Bacterial ‘syringes’ could inject drugs directly into human cells

Benjamin Thompson

Welcome back to the Nature Podcast, this week: a new way to inject molecules directly into cells...

Nick Petrić Howe

...and the disconnect between research into, and treatment of, chronic pain. I'm Nick Petrić Howe.

Benjamin Thompson

And I'm Benjamin Thompson.

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Benjamin Thompson

One of the great challenges of modern medicine is delivery. How do you get drugs, other therapeutics, or even gene editing systems like CRISPR-Cas9 directly into the cells that you want to treat? There are a range of approaches. For example, some vaccines use harmless viruses to smuggle genetic material into cells to kickstart an immune response. And now researchers writing in Nature have come up with another approach using a type of molecular syringe made by some bacteria that can deliver proteins directly into cells. Reporter Anand Jagatia spoke to Feng Zhang, one of the researchers involved, about the new study and started by asking how these tiny syringes known as contractile injection systems or CISs work.

Feng Zhang

So contractile injection systems are really interesting systems that bacteria use in order to send signals or send proteins to other cells. These CISs are like little spring-loaded syringes, and it can get loaded with proteins on the inside. And once the CIS recognises a cell, the spring gets released, and that injects the protein that's loaded into the recipient cell. What we studied in this study, there's one particular CIS is made by a bacteria called Photorhabdus and this bacteria lives in the gut of an insect and it uses the CIS to inject a toxin to kill the insects.

Anand Jagatia

And if we could harness the power of these bacterial syringes, then they can be really useful, right? So what kinds of things could we use them for?

Feng Zhang

So cells have a membrane and the membrane protects the cell, so the cell naturally doesn't want things to get into it, whether it's protein or other molecules like RNA — they're hard to cross the cell membrane. And so one of the really tantalising things about these contractile injection needles is that it can puncture the membrane and potentially inject that therapeutic protein directly into the cell that you're trying to treat.

Anand Jagatia

So walk me through what you did with this system that normally injects toxins into an insect.

Feng Zhang

So one of the biggest challenges is to figure out, how do you reprogram this syringe to be able to inject into a human cell or other types of animal cells? And this is something that Joe Kreitz, who is a graduate student in my lab, he thought maybe we can try to change the way that these almost tentacle like things, called tail fibers, on the syringe latch onto their target cell. What Joe did is that he he used a computer program called AlphaFold to predict what the molecular shape of this latching mechanism looks like. And based on that AlphaFold prediction, he then engineered a way to replace the component that recognises the insect cell with a component that can recognise a human cell.

Anand Jagatia

And so what kinds of things were you able to demonstrate that you could inject into human cells? And what kinds of effects did they have?

Feng Zhang

So he was able to make a cell glow green, after receiving this injected protein, he was also able to deliver the Cas9 protein into a cell so that the Cas9 protein can work with a RNA that's already in the cell to then go edit a specific place in the human genome, he was also able to deliver another protein that uses zinc finger protein coupled with a deaminase to also edit specific sequences in the human genome. And so so it's very exciting that we're able to start to tinker with the system to try to deliver different useful proteins.

Anand Jagatia

And I know that one potential dream application in the future might be to use a system like this to target cancer cells in the body, and that's something that you were able to demonstrate as well in this paper.

Feng Zhang

So he showed that you can target a protein called EGFR. So this will be a marker that gets expressed on some of the cancer cells to be able to target cancer cells, but also something that will be really exciting to continue to try is to reprogram these CIS syringes to recognise other cell types so that we can deliver to specific types of cells in the brain or specific types of cells in the blood or, or other organs in the body.

Anand Jagatia

And then really excitingly, you're able to demonstrate that you could use the system in a live animal. So can you tell me about the experiments that you did in the mouse model?

Feng Zhang

Sure. In one experiment, Joe was able to inject this into the brain of a mouse. And, of course, he engineered the CIS syringe so that he can bind to neuronal cells in the brain. And then he was able to show that you can deliver proteins like Cre recombinase, directly into neurons in the injection site.

Anand Jagatia

So this seems like a really promising first step. What kinds of things are you hoping to achieve in the coming years? And what sorts of experiments are you interested in running to develop this?

Feng Zhang

There are a lot of exciting things that we want to do. One of them is to continue to test the system to evaluate how well you can work in different types of tissues and different disease models in a mouse. But at the same time, I think we have to make this technology better, we have to figure out ways to get it to be more potent, get it to be less immunogenic, so that it's safer to use in the body. And also, we want to explore the many different types of CIS systems and some of them may be better than others. And some of them may be able to deliver new types of payloads not just protein, but maybe RNA and even DNA. It's still early for this approach, but I think is really important to explore, to be able to treat you know many different diseases that affect human health

Benjamin Thompson

That was Feng Zhang from MIT in the US. For more on this study, check out the show notes for a link to the paper and an associated News and Views article.

