All three studies were phase 1, two-arm, randomized, single-dose, participant-blind, parallel design studies in healthy participants. All studies were designed to assess the PK and safety of the original and CF formulations of mirikizumab.

Table 1 summarizes the main elements of the study designs for the three studies, including participant parameters, formulation randomization, and dosing. Study A (I6T-MC-AMBV, ClinicalTrials.gov identifier NCT04548219) was an investigator-blind RBA study for 200 mg mirikizumab which informed the study design for the later BE studies. Study B (I6T-MC-AMBT, ClinicalTrials.gov identifier NCT05515601) and study C (I6T-MC-AMBY, ClinicalTrials.gov identifier NCT05644353) were BE studies for 200 mg and 300 mg mirikizumab, respectively. The 200 mg and 300 mg doses are proposed for UC and CD, respectively. In studies B and C, participants may have had chronic, stable medical conditions which, in the investigator’s opinion, did not pose an increased risk to the participant. Participants were screened for 28 days (study A) or 35 days (studies B and C) prior to day 1 of the study. In all studies, participants completed 4-h post-dose safety assessments on day 1, and returned to the clinical research unit for PK sampling, immunogenicity sampling, and safety assessments at pre-specified times up to 12 weeks post dose. Table S1 (supplementary material) details the components of the CF and original mirikizumab formulations used in the studies.

Exclusion criteria included (a) significant allergies to humanized monoclonal antibodies or mirikizumab, (b) prior or concomitant therapies such as anti-IL-12p40 or anti-IL-23p19 antibody therapy, (c) current enrollment in an incompatible clinical study or prior study participation within the last 30 days or 5 half-lives, whichever is longer, increasing to at least 3 months or 5 half-lives for biologic agents, (d) incompatible diagnostic assessment such as prior severe infections within 12 weeks, and (e) other relevant exclusions such as lactation or pregnancy.

The studies were conducted in accordance with the study protocols and with consensus ethics principles derived from international ethics guidelines, including the Declaration of Helsinki and Council for International Organizations of Medical Sciences International Ethical Guidelines, applicable International Council for Harmonisation Good Clinical Practice Guidelines, and applicable laws and regulations. The study protocols were approved by the institutional review boards before all studies were initiated. Ethical review boards were in place for all studies: the WCG – Midlands Independent Review Board and WCG Independent Review Board were the overall (“master”) ethics committees for study A, and the Salus Institutional Review Board was the overall (“master”) ethics committee for studies B and C. Informed consent forms, required to provide details about why the research was being done and what it would involve, were approved by the respective review boards and provided to participants. Subsequent dated written informed consent was required by each participant before the participant could participate in the study. The informed consent forms also noted that study data which did not directly identify participants could be published.

Table 2 outlines the study objectives and endpoints. Endpoints were identical in all studies.

For continuous data, summary statistics included the arithmetic mean and arithmetic standard deviation (SD). For categorical data, frequency count and percentages were presented. Summary statistics were presented by treatment formulation and injection site. A combination of SAS (version 9.4. or greater; SAS Institute Inc. Cary, NC, USA) and R (version 4.0.0 or greater; R Foundation for Statistical Computing, Vienna, Austria) was used for the statistical analyses.

The PK population consisted of all enrolled participants who received a dose of mirikizumab and who had evaluable PK data. Figure S1 shows that dosing and PK sampling times were the same across all studies. PK samples were collected up to day 85 ± 3 post dose in the absence of early discontinuation.

PK data were subject to data handling considerations. In study A, PK data exceeding the protocol-specified windows were excluded from the mean concentration–time profiles. Positive pre-dose samples and anomalous below the lower limit of quantitation post-dose concentrations were excluded from the PK analysis and mean concentration–time profiles. Study A was a small RBA study with insufficient sample size to achieve BE. Studies B and C were larger studies designed to have approximately 90% power to achieve BE.

