Episode Transcript
This transcript has been edited for clarity. For more episodes, download the Medscape app or subscribe to the podcast on Apple Podcasts, Spotify, or your preferred podcast provider.
Ursula A. Matulonis, MD: Hello, I'm Dr Ursula Matulonis. Welcome to Season Two of the Medscape InDiscussion: Endometrial Cancer podcast series. Today, we'll discuss targeting DNA damage and repair and replication stress in endometrial cancer. Let me introduce my guest, Dr Joyce Liu. Dr Liu serves as the associate clinical research officer for the Dana-Farber Cancer Institute in Boston, Massachusetts, as well as the associate chief and the clinical research director for the Division of Gynecologic Oncology at Dana-Farber.
Dr Liu is a medical oncologist specializing in gynecologic cancers, and she is a wonderful colleague. Joyce, welcome to the Medscape InDiscussion: Endometrial Cancer podcast.
Joyce F. Liu, MD, MPH: Thank you so much for having me.
Matulonis: This is a complicated topic, but I know you're going to take us through it expertly, because this is a new type of therapy for endometrial cancer, focusing on replication stress and DNA damage and repair. Can you briefly explain the concept of replication stress and its role in DNA repair?
Liu: It's a really complicated topic. In really broad terms, replication stress is when the process of DNA replication — by which DNA is duplicated during the cell cycle — is slowed down or halted due to issues that arise with the DNA synthesis process. As a concept, replication stress is actually a little bit different from some of the other things that we often think about as molecular alterations or sort of targetable processes in cancer.
For example, when we talk about homologous recombination deficiency, we're really talking about the inability of a cell to perform a specific process — homologous recombination — the ability to repair double-strand DNA breaks. In the case of replication stress, though, it's actually more of a secondary downstream outcome. The replication fork is slowing or stalling, and it turns out this is a result that can be caused by a number of different processes.
Some of the most common causes of replication stress are, in fact, unrepaired DNA damage. So, as you can imagine, if a cell is trying to replicate its DNA, and the replication fork is going along and encounters an area with unrepaired DNA damage, the replication fork can't progress through that area until the DNA is fixed. To do this, the replication fork has to stop; it has to stall or slow down until that area of DNA can be repaired, and then it can progress. So that is how defects in DNA repair can lead to increased replication stress.
However, there are other causes of replication stress. For example, there's something called oncogene-induced replication stress, which can happen when there's amplification or overexpression of oncogenes such as RAS or MYC or CCNE1. Some of these oncogenes can contribute to DNA repair defects. So that's one way they can cause replication stress. Additionally, oncogenes can actually drive replication stress by causing things like more frequent or aberrant origin firing. When I say origin firing, this means opening up areas of the DNA to open those pockets for replication. So more of the DNA is trying to replicate at the same time.
This, in turn, leads to things called collisions between the replication machinery and the transcription machinery, which then causes the DNA to stall again so that replication can go on. When there's a lot of origin firing, you actually deplete the nucleotide pools needed for DNA synthesis. Without enough materials, you can't replicate DNA at the same speed, which also slows down the replication process.
So, there are a lot of different causes. I've touched on two major ones. There are many more, but you can see that replication stress is conceptually a downstream effect of a number of different causes — one of which turns out to be DNA repair.
Matulonis: That's a great explanation. It is complicated. I think every time we hear it, it becomes more ingrained. So, the next question after that great explanation would be: How important do you think DNA damage repair and replication stress are in uterine cancer biology?
Liu: This is a really great question and one that we've been working hard to understand. Ultimately, we're going to find that things like replication stress and DNA damage response are going to be really important in at least a significant subpopulation of uterine cancers.
We already know that uterine cancer is a heterogeneous group of diseases. They share a single cell type of origin, but ultimately, there’s a group of them with very disparate biologies. You have your dMMR (deficient mismatch repair) endometrial cancers, your low-grade, hormonally driven endometrioid cancers, and your higher-grade p53-mutated endometrial cancers — those are the three big buckets.
