Abstract A245: Combination of the glycoengineered Type II CD20 antibody obinutuzumab (GA101), and the novel Bcl-2 selective inhibitor, ABT-199 (GDC-0199), results in superior in vitro and in vivo anti-tumor activity in models of B-cell malignancies. (2013)

Abstract Obinutuzumab (GA101) is a novel glycoengineered type II, anti-CD20 monoclonal antibody induces a high level of direct cell death. As a result of glycoengineering, GA101 has increased affinity for FcγRIIIa on effector cells resulting in enhanced direct cell death and ADCC induction. GA101 is currently in pivotal clinical trials in chronic lymphocytic leukemia (CLL), indolent non-Hodgkins lymphoma (iNHL) and diffuse large B-cell lymphoma (DLBCL). ABT-199 (GDC-0199) is a novel, orally bioavailable, selective Bcl-2 inhibitor that induces robust apoptosis in preclinical models of hematological malignancies and is currently in clinical trials for CLL, NHL and multiple myeloma. Based on their complementary mechanisms of action involving increased apoptosis (GDC-0199) or direct cell death (GA101) the combination of anti-CD20 therapy with a Bcl 2 inhibitor has the potential for greater efficacy in treating B lymphoid malignancies. The combination of GA101 or rituximab with GDC-0199 was studied in vitro utilizing assays that measure direct cell death induction/apoptosis (AxV/Pi positivity) on WSU-DLCL2 NHL, SU-DHL4 DLBCL and Z138 mantle cell lymphoma cells by FACS and the impact of Bcl-2 inhibition on ADCC induction. In vivo efficacy of the combination of GA101 or rituximab and GDC-0199 was evaluated in SU-DHL4 and Z138 xenograft models. GA101 and rituximab enhanced cell death induction when combined with GDC-0199 in SU-DHL4, WSU-DLCL2 and Z138 cell lines. When combined at optimal doses of GA101 and GDC-0199 an additive effect of the two drugs was observed. GDC-0199 did not negatively impact the capability of GA101 or rituximab to induce NK-cell mediated ADCC. Combination of GDC 0199 with GA101 or rituximab in vivo induced greater than additive anti-tumor effects in the SU DHL4 and Z138 xenograft models resulting in tumor regressions and delay in tumor regrowth when compared to monotherapy. Importantly, continued single-agent treatment with GDC-0199 after combination with GA101 resulted in sustained in vivo efficacy in the SU-DHL4 xenograft model. Our data demonstrate that the combination of GA101 with GDC-0199 results in enhanced cell death and robust anti-tumor efficacy in xenograft models representing NHL sub-types that is comparable to combination therapy with rituximab. In addition, single-agent treatment with GDC-0199 following combination with GA101 sustains efficacy in vivo suggesting a potential benefit in continued maintenance therapy with GDC-0199. Collectively, our preclinical data strongly supports clinical investigation of GA101 and GDC-0199 combination therapy, which is currently being evaluated in a phase Ib clinical trial (clinical trial.gov identifier NCT01685892). Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A245. Citation Format: Deepak Sampath, Sylvia Herter, Ellen Ingalla, Frank Herting, Marina Bacac, Michelle Nannini, Wayne J. Fairbrother, Christian Klein. Combination of the glycoengineered Type II CD20 antibody obinutuzumab (GA101), and the novel Bcl-2 selective inhibitor, ABT-199 (GDC-0199), results in superior in vitro and in vivo anti-tumor activity in models of B-cell malignancies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A245.