Oral cancer induced in hamsters with herpes simplex infection and simulated snuff dipping

Conversion of Normal To Malignant Phenotype: Telomere Shortening, Telomerase Activation, and Genomic Instability During Immortalization of Human Oral Keratinocytes

Normal somatic cells terminate their replicative life span through a pathway leading to cellular senescence, which is triggered by activation of p53 and/or pRb in response to critically shortened telomere DNA. Potentially neoplastic cells must first overcome the senescence checkpoint mechanisms and subsequently activate telomerase to propagate indefinitely. Although telomerase activation is closely associated with cellular immortality, telomerase alone is not sufficient to warrant tumorigenicity. Environmental factors, including chemical carcinogens and viral infection, often contribute to aberrant changes leading to tumorigenic conversion of normal cells. Of particular importance in oral cancer development are tobacco-related chemical carcinogens and human papillomavirus (HPV) infection. To describe the molecular mechanisms by which these environmental factors facilitate the genesis of oral cancer, we first established an in vitro multistep oral carcinogenesis model by sequential exposure of normal human oral keratinocytes (NHOK) to "high risk" HPV and chemical carcinogens. Upon introduction of the HPV genome, the cells bypassed the senescence checkpoint and entered into an extended, but not immortal, life span during which telomere DNA continued to shorten. In a few immortal clones surviving beyond the crisis, we found a marked elevation of telomerase activity and stabilization of telomere length. Furthermore, the E6 and E7 oncoproteins of "high risk" HPV disrupted the cell cycle control and DNA repair in immortalized HOK, and enhanced mutation frequency resulting from genomic instability. However, HPV infection alone failed to give rise to a tumorigenic cell population, which required further exposure to chemical carcinogens in addition to HPV infection. Analysis of the data presented suggests that oral carcinogenesis is a series of discrete genetic alterations that result from a continued genotoxic challenge by environmental risk factors. Our in vitro model may be useful for investigators with interest in furthering our understanding of oral carcinogenesis.

Oncoapoptotic signaling and deregulated target genes in cancers: special reference to oral cancer

Cancer is a class of diseases characterized by uncontrolled cell growth. The development of cancer takes place in a multi-step process during which cells acquire a series of mutations that eventually lead to unrestrained cell growth and division, inhibition of cell differentiation, and evasion of cell death. Dysregulation of oncoapoptotic genes, growth factors, receptors and their downstream signaling pathway components represent a central driving force in tumor development. The detailed studies of signal transduction pathways for mechanisms of cell growth and apoptosis have significantly advanced our understanding of human cancers, subsequently leading to more effective treatments. Oral squamous cell carcinoma represents a classic example of multi-stage carcinogenesis. It gradually evolves through transitional precursor lesions from normal epithelium to a full-blown metastatic phenotype. Genetic alterations in many genes encoding crucial proteins, which regulate cell proliferation, differentiation, survival and apoptosis, have been implicated in oral cancer. As like other solid tumors, in oral cancer these genes include the ones coding for cell cycle regulators or oncoproteins (e.g. Ras, Myc, cyclins, CDKs, and CKIs), tumor suppressors (e.g. p53 and pRb), pro-survival proteins (e.g. telomerase, growth factors or their receptors), anti-apoptotic proteins (e.g. Bcl2 family, IAPs, and NF-kB), pro-apoptotic proteins (e.g. Bax and BH-3 family, Fas, TNF-R, and caspases), and the genes encoding key transcription factors or elements for signal transduction leading to cell growth and apoptosis. Here we discuss the current knowledge of oncoapoptotic regulation in human cancers with special reference to oral cancers.

[Smokeless tobacco]

Use of smokeless tobacco (ST) (chewing tobacco and snuff) can lead to a number of consequences detrimental to health. ST rapidly delivers high doses of nicotine, which can lead to dependence and is also a source of carcinogenic nitrosamines. Changes usually develop in the mouth area where the ST is most often placed. Non-malignant oral lesions include leuko-oedema, hyperkeratotic lesions of the oral mucosa and localised periodontal disease. Oral premalignant lesions are leukoplakia, erythroplakia, submucosal fibrosis and lichen planus. Betel chewing, with or without tobacco, may increase the incidence of oral cancer. There is conflicting evidence with regard to snuff users about the risk of oral and gastro-oesophageal cancer. ST use is a risk factor for pancreatic cancer and may increase the risk of fatal myocardial infarction and ischemic stroke. During pregnancy, ST is associated with an increase in pre-eclampsia, preterm delivery and stillbirth. Nicotine replacement therapy and bupropion reduce withdrawal symptoms and tobacco craving during ST cessation. However, they have not been shown to help long-term abstinence. Information concerning the potential hazards of ST products should be incorporated into educational programmes to discourage its use and to help users to quit. Smokeless tobacco is not recommended to help smoking cessation.

