A Phase 3, Randomized, Double-blind, Placebo-controlled, Multicenter Study of Upifitamab Rilsodotin (XMT-1536) as Post-Platinum Maintenance Therapy for Participants With Recurrent, Platinum-Sensitive, Ovarian Cancer (UP-NEXT)

UP-NEXT is a double-blind, randomized, placebo-controlled study of the antibody-drug conjugate (ADC) XMT-1536 (upifitamab rilsodotin) administered as an intravenous infusion once every four weeks in patients with recurrent, platinum-sensitive high-grade serous ovarian cancer (HGSOC), including fallopian tube and primary peritoneal cancer, expressing high levels of NaPi2b.

Start Date23 Jun 2022

Sponsor / Collaborator

Mersana Therapeutics, Inc.

[+2]

NCT04907968 / TerminatedPhase 1

Upifitamab Rilsodotin (Xmt-1536) An Open-Label, Multicenter, Dose Escalation And Expansion Study Of Upifitamab Rilsodotin In Combination With Carboplatin In Participants With High Grade Serous Ovarian Cancer (Upgrade-A)

Phase 1 safety study of the antibody-drug conjugate (ADC) XMT-1536 (upifitamab rilsodotin) administered as an intravenous infusion once every four weeks in combination with Carboplatin in participants with high-grade serous ovarian cancer (HGSOC, including fallopian tube and primary peritoneal cancer). The trial consists of dose escalation (DES) and expansion (EXP) portion. In addition to safety assessments, the pharmacokinetics of the drug will be assessed along with ADC activity.

Start Date11 Jun 2021

Sponsor / Collaborator

Mersana Therapeutics, Inc.

[+2]

NCT06517485 / CompletedPhase 1

A Phase 1b/2, First-in-Human, Dose Expansion Study of XMT-1536 In Patients With Solid Tumors Likely to Express NaPi2b

First-in-human, Phase 1b/2 safety study of the antibody-drug conjugate (ADC) XMT-1536 (upifitamab rilsodotin) administered as an intravenous infusion once every four weeks. Patients with platinum-resistant ovarian cancer and non-small cell lung cancer (adenocarcinoma subtype) were enrolled in the expansion segment of this study. In addition to safety assessments, the pharmacokinetics of the drug were assessed along with ADC activity.

Start Date30 Jul 2019

Sponsor / Collaborator

Mersana Therapeutics, Inc.

100 Clinical Results associated with Upifitamab Rilsodotin

100 Translational Medicine associated with Upifitamab Rilsodotin

100 Patents (Medical) associated with Upifitamab Rilsodotin

Literatures (Medical) associated with Upifitamab Rilsodotin

01 May 2023·American Society of Clinical Oncology educational book. American Society of Clinical Oncology. Annual Meeting

Antibody-Drug Conjugates in Gynecologic Cancer.

Review

Author: Powell, Sachia Stonefeld ; Pothuri, Bhavana ; Karpel, Hannah C

The present article reviews the current evidence for antibody-drug conjugates (ADCs) in gynecologic cancer. ADCs consist of a highly selective monoclonal antibody for a tumor-associated antigen and a potent cytotoxic payload conjugated through a linker. Overall, the toxicity profiles of ADCs are manageable. Ocular toxicity is a known class effect of some ADCs and is managed with prophylactic corticosteroid and vasoconstrictor eye drops as well as dose interruptions/holds and dose modifications. In ovarian cancer, mirvetuximab soravtansine, an ADC targeting alpha-folate receptor (FRα), received US Food and Drug Administration (FDA) accelerated approval in November 2022 after data from the single-arm phase III SORAYA trial. A second ADC targeting FRα, STRO-002, received FDA fast track designation in August 2021. Multiple studies with upifitamab rilsodotin, an ADC comprising a NaPi2B-binding antibody, are underway. In cervical cancer, tisotumab vedotin, an ADC-targeting tissue factor, received FDA accelerated approval in September 2021 after the phase II innovaTV 204 trial. Tisotumab vedotin in combination with chemotherapy and other targeted agents is currently being evaluated. Although there are no currently approved ADCs for endometrial cancer, there are many under active evaluation, including mirvetuximab soravtansine. Trastuzumab-deruxtecan (T-DXd), an ADC targeting human epidermal growth factor receptor 2 (HER2), is currently approved for HER2-positive and HER2-low breast cancer and shows promise in endometrial cancer. Like all anticancer treatments, the decision for a patient to undergo therapy with an ADC is a personal choice that balances the potential benefits with the side effects and requires thorough and compassionate support of their physician and care team and shared decision making.

