Scientists have engineered a virus that when injected into the blood, can selectively target cancer cells throughout the body. The virus attacked only tumours, leaving the healthy tissue alone, in a small trial on 23 patients, according to the journal Nature.
Researchers said the findings could one day “truly transform” therapies. Cancer specialists said using viruses showed “real promise”.
Using viruses to attack cancers is not a new concept, but they have needed to be injected directly into tumors in order to evade the immune system. Scientists modified the vaccinia virus, which is more famous for being used to develop a smallpox vaccine. The virus, named JX-594, is dependent upon a chemical pathway, common in some cancers, in order to replicate. It was injected at different doses into the blood of 23 patients with cancers which had spread to multiple organs in the body. In the eight patients receiving the highest dose, seven had the virus replicating in their tumors, but not in healthy tissue.
Prof John Bell, lead researcher and from the University of Ottawa, said, “We are very excited because this is the first time in medical history that a viral therapy has been shown to consistently and selectively replicate in cancer tissue after intravenous infusion in humans. Intravenous delivery is crucial for cancer treatment because it allows us to target tumors throughout the body as opposed to just those that we can directly inject.”
Infection prevented further tumor growth in six patients for a time. However, the virus did not cure cancer. Patients were given only one dose of the virus as the trial was designed to test the safety of the virus. It is thought that the virus could be used to deliver treatments directly to cancerous cells in high concentrations.
Prof Bell acknowledges that the research is still in the very early stages, but he said, “I believe that someday, viruses and other biological therapies could truly transform our approach for treating cancer.”
Cancer Research UK's Prof Nick Lemoine, also director of Barts Cancer Institute, added, “Viruses that multiply in just tumor cells - avoiding healthy cells - are showing real promise as a new biological approach to target hard-to-treat cancers. This new study is important because it shows that a virus previously used safely to vaccinate against smallpox in millions of people can now be modified to reach cancers through the bloodstream - even after cancer has spread widely through the patient's body. It is particularly encouraging that responses were seen even in tumors like mesothelioma, a cancer which can be particularly hard to treat.”
The field received a boost in January when biotech giant Amgen Inc agreed to pay up to $1 billion for BioVex, the developer of experimental cancer-fighting virus OncoVex. But the only “oncolytic virus” so far approved by a regulatory agency is for treatment of head and neck cancer in China.
Dr. Bell said the next step is a Phase 2b trial of the viral therapy in 120 patients with primary liver cancer, known as hepatocellular carcinoma. He said earlier trials of JX-954 showed really strong activity in liver cancer. Since some kinds of liver cancer are caused by viruses - like hepatitis B - the theory is that those tumor cells may be more susceptible to a second virus.
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