Cancer-fighting version of herpes shows promise in early human trials

Cancer-fighting version of herpes shows promise in early human trials

An illustration of a herpes simplex virus.

An illustration of a herpes simplex virus.
Drawing: Shutterstock (Shutterstock)

Scientists may be able to turn a longtime enemy germ into an ally against cancer, according to new research this week. In preliminary data from a phase I trial, a genetically modified version of the herpes virus has shown promise in treating hard-to-eradicate tumors, with one patient experiencing complete remission for 15 months so far . However, much more research will be needed to confirm early treatment success.

The viral treatment is known as RP2 and is a genetically modified strain of herpes simplex 1, the virus responsible for most cases of oral herpes in humans, as well as some cases of genital herpes. Developed by Replimune, RP2 is designed work on two fronts. Injected directly into the tumor, the virus is believed to selectively infect and kill certain cancer cells. But it also blocks the expression of a protein known as CTLA-4 produced by these cells, and it hijacks their machinery to produce another molecule called GM-CSF. The net result of these cellular changes is to weaken the cancer’s ability to hide and fend off the immune system.

In a phase I trial led by scientists from the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust in the UK, RP2 was given as the only treatment to nine patients with advanced cancers who did not respond. other therapies; it was also given in combination with another immunotherapy drug to 30 patients. Three patients on RP2 alone appeared to respond to treatment, meaning their cancers shrank or stopped growing, and seven patients on combination therapy also responded. One patient in particular, with a form of carcinoma along his salivary gland, showed no signs of cancer for at least 15 months after treatment with RP2 alone. No life-threatening adverse events were reported in the trial, with the most common symptoms after treatment being fever, chills and other flu-like illnesses.

The results, present this week at the European Society for Medical Oncology (ESMO) Congress 2022, are preliminary, as they have not yet gone through the formal peer review process. They are also based on a very small sample size, which means any results should be taken with caution. But phase I trials are not intended to show that a treatment is effective, only that it is safe enough to be taken by humans. So the fact that some people with seemingly incurable cancers already seem to be responding to RP2, according to the team, is a very good sign that it may be living up to its potential.

“Our study shows that a genetically engineered, anti-cancer virus can deliver a punch against tumors, by directly destroying cancer cells from the inside while appealing to the immune system against them,” said lead author Kevin Harrington, professor of biology. therapies at the Cancer Research Institute, in a statement organisation.

Scientists have been optimistic on cancer viruses for a long time. But it is only recently that this hope is finally beginning to bear fruit. In 2015, the first viral therapy was approved in the United States for certain advanced cases of melanoma. Last May, scientists in California launched a phase I clinical trial of their anti-cancer virus, called Vaxinia. Other companies are developing their own candidates, alone or in combination with other treatments. And Replimune is developing two other candidates based on their modified herpes virus.

While many experimental therapies ultimately fail to cross the finish line and reach the public, it’s possible that at least some of these viruses could one day become a new standard cancer treatment.

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