Dr. Samuel Denmeade Video (Text Version)
Title of Talk: Development of a PSMA-Activated Prodrug as Therapy for Metastatic Prostate Cancer
Speaker
Our first speaker is Dr. Samuel Denmeade. Sam is an old friend and colleague of mine from Johns Hopkins where he is now a full Professor in both Oncology and Pharmacology and Molecular Sciences. His research focus has primarily been on the identification and study of novel cancer selective targets for enzymatic function that can be exploited for therapeutic and diagnostic purposes. He’s earned his medical degree from Columbia and before going onto Chicago for his residency he did his Fellowship at Johns Hopkins and has been there ever since. He worked under my former mentor as well, John Isaacs and it’s a pleasure to welcome Sam to the podium; thank you, Sam.
Samuel Denmeade, M.D.; The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins Cancer Center
Thanks Dan for that introduction. So I’m going to talk to you today about a long-standing project in our lab and sort of give you some of the history of it and how we’ve managed to take it from an idea to clinical trial at the end. And so I’ll begin with my necessary disclosure.
So I am a founder and consultant for a company called GenSpera which is trying to tell you what I’m going to tell you today into patients and that’s all being managed by Johns Hopkins as they do for us. So I stole this from Jianfeng Xu who showed you this earlier and I just wanted to myself thank the DoD. I had the honor to—and opportunity to go to Fort Detrick about 10 years ago to present some of our work and I’m amazed and—and really to see that most of the folks that were there then are still there now, so it’s—it’s a dedicated group and I—like many people here my first grant I ever had was a New Investigator Grant from DoD. I had a few of the Idea Grants as well and the research I’m showing you here has primarily been supported by the DoD and Prostate Cancer Foundation.
So I want to change this a little bit in my own way to—to make it look like that. I—I hope I can come back and talk to you again about the clinical work we’re doing with this stuff and so I thank you all for your advocacy because I—I really hope we can keep this alive because it’s—I think it’s a great thing, the whole grant mechanism we have.
So my talk starts with some initial observations that go way back to the 19—late 1980s and these were made by John Isaacs who was my mentor and now my colleague and my long-term friend as well, and what John’s lab had—had showed was that before the word apoptosis was even a word John was studying program cell death which was what we called it at that point. And what John showed was that androgen-independent cells just like androgen-dependent cells die by all the same pathways; they just don’t initiate death when you take away androgen.
The second thing they observed in his lab and others is that prostate cancer grows really slowly compared to other cancers, and this may explain in some ways why prostate cancer is somewhat resistant to chemotherapy because chemotherapy kills cells trying to grow fast. And then the last observation was that if you could interfere with the calcium levels in the cell, you could trigger the cells to die. And so that led us on this path of how can we do this in prostate cancer and make a drug.
So this just shows you some data on the growth rates of cancer, so prostate cancer is way down here. You can see that compared to other cancers, the proliferative rate, how many cells are actually growing in the cancer at a particular time is extremely low for prostate cancer, much lower than the normal bone marrow and your colon and the skin, and so some of the problems we see with chemotherapy relate to these cells are actually growing faster than the cancer.
So our goal was to figure out a way to try to kill cells without requiring them to have to grow as a mechanism. So we became very interested in this drug I’m going to tell you a bit about called Thapsigargin. Thapsigargin was discovered by our collaborator and colleague Dr. Soren Christianson at the University of Copenhagen. This is a very complicated molecule that’s a natural product made by a plant. And I’ll show you a picture of that in a second. And the way Thapsigargin works is—is normally in the cell there’s a pump that keeps the calcium levels at a very low level in what’s called the cytosol of the cell and at very high levels in a part of the cell called the endoplasm reticulum where—where proteins are made in the cell. Thapsigargin actually is able to block that pump and by doing so it causes the calcium to leave this compartment and enter this compartment. And when the calcium is in the wrong compartment all hell kind of breaks loose in the cell; the cell kills itself by apoptosis because it can't handle that influx of calcium in the wrong place.
So Thapsigargin comes from this plant called Thapsia Garganica; it’s a beautiful yellow flower in the late spring and early summer and then it turns to these seeds in the—in the early summer. It’s a plant that’s been known for a very long time to—to sort of medicine I guess you can call it. It grows as a weed. It was known to the ancient Greeks and it was—there’s literature by Pliny and Aristotle and the Romans, by Galen describing Thapsigargin. It was known at the time to be very toxic so in—in Arabic literature it’s known as the death carrot because if camels would eat this plant they would die. It could kill sheep; it could kill cows and as early as—up until the 1900s it was used as a blistering agent and so you could buy this at the drugstore as—as a drug.
