By Bruce Mirken
For three and a half decades, lab and animal studies have reported that cannabinoids have relatively potent anti-cancer properties. While politics and bureaucracy continue to thwart human clinical trials — which, in a rational world, would have happened decades ago — interesting new results continue to come from laboratories around the world. The latest suggest that the combination of THC and cannabidiol (CBD) may be more potent against brain tumors than either drug alone.
The journal Molecular Cancer Therapeutics published a new study in January providing the first evidence that combination cannabinoid therapy is more potent against cancer than using THC or other cannabinoids as single agents.
Sean McAllister and colleagues from the California Pacific Medical Center Research Institute in San Francisco tested THC and CBD, and the two combined, on human glioblastoma brain cancer cells. In all three cell lines tested, both drugs showed antitumor activity, with CBD the more potent. In two of the three cell lines, the THC/CBD combination proved more potent, presumably adding the anti-cancer effects of the two drugs together and suggesting a synergistic action.
“Combinations, compared to individual drug treatments with specific cannabinoid- based compounds, may represent an improvement for the treatment of patients with glioblastoma and perhaps additional cancers,” McAllister says. “It is also possible that other constituents of cannabis sativa which are not structurally related to cannabinoids could improve antitumor activity when combined.”
One obvious way to combine multiple cannabinoids with other components of the cannabis plant is to simply use the plant itself — whether smoked, vaporized, or in some sort of extract. McAllister isn’t quite ready to jump on that bandwagon yet. “In regard to brain cancer, it is highly unlikely that effective concentrations of either Δ9-THC or CBD could be reached by smoking cannabis,” he says. “In regard to additional cancers, I feel defined formulations and dosing will be needed in order to effectively treat patients.”
McAllister says his team is moving toward “clinical trials in both breast and brain cancer, but it is a slow process.” His next step will be to try to replicate test-tube results in animals. “No agency in the US would allow me to move forward to clinical trials without some form of proof of concept data in a relevant preclinical in vivo model.” That may well be an accurate assessment of the regulatory environment in which researchers operate, but it’s frustrating to cannabis activists. They note that test-tube data on the antitumor action of THC goes back to 1975, and argue that the safety of cannabinoids is clearly established. The politicization of science regarding cannabis, they argue, is the reason that only one human study of cannabinoids for cancer treatment has been published so far — a tiny pilot study which found THC infusions into terminal brain tumors to be safe. The study was not designed to confirm whether the treatment worked.
* Mirken is a writer and media consultant in San Francisco. He served as director of communications for the Marijuana Policy Project from 2001 to 2009. Mol. Cancer Ther. abstract available at mct.aacrjournals.org/content/9/1/180.abstract).