Clinical Pharmacokinetic (PK) and Safety (Immunogenicity) of Rituximab Biosimilar RTXM83 in Combination with Chemotherapy CHOP in Patients with Diffuse Large B-Cell Lymphoma (DLBCL)

Background: RTXM83 is a rituximab biosimilar candidate manufactured by MAbxience Company. Full spectrum of physicochemical and preclinical studies showed biosimilarity of RTXM83 and originator drug MabThera^®/Rituxan^® marketed by Roche. MabThera®/Rituxan® product is approved to treat Non-Hodgkin´s Lymphoma, chronic lymphocytic leukemia and rheumatoid arthritis in the EU and US, plus it is approved to treat Diffuse Large B-cell lymphoma (DLBCL) in the EU. Rituximab is also used for other types of lymphoma (e.g. Mantle cell lymphoma) in certain parts of the word.

Objective: To demonstrate comparable pharmacokinetics (PK) and safety profile (immunogenicity) to MabThera®, a clinical PK/immunogenicity analysis was designed to compare RTXM83 and MabThera® when administered with CHOP to patients with DLBCL.

Methods: Analysis of an interim PK/Safety report from randomized and blinded study, where 24 patients with newly diagnosed DLBCL treated with R-CHOP as part of a multi-center study undertaken to assess the PK and immunogenicity. R-CHOP (rituximab-375mg/m2; cyclophopsphamide-750mg/m2; adriamycin-50mg/m2; vincristine-1.4mg/m2 on day 1 and prednisolone-60mg/m2 on days 1 to 5) was given every 3 weeks for a total of 6 cycles.

The PK analysis were conducted on quality control (QC) checked analytical data for Cycle 1 and Cycle 6 using nominal blood sampling times. PK parameters were determined from the serum Rituximab concentration-time profiles obtained following administration of the first (Cycle 1) and last intravenous infusion of study medication (Cycle 6) using non-compartmental procedures in Phoenix WinNonlin (Version 6.2.1).

The immunogenicity assessments were based on a specific and validated method for systematic evaluation of an unwanted immune response against RTXM83 and MabThera®. In fact, a confirmatory assay and specific cut point was established as current described recommendations in white papers and guidance documents. This part assures the assay sensitivity and a “characterization step” in the study sample analysis. A screening assay that picks up 5% positives that are subsequently shown to be due to non-specific binding in a confirmatory (immunodepletion) assay provides assurance that true low positives can be detected. Finally, the clinical immunogenicity measurements were performed on Cycle 5, Cycle 6 and follow-up patient samples.

Results: Following the end of infusion of 375 mg/m2 q3w RTXM83 or MabThera® (Rituximab) (3 hours infusion) administered in combination with CHOP in Cycle 1 and Cycle 6, serum concentrations of Rituximab declined steadily in a generally bi-phasic manner. The arithmetic mean ±SD of PK parameters (T1/2(hrs); C_max (ug/ml); C_min (ug/ml); AUC0-∞ (ug*hrs/ml) of Rituximab during cycle 1, cycle 6 and follow-up patients were determined. All these data are comparable with values previously reported for rituximab in other conditions. No anti-drug antibody case was reported, so RTXM83 and MabThera® displaying null or undetectable immunogenicity.

Conclusions: The data indicate that therapeutic levels of rituximab (RTXM83/Mabthera®) were observed across studied cycles. All data are comparable with values previously reported for rituximab. Therefore, PK profile and immunogenicity profile of RTXM83 is comparable with Mabthera® in treating DLBCL.