A method for scoring 4-nitroquinoline 1-oxide-induced murine esophageal squamous neoplasia

A mouse model for esophageal squamous cell carcinoma (ESCC) is induced by oral administration of the carcinogen 4-nitroquinoline 1-oxide (4-NQO). There is not an objective method for determining histopathologic severity of disease in this model. We aim to create a clearly defined and easily applied scoring system that can quantify the severity of 4-NQO-induced murine ESCC. Fifteen wild-type C57BL/6J mice were treated with 4-NQO for 8 (n = 8) or 16 (n = 7) weeks, while the rest (n = 9) were treated with vehicle, as 8 weeks of 4-NQO typically results in dysplasia and 16 weeks in carcinoma. We identified histologic abnormalities of the esophagus in this model and developed metrics to grade severity of dysplasia, papillomas, and invasion. Scores were then calculated using quantitative digitized image analysis for measuring depth and extent of each feature within the entire sample. Each feature was also assigned a weight based on its relation to cancer severity. Histology scores were significantly different in the three groups, suggesting that this method can discriminate dysplasia from carcinoma. This model can be applied to any mouse treated with 4-NQO.

Investigating the impact of long term exposure to chemical agents on the chromosomal radiosensitivity using human lymphoblastoid GM1899A cells

This study aimed to investigate the impact of chronic low-level exposure to chemical carcinogens with different modes of action on the cellular response to ionising radiation. Human lymphoblastoid GM1899A cells were cultured in the presence of 4-nitroquinoline N-oxide (4NQO), N-nitroso-N-methylurea (MNU) and hydrogen peroxide (H2O2) for up to 6 months at the highest non-(geno)toxic concentration identified in pilot experiments. Acute challenge doses of 1 Gy X-rays were given and chromosome damage (dicentrics, acentric fragments, micronuclei, chromatid gaps/breaks) was scored. Chronic exposure to 20 ng/ml 4NQO, 0.25 μg/ml MNU or 10 μM H2O2 hardly induced dicentrics and did not significantly alter the yield of X-ray-induced dicentrics. Significant levels of acentric fragments were induced by all chemicals, which did not change during long-term exposure. Fragment data in combined treatment samples compared to single treatments were consistent with an additive effect of chemical and radiation exposure. Low level exposure to 4NQO induced micronuclei, the yields of which did not change throughout the 6 month exposure period. As for fragments, micronuclei yields for combined treatments were consistent with an additive effect of chemical and radiation. These results suggest that cellular radiation responses are not affected by long-term low-level chemical exposure.

Genomic landscape and clonal architecture of mouse oral squamous cell carcinomas dictate tumour ecology

To establish whether 4-nitroquinoline N-oxide-induced carcinogenesis mirrors the heterogeneity of human oral squamous cell carcinoma (OSCC), we have performed genomic analysis of mouse tongue lesions. The mutational signatures of human and mouse OSCC overlap extensively. Mutational burden is higher in moderate dysplasias and invasive SCCs than in hyperplasias and mild dysplasias, although mutations in p53, Notch1 and Fat1 occur in early lesions. Laminin-α3 mutations are associated with tumour invasiveness and Notch1 mutant tumours have an increased immune infiltrate. Computational modelling of clonal dynamics indicates that high genetic heterogeneity may be a feature of those mild dysplasias that are likely to progress to more aggressive tumours. These studies provide a foundation for exploring OSCC evolution, heterogeneity and progression.

Multiple modulatory activities of Andrographis paniculata on immune responses and xenograft growth in esophageal cancer preclinical models

BACKGROUND

Esophageal cancer (EC) is a malignant gastrointestinal cancer with high morbidity worldwide and is the fourth leading cause of cancer-related deaths in China. Even though surgery and/or chemotherapy/chemoradiation might achieve good therapeutic response, recurrence rate is high due to cancer metastasis. Hence, the use of alternative adjuvant treatments, such as herbal medicines, for metastatic EC remains a great desire of the patients. Our previous studies have demonstrated the anti-metastatic efficacy of hot water extract of Andrographis paniculata (APW) in human esophageal cancer cells and tumor-bearing nude mice.

PURPOSE

In the present study, the immunomodulatory activities of APW were further evaluated in human peripheral blood mononuclear cells (PBMCs) and in a carcinogen-induced esophageal tumorigenesis model using immune-competent C57BL/6 mice. Besides, the inhibitory effects of APW on esophageal cancer cell line-based xenografts and patient-derived xenografts (PDX) were examined so as to illustrate the potential multi-targeted efficacies of APW in esophageal cancer in pre-clinical models.

