A phase II/III study of ozoralizumab was conducted to assess the early improvement in clinical symptoms, sustained efficacy up to 52 weeks, and acceptable tolerability afforded by this agent [40, 41]. The following subsection outlines the results of the phase II/III study (OHZORA trial) [40, 41], the phase III study (NATSUZORA trial) [42], and the results of the extended dosing interval conducted in the long-term extension study (HOSHIZORA trial) [43]. The designs of these clinical studies are summarized in Table 2.

Table 2 Design of major clinical trials for OZR4.1 Efficacy in Patients with RA4.1.1 Phase II/III Trial (OHZORA Trial)

A multicenter, double-blind, parallel-group, placebo-controlled, phase II/III trial (JapicCTI-184029) was conducted to evaluate the efficacy and safety of the subcutaneous administration of ozoralizumab plus methotrexate (MTX) in patients with active RA despite MTX therapy [40, 41]. In this trial, a total of 381 patients were allocated to receive placebo, ozoralizumab 30 mg, or ozoralizumab 80 mg at a ratio of 1:2:2. These drugs were administered subcutaneously every 4 weeks for 24 weeks in combination with MTX. The primary endpoint of the American College of Rheumatology (ACR) 20 response rate at week 16 was significantly higher in the two ozoralizumab groups (30 mg: 79.6%; 80 mg: 75.3%) compared with the placebo group (37.3%) [p < 0.001] [40]. Similar results were obtained for the ACR50 and ACR70 response rates. Furthermore, the results obtained at week 24 were comparable. However, there was no significant difference in the other primary endpoint, i.e., the amount of change from the baseline in the modified total sharp score at week 24 in the ozoralizumab 30-mg and 80-mg groups compared with the placebo group. However, the proportion of patients without progression of structural damage (change from the baseline in the modified total sharp score ≤ 0) was smaller in the 30-mg and 80-mg groups compared with the placebo group, and a significant difference was observed [40]. In addition, a significant improvement was observed in the ozoralizumab 30-mg and 80-mg groups compared with the placebo group from day 3 of treatment in terms of disease activity evaluation indices, such as the Disease Activity Score 28 (DAS28) using the C-reactive protein, patient-reported outcomes (such as the visual analog scale [VAS] for patient pain), and inflammatory markers (such as high-sensitivity C-reactive protein) [40]. In this trial, all patients received ozoralizumab 30 mg or 80 mg from week 24 onward. In the non-blinded evaluations, the effects were maintained for 52 weeks at both ozoralizumab doses [41].

4.1.2 Phase III Trial (NATSUZORA Trial)

The safety and efficacy of ozoralizumab were examined in an open phase III trial (JapicCTI-184031) that included 140 Japanese patients with RA who had discontinued conventional synthetic disease-modifying anti-rheumatic drugs because of safety reasons or an inadequate response [42]. Ozoralizumab (30 mg: 80 mg at a ratio of 2:1) was administered subcutaneously every 4 weeks for 52 weeks without MTX, yielding continuation rates of 87.1% up to week 24 and 72.1% up to week 52. The ACR20, ACR50, and ACR70 response rates improved from the timepoint of the initial evaluation at week 1, with the effects being maintained for 52 weeks (72.3%/51.1%/30.9% in the 30-mg group and 78.3%/54.3%/37.0% in the 80-mg group) [42]. A similar tendency was observed for the remaining efficacy endpoints, including physician’s global VAS, patient’s global VAS, patient pain VAS, and the number of tender or swollen joints, as well as for the inflammatory markers.

4.2 Pharmacodynamics and Effect of Trough Concentration on Drug Efficacy

In the OHZORA trial, the plasma concentrations of ozoralizumab after the single subcutaneous administration of ozoralizumab 30 mg in combination with MTX in Japanese patients with RA reached a maximum concentration on day 6 after the administration (time to maximum concentration), and then slowly disappeared with a half-life of approximately 18 days. The maximum concentration was 4.55 ± 1.1 μg/mL, and the area under the concentration–time curve from zero to infinity was 3280 ± 1280 h/μg/mL [44]. The plasma concentration after a repeated subcutaneous administration of ozoralizumab 30 mg every 4 weeks stabilized by week 16 after the start of the administration regardless of the presence or absence of MTX and was maintained at approximately 2 μg/mL up to week 52. This suggests that ozoralizumab obtained long-term retention benefits from the albumin recycling mechanism through the anti-HSA VHH.

