Oncolytic viruses (OV)—a novel family of cancer therapies—have varying degrees of selective replication in cancer cells.
Cancer has claimed the lives of more than 10 million people worldwide since its discovery in 1500 B.C. It was the second biggest cause of mortality in 1990. However, in recent years, it has overtaken cardiovascular disease as the major cause of death
Several treatment options have been discovered in a bid to combat this menace. Some of them include surgery, radiotherapy, chemotherapy and immunotherapy. But their limitations have proven to outweigh their successes, in most cases.
For instance, surgical treatments are mainly used for patients with early-stage cancer, and severe side effects make radiation and chemotherapy intolerable to patients.
Overall, the imperfections of existing cancer therapeutic strategies have led to the development of new therapies with precise tumour targeting, potent tumoricidal properties and few toxic side effects.
OV has emerged as a promising new-age cancer therapy.
What Are Oncolytic Viruses?
Oncolytic viruses are genetically engineered or naturally occurring viruses that can selectively replicate themselves in cancer cells and kill cancer cells without harming healthy cells.
The concept of using viruses to treat tumours has been around for over 100 years. In 1904, it was reported that influenza had shrunk a tumour in a 42-year-old woman with leukaemia.
Then, in 1912, Italian doctors discovered that rabies vaccine injections could reverse cervical cancer, leading to the new concept of OV therapy.
How Do Oncolytic Viruses Kill Cancer?
This therapy involves injecting a genetically modified virus or an oncolytic virus directly into the cancer cell.
It is known that cancer cells often have weak antiviral defences, making them defenceless against viral infection.
After the virus has been injected into the cancer cell, it makes several copies of itself, causes an infection and begins to destroy the cancer.
Excess copies cause cancer cells to explode and die. The death of the cancer cells facilitates the release of previously hidden antigens (proteins) that are unique to cancer.
These antigens leave traces of the areas where the cancers exist in the body and prompt the immune system to target the remaining cancer cells.
This will cause the immune system to kill nearby tumours or cancer cells in other parts of the body.
Why Is Viral Therapy a Promising Cancer Treatment?
Genetically modified viruses have shown a promising approach to cancer treatment for several reasons:
- Reduced ability to damage healthy cells in the body.
- The ability to specifically target and infect tumours.
- The ability to produce molecules that strengthen the immune system after the cancer cells have been infected.
- Minimal side effects compared to other treatment options.
- Drug resistance.
- Low cost.
Which Viruses Are Used for Cancer Virotherapy?
Several viruses are being investigated for potential oncolytic virotherapy. The most common is the modified herpes simplex virus (HSV), which infects tumour cells and promotes their destruction.
This virus is currently being used in clinical trials for oncolytic virotherapy in glioblastoma.
Other viruses used in cancer virotherapy include Adenoviruses (a group of viruses that cause sore throats, colds, and other minor infections) and Measles Vaccinia virus (used in vaccination against smallpox).
Contraindications of Oncolytic Virus Therapy
Oncolytic virus therapy should be avoided under the following conditions:
- In pregnancy or if planning to become pregnant.
- Leukaemia, lymphoma, AIDS or other human immunodeficiency viruses.
- During Immunosuppressive treatment
- When taking steroids.
What Are the Side Effects of Viral Therapy?
Most studies have shown that viral therapy has been effective in many cancer patients with fewer reported side effects. However, some people may experience any of these side effects, including:
- Flu symptoms
- Pain at the injection site
The least reported side effects include:
- Difficulty in breathing
- Deep vein thrombosis
- Oral herpes
- Worsening of psoriasis
What Is the Result of Viral Therapy?
Some studies suggest that oncolytic virus therapy is most effective when combined with other immunotherapies, such as immune checkpoint inhibitors and drugs that boost the immune system to fight cancer.
Another research shows that if oncolytic virus therapy is given before melanoma surgery, it usually boosts the body’s immune response and improves the effectiveness of treatment.
Nonetheless, this therapy has several disadvantages and they include:
- No stable therapeutic effect in individuals due to different physical environments.
- The body’s ability to quickly clear the virus.
- Limited availability of oncolytic virus.
- Safety of oncolytic viruses in immunocompromised individuals.
Despite the success stories of oncolytic virus therapy, further research and trials are needed to ensure the full efficacy and safety of oncolytic virus therapy.