SINOMAB BIO-B (03681) has announced that its SM17 drug candidate has achieved positive topline results in a Phase 1 bridging study in China evaluating a route of administration conversion. The first group of healthy participants received a subcutaneous injection of SM17 on October 14, 2025, and all follow-up visits for the total of 30 healthy participants were completed in February 2026.

This bridging trial was a randomized, double-blind, placebo-controlled study designed to assess the safety, tolerability, and pharmacokinetic profile of subcutaneously administered SM17, and to explore its bioavailability in humans via this route. A total of 30 healthy participants were enrolled and randomly assigned to receive single ascending doses of subcutaneous SM17, which were compared with intravenous administration of SM17 and with a placebo.

The primary endpoints were the tolerability and safety of SM17, measured by the incidence of treatment-emergent adverse events and serious adverse events, changes in vital signs and laboratory tests, as well as absolute bioavailability. Secondary endpoints included pharmacokinetic parameters, bioavailability, and immunogenicity.

The study results were as follows:

**Safety and Tolerability:** The incidence of treatment-emergent adverse events was similar across all study groups and did not indicate any dose-related safety risks. No serious adverse events were reported in any group. Importantly, all treatment-emergent adverse events in the subcutaneous injection group were of Grade 1 or 2 severity, with no Grade 3 or higher events considered related to the study drug. No adverse events led to study discontinuation, and no clinically relevant findings were observed in vital signs, laboratory parameters, or electrocardiograms. Only one injection site reaction was reported, a Grade 1 rash that resolved on its own within one hour.

**Pharmacokinetics and Bioavailability:** The pharmacokinetic profile of the subcutaneous formulation was in line with expectations. Subcutaneous administration resulted in a prolonged absorption phase, while the terminal half-life was similar between the intravenous and subcutaneous routes. Within the tested subcutaneous dose range, exposure (maximum concentration and area under the curve) increased in an approximately dose-proportional manner. The absolute bioavailability of the subcutaneous formulation, calculated relative to a potential effective intravenous dose, was robust and competitive.

**Immunogenicity:** Although a low percentage of anti-drug antibody positivity was detected, these responses were considered non-neutralizing and had no detectable impact on safety or pharmacokinetic parameters. Therefore, the subcutaneous formulation did not demonstrate clinically significant immunogenicity.

These encouraging results are consistent with previously released data from healthy participants and partial data from a proof-of-concept study of intravenous SM17 in atopic dermatitis (AD), which demonstrated a clear safety profile and compelling efficacy. The successful completion of this bridging study supports the continued development of the more convenient subcutaneous formulation, which has the potential to improve patient experience and expand treatment options for inflammatory diseases.

SM17 is a novel, first-in-class humanized IgG4-k monoclonal antibody designed to modulate type 2 inflammation by targeting the interleukin-25 (IL-25) receptor, a core "alarmin" molecule in type 2 immunity. By binding to the IL-25 receptor (IL17RB) on type 2 innate lymphoid cells (ILC2s) and Th2 cells, SM17 inhibits IL-25-mediated signaling and downregulates downstream inflammatory cytokines, including IL-4, IL-5, and IL-13. IL-25 is a key cytokine classified as an "alarmin," and research shows it is involved in the pathogenesis of various inflammatory and immune diseases, such as asthma, AD, and inflammatory bowel disease (IBD).

Despite advances in targeted therapies, these chronic inflammatory and immune-mediated diseases are still associated with a significant burden, including persistent symptoms, progressive tissue damage, and severely impaired quality of life. While current treatments are effective for many patients, they are often limited by safety concerns, suboptimal adherence, and a failure to achieve sustained remission in some individuals. These unmet needs highlight the persistent demand for novel treatment options with improved convenience, a favorable safety profile, and differentiated efficacy.

The company previously conducted a Phase 1 first-in-human clinical trial in the United States to evaluate the safety and tolerability of SM17 in healthy participants. The clinical report received in the first quarter of 2024 showed that SM17 had a favorable safety profile, with no drug-related serious adverse events reported. On April 7, 2025, the company announced positive primary results from a proof-of-concept Phase 1b clinical trial evaluating the preliminary efficacy of SM17 in Chinese patients with moderate-to-severe AD. In February 2026, an Investigational New Drug application for a clinical study of SM17 in IBD patients was approved by China's National Medical Products Administration.

The company believes that targeting the IL-25 receptor, an upstream node, enables broad-spectrum immunomodulation with the potential to simultaneously regulate both Th2 and Th17 pathways. This dual mechanism of action differentiates SM17 as a candidate drug applicable to a range of inflammatory and immune disease indications beyond AD, including asthma, IBD, chronic rhinosinusitis with nasal polyps, and idiopathic pulmonary fibrosis, while maintaining a favorable safety profile.

The company anticipates initiating a Phase 2 clinical study for AD in China as early as mid-2026.