Venoms and Toxins - Natures Arsenal

Lung cancer has a very poor survival rate, which is often due to the fact that the disease isn't diagnosed until it has spread around the body, making treatment difficult. Now a team of researchers in the US have found that faults in a gene called LKB1 may be responsible for causing lung cancer cells to spread aggressively.

In experiments published in the journal Nature this week, the scientists took some mice carrying faults in genes that are known to increase the development of cancers, and bred them with mice carrying faults in LKB1. These double-fault mice developed highly aggressive lung tumours that quickly spread.

In healthy cells, LKB1 acts to protect us from cancer - it's a type of gene known as a tumour suppressor. In order for cancer to develop, cells need to pick up faults in several different genes - a bit like mixing a cocktail of genetic mistakes. But it seems that faults in LKB1 act like the "vodka in the cocktail", causing the cancer to spread.

Although it's still very early days, the researchers hope that their research may help to shed light on what makes some lung cancers grow so aggressively. The new mice they have created are a good model for human lung cancer, and will help to accelerate research into urgently-needed cures.

It is also possible that LKB1 may become a future drug target, if scientists can find some way to reactivate its function. And it could also be used as a prognostic tool - to predict how a person's cancer might progress, or how best to treat them. The team is now carrying out experiments to test this idea in cancer patients. But work like this needs to go hand in hand with better ways to pick up lung cancer at an earlier stage.

Of course, we don't need to tell you that the best way to avoid lung cancer is to quit smoking - a habit that causes more that 9 out of ten cases of lung cancer in the UK.

The main thing that smokers are addicted to is nicotine, which is a drug that your brain starts to crave after you've been exposed to it. There's more than 4000 chemicals in cigarettes, and they come from a variety of sources. Some of them are in the tobacco plant itself, absorbed from the air by the plants including chemicals such as polonium. Some chemicals are produced when the tobacco is processed, some are added in when cigarettes are made. The most dangerous chemicals in tobacco are actually created when you burn a cigarette; the chemicals of burning are produced by the act of lighting a cigarette and inhaling something that is burning.There are a few extra chemicals added during the process of making a cigarette, and so smoking straight tobacco would lack these, but the important chemicals are created by the simple act of burning the tobacco.A lot more information is available from Cancer Research UK's smoke is poison campaign, www.smokeispoison.com.

Jim Olsen and his team from the Fred Hutchinson Cancer Research Centre in Seattle have found a way to use scorpion venom to make a 'paint' which shows up cancer cells.  This means that surgeons can be more certain that they are taking out an entire tumour, which can limit the damage to healthy tissue. Chris Smith heard how it works...

Jim -   We took a peptide which comes from scorpion venom, called chlorotoxin, and we linked it to a molecule called Cy5.5 which is a little molecular beacon; it lights up.  The scorpion toxin binds to cancer cells, but not to normal cells, so our idea was to inject this into the veins of a mouse that has cancer and see whether or not the chlorotoxin could carry the molecular beacon to the cancer cells and make them glow.  Indeed, when we inject mice that have tumours and wait about a day or two, we can put the mice under a camera that picks up near-infrared light, the type emitted by the molecular beacon, and it's really easy to see the tumour compared to the normal brain around it.

Kat -   So you can see the tumour even inside a mouse?

Jim -   The light waves that are emitted by the molecule that we made have a very short path length.  This is developed mainly for surgeons who want to see whether they got all of the cancer while they were doing their operation.  So the point is that the whole tumour when they open up the cavity will be glowing, and then as they take more and more of it out, the pieces that are still glowing are where the cancer is left behind.

Kat -   And how sensitive is this technique? Part of the problem with cancer is it only takes a few cells to start the cancer growing again.

Jim -   Well that was one of the big surprises of our study; we initially started working on this for brain cancer, and when we tested it on other models such as prostate cancer and colon cancer we found that it was sensitive for picking up these kinds of cancer as well. In one case we had an instance where it picked up a cancer as small as 2000 cells, and that's 5000 times more sensitive than an MRI.

Kat -   That's really tiny.  Tell us a bit more about this toxin, this chlorotoxin, how does it recognise cancer cells and not target healthy cells?

Jim -   We believe that it's binding to a component of the matrix metaloproteinase-2 complex, and in easy to understand terms the matrix metaloproteinase-2 complex is what cancer cells use to eat away normal tissue to make space for the cancer to grow.  For that reason this complex is expressed in cancer cells but not in normal tissue.

Kat -   And do you think that this paint might also be useful for spotting cancers that have spread throughout the body, or is the wavelength not strong enough to get it out of the body again?

