Zymeworks Inc (NASDAQ:ZYME) stock declined 9.1% in premarket trading Tuesday after the clinical-stage biotech company announced it will voluntarily cease clinical development of ZW171, a T cell engager aimed at treating gynecological, thoracic, and digestive system cancers.
The decision followed the completion of the planned cohorts in the dose-escalation phase of the Phase 1 trial in patients with ovarian cancer and non-small cell lung cancer. Zymeworks determined that further dose evaluation “would be unlikely to support a benefit-risk profile consistent with the desired monotherapy target product profile.”
Although cytokine release syndrome was effectively managed during the study, the company encountered dose-limiting toxicities related to mesothelin-targeted off-tumor effects. Mesothelin, the protein targeted by ZW171, is described by Zymeworks as “a well-recognized but historically challenging target.”
“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.
The company confirmed that participants still enrolled in the Phase 1 trial will continue treatment at the discretion of their investigators, while those discontinuing will remain under safety follow-up according to the study protocol.
Zymeworks emphasized its commitment to advancing its broader pipeline, including the ongoing Phase 1 study of ZW191 and plans to start a Phase 1 trial for ZW251 in 2025. Additionally, the company is preparing an IND submission for ZW209, a DLL3-directed trispecific T cell engager, expected in the first half of 2026.
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