Smokeless tobacco and cancer

Use of smokeless tobacco products is common worldwide, with increasing consumption in many countries. Although epidemiological data from the USA and Asia show a raised risk of oral cancer (overall relative risk 2.6 [95% CI 1.3-5.2]), these are not confirmed in northern European studies (1.0 [0.7-1.3]). Risks of oesophageal cancer (1.6 [1.1-2.3]) and pancreatic cancer (1.6 [1.1-2.2]) have also increased, as shown in northern European studies. Results on lung cancer have been inconsistent, with northern European studies suggesting no excess risk. In India and Sudan, more than 50% of oral cancers are attributable to smokeless tobacco products used in those countries, as are about 4% of oral cancers in US men and 20% of oesophageal and pancreatic cancers in Swedish men. Smokeless tobacco products are a major source of carcinogenic nitrosamines; biomarkers of exposure have been developed to quantify exposure as a framework for a carcinogenesis model in people. Animal carcinogenicity studies strongly support clinical results. Cancer risk of smokeless tobacco users is probably lower than that of smokers, but higher than that of non-tobacco users.

Herpes Simplex Virus Infection Presenting as a Piriform Sinus Mass

Evidence is accumulating that herpes simplex virus (HSV) infection is implicated in oncogenesis. HSV antigens have been observed in some oral cancers. We present the case of a 62-year-old man who presented with dysphagia, odynophagia, and dysphonia and who was found on computed tomography (CT) to have a mass in his piriform sinus. We suspected a malignancy, but histopathology of biopsy specimens revealed that the mass exhibited the classic signs of the HSV cytopathic effect, including the presence of intranuclear inclusion bodies, ballooning degeneration of epithelial cells, and a ground-glass appearance of some nuclei. The patient responded well to antiviral therapy, and posttherapy CT revealed that the mass had resolved completely. To the best of our knowledge, this is the first report in the literature of a case of HSV infection presenting as a piriform sinus mass.

Smokeless tobacco extracts modulate exogenous gene expression in early passage cultured human oral epithelial cells: an in vitro system to study chemical and viral enhancer/promoter interaction

The increased risk for cancers of the oral cavity from smokeless tobacco use may reflect the interaction of tobacco with genetic factors, such as oncogenes, and other exogenous factors, such as viruses. An in vitro system was developed based on expression of the chloramphenicol acetyltransferase (CAT) reporter gene to study interactions of chemical treatments with viral enhancer/promoters in early passage cell cultures of oral cavity-derived epithelial cells. Expression of CAT in transfected cells was significantly greater with CAT under the control of the cytomegalovirus immediate early enhancer/promoter (pCEP4/CAT) compared to the Rous sarcoma virus long terminal repeat enhancer/promoter (pRSV-cat) and the simian virus 40 (SV40) early promoter (pSV2-cat). No CAT expression was detected using corresponding control plasmids without the CAT reporter gene. Using this system, smokeless tobacco extracts prepared from either dry snuff or moist snuff delayed maximum CAT expression from Day 4 to Day 5, with sustained, significantly increased CAT expression at 12 days compared to the declining CAT expression observed in untreated control cells. Smokeless tobacco extracts can modulate intracellular gene expression. This system provides an in vitro model to test specificity of toxic agents on enhancer/promoter activity and the interaction on exogenous gene expression.

Smokeless tobacco and oral cancer: an assessment of evidence derived from laboratory animals

No carcinogenic activity was observed when snuff was inserted into the cheek pouch of the hamster or spread over the oral mucosa. This negative result was obtained in a number of experiments whether snuff was applied once only and left in place for several months or inserted repeatedly for up to 2 years. In the rat, a few tumours were observed when snuff was inserted into the artificial lip canal. The insertion appeared to cause a considerable reaction in the surrounding tissue so it is plausible to assume that trauma plays an important role in the development of these tumours. An extract of snuff applied to the oral mucosa of the rat did not produce any tumours, but an extract enriched by the addition of 10 times the naturally-occurring amounts of NNN and NNK produced a few benign tumours at the site of application. A higher incidence of tumours was produced when an equivalent amount of an aqueous solution of these two nitrosamines was applied directly to the oral mucosa, suggesting, according to the authors, that snuff inhibits the carcinogenic activity of TSNAs. Initiation/promotion studies were carried out on snuff in the rat in order to explore further its carcinogenic potential. The results were consistent with the conclusion that snuff does not possess any promotional activity. No increase in tumour incidence was observed in mice when snuff was given in the diet at concentrations of 25% gradually decreasing to 5% in a 14 month study. A negative result was also obtained in the rat given snuff at a concentration of 5% for 18 months. In hamsters given snuff at a concentration of 20% for 2 years, forestomach tumours occurred. A comparable incidence of this type of tumour occurred in animals given 20% cellulose. The result of this study does not provide valid evidence of carcinogenicity. HSV and snuff applied orally in the hamster produced a high incidence of squamous cell carcinomas. The sustained high level of squamous cell hyperplasia generated by the experimental design could account for the development of these tumours. Despite the defects in some of the earlier studies, the sum total of this experimental work suggests that snuff is not carcinogenic to the oral mucosa of the hamster or the rat. It is also unlikely to cause tumours in other tissues in these species. These results give some degree of reassurance that snuff is not likely to be carcinogenic to the human oral mucosa. The interaction of snuff and HSV viruses is, at the moment, questionable and requires further investigation.

