-methylimidazo[4,5-f]quinoline(IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP).In the present study we examined the capacity of hepatic microsomesfrom Fischer 344 rats, cynomolgus monkeys and humans to metabolicallyactivate IQ, MeIQx and PhIP in vitro using the Ames Salmonellamutagenicity assay. The mutagenic activation of IQ was similaramong the three species; however, there were significant differencesamong the species in the activation of PhIP and MeIQx. Livermicrosomes from humans showed the greatest capacity to activatePhIP and MeIQx, followed by rats, and then monkeys. The largestdifferences between the species were observed when MeIQx wasused as the mutagen. MeIQx–DNA adducts formed in vivowere then compared among rats and monkeys given MeIQx by gavage(20 mg/kg/day, 10 doses). ³²P-Postlabeling analysis, carriedout under intensification conditions, was used to examine MeIQx–DNAadducts in the liver, kidney, heart, colon and white blood cells.MeIQx–DNA adducts were highest in all tissues examinedfrom male rats, followed by female rats, and much lower in monkeys.In the liver, the total MeIQx–DNA adduct levels of monkeyswere {small tilde}19 and {small tilde}10 times lower than inmale and female rats respectively. In extrahepatic tissues,the differences in MeIQx–DNA adduct levels between monkeysand rats were even greater. The results suggest that the lowlevel of MeIQx–DNA adducts found in vivo in cynomolgusmonkeys reflects a low capacity to activate MeIQx via the hepaticcytochrome P450 monooxygenase system.     

DNA adduct formation and tumorigenesis in mice during the chronic administration of 4-aminobiphenyl at multiple dose levels

Recent studies have demonstrated the presence of DNA adductsfrom 4-aminobiphenyl (4-ABP) in the bladder cells of humans;however, the correlation between the concentration of theseadducts and the tumorigenic response is not clear. To help elucidatethis relationship, we have investigated DNA adduct formationin experimental animals continuously administered 4-ABP. Maleand female BALB/c mice were treated for 28 days with 4-ABP hydro-chloridein their drinking water. DNA adducts in target tissues (liverof females and bladder of males) were identified and quantifiedby ³²P-postlabeling analyses and radio-immunoassays. These resultswere compared to previously reported tumor incidences obtainedfrom the lifetime administration of 4-ABP hydrochloride. Themajor adduct observed in both tissues was N-(deoxyguanosin-8-yl)-4-ABP.In the bladders of both sexes and the livers of female mice,adduct levels increased with dose at low doses, but saturationwas observed at high doses. In the livers of males, the adductlevels were linearly correlated with dose throughout the entiredose range. A comparison between DNA adducts and tumorigenesisindicated a linear correlation between adduct levels and theincidence of liver tumors in female mice. In the bladders ofmale mice, however, the relationship was markedly nonlinear.These data suggest that adduct formation alone is insufficientfor tumorigenesis in the bladder and that other factors suchas cell proliferation are necessary for tumor production.     

Dose-related differences in DNA adduct levels in rodent tissues following skin application of complex mixtures from air pollution sources

Dose-related differences in the binding of DNA reactive intermediates for three environmentally important complex mixture particulate extracts and a well-studied carcinogen, benzo[a]pyrene (BaP), were examined in female C-57 mice following multiple topical treatments ranging from 1 to 120 mg/mouse. Particulate extracts from coke oven, coal soot and diesel exhaust were selected as model complex mixtures based on short-term mutagenicity assays, animal bioassays for carcinogenicity or epidemiological studies, where increased incidences of lung cancer in exposed populations were detected. Positive and negative control animals were treated with 1.2 mg BaP or acetone respectively. DNA was isolated from skin, lung and liver 24 h following the last application and analyzed for DNA adducts using the nuclease P1 version of the 32P-postlabeling assay. Each of the particulate extracts produced distinct patterns of DNA adducts. A diagonal zone of radioactivity, presumably representing multiple putative DNA adducts, was observed for coke-oven, coal-soot- and diesel-modified DNA samples. One adduct, common to all three complex-mixture-modified DNA samples, co-migrated with the major BaP adduct observed following treatment with BaP alone. Based on the BaP concentration for each of the extracts it seems unlikely that this adduct is derived from BaP alone. It is possible that an adduct is formed with chromatographic properties similar to the major BaP-derived adduct detected in mice treated with BaP alone. This adduct was detected in all tissues examined and represented approximately 12-34% of the total number of adducts detected within the diagonal radioactive zone for all coke-oven- and coal-soot-exposed tissues (skin, lung and liver). In contrast, this adduct represented 49-67% of the total radioactivity recovered from the diagonal zone of DNA isolated from lungs of animals exposed to diesel extract. The highest total number of adducts resulted from the metabolism of coke oven extract followed by coal soot and diesel treatments respectively. A dose-dependent increase in adduct formation was observed for all tissues in the diesel- and coal-soot-treatment mice. Liver and lung, but not skin, DNA adduct levels increased in a dose-dependent manner in the coke-oven-treated mice. The percentage of dose administered, detected as DNA adducts increased in all tissues as the dose decreased for all three complex mixtures. These data have important implications for risk assessment of these complex mixtures.     