01 Dec 2021·Biochemistry and biophysics reports

Sodium-dependent phosphate transporter NaPi2b as a potential predictive marker for targeted therapy of ovarian cancer

Article

Author: Kiyamova, R G ; Popov, V E ; Vlasenkova, R A ; Safina, S Z ; Savenkova, D V ; Shakirova, E Zh ; Bulatova, L F ; Nurgalieva, A K ; Filonenko, V V ; Skripova, V S ; Bogdanov, M V

The high mortality rate from ovarian cancer is due to the asymptomatic nature of the course of the disease, which leads to the diagnosis of ovarian cancer in later stages. The sodium-dependent phosphate transporter NaPi2b encoded by SLC34A2 gene is expressed in 80-90% of epithelial ovarian cancers and used as a target for therapeutic antibodies XMT-1536, and XMT-1592, which are derived from MX35 antibodies and used in clinical trials for the treatment of ovarian and lung cancers. In this work, we aimed to evaluate NaPi2b as a molecular marker for diagnostics and predicting the course and outcome of ovarian cancer disease. Quantitative analysis of SLC34A2 gene expression in ovarian tumor tissue was performed at the level of transcription and translation using real-time PCR, droplet digital PCR and Western blot analysis respectively. Statistical analysis was performed taking into account various clinicopathological characteristics of the ovarian cancer patients, including the stage of the disease, the tumor grade, the applying of neoadjuvant chemotherapy and the presence of ascites. In this work, we demonstrated that the expression of the human NaPi2b (hNaPi2b) transporter is downregulated in the tumors of patients receiving neoadjuvant therapy and during the development of disease. The data suggest that the level of expression of the SLC34A2 gene can serve as a potential marker for the monitoring and predicting responses to neoadjuvant and targeted therapy in patients with ovarian cancer.

01 May 2021·MOLECULAR CANCER THERAPEUTICS

The Dolaflexin-based Antibody-Drug Conjugate XMT-1536 Targets the Solid Tumor Lineage Antigen SLC34A2/NaPi2b.

Article

Author: Xu, Jian ; McGillicuddy, Dennis ; Lee, Winnie ; Stevenson, Cheri A ; Yurkovetskiy, Aleksandr V ; Xiao, Dongmei ; Gumerov, Dmitry R ; Ter-Ovanesyan, Elena ; Protopova, Marina ; Park, Peter U ; Bodyak, Natalya D ; Xu, Ling ; Lowinger, Timothy B ; Gurijala, Venu R ; Bergstrom, Donald A ; Conlon, Patrick R ; Mosher, Rebecca ; Uttard, Alex ; DeVit, Michael J ; Yin, Mao ; Demady, Damon R ; Qin, LiuLiang ; Poling, Laura L ; Bu, Charlie

Target selection for antibody-drug conjugates (ADC) frequently focuses on identifying antigens with differential expression in tumor and normal tissue, to mitigate the risk of on-target toxicity. However, this strategy restricts the possible target space. SLC34A2/NaPi2b is a sodium phosphate transporter expressed in a variety of human tumors including lung and ovarian carcinoma, as well as the normal tissues from which these tumors arise. Previous clinical trials with a NaPi2b targeting MMAE-ADCs have shown objective durable responses. However, the protein-based biomarker assay developed for use in that study was unable to discern a statistically significant relationship between NaPi2b protein expression and the probability of response. XMT-1536 is a NaPi2b targeting ADC comprised of a unique humanized antibody conjugated with 10-15 auristatin F- hydroxypropylamide (AF-HPA) payload molecules via the Dolaflexin platform. AF-HPA is a cell-permeable, antimitotic compound that is slowly metabolized intratumorally to an active, very low-permeable metabolite, auristatin F (AF), resulting in controlled bystander killing. We describe the preclinical in vitro and in vivo antitumor effects of XMT-1536 in models of ovarian and lung adenocarcinoma. Pharmacokinetic analysis showed approximately proportional increases in exposure in rat and monkey. Systemic free AF-HPA and AF concentrations were observed to be low in all animal species. Finally, we describe a unique IHC reagent, generated from a chimeric construct of the therapeutic antibody, that was used to derive a target expression and efficacy relationship in a series of ovarian primary xenograft cancer models.

News (Medical) associated with Upifitamab Rilsodotin

13 Nov 2024

·www.globenewswire.com

Mersana Therapeutics Provides Business Update and Announces Third Quarter 2024 Financial Results

