Advancing Personalized Medicine: Examining Trop2 as a Biomarker to Stratify Prostate Cancer Patient Risk - Tanya Stoyanova

February 27, 2024

Tanya Stoyanova discusses research on Trop2's role in prostate cancer, published in Nature Scientific Reports. Collaborating with Drs. Michael Liss and Jim Brooks, the study reveals Trop2 as a high-potential therapeutic target due to its overexpression in various epithelial cancers, including prostate cancer, where it's linked to aggressive behavior. Their work, validated in a large patient cohort, demonstrates Trop2's prognostic significance in predicting outcomes and its potential as a urinary biomarker for non-invasive disease monitoring. Highlighting the collaborative nature of the research and the support from multiple funding sources, Dr. Stoyanova emphasizes the next steps involve validating Trop2 detection in urine and optimizing the assay for clinical application. This innovative approach offers new avenues for monitoring and potentially targeting prostate cancer therapy.


Tanya Stoyanova, PhD, Associate Professor of Molecular and Medical Pharmacology, Associate Professor of Urology University of California Los Angeles (UCLA), Los Angeles, CA

Andrea K. Miyahira, PhD, Director of Global Research & Scientific Communications, The Prostate Cancer Foundation

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Andrea Miyahira: Hi everyone, I'm Andrea Miyahira here at the Prostate Cancer Foundation. Joining me is Dr. Tanya Stoyanova, an associate professor at UCLA. Dr. Stoyanova's group recently published the paper, "High expression of Trop2 is associated with aggressive localized prostate cancer and is a candidate urinary biomarker." This was published in Nature Scientific Reports. Dr. Stoyanova, thank you for joining me today to discuss this study.

Tanya Stoyanova: Thank you, Andrea, for the nice introduction and thank you very much for giving us the opportunity to really share our work that was published in late 2023 on evaluating the expression of a cell surface molecule Trop2 in samples from prostate cancer patients and its utility as a potential urinary biomarker. This was a highly collaborative study. There were many collaborators from many institutions involved in the collection of the samples that we analyzed, and this is really close collaboration with Dr. Michael Liss from UT San Antonio as well as Dr. Jim Brooks from Stanford University.

Trop2 is a very attractive therapeutic target and has gotten a lot of attention in recent years due to its high expression in many, many epithelial cancers. We and others have shown before that this cell surface receptor is actually activated through multiple cleavages, which results in the release of the extracellular domain, as well as release of the intracellular domain. The molecule has multiple functions in cancer. In many cancers, as well as prostate cancer, it regulates calcium signaling, it also regulates the cell cycle, it's known to regulate the integrin signaling axis which induces migratory abilities and metastasis, and it's known to have quite a few downstream targets. It also can signal through the PI3 kinase and the AKT pathway.

It's found overexpressed in many epithelial cancers, and I'll show you in the next slide a few of those cancers with their percentages of overexpression. Due to this high expression in cancers, Trop2 has become a very attractive therapeutic target and one agent that targets Trop2 is a Trop2-directed antibody that's conjugated to SN-38, which is a topoisomerase inhibitor. It was FDA-approved for breast cancer and urothelial cancers, TRODELVY. In recent years, there are many companies and academic labs that are developing new agents to target this molecule, and I very much look forward to additional agents being developed to target Trop2.

It is overexpressed in many epithelial cancers. In prostate cancer, we and others have shown that about 71% of prostate cancer has overexpression of Trop2. We see that in localized prostate cancer, we also see that the percentage is even higher in metastatic disease. What we set out to evaluate a few years ago was if the high levels of Trop2 have any predictive value for outcome in prostate cancer patients.

The first study we conducted in 2020 was in collaboration with Jim Brooks from Stanford University, and here we took samples from 234 patients that were collected that underwent radical prostatectomy at Stanford University, this was part of their care, and then they were followed for 10 years. What we found is, we stained for Trop2, and here the brown staining indicates levels of Trop2. You could see that the patients who had high levels of Trop2 at the time of surgery had much shorter time to biochemical recurrence, and biochemical recurrence here is measured by prostate-specific antigens in blood. Also, we found that patients who had high levels of Trop2 at the time of surgery had a higher chance of developing lymph node and bone metastasis.

In this study, we set out to validate these findings in a much larger cohort of patients, and here we utilized the Canary Prostate Cancer Tissue Microarray. This is a tissue microarray that was built from the samples of over 1,100 patients from six different institutions. And then we also set a goal to test if we can detect the shedding of Trop2 in the urine of patients with prostate cancer and if this can be used as a minimally invasive approach to really reflect the levels of Trop2 in prostate cancer tissues. Here is the immunohistochemical analysis of the tissues that we have analyzed. The patient number was 1,153. We stained them for Trop2 and they were stratified as Trop2 negative/low, which here is shown in 0 or 1 score, or Trop2 positive, which is a score of 2 and 3. These scores were based on the intensity of staining which reflects the levels of Trop2 in these tissues. Then we correlated the levels of Trop2 negative/low or positive with overall survival in these patients. These patients had a 20-year follow-up.

In this TMA here, again, it's just one example, one representative of the many tissues that we have stained, what we found is that high or Trop2-positive samples, Trop2-positive patients, have much shorter overall survival when compared to patients that, at the time of surgery, had low or negative Trop2.

