#09 – David Sabatini, M.D., Ph.D.: rapamycin and the discovery of mTOR

1. 0:00 – 0:04

   Intro

   1. PAPeter Attia0:00

      [upbeat music]

2. 0:04 – 5:40

   Intro and David Sabatini's Path to mTOR

   1. PAPeter Attia0:04

      Hey, everyone. Welcome to The Peter Attia Drive. I'm your host, Peter Attia. [upbeat music] The Drive is a result of my hunger for optimizing performance, health, longevity, critical thinking, along with a few other obsessions along the way. I've spent the last several years working with some of the most successful top-performing individuals in the world, and this podcast is my attempt to synthesize what I've learned along the way to help you live a higher quality, more fulfilling life. If you enjoy this podcast, you can find more information on today's episode and other topics at peterattiamd.com. [upbeat music] In this podcast, I'll be speaking with my close friend and amazing scientist, David Sabatini. David's a professor of biology and a member of the Whitehead Institute at MIT. He's also an investigator at the Howard Hughes Medical Institute and a senior member of the Broad Institute, along with a bunch of other accolades that would take too long to get into here. This podcast was actually recorded initially as part of an interview series I was doing for research around my book, and this was recorded in August of 2017. Maybe at some point, we'll even just put the video up as this was actually done as a video interview with David, along with a number of his amazing post-docs, and certainly, some of those will probably make their way into the podcast as well. Now, in this episode, we talk about his amazing journey in science and the work and stuff that he's done around mTOR and rapamycin, and if you've been following the blog and/or paying attention to stuff that I'm interested in, you'll know that mTOR and rapamycin sit kind of at the heart of it. Now, about four years ago, David and I were having lunch one day, and it was kind of the first time that he ever really told me the full story of his work as a graduate student at Hopkins, where he was part of the MD-PhD program. And I was just ... You know, I remember sitting there taking notes on a napkin and thinking, "God, this is such an incredible story of science." And I remember thinking, "God, you know, one day we have to have this discussion again, but such that most people can actually hear it besides just me." [laughs] So part of what we discuss on this podcast is actually that journey and how, as a young PhD newbie grad student, David methodically went after a problem that really wasn't even deemed particularly interesting at the time, which was to basically figure out how this thing called rapamycin actually worked, and of course, through the process, ended up being the first person to identify this mechanistic target of rapamycin in mammalian cells. Now, stuff that I found really interesting in this podcast is that David points out that he's, from an academic standpoint, kind of an unusual bird in that he's one of the few people who has carried his work from graduate school into his career, and that's, that's actually pretty unusual. He's incredibly thoughtful, and some of you may have already heard a podcast that David, myself, and Nav Chandel, another good friend who will also be on the podcast, recorded back with Tim Ferriss on Easter Island back in the fall of 2016. We'll link to that here as well. And obviously, the reason we went to Easter Island was as sort of a pilgrimage based on the discovery of the bacteria that ultimately led to rapamycin, a bacteria by the name of Streptomyces hygroscopicus. The interest I have in mTOR, of course, has to do with its central role in nutrient sensing and, of course, its, I believe, and many believe, its central role in longevity. So if you are interested in longevity, if you're interested in fasting, if you're interested in rapamycin, you're really gonna wanna listen to this podcast because David is effectively mTOR man. I don't think there really is a person on the planet, and I'm saying that without trying to be hyperbolic, but I don't think there's anybody on the planet who knows more about rapamycin and mTOR than David Sabatini. And if you like this podcast, please make sure to check out the one that's, uh, going to be out soon with Matt Kaeberlein, which will take this discussion to another level as well, uh, looking at Matt's work in dogs. So without further delay, here's my discussion and conversation with David Sabatini. [upbeat music] Well, David, thank you so much for, uh, making time to sit down today and talk about what is potentially mutually our favorite topic of discussion. Before we jump into it, though, maybe for people who don't know you, can you tell us a little bit about how you got here and what it is you do specifically?

   2. DSDavid Sabatini4:18

      Sure, sure. So thank you, Peter, for coming and for visiting and, and both of you and for wanting to talk to me. So I am, uh, I guess, a biologist. I'm a professor of biology at MIT, and I'm also a, a member of the Whitehead Institute, which is where we are today. And I receive a lot of funding from the Howard Hughes Medical Institute, which is a, a key, uh, charity that works with biomedical researchers. I have studied this protein that I'm glad you like a lot. It's my favorite protein, called the mTOR protein, which is the protein through which this drug, rapamycin, which gets quite a bit of attention now, acts. And I basically worked on that from the earliest point. We, we discovered that when I was a student. And so my career is as an MD-PhD, never really following the clinical track, though, and, and staying on the research side and finishing that and actually coming to the Whitehead in a program that is quite interesting and very unique at the time, which was that you could start your own lab after graduate school. And so I did that, and I eventually joined the faculty here, and now I've moved up the academic ranks. And to some extent I'm, I'm a little bit strange from an academic point of view because I've continued to work on, not exclusively, but to a large extent what I started in my graduate school. So most people, as you know, do something in graduate school, they do something in their postdoc, and then they sort of morph along the way. I've kind of stuck with this mTOR protein and, and in many ways I was very lucky because we were there at the beginning, and it turned out to be such an exciting thing to work on.

3. 5:40 – 11:58

   Choosing a Project in Solomon Snyder's Lab

   1. PAPeter Attia5:40

      So let's go back to the beginning a little bit. You were an MD-PhD student at Hopkins, and after a couple of years of doing preclinical stuff, you pick a lab.

   2. DSDavid Sabatini5:51

      Exactly, right? So you do two years of, of medical school, and then you pick a lab, and I was very fortunate to be taken by Solomon Snyder, who was at the time the head of neuroscience. He had a very big lab, lots of MD-PhDs. A lot of MD-PhDs wanted to go to his lab. And I was lucky that he let me go. And Sol was a, is a really interesting man. He still has actually a really prominent lab at Hopkins. In fact, the department is now named after him. And he was that person who had a lot of varied interests, or he was a neuroscientist, but he was also a psychiatrist, and he was also a pharmacologist. So he, he really loved Small molecules. In his lab, particularly potent small molecules. That is mo- small molecules that act at low doses

   3. PAPeter Attia6:32

      How do we define in pharmacology a small molecule? What's the cutoff point?

   4. DSDavid Sabatini6:35

      [sighs] You know, some people say a thousand daltons, which rapamycin is about that. To a larger extent, it's sort of a non-peptide also-

   5. PAPeter Attia6:43

      Yeah

   6. DSDavid Sabatini6:43

      ... so it's not a piece of a protein. In many cases, it's not a natural molecule, although in our case, it's made by microorganisms. It's not natural to our body, so probably a thousand daltons.

   7. PAPeter Attia6:54

      Okay.

   8. DSDavid Sabatini6:54

      And so he had these set of interests, and when I went to his lab, I was actually really interested in neuroscience. So I'd had some classes-

   9. PAPeter Attia7:00

      I see

   10. DSDavid Sabatini7:00

       ... in which I was sort of fascinated by some neuro questions. But when I got to his lab, I actually never did anything on neuroscience. And I often told the story that the most influential scientific discussion I probably ever had is when I went to talk to Saul. And basically, as a student, you need to pick a project. This is something that, that is quite challenging, and I see with my own students, they really get quite apprehensive about their projects. So I went to talk to Saul, and I went to his office, and I only met with Saul, like, I don't know, maybe five or six times during my PhD. So this was, like, a, a big deal. And so I went to talk to him, and he basically said, "David, we work on the brain." And I thought that was great 'cause I wanted to do neuroscience, but then he didn't say anything else. So that was it. And so I remember leaving his office really anxious because basically, like, I didn't have a project. But I realize now in retrospect what he did is he actually was giving me complete freedom to do what I wanted to do, and that was, as I said, probably the most important thing anyone's ever done for me. 'Cause it really forced me to come up with my own project, and I think was a key sort of foundation in becoming the scientist I have, and it's something that I try to foster amongst my own people. So anyways, I was in his lab, and I didn't have a project, and at the time, they were actually working with this other drug called FK506, which is a well-known-

   11. PAPeter Attia8:15

       It's an immunosuppressant

   12. DSDavid Sabatini8:16

       ... immunosuppressant. It's used clinically still. Mechanism of action, although structurally it's very different than cyclosporine, it actually mechanistically works on the same target, which is calcineurin. And at the time, this is before we had a lot of the tools we have now, like RNAi or CRISPR, and so you needed controls. So if you had a drug, what you tended to use was another drug that kinda looked like it but didn't do the same thing, and so their control was rapamycin. And when I started reading about rapamycin-

   13. PAPeter Attia8:44

       And this is what year?

