Dr. James L. Mohler Video (Text Version)
Intracrine Metabolism of Testicular Androgens by Castration-Recurrent Prostate Cancer
Natasha Kyprianou
Our next speaker will cover steroid metabolism. Dr. Jim Mohler is an Associate Director and Senior Vice President for Translational Research, Professor of Oncology, the Chair of the Department of Urology and the founder of the Prostate Program at Roswell Park Cancer Institute in New York. Dr. Mohler’s research interests include the role of androgen signaling and the androgen receptor and the mechanismsdriving prostate cancer growth to androgen independence after castration of—castration-induced deprivation. He is also interested in studying racial differences in the androgen-signaling axis and active surveillance for low-risk prostate cancer patients.
Dr. Mohler has made seminal contributions to prostate cancer in both the research as well as the clinical setting, both with equal vitality. He has been leading the North Carolina, Louisiana Prostate Cancer Program supported by the Department of Defense PCRP. This morning Dr. Mohler will share his insights on a provocative theme that androgen independent prostate is not really androgen independent; Dr. Mohler.
James L. Mohler, M.D.; Associate Director and Senior Vice President for Translational Research; Chair, Department of Urology; Professor of Oncology, Roswell Park Cancer Institute, Buffalo, NY
Thank you. It is an honor to be introduced by Natasha and follow the previous speakers. Arul is actually helping me with the DoD-funded award to look at the role of gene fusions and are there racial differences in gene fusion. Scott, I tried unsuccessfully to hire, and you all can see why. So I am going to blow through what is really something important that I think I did kind of out of naiveté in 2004, so I am old enough that I can talk about things from a while ago. The androgen receptor responds to castration as you have just learned with molecular and biochemical alterations that cause hypersensitivity to low levels of androgen. Our laboratory was the first to show that the androgen receptor actually can become 10,000 times more sensitive in androgen independent than the androgen-sensitive cell lines. Now the mechanism, the molecular mechanism for that has been shown to be co-activator rearrangement and more recently differences in AR phosphorylation relation status.
Now prostate cancer also responds to castration by synthesizing ligand. In 2004 we published this paper that was actually the result of 7 years of work. The first 3 years were devoted to modifying radioimmunoassay that is used to measure androgens in Olympic athletes in their saliva or their urine. I asked the naïve question; why is the androgen receptor expressed at high levels in androgen-independent prostate cancer when there is no androgen around? I said how do we know there’s no androgen? So we had to modify this assay for use in tissue and it’s very difficult to do radioimmunoassay in tissue because the prostate is a factory of proteolytic enzymes.
And so Peter Petrus who is one of the world’s experts in how to do this and I worked for 3 years and the result was this paper on a series of specimens collected from men who went into urinary retention from castration-recurrent prostate cancer. Much to our surprise, the levels of testosterone were the same in castration-recurrent cancer as it was in androgen-stimulated benign prostate tissue. We at first didn't believe this and neither did many other people, so we spent the next several years modifying mass spectrometry assays for use in prostate tissue. And to make a long story short, working with the laboratory (mass spectrometry laboratory at NIEHS under Ken Tomer’s leadership) we develop mass spectrometry assays suitable for prostate tissue that detected both T and DHT. We confirmed the results by RIA that castration-recurrent prostate cancer had essentially the same levels of testosterone as did benign prostate and that the levels of DHT were diminished but they were still sufficient to activate an even molecularly normal androgen receptor.
So we were excited by this and dropped the use of the term androgen-independent prostate cancer. In fact, in the 37 specimens that we have analyzed, we have only found a single specimen in which we could not detect or T or DHT. And this is probably the one specimen where the tissue was degraded so that the T and DHT were gone. I do not think there’s any such thing as androgen-independent prostate cancer. Now are we really smart? Well the Seattle group confirmed that the situation was the same using mass spec analyzing castration-recurrent prostate cancer harvested in their autopsy series from bone metastasis, so the situation that we looked at in the primary seems to be the same in the metastasis. Now John Isaacs who is sitting right over there said, well Jim; you haven't done anything new. You published this in 2004 and Geller actually showed this in 1979. And this was before Pub-Med so it’s unknown to all the young people in the audience and this was unknown to me at the time.
