Cristina
Sanchez, a young biologist at Complutense University in Madrid, was
studying cell metabolism when she noticed something peculiar. She had
been screening brain cancer cells because they grow faster than normal cell lines and thus are useful for research purposes. But the cancer cells died each time they were exposed to tetrahydrocannabinol (THC), the principal psychoactive ingredient of marijuana.
Instead of gaining insight into how cells function, Sanchez had stumbled upon the anti-cancer properties of THC. In 1998, she reported
in a European biochemistry journal that THC “induces apoptosis [cell
death] in C6 glioma cells,” an aggressive form of brain cancer.
Subsequent
peer-reviewed studies in several countries would show that THC and
other marijuana-derived compounds, known as “cannabinoids,” are
effective not only for cancer-symptom management (nausea, pain, loss of
appetite, fatigue), they also confer a direct antitumoral effect.
A
team of Spanish scientists led by Manuel Guzman conducted the first
clinical trial assessing the antitumoral action of THC on human beings.
Guzman administered pure THC via a catheter into the tumors of nine
hospitalized patients with glioblastoma, who had failed to respond to
standard brain-cancer therapies. The results were published in 2006 in
the British Journal of Pharmacology: THC treatment was associated with significantly reduced tumor cell proliferation in every test subject.
Around the same time, Harvard University scientists reported
that THC slows tumor growth in common lung cancer and “significantly
reduces the ability of the cancer to spread.” What’s more, like a
heat-seeking missile, THC selectively targets and destroys tumor cells
while leaving healthy cells unscathed. Conventional chemotherapy drugs,
by contrast, are highly toxic; they indiscriminately damage the brain
and body.
There is mounting evidence, according to a report in Mini-Reviews in Medicinal Chemistry, that cannabinoids “represent a new class of anticancer drugs
that retard cancer growth, inhibit angiogenesis [the formation of new
blood cells that feed a tumor] and the metastatic spreading of cancer
cells.”
Dr.
Sean McAllister, a scientist at the Pacific Medical Center in San
Francisco, has been studying cannabinoid compounds for 10 years in a
quest to develop new therapeutic interventions for various cancers.
Backed by grants from the National Institute of Health (and with a
license from the DEA), McAllister discovered
that cannabidiol (CBD), a nonpsychoactive component of the marijuana
plant, is a potent inhibitor of breast cancer cell proliferation,
metastasis, and tumor growth.
In 2007, McAllister published a detailed account
of how cannabidiol kills breast cancer cells and destroys malignant
tumors by switching off expression of the ID-1 gene, a protein that
appears to play a major role as a cancer cell conductor.
The
ID-1 gene is active during human embryonic development, after which it
turns off and stays off. But in breast cancer and several other types of
metastatic cancer, the ID-1 gene becomes active again, causing
malignant cells to invade and metastasize. “Dozens of aggressive cancers
express this gene,” explains McAllister. He postulates that CBD, by
virtue of its ability to silence ID-1 expression, could be a
breakthrough anti-cancer medication.
“Cannabidiol
offers hope of a non-toxic therapy that could treat aggressive forms of
cancer without any of the painful side effects of chemotherapy,” says
McAllister, who is seeking support to conduct clinical trials with the marijuana compound on breast cancer patients.
McAllister’s
lab also is analyzing how CBD works in combination with first-line
chemotherapy agents. His research shows that cannabidiol, a potent
antitumoral compound in its own right, acts synergistically with various
anti-cancer pharmaceuticals, enhancing their impact while cutting the
toxic dosage necessary for maximum effect.
“Cannabidiol offers hope of a non-toxic therapy that could treat aggressive forms of cancer without any of the painful side effects of chemotherapy.
Investigators
at St. George’s University in London observed a similar pattern with
THC, which magnified the effectiveness of conventional antileukemia
therapies in preclinical studies. THC and cannabidiol both induce
apoptosis in leukemic cell lines.
At
the annual summer conference of the International Cannabinoid Research
Society, held this year in Freiburg, Germany, 300 scientists from around
the world discussed their latest findings, which are pointing the way
toward novel treatment strategies for cancer and other degenerative
diseases. Italian investigators described CBD as “the most efficacious
inducer of apoptosis” in prostate cancer. Ditto for cannabidiol and
colon cancer, according to British researchers at Lancaster University.
Within
the medical science community, the discovery that cannabinoids have
anti-tumoral properties is increasingly recognized as a seminal
advancement in cancer therapeutics.
