Good day, and welcome everyone to the Aprea Therapeutics KOL event, featuring presentations by esteemed key opinion leaders, Dr. Fiona Simpkins, Professor in the Division of Gynecology Oncology and Department of OB-GYN at the University of Pennsylvania, and Dr. Tim Yap, Medical Oncology Physician, Scientist, and Professor based at the University of Texas MD Anderson Cancer Center, who will speak today about key targets in oncology and tumor suppression, specifically synthetic lethality and DNA damage response pathways. We will also hear from Dr. Eric Brown, Professor at the University of Pennsylvania, and a member of the Abramson Family Cancer Research Institute, Dr. Nadeem Mirza, Senior Medical Advisor at Aprea, and Dr. Oren Gilad, President and Chief Executive Officer at Aprea. Dr. Gilad is a pioneer in the field of cancer research, having authored several scientific publications during his thirteen-year academic career, including on the ATR pathway.
All speakers will be available for a Q&A session following the formal presentations. Let me remind everyone that during the event, speakers may make forward-looking statements. Forward-looking statements are subject to numerous risks and uncertainties as described in the company's SEC filings. Also, I would like to note that this call is being recorded on the date of today's event, October 31st, 2023. Now, I would like to turn the call over to Dr. Oren Gilad, President and Chief Executive Officer of Aprea, who will begin today's event with an overview of the company and agenda. Oren?
Thank you, Tara, and welcome everyone to our event today. It is a pleasure to be here and discuss synthetic lethality, DDR pathway, and our development program addressing these key pathways. We're very excited about the opportunity for our key program in development, and hopefully by the end of this event, you will share our enthusiasm. Let me first introduce the speakers on our call today before I provide a quick overview of our company. In addition to Dr. Nadeem Mirza, our Senior Medical Advisor, we are honored to have three esteemed key opinion leaders in the field: Dr. Fiona Simpkins, Dr. Eric Brown, and Dr. Tim Yap. Dr. Mirza, who will be speaking about our ATR inhibitor program, has served as Senior Medical Advisor to Aprea since February 2023. Dr.
Mirza brings over 30 years of clinical and development experience in solid tumors and hematological malignancies. In the past, Dr. Mirza served on multiple leadership roles, including Global Head Hematology and Solid Tumors at AbbVie. He was Vice President, Head of Oncology, North America Medical Affairs at Sanofi, where he was responsible for medical affairs programs to support 12 products across several oncology indications. Dr. Mirza also held leadership roles in medical affairs and clinical development at Genzyme, Sanofi, Onyx, AbbVie, and Berlex. We're honored to have him on our team. Dr. Brown, who will be speaking about our WEE1 inhibitor program, is a consultant to Aprea. He's a Professor of Cancer Biology at the University of Pennsylvania and a member of the Abramson Family Cancer Research Institute. The first demonstration that ATR loss caused genomic instability was part of his postdoctoral research.
His laboratory has investigated the effect of ATR suppression in cancer progression, inflammation, and tissue homeostasis. We worked together at his laboratory to demonstrate that the DNA replication of abnormalities caused by oncogenic stress is synthetic lethal with ATR suppression. Furthermore, they showed that hypomorphic suppression of ATR expression is sufficient to limit tumor growth while leaving normal tissue intact. Dr. Simpkins, who will be covering DDR and synthetic lethality, is a professor at the University of Pennsylvania and a Director of Preclinical Drug Development for the Ovarian Cancer Research Center. She's the lead PI on our ATR trial and a principal investigator on several early-phase ovarian cancer clinical trials, evaluating novel therapies emanating from her laboratory, where she focuses on developing strategies to circumvent drug resistance in GYN cancer. Dr.
Yap, who was just named as principal investigator on our WEE1 trial, is a medical oncology physician-scientist focused on first-in-human and combination development of molecular-targeted agents and immunotherapies. He will discuss the unmet medical need in the WEE1 space. His main interests include DDR targeting, such as ATR, PARP, POLQ, USP1, PARP, CHK1, ATM, and of course, WEE1 inhibitors, along with next-generation CDK4 and CDK2 selective inhibitors. Now, let me provide a brief overview of Aprea. We are a biopharmaceutical company focused on developing and commercializing novel synthetic lethality-based cancer therapeutics targeting the DNA damage response pathways. We have an outstanding team that includes world-class scientific and clinical oncology leaders, all focused on developing novel cancer therapies to address the significant unmet medical needs in for patients with cancer.
Our synthetic lethality portfolio came to us through the acquisition of Atrin Pharmaceuticals last year, which I founded in 2011, and we have since focused on advancing our targets into the clinic. Our lead candidate, ATRN-119, an ATR inhibitor, is currently in phase I, II-A trial, and we have second candidate, APR-1051, a WEE1 inhibitor, which we are expecting an IND by the end of the year, and we'll begin clinical studies early next year. We recently presented initial clinical findings and data at the Triple Meeting earlier this month, which we believe provide rationale and foundation for moving forward in both of these programs. We will begin the presentation with Dr. Simpkins, who will provide an overview of the clinically validated synthetic lethality approach and rationale for combination strategies for overcoming drug resistance.
Next, we will hear from our internal expert, Dr. Nadeem Mirza, who will articulate our first-in-human phase I, II-A trial of a macrocyclic ATR inhibitor, ATRN-119, in patients with advanced solid tumors. Dr. Brown will follow with the preclinical development strategy and differentiation of our WEE1 inhibitor, APR-1051. And finally, we will hear from Dr. Yap on the clinical strategy for our WEE1 inhibitor, APR-1051, and why he selected to be principal investigator and part of our clinical development program. We will then open the call for question and answer session. And now, without further delay, it is my pleasure to turn the call over to Dr. Fiona Simpkins. Fiona?
Good morning. I've focused the past 10 years on developing synthetic lethal approaches in the lab, with a goal in moving them to the clinic for patients with gynecological cancers. This morning, I will show you how this strategy really works. Next slide. So synthetic lethality is a very promising approach in cancer therapy. So what is it? In the green panel, when an individual genetic event occurs, such as a single mutation like BRCA loss or overexpression like CCNE1, cells survive. On the right pink panel, when co-occurrence of two genetic events, such as a BRCA mutation and blockage of PARP1, for example, treatment with a PARP inhibitor, this leads to cell death. Also, when gene alterations result in overexpression, like CCNE1, treatment with a WEE1 inhibitor hits WEE1 inhibitor signaling, and that leads to cell death, and this is shown in the right.