Snuff use and smoking among senior high school students: effects of a snuff sales ban

OBJECTIVES

The popularity of snuff especially among adolescents is rising. The association between long-term snuff use and oral cancer discovered in epidemiological studies has prompted a variety of preventive measures to be taken to reduce snuff use and prevent adoption of the habit. In this study, the effect of a recent (1 March, 1995) snuff sales ban introduced in Finland was investigated. Further, the rates of smoking, snuff use, alcohol use and drug experimenting were investigated before the introduction of the ban to characterize the study population.

DESIGN AND SUBJECTS

Two questionnaire studies were carried out. The first was carried out 3 months prior to the ban in 1994 and the second 9 months after the ban in 1995 in a senior high school population in southwestern Finland. The participants were 793 students (aged 15-22 years) in the first survey and 545 students (aged 16-23) in the second. Associations between variables were analyzed using cross-tabulation and step-wise logistic regression. The effects of the ban were determined on the basis of direct questions in the second questionnaire relating to the snuff sales ban.

RESULTS

Snuff was used by 9% of the students participating in the first study. The results of the second questionnaire indicate that the implementation of the snuff sales ban reduced the rate of snuff use by 1% in the study population. The majority of the snuff users (76%) reported that they had maintained their snuff habit. Of those reporting that they were snuff users before implementation of the snuff sales ban, 12% had switched to smoking and 5% to drugs.

CONCLUSIONS

The results of the present study suggest that the snuff sales ban in this population with a high rate of snuff use had little effect on snuff use rates and may have some short-term negative consequences as some snuff users switch to other substitutes, such as smoking, with known adverse health effects.

A qualitative and quantitative risk assessment of snuff dipping

The presence of highly carcinogenic tobacco-specific nitrosamines (TSNA) in snuff has been a matter of serious concern. However, the levels of TSNA in such products may differ by orders of magnitude depending on origin and manner of processing, and the mere presence of such agents at low levels does hardly constitute a meaningful prerequisite for classifying all types of snuff as human carcinogens. Reviewing available epidemiological evidence, a wide discrepancy is found for estimated cancer risk associated with snuff dipping derived from on one hand previous investigations conducted in the United States and on the other from recent extensive Swedish epidemiological studies. In spite of the fact that approximately 20% of all grown-up Swedish males use moist snuff, it has not been possible to detect any significant increase in the incidence of cancer of the oral cavity or pharynx-the prevalence of which by international standards remains low in this country. Further, there is insufficient evidence for a causal link between the use of Swedish snuff and increased risk for cardiovascular disease. Dissimilarities in the content of TSNA in oral snuff products may represent one important reason for the different outcomes of the epidemiological surveys conducted in the United States and Sweden. Bioassays using pure TSNA in rodents appear to give exaggerated risk estimates for humans, a discrepancy that could be ascribed to species-related differences in the relation between exposure and DNA target dose and/or adduct repair rates, as well as to the presence of anticarcinogens in snuff. Although a small risk cannot be excluded, the use of smokeless tobacco products low in TSNA which now are available on the market entails a risk that at any rate is more than 10 times lower than that associated with active smoking. Nevertheless, due to the decisive role of potent TSNA in determining possible cancer risks in users of smokeless tobacco, and due to the fact that large variations in the concentrations may occur, adequate control measures should be taken to keep the levels of these nitrosamines in smokeless tobacco products as low as is technically feasible.

Chemical composition and carcinogenicity of smokeless tobacco

In the United States, smokeless tobacco (ST) is marketed as chewing tobacco and as oral snuff. During the past 15 years, consumption of chewing tobacco has declined by 30.6%, whereas snuff use has significantly increased, namely, by 51.8%. This increase is primarily due to the growing popularity of oral snuff use among teenage and young adolescent males. Chewing of tobacco is associated with an increased risk for oral cancer. Snuff dipping is causally and specifically associated with cancer of the cheek, gum, and pharynx. In laboratory animals, snuff induces cancer of the mouth. Several carcinogens have been identified in ST, the tobacco-specific N-nitrosamine (TSNA), N'-nitrosonornicotine (NNN), and 4(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) being the most important. NNN and NNK are formed from nicotine during curing, aging, and especially during fermentation of tobacco. Oral swabbing of a low concentration of a mixture of NNN plus NNK in water induces oral tumors in rats. The concentration of the strongly carcinogenic TSNA is higher in snuff than in other ST products. According to our analytical studies, the three leading snuff brands in the US (92% of the market) contain far higher concentrations of nicotine, unprotonated nicotine, and TSNA than the less popular brands. Thus, the leading US snuff brands are the strongest inducers of nicotine dependence and also have the highest carcinogenic potential.