There's still a lot of work to be done in this space. But right now, a lot of the interest in terms of targeting DNA damage and repair and replication stress has been focused on those high-grade, p53-mutated endometrial cancers. There are some really good reasons for this.
If you have a p53 mutation, it means there’s dysregulation of the G1-S cell cycle checkpoint. This can set the stage for increased replication stress because cells with intrinsic DNA damage are supposed to pause at that GI-S checkpoint so that they don’t enter S phase and DNA synthesis and replication with unrepaired DNA damage. But if you have a p53 mutation and you have dysregulated the G1-S cell cycle checkpoint, the cell is more likely to progress into S-phase with unrepaired DNA damage and have higher replication stress.
One reason we’re also interested in this is because we’ve been guided by our experience with high-grade serous ovarian cancers, which have all those p53 mutations as being central to their biology. And so, we think that targeting DNA damage response with drugs like PARP inhibitors have been so effective in certain ovarian cancers, that we think endometrial cancer might be a place where we could see some activity as well. But it's important to remember that uterine cancers are molecularly different from ovarian cancers. About half of high-grade serous ovarian cancers have homologous recombination deficiency, but the fraction of endometrial cancers that are homologous recombination deficient is probably much lower. Uterine cancers, by contrast, are oncogenic-driven diseases. So, oncogene-driven replication stress may play a bigger role in endometrial cancer than in ovarian cancer.
Matulonis: That's a great entry into talking about more therapies focused on this area. I am going to credit you, Joyce, with starting the study of targeting replication stress with your original trial of a WEE1 inhibitor a number of years ago. You can tell us about that and also how you became interested in studying this class of drugs in these higher-grade, harder-to-treat uterine cancers like serous, clear cell, and carcinosarcoma.
Liu: Thanks so much, Ursula. Our experience with the WEE1 inhibitors has been one of the exciting areas that I've seen develop career-wise. I can't take sole credit for it. The idea of targeting WEE1 in uterine cancers actually came from a conversation that our colleague Panos Konstantinopoulos and I were having about new therapies we thought we could develop in the endometrial cancer space.
We'd been talking about replication stress and how WEE1 really plays into it. WEE1 is a kinase that has a key role in regulating the G2-M checkpoint of the cell cycle. If we go back to high school biology, there are several cell cycle checkpoints that help regulate progression through the cycle. Two of the most important are the G1-S checkpoint and the G2-M checkpoint. G1-S is also known as the restriction checkpoint; it's basically where the cell does a systems check before entering S phase and triggering cell division. P53, as I mentioned earlier, plays a major role in regulating this checkpoint.
At the same time, the G2-M checkpoint — where WEE1 is a key regulator — is where the cell does a final check of how well DNA replication has occurred before entering M phase mitosis and starts the process of physical division. What WEE1 inhibitors are really doing is releasing control of the G2-M checkpoint.
We got really interested in this in endometrial cancer because we hypothesized — again, this came from conversations with Panos — that cells with poor G1-S checkpoint regulation and high intrinsic replication stress would become really dependent on the G2-M checkpoint. These cells would go through the G1-S checkpoint unregulated, try to replicate their DNA under stress, and be very dependent on the G2-M checkpoint to stop them from entering mitosis before all of their DNA replication was complete.
Cells that enter mitosis with under replicated DNA or unrepaired DNA damage often undergo mitotic catastrophe — they try to line up the DNA during metaphase, but it can’t divide properly. So, the DNA kind of falls apart, leading to mitotic catastrophe events. We thought that these cells that might be at high-risk cells for having under-replicated DNA or DNA damage would become dependent on the G2-M checkpoint.
