Efficacy and safety of biosimilar CT-P17 versus reference adalimumab in subjects with rheumatoid arthritis: 24-week results from a randomized study

Background To demonstrate equivalent efficacy of the proposed high-concentration (100 mg/ml), citrate-free adalimumab biosimilar CT-P17 to European Union-approved adalimumab (EU-adalimumab) in subjects with active rheumatoid arthritis (RA). Methods This randomized, double-blind phase III study (ClinicalTrials.gov, NCT03789292) randomized (1:1) subjects with active RA at 52 centers to receive CT-P17 or EU-adalimumab 40 mg subcutaneously every 2 weeks until week 52. Results to week 24 are reported here. The primary endpoint was 20% improvement by American College of Rheumatology criteria (ACR20) response rate at week 24. Equivalence was concluded if the corresponding confidence intervals (CIs) for the estimate of treatment difference were within predefined equivalence margins: − 15 to 15% (95% CI; European Medicines Agency assumption); − 12 to 15% (90% CI; Food and Drug Administration assumption). Additional efficacy, pharmacokinetic, usability, safety, and immunogenicity endpoints were evaluated. Results 648 subjects were randomized (324 CT-P17; 324 EU-adalimumab). The ACR20 response rate at week 24 was 82.7% (n = 268/324) in both groups (intention-to-treat population). The 95% CI (− 5.94 to 5.94) and 90% CI (− 4.98 to 4.98) were within predefined equivalence margins for both assumptions and equivalent efficacy was concluded. Additional endpoints and overall safety were comparable between groups. Mean trough serum concentrations of CT-P17 were slightly higher than those of EU-adalimumab. Immunogenicity was slightly lower numerically for the CT-P17 group than for the EU-adalimumab group. Conclusions CT-P17 and EU-adalimumab have equivalent efficacy and comparable safety and immunogenicity in subjects with active RA. Overall safety of CT-P17 is consistent with the known safety profile of reference adalimumab. Trial registration ClinicalTrials.gov, NCT03789292. Registered 28 December 2018—retrospectively registered.


Background
Biological disease-modifying antirheumatic drugs (bDMARDs), such as tumor necrosis factor (TNF) inhibitors, are recommended for the treatment of rheumatoid arthritis (RA) when disease activity remains moderate or high despite conventional synthetic DMARD (csDMARD) monotherapy [1]. Adalimumab is an anti-TNF monoclonal antibody that effectively treats RA [2][3][4][5]. Biosimilars are highly similar to their reference products in terms of quality characteristics, biological activity, safety, and efficacy [6]. Since 2016, several adalimumab biosimilars have been licensed by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) [7,8]. European League Against Rheumatism (EULAR) recommendations for the treatment of RA position biosimilar DMARDs (bsDMARDs) equivalently to their reference products in treatment algorithms, and suggest that lower-priced biosimilars are preferred for their potential to reduce healthcare expenditures [9].
This randomized, active-controlled, double-blind, multicenter, phase III study was designed to demonstrate that the efficacy of CT-P17 at week 24 is equivalent to that of EU-adalimumab. The study also evaluated PK, usability, and overall safety, including immunogenicity.
CT-P17 and EU-adalimumab were administered by subcutaneous injection via prefilled syringe. After training in proper injection technique, subjects (or caregivers, as needed) could self-administer injections at home, unless injection at the study center was required for usability assessment. Subjects also received treatment with methotrexate (MTX; 12.5-25 mg/week, or 10 mg/week if intolerant to a higher dose, oral or parenteral [intramuscular or subcutaneous] dose) and folic acid (≥ 5 mg/week, oral).
Randomization was conducted using an interactive web response system (IWRS). The biostatistics team used Rave Randomization and Trial Supply Management (Medidata Solutions, New York) to generate the randomization schedule for the IWRS, which linked sequential subject randomization numbers to treatment codes. Randomization was by permuted block (block size remains blinded until final database lock) and was stratified by country and Simplified Disease Activity Index (SDAI) at screening (> 26 vs ≤ 26). As prespecified in the protocol, the study was unblinded for reporting purposes after the database lock for data up to week 24. Efficacy, PK, usability, immunogenicity, and safety endpoints were evaluated by separate, predefined unblinded teams constituted by the sponsor and by the Contract Research Organization (CRO). The investigators, subjects, and other teams in the CRO and the sponsor will remain blinded until the end of the study.
The study was performed in accordance with the Declaration of Helsinki [17] and Good Clinical Practice guidelines [18]. All national, state, and local laws or regulations were followed. Before study initiation, the study protocol was reviewed and approved by the independent ethics committee/institutional review board at each site (see Supplementary Table 1, Additional file 1). All subjects provided written informed consent. The study was registered with ClinicalTrials.gov (NCT03789292).

