Dear Shareholders,
In this quieter summer month, I wanted to focus on SDC-1801, our selective oral TYK2/JAK1 inhibitor, specifically on a single measure that we have highlighted in recent presentations: Psoriasis Area and Severity Index (PASI) 90. For readers less familiar with dermatology, PASI 90 is the “gold standard” clinical benchmark in psoriasis, representing a 90% improvement in a patient’s skin symptoms. It is the bar that regulators and physicians use as a sign of therapeutic success.
The current psoriasis treatment landscape provides useful context for this measure. Injectable biologics such as AbbVie’s IL-23 antibody, Skyrizi® set a high bar, with around 75% of patients achieving PASI 90 after 16 weeks, though this requires an injectable dosing regimen.[1] Oral IL-23 inhibitors, such as Johnson & Johnson’s Icotyde™, offer the convenience of a tablet and achieve a 65% PASI 90 response by 24 weeks.[2] Single TYK2 inhibitors, including Bristol Myers Squibb’s Sotyktu® and Takeda’s zasocitinib, sit in a similar range to the oral IL-23 class, with PASI 90 responses of 42% and 66% respectively by 24 weeks, but have generally been less effective than injectable biologics.[3],[4]
This is where dual TYK2/JAK1 inhibition, the mechanism behind both SDC-1801 and Priovant’s brepocitinib, becomes particularly interesting. Phase Ib clinical data for brepocitinib at a 100mg once-daily dose showed that around 90% of psoriasis patients achieved PASI 90 within four weeks, putting it ahead of injectable biologics on speed and depth of effect. However, this dose has also been associated with dose-limiting toxicities meaning that brepocitinib can only be administered at much lower doses, typically 30-45mg per day, at which significantly fewer patients achieve PASI 90; 52% after 12 weeks.[5],[6]
As we announced on 22 June 2026, our Phase 1 data showed that SDC-1801 has the potential to achieve a systemic drug exposure (measured as AuC) comparable to brepocitinib’s 100mg dose, while remaining well tolerated. SDC-1801 also demonstrated similar potency to brepocitinib in whole blood cytokine assays, a laboratory measure of how strongly a drug dampens the inflammatory signalling pathways implicated in autoimmune diseases such as psoriasis. Taken together, this gives us confidence that SDC-1801 has the potential to achieve a comparable depth of clinical response to 100mg brepocitinib, while minimising dose-limiting toxicities. While this remains a hypothesis grounded in preclinical and Phase 1 pharmacokinetic data rather than clinical efficacy demonstrated in patients, we are striving to complete the Phase-2 enabling regulatory package by Q4 2026 and position SDC-1801 for Phase 2 clinical development.
Following the completion of dosing in our toxicology programme, announced in July, the “live-phase” has concluded and we are now working through data analysis alongside the necessary chemistry, manufacturing and controls (CMC) and formulation activities. Psoriasis remains our planned initial indication, and the differentiated safety and exposure profile described above underpins our continued conviction in SDC-1801’s potential as a well-tolerated, once-daily therapy in a validated and commercially attractive drug class.
As always, we are grateful for your continued support and interest in Sareum, and we look forward to updating you further as our Phase 2-enabling work progresses.
Stephen Parker
Executive Chairman
Sareum Holdings plc
[1] Gordon KB, Strober B, Lebwohl M, et al. Efficacy and safety of risankizumab in moderate-to-severe plaque psoriasis (UltIMMa-1 and UltIMMa-2): results from two double-blind, randomised, placebo-controlled and ustekinumab-controlled phase 3 trials. Lancet. 2018;392(10148):650-661. See also https://www.skyrizihcp.com/dermatology/psoriasis-efficacy
[2] https://www.jnj.com/media-center/press-releases/icotrokinra-results-show-potential-to-set-a-new-standard-of-treatment-in-plaque-psoriasis
[3] Armstrong et al. J Am Acad Dermatol, January 2023, Pg 29. https://doi.org/10.1016/j.jaad.2022.07.002
[4] American Academy of Dermatology Annual Meeting; March 27-31, 2026; Denver, CO: Gooderham M. Once-daily oral zasocitinib demonstrates rapid and reproducible skin clearance with a consistent safety profile in moderate-to-severe plaque psoriasis: results from two randomized phase 3 trials (LATITUDE-PsO-3001 and 3002). See https://www.takeda.com/newsroom/newsreleases/2026/zasocitinib-phase3-clinical-trial-results/
[5] Banfield et al. The Journal of Clinical Pharmacology, 2017, 00(0) 1 – 14 https://DOI: 10.1002/jcph.1046
[6] clinicaltrials.gov/ct2/show/results/NCT02969018