When you look at the molecular features of these high-grade uterine cancers, especially uterine serous cancers and uterine carcinosarcomas, almost all of them have p53 mutations. In addition to that p53 mutation, which sets the stage with that G1-S checkpoint dysregulation, many also have other features suggesting high replication stress — such as RAS alterations MYC alterations, CCNE1 amplifications, and FBXW7 mutations. FBXW7 regulates MYC and CCNE1. We hypothesized that these cancers would have a vulnerability to targeting of the G2-M checkpoint with a drug like a WEE1 inhibitor.
Matulonis: That's great. It’s amazing that you and Panos came up with this idea years ago. You started with a drug called adavosertib, performing a phase 2 trial that’s now been published. Now, there are a number of other WEE1 inhibitors in clinical trials. I think you’ve already touched on the importance of this class of drug, but it would be great to hear more about your initial experience with adavosertib, what other WEE1 inhibitors are in clinical trials now, and where you think WEE1 inhibition is going as a therapeutic modality.
Liu: I think it's been a bit of a tricky time in the development of WEE1 inhibitors in the endometrial cancer space, and I'll mention that in a moment. Just looking back historically — when we first launched the trial of adavosertib in uterine serous cancer, it was a proof-of-concept phase 2 trial. We launched it based on a hypothesis drawn from molecular alterations and what we knew about the mechanism of WEE1 inhibitors and adavosertib worked. But we didn't yet have evidence that it would be active.
In that trial, it was really gratifying to see the hypothesis play out in a clinical setting. We enrolled 34 patients with evaluable disease over about a year and saw a response rate just under 30%, with durable responses lasting about 9 months. The median progression-free survival was just over 6 months.
To put that in context, we conducted the trial in 2018-2019 — before lenvatinib and pembrolizumab were available and before antibody-drug conjugates were entering the space. The alternative standard of care at that time was chemotherapy, which, as we know, is not very active in this setting and has a response rate of maybe 10%-15%. So this was really exciting to see.
Based upon that, we then launched the next trial, an international phase 2 trial, which accrued a little over 100 patients. Interestingly, the response rate was similar — around 26% — but the duration of response didn’t hold up. It was about 4 and a half months, and median progression-free survival dropped to just under 3 months.
There are a lot of questions about why that happened. One thing we saw in this trial was that treatment intensity was much less. That’s something you often see when moving from a controlled single-center trial to a broader, international one. Patients may not have been able to stay on the drug due to side effects, most notably decreases in blood counts and fatigue.
Ultimately, adavosertib was deprioritized by AstraZeneca as they focused on other parts of their portfolio. But as you mentioned, other companies are developing drugs that are targeting replication stress and WEE1. Zentalis is one of the leaders in this space, and their WEE1 inhibitor, azenosertib, has been developed for ovarian and endometrial cancers. We saw a nice presentation just last month at SGO (Society of Gynecologic Oncology), showing activity in platinum-resistant ovarian cancer.
Other companies are developing WEE1-targeting agents. Some of them are dual agents, looking at WEE1 and PKMYT1. WEE1 remains a tantalizing target. The biology is really interesting, and we have proof-of-concept that it can be an important target for certain cancers. But the therapeutic window is something we’re going to have to be aware of. That will play a major role in how successful we are at advancing these agents in their current form into the clinical arena.
Matulonis: Very well said. Thank you so much. I really want to talk about a potential biomarker for responsiveness to WEE1 inhibition, and that’s Cyclin E1 amplification. Certainly, in uterine cancer, we sometimes pick up Cyclin E1 amplification in serous carcinosarcomas, sometimes in clear cell, and certainly in some high-grade serous ovarian cancers as well.
But I think there has been some uncertainty moving forward about how to measure that. Should we be measuring it via true amplification — and if so, exactly what copy number would be sufficient to call it amplification — or through immunohistochemistry (IHC) measures? That’s exactly what the azenosertib trial that was presented at SGO did, where they probably captured a higher proportion of ovarian cancer patients using that IHC marker rather than focusing on copy number. Do you have any thoughts about where that biomarker field is going?