DNA adduct levels in congenic rapid and slow acetylator mouse strains following chronic administration of 4-aminobiphenyl.

4-Aminobiphenyl (4-ABP) is a human and mouse bladder carcinogen. Epidemiological studies have shown that individuals with a slow acetylator phenotype, especially those exposed to high levels of carcinogenic aromatic amines, show an increased susceptibility to bladder cancer. In order to determine if a slow acetylator phenotype results in increased DNA damage, congenic mouse strains C57BL/6J and B6.A-Nat(s), which differ genetically at the acetyltransferase (EC 2.3.1.5) locus as homozygous rapid (Natr/Natr) and homozygous slow (Nat(s)/Nat(s)) acetylators respectively, were continuously administered 4-ABP.HCl (55-300 p.p.m.) in their drinking water for 28 days. The levels of covalently bound N-(deoxyguanosin-8-yl)-4-ABP-DNA adducts, which are believed to be critical for the initiation of tumors, were quantitated in the liver and bladder by 32P-postlabeling analysis. The levels of the hepatic DNA adduct increased with dose in both sexes, but were independent of the mouse acetylator genotype. At comparable doses, however, the levels of DNA adducts were 2-fold higher in the liver of the female as compared to the male animals. The DNA adducts also increased with dose in bladder of the male mice, but in contrast to the liver, the adduct levels were approximately 2-fold lower in the bladder DNA of the female mice. Also in contrast to the liver, the levels of bladder DNA adducts were significantly higher (P < or = 0.03) in the phenotypic rapid acetylator females compared to the slow acetylators at both 75 and 150 p.p.m. doses; the median levels of adducts were 10-20% higher in the phenotypic slow acetylator male bladders compared to their rapid acetylator counterparts. The results of these studies are consistent with the increased carcinogenicity of 4-ABP to the liver of female mice and the bladder of male mice. They further suggest that factors other than acetylator phenotype limit the extent of DNA adduct formation from 4-ABP in these mice.     

Comparison of glutathione levels in rodent and human tumor cells grown in vitro and in vivo

Cellular glutathione (GSH) levels were compared in human and rodent tumor cells grown both in vivo and in vitro. Three human (A431, HEp3, ME180) and two murine (KHT and RIF-1) tumor cell lines were used. The average GSH contents for exponentially growing human cells in vitro were 14.2, 10.9, and 17.0 fmol/cell for ME180, A431, and HEp3 cells, respectively. These cells also were grown as tumors in nude mice. Following dissociation, greater than 90% pure populations of neoplastic and nonneoplastic cells were isolated by centrifugal elutriation prior to GSH determination. The data showed that the GSH levels of the tumor associated host cells were appreciably lower than those of the neoplastic cells. In addition, in contrast to the values obtained for the exponential cells, neoplastic cells grown in vivo showed a 2- to 3-fold reduction in GSH. However, the values for in vivo cells were similar to those obtained for the same tumor cells grown in vitro in the plateau phase. Compared to the human tumor cells the GSH contents of murine tumor cells always were lower. For example, RIF-1 and KHT cells in the exponential growth phase had GSH contents of 3.3 and 7.5 fmol/cell, respectively. Also, as was observed with the human cells, the GSH content of KHT cells in plateau phase of growth was 2-3 times less than that of cells in the exponential phase of growth. Similarly, the GSH content of KHT cells grown as in situ tumors prior to dissociation and isolation by centrifugal elutriation also was reduced by a factor of 3 compared to exponential phase cells. Although the average volume of tumor cells grown in vivo was less than that of cells grown in vitro, this did not account for the differences in GSH values observed when in vitro and in vivo derived cells were compared. Finally, GSH measurements made on multiple biopsies of individual human tumor xenografts varied by a factor of 2-3 within each tumor type studied. This variation, likely due to host cell fluctuations, may present a complicating feature in the interpretation of solid tumor GSH levels.     

