# From the Lab: Treating cancer with light through photodynamic therapy  - with Stephen Bown

## Метаданные

- **Канал:** The Royal Institution
- **YouTube:** https://www.youtube.com/watch?v=69RF1rVQ9NI
- **Дата:** 20.05.2026
- **Длительность:** 22:47
- **Просмотры:** 1,700

## Описание

Photodynamic Therapy (PDT) is offering a revolutionary new treatment option for a range of diseases, particularly cancers. By combining the skills of physicists and physicians, PDT uses light to kill living cells without damaging the structural integrity of the surrounding tissue.
Stephen Bown is the founder of the National Medical Laser Centre, and has decades of experience both developing and implementing PDT. He joins us for this month's From the Lab episode ahead of his Discourse on Friday 29 May.

About 'From the Lab':
This is the fifth of our new 'From the Lab' series, taking the place of our 'From the Theatre' episodes. UCL are celebrating their 200th anniversary in 2026, and we've collaborated with them to host UCL researchers as our Discourse speakers throughout 2026. As part of this collaboration, we'll be bringing you episodes with each of these speakers two weeks before their Discourses to explore their research topics further and give you a sneak peek of what's to come in their Discourse.
Buy tickets to Stephen's Discourse on Friday 29 May on our website.
Ri Science Podcast episodes are released on the last Wednesday of every month, and our new ‘From the Theatre’ episodes are released on the second Wednesday of the month. Subscribe to be notified as soon as the next episode is released!
• Book tickets to upcoming talks on our website
• Subscribe to our YouTube channel
• Follow us: @ri_science on Instagram and TikTok
Producer and presenter: Lia Hale
Music: Joseph Sandy

## Содержание

### [0:00](https://www.youtube.com/watch?v=69RF1rVQ9NI) Segment 1 (00:00 - 05:00)

How do physicists and physicians work together to treat cancers? The answer lies in photodynamic therapy. Stephen Bown is an expert in laser medicine and founder of the National Medical Laser Centre at UCL. As the May Discourse speaker, Steve joined me at UCL to explore the history of photodynamic therapy and how exactly it works. Steve, thank you so much for joining me here at UCL for this month's from the lab episode. You're an expert in laser medicine and have decades of experience working with and around photodynamic therapy or PDT as we'll refer to it throughout the rest of this episode. And this area of research has a really rich history between UCL and the RI which will get into a bit later, but I wanted to start by establishing a bit of a scientific foundation of the area and what this therapy is. So, PDT is a collaboration between physics and medicine and involves primarily involves two aspects, light and a photosensitizer. What is a photosensitizer to start with and how do these two things work together in PDT? Well, first thank you for the invitation to give this lecture and this opportunity to give an outline of our activities. A photosensitizer is a chemical. In many ways it's like a drug, but in most cases it has little effect on living tissue unless it is activated by light. Nevertheless, most photosensitizers are taken up with some degree of selectivity in cancerous tissues and many of them actually fluoresce under blue light. This is the first application of the combination of photosensitizer and light and is called photodiagnosis. It is a surface effect and can often be used to detect areas of cancer that are not visible just in white light. It is important in procedures such as brain cancer surgery to help the surgeon distinguish between cancer and normal brain. The therapeutic combination of photosensitizer and light is what we call photodynamic therapy, PDT. PDT is an active treatment and requires photosensitizer activation by red light. This is the color that penetrates tissue best. The intensity of light required for PDT is not enough to produce any thermal effects on tissue, but in the presence of oxygen, it can excite the photosensitizer to an energy level that converts ground state oxygen to singlet oxygen, which is the ultimate cytotoxic agent. This requires three things: a threshold level of photosensitizer in the tissues, absorption of a threshold amount of light energy in joules per cc at every point where an effect is required, and adequate tissue oxygenation. Achieving an adequate concentration of photosensitizer is usually reasonably easy, but getting enough light to every part of the target tissue is the most difficult part as the intensity of light drops rapidly as it penetrates deeper into living tissue. The wavelength of the light has to be matched to an absorption peak of the photosensitizer, and is typically in the range of 630 to 690 nanometers. This can give a depth of tissue necrosis of up to about 10 to 15 mm from the light source, which is usually a laser. One of the beauties of PDT is that the tissue effect is relatively gentle. Living cells can be killed with PDT, but the underlying connective tissue that holds body organs together is largely unaffected. So, PDT treated areas heal well. In contrast, any form of heat treatment affects all components of tissue. There are no absolutes in medicine, but a simple way of thinking about PDT is to say that in relative terms, PDT is a gentle way of treating nasty bits of tissue without upsetting all the nice bits. PDT does have some effects on normal tissues, but these areas heal much better than after any form of heat treatment. Further, PDT does not have the cumulative toxicity of other treatments like radiotherapy and chemotherapy, and so it can be repeated at the same site if required. You mentioned that cancer is what PDT is applied for. How does PDT apply to other conditions, or is it a cancer-specific treatment method? PDT is explored mainly for the treatment of cancer, but it does affect normal tissues.

