The proposed omalizumab biosimilar KA (Shanghai Taiyin Biotechnology) demonstrated similar analytical characteristics, in vitro biological activity, and pharmacology and toxicology in animals compared to the originator, according to investigators.

Omalizumab is a monoclonal antibody targeting immunoglobulin E (IgE) that is used to treat moderate-to-severe asthma. Several biosimilar candidates referencing the originator Xolair are in development.

Structure and Binding Activity Were Similar to the Reference Product

Similarities in primary structure were confirmed by analysis of molecular weight, N- and C-terminal amino acid sequences, peptide profiles, and disulfide bonds. The proposed biosimilar had “identical” primary structure to the originator, according to the authors. Similarity in secondary structure was confirmed by circular dichroism experiments.

The investigators noted some differences in charge variants and post-translational modifications. KA contained 22.5% acid components and 11.6% basic components compared to 12.1% and 8.2% in the reference product. The isoelectric points were the same, “although there was a slight variation between batches.”

There were more post-translational modifications in the biosimilar, including deamidation and oxidation, and “minor differences” in glycosylation. The differences in post-translational modifications “led to the heterogeneous charge variants,” according to the investigators.

Similar in vitro Biological Activity Between KA and Omalizumab Originator

The investigators wrote that the differences in post-translational modifications and glycosylation “did not have a negative impact on the biological activity of KA.” The biosimilar and originator showed “comparable” results in the IgE binding assay, FcεRI-ɑ binding inhibition assay, and cell based anti-degranulation assay, they said. Association and dissociation rates and equilibrium constants were also similar between the 2 antibodies.

In allergic asthma, inhaled allergens bind to antigen-specific IgE, which then binds to the FcεRI receptor, leading to degranulation of mast cells and basophils and an allergic response. Omalizumab acts by inhibiting IgE binding to the receptor, preventing degranulation of mast cells and the subsequent release of inflammatory mediators.

The average binding activity of the reference product relative to the biosimilar was 96.5%, within the acceptable 70% to 130% range set by China’s National Medical Products Administration. Average relative degranulation activity was 98.9%, also suggesting similarity, the authors said.

“No significant differences in pharmacological, pharmacokinetic, and toxicity profiles.”

A mouse model using transplanted human peripheral blood mononuclear cells and stimulation with peanut extracts confirmed that both the reference product and biosimilar candidate promoted IgE polymerization, leading to a change from the active to inactive form of IgE, “resulting in a significant reduction of the allergic symptoms.” Results from the mouse model also showed that “in vivo pharmacologic effects were similar,” the authors wrote.

Pharmacokinetic parameters were evaluated in cynomolgus monkeys, who received 1 of 3 dosage levels of the biosimilar candidate or the reference product each week for 3 weeks. According to the authors, “during the entire administration period, the mean serum antibody concentration-time profiles were superimposable.” There were no significant differences in pharmacokinetic parameters, including maximum drug concentration (Cmax) and area under the curve (AUC), for the same dosage level of the 2 antibodies.

With the exception of a bone fracture in 1 animal 6 hours after administration of the drug, no deaths or “signs of un-wellness” were observed. There were no abnormalities in electrocardiograms, blood pressure, or respiratory rates, “no noteworthy findings in microscopic and pathology evaluation,” and no significant differences in organ weights between groups.

The authors did find “few mild inflammatory lesions in both the control and treated groups,” and the main adverse reactions they observed were alterations in red blood cells and platelets, including anemia and thrombocytopenia. These adverse effects have been reported in the literature, according to the authors, and were reversible with cessation of treatment. They also noted a decrease in serum potassium and calcium levels only in female animals treated with medium and high doses, saying “there is no reasonable explanation for these gender differences, and further studies may be needed.” They added that the doses used in these toxicity tests were much higher than therapeutic doses (30 to 300 mg/kg vs 1 to 10 mg/kg).

Anti-drug antibodies (ADA) appeared in both groups, but a decrease in omalizumab AUC was only observed in 1 animal following detection of an ADA. “These results suggested that the formation of ADA would rarely affect the metabolism of the antibodies in cynomolgus monkeys,” the authors wrote.

The authors concluded that KA has similar activity to the omalizumab reference product in cell-free, in vitro, and relevant in vivo preclinical models, and that their results call for clinical evaluation of biosimilarity.