New cancer therapies: Viruses look promising as safe, effective treatment

TOKYO — An exciting new cancer treatment is being developed in Japan — deploying viruses that selectively infect cancer cells and kill them.

Tottori University and the Institute of Medical Science of the University of Tokyo have confirmed the effectiveness of their methods in animal experiments, using viruses for smallpox vaccination and measles, respectively. In each method, the virus is genetically engineered to prevent it from infecting normal cells and is injected into the bloodstream.

The researchers at both institutions believe their methods could lead to new therapies that will supplement surgery, chemotherapy using cancer drugs, and radiation therapy. But first they must confirm the effectiveness and safety of the new methods in humans.

A cancerous tumor produces new blood vessels around itself to obtain nutrients necessary for growth. When a therapeutic virus is injected into the bloodstream, it circulates through the body until it reaches the tumor. It then infects the cancer cells. The virus kills the cancer cells while it spreads in the tumor, causing it to diminish or disappear. The virus infection can also be expected to incite the immune system, which protects the body from pathogens, to attack the cancer cells.

Cancer-specific viruses

A research team led by associate professor Takafumi Nakamura at Tottori University has developed a method for using vaccinia virus, which is used for smallpox vaccination, to treat lung and pancreatic cancers. The team genetically manipulated the virus to ensure that it multiplies in cancer cells but is unable to multiply in normal cells.

The researchers injected human pancreatic cancer cells into the abdomens of mice, causing tumors to grow in them, and later injected vaccinia virus into the mice. In the experiment, they found that more than 90% of the cancer cells had died. "The virus was originally used in vaccination, so it is very safe," Nakamura said. His team hopes to confirm the safety of the virus for animals closer to humans, including monkeys, and to start clinical trials in five years.

Professor Chieko Kai and her team at the University of Tokyo's Institute of Medical Science have developed a method of using a type of measles virus to treat breast cancer. The researchers found that the virus infects breast cancer cells by sticking to a protein, PVRL4, on the surface of the cancer cells. They genetically manipulated the virus so that it would multiply only in breast cancer cells and would not infect normal cells.

When the virus was injected into mice that had received transplantation of cancerous human breast tissue, the cancer scarcely grew and most cancer cells in the tumors died. When the virus was administered to healthy monkeys and dogs, it did not produce side effects on the animals and showed no safety problems. Kai said, "The likelihood of the virus infecting non-cancerous cells is low." She wants to start clinical studies as early as in 2016.

Bearable therapy

Cancer treatment using viruses is easier on patients than traditional surgery and chemotherapy. When the injected virus is carried throughout the body by the bloodstream, it can be expected to attack small cancers that have not been removed by surgery as well as metastatic cancers. This approach, however, has weaknesses due to the use of viruses.

First of all, when a therapeutic virus is injected, it may be removed by the patient's own immune system before reaching the tumor. If the virus is repeatedly used, its effects may be reduced by the body's immune response. Therefore, viruses that can avoid the immune response and reach cancer cells have to be developed.

There is also concern that therapeutic viruses could mutate while multiplying in the body and begin attacking normal cells. The effect and safety of cancer treatment that involves an intravenous injection of viruses have been confirmed only in animal experiments. What influence the treatment might have on health in the long term has to be studied on humans. Researchers will also have to find ways of treating side effects that could result from mutation.

Tomoki Todo, professor at the University of Tokyo medical institute, who is in the vanguard of this field of research in Japan, started a clinical trial in late December for a brain tumor treatment method that involves injecting a genetically modified herpes virus and letting it reach the affected part of the body. In the clinical studies so far, there have been few side effects, and therapeutic effects have been confirmed, Todo said.

Cancer therapy that uses viruses is effective in many ways that are unavailable with traditional therapeutic methods. For the therapy to become a viable option for cancer treatment, researchers will have to steadily overcome the problems that remain.

(Nikkei)

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