Mersana Therapeutics Inc

NASDAQ:MRSN

Earnings Call Transcript

[Operator]

Good morning, and welcome to Mersana Therapeutics Second Quarter 2024 Conference Call and Webcast. [Operator Instructions] Please note this call is being recorded.

I would now like to turn the call over to Jason Fredette, Senior Vice President, Investor Relations and Corporate Communications.

[Jason Fredette, executive]

Thank you, operator, and good morning, everyone. Before we begin, please note that this call will contain forward-looking statements within the meaning of federal securities laws. These statements may include, but are not limited to, those related to our platforms, product candidates, business strategy, clinical trial execution and data, business development efforts and cash runway. .

Each of these forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially from those projected in such statements. These risks and uncertainties are discussed in our quarterly report on Form 10-Q filed with the Securities and Exchange Commission on May 9, 2024, and in subsequent SEC filings. Our filings are available at sec.gov and on our website, mersana.com.

Except as required by law, we assume no obligation to update forward-looking statements publicly even if new information becomes available in the future. On today's call, we have Mersana's President and Chief Executive Officer, Dr. Martin Huber and our Chief Operating Officer and Chief Financial Officer, Brian DeSchuytner. With that, let me turn the call over to Marty to begin our discussion.

[Martin Huber, executive]

Thank you, Jason, and good morning, everyone. The second quarter of 2024 was the time of continued progress at Mersana as we advanced dose escalation in Phase I clinical trials of XMT-1660, our lead Dolasynthen ADC candidate and XMT-2056, our lead Immunosynthen ADC candidate. At the same time, we made further progress in our collaborations while also benefiting from our efforts to reduce our operating expenses last year.

We believe these collective accomplishments have put us in a strong position as we approach our initial clinical data readout for XMT-1660, which is planned for the second half of this year. Let's begin with that program. XMT-1660 is an ADC we developed using Dolasynthen, our next-generation cytotoxic ADC platform. This candidate targets B7-H4, a cell surface protein within the B7 family that can suppress antitumor immunity and can serve as a negative prognostic indicator for multiple tumor types.

In the dose escalation portion of our ongoing Phase I clinical trial, we are enrolling patients with tumor types that most commonly express high levels of B7-H4. These include patients with recurrent triple-negative and hormone receptor positive breast cancers as well as endometrial and ovarian cancers, all areas with high unmet medical need. For instance, as many know, Trodelvy and/or in HER2 are being used to treat the vast majority of recurrent triple-negative breast cancer patients in the U.S. today. Emerging clinical data continue to suggest that patients can develop resistance to ADCs with Topo 1 inhibitor payloads.

As a result, we are hearing an increasing call among treating physicians for new ADCs with alternative payloads that aren't subject to Topo 1 or PGP ePlex resistance mechanisms. XMT-1660 fits this profile. And we are enrolling many patients who have received a prior Topo 1 ADC in our trial. Dose escalation remains ongoing, and we still have not established a maximum tolerated dose. In fact, we are currently at a dose of 80 milligrams per meter squared in escalation. This is well beyond the dose levels we were able to reach clinically with any of our prior ADCs.

We believe our ability to continue to dose escalate can be attributed to 2 factors. The first is Dolasynthen's ability to reduce toxicities commonly associated with other ADC platforms like neutropenia, neuropathy and ocular toxicity as well as those that we're seeing with our first-generation platform, Dolaflexin. And the second factor is that based on data that has been reported to date there does not appear to be an obvious on-target liability with B7-H4. In parallel, with our dose escalation work, which includes the enrollment of backfill cohorts, we are also proactively exploring different dosing schedules with XMT-1660 with the aim to optimize efficacy and safety.

