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

Experimental Modeling of Host-Bacterial Interactions in Head and Neck Squamous Cell Carcinoma

The microscopic species colonizing the human body, collectively referred to as the microbiome, play a crucial role in the maintenance of tissue homeostasis, immunity, and the development of disease. There is evidence to suggest associations between alterations in the microbiome and the development of head and neck squamous cell carcinomas (HNSCC). The use of two-dimensional (2D) modeling systems has made significant strides in uncovering the role of microbes in carcinogenesis; however, direct mechanistic links remain in their infancy. Patient-derived three-dimensional (3D) HNSCC organoid and organotypic models have recently been described. Compared to 2D models, 3D organoid culture systems effectively capture the genetic and epigenetic features of parent tissue in a patient-specific manner and may offer a more nuanced understanding of the role of host-microbe responses in carcinogenesis. This review provides a topical literature review assessing the current state of the field investigating the role of the microbiome in HNSCC; including in vivo and in vitro modeling methods that may be used to characterize microbiome-epithelial interactions.

Targeting M-MDSCs enhances the therapeutic effect of BNCT in the 4-NQO-induced murine head and neck squamous cell carcinoma model

Purpose

Malignant head and neck squamous cell carcinoma (HNSCC) is characterized by a poor prognosis and resistance to conventional radiotherapy. Infiltrating myeloid-derived suppressive cells (MDSCs) is prominent in HNSCC and is linked to immune suppression and tumor aggressiveness. This study aimed to investigate the impact of boron neutron capture therapy (BNCT) on the MDSCs in the tumor microenvironment and peripheral blood and to explore the potential for MDSCs depletion combined with BNCT to reactivate antitumor immunity.

Methods and materials

Carcinogen, 4-NQO, -induced oral tumors were irradiated with a total physical dose of 2 Gy BNCT in Tsing Hua Open Reactor (THOR). Flow cytometry and immunohistochemistry accessed the dynamics of peripheral MDSCs and infiltrated MDSCs within the tumor microenvironment. Mice were injected with an inhibitor of CSF-1 receptor (CSF-1R), PLX3397, to determine whether modulating M-MDSCs could affect mice survival after BNCT.

Results

Peripheral CD11b+Ly6ChighLy6G- monocytic-MDSCs (M-MDSCs), but not CD11b+Ly6CloLy6Ghigh polymorphonuclear-MDSCs (PMN-MDSCs), increased as tumor progression. After BNCT treatment, there were temporarily decreased and persistent increases of M-MDSCs thereafter, either in peripheral blood or in tumors. The administration of PLX-3397 hindered BNCT-caused M-MDSCs infiltration, prolonged mice survival, and activated tumor immunity by decreasing tumor-associated macrophages (TAMs) and increasing CD8+ T cells.

Conclusion

M-MDSCs were recruited into 4-NQO-induced tumors after BNCT, and their number was also increased in peripheral blood. Assessment of M-MDSCs levels in peripheral blood could be an index to determine the optimal intervention window. Their temporal alteration suggests an association with tumor recurrence after BNCT, making M-MDSCs a potential intervention target. Our preliminary results showed that PLX-3397 had strong M-MDSCs, TAMs, and TIL (tumor-infiltrating lymphocyte) modulating effects that could synergize tumor control when combined with BNCT.

IL-1β transgenic mouse model of inflammation driven esophageal and oral squamous cell carcinoma

Chronic inflammation is integral to the development of esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC), although the latter has not been associated with reflux esophagitis. The L2-IL-1β transgenic mice, expressing human interleukin (IL)-1β in the oral, esophageal and forestomach squamous epithelia feature chronic inflammation and a stepwise development of Barrett's esophagus-like metaplasia, dysplasia and adenocarcinoma at the squamo-columnar junction. However, the functional consequences of IL-1β-mediated chronic inflammation in the oral and esophageal squamous epithelia remain elusive. We report for the first time that in addition to the previously described Barrett's esophagus-like metaplasia, the L2-IL-1β mice also develop squamous epithelial dysplasia with progression to squamous cell carcinoma (SCC) in the esophagus and the tongue. L2-IL-1β showed age-dependent progression of squamous dysplasia to SCC with approximately 40% (n = 49) and 23.5% (n = 17) incidence rates for esophageal and tongue invasive SCC respectively, by 12-15 months of age. Interestingly, SCC development and progression in L2-IL-1β was similar in both Germ Free (GF) and Specific Pathogen Free (SPF) conditions. Immunohistochemistry revealed a T cell predominant inflammatory profile with enhanced expression of Ki67, Sox2 and the DNA double-strand break marker, γ-H2AX, in the dysplastic squamous epithelia of L2-IL-1β mice. Pro-inflammatory cytokines, immunomodulatory players, chemoattractants for inflammatory cells (T cells, neutrophils, eosinophils, and macrophages) and oxidative damage marker, iNOS, were significantly increased in the esophageal and tongue tissues of L2-IL-1β mice. Our recent findings have expanded the translational utility of the IL-1β mouse model to aid in further characterization of the key pathways of inflammation driven BE and EAC as well as ESCC and Oral SCC.

The 4-NQO mouse model: An update on a well-established in vivo model of oral carcinogenesis

The early detection and management of oral premalignant lesions (OPMDs) improve their outcomes. Animal models that mimic histological and biological processes of human oral carcinogenesis may help to improve the identification of OPMD at-risk of progression into oral squamous cell carcinoma and to develop preventive strategies for the entire field of cancerization. No animal model is perfectly applicable for investigating human oral carcinogenesis. However, the 4-nitroquinoline 1-oxide (4-NQO) mouse model is well established and mimics several morphological, histological, genomic and molecular features of human oral carcinogenesis. Some of the reasons for the success of this model include its reproducible experimental conditions with limited variation, the possibility of realizing longitudinal studies with invasive intervention or gene manipulation, and sample availability for all stages of oral carcinogenesis, especially premalignant lesions. Moreover, the role of histological and molecular alterations in the field of cancerization (i.e., macroscopically healthy mucosa exposed to a carcinogen) during oral carcinogenesis can be easily explored using this model. In this review, we discuss the advantages and drawbacks of this model for studying human oral carcinogenesis. In summary, the 4-NQO-induced murine oral cancer model is relevant for investigating human oral carcinogenesis, including the immune microenvironment, and for evaluating therapeutic and chemoprevention agents.

