Oncovirus & Retrovirus

      An oncovirus is a virus that can cause cancer. In the 1950-60s, these acutely transforming retroviruses were often called oncornaviruses to show their RNA virus origin. Now it refers to any virus with a DNA or RNA genome causing cancer and can be used synonymously with “tumor virus” or “cancer virus”. However, the majority of animal and human viruses to do not cause cancer; this is probably because of the coevolution between the virus and its host.  In most viruses, DNA is transcribed into RNA, and then the RNA is translated into a protein through protein synthesis. However, retroviruses (mentioned above) are a single-stranded RNA virus that stores its nucleic acid in the form of mRNA and then targets a host cell as an obligate parasite. Once it gets inside the hosts cells cytoplasm, the virus transcribes differently than most viruses. The virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, in reverse of the usual pattern. When the new DNA is incorporated into the host cell’s genome by an integrate enzyme, the retroviral DNA is referred to as a provirus. This DNA becomes integrated into the host cell’s genome and then undergoes the usual transcriptional and translational processes to express the genes carried by the virus, producing the proteins required to assemble new copies of the virus. It is difficult to detect the virus until it has infected the host, which makes research an early detection hard.

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     It is not all severe news though. The WHO International Agency for Research on Cancer estimated in 2002 that 17.8 percent of human cancers were caused by infection, with 11.9 percent of those being caused by one of seven different viruses. This is advantageous because these cancers might be easily prevented through vaccination, diagnosed with simple blood test, and treated with less-toxic antiviral compounds.

     Tumor-selective replicating viruses are offering advantages over conventional cancer therapy and are forming a new approach for the treatment of human cancer. For example, virotherapeutics is being developed based on several strategies. Virotherapy is not a new concept; however, recent technical advances in the genetic modification of oncolytic viruses have improved tumor specificity, which is leading to the development of new ways to fight cancer. Clinical trials with oncolytic viruses have been demonstrating the safety and feasibility of an effective virotherapeutic approach. Strategies to overcome some possible obstacles and challenges with this therapy are currently being explored. Hopefully combination therapy will continue to show encouraging antitumor responses by eliciting strong immunity against established cancer, and we can get closer to finding a cure for cancer.

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