### [5:00](https://www.youtube.com/watch?v=69RF1rVQ9NI&t=300s) Segment 2 (05:00 - 10:00)

It's a relative difference, not an absolute. But the beauty of PDT is if you're treating tissue, particularly at the junction of the normal and the malignant regions, the underlying scaffolding that holds tissue together is largely unaffected. So, the PDT tumor-treated area is healed by regeneration of normal tissue. That doesn't happen normally, but that's the general principle, which makes it particularly attractive for treating superficial lesions. Is this a treatment that can then be used for internal organs as well, or is that process harder because you've obviously got a lot more tissue to get through and penetrate through with that laser, like you mentioned before. So, how is that How does that make the treatment process different to say skin lesions, like you said, or more surface level treatments? Well, the answer to that lies in technology and endoscopes. Endoscopes, as most people are aware, are flexible telescopes that can be inserted in virtually every hollow organ within the body. And it is also very easy to pass laser fibers through the operating channel of endoscopes and deliver light to the lining of hollow organs. PDT requires a relatively uniform threshold concentration of photosensitizer in the target tissue, which can be given as a cream for skin or by mouth or injection for other organs. It is more difficult to get enough light to all relevant areas inside the body, as away from an organ surface, the intensity of light falls rapidly at increasing depths. For this reason, much of the work of PDT has been on superficial cancers and pre-cancers, which can develop on the skin and on the inner surface of hollow organs, like the esophagus, the bladder, and the lungs. As it is easy and safe to access and deliver light to these areas with endoscopes. This can often avoid the need for major surgery. PDT is relatively complex, and there are other options for treating these patients, but PDT is the option that has been studied most. Comparisons with alternative treatments are ongoing. For treating cancers in large solid organs, like the pancreas and prostate, the way to get light in is to insert multiple needles through the overlying skin and pass laser fibers through the needles into the target under image guidance. However, treating cancers in these organs with PDT has been slow to develop due to the problems of getting adequate light to all relevant areas. Nevertheless, there is considerable promise. The biology of PDT is exciting, but it is relatively difficult to optimize the treatment parameters for any specific condition as there are so many variables related to the delivery of photosensitizer and light. Clinical trials should be led by a senior clinician with a special interest in a particular clinical problem, and this is the only realistic way to establish the best way to apply PDT for specific indications. The future of PDT in cancer treatment is likely to be in its use in conjunction with other techniques such as radiotherapy and chemotherapy. One of the most exciting possibilities is as a primer for immunotherapy. Experimentally, if a small cancer in a mouse is treated with PDT, then there is an increasing evidence that the tissue left after treatment in that animal can act as an immune stimulant as though the cancer was effectively vaccinating its own host against the cancer itself. This sounds very complex, but clearly is a very [clears throat] exciting prospect, and the experimental evidence for it is steadily increasing. Further, PDT can have an important role as a last-ditch treatment. If all else fails, if a patient has already had maximum doses of radiotherapy, chemotherapy, and there are no further surgical options, PDT may provide significant benefit mainly because it is repeatable, it doesn't have the cumulative toxicity of treatments like radiotherapy and chemotherapy. And it's relatively simple to deliver. I will talk about one lung cancer patient in exactly that situation. And show him describing his own experience, which gave him an extra 6 years of good quality life. This series that we're recording is a result of a collaboration between UCL and the RI for UCL's 200th anniversary