And through the power of Google, we found out all kinds of stuff about it on the Internet. This is a recipe of how to make a resin on a plaster and we even found that at some point this was something sold by Johnson & Johnson when they were called the Manufacturing Chemist in New Jersey. So this was a warning about the—to make sure you buy Johnson & Johnson Thapsia plasters because they make it the best way.
So it’s—it’s a lot of stuff is known about the plant and in the 1970s, Dr. Christianson discovered the active agent. So Thapsigargin is really potent. This is the NCI screen where they take natural products and different drugs and run them through 60 different cell lines and they look how toxic they are, so you can see Thapsigargin really kills everything. We’ve learned also that it kills all normal cells so it’s not specific to prostate cancer; it’s a very potent killer of—of cells. And in this assay at least, it was 100-times more potent than Taxol or Docetaxel in these assays. So this is just a—how well it kills, and the smaller number is more potent.
And the thing we got excited about Thapsigargin based on prostate cancer is if you take cells that grow in tissue culture like we all do our assays, they grow very fast—these cells. So they—almost all the cells are in a growth phase in the plastic dish. And I showed you that prostate cancer grows very slowly, so that is not a very good model of prostate cancer but it’s what we use to screen for drugs. And if you look at the drugs we use as chemotherapies they’re very effective; these blue lines—at killing those cells when they’re growing fast in their—in their normal state as is Thapsigargin. And then we—we developed a system where we could make it grow slower and approximating how slow prostate cancers grow and now you see the—the chemotherapy drugs we use are relatively ineffective at those—at killing those cells whereas this drug, Thapsigargin remains very effective. So we think this is a good drug for prostate cancer based on some of the biology we know based on the growth rate.
The problem is because it kills everything, as you would imagine it’s a very potent rodenticide and so when we put this into mice we can't give enough of it, so the mice kind of look like this when we start and then eventually they look like this, so we—we can't use it by itself as a drug. And so the mission statement of the lab has been can we really figure out a way to make Thapsigargin a drug? Can we come up with a therapeutic index so we can treat people? So that—we—we sort of developed this idea, John initially and then together as a—can we make a pro-drug? And so what a pro-drug is—we take a drug which is very toxic and in our case we add a peptide to it and the goal is to inactivate the drug by hooking something large to it, so it can't get into cells; it can't get to the right place in the cell. It can't do what it has to do. And then we take advantage of the fact that cancers make proteases which are able to cut peptides into—off of things so that only in—in the setting of the right protease would the drug be activated. And we can take advantage of the fact that prostate cancer makes a number of different proteases. We started out by trying to target PSA and there’s another story behind that I could tell on another day. We looked at another protease of the prostate called HK2 and then most recently in the subject of our Idea Grant was prostate-specific membrane antigen which you heard Dan talk a little bit about.
We’ve also focused on some cell—some targets in the stroma. PMSA is also made by endothelial cells in cancer and another protein which I had a poster on earlier on something called fibroblast activation protein which is made by fibroblasts. So we’ve been looking at all these but today I’m telling you mostly about PMSA. So the—the design here is that we would give a drug in the blood and this drug would leak into the tumor area where the protease PMSA is. The drug would be liberated from the peptide and then the drug would be able to enter the cells—switch back—and kill them.
So we call this—we’ve been calling this lately molecular grenade. So a lot of the therapies you’re going to hear about are more snipered therapies where the sniper is able to kill the cell, let’s say an antibody combined with the target and kill that cell. But the antibodies typically won't kill the cell if it doesn’t have the target. Just as an example, other cells are like that. The way we’ve designed this we think of more of a grenade approach where we’re going to be activated this drug in the milieu of a cancer. So the—the—we’re going to kill cells that make the target PMSA; we’re going to kill cells next to it that don’t make the target. We’re going to kill endothelial cells that don’t make the target and fibroblasts and other cancers—now other cells in the tumor microenvironment, so we think of it as a grenade because we’re targeting it, but once it explodes it kills that whole environment of the tumor.
So we focused on PMSA for a number of reasons; one it—it sticks out into the microenvironment as a protease. It’s made in very high levels by the normal—normal prostate and even higher levels in prostate cancer cells. And another advantage of this is it’s also made by other tumors—the endothelial cells, the blood cells that grow into those tumors for reasons that nobody understands. But they make PMSA. And it’s also really not known yet what PMSA does. There was a—Dr. [Basich] had a—a poster showing that maybe it’s involved in folate regulation in the prostate cancer but it’s not completely known what—what PMSA does in prostate cancer or in the endothelial cells.
