Functional Similarity of Proposed Biosimilar ABP 798 with Rituximab

Background

Regulatory guidelines governing the development of biosimilars require that proposed biosimilars undergo comprehensive structural and functional characterization prior to the initiation of clinical investigation. ABP 798 is being developed as a biosimilar to rituximab. The reference product is approved in the US for treatment of non-Hodgkin's lymphoma, chronic lymphocytic leukemia, severe rheumatoid arthritis, granulomatosis with polyangiitis, and microscopic polyangiitis. Development of biosimilars is challenging as even small variations in structure have the potential to alter the function of the molecule and thus may impact efficacy, safety, and/or bioavailability. Here we compare ABP 798 and rituximab reference product with respect to binding properties (CD20, C1q, FcRn, and Fcγ receptors), antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and induction of apoptosis. The reference product was sourced from the US (rituximab US) and the EU (rituximab EU).

Methods

Binding of ABP 798 and rituximab to the CD20 antigen was characterized using a cell-based CD20 binding assay utilizing the CD20 expressing WIL2-S human B-lymphoblastoid cell line. A direct binding ELISA was used to assess the binding of the Fc domain of ABP 798 to C1q. Binding of the Fc moiety of ABP 798 and rituximab to FcγRIa, FcγRIIa, FcγRIIb, and FcγRIIIa (158V and 158F) were evaluated in AlphaLISA^Ò competitive binding assays. Binding to FcRn was evaluated by an AlphaScreen^Ò competitive binding assay. ADCC activity was evaluated in a functional cell-based assay, with WIL2-S cells used as target cells and NK92-MI cells, stably transfected with human CD16 (FcγRIIIa [158V]), used as effector cells. CDC activity was evaluated in a functional cell-based assay using the WIL2-S cell line and baby rabbit complement. Induction of apoptosis was assessed by measuring activation of caspase 3/7 in SU-DHL-4 cells, a CD20 expressing human B cell lymphoma cell line.

Results

Relative binding (%) as compared to an ABP 798 reference standard was similar between ABP 798 and rituximab (Table 1).

The dose response profiles and relative activity for ADCC and CDC were also similar (ADCC relative cytotoxicity: ABP 798, 88%; rituximab US, 85%; rituximab EU, 86%; CDC relative cytotoxicity: ABP 798, 103%; rituximab US, 102%; rituximab EU, 104%). The dose-response profile for induction of caspase 3/7 was similar between ABP 798 and rituximab as well.

Conclusions

The results presented here demonstrate that ABP 798 is similar to rituximab sourced from both US and EU in terms of biological activity across the range of tested binding and functional assays. The functional assays tested the major and minor mechanisms of action related to clinical efficacy across approved rituximab indications and these results provide a foundation for further clinical development of ABP 798.

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