Subjects
Full eligibility criteria are detailed in Additional file 1. Subjects ranged between 18 and 75 years of age, were diagnosed with RA according to the 2010 American College of Rheumatology (ACR)/EULAR classification criteria [19], and had active disease, defined by the presence of ≥ 6 swollen joints (of 66 assessed), ≥ 6 tender joints (of 68 assessed), and either erythrocyte sedimentation rate (ESR) > 28 mm/hour or serum C-reactive protein (CRP) concentration > 1.0 mg/dl (> 10 mg/l) at screening. Subjects had received oral or parenteral MTX at a dose of 12.5-25 mg/week, or 10 mg/week if intolerant to a higher dose, for ≥ 12 weeks, and had been on a stable dose and route of administration of MTX for ≥ 4 weeks before the first administration of study drug (day 1). Key exclusion criteria included prior bDMARD or targeted synthetic DMARD treatment for RA or prior TNF inhibitor treatment for any diagnosis; active or latent tuberculosis, or history of tuberculosis; or history of or current serious infection.

Study endpoints
The primary efficacy endpoint was the proportion of subjects achieving clinical response according to 20% improvement by ACR response criteria (ACR20) at week 24. Secondary efficacy endpoints up to week 24 were ACR20, ACR50, and ACR70 response, hybrid ACR response, Disease Activity Score in 28 joints (DAS28)-CRP response, EULAR (CRP) response, SDAI and Clinical Disease Activity Index (CDAI) remission rate, and 36item Short Form Health Survey (SF-36) physical and mental component scores. DAS28-CRP and Boolean remission rates were analyzed post hoc. Trough serum adalimumab concentration (C trough ) was evaluated as a secondary PK endpoint. Usability evaluations (Bulgaria and Poland only) included subject-reported outcomes from the Self-Injection Assessment Questionnaire (SIAQ) administered before (PRE-SIAQ) and after (POST-SIAQ) self-injection, and successful self-injection as determined by Self-Injection Assessment Checklist completed by study center staff. Safety was evaluated throughout; immunogenicity and local site pain were also assessed.

Study assessments
Study assessments and time points for evaluation are specified in Supplementary Table 2 (Additional file 1). For efficacy assessments, procedures were performed at the study center before study drug administration. A blinded independent joint assessor was assigned at each study center. Blood samples for PK analysis were obtained predose (immediately before study drug injection) for all PK sampling time points. Usability assessments were conducted at weeks 4, 6, 8, and 24. Safety assessments performed throughout included treatmentemergent adverse events (TEAEs), TEAEs of special interest (TEAESI), immunogenicity, clinical monitoring for tuberculosis, and review of prior and concomitant medications. TEAEs were recorded according to the Common Terminology Criteria for Adverse Events v5.0 and were coded to System Organ Class (SOC) and Preferred Term according to the Medical Dictionary for Regulatory Affairs v22.0. Prior and concomitant medications were coded using the World Health Organization Drug Dictionary (March 2019 version). Protocolspecified TEAESIs were injection-site reactions (ISRs), hypersensitivity/allergic reactions, infections, and malignancies. Local site pain was assessed by using a 100-mm visual analog scale (VAS) at all study visits (except weeks 12 and 20).
Immunogenicity was evaluated at all study visits. Antidrug antibodies (ADAs) were detected using a validated electrochemiluminescent bridging assay with acid dissociation. ADA-positive samples underwent further analysis to confirm the specificity of binding and to quantify ADA titer. If a sample was confirmed positive for specific ADAs, the presence of neutralizing antibodies (NAbs) was investigated. A validated electrochemiluminescent assay with affinity capture elution was used to measure neutralizing activity against adalimumab in human serum.