   14. DSDavid Sabatini8:45

       This would have been in probably late '91-

   15. PAPeter Attia8:51

       Okay

   16. DSDavid Sabatini8:51

       ... to '92. And it was clear to me that this molecule, in many ways, was much more interesting than FK506. And as you very well know, this had come from Wyeth-Ayers, the, the pharmaceutical company, by Suren Sehgal, who, uh, championed it. And there was a number of papers, which at the time were actually ... A few papers were largely abstracts from meetings that showed that it had antifungal effects, immunosuppressive effects, anticancer effects. So it seemed like a interesting molecule. You know, I had just come from medical school. We'd learned about immunosuppressants like cyclosporine, which at the time, you know, were really just coming on and were really seen as miracle drugs.

   17. PAPeter Attia9:26

       But your lab's interest in FK506 was not its immunosuppressive properties-

   18. DSDavid Sabatini9:31

       No

   19. PAPeter Attia9:31

       ... but its calcineurin inhibition.

   20. DSDavid Sabatini9:32

       Exactly, 'cause calcineurin, as the name implies, there's a lot of in the brain.

   21. PAPeter Attia9:36

       Mm.

   22. DSDavid Sabatini9:36

       And so in Saul's lab, they were basically studying the modulation of calcineurin in the brain using FK506 as a tool.

   23. PAPeter Attia9:43

       Okay.

   24. DSDavid Sabatini9:43

       And they were looking actually at cytotoxicity in the brain, things that at the end didn't, didn't lead, I think, in the directions they wanted to, but, but they were using it as a pharmacol- as a probe, basically. And so I basically decided why not try to work on rapamycin, and so that's what I did. And so we, we-

   25. PAPeter Attia9:59

       Which was just a control that nobody particularly cared for.

   26. DSDavid Sabatini10:02

       Yeah, I mean, there were, there were people in the world that were interested in it.

   27. PAPeter Attia10:04

       But in your lab, this is-

   28. DSDavid Sabatini10:04

       In, in our lab, yeah.

   29. PAPeter Attia10:05

       This is a very peripheral project. Yeah

   30. DSDavid Sabatini10:05

       People in our lab, no one was studying rapamycin. We had this great advantage, though, is that you couldn't buy rapamycin at the time. So rapamycin was a compound that Wyeth was developing clinically. It wasn't clinically available. You couldn't buy it. But Saul, being a very prominent scientist and having this interest in pharmacology, had actually written Suren Sehgal, and actually he had sent us, probably without any of the legalese that happens now ... Now, if you try to get a molecule out of a pharmaceutical company, the amount of paperwork and red tape is, is huge. Basically had sent us a very significant amount of rapamycin, which I remember when it did start to be sold, which was incredibly expensive, I kinda back calculated, and it was-
4. 11:58 – 16:10

   Purifying mTOR from Rat Brains

   1. DSDavid Sabatini11:58

      We actually ... Yeah, I had no idea that they ... In fact, the only point where I found out they were working on it was once our paper had been accepted, I got, and this was pre lots of email, internet, we got a fax from a journalist saying he was writing an article on our paper and another paper from Stuart Schreiber, and actually sent us Stuart's paper, which we thought was really unethical at the time, and so we, we actually at that point contacted Stuart and said, "Hey, we got your paper. You should know we're working on this too, and, and here's our paper." So it was, yeah, I, I didn't know at all. And, and in many ways, I was very naive, right? I was in this lab. Saul basically let us do whatever we wanted to. We had this drug Unbeknownst to Sol, I started working on this thing, right? And Stuart had had a history of FK506, mechanism of action, so it was a logical progression to what he was doing. Sol was not... It was funny. He came from a world where people looked for the receptors for drugs, so if you look at his history, he'd really looked for receptors for drugs, for small molecules, including the endorphins, for example-

   2. PAPeter Attia12:56

      Mm-hmm

   3. DSDavid Sabatini12:56

      ... that he had worked with. But he wasn't big on cloning, what we call cloning a gene, which is where you have that, get the DNA sequence. He almost thought you didn't need to do that. Once you purified it, you could study the protein. So I was one of the few, first people there to actually clone a, a cDNA as, as we call it, in his lab. So that wa- it was a fun time because it was clear that we'd gotten this protein, the, the pure-

   4. PAPeter Attia13:19

      But you did this in a very short period of time because your paper, which was in Cell, was 1994.

   5. DSDavid Sabatini13:24

      '94, yeah. I worked like crazy, really like crazy. So, and that lab in general worked like crazy. We were, it, it was very common to be there until 1:00 in the morning, and then I would usually show up at 7:00, 8:00 in the morning. You know, we would sleep in the lab a lot. And once, you know, once things started to go... So we were purify- I purified out of the rat, out of rat brains, and so we killed hundreds of rats to do this, and my friends would help me kill them, take the brains out. There's a method in biology to visualize proteins called a silver stain, which is a very sensitive way of seeing a protein. And the first silver taint- stain I did where I actually c- saw sort of a glimpse of mTOR on, on this method, I remember that really clearly, 'cause at that point I knew I could do it.

   6. PAPeter Attia14:08

      How did you know it was mTOR that you were looking at in the stain?

   7. DSDavid Sabatini14:11

      Well, I mean, I had all the controls, and there was this band on a, what we call a gel, that showed up just in the right place.

   8. PAPeter Attia14:18

      I see.

   9. DSDavid Sabatini14:18

      And so I was like, "Okay, there is a protein here that has all the properties that I want." And-

   10. PAPeter Attia14:23

       And at that time, what properties did you know? You didn't know its size, did you?

   11. DSDavid Sabatini14:26

       Didn't know its size, but we know it bound to FKBP rapamycin.

   12. PAPeter Attia14:30

       Mm-hmm.

   13. DSDavid Sabatini14:30

       And-

   14. PAPeter Attia14:30

       But you didn't know that that exclusively bound to it, did you?

   15. DSDavid Sabatini14:34

       We didn't. And, but we knew that it could be competed by FK506 based-

   16. PAPeter Attia14:38

       Okay

   17. DSDavid Sabatini14:38

       ... on some competition type experiments, and so we had done that. So there was these features. It was mostly the specificity that it required rapamycin to bind to FKBP, and, and that was crystal clear in the early experiments. When we had FKBP by itself, there was no band on the gel, and when we added rapamycin, there clearly was, and when we added FK506, it clearly went away.

   18. PAPeter Attia14:58

       Mm.

   19. DSDavid Sabatini14:58

       And so we knew that that thing had all the right properties. But I remember very strongly feeling, okay... A- and at the time, now we have very, very sensitive methods to sequence proteins, largely by mass spectrometry. There we didn't. And so from what I saw on that gel to actually figuring out what it sequenced and once, I knew it was hard, but I knew it could happen. That was, like, a very powerful feeling.

   20. PAPeter Attia15:19

       It was the existence principle.

   21. DSDavid Sabatini15:20

       Exactly. So I knew the thing, like, the kind of the enemy existed-

   22. PAPeter Attia15:23

       Yeah

   23. DSDavid Sabatini15:23

       ... and I could get it. But then going from that initial glimpse on a gel to then having enough to actually sequence it, that's what took hundreds of rats to actually get to enough that I could purify it. And eventually we, we collaborated with this guy called Paul Tempe at, uh, Memorial Sloan Kettering in New York, and he was able to sequence enough of the protein that then through a whole variety of molecular biology tricks, we were able to clone it. And it was a really huge cDNA, which basically is the length of the DNA sequence that encodes it. It was very big, sort of in the eight, nine kilobases, which is very hard to work with, particularly at the time. And I got very, very lucky in the sense that I did a bunch of tricks and I got the whole thing at once, which is also was kind of unheard of at the, the time.