This is synthetic lethality. Next slide, please. PARP inhibitors are an excellent example of a synthetic lethal approach that has been very successful in the clinic. PARP inhibitors are synthetically lethal with BRCA mutations. PARP inhibitors are FDA-approved for ovarian, this is the lower left-hand side of this slide, for maintenance therapy after chemotherapy, and they've been shown to increase overall survival. They've recently been approved for pancreatic maintenance after chemotherapy in the germline BRCA setting - that's shown in the upper left - and in breast cancer. Adjuvant olaparib in metastatic setting for germline BRCA mutant, HER2 negative breast cancers, that's shown in the upper right. And then on the lower right, in metastatic castrate-resistant prostate cancer with BRCA or ATM mutations. Unfortunately, patients will either progress on a PARP inhibitor or complete PARP inhibitor and recur at a later time.
So moving forward, we need to think about next treatment options for PARP inhibitor-resistant cancers. Next slide, please. We asked: How can we potentially prevent or overcome PARP inhibitor resistance? We hypothesized that by targeting two unique DNA repair pathways, such as ATR on the left and PARP-1 on the right, by combining a PARP inhibitor with an ATR inhibitor, this would lead to increased DNA double-strand breaks by two different fork-stabilizing mechanisms to overcome resistance. So ATR, the red box, is activated by replication stress. It prevents replication fork collapse. CHK1 is then activated, leading to G2/M arrest to allow DNA to repair, and this is all shown on the left. Treatment with an ATR inhibitor, the green box, now results in loss of the G2/M checkpoint replication fork collapse and double-strand breaks.
On the right hand, you can see PARP-1 is activated by single-strand breaks, and treatment with a PARP inhibitor results in double-strand breaks. So you get double-strand breaks, ultimately mitotic catastrophe and cell death occurring by two independent mechanisms with combination PARP and ATR inhibition. Next slide, please. We next evaluated combination PARP and ATR inhibition in acquired PARP inhibitor-resistant PDX models. In the top panel, PDX, PDX tumors were generated from a BRCA2 mutation carrier that actually progressed on a PARP inhibitor. Sequencing data showed 22 new mutations in DNA repair, no BRCA reversion. And with the purple line, you can see a twofold increase in tumor, a twofold decrease in tumor volume compared to ATR inhibition alone.... And then an increase in overall survival of about fivefold compared to either drug alone.
In the lower panel, this is a PDX model generated from a patient with who was on a PARP inhibitor for two years. Sequencing showed a BRCA reversion mutation. The middle panel, you can see that combination treatment with the purple line results in complete tumor regression compared to ATR alone, and an increase in overall survival similarly. So here we show that this combination leads to tumor regression that's durable in acquired PARP inhibitor-resistant PDX models from BRCA mutant patients, overcoming multiple mechanisms of drug resistance. Next slide, please. We then went on to the clinic to evaluate if the addition of an ATR inhibitor to PARP inhibitor can resensitize PARP inhibitor-resistant, HR deficient or BRCA mutant ovarian cancers to PARP inhibitor and showed that it indeed does.
This is a waterfall plot showing best response, and we found an overall response rate of about 50%, with a progression-free survival or time to where the tumor recurs, of about 7.4 months. This is a small sample size, however. Dr. Yap, an international expert in DDR in early phase clinical trials, who you'll hear from shortly, presented at AACR recently, similarly, that another ATR inhibitor in combination with multiple PARP inhibitors is quite active in multiple disease sites as, as subtypes, especially ovarian cancer. So ATR inhibitors resensitize PARP inhibitor-resistant tumors to PARP inhibitors, supporting further evaluation of this combination of PARP ATR in the clinic. Next slide, please. What about WEE1 inhibitors? WEE1 inhibitor monotherapy is a new strategy targeting cyclin E amplification or expressing cancers.
WEE1 blocks cell cycle progression from G1 to S and G2 to M by inhibiting CDK2 and CDK1, respectively. WEE1 inhibitors thereby abrogate both the G1/S and the G2/M checkpoints, leading to both premature S phase entry and M phase entry. WEE1 inhibitor treatment will exacerbate high levels of replication stress associated with cyclin E overexpression, ultimately causing mitotic catastrophe. Next slide. WEE1 inhibitors as monotherapy have recently shown activity in cyclin E amplified solid tumors in a phase II clinical trial by Fu et al. They found an overall response rate of 27% and but an even higher response rate in ovarian cancers of 36%, with 61% of patients remaining disease-free at six months. However, 23 out of 27 patients required dose reduction, and a high number experienced Grade 3 or higher toxicity.
This WEE1, in particular, adavosertib, is no longer being developed by AZ, and it's really because of financial reasons. Next slide, please. WEE1 inhibitors work in cyclin E amplified cancers for about four months in the clinical trial I just talked about, until resistance emerges. So going back to the bench, we indeed show that WEE1 inhibitor monotherapy results in tumor regression, as you can see in the upper right panel, but with rapid emergence of resistance in CCNE1 amplified PDX tumors. So we hypothesized that this dysregulated cell cycle progression, promoted by cyclin E amplification, would lead to an increased sensitivity to low-dose WEE1 and ATR inhibition, thereby optimizing efficacy and tolerability. Next slide, please. Here we see that combination WEE1 and ATR inhibition, as shown in red, leads to significant tumor regression.
Not only, not just depression, but increased overall survival, as you can see in the lower panels in red. And this is not the case in the cyclin E copy number low models, as shown on the right. This overall suggests that cyclin E amplification might be a clinically reliable biomarker predictive of response to this combination. Next slide, please. So what have I shown today? I think we really can say that synthetic lethality is a validated approach to cancer therapy. PARP inhibitors are FDA-approved and have increased overall survival in cancer patients with BRCA mutations. We've also shown that the addition of an ATR inhibitor to PARP inhibitor-resistant ovarian cancers resensitizes tumors to PARP inhibition. WEE1 inhibitor monotherapy is showing a signal of activity in phase I and phase II clinical trials. Stay tuned.
