Another Brick in the Wall: Turning cancer’s strengths against it

A mutation that allows cells to grow out of control could also provide a new way to target and destroy cancer cells. This potential Achilles’ heel comes from a mutation in a gene called PTEN, which is found in a wide range of cancers.

PTEN is one of many tumour suppressor genes that we have to prevent our cells from growing out of control. If the PTEN gene stops working because of a mutation, it can cause tumours to develop – indeed many tumours have a mutated form of PTEN. However when a door closes, a window opens: the PTEN mutation helps the tumour to grow, but it could also mark it out as a target.

Researchers from the Institute of Cancer Research, London, found that switching off another gene known as NLK killed tumour cells that had the PTEN mutation. This makes NLK a good target for drug developers to create a new cancer treatment.

The difficult thing about cancer is that it is made of us – it is our own cells that have mutated and grow wildly out of control. That means it is unlikely there will ever be a quick fix. Antibiotics work efficiently because bacteria are so different to us that we can develop drugs that target their weaknesses yet barely affect our own cells. But how do you kill something that is the same as you? Current treatments for cancer cause a lot of side-effects in patients because as they try to kill the cancer they also do damage everything else in the body. This is why finding ways to target cancer specifically is so important.

There are several proteins which we cannot live without, and our cells die if the genes responsible for producing those proteins are mutated or switched off. Targeting these proteins and genes are rarely going to be useful for treatments, as they will kill the patient about as quickly as they kill the cancer. So Alan Ashworth and colleagues set out to find proteins that are not essential in healthy cells, but cells with the PTEN mutation cannot live without. This would pave the way for designing drugs that target the tumour and leave healthy cells alone.

The researchers took samples of tumour cells with and without the mutation, and switched off genes for important proteins that are used for regulating lots of processes in the cell. To do this they used small molecules of RNA (DNA’s less famous cousin) which interfere with the processes of specific genes. This is why these molecules are known as small interfering RNA (or siRNA). They block the chain of events that allow a gene to produce a protein, effectively switching it off. By switching off 779 genes individually, they could look for ones where cells with the PTEN mutation died and cells without the mutation survived.

This is how the researchers discovered the powerful effect of switching off the NLK gene. They are not certain how this works but it appears to protect a protein called FOXO1 that can act as a backup tumour suppressor and cause the cancer cell to die. When PTEN is mutated, the FOXO1 protein becomes vulnerable to a process called phosphorylation, which means it is ejected from the cell nucleus and destroyed. NLK is one of the proteins that phosphorylates FOXO1 and so by switching off the NLK gene, FOXO1 is able to do its job.

The phosphate group, shown at the top, consists of one phosphorus atom (in orange) and three oxygen atoms (in red). This can be added to certain amino acids to control the behaviour of the whole protein

Phosphorylation is the process of adding a phosphate group, shown at the top, to certain amino acids to control the behaviour of the whole protein. This group consists of one phosphorus atom (in orange) and three oxygen atoms (in red) and has a strong negative charge.

This is just the start of a long journey from the lab to (potentially) the hospital. The researchers have shown that targeting NLK is more likely to kill mutated cells than normal cells, but that does not mean it is safe. NLK still has a role to play in healthy cells and preventing it from working is likely to have side-effects, but it could be worthwhile if this approach can kill tumours. The next stage is to develop a drug to stop the NLK protein from working, so that it can be tested further in cells and in living organisms.

Promising leads against cancer appear often, yet very few ever make it as treatments. One big hurdle is making it through clinical trials; the new drug has to be better than currently available treatments. Targeting NLK would only work against cancers with the PTEN mutation, but now we can use the mutation as a marker to find out which patients that applies to. We are now in the age of personalised medicine, where we can have 100 different treatments for 100 different people with 100 different cancers. Gradually, we are finding ways to attack cancer in whichever form it appears and build up our range of treatments. The weaknesses that we find are not going to cure all cancers, but each one provides another brick in the wall.

This article was originally written for the Access to Understanding competition run by Europe PubMed Central

Finding a needle in a haystack: How RecA slides in to the rescue

RecA is well-practiced at finding a needle in a haystack – its job is to track down the right sequence of DNA out of 3,000,000,000 letters. But until now, it was not clear how it did this: does it jump from one bit of DNA to the next or does it slide along?

Damage to DNA is one of the biggest threats that we face – it is one the main driving factors in developing cancer. However, evolution has provided us with many tools to prevent and fix any problems. One advantage of DNA being a double helix is that if only one strand of the helix breaks, the DNA is still held in place by the second and so it can be easily fixed. However, if both strands break it becomes far more difficult to piece the DNA back together.

The single strand break (left) can be easily patched up - the DNA helix is still held in one piece. However, the double strand break (right) means that the sequence is split into two and it's not possible to stitch them back together.