Jim -   Well, in some cases yes.  For example, if a person has breast, prostate or testicular cancer and the surgeons have the cavity open, and they're interested in seeing whether the lymph nodes are involved, the wavelength is long enough that they would be able to see whether the lymph nodes are involved.  You really couldn't do that in a scan, and be able to see things that deep in the body.  We're really talking about superficial cancers or cancers that are surgically open.

Kat -   So what's the next step for this?  Are you going to start testing in patients soon?

Jim -   Yeah, there are two directions that we're going.  One is to test it in patients and we're working with a company in Cambridge, Massachusetts, to advance this as quickly as possible to human clinical trials.  Because this company has already brought cholortoxin into humans there's a lot of safety data already available and we think we could be in clinical trials within 18-24 months.  The other direction we're going with this is to see whether it could be used as a cancer screening method, so for example people who are at risk for skin cancer, would they be able to take a dose of this tracer and then go to their dermatologist and have a scan to see which moles or which areas of their skin should be biopsied.  So we're thinking about that for the more superficial cancers, like skin cancer or colon cancer.

Chris -   Jim, just to finish off, are you confident that this scorpion venom based marker will bind to all kinds of cancer cells? One of the things we've learned about cancer is that they're a very heterogeneous cell population, there are stem cells in there, there are mature cancer cells.  Will it bind to everything, or are we going to miss some cells?

Jim -   So far we've tested it in six different kinds of cancer, and it has lit up all of those tumours.  Within an individual tumour, it looks as though in certain types of cancer it's lighting up almost every cell, and in others there are some cells that are lighting up and some that are not.  But they are so intermixed that at the level of surgery the ones that are not lighting up are entangled with the ones that are lighting up, so you can take that whole group of cells.

Bruce -   What I've been doing is exploring the potential of animals that live in the great barrier reef for production of novel painkillers.

Chris - Specifically what are you been looking at?

Bruce - Well we've been looking at venomous cone shells. These creatures developed just after the death of the dinosaurs and in the 500 million years since, they've developed a very sophisticated venom apparatus. They go out each night and they hunt down their prey. They do this by injecting them with a cocktail of very small molecules called peptides that make up the venom. One of those peptides is of particular importance to us, because its a very potent analgesic and we hope the develop this for the treatment of some very painful conditions, like neuropathic pain. That's the kind of pain you would have if you were to lose a limb-you may have heard of phantom limb syndrome? Where people have had an accident, lost a a limb, can't get to sleep at night because of the pain in their so-called phantom limb, which is very real to them. Another really painful condition, which happens mainly in older people, is shingles. Once again a very painful condition and a large unmet need with existing medicines not being very good at curing the pain.

Chris -   How does the cone shell actually use this? Why does it actually want to use a painkiller to kill something?

Bruce -   Well I think it perhaps doesn't need the painkiller, but it uses something like 200 other components in the venom. It uses these components to put its animal to sleep. That means the animal is not going to thrash around and they can eat it quite quietly without it feeling apprehensive, and maybe thats where the painkiller come in.

Chris -   What do these shells actually look like then and how do they catch things?

Bruce -   Well they're very pretty. There are over 500 different varieties of cone shell and they've been collectors pieces for hundreds of years. In fact, everybody in the 1600's who had a curiosity cabinet where they kept biological specimens wanted a cone shell. They were highly prized because they came mainly from the Indo-Pacific region and that meant they were quite expensive to buy. In fact, some of these cone shells sold at auction in the Hague for more than a Vermeer painting. These day, you can still pay up to $1000 for a very rare cone shell, but mostly you can get a very good collection, such as the one I have behind me, for 5 to 10 dollars a piece.

Chris -   But how do they actually catch stuff? How do they use this amazing example of overkill, these toxins, to catch things?

Bruce -   It's amazing that they need this overkill. I mean one of the toxins would probably serve the purpose well. I think the variety of toxins is there because their prey changes and they have to adapt their venom to the prey. So they make thus suite of toxins in the hope that one of them will kill their prey. Cone shells are marine snails, so like a garden snail, they're pretty slow moving and they need some benefits. What they do is they lay and wait, then put this long tongue out of their mouth, called a proboscis, and on the end of the tongue they've loaded it up with a modified, hollow, tooth, called a Radula. That tooth is stuffed full of venom, and they actually make a whole quiver of these arrows, harpoons if you like, they make the in one of the sacs in their internal digestive system, and they move them into an adjacent sac. They put their tongue back and pick up, with the muscular end of the tongue, they pick up one of these arrows stuffed full of venom and then they impale their victim with this. Now the victim, it depends on the kind of cone snail involved, but there are basically three kinds of victim. There are 'fish', some of these cone snails hunt fish, and they're the ones that are dangerous to us. There are 'others', the majority of them hunt marine worms, and then there's still another group that hunt other molluscs.

