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Cannabinoids for treating cancer?

Category: Science blog August 19, 2009 Kat Arney 33 comments

Cannabinoids could be useful for treating cancer but cannabis is not.

Researchers in Spain have published results in this week’s British Journal of Cancer showing that certain cannabinoids – molecules so-called because they were originally found in cannabis – could hold promise for treating prostate cancer.

So does this mean that smoking cannabis could treat the disease?

Certainly not.  In this paper the researchers were using purified man-made cannabinoids. And they were investigating how to harness the cancer-fighting powers of these chemicals without the mind-bending ones.

Cannabinoids and cancer

Certain cannabinoids, such as THC, the main active ingredient in cannabis, have well-documented mind-altering properties. But other cannabinoids have been known for some years to have biological effects elsewhere in the body. Of most interest to cancer researchers is the evidence showing that they can slow the growth and spread of cancer cells, or even kill them.

For example, Cancer Research UK is funding the work of Professor Chris Paraskeva in Bristol, who is investigating the anti-cancer properties of cannabinoids, as part of his research into the prevention and treatment of bowel cancer.

It needs to be stressed that these studies have all been done with purified cannabinoid chemicals – not cannabis itself, which contains cannabinoids along with a cocktail of other chemicals. There is no reliable evidence to suggest that smoking cannabis can treat cancer.

How do they work?

Cannabinoids affect cells’ behaviour by sticking to receptor molecules on their surface, and triggering a cascade of events within them. There are two main types of cannabinoid receptor, known as CB1 and CB2, although researchers think there may be others out there.

CB1 is mainly found on nerve cells in the brain – so its likely to be the important one when it comes to the mind-altering effects of cannabis.  CB2 is mainly found elsewhere in the body, and is the prime suspect for controlling the other effects of cannabinoids on the body.

In nerve cells, cannabinoids sticking to CB1 receptors  can lead to changes in the signalling pathways (causing the mind-altering and pain-relieving effects of cannabis). We also now know that cannabinoids can trigger other events within the cell, including halting growth or even kick-starting cell death.

The new research

In their recent paper, Professor Ines Diaz-Laviada and her team at the University of Alcala in Madrid studied the effects of two cannabinoids – the catchily named Methanandamide (MET) and JWH-015.  These are synthetic chemicals that don’t occur naturally in cannabis, although they are similar to compounds found in the plant.

The researchers tested the chemicals on different human prostate cancer cell lines grown in the lab, and found that they could slow down their growth and trigger cell death.  An interesting finding, but which of the two cannabinoid receptors is at work?

By using drugs that block either one receptor or the other,  or a genetic technique called RNA interference to ‘knock out’ CB1 or CB2 in turn, the scientists found that the anti-cancer effects of MET and JWH-015 were brought about by CB2.

This is an important finding, because it tells us that it should be possible to develop drugs that target CB2, which will have an anti-cancer effect, but which – crucially – won’t have the mind-altering effects of many cannabinoids.

As a last step, the researchers tested the effects of JWH-015 on mice that had been transplanted with human prostate cancer cells. The chemical helped to slow the growth of tumours, compared with a saltwater control. And blocking the CB2 receptors with a highly-specific drug called SR2 wiped out the effect of JWH-015, proving that it works through the CB2 pathway.

What does it mean for cancer treatment?

Although this work is still at an early stage, it provides a tantalising suggestion that drugs that activate the CB2 receptor could be useful for treating prostate cancer.  There’s still more research to be done before we know if MET or JWH-015 are suitable for testing in clinical trials involving patients – and no guarantee that these trials would be successful.

As part of this research, the scientists also investigated the cellular pathways that cannabinoids activate (or block) when they bind to CB2 receptors on prostate cancer cells. By understanding these cellular responses in greater detail, we might discover new targets for cancer treatment.

So can smoking cannabis treat cancer?

No.  This is a classic fallacy – assuming that because cannabinoids can kill cancer cells in the lab, then cannabis (containing cannabinoids) must be able to treat cancer. Ed has previously written extensively about this, with regard to red wine and cancer.

This research has been done using man-made chemicals that mimic the compounds found in cannabis, rather than unpurified marijuana.  Smoking cannabis, particularly when mixed with tobacco, is likely to increase rather that decrease cancer risk, although the evidence for this is mixed.   And, of course, cannabis is classified as an illegal drug in the UK.

Kat


Reference:

Olea-Herrero, N. et al. (2009). Inhibition of human tumour prostate PC-3 cell growth by cannabinoids R(+)-Methanandamide and JWH-015: Involvement of CB2 British Journal of Cancer DOI: 10.1038/sj.bjc.6605248

Cannabinoids for treating cancer?