So Dan already gave you some background on this; PMSA is a very unique protease in that it can cleave this neurotransmitter, so this is just two amino acids stuck together. PMSA can cleave this into two pieces. It releases glutamate and—and aspartate compound. PMSA is also present in the brain and it’s thought in the brain that this may play a role in some neuro-degenerative diseases because glutamate is toxic if it’s too high a concentration in the brain. And then the other thing PMSA does is it’s able to take folate, so what we just ate for breakfast had folate in it and folate has a series of amino acids that are attached to it that are called glutamic acid. To digest folate, you have to take all these glutamic acids off to get the folic acid; there are—there are other enzymes in the gut that do that. PSMA does it as well. So we decided we wanted to take advantage of—of—let me go back here before I show you my picture of Ibiza.
We wanted to take advantage of this—of this dual enzymatic activity to try to design a pro-drug and so that was our background going in. The next step we had to do was actually get—get the material I guess—the stuff and so we—we knew that this plant grew on this island called Ibiza which is off the Coast of Spain and so we started this project by having to actually go pick Thapsigargin and so this is us on a nice trip—John Isaacs and I and—and this is John’s wife Sally in a field in Ibiza picking the seeds. And so we started by harvesting a lot of these garbage bags and just to get enough of the starting material I guess to—to—to go forward with the research.
And this slide really summarizes about 9 years of work in one slide and so what we had to do was figure out a way to hook Thapsigargin to a peptide and we did that by doing a lot of chemistry around Thapsigargin with Dr. Christianson. We had to develop a linker to allow us to couple these two together which we eventually did. We had to screen a whole series of peptides that could be broken down by PMSA and we came up with one that worked the best and we had to figure out how to couple these two together and make a drug.
We call the drug G202; it’s a little shorter. It sounds like more what a drug company would make and so from now I’m going to call it G202. So we did a lot of stuff I’m not showing you based—limits on time but—but here I’m just going to show you some of the animal data we had. So we—we put G202 into animals; first in prostate cancer—this is the LNCap model that makes PMSA. You can see we get very nice regressions. This is just one single cycle. Similarly we used a line called CWR22. We made a line that grew in a castrated animal because we wanted to make sure we weren't just affecting testicular function with the drug, and again we saw very nice effects that were quite prolonged with this drug. And then this is another animal model called MDAPCA to be—again that makes PSMA. So in each case we saw very dramatic effects on growth for these pro-drugs and relatively little toxicity. The animals lose a little bit of weight transiently and then gain it back and get back to normal.
This is kind of what the tumors look like. This is what a normal tumor looks like under the microscope with just a big very solid purple mass. Those are all cells. You can see the pink is really just dead tissue. So really sort of wiped out the tumor when we used this drug, and this is really after a couple days of treatment.
The other thing we see that’s quite interesting is the drug is very lipophilic so it has a tendency to want to stick inside the tumor and not leak back into the blood and accumulate in the tumor and that’s what we saw. We see very high levels of the active drug, so this is—this is the starting material; this is what we were hoping to see—this is the drug—accumulate in the tumor and very low levels in other tissues. And we think this is consistent with the targeting of the enzyme.
And then lastly, because this was shown to be a target in other tumors in the endothelium, we did our own screen. This is sort of confirming a lot of other work and what we see is that this is a liver cancer, renal cancer, breast—a lot of cancers make PSMA—and this is scoring for the—the tumor vascular PMSA, not the tumor itself—in contrast none of the normal tissues make PSMA. So again pointing to maybe we can even use this in other tumor types and—and this shows some data with breast cancer. We get a very dramatic effect on breast cancer lines. This is a kidney cancer line that is a little bit more resistant to Thapsigargin. We had to give a little bit more of it, but we could see nice effects there as well.
So this is a bit of a time line of what we had to do, so Thapsigargin was—Thapsia was described in 300 BC. The Greeks did not have a DoD research program and so nothing really happened for about 2,000 years. In 1970, Thapsigargin was discovered. We began work in about 1998 with an Idea Award. After a lot of hand wringing and a lot of research, we licensed this to this company that we started; we started another company called Thapsibiza which is a company on Ibiza that picks the seeds for us. We were able to get the seeds into the United States which was no small task given the Department of Agriculture. And we started making the drug in—so we sort of got started about 2007. We made enough of the drug which was—was difficult; we’ve done all the stuff you need to do—pharmacokinetics and bio-distribution. We developed the formulation that we can put this into people. We did all of the talks that the FDA requires in the rat and monkey and we got an IND in 2009. And we started our trial—our first trial in 2010; our first patient was treated in January. The trial is at Johns Hopkins and the University of Wisconsin. We just added a site in San Antonio, the CTCR. It’s in—right now it’s in patients with advanced cancer, so not just prostate. GenSpera again is the sponsor; we’re—right now we’ve treated 15 patients and our plan is later this year to—to expand to just a prostate cancer-specific trial in the latter half of 2001 [meant 2011?].