   24. PAPeter Attia16:08

       How did you do that?

5. 16:10 – 21:51

   Cloning the Full-Length mTOR cDNA

   1. DSDavid Sabatini16:10

      Yeah, so back in the time what people would do is they would get pieces, and then they would sequence them, and they would sort of-

   2. PAPeter Attia16:14

      With overlapping-

   3. DSDavid Sabatini16:15

      They would overlap-

   4. PAPeter Attia16:16

      Yeah

   5. DSDavid Sabatini16:16

      ... and stitch them together. But what I did when I screened what we called libraries at the time for, for these pieces, I would get some pretty big pieces, but I knew, when I would sequence it, I knew that the front of the protein was missing, like I was missing. And I couldn't get it. It would never, I could never get beyond a certain point of the protein. And so then what I, what I did, which, you know, really, uh, turned out to be, like, incredibly lucky... So what we would do is we would screen libraries of phages. And so this was basically, people would take cDNA, complementary DNA, from rat brain, and they would clone it into these bacterial virus called phages. And so now you, every little cDNA was in a virus, and you'd have hundreds of millions-

   6. PAPeter Attia17:03

      Mm-hmm

   7. DSDavid Sabatini17:03

      ... of this library. And you would plate it out on these plates, and the phage would make little plaques, and then you would screen those plaques. And so you'd have, you know, dozens of these plates, each with thousands and thousands of these little dots on them. And so what I decided to do is that I would screen this library with a piece that I knew was a- as far towards one end and as far toward the other end. And so I screened it with both, and I looked for plaques that hybridized both. And in fact, when I first did it, I got nothing. It was really disappointing. I got plaques that had one piece, and I had plaques that had another piece, but I didn't have any plaques that had this thing. And then what I realized, and this was really key, I realized that the so-called full-length cDNA was so big that it was gonna make the phage replicate slowly. 'Cause basically, their genome was so much bigger now that to replicate it would take longer.

   8. PAPeter Attia17:57

      And on what order of times?

   9. DSDavid Sabatini17:58

      It was probably two to three times more that it would take.

   10. PAPeter Attia18:01

       I got it.

   11. DSDavid Sabatini18:01

       And so-

   12. PAPeter Attia18:01

       So you could have been missing it.

   13. DSDavid Sabatini18:02

       I could have missing it because the plaque that would have this would be incredibly small. And so what I did is I went back and redid it, and now I let the plaques grow longer, and I re-screened it, and in fact, I got one plaque that a tiny, tiny little plaque that hybridized with both. Both probes. And when I looked at what was in there, it turned out to be the, the complete full-length cDNA, which was amazing because it was unheard of that these libraries would give you something like 9,000 base pairs, but it was. When I sequenced it, it was literally the intact thing from one end to the other. So I got very lucky because that would've been pretty hard to assemble at, at the time.

   14. PAPeter Attia18:39

       So you knew at the time, had Michael Hall's work in yeast been published yet?

   15. DSDavid Sabatini18:44

       It had been published sometime during this period of time, but we didn't-

   16. PAPeter Attia18:48

       But you didn't know anything. You didn't know even what the yeast form of this protein-

   17. DSDavid Sabatini18:51

       No, no. When we started, we weren't doing... And in fact, when we first started getting sequenced, there was no sequence out there. And the yeast protein, really only the kinase domain is conserved.

   18. PAPeter Attia19:00

       I see.

   19. DSDavid Sabatini19:00

       And so most of the peptide sequences that we had that Paul Temps had sequenced for us, we didn't know at all where they were, right? And so these are kind of fun things that used to happen in the past. You used to collaborate with a, a person to do protein sequencing, and they would give you back a series of peptide sequences, but you didn't know what order they went in. So let's say he gave you back, I think Paul gave me... Paul was amazing, 'cause he would give you, let's say, 15 peptide sequences. He'd say, "Look, your protein, these 15 peptides exist in your protein." And then some-

   20. PAPeter Attia19:31

       With or without overlap in those peptides?

   21. DSDavid Sabatini19:33

       No overlap. These are short.

   22. PAPeter Attia19:35

       Mathematically, it's impossible to, by chance, figure out... Like, you need more clues to figure out the order because it's combinatorially impossible.

   23. DSDavid Sabatini19:43

       Yeah. You have no idea what the order is.

   24. PAPeter Attia19:44

       Yeah.

   25. DSDavid Sabatini19:44

       And so what you end up doing is a kind of a cool thing. And Paul was really cool because he would actually, in the sequence of the peptides, he also had uncertainty. Sometimes he'd say, "This amino acid-

   26. PAPeter Attia19:53

       Plus or minus

   27. DSDavid Sabatini19:54

       ... could be this or it could be that," and he would tell you what he thought it was. And it turned out he was so good that when I actually figured out the sequence, every one that he said it could be this or that, he was right, his prediction. But so what you would do is you'd have these peptide sequences, and what you could do now is design, we know the, obviously the code, the amino acid code, so we can predict what the DNA sequence would encode. But as you know, the DNA sequence is degenerate.

   28. PAPeter Attia20:19

       Mm-hmm.

   29. DSDavid Sabatini20:19

       Right? So one peptide sequence can be encoded at the DNA level.

   30. PAPeter Attia20:23

       You don't know what the exons and introns look like around it.
6. 21:51 – 28:31

   Starting a Lab at Whitehead and the Hunt for mTOR Complexes

   1. DSDavid Sabatini21:51

      Saul's lab was big and I was very independent, so the people said, "Why don't you do one of these fellows positions where you can start your own lab?" And at the time, there was only three. There was the Whitehead one, there was one at Carnegie Institute, which is in Baltimore, and there was one at Cold Spring Harbor, New York, and I applied to all of them. And I got accepted pretty quickly, although after I graduated, to Cold Spring Harbor and to Carnegie, but I didn't hear anything from Whitehead, like nothing. And only, like, basically once I graduated and I was kind of unemployed at that point, I was technically a postdoc in Saul's lab, but I hadn't taken, like, the boards, which Hopkins, you know, Bar- Hopkins didn't make you take the boards, the medical boards to graduate, which was a nice thing. My mother was like, "You're gonna starve. You don't have a job. You can't do residency now 'cause you didn't apply- you didn't take the boards." And then I got a call from Whitehead actually inviting me to interview, and I did. And then it took, again, a lot of time to, like, hear back. And I remember they called me and said, "Look, we're gonna offer you a position, but you need to understand you will never, ever stay here as a faculty member, ever." I was like, "Okay." I realized I was applying for this-

   2. PAPeter Attia22:56

      Right

   3. DSDavid Sabatini22:56

      ... Whitehead fellow position, not a faculty position. But then eventually I came, and eventually I did stay. And, and when I look actually at history, it's, they do keep, you know, about a third of the people who come through, but they give you this sort of speech that you will never, ever stay.

   4. PAPeter Attia23:09

      Set the expectation.

   5. DSDavid Sabatini23:11

      Yeah. And incidentally, many of the people named David have stayed, so it's actually a good thing to be named David. [laughs] Actually, our current director was a Whitehead fellow. His name is David. One of the other faculty members' name is David as well. So I didn't know at the time, but now I realize that David was a, was a big advantage.

   6. PAPeter Attia23:24

      So how has your work evolved? I mean, you came here in the late '90s, right?

   7. DSDavid Sabatini23:28

      The late '90s, exactly.

   8. PAPeter Attia23:29

      Rapamycin would go on to be approved by the FDA in 1999 as a frontline treatment as part of the double or triple cocktail for patients, uh-

   9. DSDavid Sabatini23:38

      As Rapamune, right?

   10. PAPeter Attia23:39

       Right, as Rapamune, along with often prednisone, cyclosporine, or MMF. So now you're here, and I mean, we're gonna get into much more detail, but effectively you've never looked back. You've never really left this space.

