Abstract 2902: Obinutuzumab (GA101) significantly increases overall survival against CD20+ rituximab-sensitive and -resistant Burkitt (BL) and acute lymphoblastic leukemia (B-ALL): potential targeted therapy in patients with high risk BL and pre-B-ALL

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Patients who relapse with CD20+ B-NHL and B cell Acute lymphoblastic leukemia (B-LL) have a dismal prognosis, which is often associated with chemotherapy resistance and may require alternative therapeutic strategies (Cairo et al. JCO, 2012, Barth/Cairo et al. BJH, 2013). Rituximab (RTX) in combination with FAB 96 chemotherapy is a safe and well-tolerated and is associated with > 90% EFS in children with newly diagnosed and advanced mature B-Cell NHL (Goldman/Cairo et al. Leukemia, 2013). Resistance to RTX, however, may predispose patients with CD20+ B-LL to an increase risk of relapse and/or disease progression (Barth/Cairo et al. BJH, 2012; Tsai et al. Cl. Can. Res, 2012). Obinutuzumab, a novel type II glycoengineered CD20 antibody, mediates enhanced cell death and ADCC vs. RTX (Bologna L et al. JI, 2012), and was recently approved by FDA for first line treatment of CLL in combination with chlorambucil. Objective: To evaluate anti-tumor activity of obinutuzumab vs RTX against RTX resistant and sensitive BL and pre-B-ALL in xenografted NSG mice. Methods: Raji (CD20+) and Loucy (T-ALL, 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. The lentiviral construct, pSico PolII-eGFP-Luc2, was transfected into Raji, Raji 4RH (RTX resistant), U698M and Loucy. Six to 8 week old female NSG (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ), mice were bred in house under pathogen free conditions, NSG mice were divided into 5 groups: PBS only (control), isotype control (IgG), obinutuzumab 10 mg/kg (generously supplied by Christian Klein, PhD (Roche)), obinutuzumab (30 mg/kg), and rituximab (30 mg/kg). Mice were xenografted with intravenous injections of Luc+ Raji, Raji4RH, U698M and Loucy cells at 5x106 tumor cells/mouse. 6-8 days after tumor cell injection, mice were then injected every 7 days with the respective therapy for 8 weeks. Mice were closely monitored for tumor burden and survival for up to 12 weeks ( approx. 80 days) via bioluminescent imaging (BLI) using the IVIS Spectrum system. Results: We demonstrated that obinutuzumab was significantly more effective than RTX when administered at the same doses in BL (RTX resistant/sensitive) and pre-B-ALL xenografts. Overall survival in mice receiving 30 mg/kg of obinutuzumab was significantly increased when compared to mice receiving 30 mg/kg of RTX in BL; Raji (p=0.0002), Raji4RH (p=0.01) and U698-M (p=0.001), respectively. Conclusion: These preliminary studies demonstrate that RTX sensitive/resistant BL and pre-B-ALL xenografted mice display significantly increased survival when given 30 mg/kg of obinutuzumab and decreased tumor burden in BL and Pre-B-ALL xenografts compared to equal dose of RTX. Citation Format: Aradhana A. Tiwari, Janet Ayello, Carmella van de Ven, Matthew J. Barth, Mitchell S. Cairo. Obinutuzumab (GA101) significantly increases overall survival against CD20+ rituximab-sensitive and -resistant Burkitt (BL) and acute lymphoblastic leukemia (B-ALL): potential targeted therapy in patients with high risk BL and pre-B-ALL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2902. doi:10.1158/1538-7445.AM2014-2902