Mersana Therapeutics only has eyes for Emi-Le. Seeking to extend its cash runway into mid-2026, the biotech is laying off 55% of its employees and cutting back internal R&D work to focus on lead program emiltatug ledadotin (Emi-Le).
Massachusetts-based Mersana shared initial phase 1 data on Emi-Le, an antibody-drug conjugate (ADC) that targets B7-H4, in January. The biotech is now running the expansion portion of the study in people with triple-negative breast cancer. Mersana, which ended last year with enough cash to keep going into 2026, has decided the breast cancer opportunity is the best use of its remaining money.
The decision led Mersana to reduce research activities and eliminate its internal pipeline development efforts. In the near term, the biotech will focus on generating safety, tolerability and clinical activity data on Emi-Le in breast cancer, handling dose escalation for XMT-2056 and supporting its collaborations.
GSK paid $100 million upfront for an option on the HER2-directed ADC XMT-2056 in 2022. Mersana needs to complete dose escalation with enrichment for breast cancer patients in a phase 1 single-agent trial to generate a data package to support GSK’s opt-in decision. The company also has collaborations with Johnson & Johnson and Merck KGaA that it will continue to support.
Mersana has calculated it can manage those activities with a reduced workforce. The company, which ended last year with 102 full time employees, plans to reduce its headcount by 55% by the end of the third quarter. The layoffs come less than two years after Mersana halved its workforce in response to the failure of its former lead candidate.
The biotech’s timeline for 2025 includes data from Emi-Le dose escalation and backfill cohorts and initial clinical pharmacodynamic STING activation data for XMT-2056. The readouts offer opportunities to try to revitalize interest in Mersana, which has seen its share price slump to $0.36.
Mersana needs data to back up its claims that Emi-Le has a differentiated profile that will meaningfully benefit patients. B7-H4 is a competitive field, with AstraZeneca, BeiGene and GSK among the companies with ADCs in the clinic. Most of the rival candidates use topo-1 payloads. Emi-Le delivers dolasynthen, a proprietary payload, and as such could carve out a niche in people previously treated with topo-1 ADCs.