Statistical analyses
A sample size of 450 subjects (225 per treatment group) was determined to provide ≥ 80% statistical power to demonstrate equivalence of ACR20 response at week 24, using nQuery Adviser (v7.0; nQuery, Boston, MA). This calculation was based on two sets of statistical assumptions to meet the different requirements of regulatory authorities in the European Union and the USA: an equivalence margin of − 15 to 15% using a 2 1-sided 2.5% significance level of an equivalence test (predefined in the protocol; EMA assumption), and an asymmetric equivalence margin of − 12 to 15% using a 2 1-sided 5% significance level of an equivalence test (FDA assumption). To allow for a possible dropout rate of 20%, the target sample size was 564 subjects (282 per treatment group).
Analysis populations are described in Additional file 1. The intention-to-treat (ITT) population included all subjects enrolled and randomized to receive a dose of either study drug, regardless of whether study drug dosing was completed. The ITT population was the primary analysis population for the primary endpoint, which was also assessed in the per-protocol (PP) population as a supportive analysis. The analysis was conducted by the exact binomial approach using a Farrington-Manning score method (inverting 2 1-sided test) [20]. A sensitivity analysis for the primary efficacy endpoint was performed in both the ITT and the PP populations using logistic regression with treatment group as a fixed effect and country and disease activity by SDAI at screening as covariates. Selected analyses were also conducted by ADA status. Post hoc analyses were conducted to compare parameters between treatment groups (Tables 1, 2, and  3), with p values generated by the Wald test (for proportional values) or t test (for mean values). All statistical analyses were performed using SAS software v9.4 (SAS Institute, Cary, NC).

Subject disposition and baseline characteristics
Subjects were recruited between December 5, 2018, and April 25, 2019 (last subject week 24 visit: October 8, 2019). Of the 648 subjects who were randomized, 324 to each of the CT-P17 and EU-adalimumab groups ( Fig. 1

Primary efficacy analysis
The ACR20 response rate at week 24 ( Fig. 2a) was 82.7% (n = 268/324) for both the CT-P17 and EU-adalimumab  were entirely within the asymmetric equivalence margin of − 12 to 15% (FDA assumption), thereby also demonstrating therapeutic equivalence between treatment groups. Sensitivity analysis using logistic regression with covariates for the primary endpoint provided similar results, − 5.75 to 5.86 (ITT population) and − 5.07 to 5.93 (PP population) for 95% CI.

Secondary and additional efficacy analyses
The proportions of subjects achieving ACR20, ACR50, and ACR70 responses up to week 24 were similar between the CT-P17 and EU-adalimumab groups (Fig. 2a 2c), CDAI (Fig. 2d), and SDAI (Fig. 2e) were comparable between groups up to week 24, as were EULAR (CRP) response rates and SDAI, CDAI, DAS28 (CRP), and Boolean remission rates (Table 2). Mean hybrid ACR scores increased from week 2 to week 24 and were similar between groups (Supplementary Table 3

Pharmacokinetic analysis
The mean adalimumab C trough was comparable between groups in the PK population, although values were slightly higher in the CT-P17 than in the EU-adalimumab group (Supplementary Table 4, Additional file 1). Mean C trough increased gradually from baseline to week 22 for both groups (Supplementary Figure 1, Additional file 1).

Usability analysis
Mean scores for each domain of the PRE-SIAQ and POST-SIAQ were comparable between treatment groups (Supplementary Table 5, Additional file 1). All subjects in the population in which usability was assessed completed self-injection successfully.

