Leukemic cells expressing NCOR1-LYN are sensitive to dasatinib in vivo in a patient-derived xenograft mouse model

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a distinct subtype of B-ALL with a poor prognosis. Rearrangement of LYN is a recurrent genetic abnormality in Ph-like ALL, but functional analysis of LYN-related fusion genes identified in ALL has not been reported. In this study, we performed functional analysis of the NCOR1-LYN fusion gene identified in a pediatric Ph-like ALL patient to establish its potential for molecular targeted therapy. Retroviral transduction of interleukin (IL)-3-dependent Ba/F3 cells with NCOR1-LYN enabled IL-3-independent proliferation, with constitutive phosphorylation of the tyrosine residues of the LYN kinase domain in the fusion protein. Replacing tyrosine residues with phenylalanine in the LYN kinase domain abolished IL-3 independence. Tyrosine kinase inhibitor dasatinib killed Ba/F3 cells expressing NCOR1-LYN in vitro accompanied by dephosphorylation of the tyrosine residues of the LYN kinase domain in the fusion protein. In a patient-derived xenograft (PDX) mouse model, generated using leukemic cells from the NCOR1-LYN positive Ph-like ALL patient, dasatinib controlled the growth of leukemic cells in vivo and significantly extended the survival time of the PDX mice (p=0.03). Our data demonstrate that, like other kinase fusions identified in Ph-like ALL, the NCOR1-LYN rearrangement has proliferative activity, and that tyrosine phosphorylation of the LYN kinase domain is critical for IL-3 independent growth. Furthermore, in a preclinical model we demonstrate the efficacy in vivo of dasatinib as therapy for Ph-like ALL with a LYN rearrangement. Ba/F3 cells were transduced with NCOR1-LYN protein by the Retro-X Tet-on Advanced Inducible System (Clontech), and Ba/F3 cells expressing NCOR1-LYN under doxycycline (DOX) dependent manner were established. To reveal which pathways affected by introducing NCOR1-LYN, Ba/F3 cells expressing NCOR1-LYN induced by DOX (Ba/F3-NCOR1-LYN) and uninduced Ba/F3 cells (mock Ba / F3) were cultured in triplicate, and total RNA was extracted from Ba/F3-NCOR1-LYN and mock Ba/F3.