Mersana Therapeutics, Inc.

Good morning and welcome to Mursana Therapeutics' first quarter 2024 conference call and webcast. Currently, all participants are in listen-only mode. There will be a question and answer session at the end of this call. I would like now to turn the call over to Jason Fredette, Senior Vice President, Investor Relations and Corporate Communications. Please note, this call is being recorded.

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 is 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 annual report on Form 10-K filed with the Securities and Exchange Commission on February 28, 2024, and in subsequent SEC filings. Our filings are available at sec.gov and on our website, mursana.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 Mursana's President and Chief Executive Officer, Dr. Marty Huber, and our Chief Operating Officer and Chief Financial Officer, Brian Descheitner. With that, let me turn the call over to Marty to begin our discussion.

Thank you, Jason, and good morning, everyone. As most of you know, Mursana is an ADC innovator that's advancing product candidates based on its two proprietary platforms. The first of these is dolosynthin, our next generation cytotoxic ADC platform, and the second is immunosynthin, a novel platform that utilizes a sting agonist payload. Let's begin today's call with a brief discussion of new insights about dolosynthin that we recently shared at both ESGO and AACR. As many of you know, severe neutropenia, peripheral neuropathy and ocular toxicity have served as key limitations for today's leading ADC platforms. At those congresses, we presented preclinical and clinical data that we believe demonstrates DolaSynthin's ability to significantly reduce these types of off-target platform-related toxicities, as well as other presumed platform-related adverse events that we saw with our own first-generation ADC platform, Dolaflexin. Ultimately, our goal is to reduce ADC platform toxicities to the greatest extent possible in order to both maximize monotherapy efficacy and open the door to combination approaches with other chemotherapy and ADC standards of care. That's something that simply isn't possible with many of today's approved ADCs. Now, let's move on to XMT1660, our lead dolosynthin ADC that targets B7H4. We're in the midst of a phase one clinical trial that's enrolling patients with solid tumors, including triple negative and ER positive breast cancer, ovarian cancer, and endometrial cancers. B7H4 is a member of the B7 family of immune checkpoint markers. The scientific literature suggests that B7H4 is selectively expressed in tumors with limited healthy tissue expression. Additionally, we have not seen any clear signs of on-target toxicities in the clinical data presented by our competitors. We believe B7H4's selective expression and dolesynthin's ability to reduce off-target platform toxicity have helped us continue advancing the dose escalation portion of our ongoing trial. We are now beyond the dose levels previously investigated clinically with either dolosynthin or our first-generation platform, and we still have not established a maximum tolerated dose for 1660. Based on preclinical models, we have identified exposure thresholds that we believe are key to clinical activity. We also have leveraged our clinical data for 1660 to identify doses and schedules that increase the time above this exposure threshold. Additionally, based on emerging data in the B7H4 space, we also are progressing our biomarker strategy in preparation for expansion and later stages of development. Given that a maximum tolerated dose has not yet been established and objective responses have been seen in this trial, we are continuing to advance dose escalation and backfill cohorts in parallel to optimize our dose, schedule, and biomarker. We now expect to be in a position to announce our initial clinical data and initiate expansion in the second half of this year. All of this work is aimed at positioning XMT1660 as a potential best-in-class asset, and we are taking the time needed to accomplish our objective. Now let's shift to XMT2056, which is the lead candidate we are developed utilizing immunosynthin. Our immunosynthin platform is designed to deliver a one-two punch by activating sting in a target-dependent manner in both tumor cells and in tumor-resident myeloid cells. XMT2056 is an ADC targeting a novel epitope of HER2 that's distinct from both pertuzumab and trastuzumab. So in addition to its potential as a monotherapy, we believe there may be a range of intriguing paths to pursue for combination treatments with 2056, including combos with other HER2-targeted agents. That said, our near-term goal is to advance the dose escalation portion of our Phase I clinical trial of 2056. Multiple clinical sites are now open, and we're actively recruiting patients with a range of HER2-positive tumors, including breast, gastric, colorectal, and non-small-cell lung cancer. In addition to these lead programs, we also continue making progress with the collaborations we have in place with Johnson & Johnson, focusing on dolosynthin ADC discovery efforts, and with Merck KGA for immunosynthin discovery efforts. With that, let's turn the call over to our Chief Operating and Financial Officer, Brian Descheitner, to provide a financial update.