A Phase 1, Randomized, Double‐Blind, Placebo‐Controlled, Single Ascending Dose Study to Evaluate the Pharmacokinetics, Immunogenicity, Safety, and Tolerability After Subcutaneous Administration of Tozorakimab in Healthy Chinese Participants

Tozorakimab is a high‐affinity human immunoglobulin G1 monoclonal antibody that neutralizes interleukin (IL)‐33, an IL‐1 family cytokine. This phase 1, single‐center, randomized, double‐blind, placebo‐controlled, single ascending dose study (NCT05070312) evaluated tozorakimab in a healthy Chinese population. Outcomes included the characterization of the pharmacokinetic (PK) profile and immunogenicity of tozorakimab. Safety outcomes included treatment‐emergent adverse events (TEAEs) and clinical laboratory, electrocardiogram, and vital sign parameters. Healthy, non‐smoking, male, and female Chinese participants aged 18‐45 years with a body mass index 19‐24 kg/m2 were enrolled. In total, 36 participants across 2 cohorts of 18 participants were randomized 2:1 to receive a single subcutaneous dose of tozorakimab (300 mg [2 mL] or 600 mg [4 mL]) or matching placebo (2 or 4 mL). Tozorakimab showed dose‐dependent serum PK concentrations with an approximate monophasic distribution in serum over time and a maximum observed peak concentration of 20.1 and 33.7 μg/mL in the 300‐ and 600‐mg cohorts, respectively. No treatment‐emergent anti‐drug antibodies for tozorakimab were observed in any of the participants. There were no clinically relevant trends in the occurrence of TEAEs across the treatment groups. There were no clinically relevant trends over time in clinical laboratory (hematology, clinical chemistry, and urinalysis), electrocardiogram, or vital sign parameters in any treatment group. Overall, tozorakimab demonstrated dose‐dependent systemic exposure in healthy Chinese participants and was well tolerated, with no safety concerns identified in this study.

occurrence of TEAEs across the treatment groups.There were no clinically relevant trends over time in clinical laboratory (hematology, clinical chemistry, and urinalysis), electrocardiogram, or vital sign parameters in any treatment group.Overall, tozorakimab demonstrated dose-dependent systemic exposure in healthy Chinese participants and was well tolerated, with no safety concerns identified in this study.

Keywords
tozorakimab, China, pharmacokinetics, safety Interleukin (IL)-33 is a cytokine in the IL-1 family with roles in immunity, inflammation, tissue homeostasis and repair, viral infection, and disease. 1 IL-33 is stored in epithelial and endothelial cell nuclei in a reduced form (IL-33 red ) that is rapidly oxidized on release (IL-33 ox ). 2,3Interestingly, these alternate forms of IL-33 can activate independent signaling pathways.IL-33 red signals via the membrane-bound receptor, serum stimulated-2 (ST2), whereas IL-33 ox signals via a complex comprising the receptor for advanced glycation end products (RAGE) and the epidermal growth factor receptor (EGFR). 2,4[7][8][9][10] Tozorakimab is a high-affinity human immunoglobulin G1 monoclonal antibody that neutralizes IL-33. 11ozorakimab binds to IL-33 red ligands to block signaling via the ST2 pathway, and also prevents the formation of IL-33 ox and thereby reduces signaling via the RAGE/EGFR pathway. 11Tozorakimab has previously been evaluated in a first-in-human phase 1, randomized, double-blind, placebo-controlled study in the UK that characterized the safety, tolerability, pharmacokinetics (PKs), immunogenicity, target engagement, and pharmacodynamics of tozorakimab in healthy participants and those with mild COPD. 12Tozorakimab was well tolerated with no safety concerns identified, it had a linear serum PK profile for 1-300 mg doses, and target engagement was observed in the blood and nasal airway.Tozorakimab is being investigated in COPD (NCT04631016, NCT05166889, NCT05158387, NCT05742802, NCT06040086), asthma (NCT04570657), diabetic kidney disease (NCT04170543), and severe viral lower respiratory tract disease (NCT05624450, EudraCT: 2020-001736-95).
The aim of this phase 1 study was to evaluate the PKs, immunogenicity, safety, and tolerability of tozorakimab after a single 300 or 600 mg dose administered subcutaneously in healthy Chinese participants.Comparisons with the first-in-human phase 1 trial 12 were used to determine if differences in the PK char-acteristics of tozorakimab exist between Chinese and UK populations.Such comparisons are important for the inclusion of Chinese participants in ongoing and future clinical studies of tozorakimab to promote a diverse clinical study population.