Chris -   Say I was to go near one and it stuck one of these things in my foot, what would I notice then?

Bruce -   Well if it was the kind that hunt fish, you could be in trouble. There have been thirty deaths from cone shell in envenomation worldwide and there's no antidote to it. The first hint that you would have would be that you would have blurred vision, and then your respiration starts to slow and then you would die from asphyxia up to 7-9 hours later. The things that interested us was, in the descriptions of such envenomations, that they said the patient dies a painless death. So I thought, I know what kills the person, but what is component there that acts as an analgesic? We went out on purpose  to look for the analgesic component.

Chris -   Have you tracked it down?

Bruce - Yeah, there are actually a number of different components but the one that we tracked down we got from a cone shell from Broome, in Western Australia. Conus Victorii  its name is. Named after Queen Victoria but in fact its not in the state of Victoria, its in western Australia. This component is a small peptide of 16 amino acids and that acts as a very potent analgesic between 1000 and 10,000 more portent than morphine.

Chris -   How do you know its going to work in us?

Bruce -   We don't. We know that it works in animal models of pain and we're current in phase 2 clinical trials, testing it on people who have painful sciatica. The results of those studies will be known mid-year. At this stage everything is coded, so the patients don't know if they're receiving a placebo or the real drug. And the results will be analysed and well the results will tell us if it's going to be an effective medicine or not. We've got out fingers crossed, as you can see I've got both fingers crossed and my legs crossed.  We're hoping for a good result because there's really a big unmet need of patients for whom conventional analgesics are not working and they need something else. We hope that the cone shell has the solution to their problems.

We put this question to Gavin Laing, of the Liverpool School of Tropical Medicine:Okay, antivenom has been around for at least 100 years, but the techniques of producing antivenom have not really altered a lot in that time. What normally happens is a very large animal is immunised over a long time with very small amounts of snake venom, so it won't harm the animal; traditionally they have used horses.Chris: So what you would do is milk the snake, get some of its venom and then inject that into the horse.Gavin: Yes, in very small quantities, so the horse will not be affected at all, it's only a tiny amount. The horse will then raise antibodies against this antigen that's been injected in the same way that humans immunised with smallpox would be raising antibodies against that.Chris: So the horse gets antibodies in the bloodstream.Gavin: That's correct, and over a long period of time, say eight months or so, the horse will then become hyper-immune. Every so often, some serum is then drawn from the horse and immunoglobulins are purified from that, and from that you can split the immunoglobulins into smaller components such as the FAB or the FAB prime-2. And these would then be infused intravenously to a person who presents themselves in hospital who has been envenomed.Chris: And so the antibodies would, in that victim, lock on to the venom and neutralise it?Gavin: They would. They would seek out the circulating venom in the patient and immobilise it. They would form an immune complex and would be completely harmless and would then be flushed away normally.You can read the whole interview with Gavin here, or listen to it as part of the podcast.

This week we are looking at nature's arsenal, and we thought that probably the part of nature's arsenal you're most likely to come into contact with will be stinging nettles. So Ben Valsler went to Cambridge University's Department of Plant Sciences to talk to Dr Beverley Glover about exactly what they are. So Beverley, why is it that nettles sting?

Beverley - Well they sting you in order to try to protect themselves. It's a mechanism to stop being eaten by rabbits, by cows, by things that would normally damage a plant out there in the wild.

Ben - What advantage does stinging offer over say just tasting bitter?

Beverley - There are all sorts of different ways plants defend themselves, some taste bitter some make poisonous chemicals, some make cyanide even. And some go about it by having a combination of physical defense, say a sharp hair and a chemical component in it. So they really do put things off and they're very successful as a result.

Ben - So the way a nettle stings is by effectively stabbing you with a really sharp hair and then injecting a bunch of poisons in. What sort of chemicals are they're using?.

Beverley - Well its not a straight stabbing mechanism. The hair is very brittle its got silica in the cell wall. What actually happens is that when you brush against the nettle you break the hair, leaving a sharp edge to the silica wall which scratches you and then the chemicals flow up the hair and into the scratch. It doesn't stab you so much as scratch you. The chemicals it's using are an interesting question, people used to think it was formic acid because the sting feels like the sting you get from an ant or bee and that's formic acid but it turns out it's not. It's a mix of acetylcholine, serotonin and histamine. So it's basically the neurotoxins in there that are hitting a nerve and making it sting.

