Background/Purpose:   ABP 501 is a biosimilar candidate to adalimumab, a fully human recombinant monoclonal antibody. Totality of evidence to date suggests that ABP 501 is similar to adalimumab. Subjects receiving either ABP 501 or adalimumab in the active-controlled comparative pivotal phase 3 study in rheumatoid arthritis continued on to this ongoing open-label extension (OLE) study if they had completed the week 26 visit of the active-controlled pivotal phase 3 study (parent study) and met study entry criteria. Objective: To report results from the interim analysis of this OLE study.

Methods:   This was a single-arm OLE of the parent study; the objective was to assess long-term safety and efficacy of ABP 501. The study design included 68 weeks of treatment followed by an assessment at week 70 and an end of study visit at week 72. All subjects received 40 mg ABP 501 every other week; starting earliest at the week 26 visit of the parent study.

Results:   Of the 466/467 treated subjects, 237 transitioned from adalimumab to ABP 501. At the time of this interim analysis one (0.2%) subject had completed the OLE study and 37 (7.9%) had terminated early, mostly due to consent withdrawal. Demographics and disease characteristics were balanced between subjects who transitioned from adalimumab and those who continued on ABP 501. The incidence of treatment-emergent adverse events (TEAEs) was 57.1% (266/466) and that of grade ≥3 TEAEs was 6.2% (29/466); incidence of TEAEs leading to discontinuation of investigational product was 1.7% (8/466). The most frequently reported TEAEs included nasopharyngitis (8.2%), upper respiratory tract infection (7.3%), and bronchitis (4.3%). No fatal adverse events were reported; 6.9% (32/466) subjects experienced serious adverse events (SAEs), of which 1.9% (9/466) experienced musculoskeletal and connective tissue disorders. There were 2 SAEs of interest (infections: n=1; malignancies: n=1). The overall exposure-adjusted incidence rate for SAEs occurring in the OLE study was 8.4 per 100 patient-years (32 subjects/382.4 total subject exposure-time [patient-year]). At the time of this interim analysis, 45.9% (214/466) subjects had developed binding antidrug antibodies (ADAs), 11.6% (54/466) had developed neutralizing ADAs in the OLE study. The rates of TEAEs and ADAs were similar between subjects with single transition from adalimumab and those who continued on ABP 501. The ACR20 response rate (using the parent study baseline) was 73.3% (340/464) at the OLE study baseline, 77.6% (361/465) at week 4, 74.2% (336/453) at week 24, 76.5% (224/293) at week 48. The overall mean DAS28-CRP change from parent study baseline was −2.25 (n=440) at the OLE study baseline, −2.36 (n=463) at week 4, −2.41 (n=450) at week 24 and −2.52 (n=292) at week 48. Efficacy was similar in subjects who transitioned from adalimumab as compared with the subjects who continued on ABP 501.

Conclusion:   In this ongoing OLE study of ABP 501, efficacy was maintained with no new safety findings. Long term safety and efficacy results were similar between subjects who transitioned from adalimumab and those who continued on ABP 501.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/abp-501-long-term-safetyefficacy-interim-results-from-an-open-label-extension-study/