The single strand break (left) can be easily patched up – the DNA helix is still held in one piece. However, the double strand break (right) means that the sequence is split into two and it’s not possible to stitch them back together.

In a double-strand break, the broken strands separate from each other because they can’t be put back together. To be repaired, a broken strand needs to line up with an undamaged molecule of DNA and use it as a template. However, finding the right sequence to align with is not easy when there are 3 billion nucleotides to search through.

These broken strands rely on a protein known as RecA to act as matchmaker and find the perfect partner sequence of DNA. Several molecules of RecA attach themselves to the strand, straightening it out and forming what is called the pre-synaptic filament. Taekjip Ha from the University of Illinois wanted to find out if this filament is able to slide along the DNA or if it has to rely on jumping from place to place. To test this they used a technique known as FRET (fluorescence resonance energy transfer), which can tell you the distance between two fluorescent tags that are attached to different molecules. One tag was attached to the filament and the other was attached to a short stretch of DNA that would not match with the filament. The researchers were able to see the distance changing very quickly, showing that the RecA-DNA filament was sliding back and forth along the short length of DNA, unsuccessfully trying to find a match.

Several copies of RecA bind to a stretch of single-stranded DNA

Several copies of RecA bind to a stretch of single-stranded DNA (shown in black) to help it find a match

The ‘bait’ DNA was then changed so that it had two patches that matched the sequence of the filament. By attaching fluorescent tags to each patch, the filament could be seen sticking to one of the two sections, and then sliding along and binding to the other. From the speed of the sliding, the researchers estimated that RecA could help to slide along up to 300 base pairs of DNA before reattaching somewhere else. This could help speed up the search for the matching sequence by over 200-fold, making it a much more efficient technique than randomly hopping from sequence to sequence.

This kind of sliding movement is the first that has been seen in a protein-DNA complex and improves our understanding of this highly important process. Fortunately, one lab has made a (low-budget) video to show how RecA works. Enjoy…

The hidden potential of MDMA and psilocybin

Earlier this week I went to a talk by Professor David Nutt entitled ‘Time to Grow Up?’ where he spoke about the damage caused by the UK government’s approach towards drugs. David Nutt has become quite well known in the UK after he was fired in 2009 by the Home Secretary as the chairman of the Advisory Council on the Misuse of Drugs for clashing with government policy. Most notably, he published an editorial in the Journal of Psychopharmacology in which he said that the dangers from ecstasy were comparable to that of horse-riding.

I was already well aware of his views on the relative risks of drugs (alcohol causes far more damage overall than anything else) and his views on the government’s approach to banning new drugs (such as mephedrone, which potentially saved more lives than it took). He laid out the evidence very clearly and presented it in a very engaging manner – I would recommend checking out his blog if you’re interested.

When adding together harm to self and harm to others, alcohol tops the list of most harmful drugs. Image credit: The Economist

When adding together harm to self and harm to others, alcohol tops the list of most harmful drugs. Image credit: The Economist

However, one aspect really caught my attention – the study of illegal drugs as therapeutics or medicine. The case for cannabis is well-known: its potency as a pain reliever has led to it now being prescribed by doctors in some countries. But what about MDMA (ecstasy) used to treat post-traumatic stress disorder, or psilocybin (the hallucinogen found in magic mushrooms) used to treat depression or obsessive-compulsive disorder? These drugs have been suggested as potential treatments but there are so few studies conducted that we can’t be sure.

Science on drugs

Cannabis, MDMA and psilocybin are all considered have no therapeutic value by the UK government and so are listed as Schedule 1 drugs. This means that not only are researchers required to get a licence from the Home Office, but they also have to find a supplier who also has the correct licence. These licences cost thousands of pounds, take about a year to be approved and then result in police inspections on a regular basis. Not only that, many research funding bodies are reluctant to sponsor studies on illegal drugs or refuse to fund it altogether.

It is easy to see why there hasn’t been much research done.

Nonetheless, David Nutt made a big splash two months ago when he televised a study on the neurological effects of MDMA. In Drugs Live: The Ecstasy Trial, 25 volunteers were studied by fMRI after taking either the drug or a placebo in a double-blind trial – making it the largest ever brain-imaging study of MDMA conducted. In time, the full results will be published in peer-reviewed journals and they are actually expecting to publish 5-6 papers from this single study.