And so why did I and everybody else forget about this? Well I think it is because of Ferdinand Labrie’s publication that when you used an anti-androgen in combination with LHRH your DHT went away. And this has been quoted in every book and paper written since 1989, and it was based upon a study of four men who had flutamide for 2 months and it turns out the ND in this paper stands for not detectable and the radioimmunoassay he was using probably had a lower limit of detection of about two nanomolar and as I showed you before, the DHT levels are usually in the one to two nanomolar range. So we went on this decade or two-decade long fascination with very poor performing anti-androgens and forgot about Dr. Geller’s hypothesis in 1979.
Now we need to make up for lost time. So how do we do that today based on our recognition that there is intracrine metabolism of testicular androgens going on within prostate cancer that recurs during androgen deprivation? So the first thing I want to tell everybody is that our group has published extensively about AR mutations that broaden ligand specificity and this is a mistake, so all our papers are wrong. So AR is not promiscuous in CWR R1 like we published; we said that diol can activate the androgen receptor because of the mutation and in fact, the diol was being metabolized to DHT which is responsible for the activation of the androgen receptor and this is a unique characteristic of prostate cancer cell lines. Other cell lines, for instance from cervical cancer and kidney cancer do not have this ability. We even proved that this happens in vivo. If you have a mouse bearing a recurrent tumor and you give the mouse human levels of androstanediol, an adrenal androgen, look at the levels of DHT. Without the human levels of androstanediol they’re four nanomolar; with androstanediol provided the DHT levels are 112 nanomolar. So the human prostate tissue implanted in the mouse can make astronomical levels of DHT to drive its growth. So DHT comes from weak adrenal androgens. The Harvard group helped us show that immediately after castration, enzyme metabolism changes to favor enzymes that make testosterone from adrenal androgens. The group from Vancouver showed us that if there are not adrenal androgens available, the prostate cancer could make it all the way from cholesterol.
What do we do in 2011? We need to learn how to prevent the synthesis of tissue androgens. When I went to medical school, this is what was known about making DHT from adrenal androgens. Three enzymes were involved; I can't remember names, so I just refer to them as the green one, the red one, and the blue one and this is pretty simple, so any drug company should be able to figure out how to block this. Here’s the barriers to understanding androgen metabolism. There are lots of enzymes; most of them have isozymes. Many of them have several different names for the same enzyme and for any urologist to understand this is a daunting task. This is what Locke and the group at Vancouver now suggest is the pathways to DHT synthesis. In yellow, is the situation when you have intact testicles and then when you lose your testicles, you make DHT from adrenal androgens. If you lose that as a source, you make them from cholesterol and then you have to worry about backdoor pathways.
This has become very complicated but common to the synthesis, is the need for SIP21 to turn your adrenaline androgens into DHT and this is now led pharma to develop 3 new drugs that show great promise for treatment of advanced prostate cancer. The first to be published in a Phase 3 clinical trial, abiraterone, shows an extension of survival in men who have failed taxotere for castration-recurrent prostate cancer. We can apply science to understanding these pathways better and this is our current mass spectrometry assay that measures simultaneously eight androgens, abiraterone and abiraterone Acetate. We can use this to study on how to better block these androgen metabolism pathways.
Here’s testosterone in testicles; the green is from adrenal androgens—there’s all the way from cholesterol, there’s the backdoor pathway, and we are now proposing through overexpression of 5 alpha reductase 3 that this is even more complicated—that there’s a degradative pathway that prostate cancer uses to make DHT. So attacking androgen metabolism is a daunting task but one that should be pursued.
I always point out to everybody that I’m the conductor of an orchestra. I don’t really know how to do much of anything; I just think up the ideas and these are all the people that contributed to the work that I just blew through in 10 minutes and 15 seconds. Notice at the bottom the support, NCI, NIA, and of course DoD. Thank you.