Fluorescence-guided resection of tumors in mouse models of oral cancer

Complete removal and negative margins are the goal of any surgical resection of primary oral cavity carcinoma. Current approaches to determine tumor boundaries rely heavily on surgeons' expertise, and final histopathological reports are usually only available days after surgery, precluding contemporaneous re-assessment of positive margins. Intraoperative optical imaging could address this unmet clinical need. Using mouse models of oral cavity carcinoma, we demonstrated that PARPi-FL, a fluorescent PARP inhibitor targeting the enzyme PARP1/2, can delineate oral cancer and accurately identify positive margins, both macroscopically and at cellular resolution. PARPi-FL also allowed identification of compromised margins based on fluorescence hotspots, which were not seen in margin-negative resections and control tongues. PARPi-FL was further able to differentiate tumor from low-grade dysplasia. Intravenous injection of PARPi-FL has significant potential for clinical translation and could aid surgeons in assessing oral cancer margins in vivo.

The Oral Mouse Microbiome Promotes Tumorigenesis in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the head and neck worldwide. Dysbiosis of the microbiome has increasingly been linked to the development of different kinds of cancer. Applying 16S rRNA gene sequence analysis and metatranscriptomic analyses, we characterized the longitudinal changes in the profiles and the function of the oral microbiome in a 4-nitroquinoline-1-oxide (4-NQO)-induced model of OSCC in gnotobiotic mice. We characterized the dynamics of the oral microbiome in this model using two different microbiome inocula: one from healthy mice and the other from mice bearing a 4-NQO-induced tumor. Mice colonized with different oral microbiomes and exposed to 4-NQO had increased tumor numbers and sizes compared to controls exposed to 4-NQO but lacking a microbiome. We observed an overall increase in diversity in the tumorigenic samples compared to that in the nontumor group not exposed to 4-NQO. Despite the variability in community dynamics, specific patterns emerged during the progression of the disease. In the two groups that were inoculated with the OSCC-associated microbiome, we observed opposite profiles of abundance in Parabacteroides and Corynebacterium While the percentage of Parabacteroides bacteria decreased in the control group, it increased in the OSCC group, and the opposite was observed for Corynebacterium The metatranscriptomic analysis revealed overexpression of the same metabolic signatures associated with OSCC regardless of the community profile. These included nitrogen transport, response to stress, interspecies interactions, Wnt pathway modulation, and amino acid and lipid biosynthesis. Thus, these results seem to suggest that certain collective physiological activities are critical for microbiome-mediated OSCC progression.IMPORTANCE There is growing evidence that changes in the microbiome are associated with carcinogenesis. To date, no consistent oral microbiome composition associated with OSCC has been identified. Longitudinal and functional studies like the study presented here should yield a better understanding of the role that the oral microbiome plays in OSCC. Our findings, obtained using a germ-free mouse model, indicate that the presence of different oral microbiomes enhances tumorigenesis and increases the final number of tumors in mice. By studying community-wide expression profiles, we found that regardless of the phylogenetic composition of the microbiome, the same metabolic activities were consistently associated with OSCC. Therefore, due to the functional redundancy of the microbiome, the critical element in explaining the contribution of the microbiota in OSCC is the collective physiological activity of the community, thus accounting for the previous inability to identify a consensus community profile or etiologic agents for OSCC.

Acquisition of Relative Interstrand Crosslinker Resistance and PARP Inhibitor Sensitivity in Fanconi Anemia Head and Neck Cancers

PURPOSE

Fanconi anemia is an inherited disorder associated with a constitutional defect in the Fanconi anemia DNA repair machinery that is essential for resolution of DNA interstrand crosslinks. Individuals with Fanconi anemia are predisposed to formation of head and neck squamous cell carcinomas (HNSCC) at a young age. Prognosis is poor, partly due to patient intolerance of chemotherapy and radiation requiring dose reduction, which may lead to early recurrence of disease.

EXPERIMENTAL DESIGN

Using HNSCC cell lines derived from the tumors of patients with Fanconi anemia, and murine HNSCC cell lines derived from the tumors of wild-type and Fancc(-/-) mice, we sought to define Fanconi anemia-dependent chemosensitivity and DNA repair characteristics. We utilized DNA repair reporter assays to explore the preference of Fanconi anemia HNSCC cells for non-homologous end joining (NHEJ).

RESULTS

Surprisingly, interstrand crosslinker (ICL) sensitivity was not necessarily Fanconi anemia-dependent in human or murine cell systems. Our results suggest that the increased Ku-dependent NHEJ that is expected in Fanconi anemia cells did not mediate relative ICL resistance. ICL exposure resulted in increased DNA damage sensing and repair by PARP in Fanconi anemia-deficient cells. Moreover, human and murine Fanconi anemia HNSCC cells were sensitive to PARP inhibition, and sensitivity of human cells was attenuated by Fanconi anemia gene complementation.

CONCLUSIONS

The observed reliance upon PARP-mediated mechanisms reveals a means by which Fanconi anemia HNSCCs can acquire relative resistance to the ICL-based chemotherapy that is a foundation of HNSCC treatment, as well as a potential target for overcoming chemoresistance in the chemosensitive individual.

A toxicity-based method for evaluating safety of reclaimed water for environmental reuses

A large quantity of toxic chemical pollutants possibly remains in reclaimed water due to the limited removal efficiency in traditional reclamation processes. It is not enough to guarantee the safety of reclaimed water using conventional water quality criteria. An integrated assessment method based on toxicity test is necessary to vividly depict the safety of reclaimed water for reuse. A toxicity test battery consisting of lethality, genotoxicity and endocrine disrupting effect was designed to screen the multiple biological effects of residual toxic chemicals in reclaimed water. The toxicity results of reclaimed water were converted into the equivalent concentrations of the corresponding positive reference substances (EQC). Simultaneously, the predicted no-effect concentration (PNEC) of each positive reference substance was obtained by analyzing the species sensitivity distribution (SSD) of toxicity data. An index "toxicity score" was proposed and valued as 1, 2, 3, or 4 depending on the ratio of the corresponding EQC to PNEC. For vividly ranking the safety of reclaimed water, an integrated assessment index "toxicity rank" was proposed, which was classified into A, B, C, or D rank with A being the safest. The proposed method was proved to be effective in evaluating reclaimed water samples in case studies.

Systemic toxic effects during early phases of topical 4-NQO-induced oral carcinogenesis in rats

BACKGROUND

Most studies have demonstrated 4-NQO toxicity to oral epithelium during oral carcinogenesis induction, but systemic toxicity has been poorly addressed. The aim of this study was to describe the systemic effect of 4-NQO topical application during early phases of oral cancer induction.

METHODS

A 4-NQO propylene glycol ointment was topically applied on the rat tongue three times a week for 16 weeks. Local and systemic 4-NQO toxicity was evaluated by body weight gain, hematology, and serum chemistry analyses, histopathology, and proliferating cell nuclear antigen (PCNA) immunohistochemistry.

RESULTS

Significant reduction in body weight gain and in white blood cell count as well as significant increase in serum ALT and AST was observed after 16 weeks of 4-NQO topical application. Focal hepatic lobular necrosis, renal tubular degeneration, and decreased cellularity in the splenic white pulp were also detected.