The effect of N-nitrosonornicotine on the buccal mucosa of Syrian hamsters

PURPOSE

The carcinogens in smokeless tobacco have been identified as the tobacco-specific nitrosamines and the effect of one of these, N-Nitrosonornicotine (NNN), on the buccal mucosa of the Syrian hamster was studied.

MATERIALS AND METHODS

Buccal pouches of 36 Syrian hamsters were painted five times per week for 24 weeks with 10 mg/mL 98% pure NNN in suspension with mineral oil. Animals were killed at 6, 8, 12, and 24 weeks.

RESULTS

At 6 weeks, the buccal pouch mucosa of the experimental animals appeared clinically more hyperemic than those of the controls. From 12 weeks onward, all experimental animals showed epithelial hyperplasia and inflammation on histologic examination. Three animals killed at 24 weeks showed mild epithelial dysplasia.

CONCLUSIONS

Exposure of Syrian hamster buccal mucosa to NNN, five times per week for 24 weeks, did not result in clinical or histologic cancerous changes. NNN may require other factors for cancer production, such as a cocarcinogen, a higher concentration, or a longer period of application.

Attenuation of the natural course of herpes simplex virus infection in human oral epithelial cell cultures by smokeless tobacco extracts suggests the possibility of a synergistic mechanism for carcinogenesis

High prevalence of both tobacco use and latent herpes simplex virus type 1 suggests the opportunity for synergism between these agents as cocarcinogens. In this study, postprimary human oral epithelial cell cultures were infected with herpes simplex virus type 1 pretreated with 2% extracts of either loose leaf, moist, or dry snuffs. Cultures were subsequently periodically exposed to the tobacco. Parameters measured included percentage of cultures undergoing active virus production, onset and time course of cytopathic effects, and concentration of virus released into the media over time. Results showed inhibition of both herpes simplex virus-mediated cell lysis and viral replication by tobacco extracts. This is the first time that these phenomena have been demonstrated in normal human oral epithelial cells. The work described here provides evidence to support a hypothesis that herpes simplex virus type 1 and smokeless tobacco may act synergistically in oral carcinogenesis.

Tobacco use and cancer. A reappraisal

With approximately six million users, smokeless tobacco has received considerable scrutiny as a risk factor for oral cancer. We review the relationship between smokeless tobacco use, keratosis, and oral cancer. Several features of smokeless tobacco keratosis, including the natural history, clinical presentation, and biologic behavior, differentiate it from other leukoplakias that exhibit greater malignant potential. Previous research has demonstrated that the relative risk of oral cancer with smokeless tobacco use is 4.2, about half of the risk from smoking (relative risk = 10 to 15). Mortality data from populations with sustained high-frequency smokeless tobacco use do not support the mistaken prediction of an epidemic of oral cancer with increasing smokeless tobacco use. In fact, the risks of smokeless tobacco use compare so favorably with those of smoking that smokers who switch to smokeless tobacco reduce their risks for all tobacco-related illnesses including oral cancer. Although some criticize this proposal as less than an ideal solution for the nation's smokers, full adoption of this strategy would eventually save over 400,000 lives each year.

Effect of vitamin E succinate on smokeless tobacco-induced production of nitric oxide by rat peritoneal macrophages and J774A.1 macrophage cells in culture

Previous studies have shown that an aqueous smokeless tobacco extract when administered in a single oral dose to rats results in an enhanced induction of hepatic lipid peroxidation, hepatic DNA single strand breaks, and a marked increase in the urinary excretion of the lipid metabolites malondialdehyde, formaldehyde, acetaldehyde, and acetone. These observations strongly suggest that STE induces the production of reactive oxygen species. We have therefore examined the effects of STE in vivo in rats on the production of nitric oxide (NO) by isolated peritoneal exudate (macrophage) cells and when incubated with cultured J774A.1 macrophage cells. In both cases, a significant increase in NO production was observed. When the antioxidant vitamin E succinate was preadministered to rats, a marked decrease in NO production in response to STE by isolated peritoneal macrophages was observed. Similar results were observed when J774A.1 macrophages were cultured in the presence of vitamin E succinate and STE. When vitamin E succinate alone was cultured with macrophages, an increase in NO production was observed. A similar increase was observed when the vitamin E succinate was administered to rats, and NO production by isolated peritoneal macrophages was assessed. The results demonstrated that the increase in NO production by macrophages in response to vitamin E succinate was due to a succinate moiety. Taken together with previous studies, the results indicate that STE activates macrophages, which result in the production of reactive oxygen species. These reactive oxygen species may be responsible for tissue damaging effects including lipid peroxidation and DNA damage, which may be associated with the cytotoxicity and mutagenicity of smokeless tobacco products.