RESULTS

In vitro results showed that APW could stimulate proliferation of PBMCs, as well as TNF-α and IFN-γproductions. In mice with 4-nitroquinoline 1-oxide-induced tumorigenesis, 21-day oral treatment with APW (1600 mg/kg) decreased the level of dysplasia in esophagus and significantly modulated the population of regulatory T cells. The cytokines productions by spleen lymphocytes of APW-treated mice were shifted towards normal resting state (i.e. unchallenged with carcinogen). Furthermore, APW treatment suppressed the growth of cell line-based xenografts by significantly increasing apoptosis in tumors, without causing severe body weight loss as chemotherapeutics did. Most importantly, the inhibitory effects of APW treatment on esophageal patient-derived xenografts growth were demonstrated for the first time. Besides, several diterpenes were detected in the plasma after oral administration of APW in mice, suggesting that multi-components of APW were bioavailable and might have contributed towards the varied pharmacological activities demonstrated in our studies.

CONCLUSION

APW was shown to possess anti-tumor, anti-metastatic and immunomodulatory activities in esophageal cancer cell-based and animal models, including immunocompromised mice model and clinically relevant PDX model. Our findings illustrated the potential multi-targeted efficacies of APW in esophageal cancer management.

Inhibition of 4-nitroquinoline-1-oxide-induced oral carcinogenesis by dietary calcium

Calcium is a strong inducer of keratinocyte differentiation. We have previously demonstrated that extracellular calcium promotes keratinocyte differentiation via E-cadherin-catenin complex-mediated phospholipase C-γ1 (PLC-γ1) activation in the plasma membrane. However, it is unclear whether dietary calcium regulates keratinocyte proliferation, differentiation or carcinogenesis. To address this issue, the rates of oral tumor and levels of proliferation and differentiation in the oral epithelium were assessed in mice on different calcium diets and the carcinogen 4-nitroquinoline-1-oxide. The results showed that mice on the high calcium diet had lower rates of oral tumors, lower levels of proliferation and higher levels of differentiation in the normal oral epithelium than those on the normal calcium diet. Higher levels of E-cadherin, β-catenin, p120-catenin (p120), epidermal growth factor receptor (EGFR), and calcium and lower levels of PLC-γ1 were also noted in the normal oral epithelium in mice on high calcium diet than the control mice. In contrast, mice on low calcium diet had opposite effects. However, dietary calcium had no effect on the proliferation, differentiation or the levels of E-cadherin, β-catenin, p120, PLC-γ1 and EGFR in oral tumors. These data indicate that dietary calcium increases calcium levels in oral epithelium, suppresses oral carcinogenesis, inhibits proliferation and promotes differentiation of normal oral epithelium. Increased E-cadherin, β-catenin, p120 and EGFR and decreased PLC-γ1 may participate in the inhibitory effect of dietary calcium in oral carcinogenesis.

Comparable molecular alterations in 4-nitroquinoline 1-oxide-induced oral and esophageal cancer in mice and in human esophageal cancer, associated with poor prognosis of patients

BACKGROUND

The murine model of 4-nitroquinoline 1-oxide (4-NQO)-induced oral and esophageal cancer is frequently used to assess the effects of different cancer prevention/ therapy agents in vivo, but the molecular mechanisms in those 4-NQO-induced carcinogenesis are unknown. This study investigated aberrant expression of cell growth-critical genes in 4-NQO-induced oral and esophageal cancer tissues in mice compared to those present in the human disease for association with survival of patients.

MATERIALS AND METHODS

C57LB6/129Sv mice were given 4-NQO in their drinking water to induce oral and esophageal cancer. Quantitative-reverse transcription polymerase chain reaction (qRT-PCR), western blot, and immunohistochemistry were used to detect gene expression in the cancer tissues from mice and in 4-NQO-treated human esophageal cancer cell lines and esophageal cancer tissues. Methylation-specific PCR and DNA sequencing were performed to assess methylation of the Rarb2 promoter in murine tissues. Kaplan-Meier analysis was performed to associate gene expression in esophageal cancer tissues with survival data for patients with esophageal cancer.

RESULTS

4-NQO dose-dependently induced pre-malignant and malignant lesions in the oral cavity and esophagus in mice that pathologically and morphologically mimicked human oral and esophageal cancer. Molecularly, 4-NQO inhibited Rarβ₂ but induced expression of phosphorylated extracellular-signal-regulated kinase-1 and -2 (p-ERK1/2) and Cox2 proteins and Rarβ₂ gene promoter methylation in murine tumors. In vitro treatment with 4-NQO altered expression of RARβ₂, p-ERK1/2, and COX2 in human esophageal cancer cells. In tissues from 90 patients with esophageal cancer, expression of p-ERK1/2 and COX2 was up-regulated, and p-ERK1/2 expression was associated with advanced clinical tumor stage and consumption of hot beverages, while COX2 expression was associated with tumor de-differentiation in esophageal cancer. Furthermore, expression of p-ERK1/2 was associated with a worse overall survival rate of patients (p=0.014), whereas the association of COX2 expression with worse overall survival rate did not reach statistical significance (p=0.19). Knockdown of COX2 expression using transient transfection of a COX2 antisense expression vector inhibited Ki67 expression, an indicator of cell proliferation, in human esophageal cancer cells.

