Zymeworks Announces Decision to Discontinue Clinical Development of ZW171, a Mesothelin-directed T Cell Engager

VANCOUVER, British Columbia, Sept. 02, 2025 (GLOBE NEWSWIRE) -- Zymeworks Inc. (Nasdaq: ZYME), a clinical-stage biotechnology company developing a diverse pipeline of novel, multifunctional biotherapeutics to improve the standard of care for difficult-to-treat diseases, including cancer, inflammation, and autoimmune disease, today announced its decision to voluntarily discontinue clinical development of ZW171, a T cell engager designed to target gynecological, thoracic, and digestive system cancers.
 
ZW171 is designed to address cancers driven by mesothelin, a well-recognized but historically challenging target.
 
The decision to discontinue clinical development of ZW171 was based on completion of the planned cohorts of the dose escalation portion of the Phase 1 trial of ZW171 in patients with ovarian cancer and non-small cell lung cancer. After completing the planned dose escalation cohorts and establishing a maximum tolerated dose, Zymeworks determined that further dose evaluation in the current trial would be unlikely to support a benefit-risk profile consistent with the desired monotherapy target product profile. While cytokine release syndrome was well-managed in the Phase 1 study, dose-limiting toxicities were consistent with mesothelin-related on-target off-tumor toxicity. Ongoing participants in the Phase 1 trial will continue treatment at the discretion of their investigator, and participants who have discontinued treatment will continue safety follow-up as per the study protocol.
 
“While this is a disappointing outcome given the promising preclinical activity observed with ZW171, we are deeply grateful to the patients, providers, and caregivers for their support and participation in the ZW171 Phase 1 study,” said Kenneth Galbraith, Chair and Chief Executive Officer of Zymeworks. “As part of Zymeworks’ disciplined approach to the management of our broad product portfolio, we are committed to careful and consistent evaluation of clinical progress for each product candidate to ensure our resources are directed towards those product candidates with the greatest potential impact for patients. We continue to advance our broader product pipeline, including the ongoing Phase 1 trial of ZW191 and the initiation of a Phase 1 study for ZW251 expected in 2025. We are also preparing an IND filing for ZW209, our DLL3-directed trispecific T cell engager, planned in the first half of 2026.”
 
About Zymeworks Inc.
Zymeworks is a global clinical-stage biotechnology company committed to the discovery, development, and commercialization of novel, multifunctional biotherapeutics. Zymeworks’ mission is to make a meaningful difference in the lives of people impacted by difficult-to-treat conditions such as cancer, inflammation, and autoimmune disease. The Company’s complementary therapeutic platforms and fully integrated drug development engine provide the flexibility and compatibility to precisely engineer and develop highly differentiated antibody-based therapeutic candidates. Zymeworks engineered and developed zanidatamab, a HER2-targeted bispecific antibody using the Company’s proprietary Azymetric™ technology. Zymeworks has entered into separate agreements with BeOne Medicines Ltd. (formerly BeiGene, Ltd.) and Jazz Pharmaceuticals Ireland Limited, granting each exclusive rights to develop and commercialize zanidatamab in different territories. Zanidatamab has received accelerated approval from the U.S. FDA, conditional approval from the NMPA in China, and conditional marketing authorization from the European Commission for the treatment of adults with previously treated, unresectable or metastatic HER2-positive (IHC 3+) biliary tract cancer. It is the first and only dual HER2-targeted bispecific antibody approved for this indication in the U.S., Europe, and China. Zanidatamab is also being evaluated in multiple global clinical trials as a potential best-in-class treatment for patients with multiple HER2-expressing cancers. Zymeworks is rapidly advancing a robust pipeline of wholly-owned product candidates, leveraging its expertise in both antibody drug conjugates and multispecific antibody therapeutics targeting novel pathways in areas of significant unmet medical need. A Phase 1 study for ZW191 is actively recruiting and ZW251 is expected to enter clinical trials in 2025. In addition to Zymeworks’ pipeline, its therapeutic platforms have been further leveraged through strategic partnerships with global biopharmaceutical companies. For information about Zymeworks, visit www.zymeworks.com and follow @ZymeworksInc on X.

Investor inquiries:
Shrinal Inamdar
Senior Director, Investor Relations
(604) 678-1388
ir@zymeworks.com