Evidence of anti-benzo[a]pyrene diolepoxide-DNA adduct formation in human colon mucosa

As risk factors for colorectal cancer include consumption offoods potentially contaminated with polycyclic aromatic hydrocarbons(PAHs), the level of ( + )-r-7, t-8-dihydroxy-t-9, 10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene[(+ )-anti-BPDE] bound to DNA of human colon mucosa sampleswas quantified by a sensitive and specific HPLC/fluorescencemethod (Alexandrov et al., Cancer Res. 51, 6248–6253,1992). (+ )-anti-BPDE-DNA adducts were detected in four outof seven colon mucosa samples but not in any of 11 human pancreassamples from smokers and non-smokers. Adduct levels in humancolon varied between 0.2 and 1.0 ( + )-anti-BPDE-DNA adducts/10⁸nucleotides. Our results provide evidence that: (i) the DNAin human colon cells can be damaged by benzo[a]pyrene, possiblyderived from diet and/or tobacco smoke; (ii) DNA adduct formationin human colon epithelium proceeds via the diol epoxide pathway;(iii) benzo[a]pyrene and other PAHs could play a role in theetiology of human colorectal cancer.     

Tamoxifen forms DNA adducts in human colon after administration of a single [14C]-labeled therapeutic dose

Tamoxifen is widely prescribed for the treatment of breast cancer and is also licensed in the United States for the prevention of this disease. However, tamoxifen therapy is associated with an increased occurrence of endometrial cancer in women, and there is also evidence that it may elevate the risk of colorectal cancer. The underlying mechanisms responsible for tamoxifen-induced carcinogenesis in women have not yet been elucidated, but much interest has focused on the role of DNA adduct formation. We investigated the propensity of tamoxifen to bind irreversibly to colorectal DNA when given to 10 women as a single [(14)C]-labeled therapeutic (20 mg) dose, approximately 18 h before undergoing colon resections. Using the sensitive technique of accelerator mass spectrometry, coupled with high-performance liquid chromatography separation of enzymatically digested DNA, a peak corresponding to authentic dG-N(2)-tamoxifen adduct was detected in samples from three patients, at levels ranging from 1 to 7 adducts/10(9) nucleotides. No [(14)C]-radiolabel associated with tamoxifen or its major metabolites was detected. The presence of detectable CYP3A4 protein in all colon samples suggests that this tissue has the potential to activate tamoxifen to alpha-hydroxytamoxifen, in addition to that occurring in the systemic circulation, and direct interaction of this metabolite with DNA could account for the binding observed. Although the level of tamoxifen-induced damage displayed a degree of interindividual variability, when present, it was approximately 10 to 100 times higher than that reported for other suspect human colon carcinogens such as 2-amino-1-methyl-6-phenyimidazo[4,5-b]pyridine. These findings provide a mechanistic basis through which tamoxifen could increase the incidence of colon cancers in women.     

Chemopreventive activity of very low dose dietary tannic acid administration in hepatoma bearing C3H male mice.

Tannins are plant polyphenols comprising a heterogeneous group of compounds. Tannic acid is a common tannin found in tea, coffee, immature fruits, etc. and it has also been used as a food additive. An increasing body of experimental evidence supports the hypothesis that tannins exert anticarcinogenic activity in chemically induced cancers in animal models. In the present study, tannic acid was administered in very low doses in the drinking water of C3H male mice divided into three groups (75 mg/l, 150 mg/l and 300 mg/l). These animals carry a genetic defect and show a high incidence of spontaneous liver tumors (> 50%) at an age older than 12 months. The results showed a decrease in the overall incidence of hepatic neoplasms (adenomas plus carcinomas): 53.3% of animals in the control group developed hepatic neoplasms versus 33.3% in the group given a low dose of tannic acid, 26.6% in the group given a medium dose and 13.3% in the high dosage group. The difference was more pronounced in the animals with carcinomas: 4.44% of mice who received tannic acid developed carcinomas versus 33.3% of those in the control group. Tannic acid administration did not affect the PCNA labeling index of normal hepatocytes. It is concluded that tannic acid dietary intake in low doses can exert a strong dose-dependent chemoprotective activity against spontaneous hepatic neoplasm development in C3H male mice, most probably through antipromoting mechanisms.     

