Latest Izokibep Trial for PsA Shows Promise But Misses on Enthesitis
FROM EULAR 2024
VIENNA — The investigational interleukin (IL)-17 inhibitor izokibep hit its mark when it came to improving overall disease activity in people with active psoriatic arthritis (PsA) in a phase 2b/3 trial, but it was no better than placebo at reducing inflammation of the entheses.
This apparent and unexpected lack of effect in the entheses was a key talking point after Philip J. Mease, MD, presented the late-breaking trial findings at the annual European Congress of Rheumatology.
At just 18.6 kilodaltons in size, izokibep is just “one tenth the size of a standard monoclonal antibody” and is classed as a small protein therapeutic, Dr. Mease said. It has a “very tight” binding affinity for IL-17A, and because it also binds to albumin, it has a prolonged half-life compared with other IL-17 inhibitors. Potentially, it should be able to “penetrate into difficult areas,” such as the entheses, he said.
Prespecified Enthesitis Analysis
However, results of a prespecified secondary analysis conducted in 209 of the 343 trial participants who had received treatment showed no significant difference in the proportions with enthesis resolution at 16 weeks, defined as a Leeds Enthesitis Index (LEI) of 0.
Comparing two dosing regimens of izokibep 160 mg once weekly (QW) vs every other week (Q2W) with placebo, enthesitis resolution was seen in 45%, 56%, and 47%, respectively, of patients.
The LEI is “sometimes subject to problems with evaluation because of placebo response, which is what we see here,” noted Dr. Mease, director of rheumatology research at the Providence Swedish Medical Center and a rheumatology professor at the University of Washington School of Medicine in Seattle.
An exploratory analysis showed that there was a better response for izokibep vs placebo if the analysis included only patients with higher LEI scores at baseline, at 8.0% (n = 12) for placebo, 22.0% (n = 9) for izokibep 160 mg QW, and 50.0% (n = 12) for izokibep 160 mg Q2W.
Main Efficacy Data
The primary endpoint for the trial was the proportion of patients who had 50% improvement in American College of Rheumatology response criteria (ACR50) at 16 weeks. This showed a clear advantage for treatment with izokibep 160 QW and Q2W compared with placebo, with a respective 40%, 43%, and 15% of patients meeting this endpoint.
Corresponding ACR20 response rates were 59%, 64%, and 35%, respectively; ACR70 response rates were a respective 25%, 23%, and 5%.
In addition to ACR70, izokibep 160 QW and Q2W met a number of other “high hurdle” efficacy endpoints better than did placebo, Dr. Mease reported. A 90% reduction from baseline in the Psoriasis Area and Severity Index (PASI90) was achieved by a respective 64%, 58%, and 12% of patients, and a 100% reduction in this index (PASI100) was achieved by a respective 51%, 47%, and 12%. And 41%, 42%, and 14% of patients, respectively, met the criteria for minimal disease activity.
