Cell lines generated from a chronic lymphocytic leukemia mouse model exhibit constitutive Btk and Akt signaling

// Simar Pal Singh 1, 2, 3 , Saravanan Y. Pillai 1 , Marjolein J.W. de Bruijn 1 , Ralph Stadhouders 1, 4 , Odilia B.J. Corneth 1 , Henk Jan van den Ham 5 , Alice Muggen 2 , Wilfred van IJcken 6 , Erik Slinger 7 , Annemieke Kuil 8 , Marcel Spaargaren 8 , Arnon P. Kater 7 , Anton W. Langerak 2 and Rudi W. Hendriks 1 1 Department of Pulmonary Medicine, Erasmus MC, Rotterdam, The Netherlands 2 Department of Immunology, Erasmus MC, Rotterdam, The Netherlands 3 Post graduate school Molecular Medicine, Erasmus MC, Rotterdam, The Netherlands 4 Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona Spain 5 Department of Virosciences, Erasmus MC, Rotterdam, The Netherlands 6 Center for Biomics, Erasmus MC, Rotterdam, The Netherlands 7 Department of Hematology, Academic Medical Center, Amsterdam, The Netherlands 8 Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands Correspondence to: Rudi W. Hendriks, email: r.hendriks@erasmusmc.nl Keywords: B-cell receptor (BCR), bruton’s tyrosine kinase (Btk), chronic lymphocytic leukemia (CLL), ibrutinib, idelalisib Received: March 02, 2017      Accepted: May 03, 2017      Published: May 26, 2017 ABSTRACT Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature CD5 + B cells in blood. Spontaneous apoptosis of CLL cells in vitro has hampered in-depth investigation of CLL pathogenesis. Here we describe the generation of three monoclonal mouse cell lines, EMC2, EMC4 and EMC6, from the IgH.TEμ CLL mouse model based on sporadic expression of SV40 large T antigen. The cell lines exhibit a stable CD5 + CD43 + IgM + CD19 + CLL phenotype in culture and can be adoptively transferred into Rag1 –/– mice. RNA-seq analysis revealed only minor differences between the cell lines and their primary tumors and suggested that NF-κB and mTOR signaling pathways were involved in cell line outgrowth. In vitro survival and proliferation was dependent on constitutive phosphorylation of Bruton’s tyrosine kinase (Btk) at Y551/Y223, and Akt(S473). Treatment of the cell lines with small molecule inhibitors specific for Btk (ibrutinib) or PI3K (idelalisib), which is upstream of Akt, resulted in reduced viability, proliferation and fibronectin-dependent cell adhesion. Treatment of cell line-engrafted Rag1 –/– mice with ibrutinib was associated with transient lymphocytosis, reduced splenomegaly and increased overall survival. Thus, by generating stable cell lines we established a novel platform for in vitro and in vivo investigation of CLL signal transduction and treatment modalities.