The California study authored by Sean McCallister was reported in the January 2010 issue of Molecular Cancer Therapeutics. In this new study researchers looked at both THC and cannabidiol, another compound from marijuana, on brain cancer cells. Researchers found that a combination treatment of both compounds together were more effective at better at killing the cancerous cells and preventing them from growing back than when used separately.
This initial study was performed in the laboratory. McCallister and his team now want to extend their testing on laboratory animals and then humans. Human studies though would be expensive and difficult as the compounds would have to be delivered directly into the brain.
Guillermo Velasco and colleagues reported their findings appear in a 2009 issue of the Journal of Clinical Investigation.
In the Spanish study mice were ‘engineered” to carry forms of cancerous human brain. They found that when an active ingredient of marijuana THC was injected directly into the brain the active ingredient in marijuana, THC, caused brain cancer cells to undergo a process called autophagy. In cell biology, autophagy, is a catabolic process involving the degradation of a cell's own components.
It is a tightly-regulated process that plays a normal part in cell growth, development, and homeostasis, helping to maintain a balance between the synthesis, degradation, and subsequent recycling of cellular products.
In this case the THC in marijuana caused the cancerous cells in the mice to die off and the tumors shrank.
The Spanish researchers also tested the effect of THC on two human patients suffering from "recurrent glioblastoma multiforme," a form of brain cancer. Both patients had been enrolled in a clinical trial designed to test THC's potential as a cancer therapy.
The research team took biopsies of the brain tissue both before and after a one-month regimen of THC therapy. Electron microscopic analysis showed that the treatment apparently eliminated cancer cells while sparing healthy brain cells.
"These results may help to design new cancer therapies based on the use of medicines containing the active principle of marijuana and/or in the activation of autophagy," Velasco said.
About 9,000 people in the United States develop glioblastomas each year. Because these tumors spread throughout the brain they are difficult to treat effectively without damaging the brain itself.
However, both groups of researchers warned that no matter how encouraging their research may be, we are still a long way away before doctors will be prescribing marijuana compounds to treat brain cancer. In addition, the doctors warned against simply smoking marijuana as an adjunct therapy:
"It's unlikely that you could reach effective concentrations by smoking the plant."