Abstract 516: Obinutuzumab (GA101): A novel type II glycoengineered CD20 antibody exhibits enhanced cell death against Rituximab-resistant and -sensitive cell lines in B-cell non-Hodgkin lymphoma

Abstract

Abstract Background: Rituximab (RTX), an antibody targeting the B-cell antigen CD20, in combination with chemotherapy, is safe, well tolerated and associated with > 90% EFS in children with advanced mature B-Cell NHL (Cairo M.S. et al, ASCO 2010). However, RTX resistance has evolved as one of the limiting factors of such therapy and the exact cause of this resistance is not well understood. C-terminal deletion mutations of CD20 may be one possible reason such resistance or for relapse (Mishima Y. et al, Blood Cancer Journal 2011). Obinutuzumab (GA101), a novel type II glycoengineered CD20 antibody of the IgG1 isotype, demonstrates superior cell death induction and its glyco-engineered Fc region has shown to cause significant enhanced ADCC (Mössner et al, Blood 2010; Niederfellner G. et al, Blood 2011). The objective of this study was to evaluate the efficacy of GA101 as compared to RTX against RTX resistant cell lines (Raji-2R and Raji-4RH, generously supplied by M. Barth, MD, Roswell Park Cancer Center, Buffalo, NY) in-vitro. Methods: 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-4R (Barth M. et al, ASH 2010). All cell lines were cultured in RPMI with 10% FBS and incubated with dose escalation of GA101 (1-100 µg/ml) for 24 hrs. Cell death was evaluated by staining with AnnexinV/7AAD using a standard kit (BD Biosciences) and flow-cytometry. B-Cell Leukemia-Lymphoma (BLL) U-698-M cells (CD20+) (DSMZ, Germany) were used as the positive control; whereas, Loucy cells (CD20−) (T-ALL) (ATCC, Manhass, VA) were used as the negative control. Results: At 100 µg/ml of GA101 when incubated for 24 hrs, Raji and U-698-M demonstrated 26.5±0.42% and 32.4±1.9% cell death, respectively. Cell death of the RRCL, Raji-2R and Raji-4RH, was 16.3±3.4% and 17.5±0.07% respectively, at 100 µg/ml of GA101 at 24 hrs. Significant cell death was demonstrated with RSCL as compared to the RRCL, Raji vs Raji-2R (p<0.05) and Raji vs Raji-4RH (p<0.01). There was no significant change in cell death with any concentration of GA101 with the Loucy cell line. Conclusion: Based on these findings, GA101 is a promising novel CD20 antibody for the treatment of RTX resistant B-Cell Lymphomas and related B-Cell malignancies. Further studies are aimed to identify novel candidates that may increase the efficacy of GA101 against RTX resistant cell lines in-vitro and in-vivo. One such approach is to combine GA101 with activated NK cells or a chemotherapeutic agent. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 516. doi:1538-7445.AM2012-516