Immunocytochemical localization of DNA adducts induced by a single dose of N-nitroso-N-methylbenzylamine in target and non-target tissues of tumor formation in the rat

Effect of N-nitrosomethylbenzylamine on nasal mucosa in rats

N-nitrosomethylbenzylamine (NMBA) is one of the most potent organ-specific carcinogens routinely used in rat esophageal tumorigenesis. The aim of the study was to evaluate NMBA effect on nasal mucosa, one of the non-target organs. NMBA was administered subcutaneously to 20 male albino rats of Wistar strain for 5 weeks (0.5mg/kg/dose; three doses/week). The experiment was terminated on week 22. In each case, seven standard frontal sections of the nose were taken after fixation for assessment of all the parts of the nasal mucosa. Microscopic examination revealed one small squamous cell papilloma located on the ventro-lateral surface of the left superior nasal concha, one focus on simple hyperplasia and two foci of squamous epithelium dysplasia within the mucosa covering nasal vestibule near the respiratory part of the nasal cavity. Furthermore, statistically significant increase of proliferation activity in both lesional and non-lesional nasal squamous epithelium in NMBA-exposed animals was also found. These phenomena could be potentially induced by carcinogen exposure.

Functional role of cytochrome p-450 2a3 in N-nitrosomethylbenzylamine metabolism in rat esophagus

Previous in vitro studies demonstrated that the rat esophageal carcinogen N-nitrosomethylbenzylamine (NMBA) is metabolically activated by cytochrome P-450s (CYP) 2A3 and 2E1. However, the in vivo role of these P-450s in the metabolism of NMBA has not been fully evaluated. In this study, the effects of single and multiple doses of NMBA were investigated on CYP2A3 and CYP2E1 mRNA expression in the rat esophagus and lung. Seven- to 8-wk old male Fischer 344 rats were administered a single subcutaneous dose of NMBA at either 0.5 mg/kg or 2 mg/kg body weight, after which the rats were sacrificed at 1, 3, 6, 12, 24, 48, and 72 h. In the multiple-dose experiment, 2 groups of rats were dosed with 0.5 mg/kg body weight NMBA 3 times per week for 1 wk or 3 wk. The animals were sacrificed 24 h following the last treatment. Semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis demonstrated a reduction of CYP2A3 mRNA expression in lung and esophagus from NMBA-treated animals compared to dimethyl sulfoxide (DMSO)-treated vehicle controls. This reduction in CYP2A3 mRNA was significant at 48 h in the esophagus and at 24 and 48 h in the lung following a single dose of 2 mg/kg body weight NMBA. In contrast, CYP2E1 mRNA expression remained unchanged in rat lung following NMBA treatment and no consistent pattern of expression could be observed in the esophagus. In the multiple-dose study, a 32% and 25% reduction in esophageal CYP2A3 mRNA expression was observed at 1 and 3 wk, respectively. Similar reductions in CYP2A3 mRNA expression were also observed in the lung. Further, esophageal explants derived from animals pretreated with NMBA in vivo demonstrated a reduced ability to metabolize the carcinogen in vitro as compared to explants from vehicle control animals. Taken together, these data provide further support for a potential role of CYP2A3 in NMBA metabolism in the rat esophagus. Data suggest that CYP2A3 levels in the rat esophagus can be a determinant of its ability to metabolize this carcinogen in vivo.

The formation and repair of cisplatin-DNA adducts in wild-type and cisplatin-resistant L1210 cells: comparison of immunocytochemical determination with detection in isolated DNA

We have studied the formation and repair of cisplatin-DNA adducts in wild-type mouse leukemia L1210/0 cells and in the sublines L1210/2 and L1210/5, which differ in cisplatin sensitivity. In a colony-formation assay these sublines were 9- and 22-fold more resistant compared to L1210/0, respectively. Cisplatin-induced DNA modification was studied at the cellular level by immunocytochemistry with antiserum NKI-A59 raised against cisplatin-treated DNA. Levels of nuclear staining immediately after a 1-h treatment were similar to those seen after a 24-h post-incubation in drug-free medium. Clear differences in DNA platination were found between the cell lines: immediately after exposure, L1210/2 and L1210/5 showed only 32 and 14%, respectively, of the nuclear staining observed in L1210/0, and 48 and 13% after 24 h. In these experiments, adduct-specific nuclear staining was quantified as the area under the adduct versus concentration curves (AUC). The formation and repair in these cell lines of the bifunctional adducts cis-Pt(NH3)2d(pGpG) (Pt-GG), cis-Pt(NH3)2d(pApG) (Pt-AG) and cis-Pt(NH3)2(dGMP)2 (G-Pt-G) were studied with an enzyme-linked immunosorbent assay (ELISA). No relation between repair and resistance was observed. The results suggest that differences in induced DNA platination levels, rather than in repair, are responsible--at least in part--for the differences in cisplatin resistance. A mechanism such as an increased tolerance of the resistant cells to plantinum-DNA damage may also be involved.