Regression of human colon cancer xenografts in SCID mice following oral administration of water-insoluble camptothecins

Gastrointestinal cancers pose major public health problems worldwide, in part because little progress has been made in the treatment of colorectal cancers. The present study explored the potential use of natural product topoisomerase I inhibitors, 10-hydroxycamptothecin (HCPT) and camptothecin (CPT), in the treatment of human colon cancers. HCPT and CPT are indole alkaloids originally isolated from th. Chinese tree, Camptotheca acuminata. They have been shown to have a wide spectrum of anticancer activity both in vitro and in vivo. The use of these camptothecins, however, has been hampered by their water-insolubility. In the present study, following screening of their in vitro antitumor activity, we determined their in vivo antitumor effects using C.B-17-scid/scid mice bearing LS174T or DLD-1 xenografts. Tumor-bearing mice were treated with oral doses of HCPT (1, 3, or 6 mg/kg/day) or CPT (1 or 3 mg/kg/day), 5 days per week for 2 weeks (LS 174T) or 3 weeks (DLD-1). Growth of the xenografts was significantly inhibited by HCPT and CPT in a dose-dependent manner, with marked reductions in tumor mass occurring in those groups given HCPT at 6 mg/kg/day or CPT at 3 mg/kg/day. Pathologic examination confirmed the dose-dependent atrophy of the adenocarcinomas. In summary, this study demonstrates the potential use of water-insoluble camptothecins when given by the oral route for treatment of human colon cancer, and provides the basis for the design of future human trials with these anticancer drugs.     

Comparison of benzo[a]pyrene-DNA adduct levels in mouse and rat epidermis and dermis

Male Swiss mice and Wistar rats were treated topically with 250 nmol/mouse and 750 nmol/rat of [3H]benzo[a]pyrene ([3H]BaP). The initial level of total BaP--DNA and the individual modified deoxyribonucleoside adducts were similar in the skin epidermis of the two species. The concentration of these adducts was approximately 3 times less in both mouse and rat dermis. The decreased amount of BaP bound to DNA of mouse dermis may be related to the resistance of this tissue to the carcinogenic action of BaP. The ability of both the mouse (susceptible) and rat (resistant) skin to form BaP-bound products similar in nature and ratio in the epidermal and dermal DNA, suggests that other mechanisms are involved in the difference in the biological response of epidermis versus dermis to the carcinogenic effect of BaP.     

High‐dose methotrexate following intravitreal methotrexate administration in preventing central nervous system involvement of primary intraocular lymphoma

In order to prevent central nervous system (CNS) involvement and improve the prognosis of primary intraocular lymphoma (PIOL), we prospectively evaluated the efficacy of combined therapy using intravitreal methotrexate (MTX) and systemic high‐dose MTX on treatment‐naïve PIOL. Patients with newly diagnosed PIOL whose lymphoma was limited to the eyes were enrolled. The patients were treated with weekly intravitreal MTX until the ocular lesions were resolved, followed by five cycles of systemic high‐dose MTX (3.5 g/m²) every other week. Ten patients were enrolled in this study and completed the treatment. All patients achieved complete response for their ocular lesions with rapid decrease of intravitreal interleukin‐10 concentration. Adverse events of intravitreal and systemic high‐dose MTX were mild and tolerable. With a median follow‐up of 29.5 months, four patients (40%) experienced the CNS disease development and the mean CNS lymphoma‐free survival (CLFS) time was 51.1 months. Two‐year CLFS, which was the primary end‐point of the study, was 58.3% (95% confidence interval, 23.0–82.1%). In contrast, eight patients were treated with intravitreal MTX alone in our institute, and their 2‐year CLFS was 37.5% (95% confidence interval, 8.7–67.4%). In conclusion, systemic high‐dose MTX following intravitreal MTX is feasible and might be effective in preventing CNS involvement of PIOL. Further arrangements are worth considering in order to improve the effects. This study was registered with UMIN Clinical Trials Registry (UMIN000003921).     