Safety
Overall, the proportion of subjects experiencing ≥   TEAEs classified as hypersensitivity/allergic reactions, ISRs, or infections were experienced by similar proportions of subjects in each group (Table 3). Conversion to positive interferon-γ release assay, up to week 24, was experienced by 12 (3.7%) and 17 (5.2%) subjects in the CT-P17 and EU-adalimumab groups, respectively. Latent tuberculosis was reported in 12 (3.7%) and 15 (4.6%) subjects in the CT-P17 and EU-adalimumab groups, respectively; for 7 (2.2%) and 10 (3.1%) of these subjects, this was considered study drug-related. All these subjects began tuberculosis prophylaxis, except for the single subject in each group who terminated study participation. Two (0.6%) subjects in the EU-adalimumab group reported active tuberculosis and discontinued study treatment. One (0.3%) subject experienced a TEAE classified as malignancy (breast cancer) in the CT-P17 group (Table 3); however, the site investigator considered this event to be unrelated to study drug. Fig. 1 Subject disposition (ITT population). a Subject discontinued CT-P17 treatment due to significant dose delay due to adverse event. b Two subjects discontinued EU-adalimumab treatment due to subject decision due to adverse event. EU-adalimumab, European Union-approved adalimumab; ITT, intention-to-treat Small imbalances were identified in the proportions of subjects reporting TEAEs classified in the SOC of gastrointestinal disorders (CT-P17, 24 Table 7, Additional file 1). However, among these SOCs, other than for two grade 3 TEAEs that were considered unrelated to study drug in the EU-adalimumab group (1 nervous system disorder of carotid arteriosclerosis, and 1 metabolism and nutrition disorder of hypertriglyceridemia), all TEAEs were grade 1-2 in intensity.
Mean (SD) 100-mm VAS scores for local site pain measurements decreased over time. Results at each visit were comparable between treatment groups. At week 0, mean (SD) VAS scores for local site pain were 6.64 Mean change from baseline in SDAI value up to week 24 (e). ACR, American College of Rheumatology; ACR20, 20% improvement according to American College of Rheumatology criteria; ACR50, 50% improvement according to American College of Rheumatology criteria; ACR70, 70% improvement according to American College of Rheumatology criteria; CDAI, Clinical Disease Activity Index; DAS28-CRP, Disease Activity Score in 28 joints C-reactive protein; EU-adalimumab, European Union-approved adalimumab; ITT, intention-to-treat; SDAI, Simplified Disease Activity Index (10.887) for CT-P17 and 4.85 (7.300) for EUadalimumab, while mean VAS scores at week 24 had decreased to 4.45 (8.393) for CT-P17 and to 4.32 (8.651) for EU-adalimumab.

ADA subgroup analysis
The proportions of subjects achieving an ACR20 response at week 24 were similar between the CT-P17 and the EU-adalimumab treatment groups in both the ADApositive and ADA-negative subgroups (Supplementary Table 9, Additional file 1). Mean C trough was lower in the ADA-positive subgroup than in the ADA-negative subgroup for both treatment groups (Supplementary Figure 1 and Supplementary Table 4, Additional file 1). A lower proportion of subjects in the ADA-negative subgroup experienced ≥1 TEAE than did those in the ADApositive subgroup (49.7% and 59.8%, respectively); however, with a limited number of events, there was no apparent correlation between the presence of ADA and the incidence of TESAEs, TEAEs classified as hypersensitivity/reactions, or TEAEs classified as ISRs (Supplementary Table 10, Additional file 1).