Nasal cavity carcinogenesis by N-nitrosamines: a critical appraisal

This review is a critical appraisal of our current knowledge on nasal cavity carcinogenesis by nitrosamines. The pathology and pathogenesis of nitrosamine-induced tumors in the nasal cavity of rodents is summarized while controversies on the underlying molecular mechanisms are discussed in more detail. Investigations on the distribution of metabolically competent cell types, the cellular site(s) of nitrosamine metabolism, as well as reports on the cellular distribution and persistence of DNA-adducts strongly suggest that DNA-adducts formed from reactive metabolites are not immediately responsible for the genesis of nasal cavity tumors. A preexisting high proliferative ability has also been suggested as a factor rendering certain cell types more susceptible to the carcinogenic actions of nitrosamines in the nasal cavity. However, this hypothesis has been clearly rejected by more recent investigations. Recent studies have shown that nitrosamines can stimulate the secretion of growth factors via interaction with neurotransmitter receptors in the lungs and that this molecular mechanism is an important factor in determining the histological phenotype of the developing lung tumors. In light of the fact that secretory cells are the main sites of DNA-adduct accumulation and toxic lesions in the nasal cavities of nitrosamine treated rodents, it is suggested that similar mechanisms may mediate the genesis of nitrosamine-induced nasal cavity tumors.

DNA damage in the nasal passageway: a literature review

The purpose of this review is to provide a compilation of work examining DNA damage in the nasal cavity. There are numerous methods to identify and quantify damage to DNA and the diversity of methods and toxicologic endpoints is illustrated by the range of studies presented here. There are a large number of independent studies measuring endpoints in the upper respiratory tract; however, with regard to toxicant induced DNA damage in the nasal passageway, the effects of two compounds, 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and formaldehyde (HCHO), appear to have been extensively characterized. The body of work on NNK and formaldehyde have provided insights into molecular mechanisms of DNA damage and repair and induced cell replication and its relationship to nasal cancer. With new technologies and molecular techniques, the sensitivity to enable evaluations of the minute quantities of nasal tissue available in test species and human biopsy impact the study of the nasal-toxicant interactions. As methods used to characterize DNA damage increase in sensitivity, the importance of both exogenous and endogenous sources of DNA damage, steady-state levels of cellular damage, repair, and resulting mutations, low-dose exposure assessments and inter-species extrapolation will become increasingly complex. Additional studies of DNA damage in the nasal passage will undoubtedly challenge future estimations of risk and impact what are perceived to be acceptable levels of exposure to known and predicted carcinogens. The aim of this paper is to provide to the interested scientist literature relevant to the effects of agents on nasal DNA, so that areas of insufficient information can be identified and used to further develop and expand the knowledge base for nasal DNA toxicant interactions.

Hyperthermia enhances the cytotoxicity and platinum-DNA adduct formation of lobaplatin and oxaliplatin in cultured SW 1573 cells

The cytotoxicity of cisplatin and cisplatin-DNA adduct formation in vitro and in vivo is clearly enhanced by hyperthermia. We investigated whether cytotoxicity and platinum-DNA adduct formation of two promising new third-generation platinum derivatives, lobaplatin [1,2-diamminomethylcyclobutane platinum(II) lactate] and oxaliplatin [oxalato-1,2-diaminocyclohexane platinum(II)], are also enhanced by hyperthermia. Cisplatin was used for comparison. SW 1573 cells were incubated with cisplatin, lobaplatin or oxaliplatin at different concentrations for 1 h at 37 degrees, 41 degrees and 43 degrees C. The reproductive capacity of cells was determined by cloning experiments. Immunocytochemical detection of platinum-DNA adducts was performed with the rabbit antiserum NKI-A59. At 37 degrees C, cisplatin was the most cytotoxic, followed by oxaliplatin and lobaplatin. Hyperthermia clearly enhanced the cytotoxicity of cisplatin, lobaplatin and oxaliplatin. There was no further increase in cytotoxicity at 43 degrees C compared to 41 degrees C for cisplatin and oxaliplatin. A further increase in cytotoxicity at 43 degrees C was observed for lobaplatin. At 43 degrees C thermal enhancement was higher for lobaplatin than for oxaliplatin, with the reverse pattern at 41 degrees C. For both drugs, thermal enhancement of cytotoxicity was lower than observed for cisplatin. Immunocytochemical detection of platinum-DNA adducts was feasible for all the drugs. Adduct formation was enhanced at 43 degrees C for cisplatin, lobaplatin and oxaliplatin with a relative increase of 410%, 170% and 180%. These results seem to confirm that an increase in platinum-DNA adduct formation is involved in the in vitro thermal enhancement of cytotoxicity. The observed thermal enhancement of cytotoxicity of lobaplatin and oxaliplatin in vitro warrants further in vivo investigations.

