Hangzhou, China; Shanghai, China; and Boston, Massachusetts, USA, October 27, 2026
Lynk Pharmaceuticals Co., Ltd. has announced positive long-term Phase III clinical results for zemprocitinib, an investigational, selective, second-generation oral Janus kinase 1 (JAK1) inhibitor, in adults with moderate-to-severe active rheumatoid arthritis (RA). The treatment is being evaluated in patients who experienced an inadequate response or intolerance to biologic disease-modifying antirheumatic drugs (bDMARDs). The results showed sustained clinical responses, improvements in disease activity, and better physical function through Week 76 in the pivotal study. The Phase III trial met its primary endpoint and key secondary endpoints at Week 24, with statistically significant improvements compared with placebo. The findings provide additional long-term evidence supporting the continued development of zemprocitinib for people whose rheumatoid arthritis remains inadequately controlled by existing biologic therapies. However, zemprocitinib remains investigational for rheumatoid arthritis, and these findings do not establish regulatory approval for this indication.
Phase III Trial Shows Sustained Clinical Responses
The randomized, double-blind, placebo-controlled Phase III study enrolled 430 patients with moderate-to-severe active rheumatoid arthritis who had experienced inadequate response or intolerance to previous bDMARD treatment. Of these participants, 429 received at least one dose of study treatment. During the initial 24-week period, patients received either zemprocitinib at 12 mg twice daily or placebo. After Week 24, participants continued or transitioned to active treatment, and researchers assessed efficacy and safety through Week 76. The primary endpoint was the proportion of patients achieving an ACR20 response, which represents an improvement of at least 20% in American College of Rheumatology-defined disease activity measures. The study met this endpoint and key secondary endpoints at Week 24, with results significantly favoring zemprocitinib over placebo (p less than 0.0001). Long-term findings showed that among patients receiving continuous zemprocitinib treatment, ACR20 response rates reached 93.0% at Week 52 and remained at 91.8% at Week 76. ACR50 responses were 79.9% and 80.5%, respectively, while ACR70 responses increased from 52.5% at Week 52 to 62.4% at Week 76. These measures indicate different levels of improvement in rheumatoid arthritis symptoms and disease activity.
Improvements in Disease Activity and Physical Function
Beyond response rates, zemprocitinib demonstrated sustained improvements across several measures of rheumatoid arthritis activity and patient function. Among participants receiving continuous treatment, 85.5% achieved low disease activity at Week 52, based on a DAS28-CRP score of 3.2 or lower. At Week 76, 81.4% continued to meet this threshold. Using the Clinical Disease Activity Index (CDAI), low disease activity was reported in 81.5% of patients at Week 52 and 81.0% at Week 76. Improvements were also observed in physical function, an important treatment goal for people living with chronic inflammatory joint disease. Based on the Health Assessment Questionnaire–Disability Index (HAQ-DI), 84.5% of patients at Week 52 and 86.7% at Week 76 achieved an improvement of at least 0.22 points from baseline. Patients who initially received placebo and switched to zemprocitinib at Week 24 also demonstrated clinical responses by Week 76, including ACR20, ACR50 and ACR70 response rates of 92.0%, 77.6% and 55.1%, respectively. These findings suggest that improvements were observed following treatment initiation in both groups, although long-term results should be interpreted in the context of the study design and treatment changes after Week 24.
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Long-Term Safety Supports Further Development
Lynk Pharmaceuticals reported that the safety profile observed through Week 76 remained consistent with earlier findings, with no new safety signals identified during long-term treatment. During the initial 24-week placebo-controlled period, the company described zemprocitinib’s safety profile as generally comparable to placebo. Long-term laboratory assessments included observations involving hemoglobin levels and liver enzymes, including alanine aminotransferase (ALT) and aspartate aminotransferase (AST). The company reported an increase in mean hemoglobin levels, rare Grade 3 or 4 ALT elevations, rare Grade 3 AST elevations, and no Grade 4 AST elevations. These observations add to the available safety information but do not eliminate the need for continued monitoring in future studies and clinical use, if approved. Zemprocitinib is also being developed for other inflammatory and autoimmune conditions, including atopic dermatitis and ankylosing spondylitis. Lynk has reported that a new drug application for atopic dermatitis has been accepted for review by China’s National Medical Products Administration. Simcere Pharmaceutical Group is the company’s commercialization partner for zemprocitinib in Greater China. The latest rheumatoid arthritis findings represent a further development milestone, while additional regulatory review and evidence will be necessary before the drug can become an approved treatment for this condition.
Source: Lynk Pharmaceuticals press release