### [10:00](https://www.youtube.com/watch?v=69RF1rVQ9NI&t=600s) Segment 3 (10:00 - 15:00)

celebrations, which are going on throughout this year. And as I mentioned at the start, this area of research has a particularly long-standing history between the RI and UCL. But as do you. So, could you tell me a bit about how you first encountered the RI and the first work that you did in that overlap between UCL and the RI? Well, my first contacts with the RI were back in the 19 late 1970s, believe it or not. And I met David Phillips. I think it was actually at a disco. Oh, really? — To be honest, I can't remember. [clears throat] At that time At that time, Sandy MacRobert, who is a photochemist, was working with David Phillips in the Royal Institution. And they realized that one of the chemicals they were developing for something entirely different from photodynamic therapy, but this chemical had many of the right properties to be a photosensitizer. In view of this, we started a joint project. And then Sandy MacRobert got so involved in this that he actually moved to UCL, where he has been Professor of photochemistry and has worked with me on PDT for more than 20 years. But we retained the links with the RI through David Phillips. The chemical involved is aluminum disulfonated phthalocyanine. We undertook many of our early fundamental laboratory experiments establishing what PDT did to normal and diseased tissue, and that provided us with material we needed to be able to start clinical work in UCH. This actually isn't your first discourse at the RI. You first gave one 45 years ago exactly. What did you speak about in that discourse and how has the field changed from that discourse to this one? My subject of the discourse was the internal surgeons without a knife, the laser and the endoscopes. At that time I was working with lasers in medicine but not PDT. It was just thermal lasers. So, the laser was a convenient way of delivering predictable amounts of energy at precise points within the body. And that included through endoscopes as well as directly from the outside. While I was doing that project, I came in contact with David Phillips and that's how our links developed and he invited me to give that discourse on where we'd got to with the thermal lasers. But it was again a way of developing closer links with the Royal Institution. And it was shortly after that we got involved in the joint experiments on PDT. That first laser project was about using lasers to stop ulcers bleeding endoscopically. We did the preliminary experiments to work out how a thermal laser could be used to stop arteries bleeding within the stomach and the duodenum and carried out clinical trials. We were one of the first group to show that worked. Previously, such patients would likely be requiring major operations to open their stomach and seal the bleeding vessel. But with the laser endoscopy, this was just a simple endoscopic procedure. And often we could get patients home within a few days. Another major thing that thermal laser work enabled us to do was to core out cancers that were blocking particularly the esophagus and also the airways. Again, endoscopically the beauty of the laser was that you could do a superficial ablation of tissue and coagulate the slightly deeper layers, so you didn't stir up any bleeding. And that way it was rapid palliation of difficulties in breathing and swallowing. And then when the patients were better from that point of view the other team could throw the book at them with chemotherapy, radiotherapy, and sometimes surgery. Throughout your career, you were splitting your time essentially between being a an active practicing clinician and also doing this research. So how did you find that those two things helped each other and were you able to put your research into practice quicker than you maybe would if you were just on one side of those two things? Absolutely. I was very lucky that at an early stage I was funded actually by a charity, Imperial Cancer Research Fund, later became part of Cancer Research UK. And 50% of my life was devoted to the