   11. DSDavid Sabatini23:53

       I got here, and I was incredibly naive. I realized at this point how I thought, you know, I knew a lot. I thought I knew how to run a lab. I had been very independent on my own, but that doesn't mean that I was sort of independent from, like, running a lab. You know, behind the scenes in Saul's lab, obviously it was the entire finances. I had written grants and things, entire finances, organization, but there was a lot. Like, I could be independent, me, but then a lab is a different thing. And so that was a hard transition to run, even though it was a small lab, to run a lab. And it was clear that at that time, I felt that this field had kind of plateaued. There had been the discovery of mTOR, but we weren't getting very far. People were using rapamycin to look at lots of different things, and mTOR by implication through rapamycin was being connected to lots of different things. But one of the things that was obvious to me, and I think to others as well, was that mTOR had to act with partner proteins. And so we set about trying to identify what we now know are these mTOR-containing complexes, mTORC1 and mTORC2, mTOR complex 1 and 2. But that was... It was really hard. We failed for years. And it was, again, one of... This field has had a series of just, like, little things that until you figure them out, you make no progress. And so we would purify mTOR, and we'd look for other proteins. We would continue to work with Paul Thamps, and we just wouldn't find anything.

   12. PAPeter Attia25:12

       To be clear, you, you knew that you had discovered the gene for TOR.

   13. DSDavid Sabatini25:17

       Right.

   14. PAPeter Attia25:18

       You suspected that this thing exists in different complexes.

   15. DSDavid Sabatini25:21

       And I already knew that there was other proteins 'cause when I was doing the mTOR original purification, the way that, that I was following mTOR with was with a, kind of a funky cross-linking assay, where I was cross-linking a radioactive FKBP to the putative target, and there was always two bands on the gels. There was the protein mTOR, which I eventually purified, but there was a smaller one, which I could never get, either because it was just low abundance, I couldn't det- I don't know what. But that little protein, which at the time I called Raf-2, actually-

   16. PAPeter Attia25:52

       Mm-hmm

   17. DSDavid Sabatini25:52

       ... basically remained unidentified. So I knew that there was something-

   18. PAPeter Attia25:56

       So basically, the first version of mTOR complex 1 was TOR, and the version of mTOR complex 2 was Raf-2.

   19. DSDavid Sabatini26:02

       No, no, no. That protein actually, now that we found it, turns out to be in both complexes.

   20. PAPeter Attia26:06

       Oh, I see.

   21. DSDavid Sabatini26:06

       But what I knew was that there was an associated protein with mTOR. I knew from... I didn't know what its identity was-

   22. PAPeter Attia26:12

       Mm

   23. DSDavid Sabatini26:12

       ... but it was very clear on all my experiments that there was a small... mTOR is very big. It's around 300 kilodaltons, which is a big protein.

   24. PAPeter Attia26:19

       Mm.

   25. DSDavid Sabatini26:19

       This was a little protein. It was around 30. So it was about 10 times smaller.

   26. PAPeter Attia26:23

       Wow.

   27. DSDavid Sabatini26:23

       So from a technical point of view, it's about 10 times harder to get because there's about 10 times less peptides in that protein.

   28. PAPeter Attia26:30

       Yeah.

   29. DSDavid Sabatini26:30

       So I failed to get it. So when I got here to the Whitehead, I knew there was another protein to find, and we kept trying to go after this protein, and others. We knew it had to work. You know, it's a really big protein. Big proteins work with friends. And it turned out, this is again, these, these little things, it turned out that the detergent... So when you, when you're working with mammalian cells, you have to lyse them.

   30. PAPeter Attia26:52

       Mm-hmm.
7. 28:31 – 33:47

   What mTORC1 and mTORC2 Do, and the Link to Longevity

   1. DSDavid Sabatini28:31

      Right. So it was very clear early on that mTORC1 was doing most of the things that we had connected before to mTOR.

   2. PAPeter Attia28:38

      Mm-hmm.

   3. DSDavid Sabatini28:38

      So, you know, we'd had rapamycin, and so rapamycin in a way had allowed us to know a lot about mTORC1, we now realize, than otherwise we would have known. 'Cause we didn't have really genetics. We didn't have easy ways of modulating mTOR.

   4. PAPeter Attia28:52

      Right.

   5. DSDavid Sabatini28:52

      But we had rapamycin, and so there was a body of knowledge acquired by many different investigators about what was so-called downstream of mTOR. What did mTOR do? We had some ideas. It was a growth regulator. It regulated translation. It regulated autophagy, right? It regulates many, many metabolic pathways. It would regulate cell size. We knew that largely through the use of rapamycin.

   6. PAPeter Attia29:14

      Mm-hmm.

   7. DSDavid Sabatini29:14

      And so now when we discovered mTORC1, which, you know, the, the first part we discovered was this protein called raptor, we now could go and say, "Well, does raptor matter for all those things?"

   8. PAPeter Attia29:24

      Mm.

   9. DSDavid Sabatini29:24

      And it turned out it did. So it was very clear that mTORC1 must be doing the things that we ascribe to rapamycin. mTORC2, therefore, remained very mysterious for a long period of time because it wasn't doing those other things. And only later did we find that it was actually part of the PI3 kinase pathway and it regulated AKT. And that clarified lots of things. A- and in many ways, mTORC2, you could actually even say, and we've written papers arguing this, that it's almost like upstream of mTORC1 because the PI3 kinase pathway-

   10. PAPeter Attia29:55

       Mm-hmm

   11. DSDavid Sabatini29:55

       ... is one of the inputs into mTORC1. In many ways, mTORC2 is less important than mTORC1. I mean, you can modulate it more and still survive more. So we've really focused largely on, on mTORC1. And when I first got here, you, you sort of asked me, "Okay, well, what did you end up doing," right? And, and, and I was pretty worked up when I got here, and I had to real- realize I was sort of running a lab and, and unclear exactly what I was gonna do. And I ended up working on mTORC1- Or mTOR, I should say, largely 'cause I didn't know anything [laughs] else. And so I basically had to work on something. And I remember some people here were pretty critical of me working on rapamycin. They were like, "Why are you working that silly molecule? Okay, now you have the target." And, and the truth was that's what I knew how to do.

   12. PAPeter Attia30:39

       Even at the time, you didn't appreciate what you do now, which is that effectively mTOR sits at the center of the universe for at least some of the things that we care a lot about, including potentially longevity.

   13. DSDavid Sabatini30:54

       We did not. We did not.

   14. PAPeter Attia30:55

       When did that become clear to you? Is this-

   15. DSDavid Sabatini30:57

       That became clear ... You know, we tried ... When we started to understand the connection to nutrients and the fact that caloric restriction had been connected to longevity, we started thinking, okay. We, we actually tried doing experiments on worms at the time with rapamycin. Turns out-

   16. PAPeter Attia31:10

       Hm

   17. DSDavid Sabatini31:10

       ... rapamycin doesn't get into worms. But there was really some im- it was an important paper in worms where there was a mutant in the C. elegans version of mTOR that had longevity effects. I would say that was sort of the key paper.

   18. PAPeter Attia31:24

       And this is unrelated to DAF-2.

   19. DSDavid Sabatini31:26

       Unrelated to DAF-2, although interestingly, in the screens, they gave the DAF mutants, one of the DAF mutants, in retrospect, one of the ones actually had never been identified what the gene was. It was simply a mutant that had-

   20. PAPeter Attia31:37

       Hm

   21. DSDavid Sabatini31:37

       ... a mutation, turns out to be raptor. I think it's DAF-15. I don't quite remember.

   22. PAPeter Attia31:42

       Okay.

   23. DSDavid Sabatini31:42

       So there was a-

   24. PAPeter Attia31:43

       Not 16, I'm tr- okay.

   25. DSDavid Sabatini31:45

       I don't remember. We, we could look it up.

   26. PAPeter Attia31:46

       We'll, we'll look that up. Yeah.

   27. DSDavid Sabatini31:47

       But so it was interesting. There was all these DAF mutants that had these interesting phenotypes, and once we found raptor, someone went back and found that one of the DAF mutants was actually raptor. So that connected again to mTORC1. Now not only were there mutations in mTOR itself, the C. elegans mTOR, but also in the C. elegans raptor that connected it to it. We did not realize ... Now, you know, of course our paper was published in Cell, Stuart Schreiber's paper was published in Nature. I remember Nature wrote a news and view, so people appreciated that the finding of mTOR mattered, but I think more from, okay, this is a new signaling pathway, this is a new component. I don't think we realized that it really, we certainly didn't, at the center of so many important processes as we do now. People sometimes joke and say, "Well, you know, mTOR does everything." Right? So if something does everything, at some point, okay, how interesting is it, right?

