Publication of Phase 1 data on SDC-1801 in BJCP

• SDC-1801 demonstrated a well-tolerated safety profile with clear TYK2/JAK1 target engagement and reinforces the Company's confidence in SDC-1801's potential as a best-in-class, once-daily oral therapy for autoimmune diseases
• PK/PD data from the Phase 1 trial informed the ongoing toxicology programme with a complete Phase 2‑enabling regulatory package anticipated by year-end

Cambridge, UK, 22 June 2026 - Sareum Holdings plc (AIM: SAR), a clinical-stage biotechnology company developing next-generation kinase inhibitors for autoimmune disease and cancer, announces the publication of the full dataset from the Phase 1 clinical trial of its lead asset, SDC-1801, in the peer-reviewed British Journal of Clinical Pharmacology.

The paper, titled 'First-in-human, phase I, randomised, safety, pharmacokinetic, food-effect, and pharmacodynamic study of a tyrosine kinase 2/janus kinase 1 inhibitor, SDC-1801', presents the findings from a randomised, double-blind, placebo-controlled study conducted in 95 healthy adult participants. The paper confirms the results previously disclosed by the Company with comprehensive clinical and pharmacological characterisation of SDC-1801.

Key results include:

• SDC-1801 was well tolerated across all doses tested, from 5-150 mg, with no deaths and no treatment-related serious adverse events
• Pharmacokinetics (PK) analysis demonstrated a half-life of approximately 15-27 hours, supporting once or twice-daily oral dosing
• Computational PK modelling demonstrated that SDC-1801 at 70mg twice-daily achieved blood exposure levels comparable to brepocitinib, a clinically validated dual TYK2/JAK1 inhibitor, at 100mg once-daily without the side effects observed with brepocitinib at this exposure level
• Pharmacodynamic biomarker analysis provided evidence of sustained target engagement of both TYK2 and JAK1

The PK data from the Phase 1 trial informed the ongoing Phase 2-enabling formulation programme to optimise the capsule, aimed at improving drug release at higher doses and reducing the capsule burden in future clinical trials. Formulation optimisation and the ongoing toxicology programme is being undertaken using the Company's existing cash resources, with a complete Phase 2‑enabling regulatory package anticipated by year-end.

Dr John Reader, Chief Scientific Officer of Sareum, commented: "The publication of the Phase 1 data in the British Journal of Clinical Pharmacology provides independent scientific validation of the strong clinical profile of SDC-1801, including good tolerability, a pharmacokinetic profile consistent with once-daily oral dosing, and clear evidence of target engagement through dose-dependent reductions in established inflammatory biomarkers."

"These biomarker findings are predictive of SDC-1801's potential efficacy in patients and reinforce our confidence in SDC-1801's potential as a differentiated therapy for autoimmune diseases. With the Phase 2-enabling toxicology programme well underway, we are focused on translating this clinical evidence into the next stage of development."

The full paper is available via the British Journal of Clinical Pharmacology here: https://bpspubs.onlinelibrary.wiley.com/doi/10.1002/bcp.70642