Cells On The Move

Have you ever heard of a nocebo? Possibly not, but it’s effectively the opposite of a placebo: you expect to experience side effects when you take a drug, so you do! And a study out this week suggests this nocebo effect could be playing a significant role in the difficulties some people have with taking cholesterol-lowering drugs called statins, as Katie Haylor has been hearing...

James - Most of the time when patients suffer side effects from statins, although they are real, they are probably not caused by the statin molecule themselves, but rather by the act of taking a tablet.

Katie - That's cardiologist James Howard from Imperial College London. James and colleagues have recently published the findings of a clinical trial called SAMSON, which sought to better understand why some people have such a difficult time taking cholesterol lowering drugs called statins.

James - Statins are actually one of the most prescribed medicines in the UK because they can help prevent heart attacks and strokes. But so many of our patients suffer from side effects, and some people have estimated that half of patients have had to stop taking statins within two years of being prescribed to them.

Katie - The team recruited 60 people who'd all actually stopped taking statins in the past due to side effects. These can be wide ranging in severity and type, but in this study, 60% of people had experienced muscle aches and pains.

James - We gave them a suitcase, and inside that suitcase there were twelve jars. And four of those jars contained these statin tablets; four of the jars contained what we call placebos, which are just sugar tablets that look identical to the statins; and four of them were empty. And for every month of the following year, they were told to start a different jar in a random order that we told them. And we also - if they didn't own their own - gave them a smartphone, and they used that to tell us every day, on a scale of 0 to 100, how good or bad they felt.

Katie - Crucially neither the participants nor the scientists knew who was taking what throughout the study.

James - The patients of course knew when they weren't taking tablets, which was the case for four months of the year. But for the other eight months of the year, they didn't know if the tablets they were taking were statin tablets or the sugar tablets.

Katie - And it was tough going for some.

James - 49 of them managed to complete the full year. That means 11 of them didn't. And of those, around half of those had to stop because they found the side effects so bad they didn't want to carry on.

James -  Now the 49 that did finish, they also occasionally had to stop their tablets because the side effects were so bad, but the next month they were willing to come back and keep doing the experiment.

Katie - Well the team sat down with the participants and showed them the scores of how they'd been feeling throughout the year and which tablets - statins, sugar pills, or none - they'd been taking.

James - When people don't take tablets, they don't get very many symptoms at all. When they take statins, they actually feel much worse, but they feel 90% as bad taking the sugar tablets. So what we think is going on is that when people take statins, they are concerned that they will feel worse. And actually, this does make them feel worse. And we call this the nocebo effect.

Katie - The team actually found that explaining this nocebo effect to the people on the trial had a pretty big impact.

James - When we sat down with patients and talked about their symptoms and showed them their results, half of them were able to go back on to statins, without problems, and were still taking them six months later. For the half that aren't back on statins yet, a lot of them say they actually want to go back, but because of the COVID crisis and things like that, they haven't been able to make appointments with their GP doctors. So only around half of half of our patients refuse to go back on the statins because they felt they really did have side effects.

Katie - So what about that 10% that wasn't reflected in the placebo group? Are they drug-related side effects?

James - So it's a little bit difficult to say that because whenever you make a measurement in a clinical trial, you know you're not going to be quite precise enough. And because of that, we are saying most side effects seem to be caused by this very interesting nocebo effect. Some patients do get satin side effects caused by the drug themselves because that's the case with all drugs. We're just saying it's probably a lot rarer than we previously thought. By sitting down with patients and showing them the science, you can get them back on tablets that previously they haven't been able to take. So communication is the most important thing.

Over the past few years, medical scientists have been using 3D printing to create artificial human tissues with the goal of, one day, replacing their natural diseased counterparts. But cells need oxygen, and it’s tough to engineer these ‘bioprinted’ body parts so - that while they’re growing - they don’t die of oxygen starvation or a toxic build up of carbon dioxide before blood vessels can plumb themselves in. So a team in the US are trying to solve the problem using algae. Yes, it does sound strange, but algae are plants: they use light to drive the process of capturing carbon dioxide and releasing oxygen, so by laying down algal cells alongside human cells, one can feed the other and keep both healthy in the process, while an organ develops. Eva Higginbotham heard how it works from Shrike Zhang...

