Mersana goes all in on B7-H4

So far B7-H4 hasn't convinced as a target, but Mersana is now putting all its hopes here, following a cost-cutting exercise announced Tuesday. Specifically, the company is focusing its ADC emiltatug ledadotin on triple-negative breast cancer, where the project produced a 23% ORR in phase 1 – albeit in a curated dataset that involved just 13 B7-H4-high patients receiving “intermediate” doses of 38.1-67.4mg/m². The phase 1 study also enrolled patients with ovarian and endometrial cancers, among others, which are no longer a priority. As well as pushing on with emilta-L, Mersana will continue with phase 1 dose-escalation work on XMT-2056, a HER2-targeting immune-stimulating antibody conjugate (ISAC) that GSK has an exclusive option to co-develop, under a 2022 deal. Mersana also signed agreements that year with Johnson & Johnson, on ADCs, and Merck KGaA, on ISACs, which apparently remain in play, with Mersana also saying it would also support ongoing collaborations. However, it appears that earlier-stage wholly owned ISACs against undisclosed targets, XMT-2068 and XMT-2175, have fallen by the wayside. Mersana’s 55% workforce reduction could keep it going into mid-2026; more details could be available at the group’s first-quarter earnings call on 15 May. 

Mersana’s clinical-stage pipeline

Note: ISAC=immune-stimulating antibody conjugate; *among B7-H4-high pts receiving intermediate doses (38.1-67.4mg/m²). Source: OncologyPipeline & company releases.