Voiceover: Welcome to the Salk Institute’s Where Cures Begin podcast, where scientists talk about breakthrough discoveries with your hosts Allie Akmal and Brittany Fair.
Allie Akmal: Salk professor Tony Hunter has been on the faculty of the institute for 45 years. As a cancer researcher, he is known for his 1979 discovery of a genetic switch that, when flipped, can turn cancer on. Since then, he has won almost every award for cancer research there is, and yet he remains one of the most down to earth people you’ll ever come across. He is a beloved figure at Salk, usually seen wearing sandals and one of his signature tee shirts. We were thrilled to have the chance to sit down and talk with Dr. Hunter, Salk’s Renato Dulbecco chair in cancer research, about his long tenure in science.You’re wearing an interesting tee shirt today. It has an up arrow and the words collaborate, accelerate. What does that mean?
Tony Hunter: This is one of the stand up to cancer tee shirts that they gave us at various meetings to try and promote the speed of finding treatments for deadly cancers.
Allie Akmal: You’re quite a tee shirt collector. Is there a story behind that or do you just like tee shirts?
Tony Hunter: Yeah, I have several hundred tee shirts, usually from meetings one or two from vendors. I just sort of like collecting them. My wife doesn’t like me collecting, however, because she thinks they take up unnecessary space in our closet. Yes. But I have tee shirts from all the Salk meetings where we made them. So that’s probably 40 or 50 over the years.
Allie Akmal: How did you first become interested in science?
Tony Hunter: Yes. I had a teacher in high school who was very influential.
Allie Akmal: And the humanities didn’t seem like quite the right fit?
Tony Hunter: Greek and Latin didn’t really appeal to me that much. My dad was an MD and I think he influenced the decision, no doubt, and got me interested in biology in general. Medicine particularly, because of his profession. Yeah, so it was really as a result of this teacher, biology teacher in my last two years at school, that I ended up in Cambridge reading Natural Sciences. That’s a collection of sciences, and then specializing for my final year in biochemistry. I didn’t really know what I was going to do when I graduated with my BA from Cambridge, and someone suggested that I should apply for a studentship in the department of biochemistry to do graduate studies. I started as a graduate student in 1965.
Tony Hunter: My first Nature paper was published while I was still a graduate student, and I never really thought that I’d still be doing science 50 years later. Just seems to have happened and the time seems to have flashed past. I have an almost accidental career, I would say.
Allie Akmal: You ended up coming to San Diego in 1971 and doing a postdoctoral fellowship at Salk, and then you returned briefly to England before being offered an assistant professorship at the Institute. That must have been so exciting.
Tony Hunter: Well, I was lucky to be in the right place at the right time. I think particularly coming back here in 1975 put me right in the middle of a really exciting revolution in cancer biology.
Tony Hunter: I was lucky to stumble across tyrosine phosphorylation, because as I’ve said many times, I was too lazy to make up a fresh buffer solution. Also, tyrosine emerged unexpectedly, so there’s a lot of luck involved in science. People, they think it’s all having good ideas. And good ideas are important, but sometimes isn’t the good idea. You stumble across it, and provided you recognize what it is, and then you’ve made a discovery.
Allie Akmal: Dr. Hunter’s serendipitous 1979 discovery of a genetic switch that turns genes off or on was groundbreaking for cancer research. The switch is the process by which a protein called a kinase attaches a phosphate chemical group to an amino acid called tyrosine. Malfunctions of the switch, called tyrosine phosphorylation, often lead to cancer. Here, Dr. Hunter tells us how the discovery happened.
Tony Hunter: Yeah, so we were working on this small DNA tumor virus called polyomavirus. It is, as the name suggests, it causes multiple sorts of tumors, and particularly in rodents like hamsters. It was late at night in June, June 21st, 1979 …
Tony Hunter: That I was too lazy to make up a fresh buffer solution to separate the amino acids on a plate covered with cellulose powder. Yeah, so then I was doing a routine experiment to try and figure out which amino acid was being phosphorylated—had phosphate added, and we believed it would be either serine or threonine, in which were the two amino acids which have been reported over many, many years since the 1920s to be the phosphorylated residues in proteins.
Tony Hunter: I set up the experiment where I took this radioactively labeled middle T protein out of the gel and treated it with strong acid to chop it up into single amino acids and then separated these amino acids together with some… mixed in some marker phosphoserine and phosphothreonine, the phosphorylated forms of serine and threonine.