Plan to announce initial clinical data for XMT-1660 at a company event by the end of 2024 Dose escalation advancing in Phase 1 clinical trial of XMT-2056 Conference call today at 8:00 a.m. ET CAMBRIDGE, Mass., Nov. 13, 2024 (GLOBE NEWSWIRE) -- Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today provided a business update and reported financial results for the third quarter ended September 30, 2024. “During the third quarter of 2024, our team continued its strong execution as we advanced the dose escalation portions of our Phase 1 clinical trials of XMT-1660 and XMT-2056, made further progress in our collaborations and maintained the strength of our balance sheet,” said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. “In multiple presentations over the course of the past year, we shared data demonstrating the potential for Dolasynthen ADCs to generate anti-tumor activity and avoid many of the toxicities that have limited other ADC platforms. We are looking forward to presenting initial XMT-1660 clinical data later this year. We also are finalizing plans to begin the expansion portion of our trial, with an initial focus on patients with triple-negative breast cancer who have previously been treated with at least one topoisomerase-1 ADC.” Recent Accomplishments, Strategic Priorities and Expected Milestones XMT-1660: Mersana continues to advance its Phase 1 clinical trial of XMT-1660, the company’s lead Dolasynthen ADC candidate targeting B7-H4. The dose escalation portion of the trial is ongoing, with the company having recently escalated to a dose of 115 milligrams per meter squared administered every four weeks. A maximum tolerated dose has not yet been established. Approximately 75 percent of the patients that have been enrolled in the trial to date have triple-negative breast cancer (TNBC) or hormone receptor-positive breast cancer (HR+BC). Among the enrolled patients with TNBC, approximately 90 percent have received a prior topoisomerase-1 (topo-1) ADC, and among the enrolled patients with HR+BC, approximately half have received a prior topo-1 ADC. Last week at World ADC 2024, Mersana presented new preclinical data demonstrating XMT-1660’s anti-tumor activity following topo-1 treatment. By the end of 2024, Mersana plans both to share initial safety, tolerability, efficacy and biomarker data from its Phase 1 dose escalation and backfill cohorts at a company event and to initiate the expansion portion of the trial in patients with TNBC who have previously been treated with at least one topo-1 ADC. XMT-2056: Mersana continues to escalate dosing in its Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen ADC candidate targeting a novel HER2 epitope. GSK plc has an exclusive global license option to co-develop and commercialize XMT-2056. At the Society for Immunotherapy of Cancer (SITC) 2024 Annual Meeting last week, Mersana presented new preclinical data demonstrating XMT-2056’s ability to activate STING signaling and inhibit tumor growth at very low doses. Collaborations: Mersana continues to advance its Johnson & Johnson and Merck KGaA, Darmstadt, Germany collaborations. The collaboration with Merck KGaA, Darmstadt, Germany focuses on discovering novel Immunosynthen ADCs for up to two targets. The collaboration with Johnson & Johnson focuses on discovering novel Dolasynthen ADCs for up to three targets. In the third quarter of 2024, Mersana achieved and received payment for an $8 million development milestone under the Johnson & Johnson collaboration and achieved a $1 million development milestone under the Merck KGaA, Darmstadt, Germany collaboration, for which payment was received in the fourth quarter of 2024. Third Quarter 2024 Financial Results Cash, cash equivalents and marketable securities as of September 30, 2024, were $155.2 million. Mersana continues to expect that its capital resources will be sufficient to support its current operating plan commitments into 2026.Net cash used in operating activities for the third quarter of 2024 was $8.6 million, which reflects the impact of the aforementioned $8 million milestone payment and a $3.5 million payment for manufacturing activities from Johnson & Johnson. Collaboration revenue for the third quarter of 2024 was $12.6 million, compared to $7.7 million for the same period in 2023. The year-over-year change was primarily related to an increase in revenue recognized under Mersana’s collaboration and license agreements with Johnson & Johnson and Merck KGaA, Darmstadt, Germany.Research and development (R&D) expenses for the third quarter of 2024 were $14.8 million, compared to $30.5 million for the same period in 2023. Included in the third quarter of 2024 R&D expenses were $2.3 million in non-cash stock-based compensation expenses. The year-over-year decline in R&D expenses was primarily related to reduced costs associated with manufacturing and clinical development activities for UpRi, a discontinued ADC candidate, and reduced employee compensation expense following the company’s restructuring in 2023.General and administrative (G&A) expenses for the third quarter of 2024 were $9.9 million, compared to $12.9 million during the same period in 2023. Included in the third quarter of 2024 G&A expenses were $1.7 million in non-cash stock-based compensation