CONCLUSIONS

4-NQO topical application on the tongue of rats for 16 weeks seems to have caused hepatic, renal, and splenic toxicity. Potential systemic toxicity should be considered to monitor for variables that could interfere in topical oral carcinogenesis experiments.

Development of a 4-nitroquinoline-1-oxide model of lymph node metastasis in oral squamous cell carcinoma

OBJECTIVES

Lymph node metastasis is one of the most important prognostic factors in oral squamous cell carcinoma. However, regional lymph node metastasis from oral cancer has barely been investigated in 4-nitroquinoline-1-oxide (4NQO) models. In this study, we developed a 4NQO-treated mouse model of oral squamous cell carcinoma that displayed lymph node metastasis and examined the occurrence and timing of the lymph node metastasis.

MATERIALS AND METHODS

BALB/c mice were treated with 200 μg/ml 4NQO in drinking water for 20 weeks and then followed for 4 weeks. Four mice were sacrificed bi-weekly, and oral lesion and regional lymph node metastasis were assessed during the week 25-32 and week 33-40 observation periods.

RESULTS

Tumor formation and local lymph enlargement were observed from 25 weeks onwards. The presence of metastatic tumor cells in the enlarged lymph nodes was confirmed via the detection of tumor infiltration by HE staining and cytokeratin positivity by immunostaining at both 28 and 36 weeks. The incidence rates of oral squamous cell carcinoma and local lymph node metastasis were 68.8% and 12.5% in the week 25-32 observation period, and 100% and 100% in the week 33-40 observation period, respectively.

CONCLUSIONS

A lymph node metastasis model involving mice being subjected to high-dose 4NQO treatment for a long period and then followed for a prolonged period was established. This model might provide a platform for studying the mechanism of lymphatic metastasis in oral carcinoma, leading to the development of new therapies for advanced oral carcinoma.

Chemopreventive effect of a mixture of Chinese Herbs (antitumor B) on chemically induced oral carcinogenesis

In this study, we evaluated chemopreventive efficacy of Antitumor B, a Chinese herbal mixture of six plants (Sophora tonkinensis, Polygonum bistorta, Prunella vulgaris, Sonchus arvensis L., Dictamnus dasycarpus, and Dioscorea bulbifera) on the development of 4-nitroquinoline-1-oxide (4NQO) induced oral squamous cell carcinomas in A/J mice. Antitumor B, delivered through diet, inhibited 4NQO-induced oral cancer development by 59.19%. The reduction of cell proliferation appears to be associated with efficacy of Antitumor B against 4NQO-induced oral cancer in A/J mice. The expression of epidermal growth factor receptor (EGFR) and phosphorylated EGFR (Tyr1173) were down-regulated by Antitumor B. Tissue distribution of Antitumor B was determined using obacunone, matrine, and maackiain as marker chemicals. We found significant amounts of obacunone, matrine, and maackiain in the blood after 1-wk treatment. The concentrations of these three compounds did not increase further at 18  wk, suggesting that plasma concentrations had reached a steady-state level at 1  wk. There was no significant body weight loss and there was no other obvious sign of toxicity in Antitumor B-treated mice. These results suggest that Antitumor B is a promising agent for human oral cancer chemoprevention.

DMBA-induced hamster buccal pouch carcinoma and VX2-induced rabbit cancer as a model for human oral carcinogenesis

In this article, we have described and compared the advantages and disadvantages of two potential animal cancer models (the hamster buccal pouch cancer model and the VX2-induced rabbit cancer model) for human squamous cell carcinomas of the oral mucosa. Currently, no animal cancer model is perfectly applicable to human oral squamous cell carcinomas. This is because the hamster buccal pouch cancer model has a different etiology and genetic constitution compared with human oral carcinomas. In addition, the VX2-induced rabbit cancer model is not produced in situ and, consequently, its natural behavior is totally reliant on the location of transplantation. Nonetheless, with the use of these two animal cancer models together, researchers could evaluate different aspects of the cellular and molecular biological characteristics or assess potential novel treatment regimens for squamous cell carcinomas of the human oral mucosa.

Co-treating with arecoline and 4-nitroquinoline 1-oxide to establish a mouse model mimicking oral tumorigenesis

The aim of this study was to establish an effective mouse model of oral cancer and to use this model to identify potential markers of oral tumor progression. C57BL/6JNarl mice were treated with arecoline, 4-nitroquinoline 1-oxide (4-NQO), or both arecoline and 4-NQO in high and low doses for 8 weeks to induce oral tumor. The induced oral lesions were observed for 20 weeks to assess the efficiency of cancer induction and survival rate of the mice. In addition, two target proteins that are frequently overexpressed during tongue cancer tumorigenesis, alphaB-crystallin and Hsp27, were examined by immunohistochemical analysis. In mice exposed to 4-NQO (200 microg/mL) and arecoline (500 microg/mL), the tongue lesions showed evidence of hyperplasia, papilloma, dysplasia, and carcinoma, and the lesions were pathologically similar to those lesions in human oral cancer. The tongue tumor incidence rate was 100% in mice exposed to concomitant 4-NQO (200 microg/mL) and arecoline (500 microg/mL) treatment, 57% in mice exposed to 4-NQO only, and 0% in mice exposed to arecoline only. Immunohistochemical analysis demonstrated that, consistent with human studies, alphaB-crystallin and Hsp27 were upregulated in murine oral tumors. In conclusion, we have established a powerful animal model that enables the study of the promoting effects of arecoline on tongue tumorigenesis. Data subsequently attained from this mouse model support a role for alphaB-crystallin and Hsp27 as clinical markers for tumor progression.

ABT-510 is an effective chemopreventive agent in the mouse 4-nitroquinoline 1-oxide model of oral carcinogenesis

Despite numerous advances, the 5-year survival rate for head and neck squamous cell cancer (HNSCC) has remained largely unchanged. This poor outcome is due to several variables, including the development of multiple primary tumors. Therefore, it is essential to supplement early detection with preventive strategies. Using the 4-nitroquinoline 1-oxide (4-NQO) mouse model, we sought to define an appropriate dose and duration of administration that would predict the histologic timeline of HNSCC progression. Additionally, we sought to determine the timing of the onset of the angiogenic phenotype. Finally, using ABT-510 as a proof-of-principle drug, we tested the hypothesis that inhibitors of angiogenesis can slow/delay the development of HNSCC. We determined that 8 weeks of 100 microg/mL 4-NQO in the drinking water was the optimal dosage and duration to cause a sufficient incidence of hyperkeratoses, dysplasias, and HNSCC over a period of 32 weeks with minimal morbidity and mortality. Increased microvessel density and vascular endothelial growth factor expression in hyperkeratotic lesions provided evidence that the initiation of the angiogenic phenotype occurred before the development of dysplasia. Importantly, ABT-510 significantly decreased the overall incidence of HNSCC from 37.3% to 20.3% (P = 0.021) as well as the combined incidence of dysplasia and HNSCC from 82.7% to 50.6% (P < 0.001). These findings suggest that our refinement of the 4-NQO model allows for the investigation of the histologic, molecular, and biological alterations that occur during the premalignant phase of HNSCC. In addition, these data support the hypothesis that inhibitors of angiogenesis may be promising chemopreventive agents.

