Chapter 12: Research Advances with Fludarabine and Cytarabine

Chapter 12: Research Advances with Fludarabine and Cytarabine

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In this chapter, Dr. Keating explains how he became interested in Fludarabine, which had been tested for use with rapidly dividing cells. He explains how his studies (early eighties) with the drug worked against acute leukemia and slow-growing CLL and hairy cell leukemia, and notes toxicities, the relatively small number of patients involved in trials, and the remarkably short time frames in which results were obtained. Dr. Keating notes how much he learned from his collaborator, William Plunkett, Ph.D. (interviewed for project, 2013), particularly regarding the effects of the drug inside the cell. [[CLIP Dr. Keating tells an anecdote that illustrates in very practical terms how the clinical and basic science sides of their collaboration worked in obtaining results and creating a molecular portrait of the disease.]] Dr. Keating sketches the research questions behind his studies and briefly explains work integrating the drug Cytarabine into his trials. He notes that the research into these drugs led to a very sophisticated understanding of molecular processes, leading to a targeted therapy approach to CLL. He also lists some challenges that arose in understanding how to block enzymes and pathways, noting that concepts are continually being developed and added.

Dr. Keating then lists the milestone discoveries emerging from his work on Fludarabine, noting that the drug created remission with CLL, with twenty to thirty percent of patients manifesting complete remission. He then explains how the drug regimen was expanded to include Cyclophosphamide, resulting in a new standard of care. He explains that Dr. Plunkett demonstrated that Fludarabine prevented the DNA damage created by other drugs. He notes that he has a small percentage of patients who have survived for twenty years beyond treatment.

Identifier

KeatingM_02_20140520_C12

Publication Date

5-20-2014

City

Houston, Texas

Topics Covered

The Interview Subject's Story - The Researcher; The Researcher; Discovery and Success; Patients, Treatment, Survivors; Professional Path; Obstacles, Challenges; Career and Accomplishments; MD Anderson Impact; Multi-disciplinary Approaches; Professional Practice; Collaborations; The Professional at Work

Transcript

Tacey Ann Rosolowski, PhD:

So you were talking about Fludarabine and—

Michael Keating, MD:

Fludarabine was interesting because the whole concept of it being used to work against rapidly dividing cells and ended up being semi true, but much more dramatically true in diseases where there wasn’t very much in the way of dividing cells, and we still really don’t know how it works. A lot of drugs, we still don’t know how they work. But at the same time as we were getting this catastrophic neurotoxicity with people becoming blind and paraplegic at the high doses in the acute leukemias, there was none of this in the much lower doses, and this has led to the survival of the drug in leukemias and lymphomas.

Tacey Ann Rosolowski, PhD:

Can I ask you what was the entity that provided the drug, and how did you go about setting up the study? I know you worked with Bill Plunkett [Oral History Interview], who I also interviewed for this project.

Michael Keating, MD:

Yes.

Tacey Ann Rosolowski, PhD:

So tell me a bit about kind of the whole process of setting it up.

Michael Keating, MD:

Well, when you would get a new drug to study, in those days it depended entirely on who the principal investigator was as to who was eligible to go on to the study, and in those days it wasn’t nearly as restrictive in a protocol for a particular subset of patients. So the Fludarabine study, you were able to do a two-tiered approach, and the first tier was in the acute leukemias with rapidly developing disease and a much higher dose being given, which is customary in the acute leukemias, and the slow-growing leukemias such as chronic lymphocytic leukemia and hairy cell leukemia and the low-grade lymphomas, etc., and we were able to do that with the drug being manufactured under the guidance of the National Cancer Institute and a lot of the early studies in mouse models, etc., being conducted there.

Tacey Ann Rosolowski, PhD:

And what were the years that we’re talking about here?

Michael Keating, MD:

The early 1980s is when the Fludarabine first came along, and the nerve damage was just at the high doses, but there were these dramatic responses that were occurring in the slow-growing tumors.

Tacey Ann Rosolowski, PhD:

How many patients did you have involved in these studies?

Michael Keating, MD:

It was a relatively small number. It would have been—I think the first Fludarabine study we might have had seventy or eighty patients, and half of them ended up being lymphomas and half of them ended up being chronic lymphocytic leukemia and a smattering of other less common blood malignancies, so that from that point of view, the acute leukemia studies stopped very early because of the toxicity. So that we were able to explore a lot of features of the side-effect profile broadly, and this you usually do in Phase 1, but when you do Phase 1, sometimes you get pleasantly surprised that even at the Phase 1 dose there are very dramatic responses, so that it rapidly becomes a Phase 2 study that you find out where it’s working, and you enrich the study for the patient population that it’s working in.

Tacey Ann Rosolowski, PhD:

What’s the time frame we’re talking about here for seeing the results and being able to make a decision, for example, to take a trial from Phase 1 to Phase 2?

Michael Keating, MD:

Oh, in those days it was probably only six months.

Tacey Ann Rosolowski, PhD:

Wow. That’s amazing. I had no idea.

Michael Keating, MD:

Because you would see it very, very quickly, that always the lymph gland would dissolve very quickly, and we hadn’t see that before. And our lymphoma colleagues were seeing the same thing in lymphomas as we were seeing in the chronic lymphocytic leukemia, so it was then the question, okay, well, let’s concentrate on these, and these other less common diseases would come along.

Tacey Ann Rosolowski, PhD:

Now, were you collaborating with Dr. Plunkett at the time?

Michael Keating, MD:

Yeah. Bill was teaching us a lot about the concentration of the drug inside the cell, because in the past, there was a lot of emphasis on the plasma levels of the drugs so that they were given intravenously, they were drug outside the cancer cell, and you were measuring that, and that was convenient, but that was not convenient to get solid tumor cancer cells all the time to measure what was happening inside the cell.

