Abstract 3096: Obinutuzumab (GA101) significantly induces antiproliferative effects and programmed cell death, and significantly downregulates cell signaling pathways in primary mediastinal B-cell lymphoma (PMBL): Obinutuzumab may be a future potential targeted agent for treatment of PMBL
Authors: Yin Changhong , O'Connell Timmy , Ayello Janet , Ven Carmella van de , Lee Sanghoon , Cairo Mitchell 
Published: May 2015

BACKGROUND: Primary Mediastinal large B-cell lymphoma (PMBL) is a rare form of non-Hodgkin Lymphoma (NHL) representing 2% of mature B-cell NHL in patients ≤ 18 years of age (Lones/Cairo et al., JCO, 2000). PMBL is classified as a distinct mature B-Cell lymphoma and is considered midway in the biologic spectrum between Diffuse Large B-Cell Lymphoma (DLBCL) and classical HL (Abramson et al., Blood, 2005). We have recently reported a significant decrease in EFS among children and adolescent PMBL patients compared with other stage III non-PMBL pediatric DLBCL patients following FAB/LMB 96 therapy, suggesting that children and adolescent PMBL may be an inherently different B-NHL (Gerrard/Cairo et al., Blood, 2013). Since 98% of PMBL express CD20, targeting the CD20 receptor with a CD20 antibody is of high clinical interest. Obinutuzumab (GA101) is a novel, anti-CD20 targeted monoclonal antibody recognizing a unique CD20 type II epitope and has been demonstrated to have efficacy in reducing tumor size and improving survival in other B-NHL xenograft models (Mössner et al., Blood, 2010).

OBJECTIVES: We hypothesize that obinutuzumab may be a future potential targeted agent for the treatment of PMBL, and therefore, we investigated the effect of obinutuzumab on cell proliferation, programmed cell death, and cell signaling pathways in PMBL.

METHODS: CD20+ PMBL, Karpas-1106P cells (Karpas) were obtained from the DSMZ, Germany and obinutuzumab was generously provided by C. Klein, Roche. Cell proliferation and apoptotic rate were assessed using MTS and FACS analysis, respectively. Statistical significance was determined by one-tailed Student's t-test.

RESULTS: There was a significant decrease of cell proliferation in obinutuzumab-treated Karpas vs PBS-treated Karpas (1.000 ± 0.000) at 48 hours with 1ug/ml (0.723 ± 0.005, p=0.0007), 10ug/ml (0.688 ± 0.025, p=0.0033), and 20ug/ml (0.627 ± 0.042, p=0.0092) obinutuzumab treatment. There was a significant increase in cell death in Karpas following 10ug/ml obinutuzumab treatment (37.790 ± 10.096, p=0.018) as compared to IgG isotope (1.040 ± 0.834, p=0.340) and PBS control (1.190 ± 0.762) at 48 hours by FACS analysis. We also observed significant decreases in the phosphorylation of Stat6 (0.730 ± 0.005, p=0.0001), Akt (0.691 ± 0.002, p&lt;0.0001), IkBa (0.706 ± 0.006, p=0.0002) and Erk (0.578 ± 0.001, p&lt;0.0001) in 10ug/ml obinutuzumab-treated Karpas as compared to control (1.000 ± 0.000).

CONCLUSIONS: Obinutuzumab significantly induced antiproliferative effects and cell death in PMBL and may be a future potential targeted agent for the treatment of PMBL. The effect(s) of obinutuzumab will be evaluated in vivo in a NOD/SCID PMBL xenograft mouse model.

Citation Format: Changhong Yin, Timmy O'Connell, Janet Ayello, Carmella van de Ven, Sanghoon Lee, Mitchell Cairo. Obinutuzumab (GA101) significantly induces antiproliferative effects and programmed cell death, and significantly downregulates cell signaling pathways in primary mediastinal B-cell lymphoma (PMBL): Obinutuzumab may be a future potential targeted agent for treatment of PMBL. [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 3096. doi:10.1158/1538-7445.AM2014-3096