expenses. The year-over-year decline in G&A expenses was primarily related to reduced consulting and professional services fees and reduced employee compensation expense following the aforementioned restructuring.Net loss for the third quarter of 2024 was $11.5 million, or $0.09 per share, compared to a net loss of $41.7 million, or $0.35 per share, for the same period in 2023. Conference Call ReminderMersana will host a conference call today at 8:00 a.m. ET to discuss business updates and its financial results for the third quarter of 2024. To access the call, please dial 833-255-2826 (domestic) or 412-317-0689 (international). A live webcast of the presentation will be available on the Investors & Media section of the Mersana website at www.mersana.com, and a replay of the webcast will be available in the same location following the conference call for approximately 90 days. About Mersana TherapeuticsMersana Therapeutics is a clinical-stage biopharmaceutical company focused on the development of novel antibody-drug conjugates (ADCs) and driven by the knowledge that patients are waiting for new treatment options. The company has developed proprietary cytotoxic (Dolasynthen) and immunostimulatory (Immunosynthen) ADC platforms that are generating a pipeline of wholly-owned and partnered product candidates with the potential to treat a range of cancers. Its pipeline includes XMT-1660, a Dolasynthen ADC targeting B7-H4, and XMT-2056, an Immunosynthen ADC targeting a novel epitope of human epidermal growth factor receptor 2 (HER2). Mersana routinely posts information that may be useful to investors on the “Investors & Media” section of its website at www.mersana.com. Forward-Looking StatementsThis press release contains “forward-looking” statements and information within the meaning of the Private Securities Litigation Reform Act of 1995. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “could,” “estimates,” “expects,” “forecasts,” “goal,” “intends,” “may,” “plans,” “possible,” “potential,” “seeks,” “will” and variations of these words or similar expressions, although not all forward-looking statements contain these words. Forward-looking statements in this press release include, but are not limited to, statements concerning Mersana’s plans regarding the clinical development of XMT-1660 and XMT-2056, including with respect to the progress and design of the clinical trials of these product candidates; Mersana’s planned data presentations, including with respect to its Phase 1 clinical trial of XMT-1660; Mersana’s cash runway; Mersana’s collaborations with third parties; and the development and potential of Mersana’s product candidates, platforms, technology and pipeline of ADC candidates. Mersana may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including, among other things, uncertainties inherent in research and development, in the advancement, progression and completion of clinical trials and in the clinical development of Mersana’s product candidates, including XMT-1660 and XMT-2056; the risk that Mersana may face delays in patient enrollment in its Phase 1 clinical trial of XMT-2056; the risk that Mersana may not realize the intended benefits of its platforms, technology and collaborations; and other important factors, any of which could cause Mersana’s actual results to differ from those contained in the forward-looking statements, that are described in greater detail in the section entitled “Risk Factors” in Mersana’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (“SEC”) on August 13, 2024, as well as in other filings Mersana may make with the SEC in the future. Any forward-looking statements contained in this press release speak only as of the date hereof, and Mersana expressly disclaims any obligation to update any forward-looking statements contained herein, whether because of any new information, future events, changed circumstances or otherwise, except as otherwise required by law. Mersana Therapeutics, Inc.Selected Condensed Consolidated Balance Sheet Data(in thousands and unaudited) September 30,2024 December 31,2023 Cash, cash equivalents and marketable securities$155,171 $209,084 Working capital(1) 92,256 150,420 Total assets169,530 226,060 Total stockholders' equity1,049 36,904 (1) The company defines working capital as current assets less current liabilities. Mersana Therapeutics, Inc.Condensed Consolidated Statement of Operations(in thousands, except share and per share data, and unaudited) Three months ended Nine months ended September 30, September 30, September 30, September 30, 2024202320242023 Collaboration revenue$12,598 $7,698 $24,136 $26,154 Operating expenses: Research and development14,803 30,531 50,734 126,774 General and administrative9,864 12,894 31,927 49,409 Restructuring expenses- 8,214 - 8,214 Total operating expenses24,667 51,639 82,661 184,397 Total other income, net986 2,285 3,868 6,117 Loss before income taxes (11,083) (41,656) (54,657) (152,126)Income tax expense (418) - (418) - Net loss$(11,501) $(41,656) $(55,075) $(152,126)Net loss per share — basic and diluted$(0.09) $(0.35) $(0.45) $(1.33)Weighted-average number of common shares — basic and diluted122,721,918 120,521,985 122,197,585 114,595,910 Contact:Jason Fredette 617-498-0020jason.fredette@mersana.com