CONCLUSION

4-NQO-induced cancer in oral cavity and esophagus of mice not only pathologically and morphologically mimicked human oral and esophageal cancer, but also shared some molecular alterations (e.g. aberrant expression of Rarb2, p-ERK1/2, and Cox2). This study further demonstrated that targeting of the altered RARβ₂-led gene pathway could effectively suppress the development of this deadly type of cancer.

Enhancement of tongue carcinogenesis in Hras128 transgenic rats treated with 4-nitroquinoline 1-oxide

Transgenic rats carrying human c-Ha-ras proto-oncogene (Hras128 rats) have been shown to be highly susceptible to induction of tumors. We have found an early induction of tongue tumors in Hras128 rats treated with 4-nitroquinoline 1-oxide (4NQO). 4NQO was administered to the Hras128 and wild-type Sprague-Dawley (SD) rats for 4 and 8 weeks, respectively. The experiment was terminated at 14 (Hras128 rats) and 28 (SD rats) weeks. Either during or after treatment with 4NQO, dysplastic hyperplasia, papilloma and squamous cell carcinoma were found on the tongue of both Hras128 and wild-type rats, with a higher incidence and multiplicity in Hras128 rats. Treatment of the Hras128 rats with 4NQO significantly increased cell proliferation in the tumor compared to the control rats. In the tongue tumors of the Hras128 rats, there was a significant increase in the mRNA expression levels of cyclin D1 and COX2. To examine whether this experimental system is useful for screening of the candidate agents for cancer preventive effect, nimesulide, a selective COX2 inhibitor, was tested in the present model. Nimesulide significantly decreased total multiplicity of tongue lesions compared to the control rats. Treatment of Hras128 rats with nimesulide caused a significant decrease in the levels of mRNA expression of cyclin D1 and COX2 in the tumor. Therefore, the current 4NQO-induced Hras128 rat tongue carcinogenesis model provides a simple and rapid system for investigating carcinogenesis process and evaluating the effect of possible cancer preventive agents for human tongue cancer.

[Expression of survivin, Bcl-2 and p53 during 4-nitro-quinoline 1-oxide-induced rat tongue carcinogenesis]

OBJECTIVE

To investigate the expression of survivin during oral carcinogenesis and its relationship with the expression of Bcl-2 and p53.

METHODS

Two-step immunohistochemical method was employed to detect the expression of survivin, Bcl-2 and p53 in 60 rat tongue carcinogenesis specimens induced by 4-nitro-quinoline 1-oxide (4NQO).

RESULTS

Survivin was present in 1/36 cases of normal mucosa, 6/11 cases of oral epithelial dysplasia and 10/11 cases of oral carcinoma. There were significant difference in the expression of survivin among normal mucosa, oral epithelial dysplasia and carcinoma (P < 0.001). While in the 17 cases of positive expression of survivin, Bcl-2 was present in 12 cases and p53 was present in 8 cases. The expression of survivin in oral epithelial dysplasia and carcinoma were significantly higher than that in normal oral mucosa (P < 0.01). The expression of survivin was positively correlated to the expression of Bcl-2 and p53 in rat tongue (P < 0.01).

CONCLUSIONS

The expression of survivin may play an important role in oral carcinogenesis. Survivin, Bcl-2 and p53 may be synergetic in the carcinogenesis of oral cancer.

The Werner syndrome protein confers resistance to the DNA lesions N3-methyladenine and O6-methylguanine: implications for WRN function

The Werner syndrome (WS) protein (WRN), a DNA helicase/exonuclease, is required for genomic stability and avoidance of cancer. Current evidence suggests that WRN is involved in the resolution of stalled and/or collapsed replication forks. This function is indicated, in part, by replication defects in WS cells and by hypersensitivity to agents causing major structural aberrations in DNA that block replication. We show here that antisense suppression of WRN in two human glioma cell lines reproduces hallmarks of the drug cytotoxicity profile of WS cells, namely, hypersensitivity to 4-nitroquinoline 1-oxide, camptothecin and hydroxyurea. We also show that antisense-treated cells are hypersensitive to methyl-lexitropsin, a site-specific alkylating agent that produces mainly N3-methyladenine, a cytotoxic and replication-blocking lesion. Antisense-treated cells are hypersensitive to O(6)-methylguanine adducts as well, but only when repair by O(6)-methylguanine-DNA methyltransferase is lacking. Our results illustrate the drug sensitivity caused by deficiency of WRN in a uniform genetic background. They extend the WRN DNA damage sensitivity spectrum to methyl base adducts that can result in blocked replication, and suggest that WRN may be required for resumption of processive replication when incomplete repair of DNA damage leaves blocking lesions at forks. The evidence that highly disparate lesions fall within the purview of WRN, and that abrogating DNA repair can reveal dependence on WRN, suggests that WRN may protect the genome from the lethal, mutagenic and carcinogenic effects of widely diverse DNA damage arising from endogenous processes and environmental agents.