Global and gene‐specific promoter methylation changes are related to anti‐B[a]PDE‐DNA adduct levels and influence micronuclei levels in polycyclic aromatic hydrocarbon‐exposed individuals

We investigated the effect of chronic exposure to polycyclic aromatic hydrocarbons (PAHs) on DNA methylation states (percentage of methylated cytosines (%mC)) in Polish male nonsmoking coke‐oven workers and matched controls. Methylation states of gene‐specific promoters (p53, p16, HIC1 and IL‐6) and of Alu and LINE‐1 repetitive elements, as surrogate measures of global methylation, were quantified by pyrosequencing in peripheral blood lymphocytes (PBLs). DNA methylation was evaluated in relation to PAH exposure, assessed by urinary 1‐pyrenol and anti‐benzo[a]pyrene diolepoxide (anti‐B[a]PDE)‐DNA adduct levels, a critical genetic damage from B[a]P. We also evaluated whether PAH‐induced DNA methylation states were in turn associated with micronuclei in PBLs, an indicator of chromosomal instability. © 2009 UICC     

MicroRNA‐135a acts as a putative tumor suppressor by directly targeting very low density lipoprotein receptor in human gallbladder cancer

The precise functions and mechanisms of microRNAs (miR) in gallbladder cancer (GBC) remain elusive. In this study, we found that miR‐135a‐5p expression is often dampened and correlated with neoplasm histologic grade in GBC. MicroRNA‐135a‐5p introduction clearly inhibited GBC cell proliferation in vitro and in vivo. Moreover, very low density lipoprotein receptor (VLDLR), which is often upregulated in GBC tissues, was identified as a direct functional target of miR‐135a‐5p. Furthermore, the p38 MAPK pathway was proven to be involved in miR‐135a‐VLDLR downstream signaling. Together, these results suggested that the miR‐135a–VLDLR–p38 axis may contribute to GBC cell proliferation.     

Comparison of radiosensitization by 41 degrees C hyperthermia during low dose rate irradiation and during pulsed simulated low dose rate irradiation in human glioma cells

PURPOSE: Long duration mild hyperthermia has been shown to be an effective radiosensitizer when given concurrently with low dose rate irradiation. Pulsed simulated low dose rate (PSLDR) is now being used clinically, and we have set out to determine whether concurrent mild hyperthermia can be an effective radiosensitizer for the PSLDR protocol. MATERIALS AND METHODS: Human glioma cells (U-87MG) were grown to plateau phase and treated in plateau phase in order to minimize cell cycle redistribution during protracted treatments. Low dose rate (LDR) irradiation and 41 degrees C hyperthermia were delivered by having a radium irradiator inside a temperature-controlled incubator. PSLDR was given using a 150 kVp X-ray unit and maintaining the cells at 41 degrees C between irradiations. The duration of irradiation and concurrent heating depended on total dose and extended up to 48 h. RESULTS: When 41 degrees C hyperthermia was given currently with LDR or PSLDR, the thermal enhancement ratios (TER) were about the same if the average dose rate for PSLDR was the same as for LDR. At higher average dose rates for PSLDR the TERs became less. CONCLUSIONS: Our data show that concurrent mild hyperthermia can be an effective sensitizer for PSLDR. This sensitization can be as effective as for LDR if the same average dose rate is used and the TER increases with decreasing dose rate. Thus mild hyperthermia combined with PSLDR may be an effective clinical protocol.     

Increased transforming growth factor‐α levels in human colon carcinoma cell lines over‐expressing protein kinase C

Transforming growth factor‐α (TGF‐α) is synthesized as a membrane‐bound precursor protein, pro‐TGF‐α, that is converted to a soluble form by 2 endoproteolytic cleavages. Several factors have been implicated in the regulation of the second rate‐limiting step, including protein kinase C (PKC). Earlier results indicated a potential role for the conventional class of PKC isozymes in the observed increase in TGF‐α in the conditioned media of 2 human colon carcinoma cell lines. The present study addresses the potential role of specific PKC isozymes in this process using sense and anti‐sense expression vectors for PKC isozymes. Two human colon carcinoma cell lines, HCT 116 and GEO, were transfected with plasmids, leading to the over‐expression of PKC‐α, ‐βI or ‐βII; and the secretion of TGF‐α into the conditioned medium was determined. Over‐expression of either PKC‐βI or PKC‐βII in these cell lines enhanced the levels of TGF‐α in the media 2‐ to 5‐fold. Over‐expression of PKC‐α did not alter the amount of TGF‐α in the media to a significant extent. Transfection of HCT 116 cells with the anti‐sense PKC‐βI cDNA resulted in a reduction in PKC‐βI protein expression. This was accompanied by a decrease in the amount of TGF‐α in the conditioned media. Our results indicate that modulation of PKC‐β protein levels alters the amount of TGF‐α found in the conditioned media from these colon carcinoma cells. Int. J. Cancer 80:72–77, 1999. © 1999 Wiley‐Liss, Inc.     

