Enhancement of responses to chemical carcinogens by nononcogenic viruses and antimetabolites

Viruses and oral cancer. Is there a link?

Oral squamous cell carcinoma (OSCC) is the most common malignant tumour of the oral cavity. The aetiology of epithelial cancer of the head and neck is considered to be a multifactorial, sequential process. DNA viruses are found in many different cancers and are also capable of transforming cells to a malignant phenotype. Human Papilloma Virus (HPV) has been proposed as risk factors in OSCC development and HPV type 16 is the most important subtype. Other oncogenic virus species i.e., Epstein-Barr Virus and Herpes Simplex Virus Type 1 have been proposed to be involved in oral carcinogenesis. However, no convincing evidence exist that they are an established risk factor in OSCC. Therefore more studies are needed in order to clarify the different aspects of virus involvement. Here, we review the existing literature on viral involvement in oral cancer.

Role of viruses in oral squamous cell carcinoma

The etiology of oral squamous cell carcinoma (OSCC) is complex and involves many factors. The most clearly defined risk factors are smoking and alcohol, which substantially increase the risk of oral SCC. However, despite this clear association, a substantial proportion of patients develop OSCC without exposure to them, emphasizing the role of other risk factors such as genetic susceptibility and oncogenic viruses. Some viruses are strongly associated with OSCC while the association of others is less frequent and may depend on co-factors for their carcinogenic effects. Therefore, the exact role of viruses must be evaluated with care in order to improve the diagnosis and treatment of OSCC.

Association between malignancies of the upper aerodigestive tract and uterine cervix

Cancers of the cervix and buccal cavity share histologic, epidemiologic, and exposure characteristics. In particular, cigarette smoking and human papillomavirus (HPV) have been cited as etiologic cofactors of both malignancies. Using incidence data from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute for the years 1973 through 1984, we evaluated the incidence of second cancers of the buccal cavity following an initial cervical cancer. Standardized incidence ratios (SIR) were uniformly elevated for both white (SIR = 2.0), and black (SIR = 3.5) women. There were also elevated risks for the development of cervical cancer following an initial buccal cavity cancer (SIRs = 3.3 and 2.5, respectively). A similar pattern was evident for laryngeal cancer among white women. HPV transmission could account in part for the paired occurrence of these two anatomically distinct cancer sites. Cigarette smoking could act as a synergistic cofactor in the malignant transformation of viral genome-harboring tissue.

Viruses and oral cancer

Oral cancer is a disease with a complex etiology. There is evidence for important roles of smoking, drinking, and genetic susceptibility, as well as strong indications that DNA viruses could be involved. The herpes simplex virus type 1 has been associated with oral cancer by serological studies, and animal models and in vitro systems have demonstrated that it is capable of inducing oral cancer. Papillomaviruses are found in many oral cancers and are also capable of transforming cells to a malignant phenotype. However, both virus groups depend on co-factors for their carcinogenic effects. Future research on viruses and oral cancer is expected to clarify the role of these viruses, and this will lead to improvements in diagnosis and treatment of the disease.

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 and herpes simplex virus-1 on rat oral mucosa: possible associations with the development of squamous cell carcinoma

The purpose of this investigation was to study the effect of snuff and experimentally induced herpes simplex virus type 1 (HSV-1) infection in Sprague-Dawley rats. It was demonstrated that it was possible to obtain 100% development of acute HSV-1 infection in the rat oral mucosa, but only 10% of latent reactive infection of the trigeminal ganglia. The rats were, therefore, acutely infected monthly with virus to simulate recurrence of latent infection. Virus was applied topically to the mucous membrane twice with an interval of one month. Snuff was administered between the virus applications and afterwards to half the virus-exposed animals. Sham-infected rats were given snuff during the same period (18 months). A fourth group of rats were left untreated. A complete post-mortem examination was performed. Two rats exposed to snuff and HSV-1 in combination developed squamous cell carcinoma of the oral cavity. It was also found that rats exposed to snuff alone or in combination with HSV-1 had a higher incidence of tumours or tumour-like conditions than control rats exposed to HSV-1 only. The incidence of malignant tumours was significantly higher in rats exposed to snuff or HSV-1 and snuff in combination than in control animals (p less than 0.05). The results of the study indicate that HSV-1 in combination with snuff exposure may be associated with the development of squamous cell carcinomas of the oral cavity.

Neutralizing antibody to herpes simplex virus type 1 in patients with oral cancer

Neutralizing antibody to Herpes simplex virus type 1 (HSV-1), type 2, and measles virus was measured in the serum of patients with oral cancer, patients with oral leukoplakia, and in control subjects who were smokers and nonsmokers. Significantly higher titers to HSV-1 were found in controls who smoked than in controls who did not smoke. Patients with untreated oral cancer had HSV-1 neutralizing titers similar to those of the controls who smoked, but those with later stage tumors had higher titers than those with earlier stage tumors. In patients who were tumor free after treatment for oral cancer, higher antibody titers to HSV-1 were associated with longer survival times. No association was found between clinical status and antibody to measles virus. The data are consistent with a role for both HSV-1 and smoking in the pathogenesis of oral cancer.