Shrike - We combined our algae and human cells where the oxygen produced by the algae cells can promote the growth of the human cells. After removing the algae we can have a better engineered human tissue.

Eva - What is the problem that you were trying to solve by creating this?

Shrike - Oxygen supply. So providing sufficient oxygen from within engineered tissues has been a major problem or challenge over the years. And if you engineer thicker tissue, it's very hard to get oxygen into the middle of the tissue because oxygen doesn't really go through the thick tissues or dense cells 10. This way that we have devised is to really provide long-term oxygen release from within the engineered tissue. So that's perfectly solving this long-term dilemma that's faced by this whole community.

Eva - What sorts of tissue are people growing in a lab that they need to be able to get oxygen all the way in?

Shrike - This basically applies to pretty much every single type of tissue that people engineer. All the way from, for example, the brain, to the heart, to the liver - there's almost no tissue in the human system that does not have an interconnected network of blood vessels.

Eva - So how have you solved the problem?

Shrike - We use bioprinting to deposit these algae containing structures. If you shine a light across this construct then the algae can actually produce oxygen.

Eva - How on earth do you actually print algae?

Shrike - We use a Jello-like structure containing algae, which are called Bioink. And then if you control how this Bioink is extruded you can start to deposit these algae structures in three dimensions.

Eva - You know what I'm thinking of is whipped cream that comes in a can! You know, where you squeeze things out, either that or like a glue gun?

Shrike - Yeah, sort of yeah.

Eva - And you've actually sent me some pictures that show these algae and it almost looks like you've printed them to look like a honeycomb. Why did you print them in that shape?

Shrike - We printed them in this honeycomb shape just because we were trying to model or mimic human liver structures. But again, using bioprinting, you can essentially deposit any shape or structure that you want.

Eva - And so within these honeycomb circles I can see lots of bubbles, is that bubbles of oxygen?

Shrike - Yes, exactly.

Eva - And so taking this sort of structure that you've made you then throw on some liver cells, is that right?

Shrike - Yeah, basically. So you can throw your liver cells onto the structures. So then these oxygen bubbles that are created by this algae are going to be used to supply the oxygen to the cells.

Eva - Would you then be implanting algae as a part of someone's regrown heart?

Shrike - No. Once the liver tissue is sufficiently oxygenated, you can actually selectively remove these algae patterns from the liver tissue that you can then directly implant into human systems.

Every single one of us exists because a sperm successfully fertilised an egg. But the resulting embryo faces a problem: how to ensure that the trillions of cells that it gives rise to - and which make up the body - end up in the right places. One group of cells is called the neural crest. They form down the length of the embryo above what’s going to become the spinal cord. But from there, they have to migrate around to the front of the embryo - passing through lots of other developing tissues on the way - to give rise to a host of different structures including the nerves supplying the skin, melanocytes that give us our protection from the sun, and they even form the face. These feats of navigation mean the neural crest can teach us a huge amount about how cells move, and Paul Kulesa, from the Stowers Institute for medical research, studies how they do it, and what can sometimes go wrong, as he told Eva Higginbotham...

Paul - Neural crest cells are a multipotent cell type. That means they can become a number of different types of cells that include neurons and bone and cartilage and pigment cells. And they contribute to nearly every organ. But the problem is that neural crest cells must travel long distances to reach peripheral targets, where they contribute to organ assembly. They encounter complex developing tissues during migration in an embryo that's growing and undergoing tremendous amounts of dynamic movements of the underlying tissues through which they're crawling in the fibers. So it's a very dynamic microenvironment and it's as if they're crawling through a very dense like Amazon jungle, but the jungle is dynamic and moving and growing plants as they're trying to get through the jungle.

Eva - So these cells are sort of crawling through this complicated surface of other cells and other things that are going on. How do they actually move themselves forward?