Study Design and Population
This study was approved by China's Center for Drug Evaluation and the ethics committee of the conducting site, The First Affiliated Hospital of Soochow University.The study was carried out in accordance with the International Council for Harmonisation Guidance for Good Clinical Practice.Written informed consent was obtained from all participants.
This phase 1, single-center, randomized, doubleblind, placebo-controlled, single ascending dose study (ClinicalTrials.govidentifier: NCT05070312) was conducted between August 23, 2021 and February 7, 2022, at 1 study site in China.All participants underwent an initial screening evaluation up to 28 days before randomization to determine their eligibility and in total, 36 participants were randomized (Figure S1).The first 18 participants were assigned to cohort 1 and randomized 2:1 to receive either tozorakimab 300 mg (2 mL) subcutaneously or matching placebo 2 mL.The remaining 18 participants were assigned to cohort 2 and randomized 2:1 to receive either tozorakimab 600 mg (4 mL) subcutaneously or matching placebo 4 mL.Cohort assignment was not blinded owing to the difference in dose volume.Within each cohort, randomization of each participant to either tozorakimab or placebo was double blinded.
The study enrolled healthy, nonsmoking, male and female Chinese participants aged 18-45 years with a body mass index (BMI) of 19-24 kg/m 2 .During the study period, participants stayed at the study facility for 2 nights starting from the day before dosing (day −1).Participants received a single subcutaneous (SC) dose of tozorakimab or matching placebo on day 1 and were discharged on the morning of day 2. The injection site for all participants was the anterior abdominal wall, although arms or thighs were also permitted injection sites in the study protocol.Participants returned to the study site for additional blood collection and assessments during the 9 scheduled follow-up visits (day 3 to day 113; Figure S1).Pharmacokinetic samples were taken on day 1 (up to 30 minutes predose and 12 hours ± 30 minutes postdose) and days 2, 4, 5, 8, 15, 29, 43, 57, 85, and 113.Sampling time points were selected based on the results of the previous phase 1 trial. 12

Outcomes
A study objective was to characterize the PK profile of tozorakimab following a single SC administration in healthy Chinese participants.Pharmacokinetic endpoints included the maximum observed (peak) concentration (C max ), time to reach the peak observed concentration (t max ), dose normalized C max (C max /dose), half-life associated with the terminal slope of a semilogarithmic concentration-time curve (t 1 2 λz), area under the concentration-time curve from 0 to the last quantifiable concentration (AUC last ) and from 0 to infinity (AUC inf ), dose normalized AUC inf (AUC inf /dose), apparent total body clearance after extravascular administration (CL/F), and volume of distribution during the terminal phase after extravascular administration (Vz/F).
Another study objective was to evaluate the immunogenicity of tozorakimab in participants by measuring the presence of antidrug antibodies (ADAs).The safety endpoints included adverse events (AEs), vital signs, clinical laboratory measurements, and 12lead electrocardiogram findings.Vital sign parameters included systolic and diastolic blood pressure, pulse rate, respiratory rate, and body temperature.Clinical laboratory assessments included hematology, clinical chemistry, and urinalysis.

Data Analysis
As is usual with phase 1 studies, the study sample size was not based on formal statistical considerations.The planned sample size of 36 participants (12 per treatment group, including the combined placebo group) was based on practical considerations that 8-12 participants completing each active treatment would be sufficient to evaluate the PK characteristics of tozorakimab.This sample size could allow for a dropout rate of 30%, which was estimated based on a study duration of 113 days.
Pharmacokinetics, immunogenicity, safety, and tolerability data were summarized descriptively.Adverse events were coded using MedDRA version 25.0.Pharmacokinetic parameters were derived using noncompartmental methods with Phoenix WinNonlin version 8.1.1.All descriptive statistical computations were performed using SAS version 9.4.Further methods details can be found in the online Supplemental Information.

Demographics and Baseline Characteristics
The participants' baseline characteristics are shown in Table S1 and were generally well-balanced across the treatment groups.Overall, 36 Chinese participants were enrolled in the study; all participants received treatment and completed the study.The mean age of the participants was 26.1 years (standard deviation [SD] 5.7) and most of the participants were men (29 men and 7 women).The mean weight of the participants was 61.5 kg (SD 6.2), and all participants had a BMI between 19 and 24 kg/m 2 .No medical or surgical histories were reported for any of the participants, nor were any previous, concomitant, or prohibited medications.