Liu: Yes, it's really interesting. So, for context: CCNE1 is the gene that encodes the protein Cyclin E1. Cyclin E1 is the regulatory subunit for the CDK2 cell cycle kinase, and the Cyclin E-CDK2 complex facilitates the G1S transition — it moves cells from G1 into S phase.
Cyclin E overexpression has been observed in a number of cancers and really helps facilitate premature entry of cells into S phase. So it increases replication stress, which is why it’s been so interesting as a potential biomarker for WEE1 inhibitors and other drugs that target replication stress.
There are a number of ways you can have high levels of Cyclin E protein in a cell. One is gene amplification — CCNE1 amplification — which we see in a portion of endometrial cancers, most commonly the high-grade p53-mutated types. We also see it in ovarian cancers and other solid tumors. CCNE1 amplification almost always results in Cyclin E overexpression, so there's a direct linkage.
At the same time, we also know that you can have high levels of Cyclin E in the cell, so high Cyclin E that is completely independent of CCNE1 amplification. The protein is at high levels, even though you don’t have extra copies of the gene. That can be detected by immunohistochemistry. In endometrial cancer, it’s not yet clear what the clinical significance of that is.
In ovarian cancer, we saw the recent presentation at SGO using Cyclin E IHC as a biomarker for response to azenosertib and observed different response rates between Cyclin E high and Cyclin E low tumors. But we don’t have that same level of data in endometrial cancer.
When we did the adavosertib trial, we looked at CCNE1 amplification and Cyclin E levels, and it wasn’t clear there was a strong correlation. There’s still a lot to learn. Again, the biology between ovarian and endometrial cancer is not identical, so the biomarkers for response may not be either.
Matulonis: I agree. I think there's a lot of work to do. I just want to briefly get your take on the role of PARP inhibitors in the treatment of endometrial cancer right now. Do you think there is a role for these drugs in endometrial cancer?
Liu: Right now, the answer is: I don’t know where PARP inhibitors are going to end up in the endometrial cancer space. I’m not routinely using them at this point.
Again, the biology of ovarian cancer and endometrial cancer is very different. Ovarian cancers have a lot of homologous recombination deficiency — that’s not necessarily true of endometrial cancers. One of the lessons I took from ovarian cancer is that when we use PARP inhibitors without a biomarker, we may not be doing the best for all of our patients.
One of the things I've really struggled with, with the data that is starting to come out with, adding PARP inhibitors to immunotherapy and the DUO- E trial results, where numerically, the outcomes look better with that combination compared to IO alone, that study was not statistically designed to actually compare the arms. It’s not clear there’s a biomarker, and I don’t yet understand the biology.
So, from my perspective, without a better understanding of the biology, without knowing biomarkers for activity, and without knowing that there aren't any worrisome signals for long-term effects, I don’t feel that right now I am able to say PARP inhibitors today have a role in endometrial cancer. It is possible that, down the road, there will be at least a portion of endometrial cancers where PARP inhibitors have a place.
Matulonis: I agree with you. I think it’s too early. And as you said, we learned in ovarian cancer that we can actually do harm in HRP (homologous recombination proficient) tumors. Can you talk about your program project grant, which is focused on replication stress and endometrial cancer? Do you have any results to report?
Liu: We’re still in the early days, so no results to report just yet. But I think, as is probably clear from this conversation — and as you know — we’ve become really interested, based on the adavosertib data and all the preclinical work, in whether we can leverage the presence of replication stress in endometrial cancer to develop new therapies.