Paul - Well, we know from cell culture studies that cells will extend a protrusion and then anchor that protrusion and then degrade whatever fibers are in their way and attach to something that they can hold on to, and then pick up the attachments behind at the backend of the cell and then pull themselves forward.

Eva - Is that kind of like how you kind of think of a slug moving or a snail, they kind of push out some part of themselves and then drag themselves along?

Paul - Right, right. Very much so because you can see in vivo, when you're imaging, you can see bits and pieces of the cell membrane that are left behind actually, as the cells are crawling through. And so it's almost going back to the analogy of the jungle as if they're going through very dense thorny bushes and shrubs and getting pieces of clothing ripped off on the thorny bushes as you go. And it's very much so it seems like with the cells.

Eva - How do they manage to actually force a protrusion out? Cause if they're moving through this really dense forest, how do they get enough sort of energy and force behind them to push a protrusion between cells to allow them to sort of dig their way through?

Paul - Right. Well, there's a couple of different ways that we know of that cells can do this. They can start to initiate a protrusion of the membrane by bringing in machinery of the cell, which builds fibers in the cell. But there's also another way that a cell can initiate a protrusion and that's by opening water channels, aquaporins, within the cell membrane. So Aqua for water and pour for porins. And having water do the job to initiate the protrusion.

Eva - Like creating holes almost that allow the bit of the membrane that they want to force its way through, to kind of inflate?

Paul - Right. It's as if in the dense jungle, there's only small gaps, then you can stick your arm through there and then cut away at the fibers in order for you to then move more of your body through that dense jungle.

Eva - What happens if something goes wrong in that process?

Paul - Ah, well, if they can't make it to their target in the head, then the cranial facial pattern can be disrupted because they give rise to bone and cartilage of the face. And so two of the more common human birth defects are cleft lip or cleft palate, or problems with the nerves that innervate your jaw. And neural crest cells contribute to the heart. And so you can have congenital birth defects to the heart flow tracks. One of the major early pediatric cancers is neuroblastoma. It is a solid tumor that forms outside of the brain. And it's very common in infants that are zero to five years old. And what happens is the neural crest cells that are contributing to the peripheral nervous system and becoming neurons and having to wire a neural circuit have some malfunction and that can lead to pediatric neuroblastoma. We're looking to see whether aquaporins and other invasion genes that are typical of the embryonic neural crest relate at all to predicting the potential of a neuroblastoma as a solid tumor to become what's called metastatic or to leave the primary tumor site and invade other tissues.

Eva - So are these aquaporins prevalent in other cancers that we know are likely to metastasize?

Paul - Yes, well, there's been some work in glioblastoma recently. That's compared patient samples of the tumor core versus infiltrating cells. And we know that aquaporin-1 is expressed by the infiltrating cells. So certainly in glioblastoma and in other invasive cancers. So it may be that it's both predictive of metastatic potential and a clinical target.

Cancer metastais occurs when rogue cancer cells break away from a tumour and spread, often via the bloodstream or the lymphatic system to other parts of the body. But why do cancer cells but not healthy cells do this, and what determines where these cells tend to spread to? Sakari Vanharanta is a cancer biologist at the MRC Cancer Unit in Cambridge and Cancer Research UK Cambridge Centre, and his lab studies this process, as he told Chris Smith...

Sakari - I think they don't necessarily want to spread, but cancer is a disease of uncontrolled growth. And these tumour cells divide and divide. And there's so many of them that they end up just spilling out of the primary tumour and ending up in different organs. And then some of those cells eventually survive there, and form a secondary tumour. So I don't think this is an orderly process in cancer. They just move randomly and end up in secondary organs because of that.

Chris - But some cancer types do seem to "prefer" in inverted commas, to spread to certain parts of the body, and certain other organs don't they?

Sakari - Absolutely, there is organ specificity to the metastatic process. And this is something that is kind of poorly understood still, but it seems that there's a match between a certain cancer types and a certain secondary sites and cancer cells when they end up at there, or if they end up there, they have a higher chance of surviving, and that's why there's this predominance of certain types of metastatic sites.

