• Disease modifying mechanism of action: short treatment course results in significant and durable clinical response in psoriasis patients
• si-544 is the first highly potent and selective Kv1.3 blocker to safely achieve patient plasma levels suitable for high target engagement
• Excellent safety and tolerability consistent with prior clinical experience; no dose-limiting toxicities and no serious safety signals observed
• Full immunocompetence maintained in si-544 treated patients; no immunosuppression

San Diego, CA, USA, and Munich, Germany – October 21, 2025 – selectION, Inc. (“selectION” or the “Company”), a clinical-stage biopharmaceutical company developing novel treatments for T cell-mediated autoimmune diseases, today announced  the successful completion of its phase 1b proof-of-concept trial evaluating si-544, a first-in-class Kv1.3 blocker in patients diagnosed with psoriasis vulgaris.

“These results mark a significant milestone, as si-544 has, for the first time, clinically confirmed the long hypothesized and remarkable therapeutic potential of Kv1.3 in T cell autoimmunity,” said Antonius Schuh, Ph.D., CEO of selectION. “This trial clinically validates Kv1.3 dependency as an ideal clinical entry point to disrupt the chronic activation of pathogenic, autoreactive T cells. si-544 has the potential to become a disease modifying and safe treatment option, offering meaningful and durable reduction of disease burden across a broad spectrum of T cell-mediated autoimmune diseases.”

Novel Mechanism Targets Root Cause of Autoimmunity

The voltage gated potassium ion channel Kv1.3 is a well-researched clinical target in autoimmunity. Dependency on Kv1.3 is a distinct feature of autoreactive T cells. Selective blocking of Kv1.3 irreversibly disrupts the pathogenic activity of chronically activated, autoreactive T cell clones, while fully maintaining the patient’s protective immunocompetence. 

This unique mechanism supports the hypothesis that short treatment cycles with
si-544, a highly selective and potent Kv1.3 blocker, should induce a durable, disease-modifying, effect in a wide range of autoimmune conditions, including psoriasis, atopic dermatitis, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and many others. Now this hypothesis has been confirmed in a clinical setting, using si-544 in psoriasis vulgaris, an excellent clinical surrogate for T cell autoimmunity.

Trial Design and Outcomes

This Phase 1b study was a randomized, double-blind, placebo-controlled proof-of-concept trial in patients diagnosed with mild-to-severe psoriasis vulgaris. Patients received 2 subcutaneous injections of si-544 or placebo (ratio 3:1) per week over a period of 4 weeks and were monitored for a period of 12 weeks post drug washout.

The trial enrolled 45 patients across four clinical sites in Germany. Its primary objective was to evaluate the safety and tolerability of si-544, including monitoring adverse events, laboratory and ECG findings, and vital signs. Secondary endpoints included pharmacokinetics, pharmacodynamics, immunogenicity, and efficacy across key dermatologic measures, including psoriasis area and severity index (PASI), physician’s global assessment (PGA), and body surface area (BSA). Further details are available at ClinicalTrials.gov (NCT06191042).

Key findings:

• si-544 was well tolerated with no related serious adverse effects, dose-limiting toxicities, or safety signals observed
• A short 4-week treatment cycle resulted in significant clinical improvement as measured by change in Psoriasis Activity and Severity Index (PASI)
• Signs of clinical efficacy were seen as early as week 2 of the treatment period
• Disease stabilization and continued healing were observed over the entire
  12-week monitoring period, post drug washout
• Patients treated with si-544 maintained full immunocompetence

“This Phase 1b study confirms our central development hypothesis that si-544, a potent and highly selective Kv1.3 blocker, can safely achieve specific disruption of disease-driving autoreactive T cells without compromising the patient’s immune competence,” said Andreas Klostermann, Ph.D., CSO and scientific founder of selectION. “The observed durable clinical improvement and continued healing beyond drug exposure proves the disease-modifying quality of clinical response. The results observed in psoriasis echo the results from our first-in-human study in atopic dermatitis, and we are now focused on advancing the clinical development of si-544 across multiple autoimmune indications.”

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About si-544

si-544, the Company´s investigational drug, blocks Kv1.3, a specific ion channel critical for the maintained activation and proliferation of chronically activated, autoreactive effector memory T cells, with high potency and what the Company believes to be class leading selectivity. Chronically activated autoreactive effector memory T cells lie at the root of many autoimmune diseases, such as psoriasis, atopic dermatitis, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and many others.

si-544 is a potent immuno-selective agent addressing a significant unmet medical need by functionally inhibiting and eliminating disease-specific, chronically activated effector memory T cells while maintaining full immunocompetence.

si-544 has demonstrated an excellent safety and tolerability profile in two completed Phase 1b clinical trials in atopic dermatitis patients and, more recently, in psoriasis vulgaris. An initial efficacy signal has been observed in the atopic dermatitis data set. Clinical proof of concept has been achieved in the larger psoriasis vulgaris trial.

About selectION, Inc.

selectION, Inc. is a clinical-stage biopharmaceutical company developing novel peptide therapies for autoimmune diseases and select cancer indications by targeting autoreactive, chronically activated T cells.

The Company has established an efficient, unique technology platform to develop potent and highly selective peptide blockers for ion channels involved in various diseases. The platform enables systematically optimized target selectivity, providing the opportunity to develop drugs with significantly improved efficacy and safety profiles.

For further information, please visit https://selectiontherapeutics.com/

Forward Looking Statements

This press release includes forward-looking statements related to selectION, Inc. (the “Company”), including statements regarding the prospects of si-544 and the value of the phase 1b trial evaluating si-544 in patients with atopic dermatitis (the “Trial”). These forward-looking statements are based upon information that is currently available to the Company and its current expectations, speak only as of the date hereof, and are subject to risks and uncertainties that could cause actual results to differ materially from those projected, including risks that the Company does not realize the expected benefits of si-544 or the Trial; risks that the results of the Trial may not be accurate; risks that prior clinical trial results may not be repeated; regulatory risks, and general economic and market factors. Any of these may cause the Company’s actual results, performance, or achievements to differ materially and adversely from those anticipated or implied by the Company’s forward-looking statements. The Company expressly disclaims any obligation, except as required by law, or undertaking to update or revise any such forward-looking statements.

Contacts

Media Contact:                                         Investor Contact:
akampion                                                  selectION, Inc.
Dr. Ludger Wess / Ines-Regina Buth        Steve Zaniboni
Managing Partners                                   Chief Financial Officer
info@akampion.com                                 szaniboni@selectiontherapeutics.com
T: +49 40 88 16 59 64 /                             T: +1 858 967 8014
T: +49 30 23 63 27 68