Androgen Receptor Inhibition and MHC Class 1 Expression in Prostate Cancer - Lisa Chesner
March 27, 2025
Andrea Miyahira speaks with Lisa Chesner about the relationship between androgen receptor inhibition and MHC class I expression in prostate cancer. Dr. Chesner describes how her team used a whole-genome CRISPRi screen to identify the androgen receptor as a top regulator of MHC class I expression, with AR suppression significantly increasing MHC levels. She demonstrates that AR inhibition through enzalutamide, AR degraders, or ADT enhances T cell response both in vitro and in vivo, a finding validated in patient samples across primary and metastatic settings. Dr. Chesner notes that MHC expression peaks around 40 days after treatment but decreases as castration resistance develops, coinciding with increased glucocorticoid receptor expression. This research provides mechanistic support for combining AR inhibition with immunotherapy while highlighting the importance of identifying the optimal therapeutic window and patient selection for such combinations.
Biographies:
Lisa Chesner, PhD, Associate Professional Researcher, University of California San Francisco (UCSF), San Francisco, CA
Andrea K. Miyahira, PhD, Director of Global Research & Scientific Communications, The Prostate Cancer Foundation
Biographies:
Lisa Chesner, PhD, Associate Professional Researcher, University of California San Francisco (UCSF), San Francisco, CA
Andrea K. Miyahira, PhD, Director of Global Research & Scientific Communications, The Prostate Cancer Foundation
Read the Full Video Transcript
Andrea Miyahira: Hi, everyone. I'm Andrea Miyahira here at the Prostate Cancer Foundation. With me is Dr. Lisa Chesner of UCSF, who will share her recent paper, "Androgen receptor inhibition increases MHC class 1 expression and improves immune response in prostate cancer," published in Cancer Discovery. Dr. Chesner, thanks for joining us.
Lisa Chesner: Thanks so much for having me. I'm excited to share this work with you all. So thanks so much for having me. I'm excited to share this work with you that was published in Cancer Discovery just at the end of last year. And to start off with a little bit of background on what is MHC class 1, the Major Histocompatibility Complex. So it is responsible for presenting neoantigens on the surface of cancer cells to CD8 T cells, it's a part of the innate immune response. And downregulation of MHC class 1 is associated with cancer immune evasion.
And so if we look at expression of MHC class 1 in the TCGA cohort—this is RNA expression of HLA-A, B, and C—we can see in prostate cancer it is especially downregulated. And so we hypothesize that if we're able to increase MHC class 1 expression in prostate cancer, would this improve immune recognition and therefore immunotherapy response?
And so in order to address this question, we conducted a whole-genome CRISPRi screen in prostate cancer cells. This library targeted over 20,000 genes. The selected cells were then stained with a pan HLA-ABC antibody and sorted for MHC high and low expression. And what you can see on the right is a volcano plot of the gene hits, and the red are genes which downregulated MHC class 1 when suppressed. And we can see a lot of our positive controls that are actually components of the MHC class 1 complex, such as B2M and HLA-A.
On the other side, however, we see genes that increased MHC class 1 expression when repressed. And our number one hit was the androgen receptor (AR), as well as Grainyhead like-2 and FOXA1 were shown to increase MHC class 1 expression when suppressed. And so after validating the hits of the screen using sgRNA, we next wanted to test if we are able to upregulate MHC class 1 with other types of inhibitors.
So here we treated prostate cancer cells with an AR degrader, charcoal-stripped serum, or enzalutamide and looked at MHC class 1 surface expression over time. And what you can see is significantly increased expression with all three types of AR inhibitors compared to control. So this just shows that MHC class 1 expression is increased on the cell surface, but next we wanted to confirm that this also improves T cell response.
And so here I'm showing a video of our prostate cancer cell co-cultured with NY-ESO-1-specific T cells. Under control conditions, you can see the cancer cells are able to proliferate with no T cell inhibition whatsoever. However, if we pre-treat the cancer cells with the AR degrader, we are able to see dramatically improved T cell response. And we were also able to confirm that decreased AR also improves T cell response in vivo.
