Scientists from the Ottawa Hospital Research Institute have succeeded in delivering a virus intravenously that only attacks cancer tumours and doesn't harm healthy tissues, according to a new study in the scientific journal Nature.
Dr. John Bell, a senior scientist at OHRI and senior co-author of the study, said the investigators were trying to demonstrate that it is possible to deliver such a virus intravenously in people. Previously, it had only been done in animals.
Ultimately, the goal is to use viruses as a cancer treatment, likely in combination with chemotherapy.
"In this study, the way we designed the virus is that it can only grow in cancers and cannot grow in any normal tissues," Bell said. "We think that with this selective approach we may be able to treat cancer continuously with the virus and hopefully effect a complete remission of the disease."
The study involved 23 patients (seven from Ottawa Hospital) who had advanced cancers that had spread to multiple organs. The objective was to prove that viruses could be delivered to tumours through the bloodstream, not to actually treat the patients involved.
"Intravenous delivery is crucial for cancer treatment because it allows us to target tumours throughout the body as opposed to just those that we can directly inject," Bell said, "The study is also important because it shows that we can use this approach to selectively express foreign genes in tumours, opening the door to a whole new suite of targeted cancer therapies."
Bell said those kinds of therapies are desirable because of the restrictions of current forms of treatment.
"The limitations of [chemotherapy and radiation therapy] are that they not only attack the cancer but unfortunately they also attack normal tissues," Bell said.
Bell added that the virus is particularly effective on solid tumors such as in the skin, breast, prostate or pancreas but less effective in leukemia and lymphoma.
Dr. Michael Baker, cancer researcher and professor of medicine at the University of Toronto, said the study is extremely promising but there is a way to go before it translates into a way of treating cancer.
"My educated guess would be we're talking two to four years before this is proven to be safe enough to carry actual therapeutic drugs and other destructive items right to the cancer cell, that's still a work in progress," Baker said.
The study called for patients to receive a single intravenous infusion of the virus (JX-594) at one of five dosage levels. Biopsies of their tumours were obtained 10 days later. In the two highest dosage groups, there was evidence in seven out of eight patients of viral replication in their tumours but not in healthy normal tissue.
Patients reported some side effects consisting of flu-like symptoms for less than 24 hours.
The virus used, a distant relative of smallpox that has been used as a vaccine against smallpox, seemed to be particularly effective at searching for cancerous tumours, according to the study.
Although other viruses have been studied, Baker said this particular virus has a "peculiar capacity."
"It's actually big enough to put things into it. And this experiment showed that those viruses are capable of carrying sizable other molecules to where they are supposed to go and then they multiply — many viruses are just passive carriers that get into the cell — [whereas] these viruses are alive and multiply and spread to other parts of the body where there are other cancers that have been spread."
Bell said the next step is to have trials consisting of a multi-dose regime and open trials around the world to test the virus more thoroughly.
"We'll hope to see we can improve outcomes of patient survival in these larger trials."
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