Mersana Therapeutics, Inc.

Good morning and welcome to the Mursana Therapeutics Third Quarter 2023 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. Please note this call is being recorded. I would now like to turn the call over to Jason Prudette, Senior Vice President, Investor Relations and Corporate Communications. Please go ahead.

Thank you, operator, and good morning, everyone. Before we begin, please note that this call will contain forward-looking statements within the meeting 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 results, 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 quarterly report on Form 10-Q filed with the Securities and Exchange Commission on August 8, 2023, 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 the call today, 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. It's a pleasure to be speaking with you about eight weeks into my tenure as Mursana's CEO. Over the course of these two months, many investors and analysts have asked why I chose the role. So let's start there. It's really because of our people, platforms, product candidates, and our financial position. Having served as a MRSANA board member since 2020 and having worked with several of our executives in a prior role, I knew this was a high-caliber, high-functioning team that was driven by a mission to make a real difference for patients. In addition, my role as a director provided a clear view that from an innovation standpoint, we had advanced well beyond Doloflexin, our first-generation ADC platform. and that we were making meaningful progress with our next generation platforms, Dolosynthin and Aminosynthin. Not only that, but thanks in part to the difficult decisions that were made in the wake of uplift, we also have a balance sheet providing an opportunity to accomplish our objectives. My time in the CEO role has only strengthened my conviction about these factors and my excitement about Rosana's potential. Now let's move on to our core areas of focus. The first is XMT1660, which was developed utilizing Dolacinthin, our next-generation cytotoxic ADC platform. Our preclinical work has shown that Dolacinthin has numerous potential advantages over Dolaflexin, our first-generation ADC platform that was utilized to develop UPRI. Like many first-generation platforms, Dolaflexin produced a heterogeneous population of ADCs, Published data from other platforms have shown that some species within heterogeneous ADC mixtures, specifically hydrophobic high DAR subpopulations, can negatively impact safety and tolerability while having limited to no contribution in terms of efficacy. We spent years developing a technology that improved upon both first-gen platforms and Doloflexin. Specifically, we wanted the ability to identify an ADC outperformer and then produce that outperformer in a completely homogeneous fashion. We believe this would result in improved drug-like properties, the potential for enhanced efficacy, and further reductions in off-target toxicity. Additionally, we wanted the ability to optimize both drug-to-antibody ratios and site-specific conjugation approaches. Dolacentin is the result of that effort. Across preclinical models, when we compare dolosynthin ADCs to those from doloflexin and first-gen platforms like BCMMAE, we see clear benefits in terms of pharmacokinetics, tumor delivery, efficacy, and toxicity. XMT1660, our lead dolosynthin ADC, now provides a near-term opportunity to demonstrate these advantages clinically. XMT1660 is a DAR6 ADC targeting B7H4, a member of the B7 family of immune checkpoint markers that's been shown to have limited expression in healthy tissue and overexpression in multiple tumor types with high medical need, including breast, ovarian, and endometrial cancers. At ESMO last month, initial clinical data was shared by others in the field, helping to validate B7H4 as an intriguing target. In light of these early data, we believe there are opportunities to differentiate XMT1660 from others in this space. We continue to advance 1660 in the dose escalation portion of our Phase I trial. Additionally, we have begun to enroll patients in backfill cohorts at clinically relevant doses as part of our dose escalation design. By the end of this year, we expect to complete dose escalation with dose expansion planned for 2024. It also is worth noting that we have been making good progress in our collaboration with Janssen that focuses on discovering novel dole-sensitive ADCs for up to three targets. Janssen has shared publicly that it chose Dolescentin following a comprehensive review of the ADC landscape. Now let's move on to XMT2056 and Immunosynthin. As many of you know, the ADC field has focused almost exclusively on attacking tumors with cytotoxic payloads for the past two decades. Several years ago, we began to explore how we might be able to leverage the benefits of an ADC approach to activate an innate immune response selectively in the tumor microenvironment. Immunosynthin is the result of this effort. Immunosynthin is an entirely unique platform that leverages a sting agonist payload with the goal of activating sting signaling in both tumor resident immune cells and in antigen expressing tumor cells. We initiated a phase one clinical trial of XMT2056, our first immunosynthetic ADC candidate, earlier this year. This trial was placed on clinical hold following a grade five adverse event in one of the initial patients that had been dosed. This served as an unfortunate reminder that when developing truly novel mechanisms, the translation from preclinical to clinical can sometimes be less predictable. We delve deeply into cytokine, pharmacokinetic, and other clinical data from the patient's dose in this trial. The findings from the initial patient's dose in our Phase I clearly indicated that XMT2056 is a much more potent innate immune stimulator in humans than we'd seen preclinically. As a result, we developed a response to the FDA that included a lowered starting dose in our Phase I dose escalation design. We were very pleased to share the news last week that the clinical hold on the phase one trial of XMT 2056 has been lifted by the FDA. Our attention has now turned to re-engaging with clinical sites to reinitiate enrollment. And finally, I would also like to mention that our analysis of the results from uplift in ovarian cancer is nearing its completion. We plan to present the data at a medical meeting during the first half of 2024. In summary, I'm proud of all the recent progress that has been made by the Mursana team, and my excitement about what lies ahead for the company continues to build. With highly differentiated platforms and clinical stage molecules, strong collaborations, a great team, and a healthy balance sheet, Mursana has an opportunity to make a difference for patients with a range of cancers, and we are working hard to deliver on this promise. We look forward to sharing more with you about our outlook for 2024 and key upcoming milestones in January. With that, let's turn things over to you, Brian.