Tony Hunter: So I finished the run. That takes about 20 minutes. I dried the plate to get the buffer off it and then to find where the radioactivity was, you put the plate against a sheet of X-ray film, which detects x rays but also to the texts radioactive decay. Came back the next morning and developed the x ray film, and there indeed was a very faint but a real spot, but it didn’t overlap with either the phosphoserine or phosphothreonine. So it was something new.
Allie Akmal: So if you would use fresh buffer solution to begin with,with a higher pH, you might never have discovered tyrosine phosphorylation?
Tony Hunter: It was pure luck, right, that I happened to be too lazy. That led to the understanding that this is really how the virus is making tumors.
Allie Akmal: So at what point … Did you ever have an Eureka moment?
Tony Hunter: It wasn’t really a Eureka moment. It was a Eureka two months, I guess. there was a lot of excitement on the floor at the time when we presented this at lab meeting, you know, people were very excited.
Allie Akmal: Dr. Hunter is characteristically understated about just how big a discovery tyrosine phosphorylationwas. Identifying it gave researchers a mechanism that could be targeted with drugs like the anti-leukemia drug Gleevec, which was developed in the 1990s.
Tony Hunter: It took a few more years before we realized that this was also true in human cancers, particularly in chronic myelogenous leukemia, which is usually called CML, which is driven by the BCR ABL protein, which is a tyrosine kinase. So that was really the first evidence that tyrosine phosphorylation could play a role in human cancer. And then subsequently several other human cancers and human oncogenes were shown to be tyrosine kinases. So that then led to interest in potentially targeting the tyrosine kinases in human cancer, but at that time, there weren’t any selective kinase inhibitors known, and so that whole field had to evolve.
Allie Akmal: And it’s been able to turn basically a death sentence for CML into just making it a chronic disease that’s entirely manageable.
Tony Hunter: Right. If the disease is diagnosed early enough when it’s still in the chronic phase, the indolent phase, then yes. Many, perhaps 90% of the patients who go on Gleevec then, the disease goes into remission. Many of the patients who went on Gleevec in 2001 when it was approved are still taking Gleevec. A few of them actually even stopped because it looks like the disease is being molecularly cured. It’s eradicated.
Allie Akmal: That’s remarkable.
Allie Akmal: You’re part of the Conquering Cancer Initiative. Could you tell me about what it is, why it’s important?
Tony Hunter: Well, Salk has had a cancer center since 1973. The institute’s always been interested in cancer as a disease to understand and hopefully to cure. So the cancer center has the last … Whatever it is, 45 years, 46 years now I guess, has been pursuing this mission to try and understand cancer at a basic level, fundamental level, and then to try and promote the translation of some of our discoveries into treatments. So this is our latest effort to try and really focus on specific cancers that are the most intractable cancers for which the current treatments are not very adequate. They include pancreatic cancer, which is by some measures the most deadly cancer.
Allie Akmal: The tyrosine phosphorylation discovery was one milestone, and another was the 50th anniversary this year of his first paper in the prestigious journal Nature.
Tony Hunter: Well, I brought a copy with me, right? I wouldn’t make it into Nature now, I can tell you, but then it was a lot easier. And yeah, it was really exciting to get. I’ve had a couple of other papers before that. I was really excited get a first Nature paper and since then we’ve published 26 Nature papers over the years.
Allie Akmal: Your latest one just this year is about pancreatic cancer. Can you tell us more about it?
Tony Hunter: Yes. I started working on pancreatic cancer because my colleagues, Ron Evans and Geoff Wahl, suggested I should join them in applying for as part of a Stand Up to Cancer dream team to work on pancreatic cancer. Our goal was to try and understand the role of the non tumor cells in the tumor, and so my groups’ project was to try and figure out whether there were proteins, particularly cytokines, protein messengers that are able to communicate with the tumor cells.
Allie Akmal: Pancreatic cancer is one of the deadliest cancers, because the tumor is surrounded by an impenetrable shell of fibers, proteins, and immune cells. These make the tumor harder to detect and hard to treat. Scientists have found that normal pancreatic cells, called stellate cells, can get inflamed and begin communicating with tumor cells in ways that promote the cancer’s growth.
Tony Hunter: Yeah, that was our model. It will be crosstalk between the two cell types. It’s sort of a vicious cycle, if you like, of both cells maintaining each other. We generated a catalog of all the proteins that the stellate cells make using a technique known as mass spectrometry to identify these proteins.
Allie Akmal: And you zeroed in on one particular protein, is that right?