Formation of DNA adducts by the anticancer drug carboplatin: different nucleotide sequence preferences in vitro and in cells

We have studied the formation of adducts upon carboplatin treatment of isolated DNA and in cells. The major adduct formed in vitro, determined with atomic absorption spectroscopy and enzyme-linked immunosorbent assay, was the intrastrand cross-link cis-Pt(NH3)2d(pGpG)(Pt-GG) (58%). cis-Pt-(NH3)2d(pApG) (Pt-AG) (11%), cis-Pt(NH3)2d(GMP)2 (G-Pt-G) (9%), and monofunctionally bound platinum (cis-Pt(NH3)3dGMP (Pt-G), 22%) were formed in smaller amounts. These relative occurrences of the adducts, average values found between 1 and 16 h of incubation, are comparable with those after incubation with cisplatin. The formation of carboplatin-DNA adducts was slow, and about 230-fold more carboplatin than cisplatin (molar dose) was required to obtain equal levels of platination after 4 h of incubation. However, less than 20 times more carboplatin was needed to obtain equal levels of cytotoxicity after 1 h of exposure of CHO cells. The percentages of the carboplatin-DNA adducts after 7-12 h postincubation of the cells (determined with ELISA), Pt-GG (30%), Pt-AG (16%), G-Pt-G (40%), and Pt-G (14%), were different from those of the in vitro data. After 12 h postincubation, the number of interstrand cross-links (determined by alkaline elution) amounted to about 10% of the G-Pt-G adducts and 3-4% of the total amount of adducts. The immunocytochemical detection (with antiserum NKI-A59) of the platinum-DNA modifications showed a pattern similar to that found for the various bifunctional adducts: the initially low levels slowly increased to maximum values within 7-12 h and then slowly decreased. In conclusion, carboplatin forms the same bifunctional adducts as cisplatin.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of platinum-DNA adducts by 32P-postlabelling

We developed a sensitive 32P-postlabeling method for the detection of bifunctional intrastrand crosslinks d(Pt-GpG) and d(Pt-ApG) in DNA in vitro and in vivo. After enzymatic digestion of DNA the positively charged platinum adducts were purified from unplatinated products, using strong cation exchange chromatography. Subsequently the samples were deplatinated with cyanide, because platinated dinucleotides are very poor substrates for polynucleotide kinase. The excess of cyanide was removed using Sep-pak C18 cartridges, and the resulting dinucleoside monophosphates d(GpG) and d(ApG) were subsequently postlabelled. Analysis of the postlabelling mixture was performed by a combined TLC and HPLC-procedure. Good correlations with existing methods (AAS, immunocytochemistry and ELISA) were found in DNA samples treated in vitro and in vivo with cis- or carboplatin. The detection limit of the assay was 1 adduct/10(7) nucleotides in a 10 micrograms DNA sample.

Effects of temperature on the interaction of cisplatin and carboplatin with cellular DNA

Increased levels of cisplatin (cDDP)- and carboplatin (CBDCA)-DNA adducts were detected in cDDP (10 microM)- and CBDCA (6 mM)-treated CC531 cells when the temperature was raised from 37 degrees to 43 degrees. In the case of cDDP, increased DNA adduct formation was already detectable at 38.5 degrees; additional temperature steps led to further increases in DNA modification. Increased CBDCA-DNA adduct formation was observed only at temperatures higher than 40 degrees. In vitro studies on the interaction of CDDP and CBDCA with isolated salmon sperm DNA, however, demonstrated no significant differences in the DNA binding rate between 37 degrees and 43 degrees for cDDP and a minor effect for CBDCA only at 43 degrees, almost totally excluding a direct temperature effect on DNA platination in this temperature range. Furthermore, neither the stability of the formed platinum-DNA adducts nor the rate of adduct loss in CC531 cells was changed at higher temperatures. The observed difference in cellular adduct formation, however, could be related to increased uptake of cDDP and CBDCA into CC531 cells at higher temperatures. In the case of cDDP, a temperature shift from 37 degrees to 38.5 degrees resulted in a significantly higher intracellular platinum concentration (0.03 +/- 0.01 vs 0.071 +/- 0.021 micrograms platinum/10(6) cells, respectively); for CBDCA, temperatures > or = 41.5 degrees were needed to increase the platinum concentration significantly above 37 degree values (0.3 +/- 0.1 vs 0.6 +/- 0.1 micrograms platinum/10(6) cells, respectively). In addition, the increase in DNA adduct formation of cDDP and CBDCA at elevated temperatures was comparable with the increase in cDDP-DNA adducts after a cDDP concentration escalation at 37 degrees, indicating a concentration-dependent increase in cDDP-DNA adducts. It seems that heat affects primarily the cellular uptake of cDDP and CBDCA and not their covalent binding to DNA.