Biomarker Analysis to Identify Molecular Signatures Predictive of Response in the COMBAT Study - Emmanuel Antonarakis

December 5, 2022

Alicia Morgans and Emmanuel Antonarakis discuss an ongoing biomarker analysis aimed at identifying a molecular signature predictive of response in the COMBAT study. The COMBAT study is a multi-center, single-arm, open label Phase 2 study in asymptomatic patients with mCRPC who had soft tissue metastases amenable to biopsy, and who progressed on at least one prior novel AR-targeted therapy (and up to one prior chemo for mCRPC). A small study supported by PCF, co-led by Hopkins investigators Mark Markowski, MD, Ph.D. and Emmanuel Antonarakis, MD tested the combination of bipolar androgen therapy (BAT) and immunotherapy in 45 men with metastatic castration-resistant prostate cancer (mCRPC). The results suggested that BAT alone has significant efficacy, while nivolumab improves responses in some patients. The combination of BAT with nivolumab was safe and well tolerated by the participants. Dr. Antonarakis explains that they are now trying to uncover who are those patients that responded and in this conversation, he highlights the depth of this biomarker analysis.


Emmanuel Antonarakis, MD, Genitourinary Oncologist, Clark Endowed Professor of Medicine, Division of Hematology, Oncology and Transplantation, Associate Director of Translational Research, Masonic Cancer Center, The University of Minnesota

Alicia Morgans, MD, MPH, Genitourinary Medical Oncologist, Medical Director of Survivorship Program at Dana-Farber Cancer Institute, Boston, Massachusetts

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Alicia Morgans: Hi, I'm so excited to be here with Dr. Emmanuel Antonorakis, who is joining us from the University of Minnesota. You're working on a lot of things. Some of those are PCF funded. I really appreciate you taking the time to be here today. Can you tell us a little bit about your latest work?

Emmanuel Antonorakis: Thank you. It's a pleasure to be here. Well, the PCF has funded my research over the years, but recently we had a challenge award to conduct a study called the COMBAT Trial. The COMBAT study was our first combination study of bipolar androgen therapy. This paradoxical notion of using super high doses of testosterone, combined with, in this case, nivolumab, PD1 immunotherapy. Men with prostate cancer metastatic CRPC. We did this study at four sites. Alicia, your site, Dana-Farber was one of the four, and it was a 44 patient trial.

The trial itself was funded by other means, but the PCF funded the biomarkers. This was in my career, one of the richest and deepest biomarker interrogations that we've done. We had metastatic biopsies on these patients, all of them. In about half, we had a second biopsy during the course of therapy, and we also aimed to get a third biopsy at progression. Those were much more difficult.

Let's start with a few patients that inspired the trial, because I always like to tell this story. Why did we do this study? We did this study because we had some patients that we had treated with high dose testosterone, and then as their next course of therapy, we used the PD1 inhibitor, and we had these three anecdotal cases. Of course, their anecdotes where the gentleman received the high dose testosterone, had a beautiful response, progressed unfortunately, and then received a PD1 inhibitor as a next line of therapy and had another very profound response. We published those three cases and we thought, are these anecdotes or is there something scientific here, some synergy? That was the goal of the COMBAT study.

In the COMBAT study, we prospectively designed a trial where patients got three months of high dose testosterone. On the fourth month if their disease had not progressed, so if they had stable disease or better, we added the nivolumab and we continued the high dose testosterone. This was led by one of our faculty members, Mark Markowski, with my mentorship. The PCF Challenge award was awarded to a big team of people that I was leading. We had pathologists in there like Angela DeMarzo. We had experts on bioinformatics and genomics. We hope to get a lot of answers to explain why. We saw about a 30 to 40% response rate in that trial, which was exciting. Now we're trying to uncover who are those patients that responded.

Alicia Morgans: Well, what I think is so incredible is of course that response rate, but the depth of your biomarker analysis can actually tell you who that is. Without that, it's a really interesting trial, but not one that you can so easily apply across the board in clinical practice. What are you looking into with the correlatives?

Emmanuel Antonorakis: I don't want to spoil too much, but we've come across some interesting and maybe unexpected discoveries that we're trying to confirm. We had thought for a while that patients with DNA repair deficiencies, like the BRCA mutations might in fact do better. We did confirm that. The unexpected piece was the pathogenic P53 mutations, which are typically a poor prognostic factor. Those patients might also be responding better, not worse, but better. One of the hypotheses is that the high dose testosterone, the way that it might work is by inducing double strand DNA breaks. If you have a mutation in P53, which is the master regulator of DNA repair, those patients might do better.

The second has to do with the immune microenvironment. Dr. Angela DeMarzo very carefully characterize the immune landscape from those biopsies. In some cases, we have paired biopsies. It turns out that patients that have a higher baseline CD8 T-cell count, and patients that have a higher baseline PD1 positive immune cell count, those patients do better even before you give the nivolumab. Just on the bipolar androgen therapy by itself.

We also had a number of patients, not that many, but a few who had no response at all to the bipolar antigen therapy until the PD1 inhibitor was added. What we're trying to figure out for those patients, are these guys that would've just responded to a PD1 inhibitor anyway? Irrespectively of the high dose testosterone, or did the high dose testosterone somehow create an immunologic milieu or activated immune system such that the subsequent inhibition of PD one then caused true synergy? That's the piece that we don't quite know yet, and we're trying to uncover that too.

Alicia Morgans: Well, I think it's incredible that this work is being done and really that PCF is supporting it. It sounds like there's a lot more that can be done, and it's a very rich data set from this trial. What do you hope for next? If you get the next big grant, what are you going to look into?

Emmanuel Antonorakis: Where we go next is the key question that we all want to answer. I think for me, it would be a randomized trial. You've got 44 patients as a single arm and four sites. We now want to move this to 30 sites with 200 patients. There's a challenge then, we've started to think through this. The challenge is that neither high dose testosterone nor nivolumab as mono therapies are standard of care in our disease. How can we design the study? We can design the study comparing that combination with a chemotherapy, like docetaxel cabazitaxel. That's the challenge.

We are not quite sure what the optimal control arm would be. One idea would be to compare high dose testosterone alone, versus the combination of high dose testosterone plus nivolumab. Then the FDA would come back and say, well, high dose testosterone is not a standard in this disease. We're not going to give you FDA approval. We're thinking through all those parameters. I used to be on the NCCN panel when I was at Hopkins, and I'm trying to put my NCCN lens on and say, what would the NCCN say? Would they accept this to increase the label of high dose testosterone? I'm not sure. We do need randomized studies, and these studies can be costly. I do think that when we do those studies, hopefully we will one day, we should embed the biomarkers into those as well. We can also learn from that.

Alicia Morgans: Well, I could not agree more. I really commend you and your team for doing such innovative work and not just doing the hard part of doing a clinical trial, but digging into that evidence to understand the things that you don't even know when you're designing that trial are questions that you'd like to answer. You're really evolving as the science evolves and you're doing amazing things. PCF funding is certainly supportive of that. Your team is just wonderful. Keep up the good work. Thank you so much for sharing it, and I appreciate your time and expertise.

Emmanuel Antonorakis: Thanks very much. It's been my pleasure.

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