Update on TYK2/JAK1 and SRA737 Programmes

Cambridge, UK, 28 April 2025 - Sareum Holdings plc (AIM: SAR), a clinical-stage biotechnology company developing next-generation kinase inhibitors for autoimmune disease and cancer, today provides an update on its TYK2/JAK1 and SRA737 programmes.

"Brain-penetrant" TYK2 inhibitors

Sareum has recently conducted targeted preclinical studies to evaluate the potential of its TYK2/JAK1 compounds in central nervous system ("CNS") indications. This work reflects growing scientific and commercial interest in the role of TYK2 inhibition in neuroinflammatory diseases such as Multiple Sclerosis, Parkinson's Disease, and Alzheimer's Disease - all areas with significant unmet medical need.

The study involved six compounds from Sareum's proprietary Sareum Kinase Inhibitor Library ("SKIL") platform, tested in preclinical models to assess their ability to cross the blood-brain barrier ("BBB") - a key requirement for CNS drug development. Three compounds demonstrated meaningful BBB penetration, with one showing strong levels of free drug in the brain.

While further optimisation is still required, the results support the potential for Sareum's TYK2/JAK1 chemistry to be applied to CNS indications.

The Company is assessing the potential next steps for these compounds, including whether to progress one or more into preclinical development.

SRA737

SRA737 is a clinical-stage oral, selective Checkpoint kinase 1 inhibitor that targets cancer cell replication and DNA damage repair mechanisms. Sareum has now received the full clinical dataset for SRA737, following the termination of its licensing agreement with a US-based partner in December 2024. This includes the Trial Master File and all associated documentation - these data amount to approximately 235Gb. With full operational control attained, Sareum is now positioned to conduct a comprehensive review of the programme's potential.

Strategic options under consideration include re-licensing the asset or advancing it in-house with or without a partner. The former licensee has expressed continued confidence in SRA737's clinical profile, which Sareum believes will support potential future partnering discussions. A decision on the optimal path forward will be made in the context of broader pipeline priorities including the opportunity to enhance shareholder value through partnering or re-licensing.

Ongoing development of SDC-1801 and SDC-1802

Sareum continues to advance its lead autoimmune and oncology programmes:

• SDC-1801, a selective TYK2/JAK1 inhibitor for autoimmune diseases, has completed Phase I clinical development, demonstrating a favourable safety and pharmacokinetic profile. Comprehensive data from the Phase I study has now been published on the Australian New Zealand Clinical Trials Registry (ANZCTR). A 16-week toxicology study to support longer-term dosing is expected to commence in May 2025, with completion anticipated in Q4.
• SDC-1802, a TYK2/JAK1 inhibitor for immuno-oncology applications, remains in preclinical development. Sareum is continuing translational work to define optimal cancer indications and patient populations prior to advancing SDC-1802 toward first-in-human studies.

These programmes represent Sareum's most advanced assets and form the foundation of its near-term clinical strategy.

Dr Stephen Parker, Executive Chairman of Sareum, commented:

"Our recent preclinical findings show that our TYK2/JAK1 inhibitors have significant potential to be developed for CNS diseases - a strategically important area with high unmet need. Regaining full control of SRA737 also provides us with the flexibility to determine the best route forward based on robust data. Alongside our advancing clinical programmes, we are building optionality and long-term value across the pipeline."