New research suggests that, when used in combination with radiotherapy, compounds found in cannabis could offer a new treatment option for glioma, one of the most aggressive forms of adult brain cancers.
Cancer researchers from St George's, University of London in the UK discovered that cannabinoids can help to kill 50 percent of glioma cells in the lab - and when combined with radiotherapy, the cannabis compounds stopped the growth of the tumours entirely in mice.
"The tumours were treated in a variety of ways, either with no treatment, the cannabinoids alone, and irradiation alone or with both the cannabinoids and irradiation at the same time," said oncologist and lead researcher Wai Liu in a press release.
"Those treated with both irradiation and the cannabinoids saw the most beneficial results and a drastic reduction in size. In some cases, the tumours effectively disappeared in the animals," said Liu.
The results, which are published in the journal Molecular Cancer Therapeutics, are pretty exciting, and open up new treatment pathways for a disease that currently only has a 10 percent five-year survival rate.
But it's important to note that so far the tests have only been done on glioma in the lab and in mice models, and the effects in the human body will be far more complicated.
Still, it's not the first study to suggest that cannabis could offer new treatment options for cancer. Cannabis and its 85 active compounds, called cannabinoids, are already being used widely in a range of therapeutic ways - from relaxation and pain relief to the treatment of chemotherapy side effects.
In fact, a mixture of two common cannabinoids, tetrahydrocannabinol (THC) and cannabidiol (CBD), is already being sold as a licensed drug called Sativex, to help ease the effects of multiple sclerosis.
Previous, albeit controversial, research has already shown that both THC and CBD can induce cell death in some tumour cells in the lab - but little extensive research had been done specifically on brain tumours.
The team figured that because the receptors for THC and CBD are both found in the highest abundance in brain cells - which is why cannabis makes us high - it made sense that they might also be especially good at killing brain cancer cells, as Liu explains in a story on the study in The Conversation.
To test this theory, the team investigated the effects of Sativex, which contains an equal balance of THC and CBD, on glioma cells in the lab.
They found that, on their own, THC or CBD could kill around 50 percent of glioma cells, but they needed to be used at a concentration of 14 millimolar (mM) to 19 mM - a pretty strong dose.
However, when combined, only a 7 mM dose of each was required to achieve the same benefit. Liu explains at The Conversation that at this concentration, the cannabinoids shouldn't have a psychoactive effect.
The researchers then tested the combination of THC and CBD on mice who had glioma, and monitored the growth of their tumours using MRI technology. They also compared this to the use of traditional radiotherapy, which involves irradiating cancer cells in order to kill them.
Finally, they combined radiotherapy with cannabinoids. In this experiment, they first treated the mice with THC and CBD, which lab results had shown made tumour cells more responsive to irradiation, and then gave them radiotherapy.
They found that, on its own, irradiation didn't do much to stop tumour growth, and THC and CBD administered together only slightly slowed it down. But when combined, the cannabinoids followed by radiotherapy actually stopped the growth of the glioma cells.
"Our results showed that the dose of irradiation we used had no dramatic effect on tumour growth, whereas CBD and THC administered together marginally reduced tumour progression," writes Liu for The Conversation. "However, combining the cannabinoids with irradiation further impeded the rate at which tumour growth progressed and was virtually stagnant throughout the course of the treatment."
Impressively, at the end of the 21 day treatment process the mice that had been given the combination of cannabinoids and radiotherapy had significantly smaller tumour volumes than the other test subjects.
"The benefits of the cannabis plant elements were known before but the drastic reduction of brain cancers if used with irradiation is something new and may well prove promising for patients who are in gravely serious situations with such cancers in the future," said Liu in the release.
Of course, the next, and most important step, will be to test these results in humans, and Liu's team are now discussing the possibility of combining cannabinoids with irradiation in a human clinical trial.
Until then, it's too soon to say whether cannabis could be used to help treat glioma in humans, but it definitely opens up some interesting research possibilities.
We'll be watching this space.