This has included every 4 weeks as well as more frequent dosing regimens. At the same time, we also are progressing our biomarker strategy in preparation for expansion and potential later stages of development. All this work is aimed at building a robust data set that can inform important strategic decisions as we seek to position XMT-1660 as a potential best-in-class asset, one that we believe they have the opportunity to serve both as a monotherapy and in combination with standards of care that may be inaccessible for the other B7-H4 ADCs in development.

We continue to expect that we will be in a position to announce our initial clinical data and initiate expansion in the second half of this year. This readout will include safety, tolerability, efficacy and biomarker data.

Now let's turn to Immunosynthen and XMT-2056. Immunosynthen is an innate immune stimulating ADC platform. Last month, we were pleased to publish preclinical data in Nature communications regarding some of the key mechanistic underpinnings of our approach to activate STING in a targeted manner using an ADC. This included in vitro and in vivo data demonstrating a 1-2 punch consisting of target-dependent STING activation in both tumor cells and tumor-resident immune cells. The data also showed increased antitumor efficacy and reduced serum cytokine elevations in comparison to a free STING agonist.

XMT-2056 is our lead STING agonist ADC candidate that we developed using immunosynthen. It targets a novel HER2 epitope that we believe could enable it to not only be an effective monotherapy, but also could allow for eventual combinations with a range of other agents, including other HER2-targeted therapies. The dose escalation portion of our Phase I trial is advancing and is enrolling patients with HER2-positive tumors, including breast, gastric, colorectal and non-small cell lung cancer. We expect to make good progress in escalation this year.

And finally, I'm pleased to report that we continue to advance our discovery collaborations with Johnson & Johnson and Merck KGaA. In fact, we have been performing CMC activities to support J&J. And earlier this month, we earned another milestone, this one for $8 million related to that Dolasynthen collaboration. Payment of this milestone is due in the third quarter of 2024.

Now let's turn things over to Brian for our Q2 financial update.

[Brian DeSchuytner, executive]

Thank you, Marty. Let's get into the financial highlights for the second quarter of 2024, starting with our balance sheet. We ended the second quarter with $162.7 million in cash, cash equivalents and marketable securities. We continue to expect our available funds will support our operating plan commitments into 2026. Please note that our cash runway guidance does not assume any future milestone payments that we may earn from our current collaborations or proceeds that we may realize from future collaborations.

Net cash used in operating activities for the second quarter of 2024 was $21.8 million, down significantly from the $61.8 million in net cash used during the year ago quarter. This decrease primarily reflects the portfolio reprioritization efforts and OpEx reductions we implemented in the second half of 2023. Turning to our income statement. Collaboration revenue for the second quarter of 2024 was $2.3 million compared to $10.7 million for the same period in 2023. The year-over-year change was primarily related to reduced collaboration revenue recognized under our Johnson & Johnson and Merck KGaA collaboration agreements.

Research and development expenses for the second quarter of 2024 declined significantly to $17.2 million compared to $49 million for the same period in 2023. For the most recent quarter, approximately $2.4 million of this spending was related to noncash stock-based compensation. The year-over-year decline in R&D expenses was primarily related to reduced costs associated with manufacturing and clinical activities for our discontinued ADC [indiscernible] and reduced employee compensation expense following the restructuring we completed in 2023.

General and administrative expenses for the second quarter of 2024 declined significantly to $10.5 million compared to $18.2 million during the same period in 2023, approximately $2 million in noncash stock-based compensation expenses, were included in G&A for the most recent quarter. The year-over-year decline in G&A was primarily related to reduced consulting and professional services fees and reduced employee compensation expenses following our restructuring.

And finally, Mersana's net loss for the second quarter of 2024 was $24.3 million compared to a net loss of $54.3 million for the same period in 2023. That concludes our business update.

Operator, would you please open the call for questions from the audience.

[Operator]

[Operator Instructions] The first question today comes from Tara Bancroft with TD Cowen.

[Tara Bancroft, analyst]

So I was hoping you could give us maybe a qualitative measure of how patients are doing in the trial. I mean you previously noted that responses are being observed, but have you observed more or deepening since then? And for safety, other than no MTD being reached, are you happy with the level of grade 3 events that you're seeing?