   28. PAPeter Attia32:39

       [laughs]

   29. DSDavid Sabatini32:39

       And so i- it's a funny, uh, line-

   30. PAPeter Attia32:42

       Not a lot of people studying oxygen these days.
8. 33:47 – 39:32

   Why Inhibiting mTORC1 Extends Life: The General Contractor

   1. DSDavid Sabatini33:47

      I find that a very interesting question, and it's a question that I'm often asked. And I think we should say up front, we don't know the answer to that question. One way of addressing it is that you can eliminate many of the things that mTORC1 does and then ask, "Well, now when I inhibit mTORC1, do I still get lifespan effects?"

   2. PAPeter Attia34:06

      Mm-hmm.

   3. DSDavid Sabatini34:07

      If you do that and look at many different processes, probably you'd vote autophagy is the most important thing that it regulates, which, as you know, autophagy is this self-eating process where the cell breaks down some of its own components and presumably has to remake them. And so in a kinda naive way, you might imagine that what you're doing is throwing out the old and making new, and again, naively, you might think, well, that's gonna rejuvenate a cell, although none of that is, of course, proven. So that would be a simple answer, but it clearly is not the whole answer. So my answer to your question why mTOR modulation has these longevity effects and yet many other pathways that in some ways are as complicated and as important for a variety of other things don't, and this is the way I think about it. I think about it, like, I try to analogize it a little bit to, like, a building, right? So if I wanted to take a building like this one and make it younger, rejuvenate it, you know, I, I can't just get a plumber or electrician or a painter, right, or wood- a carpenter, 'cause the building has many different features of which all of them have aged.

   4. PAPeter Attia35:13

      Mm-hmm.

   5. DSDavid Sabatini35:14

      What you really need is a general contractor, right, who's gonna then bring in all of those people-

   6. PAPeter Attia35:18

      All the subcontractors

   7. DSDavid Sabatini35:19

      ... and fix all the subsystems. We look at an old building. An old building has lots of things that are messed up from it, from the electrical systems to the windows to everything. And to some extent, mTOR is like the general contractor for the cell. I don't know of any other pathway that does as many things, right? mTOR basically has a finger in every major process in the cell. And so I think another way of-

   8. PAPeter Attia35:43

      Hm

   9. DSDavid Sabatini35:43

      ... of thinking about your question is, what's the simplest way to manipulate a cell so that lots of things are changed? And the answer to that is to modulate mTOR. Because all of these other pathways will s- you know, maybe some of them will regulate transcription. Maybe some will do translation. Some are gonna change the shape of the cell. But if you gotta do all those things plus more, the only way of doing it with, like, a single hit is to go after mTOR. It is, like, the thing. It's like the brain of the cell, which then has all these subroutines that do all these things. And so to me, that's the simple answer, is that to impact the state of a cell, to rejuvenate it, to slow the aging process, you can't do one thing. You can't do two things. You can't do three things. You can't do 10 things. You probably have to do 100 things, and the only way you can do all of those things with one button ... is to go after mTOR

   10. PAPeter Attia36:34

       Now, in biology, that tends to be a two-edged sword, right? Because presumably if you have one switch that controls so much, you know, if you have the wrong general contractor or if the general contractor does the wrong thing, the effect is much more noticeable. So when did it become apparent to you or how is it apparent to you that this isn't just a linear relationship between signal and response?

   11. DSDavid Sabatini37:03

       This is a very good point, right? So you could say, well, as a general contractor, there's a lot of things, and so not only is anti-aging one of the things it does, but how you sort of, for example, sperm production, which is a potential target, heart function, right? All these things require it. And so, okay, you might get the anti-aging effects, but you're also gonna get all the downsides. And I think that is certainly true, and that's the major issue with targeting mTOR. And so the-

   12. PAPeter Attia37:27

       Because at the time you really kicked your efforts off here, people thought of rapamycin and mTOR as a one-trick pony, which was you give this drug every day, your immune system, specifically your cellular immune system, doesn't work as well.

   13. DSDavid Sabatini37:40

       Right.

   14. PAPeter Attia37:40

       And at least for that subset of patients who had foreign organs in their body, that's a, a reasonable thing to have.

   15. DSDavid Sabatini37:46

       And, and incidentally, you know, there is now ... So funny, rapamycin started as an immunosuppressant. The interest in mTOR in the immune system pretty much was unexistent, and now there's an entire field of so-called immunometabolism, of which mTOR is probably 50% of that whole field. And so it's mTORC1, mTORC2 in different immune cells, Tregs, right, T helpers.

   16. PAPeter Attia38:06

       How much of this came out of the Novartis work from three years ago? Was it, did this precede that or?

   17. DSDavid Sabatini38:11

       Well, it, it preceded it, that. I mean, the Novartis work was the first sort of work in humans, right-

   18. PAPeter Attia38:15

       Yeah

   19. DSDavid Sabatini38:16

       ... that clearly showed modulation, beneficial modulation of the immune system. But in terms of studying which immune cells are most affected by rapamycin and what the role of mTORC1, that's come out of the academic world-

   20. PAPeter Attia38:26

       Mm-hmm

   21. DSDavid Sabatini38:26

       ... by a number of groups that were heavily enabled by the discovery of raptor and rictor because now you could genetically inhibit each of those. And one of the things that my lab, we've really tried to do is to put our mice out there, and so people use, for example, our raptor mouse-

   22. PAPeter Attia38:41

       Mm-hmm

   23. DSDavid Sabatini38:41

       ... or flocks, so-called flocks raptor mouse a lot. But this question of, in a way what you're saying is how much can we sort of tolerate of mTOR modulation for beneficial effects versus-

   24. PAPeter Attia38:51

       Mm-hmm

   25. DSDavid Sabatini38:51

       ... non-beneficial ones? And again, I don't think we have the answer to that. To some extent, rapamycin is not a complete mTORC1 inhibition. We know that. And complete mTORC1 inhibition is probably not tolerated. And so rapamycin might be as good as you can get. You get some modulation of-

   26. PAPeter Attia39:08

       Well, say a little bit more about that. So you're saying if we could wave a magic wand, Bobby was very eloquently spoke about why inhibition of mTORC1 leads to inhibition of mTORC2 and what the temporal relationship of that might be. But I don't think we got into this issue, which is if I could wave a magic wand and completely inhibit mTOR complex 1, not lay a hand on complex 2, why wouldn't that be a good thing?

9. 39:32 – 42:57

   Limits of Rapamycin and the Ideal mTORC1 Inhibitor

   1. DSDavid Sabatini39:32

      Because mTORC1 is probably required for the growth of any normal cell. So to make, for a cell to basically make its organelles, to make its proteins, to divide, mTORC1 is probably an essential.

   2. PAPeter Attia39:46

      So at that level it would start to mimic a, you know, crude chemotherapeutic agent that modulates ... Like a, it becomes 5-FU at a ridiculous dose, or s- s- you know, something that's gonna basically slough off epithelial cells-

   3. DSDavid Sabatini40:00

      Exactly

   4. PAPeter Attia40:00

      ... your hair falls out.

   5. DSDavid Sabatini40:01

      Cause basically atrophy of everything, anti-growth, and probably cell death. And in fact, in many tissues when you delete raptor, it can be quite bad.

   6. PAPeter Attia40:10

      That's the phenotype?

   7. DSDavid Sabatini40:11

      Yeah. Like in epithelium in the gut, at least when we've looked, that's the way-

   8. PAPeter Attia40:14

      I see.

   9. DSDavid Sabatini40:15

      So I don't think there's two issues going on here. As, as Bobby surely told you, rapamycin will also with a longer time point inhibit mTORC2-

   10. PAPeter Attia40:22

       Yes

   11. DSDavid Sabatini40:22

       ... and that is potentially bad for glucose homeostasis.

   12. PAPeter Attia40:25

       Yes.

