Restart of Phase 2-enabling toxicology programme

Sareum Holdings PLC

("Sareum" or the "Company")

Restart of Phase 2-enabling toxicology programme for SDC-1801

Cambridge, UK, 17 February 2026 - Sareum Holdings plc (AIM: SAR), a clinical-stage biotechnology company developing next-generation kinase inhibitors for autoimmune disease and cancer, is pleased to announce that it has restarted the Phase 2-enabling toxicology programme for SDC-1801, a selective TYK2/JAK1 inhibitor being developed as a potential treatment for a range of autoimmune diseases, with an initial focus on psoriasis.

The Company has appointed a leading global contract research organisation (CRO), with extensive experience in long-term toxicology studies to conduct the programme following the discontinuation of a previous study, as announced on 10 October 2025.

Before restarting, the Company completed preliminary pharmacokinetic (PK) work to evaluate tolerability and exposure levels across different formulations allowing selection of a vehicle with some precedence in long-term studies.

The toxicology programme is being conducted using the Company's existing cash resources and toxicology batch of SDC-1801. Completion of this programme, together with ongoing CMC and formulation development activities, will form the Phase 2-enabling regulatory package, positioning the programme for Phase 2 clinical development. The dosing phase of the toxicology studies is expected to complete in mid-2026, with the full Phase 2-enabling package expected to be complete by year-end.

As previously reported, the Phase 1 clinical study of SDC-1801 in healthy volunteers met its primary objectives and characterised a pharmacokinetic profile consistent with once-daily dosing. No safety concerns were identified.

Dr Stephen Parker, Executive Chairman of Sareum, said: "Generating a full Phase 2 enabling toxicology package is an important step forward for SDC-1801. The appointment of an experienced global CRO and the successful completion of the preliminary PK study give us confidence as we advance through this important phase of development. Combined with the strong Phase 1 data, these studies will further support SDC-1801's potential to become a best-in-class, once-daily oral therapy for autoimmune diseases. We look forward to providing further updates as the programme progresses."

- ENDS-

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About Sareum

Sareum (AIM: SAR) is a biotechnology company developing next generation kinase inhibitors for autoimmune disease and cancer.

The Company is focused on developing next generation small molecules which modify the activity of the JAK kinase family and have best-in-class potential. Its lead candidate, SDC-1801, simultaneously inhibits TYK2 and JAK1. SDC-1801 is a potential treatment for a range of autoimmune diseases, with a planned initial focus on psoriasis.

Sareum is also developing SDC-1802, a TYK2/JAK1 inhibitor with a potential application for certain haematological cancers and has recently initiated a preclinical programme to develop TYK2/JAK1 inhibitors for neuroinflammatory diseases such as multiple sclerosis and Parkinson's disease

The Company has recently acquired the license for SRA737, a clinical-stage Checkpoint kinase 1 inhibitor that targets cancer cell replication and DNA damage repair mechanisms.

Sareum Holdings plc is based in Cambridge, UK, and is quoted on the AIM market of the London Stock Exchange, trading under the ticker SAR. For further information, please visit the Company's website at www.sareum.com