Poxvirus used to fight cancer: malignant human brain tumours ‘cured’ in mice

Calgary, AB – A cross-Canada scientific collaboration has successfully tested a potent new cancer-fighting virus that eliminates malignant brain tumours and prolongs survival in mice with a single injection.

The scientists – from Calgary and London, ON – have shown for the first time that myxoma virus, a poxvirus, will kill human brain tumours in mice and prolong the animals’ survival. Their findings are published this month in the journal Cancer Research.

“We’re extremely encouraged by these results and the apparent cure seen in the mice treated with the active virus compared to untreated mice or those injected with inactivated virus,” says virologist Grant McFadden, a scientist at Robarts Research Institute in London and Canada Research Chair in Molecular Virology. His research on poxviruses over the past two decades has shed significant light on how viruses disarm their hosts’ immune systems and their potency as anti-cancer and anti-inflammatory agents.

For the brain tumour experiments, Dr McFadden teamed up with Dr Peter Forsyth of the University of Calgary, a professor in the departments of oncology, and biochemistry & molecular biology, who has developed a mouse model with human gliomas, a malignant form of brain tumour that strikes 2500 people each year. Over the past two years, their laboratories have tested the virus against experimental models of human malignant tumours, both in cell culture and in living animals. Injecting the tumour with the virus was not only well-tolerated – with only minimal inflammation at the site of the inoculation – but 92% of the 13 mice treated were alive and apparently “cured” when the experiment was finished (after more than 130 days).

“Those animals continued to show a selective and long-lived myxoma virus infection in the tumours themselves but that infection did not spread and harm the animal,” says Dr Forsyth, director, Clark H Smith Integrative Brain Tumour Research Centre. “This and other factors suggest that myxoma virus warrants further investigation as a potential treatment for malignant brain tumours in people.”

The University of Ottawa also played a major role: Dr John Bell initiated the Canadian Oncolytic Virus Consortium, a program funded by The Terry Fox Foundation, to study various viruses with the potential to treat cancer. In 2004, Dr Bell brought together the teams from London and Calgary to initiate the study reported in Cancer Research.

Drs McFadden and Forsyth are now planning to test the virus as a treatment for a deadly melanoma that is known to spread to the lung. They will be able to tag the virus with a fluorescent protein and track its progress in mice as it attacks the metastasized tumour cells.

“Oncolytic viruses are a particularly exciting weapon emerging in the fight against cancer,” says Dr McFadden. “There is a lot more preclinical work ahead but the next step is to learn how best to harness their potency and their potential.”

Dr Forsyth’s work is supported by the Canadian Cancer Society, Canadian Institutes of Health Research, Alberta Cancer Foundation, Kid’s Cancer Care Foundation, and the Clark H Smith Integrative Brain Tumour Research Centre. Dr McFadden’s research is supported by the Canadian Cancer Society, and Canadian Institutes of Health Research.