Cigarette smoke induces promoter methylation of single‐stranded DNA‐binding protein 2 in human esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the sixth most frequent cause of cancer death in the world, and cigarette smoke is a key factor in esophageal carcinogenesis. To identify molecular changes during cigarette smoke‐induced ESCC, we examined the methylation status of 13 gene promoters in the human immortalized, nontumorigenic esophageal epithelial cell line (Het‐1A) that were exposed to mainstream (MSE) or sidestream cigarette smoke extract (SSE) for 6 months in culture. The promoter of sequence‐specific single‐stranded DNA‐binding protein 2 (SSBP2) was methylated in the Het‐1A cells exposed to MSE (MSE‐Het‐1A). Promoter methylation (86%, 56/70) and downregulation of SSBP2 expression were frequently detected in tumor tissues from ESCC patients. In addition, reintroduction of SSBP2 in an ESCC cell line (TE1) that does not express SSBP2 and in the MSE‐Het‐1A cells inhibited expression of LRP6 and Dvl3, which are mediators of the Wnt signaling pathway. SSBP2 expression markedly decreased the colony‐forming ability of ESCC cell lines and significantly inhibited cell growth of the MSE‐Het‐1A cells. Our results indicate that cigarette smoking is a cause of SSBP2 promoter methylation and that SSBP2 harbors a tumor suppressive role in ESCC through inhibition of the Wnt signaling pathway.     

Comparison of basic fibroblast growth factor levels in clone A human colon cancer cells in vitro with levels in xenografted tumours.

We measured levels of basic fibroblast growth factor (FGF-2) in human colon cancer cells (clone A) in vitro and in xenografted solid tumours using a commercial enzyme-linked immunoassay. In Vitro, levels in unfed plateau phase or exponentially growing cells were low, averaging respectively about 2 and 8 pg 10(-6) cells. However, when solid tumours (average volumes 787 mm3) were cut into halves and either enzymatically disaggregated to obtain a cellular fraction or extracted in toto, levels were much higher. In the cellular fraction, values averaged 110 pg 10(-6) cells, while in whole tumour extracts, average values were 24 pg mg-1 tumour tissue. These results indicate that growth factor levels in solid neoplasms may differ markedly from those predicted from in vitro measurements. We hypothesise that the apparent increase in FGF-2 levels in vivo results primarily from the presence of a significant fraction of host cells (in particular, macrophages, which may contain high levels of FGF-2) within xenografted clone A neoplasms.     

Ethanol‐mediated carcinogenesis in the human esophagus implicates CYP2E1 induction and the generation of carcinogenic DNA‐lesions

Chronic alcohol consumption is a major risk factor for esophageal cancer. Various mechanisms may mediate carcinogenesis including the genotoxic effect of acetaldehyde and oxidative stress. Ethanol exerts its carcinogenic effect in the liver among others via the induction of cytochrome P450 2E1 (CYP2E1) and the generation of carcinogenic etheno‐DNA adducts. Here we investigated if such effects can also be observed in the human esophagus. We studied nontumorous esophageal biopsies of 37 patients with upper aerodigestive tract cancer and alcohol consumption of 102.3 ± 131.4 g/day (range: 15–600 g) as well as 16 controls without tumors (12 teetotalers and 4 subjects with a maximum of 25 g ethanol/day). CYP2E1, etheno‐DNA adducts and Ki67 as a marker for cell proliferation were determined immunohistologically. Chronic alcohol ingestion resulted in a significant induction of CYP2E1 (p = 0.015) which correlated with the amount of alcohol consumed (r = 0.6, p < 0.001). Furthermore, a significant correlation between CYP2E1 and the generation of the carcinogenic exocyclic etheno‐DNA adducts 1,N⁶‐ethenodeoxyadenosine (r = 0.93, p < 0.001) and 3,N⁴‐ethenodeoxycytidine (r = 0.92, p < 0.001) was observed. Etheno‐DNA adducts also correlated significantly with cell proliferation (p < 0.01), which was especially enhanced in patients who both drank and smoked (p < 0.001). Nonsmokers and nondrinkers had the lowest rate of cell proliferation, CYP2E1 expression and DNA lesions. Our data demonstrate for the first time an induction of CYP2E1 in the esophageal mucosa by ethanol in a dose dependent manner in man and may explain, at least in part, the generation of carcinogenic DNA lesions in this target organ.