We next wanted to look at patient data in order to see if MHC class 1 expression was increased after different types of AR signaling inhibitors, such as enzalutamide. So here we're looking at pre- and post-treatment of enzalutamide in the primary setting. We can see significantly increased expression of multiple MHC class 1 genes. We also looked in the metastatic hormone-sensitive setting, pre-treatment. We see very high expression of AR and low expression of MHC class 1 genes. However, after ADT you can see AR start to go down, and MHC class 1 expression going up. And this is further amplified by the addition of an aPD1 inhibitor.
And so finally, we wanted to investigate how MHC class 1 expression changes during the development of castration resistance. And so in order to address that question, we treated prostate cancer cell lines with enzalutamide for over 91 days. And what you can see here is we've plotted, in the black, MHC class 1 expression over time. And you can see up to a five-fold increase in MHC class 1 expression at right around 40 days. However, this then does start to decrease over time.
Interestingly, if we turn our attention to the gray line, which looks at growth response to the enzalutamide treatment, we can see the cells are initially very responsive to the enzalutamide and decrease in growth. However, as resistance starts to develop, the cells start to proliferate and start to grow. And so interestingly, this occurs right around the same time that MHC class 1 expression is starting to decrease.
And so to identify what other gene changes are happening during this window, we conducted RNA sequencing and noted that NR3C1, or the glucocorticoid receptor (GR), was actually the number one gene that was associated with treatment response, meaning that expression of GR was going up as MHC class 1 was going down. And so future directions will plan on investigating GR's role in possibly immune evasion during this later drug-resistant state.
And so to summarize, hopefully I've shown you that AR is a regulator of MHC class 1 expression, that it increases T cell response both in vitro and in vivo, and that MHC class 1 expression during AR inhibition is improved and associated with immunotherapy response. And overall, it provides support for the combination of AR inhibition and immunotherapy in select prostate cancer patients.
And so I just want to acknowledge all the authors on this paper—it was a huge team effort—and I am so grateful to my mentors, Felix Feng and Amy Moran, as well as my funding sources, especially the Prostate Cancer Foundation for my Young Investigator Award. And thanks again for having me and happy to take any questions.
Andrea Miyahira: Thank you so much, Dr. Chesner, for sharing that. So do you see greater MHC 1 repression when AR is amplified, or alternatively, are MHC 1 levels increased in AR-low or null prostate cancer subtypes such as NEPC?
Lisa Chesner: It's a great question. So I can say that, for example, in our prostate cancer cell lines, our AR-null PC3 prostate cancer cells have very high MHC class 1 expression. In regards to NEPC, we do not see elevated MHC class 1 expression, and this is likely due to the data that I showed previously, where we've gotten to a point where we're so late in the disease course that AR is actually no longer the hormone that's suppressing MHC class 1 expression.
Andrea Miyahira: OK, thank you. And you noted that MHC derepression appears only temporary with inhibition, so what mechanisms do you think are mediating rerepression of MHC under ADT, and what do you think could be done to maintain MHC levels?
Lisa Chesner: Yes, so I think the glucocorticoid receptor is a great indicator that that might be playing a role. We know that GR binds to a lot of the same recognition sites as AR does, and so one of my future goals is to investigate that mechanism and see if it's possibly just a switch in nuclear receptors—and now that GR has taken over the job of suppressing MHC from AR in this later disease setting.
Andrea Miyahira: OK, thanks. And based on these data, why do you think we haven't seen any benefit in trials testing ICi in combination with ADT or ARSI, such as KEYNOTE-991?
Lisa Chesner: Such a good question, and something that I think is really important to address. I think that it is tricky in that we need to find the right patients and also the right therapeutic window to utilize this combination treatment. You can see from in vitro data that there definitely is a point where we get where this combination treatment is no longer effective.
