Mersana Therapeutics, Inc.

Ladies and gentlemen, thank you for standing by, and welcome to Marsana First Quarter 2021 Earnings Conference Call. At this time, all participants are on a listen-only mode. After the speaker's presentation, there will be a question-and-answer session. To ask a question during the session, you will need to press the star, then the one key on your touch-tone telephone. If you recall our assistance, please press star, then zero. I would now like to hand the conference over to your speaker host, Sarah Karmody. Go ahead. Good afternoon. Welcome to Mursana's first quarter 2021 conference call. Earlier today, we issued a press release reviewing our first quarter financial results and business updates, which will be covered on this call. A replay of today's call will be available on the Investors and Media section of our website. After our prepared remarks, we will open the call for Q&A. Before we begin, I'd like to mention that our call will contain forward-looking statements within the meaning of the federal securities laws. These are not statements of historical facts and are based on management's beliefs and assumptions and on information currently available. They're subject to risks and uncertainties that could cause the actual results and the implementation of the company's plans to vary materially, including the risk that the results of our ongoing or future clinical studies may be inconclusive with respect to the efficacy of our product candidates, that we may not meet clinical endpoints with statistical significance, or there may be safety concerns or adverse events associated with our product candidates. That preclinical testing or early clinical results may not be predictive of the results or success of our ongoing or later preclinical or clinical studies. That the identification, development, and testing of the company's product candidates and new platforms will take longer and or cost more than planned. and that our clinical studies may not be initiated or completed on schedule, if at all. These risks are discussed in the company's SEC filings, including, without limitation, the company's annual report on Form 10-K filed on February 26, 2021, and subsequent filings. In addition, while we expect that the COVID-19 pandemic might adversely affect the company's preclinical and clinical development efforts, business operations, and financial results, The extent of the impact on the company's operations and the value of the market for the company's stock will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantine, physical distancing, and business closure requirements in the U.S. and in other countries, and the effectiveness of actions taken globally to contain and treat the disease. Except as required by law, the company assumes no obligation to update these forward-looking statements publicly, even if new information becomes available in the future. And with that, I'll turn the call over to Anna Protopopis, Murasana's President and Chief Executive Officer.

Thank you, Sarah. Good afternoon, everyone, and welcome to our first quarter 2021 Corporate and Financial Update call. Joining me today with prepared remarks are Arvind Yang, Chief Medical Officer, Tim Loewinger, our Chief Science and Technology Officer, and Brian Descheidner, our Senior VP of Finance and Product Strategy. I'm also joined by the rest of the executive team, who will be available for your questions, including the newest member, Alejandra Carvajal, Chief Legal Officer, who joined us in April. Before we start, I want to take the opportunity to introduce and welcome Alejandra. Alejandra brings with her 20 years of legal leadership experience in various pharmaceutical and biotech companies and a demonstrated ability to work cross-functionally. Most recently, Alejandra served as the chief legal officer of Momenta Pharmaceuticals, where she led the company's legal operations through both restructuring and the successful acquisition by Johnson & Johnson. Brian, Michael, and I have had the pleasure of working with Alejandra at Millennium Pharmaceuticals, and we are very excited to have the opportunity to work with her again. I am confident of the positive impact she will have on MERSANA. Welcome, Alejandra. I'll now move on to the business update. Since the beginning of the year, we've made important progress in our endeavors to build UPRI as a foundational medicine in the treatment of ovarian cancer. and in building out our innovative pipeline of ADC candidates addressing areas of high unmet medical need. With respect to building UPRI, in January we disclosed further data from the expansion portion of the UPRI phase one study in ovarian cancer and showed consistent robust activity with a response rate of approximately 30%, substantially above the current standard of care including complete responses in heavily pretreated patients and a tolerability profile without the severe neutropenia, neuropathy, and ocular toxicities seen with other ADC platforms. The data also demonstrated a clear biomarker response relationship, which leads me to the next important step in building UPRI, Uplift, our single arm registration strategy informed by FDA feedback. In April, we announced that we have initiated patient dosing. This is an important milestone in our efforts to bring Uplift to patients living with heavily pretreated ovarian cancer who have an acute need for new therapeutic options. The design of Uplift focuses both on increasing the potential for label differentiation and the probability of success. As a reminder, Uplift is enrolling a broader patient population than other studies in this space, consistent with where we observed activity in the expansion cohort. More prior lines, more flexible inclusion of prior Bevacizumab treatment, consistent with the Bevacizumab label, and there is no exclusion for baseline peripheral neuropathy. By enrolling patients regardless of NAPI-to-be expression, Uplift also offers two shots on goal with a primary endpoint in the high NAPI2B population and a secondary endpoint in the overall population, allowing us to fully evaluate the role of the biomarker in enriching for patient outcomes. We plan to present a trial in progress poster at the upcoming virtual ASCO meeting in June, detailing the design of the Uplift study. In addition to initiating Uplift, we also provided an update on the final selection of the NAPI-2B biomarker cutoff, its role in Uplift, and our expected commercial diagnostic development path. The development of the diagnostic is a result of a multi-year program encompassing research, translational, and clinical work, advanced at each stage in tandem with the development of Uplift. Through this work, we believe we have designed an optimal diagnostic assay in terms of its robustness, predictiveness, and reproducibility. Importantly, while we have previously shown that an age score of 110 enriches for a response, we demonstrated that tumor proportion score, or TPS, greater than or equal to 75%, which is derived from the same values as age score, also enriches for response just as well and can be operationally more straightforward to perform. When we looked at the same ovarian cancer expansion data set that we showed you back in January, but evaluated this data by TPS methodology based on the TPS75 cutoff, the high NAPI-2B patients have an enriched overall response rate of 39%. relative to the overall response rate of 28% in the total population. These results are comparable to the age score results that we have demonstrated to date. TPS 75 is the predefined threshold that we will use to define our high NAPI 2B population in Uplift, where we will look to validate the proposed commercial assay. In summary, the strong proof of concept data from the expansion cohort, the robust, predictable, and reproducible assay we have developed, and the design of UPRI informed by FDA feedback contribute to our belief that we will be able to deliver UPRI to patients that are in dire need of therapeutic options. Finally, for UPRI, we've made progress in preparing for the initiation of the upgrade umbrella study. a first step in bringing UPRI to patients in earlier lines of therapy as we seek to establish it as a foundational medicine in ovarian cancer. Arvind will discuss the design of UPRI in a moment, but we believe we're on track to initiate this study in the third quarter of this year. With respect to building out the pipeline, the UPRI lung adenocarcinoma expansion cohort continues to enroll patients and we believe we will remain on track to reach our goal of enrolling approximately 40 to 45 patients this year and plan to report data in the second half of this year. At the same time, XMT1592 is still in dose exploration phase of the study, using the clinical experience to validate the preclinical finding of greater potency. We have exceeded the MTD, and are doing further exploration of dose and schedule. We plan to disclose interim data in the second half of the year. Finally, we have continued to advance our next two earliest stage candidates, XMT1660, our dolosynthin B7 H4 ADC, and XMT2056, our first immunosynthin sting agonist ADC. through IND-enabling studies with the goal of initiating clinical studies in early 2022. In April, we presented preclinical data highlighting the potential for both programs at the virtual AACR conference, which Tim will review shortly. As I stated earlier, we continue to make important progress across each of our programs and look forward to continuing to make progress on uplift, and the rest of our ATC pipeline, providing the potential for multiple value inflection points and bringing us even closer to reaching our overarching mission to develop life-changing ATCs for patients fighting cancer. With that, I will turn the call over to Arvind to discuss the design of the upgrade study for upbringing in ovarian cancer.