Tony Hunter: Yes, and this protein is a cytokine called leukemia inhibitory factor, or L-I-F or short, or we call it LIF. We focused on this partly because we knew that this cytokine was important in stem cell function, particularly in the embryos. LIF is important for maintaining embryonic stem cells in a pluripotent state where they can make many different cell types from a single cell. And so it had
interesting properties that it could potentially maintain a population of tumor stem cells and it could also potentially be involved in their invasive behavior.
Allie Akmal: Dr. Hunter and his colleagues found that pancreatic tumors have high levels of LIF, which increase as the tumor progresses, but just because there is a correlation between two things doesn’t mean one causes the other. The team needed a more direct connection between LIF and tumors.
Tony Hunter: And so at that point we decided we ought to test whether LIF is playing a role in the cancer. So we obtained a monoclonal antibody, an antibody that can bind to LIF and neutralize its activity, and then we set up a preclinical model of pancreatic cancer. It’s a mouse genetic model. Yeah. We treated the mice three times a week with an injection of the antibody, and we also combined that in half the mice with a chemotherapeutic drug, gemcitabine, which was the standard of care for pancreatic cancer patients. It’s still used, but now in combination with other things. And we found that the antibody combined with gemcitabine slowed the progression of the tumor particularly.
Allie Akmal: Wow. So that meant LIF was actually promoting tumor growth.
Tony Hunter: Yeah, that was exciting.
Allie Akmal: So it’s something that you could target in human tumors as well.
Tony Hunter: The idea is that we could, and the other thing we found out was that we could detect LIF in the serum of both mice and importantly in the serum of pancreatic cancer patients. So it could potentially be used as a biomarker for response to therapy in people.
Allie Akmal: That’s a pretty exciting translational result.
Tony Hunter: Yeah. So this was really the first project I’ve ever had in the lab that’s actually been translated into something useful.
Allie Akmal: Wow.
Tony Hunter: Directly, I mean. Obviously many of the things we’d done have been used by others to translate, but we haven’t done that before. So towards the end of my career, it’s exciting to have done at least one thing that’s translatable.
Allie Akmal: So it’s going into clinical trials, is that right?
Tony Hunter: So a small company in Toronto developed another antibody that neutralizes LIF, the human LIF protein, and they initiated clinical trials in August last year. August, 2018.
Allie Akmal: If you go back in time, what about the work you’ve done or the life you’ve led as a scientist would have surprise your undergraduate self or your graduate school self? You said you didn’t think you’d be in science this long.
Tony Hunter: It’s pretty remarkable to think that I’ve been doing this for over 50 years now. I started as a graduate student, you know, really even before the genetic code had been solved. We had no idea how many genes there were in an organism, and for a while during these early sequencing days, there were numbers ranging from 150,000 down to as many as 30,000.It turns out it’s less than 30,000. I think that is a surprise, that given the complexity of the human being, that you only need 20,000 different genes to develop the body and to behave the way that we all do. That was a big surprise. So we had no real understanding of how DNA encoded information and could direct the formation of cells and organisms.So it was really the molecular biology revolution starting in the late sixties. Once the genome was sequenced, obviously we could catalog how many protein kinase genes an organism had. We were the first to do that for the human genome and reported that the kinome—that’s the collection of the protein kinase genes—is 518 in people. What else? I mean, there have been so many surprises along the way. I don’t think it would have been easy to predict, you know, many of these things. And I certainly didn’t. I’m just happy to be part of some discoveries and to wonder at the beauty of nature, right?
Allie Akmal: Just one of my last questions. Did you have any specific advice you would give graduate students or people considering graduate school in science?
Tony Hunter: Well, in science in general, I mean, because of the rapid progress in the rate of discovery, sometimes people feel there isn’t anything left to discover. And that’s absolutely not true. There’s going to be a lot more still to discover. I always tell people when they’re embarking on a career in science, when I’m interviewing prospective graduate students for the biology program, it’s important to ask a question that if it’s answered will have an important outcome.You know, it’s a hard job in the sense that it’s not really a nine to five job. You spend extra hours in the lab and even on weekends, but you’re rewarded by being able to travel around the world to meetings. And you know, you can take a day off when you feel like it, as long as you can organize your experiments. It’s not as though you have to be in the lab nine to five. You can do it on your own time, provided you get it done.
Allie Akmal: And there’s lots of great tee shirts in it.
Tony Hunter: Lots of great tee shirts, right.
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Voiceover: Where Cures Begin is a production of the Salk Institute’s Office of Communications.