Preclinical work shows that the addition of an ATR inhibitor to WEE1 inhibitor overcomes and may present... prevent WEE1 inhibitor resistance. We are at the beginning stages for next-generation cancer therapies. Next slide. Thank you so much. I can, you know, it's always important team science, and the folks listed on this slide are all my partners, and this work could not have been done without them. So thank you.
Thank you, Dr. Simpkins. Now, I would like to turn the call over to Dr. Nadeem Mirza, Senior Medical Advisor at Aprea Therapeutics, who will provide insight and details on our clinical development programs for ATRN-119, our ATR inhibitor for the treatment of solid tumors. Nadeem, please go ahead.
Thank you, Oren. As mentioned, I will provide an overview of our ongoing phase I clinical trial and share some preliminary data that was presented at the recently held Triple Meeting in Boston this month. We are investigating first in human phase I, II-A trial of macrocyclic ATR inhibitor, also known as ATRN-119, in patients with advanced solid tumor. This trial is being conducted at four sites with Dr. Simpkins from University of Pennsylvania as the lead principal investigator, Dr. Reva Schneider from Mary Crowley Cancer Research Institute, Dr. Amit Mahipal from University Hospital Cleveland Medical Center, and Dr. Patricia LoRusso from Yale Cancer Center, our participating investigators. ATRN-119 is highly specific ATR inhibitor that is given orally on daily basis. Preliminary studies have shown that high specificity for ATR kinase correlates with increased tolerability, can be given daily, and reduces hematological toxicity.
Single agent ATRN-119 in vitro has shown to increase cytotoxicity against broad spectrum of cancer cell lines that harbor DDR gene alteration and inhibit tumor growth in cell line-derived and patient-derived xenografts in in vivo models. In addition, in vivo combination studies have demonstrated significant synergy between ATRN-119 and PARP inhibition. The primary objective of the study is to evaluate safety profile of daily dose escalation of ATRN-119, determine the maximum tolerated dose, and recommended phase II dose. To characterize the pharmacokinetics profile of ATRN-119 and its active metabolite. Secondary objective includes evaluation of antitumor activity of ATRN-119 among advanced solid tumors. Additionally, we are exploring the association between identified mutations and clinical outcome as an exploratory objective. Key eligibility criteria are shown here.
Patients must be at least 12 years or older with advanced solid tumor that harbor at least one or more documented DDR mutation, such as ARID1A per Next Gen sequence. Patients have measurable disease per RECIST version 1.1 for solid tumors or must meet PCWG-3 criteria for patients with metastatic prostate cancer. Patients must have failed at least one prior therapy, have ECOG performance status of zero or one, and have adequate bone marrow and renal function. Exclusion criteria includes prior chemotherapy, immunotherapy, radiotherapy, or targeted therapies within four weeks or greater or equal to five half-lives at the time of enrollment. Adverse events related to prior therapy must be at baseline or stable. Investigational agent within five half-lives or within 30 days of drug inclusion are excluded.
Patients with known CNS metastases or CNS involvement that is not stable for prior 1 month are also excluded. Concomitant treatment with strong inhibitors or inducers of CYP3A4 or CYP2D6 is not allowed. The dose, the dose escalation schema, as 3+3 design, and we expect to treat approximately 18 patients in the dose escalation part. The starting dose level is 50 milligrams once daily, continuously, and we have cleared dose level three of 200 milligrams once daily, and are currently enrolling patients at dose level four of 350 milligrams once daily. After determination of the recommended phase II dose by the Safety Review Committee, dose expansion arm will enroll 30 patients with specific mutations such as BRCA1 and BRCA2, and some undisclosed at this time. We plan to focus on specific indications that may include breast, colorectal, and ovarian cancer.
We have enrolled nine patients, and their demographics are listed here. Median age was 62 years, with slightly more females than males in the study. Two-thirds of patients had ECOG performance status of one. Median of three prior lines of therapy with range of one to five, including 100% of patients receiving prior platinum-containing therapy. Majority of patients enrolled had p53 mutation, followed by CDKN2A. In terms of tumor types, 44% were GI cancers and one each of adrenal cortical carcinoma, endometrial cancer, fallopian tube carcinoma, pancreatic cancer, and carcinoma of unknown primary were enrolled. Overall, the study drug was well tolerated. Most drug-related adverse events were Grade 1 GI adverse events that were manageable, and no Grade 3 or higher adverse events were reported. We did not observe heme toxicity as of today. This graph shows duration of treatment and patient outcome.
As expected, at this stage of development, most patients came off treatment due to disease progression, as these were heavily pretreated patients with advanced solid tumors. There was one patient with colorectal cancer who had stable disease at two months but later progressed. This patient had failed several prior therapy before enrolling in the study. None of the patients came off treatment due to toxicity. In summary, daily dosing of ATRN-119 is possible and may result in persistent tumor reduction. To date, we have not observed any dose-limiting toxicities, and ATRN-119 appears to be well tolerated with manageable safety profile. PK data analysis is ongoing and will be presented at future meetings. We continue to enroll patients at the four U.S. sites with expectation of starting dose expansion in second quarter of next year. Thank you.
Thank you, Nadeem. Next, it is my pleasure to introduce Dr. Eric Brown, who will review our strategy and development plans for WEE1 inhibitor, APR-1051. Eric, please take it away.
Thank you so much, Oren. It's really a pleasure to be telling you about our work today. The work I'll be telling you about is in part sponsored by a $2 million grant awarded by the NIH to both Aprea Therapeutics, as well as to the laboratories of Dr. Simpkins and my laboratory. What we've been able to do with that money is work on a next-generation WEE1 inhibitor, which I believe for a couple of different reasons I'll tell you about, is extremely promising. So as Dr. Simpkins already told you about, WEE1 is an important target. Just to go over that briefly on the top part of this panel, WEE1 is different from ATR inhibition in the following ways. It not only overcomes the G2/M phase checkpoint, it also overcomes the G1/S checkpoint.