Phase 1Financial StatementLicense out/inADCImmunotherapy

13 Aug 2024

·www.globenewswire.com

Mersana Therapeutics Provides Business Update and Announces Second Quarter 2024 Financial Results

Dose escalation advancing in Phase 1 clinical trials of both XMT-1660 and XMT-2056 Continue to expect to announce initial XMT-1660 clinical data and initiate expansion in the second half of 2024 Capital resources expected to support current operating plan commitments into 2026 Conference call today at 8:00 a.m. ET CAMBRIDGE, Mass., Aug. 13, 2024 (GLOBE NEWSWIRE) -- Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today provided a business update and reported financial results for the second quarter ended June 30, 2024. “The second quarter of 2024 was a time of continued progress at Mersana as we advanced dose escalation in Phase 1 clinical trials of XMT-1660, our lead Dolasynthen ADC candidate, and XMT-2056, our lead Immunosynthen ADC candidate,” said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. “At the same time, we made further progress in our collaborations while also benefiting from last year’s efforts to reduce operating expenses. 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.” Recent Accomplishments, Strategic Priorities and Expected Milestones XMT-1660: Mersana continues to advance its Phase 1 clinical trial of XMT-1660, the company’s lead Dolasynthen ADC candidate targeting B7-H4. The dose escalation portion of the trial is ongoing at a dose level of 80 milligrams per meter squared every four weeks, and a maximum tolerated dose has yet to be established. Additionally, the company has been proactively exploring more frequent dosing and enrolling patients in backfill cohorts to inform the optimal dose and schedule for expansion. Mersana plans to share initial safety, tolerability, efficacy and biomarker data from dose escalation and backfill cohorts and plans to initiate the expansion portion of the trial in the second half of 2024. XMT-2056: Mersana continues to enroll patients in the dose escalation portion of its Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen ADC candidate targeting a novel HER2 epitope. GSK plc has an exclusive global license option to co-develop and commercialize XMT-2056. Additionally, mechanistic underpinnings related to Mersana’s Immunosynthen platform were recently described in a Nature Communications publication entitled, “Tumor Cell-Directed STING Agonist Antibody Drug Conjugates Induce Type III Interferons and Anti-Tumor Innate Immune Responses.” Collaborations: Mersana continues to advance its Johnson & Johnson and Merck KGaA, Darmstadt, Germany collaborations. The collaboration with Merck KGaA, Darmstadt, Germany focuses on the discovery of novel Immunosynthen ADCs for up to two targets. The collaboration with Johnson & Johnson focuses on the discovery of novel Dolasynthen ADCs for up to three targets. In August 2024, Mersana earned an $8 million development milestone under the Johnson & Johnson collaboration, for which payment is due in the third quarter of 2024. Second Quarter 2024 Financial Results Cash, cash equivalents and marketable securities as of June 30, 2024 were $162.7 million. Mersana continues to expect that its capital resources will be sufficient to support its current operating plan commitments into 2026.Net cash used in operating activities for the second quarter of 2024 was $21.8 million. 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 Mersana’s collaboration and license agreements with Johnson & Johnson and Merck KGaA, Darmstadt, Germany.Research and development (R&D) expenses for the second quarter of 2024 were $17.2 million, compared to $49.0 million for the same period in 2023. Included in R&D expenses for the second quarter of 2024 were $2.4 million in non-cash stock-based compensation expenses. The year-over-year decline in R&D expenses was primarily related to reduced costs associated with manufacturing and clinical activities for UpRi, a discontinued ADC candidate, and reduced employee compensation expense following the company’s restructuring in 2023.General and administrative (G&A) expenses for the second quarter of 2024 were $10.5 million, compared to $18.2 million during the same period in 2023. Included in G&A expenses for the second quarter of 2024 were $2.0 million in non-cash stock-based compensation expenses. The year-over-year decline in G&A expenses was primarily related to reduced consulting and professional services fees and reduced employee compensation expense following the aforementioned restructuring.Net loss for the second quarter of 2024 was $24.3 million, or $0.20 per share, compared to a net loss of $54.3 million, or $0.47 per share, for the same period in 2023. Conference Call ReminderMersana will