After validating the findings at tissue levels, we went ahead and asked, can we now detect shed Trop2 or Trop2 in the urine of these patients? We started with a small cohort of patients. Those patient samples were collected at UT San Antonio. Here what we had is urine samples from 40 confirmed cancer-free patients and 39 confirmed patients with high-risk prostate cancer. We also had patient-matched tissue samples from these patients and we developed an ELISA and we conducted ELISA to detect Trop2 in the urine and performed immunohistochemical analysis to detect Trop2 in the tissues of these patient-matched samples.

What we were excited to see is that we indeed were able to detect Trop2 in the urine of patients with prostate cancer. To validate this assay, we also performed a secondary assay, which is a Western blot, and we were able to see that actually what we see on our ELISA is confirmed by two different assays. So the results from the two assays correlate. We were very excited about these findings. And then we went ahead and stained the tissues from these prostate cancer patients to see if what we see in the urine actually reflects what is happening in the tissue. So here you can see this is a few examples, and indeed, the patients that had higher levels of Trop2 in the urine or where Trop2 was detected in the urine now we see high levels of Trop2 in the tissues of these particular patient samples.

What we have demonstrated with this study is that Trop2 is a prognostic tissue biomarker, this was validated for clinically significant prostate cancer. We also have shown that it correlates with worse clinical features including Gleason score, age, and PSA prior to surgery, and that high expression of Trop2 at the time of radical prostatectomy actually predicts worse overall survival in men that are having surgery for prostate cancer. We're very excited that we could detect shed Trop2 in urine from men with clinically significant prostate cancer, and these preliminary studies in urine really set the foundation to start to expand the cohort and perform this evaluation of urine Trop2 in a very large cohort of samples and correlate it also with outcome as well as tissue levels of Trop2.
With that, I would like to emphasize, again, these are really collaborative studies. Many institutions and many collaborators have participated in the collection of these samples and evaluation of this biomarker. I also would like to thank my lab, very bright individuals who work very, very hard, as well as our funding sources who have been very supportive with this and other studies in the lab. Thank you very much.

Andrea Miyahira: Thank you so much, Dr. Stoyanova, for that presentation. Have you looked for Trop2 in blood or urine exosomes?

Tanya Stoyanova: That is a great question. In urine exosomes, we haven't isolated specifically exosomes to look for Trop2. With that being said, the ELISA that we use, it's whole urine, so we cannot rule out that we are not detecting exosomes. So we may be detecting shed extracellular Trop2 as well as exosomal Trop2.

In blood, we have a study that we are actually about to submit where we isolated exosomes from the serum of patients with high-risk prostate cancer and we find that high levels of Trop2 in these exosomes are actually correlated with high-risk prostate cancer when compared to low-risk and cancer-free patients. So in blood, we use exosomes because we faced some technical challenges to use just ELISA in blood. There was a lot of background. With urine, we were able to use ELISA, so we decided not to preisolate exosomes to actually shorten the time of the assay and make it more high throughput. But for serum, yes. For serum and plasma, we have actually done both. We do see exosomal Trop2 in those. Collaborative studies with Dr. Utkan Demirci at Stanford who developed this very elegant tool to isolate exosomes based on different filters and size exclusion.

Andrea Miyahira: Okay, thank you. Have you compared the prognostic significance of Trop2 expression with other molecular biomarker tests that are available in localized settings, such as Decipher?

Tanya Stoyanova: We have not. We are planning to do that, and this is a great question and a great idea. We will most certainly do that. We have not done it, and I'm not sure if the patients that we have analyzed here, this very small cohort, have had Decipher done on them. But we would like to do that to compare it. Again, we think that this may add prognostic value rather than replace a test. But we would be very interested to look if, together, the two tests, Trop2 can add more information to it.

Andrea Miyahira: Okay. What clinical applications and disease settings do you envision Trop2 biomarkers may be most informative?

Tanya Stoyanova: The most informative would be to predict and monitor therapy, if you will, to an agent that's targeting Trop2, because that will really, really reflect the protein that is being targeted. However, I think from what we see, it can be very useful to predict the outcome in conjunction with other assays and current biomarkers. It's a very high-throughput assay detecting just one protein; it's a very straightforward assay. So it can be used in localized disease to predict outcome. It can be used to monitor responses in the settings of prostate cancer. Since it's overexpressed in a very high percentage of patients, it can monitor responses not only to Trop2-targeted therapies but to any therapies.

Andrea Miyahira: Okay, thanks. What are the next steps in these studies? Do you have translational plans?

Tanya Stoyanova: The next steps will be to really validate the urine biomarker part of the study in a large cohort of samples, and again, to compare it or add it to existing tests. That is the next step. In terms of translating it, we are also working on further optimizing the ELISA. We have developed a series of human antibodies, and we are currently trying to further optimize the ELISA to make the time of the assay even shorter, which will make it even closer to the clinic. So the first step will be to validate it in a very large cohort.

Andrea Miyahira: All right. Well, this was such wonderful work, and I look forward to the next studies. Thank you for sharing this with us today.

Tanya Stoyanova: Thank you, Andrea. It was a pleasure.