Whereas ATR really is focused more on the G2 to M phase checkpoint. And so that has a couple of different qualities. One of the things it does is it drives cells into the DNA synthetic phase of the cell cycle, and the next thing it does is drive cells further into mitosis. As you can imagine, if cells go into mitosis with unreplicated DNA, it's catastrophic. And one of the things that we've learned from Dr. Simpkins' work, and it's been validated by multiple laboratories around the world, is that, if cyclin E is overexpressed and CDK2 is activated by WEE1 inhibition, then it even further drives cells in the S phase and causes a synthetic lethality effect when WEE1 is inhibited.
So we think that WEE1 inhibition is going to be a very promising target in cyclin E overexpressing cancers, which occurs both in ovarian cancer as well as drug-resistant breast cancers and a number of other cancer types. In the bottom panels, what it's showing is some, you know, just some basic information on what you would expect a WEE1 inhibitor to do. It binds WEE1 selectively. This is all APR-1051 data. It inhibits the phosphorylation of its direct target, CDK1, and it can kill cyclin E overexpressing cancer cells. So if this was the first WEE1 inhibitor to ever be developed, you would say, "Wow, that's pretty impressive." Now, there are a few others, and you've probably heard of this before, that WEE1 inhibitors are in the clinic right now.
But there have been a couple of problems, and I would just say that, you know, some of the prior WEE1 inhibitors have been a little bit unlucky. And so I'll, I'll tell you a little bit about that and why we think APR-1051 solves some of those problems. Okay, so here are two that you might be familiar with. AZD1775, which is now discontinued from AstraZeneca, originally from Merck, and Zentalis's zennasertib. Now, one of the problems with WEE1 inhibition for some time now has been that the first WEE1 inhibitors have also off-targeted the PLK family of kinases, and specifically, I'm talking about PLK1, PLK2, and PLK3. And I'm going to show you some data from this SBIR grant that we've worked on together that indicates this is a significant liability.
It's not just the liability that PLK1 inhibition has overlapping toxicity with WEE1 in myelosuppression, but also that it's countering some of the effects of WEE1. One of the things Aprea did right from the start was to say: Can we get rid of this liability? Can we reduce off-targeting of the PLK family? And they were successful. If you look in the middle column there, WEE1 inhibition, 1051 is a very potent WEE1 inhibitor that shows less WEE1—sorry, PLK inhibitory activity looking at PLK1, 2, or 3. All those are percent inhibition activities. Whereas with zennasertib, Zentalis and AstraZeneca, this is all done at the same company.
You can see that they're inhibiting PLK1, PLK2, and PLK3 about the same, in some cases, almost 100% inhibition of PLK at this dose. So, one of the problems, as I mentioned, with targeting the PLK family, is that it can counter the effects of WEE1, and I'm going to take you through that in the next slide. So I'll go slow on this. I know it's a lot to digest, but if you were to look at the left-hand panel and look at the second lane and look at the top panel, that's H2AX. So that's basically a marker of DNA damage. That's how we think these WEE1 inhibitors work, is that they cause DNA damage. And as you see, once 1051 is added, we see more DNA damage.
But if you were to dose in a little bit of a PLK inhibitor in the second, excuse me, in the third lane there, you see there's less H2AX. So that means that PLK inhibition is countering the effects of our WEE1 inhibitor, and that's not good. You can also go down to the second panel below, and you see that CDK1 phosphorylation, that's the direct target of WEE1. It's down when we treat with 1051. That's what you expect. But if you dose in a little bit of a PLK inhibitor, it goes back up. That's not good. That's not what is supposed to be happening here. And if we did the flip experiment as part of this SBIR grant, if we dose in 1051 at different concentrations, you can see, again, the H2AX in the top panel.
At different doses, you see, you know, an increasing level of DNA damage, and you see a decreasing ability to inhibit CHK1 phosphorylation. But if you add the IC50 dose of this particular PLK1 inhibitor, 75 nanomolar, the GSK compound, you see less H2AX. And off to the right, in the third panel, it's the same thing, but it's just a different PLK inhibitor. So this indicates that when compounds inhibit both WEE1 and PLK, it's countering the effects of the WEE1 inhibitor. That can't be helpful, and at the same time, they're off-targeting, the off-targeting of PLK1 is expected to have overlapping myelosuppression.
So it's two things that are sort of working against a drug that inhibits both WEE1 and PLK-one, which is why we thought that solving this problem by eliminating PLK inhibition was a good idea. And I have to say that at least Zentalis and AstraZeneca, maybe they got a little bit unlucky with, in my opinion, the PK properties. So if you were to look at the second column, that's Aprea's APR-1051. At 10 mg per kg per day, they have an AUC, which is the general metric of the exposure to the drug, of 16,739. Okay, so then that sets 10 as the number to be looking at here.
You have to go up to 40 of Zentalis to hit approximately that level, and you have to go above 80 of AstraZeneca to hit about that level. So, this is another good quality of 1051. It inhibits WEE1 very selectively, doesn't inhibit the PLK family, it's very potent towards WEE1, and it's got great exposure in these preclinical studies. Also, a very good sign. And then finally, you know, Aprea wasn't the only company to recognize PLK1 off-targeting as a problem. There are a couple of other companies out there that have also developed drugs that don't inhibit PLK1. Unfortunately, those companies have seen some cardiotoxicity in their clinical trials, QT prolongation.
So one of the things that Aprea wanted to look at, first off, was there any indication that there might be cardiotoxicity with its next generation WEE1 inhibitor? So they did two different kinase assays. You know, the more, the better, because different types of assays give you different values. These are two different types of assays, a LanthaScreen and a HotSpot screen. If you average those, you get about 21 nanomolar of an IC50 dose. If you do the other different ways of screens, you get a bunch of other numbers, but that's very potent WEE1 inhibition. And then two different screens looking at hERG inhibition, which is a potassium channel that's expressed in the heart. You see on average about 4,700 nanomolar is the average hERG inhibition.