Risk factors and genetic susceptibility

Tobacco use is such a major determinant of head and neck cancer risk that classical epidemiologic techniques were more than adequate to document and characterize the etiologic association. However, the new emphasis in epidemiologic research is multidisciplinary, centering on the role of interindividual differences in susceptibility to carcinogenic exposures and particularly on the interaction of genetic susceptibility and environmental forces, that is, ecogenetics. For upper aerodigestive tract cancers, measurements of carcinogen metabolic activation and DNA repair capability are especially relevant. These susceptibility markers will enable the identification of high-risk population subgroups who can be targeted for the most intensive primary and secondary preventive strategies.

Effects of nicotine and tobacco-specific nitrosamines on hamster cheek pouch and gastric mucosa

Fifty-two hamsters were divided into 6 groups and their cheek pouches treated with either 0.01% NNN, 0.01% NNN and 6% nicotine, 0.01% NNK, 0.01% NNK and 6% nicotine, 6% nicotine, or sesame oil. After painting each pouch 3 times per week for 13 months, the animals were killed and specimens from the cheek pouch and forestomach examined. Cheek pouch epithelium showed more frequent histologic changes, including hyperplasia, hyperkeratosis and, in one animal, moderate dysplasia, when nicotine was combined with NNN than after treatment with NNN (or nicotine) alone. There was a higher frequency of hyperplasia with hyperkeratosis in the forestomach when nicotine was combined with NNK than following NNK, or nicotine treatment alone, and squamous cell papillomas were evident in animals treated with both NNK and nicotine. These results suggest that in mucosal tissues nicotine may enhance the effect of weak carcinogens such as the nitrosamines.

Oncogenes, tumor suppressors and viruses in oral squamous carcinoma

The pathogenesis of oral squamous cell carcinoma involves recognised carcinogens in tobacco and/or alcohol but other factors, including viruses, may also have a role. This paper reviews the gene changes revealed in oral carcinoma, the evidence implicating viruses, and mechanisms whereby viruses may affect gene function.

Inhibition of herpes simplex virus replication and protein synthesis by non-smoked tobacco, tobacco alkaloids and nitrosamines

Inhibitory effects of snuff extract and the tobacco chemicals nicotine, anabasine, diethyl-N-nitrosamine (DEN), and the tobacco-specific nitrosamines (TSNA), N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on herpes simplex virus type 1 (HSV-1) replication in vitro and on HSV-1 protein synthesis in infected cells were analysed. Snuff extract and nicotine caused a significant reduction of HSV-1 attachment to cell membranes whereas anabasine, DEN, NNN and NNK did not affect adsorption of HSV-1. Virus production assays in the presence of snuff added after virus adsorption resulted in a significantly reduced production of virus at low multiplicities of infection (MOI), but at high MOI the inhibitory effect of snuff extract was less pronounced. DEN, NNN and NNK only affected virus production at toxic concentrations. Nicotine and anabasine reduced virus production in non-toxic doses but not at the concentrations present in snuff extract. In HSV-infected cells exposed to snuff extract, the immediate early (alpha-) infected cell proteins (ICPs) 4 and 27 (as well as the early (beta-) ICPs 6 and 8) were markedly increased, whereas the late (gamma-) ICPs 5, 11 and 29 were reduced. Nicotine had a less pronounced stimulating effect on the production of alpha-proteins but no detectable effect on production of beta- or gamma-proteins. Anabasine, DEN, NNN and NNK did not affect HSV protein synthesis at non-toxic concentrations. Synthesis of thymidine kinase and DNA polymerase was significantly reduced by snuff extract. Also nicotine and anabasine affected thymidine kinase and DNA polymerase but only at toxic concentrations. The production of the cellular protein actin, which almost disappears a few hours after HSV-1 infection, remained at a significant level in HSV-infected cells exposed to snuff. Thus snuff extract blocks the replicative cycle of HSV at an early stage, which results in an increased production of alpha-proteins in the infected cells and in prolonged maintenance of cellular functions. This may be of importance for HSV-induced transformation and the development of HSV-associated tumours.

