Cancer viruses

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. 

An antimetabolite is a compound that is (1) similar to a compound required for normal cellular function and (2) interferes with cellular processes. Based on this definition, many drugs technically qualify as antimetabolites. The term antimetabolite is, however, most closely associated with drugs that interfere with the synthesis or action of nucleic acids. Antimetabolites are commonly discussed in the treatment of cancer, viruses, and bacterial infections. 

Buchschacher GL Jr, Wong-Staal F. Etiology of cancer viruses RNA viruses. In DeVita VT Jr, Heilman S, Rosenberg SA, eds. Cancer Principles and Practice of Oncology. 7th Ed. Baltimore Lippincott Williams Wilkins, 2005 165-173. 

DEAD also increases the cellular uptake of viral RNA by cells in tissue culture by a factor of up to 10 [12]. Thus DEAD can be employed to increase the transfer of immunity by means of immune RNA to non-immune cells and prolong the survival of animals [13]. The ability of a cancer virus to cause tumors in mice can be increased up to 10-fold following administration of DEAD. Hence as a research tool, DEAD may be of use in the detection of viruses with low cancer-causing activity in mice and other species. The recently reported carcinogenicity of DEAD in mice may be due to this mode of action, therefore care should be exercised in the handling of this compound. 

Both viral and non-viral approaches to gene therapy have been used in clinical trials to treat illnesses such as cystic fibrosis and several forms of cancer. Viruses have evolved efficient ways of targeting cells, delivering genetic material and expressing it. However, inflammatory and immunological responses induced by viruses may limit their utility for repeated administration. 

In this classification the basic facility is used for work with the least hazardous agents and the total containment facility is used for the most hazardous agents. For recombinant DNA research, the biosafety levels of these facilities have been abbreviated as BLl, BL2, BL3, and BL4 (previously called PI to P4) these terms are also used to refer to the corresponding facilities for other kinds of biohazard research (see Section 11.4). Table 10.1 indicates the level of facility that is appropriate for work with cancer viruses, recombinant DNA, and human pathogens. 

The evaluation of the risks associated with cancer virus research is extremely difficult, since we lack much scientific data on such vital characteristics as agent host range, infec-tivity, host susceptibility, and infectious dose (see Section 11.2). Because the potential consequences of accidental inoculation of laboratory workers with oncogenic viruses are so serious, standards have been developed for work with these agents (476, 477). The technique of risk assessment, which classifies both agents and experimental procedures on the basis of their relative hazards, is very useful for assigning particular ents into hazard categories based upon available data. 

If the experimental procedure requires the use of laboratory animals, special precautions must be taken based upon the assumption that the animal may excrete tumor virus in its urine, feces, sputum, or other sources (Table 11.6). Although the chances for transmission of cancer virus from animal to human (221) seem to be minimal at this time, the occurrence of this should be considered as a possibility since horizontal transmission, the spread of disease from an inoculated animal to its cagemate, of oncogenic disease is known to occur in animals (Table 11.7). Furthermore, the presence or absence of horizontal trans-... 

Table 11.11 Tumorigenic properties of nucleic acids from cancer viruses...

To illustrate the potential risks to a laboratory worker who handles cancer viruses, consider a statement made by the National Cancer Institute The most likely candidate for laboratory-acquired human cancer is the predisposed person self-inoculated with or inhaling a highly concentrated viral preparation (477). Other types of research present... 

Selecting a Biological Safety Cabinet Assessment of Risk in the Cancer Virus Laboratory ... 

Trentin JJ, Yabe Y, Taylor G. The quest for human cancer viruses. Science 1962 137 835-849. 

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