Mestag Therapeutics Announces the First Patient Dosed with MST-0312 in the Phase I STARLYS Trial

Mestag Therapeutics, a clinical-stage biotech company specializing in fibroblast immunology, has dosed the first patient in the Phase I STARLYS trial. The trial assesses MST-0312, a bispecific antibody designed to activate lymphotoxin-beta receptor (LTBR) in the tumor microenvironment, promoting the formation of tertiary lymphoid structures (TLS) and high endothelial venules (HEV). TLS are linked to improved anti-tumor immunity and better patient outcomes. The adaptive, multi-arm study will evaluate MST-0312 alone and in combination with pembrolizumab (Keytruda) in patients with advanced solid tumors, initially targeting tumors in barrier organs such as lung, gut, bladder, breast, and skin. The trial aims to assess safety, tolerability, pharmacodynamics, pharmacokinetics, and anti-tumor activity. MST-0312 works by inducing TLS—aggregates of immune cells including T, B, and dendritic cells—which are associated with enhanced immune responses against tumors. Dr. Lindsey Rolfe, Mestag’s Chief Medical Officer, highlighted the study’s focus on both monotherapy and combination therapy, emphasizing its potential to provide insights for future cancer treatments. The STARLYS trial is coordinated by Dr. Elena Garralda, Head of Early Drug Development at Vall d’Hebron Institute of Oncology in Barcelona, Spain, with Dr. Emiliano Calvo of START Madrid-CIOCC Hospital serving as a Principal Investigator. The first patient was dosed at START Madrid-CIOCC in Spain. Both researchers expressed optimism about MST-0312’s potential to address unmet needs in solid tumor treatment by reshaping anti-tumor immunity. MST-0312 is a FAP-targeted bispecific agonist antibody designed to induce TLS and HEV formation in tumors. The trial’s findings could inform broader therapeutic strategies for patients with immunologically ‘cold’ or ‘warm’ tumors, where current treatments often yield limited benefits.