Cancer-killing virus becomes more effective when shielded by bacteria

Viruses have shown enormous potential in the treatment of various types of cancer, but the immune response limited their application to tumors near the body surface. Now scientists have shown that the shielding of viruses with genetically modified bacteria bypass this problem, slowing down the growth of serious tumors in mice.

Some therapies that use viruses killing cancer or oncolytics have been approved worldwide to treat cancers in the skin, brain and head and neck. These involve injecting the viruses genetically modified directly into tumors, where they infect and kill cancer cells by bursting them.

But for tumors that are more difficult to reach deeper into the body, such viruses must be injected into the blood, where the immune system quickly destroys them before reaching the planned target.

To get around this obstacle, Zakary singer at Columbia University in New York and her colleagues used Salmonella typhimurium Bacteria that has been genetically designed to be harmless and cause a lower immune response than oncolytic viruses. They also designed bacteria to carry the genome of Sénécavirus A, a virus which turned out to have killed human cancer cells in laboratory and animal experiences.

“We are talking about a Trojan horse approach, where bacteria hide this virus [from the immune system]The shuttle where she has to go and deliver it to be able to do her activities killing cancer, ”explains the singer. The bacteria are designed to enter cancer cells, then release copies from the viral genome, he says.

To put their approach to the test, the researchers cultivated nerve tumors on the back of the mouse. A week later, they injected the bacteria bearing the virus, which they called Cappsid, in the blood of half of the mice. The remaining mice received the Senecavirus A without bacteria.

In one day, the team noted that Cappsid – which they marked with a fluorescent label – had accumulated in tumors, where immune responses are generally deleted. Meanwhile, any cappsid remaining in the blood or which had reached healthy tissue was quickly eliminated by the immune system, explains Singer.

It took 11 days, on average, for the tumors of the Seneca group to only reach the maximum authorized size before ethical regulations dictate that mice had to be euthanasic. On the other hand, tumors took 21 days to reach this size at the mouse which received the Cappsid. None of the mice has experienced apparent side effects.

“The data is absolutely wonderful,” said Guy Simpson at the University of Surrey in the United Kingdom. The team has shown that this approach works well against rapid growth tumors, such as those derived from nerve cells, but it could be even more effective against the slowest, he said.

In another part of the experience, the researchers noted that the cappsy completely eradicated human pulmonary tumors located in the back of the mouse, but they did not include a control group which only received Sénécavirus A.

Before it can be deployed to people, other studies on mice and non -human primates should test it against a wider range of tumors, such as pancreatic cancer, which has a particularly mediocre survival rate, explains Simpson.