Abstract 2479: Obinutuzumab compared to Rituximab significantly enhances cell death, antibody dependent cytotoxicity (ADCC) and improves overall survival against CD20+ rituximab-sensitive/-resistant Burkitt Lymphoma (BL) and precursor Lymphoblastic L

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Background: CD20, expressed on normal and malignant B-cells, has proven to be a useful target for immunotherapeutic approaches in hematological malignancies. (Dalle, S et al. Mol. Can. Ther., 2011) Patients who relapse with CD20+ BL/ B-ALL have a dismal prognosis, often associated with chemotherapy resistance and may require alternative therapeutic strategies (Cairo et al. Blood, 2007, Cairo et al. JCO, 2012, Barth/Cairo et al. BJH, 2013,Goldman/Cairo et al. Leukemia, 2013). Obinutuzumab, a novel glycoengineered type II CD20 antibody, has been shown to enhance cell death and ADCC vs. RTX (Herter et al, Clinc Can Res, 2013), and was recently approved by FDA and EMA for first line treatment of CLL in combination with chlorambucil. Objective: To evaluate anti-tumor activity of obinutuzumab vs RTX against RTX resistant/sensitive BL and pre-B-ALL tumor targets in-vitro/ in-vivo in xenografted NSG mice. Methods: Raji (CD20+), (ATCC, Manhass, VA), U698-M (CD20+, DSMZ, Germany) and Raji-4RH (provided by M. Barth, Roswell Park Cancer Institute) were cultured in RPMI with 10% FBS. Tumor cells were incubated with 100 μg/ml obinutuzumab (Hoffmann La Roche (Switzerland)), and/or RTX for 48 hrs. Cell death was evaluated by staining with Ann.V/7AAD by flow-cytometry. ADCC were performed with K562-IL-15-41BBL expanded NK cells at 20:1E: T ratio. Six to 8 week old female NSG (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ), were divided into 5 groups: PBS only (control), isotype control (IgG), obinutuzumab (10 and 30 mg/kg), and RTX (30 mg/kg). Mice were xenografted with intravenous injections of Luc+ Raji, Raji4RH and U698M cells at 5×106 tumor cells/mouse. Mice were treated every 7 days for 8 weeks. Tumor burden was monitored by IVIS spectrum system. Results: Obinutuzumab vs. RTX (100 μg/ml), significantly enhanced cell death in Raji, 35.6 ± 3.1 vs. 25.1± 2.0% (p = 0.001), Raji2R, 18.2 ± 0.9 vs. 7.8 ± 2.4% (p = 0.001), Raji4RH, 19.7 ± 2.2 vs. 7.97 ± 3.4% (p = 0.001) and U698-M 47.3 ± 4.9 vs 23.2 ± 0.50%, (p = 0.001). Obinutuzumab vs RTX also elicited a significant increase in ADCC in expanded NK cells, Raji 73.8± 8.1% vs 56.81± 4.6% (p = 0.001), Raji-2R, 38.0 ± 2.0 vs 21.6 ± 1.2% (p = 0.0001), Raji-4RH 40.0±1.6% vs 0.5±1.1%, (p = 0.001), and U-698-M 70.0±6% vs. 45.56± 0.1%, (p = 0.001). Further, overall survival in mice receiving 30 mg/kg of obinutuzumab was significantly increased when compared to mice receiving 30 mg/kg of RTX; Raji (p = 0.05), Raji4RH (p = 0.024) and U698-M (p = 0.03). Conclusion: Obinutuzumab significantly enhances cell death and NK mediated ADCC in RTX sensitive/ resistant CD20+ BL and pre-B-ALL vs. RTX. Furthermore, obinutuzumanb significantly increased survival and decreased tumor burden in BL and Pre-B-ALL xenografts compared to an equal dose of RTX. Citation Format: Aradhana Awasthi Tiwari, Janet Ayello, Carmella Vandeven, Mona Elmacken, Matthew J. Barth, Christian Klein, Mitchell S. Cairo. Obinutuzumab compared to Rituximab significantly enhances cell death, antibody dependent cytotoxicity (ADCC) and improves overall survival against CD20+ rituximab-sensitive/-resistant Burkitt Lymphoma (BL) and precursor Lymphoblastic L [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2479. doi:10.1158/1538-7445.AM2015-2479