Changing expression of E- and P-cadherin during rat tongue carcinogenesis induced by 4-nitroquinoline 1-oxide

BACKGROUND

Oral squamous cell carcinoma (SCC) develops from pre-malignant lesions, but the role of cell adhesion molecules such as E-cadherin (E-CD) and P-cadherin (P-CD) in the pre-malignant stage has not been elucidated.

METHODS

The expression of E-CD and P-CD was examined immunohistochemically and biochemically in a 4-nitroquinoline 1-oxide (4NQO)-induced rat model of carcinogenesis.

RESULTS

The expression of E-CD in the pre-malignant stage was the same as that in the normal epithelium. The expression of P-CD was even throughout the prickle cell layer in the dysplasia stage. E-CD and P-CD were expressed in essentially the same locations in SCC and in the pre-malignant stage. P-CD expression was very strong in the pre-malignant stage, compared to that in normal epithelium.

CONCLUSIONS

Aberrant P-CD expression in E-CD-positive cells may play a crucial role in the progression of the pre-malignant stage of 4NQO-induced carcinogenesis, and may activate mechanisms responsible for cell proliferation.

Epithelial-mesenchymal interactions in experimental oral mucosal carcinogenesis

In an effort to come to a better understanding of human oral mucosal carcinogenesis, an animal model was used in which the carcinogen 4-nitroquinoline-1-oxide was applied to rat palatal mucosa for varying periods of time. Histological and histometric analyses showed that there were quantifiable differences in the palatal epithelium to which carcinogen had been applied in comparison with control tissue. Tissue recombination experiments, using various combinations of the palatal mucosa and analysed after recovery from transplantation to hypothymic BALB/c mice, showed that control epithelium recombined with connective tissue from carcinogen-treated mucosa was altered, indicating that the underlying connective tissue modified histomorphological aspects of the epithelium in the later stages of carcinogenesis.

Prevention of 4-nitroquinoline 1-oxide-induced rat tongue carcinogenesis by garlic

The present study was undertaken to examine the inhibitory effect of garlic (Allium sativum) on 4-nitroquinoline 1-oxide (4NQO)-induced tongue carcinogenesis in male rats, both in the initiation and post-initiation phases. Lipid peroxidation, reduced glutathione (GSH), glutathione peroxidase (GPx), and glutathione S-transferase (GST) were used to monitor the chemopreventive potential of garlic. Biochemical estimations were carried out on tumour and normal tongue tissues. Diminished lipid peroxidation in the tumour tissue was accompanied by a significant increase in the levels of GSH, GPx and GST. Administration of garlic (250 mg/kg, p.o., three times a week) effectively suppressed 4NQO-induced tongue carcinogenesis as revealed by the absence of carcinomas in the initiation phase and their reduced incidence in the post-initiation phase. The results of the present study suggest that garlic may exert its chemopreventive effects by modulating lipid peroxidation and enhancing the levels of GSH, GPx and GST.

Cell division transforms mutagenic lesions into deletion-recombinagenic lesions in yeast cells

Cell proliferation has been recognized as an important factor in human and experimental carcinogenesis. Point mutations as well as larger chromosomal rearrangements are involved in the initiation of cancer. In this paper we compared the relative potencies of radiation and chemical carcinogens for inducing point mutations vs. deletions in cell cycle arrested with dividing cells of Saccharomyces cerevisiae. Point mutation substrates and deletion (DEL) recombination substrates were constructed with the genes CDC28 and TUB2 that are required for cell cycle progression through G1 and G2, respectively. The carcinogens ionizing radiation, UV, MMS, EMS and 4-NQO induced point mutations in G1 and in G2 arrested as well as in dividing cells. UV, MMS, EMS and 4-NQO caused very weak if any increases in DEL recombination in G1 or G2 arrested cells, but large increases in dividing cells. When cells treated with carcinogen either in G1 or G2 were allowed to progress through the cell cycle, a time-dependent increase in DEL recombination was seen. Ionizing radiation and the site-specific endonuclease I-SceI, which both directly create double-strand breaks, induced DEL recombination in G1 as well as in G2 arrested cells. In conclusion, UV-, MMS-, EMS- and 4-NQO-induced DNA damage was converted during DNA replication to a lesion capable of inducing DEL recombination which is probably a DNA strand break. Thus, cell proliferation is not necessary to turn DNA alkylation or UV damage into a mutagenic lesion but to convert the damage into a lesion that induces DNA deletions. These results are discussed with respect to mechanisms of carcinogenesis.