host a conference call today at 8:00 a.m. ET to discuss business updates and its financial results for the second quarter of 2024. To access the call, please dial 833-255-2826 (domestic) or 412-317-0689 (international). A live webcast of the presentation will be available on the Investors & Media section of the Mersana website at www.mersana.com, and a replay of the webcast will be available in the same location following the conference call for approximately 90 days. About Mersana TherapeuticsMersana Therapeutics is a clinical-stage biopharmaceutical company focused on the development of novel antibody-drug conjugates (ADCs) and driven by the knowledge that patients are waiting for new treatment options. The company has developed proprietary cytotoxic (Dolasynthen) and immunostimulatory (Immunosynthen) ADC platforms that are generating a pipeline of wholly-owned and partnered product candidates with the potential to treat a range of cancers. Its pipeline includes XMT-1660, a Dolasynthen ADC targeting B7-H4, and XMT-2056, an Immunosynthen ADC targeting a novel epitope of human epidermal growth factor receptor 2 (HER2). Mersana routinely posts information that may be useful to investors on the “Investors & Media” section of its website at www.mersana.com. Forward-Looking StatementsThis press release contains “forward-looking” statements and information within the meaning of the Private Securities Litigation Reform Act of 1995. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “could,” “estimates,” “expects,” “forecasts,” “goal,” “intends,” “may,” “plans,” “possible,” “potential,” “seeks,” “will” and variations of these words or similar expressions, although not all forward-looking statements contain these words. Forward-looking statements in this press release include, but are not limited to, statements concerning Mersana’s plans regarding the clinical development of XMT-1660 and XMT-2056, including with respect to the progress and design of the clinical trials of these product candidates; Mersana’s planned data presentations, including with respect to its Phase 1 clinical trial of XMT-1660; Mersana’s cash runway; Mersana’s collaborations with third parties; and the development and potential of Mersana’s product candidates, platforms, technology and pipeline of ADC candidates. Mersana may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including, among other things, uncertainties inherent in research and development, in the advancement, progression and completion of clinical trials and in the clinical development of Mersana’s product candidates, including XMT-1660 and XMT-2056; the risk that Mersana may face delays in patient enrollment in its Phase 1 clinical trial of XMT-2056; the risk that Mersana may not realize the intended benefits of its platforms, technology and collaborations; and other important factors, any of which could cause Mersana’s actual results to differ from those contained in the forward-looking statements, that are described in greater detail in the section entitled “Risk Factors” in Mersana’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (“SEC”) on May 9, 2024, as well as in other filings Mersana may make with the SEC in the future. Any forward-looking statements contained in this press release speak only as of the date hereof, and Mersana expressly disclaims any obligation to update any forward-looking statements contained herein, whether because of any new information, future events, changed circumstances or otherwise, except as otherwise required by law. Mersana Therapeutics, Inc.Selected Condensed Consolidated Balance Sheet Data(in thousands and unaudited) June 30,2024 December 31,2023 Cash, cash equivalents and marketable securities$162,742 $209,084 Working capital(1)106,779 150,420 Total assets179,128 226,060 Total stockholders' equity8,427 36,904 (1)The company defines working capital as current assets less current liabilities. Mersana Therapeutics, Inc.Condensed Consolidated Statement of Operations(in thousands, except share and per share data, and unaudited) Three months ended Six months ended June 30,2024 June 30,2023 June 30,2024 June 30,2023 Collaboration revenue$2,293 $10,654 $11,538 $18,456 Operating expenses: Research and development17,245 48,968 35,931 96,243 General and administrative10,503 18,187 22,063 36,515 Total operating expenses27,748 67,155 57,994 132,758 Total other income, net1,187 2,194 2,882 3,832 Net loss$(24,268) $(54,307) $(43,574) $(110,470)Net loss per share — basic and diluted$(0.20) $(0.47) $(0.36) $(0.99)Weighted-average number of common shares — basic and diluted122,440,124 115,608,156 121,932,540 111,583,765 Contact:Jason Fredette 617-498-0020jason.fredette@mersana.com This press release was published by a CLEAR® Verified individual.