[Brian DeSchuytner, executive]

Thank you, Tara. While we're not giving any details on the 1660 clinical data, I think there are a couple of points is, one, we are at 80 milligrams per meter square. And this is a dose that equates to roughly 2.2 milligrams per kilogram, which is much higher than we've previously gone on the platform. So while we're not talking about details of Grade 3, et cetera events, we are comfortable that we're able to escalate to this dose range.

We're not getting into any details on the responses at this point in time. That information will be included in our second half data disclosure.

[Operator]

The next question comes from Jonathan Chang with Leerink Partners.

[Jonathan Chang, analyst]

First question on 1660. Can you discuss the progress you're making on the biomarker front and how much and what biomarker data we could see in the second half disclosure? And second question, can you provide any more granularity on when and how you plan to disclose the initial 1660 clinical data?

[Brian DeSchuytner, executive]

I'm going to cover the biomarker answer, and then I'm going to turn it over to Jason regarding the future disclosure. With regards to biomarker, just to remind everybody, we selected patient populations that with the tumor types, triple-negative breast cancer, hormone receptor-positive breast cancer, endometrial and ovarian that all have higher levels of expression of B7-H4. However, within those populations, we are not requiring a patient to be biomarker positive to be enrolled.

In other words, we're enrolling all comers across that. We are capturing tissue, which we are analyzing retrospectively for the expression of B7-H4. So what our plan would be in the initial data disclosure is to provide some information that would allow us -- we'll share with you kind of our thinking on do we believe a biomarker will be necessary for patient selection going forward or not. As of today, we have not made that decision, but we'll continue to gather data on biomarker negative and positive to inform that decision.

[Jason Fredette, executive]

And Jonathan on additional color. We really don't have additional color to share at this stage. We're keeping the guidance at second half, if that could be a company event or it could be a medical congress at this stage, we haven't defined that. .

[Jonathan Chang, analyst]

Got it. If I could just maybe fill in 1 more follow-up question here. Also on 1660. Just to clarify, have you already committed to this expansion portion of the study? I guess, what do you need to see in address before initiating the expansion portion of the study.

[Brian DeSchuytner, executive]

We have built the expansion cohorts into the existing protocol. So that work has all been done. The step we're left is the identification of a recommended phase to at least 1 recommended Phase II dose to take forward into the expansion. And as we have not yet defined an MTD, we are not yet ready to declare a recommended Phase II dose at this point in time.

[Operator]

The next question comes from Ashiq Mubarack with Citi.

[Ashiq Mubarack, analyst]

In the press release, you called out the 80 mg dose every 4 weeks, which seems to be less frequent dosing compared with some of the data we've seen from your peers in the B7-H4 space. I'm just curious how important you think dosing frequency could be as a potential differentiator. And on a similar point, I think in the past, you've talked about the need to sort of work through the exposure optimization. I'm wondering if you could share any color on where you are in that process and how close you are to figuring out optimal exposure?

[Martin Huber, executive]

Thank you for the question. First of all, we -- we have spoken about the every 4 weeks, and 1 of the reasons we're able to explore the every 4-week schedule is because our molecule and we have shared preclinical data shows an extended half-life compared to other molecules. We have antibody-like half-life for our Dolasynthen ADCs. So when you have that long half-life that allows you to explore these longer schedules which we do think could be a potential advantage in the clinic. But at the same time, it may be more effective to have more frequent dosing to decrease Cmax relative to AUC and maintain more exposure over time. That is an unknown -- we got the question we don't have an answer for. And that's one of the reasons we made the decision to proactively explore the every 4-week schedule dose escalation in parallel to more frequent dose -- more frequent schedules.

So we are generating data on both every 4 week as well as shorter intervals, and we should have that data as part of the second half presentation, which would then allow us, as part of the recommended Phase II dose, to define not only with that dose is, but also the appropriate schedule.