Oral cancer: role of the basement membrane in invasion

Invasive growth of cancer cells is a complex process involving specific interactions between tumour cells and the orderly, integrated complexes of the extracellular matrix. Basement membranes have been proposed as one constituent of extracellular matrix which carries responsibility for regulating invasion and metastasis. Using a chemically induced rat tongue carcinoma model, it has been shown that components of the basement membrane and its overall structure are altered during tumour invasion, and methods have been developed to quantitate some of these differences. Since the basement membrane can be specifically characterized by its fibrous protein network of Type IV collagen and laminin, which is embedded in a heparan sulphate-rich proteoglycan matrix, these components have been targeted. In particular, the current paper presents results in the context of current concepts of early changes in neoplastic invasion of underlying connective tissues. In consequence, further elaboration of the underlying mechanisms of epithelial migration in oral cancer may allow an exploration of the use of alterations in expression of basement membrane components as prognostic indicators.

Changes in Bcl-2 and Bax expression in rat tongue during 4-nitroquinoline 1-oxide-induced carcinogenesis

Bax is considered as a main effector of apoptosis. Bax forms homodimers and also heterodimers with Bcl-2. The function of the Bax-Bax dimer in active cell death is antagonized by Bax-Bcl-2 heterodimers. Thus, the ratio of Bcl-2 and Bax should control the susceptibility of cells to those stimuli that induce apoptotic cell death. An increase in apoptotic change has been shown in many carcinomas. In the present study, the changes in Bcl-2 and Bax expression in the tissue during carcinogenic transformation were examined immunohistochemically by means of the 4-nitroquinoline 1-oxide (4NQO)-induced carcinoma model. Animals were divided into 7 groups of 10 rats each, and given 50 ppm 4NQO solution as drinking water for 4, 8, 12, 16, 20, or 24 weeks. Ten animals were used as controls. Gradual increases in the numbers of Bcl-2- and Bax-positive cells were shown corresponding to the progression of experimental carcinogenesis. Statistically significant differences in Bcl-2 and Bax expression were demonstrated between control and four-week treatment groups (p < 0.01), and between control and eight-week treatment groups (p < 0.05), respectively. Levels of both proteins remained high after the period of dysplastic change of the epithelium. In conclusion, Bcl-2 and Bax are involved in the progression of 4NQO-induced carcinoma.

Experimental odontogenic cysts induced by in vitro 4-nitroquinoline 1-oxide (4NQO) treatment of F344 rat incisor tooth germs

This study was designed to establish an experimental animal model for elucidating the early stages of odontogenic cysts and tumors. It involves the in vitro treatment of tooth germs with 4-nitroquinoline 1-oxide (4NQO) at the early bell stage and their subsequent transplantation into the kidney subcapsular space. While all tooth germ transplants of the control group not exposed to the carcinogen showed continued tooth development with no pathological lesions, 21 of 23 4NQO-treated tooth germs developed into similar appearing keratinized cysts with or without associated tooth structures. The remaining two transplants failed to develop cysts and formed only a tooth. The present experimental procedure was effective in inducing keratinized cystic lesions that exhibit some similarities to human odontogenic keratocysts or primordial cysts.

Glutathione S-transferase pi-class as a tumour marker in lingual preneoplastic and neoplastic lesions of rats and humans

Immunocytochemical expression of the pi class glutathione S-transferase (GST) was investigated in preneoplastic and neoplastic lingual lesions in a 4-nitro-quinoline 1-oxide (4NQO)-induced rat genetic model [Wistar/Furth rats (WF) and Dark-Agouti rats (DA)] and in human surgical material [fibrous polyp, mild to moderate dysplasia, severe dysplasia, carcinoma in situ (CIS), squamous cell carcinoma (SCC)]. Two polyclonal antibodies raised against rat (GST-P) and human (GST-pi) antigens were used. In the rat model, DA and WF rats showed contrasting susceptibility to 4NQO, DA rats having a much higher tumour incidence and a significantly shorter survival time than WF rats. While the established lingual SCC in DA and WF rats all expressed GST-P, the number of GST-P+ foci in the preneoplastic lingual epithelium was significantly higher in DA (14.5 +/- 6.5) than in WF rats (5.5 +/- 2.6; P < 0.0001). In contrast, GST-pi epithelial staining in human specimens was more variable and the results overlapped in different groups. More frequent nuclear and/or basal cell staining was detected in severe dysplasia, CIS and SCC than in benign and mild to moderate dysplastic lesions. Although the pi class GST may be a useful marker for rat lingual carcinogenesis, its value in clinical applications is unclear. GST-pi staining patterns and their distribution may be helpful in identifying high-risk lingual lesions in humans.