A novel immunocompetent murine model for Candida albicans-promoted oral epithelial dysplasia

Candida albicans is a common opportunistic pathogen found in the oral mucosa. Clinical observations indicate a significant positive association between oral Candida carriage or infection and oral epithelial dysplasia/neoplasia. The aim of this study was to test whether C. albicans is able to promote epithelial dysplasia or carcinoma in a mouse model of infection where a carcinogen (4 Nitroquinoline 1-oxide [4NQO]) was used as initiator of neoplasia. Mice were divided into four groups: group 1 received 4NQO alone; group 2 received 4NQO followed by C. albicans (ATCC 90234); group 3 received vehicle dimethyl sulfoxide (DMSO) followed by C. albicans and group 4 was untreated. Although 4NQO treated mice did not develop oral lesions, mice exposed to both 4NQO and C. albicans developed oral dysplastic lesions 19 weeks after exposure to 4NQO. Mice challenged with C. albicans only developed hyperplastic lesions. The expression of Ki-67 and p16, two cell-cycle associated proteins that are frequently deregulated in oral dysplasia/neoplasia, was also tested in these lesions. Ki-67 and p16 expression increased from normal to hyperplastic to dysplastic mucosa and was highest in the group exposed to both 4NQO and C. albicans. In conclusion, we showed that C. albicans plays a role in the promotion of oral dysplasia in a mouse model of infection when 4NQO was used as initiator of oral neoplasia.

Collagenase-2 (matrix metalloproteinase-8) plays a protective role in tongue cancer

Squamous cell carcinoma (SCC) of the tongue is the most common cancer in the oral cavity and has a high mortality rate. A total of 90 mobile tongue SCC samples were analysed for Bryne's malignancy scores, microvascular density, and thickness of the SCC sections. In addition, the staining pattern of cyclooxygenase-2, αvβ6 integrin, the laminin-5 γ2-chain, and matrix metalloproteinases (MMPs) -2, -7, -8, -9, -20, and -28 were analysed. The expression of MMP-8 (collagenase-2) was positively associated with improved survival of the patients and the tendency was particularly prominent in females. No sufficient evidence for a correlation with the clinical outcome was found for any other immunohistological marker. To test the protective role of MMP-8 in tongue carcinogenesis, MMP-8 knockout mice were used. MMP-8 deficient female mice developed tongue SCCs at a significantly higher incidence than wild-type mice exposed to carcinogen 4-Nitroquinoline-N-oxide. Consistently, oestrogen-induced MMP-8 expression in cultured HSC-3 tongue carcinoma cells, and MMP-8 cleaved oestrogen receptor (ER) α and β. According to these data, we propose that, contrary to the role of most proteases produced by human carcinomas, MMP-8 has a protective, probably oestrogen-related role in the growth of mobile tongue SCCs.

The hamster model of sequential oral oncogenesis

Oral squamous cell carcinoma (OSCC) is a common cancer characterised by low survival rate and poor prognosis. The multistep process of oral carcinogenesis is affected by multiple genetic events such as alterations of oncogenes and tumour suppressor genes. The use of appropriate experimental animal models that accurately represent the cellular and molecular changes which are associated with the initiation and progression of human oral cancer is of crucial importance. The Syrian golden hamster cheek pouch oral carcinogenesis model is the best known animal system that closely correlates events involved in the development of premalignant and malignant human oral cancers. Therefore, we established an experimental system of chemically induced oral carcinogenesis in hamsters, in order to study different stages of tumour formation: normal mucosa, hyperkeratosis, hyperplasia, dysplasia, early invasion, well differentiated OSCC and moderately differentiated OSCC. We investigated the expression of oncogenes EGFR, erbB2, erbB3, FGFR-2, FGFR-3, c-myc, N-ras, ets-1, H-ras, c-fos and c-jun, apoptosis markers Bax and Bcl-2, tumour suppressor genes p53 and p16, and cell proliferation marker Ki-67 in the sequential stages of hamster oral oncogenesis. Here, we describe the findings of the experimental model in regard to the involvement of signal transduction pathways in every stage of cancer development. Increased apoptosis and cell proliferation were observed in early stages of oral oncogenesis. Furthermore, the increased expression of transmembrane receptors (EGFR, erbB2, FGFR-2 and FGFR-3) as well as the increased expression of nuclear transcriptional factors in early stages of oral cancer indicates that these molecules may be used as early prognostic factors for the progression of OSCC. Since the expression of both H-ras and N-ras do not seem to affect signal transduction during oral oncogenesis, it can be assumed that a different signalling pathway, such as the PI3K and/or PLCgamma pathway, may be implicated in the pathogenesis of OSCC.

p53 Transgenic mice are highly susceptible to 4-nitroquinoline-1-oxide-induced oral cancer

In this study, we did a bioassay employing mice with a dominant-negative p53 mutation (p53(Val135/WT)) to assess whether a germ-line p53 mutation predisposed mice toward the development of squamous cell carcinomas (SCC) in the oral cavity. Treatment of the mouse oral cavity with 4-nitroquinoline-1-oxide produced a 66%, 91%, and 20% tumor incidence in the oral cavity, esophagus, and forestomach/stomach, respectively, in p53(Val135/WT) mice. In contrast, only a 25%, 58%, and 4% tumor incidence was observed in oral cavity, esophagus, and forestomach/stomach, respectively, in wild-type littermates (p53(WT/WT)). The most striking difference between p53(Val135/WT) and p53(WT/WT) mice following the carcinogen treatment was the higher prevalence and more rapid development of SSC in p53(Val135/WT) mice than in wild-type mice. To identify the precise genes or pathways involved in these differences during tumor development, we examined gene expression profiles of 4-nitroquinoline-1-oxide-treated normal tongues as well as tongue SCC in p53(Val135/WT) and p53(WT/WT) mice. Microarray and GenMAPP analysis revealed that dominant-negative p53 ((135)Valp53) affects several cellular processes involved in SCC development. Affected processes included apoptosis and cell cycle arrest pathways, which were modulated in both tumor and normal epithelium. These results showed that reduction of p53-dependent apoptosis and increases in cell proliferation might contribute to the observed increase in oral cavity and gastroesophageal malignancies in p53(Val135/WT) mice as well as to the more rapid growth and progression of tumors.

Animal models in oral cancer research

Biologically and clinically relevant animal models are essential in investigation of the progression of diseases and the elaboration of diagnostic or therapeutic protocols. The several rodent models used for in vivo evaluation for oral cancer employ chemical, transplantation and genetic (knockout and transgenic) induction methods. These models are described together with their advantages and disadvantages. Their optimization and application in future research may improve the early detection and treatment of oral cancer.

