Aclaris Therapeutics Inc (NASDAQ:ACRS) shares plunged after the company released topline results from a Phase 2b study of zunsemetinib (ATI-450) in subjects with moderate to severe rheumatoid arthritis.

The study evaluated two doses of zunsemetinib plus methotrexate (MTX) versus placebo plus MTX in patients with moderate to severe RA who have had an inadequate response to MTX alone.

The study enrolled 251 patients across three treatment arms (ATI-450 20mg BID, ATI-450 50mg BID, and Placebo BID).

The primary efficacy endpoint is the proportion of patients achieving an ACR20 response following 12 weeks of treatment. 

Secondary efficacy endpoints included ACR50 response, ACR70 response, DAS28-CRP and other pertinent RA measures.

In the trial, patients administered either the 20mg or 50mg dose did not meet the primary endpoint of ACR20 response or any secondary efficacy endpoints at 12 weeks, including ACR50 response, ACR70 response, and DAS28-CRP.

There was no notable differentiation between zunsemetinib and placebo across any efficacy measures at week 12.

No meaningful safety findings were observed.  

Based on the overall program results, Aclaris will discontinue further development of the ATI-450 program, including halting enrollment of Aclaris' ongoing Phase 2a trial of zunsemetinib in psoriatic arthritis.

Price Action: ACRS shares are down 85.5% at $0.69 on the last check Monday.