Cannabis, cannabinoids and cancer – the evidence so far

Cannabis, cannabinoids and cancer – the evidence so far

Here is a solid article that I found on the subject. It’s long and I’m only sharing a excerpt. For the entire article please go to the source at; http://scienceblog.cancerresearchuk.org/2012/07/25/cannabis-cannabinoids-and-cancer-the-evidence-so-far/#can-treat

We’ve broken it down under a number of headings:

This post is long, but can be summarised by saying that at the moment there isn’t enough reliable evidence to prove that cannabinoids – whether natural or synthetic – can effectively treat cancer in patients, although research is ongoing around the world.

And in case you’ve seen articles on the internet about it – no, the US government hasn’t “just admitted that cannabis kills cancer”, as we explain in this comment[Updated KA 01/10/15]

Read on to get the full picture.

What are cannabinoids and how do they work?

Cannabinoids” is a blanket term covering a family of complex chemicals (both natural and man-made) that lock on to cannabinoid receptors – protein molecules on the surface of cells.

Humans have been using cannabis plants for medicinal and recreational purposes for thousands of years, but cannabinoids themselves were first purified from cannabis plants in the 1940s. The structure of the main active ingredient of cannabis plants – delta-9 tetrahydrocannabinol (THC) – was discovered in the 60s. It wasn’t until the late 1980s that researchers found the first cannabinoid receptor, followed shortly by the discovery that we create cannabinoid-like chemicals within our own bodies, known as endocannabinoids.

The CB1 and CB2 receptors

The CB1 and CB2 receptors.Image source

We have two main types of cannabinoid receptor, CB1 and CB2, which are found in different locations and do different things. CB1 is mostly found on cells in the nervous system, including certain areas of the brain and the ends of nerves throughout the body, while CB2 receptors are mostly found in cells from the immune system. Because of their location in the brain, it’s thought that CB1 receptors are responsible for the infamous ‘high’ (known as psychoactive effects) resulting from using cannabis.

There is also a third family of cannabinoid receptors, known as GPR, of which the main type is GPR55. Less is known about these receptors, but researchers are investigating them to see if they could lead to effective approaches for treating cancer. [Updated KA 14/08/14]

Over the past couple of decades scientists have found that endocannabinoids and cannabinoid receptors are involved in a vast array of functions in our bodies, including helping to control brain and nerve activity (including memory and pain), energy metabolism, heart function, the immune system and even reproduction. Because of this molecular multitasking, they’re implicated in a huge range of illnesses, from cancer to neurodegenerative diseases.

Can cannabinoids treat cancer?

There is no doubt that cannabinoids – both natural and synthetic – are interesting biological molecules. Hundreds of scientists around the world are investigating their potential in cancer and other diseases – as well as the harms they can cause – brought together under the blanket organisation The International Cannabinoid Research Society.

Researchers first looked at the anticancer properties of cannabinoids back in the 1970s, andmany hundreds of scientific papers looking at cannabinoids and cancer have been published since then. This Wellcome Witness seminar is also fascinating reading for aficionados of the history of medical cannabis, including the scientific, political and legal twists. [Updated KA 26/03/14] 

The scientific journal Nature has also published a supplement containing a number of review articles about various aspects of cannabis. It’s free to access and worth a read. [Updated KA 24/09/15]

But claims that this body of preclinical research is solid “proof” that cannabis or cannabinoids can cure cancer is highly misleading to patients and their families, and builds a false picture of the state of progress in this area. For example, we’ve taken a look at more than 30 scientific papers that are often claimed to “prove” that cannabis cures various types of cancer[Updated KA 21/07/14]

Let’s take a closer look at the evidence.

Lab research

Virtually all the scientific research investigating whether cannabinoids can treat cancer has been done using cancer cells grown in the lab or animal models. It’s important to be cautious when extrapolating these results up to real live patients, who tend to be a lot more complex than a Petri dish or a mouse.

A researcher with some cells in a Petri dish

Virtually all the research into cannabinoids and cancer so far has been done in the lab.

Through many detailed experiments, handily summarised in this recent article in the journal Nature Reviews Cancer, scientists have discovered that various cannabinoids (both natural and synthetic) have a wide range of effects in the lab, including:

  • Triggering cell death, through a mechanism called apoptosis
  • Stopping cells from dividing
  • Preventing new blood vessels from growing into tumours
  • Reducing the chances of cancer cells spreading through the body, by stopping cells from moving or invading neighbouring tissue
  • Speeding up the cell’s internal ‘waste disposal machine’ – a process known as autophagy – which can lead to cell death

All these effects are thought to be caused by cannabinoids locking onto the CB1 and CB2 cannabinoid receptors. It also looks like cannabinoids can exert effects on cancer cells that don’t involve cannabinoid receptors, although it isn’t yet clear exactly what’s going on there.

So far, the best results in the lab or animal models have come from using a combination of highly purified THC and cannabidiol (CBD), a cannabinoid found in cannabis plants that counteracts the psychoactive effects of THC. But researchers have also found positive results using synthetic cannabinoids, such as a molecule called JWH-133.

It’s not all good news though, as there’s also evidence that cannabinoids may also have undesirable effects on cancer.

For example, some researchers have found that although high doses of THC can kill cancer cells, they also harm crucial blood vessel cells, although this may help their anti-cancer effect by preventing blood vessels growing into a tumour. And under some circumstances, cannabinoids can actually encourage cancer cells to grow, or have different effects depending on the dosage and levels of cannabinoid receptors present on the cancer cells[Edited for clarity and to add reference – KA 27/07/12]

Others have discovered that activating CB2 receptors may actually interfere with the ability of the immune system to recognise and destroy tumour cells, although some scientists have found that certain synthetic cannabinoids may enhance immune defences against cancer.

Furthermore, cancer cells can develop resistance to cannabinoids and start growing again, although this can be got round by blocking a certain molecular pathway in the cells known as ALK.

Combining cannabinoids with other chemotherapy drugs may be a much more effective approach

And yet more research suggests that combining cannabinoids with other chemotherapy drugs may be a much more effective approach. This idea is supported by lab experiments combining cannabinoids with other drugs including gemcitabine andtemozolomide.

As might be expected, whenever research about cannabis or cannabinoids hits the news there is a lot of  interest on social media. But often it turns out that the hype doesn’t realistically reflect the work. For example, this study from researchers at the University of East Anglia was done using cancer cells grown in the lab or transplanted into mice, to try and understand why different levels of purified THC seem to have different effects on cancer cells – something that has been noticed from previous experiments on cannabinoids and cancer cells.

The researchers found that THC seems to work through two different receptor molecules coming together – CB2 and GPR55 – and that high doses slow cancer cells growth while low doses don’t. So they think that designing drugs that make sure the receptors come together in the right way to kill cancer cells could be a good way to harness the potential power of cannabinoids to treat cancer in a much more effective and targeted way.

But while it’s an interesting scientific paper and helps to shed light on the molecular “nuts and bolts” that underpin how some cancer cells may respond to cannabinoids, and could point to ways to make cannabinoid drugs more effective in the future, it certainly doesn’t tell us that cannabis can effectively treat cancer in patients at the moment.

There are long lists of scientific papers circulating on various internet sites claiming that they “prove” that “cannabis cures” all sorts of different types of cancer. Virtually all this work has been done in cells grown in the lab or in animal models of cancer, and certainly doesn’t “prove” that cannabis or cannabinoids can cure cancer in patients. We’ve looked at the actual evidence presented in around 30 of these papers in the extensive comment below this post.

 

 

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