Animal models for the study of squamous cell carcinoma of the upper aerodigestive tract: a historical perspective with review of their utility and limitations. Part A. Chemically-induced de novo cancer, syngeneic animal models of HNSCC, animal models of transplanted xenogeneic human tumors

Understanding the complex histological, genetic and molecular changes that lead to malignant transformation of squamous epithelia of the head and neck will likely guide the development of methods for improved diagnosis, monitoring and treatment of head and neck squamous cell carcinoma (HNSCC). The development and use of animal models that closely mimic the histopathology and molecular pathogenesis of HNSCC in humans would greatly expand the research possibilities and provide a means of testing potential therapeutic agents. However, many available animal models of HNSCC fall short of this objective. In order for investigators to select the appropriate model to answer scientific questions, it is important to understand the benefits and limitations of available animal models for the study of HNSCC. The purpose of this work is to give an overview of the most pertinent animal models of HNSCC, and to discuss future directions of research in this field.

Ultrastructural changes of the palatal mucosa following application of 4-nitroquinoline-l-oxide (4NQO) in rats subjected to major salivary gland excision

OBJECTIVE

It has been suggested that saliva exerts a protective role against the carcinogenic effect of various substances in the oral cavity. The objective of this study was to examine the ultrastructural changes of the palatal mucosa caused by the application of 4-nitroquinoline-l-oxide (4NQO) in the presence or absence of saliva.

STUDY DESIGN

Wistar-Furth rats subjected and not subjected to total bilateral excision of the major salivary glands were either painted with an aqueous solution of 4NQO or with propylene glycol only (controls). Two animals of each group were humanely killed periodically. The areas of the palatal lesions were immediately sliced and processed for TEM examination.

RESULTS

Ultrastructurally, the progressive changes to squamous cell carcinoma were observed in the animals painted with 4NQO. In the desalivated animals group, the ultrastructural alterations appeared earlier than in the group with salivary glands.

CONCLUSIONS

Saliva appeared to delay but not hinder tumor induction by 4NQO.

Parp-1 deficiency does not increase the frequency of tumors in the oral cavity and esophagus of ICR/129Sv mice by 4-nitroquinoline 1-oxide, a carcinogen producing bulky adducts

The impact of poly(ADP-ribose) polymerase-1 (Parp-1)-deficiency on 4-nitroquinoline 1-oxide (4NQO)-induced carcinogenesis was studied in mice with an ICR/129Sv mixed genetic background. Parp-1(+/+), Parp-1(+/-) and Parp-1(-/-) animals given 4NQO for thirty-two weeks at 0.001% in their drinking water developed papillomas and squamous cell carcinomas of the tongue, palate and esophagus, but with no statistically significant variation with the Parp-1 genotype. Thus Parp-1 deficiency does not elevate susceptibility to carcinogenesis induced by a carcinogen which gives rise to bulky DNA lesions. This study also indicated that the ICR/129Sv mixed genetic background is associated with high yield induction of esophageal tumors by 4NQO.

Oral cavity and esophageal carcinogenesis modeled in carcinogen-treated mice

PURPOSE

Squamous cell carcinoma of the oral cavity is one of the most common human neoplasms, and prevention of these carcinomas requires a better understanding of the carcinogenesis process and a model system in which cancer chemoprevention agents can be tested. We have developed a mouse model using the carcinogen 4-nitroquinoline 1-oxide (4-NQO) in the drinking water to induce tumorigenesis in the mouse oral cavity.

EXPERIMENTAL DESIGN

4-NQO was delivered by tongue painting or drinking water to two mouse strains, CBA and C57Bl/6. The incidences of oral cavity carcinogenesis were then compared. In addition, we examined the expression of some of the molecular markers associated with the process of human oral cavity and esophageal carcinogenesis, such as keratin (K) 1, K14, p16, and epidermal growth factor receptor, by immunohistochemistry.

RESULTS

After treatment with 4-NQO in the drinking water, massive tumors were observed on the tongues of both CBA and C57Bl/6 female mice. Pathological analyses indicated that flat squamous dysplasias, exophytic papillary squamous tumors (papillomas), and invasive squamous cell carcinomas were present. Immunohistochemistry analyses showed that 4-NQO changed the expression patterns of the intermediate filament proteins K14 and K1. K14 was expressed in the epithelial suprabasal layers, in addition to the basal layer, in tongues from carcinogen-treated animals. In contrast, control animals expressed K14 only in the basal layer. Moreover, we observed more bromodeoxyuridine staining in the tongue epithelia of 4-NQO-treated mice. Reduced expression of the cell cycle inhibitor, p16, was observed, whereas 4-NQO treatment caused an increase in epidermal growth factor receptor expression in the mouse tongues. Interestingly, similar features of carcinogenesis, including multiple, large (up to 0.5 cm) exophytic papillary squamous tumors and invasive squamous cell carcinomas, increased bromodeoxyuridine staining, and increased K14 expression, were also observed in the esophagi of 4-NQO-treated mice. However, no tumors were observed in the remainder of digestive tract (including the forestomach, intestine, and colon) or in the lungs or livers of 4-NQO-treated mice. These results indicate that this murine 4-NQO-induced oral and esophageal carcinogenesis model simulates many aspects of human oral cavity and esophageal carcinogenesis.

CONCLUSIONS

The availability of this mouse model should permit analysis of oral cavity and esophageal cancer development in various mutant and transgenic mouse strains. This model will also allow testing of cancer chemopreventive drugs in various transgenic mouse strains.

Interaction between the immune system and tongue squamous cell carcinoma induced by 4-nitroquinoline N-oxide in mice

Squamous cell carcinoma of the oral cavity (SCC) accounts for 3% of cancers in the western world and 40% of cancers in India. The overall 5-year survival rate is only 50%. Most of the lesions appear intra-orally on the tongue. Results from a previous study demonstrated a significant increase in T and B-lymphocytes under the transformed epithelium when examining human lesions of hyperkeratosis, dysplasia and carcinoma of the tongue. In order to investigate the interaction between the host immunity and SCC, carcinogen induced SCC of the tongue was studied in mice. The water-soluble carcinogen, 4 nitroquinoline N-oxide (4NQO), was applied to BALB/c mice tongues and produced tongue SCC after a long incubation period of several months. Immunologic properties were examined systemically in the spleens and locally, at the tumor site. Examination of spleen lymphocytes from 4NQO induced mice revealed enlargement of the spleens and a significant decrease in the CD3, CD4, CD8 and CD19 cells. In the tongues, expression of TGF-beta, TNF-alpha, GM-CSF, and IL-1 beta mRNA were detected. TNF-alpha protein was detected in the affected tongues using immunoassays. mRNA expression of TNF-alpha was detected in the cancerous epithelium when extracted from the connective tissue. CD11b and CD3 cells were detected in the connective tissue under the developing carcinoma. CD11b positive cells were more prominent. The infiltrate was very scattered and not prominent as the infiltrate in the human tongue tissues. These results indicate that the growing tumor affected the immune response around the tumor and systemically. Most of the cytokines, which appeared in the affected tongues, originated from the tumor surroundings, but TNF-alpha was found also in the tumor. The interaction between the tumor and immune response components is important for diagnosis and treatment purposes.