That's a pretty big fold difference, 218-fold. So right now, it's looking very promising that 1051 will not suffer the same cardiotoxicity as the other inhibitors. And all told, this says that, you know, you know, everything is go for further studies. Okay, so here's, you know, here's something you really want to, to work on.
I said before that WEE1 is expected to have some myelosuppression, and in order to deal with that myelosuppression, you can schedule, so you can take the drug off for a few days. So that's one of the things that we've been doing as part of this SBIR grant, is, as you can see here on the left-hand panel, the blue line is vehicle-treated, so that's tumor growth over time, and then 1051 was added at 50 mg per kg BID, two days on—five days on, two days off. So the two days off is allowing the red blood cells to recover. Okay, so can you get the benefit of tumor suppression without having to have anemia? That's the goal. And it looks like this is already promising, as a schedule. We're not done yet, but we're continuing.
Already we see that after 28 days and four cycles of treatment, what we see is that there's a very small decrease in red blood cells with this schedule of treatment, even though tumors are suppressed. And what we saw in that two-day off period is that reticulocytes, the predecessors to red blood cells, are expanding during that time. So that's actually beneficial that we're seeing that expansion of red blood cells during the off period, and there was no loss of body weight during this time. Dr. Simpkins mentioned that a combination of WEE1 and ATR inhibition is very favorable, and Aprea is very well situated in that regard, and that has both drugs. And not only does it have ATRN-119, but it's also developing some next-generation ATR inhibitors for the future.
So that's what's shown in this slide, and the green line is vehicle control. So this is a cyclin E overexpressing xenograft model. That's tumor growth with the blue line, with the blue line. And then with a partially suppressive, you know, by basically half the dose of what I just showed you, of 1051, you see some suppression of growth. We actually purposefully didn't add too much. And in the green, you see the next-generation ATR inhibitor. Again, a partially suppressive, not maximal dose of 330, the next-generation ATR inhibitor. But when you combine those two, then you see a flat line in the tumor. And not only that, but with another next-generation ATR inhibitor that Aprea has, you also see a flat line in the tumor.
So this is very promising that we can combine these two drugs and completely suppress tumor growth. And what Dr. Simpkins demonstrated is that in PDX models, this is also looking very promising. Okay, so I just want to summarize and say that 1051 is very potent. It doesn't off-target or significantly off-target the PLK family of kinases. It has very favorable PK properties. It appears to have low inhibition of hERG relative to inhibition of WEE1, therefore predicting that it may have low cardiotoxicity as opposed to other WEE1 inhibitors that have been developed. We are working on dose and scheduling that suppress tumor growth, but allow us to have very little effect on red blood cell generation. And these studies have justified IND-enabling studies, studies for clinical development of 1051. And thank you so much. I'll hand it back to Oren.
Thank you, Eric. Now it is my pleasure to introduce our last speaker, Dr. Tim Yap. Dr. Yap, please go ahead.
Thanks very much, Oren, and thanks to the organizers for the very kind invitation to cover really the unmet clinical needs in the WEE1 space, and really the upcoming clinical trial. Next slide, please. So you've already heard from both Fiona and also Eric about how DDR inhibition via various agents has really changed and evolved over time. And we now have obviously four different PARP inhibitors that are FDA approved in different settings and different cancer types, so on and so forth. But there are still critical areas of unmet medical need, specifically in ovarian cancer, for example, in platinum-resistant patients, and also what we do in patients who've already had a PARP inhibitors. We know that PARP inhibitor resistance is complex and still remains a real challenge in the field.
We're also seeing, as Eric has alluded to, dose-limiting toxicities and also chronic toxicities with WEE1 inhibitors that are currently in clinical development. And these are primarily hematological toxicities with myelosuppression, GI toxicities such as nausea, vomiting, diarrhea, and also cardiac toxicities such as prolonged QTc. And then as we go ahead with WEE1 inhibitor drug development, it's likely that acquired resistance will also be a challenge, and that's probably where combinations such as the one that Eric and Fiona mentioned, I, I think, will really come into play. Next slide, please. So in the phase I clinical trial, this will be a multicenter first-in-human study to investigate not just safety tolerability, but also PK, biomarkers, and also preliminary efficacy of APR-1051 in patients with advanced solid tumors.
This will 3+3 phase I clinical trial design as monotherapy in patients with advanced solid tumors harboring DDR alterations. Following this, there'll be a dose expansion at the recommended phase II dose in ovarian cancer and also in solid tumors. The study objectives include the following. Primary objectives include the safety and tolerability of 1051, and ultimately to establish the recommended phase II dose of this drug. Secondary objectives will be to characterize the PK of 1051 following a single dose and also at steady state after multiple dosing, and also ultimately to assess the preliminary anti-tumor activity of 1051. As exploratory objective, we'll also investigate the biomarkers of 1051 activity.
You can see there at the bottom, the phase I trial design, as mentioned earlier, 3+3 trial design. Drug will be given QD in 28-day cycles. And the key inclusion criteria include patients who are at least 18 years of age with advanced or metastatic solid tumors, without standard of care treatment options and those harboring biomarkers related to DDR pathways. Patients will be required to have either measurable or evaluable disease, an ECOG performance status of one or better, adequate bone marrow and organ function, and a life expectancy of at least three months. Next slide, please. Thank you.
Thank you, Dr. Yap. Before opening the floor to any questions or comments, as a reminder, it is possible that today's meeting, including some of our comments and responses to your questions, may include forward-looking statements that are based on certain assumptions and are subject to a number of risks and uncertainties. The risks, uncertainties and assumptions that could affect these forward-looking statements include risks that are included in the company's SEC reports, including our Form 10-K for the fiscal year ended December 31st, 2022, and Form 10-Qs for the first and second fiscal quarters of 2023. We qualify all of our forward-looking statements by these cautionary statements, and except as required by law, we assume no responsibility for updating any forward-looking statements.
In addition, with respect to all of our forward-looking statements, we claim the protection and the safe harbor for forward-looking statements. I hope you can see how we are so... Why we're so excited about our two promising programs. We believe we have some meaningful upcoming news, beginning with our IND for APR-1051, expected by the end of the year, and initiation of the clinical trial early next year, followed by anticipated additional data readouts in our study for ATRN-119 in solid tumors. With that, it is now my pleasure to open the call for our Q&A session. Dara?