Phase 1ADCFinancial StatementLicense out/in

13 Aug 2024

·ir.mersana.com

Mersana Therapeutics Provides Business Update and Announces Second Quarter 2024 Financial Results

Dose escalation advancing in Phase 1 clinical trials of both XMT-1660 and XMT-2056 Continue to expect to announce initial XMT-1660 clinical data and initiate expansion in the second half of 2024 Capital resources expected to support current operating plan commitments into 2026 Conference call today at 8:00 a.m. ET CAMBRIDGE, Mass., Aug. 13, 2024 (GLOBE NEWSWIRE) -- Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today provided a business update and reported financial results for the second quarter ended June 30, 2024. “The second quarter of 2024 was a time of continued progress at Mersana as we advanced dose escalation in Phase 1 clinical trials of XMT-1660, our lead Dolasynthen ADC candidate, and XMT-2056, our lead Immunosynthen ADC candidate,” said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. “At the same time, we made further progress in our collaborations while also benefiting from last year’s efforts to reduce operating expenses. 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.” Recent Accomplishments, Strategic Priorities and Expected Milestones XMT-1660: Mersana continues to advance its Phase 1 clinical trial of XMT-1660, the company’s lead Dolasynthen ADC candidate targeting B7-H4. The dose escalation portion of the trial is ongoing at a dose level of 80 milligrams per meter squared every four weeks, and a maximum tolerated dose has yet to be established. Additionally, the company has been proactively exploring more frequent dosing and enrolling patients in backfill cohorts to inform the optimal dose and schedule for expansion. Mersana plans to share initial safety, tolerability, efficacy and biomarker data from dose escalation and backfill cohorts and plans to initiate the expansion portion of the trial in the second half of 2024. XMT-2056: Mersana continues to enroll patients in the dose escalation portion of its Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen ADC candidate targeting a novel HER2 epitope. GSK plc has an exclusive global license option to co-develop and commercialize XMT-2056. Additionally, mechanistic underpinnings related to Mersana’s Immunosynthen platform were recently described in a Nature Communications publication entitled, “Tumor Cell-Directed STING Agonist Antibody Drug Conjugates Induce Type III Interferons and Anti-Tumor Innate Immune Responses.” Collaborations: Mersana continues to advance its Johnson & Johnson and Merck KGaA, Darmstadt, Germany collaborations. The collaboration with Merck KGaA, Darmstadt, Germany focuses on the discovery of novel Immunosynthen ADCs for up to two targets. The collaboration with Johnson & Johnson focuses on the discovery of novel Dolasynthen ADCs for up to three targets. In August 2024, Mersana earned an $8 million development milestone under the Johnson & Johnson collaboration, for which payment is due in the third quarter of 2024. Second Quarter 2024 Financial Results Cash, cash equivalents and marketable securities as of June 30, 2024 were $162.7 million. Mersana continues to expect that its capital resources will be sufficient to support its current operating plan commitments into 2026. Net cash used in operating activities for the second quarter of 2024 was $21.8 million. 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 Mersana’s collaboration and license agreements with Johnson & Johnson and Merck KGaA, Darmstadt, Germany. Research and development (R&D) expenses for the second quarter of 2024 were $17.2 million, compared to $49.0 million for the same period in 2023. Included in R&D expenses for the second quarter of 2024 were $2.4 million in non-cash stock-based compensation expenses. The year-over-year decline in R&D expenses was primarily related to reduced costs associated with manufacturing and clinical activities for UpRi, a discontinued ADC candidate, and reduced employee compensation expense following the company’s restructuring in 2023. General and administrative (G&A) expenses for the second quarter of 2024 were $10.5 million, compared to $18.2 million during the same period in 2023. Included in G&A expenses for the second quarter of 2024 were $2.0 million in non-cash stock-based compensation expenses. The year-over-year decline in G&A expenses was primarily related to reduced consulting and professional services fees and reduced employee compensation expense following the aforementioned restructuring. Net loss for the second quarter of 2024 was $24.3 million, or $0.20 per share, compared to a net loss of $54.3 million, or $0.47 per share, for the same period in 2023. Conference Call Reminder Mersana will host a conference call today at 8:00 a.m. ET to discuss business updates and its financial results for the second quarter of 2024. To access the call, please dial 833-255-2826 (domestic) or 412-317-0689 (international). A live webcast of the presentation will be available on the Investors & Media section of the Mersana website at www.mersana.com, and a replay of the webcast will be available in the same location following the conference call for approximately 90 days. About Mersana Therapeutics Mersana Therapeutics is a clinical-stage biopharmaceutical company focused on the development of novel antibody-drug conjugates (ADCs) and driven by the knowledge that patients are waiting for new treatment options. The company has developed proprietary cytotoxic (Dolasynthen) and immunostimulatory (Immunosynthen) ADC platforms that are generating a pipeline of wholly-owned and partnered product candidates with the potential to treat a range of cancers. Its pipeline includes XMT-1660, a Dolasynthen ADC targeting B7-H4, and XMT-2056, an Immunosynthen ADC targeting a novel epitope of human epidermal growth factor receptor 2 (HER2). Mersana routinely posts information that may be useful to investors on the “Investors & Media” section of its website at www.mersana.com. Forward-Looking Statements This press release contains “forward-looking” statements and information within the meaning of the Private Securities Litigation Reform Act of 1995. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “could,” “estimates,” “expects,” “forecasts,” “goal,” “intends,” “may,” “plans,” “possible,” “potential,” “seeks,” “will” and variations of these words or similar expressions, although not all forward-looking statements contain these words. Forward-looking statements in this press release include, but are not limited to, statements concerning Mersana’s plans regarding the clinical development of XMT-1660 and XMT-2056, including with respect to the progress and design of the clinical trials of these product candidates; Mersana’s planned data presentations, including with respect to its Phase 1 clinical trial of XMT-1660; Mersana’s cash runway; Mersana’s collaborations with third parties; and the development and potential of Mersana’s product candidates, platforms, technology and pipeline of ADC candidates. Mersana may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including, among other things, uncertainties inherent in research and development, in the advancement, progression and completion of clinical trials and in the clinical development of Mersana’s product candidates, including XMT-1660 and XMT-2056; the risk that Mersana may face delays in patient enrollment in its Phase 1 clinical trial of XMT-2056; the risk that Mersana may not realize the intended benefits of its platforms, technology and collaborations; and other important factors, any of which could cause Mersana’s actual results to differ from those contained in the forward-looking statements, that are described in greater detail in the section entitled “Risk Factors” in Mersana’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (“SEC”) on May 9, 2024, as well as in other filings Mersana may make with the SEC in the future. Any forward-looking statements contained in this press release speak only as of the date hereof, and Mersana expressly disclaims any obligation to update any forward-looking statements contained herein, whether because of any new information, future events, changed circumstances or otherwise, except as otherwise required by law. Contact: Jason Fredette 617-498-0020 jason.fredette@mersana.com This press release was published by a CLEAR® Verified individual.