   13. DSDavid Sabatini40:26

       The other issue is that rapamycin doesn't fully inhibit mTORC1. So in an ideal world you'd like to have ... And what I mean by that is that mTORC1 probably has dozens of substrates, and rapamycin only ef- effectively inhibits some of them and not others, including, for example, autophagy is relatively weakly modulated by rapamycin. So-

   14. PAPeter Attia40:45

       Why is that?

   15. DSDavid Sabatini40:45

       Because the substrate ... What rapamycin basically does is sort of occlude the substrate binding channel-

   16. PAPeter Attia40:52

       Uh-huh

   17. DSDavid Sabatini40:52

       ... in mTORC1, and it's basically physically occluding. And depending probably, we don't, you know, this is somewhat, uh, hand waving, but there's some evidence for this. Probably the size of the substrate, if it's smaller, it might get in easier and it's not occluded. If it's bigger, it's gonna get blocked.

   18. PAPeter Attia41:07

       Right.

   19. DSDavid Sabatini41:07

       And so probably the key substrates in the autophagy pathway simply are not as affected because they get into the kinase domain of mTORC1 still.

   20. PAPeter Attia41:14

       By the way, is this issue different for any of the rapalogs?

   21. DSDavid Sabatini41:18

       No. I-

   22. PAPeter Attia41:18

       They're all basically producing the same effect as rapamycin.

   23. DSDavid Sabatini41:23

       Some people might argue differently from that, but in my experience of them, they are basically like rapamycin with maybe different PK/PD properties. But from a mechanistic point of view, I wouldn't expect differences in this, and I, and I haven't seen those differences. But so in, in an ideal world, you might want a molecule that would inhibit all the substrates of mTORC1, not touch mTORC2, but then let the-

   24. PAPeter Attia41:46

       But not do it constitutively.

   25. DSDavid Sabatini41:47

       Not do it constitutively, but also maybe not to 100% inhibition.

   26. PAPeter Attia41:50

       Mm.

   27. DSDavid Sabatini41:50

       Right? So I'm not sure I would use that molecule to wipe out mTORC1.

   28. PAPeter Attia41:54

       Yeah.

   29. DSDavid Sabatini41:55

       I would use it to bring down all the mTORC1 activity of all towards our service to some extent, leaving mTORC2 intact. I think that's gonna be very hard to do by targeting mTORC1 itself, because mTORC1 and mTORC2 share the same kinase domain, and so you can't go for the ATP binding site, which is most kinase inhibitors. mTOR is a, is a kinase, a protein kinase. Like Gleevec, for example, they all go for the ATP binding site. So we're probably not gonna be able to do it for that. And so our view is that the way to accomplish that is not to go after mTORC1 itself, but to go after its upstream regulators. And the big benefit in my view of doing that is that you should be able to have something now that modulates all mTORC1 substrate, and you can also start to get tissue specificity 'cause these regulators vary in importance across tissues. The aspect of this pathway that's kept our attention for two decades at this point is that mTORC1 is basically regulated by everything Anything I do to the cell, whether I change nutrients, oxygens, pH, growth factors, osmotic-

10. 42:57 – 50:00

    Nutrient Sensing: Insulin, Glucose, Leucine and Arginine

    1. PAPeter Attia42:57

       What's the direct effect of glucose and/or insulin on mTORC1? It obviously plays an enormous role on complex two.

    2. DSDavid Sabatini43:04

       It seems to activate them, right? So through independent pathways. There seems to be a pathway through which insulin acts, and there seems to be a pathway through which glucose acts, and even the glucose pathway probably has several sub-branches to it.

    3. PAPeter Attia43:14

       I see, which again, teleologically makes sense because if it's a nutrient sensor, it should be activated by nutrients, but it becomes very complicated now because you have the same nutrient acting-

    4. DSDavid Sabatini43:27

       In-

    5. PAPeter Attia43:27

       ... on completely different areas.

    6. DSDavid Sabatini43:28

       Right, and that's probably-

    7. PAPeter Attia43:29

       With great redundancy

    8. DSDavid Sabatini43:30

       ... because you're looking at ... In the cells that we use in culture, we can get both of these sensing systems, where probably in vivo, there's tissues are gonna care more about the insulin arm, there's tissues that are gonna care much more about the glucose arm, and there's some that are gonna care about both, right? So if you think about being a peripheral tissue, let's say you're, you're a cell somewhere in your leg, and you need to make a decision.

    9. PAPeter Attia43:49

       A muscle cell.

    10. DSDavid Sabatini43:50

        Let's say a muscle cell. You need to decide whether you're an anabolic state or a catabolic one. So clearly there's things of use and all that. But let's say just in response to nutrition, you kind of want two pieces of information, right? One, you wanna know that the organism that you live in as a whole is in a fed state. You wanna be a good member of the community, and that is reflected by things like insulin-

    11. PAPeter Attia44:12

        Mm-hmm

    12. DSDavid Sabatini44:12

        ... which basically tells you the pancreas-

    13. PAPeter Attia44:13

        It's a global metric.

    14. DSDavid Sabatini44:14

        Right. Pancreas saw glucose. We sent out insulin.

    15. PAPeter Attia44:17

        Yep.

    16. DSDavid Sabatini44:18

        And the other one is you actually wanna know that you have the nutrient that you need. You could have, like, central command telling you, "Hey, I got glucose," but if you don't have glucose, you can't do anything, right?

    17. PAPeter Attia44:27

        It's a local issue.

    18. DSDavid Sabatini44:29

        And so you really want, like, the central signal and you want the local signal.

    19. PAPeter Attia44:32

        Mm.

    20. DSDavid Sabatini44:33

        So I think one can interpret that the pathway senses both the nutrient and-

    21. PAPeter Attia44:37

        So the amino acid could be a local ...

    22. DSDavid Sabatini44:39

        Right.

    23. PAPeter Attia44:39

        And the glucose molecule itself-

    24. DSDavid Sabatini44:40

        Itself-

    25. PAPeter Attia44:41

        Yeah

    26. DSDavid Sabatini44:41

        ... is a local one.

    27. PAPeter Attia44:41

        Yeah.

    28. DSDavid Sabatini44:41

        And for sure, we, we know it is, right? And the-

    29. PAPeter Attia44:43

        Whereas the larger peptide can be-

    30. DSDavid Sabatini44:45

        Exactly
11. 50:00 – 54:35

    Sensing Across Species and the Methionine/SAM Sensor

    1. PAPeter Attia50:00

       So say more about methionine because in the protein restriction literature, certainly one argument is that methionine restriction specifically could be beneficial if one believes that low IGF is beneficial.

    2. DSDavid Sabatini50:13

       Mm-hmm.

    3. PAPeter Attia50:13

       And we can talk about whether that's causally the case or not, not even getting into the IGF binding proteins. Where does methionine fit into TOR?

    4. DSDavid Sabatini50:22

       Right. So, so methionine actually is a very interesting one. As you said, there's extensive literature on what's so-called methionine restriction having quite beneficial effects-

    5. PAPeter Attia50:29

       Mm-hmm

    6. DSDavid Sabatini50:29

       ... from glucose homeostasis actually to quite very reasonable lifespan extension effect, as good as caloric restriction. And there are some papers in flies, genetic papers, that suggest that some of the methionine restriction effects go through the TOR pathway in flies. We got to this basically through the protein. We found a protein of unknown function, and we tried to figure out what it did, and it turned out to be a sensor of this metabolite called SAM, S-adenosylmethionine-

    7. PAPeter Attia50:56

       Mm-hmm

    8. DSDavid Sabatini50:56

       ... which is basically made by methionine. So it's actually quite interesting as a sensor.

    9. PAPeter Attia50:59

       And people supplement with a variant of SAM, SAMe. Yeah.