Chris - Is it just the cancer cells, the abnormal cells that have made the primary tumour, that then go off and spread, or do they have the potential to subvert and manipulate other healthy cells in other places, to make their spread and invasion into other sites in the body, more likely?

Sakari - Cancers are more like ecosystems, there's multiple different cell types there. And cancer cells recruit various types of normal cells, and they exploit those, and they do this for many purposes, including migration and for the purpose of leaving. So some cancer cells can follow, or tag along with other normal cells, and that will help them move. So absolutely it's a process in which cancers very much exploit normal cells.

Chris - We were hearing earlier about the amazing journey that these neural crest cells take when they're migrating from where they're formed, in a developing embryo, to end up all over the body and giving rise to all kinds of important structures, presumably since cancer cells have access to all of the same genetic programs that a developing embryo would have, can they just turn on those developmental programs and basically pretend as though they're back in an embryo, and go wherever they want, is that part of the reason why they're so destructive?

Sakari - So in cancer, many of these developmental programs are activated in the wrong place. And I think an example of this would be melanomas, which develop from the melanocytes that were just discussed in the context of neural crests. So the normal function of the developing neural crest, is to migrate through the developing embryo. Now melanocytes don't normally do that, but the cancer causing mutations may allow them to activate the same programs. And that's one of the reasons melanomas can form metastases in many secondary sites.

Chris - And is there any evidence that cancers, when they're in situ, and they've got these distant metastases, these deposits in other parts of the body, are those cancers in cahoots? Do they talk to each other? Is there a sort of chemical conversation going on between tumour deposits around the body?

Sakari - Between the different metastatic sites I think it is difficult to measure whether those sites communicate, but cells travel from one metastatic site to the next. So through these kind of messengers, they would be exchanging information.

Chris - So you're saying a cancer can not only spawn a new tumour in a new place, but sometimes cancer cells will come out of one metastatic deposit and go to another one?

Sakari - Absolutely. So there's genetic evidence showing that again, like an ecosystem of different tumours in different parts of the body, and there's clones that move from one place to another, and then start growing there.

Chris - And does that affect the way that the tumours grow? If one of them discovers a really good way to grow, can it take that information or that know-how to another tumour site, and stimulate that to grow more?

Sakari - Yes. For example, if you have cancers under therapy, you could have resistant clones that emerge in one metastatic site, and then if it's migratory, it could colonise new sites or preexisting metastatic sites, and then help them grow as well.

Chris - Oh goodness. So that would explain why, when you have advanced disease, it can suddenly accelerate uniformly. So it's not just one bit of it that discovers how to grow better. The whole lot seems to progress, and progress increasingly quickly as the disease advances.

Sakari - Very true. So metastatic tumours can behave exactly like that, when you get resistance, it can happen in multiple places simultaneously, but it can also happen independently. So they could have mutations that target the same gene, independent mutations in different sites. And that could also lead to the same outcome.

Chris - But now that we know all these things, and we understand a lot more about the processes that lead up to cancers beginning to spread, the fact they get into tissues and establish metastases. How does an understanding of that mechanism inform how we treat patients?

Sakari - I think if we understand how metastatic sites, for example grow, of course it can help us develop targeted therapies for those very specific processes. And there are examples, like anti-oestrogen therapy in breast cancer. We know that breast cancer cells like oestrogen, so to prevent metastasis, we give patients anti-oestrogens to prevent that from happening.

Chris - And are there any specific things we've noticed that do by and large repeatedly lead to cells wanting to go walkabout? And by interrupting that, we have a chance to interrupt across the board, the spread of cancer? So we would turn a cancer from something that's highly progressive and virulent and nasty, into just a chronic indolent thing that we live with, a bit like high blood pressure, I suppose.

Sakari - I think that's the hope, but I don't think we are there yet, because we don't understand the process well enough. I think to inhibit the initial spread of cancer is very difficult because it's difficult to find the time window of applying such a therapy, but trying to prevent already disseminated cells from forming clinically meaningful metastases, I think that's why we should try to go.