Biomarkers and molecular epidemiology and chemoprevention of oral carcinogenesis

Chemopreventives are chemicals that prevent the formation of cancers such as oral cancer. They can take the form of nutrients or synthetic molecules, and their fundamental characteristic is that they do not produce disease processes that would result in debilitating symptoms. Current evidence indicates that they function by modifying the oxidative state of transforming cells. Biomarkers can take the form of genetic and molecular indicators, which characterize the function of chemopreventives and cancer processes such as oral carcinogenesis. Biomarkers cannot provide all the required information for risk assessment or possible activity of the chemopreventives. Other methods, such as epidemiological analyses and techniques, must be used to enhance our understanding of the risk for oral cancer in human populations. One common epidemiologic method, the questionnaire, helps to determine the use and carcinogenic potential of tobacco and alcohol during oral carcinogenesis. Genetic and molecular changes in human patient populations may result in a reduction in the number and function of tumor suppressor genes. If these changes are to be assessed, the tissues (e.g., buccal mucosa) must be accessible and harvested in a reliable and consistent manner for the acquisition of DNA, mRNA, and protein. Oral tissues provide sufficient quantities of these molecules and, under stringent conditions, the quality required for the isolation of these molecular constituents. In conjunction with epidemiologic techniques, various genotypic polymorphisms, such as glutathione-S-transferase (GSTM1) or cytochrome P450 (CYP450A1), have indicated a loss in carcinogen detoxification or the processing of internal growth control signals. Biomarkers are composed of a large diverse group of genetic and molecular structures. Some of these biomarkers are indicators for programmed cell death (PCD), while others describe malignant tumor growth. Many of these classes of molecules are oxidative-responsive (e.g., tumor suppressor p53, Bcl-2, growth factors, immune-derived proteins, and death-inducing molecules) and induce PCD by triggering a cascade of cysteine proteases and regulators (e.g., caspases, death receptors). This pathway results in cell-cycle alterations and DNA fragmentation. It is hoped that a detailed knowledge of the processes involved in malignant transformation will better define the biomarker-screening tools for oral cancer. These tools will enhance our ability to predict the incidence of cancer, detect early malignant change, and quantitate chemoprevention during oral carcinogenesis. Chemopreventives such as the retinoids have already demonstrated their ability to suppress potential malignant changes in pre-malignant oral leukoplakias and decrease the incidence of second head-and-neck cancer primaries. It is our hope that this review will increase investigators' interest in developing new screening and detection systems for oral cancer.

Promotional effects of CO(2) laser and scalpel incision on 4-NQO-induced premalignant lesions of mouse tongue

BACKGROUND AND OBJECTIVES

CO(2) laser and scalpel incision have been demonstrated to have promotional effects on oral neoplastic lesions. However, a precise understanding has not been achieved as to which modality has a more significant effect on cancer promotion. The purpose of this study was to determine the histological and biological changes after CO(2) laser surgery and scalpel incision in oral premalignant lesions.

STUDY DESIGN/MATERIALS AND METHODS

Premalignant lesions of mouse tongue induced by 4-nitroquinoline-1-oxide (4NQO) in drinking water for 4 months were used in this study. A 2-mm incision was made on the right margin of each mouse tongue, using either a CO(2) laser (group A) or a scalpel (group B). Mice without incisional treatment were used as controls (group C). Seven months after laser and scalpel treatments, hematoxylin-eosin staining and proliferating cell nuclear antigen (PCNA), epidermal growth factor receptor (EGFR), and p53 immunostaining were performed for tongue specimens.

RESULTS

The epithelia of right tongue margins showed more severe dysplasia than those of left tongue margins in both group A and group B. The PCNA labeling indices (LIs) and EGFR expression for right tongue margins were also higher than for left margins in both group A and group B. There was no obvious difference between these two groups. Almost no p53-positive staining was found in either group.

CONCLUSION

CO(2) laser surgery and scalpel incision seem to have similar promotional effects on oral premalignant lesions.

Effect of photodynamic therapy using 5-aminolevulinic acid on 4-nitroquinoline-1-oxide-induced premalignant and malignant lesions of mouse tongue

A new photosensitizing agent 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) has been demonstrated as a useful method for treatment of superficial neoplastic lesions. The aim of this study was to determine the effects of topically and systemically ALA-based PDT in neoplastic lesions of the oral cavity. Premalignant and malignant lesions of mouse tongue induced by 4-nitroquinoline-l-oxide (4NQO) were used in this study. At 1, 2 and 3 h after topical application of ALA or 3 h after systemic administration of ALA (250 or 1000 mg/kg), the lesions were irradiated with Nd: YAG dye laser at 630 nm (200 J/cm2). Both premalignant and early malignant lesions showed complete response to systemically ALA-based PDT. In an invasive nodular malignant lesion, however, only the superficial portion was affected. There was no apparent difference in the PDT effect between 250 and 1000 mg/kg doses of ALA. In contrast, topically ALA-based PDT had virtually no effect on most lesions. It was concluded that systemically ALA-based PDT is a useful method for treating premalignant and early malignant lesions in the oral cavity, while topically ALA-based PDT using this preparation may be unsuitable for treatment of oral lesions.

Consistent allelic loss on mouse chromosome 7 distal to tyrosinase in 4-nitroquinoline-1-oxide-induced oral cavity tumors with loss of heterozygosity at Ha-ras-1

We have previously shown that all CBA/J mice exposed to 4-nitroquinoline-1-oxide (4NQO) eventually develop oral cavity squamous cell carcinomas, and two-thirds of these tumors have Ha-ras-1 (Hras1) point mutations at codon 12. Half of the tumors with Hras1 mutations have loss of heterozygosity (LOH) at Hras1. In the study reported here, seven tumors with LOH at Hras1, six heterozygous for Hras1, and six without Hras1 mutations were analyzed to define the extent of LOH on chromosome (Chr) 7. Microsatellite polymorphisms present in CBA/J mice were used as informative allelic markers. Tumors with LOH at Hras1 showed consistent allelic loss at the distal portion of Chr 7. The boundary of allelic loss lay between the tyrosinase and hemoglobin beta chain loci, which are 6 cM apart. None of the tumors that remained heterozygous for Hras1 or had no Hras1 mutations had evidence of chromosomal loss involving Chr 7. Because LOH was only detected in advanced lesions long after exposure to 4NQO had ceased, we presume that the chromosomal alterations by which LOH occurred were independent of the carcinogen exposure. The development of LOH in only half of the tumors with Hras1 point mutations suggests that LOH was not caused by the initial Hras1 point mutation but was a highly selected event during tumorigenesis.