[Ashiq Mubarack, analyst]

Okay. Okay. Got it. And I could ask one follow-up. I think you've alluded in the past to maybe needing to establish a Phase II dose before sharing the data with us. Is it also necessary to establish an MTD as per the primary end point of the study before you show the data? Or is that not necessary? .

[Martin Huber, executive]

MTD is not critical. We don't necessarily have to get to an MTD. I think we want to -- before we declare a recommended Phase II dose, though, is to have some understanding of kind of where is the upper bound that you can get to, whether that's a formal protocol specified MTD or just a general observation of you're starting to see payload effects. So I think we want to be a little careful saying we have to see an MTD. But I think we -- given the fact that ADCs historically have had relatively narrow therapeutic indices. I think we do want to see kind of where is that upper bound before we make a call on which dose we're taking to expansion.

[Operator]

The next question comes from Michael Schmidt with Guggenheim.

[Michael Schmidt, analyst]

I was wondering if you could comment a bit more on whether you have observed a dose response in the every 4 weeks dosing cohort so far. I know you've commented on seeing responses earlier than the 80 milligram dose. So just curious. And then also, what magnitude of increase in those exposure one would expect perhaps with a more frequent dosing schedule?

[Brian DeSchuytner, executive]

Thank you, Michael. We're not sharing any further color on exposure response relationships. I think we did disclose that we had responses at doses previously before we got to [indiscernible]. So I think what we -- we can be explicit that we have seen responses at the lower doses lower than 80 and that was in our previous disclosure. And with regards to exposure response relationships that would be premature at this point in time, and that will be part of the second half data disclosure. .

The second part of your question was.

[Michael Schmidt, analyst]

I think there was -- it on that. And yes, the other question I had is as we monitor forthcoming data from other companies pursuing B7-H4, for example, AstraZeneca, who will have some [indiscernible]. I'm just curious how [indiscernible].

[Jason Fredette, executive]

Yes, Michael, you're coming in and out. Are you asking for some speculation about AZ? .

[Michael Schmidt, analyst]

Yes, I'm just curious as we kind of look forward to [indiscernible] they have an update on their data, how investors should interpret there and how it may reprove your program, if you [indiscernible] that?

[Brian DeSchuytner, executive]

Sure, Michael, maybe I can handle that. From a safety and tolerability perspective, we would expect to see the typical Topo 1 platform toxicity. Those include things like myelosuppression. I think that's relevant because it speaks to which combination opportunities may be more or less challenging for an asset like that. From an efficacy standpoint, to the extent that AZ shows responses in breast cancer, we frankly believe the question in this space will be how many of those responses were generated in patients who have been previously treated with the prior Topo 1 ADCs. .

[indiscernible] has been enrolling its trial globally, including in potentially locations where patients are more likely to be naive to Topo 1 ADCs. Here in the U.S., the vast majority of recurrent triple-negative break cancer patients are being treated with TRODELVY and/or in HER2. Emerging data, and we've spoken about this before, continue to suggest that patients can develop resistance to ADCs with those Topo 1 payloads. As a result, as Marty noted in the opening remarks, there's an increasing call from physicians to find ADCs with new sort of fatal payloads that aren't subject to the Topo resistance mechanisms or PGP pump. So I guess the key question that people should be looking for is what are those prior treatments and the demographics of those patients.

[Operator]

[Operator Instructions] The next question comes from [indiscernible] with LifeSci.

[Unknown Analyst]

Given that your XMT-1660 protocol allows for pretty sizable backfilling, how are you thinking or have been thinking about prioritizing enrollment towards further advancing dose-escalation/exporation versus collecting more data at any given backfill cohort. And has this thinking evolved as you've continued to advance further into clinically relevant doses and schedules.