Ben - So you mention that it's good to defend them from cows and that sort of thing. Are all animals effected equally?

Beverley - I'm not aware of anybody having tested a whole batch of animals but there is some interesting data out there that says that rats aren't that effected by them. They tested some of the chemicals from the nettle sting on cell cultures and while human cell cultures respond by producing various chemicals in response, rat cell cultures were apparently not affected at all. So it seems rats are immune. But certainly if you watch rabbits they'll graze around them and cows will as well.

Ben - So they sting in order to defend themselves, to stop themselves being eaten, but is there actually anything in them worth eating?

Beverley - Yes, very much so. Well all plants are full of sugar because they photosynthesize, but nettles grow in places that have got a lot of phosphate in the soil so thats why they grow round farms and around human habitation. They grow on run-off from agriculture. Phosphates are expensive for plants to acquire, the fact that nettles have got a lot of it in them makes them interesting for most animals to eat. But apparently they are also quite high in Vitamin C and Vitamin A which is why people eat them sometimes. You can make nettle tea and nettle soup and they were apparently used a lot in the Irish potato famine as a standby food source when things got really bad.

Ben - Is there any way to avoid being stung?

Beverley - Well there's lots of different ways. The theory goes that because the hair breaks as you brush against it, then if you actually grab it and press it quite firmly then you'll bend it over and it won't break, won't be able to scratch you and you won't get stung. Another way is to choose your nettle carefully so theres a lot of evidence to say that the frequency of the stinging hairs increases in fields where theres a lot of grazing. If you're looking at a nettle in a field full of cows chances are its pretty spiky but if you go somewhere there aren't many cows or rabbits around the nettles will be less stingy, and so you might actually find it's easier to grab them. In my experience, if you go down to to the base of the stem and actually grab the nettle down near the roots as close to the soil as possible there are very few hairs usually down there as well.

Once you've got your nettle the way then to stop it stinging you is to heat it in some way because heat denatures the chemicals in the sting.

Ben - Fantastic. If you have been stung and its itching and stinging is there anything you can do to stop it?

Beverley - Because one of the chemicals is a histamine then applying/taking an antihistamine will stop the sting happening fairly quickly, but usually it only stings for about 20 minutes so anything to take your mind of it, a nice ice cream or something, will probably do the trick.

Ben - Beverley Glover, thank you very much.

Beverley - It's been a pleasure. Thank you.

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Ben - Now, armed with Beverley's advice I'm going to try and make myself a cup of nettle tea without getting stung. I have come somewhere where there's no grazing and that's my own garden. I don't keep rabbits or anything like that. I need to find a nettle and grab it from near the root, just down near the soil there and grab it really hard and pull.....this is a success. I have myself a nettle, I'm going to take it inside and see if I can make some nettle tea.

Ok, I'm on my way into my kitchen now, so the first thing I need to do is to rinse these nettles off. So now that I've got my nettles all rinsed, the next thing I need to do is to cut the leaves off, I don't really want to use the stem in my cup of nettle tea.

Now I'm going to take a hand full of my nettles and put them in my kettle, [Agh!] thats strike one for the nettles. I'll put them in my cup and set the kettle boiling.....

Now while the kettle's boiling, I'd just like to say if you do want to do this at home feel free to try it out, but if you want to you can wear rubber gloves, they will keep you safe from the nettle stings but I thought I'd just give this a go with no protection whatsoever.

The kettle's boiled now so lets pour my tea.....already that smells very plant-like, like a herbal tea. I'm going to leave it to brew for a bit and come back to you later when I'm ready to drink it.

It's now been about 10 minutes, I've let my nettle tea brew and cool down. I'm now going to scoop out all the nettles, I don't want bits of nettles getting stuck in my teeth... There we go, nows its just time to drink it I guess....

(SIP)

Ooh, well it tastes quite good really. A bit like green tea, its got that fresh leafy flavour but its a bit more bitter and I've actually heard that if you add lemon to nettle tea it will change colour, a bit like a pH indicator, but I think I will save that for a different kitchen science.

So there we go, you can make your own nettle tea and you can avoid, almost avoid, being stung if you follow some simple rules:

1. Try and find your nettles in a place where there's little grazing so the nettles have developed fewer stings.

2. Grab the nettles firmly so you just push the spikes away instead of breaking them into your skin.

3. Try and grab them at the base where there should be fewer spikes.

4. Heat them up. It's the heating stage that's really important as it denatures some of the proteins in the poison, it denatures the proteins that makes those spikes so it stops the nettles from being able to inject that into you.