Anti-CD20 Antibody GA101 Shows Higher Cytotoxicity but Is Competitively Displaced by Rituximab in Mantle Cell Lymphoma.

Mantle cell lymphoma (MCL) is characterized by a poor long-term prognosis with a median survival of 3–5 years. Type I anti-CD20 antibody rituximab has demonstrated a clear anti-proliferative effect in MCL and achieves increased response rates in combination with chemotherapy. GA101, a third-generation IgG1 anti-CD20 antibody displays improved ADCC and superior direct cell death induction by virtue of glycoengineering compared to rituximab and its targeting a type II epitope on CD20, respectively.

Using a panel of MCL cell lines (Rec-1, HBL-2, Jeko-1, Granta-519, JVM-2 and Z-138) we determined the effect of GA101 alone as well as in combination with rituximab on cell viability and proliferation. Karpas-422 (Diffuse Large B-Cell Lymphoma) was used as a control cell line. MCL and Karpas-422 cells were treated with GA101 or rituximab at concentrations of 1 – 20μg/ml and rituximab. Cell viability was analyzed by trypan-blue exclusion tests at 0h, 24h, 48h and 72h. The panel of MCL cell lines and Karpas-422 were then treated with GA101 and rituximab each at 1 and 10 μg/ml to determine potential synergism of antibody combinations. Accordingly, a fractional product calculation was performed: synergism > 0,1; antagonism < −0,1. In addition, Western-blot and RNA-array-analyses were performed to elucidate potential intra-cellular downstream pathway mechanisms.

After mono-exposure with GA101 (1 μg/ml), Granta-519 and Rec-1 showed the highest sensitivity (65–75% cell reduction in Granta-519 and 35–40% in Rec-1). Intermediate results were gained for Z-138, HBL-2, Jeko-1 and JVM-2 and Karpas-422 (15–20%). rituximab mono-exposure at 12,5 μg/ml showed a 25% reduction of cell count in Granta-519, 20% in HBL-2 and < 5% in Rec-1, Jeko-1 and Z-138. Combination experiments suggested the competitive binding of the two antibodies. Thus, GA101 plus rituximab combination experiments resulted in a lower cytotoxicity than GA101 alone, according to fractional product calculations.

Although GA101 is competitively displaced by rituximab, GA101 demonstrates higher efficacy in MCL cell lines than rituximab, even at a more than 10-fold lower concentration. Currently RNA-array- and Western blot analysis are being performed to identify the critical pathways responsible for the superior cytotoxicity of GA101.

Klein:Discovery Oncology, Roche Diagnostics GmbH: Employment. Weinkauf:Lilly Deutschland GmbH: Research Funding. Hutter:Lilly Deutschland GmbH: Research Funding. Zimmermann:Lilly Deutschland GmbH: Research Funding. Dreyling:Roche: Honoraria, Research Funding.