In vitro and animal studies of the role of viruses in oral carcinogenesis

The linkage of herpes simplex virus (HSV) and human papillomavirus (HPV) to the development of oral cancer has been studied. In spite of the presence of viral nucleic acids in some human oral cancer specimens, HSV alone is not carcinogenic in animals: repeated viral inoculation to mouse or hamster oral mucosa fails to produce tumours or histopathological evidence of malignancy. However, HSV demonstrates co-carcinogenicity in vivo: viral inoculation significantly enhances the oncogenic capacity of chemical carcinogens in the oral cavity of mice and hamsters. Though the detailed mechanisms of HSV cocarcinogenicity are unknown, HSV promotes the chemical carcinogen-induced activation of certain cellular proto-oncogenes and inactivation of p53 tumour suppressor gene. Human papillomaviruses type 16 (HPV-16) and 18 (HPV-18) demonstrate oncogenicity by transforming normal human oral keratinocytes in vitro. While normal cells exhibit a limited life-span, cells transformed by these viruses show immortality and altered morphology in comparison with their normal counterparts. The HPV-immortalised cells contain multiple copies of intact viral genome integrated into cellular chromosomes. These cells also express several viral-specific mRNAs including viral E6/E7 mRNAs. Notably, these cells contain low levels of p53 protein and overexpressed cellular myc proto-oncogene compared to their normal counterpart; however, the immortilised cell lines are non-tumorigenic in nude mice.

Pathogenesis of oral submucous fibrosis. Relationship to risk factors associated with oral cancer

Oral submucous fibrosis (OSF) is a chronic disease of the oral mucosa characterized by inflammation and a progressive fibrosis of the lamina propria and deeper connective tissues. It is a condition predominantly seen among people of Indian origin, and an epidemiologic survey done a decade ago showed no less than 250,000 cases in India, a figure that must have increased sharply. OSF is a condition with a high risk of malignant transformation; to date, no conclusive etiologic agent has been identified, although plenty of data have been generated on various aspects of the disease. These include genetic, carcinogenic, immunologic, viral, nutritional, and autoimmune possibilities, all of which also have been implicated in the development of oral cancer. This article reviews existing evidence on the pathogenesis of OSF and its relation to oral cancer and suggests a possible multifactorial model to explain the disease process.

Viruses in the aetiology of oral carcinoma? Examination of the evidence

This paper examines the evidence for an aetiological role for viruses in the development of oral carcinoma. Several viruses have been sought in oral cancer and evidence found for some, particularly herpes simplex and human papillomavirus. However, the evidence also suggests that these viruses are ubiquitous agents and a number of criteria must be met before these potentially oncogenic agents can reliably be implicated in human carcinogenesis. In contrast, there is no evidence that viruses such as adenovirus, Epstein-Barr virus, and retroviruses play any role in oral carcinogenesis.

Viruses and chronic disorders involving the human oral mucosa

Viruses have been implicated in the etiology of several chronic disorders of the oral mucosa. Most of these associations have been with DNA viruses, particularly certain herpesviruses, which are associated, for example, with some cases of erythema multiforme and with hairy leukoplakia. Papillomaviruses are associated with various papillomatous lesions, focal epithelial hyperplasia, and possibly with some carcinomas. Viruses may possibly be associated with recurrent aphthae, Behçet's syndrome, and some dermatoses. The literature concerning these possible associations is reviewed. However, much more research needs to be done before the full story of viral associations with oral mucosal disorders can be written.

Reactivity against herpes simplex virus in patients with head and neck cancer

The relation between herpes simplex virus (HSV) and head and neck cancer was examined. A total of ninety patients were analyzed for IgG antibodies against HSV. Antibody titers were established with an enzyme-linked immunosorbent assay and antibodies against specific HSV-antigens were analyzed by Western blot. These patients' seroreactivity was compared to that of an age-matched control group of patients with arteriosclerotic disease in their lower limbs, a disease also closely related to heavy tobacco consumption. Prevalence of antibodies against HSV was around 90% and did not differ significantly between cancer patients and controls, but antibody titers against HSV were significantly higher in the cancer patients. The cancer patients also reacted more constantly (80%) in Western blot analysis against the early immediate protein, ICP-4, than controls (50%). This suggests a different course of an earlier herpetic infection in these patients with a prolonged exposure to early immediate HSV-proteins which may be related to an increased risk of developing head and neck cancer. We propose that heavy smoking may contribute to this phenomenon.

Synergism of herpes simplex virus and tobacco-specific N'-nitrosamines in cell transformation

Previous studies indicate that herpes simplex virus (HSV) enhances the carcinogenic activity of smokeless tobacco and tobacco-related chemical carcinogens in animals. Since tobacco-specific N'-nitrosamines (TSNAs) such as N'-nitrosonornicotine (NNN) and 4-(N-methyl-N'-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are major chemical carcinogens of smokeless tobacco and are known to be responsible for the development of oral cancers in smokeless tobacco users, the combined effects of TSNAs and HSV in cell transformation were investigated. Exposure of cells to NNN or NNK followed by virus infection resulted in a significant enhancement of transformation frequency when compared with that observed with chemical carcinogens or virus alone. This study suggests that TSNAs and HSV can interact together and show synergism in cell transformation.

