P687 Early and sustained improvement in stool frequency and rectal bleeding following 52 weeks of mirikizumab treatment

Abstract Background Interleukin (IL)-23 is a key cytokine in inflammatory bowel disease pathogenesis. Mirikizumab (miri), a p19-directed IL-23 antibody, demonstrated efficacy and was well-tolerated in patients with moderate-to-severely active ulcerative colitis (UC) during 52 weeks of a Phase 2 randomised clinical trial (AMAC, NCT02589665). The effects of miri on stool frequency (SF) and rectal bleeding (RB) through Week 52 are reported. Methods Patients (Mayo score 6–12 with endoscopic subscore [ES] ≥2) were randomised 1:1:1:1 to receive intravenous (IV) placebo (n = 63), miri 50 mg (n = 63) or 200 mg (n = 62) with possibility of exposure-based (EB) dose increases, or fixed miri 600 mg (n = 61) every 4 weeks (Q4W). Responders to miri at Week 12 (9-point Mayo score decrease ≥2 points and ≥35% change from baseline, with RB=0 or 1 or decrease ≥1) were re-randomised 1:1 into a double-blind maintenance period to receive miri 200 mg subcutaneously (SC) Q4W (n = 47) or every 12 weeks (Q12W; n = 46), and were treated through Week 52. Patients reported UC symptoms, including SF and RB, via a daily diary. Changes from baseline in average Mayo SF and RB subscores at Weeks 2, 4, and 12 were analysed using a mixed model repeated-measures method to account for missingness and baseline characteristics. Results Significant improvement in SF was observed as early as Week 2 in the miri 600 mg Q4W group and as early as Week 4 in the miri 200 mg Q4W group (Figure). Similarly, significant improvement in RB was observed as early as Week 2 in both the miri 200 mg Q4W and 600 mg Q4W groups. Patients who received miri 200 mg Q4W or 600 mg Q4W had a significantly greater reduction in both SF and RB compared with placebo at Week 12 (all p < 0.001) (Figure). Patients who achieved clinical response at Week 12 and were treated with miri 200 mg SC Q4W or SC Q12W maintained a low average SF and RB score at Week 52. Conclusion Significant improvements in SF and RB occurred as early as Week 2 of induction treatment and continued to improve during maintenance treatment with mirikizumab. These data demonstrate the early efficacy and longer-term effects of an IL-23p19 antibody on these patient-reported outcomes.