In the latest installment of our occasional conversations with Fort Worth leaders, Sherri McFarland, a professor of chemistry at the University of Texas at Arlington, discusses a bright spot in her work: She’s studying how light can destroy cancer cells.
This conversation has been edited for length and clarity. For an unabridged version, please listen to the audio file attached to this article.
Alexis Allison: Tell us about photodynamic therapy.
Sherri McFarland: Photodynamic therapy is a light-based or light-triggered cancer therapy and sometimes it’s referred to as PDT for short. PDT is a cancer treatment option that can be used in combination with other things that one would be familiar with, like chemotherapy, or surgery or radiation. The goal is to, of course, destroy the cancer. PDT is a little different than traditional forms of therapy in that it does use a drug, but the drug is inactive until you turn it on with light. And when you turn the drug on with light in the presence of oxygen, it creates what we call reactive oxygen species, which are just very reactive forms of oxygen that can kill cancer cells in the surrounding areas. It’s a highly selective form of cancer therapy, because you can choose where you shine the light, and then the cells that are affected are only affected in regions where the drug, the light and oxygen overlap in space and time. This is very important because it minimizes side effects. So you can selectively target the cancer cells over normal, healthy, non-cancerous cells.
Allison: Out of curiosity, how does the experience for the patient change between this therapy and, say, chemotherapy?
McFarland: Something that would be very beneficial from the patient’s point of view is that the PDT treatment is one treatment. Whereas with chemotherapy, you would be doing a course of chemotherapy and getting multiple treatments. And as anybody who’s been around somebody that’s had chemotherapy, or maybe had chemotherapy themselves, they know that it’s sort of an up-and-down in terms of side effects and being sick after the treatments. So it’s one treatment and also the fact that there are virtually no side effects.
Allison: That’s amazing. Say you’re a patient who’s going to receive this therapy. What is happening to you?
McFarland: It depends on the type of cancer that you have and how the PDT will be delivered. I can give an example for a drug that we developed, and it’s for bladder cancer. And in the case of bladder cancer, these patients have already failed other forms of cancer therapy, and their only option at this point is to have their bladder removed. And the patients in our clinical trial either are unfit for the procedure and can’t have it for that reason, or they refuse to have it, which is understandable. It is not without its complications. So that being said, the patients are cancer patients that have tumors in the bladder, and what we can do is come in with our drug and infuse it directly into the bladder. And we do that over about one hour under sedation. And then, at the end of that period, we come in with the light, and we just feed it in through what you might think of as a catheter or a cystoscope, and we illuminate the bladder. The time for illuminating the bladder really depends on the patient, the bladder volume, as well as how much scarring the patient already had in the bladder. But generally, it may be anywhere from a half an hour up to an hour for the illumination of the bladder, and then that’s it.
Allison: So the patient’s asleep the whole time?
McFarland: Yes. So the whole procedure from start to finish is maybe three or four hours getting ready, being sedated, having the drug infused over about an hour and then having the illumination and then recovering, and then the patient goes home.
Allison: This is kind of a random question, but what kind of light do you use?
McFarland: Oh, we use green light. Green light from a little portable laser.
Allison: Why green light?
McFarland: So these compounds that can be activated with light, they can be designed to work with different wavelengths of light or different colors of light. And the color that you might choose, for example, would depend on how far you might want to penetrate tissue. And for our drug, we chose green light, because green light doesn’t penetrate very far. With bladder cancer patients, it’s very important that we not damage the underlying muscle layer, because if we damage that muscle layer, it’s going to compromise bladder function. These patients could have problems with their bladders after the treatment, so green light is very important to eliminate that from happening.
Allison: How effective is the treatment so far?
McFarland: Well, we’re in a phase two clinical trial. So you know, I probably shouldn’t comment on what I think the outcomes will be. But in the phase one clinical trial, our response rate was “complete response, two-thirds.” And that’s for “complete response,” so that’s pretty good.
Allison: And what does “complete response” mean?
McFarland: No evidence of cancer whatsoever.
Allison: Wow. And for people who may not know the research path when it comes to clinical trials, what would be next after the second clinical trial?
McFarland: Normally, the clinical trials consist of a first phase, which tests safety, and a second phase, which tests efficacy, and then a third phase, which usually compares your new treatment against standard of care for that particular cancer. Ours is a bit different, because our patient population has already failed other cancer therapies, and so they don’t have any options because they’re unfit or refusing to have the bladder removal. So in our phase one study, we looked primarily at safety. But since these were diseased patients, we got an idea of efficacy as well. And then our phase two, of course, is looking at efficacy, but also tracking safety alongside. Because there is no standard of care for this patient population, because they’ve already failed the standard of care, we don’t need to have a phase three.
Allison: So then, if everything goes well in this phase two, what would happen next?
McFarland: Then we would get approval to bring the drug to patients.
Allison: Okay. And hypothetically, will the drug work on other types of cancers?
McFarland: Yes, we are exploring the same drug with other forms of cancer, such as brain cancer, lung cancer, and we also design other drugs to work with other colors of light for different applications as well.
Allison: Beautiful. And can you tell us a little bit about how you got into cancer research?
McFarland: Sure. I mean, probably like many people, you’ve probably known someone with cancer along the way. So when I was starting my career, I was trying to think, “What will I do to bring my background in chemistry together with an application?” When I was thinking of application, I had a good friend who had had childhood cancer, my mother had cancer. And of course, I knew many other people around me that had been affected by cancer, so I thought that would be a good application to pursue. And because my background as a chemist had been in looking at how molecules interact with light, I thought that PDT was quite a good area for me to use the knowledge I already had.
One thing that struck me about PDT was the selectivity and the opportunity to minimize side effects, and that was probably the thing that caught my attention. Well, there were two things that caught my attention. One would be to develop therapies for patients that didn’t have any other options. That was one goal. And then the other would be to minimize side effects that can be quite debilitating and even lead to secondary cancers in some cases.
Allison: Thank you for sharing with us and is there anything else that you’d like to share?
McFarland: I would just like for the general population to know that PDT exists and is complementary to surgery, radiation, radiation therapy, chemotherapy, immunotherapy, and can be used in combination. So it’s worth researching if you or your family member may have a diagnosis and you’re thinking about what else might be out there to complement existing forms of therapy.
Allison: So other forms of photodynamic therapy already exist and are already available to patients in the general public?
What’s one difference between McFarland’s drug and Photofrin, an already FDA-approved photodynamic therapy drug?
Photofrin requires an IV infusion over two appointments. Because an IV-infused drug can spread through the body, including the skin, patients may become temporarily sensitive to sunlight. McFarland’s drug requires a one-time infusion directly into the cancer-affected region, thus avoiding the side effect of sunlight sensitivity.
Alexis Allison is the health reporter at the Fort Worth Report. Her position is supported by a grant from Texas Health Resources. Contact her by email or via Twitter. At the Fort Worth Report, news decisions are made independently of our board members and financial supporters. Read more about our editorial independence policy here.