The Role of Oncolytic Viruses in Cancer Treatment

Written by Kranti Kaur

The search for a cure to cancer has been ongoing for decades now, but no “cure” that can effectively eradicate the disease has been found. Currently, surgery is used to remove cancerous tumors, chemotherapy uses a mix of different drugs to kill off cancerous cells throughout the body, and radiation treatment kills cancer cells. There are many other treatments, but no treatment can be considered a “cure”, as they don’t exclusively target cancer cells or simply are not effective for different types of cancer. However, the results of a new study on a modified herpes virus allow us to hope.

When one thinks of a virus, one assumes something negative, as viruses have always been a source of disease and sickness. But what would happen if a virus was modified to treat cancer? This is exactly what happened in a study that genetically modified the herpes virus to fight advanced cancers. This virus, called RP2, has been shown to be effective in 25% of patients with advanced cancers. The treatment works by multiplying inside of cancerous cells, causing them to burst. Additionally, it blocks a protein, CTLA-4, which allows the immune system to kill the cancer cells with greater efficiency. The herpes virus was used as the model virus because it is easily modifiable genetically and is very effective at reaching epithelial cells.

Three out of nine patients treated with RP2 saw shrinkage in their tumors. One of these three patients saw complete eradication of his cancer. This patient, Kryzysztof Wojkowski, a 39-year-old builder from West London, suffered from a cancer of the salivary glands. He had undergone surgery and many different treatments to no avail. He was receiving end-of-life care when he was given the opportunity to participate in the trial with this modified herpes virus. After five weeks of injections every two weeks, his cancer completely disappeared. He has been cancer-free for two years now. 

The trial in which these results were found tested RP2 alone in nine patients and RP2 with another cancer treatment, nivolumab, in 30 patients. Seven out of the thirty patients receiving the combined treatments saw benefits. The phase 1 trial, which is currently ongoing,  attempts to test the safety and dosages of RP2 in patients as well as its ability to shrink tumors. There appeared to be only mild tiredness as a side effect of the treatment. 

The genetically modified herpes virus is not the only virus being used to treat cancers. In another study, an oncolytic virus, which is a virus that can kill cancerous cells without damaging healthy cells, was used to reduce the size of cancerous tumors. This drug is called CF33-hNIS, or Vaxinia, and appears to be more effective than previous attempts to make oncolytic viruses shrink tumors. Vaxinia also attempts to target all cancers rather than one specific cancer. Additionally, there appear to be only mild side effects, including fever, fatigue, and chills, which is a major upgrade from the aggressive side effects of other cancer treatments such as hair loss. 

The immune system can develop a “memory” of the tumor antigens and therefore fight them more effectively with the aid of oncolytic viruses. When oncolytic viruses replicate inside of cancer cells, they burst, releasing all of the antigens in the cell which are recognized by the immune system. Not only do the oncolytic viruses kill the cancer cells, but they discourage the recurrence of cancer since the immune system is able to recognize the antigens from cancer cells and target them. Cancer cells are able to metastasize and prevent cell death because of specific proteins and receptors. These proteins are what oncolytic viruses use to selectively target cancer cells; the proteins are also present universally in cancer, which allows oncolytic viruses to treat most cancers. 

Although these modified viruses appear to be effective in cancer treatment, they cannot be considered perfect treatments. In theory, they are exactly what a cancer cure should be: able to target and kill all types of cancerous cells without damaging healthy cells. However, it is important to be realistic in situations where there is cause of excitement. First of all, oncolytic viruses have been used for a long time in an attempt to treat diseases and cancers: but it is very difficult to control viruses. Additionally, the study has a very small sample size, so the results, though promising, must not be interpreted to be a very representative depiction of what the oncolytic viruses can do to cancer. However, the results are promising and there is hope for the results of further trials to be very good. 

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