Nick Petrić Howe

Coming up, why people who experience chronic, persistent pain are still not getting the best treatment outcomes. Right now though, it's time for the research highlights with Dan Fox.

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Dan Fox

A lightweight radiation resistant coating could one day be used to protect spacecraft and their scientific payloads from the harsh conditions of outer space. Many spacecraft parts are made of plastics containing carbon fibers. These composites are lightweight and strong, but space radiation can cause microscopic cracks and static electricity buildup that can damage electronic instruments on the spacecraft. To solve this problem, researchers coated carbon fiber composites with alternate layers of two materials: a water repelling polymer and a carbon layer in which the atoms are arranged in the same way as in diamond. The carbon barrier absorbs radiation while the polymer helps the layers stick together and to the surface being coated. Unlike other proposed coatings, this one tightly encases the fibres offering better protection, while only adding minimal mass. Read that research in full, in Science Advances.

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Dan Fox

CD3δ severe combined immune deficiency is a rare genetic condition. Babies born with the condition have just one abnormal pair of DNA bases in a single gene. But that is all it takes to derail the immune system, with the mutation preventing T cells from detecting pathogens, but gene editing might bring a cure. Researchers used Cas9n, an enzyme capable of nicking a single strand of DNA on stem cells, opening the cell's DNA near a disease conferring mutation. A DNA editing protein fused to the Cas9n then swapped the erroneous bases for the correct ones. When transplanted into mice, the repaired stem cells became functional T cells. Gene editing can cause undesirable mutations and the researchers did occasionally find some unintended DNA changes. These new mutations will need to be analysed if the technique is to be used clinically. Read that paper in Cell.

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Nick Petrić Howe

Chronic Pain is pain that persists for more than three months. It affects millions of people around the world, and it can be debilitating. Over the past few decades, researchers have made strides in their understanding of chronic pain. And yet that knowledge hasn't necessarily translated into better outcomes for those who experience it. Now in a very personal News Feature, Lucy Odling-Smee, Senior Comment Editor here at Nature, has been asking why. She joined me in the studio last week to tell me more. Just so you know, this story includes a reference to suicide, which may be difficult for some listeners to hear.

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Nick Petrić Howe

Lucy Hi, how's it going?

Lucy Odling-Smee

Hello, I'm doing well. Thank you.

Nick Petrić Howe

Well, I'm so happy that you're here to go through this Feature with me. And I wanted to ask you, what was your sort of motivation for writing this article?

Lucy Odling-Smee

So I've had several episodes in my life of severe debilitating pain when I've been lying on the floor for many months, more than a year each time, always spinal pain. And what really motivated me to write this feature was in the latest episode I had, during 2020/2021, I was starting to read about pain again, to try and understand why my pain persisted, why it was escalating instead of subsiding. And many of the things I read were books written by doctors who got into trouble with pain themselves, and then tried to understand more about the science. And I was really struck at how much the science seemed to have moved along, compared to when I was last reading about pain when I'd been in trouble more than a decade ago. So there was this disconnect. On the one hand, the science seemed to be moving and there was so much more we understood. And yet, as someone who was dealing with pain, I was still in the same wilderness, I was still struggling to find anyone who would actually engage with the level of pain I was in, anyone who would offer anything besides more MRIs, possible surgery, more steroid injections, all the usual things that I knew probably weren't going to work for me. So I was really fascinated why there's this disconnect, the science seems to be moving so fast. And yet, actually, as a patient, you're dealing with the same struggles.

Nick Petrić Howe

And we'll touch on that disconnect in a second, but I was also very moved by some of the things you wrote in the Feature about people's actual experiences of chronic pain. So what what is the experience like of living with chronic pain?