To evaluate the relationship between pharmacodynamics and efficacy, a receiver operating characteristic analysis was performed using the ACR20 and ACR50 response rates and the trough concentrations of ozoralizumab [44]. As a result, a cut-off value of 1 μg/mL for the trough concentration at week 16 was obtained in both the OHZORA trial with MTX and the NATSUZORA trial without MTX. In groups with plasma concentrations above this cut-off value, a high response was confirmed regarding the efficacy indices. In contrast, at week 24, the cut-off value was reduced or could no longer be obtained, and at week 52, the cut-off value could no longer be obtained in either of the trials. The effect of the plasma trough concentration of ozoralizumab on its efficacy decreased with long-term continued treatment, suggesting that the effect was to be expected independent of the trough concentration of the drug. Furthermore, the simulation of the trough concentration when ozoralizumab 30 mg was administered every 6 weeks resulted in a trough concentration of 1.2 μg/mL. This finding suggests that the effect can be maintained even when treatment is administered at intervals of 6 weeks because of factors such as the delay in hospital visits.

4.3 Prolongation of the Treatment Interval (Administration Every 8 Weeks)

The HOSHIZORA trial (NCT04077567) was a multicenter, open, long-term extension study that evaluated the long-term efficacy and safety of ozoralizumab in patients who had completed the OHZORA and NATSUZORA trials [43]. In the HOSHIZORA trial, the treatment interval was allowed to extend from every 4 weeks to every 8 weeks at the doctor’s discretion for patients receiving ozoralizumab 30 mg and exhibiting a 28-Joint DAS that was maintained at < 3.2 based on the DAS28 erythrocyte sedimentation rate (ESR). The treatment interval was extended in 32 patients, and 28 (87.5%) patients remained on every 8 weeks for 24 weeks. Furthermore, at week 24, 23 of these 32 patients achieved a DAS28-ESR of < 2.6, and 27 patients achieved a DAS28-ESR of < 3.2. Importantly, there were no safety concerns associated with the extension of the treatment interval [43]. These results suggest that the treatment interval can be extended in patients who maintain a DAS28-ESR < 3.2 during the long-term administration of ozoralizumab. Although the concentration of ozoralizumab was not evaluated in this study, these results supported the hypothesis that efficacy is independent of the trough concentration in long-term continuous treatment with ozoralizumab.

4.4 Immunogenicity

Regarding the development of ADAs against ozoralizumab, 29.2–46.8% of the patients showed an increase in the antibody titer or newly generated antibodies by week 52 regardless of the dose of ozoralizumab administered and of whether MTX was used concomitantly [41, 42]. The proportion of neutralizing antibody-positive patients detected by week 52 was 7.0% (10/143 patients) and 5.2% (8/154 patients) for ozoralizumab 30 mg and 80 mg in the OHZORA trial, respectively [41]; and 27.7% (26/94 patients) and 2.2% (1/46 patients) for ozoralizumab 30 mg and 80 mg in the NATSUZORA trial, respectively [42]. Although a reduced efficacy was observed in some patients who were positive for neutralizing antibodies in the 30 mg in the NATSUZORA trial, only 11.5% of them (3/26 patients) discontinued the study because of disease progression.

4.5 Safety

A summary of safety through week 24 (period A; the double-blind treatment period) in the OHZORA trial is shown in Table 3. Most adverse events were mild or moderate. In the ozoralizumab 80-mg group, one event of disseminated tuberculosis was reported as an adverse event leading to death and was determined to be causally related to the drug [40].

Table 3 Occurrence of AEs up to 24 weeks (period Aa) in the OHZORA trial (adapted from Takeuchi et al. [40])

Safety data obtained for up to 52 weeks after drug administration in the OHZORA and NATSUZORA trials were combined and evaluated [45]. The incidence of adverse events was 83.8% (243/290 patients) in the 30-mg group and 88.8% (206/232 patients) in the 80-mg group; moreover, the incidences of adverse drug reactions were similar, i.e., 41.0% (119/290 patients) and 41.4% (96/232 patients), respectively. During the safety evaluation of ozoralizumab, adverse events of special interest (such as serious infections and malignancies) were assessed based on the characteristic side-effect profiles identified for existing TNFα inhibitors; however, no events were considered to be at a particularly high risk of occurrence after the administration of ozoralizumab treatment. Furthermore, the incidence of adverse events corresponding to a “reaction at injection site” was 1.4% (4/290 patients) in the 30-mg group and 1.3% (3/232 patients) in the 80-mg group. There was no clear impact on safety based on the presence or absence of expression of ADAs and neutralizing antibodies [45].