[Martin Huber, executive]

Well, first of all, yes, the protocol, just to remind you for everybody, allows up to 12 patients at a given dose as well as at a given indication. So it does give us a lot of flexibility to get significant patient numbers at a given dose and tumor type. How do we think about that? I think we've probably been fairly explicit that TNBC is probably the one we spend the most time talking about as it's the area of highest unmet medical need. So I do think what we would look toward in this data set is how to -- one, we're getting TNBC patients, high unmet medical need, B7-H4 is fairly frequent there. .

It's a second is an area, as Brian alluded to in the differentiation from the others. Looking at a U.S.-based population where most TNBC patients will have seen Trodelvy and/or in HER2 is a great place to explore the hypothesis that our ADC with its novel scaffold linker payload will have an opportunity to show activity in settings where topo payloads are unlikely to be effective. So I think for us, the -- while we're not giving details of exactly what patient types, the way the protocol is designed, we can enroll expand backfills that with TNBC or other tumor types and really try to answer that question of what's the activity of this kind of post [indiscernible]. So that would be one of the data sets that we should -- but one of the data points we should be able to include in our second half disclosure.

[Unknown Analyst]

Got it. And maybe if I could just ask one follow-up on that. Just given the FDA project optimist environment and what sounds like your intention to take on go-forward dose as opposed to more than one I guess then, is it fair to assume then that you would have backfilled across or backfilled enough patients at each given dose level to have made that determination by end of this year?

[Unknown Executive]

One of the things we're careful and we need at least one recommended Phase II dose. I want to be careful. It could be 2. The way expansion is written in the protocol, it gives us the flexibility to take 1 or 2. We do recognize that with the way Project Optimus is rolling out, at some point in time, we will formally -- will likely formally have to study 2 doses. But if you look at the precedent here and some of the guidance from the agency, having meaningful backfill patients at multiple doses does go in the direction of [indiscernible] answering questions for project Optimis. So hopefully, it will minimize the number of doses we would have to take into the actual pivotal programs.

I mean, there are folks out there today who are taking 3 or 4 doses and schedules into large registration-enabling or registration targeted programs. And we think there is an opportunity based on precedent to narrow down. Are we going to have to study 2 doses in the pivotal potentially. But the more information we get out of these backfills at multiple doses, the better we'll inform that discussion with the agency.

[Operator]

The next question comes from Colleen Kusy with Baird. .

[Colleen Hanley, analyst]

On the upcoming 1660 readout, can we expect biomarker data from all patients enrolled in escalation backfill? And will that be meaningful enough data set to determine an ORR in that biomarker positive subgroup. And then for the expansion cohorts that you plan to open in the second half of this year, would you be looking to open one or multiple tumor specific expansion cohorts.

[Brian DeSchuytner, executive]

With regards to the biomarker, I mean, one of the challenges of a retrospective analysis is since you don't require the patient to have a documented positive before they roll you will have samples that will be invaluable for the biomarker. So it would be -- I just mean to sit here and say, we're going to have 100% of the data on that topic. But what we -- and the second thing -- remember, these are backfills. This is not a full expansion. So your confidence intervals around any point estimate. And by the way, this applies to the seen data set as well as the [indiscernible] that they presented last year [indiscernible] are going to be relatively wide.

So trying to say we have a definitive response rate determination out of a Phase I dose escalation would be overreaching. However, I do think we should have sufficient patients to get a directional answer is, how do these data look in the greater universe of data out there. And two, is there some differentiation in biomarker positive versus negative. We may still need to carry into expansion and/or for that matter, pivotal studies all [indiscernible] based on the evolving data. One of the things I learned back on the KEYTRUDA experience, if you don't have a clear signal, you want to be really careful. There after less than 100 lung cancer patients, we had quite a clear signal that we were able to select out a subset.