Pharmacokinetics
All participants were included in the PK analysis.Tozorakimab showed a dose-dependent increase in serum PK concentrations (Table 1 and Figure 1).Tozorakimab exposure increased between the 300 and 600 mg SC doses (Figure 2), with a 1.7-and 1.8-fold increase in geometric mean C max and AUC last , respectively (Table 1).The geometric mean concentrationtime profiles indicate an approximate monophasic distribution of tozorakimab in serum over time, and the rates of decline were consistent between the 300 and 600 mg SC dose groups, with a geometric mean t 1 2 λz of 12.7 and 13.4 days, respectively.The maximum serum concentrations of tozorakimab were demonstrated approximately 7 days after administration for both the 300 and 600 mg SC doses.CL/F and Vz/F were generally consistent between the 2 dose groups.
Variability was lower in the tozorakimab 300 mg SC dose group (C max arithmetic coefficient of variation [CV] 33.2%, geometric CV 36.4%,AUC inf arithmetic CV 34.0%, geometric CV 35.0%) compared with the 600 mg SC dose group (C max arithmetic CV 34.9%, geometric CV 48.6%, AUC inf arithmetic CV 39.8%, geometric CV 47.6%).Serum concentrations were quantifiable to the last collection time point on day 113 for all except 1 participant in the 300 mg SC dose group, who had detectable concentrations until day 84.

Immunogenicity
All participants who received tozorakimab or placebo were ADA-negative at baseline and at all postbaseline time points.

Safety
Overall, at least half of all study participants, including those treated with the placebo, experienced at least 1 treatment-emergent AE (TEAE; Table 2).Although a numerically higher proportion of participants who received tozorakimab experienced a TEAE than placebo (66.7% vs 50.0%), there were no clinically  The table includes TEAEs with an onset date on or after the date of first dose of tozorakimab or placebo.
Participants with multiple occurrences in the same category are counted once per category regardless of the number of occurrences.AE, adverse event; AESI, adverse event of special interest; n, number of participants per category; TEAE, treatment-emergent adverse event; TESAE, treatment-emergent serious adverse event.
a The causality of any TEAE was judged by the investigator, who was blinded to the treatment received by the study participant.
relevant trends in the occurrence of TEAEs across the treatment groups.No TEAEs led to discontinuation or participant withdrawal from the study and no deaths or treatment-emergent serious AEs were reported.An AE of special interest with the preferred term of injection site erythema with mild intensity was reported by 1 individual in the tozorakimab 300 mg SC dose group, which resolved without medical treatment within 1 day.The most common TEAEs by preferred term (≥3 participants combined across the 300 and 600 mg  SC dose groups) in those who received tozorakimab were increased blood uric acid, increased C-reactive protein, increased alanine aminotransferase, and decreased white blood cell count.In the placebo group, the most common TEAEs by preferred term (≥3 participants) were white blood cells urine positive and increased blood uric acid (Table S2).There were no clinically relevant trends over time in clinical laboratory (hematology, clinical chemistry, or urinalysis), vital signs, or electrocardiogram parameters in any treatment group.