Photofrin-mediated photodynamic therapy of chemically-induced premalignant lesions and squamous cell carcinoma of the palatal mucosa in rats

Photodynamic therapy (PDT), an experimental cancer therapy, was studied in an animal model of chemically-induced epithelial dysplasia and squamous cell carcinoma. PDT was performed 24 hours after i.v. injection of 2.5 mg/kg bw Photofrin, and using 100 J/cm2 incident light at two activation wavelengths (514.5 nm or 625 nm). Two days after PDT, the majority of rats macroscopically showed a marked erythema of the entire palatal region. Microscopically all the rats showed oedema, haemorrhage, and necrosis of the epithelium of the intermolar area. The long-term results were not so favourable. No evidence of disease was found in 6 out of 20 rats in the 514.5 nm group and in 2 out of 20 rats in the 625 nm treated group. Epithelial dysplasia was found in 14 out of 20 rats in the 514.5 nm group, and in 18 out of 20 rats of the 625 nm treated group. Squamous cell carcinomas were found in 4 out of 20 rats treated with 514.5 nm and in 7 out of 20 rats in the 625 nm treated groups. Comparing both treatment wavelengths, better results were obtained in the 514.5 nm groups as this wavelength gave less normal tissue damage. Based on the results of this study the application of PDT for the treatment of field cancerization and squamous cell carcinoma of the oral cavity, is discussed.

DNA repair capacity correlates with mutagen sensitivity in lymphoblastoid cell lines

This study describes a correlation between cellular DNA repair capacity and the frequency of mutagen-induced in vitro chromosomal breaks in selected lymphoblastoid cell lines. Two assays, host cell reactivation (HCR) assay for measuring cellular DNA repair capacity and in vitro mutagen sensitivity assay, have recently been shown to be useful biomarkers for such susceptibility. Increased in vitro mutagen sensitivity, measured by the number of induced chromatid breaks, has been postulated to reflect decreased capacity of DNA repair, as measured by the HCR assay. However, these two assays have not been examined in parallel to test this hypothesis. In this study, we performed both assays in 16 established lymphoblastoid cell lines derived from patients with xeroderma pigmentosum (n = 3), ataxia telangiectasia (n = 2), head and neck cancer (n = 3), and melanoma (n = 2), and from normal human subjects (n = 6) using UV light, 4-nitroquinoline-1-oxide (4-NQO; an UV-mimetic agent), and gamma-irradiation as the test agents. The measurements from the HCR assay correlated significantly with the frequency of chromatid breaks induced by either UV irradiation (r = -0.69; P < 0.01) or 4-NQO (r = -0.70; P < 0.01). Although published data suggest that damage induced by UV and 4-NQO may be repaired by different pathways, the two agents induced similar frequencies of chromatid breaks (r = 0.68; P < 0.01) in the tested cell lines. Our results also indicated that the HCR assay is not suitable to test agents that cause DNA strand breaks, such as gamma-irradiation, whereas the mutagen sensitivity assay is. Although reduced cellular DNA repair capacity correlated with increased frequency of mutagen-induced chromatid breaks in these cell lines, these two assays have different sensitivities in measuring the repair of damage induced by different carcinogens; therefore, the use of both assays is recommended for future molecular epidemiological studies of cancer susceptibility.

Proteoglycan changes in carcinogen (4NQO)-treated rat tongue mucosa

The purpose of this study was to undertake preliminary analyses of the extracellular proteoglycans in carcinogen [4-nitroquinoline N-oxide (4NQO)]-treated rat tongue mucosa. Experimental rats were exposed to twice-weekly applications of 4NQO in propylene glycol for six months, after which the animals were killed. Control and 4NQO-treated tissues were subjected to sequential aqueous extractions of proteoglycans under associative and dissociative conditions, followed by alkaline cleavage of protein-glycosaminoglycan linkages to yield a glycosaminoglycan residue. Tissues subjected to 4NQO applications contained smaller proportions of proteoglycans which were readily soluble under associative and dissociative conditions. Proportionately more proteoglycan remained strongly associated with other intercellular tissue components, being released only by alkaline cleavage. These biochemical alterations in preinvasive 4NQO-treated epithelium and connective tissues, together with an observed associated change in water retention by the connective tissue, occurred prior to actual neoplastic invasion and suggest differences in macromolecular conformation and orderliness. We hypothesize that these changes are related to the phenomenon of neoplastic epithelial invasion.

4NQO carcinogenesis: a mouse model of oral cavity squamous cell carcinoma

BACKGROUND

A murine model of oral cavity carcinogenesis is needed to study the molecular aspects of malignant transformation. 4-Nitroquinoline-1-oxide (4NQO), a water-soluble carcinogen, produces squamous cell carcinoma in rodents. Protocols were designed to investigate the temporal aspects of neoplastic transformation.

METHODS

4NQO was applied topically to mouse palates for up to 16 weeks. Mice were observed and killed from 24 to 49 weeks.

RESULTS

A spectrum of lesions ranging from atypia to moderately differentiated invasive squamous cell carcinoma (SCC) was produced. The severity of the lesions corresponded to the duration of treatment and the length of observation. There was no gross or microscopic evidence of an inflammatory reaction to 4NQO. The lesions were focal and normal mucosa predominated in the treated mice.

CONCLUSION

4NQO reliably produced preneoplastic and malignant oral cavity lesions, which morphologically and histologically mimic human head and neck cancer. Lesions develop long after 4NQO exposure and without an inflammatory response. Thus, the model should be useful for molecular analysis of neoplastic transformation.

