Evidências crescentes mostram que os canabinóides na maconha retardam o crescimento do câncer, inibem a formação de novas células sanguíneas que alimentam o tumor e ajudam a controlar a dor, a fadiga, a náusea e outros efeitos colaterais.
Cristina Sanchez, jovem bióloga da Universidade Complutense de Madri, estudava o metabolismo celular quando percebeu algo peculiar. Ela havia triagem de células de câncer no cérebro porque elas crescem mais rápido que as linhas celulares normais e, portanto, são úteis para fins de pesquisa. Mas as células cancerosas morreram cada vez que foram expostas ao tetrahidrocanabinol (THC), o principal ingrediente psicoativo da maconha.
Em vez de obter informações sobre como as células funcionam, Sanchez descobriu as propriedades anticancerígenas do THC. Em 1998, ela relatou em uma revista de bioquímica européia que o THC “induz a apoptose [morte celular] em células de glioma C6”, uma forma agressiva de câncer no cérebro.
Estudos subseqüentes revisados por pares em vários países mostrariam que o THC e outros compostos derivados da maconha, conhecidos como “canabinóides” são eficazes não apenas para o manejo do sintoma de câncer (náusea, dor, perda de apetite, fadiga) Eles também conferem o efeito antitumoral direto .
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 catheter into the tumors of nine hospitalized patients with glioblastoma, who 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.
At the annual international conference of the International Cannabinoid Research Society, held this year in Freiburg, Germany, 300 scientists from around the world have discussed their latest findings, which are pointing to 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-tumor properties is increasingly recognized as the seminal advancement in cancer therapeutics.