Analytical and Functional Similarity of Aflibercept Biosimilar ABP 938 with Aflibercept Reference Product.

INTRODUCTION: ABP 938 is being developed as a biosimilar candidate to aflibercept reference product (RP), a biologic used for certain angiogenic eye disorders. This study was designed to provide a comparative analytical assessment of the structural and functional attributes of ABP 938 and aflibercept RP sourced from the United States (US) and the European Union (EU). METHODS: Structural and functional characterization studies were performed using state-of-the-art analytical techniques that were appropriate to assess relevant quality attributes and capable of detecting qualitative and quantitative differences in primary structure, higher-order structure and biophysical properties, product-related substances and impurities, general properties, and biological activities. RESULTS: ABP 938 had the same amino acid sequence and exhibited similar secondary and tertiary structures, and biological activity as aflibercept RP. There were minor differences in a small number of biochemical attributes which are not expected to impact clinical performance. In addition, aflibercept RP sourced from the US and EU were analytically similar. CONCLUSIONS: ABP 938 was structurally and functionally similar to aflibercept RP. Since aflibercept RP sourced from the US and EU were analytically similar, this allows for the development of a scientific bridge such that a single-source RP can be used in nonclinical and clinical studies.

Eylea^® (aflibercept) is a biologic medication approved for the treatment of patients with certain eye diseases that can result in low vision or blindness. Biosimilars are biologic medications that are highly similar to an existing approved biologic medication, often called a reference product. Biosimilars have the potential to reduce medication costs despite having no clinically significant differences in quality, efficacy, and safety from their reference products. ABP 938 is currently being developed as a biosimilar to aflibercept reference product. We have conducted similarity studies to compare multiple batches of ABP 938 and aflibercept reference product sourced from both the United States and the European Union, using state-of-the-art analytical methods. The results demonstrated that ABP 938 had the same amino acid sequence and similar structural and biological activities as aflibercept reference product. Before biosimilars can be used as medicines, studies such as this one are required by the Food and Drug Administration and other regulatory authorities to ensure that biosimilars are as safe and effective as their reference products.

Target cell line characterization reveals changes in expression of a key antigen that impacts T cell dependent cellular cytotoxicity assay performance.

Cell lines are important tools regularly used for in-vitro potency assays employed in Good Manufacturing Process (GMP) lot release and stability testing of different therapeutic modalities. Characterization of these cell lines is key to understanding their performance. Bispecific T cell engager (BiTE®) molecules are an exciting modality in Amgen's therapeutic product portfolio. BiTE® molecules are engineered as two linked, single chain antibody domains. One domain targets the cluster of differentiation 3 (CD3) domain of T cells, and the other domain targets a specific antigen. The mechanism of action of the BiTE® molecule is to bring T cells into close proximity of tumor cells to facilitate tumor cell killing. One BiTE® molecule in development, AMG 757, is directed against delta-like ligand 3 (DLL3), which is expressed in small cell lung cancer tumor cells. AMG 757 is a half-life extended bispecific T cell engager (HLE BiTE®) construct. The bioassay employed to demonstrate the mechanism of action of AMG 757 is a T cell dependent cellular cytotoxicity (TDCC) cell-based assay requiring two cell lines, the effector T cell line HuT-78, and engineered tumor target cells, SHP-77-Luc. During the course of development of this bioassay, characterization of the SHP-77-Luc line showed an increase in the luminescence assay signal and Maximum-to-Minimum (Max-to-Min) ratio of the dose response curve as the passage number of the cells increased. Our research revealed an increase in not only luciferase expression but also an increase in the cell surface and intracellular expression levels of DLL3 over time in culture, which ultimately resulted in the increased assay signal window.

Qualification of a homogeneous cell-based neonatal Fc receptor (FcRn) binding assay and its application to studies on Fc functionality of IgG-based therapeutics.