Thank you, Oren. At this time, we will be conducting a question-and-answer session with our speakers. As a reminder to the audience watching on the webcast, if you'd like to submit a question, please use the Q&A text box at the bottom of the webcast player. And to our covering analysts who are joining us live, please raise your hand to indicate you have a question. Please hold for a brief moment. Our first question comes from Jason McCarthy from Maxim Group. Please go ahead, Jason.
Hi, all. Very nice presentation. And this is kind of a question for the field here. Anybody could take it. Can you talk a little bit about the half-life of these SL molecules, particularly the WEE1, and how that can impact synthetic lethal phenotype when you're talking about intermittent dosing versus continuous dosing? And I'd add to that, you know, around the WEE1 inhibitor, because you have seemingly such better or higher potency and less interaction with PLK1 in your clinical trial, even if you can't, or you find that you can't continuously dose, do you have a little bit more wiggle room to get more days on drug if you have to roll back to intermittent dosing over what Zentalis is showing?
Thank you, Jason. Tim, maybe you can start with the clinical strategy, and then we can hand it over to Eric to talk about the mechanism.
Sure. I think ultimately, you know, we need to see what the clinical data show. You know, ultimately, we need to see what the clinical data show, starting with the QD dosing. I think will tell us a lot, not just about the safety, but also the PK, PD and, and ultimately efficacy. And then, one can actually pivot from that, from a continuous dosing to a, intermittent dosing if needed. And, you know, Jason, to answer your question, I think it will be the clinical data that will speak the loudest, with regards to, what we will see. I think Eric can probably talk about, you know, preclinical data and modeling in terms of, what we would expect to see, both with continuous and also intermittent dosing.
Yeah, Jason, you pretty much read our minds on this, is that, you know, going into QD dosing is the, the logical thing to start off with, but we're, you know.
taking advantage of all of our preclinical models and the expertise, we have. I should also mention that the other person that's funded by this SBIR grant is actually Fiona Simpkins, who has a number of models that could be put to bear on this problem. Our objective here is to really find the optimal dosing and scheduling for this drug, which we think is extremely promising because it lacks PLK inhibitory activity. Apparently, it's also looking pretty clean for cardio too, so.
Got it. And just briefly, on the CCNE overexpression of the amplification, when you're talking about the ATR/WEE1 combination, is there a threshold in that level of amplification that you or maybe a range that you've established that you would use going forward in the clinic?
Dr. Simpkins has done a lot of work on this, so she would be good to.
She's the expert. Yeah.
Happy to talk about this, but we don't have an answer. Bottom line, we do see that we can dose down the combination, the higher the Cyclin E expression level is, and we see that efficacy does correlate with Cyclin E expression. So, amplification with correlating protein expression, the higher it is, the better the combination works. But how we translate that to the clinic, I think is really yet to be determined. But great question.
And if I can just add, you know, I think certainly a copy number of six or seven has been routinely used by you know different NGS panels to be considered as amplification. So I think that would probably be a good starting point. But as Fiona said, I think that needs to be correlated clinically with expression, so on and so forth. So and balanced off against efficacy that's seen as well. So I would say watch this space.
Great. Thank you. I'll pass that along from here.
Thanks for the questions, Jason. Our next question comes from Sam Ravina from Wedbush. Please go ahead, Sam.
Hi. Thanks for taking the question, and great presentation. I'm just wondering what your thoughts are around how combination toxicities have limited development for other ATR inhibitors to date. And then I have one more question after that.
Tim, can you please address?
Yeah, I think that's a great point to raise, Sam. I think what we have found is that the traditional ways of combining drugs concomitantly at full doses of each component part are just not ideal. And what we have been doing with ATR inhibitors, and to be honest, with PARP inhibitors as well, and other DDR agents, is to really try and think outside the box and to be a little bit more creative, to think about sequential dosing, to think about low-dose, intermittent dosing of both drugs. I think it's absolutely critical as we think about the biology in terms of the of what we're trying to achieve ultimately, right? What we're really trying to do is to drive cells into premature mitosis and ultimately mitotic catastrophe.
And I think, you know, going in hard with intermittent doses would be a logical approach. We've also found in Gordon Mills's lab and also actually with Fiona's lab, that the sequential dosing of these drugs actually maintains the efficacy and minimizes the toxicity as well. So I think there are different ways to get around the challenges of a narrow therapeutic index. We know these are great drugs. It's just how to put them together to really generate the widest therapeutic index and window for our patients.
Okay. Thank you. And then I'm wondering, kind of aside from or in addition to, BRCA alterations, which mutations or signatures do you see as most intriguing, maybe in combination with an ATR inhibitor?
Eric?
Yeah. So we've actually developed a whole panel of biomarkers, and in terms of which, you know, it's which, you know, which one turns out to be the most effective. Now, based on our preclinical studies, we have some favorites, but we have a general approach that we think is going to be very strong. And that's really looking at not only just the oncogenic stress synthetic lethality that actually was first demonstrated by Dr. Gilad, the CEO and President of Aprea Therapeutics, but also with other mutations that cause defects in DNA repair, for example, ATM, BRCA1, BRCA2, so on.
So we've developed an overall strategy for that, also using a platform that is part of this collaboration called RepliBiome, which uses a number of different approaches, orthogonal approaches, to identify biomarkers that are responding to the drug at the replication fork. And also have been proven to be mutated and synthetic lethal based on publicly available genomic databases. So I think we've defined you know a whole slew of different biomarkers, and we're applying those you know in the future.
Okay. Thank you very much. I'll pass it off now.
Thank you for the question, Sam. Our next question comes from Joe Pantginis from HC Wainwright. Please go ahead, Joe.
Hi, everybody. Thanks for taking the questions. First, a logistical question for the upcoming WEE1 clinical study next year. Can you remind the audience, the broader audience, about the availability and the ease of the diagnostic for DDR mutation?
Tim?
Well, I think it's gonna be a CLIA-certified NGS panel that will be used in the clinical trial.