Nicotine-derived N-nitrosamines (TSNA) and their relevance in tobacco carcinogenesis

Biochemical studies and bioassays support the concept that the increased risk for cancer of the oral cavity in snuff dippers and cancer of the lung, upper aerodigestive tract, and pancreas in smokers is most likely associated with the exposure to tobacco-specific N-nitrosamines. The doses of TSNA required to induce tumors in the oral cavity in rats and tumors in the lungs of rats and hamsters are comparable to the total doses of TSNA to which a long-term snuff dipper, respectively a cigarette smoker, are exposed over 4 decades. The carcinogenic NNN and NNK are metabolized to highly reactive electrophiles which react with nucleophilic centers of DNA and with proteins. The DNA-adducts are known to cause miscoding which can activate K-ras proto-oncogenes. K-ras oncogenes have been detected in adenocarcinomas of the lung of smokers. TSNA also form globin adducts in the blood of laboratory animals as well as of snuff dippers and smokers. Such adducts are currently being evaluated for their significance as biochemical markers of exposure to TSNA. These biomarkers may also serve as indicators for the possible endogenous formation of TSNA in tobacco chewers and smokers. Additional research needs in TSNA carcinogenesis include the development of modified methods for the reduction of TSNA in tobacco and smoke, inhibition of TSNA carcinogenesis by nutrients and micro-nutrients and the testing of chemopreventive agents.

Effect of repeated oral administration of tobacco snuff on natural killer-cell activity in the rat

The possible immune effect of oral snuff was investigated. In male adult rats, oral snuff given for 15 weeks significantly decreased NK-cell activity in peripheral blood against murine NK cell-sensitive target cells (YAC-1 lymphoma).

Oral cancer

In the U.S. oral cancer accounts for 2.1% of all cancers and 1% of cancer deaths. Two to three times as many males as females are affected. Blacks have more intra-oral cancer than whites, and their incidence and mortality rates have increased in recent years. The etiologic process very likely involves several factors. The major etiologic agents are tobacco (all types) and alcoholic beverages. Herpes simplex virus, human papilloma virus, and Candida have been implicated. Host factors include poor state of dentition, nutritional aberrations, cirrhosis of liver, lichen planus, and immunologic impairmant. Cellular changes include amplification of some oncogenes, alterations in antigen expression, production of gamma-glutamyl transpeptidase, and disturbance of keratin and involucrin production. Experimentally, cancer is readily produced on the hamster cheek pouch and rat oral mucosa. Unlike oral cancer in humans, most experimental lesions are exophytic, and they rarely metastasize.

Effect of snuff extract on the replication and synthesis of viral DNA and proteins in cells infected with herpes simplex virus

The water-extractable component of snuff (snuff extract) inhibits the replication of herpes simplex virus (HSV) by suppressing the synthesis of viral DNA. This process probably causes HSV to be oncogenic. To further understand the mechanism of inhibitory action of snuff extract on HSV replication, the effect of snuff extract on the synthesis of viral DNA and proteins in type 1 HSV (HSV-1) infected cells was investigated. Snuff extract inhibited the synthesis of viral DNA and altered the production of certain classes of viral proteins. The syntheses of ICP4, a viral alpha-protein, and ICP8, a beta-protein, were not generally reduced by noncytotoxic concentrations of snuff extract (where ICP = infected cell polypeptide). However, snuff extracts significantly inhibited the production of ICP gC (glycoprotein C), a gamma 2-protein, and the inhibition was in a concentration-dependent fashion: the higher the concentration of snuff extracts, the greater the inhibition. Based on the fact that the production of alpha- and beta-proteins is absolutely necessary for and precedes the viral DNA synthesis and that viral gamma 2-proteins are mostly produced by the newly synthesized viral DNA, it is concluded that snuff extract inhibits HSV-1 DNA replication directly rather than indirectly via the alteration of viral protein synthesis.

Occurrence of recurrent herpes labialis in an adult Swedish population

In a general adult Swedish population recurrent herpes labialis (RHL) was found in 3.1% of 20,333 people aged 15 years and more. When a 2-year history of RHL was considered, the total prevalence was 17.4%. There was a slight predominance among women. Only slight differences were found between various age groups. In a fraction of the population studied, constituting 2771 people, interviews concerning cases of RHL were carried out. Thus, for example, most individuals referred to only one herpes episode a year; the most prevalent site of eruption was an area comprising both the vermilion border and the skin, and most of the lesions showed healing times of 5-8 days. The prevalence of RHL was influenced by some tobacco habits. Thus, the prevalence was significantly lower among smokers, and especially among pipe smokers, than among people with no tobacco habit at all. Snuff dipping did not seem to influence the prevalence values.