The researchers used pure MDMA, avoiding the contaminants usually found in ecstasy

The researchers used pure MDMA, avoiding the contaminants usually found in ecstasy pills

This research was not just to look at the effects of taking an illegal drug – understanding the neurological mechanism of MDMA could potentially help millions. Back in 2010, a US study of patients with post-traumatic stress disorder showed that MDMA, combined with psychotherapy, cured 10 out of the 12 people given the drug in a randomized-control trial. These were people who had not responded to government-approved drugs or psychotherapy alone, and two months after the study they were free of symptoms. MDMA appears to dampen negative emotions, which allows a patient to revisit their traumatic memories without the associated emotional pain. This can be the starting point for the patient to come to terms with their trauma and deal it with through therapy. These results, although from a very small sample size, are near miraculous and yet it took over ten years for the researchers to get approval.

The magic of mushrooms

David Nutt has also previously studied the effects of psilocybin on the brain and the results were surprising. Psilocybin is a hallucinogen, causing colours, sounds and memories to appear much more vivid than usual. With this kind of effect it was expected that psilocybin would activate certain areas of brain, which would be seen as bright patches on an fMRI scan. However, they actually saw dark blue patches of decreased brain activity, but only in a specific area of the brain that acts as a central hub for connections.

Psilocybin is the hallucinogen in magic mushrooms. Like MDMA is a class A drug in the UK

Psilocybin is the hallucinogen in magic mushrooms. Like MDMA, it is a class A drug in the UK but could it used to treat depression?

Decreasing brain activity doesn’t sound like a good thing, but one of these connector hubs, known as the posterior cingulate cortex, is over-active in people with depression. This area is responsible for several roles but can cause anxiety, particularly when it is over-active. When David Nutt and his colleagues asked people on psilocybin to think of a happy memory, they found that the volunteers could remember happy memories more vividly – almost as if they were reliving them. These test subjects were also much happier after recalling positive memories. Dampening the activity in the connector hubs and getting a boost from recalling happier times could be enough to get people out of the vicious circle of depression. Fortunately, the Medical Research Council has since funded David Nutt to conduct further studies into the use of psilocybin as a treatment for depression.

Post-traumatic stress disorder and depression are two of the biggest mental health issues that we face and current treatments are plainly inadequate. It seems ridiculous that the government’s policies on drugs prevent scientific studies aiming to reap benefits from them. These treatments show good potential and yet little is being done to take advantage of them. This situation is nothing new – after being fêted as a treatment for alcoholism in the 1960s, LSD has largely been ignored ever since it was declared illegal. Even though, according to David Nutt, it is probably as good at treating alcoholism as anything we’ve got now, researchers are limited to reanalysing studies completed 50 years ago.

What treatments are out there, undiscovered because of governments’ heavy-handed approaches towards recreational drugs? I’m just glad that there are researchers like David Nutt who are willing to make the effort, and take the flak, in order to find out.

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Red Alert: How red hair can cause skin cancer without sun exposure

I’m not usually that interested in research completely based on mouse studies, but any paper that starts with ‘People with pale skin, red hair, freckles and an inability to tan…‘ is always going to get my attention.

People like me, with the ‘red hair/fair skin’ phenotype, are pretty bad at dealing with the sun. Not only do we get sunburnt much more easily, but we have the highest risk of developing melanoma, the deadliest form of skin cancer. It is (hopefully) very well known that exposure to UV light increases the risk of melanoma. However, unlike other other skin cancers, melanoma also appears to develop independently of UV light, although this has been poorly studied to date.

The sun can be your worst enemy when you’re ginger. (Photo credit: coltera)

In a letter published in Nature this week, researchers wanted to see if hair-colour pigments affect this UV-independent pathway for melanoma. To do this, they engineered mice to mimic human complexions by mutating a gene known as MC1R. This is responsible for producing the pigment eumelanin which is dark coloured and results in dark hair. Most people with red hair have an inactive form of MC1R, which instead leads to the red-coloured pheomelanin being produced.

The researchers compared mice with black hair (active MC1R), red hair (inactivated MC1R) and albinism (produces neither pigment). In addition, all the mice had a specific mutation that causes benign moles, but leaves them predisposed to developing melanoma. The mice were kept away from sources of UV light and their health was charted over time.

The differences are startling. In under a year 50% of the red-haired mice had died compared to only 20% of the black-haired or albino mice. This, and further tests, seem to suggest that producing pheomelanin is actually harmful, increasing the rate of melanoma when there is no UV light.

Pheomelanin is responsible for the colour of red hair, but could also cause cancer

It was also apparent that the DNA of the red-haired mice had suffered twice as much oxidative damage as the albino mice. It is known that UV light causes oxidative DNA damage and that this increases the chances of mutations occurring. In previous studies looking at UV radiation, it was thought that eumelanin protects against this damage. However, the mice in this study show that pheomelanin is actually harmful and eumelanin has little effect under these conditions. It’s still not clear how this damage was created in the absence of UV light or why production of pheomelanin made it worse.