    10. DSDavid Sabatini51:02

        Exactly. Right. SAM actually has some pretty interesting clinical effects. I've seen some quite convincing data on antidepressive effects of SAM-

    11. PAPeter Attia51:09

        Mm-hmm

    12. DSDavid Sabatini51:10

        ... out there. So this is, the sensor here is interesting 'cause the other sensors we have directly bind leucine, directly bind arginine. This one doesn't bind directly to methionine. It binds to a metabolite made by methionine, which is SAM. Which SAM, many things can feed into SAM, so it actually can integrate lots of signals. So this sensor basically behaves like the other ones. As soon as methionine levels go down, SAM levels go down. This sensor therefore inhibits this pathway. And so-

    13. PAPeter Attia51:38

        So SAM would not be a longevity agent by the oversimplification that excess SAM would be akin to excess methionine would be akin to-

    14. DSDavid Sabatini51:47

        Exactly

    15. PAPeter Attia51:47

        ... failing to inhibit TOR.

    16. DSDavid Sabatini51:48

        Exactly.

    17. PAPeter Attia51:49

        TOR complex 1.

    18. DSDavid Sabatini51:49

        So, so methionine restriction could be presumably rescued by giving SAM.

    19. PAPeter Attia51:54

        Mm-hmm.

    20. DSDavid Sabatini51:54

        Right? And we actually know in the pathway that we've built in cells that that's true. You can bypass methionine simply by giving SAM. So a molecule that could basically trick this sensor into thinking that SAM was not there-

    21. PAPeter Attia52:07

        Yeah

    22. DSDavid Sabatini52:07

        ... would be a quite interesting one. I think methionine is probably the most interesting of these amino acids because if you fast an animal, methionine is the amino acid that drops the most. And the reason for this-

    23. PAPeter Attia52:18

        And you looked at all of the amino acids, and that's-

    24. DSDavid Sabatini52:21

        In, in mice.

    25. PAPeter Attia52:22

        Okay.

    26. DSDavid Sabatini52:22

        Okay? So we should do some of this in humans. But it, it kinda makes sense.

    27. PAPeter Attia52:25

        I, I can volunteer if you want.

    28. DSDavid Sabatini52:27

        For sure, yeah. Well, we could definitely profile.

    29. PAPeter Attia52:29

        Yeah.

    30. DSDavid Sabatini52:29

        The reason probably is that arginine you can make some.
12. 54:35 – 59:40

    Intermittent Dosing, Cancer, and the Balance of Anabolism and Catabolism

    1. PAPeter Attia54:35

       So coming back to rapamycin specifically and all of its limitations, so we've established that you can't just take rapamycin all day every day because that experiment's been done. That's the, that's the clinical utilization of it.

    2. DSDavid Sabatini54:47

       Right.

    3. PAPeter Attia54:47

       Certainly the animal data have suggested, and the human data have suggested, that an intermittent dosing of rapamycin could produce a beneficial phenotype with respect to longevity specifically, and also with respect to immune function. So if you had to guess based on triangulating these data, assuming no new drug came along that was going to selectively do some of the things that, you know, we've discussed, how would one dose in an animal or a human for that matter rapamycin to increase the odds in favor of longevity and against harmful side effects? Which presumably the most obvious ones would be immune suppression and/or glucose homeostasis disruption.

    4. DSDavid Sabatini55:30

       Yeah, and also epithelial sort of toxicity-

    5. PAPeter Attia55:32

       Yeah, yeah

    6. DSDavid Sabatini55:32

       ... or particularly the GI epithelium. So I think the intermittent approach is definitely the one that makes sense because if, if you buy the idea that you want to induce autophagy, which you know a lot of people of course, like yourself, who study the effects of a- fasting also view that that's one of the goals of fasting, is to induce autophagy. So if we basically wanna chemically induce autophagy without fasting, I think the intermittent dose is what makes sense, is you, you basically let have a induction autophagy, a relatively weak one with rapamycin, but then let the system rebuild. It's clear that both mTOR, you need just right amounts, right? You can't have too little, it's toxic. You have too much, it's toxic. The same thing with autophagy. If you remove autophagy, it's really toxic. If you have too much autophagy, it's really toxic.

    7. PAPeter Attia56:14

       Cycling anabolism catabolism might be the single most important thing to do.

    8. DSDavid Sabatini56:19

       It might be, right? And I think it's hard for us to know, but those intermittent dosing strategies, every other day feeding strategies all point to that. And the genetics where too much is bad and too little is bad also point to that, right? So if you genetically inhibit this pathway by deleting raptor, if you genetically activate it by deleting these repressors called the tuberous sclerosis complex, both are bad. Both, in fact, in many tissues, like the muscle, give the same output.

    9. PAPeter Attia56:47

       What's-

    10. DSDavid Sabatini56:47

        They get muscular dystrophy.

    11. PAPeter Attia56:48

        I was ... Yeah, I was just about to say, there's an overlap with muscular dystrophy here, isn't there?

    12. DSDavid Sabatini56:51

        Yeah, exactly.

    13. PAPeter Attia56:52

        So this may be a theoretical question, but when we think about the life-extending properties of rapamycin, do we believe that it is a result of delaying the clinical onset of disease? Let's use a disease where that tends to be more binary, like cancer. But obviously cancer spends probably 70 to 80% of its time undetectable, but due to the, just the law of growth, it becomes detectable only at the end. So do we think that inasmuch as, say, taking, you know, these agents would allow you to live longer by not dying from cancer at the same period of time, does it delay the time it takes for cancer to become clinically detectable and/or delay the demise of the animal once it has that cancer?

    14. DSDavid Sabatini57:39

        Yeah, I think it specifically, you know, in the case of cancer, rapamycin is ... There are some situations where it has some decent activity, but in general, it's not a cytotoxic agent, right? It's not gonna kill a cancer cell. It's really gonna s- s-

    15. PAPeter Attia57:49

        Once an organism has cancer-

    16. DSDavid Sabatini57:51

        Once it has

    17. PAPeter Attia57:51

        ... do we know if it's doing anything to prevent the development of cancer?

    18. DSDavid Sabatini57:54

        We don't know that well, and the only ... There actually has been some epidemiological data where people have compared cancer rates in transplant patients-

    19. PAPeter Attia58:02

        Identical patients who are with and without rapa

    20. DSDavid Sabatini58:04

        ... FK506 versus rapamycin. And it's actually quite interesting because, as you know, immunosuppression in general is associated with higher cancer rates, right?

    21. PAPeter Attia58:12

        Yeah.

    22. DSDavid Sabatini58:12

        The idea that you have less immune surveillance.

    23. PAPeter Attia58:14

        Of course.

    24. DSDavid Sabatini58:15

        That's not seen with rapamycin. So it is seen with FK506. It's not seen with rapamycin. And the argument has been that rapamycin itself has cancer cell autonomous effect.

    25. PAPeter Attia58:25

        Independent of the immune modulation problem.

    26. DSDavid Sabatini58:28

        Immune, exactly. So you're presumably getting less immune surveillance 'cause it's immunosuppressant, although of course that's not proven. But you're mitigating that-

    27. PAPeter Attia58:35

        Yeah

    28. DSDavid Sabatini58:35

        ... by now directly targeting the cancer.

    29. PAPeter Attia58:36

        And they've canceled each other out.

    30. DSDavid Sabatini58:37

        They cancel each other out.
13. 59:40 – 1:03:17

    mTOR in the Brain

    1. PAPeter Attia59:40

       What do we know about rapamycin and TOR in the brain, especially with respect to neurodegeneration?

    2. DSDavid Sabatini59:47

       Yeah, that's a, that's a really interesting one, and that probably is, is a really important question for the future. So we know autophagy matters a lot in the brain. If you delete autophagy ... And really Mitsushima was the person who kind of made autophagy interesting to lots of people.

    3. PAPeter Attia1:00:01

       And he was awarded the Nobel Prize.

    4. DSDavid Sabatini1:00:03

       No, no, he wasn't.

    5. PAPeter Attia1:00:04

       Oh, he wasn't?

    6. DSDavid Sabatini1:00:04

       Oh, Yoshimi was for original s-

    7. PAPeter Attia1:00:05

       But he didn't share.

    8. DSDavid Sabatini1:00:06

       He didn't, no.

    9. PAPeter Attia1:00:07

       Oh, oh.

    10. DSDavid Sabatini1:00:07

        Which I think was a bit of an oversight in my view, but ... Anyhow, he, he basically studied autophagy in the brain, made mutations, showed you got neurodegeneration, right? So that was a really important finding.

    11. PAPeter Attia1:00:16

        Mm-hmm.