The Fc region of IgG-based molecules plays an important role in determining their in vivo pharmacokinetic profile by its pH-dependent binding to the neonatal Fc receptor (FcRn) which is expressed on the endothelial cells lining blood vessels. By virtue of this pH-specific interaction with IgG-Fc, FcRn mediates IgG homeostasis in human adults by maintaining serum IgG levels, and also transfers maternal IgGs from mother to fetus via the placenta. The Fc-FcRn interaction is also critical for keeping IgG-based therapeutic molecules in circulation thereby enhancing their serum half life. A homogeneous cell-based flow cytometric FcRn binding assay was established to characterize the Fc-FcRn interaction of therapeutic IgG-based molecules. It is a competition-based assay, wherein the IgG-Fc containing test molecule competes with a fixed concentration of fluorescently-labeled IgG-Fc moiety in solution for binding to the cell-expressed FcRn. The cell-bound fluorescence is read on a flow cytometer. Response of the test sample is analyzed relative to the standard sample and the results are reported as % relative binding. The assay is robust and meets the qualification criteria for specificity, method linearity, accuracy and precision over the relative binding range of 60%-160%. This assay was shown to effectively characterize altered Fc-FcRn interactions for photo-stressed, heat-stressed, oxidized, and Fc mutant samples. It was observed that the relative binding of the IgG-Fc to the cell-surface-expressed FcRn in the assay varies across different molecules, even within the same IgG subclass. This indicates that the Fc-FcRn binding can be influenced by the antigen-binding region of the molecules in addition to the IgG subclass. Overall, this assay is reflective of the in vivo mechanism of immunoglobulin binding to membrane-bound FcRn, and can be used as an analytical tool for assessing lot-to-lot consistency and stability testing across different batches of the same molecule. Additionally, the assay can be used as an effective tool for elucidating the amino acids in the IgG-Fc domain that are critical for FcRn binding and also for comparing the binding of different IgG-Fc containing molecules to FcRn.

Biochemical assessment of erythropoietin products from Asia versus US Epoetin alfa manufactured by Amgen.

We compared the physical and chemical properties of purported copies of recombinant human erythropoietin (rHuEPO) purchased from Korea, China, and India with the innovator product, Epoetin alfa, manufactured by Amgen Inc. The products were characterized for similarity in the types of glycoforms present, the relative degree of unfolding, in vitro potency, presence of covalent aggregates, and presence of cleavage products using established analytical methods. All products were different from Epoetin alfa (Epogen). The purported copies of rHuEPO from Korea, India, and China contained more glycoforms and other impurities. The in vitro relative potency varied for each product when based on the labeled concentration, while the concentration based on ELISA analysis brought the relative potency, for most products closer to 100%. These data emphasize potential biochemical discrepancies resulting from different cell lines and manufacturing processes. Concentrations varied within products and did not always match the information provided on the product label. As it is not possible to reliably correlate such biochemical discrepancies to clinical consequences, or the lack thereof, these data support the need for extensive preclinical testing and clinical testing of all investigational products as not all safety and efficacy aspects can be assessed during preclinical evaluation.

Isomerization of a single aspartyl residue of anti-epidermal growth factor receptor immunoglobulin gamma2 antibody highlights the role avidity plays in antibody activity.

A new isoform of the light chain of a fully human monoclonal immunoglobulin gamma2 (IgG2) antibody panitumumab against human epidermal growth factor receptor (EGFR) was generated by in vitro aging. The isoform was attributed to the isomerization of aspartate 92 located between phenylalanine 91 and histidine 93 residues in the antigen-binding region. The isomerization rate increased with increased temperature and decreased pH. A size-exclusion chromatography binding assay was used to show that one antibody molecule was able to bind two soluble extracellular EGFR molecules in solution, and isomerization of one or both Asp-92 residues deactivated one or both antigen-binding regions, respectively. In addition, isomerization of Asp-92 showed a decrease in in vitro potency as measured by a cell proliferation assay with a 32D cell line that expressed the full-length human EGFR. The data indicate that antibodies containing either one or two isomerized residues were not effective in inhibiting EGFR-mediated cell proliferation, and that two unmodified antigen binding regions were needed to achieve full efficacy. For comparison, the potency of an intact IgG1 antibody cetuximab against the same receptor was correlated with the bioactivity of its individual antigen-binding fragments. The intact IgG1 antibody with two antigen-binding fragments was also much more active in suppressing cell proliferation than the individual fragments, similar to the IgG2 results. These results indicated that avidity played a key role in the inhibition of cell proliferation by these antibodies against the human EGFR, suggesting that their mechanisms of action are similar.