Effect of obinutuzumab (GA101), a type II glycoengineered monoclonal antibody targeting CD20, against rituximab resistant and sensitive cell lines in B-cell non-Hodgkin lymphoma.

Abstract

e21150 Background: : Relapse or insufficient response or resistance to Rituximab (RTX) has evolved as a challenge in therapy of B-cell NHL. RTX in combination with FAB chemotherapy is a safe, well tolerated and associated with > 90% EFS in children with advanced mature B-Cell NHL (Cairo M.S. et al, ASCO 2010). Obinutuzumab (GA101), a novel type II glyco-engineered CD20 antibody of the IgG1 isotype, demonstrates superior cell death induction and its glycoengineered Fc region has shown to cause significantly enhanced ADCC (Mössner et al, Bld 2010; Niederfellner G. et al, Bld 2011). We evaluated the efficacy of GA101 against Raji (Burkitt Lymphoma), a RTX sensitive cell line (RSCL) and RTX resistant cell lines(RRCL), Raji-2R and Raji-4RH, respectively (generously supplied by M. Barth, MD, Roswell Park Cancer Center, Buffalo, NY. Barth M. et al, ASH 2010). Methods: All cell lines were cultured in RPMI with 10% FBS and incubated with escalating doses of GA101 (1-1000 µg/ml) for 24 hrs (n=10), 48 and 72 hrs (n=6). Cell death was evaluated by staining with AnnexinV/7AAD and flow-cytometry. B-Cell Lymphoblastic Lymphoma (BLL) U-698-M cells (CD20+) were used as the positive and Loucy cells (CD20-) (T-ALL) were used as the negative controls. Results: At 48 hrs 100 µg/ml of GA101, Raji and U-698-M demonstrated highest cell death of 33.62±5.7% and 37.8± 3.9%, respectively; while Raji-2R and Raji-4RH cell death was 22.8±1.8% and 10.31±0.81% (p<0.02) and (p<0.001) respectively. At 1000 µg/ml of GA101 at 24 hrs, Raji demonstrated increased cell death 40.27±9.1% compared with Raji2R 14.1±0.07 and Raji4RH 20.3± 3.2 (p<0.001) and (p<0.001) respectively. Conclusions: GA101 represents a promising candidate for treating RTX resistant B-Cell Lymphomas and related CD20+B-Cell malignancies. Further studies should aim to identify novel approaches such as combination with activated NK Cells or chemotherapeutic agents that may enhance or synergize with the efficacy of GA101. Further investigations aim to elucidate the mechanisms responsible for minimal cell death induction on the U698M and Raji cell lines.