I think when we go back to our [indiscernible] experience, the biomarker there didn't perform so well. And that, ultimately, the pivotal study had a negative consequence on our ability to -- on the data. So I think it really is a data-driven decision based on not only the the performance -- I mean the biology of a specific biomarker, how the drug performs, but also then the performance of the biomarker itself. So there are a lot of questions that we want to answer based on data.

[Colleen Hanley, analyst]

Great. That's helpful. And then just on the expansion cohorts, if you would open one or multiple in the second half.

[Brian DeSchuytner, executive]

We have all 4 written in -- at least 4 written into the protocol. However, based -- we'll probably make some decisions on which ones we prioritize based on the data from the Phase I. We can flexibly either do them or stage or more, however, and that will be a data-driven decision at that point in time. .

[Operator]

The next question comes from Brian Cheng with JPMorgan.

[Unknown Analyst]

Just want to follow up on your comments earlier -- do you need to reach MTD to declare the recommended Phase II dose and then move into expansion? And then secondly, related to your ongoing work around more frequent dosing, is that just a typical part of any development plan to satisfy perhaps some of the requirement by project optimist? Or is that actively driven by our observation to [indiscernible] in the clinics?

[Brian DeSchuytner, executive]

With regards to the first question on MTD, I think what we want to say in a perfect world, we would actually define a formal MTD and know what that is before we pick a recommended Phase II dose. The 1 thing we'd like to highlight on, especially when we see these ADCs is sometimes you can have toxicities that don't achieve the level of a formal protocol specified MTD, but patients aren't able to stay on that dose for more than a couple of cycles. And then you end up in this project [indiscernible] situation where late in your program, you get taken to a lower dose. So part of it is we want to understand we say we want to make sure our recommended Phase II dose has an opportunity to be truly tolerable, which means the vast majority of patients can stay on that dose throughout their treatment cycle. But it may not be a formal MTD per protocol. That's where I want to clarify. We do want to see where does toxicity become dose limiting.

With regards to your second question was the.

[Unknown Analyst]

What was the more frequent.

[Unknown Executive]

Yes. We -- if you look at data on ADCs and we looked at data from the [indiscernible] platform with the [indiscernible], there's this observation that certain toxicities tend to be Cmax related. We made the decision with the initial delay that we announced in that instead of doing a sequential, see how high we can go with in every 3- or 4-week schedule. And then at that point, going back and saying, could we increase exposure by doing a more frequent dosing, we made the decision to explore in parallel. So today, we don't know if dose-limiting toxicity is going to be Cmax or AUC related for this platform.

One of the things we like to remind people, this is the first molecule on this platform that we've been able to get into this dose range. So we are still learning how the platform behaves. As you recall, for our initial molecules, the 1592, the NAPI 2b, the dose-limiting toxicity was driven by on-target toxicity. And that's where we saw the NAPI mediated ILD in the so far B7-H4, not just -- when we look at the competitors, has not really shown target mediated dose-limiting toxicity. So this is an opportunity for us to really learn about our platform in these higher doses and exposures.

[Unknown Analyst]

Got it. And maybe just one more follow-up, if I may. I think it's interesting that you talked about the Cmax, your thoughts around Cmax and how you're thinking about evaluating it to make sure that you have the optimal profile. Just going back to your comments and your press release, I think you emphasized a lot on your current efforts in understanding how to optimize the frequent dosing. So as you think about your current progress to date, are you close in understanding how high you can go with 1660 or this platform?

[Jason Fredette, executive]

Yes. I think, Brian, we've probably said as much as we can. We're still in dose escalation have not hit an MTD, and we'll just have to leave it at that for the time being. .

[Operator]

[Operator Instructions] The next question comes from Asthika Gunawarden with Truist.

[Asthika Goonewardene, analyst]

So I appreciate that you might be taking more than 1 dose level into the expansion cohort and that makes sense. But would you be conducting expansion cohorts with multiple frequencies running in parallel. So maybe [indiscernible] running in [indiscernible] the same dose cohort at the same dose level. And then, Marty, would you not be able to make project [indiscernible] requirements with the pension cohorts, let's say, if you were to recruit maybe 30 to 40 patients in each cohort at a couple of different dose levels. Would that not meet the SS requirements? Or do you think you need to do that in the pivotal phase study? And then I have a quick follow-up.