In regards to the KEYNOTE-991 trial, the patients were able to be on ADT therapy up to 3 months before enrollment, and so it's possible that that had an effect on the dampened response. If you do look at subsets of patients in these types of trials, there are responders. So there are individual patients that do respond to this combination and treatment, and so I think the goal really is trying to better select for those patients and optimize the timing of their treatment.
Andrea Miyahira: Thank you. And what are your next steps, and do you have any translational plans?
Lisa Chesner: Yes, so as I mentioned, the role of GR in this I think would be really important to understand in the later phases of this disease. I'm also interested in trying to identify any neoantigens that are being presented during AR inhibition that are possibly different. And that could be new targets for combination therapy with AR inhibition specifically.
Andrea Miyahira: OK, well, thank you so much, Dr. Chesner, for sharing this with us.
Lisa Chesner: Thank you so much for having me.
Andrea Miyahira: Hi, everyone. I'm Andrea Miyahira here at the Prostate Cancer Foundation. With me is Dr. Lisa Chesner of UCSF, who will share her recent paper, "Androgen receptor inhibition increases MHC class 1 expression and improves immune response in prostate cancer," published in Cancer Discovery. Dr. Chesner, thanks for joining us.
Lisa Chesner: Thanks so much for having me. I'm excited to share this work with you all. So thanks so much for having me. I'm excited to share this work with you that was published in Cancer Discovery just at the end of last year. And to start off with a little bit of background on what is MHC class 1, the Major Histocompatibility Complex. So it is responsible for presenting neoantigens on the surface of cancer cells to CD8 T cells, it's a part of the innate immune response. And downregulation of MHC class 1 is associated with cancer immune evasion.
And so if we look at expression of MHC class 1 in the TCGA cohort—this is RNA expression of HLA-A, B, and C—we can see in prostate cancer it is especially downregulated. And so we hypothesize that if we're able to increase MHC class 1 expression in prostate cancer, would this improve immune recognition and therefore immunotherapy response?
And so in order to address this question, we conducted a whole-genome CRISPRi screen in prostate cancer cells. This library targeted over 20,000 genes. The selected cells were then stained with a pan HLA-ABC antibody and sorted for MHC high and low expression. And what you can see on the right is a volcano plot of the gene hits, and the red are genes which downregulated MHC class 1 when suppressed. And we can see a lot of our positive controls that are actually components of the MHC class 1 complex, such as B2M and HLA-A.
On the other side, however, we see genes that increased MHC class 1 expression when repressed. And our number one hit was the androgen receptor (AR), as well as Grainyhead like-2 and FOXA1 were shown to increase MHC class 1 expression when suppressed. And so after validating the hits of the screen using sgRNA, we next wanted to test if we are able to upregulate MHC class 1 with other types of inhibitors.
So here we treated prostate cancer cells with an AR degrader, charcoal-stripped serum, or enzalutamide and looked at MHC class 1 surface expression over time. And what you can see is significantly increased expression with all three types of AR inhibitors compared to control. So this just shows that MHC class 1 expression is increased on the cell surface, but next we wanted to confirm that this also improves T cell response.
And so here I'm showing a video of our prostate cancer cell co-cultured with NY-ESO-1-specific T cells. Under control conditions, you can see the cancer cells are able to proliferate with no T cell inhibition whatsoever. However, if we pre-treat the cancer cells with the AR degrader, we are able to see dramatically improved T cell response. And we were also able to confirm that decreased AR also improves T cell response in vivo.
We next wanted to look at patient data in order to see if MHC class 1 expression was increased after different types of AR signaling inhibitors, such as enzalutamide. So here we're looking at pre- and post-treatment of enzalutamide in the primary setting. We can see significantly increased expression of multiple MHC class 1 genes. We also looked in the metastatic hormone-sensitive setting, pre-treatment. We see very high expression of AR and low expression of MHC class 1 genes. However, after ADT you can see AR start to go down, and MHC class 1 expression going up. And this is further amplified by the addition of an aPD1 inhibitor.
