The blowup in phase II with Aclaris Pharmaceuticals Inc.’s oral MK2 inhibitor zunsemetinib (ATI-450) for moderate to severe rheumatoid arthritis (RA) sent shares (NASDAQ:ACRS) into a tailspin and sparked Wall Street speculation about the firm’s other mid-stage prospect. Wayne, Pa.-based Aclaris’ stock ended Nov. 13 at 64 cents, down $4.11, or 86%, after investors learned that ATI-450 missed the study’s primary and secondary endpoints. Development of the candidate, which was also under phase IIa investigation in psoriatic arthritis, will be stopped.