Mestag Therapeutics raises $40M and adds two senior biotech executives as lead cancer program nears the clinic
UK biotech Mestag Therapeutics has raised $40 million and appointed veteran drug developers Lindsey Rolfe as chief medical officer and Pascal Merchiers as chief development officer, as the company prepares to start its first clinical trial in cancer in mid-2026. The new financing brings total capital committed to the Cambridge-based company to more than $95 million, following its $11 million launch round in April 2021 and a seed extension that took total seed financing to $45 million in August 2021.
The money will fund the Phase 1 STARLYS study of MST-0312, Mestag’s lead program, in patients with solid tumors. The drug is designed as a fibroblast activation protein, or FAP, targeted bispecific antibody that agonizes lymphotoxin-beta receptor (LTBR), with the aim of inducing tertiary lymphoid structures (TLS) and high endothelial venules (HEV) inside tumors. Mestag says that the mechanism could help turn immunologically “cold” tumors into sites that are more accessible to anti-tumor immune responses.
That scientific rationale is drawing increasing attention across immuno-oncology. Scientific reviews have highlighted that TLS in tumors are associated with better prognosis and, in some settings, improved responses to immunotherapy, while HEVs are thought to help lymphocytes enter tumors more efficiently. Other academic sources also linked intratumoral HEVs with favorable outcomes across solid tumors.
Mestag has been building toward this point for several years. The company launched in 2021 around a fibroblast-focused platform and quickly attracted backing from SV Health Investors and Johnson & Johnson Innovation’s venture arm JJDC, later adding Forbion, GV (Google Ventures) and Northpond Ventures in its seed extension. Since then, the company has also used its platform to strike partnerships with large pharma.
In 2021, Mestag signed a target discovery, option and license deal with Janssen Biotech focused on inflammatory disease, and in October 2024 it entered a research and licensing collaboration with MSD to identify targets for inflammatory diseases in a deal valued at up to $1.9 billion in potential payments.
The two executive hires suggest the company is shifting from platform-building into clinical execution. Rolfe most recently served as chief medical officer at targeted radiotherapy company 3B Pharmaceuticals, and previously held the CMO role at Clovis Oncology, where she helped lead development of Rubraca, a PARP inhibitor that won approvals in the US and Europe in ovarian and prostate cancer. Merchiers joins from Commit Biologics and has also held senior R&D roles at Aboleris, Oncurious and Tusk Therapeutics, the latter of which was acquired by Roche in 2018.
For Mestag, the key test now is whether the biology behind fibroblast-directed immune remodeling can translate in patients. The broader field has already shown interest in FAP-targeted immune agonists as a way to localize activity in tumors and potentially widen the therapeutic window of immune stimulatory drugs but clinical proof remains limited, and the STARLYS trial will likely determine how much enthusiasm follows MST-0312 into later development.
Engitix