And so finally, we wanted to investigate how MHC class 1 expression changes during the development of castration resistance. And so in order to address that question, we treated prostate cancer cell lines with enzalutamide for over 91 days. And what you can see here is we've plotted, in the black, MHC class 1 expression over time. And you can see up to a five-fold increase in MHC class 1 expression at right around 40 days. However, this then does start to decrease over time.
Interestingly, if we turn our attention to the gray line, which looks at growth response to the enzalutamide treatment, we can see the cells are initially very responsive to the enzalutamide and decrease in growth. However, as resistance starts to develop, the cells start to proliferate and start to grow. And so interestingly, this occurs right around the same time that MHC class 1 expression is starting to decrease.
And so to identify what other gene changes are happening during this window, we conducted RNA sequencing and noted that NR3C1, or the glucocorticoid receptor (GR), was actually the number one gene that was associated with treatment response, meaning that expression of GR was going up as MHC class 1 was going down. And so future directions will plan on investigating GR's role in possibly immune evasion during this later drug-resistant state.
And so to summarize, hopefully I've shown you that AR is a regulator of MHC class 1 expression, that it increases T cell response both in vitro and in vivo, and that MHC class 1 expression during AR inhibition is improved and associated with immunotherapy response. And overall, it provides support for the combination of AR inhibition and immunotherapy in select prostate cancer patients.
And so I just want to acknowledge all the authors on this paper—it was a huge team effort—and I am so grateful to my mentors, Felix Feng and Amy Moran, as well as my funding sources, especially the Prostate Cancer Foundation for my Young Investigator Award. And thanks again for having me and happy to take any questions.
Andrea Miyahira: Thank you so much, Dr. Chesner, for sharing that. So do you see greater MHC 1 repression when AR is amplified, or alternatively, are MHC 1 levels increased in AR-low or null prostate cancer subtypes such as NEPC?
Lisa Chesner: It's a great question. So I can say that, for example, in our prostate cancer cell lines, our AR-null PC3 prostate cancer cells have very high MHC class 1 expression. In regards to NEPC, we do not see elevated MHC class 1 expression, and this is likely due to the data that I showed previously, where we've gotten to a point where we're so late in the disease course that AR is actually no longer the hormone that's suppressing MHC class 1 expression.
Andrea Miyahira: OK, thank you. And you noted that MHC derepression appears only temporary with inhibition, so what mechanisms do you think are mediating rerepression of MHC under ADT, and what do you think could be done to maintain MHC levels?
Lisa Chesner: Yes, so I think the glucocorticoid receptor is a great indicator that that might be playing a role. We know that GR binds to a lot of the same recognition sites as AR does, and so one of my future goals is to investigate that mechanism and see if it's possibly just a switch in nuclear receptors—and now that GR has taken over the job of suppressing MHC from AR in this later disease setting.
Andrea Miyahira: OK, thanks. And based on these data, why do you think we haven't seen any benefit in trials testing ICi in combination with ADT or ARSI, such as KEYNOTE-991?
Lisa Chesner: Such a good question, and something that I think is really important to address. I think that it is tricky in that we need to find the right patients and also the right therapeutic window to utilize this combination treatment. You can see from in vitro data that there definitely is a point where we get where this combination treatment is no longer effective.
In regards to the KEYNOTE-991 trial, the patients were able to be on ADT therapy up to 3 months before enrollment, and so it's possible that that had an effect on the dampened response. If you do look at subsets of patients in these types of trials, there are responders. So there are individual patients that do respond to this combination and treatment, and so I think the goal really is trying to better select for those patients and optimize the timing of their treatment.
Andrea Miyahira: Thank you. And what are your next steps, and do you have any translational plans?
Lisa Chesner: Yes, so as I mentioned, the role of GR in this I think would be really important to understand in the later phases of this disease. I'm also interested in trying to identify any neoantigens that are being presented during AR inhibition that are possibly different. And that could be new targets for combination therapy with AR inhibition specifically.
Andrea Miyahira: OK, well, thank you so much, Dr. Chesner, for sharing this with us.
Lisa Chesner: Thank you so much for having me.