Epithelial dysplasia and squamous cell carcinoma of the Wistar rat palatal mucosa: 4NQO model

BACKGROUND

The carcinogen 4-nitroquinoline 1-oxide (4NQO) has been used in several studies concerning experimental oral carcinogenesis to induce squamous cell carcinoma in the palatal mucosa of rats, whereas limited attention has been paid to preceding premalignant mucosal changes. The aim of this study was to describe the macroscopic and microscopic changes of the rat palatal mucosa treated with 4NQO as a function of the application time of this carcinogen.

METHODS

The carcinogen 4NQO was applied to the palatal mucosa of male Wistar rats three times a week for 2-26 weeks. The Epithelial Atypia Index (EAI) was used to quantify the degree of dysplasia induced by the application of 4NQO for various time intervals.

RESULTS

This study shows that the EAI increases as a function of the application time. As soon as 2 weeks following application of the carcinogen, dysplastic alterations in the mucosa were observed. The extent and grade of the dysplastic changes increased with time. At week 26, squamous cell carcinoma developed. In rats in which the application of 4NQO was discontinued earlier, the application period appeared to be in inverse proportion to the latency period i.e., the period between the last application of the carcinogen and the first clinical sign of squamous cell carcinoma. This emphasizes the premalignant character of the induced epithelial changes, because in all the rats squamous cell carcinoma eventually developed.

CONCLUSIONS

From this study, we concluded that the 4NQO rat palate model is a proper model in which both premalignant epithelial lesions and squamous cell carcinoma of the oral mucosa can be studied.

Cell, tissue and organ culture as in vitro models to study the biology of squamous cell carcinomas of the head and neck

In vitro models are currently being used to study head and neck squamous cell carcinoma (HNSCC). Several hundred HNSCC cell lines have been established by various investigators and used to study a broad spectrum of questions related to head and neck cancer. The head and neck model with respect to multistage carcinogenesis is now complete. Several techniques exist for the culture of normal epithelial cells from the upper aerodigestive tract (UADT). The biology of these UADT cells (oral cavity, oropharynx, hypopharynx and larynx) is being studied. Successful culture of premalignant lesions (dysplastic mucosa, leukoplakia, erythroplakia) has resulted in establishment of a limited number of premalignant cell lines and cell cultures. HPV infection of normal oral epithelial cells for immortalization (approximately premalignant cells) coupled with transformation with carcinogens (malignant cells) has established an experimental model for progression. Two in vivo models for oral carcinogenesis, the 7,12 dimethylbenz(a)anthracene-induced hamster cheek pouch model and the 4-nitroquinoline-N-oxide rat oral model, have been established in culture. Thus, multistage carcinogenesis models have been established from both human tissues and animal models and include cultures of normal, premalignant and malignant cells. Culture techniques for growing dissociated primary tumor cells for short term experimental analysis are being used. The culture of normal or tumor tissue as organ/explant cultures allows for the maintenance of normal cell-cell and cell-matrix interaction, but limits experimentation since these cultures cannot be propagated. Several three dimensional model systems are being used to obtain this histological complexity but allow for experimentation. The ability to culture normal, premalignant and malignant cells coupled with the use of a variety of culture techniques, should allow for the continued growth and experimentation in head and neck cancer research.

Structure of hamster palatal gingiva and intermolar mucosa after intraperitoneal dosing with N-methyl-N-nitrosourea: a scanning electron microscope study

The palatal gingiva and intermolar mucosa from normal hamsters and from hamsters that had received N-methyl-N-nitrosourea (NMU) intraperitoneally were examined by scanning electron microscopy over a 22-week period. The normal gingiva and rostral two-thirds of the intermolar mucosa were covered by flat polygonal cells that had a regular honeycomb surface pattern of interconnecting micro-ridges, distinct cell boundaries and imprints of cells that had been desquamated. The caudal third of the intermolar mucosa in normal and NMU-treated hamsters was covered by soft-palate type mucosa whose smooth surfaced cells surrounded scattered fungiform-like papillae. In NMU-treated hamsters changes were more common in the rostral two-thirds of the intermolar mucosa than in the gingiva. At 10 weeks there were sessile and conical surface projections and saucer-shaped and conical epithelial-lined depressions. At 16 weeks these projections and depressions were larger and more numerous, and groups of conical projections formed papillomatous-like lesions. At 22 weeks the projections and depressions were further increased in number and size and there were distinct papillomas. At 10 and 16 weeks the entire epithelium showed cells, cell boundaries and cell imprints resembling those in the controls, except that there were defects or dilated intercellular spaces at the base of the conical depressions and some of the cells were thicker. Much of the 22-week epithelial had a similar structure, but in some areas that did not show the projections or depressions the cells varied in size and shape and were covered by elongated micro-ridges. Here the surface was irregular as were the cell boundaries. Examination of sections by light microscopy, both from these irregular areas and from areas that appeared normal by scanning electron microscopy, revealed that the deeper epithelial strata could be either normal, dysplastic or at times malignant. However, scanning electron microscopy failed to reveal dysplastic or malignant epithelium.

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.

The effect of intraperitoneal N-methyl-N-nitrosourea on hamster palatal gingiva and intermolar mucosa

Fifty 4- to 6-week-old male random-bred golden hamsters were injected intraperitoneally with a weight-related dose (12.5 mg/kg body weight) of N-methyl-N-nitrosourea (NMU) three times a week for 4 weeks. Groups of seven animals were killed 10, 16 and 22 weeks after the first injection. The palatal gingiva from six animals and the intermolar mucosa from 21 animals was examined. Seven male age-matched untreated control animals were killed at each period. Although all NMU-treated hamsters showed dysplastic and neoplastic changes similar to those in human oral squamous-cell carcinoma, other changes such as acantholytic dyskeratosis, invading cysts, duct-like structures and basaloid islands and cords were not. The extent and severity of the changes increased with time so that by 22 weeks there was extensive involvement of the palatal bone and marrow spaces, the molar periodontal ligament and the greater palatine neurovascular bundle by neoplastic epithelium. The invading epithelium was derived from the junctional, crevicular and palatal gingival and intermolar epithelium. The latent period for the crevicular and junctional epithelia was shorter than that for the palatal gingival and intermolar epithelium. The invasive changes from the latter epithelium were often preceded by exophytic changes such as epithelial projections, papillae and papillomas. Such changes were infrequent for the gingival, crevicular and junctional epithelia. The study shows that intraperitoneal NMU acts as a complete carcinogen on the palatal gingival and intermolar epithelium in hamsters.