Some subjects were excluded from PK statistical analysis because of insufficient concentration data for estimating PK parameters. For study A, no subjects were excluded, with a total of 60 subjects in the analysis. For study B, 8 subjects were excluded as a result of the area under the concentration versus time curve from time zero to time t, where t is the last time point with a measurable concentration, AUC(0–tlast), not meeting the minimum requirement of three consecutive concentrations above the lower limit of quantitation, with at least one concentration following Cmax, due to missing mirikizumab concentration values. This resulted in a total of 388 subjects in the analysis. For study C, 34 subjects were excluded because of insufficient concentration data (1 participant with only a day 1 pre-dose sample and 2 participants who had insufficient concentration data were excluded) and incorrectly administered doses (17 participants receiving 300 mg original mirikizumab and 14 receiving 300 mg CF mirikizumab), with a total of 416 subjects in the analysis.

The Cmax, area under the concentration versus time curve from time zero to infinity, AUC(0–∞), and AUC(0–tlast) were log-transformed and were evaluated in the linear fixed-effects model, with mirikizumab formulation (original vs CF) and injection location as fixed-effects. The least squares mean (LSM) differences between the CF and original formulations were backtransformed to present the ratios of geometric LSM and the corresponding 90% confidence interval (CI). Bioequivalence was concluded if this 90% CI falls within a pre-specified interval of 0.80 to 1.25. The time of maximum observed drug concentration (tmax) was analyzed using a Wilcoxon rank sum test. Estimates of the median difference based on the observed means, 90% CI, and p values from Wilcoxon rank sum test were calculated. Comparisons were also made for three injection locations, with all possible comparisons. The analysis assessing the difference by injection location was not statistically powered, so formal bioequivalence for three injection locations was not determined. PK parameter estimates were determined using non-compartmental procedures in validated software program (Phoenix WinNonlin Version 8.1. or later) for the serum concentration of mirikizumab.

The safety population, which consisted of all participants who were exposed to mirikizumab, was used when reporting summary statistics for both safety and demographics. Safety assessments included clinical laboratory parameters, vital signs assessments, electrocardiogram, hepatic monitoring, and immunogenicity assessments.

All adverse events (AE) were listed. TEAEs were summarized related to study treatment and severity. The number of AEs, the number of participants experiencing an AE, and the percentage of participants experiencing an AE were summarized by treatment, using the Medical Dictionary for Regulatory Activities (MedDRA) preferred term.

ISRs and ISP were assessed differently for study A compared to studies B and C. For study A, prospective assessments were conducted, with spontaneous subject-reported ISRs also recorded. Events relating to injection site were captured as a study exploratory endpoint and were not recorded as an AE unless that event was a serious adverse event (SAE). For studies B and C, there was no prospective collection of ISR information; however, spontaneously reported ISRs were recorded as AEs. ISR findings for a specific injection were captured as a single AE, with severity recorded as the highest severity. Frequency and type of ISR were also recorded.

In study A, VAS analyses were performed as follows: after the first injection, the investigator or designee quantified ISP for subjects at 1, 5, and 15 min using the 100-mm validated VAS Assessment form [9]. Additional scheduled timepoints were at 30, 60, 120, and 240 min. VAS pain assessment was not performed for pain reported spontaneously. In the event of reported ISP, pain intensity was quantified using the following VAS pain score categories: (a) no pain, VAS pain score of 0 mm, (b) mild pain, VAS pain score of 30 mm or less, (c) moderate pain, VAS pain score more than 30 mm and at most 70 mm, and (d) severe pain, VAS pain score more than 70 mm. Data were summarized by treatment, treatment subset by injection location, and timepoint. The 1-min post-injection pain score was also evaluated in a linear fixed-effects model with fixed-effects for treatment formulation and injection site location. The LSM, differences between the formulations, and corresponding 90% CI for the difference were presented.

Mirikizumab concentrations in the serum samples collected during these studies were analyzed via a validated enzyme-linked immunosorbent assay. The validated assay range was 100 to 10,000 ng/mL, which comprised the lower and upper limits of quantitation, respectively. Quality control concentrations were 250, 1000, and 7500 ng/mL.