Virotherapy , a new way of cancer treatment
,1,* Foad ramasi
1. shahid beheshti university of tehran
2. shahid beheshti university of tehran
Cancer, such a harmful disease which annually drags lots of people to death, is defined as growth, multiplication and disorders in cell cycle and sometimes is caused by metastasis. both genetics and environment are involved with cancer and tumor has different receptors compared with normal cells. different therapies have been tested for cancer, such as anti-angiogenesis, gene therapy and most prevalent are chemotherapy and radiotherapy. chemotherapy not only eliminates tumors, but also disrupts the function of normal cells and has lots of side effects specially in metastatic cancers. therefore, new methods should be taken. viruses have strategies that enable them using the host cells in the way they can replicate, express their proteins, and finally yielding to disorders in host cells and apoptosis. according to these, 15 percent of cancers are related to viruses. virus therapy started in 1950 and in this case for eliminating tumor cells, we depend on the natural ability of viruses in polluting cells, multiplication and finally lysing host tumor cells.
In 1800 scientists indicated that their patients with cancer interestingly got better after getting polluted with virus infections. some years later, they injected different species of viruses to patients that results in some led to recovery and in some yielded to death. in order to decrease pathogenicity of viruses, they made genetically engineered viruses, for instance t-vec engineered to reduce the incidence of herpes. scientists also made these agents stronger against cancer by adding an immune system motive protein to viruses. in 2005, after some evidence of shrinking the size of the tumors by these agents, chinese scientists approved an adenovirus called h-101 that was able to destroy the tissue of head and neck tumors. afterwards, amgen institute which works in biotechnology fields in california, declared that genetically engineered virus t-vec not only can shrink the size of tumors in patients being afflicted with malignant melanoma but also is able to increase the life span of patients about 4.4 months more. generally, one way among numerous ways for using viruses as anti-cancer agents, is eliminating an important gene in host cells that virus highly needs it to survive in normal cells, such as eliminating thymidine-kinase that is responsible for the metabolism of nucleic acid that leads to dependence of viruses like hsv to cancer cells which they express thymidine-kinase in higher rates, so viruses attack to these cells for growth.
Based on trials, viruses like t-vec attack the tumor and eliminate it by motivating immune system. cancer-therapy with common methods like chemo and radiotherapy, destroys the function of normal cells too, but using oncolytic viruses has some benefits over than those common methods: 1.oncolytic viruses are more allocated like ndv virus that uses sialic acid as its acceptor and alpha viruses show more intention to heparin sulfate. these two chemical materials are more on the cancer cell surface. 2. there is no need of extra injections after once it entered the cells. viruses multiplicate very fast and attack each cell one by one, so this process continues to the point which immune system get activated, but chemical drugs should have been injected regularly. 3. these agents because of their natural ability, impact the metabolic paths of cancer cells specifically, but chemotherapy involves the most biochemistry paths in most of the cells. of course virus therapy has some disadvantages due to its pathogenic aspect, another limitation of it, could be vulnerability of viruses from the immune system of the host, therefore before a virus can destroy cancer cells, defensive functions of the host body like releasing interferons and antibodies, eliminate viruses from the cell. hence, immune responses must be suppressed to the point that virus can harm the tumor cells.
Genetically engineered viruses, especially oncolytic viruses and recombinant, allocated, anti-tumor proteins derived from them, are being studied more in the field of cancer-therapy. even though pathogenicity of viruses prohibits using them as human anti-cancer agents, one way to overcome this issue is understanding the mechanisms that viruses can attack to the tumor cell specifically. oncolytic therapy that is defined as using viruses to treat cancer is an impressive relationship of basic sciences and medical sciences as well.
Oncolytic viruses - cancer - chemotherapy - virotherpy