[Martin Huber, executive]

With regards to your first question, yes, when I say dose for recommended Phase II dose, I probably should be more explicit. It's recommended Phase II dose and schedule. And yes, it is possible that you would take 2 different dose schedules forward. If that's the question is, you really want to answer. But at this point in time, it would be premature to speculate on how we're going to do that. just the protocol is written so we have the flexibility that if we want to take a more frequent dose versus a less frequent dose forward, we could do that.

With regards to your second question, we are now getting purely into speculation as we have not had -- we're not coming forward with a specified registration-enabling studies. So I want to be clear what I'm giving you is a theoretical -- to your point, generally, most people are having to do some form of randomization for dose in the current environment.

I think if you look at all the precedents out there today in the ADC space, they're doing randomization somewhere. I don't think there's a strong rule on whether you do that as part of expansion or whether you do that as part of your pivotal. Ultimately, you're going to need some data justifying the therapeutic index, the benefit risk of your dose versus an alternative dose. And I think with that becomes a matter of, to be frank, efficiency of execution, et cetera. And those are all details that when we start talking about our expansion of registration plans, which we're not doing at this time, will go into our thinking there.

[Unknown Analyst]

Got it. And then -- if you're in the enviable situation where you have pushed the dosing escalation and you're not seeing a big signal that you're approaching dose-limiting that's going to be dose limiting. Would you continue the escalation while also running the expansion at a couple of cohorts? .

[Martin Huber, executive]

I mean it's possible if we get into that scenario. We did -- as we say, we don't have to get to an MTD to declare a recommended Phase II dose to move forward, and that can be part of our judgment as the data emerges. If we're comfortable that we've got enough confidence in the dose, and we want to continue to escalate and initiate expansion in parallel. That is an option for us. We have not made that decision today, and that will be based on data.

[Operator]

The next question comes from Justin Zelin with BTIG.

[Justin Zelin, analyst]

With the discussion of unmet need for Topoisomerase experience in resistant patients. Can you talk to your confidence of differential activity of 1660 [indiscernible] patients?

[Brian DeSchuytner, executive]

Yes. Maybe I can take that. I think there are a number of hypotheses that would maybe lend themselves to think that our payload might not be subject to the same resistance mechanism. So as you're probably well aware, there have been a number of real-world data sets, retrospective analyses and single sites that have shown that topoisomerase ADCs used after other topoisomerase ADCs have a substantial degradation in time-to-event end points. And this data really started to come out last ESMO, and it's been reinforced at ASCO and SABCS and other places. .

There are papers out there that really speak to the mechanisms for how that resistance might occur. It might be related to the switch of Topo enzyme complexes to Topo 2, which don't share a sort of a chemical similarity or could also be up regulation of PGP pumps -- that's a pretty common resistance mechanism in cancer just reducing drug concentrations in the cancer cells themselves.

Our payload, a novel or a statin with a controlled bystander effect, is not subject to either of those mechanisms. It's not acting on topoisomerase, not acting on DNA, acting on the microtubules. And once metabolized, that payload is not a PGP pump substrate. So those are at least theoretically, reasons we would think that you might see some differential activity.

[Operator]

This concludes our question-and-answer session. I would like to turn the conference back over to CEO, Dr. Marty Huber, for any closing remarks. .

[Martin Huber, executive]

Thank you, operator, and thanks, everyone, for dialing in. We'll be seeing some of you in New York at the Wedbush Healthcare Conference and hope the rest of you enjoy the rest of your summer. This concludes the call, operator. Thank you.

[Operator]

The conference has now concluded. Thank you for attending today's presentation. You may now disconnect.