Perfect. Thank you for that. And then, with regard to the 119 clinical study, glad it's ongoing, the dose escalation continues. Just curious about what some of your dose increase assumptions are and where you feel you are right now or provide data with regard to target coverage and engagement, based on the dose against ATR.
Thank you, Joe. Nadeem, please.
Yeah, thank you for the question. So as I showed you, we have completed the third cohort of 200 milligrams once a day. We have started enrolling patients at 350. I think at this dose and levels above, we should start seeing some target engagement.
That's helpful. And then, and then lastly, I guess this is truly a forward-looking statement for everybody, and especially maybe Dr. Simpkins as well. So whether it's ATR inhibition or WEE1, what are you excited about with regard to future combinations? You know, anything that might have done, you know, early in the labs or even hypothetical right now that you look might combine well?
That's a great question. You know, in terms of, you know, what I presented today, you know, the PARP inhibitor, you know, ATR/WEE1 combinations, it's just, you know, super important in terms of the PARP inhibitor used. Excited about the PARP-1 selective inhibitor that's being developed. And Dr. Yap here might want to comment after, as he led the phase I for that drug. But the hopes, it... You know, again, it's choosing drugs that are selective, with less off, you know, off-target tox, to decrease toxicity. So PARP/ATR combinations with the PARP-1 selective, potentially. And then, you know, I, you know, CCNE1 amplification, it's such an awful disease in ovarian cancer.
So I'm really excited about WEE1 inhibitor combinations, in particular, in combination with ATR, because we really can tone it, tone, you know, tune down the dose to really exploit the replication stress, in terms of cyclin E, to see efficacy and tolerability. So that's kind of where I am right now. There's CDK2 inhibitors out there, but, you know, really early on. Yeah, I mean, I can go on about all the other DDR inhibitors, but these, I think, PARP/ATR and WEE1/ATR for right now.
Joe, can I add a little something to that?
Please.
Of course.
Okay. So this is just a... You said forward-looking statement, so that's my favorite. So wait, the way I think about this, because I've been studying this now for, well, it's been over 20 years. It's actually more like 25, is that ATR plays such essential, such an essential role in the replication checkpoint. You know, in terms of PIK-related kinases that are active, there's only five or so. In terms of protein kinases, hundreds, literally hundreds. So each one of them plays a key role in what they do, mTOR G1 to S, for instance. But ATR is the key regulator of replication stress responses. And you think about so many different agents, and in fact, this was a big question early on in the field: How can ATR be responding to so many different types of DNA damage?
We figured it out later. It has to do with single-stranded DNA. But it's really that ability to respond to so many different types of damage that make it a key contributor to any type of therapy that is applied. For example, radiotherapies, like especially radiopharmaceuticals, or biologics, that you can basically target the tumor selectively. ADCs that add a DNA-damaging agent plus an ATR inhibitor is a very promising approach. And now, obviously, the ones that Fiona was just talking about, combining with other targeted agents and combining that with biomarkers that would lead to greater sensitivity. It really is, you know, it's sort of like, you know, you can have lots of different recipes, but most of them include salt.
I think, ATR inhibition is the salt of cooking and the salt of cancer therapy in this case.
Well, fantastic. Appreciate all the color, guys. Thank you.
Great. Thanks for the questions, Joe. This concludes the verbal portion of our Q&A session. I'll now turn it over to Monique Kosse of LifeSci Advisors to read the remainder of the questions from the webcast.
Hello, everyone. We did get some questions in from our audience and let me turn to them here. The first one is for Dr. Yap, and the question is: What is it about the WEE1 that got your attention, and why this program?
... I think it's the answer to that is really summarized in Eric's slides. I think, you know, they've learned, I think, from 10 years of adavosertib development and benefited from hindsight of issues that arose. You know, the points that Eric had mentioned included myelosuppression, dealing with GI toxicities, and also with other toxicities observed with other agents like QT prolongation, so on and so forth. And I think Aprea certainly benefited from the learnings over all of those different compounds and different and over many years. And so they've managed to develop what we hope to be a very selective and clean compound, and potent one, that will hopefully benefit patients. And so that was essentially what attracted me to the program.
Excellent. Thank you, Dr. Yap. We have another question here. When do you expect to finish the dose escalation study?
Nadeem?
Sorry, go ahead. Are you talking about 119?
Yes, I believe that was in the 119.
So yeah, we are on track, and we expect to complete the dose escalation by first quarter of next year and then start the expansion phase soon after.
Okay. Okay, thank you. Another question here. Are you expecting to see any heme toxicity?
Nadeem?
Yeah, it's not entirely clear at this time, but we are pleased to see that there is nothing that is preventing the study from progressing and moving forward.
And if I can just, you know, add to that a little bit. You know, if you completely delete ATR, you expect heme toxicity for sure. And we, we demonstrated that over 15 years ago in a mouse model where we knocked out ATR, so it can't be more selective than a knockout. But what we also found is with a, a model in which we just suppressed the expression of ATR, again, there's no off-target activity here. It had very little hematologic toxicity, had no gut toxicity, yet it was still able to suppress the growth of an AML, a transplanted AML. Okay, so it, it's possible to reach a level of ATR suppression or inhibition. These are all targeted, and this is not a, a, you know... There's no off-target with a, with a, a genetic manipulation like this.
It's possible to have a level of suppression that is well-tolerated, yet is still suppressing the growth of these tumors, and that has to do with the biomarkers that are in the tumors, the oncogenic stress, whatever other mutations that would cause defects in DNA repair. So is it possible that there are off-targets in some of the previously generated ATR inhibitors that are synergizing with their inhibition of ATR as well? Well, I just have to say that people have to be careful about this because these are PIK-related kinases, PI kinase-related kinases. They're not the conventional protein kinases. You know, like I said, there's only five of these things. They look much more like phosphatidylinositol kinases. Is it possible there are off-targets that they're not seeing?
Are the compounds that have been tested thus far in the clinic structure related to one another, and so they're seeing some of the same off-targets? Could be same off-targets? That's, you know, I'm just saying unknown, right? Unknown is risk. So one of the things that Aprea did, and this is why I'm fascinated with Aprea's approach here, is they used a macrocycle. What's a macrocycle? Well, in case you didn't know, a macrocycle is where you're constraining the conformation of the molecule by turning it into a large circle, right? That constrains its conformation. That means it can't bind as many things because it can't assume as many conformations. So it is more selective when you look at the other PIK-related kinases, according to assays that have been, you know, disclosed.
