Researchers Report on the Analytical Similarity of ABP 980 and Reference Herceptin

Amgen’s biosimilar trastuzumab, ABP 980, referencing Herceptin, has been approved in the European Union under the name Kanjinti, while in the United States, the product received a Complete Response Letter from the FDA in July 2018. The biosimilar earned its European approval on the basis of a data package that showed the product to be similar to the reference in nonclinical xenograft models, a phase 1 pharmacokinetic (PK) study, and a phase 3 study in patients with HER2-positive early breast cancer. The drug was also assessed versus 23 lots of the US-licensed reference and 33 lots of the EU-licensed reference that were obtained over a period of 5 years, and a paper recently published in BioDrugs describes the process of assessing the analytical and functional similarity of the 2 reference and 1 biosimilar trastuzumab products.

First, the primary structures of the trastuzumab products were investigated by methods including intact mass, reduced and deglycosylated heavy-chain and light-chain mass analysis, peptide mapping, and glycan mapping, showing that the reference and biosimilar have the same molecular mass. Furthermore, the same N-linked glycosylation site was detected in the same glycopeptide in the biosimilar and the reference products, showing that the products have the same amino acid sequences.

The researchers found some differences among individual glycan species, but they note that the ranges of afucosylated and galactosylated species for the US- and EU-licensed references are “fairly wide,” and all 3 products followed the same glycan antibody—dependent cellular cytotoxicity (ADCC).

The higher-order structure for the biosimilar and the reference were characterized by Fourier-transformed infrared spectroscopy (FTIR), as well as by near ultra-violet circular dichroism for tertiary structure, and differential scanning calorimetry for thermal stability. The FTIR profiles were visually similar, and the spectral similarity analysis demonstrated that the FTIR spectra among the 3 products have 95% or greater similarity. The near ultraviolet circular dichroism (UV CD) profiles were also visually similar, and both the disulfide bonds and aromatic amino acids were in the expected environment as a result of proper protein folding. Spectral similarity analysis showed that the near UV CD spectra have 95% or greater similarity.

Particles and aggregates were assessed via a combination of methods, and the researchers focused on proteinaceous particles. Analysis of subvisible particles show that the reference products and the biosimilar have similar amounts of subvisible particles, and similar amounts of non-spherical particles. Detected aggregates were below the limits of quantification for all products, and the aggregates in all 3 products were similar in terms of size and level.

A slightly lower level of non—glycosylated heavy chain clips was found in ABP 980, but it did not impact the biological activity of the product as demonstrated by a panel of biological assays. Protein content and concentration were similar.

All 3 products were found to have similar HER2 target binding, and potency among the products was also similar. Relative FcRn binding ranges for the 3 products were also found to be similar, which supports the PK equivalence reported in the PK study. FcγRIIa binding, which mediates ADCC activity, was similar among the 3 products, though the researchers note that they observed high variability in FcγRIIa binding in a subset of trastuzumab lots that correlated with specific glycans.

Two methods to assess ADCC were used: an assay using PBMC and SKBR3 cells, and an assay using NK92 effector cells and HCC2218 target cells. The researchers report that the use of NK 92 cells provided a consistent source of effector cells for the entire 5-year period of research. The authors write that the biosimilar and the reference products demonstrated similar ADCC activities in both assays, and the results for the biosimilar were consistent with the wide ranges of glycan and FcγRIIa binding that were found in the references.

The researchers concluded that these results demonstrate that the biosimilar is highly analytically similar to the reference with respect to identity, general properties, primary and higher-order structures, biological activity, and carbohydrate structure. Where there were minor differences, those differences were deemed to be unlikely to impact the therapies’ clinical performance.

Reference

Hutterer KM, Polozova A, Kuhns S, McBride HJ, Cao X, Liu J. Assessing analytical and functional similarity of proposed Amgen biosimilar ABP 980 to trastuzumab [published online April 10, 2019]. BioDrugs. doi: 10.1007/s40259-019-00350-9.