Cannabis: Medicine or Malady?

Brain tumours, one of the most aggressive forms of cancer, are currently treated by surgery but often the whole tumour is not removed and grows back, eventually killing the cancer patient. To prevent tumours growing from the site of earlier cancer surgery, all tumour cells need to be killed off and starved of nutrients.

Researchers have found that the cannabis component THC can do just that. Importantly, they found that the drug specifically targeted cancer cells and hardly affected healthy cells outside the tumour.

Dr Manuel Guzmán, who led the study, said: “Cannabinoids seem to be selective anti-tumoral compounds as they can kill tumor cells without significantly affecting the viability of their non-transformed counterparts.”

The study, published in Cancer Research in 2004, involved analysing removed cancerous tissue from brain tumour patients.

How does THC kill cancer cells? Tumorous cells thrive on essential nutrients delivered via the blood. New blood vessels are formed through the process of angiogenesis to deliver blood and nutrients to the cancer. The signalling protein VEGF, Vascular Endothelial Growth Factor, is produced by the body to allow this new vessel-sprouting process to occur. THC inhibits the expression of genes needed to produce VEGF, thereby starving the tumour of nutrients needed for growth.

Guzmán said: “Blockade of the VEGF pathway constitutes one of the most promising anti-tumoral approaches currently available. These findings provide a novel pharmacological target for cannabinoid-based therapies.”

THC also induces apoptosis – the process of programmed cell death – in cancerous cells.

Guzmán concluded: “The fair safety profile of THC, together with its possible growth-inhibiting action on tumour cells, may set the basis for future trials aimed at evaluating the potential antitumoral activity of cannabinoids.”

Substances responsible for lowering blood pressure also trigger the release of endocannabinoids. In 2001 the researchers Langneux and Lomontagne suggested that excess endocannabinoids could enhance this blood pressure lowering effect. They injected a drug to inhibit a cannabinoid receptor and reported a loss of the blood pressure lowering effect. This suggests that cannabinoids could be used to treat high blood pressure and heart disease.

A further study by Joyeux and colleagues in 2002 showed that cannabinoids could lower the severity of heart attacks in rodents.

Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation (BHF) said: "There is increasing experimental evidence that cannabinoid drugs may be useful in limiting damage to diseased hearts or blood vessels, though much more work needs to be done to understand how effective these drugs may be compared to current cardiovascular drugs. We also need to look at what their side effects are likely to be before clinical trials could take place.”

In addition to possibly treating depression, obesity and nicotine addiction, cannabinoids can also be used in allergy creams. Although the way in which this works is not known, Andreas Zimmer and colleagues in 2007 found the expression of genes involved in the inflammatory allergic response were changed as a result of the application of a cannabis-based cream.

Cannabinoids are a promising group of drugs that have been implicated in various fields of clinical research. However, legal issues surrounding the drug have scared off researchers from working in this field, particularly in the United States., Cannabinoid research joins stem cell research and xenotransplantation – the transplantation of an organ from one species to another – on the list of potentially life-saving technologies that have been held back for legal reasons.

The Multidisciplinary Association for Psychedelic Studies (MAPS) hold a different view from many of these researchers. They are an independent US-based research funding body and aim to “initiate and fund a serious drug development research program aimed at proving to the satisfaction of the FDA (the US Food and Drug Administration) that marijuana is safe and efficacious for specific medical uses and should become a legal, FDA-approved prescription medicine.”

They claim that “The National Institute on Drug Abuse (NIDA) has a monopoly on the supply of marijuana that can be used in research, provides low-potency material, and only makes it available to projects it approves. MAPS needs its own independent source of supply since NIDA's arbitrary and lengthy review process for providing marijuana essential to research can derail any drug development plan.”

Is this the way forward? Should more money be invested in cannabinoid research? Perhaps. But this should be done with caution. As in the case of MAPS, a political motive can sometimes override scientific interests. This exciting field in clinical research is definitely one to keep an eye on.

For more information

National Institute of Health (USA) - Workshop on the Medical Utility of Marijuana (1997)
http://www.nih.gov/news/medmarijuana/MedicalMarijuana.htm

UK House of Lords - Science and Technology Ninth Report 1998 - Cannabis, The Scientific and Medical Evidence
http://www.parliament.the-stationery-office.co.uk/pa/ld199798/ldselect/ldsctech/151/15109.htm