This is just briefly our dosing scheme; patients come in and they get three doses. We repeat it every 28 days. We do a lot of blood tests around it to look for the blood levels.
Finally, just to acknowledge, I already mentioned John as my long-term collaborator. Angelo De Marzo has helped us with a lot of the staining. Anastasia Mhaka was a student who did all the initial work. Bora has also helped us do the staining and Mark is my able technician who does all the IV injections. Dr. Christiansen is at the University of Copenhagen—is the—our source of Thapsigargin analogs. Craig Dion is the—the hardest working guy I know who is at GenSpera who—who does all the business for us and raises the money to get the trials done. And then we initially had funding from the Prostate Cancer Foundation as the only funding and so that—I think the partnership of the—of the DoD and the Prostate Cancer Foundation is fantastic. And then we were able to use that foundation funding to get enough data to compete for a DoD Award and we’ve had some nice funding from DoD.
So I’ll stop there and I guess we’ll do questions later or we can do questions now. Thank you for your attention.
Yes, sir?
Question
Good morning. I’m—is that on? Okay; good morning. I’m Glen Spielman and I’m with the Man to Man in Albany for Northeastern New York and I want to thank you for your presentation. It’s made me excited. You said it’s available—it would be effective on all cancers. I have a question about timing. Would this be effective—go to the end saying those with metastases in—in bone or soft tissue or—and—or will it be effective as a preventative when someone’s PSA rises enough that you suspect cancer?
Dr. Denmeade
Well I think we’re going to develop it and test it in the first group, in the patients who have advanced cancer just because we’re in an early stage and that’s kind of how we—we start. There’s no reason why it wouldn’t work in an earlier stage of the cancer. The target is still there. It gets a little—as we all know from this meeting, it’s a little bit harder to image those folks and get a read-out of whether it’s working at that early stage. But certainly we would expect it to work in either stage of cancer and probably eventually would do testing in an earlier stage as well. But the initial stuff is going to be mostly likely in patients who’ve had Taxotere chemotherapy for instance and you know as the next thing to try.
Question
Okay; so it likely will be that it’s post-Taxotere and some chemotherapy?
Dr. Denmeade
Yeah; I think in the—in the clinical testing phase that would be the most likely scenario. And then if it worked you know hopefully it works and we would most likely be able to use it even earlier. You know whether we did it before Taxotere, I don’t know; that would—that’s sort of way out there right now. But—but there’s no reason sort of intellectually why it wouldn’t work earlier.
Question
I’d like to see it started that way by noon on Monday please.
Dr. Denmeade
Okay. How big is your bank account? I’ll just give you my address afterward and you can fund that. Yes, sir?
Question
Harley Vander-Lou—Us Too, Ventura, California—these trials that UW and Johns Hopkins are they Phase 1 and what are the requirements for—are they open, closed—what?
Dr. Denmeade
It’s Phase 1; they’re—they’re open. Right now it’s—we have a third site as well. It’s a Phase 1 so it has to be staggered, so we put a few people on at a time. We have to wait a while and we go up to the next dose. We anticipate if all goes well, later this year, starting a prostate cancer-specific trial. That will have a Phase 1 part; we’ll probably do a couple doses and then get into a—more of a Phase 2 which means we’ll be able to put more people on more quickly. But right now those are the sites. You know whether we’ll add anymore sites I don’t know. I think there’s going to be a site in England as well or in—somewhere in Europe but I don’t know the answer—where exactly it is.
Question
Are you doing all types of cancers right now?
Dr. Denmeade
Right now it’s all types, so we’ve had I think in the 15 patients at least one prostate cancer patient on a very early dose. But we—we—right now we’re just focused on looking at the toxicity and hopefully getting some readout that it does something at the higher doses. Thank you; thank you very much.
Question
One quick question; what toxicity would you anticipate for this? I mean you mentioned the brain and neuropathy; is that sort of what you think is going to be your dose limiting toxicity or do you have any other thoughts?
Dr. Denmeade
Well we you know—we have—the only data we have so far is from monkeys and what we saw in the monkey—so PSMA is also made in the kidney a little bit and so what we saw in the animals is no toxicity to the brain, no neuropathy, no bone marrow toxicity but we saw some toxicity to the kidney at the higher doses. So we think that may end up being our dose limiting toxicity is some—and we think that’s not a non-specific. That’s sort of an on-target because there’s the enzyme in the kidney as well. Thank you.