Mestag Therapeutics has dosed the first patient in its Phase 1 Starlys trial evaluating MST-0312, a bispecific antibody designed to stimulate anti-tumour immune responses in patients with advanced solid tumours.

The first-in-human study is assessing MST-0312 as both a monotherapy and in combination with Merck’s PD-1 inhibitor Keytruda (pembrolizumab) in selected advanced solid tumours.

MST-0312 targets the lymphotoxin-beta receptor pathway in the tumour microenvironment with the aim of inducing tertiary lymphoid structures and high endothelial venules within tumours. These immune structures are associated with stronger anti-tumour immune activity and improved clinical outcomes in several cancer types.

The adaptive open-label Phase 1 study will evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and anti-tumour activity of the therapy.

Initially, the Starlys trial will focus on tumours arising in barrier organs including lung, gut, bladder, breast and skin cancers, which the company believes may be particularly responsive to tertiary lymphoid structure formation.

Dr Lindsey Rolfe, chief medical officer of Mestag Therapeutics, said: “Dosing the first patient with MST-0312 is a significant milestone in developing this potential new therapeutic class.

“Our carefully designed study evaluates monotherapy and combination therapy in immunologically ‘cold’ and ‘warm’ tumors, generating multiple mechanistic and clinical insights to inform future development.”

The first patient was dosed at START Madrid-CIOCC in Spain.

Dr Emiliano Calvo, principal investigator of the study and director of clinical research at START Madrid-CIOCC, said: “MST-0312 is an exciting new investigative approach for the treatment of solid tumors and we are thrilled to have dosed the first patient in the STARLYS trial.”

The study is also being coordinated by Vall d’Hebron Institute of Oncology in Barcelona.

Dr Elena Garralda, co-director of the clinical research programme and head of early drug development at Vall d’Hebron Institute of Oncology, said: “Published data show that the presence of TLS is associated with significantly improved outcomes for patients.

“Despite recent therapeutic advances, many patients with solid tumors derive limited benefit from current therapies. MST-0312 is designed to address this unmet need by inducing TLS and reshaping anti-tumor immunity.”

Mestag Therapeutics is developing therapies based on fibroblast immunology, targeting interactions within the tumour microenvironment and inflammatory disease pathways.