Carcinogens viruses

In an alternate form of tumor promotion, referred to as atypical tumor promoters (ATPs), elimination of the nascent clones may be blocked by inhibiting apoptosis [19], by failure to eliminate nascent transformed cells, or by failure to control an active infection (or activation of a latent viral infection [20]) of a carcinogenic virus. Host defense mechanisms are primarily responsible for regulating extrinsic apoptosis, cytotoxicity, and control of viral infections. If an IMBP were to mediate tumor promotion, it would be acting through such a mechanism. 

Powers A, Carbone M (2002) The role of environmental carcinogens, viruses and genetic predisposition in the pathogenesis of mesothelioma. Cancer Biol Ther 1 348-353... 

Carcinogenic agents include chemicals in the environment, such as aniline and benzene, which are associated with the development of bladder cancer and leukemia, respectively. Environmental factors, such as excessive sun exposure, also may result in cancer. Viruses, including the human papilloma virus and hepatitis B, maybe associated with the development of cancer. Some of the chemotherapy agents cause secondary cancers after therapy has been completed. Numerous factors may contribute to the development of cancer. 

Other factors associated with the risk of NMSC include exposure to ionizing radiation and arsenic, which is connected with BCC. Chemical carcinogens that give rise to NMSC include industrial hydrocarbons that are found in coal tars, soot, asphalt, paraffin waxes, and tobacco.21 Exposure to the human papilloma virus (HPV-6, -11, -16, and -18) has been linked to SCC.31 Lastly, a personal history of previous melanoma is a risk factor for developing another primary melanoma. 

It has recently been claimed that peptide-bound N-hydroxy amino acids occur in human brain tumor, in virus-induced tumor of mouse spleen, and in carcinogen-induced tumors in the rat (112). 

Dunkel VC, Pienta RJ, Sivak A, et al. 1981. Comparative neoplastic transformation responses of Balb/3T-3 cells, Syrian hamster embryo cells, and Rauscher murine leukemia virus-infected Fischer 344 rat embryo cells to chemical carcinogens. J Nat Cancer Inst 67 1303-1315. 

Because of the long duration and expense of carcinogenicity studies, the care of animals used in these studies is of paramount importance. Various physical and biological factors can affect the outcome of these studies. Some important physical factors include light, temperature, relative humidity, ventilation, atmospheric conditions, noise, diet, housing, and bedding (Rao and Huff, 1990). Biological factors include bacteria and viruses that may cause infections and diseases. 

Common viral infections may affect the outcome of carcinogenicity studies by altering survival or tumor incidence. Nevertheless, viral infections did not cause consistent adverse effects on survival or tumor prevalence in control F344 rats from 28 NCI-NTP studies, though body weights were reduced by Sendai and pneumonia viruses of mice (Rao et al., 1989). The probability of such infections can be minimized by using viral-antibody-free animals, which are readily available. 

The results from a study employing a human cell line showed that neither 5 nor 50 ppm petroleum-derived JP-5 (PD-JP5) interfered with Snyder-Theilen feline sarcoma virus (ST-FeSV)-directed transformation of human foreskin fibroblastic cells (Blakeslee et al. 1983). Higher concentrations ( 100 ppm) were cytotoxic. It was reported that marine diesel fuel failed to inhibit transformation in this assay, but data were not shown. The study authors consider this in vitro assay to be a useful predictor of carcinogenesis since several known carcinogens have been shown to suppress transformation in cells infected with the ST-FeSV virus by blocking a specific virus gene function (i.e., transformation) noncarcinogens do not inhibit virus-induced cell transformation in this test system. 

It has been known for a long time that external agents (carcinogens) are capable of causing cancer, namely viruses, radiation, and chemicals, both natural and man-made. This information has been derived from both epidemiology and experiments in animals. 

Price, P.J. Mishra, N.K. (1980) The use of Fischer rat embryo cells as a screen for chemical carcinogens and the role of the nontransforming type C RNA tumor viruses in the assay. Adv. mod. environ. Toxicol.. 1. 213-239... 

Warren, W, Clark, J.P, Gardner, E., Harris, G, Cooper, C.S. Lawley, PD. (1990) Chemical induction of thymomas in AKR mice interaction of chemical carcinogens and endogenous murine leukemia viruses. Comparison of W-methyl-A-nitrosourea and methyl methane-sulphonate. Mol. Carcinog., 3, 126-133... 

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