Discussion
In this phase 1 study of healthy Chinese participants, tozorakimab demonstrated dose-dependent PKs.Both the tozorakimab 300 and 600 mg SC dose groups had a median t max of 7.1 days and a linear serum profile.Variability in PK parameters was higher for the tozorakimab 600 mg SC dose group versus the 300 mg SC dose group.Two participants in the tozorakimab 600 mg SC dose group showed lower serum concentrations and corresponding lower C max and AUC inf values compared with the other participants in the same cohort, which may have contributed to the higher variability observed for these parameters at the 600 mg SC dose level.No reasons were identified to explain the lower exposures in these participants.Any influence of participant demographics on tozorakimab PKs may be explored in ongoing phase 2 and phase 3 studies.
No ADAs were detected in any study participants.This is consistent with the low incidence of immunogenicity previously reported for tozorakimab in a single ascending dose study of a UK population. 12The low immunogenicity observed after a single dose of tozorakimab is in line with other monoclonal antibody therapies, where an increase in the number of injections has been associated with a greater immune response. 13ecause no ADAs were detected, the potential effects on the PKs and safety characteristics of tozorakimab cannot be established.The results from this study demonstrated that tozorakimab was well tolerated, and no safety concerns were identified with the doses evaluated in healthy Chinese participants.
The UK-based first-in-human phase 1 study of tozorakimab 12 included a cohort of healthy participants with a history of mild atopy who received a single tozorakimab 300 mg SC dose, allowing comparisons with the Chinese population treated with tozorakimab 300 mg subcutaneously in this study.Tozorakimab exposure was higher in the Chinese population than the UK population, with a 27.7% increase in arithmetic mean C max (21.2 μg/mL in the Chinese population vs 16.6 μg/mL in the UK population) and a 10.6% increase in arithmetic mean AUC inf (385 vs 348 day•μg/mL).The t max in the Chinese population was longer than in the UK population (7.1 vs 4.0 days) and the arithmetic mean half-life of tozorakimab in the Chinese population was numerically lower than the UK population (12.9 vs 17.3 days).The observed differences in tozorakimab PK parameters between Chinese and UK populations may be partially explained by the 12.6% lower mean BMI of those treated with tozorakimab in the Chinese population compared with the UK population (21.6 vs 24.7 kg/m 2 ).Additionally, the tozorakimab formulation differed between studies, which might have contributed to the observed differences in PK parameters.However, the overall safety data and similar PK profile observed between Chinese and UK populations may suggest that no dose adjustment will be required for tozorakimab in future studies in the Chinese population.
The limitations of this study must also be considered.Although there were more male than female participants, the distribution of female participants was even across the tozorakimab and placebo groups and between the tozorakimab dose levels.Pharmacokinetic parameters of tozorakimab will be further assessed in female participants as part of the phase 2 and phase 3 trials.Although the planned study size of 36 participants was small, it was based on practical considerations to ensure that a minimum of 8 participants completed each active treatment group after predicted participant dropout.

Conclusions
The PKs of tozorakimab were characterized in a Chinese population and showed dose-dependent systemic exposure.No detectable ADAs were found in any participants receiving single SC doses of tozorakimab.The doses of tozorakimab investigated in this study were well tolerated in healthy participants, and no safety concerns were identified.This early study, together with the first-in-human study, 12 suggest that there are no relevant differences in PK parameters between Chinese and UK populations.This provides the first evidence that dose adjustment would not be required for Chinese participants to join ongoing and future global studies of tozorakimab.

Figure 1 .
Figure 1.Arithmetic mean (arithmetic standard deviation) serum concentrations of tozorakimab versus time since dosing on (A) a linear scale and (B) a semilogarithmic scale.n, number of participants per category; SC, subcutaneous.

Figure 2 .
Figure 2. (A) Maximum observed (peak) concentration and (B) area under the concentration-time curve from 0 to the last quantifiable concentration, calculated using the linear-up log-down method, for tozorakimab 300 and 600 mg subcutaneous doses.The box plots display the lower quartile, median, and upper quartile of each dataset.Whiskers extend from each box to indicate the minimum and maximum values.Each dot represents a single data point.AUC last , area under the concentration-time curve from time 0 to time of last quantifiable analyte concentration divided by the dose administered; C max , maximum observed (peak) concentration divided by the dose administered.

Table 1 .
Summary of Tozorakimab Pharmacokinetic Parameters AUC inf , area under the concentration-time curve from 0 to infinity; AUC last , area under the concentration-time curve from 0 to the last quantifiable concentration; CL/F, apparent total body clearance of drug after extravascular administration; C max , maximum observed (peak) concentration; CV, coefficient of variation; dose-normalized AUC inf , area under the concentration-time curve from time 0 extrapolated to infinity divided by the dose administered; dose-normalized AUC last , area under the concentration-time curve from time 0 to time of last quantifiable analyte concentration divided by the dose administered; dose-normalized C max , maximum observed (peak) concentration divided by the dose administered; n, number of participants in analysis; SC, subcutaneous; SD, standard deviation; t 1/2 λz, half-life associated with terminal slope of a semi-logarithmic concentration-time curve; t max , time to reach peak or maximum observed concentration following drug administration; Vz/F, volume of distribution during the terminal phase after extravascular administration.

Table 2 .
Summary of Adverse Events