We have this program project grant that’s really focused on targeting replication stress in endometrial cancer. It’s been a rewarding collaboration with the groups here, including you, Ursula. The questions we’re asking are focused on a number of different topics
First, we talk a lot about replication stress as a concept, but the truth is, we don’t yet have a good biomarker for it. No one has been able to definitively say: “Here is what replication stress looks like,” or “This is what shows a cell is under high replication stress.” Even though we hypothesize that high replication stress leads to sensitivity to WEE1 inhibitors, we haven’t shown that directly. So one thing we are trying to do is really draw that connection more clearly, understand if there are biomarkers there that we could leverage to see when we can target replication stress.
Another project, led by Dr Konstantinopoulos, is looking at whether we can combine other replication stress-targeting agents like ATR inhibitors with PI3K pathway inhibitors, really trying to leverage that.
A third project is investigating whether targeting replication stress can actually create a more immunogenic environment and increase the effectiveness of immune-based therapies in endometrial cancer.
Matulonis: It’s been a great grant, and there’s lots more to come as we head into year two. Lastly, can you tell us about any therapeutic targets or treatments that target replication stress in endometrial cancer that you're especially excited about?
Liu: I’m still excited about WEE1, caveats and all. ATR inhibitors are another area of active development across solid tumors, and they could be very interesting in targeting replication stress, potentially in combination with other agents.
There are drugs that target a parallel to WEE1, which is PKMYT1. It also regulates the G2-M checkpoint. The lead compound in that space was recently deprioritized, unfortunately, but there are others in development, and I think PKMYT1 is going to be an interesting target.
There are these dual inhibitors of the combination of WEE1 and PKMYT1 that are also being developed — they’re just entering phase 1 trials. The therapeutic window and tolerability will be key questions there. And finally, degraders are entering the space — WEE1 degraders, CDK2 degraders — agents that could help us hone in on particular proteins of interest.
These are all going to be really interesting in seeing if we can tease out the ability to target replication stress while creating a window of tolerability where we don't run into the same hematologic or other side effects that have, to date, made it harder to bring those agents forward in clinical development.
Matulonis: Joyce, thank you so much for your thoughts, your insights, and your knowledge. It’s always great to chat. Thank you for helping us focus on this topic, which is no longer emerging — it’s very much on its way. Thank you so much.
Liu: Thank you for having me.
Matulonis: Today, we’ve talked to Dr. Joyce Liu about the role of replication stress and DNA damage and repair in endometrial cancer. We explored different potential therapeutic targets currently being tested, as well as future treatments focused on replication stress and DNA repair in this disease.
Thank you so much for tuning in. Please take a moment to download the Medscape app to listen and subscribe to this podcast series on endometrial cancer. This is Dr. Ursula Matulonis for the Medscape InDiscussion: Endometrial Cancer podcast.
Resources
- Endometrial Carcinoma
- Exploiting Replicative Stress in Gynecological Cancers as a Therapeutic Strategy
- Mechanisms of Oncogene-Induced Replication Stress: Jigsaw Falling Into Place
- WEE1 Inhibition in Cancer Therapy: Mechanisms, Synergies, Preclinical Insights, and Clinical Trials
- Phase 2 Study of the WEE1 Inhibitor Adavosertib in Recurrent Uterine Serous Carcinoma
- ADAGIO: A Phase 2b, Open-Label, Single-Arm, Multicenter Study Assessing the Efficacy and Safety of Adavosertib (AZD1775) as Treatment for Recurrent or Persistent Uterine Serous Carcinoma
- Azenosertib Monotherapy Yields Encouraging Responses in Cyclin E1+ Proc
- Durvalumab Plus Carboplatin/Paclitaxel Followed by Maintenance Durvalumab With or Without Olaparib as First-Line Treatment for Advanced Endometrial Cancer: The Phase 3 Duo-E Trial
- Homologous Recombination Deficiency: Concepts, Definitions, and Assays
- A Replication Stress Biomarker Is Associated With Response to Gemcitabine vs Combined Gemcitabine and ATR Inhibitor Therapy in Ovarian Cancer
- Abstract B144: Discovery and Preclinical Evaluation of Novel Oral WEE1 Degraders
