A team of Canadian and US-based research groups co-led by the Singh Lab at McMaster University have discovered a new pathway that is used by cancer cells to infiltrate the brain. The research, which includes work funded by the Terry Fox Research Institute, also reveals a new therapy that shows promise in blocking and killing these tumours.
The research, published in Nature Medicine, offers new hope and potential treatments for glioblastoma, the most aggressive form of brain cancer. With existing treatments like surgery, radiation therapy and chemotherapy, the tumours often return, and patient survival is limited to only a few months. With this new treatment, the returning cancer cells were destroyed at least 50 per cent of the time in two of the three diseases tested in preclinical animal models.
To discover the pathway cancer cells use to infiltrate the brain, researchers used large-scale gene editing technology to compare gene dependencies in glioblastoma when it was initially diagnosed and after it returned following standard treatments. By doing this, researchers discovered a new pathway used for axonal guidance – a signalling axis that helps establish normal brain architecture – that can become overrun by cancer cells.
“In glioblastoma, we believe that the tumour hijacks this signalling pathway and uses it to invade and infiltrate the brain,” says co-senior author Dr. Sheila Singh, professor with McMaster’s Department of Surgery and director of the Centre for Discovery in Cancer Research. The research was also co-led by Dr. Jason Moffat, head of genetics and genome biology at The Hospital for Sick Children (SickKids).
“If we can block this pathway, the hope is that we can block the invasive spread of glioblastoma and kill tumour cells that cannot be removed surgically,” says Dr. Singh.
Promising new therapeutic
To stop the invasion of cancer cells, researchers targeted the hijacked signalling pathway using different strategies including a drug developed in Dr. John Lazo’s group at the University of Virginia, and also by developing a new therapy with help from Drs. Kevin Henry and Martin Rossotti at the National Research Council Canada using CAR T cells to target the pathway in the brain. They honed in on a protein called roundabout guidance receptor 1 (ROBO1) that helps guide certain cells, similar to a GPS.
“We created a type of cell therapy where cells are taken from a patient, edited and then put back in with a new function. In this case, the CAR T cells were genetically edited to have the knowledge and ability to go and find ROBO1 on tumour cells in animal models,” says lead author Dr. Chirayu Chokshi, a former PhD student who worked alongside Dr. Singh at McMaster University.
Drs. Singh and Chokshi say the treatment can also apply to other invasive brain cancers. In the study, researchers examined models for three different types of cancer including adult glioblastoma, adult lung-to-brain metastasis and pediatric medulloblastoma. In all three models, treatment led to a doubling of survival time. In two of the three diseases, it led to tumour eradication in at least 50 per cent of the mice.
“In this study, we present a new CAR T therapy that is showing very promising preclinical results in multiple malignant brain cancer models, including recurrent glioblastoma. We believe our new CAR T therapy is poised for further development and clinical trials,” says Dr. Singh.
Work on the study was performed with samples derived from patients treated by neurosurgeons at Hamilton Health Sciences. Proteomics discovery which helped to elucidate the new glioblastoma targets was done in collaboration with Dr. Thomas Kislinger at Princess Margaret Cancer Centre and University of Toronto. The research was made possible through collaborations among the National Research Council Canada, University of Virginia, University of Pittsburgh and the Princess Margaret Cancer Centre.
The study also received funding from Brain Cancer Canada, the Brain Tumour Foundation of Canada, the Canadian Institutes of Health Research, the Foundation for the National Institutes of Health, the US National Institutes of Health and Mitacs.