Zymeworks Discontinues Clinical Development of ZW171, a Mesothelin-directed T Cell Engager.

Zymeworks has discontinued the clinical development of ZW171, a T cell engager targeting mesothelin-driven cancers, due to dose-limiting toxicities and a lack of benefit-risk profile. The Phase 1 trial will continue, and the company will focus on advancing its broader pipeline, including the ongoing Phase 1 trial of ZW191 and the planned Phase 1 study for ZW251 in 2025.

September 02, 2025

Vancouver, British Columbia — Zymeworks Inc. (Nasdaq: ZYME), a leading clinical-stage biotechnology company, has announced the discontinuation of clinical development for ZW171, a T cell engager targeting mesothelin-driven cancers. The decision follows the completion of Phase 1 trial dose escalation cohorts in ovarian cancer and non-small cell lung cancer patients.

During the trial, while cytokine release syndrome was manageable, dose-limiting toxicities related to mesothelin-targeted effects were observed. Zymeworks determined that further dose evaluation would not support a favorable benefit-risk profile for ZW171. As a result, the company has decided to discontinue the clinical development of this drug candidate.

Current trial participants may continue treatment at their investigator's discretion. Zymeworks remains committed to advancing its broader pipeline, including the ongoing Phase 1 trial of ZW191 and the planned Phase 1 study for ZW251 in 2025. The company also intends to file an Investigational New Drug (IND) application for ZW209, a DLL3-directed trispecific T cell engager, in the first half of 2026.

Zymeworks' decision to discontinue ZW171 represents a significant setback in their oncology pipeline, particularly in the areas of gynecological, thoracic, and digestive system cancers, which have substantial unmet needs. The company has demonstrated a disciplined approach to the management of its product portfolio, ensuring that resources are directed towards the most promising candidates.

Zymeworks' commitment to its mission of making a meaningful difference in the lives of people impacted by difficult-to-treat conditions remains steadfast. The company's focus on novel, multifunctional biotherapeutics and its robust pipeline of wholly-owned product candidates positions it as a key player in the biotechnology sector.

References:
[1] https://www.streetinsider.com/Globe+Newswire/Zymeworks+Announces+Decision+to+Discontinue+Clinical+Development+of+ZW171%2C+a+Mesothelin-directed+T+cell+Engager/25280205.html
[2] https://www.stocktitan.net/news/ZYME/zymeworks-announces-decision-to-discontinue-clinical-development-of-qezs3habk5i6.html