Herpes simplex virus enhances the 7,12-dimethylbenz[a]anthracene (DMBA)-induced carcinogenesis and amplification and overexpression of c-erb-B-1 proto-oncogene in hamster buccal pouch epithelium

We studied the effects of herpes simplex virus type 1 (HSV-1) inoculation and topical 7,12-dimethylbenz[a]anthracene (DMBA) application, alone or in combination, on the carcinogenesis and on the amplification and expression of various cellular proto-oncogenes in hamster buccal pouch tissue. Topical DMBA treatment produced tumor formation in pouches, but HSV-1 inoculation, alone caused no neoplastic changes. In pouch tissues receiving both DMBA application and HSV-1 inoculation, the development of initial leukoplakia and tumor has hastened and enhanced in comparison with those receiving DMBA alone. Topical DMBA application to pouch tissue induced an amplification and an increase in the expression of cellular erb-B-1 (c-erb-B-1) proto-oncogene in the epithelial tissue, whereas repeated infection with HSV-1 alone did not. Topical DMBA combined with HSV-1 inoculation, however, resulted in greater amplification and expression of c-erb-B-1 proto-oncogene in the pouch epithelial tissue compared to the DMBA alone. These data indicate that HSV-1 inoculation significantly increases the carcinogenic activity of DMBA, in part, by probably enhancing DMBA-induced amplification and expression of c-erb-B-1 proto-oncogene in hamster buccal pouch tissue.

Snuff dipping and oral cancer in Sudan: a retrospective study

A retrospective study involving 78 cases of oral carcinoma was conducted to investigate their association with the habit of taking snuff orally known as 'snuff-dipping' and locally termed 'saffa'. It was found that 50 (81%) of the 62 questioned patients used snuff in the form of saffa. It was also found that carcinomatous changes usually developed in the area of the mouth where the snuff was habitually placed. It was concluded that the association between saffa and development of oral carcinoma is likely to be causal.

Snuff tumorigenesis: effects of long-term snuff administration after initiation with 4-nitroquinoline-N-oxide and herpes simplex virus type 1

The tumor promoting effects of snuff was studied in Lewis rats initiated with 4-nitroquinoline-N-oxide (4-NQO) and Sprague Dawley rats repeatedly inoculated with herpes simplex virus type 1 (HSV-1). The test substances were administered in a surgically created canal in the lower lips of the rats. There were 15 rats in each test group and 10 rats in the control group. In the groups treated with 4-NQO and 4-NQO + snuff, 8 and 12 tumors (5 and 9 malignant) were found, respectively. In the group subjected to HSV-1 only, 3 tumors were found (2 malignant), in the group subjected to snuff only, 4 tumors were found (3 malignant) and in the group subjected to the combination of HSV-1 and snuff, 13 tumors were found (7 malignant). In the control group only one malignancy was found. The study did not show any promoting effects of snuff in the oral cavity after initiation with 4-NQO. Neither was there any increase in the number of oral tumors in rats treated with HSV-1 and snuff. However, there was a marked increase in the number of malignant tumors outside the oral cavity in the group treated with HSV-1 and snuff, underlining the importance of interactions between these two agents in the development of malignant lesions.

The effects of benzo(a)pyrene, nicotine, and tobacco-specific N-nitrosamines on the generation of human lymphokine-activated killer cells

The effects of four major components of snuff (fine-cut smokeless tobacco) on the development of lymphokine-activated killer cells (LAK) were measured in vitro. Of the components tested: nicotine, N'-nitrosonornicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and benzo(a)pyrene (BaP), only BaP suppressed LAK cytotoxicity against tumour targets and LAK DNA synthesis during 3- and 7-day incubations. BaP concentrations of 0.1-1.0 micrograms/ml suppressed lymphocyte proliferation only; there was no effect on tumour cell proliferation at these concentrations. BaP had no effect on tumour target killing when incubated during 4 h natural killer (NK) or LAK cytotoxicity assays. There was no effect on LAK binding of tumour targets after 3 days culture with BaP concentration of 0.1-1.0 micrograms/ml. These data confirm that a water-soluble extract of snuff has anti-cytolytic and anti-proliferative effects on peripheral blood lymphocytes. As NK and LAK cells are important in preventing tumourigenesis and metastasis, suppression of these cells may favour neoplastic growth associated with snuff-dipping.

Inhibition of human lymphokine-activated killer activity by smokeless tobacco (snuff) extract

Chronic snuff dipping has been associated with oral cancer in man and experimental animals. Here, the effects of a water-extract of snuff on the in-vitro development of human lymphokine-activated killer (LAK) activity were examined. The snuff extract inhibited both LAK cytotoxicity and DNA synthesis in a dose-dependent fashion at concentrations of 0.125 to 2.0 per cent; above 2.0 per cent, cell viability decreased significantly. In contrast, the snuff extract had no effect on natural killer-cell cytotoxicity when incubated with fresh peripheral blood lymphocytes in a standard 4 h assay, or on LAK cytotoxicity when incubated only during the final 4 h effector phase. Lymphocyte protein synthesis was generally unaffected by the addition of this extract. Thus, a water-soluble snuff extract appears to suppress LAK activity by inhibiting DNA synthesis. Altered LAK function in the oral mucosa might permit the development of snuff-associated carcinogenesis.