Lucy Odling-Smee

I think the experience is so diverse, obviously, for so many different people. And pain is such a hopeless word in a way, because it really depends on what level of pain you're in, and how it impacts your life. But there were many people I spoke to for this Feature, maybe half a dozen. And unfortunately, I could only fit in a couple of stories into the piece. I decided in the end to focus on this man called Philip Kass, partly because the nature of his pain was familiar to me — he also has had spinal pain, so it resonated with me personally. I wanted to focus on Philip, because he's had such a appalling time with pain. He's unusual, and that he made the terrible decision of deciding to try and end his own life. He's not at all unusual in the level of despair he's experienced, so I felt his story really illustrated just how hard things can get and how impossible it can be to try and live your life with this relentless alarm bell playing all the time. So that's why I chose Philip. But there were other people who were dealing with pain. There was a woman called Jemela Williams, who I couldn't fit her story into the piece, but she was diagnosed with sickle-cell disease. And there's some debate about what the source of pain is for people who are dealing with this disease. In people with sickle-cell disease, your bloods are a different shape from the rest of ours, and they can't move through the blood vessels so easily, and they get blocked up. And the lack of oxygen can in itself caused pain. But several studies indicating that even for people with sickle-cell disease, there are changes neurological changes, just as there are with any patient who has been in pain for a long time. And her story really just resonated with me as an example of what it is like to deal with pain and disability in the United States, particularly if you're Black. Jemela really started to get in trouble with her pain only when she was a teenager when she was at middle school. And it got to the point where she was having to use crutches, she had so much pain in her legs. And she was struggling to get from the lower floors of her school up to the higher floors. And they had this system which they called hall freeze, where if you didn't get into your classroom on time, the doors were locked, and then you would receive a suspension if you didn't make it. So I just imagine this 14... 13/14-year-old girl struggling to get up the stairs with her crutches, and that that image just really stayed with me as if this is kind of how society deals with pain and disability.

Nick Petrić Howe

So pain is kind of an all encompassing thing. So I guess I'm wondering who is it that studying chronic pain?

Lucy Odling-Smee

So there's a bunch of different people from different fields studying different aspects of pain, and that's been one of the challenging things of trying to get your head around this vast field, which has so many disparate pieces, but I suppose the way to think about it is just these different parts of research. So neuroscientists have done a lot of work looking at the brain. And using brain imaging, looking at how firing patterns, connectivity patterns change in people who've been in pain for a long time. And so they're kind of coming at it from the, from the top down, in a way. And then there's other researchers who are looking more at the sort of molecular/cellular level of what's going on. And they've been trying to tease apart these interactions between the immune system and the nervous system. And it turns out that there's all this crosstalk between nociceptors, which are the neurons that detect things like heat that's too hot, that's going to burn your pressure that's so strong, it's going to potentially harm tissues. So you have all these nociceptors in your peripheral nervous systems that are out in your body away from your central nervous system — your brainstem, your brain, your spinal column — and how do those nerves interact with the immune system? And it seems that there's all this crosstalk that doesn't even have to involve the brain. It's quite extraordinary. So there's a bunch of people looking at well, what are the factors that are produced by the immune system that turn on those nociceptors? And then there's more the sort of approach of using surveys, that epidemiologists do, to try and understand well, why do some people have more chronic pain? Why do... Why does it affect certain sector of the population to try and figure out well, what is it that's predisposing people to develop these persistent pain problems? And then genetics is a whole other area where there's been a lot of genome-wide association studies, mainly looking at people with migraines, to try and figure out well what are the genetic variants associated with chronic pain, and a lot of variants have been uncovered, but they each have individually quite small effects. So I think it's very useful to look at what kinds of mechanisms might be going on with pain, but it's not looking as if you can just get a clear genetic predictor that if you have that gene, then you're going to have this kind of pain, that doesn't seem to be the picture that's emerging.

Nick Petrić Howe

So has science been moving forwards with it?

Lucy Odling-Smee

So the science, I think, it's just extraordinary. It's so beautiful and diverse, there's so many different areas of research going on. At the moment, they're all a little bit disconnected. I think in time, the dots will be joined up. There's been a ton of work looking at brain imaging, and seeing what are the changes that happen to a person's brain when they've been in pain for a long time? They've actually been able to find out by looking at certain properties of people's brains, who's going to be vulnerable to developing a chronic pain condition? Who isn't? There's also been a lot of work by geneticists, epidemiologists trying to work out well, what is it that makes someone vulnerable to developing a chronic pain condition. And as with everything to do with pain, it's complicated, there's many factors. You're much more likely to develop chronic pain as a woman than as a man, at least in certain conditions. And we've really haven't figured out why that is. Age is a factor; as you get older, you're more likely to develop chronic pain until you reach about 60 and then your risk drops off. Socioeconomic status is a big factor, how well supported you are. And then whether you bringing already whether you're bringing depression, anxiety, all these things are massively amplified by pain. But if you already have depression, and high levels of depression and anxiety that predisposes you to developing a long term pain problem.

Nick Petrić Howe

And are we getting any closer... I mean, I guess it's diverse, why people have chronic pain and what's causing it. But are we getting any closer to sort of more effective treatments?