### [15:00](https://www.youtube.com/watch?v=69RF1rVQ9NI&t=900s) Segment 4 (15:00 - 20:00)

medical laser center for laboratory work. And the other 50% was treating patients. But the joy of that was that if something looked good in the laboratory we could walk across the road and try some patients. And if it didn't look good, we would shrug our shoulders and try something else. And that went on for many years. We actually got involved in experimental work in 11 different specialties in medicine. Personally, I was a gastroenterologist, so my main interest was in the esophageal work and some rectal work. But essentially, we tried all the others as well and have made different degrees of progress in each. But always the concept was understand the biology of what happens to thermal lasers and to PDT in these organs, and then we could decide which ones were likely to be relevant in the management of human disease. As we were doing before taking your last discourse and this discourse as a bit of a uh time frame to look at how the field has changed, if there was to be a discourse on this topic in another 45 years, how different do you think that could look to what you'll be speaking about now? I think the difference will be the development of multiple treatments being applied to individual patients. — Mhm. One of the most exciting probabilities or possibilities of PDT is that it will act as an immunostimulant. What this means is that you're stirring the body up to react against its own cancer. Now, if this worked for cancers right from the beginning, the cancers wouldn't grow because the body would get rid of them. But an interesting observation with PDT is that the chemicals left in the tissue after PDT seem to stimulate the body's own immunological system, whereas the original cancer itself did not do that. As a simple expression of this, if a small cancer was treated in a rat, and then after that had healed, the same tumor was transplanted into the same animal, it didn't grow. So, effectively, the first treatment had vaccinated against recurrence of the same cancer. Now, this is largely at the experimental level, but it is being explored with great enthusiasm in many research centers around the world. And I think potentially this could be one of the greatest applications of PDT. Looking for other indications, one particularly of interest to gastroenterologists was a remarkable finding that type 2 diabetes, which you don't think of as a gastroenterological disease at all, can be controlled by ablating the lining of the duodenum. This came as a result of careful observation of neurosurgical procedures. That's bariatric surgery. And there is some experimental work that shows that what was achieved on bariatric surgery can be achieved without surgery by a rather complex and cumbersome technique called hydrothermal therapy to ablate the superficial layer of the duodenum. We have all the basic knowledge of how to ablate the surface layers in the esophagus. And in theory, we should be able to do the same in the duodenum. But this at the moment is ideas rather than hard data, but it's an exciting prospect. And one other major area where I think PDT has a future is in the treatment of infections. The challenge is to get the photosensitizer directly on the organisms, whether maybe bacteria, virus, maybe some fungal organisms. But if you can do that, they take up the sensitizer very rapidly, and the amount of light required is relatively little. Where this has taken off to a major extent has been in treatment infections of the nose. Because we all carry bacteria in our noses, which for the most of the time do no harm. But if these patients have subjected to major surgery, and a few of those bacteria get to the wrong places, that can prove nightmare. Mhm. Particularly for orthic procedures such as joint replacements. And the simple concept of a little swab to put some of the photosensitizer in a little pad up the nose, and then a simple device to shine light up the nose, may eradicate those. And this has been shown, particularly with a lot of studies in Canada

### [20:00](https://www.youtube.com/watch?v=69RF1rVQ9NI&t=1200s) Segment 5 (20:00 - 22:00)

that the incidence of infections after joint replacements has been significantly reduced. You'll be giving your discourse on Friday the 29th of May, in 2 weeks time when this episode comes out, in the RI Theatre. And those listening who are based in London can join us in the theater, all those further afield can join us on the live stream. All of the links that you need to purchase your tickets will be in the description of this episode. But I've asked all of our UCL discourse speakers for this series to try and give an elevator pitch of sorts for why people should come to the discourse, or why they should just be engaged in this area of research in general. So, if you had to give a little sales elevator pitch, what would it be? I think the simple answer is if one encounters new technologies like photodynamic therapy, I mean, the principle was established more than 100 years ago, but it's only relatively recently that we can really see what the potential might be. But, my personal opinion is the key thing is to understand the biology of what these techniques do before you try and apply it clinically. So, understand the principles, then look around and say when would it be relevant to get that effect in a particular condition in a patient. Then you can try and achieve that initially in the laboratory, and if that looks good, go on and cautiously start it in patients. But, it's a long process. And for PDT, it's particularly difficult because you have so many variables. How to get the drug in the right place at the right time. And even more of a challenge, how to get enough light in the right place. — Because as light goes through tissue, the intensity obviously falls off as you move away from the light source. — What you need to be sure is that the point of the target lesion that you have to be sure gets enough light, it's obviously the one furthest from the light source. If you achieve that, then all the other regions between that and the light source will get enough. — If you'd like to find out more about PDT, then make sure to grab your tickets for Steve's discourse on Friday the 29th of May. All the links you need are in the description of this episode, — and we'll be back in a couple of weeks with our regular episode.

---
*Источник: https://ekstraktznaniy.ru/video/51868*