Telomere-Based Pre-Clinical Therapy in a Murine Model of Non-Hodgkin’s Lymphoma of the Diffuse Large B Cell (DLCL)Type.

The dual bromodomain Brd2 is closely related to the basal transcription factor TAF_II250, which is essential for cyclin A transactivation and mammalian cell cycle progression. Constitutive expression of BRD2 (under Eμ control) in the lymphoid lineage of transgenic mice elevates basal transcription of cyclin A, destabilizes the cell cycle and leads to B cell leukemias and lymphomas that are monoclonal, morphologically uniform, transplantable and highly malignant. The surface immunophenotype of the lymphoma cells is: B220+, CD19+, sIgM+, CD5+, CD9+; B7-1 and B7-2 elevated, CD23low; CD11b-, Ly-6G- and CD49b-, supporting lymphoid-restricted lineage; CD117- (c-kit) and CD127- (interleukin-7 receptor α-chain), consistent with mature cells; CD25-, syndecan-1-, and CD69- and exhibit a high IgM/low IgD ratio, which taken together identify a B-1 cell type. Malignant, proliferating cells infiltrate lymph nodes, liver, lung and kidney, and at late stages, cause anemia and a fatal peripheral leukemia over a 14-day time course from tumor cell transplantation to death. Genome-wide transcriptional expression profiling of these lymphoma cells reveals a transcriptional fingerprint that is most similar to human diffuse large B cell lymphoma (DLCL) with an “activated B cell” signature, consistent with histopathology, and establishes a novel murine DLCL model. DLCL is the most common type of non-Hodgkin’s lymphoma (NHL) in humans; all lymphomas combined are the fifth most common type of cancer diagnosed and the sixth most common cause of death in the United States. We treated syngeneic transplanted mice with CHOP (i.e. cyclophosphamide 40 mg/kg i.v., doxorubicin 3.3 mg/kg i.v., vincristine 0.5 mg/kg i.v. and predisone 0.2 mg/kg p.o. every day for 14 days) and monitored individual lymphoma cells, tagged with human-CD4+, by flow cytometry of lymphoid and non-lymphoid organs. In a novel approach, we supplemented CHOP with DNA oligonucleotides that mimic the chromosomal telomere, which we call a “T-oligo.” Normal cells exposed to this drug in vitro undergo transient cell cycle arrest, but DLCL cells undergo p53-dependent apoptosis. The mechanism immediately suggests a novel method of chemotherapy for leukemia and lymphoma to supplement CHOP. In mice treated systemically with CHOP and T-oligo, we observed major reductions in the leukemic burden in peripheral blood, reduced lymphadenopathy, reduced leukemic infiltrates of non-lymphoid organs and splenomegaly in the combined (“CHOP+T”) regimen over CHOP alone. We also confirmed in normal B lymphocytes that T-oligo causes only cell cycle arrest, not apoptosis. Mice likewise showed low toxicity to T-oligo at the effective doses, opening the way to a more extensive pre-clinical trial of this novel approach to NHL therapy.