The authors of the paper make it very clear that UV radiation is still an important factor in the development of skin cancer, but suggest that this UV-independent pathway should be considered in the future for strategies to prevent melanoma, especially for gingers.

Redheads have long understood that we lack the natural sun protection that others enjoy, but it is still quite a shock to think that our distinctive colouring is actively causing us damage. However, this study was done under very artificial conditions, and the rates that the researchers saw are far higher than we can plainly observe. After all, we don’t see half of redheads dying every year. But whatever your hair colour, melanoma is still very deadly – one American dies from melanoma every hour. So make sure you don’t forget your sunscreen.

Keeping up with the Red Queen: Co-evolution of hosts and pathogens

While most micro-organisms are harmless to humans, and in some cases even beneficial, there are those that are not welcome. These are known as pathogens, from the Greek for ‘producer of suffering’. For us, pathogens can be very damaging and even deadly, and so we have evolved ways to resist their attacks. For the pathogen, infecting a human might be the only chance to survive and reproduce. The potential reward is so great that pathogens will develop ways around our defences. This becomes an ongoing battle and means that neither side can stop evolving in case the opponent becomes too dominant; in the words of the Red Queen from Lewis Carroll’s Through the Looking-Glass: “It takes all the running you can do, to keep in the same place.” This interplay between host and pathogen is known as co-evolution and can lead to very different strategies being used on both sides.

The Red Queen (not to be confused with the Queen of Hearts) and Alice

All-out war

Aggressive strategies, like that used by the malarial parasite Plasmodium falciparum, can drive co-evolution rapidly. Once it has infected a person, the pathogen replicates as quickly as possible. This is risky because it seriously affects the infected human and can even cause death, and if the host dies, the pathogen die with it. This strategy works because P. falciparum spreads between humans via mosquitoes. High concentration of the parasite in the bloodstream is the best way to ensure that they are taken up by a mosquito and passed on to a new host. However, the severity of malaria and the high likelihood of death means there is a strong evolutionary pressure for humans to develop resistance, even if that comes at a price.

Indeed resistance has developed, via a specific mutation in the gene coding for the blood protein haemoglobin. Everyone has two copies of the haemoglobin gene – one from each parent. A mutation in both copies of the gene provides malarial resistance but causes sickle cell anaemia. This causes blood flow to be restricted and eventually leads to premature death, which obviously outweigh any benefits. Fortunately, having just one copy of the mutation maintains some resistance and avoids sickle cell anaemia. However it can never be guaranteed that a child will inherit exactly one copy of the mutated gene, so there is always a risk of children being born with sickle cell anaemia. This means that the level of the mutation present in the population is determined by the balance between the risk of malaria and the risk of sickle cell anaemia. There is little risk of malaria in the UK and so the mutation is rare. In sub-Saharan Africa, where malaria causes a quarter of all deaths in children under five, the balance shifts. The mutated gene is present in up to 40% of the population, meaning that approximately 2% of children are born with sickle cell anaemia.

When a specific glutamic acid residue (highlighted in magenta on the far right) is mutated to a valine it causes haemoglobin molecules to aggregate, which distorts the shape of red blood cells

Under the radar

Evolving against every new infectious disease that we encounter is not possible. Humans, with our relatively slow reproductive rate, take a long time to develop new, beneficial mutations. This is why many infections, such as the common cold caused by the rhinovirus, have evolved to avoid affecting humans severely. Catching a cold will not affect the ability to reproduce, which is the main driving force behind evolution. Without this evolutionary pressure, humans do not appear to have developed mutations to specifically deal with the rhinovirus. Keeping the host able and mobile also has the benefit of boosting the spread of the disease. If the host feels well enough to leave bed and go to work, then the rhinovirus is presented with a wide range of potential hosts with every sneeze.

The immune system provides a flexible defence against a huge variety of diseases, lessening the need to evolve in response to new infections. The system learns to recognise a part of the pathogen known as the antigen, which allows the pathogen to be targeted. This means that a strain of rhinovirus, or any pathogen, that has mutated its antigen can evade detection by the immune system for longer. Unfortunately for us, this happens very often as the rhinovirus mutates very easily and reproduces incredibly quickly, allowing a huge number of mutations to accumulate within a population rapidly.

Gaining ground

Today the risk of dying from an infectious disease is lower than at any point in human history. After thousands of years locked in an impasse with diseases, we have finally developed an advantage through modern medicine. Although it seemed that we have surpassed the power of evolution, pathogens are still working towards breaking through our defences. Whether it is a new strain of flu or an antibiotic-resistant superbug, if we want to maintain our advantage it will take all the running we can do.

Note: this post was updated 16:53 GMT 21/10/2012 to remove any suggestions that Plasmodium falciparum is a bacterium

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