Tacey Ann Rosolowski, PhD:

So just to—the significance of the drug inside the cell was greater penetration throughout the system?

Michael Keating, MD:

Greater penetration and also activation in that Fludarabine and there’s a family of drugs called the purines and a family of drugs called the pyrimidines, and these were the building blocks of DNA, purine and pyrimidine molecules. And whereas Fludarabine by itself was not very soluble, so that you had to add a phosphate to it so it became a Fludarabine monophosphate, and that was a good carrier to get the Fludarabine molecule into the cell. Then it had to be transported through specific transporters, as we now know for these drugs, that carry it into certain cells in a high concentration.

Tacey Ann Rosolowski, PhD:

And that’s the basic researcher phase, yeah.

Michael Keating, MD:

And that’s when you have to then say, okay, it’s carried in there or it gets to this point. What happened to them from then on? And there are activating proteins called kinases, and in many of these drugs there were inactivating enzymes called deaminases that took off the amino acid sequence, so this ratio of the two was important. So the drug didn’t work unless it had three phosphates on it, and so that you would then give the drug, and at certain times you would collect the leukemic cells and you would measure the triphosphate level inside the cell, and that correlated beautifully with the likelihood of response.

Tacey Ann Rosolowski, PhD:

So just so I get a sense of how this worked, you’re working with the patients on the clinical side, providing them with the drug and then deciding exactly what kind of samples needs to be taken to send them over to the lab, and then Plunkett and his team do all of this so you get a fuller and fuller and fuller picture of what’s happening at a molecular and genetic level.

Michael Keating, MD:

More at a molecular level, because in those days, there really wasn’t very much information, because they were considered sort of generic drugs to get into DNA and to interfere with some of the elements of the activation or inactivation of enzymes that were important in making RNA effective. So that there was a lot of general concept, and the question was why didn’t these drugs, which worked so well in these slow-growing tumors, when we anticipated that it would be more effective in the fast-growing tumors, why did that happen? Why don’t drugs work in solid cancers when they work so well in a lot of the leukemias and lymphomas, and whether it’s a transport mechanism or whether the activation and inactivation enzymes were different. And that’s still very hard to measure in solid tumors because they’re so hard to access and collect chunks of tumor on a serial fashion. When Bill Plunkett was first working on the acute leukemias, we found that we could do this with cytosine arabinoside, and you would give a dose and then you would measure overnight and collect the cells and store them away in the refrigerator at one-hourly intervals, and then in the morning someone from his lab would come and collect those samples and they’d process them the next day. He would give you a level and a half life of the active form of the drug, and this led to if there’s a short half life, do you modify the schedule as to how you give it, do you give it more frequently, and this whole concept of having the drug around where it was supposed to be doing its job at the right concentration for the right length of time. So that many of these principles of intracellular pharmacology were important, and then the correlation between the levels and what happened to the cells. This is called pharmacodynamics, so that you have the plasma levels, you have the intracellular levels, and then you see what happens to the tumor, and you try and correlate all those features. So it lent a whole degree of sophistication to the whole process. We still have to give some consideration of that in the targeted therapy, even if we know the enzyme that’s there. What’s more important? Is it more important that you have a high drug level, or is it more important that the drug binds to the site in the enzyme and is not released so that it still sticks around and inhibits for a long period of time? Because sometimes it can have what they called an off-time. So how long it gets in there and how long it takes to fall off and—

Tacey Ann Rosolowski, PhD:

How interesting.

Michael Keating, MD:

—the longer it’s bound, the better.

Tacey Ann Rosolowski, PhD:

Interesting.

Michael Keating, MD:

So once you have the target, you have to have something that fits very well into the target, it has to penetrate the cell, and it has to have a fairly constant type of enzyme, or the enzymes can have different forms. So that if you block one, that may be enough. You sometimes have to block two or three before it works. So these concepts are still just being explored at the present time, and then there are pathways so that you can inhibit one step of the pathway, and there might be end-arounds, etc., and then something else can take over, and this is where the complexity gets greater and greater.

Tacey Ann Rosolowski, PhD:

Well, so you’ve worked on Fludarabine for many, many years. What would you consider to be kind of the big milestones that kind of brought things together, made you change directions over the course of that?

Michael Keating, MD:

I think the first big milestone was the dramatic effect on lymphoma and CLL, and I think this is where it depends on the investigator. I was really driven to keep on following this theme and this is probably because working with Plunkett, I was working towards analyzing all of these effects. And also at that time, Dr. Varsha Gandhi was looking at whether Fludarabine would make ara-C work better in acute leukemia, and she did really elegant work showing that it doubled the active form of ara-C, and in particular, this has led to the standard of care now in the acute leukemias with Fludarabine not so much working as a killing drug, but modulating the level of the active killing drug, the cytosine arabinoside. And that’s led to common types of acute leukemia having a cure fraction of probably around about 60-plus percent now. So it all evolved from the interaction of people thinking and sharing ideas in one particular lab, so it really is essential if you’re going to develop the translational research is that both groups have to have the same level of commitment. So Fludarabine dramatically changed things, because for the first time we were able to get complete remissions; that is, that all of the lymph glands went away, the blood counts normalized, the bone marrow had no leukemic cells there, and these were the criteria that we were using for evaluating acute leukemia. So it went from being a situation where no one got complete remissions to around about 20 to 30 percent of patients getting complete remissions.

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Chapter 12: Research Advances with Fludarabine and Cytarabine

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