LONDON — The first data to be reported from the phase 2 S-OLARIS trial of sonelokimab indicate that the novel interleukin (IL)-17A/F-inhibiting nanobody could be a promising future treatment for axial spondyloarthritis (axSpA).

Clinical responses were seen as early as 4 weeks of treatment, with 77% of the 26 patients studied achieving a 40% improvement in Assessment in SpondyloArthritis international Society (ASAS) response criteria, 89% achieving 20% improvement in ASAS response criteria, and 27% achieving an ASAS Partial Response. By week 12, a respective 81%, 92%, and 54% of the study’s participants had met these targets.

There was also rapid improvement in the mean Ankylosing Spondylitis Disease Activity Score (ASDAS), which fell from a baseline of 3.5 to 1.6 at 4 weeks and 1.4 at 12 weeks. Meanwhile, imaging results showed significant reductions in sacroiliac joint (SIJ) inflammation and inflammatory lesion burden.

“This is indeed a very encouraging proof-of-concept trial for the potential of sonelokimab in [axSpA],” said the presenting study investigator Xenofon Baraliakos, MD, PhD, president of the European Alliance of Associations for Rheumatology (EULAR); head of rheumatology at Rheumazentrum Ruhrgebiet in Herne, Germany; and professor of internal medicine and rheumatology at Ruhr University Bochum in Bochum, Germany.

György Nagy, MD, PhD, DSc, who later picked the late-breaking abstract as one of his clinical highlights of the EULAR 2026 Annual Meeting, said, “This new nanobody construct seems to work very well.”

Nagy, of Semmelweis University in Budapest, Hungary, also said, “What is important, there were no adverse events related to IBD [inflammatory bowel disease], which is always something that we are worrying about in spondyloarthritis.” There were also no major cardiovascular events, no suicidal ideation and behavior, liver injury, or uveitis, he added.

Nanobody Inhibitor of IL-17A/F

Baraliakos explained that sonelokimab, being just 40 kDa in size, was thought to have an enhanced ability to get into inflamed joint tissue as compared to larger molecule drugs. It binds to IL-17A and IL-17F with a similarly high affinity and has an anti-albumin component that helps to extend its half-life.

A phase 2 trial in psoriatic arthritis had already been completed, he said, and these were the first data from a trial looking at sonelokimab’s potential in axSpA.

S-OLARIS was an open-label, single-arm study that included people with axSpA as defined by ASAS 2009 classification criteria. For inclusion, a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score ≥ 4 despite treatment with nonsteroidal anti-inflammatory drugs was required, and there also had to be evidence of active disease on MRI and fluorine-18-labeled sodium fluoride (¹⁸F-NaF) PET scans. 

All participants were treated with 60 mg sonelokimab, which was given by subcutaneous injection every 2 weeks for the first 8 weeks of the study. The primary efficacy analyses were carried out at week 12, with further follow-up for safety at week 16.

Participants’ mean age was 30.7 years, 85% were men, and their mean time since symptom onset was 8.1 years.

MRI of the SIJ and spine could be performed in all but one of the participants. Findings showed a significant drop from baseline to week 12 in mean Spondyloarthritis Research Consortium of Canada MRI scores of -21.8 points in the SIJ (P < .001) and -3.9 points in the spine (P = .03).

PET imaging of the SIJ, performed in 24 individuals, showed a significant reduction in the uptake of ¹⁸F-NaF, a sign that joint inflammation was again reduced. 

Baraliakos also reported that there was inhibition of bone remodeling activity, adding to the suggestion that sonelokimab had “rapid disease-modifying effects” within the joints.

Disease-Modifying Effects

Most participants achieved inactive or low disease activity. At baseline, 46% of participants had an ASDAS > 3.5, indicating very high disease activity, and the remaining 54% had an ASDAS of 2.1-3.5, indicating high disease activity.

However, only 4 weeks into treatment, just 4% had an ASDAS > 3.5 and 15% had an ASDAS of 2.1-3.5. Another 35% had an ASDAS of 1.3 to < 2.1, indicating low disease activity, and 46% had an ASDAS < 1.3, suggesting inactive disease. By week 12, the percentages of patients in these categories were similar (4%, 15%, 39%, and 42%, respectively).

Patient-reported symptoms and function improved, as indicated by lowered total BASDAI scores over time, and in individual components of the score, such as back pain, fatigue, and morning stiffness.

Treatment-emergent adverse events (TEAEs) occurred in 14 (54%) of participants. Baraliakos said, however, that all adverse events were mild or moderate, and few were treatment related. The most frequent TEAEs were influenza in three individuals, fatigue in two, and increased blood creatine phosphokinase in two. Oral candidiasis was reported in one participant.

The study was funded by MoonLake Immunotherapeutics AG. Baraliakos disclosed having ties to multiple pharmaceutical companies, including acting as a paid instructor, speaker, consultant, and investigator for MoonLake Immunotherapeutics AG.

Nagy reported having ties to multiple pharmaceutical companies, including receiving consulting fees from AstraZeneca, Miltenyi, Richter, and Roche; support for attending conferences from AbbVie and Biotest; and honoraria for giving lectures from numerous others that did not include MoonLake Immunotherapeutics AG.

Sara Freeman, BSc, MSc, is a freelance medical journalist based in London, England. She has been reporting for specialist healthcare news organizations for more than 20 years.