Nucleolar organizer regions in tongue carcinomas induced in rats: comparison with DNA cytofluorometric analysis

Eleven papillomas and 25 carcinomas were induced in rat tongues by oral administration of 0.001% 4-nitroquinoline 1-oxide (4NQO) in drinking water, and the biological characteristics and proliferative activity of the tumors were investigated by both DNA cytofluorometry and the argyrophilic nucleolar organizer region (AgNOR) staining method. The histopathological characteristics, the mean number of AgNORs per cell and DNA ploidy patterns were compared. The mean AgNOR number was lowest in normal epithelium (1.65 +/- 0.10), and highest in squamous cell carcinomas (2.97 +/- 0.70) and intermediate in papillomas (1.87 +/- 0.28). The differences were statistically significant. All normal epithelium and all papillomas showed a diploid pattern. Eighteen (72%) of 25 squamous cell carcinomas showed a diploid pattern, while 7 (28%) showed a diploid plus tetraploid pattern. There was a significant difference in the mean AgNOR number between the two ploidy groups of squamous cell carcinomas. These results suggest that the mean AgNOR number may reflect the histological grade in the process of carcinogenesis and polyploidization of carcinomas.

Assessment of bromodeoxyuridine-labeled S-phase cells in experimentally induced precancerous lesions in the rat's tongue

Precancerous lesions and early invasive carcinomas were produced in the tongues of rats by oral administration of 0.001% 4-nitroquinoline 1-oxide in drinking water. The distribution and densities of S-phase cells were then studied in an attempt to clarify the mechanism of carcinogenesis from the viewpoint of cell cycle. Bromodeoxyuridine (BrdU)-labeled S-phase cells were demonstrated by an indirect peroxidase method, using anti-BrdU monoclonal antibody, and their percentage was determined as the labeling index (LI). The average BrdU LI was significantly higher in the precancerous lesions than in the normal epithelium. There was a wide range of LI found in cells showing such changes as hyperplasia, hyperparakeratosis, dysplasia and papilloma, but the differences among them were not significant. These findings also showed that there could be considerable differences in proliferative activity among lesions of the same grade, while the difference in histology did not mean a difference in proliferative activity. Additionally, many BrdU-labeled cells were seen in a few layers over the basement membranes of non-cancerous lesions immediately adjacent to early invasive carcinoma, suggesting that these layers had a higher possibility for advancing to early invasive carcinoma.

Estimation of proliferative activity of experimental tongue carcinoma in rats. Immunohistochemical and DNA cytofluorometric analysis

Precancerous lesions and carcinomas were produced in rat tongues by oral administration of 0.001% 4-nitroquinoline 1-oxide (4NQO) in drinking water, and the biological characteristics and tumor kinetics were studied. Bromodeoxyuridine labeling index (BrdU L.I.) was determined immunohistochemically, and the nuclear DNA content was measured by DNA cytofluorometry. The BrdU L.I. was lowest in normal epithelium (3.49 +/- 0.49%), higher in papillomas (8.24 +/- 1.76%) and highest in squamous cell carcinomas (13.36 +/- 4.40%). Normal lingual epithelial cells, papillomas and 18 of the 25 squamous cell carcinomas showed a diploid pattern, while 7 squamous cell carcinomas showed a diploid plus tetraploid pattern. The correlation between polyploidization and tumor progression was significant, but the correlation between BrdU L.I. and tumor progression was not significant. The results suggest that while polyploidization of tumors increases with tumor progression the growth rate of tumors does not necessarily do so.

Effect of pH on the activity and stability of clastogens in the in vitro chromosomal aberration test with Chinese hamster ovary K1 cells

The effect of the pH of the medium on the clastogenic activity of several direct-acting and indirect clastogens was evaluated in the in vitro chromosomal aberration test with Chinese hamster ovary K1 cells. Furthermore, the stability of the chemicals in the cell culture medium was measured by HPLC over the pH range of 5.0-11.0. The activity of the direct-acting clastogens mitomycin C (MMC), N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) and 4-nitroquinoline-1-oxide (4NQO) at various pH values depended on their stability. In the case of ENNG, its clastogenic activity decreased to about one-fifth at pH 9 but was about twice as high at acidic pH compared with that at pH 7.4. This is consistent with the observation that ENNG is unstable at basic pH; the residual content of ENNG was 0.5% of the initial amount in cell culture medium at pH 9.0 after a 2-h incubation. 4NQO was unstable at strongly basic pH (pH 10-11), and MMC was unstable at pH 5.0 and pH 11.0. The frequencies of chromosomal aberrations induced by MMC and ENNG were correspondingly decreased at these pH values. On the other hand, the clastogenicities of the indirect clastogens 7,12-dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (B(a)P) and dimethylnitrosamine (DMN), which require metabolic activation, were reduced at pH 10-11 and pH 5.8. The frequencies of chromosomal aberrations at these pHs were almost equal to negative control values. These chemicals were stable in the medium in the absence of S9 mix over the pH range of 5.0-11.0. Thus clastogenicity of indirect-acting clastogens is reduced under extreme pH conditions, probably because of the instability or nonformation of the active form. The present results indicate that the clastogenic activity of any compound will depend on its stability in the medium irrespective of its direct- or indirect-acting nature. In addition, some of the chemicals that are recognized as clastogens presumably might induce chromosomal aberrations by means of acidic pH itself. It is, therefore, important to take account of the pH of the treatment medium in evaluating the clastogenicity of chemicals.