Lucy Odling-Smee

This is such an interesting question. And it's one I asked so many people and every time I got a different answer, and I think it depends who you ask and what specialty they're in, and whether they're a research or whether they're a clinician. And I think there are actually many answers to this question. There isn't a single explanation. But really, if you talk to researchers, a lot of them will say, well, hang on, we're looking at the most complicated biological systems in the Universe — the the nervous system, the immune system — is it any wonder that we haven't really been able to translate all this phenomenal knowledge into new medications, new interventions. And I think that's a very valid perspective. Having said that, there are treatments, a range of treatments out there that either are not being matched to the patients who could actually benefit from them. Or it can be even worse than that, where patients really can't access treatment at all, for various reasons. So I think there's a sort of societal implementation issue with that is how Sean Mackey, physician-scientist at Stanford University, put it to me. So I think there's sort of multi layers of barriers. And when you ask questions about well, why are people not getting the treatments that are available? Why are they not being able to try the broad suite of multidisciplinary approaches that have been shown to help at least some people to some degree, why are they not getting at least that? And I think the answers to those questions are just complicated. They're about the lack of education. There was a report in 2011, that medical students at medical school get five hours of education about pain in their entire medical training, that has improved to some degree, but I don't think it's massively improved. Likewise, a lot of insurance companies, they'll reimburse a single steroid injection more generously than they will spending half an hour with a patient trying to go through a pain, pain management strategy, trying to find out what's going on in their lives, whether they're dealing with depression, anxiety, what else is going on, like, they get better reimbursed for the one stop treatment, even though there's a bunch of evidence indicating that that stuff invariably doesn't help people, and it can actually make the problem worse. So I think it's truly complicated. But I do feel hopeful that there's some low hanging fruit to pick.

Nick Petrić Howe

And what might be some examples of this low hanging fruit that, you know, we could take forward and help people?

Lucy Odling-Smee

So I think one thing that many of the researchers I spoke to are excited about is trying to match treatments better to patients. So the one thing about chronic pain being so complicated is that any two individuals, even if they are diagnosed with the same problem, they could have totally different mechanisms driving their pain. Even for one person, they may have one set of processes driving their pain, in the early months, the mechanisms driving that pain could completely change over the years. So it really is complicated. So I'll just give you an example of a study looking at people who have bladder pain syndrome. And through brain imaging work has been shown that actually, people who have pain in their pelvic area have a very different, almost really a different disease from people who have pain spread throughout their body. And it seems that when you look at the brains of these people, people with widespread pain have brains that look like those of people who have fibromyalgia, whereas the brains of people who have just pelvic pain who look healthy. So that suggests that actually quite different treatments could work for those two groups. And that for one, maybe pelvic physical therapy is really going to help them for the other, maybe you need really quite a different approach that looks more cognitive behavioral therapy and things that sort of rewire the brain.

Nick Petrić Howe

So there is a sense in the way that science has progressed with the understanding of chronic pain, but there's still this disconnect for people actually getting treatment. So I guess, where do we go from here?

Lucy Odling-Smee

I think there's so many layers of change that need to happen. So I think a lot can be achieved, with better trying to figure out what is going on in this particular person. And then improving education, improving awareness. I mean, that was such a motivator for me to write this piece, because I felt like pain is universal, right? Everybody knows what pain I mean, you know, you're very unlucky, if you haven't actually experienced pain, it's so important — it protects us from doing more damage to our bodies. So it's this universal thing. And yet, when it becomes chronic, it's almost like a big dark secret that nobody really talks about. And so busting that open and actually having people just really talk about what they're experiencing, and just increasing the awareness among physicians among patients among everybody that actually, pain can be a really complicated thing, and it's not necessarily a signal of biomechanical damage could be quite different things going on, that need to be addressed at all those different levels, like what support are you getting at your home? What... What's your diet like? What's your level of physical... How easy is it for you to go to physical therapy? Can you get the time off work? Can you do a 10-week Cognitive Behavioural Therapy to change your thinking around the pain? Do you get the time off work? It's like tackling it from all these different levels, is what's going to be so important. And that requires really a change in attitude, a change in attitude in the medical establishment, and in society at large.

Nick Petrić Howe

Lucy, thank you so much for joining me.

Lucy Odling-Smee

Thank you so much.

Nick Petrić Howe

Lucy Odling-Smee there. For more on this story, check out the show notes for link to her Feature. And if you or someone you know is contemplating suicide, please reach out to a suicide prevention line. We'll put details of where to access them in the show notes, along with some resources about chronic pain.

Benjamin Thompson

That's all for this week. As always, you can keep in touch with us on Twitter, we're @naturepodcast, or you can send an email to podcast@nature.com. I'm Benjamin Thompson.

Nick Petrić Howe

And I'm Nick Petrić Howe. See you next time.