Dear Shareholders,

I am pleased to report that we have completed dosing in the Phase 2-enabling toxicology programme for SDC-1801, our selective oral TYK2/JAK1 inhibitor for autoimmune diseases. Following the restart of the programme in February this year, dosing has been completed in line with our expectations, keeping us firmly on track towards our Phase 2-enabling milestones.

This is a significant step forward for the programme and we are now awaiting the analysis of the resulting data and progressing the necessary chemistry, manufacturing and controls (CMC) and formulation development activities, all funded from our existing cash resources. Our focus is on completing the full Phase 2-enabling regulatory package by the fourth quarter of this year which will position SDC-1801 for Phase 2 clinical development.

This progress builds on the strong foundation established by the Phase 1 clinical trial, the full dataset of which was published last month in the British Journal of Clinical Pharmacology. That publication confirmed a favourable safety and tolerability profile across all doses tested, alongside a pharmacokinetic profile supportive of once-daily dosing and sustained TYK2/JAK1 target engagement. Taken together with the completion of dosing in the toxicology programme, we continue to build the body of evidence that underpins our confidence in SDC-1801’s potential as a differentiated therapy for patients with autoimmune diseases.

Earlier in the month, our co-founder and Chief Scientific Officer, Dr John Reader, discussed the Phase 1 publication in more detail in an interview with Edison Group, explaining why we believe the results compare favourably with brepocitinib, the leading dual TYK2/JAK1 inhibitor in development. Dr Reader also previewed our preparations for Phase 2, including the toxicology and formulation work referenced above, and discussed the wider commercial opportunity for SDC-1801 across autoimmune diseases and our partnering strategy. The interview is available here.

Following brepocitinib’s positive late-stage clinical data on dermatomyositis, analysts have set ambitious sales expectations of up to $2.7 billion in peak global revenues by 2039.[1] This provides some sense of the scale of commercial opportunity that analysts attribute to this class of dual TYK2/JAK1 inhibitors. Combined with an FDA decision on brepocitinib due under its Q3 2026 PDUFA date, this reinforces why we see such a compelling opportunity for a differentiated, well-tolerated molecule in the same mechanistic class.

As we move further into the second half of the year, our priority remains clear, completing the Phase 2-enabling regulatory package for SDC-1801 and to keep advancing partnering discussions across the wider portfolio. With this dosing completion milestone achieved on schedule, we remain confident in our ability to deliver against our stated goals.

Thank you for your continued support as we steadily progress activity across our pipeline.

Stephen Parker

Executive Chairman

Sareum Holdings plc

[1] Analysts double sales forecasts for Roivant’s brepocitinib after trial success, S&P Global, 24 September 2025, https://www.spglobal.com/market-intelligence/en/news-insights/research/2025/09/analysts-double-sales-forecasts-for-roivants-brepocitinib-after-trial-success