Dislocation of chromatin elements in prophase induced by diethylstilbestrol: a novel mechanism by which micronuclei can arise

The in vitro micronucleus test with Syrian hamster embryo (SHE) cells assays the induction of micronuclei by chemical agents. Both chromosome fragments and lagging chromosomes can give rise to micronuclei. Nevertheless, only limited information is available on the ultrastructure of micronuclei and the mechanisms of their formation. Diethylstilbestrol (DES), a non-mutagenic carcinogen, as well as its analogue 3.3'-DES induce micronuclei in SHE cells. A comparison of the dose response of DES-induced micronucleus formation with the previously published ones for aneuploidy and transformation shows that all 3 run in parallel. Thus, a functional relationship between these endpoints, in the SHE system, may be implied. The present study is designed to address the formation of micronuclei using supravital UV microscopy, to test for the presence of defined chromosome domains within micronuclei using immunocytochemistry, and to define aspects of their ultrastructure by electron microscopy. Supravital UV microscopy showed that 3.3'-DES induces displacement of chromosomes/chromatids during prophase/anaphase and formation of micronuclei during cytokinesis. Immunocytochemistry revealed that micronuclei contain, at high frequencies, CREST antibody-reactive kinetochores, indicating the presence of whole chromosomes or centric fragments in these structures. Moreover, transmission electron microscopy showed that micronuclei exhibit ultrastructural details typical of interphase nuclei. Specifically, micronuclei exhibited morphological evidence of a nuclear lamina and segregation of karyoplasm into euchromatic and heterochromatic regions. All micronuclei examined were enclosed by a nuclear envelope of normal morphology and showed nuclear pore complexes. Together the findings provide evidence that DES interferes with the mitotic apparatus as early as prophase, resulting in the formation of micronuclei and, as a consequence, in the loss of chromatids or chromosomes.

Cell-stage dependence of mutagen-induced sister-chromatid exchanges in human lymphocyte cultures

The induction of sister-chromatid exchanges (SCEs) was studied in phytohemagglutinin (PHA)-stimulated human lymphocytes exposed for 1 h to mitomycin C (MMC, 3 X 10(-6) M), ethyl methanesulphonate (EMS, 2 X 10(-2) M), or 4-nitroquinoline-1-oxide (4NQO, 3 X 10(-5) M) at various cell-cycle stages of 72-h cultures. The doses of the chemical were chosen to give about 20 SCEs per cell when treated at Go. The SCE frequency increased almost linearly with MMC or EMS treatments at later times after PHA stimulation, peaking with those at 36 h (at around the first G1/S boundary in the 2 consecutive cell cycles, which was revealed by concomitant experiments), and then decreased with subsequent treatment times. Cell-cycle kinetics and the cell stages at which the cells were treated were measured by autoradiography and sister-chromatid differential staining. The data show that MMC and EMS produce larger numbers of SCEs when treated at stages closer to the beginning of S, and that the most efficient time of treatment is the G1/S boundary in the first cell cycle of the two consecutive cycles before sampling. Pulse treatment with EMS caused about 3 times larger inductions of SCEs when done at late G1/early S(G1/S boundary) in the first cell cycle compared to that at G0/early G1, whereas identical exposure to MMC at the first G1/S boundary produced only 1.5 times larger numbers of SCEs than that at G0/early G1. EMS and MMC both, however, induced 30-40% larger numbers of SCEs when treated at the G1/S boundary in the first cell cycle than when treated at the second cell cycle before sampling. On the contrary, treatment with 4NQO led to the induction of about the same numbers of SCEs even when treated at different cell-cycle stages before the second G1/S boundary. The SCE frequency in 4NQO-treated cells then decreased with subsequent treatment times.

Experimental induction of oral squamous cell carcinomas in mice with 4-nitroquinolone-1-oxide

The oral mucosa of mice is resistant to the action of a variety of carcinogens. In this study, the water-soluble carcinogen 4-nitroquinoline-1-oxide (4NQO) was applied repeatedly to the palates of male CBA mice for 2, 4, 6, 8, 12, or 16 weeks, and the animals were observed for the remainder of the 50-week experimental period. Oral epithelial atypia and squamous cell carcinoma were observed with increasing prevalence as the period of carcinogen exposure was increased. Carcinomas developed by 50 weeks in all animals that received 4NQO for 16 weeks.