A combination of the myxoma virus and the immune suppressant drug rapamycin can kill glioblastoma multiforme - the most common and deadliest malignant brain tumour, a new study claims. According to Peter A Forsyth from Moffitt Cancer Center in US, the combination has been shown to infect and kill both brain cancer stem cells and differentiated compartments of glioblastoma multiforme. The finding means that barriers to treating the disease, such as resistance to the drug temozolomide, may be overcome, researchers said. "Although temozolomide improves survival for patients with glioblastoma multiforme, drug resistance is a significant obstacle. "Oncolytic viruses that infect and break down cancer cells offer promising possibilities for overcoming resistance to targeted therapies," said Forsyth, the study lead author. Researchers note that oncolytic viruses have the potential to provoke a multipronged attack on a tumour, with the potential to kill cancer cells directly through viral infection and possibly through inducing the immune system to attack the tumour. The multipronged approach might get around some of the classical resistance mechanisms that have plagued both targeted therapies and conventional chemotherapies. Several oncolytic viruses, both alone or in combination with small molecule inhibitors, have been tested and show promise for malignant gliomas. However, most have not been effective in killing cancer cells.
Two likely obstacles may be the patient's own anti-viral immune response and limited virus distribution. The researchers found that brain cancer stem cells were susceptible to myxoma virus in the laboratory cultures and in animal models, including in temozolomide-resistant cell lines. "We also found that myxoma virus with rapamycin is a potentially useful combination. The idea that cancer cells can be killed by a harmless virus is an exciting prospect for therapy," Forsyth said. Researchers are investigating other drugs that may improve the effectiveness of myxoma virus when used in combination, and they are evaluating the use of other strains of myxoma virus that might be more effective. The study was published in the journal Neuro-Oncology.