Viruses, like the flu virus, try to enter the cells in our body because they need a host to survive. Once inside, the virus begins to use the “machinery” of the cell to make copies of itself, eventually destroying the cell. Viruses continue to spread to other cells throughout the body, breaking down and killing increasing numbers of healthy cells, until the immune system is able to regain control and destroy the virus particles.
Scientists have figured out methods of using the destructive nature of viruses to kill tumor cells in cancer patients. Oncolytic virus therapy (OVT) uses a virus that infects and destroys cancer cells but not normal cells. This promising treatment approach is a targeted therapy that is typically used in conjunction with chemotherapy and radiation therapy.
How OVT works
The viruses used in OVT are genetically engineered to exclusively replicate inside cancer cells and kill them without harming healthy cells. Typically, OVT uses a modified adenovirus, as in the case of DNX-2401, LOAd703, and ONCOS-102, or a naturally-occurring virus, like the herpes simplex virus or the anti-smallpox vaccine, as in the case of HF10 and GL-ONC1.
Researchers have found that viruses can be controlled to selectively affect cancer cells. In other words, even if a virus enters healthy cells, it will selectively replicate inside only cancer cells. In many OVTs the virus also is altered to contain genes that will boost the immune response. In these cases, as the virus is making copies of itself inside tumor cells, the role that the immune cells play becomes increasingly significant in destroying the tumor.
REIC gene therapy uses OVT in a unique way, in which the virus is modified to create a protein called REIC, triggering the normally suppressed pathway that leads to programed cell death.
Side effects of OVT
Imlygic is the first approved OVT in the Western world, and trials are continuing for the application of this therapy in pancreatic cancer and for use with chemotherapy and radiation therapy in the treatment of head and neck cancer.
A number of additional OVTs are still being tested in clinical trials, including those mentioned above.
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