Ultrastructural features of normal epithelium and 4-nitroquinoline 1-oxide-induced carcinomas of the rat tongue

An electron microscopical examination of normal rat lingual mucosa and 4-nitroquinoline 1-oxide (4NQO)-induced tongue carcinomas was undertaken. In normal rat tongue, the epithelium of papillae and interpapillary regions exhibited two distinct keratohyalin granule types and essentially similar ultrastructural cellular features in the different epithelial compartments. The interface between epithelium and connective tissue showed a continuous basal lamina. Compared with normal rat tongue epithelium, 4NQO-induced oral carcinomas revealed cellular and nuclear pleomorphism, atypical tonofilament aggregates, increased and swollen mitochondria, dilated intercellular spaces, local discontinuities and thickening of the basal lamina.

Lingual fibrosarcoma induced by 7, 12-dimethylbenzanthracene in the rat

A single injection of 5 mg of 7, 12-dimethylbenzanthracene (DMBA) resulted in a high incidence of lingual fibrosarcoma in 67 Wistar rats. No metastases were found. We studied the influence of age and sex on the incidence, latency of tumors, loss of weight and the spontaneous survival of animals. The method described offers an experimental model for the study of cachexia resulting from upper digestive and respiratory tract cancer.

Blood group antigen staining pattern during experimental carcinogenesis in rat palate

During 4-nitroquinoline-1-oxide-induced carcinogenesis in the rat palate, animals were sacrificed at various intervals and stained for blood group antigens B and H (Type 2 chain) by an immunofluorescent method. In rats without signs of epithelial dysplasia, the staining pattern was identical with that in the normal control rats. In rats with definite or questionable (borderline cases) dysplasias, marked changes in blood group antigen staining pattern were seen. Thus, changes in cell-surface carbohydrates during malignant development in the rat palate seem to follow closely the histomorphological changes. As there is good evidence that carcinomas would eventually develop in all rats if they were not sacrificed, it seems that the blood group antigen staining pattern does not predict malignant development in the absence of histological suspicion.

Dose-response relationship in complete oral 4NQO-carcinogenesis in rats

Groups of 48 Wistar rats were subjected to thrice-weekly palatal application of the carcinogen 4-nitro-quinoline 1-oxide (4NQO) in propylene glycol 18, 12, 6 or 2 times, each 255 nmol 4NQO, in order to examine the relationship between the dose of the carcinogen and the tumour response. Other groups were treated with solvent alone or were left untreated. When the carcinogen was applied 18 or 12 times, squamous cell or verrucous carcinomas developed in 50% of the rats in 11 and 12 months, respectively, whereas rats subjected to the carcinogen 6 times demonstrated a 50% cancer rate in 23 months. Rats twice exposed to the carcinogen demonstrated a tumour rate of 25% in 30 months. Decreasing doses of 4NQO thus prolonged the latency period and decreased the tumour rate. The tumour development in the animals subjected to two carcinogen applications was significantly different from the tumour development among the solvent-treated animals, indicating that application of 255 nmol may approximate the initiating dose of 4NQO to be used in a two- or multi-stage carcinogenesis protocol. Most of the carcinomas, either squamous cell or verrucous, were located to the hard palate and to the gingival region of the upper jaw. Impaction of hair, bedding material and food was thought to promote the carcinogenic process.

Oral epithelial atypia and acantholytic dyskeratosis in rats painted with 4-nitroquinoline N-oxide

Oral epithelial atypia and foci of acantholytic dyskeratosis (FAD) were investigated in 54 rats treated with the carcinogen 0.5% (w/v) 4-nitroquinoline-N-oxide in propylene glycol and in 18 rats treated with propylene glycol only. The palate of each animal was painted 3 times weekly for up to 9 months and rats were killed at monthly intervals. A gradual significant increase in the epithelial atypia indices of the palatal and lingual tissues (anterior and posterior of the intermolar tubercle) was observed with a maximum value of 17-22 of a possible 75 at 28-32 weeks. No significant differences were noted between the atypia indices of the palatal and lingual tissues. FAD were not evident in the palate or lingual tissues before 12 weeks and 16-24 weeks, respectively, and although the palate consistently showed more FAD compared with the lingual tissues the differences were not significant. Features of epithelial atypia and FAD were absent in the 18 control rats treated with propylene glycol only and in 8 untreated control animals. At 28 weeks of 4NQO treatment 2 of 5 rats, at 32 weeks 3 of 4 rats and at 36 weeks 3 of 3 rats had developed infiltrating squamous cell carcinomas in either/both the palate or tongue. The results suggest that epithelial dysplasia and acantholytic dyskeratosis may be late morphological features of a more fundamental change occurring earlier in the process of tumour development.

Initiation and promotion of experimental oral mucosal carcinogenesis in mice

While there is considerable evidence that skin carcinogenesis proceeds as a step-wise series of changes, little evidence is available to indicate that a similar mechanism applies to oral mucosal carcinogenesis. In the current study, a mouse model of mucosal carcinogenesis was used to examine the effects of repeated applications of the phorbol ester phorbol-12,13-didecanoate (PDD) following various periods of treatment with the carcinogen 4-nitroquinoline-1-oxide (4NQO). All animals were histologically examined at 50 weeks. Oral epithelial dysplasia was seen in animals treated with 4NQO for as little as 2 weeks, and oral squamous cell carcinomas developed in all animals treated with 4NQO for 16 weeks. In those mice treated with PDD as well, carcinomas developed in mice receiving as little as 2 weeks treatment with 4NQO, and 100% of mice treated with 4NQO for 12 weeks, followed by PDD treatment, developed carcinomas. The results indicate that irreversible changes in the oral mucosa of mice occur relatively early during treatment with 4NQO, and the development of carcinomas can be enhanced with subsequent PDD treatment, giving an indication of staged carcinogenesis in this model system.

Effect of excisional wounding on DMBA-induced hamster tongue carcinogenesis

The purpose of this study was to investigate histologically the effect of wounding on the hamster tongue after pretreatment with DMBA. The animals in which the tips of the tongues were pretreated with DMBA for 8 weeks, subsequently excised, and had no treatment or received applications of acetone, showed epithelial dysplasias. The animals which had the same pretreatment, excision, and received additional post-excision applications of DMBA for 9-13 days, developed squamous cell carcinomas. However, the animals which were pretreated with DMBA for 8 weeks but had no excision, did not show any pathologic changes, even though they received additional applications of DMBA for 9-13 days. The animals which received no pretreatment with DMBA for 8 weeks but had an excision, showed normal wound healing, even though they had a post-treatment with DMBA for 9-13 days. The results of the present study indicated that excisional wounding acted as a promotional stimulus in inducing the appearance of epithelial dysplasias or carcinomas of tongues initiated with the carcinogen DMBA.