Discussion
This study demonstrated equivalent efficacy of CT-P17 to EU-adalimumab in the proportion of subjects achieving an ACR20 response at week 24. This primary endpoint was met in both the ITT and PP analysis populations for both the EMA (− 15 to 15%, 95% CI) and the FDA (− 12 to 15%, 90% CI) statistical assumptions. Comparable efficacy of CT-P17 and EUadalimumab was demonstrated for secondary endpoints up to week 24. PK parameters were also comparable between groups, although mean C trough was slightly higher for CT-P17 than for EU-adalimumab. The usability of CT-P17, assessed by ability to complete successful selfinjections and subject-reported outcomes, was comparable to that of EU-adalimumab. The overall safety profile of CT-P17 was similar to that of EU-adalimumab, although there were small imbalances between the CT-P17 and EU-adalimumab groups for some SOCs.
In our study, the ACR20 response rate at week 24, using high-concentration (100 mg/ml) formulations of CT-P17 and EU-adalimumab, was 82.7% in both treatment groups (ITT population). These observed ACR20 response rates are only slightly above the range of ACR20 responses for reference adalimumab (50 mg/ml) and adalimumab biosimilars in other adalimumab biosimilar studies, in which ACR20 response rates at week 24 or week 26 ranged between 63.9 and 82.5% (Supplementary Figure 2, Additional file 1) [21][22][23][24][25]. However, our study did not compare the high-concentration formulation to the low-concentration formulation of adalimumab.
We also investigated the influence of immunogenicity status on the proportion of subjects achieving an ACR20 response at week 24. Overall, a slightly lower proportion of ADA-positive subjects achieved an ACR20 response at week 24 than did ADA-negative subjects (81.4% vs 85.1%), consistent with previous reports for reference adalimumab and adalimumab biosimilars [13,26]. However, within subject subgroups by ADA status, ACR20 response rates were similar between CT-P17 and EUadalimumab treatment groups, in line with similar data reported previously for adalimumab biosimilars [26,27].
In this study, we observed slightly higher mean C trough values in the CT-P17 group compared with the EUadalimumab group. In a separate study, ADA formation was associated with increased clearance and lower serum adalimumab concentrations [13]. However, in this study, AUC and clearance were not evaluated, so this could not be examined directly. It is possible that the differences may be associated with the lower proportion of ADApositive subjects in the CT-P17 versus EU-adalimumab group. Indeed, in our study, C trough was generally lower in the ADA-positive than in the ADA-negative subgroup; C trough values became more similar between groups when compared within these subgroups. Nevertheless, C trough values of the ADA-positive subgroup were within the therapeutic level of adalimumab (5 to 8 μg/ml) [13]. In addition, our findings are in keeping with previous reports for adalimumab biosimilars [26,28].
The overall safety profile of CT-P17 in this study was consistent with the known safety profile of reference adalimumab [13]. In both treatment groups, the most frequently reported study drug-related TEAEs were ISRs, consistent with information provided in the EUadalimumab summary of product characteristics [13]. ISRs, as well as the other protocol-specified TEAESIs of hypersensitivity/allergic reactions and infections, were experienced by similar proportions of subjects in each treatment group. There were small imbalances, at the SOC level, in the proportions of subjects reporting TEAEs for gastrointestinal disorders, nervous system disorders, and metabolism and nutrition disorders. These TEAEs were mostly grade 1-2 in intensity and, at the Preferred Term level, absolute differences between groups in the number of subjects experiencing a given TEAE were small. When analyzed by ADA status, the incidence of TEAEs, but not of TESAEs, was higher for ADA-positive than for ADA-negative subjects; there was no apparent correlation between the presence of ADAs and hypersensitivity/allergic reactions or ISRs. This is the first report of a phase III clinical trial comparing CT-P17 to reference adalimumab. Strengths of this study include its randomized, double-blind design, and the use of well-established outcome measures. Equivalent efficacy of CT-P17 and EU-adalimumab was established using both symmetric and asymmetric equivalence margins, as agreed to by the EMA and the FDA, respectively. In addition to the data reported from comparing these treatments up to week 24, this study will provide valuable information regarding the efficacy and safety of transitioning from EU-adalimumab to CT-P17 (during treatment period 2).
Limitations of this study include the relatively short follow-up period (24 weeks) reported herein; however, this study is ongoing and efficacy and safety data up to week 52 will be reported. Although sufficient testing was done for regulatory purposes, comprehensive PK data were not collected. While treatment groups were well balanced by stratification factors including country, subjects from Eastern European countries, particularly Poland, accounted for most of the study population. The races of subjects enrolled in this study included white, mestizo, and Native Peruvian. This could limit the global generalizability of the findings; however, this should be viewed in the context of the global scope of the CT-P17 clinical development program that included American Indian or Alaska Native, Black or African American, and Asian subjects, among which there were no differences in clinical responses [11,16,29]. Also, since this was a comparative study to demonstrate equivalence of CT-P17 to EU-adalimumab, it did not aim to evaluate the drugs across other ethnic groups.
The original reference adalimumab was developed as a low-concentration (50 mg/ml) formulation containing citrate. Subsequently, a high-concentration (100 mg/ml), citrate-free formulation of reference adalimumab has been developed [13,14]. While the high-concentration CT-P17 formulation is similar to the newer formulation of reference adalimumab [13,14], it differs from the low-concentration (50 mg/ml) adalimumab biosimilars that are currently approved [12,[30][31][32][33]. The highconcentration formulations of both CT-P17 and reference adalimumab offer the potential to administer highdose (80 mg/0.8 ml) induction treatment to patients with inflammatory bowel disease with a reduced number of injections. In addition, the citrate-free buffer may benefit patients by reducing discomfort during injection [12,15].