Oral cancer and herpes simplex virus--a review

Numerous studies have suggested that patients with oral cancer have an increased immune response to herpes simplex virus. However, the number of cases has always been small, and essential controls have not always been included. Laboratory experiments have shown that herpes simplex virus can be carcinogenic or cocarcinogenic under certain circumstances and so must be considered as a possible etiologic agent in oral cancer. This article reviews past research and suggests priorities for future investigations.

The carcinogenicity of anticancer drugs: a hazard in man

The carcinogenic potential of anticancer drugs is discussed in the light of selected basic principles of chemical carcinogenesis. Anticancer drugs which act by alkylation and/or by binding tightly to DNA frequently cause cancer in experimental animals and may be carcinogenic in man. In addition, certain anticancer drugs act as cocarcinogens in experimental systems and augment the tumorigenicity of chemical carcinogens. Host determinants are important in chemical carcinogenesis. Many chemical carcinogens and anticancer drugs require metabolic activation by microsomal enzymes. Studies in twins have shown interindividual variation of drug metabolism in man is greater than intraindividual variation caused by exogenous factors. Therefore, certain individuals may be unusually susceptible to the carcinogenicity of anticancer drugs on a pharmacogenetic basis. Age is also a host determinant. At a given total dose level, age at first exposure to chemical carcinogens has been shown to be an important risk factor in experimental studies and in some epidemiologic investigations in man. Therefore, children may be especially susceptible to the carcinogenicity of anticancer drugs. These treated children have the potential of a normal lifespan; the latency period between initial exposure to a carcinogen and clinical evidence of cancer in man is long, usually 2-5 decades. The problems involved in extrapolating data of carcinogenicity in experimental animals to man are discussed. A single drug may have multiple consequences in experimental studies; for example, actinomycin D can act as an anticancer drug, an anticarcinogen, and a carcinogen. These uncertainities and the clinical results concerning second neoplasms following cancer therapy in both children and adults clearly indicate the need to follow carefully long-term survivors who have received cancer therapy.

Chemical induction of sperm abnormalities in mice

The sperm of (C57BL X C3H)F1 mice were examined 1, 4, and 10 weeks after a subacute treatment with one of 25 chemicals at two or more dose levels. The fraction of sperm that were abnormal in shape was elevated above control values of 1.2-3.4% for methyl methanesulfonate, ethyl methanesulfonate, griseofulvin, benzo[a]pyrene, METEPA [tris(2-methyl-l-aziridinyl)phosphine oxide], THIO-TEPA [tris(l-aziridinyl)phosphine sulfide], mitomycin C, myleran, vinblastine sulphate, hydroxyurea, 3-methylcholanthrene, colchicine, actinomycin D, imuran, cyclophosphamide, 5-iododeoxyuridine, dichlorvos, aminopterin, and trimethylphosphate. Dimethylnitrosamine, urethane, DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], 1,1-dimethylhydrazine, caffeine, and calcium cyclamate did not induce elevated levels of sperm abnormalities. The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.

Cell-mediated immunity and antibodies to Herpesvirus hominis type 1 in oral leukoplakia and carcinoma

Cell-mediated and humoral immune responses to Herpesvirus hominis type 1 (HVH1) and Candida albicans were studied in patients with leukoplakia, showing a histological spectrum of changes from epithelial keratosis to acanthosis and atypia, and in patients with carcinoma. The results were ranked according to increasing values of stimulation indices of lymphocyte transformation to HVH1, and the corresponding macrophage migration inhibition indices, and complement fixing antibody titres of each patient were correlated. This revealed that most patients with epithelial atypia were clustered to that end of the spectrum which had the highest stimulation and migration indices to HVH1; this relationship was not evident with C. albicans. In patients with keratosis and acanthosis there was a significant lack of correlation between lymphocyte transformation and migration inhibition to both HVH1 and C. albicans. In carcinoma the indices of lymphocyte transformation and migration inhibition to HVH1 and C. albicans were depressed. Furthermore, a significant negative correlation was found between lymphocyte transformation and migration inhibition to HVH1, unlike the positive correlation in control subjects. Complement fixing antibodies to HVH1, HVH2, cytomegalovirus and adenovirus, and fluorescent antibodies to C. albicans failed to show a significant change in titre in any one group of subjects tested. The results suggest a cell-mediated immune defect in leukoplakia, with a dissociation between lymphocyte transformation and macrophage migration inhibition to HVH1 and C. albicans in cases of keratosis or acanthosis. A specific increase in cell-mediated immunity to HVH1 in leukoplakia with epithelial atypia and the sequential changes argue in favour of a possible participation of HVH1 in carcinomatous transformation of some leukoplakias.