A virus that damages tumours while sparing normal healthy tissue has passed a preliminary test. JX-594, an engineered version of smallpox virus, prevented or reduced further tumour growth in 13 of 23 patients four to ten weeks after they were treated.
Patients who were injected with higher doses during the phase I clinical trial - designed to test the safety of a single injection of JX-594 - responded better. The commonest side effect was flu-like symptoms lasting a day. Only ten days after the treatment, the virus had spread in the tumours of 87 percent of patients treated with the higher dose.
'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', said lead researcher Dr John Bell from Ottawa Hospital Research Institute in Canada.
JX-594 is an oncolytic virus – a virus designed to preferentially infect cancer cells. The virus uses the cancer cells' machinery to produce proteins that encourage the body's immune system to target and destroy the tumour.
'Oncolytic viruses are unique because they can attack tumours in multiple ways, they have very mild side effects compared to other treatments, and they can be easily customised for different kinds of cancer', said Dr Bell. The study also provides preliminary evidence that viruses carrying foreign genes - like the one JX-594 uses to produce its targeting protein - can be delivered directly to tumours.
'Viruses that multiply in just tumour cells - avoiding healthy cells - are showing real promise as a new biological approach to target hard-to-treat cancers. But up until now they have had to be directly injected into individual tumours to avoid being immediately cleared by the immune system', said Professor Nick Lemoine of Cancer Research UK.
'This 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'. He added: 'It is particularly encouraging that responses were seen even in tumours like mesothelioma, a cancer which can be particular hard to treat'.
Ottawa Hospital Research Institute and the University of Ottawa in partnership with Jennerex Biotherapeutics now plan to test the virus in a phase IIb trial on primary liver cancer patients. 'We are still in the early stage of testing these viruses in patients, but I believe that someday, viruses and other biological therapies could truly transform our approach for treating cancer', said Dr Bell.
The study was published in the journal Nature.