Conclusions
In conclusion, demonstration of equivalent efficacy and comparable safety and immunogenicity of CT-P17 to EU-adalimumab in this study support the ongoing clinical evaluation of CT-P17 as an adalimumab biosimilar.
Additional file 1: Supplementary methods, including Table S1 Study centers and IRB/IEC information, Full inclusion and exclusion criteria, Table S2 Schedule of assessments (screening and treatment period 1), and Analysis populations. Table S3 ACR50 and ACR70 response rates and hybrid ACR scores up to week 24 (ITT population). Table S4 Mean (SD) C trough overall and by ADA status (PK population). Figure S1 Mean (±SD) C trough by ADA status (PK population).  Table S9 ACR20 response rate at week 24 by ADA status (ITT population). Table S10 Treatment-emergent adverse events by ADA status (safety population). Figure S2 Historical data for ACR20 response rate at week 24 for reference or biosimilar adalimumab (50 mg/ml), compared with CT-P17 or reference adalimumab (100 mg/ml) treatment in the current study (ITT population).
Abbreviations ACR: American College of Rheumatology; ACR20: 20% improvement according to American College of Rheumatology criteria; ADA: Anti-drug antibody; bDMARD: Biological disease-modifying antirheumatic drug; bsDMARD: Biosimilar disease-modifying antirheumatic drug; CDAI: Clinical Disease Activity Index; CI: Confidence interval; CRO: Contract Research Organization; CRP: C-reactive protein; csDMARD: Conventional synthetic disease-modifying antirheumatic drug; C trough : Trough serum adalimumab concentration; DAS28: Disease Activity Score in 28 joints; EMA: European Medicines Agency; EU-adalimumab: European Union-approved adalimumab; EULAR: European League Against Rheumatism; ESR: Erythrocyte sedimentation rate; FDA: US Food and Drug Administration; ISR: Injection-site reaction; ITT: Intention-to-treat; IWRS: Interactive web response system; NAb: Neutralizing antibody; PK: Pharmacokinetics; PP: Per-protocol; q2w: Every 2 weeks; SDAI: Simplified Disease Activity Index; SF-36: 36-item Short Form Health Survey; SIAQ: Self-Injection Assessment Questionnaire; SOC: System Organ Class; TEAE: Treatment-emergent adverse event; TEAE SI: Treatment-emergent adverse event of special interest; TESAE: Treatmentemergent serious adverse event; TNF: Tumor necrosis factor; VAS: Visual analog scale and interpretation of data. SJL, YJB, GEY, and JKY made substantial contributions to the conception and design of the work and the analysis and interpretation of data. All authors contributed to drafting the work or substantially revising it and have approved the final manuscript.

Funding
This study was funded by Celltrion, Inc. (Incheon, Republic of Korea).
Availability of data and materials Available data and methodological information for this ongoing study are included in this article and accompanying supplementary materials.

Ethics approval and consent to participate
The study was performed in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. All national, state, and local laws or regulations were followed. Before study initiation, the study protocol was reviewed and approved by the independent ethics committee/institutional review board at each site (Supplementary Table 1, Additional file 1). All subjects provided written informed consent.

Consent for publication
Not applicable.