Thank you. Anna, and thank you everyone for joining us today. Let's take a step back and recap what we've demonstrated with UPRI, why we're so encouraged by Uplift, and how we envision doubling or tripling the number of patients with ovarian cancer that could benefit from UPRI through our life cycle plans. Today, we've seen positive results with UPRI in heavily refractory patients, including complete responses in patients who have failed Bevacizumab and PARP inhibitors. Antitubulins are an established class in the ovarian cancer space, but both anti-cubulants and other ADC platforms in this space have been limited by severe adverse events, including peripheral neuropathy and neutropenia, and also events deeply concerning to patients like alopecia. UPGRADE is a phase one umbrella study designed to evaluate UPRI in combination with other ovarian cancer therapies to explore the role of UPRI in earlier stages of the disease. We first intend to combine with platinum, as platinum therapy is currently the mainstay therapy in earlier-line platinum-sensitive ovarian cancer, and we expect to initiate patient dosing in the third quarter of this year. This Phase I open-label dose escalation portion of the study will determine the maximum tolerated dose and safety and tolerability of an every-four-week administration of UPRI in combination with Q4 week administration of carboplatinum for six cycles, and then upremonotherapy will be continued in platinum-sensitive patients with high-grade serous ovarian cancer who have received one to two prior platinum-based regimens. Patients will not be preselected for NAPB2B expression, but archival or fresh tissue will be required for retrospective assessment of expression. Upon completion of the dose escalation portion of the study, we plan to initiate the expansion portion in combination with carboplatinum for six cycles, and then up remonotherapy will be continued to assess the feasibility for this combination therapy, as well as efficacy in approximately 30 patients in order to inform next steps. This study could provide us proof of concept by benefiting patients earlier in their disease where they are platinum sensitive as well as by continuing up-ring monotherapy beyond what is achievable with carboplatinum and paclitaxel alone. Finally, we are excited for what this could mean for NAPI to be biomarker-positive patients. In addition, there is a higher unmet need for those patients who do not benefit from platinum. In the future, this umbrella study allows us to also evaluate non-platinum-based combinations. Future combinations could include liposomal doxorubicin, bevacizumab, PARP inhibitors, and immuno-oncology therapies. We look forward to getting this combination study underway. We believe that the differentiated tolerability profile without the severe neutropenia, peripheral neuropathy, and ocular toxicity that limit other ADC platforms provides UPRI with a significant advantage in terms of its potential as a combination therapy. Importantly, Moving UPRI into earlier lines of therapy could significantly expand the number of patients with ovarian cancer that could benefit from UPRI and the duration of time over which we can impact their disease. I will now turn the call to Tim to discuss our exciting early stage ADC candidates.