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Indication	Highest Phase	Country/Location	Organization	Date
metastatic non-small cell lung cancer	Phase 2	US	Mersana Therapeutics, Inc.	12 Dec 2017
Platinum-Resistant Ovarian Carcinoma	Phase 2	US	Mersana Therapeutics, Inc.	12 Dec 2017
high grade serous adenocarcinoma of ovary	Phase 1	US	Mersana Therapeutics, Inc.	11 Jun 2021
Platinum-Sensitive Ovarian Carcinoma	Phase 1	US	Mersana Therapeutics, Inc.	11 Jun 2021
Adenocarcinoma	Phase 1	US	Mersana Therapeutics, Inc.	30 Jul 2019

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Study	Phase	Population	Analyzed Enrollment	Group	Results	Evaluation	Publication Date


UPLIFT (ENGOT-Ov67/GOG-3048) (ESGO2024)	Phase 2	Platinum-Resistant Ovarian Carcinoma NaPi2b-positive	268	Upifitamab rilsodotin (UpRi)	ejwqcvkkuw(dudoyucbbq) = xbepuxyjby aauvbakmpn (qwvbkopxud, 10 - 22.7) View more	Negative	10 Mar 2024
				Placebo	ejwqcvkkuw(dudoyucbbq) = uxllwfbawz aauvbakmpn (qwvbkopxud, 9.3 - 17.7) View more
UPLIFT (Corporate Publications) Manual	Phase 2	Platinum-Resistant Ovarian Carcinoma NaPi2b-Positive	268	upifitamab rilsodotin (NaPi2b-Positive)	biumvsrwax(kmkcjxiqys) = uuikhqfjev oyflzhydcr (qhjnjexvah, 10.0 - 22.7) View more	Negative	27 Jul 2023
				upifitamab rilsodotin	biumvsrwax(kmkcjxiqys) = lznbbdmtqz oyflzhydcr (qhjnjexvah ) View more
EP017/#425 (IGCS2022)	Phase 1	NaPi2b	-	Upifitamab rilsodotin (UPRI; XMT-1536)	rncroemjce(omtbmacnqq) = eksobdcuyo gelttyuqqg (osecidzbdq )	-	04 Dec 2022
SGO	Not Applicable	Ovarian Cancer	-	Upifitamab rilsodotin 33-38mg/m^2	glqvmgpojh(vtotbhfvow) = antsxoebks gpqmmckain (nrwqsdshfg ) View more	-	01 Aug 2022
				Upifitamab rilsodotin >38mg/m^2	glqvmgpojh(vtotbhfvow) = ktbewtetmd gpqmmckain (nrwqsdshfg ) View more
SGO	Not Applicable	Ovarian Cancer	-	Upifitamab Rilsodotin (UpRi) 36mg/m^2	mlayupjkcw(tgbflmpzta) = The most common grade ≥3 events were transient AST increase, fatigue, anemia, and thrombocytopenia. fkqpehulvv (fhpngwrtkg ) View more	-	01 Aug 2022
				Upifitamab Rilsodotin (UpRi) 43mg/m^2
NCT03319628 (Corporate Publications) Manual	Phase 1	Ovarian Cancer NaPi2b	95	Upifitamab rilsodotin (Dose Group 36(33–38 mg/m2))	famtwsfncq(toxsrwroix) = xhhznkipid zxnveevzpe (odsaynmhrt ) View more	Positive	15 Mar 2022
				Upifitamab rilsodotin (Dose Group 43(>38–43 mg/m2))	famtwsfncq(toxsrwroix) = xlqeihljhc zxnveevzpe (odsaynmhrt ) View more
NCT03319628 (UPLIFT (ENGOT-ov67/GOG-3048), ESGO2021)	Phase 2	Platinum-Resistant Ovarian Carcinoma NaPi2b expression	180	Upifitamab rilsodotin (XMT-1536; UpRi)	wtvnmufyee(xuevngntzt) = fxdfwyeunt zrqpvzesuw (mesgkqdfpw )	Positive	12 Oct 2021
NCT03319628 (UPLIFT, ASCO2021)	Phase 2	Platinum-Resistant Ovarian Carcinoma	180	XMT-1536	vbftiurnvl(fkrjdcsupk) = spklcoormc ozumzfjosb (gwnqxxtnat ) View more	Positive	28 May 2021
NCT03319628 (ESMO2020)	Phase 1	Ovarian Cancer	27	XMT-1536 43 mg/m2	kvipwjefzn(iamwapeslf) = The most frequently (≥20%) reported treatment-related adverse events were fatigue, nausea, vomiting, pyrexia, decreased appetite, diarrhea, and transient increase in AST. lbcmdtfsru (gltenpskff )	Positive	17 Sep 2020
NCT03319628 (ASCO2019) Manual	Phase 1	Solid tumor	36	XMT-1536	bfrviqnbkj(koufsbhsxg) = vthwayunhp viomelovte (vwbinxlyor )	Positive	01 Jun 2019

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