The researchers induced tumours in mice using human cancer cells and then hit them with doses of the cannabis compound THC (tetrahydrocannabinol). Two cell receptors in particular – CB2 and GPR55 – were responsible for the drug’s anti-cancer effects.
The findings help explain some well-known but poorly understood effects of THC at low and high doses on tumour growth, according to the scientists. “There has been a great deal of interest in understanding the molecular mechanisms behind how marijuana, and specifically THC, influence cancer pathology," noted study scientist Peter McCormick at the University of East Anglia, UK. “There has also been a drive in the pharmaceutical industry to create synthetic equivalents that might have anti-cancer properties.”
THC is the most active psychoactive cannabinoid found in marijuana and is responsible for the well-known effects of cannabis consumption.
“The cannabinoid system is very widespread throughout the body and THC affects at least two receptor subtypes, but those receptors have secondary effects on lots of other biological systems,” said pharmacologist Ryan Vandrey at Johns Hopkins, who was not involved in the study.
Cristina Sánchez, study scientist at Complutense University in Spain, commented that knowledge is power. “The more we know about the way tumour cells work, the better we can attack them,” she said. “We knew that CB2 [receptor] had a role in cancer that that made this receptor a target for anticancer medicines; we knew that GPR55 had a role in cancer and that make this receptor a target for anticancer therapies.
“We have now discovered that CB2-GPR55 heteromers exist in cancer cells and that they signal differently than the individual receptors. And that makes them new targets for anticancer therapies.”
However, Vandrey cautions that the dose and duration of THC and other cannabinoids in such studies is unlikely to be representative of human use of cannabis and so unlikely to extend to current human conditions. “There is an estimated 200 million cannabis users globally, many of them frequent users. Cancer is not absent in that cohort of people.”
He added: “The goal right now for biochemical research of endocannabinoids is far beyond the scope of medical marijuana. The idea is that you want to get more targeted and specific compounds.”