Study Reports on Physiochemical and Biological Characterization of Rituximab Biosimilar RTXM83

While the United States awaits the launch of its first biosimilar rituximab, other regulatory jurisdictions have biosimilars referencing Rituxan already available on the market. One such product, available in South America, the Middle East, and Africa, is RTXM83, developed by drug maker mAbxience.

A newly published study discusses the physiochemical and biological characterization exercises that were used to demonstrate biosimilarity between RTXM83 and its reference and led to the product’s eventual regulatory approval in multiple territories.¹

According to the study’s authors, primary and higher-order protein structures were analyzed using techniques that included peptide mapping with liquid chromatography—electrospray ionization–tandem mass spectrometry (MS), fluorescence spectroscopy and circular dichroism, and microdifferential scanning calorimetry.

Charge variants were determined by cation-exchange chromatography and capillary isoelectric focusing, whereas glycosylation and glycoform distribution were analyzed using MS, normal phase high-performance liquid chromatography, and high-performance anion-exchange chromatography with pulsed amperometric detection.

Size variants were evaluated by size-exclusion chromatography, sedimentation velocity analytical ultracentrifugation, dynamic light scattering, and capillary electrophoresis—sodium dodecyl sulfate.

Biological characterization included binding assays for complement C1q, CD20, and multiple Fc receptors, along with a potency determination for in vitro apoptosis induction, complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC).

The researchers write that the biosimilar and the reference showed identical primary sequences and disulfide bridge patterns. There was also similarity among higher-order structures, posttranslational modification profiles, and levels of purity.

Functional studies showed that the biosimilar and its reference were similar in the 3 known mechanisms of action of rituximab: apoptosis induction, CDC, and ADCC. Binding affinities to CD20, complement component C1q, and Fc receptors were also equivalent.

The researchers concluded that the biosimilar and the reference product were similar in all critical quality attributes.

The biosimilar was also investigated in a phase 3 clinical study in which it was compared to the reference rituximab in 241 patient with diffuse large B-cell lymphoma.²

In the study, a difference of 3.9% in favor of the biosimilar was observed in the response rate (comprising complete response plus partial response) after 6 cycles of treatment. Safety assessments showed no obvious differences in safety between the biosimilar and the reference, and a low and similar incidence of anti-drug antibodies was observed in both arms.

Pharmacokinetics (PK) were assessed using a population PK approach, and systemic exposure was assessed at cycle 1 and steady state at cycle 6; the PK assessment comprised 5341 samples from 251 individuals, and the geometric least square means ratios fell within the prespecified equivalence margins of 80% to 125%. The pharmacodynamic profile (in terms of time of onset, magnitude, and duration of response) was also similar between RTXM83 and its reference; taken together, these data led the authors of the phase 3 study to conclude that the biosimilar and the reference product were highly similar.

Reference

1. Cerutti ML, Pesce A, Bés C, Seigelchifer M. Physiochemical and biological characterization of RTXM83, a new rituximab biosimilar [published online March 29, 2019]. BioDrugs. doi: 10.1007/s40259-019-00349-2.

2. Candelaria M, Gonzalez DE, Beniwal SK, et al. A randomized, double-blind, phase 3 study comparing proposed biosimilar rituximab (RTXM83) versus reference rituximab, both in combination with CHOP, in the first line treatment of patients with diffuse large B-cell lymphoma (DLBCL). Blood. 2017;130:1556. www.bloodjournal.org/content/130/Suppl_1/1556.