    12. DSDavid Sabatini1:00:17

        Connects up to lysosomal storage diseases, which, you know, autophagy, basically the autophagosome fuses with the lysosomes, so now you have that connection. So I think, like in all tissues, it's a bit of a double-edged sword. You clearly need mTORC1 activity to maintain healthy synapses. Certainly during brain growth-

    13. PAPeter Attia1:00:34

        Mm-hmm

    14. DSDavid Sabatini1:00:34

        ... you do. There, if you make mutations around, boy, in a growing animal, you basically don't have a cortex.

    15. PAPeter Attia1:00:38

        Yeah.

    16. DSDavid Sabatini1:00:38

        Right? On the other hand, you clearly need to be able to modulate mTORC1 to have some level of autophagy to keep the system healthy. Now, you could debate, is that in neurons? Is that in glia? It's probably in both. People have made mutants in-

    17. PAPeter Attia1:00:54

        Mm-hmm

    18. DSDavid Sabatini1:00:54

        ... certainly in neurons, which suggests it's both, but then some of those promoters are a little bit dirty. But the real question in the brain is what modulates mTORC1, because it's not probably nutrients.

    19. PAPeter Attia1:01:04

        Because they're so constant, you mean? Like me-

    20. DSDavid Sabatini1:01:06

        Exactly.

    21. PAPeter Attia1:01:06

        Yeah.

    22. DSDavid Sabatini1:01:06

        Your brain, your body ba-

    23. PAPeter Attia1:01:08

        Yeah, your brain prioritizes-

    24. DSDavid Sabatini1:01:09

        Exactly

    25. PAPeter Attia1:01:09

        ... nutrients in the brain over-

    26. DSDavid Sabatini1:01:10

        It basically protects your ... Right, so if you take an animal and you fast it for two days, a mouse, it loses a lot of weight, 25% of its weight And now you take every single tissue and you weigh it, every tissue has shrunk

    27. PAPeter Attia1:01:21

        Except the brain

    28. DSDavid Sabatini1:01:22

        Some, like the thymus, have shrunk ridiculously. The kidney shrinks, which you wouldn't expect. The heart shrinks. The brain, nothing. Now, clearly, probably if you ... In a mouse, you can't do that extreme of fast, and so the body protects the brain from a nutrient point of view, yet mTORC1 activity is high there. Clearly we know that we have to modulate autophagy, so something must be inhibiting mTORC1 in the-

    29. PAPeter Attia1:01:43

        By the way, this is my peripheral argument for why, and I'm in the huge minority here, I do not think the brain is really the appetitive center. I think it's the modulator, but I, for that exact reason, think it wouldn't make sense for evolution to put our appetite center in our brain.

    30. DSDavid Sabatini1:01:58

        Hmm.
14. 1:03:17 – 1:11:24

    Thought Experiments: Rapamycin versus Lifestyle, and Dream Studies

    1. PAPeter Attia1:03:17

       One of the challenges of studying biology in humans is that you can't do the same experiments you can do in animals. If, if we had a gedankenexperiment where you could take a sufficiently large number of human subjects and divide them into groups, and you ... So you had a control group. These guys were gonna do everything that the standard American does. You had a group that you could give rapamycin to in any way, shape, or form you decide. And then you had a group in which you could manipulate their behaviors in ... And they would behave as animals. They would do anything you want with respect to how they would eat or how much or when, exercise, whatever you like. First question is, how would you design arms two and three to have the best outcome with respect to longevity? And then I, I'm very curious to know what you think the difference between groups two and three would look like.

    2. DSDavid Sabatini1:04:04

       So I think as we spoke before, I mean, the mTOR modulator arm would probably be an intermittent-type dosing one, where hopefully we'd have biomarkers of that. And you and I have spoken in the past, a biomarker for autophagy, for example, a biomarker for mTOR activity, and you have to decide what tissues you care about. Probably the muscle would be one that you'd want to focus quite a bit on-

    3. PAPeter Attia1:04:20

       Mm-hmm

    4. DSDavid Sabatini1:04:20

       ... and perhaps the liver. Now, I don't think that mTOR modulation on its own is gonna give you all the benefits of good lifestyle modulation, right? So it might give you lots of the benefits of the dietary manipulations, the fasting manipulation, although clearly there's differences there. But I'm not sure if it will give you all the benefits of the exercise modulation, right?

    5. PAPeter Attia1:04:40

       Hmm.

    6. DSDavid Sabatini1:04:40

       And so if, on the lifestyle side, which you obviously know better than almost anyone what you'd exactly want to do, there'd clearly be an exercise component to it on top of a dietary component. I think mTOR modulation will give you a subset of that.

    7. PAPeter Attia1:04:54

       I see.

    8. DSDavid Sabatini1:04:55

       And so-

    9. PAPeter Attia1:04:55

       So let's simplify the experiment then. Let's assume that everything but food is the same in the groups, and the rapa group gets the intermittent doses you see fit, and the other group now can fast or do any sort of CR mimicry that you want. Do you think that normalizes the playing field?

    10. DSDavid Sabatini1:05:13

        I think it, it gets a lot closer for a simple reason. So if you give an mTOR modulator versus a fast, remember, there's one really important difference, is that nutrients in the mTOR modulation case are actually still high-

    11. PAPeter Attia1:05:24

        Yeah

    12. DSDavid Sabatini1:05:24

        ... 'cause the person's not fasting. In fact, if you actually look in cells, they can actually even be higher because the cell thinks it's starving, so it does all this-

    13. PAPeter Attia1:05:31

        So it, it shuts down processes that would accumulate them.

    14. DSDavid Sabatini1:05:33

        Yeah, and it upregulates more accumulation.

    15. PAPeter Attia1:05:34

        Yeah.

    16. DSDavid Sabatini1:05:34

        And so we've looked in cells, so actually they tend to go up, versus a fast, where things are gonna be lower. On the other hand, if all those nutrients are eventually doing their stuff by communicating through mTOR and you've sort of inhibited downstream, to those downstream processes, things look the same. Doesn't matter we have a lot of nutrients here and very low nutrients here, so the modulation of mTOR is what matters. And so I think to answer that question, we really need to understand whether all these nutrients, which are still there in the fed state, have a lot of other signaling effects. And it would be naive to think that they don't.

    17. PAPeter Attia1:06:09

        Mm-hmm.

    18. DSDavid Sabatini1:06:09

        They do. We know they do. Now, do they matter, and do they matter a lot? I don't think we know, and I think a lot of the genetics and pharmacology would argue that within the range that we can actually manipulate lifespan, it could be that those fasting regimens and rapamycin are somewhat similar.

    19. PAPeter Attia1:06:26

        And certainly in the mice it appears to be at least similar, if not better, in favor of rapamycin.

    20. DSDavid Sabatini1:06:34

        Exactly. And that's why I'm particularly excited about the methionine restriction work, because, you know, caloric restriction is not only hard to do in people, it's hard to do in animals, too. It's really hard. I mean, you have to weigh the food, pairwise feeding. It's a real pain and, and it's a real restriction to doing lots of experiments, while methionine restriction's a lot easier.

    21. PAPeter Attia1:06:51

        Yeah, you just buy methionine-free chow.

    22. DSDavid Sabatini1:06:53

        Yeah. Not f- totally free, but lower, right?

    23. PAPeter Attia1:06:55

        Yeah, yeah.

    24. DSDavid Sabatini1:06:56

        And so there we can do these kind of experiments where you could do methionine restriction plus rapamycin.

    25. PAPeter Attia1:07:00

        Mm-hmm.

    26. DSDavid Sabatini1:07:01

        Right? And actually ask, do you get synergy, do you not, right?

    27. PAPeter Attia1:07:03

        Mm-hmm.

    28. DSDavid Sabatini1:07:03

        So, so I think that's gonna be, uh, an, an intervention that's gonna be a lot easier for us to play with.

    29. PAPeter Attia1:07:08

        So if resources weren't constrained- What, what are the sort of dream experiments or what's a dream experiment that, that has been on your mind that you wanna do, but it's either technically we're not there yet, or it's just economically it poses-

    30. DSDavid Sabatini1:07:22

        In humans?

Episode duration: 1:11:27