So is it possible then it could be more selective and have less toxicity and less heme toxicity? Yeah. Yeah, that's definitely possible. And by the way, you know, they didn't, macrocycle, they didn't pull that out of the air. Rapamycin, which inhibits mTOR, is also a macrocycle. So they targeted ATR with a macrocycle, just as rapamycin was a, a macrocycle to inhibit mTOR selectively. So I think... I'm just saying that there's a possibility there that, Aprea may see less heme toxicity. But no question, if you completely eliminate ATR, there will be hematologic toxicity. But I'll leave it at that.
Thank you, Dr. Brown. We have another question here. When are you expecting to see a response in the 119 study?
Nadeem, please.
I'll take that, yes. You know, the data we presented is from our initial early doses, dose levels. And at those dose levels, we did not anticipate efficacy. As we are into the dose-finding stage, as we increase the dose, you know, we do expect at some point in time to start seeing some efficacy. But we are not there yet. We are still at low doses, so when we, you know, increase the dose to a certain level, we should see something.
Okay. Thank you, Nadeem. And the last question here looks like it's for Dr. Yap. What are the biomarkers for the WEE1 inhibitors?
Perhaps, Nadeem, you want to talk about what's planned in the trial?
I think some of it, we have not disclosed. I think some of those would be the ones that traditionally other people have looked at, you know, CCNE1 and others. And, you know, Eric is working on... We are trying to narrow down some of those specific biomarkers. So when the protocol will be fully developed and approved by, you know, through the IND, we'll have that. We'll be able to disclose it then.
Yeah, you could, you can imagine what they might be. We're not operating in the blind here.
Sorry. Okay. One last question here, and it came in. Dr. Simpkins, are you sure that the ATR and WEE1 inhibitors will synergize?
I think we've really shown that. You can, you know, look at our manuscript published in Cell Reports Medicine that really goes in-depth regarding the mechanism. Each, really, you know, acting uniquely, and I think, Eric Brown, do you want to comment in terms of all our beautiful,
Your beautiful work. Your beautiful work.
All of our beautiful work. But, I think in terms of cell cycle, the stress induced by, you know, ATR or the replication stress or, instability by blocking ATR, cells accumulate in S phase, and they, you know, increase breaks and then, ultimately end up in mitosis, prematurely. We can go into detail, but I think for the sake of time, I refer you to that manuscript. It's clearly they act independently, and we show the-- there's beautiful synergy, in multiple, in vitro models with the induction of cyclin E, with and without isogenic matched lines, organoids and PDX tumors.
So just to add to that... Thank you, Fiona. Just to add to that a little bit, I think one of the, one of the promising aspects to this is that we're really, truly targeting the amplification of cyclin E. So because we're on camera, I can use my hands. I have, I have to gesticulate here. So the way this is regulated, CDK2 and cyclin E is what drives cells into S phase, right? It phosphorylates a number of substrates, including, you know, the replication origins themselves. And there's two mechanisms that keep it at bay. One is the expression of cyclin E, and the other is the phosphorylation of CDK2 by WEE1. So if you have amplified cyclin E, but CDK2 is still phosphorylating, is still being phosphorylated by WEE1, it's still held at bay to some extent.
But if you've amplified cyclin E, multiple copies of cyclin E and CDK2 bound together, and you've actually inhibited WEE1, now these really push the cells into the cell cycle, many times prematurely, where there's not enough nucleotides or polymerases. All the goodies that allow replication to take place, it's not sufficiently generated. And then that leads to stalled replication forks and increased dependence on ATR. So it's really... This is the key quality of targeting WEE1 in combination with ATR versus something else that regulates the G2-M phase checkpoint. For example, ATR plus MYT1. Those are in the same-- that's in the same pathway, so they're just amplifying inhibition of the same pathway by inhibiting MYT1 and ATR. That's S into M phase. Whereas this is really capitalizing on the overexpression of cyclin E directly by inhibiting WEE1 in combination with ATR.
So, you know, maybe toxicities that are associated with combining things that both target the G2-M are going to be higher, or but we're going to be able to capitalize on cyclin E overexpressions of biomarker better. I think those are all possibilities.
Okay, great. And you thought you were off the hook, Dr. Simpkins, but one more question came in. Based on your experience in the clinic, what % of patients that are on PARP have developed resistance, and what, in your opinion, would be the best approach to address this increasing unmet medical need?
So what percentage of patients develop resistance to PARP? You know, so PARP inhibitors have moved from treatment in the recurrent setting to maintenance. And we're still following patients for survival. It looks like we're curing a lot more patients in the upfront setting, at least in ovarian cancer. I can speak to ovarian cancer. At least, so that's what I will be referring to. In terms of patients that will progress on PARP inhibitors, I think that actual number is not yet known. It's clearly occurring in the clinic, and we really don't know how to treat these patients once they progress. We're learning now that they actually respond less well to platinum-based therapy, which is the next standard of care treatment.
So it's a significant clinical unmet need to develop and identify new therapies after patients progress on PARP inhibitors. And so far, you know, in terms of our data, in terms of CAPRI, it was a really clean trial in that it required patients who immediately progressed on a PARP inhibitor to then go on to a PARP inhibitor and an ATR inhibitor. So really testing the hypothesis that ATR inhibition resensitizes tumors to PARP inhibition. And so we show it works, and that would be my probably my most exciting combination. There's other combinations that are showing activity out there, but I don't think the eligibility of the trials have been as clean, in terms of patients progressing on PARP, intermittent chemo. So I would say PARP/ATR combination.
Okay. Thank you very much for that, and I don't see any other questions coming in, so I will pass it over to Oren for any closing remarks.
Thank you. Thank you everyone for joining us today. We appreciate your support and look forward to continuing to develop and update you on both our ATR inhibitor, ATRN-119, in solid tumors, and our WEE1 inhibitor, APR-1051. Thank you all.