BCL6 enables Ph+ acute lymphoblastic leukaemia cells to survive BCR-ABL1 kinase inhibition.

Tyrosine kinase inhibitors (TKIs) are widely used to treat patients with leukaemia driven by BCR-ABL1 (ref. 1) and other oncogenic tyrosine kinases. Recent efforts have focused on developing more potent TKIs that also inhibit mutant tyrosine kinases. However, even effective TKIs typically fail to eradicate leukaemia-initiating cells (LICs), which often cause recurrence of leukaemia after initially successful treatment. Here we report the discovery of a novel mechanism of drug resistance, which is based on protective feedback signalling of leukaemia cells in response to treatment with TKI. We identify BCL6 as a central component of this drug-resistance pathway and demonstrate that targeted inhibition of BCL6 leads to eradication of drug-resistant and leukaemia-initiating subclones

Aberration in DNA Methylation in B-Cell Lymphomas Has a Complex Origin and Increases with Disease Severity

Despite mounting evidence that epigenetic abnormalities play a key role in cancer biology, their contributions to the malignant phenotype remain poorly understood. Here we studied genome-wide DNA methylation in normal B-cell populations and subtypes of B-cell non-Hodgkin lymphoma: follicular lymphoma and diffuse large B-cell lymphomas. These lymphomas display striking and progressive intra-tumor heterogeneity and also inter-patient heterogeneity in their cytosine methylation patterns. Epigenetic heterogeneity is initiated in normal germinal center B-cells, increases markedly with disease aggressiveness, and is associated with unfavorable clinical outcome. Moreover, patterns of abnormal methylation vary depending upon chromosomal regions, gene density and the status of neighboring genes. DNA methylation abnormalities arise via two distinct processes: i) lymphomagenic transcriptional regulators perturb promoter DNA methylation in a target gene-specific manner, and ii) aberrant epigenetic states tend to spread to neighboring promoters in the absence of CTCF insulator binding sites

BCL6-mediated repression of p53 is critical for leukemia stem cell survival in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is induced by the oncogenic BCR-ABL1 tyrosine kinase and can be effectively treated for many years with tyrosine kinase inhibitors (TKIs). However, unless CML patients receive life-long TKI treatment, leukemia will eventually recur; this is attributed to the failure of TKI treatment to eradicate leukemia-initiating cells (LICs). Recent work demonstrated that FoxO factors are critical for maintenance of CML-initiating cells; however, the mechanism of FoxO-dependent leukemia initiation remained elusive. Here, we identified the BCL6 protooncogene as a critical effector downstream of FoxO in self-renewal signaling of CML-initiating cells. BCL6 represses Arf and p53 in CML cells and is required for colony formation and initiation of leukemia. Importantly, peptide inhibition of BCL6 in human CML cells compromises colony formation and leukemia initiation in transplant recipients and selectively eradicates CD34+ CD38− LICs in patient-derived CML samples. These findings suggest that pharmacological inhibition of BCL6 may represent a novel strategy to eradicate LICs in CML. Clinical validation of this concept could limit the duration of TKI treatment in CML patients, which is currently life-long, and substantially decrease the risk of blast crisis transformation

Characterization of GECPAR, a noncoding RNA that regulates the transcriptional program of diffuse large B cell lymphoma

Enhancers are regulatory regions of DNA, which play a key role in cell-type specific differentiation and development. Most active enhancers are transcribed into enhancer RNAs (eRNAs) that can regulate transcription of target genes by means of in cis as well as in trans action. eRNAs stabilize contacts between distal genomic regions and mediate the interaction of DNA with master transcription factors. Here, we characterised an enhancer RNA, GECPAR (GErminal Center Proliferative Adapter RNA), that is specifically transcribed in normal and neoplastic germinal center B-cells from the super-enhancer of POU2AF1, a key regulatory gene of the germinal center reaction. Using diffuse large B cell lymphoma cell line models, we demonstrated the tumor suppressor activity of GECPAR, which is mediated via its transcriptional regulation of proliferation and differentiation genes, particularly MYC and the Wnt pathway

MALT1 Small Molecule Inhibitors Specifically Suppress ABC-DLBCL In Vitro and In Vivo

SummaryMALT1 cleavage activity is linked to the pathogenesis of activated B cell-like diffuse large B cell lymphoma (ABC-DLBCL), a chemoresistant form of DLBCL. We developed a MALT1 activity assay and identified chemically diverse MALT1 inhibitors. A selected lead compound, MI-2, featured direct binding to MALT1 and suppression of its protease function. MI-2 concentrated within human ABC-DLBCL cells and irreversibly inhibited cleavage of MALT1 substrates. This was accompanied by NF-κB reporter activity suppression, c-REL nuclear localization inhibition, and NF-κB target gene downregulation. Most notably, MI-2 was nontoxic to mice, and displayed selective activity against ABC-DLBCL cell lines in vitro and xenotransplanted ABC-DLBCL tumors in vivo. The compound was also effective against primary human non-germinal center B cell-like DLBCLs ex vivo

The metabolic adaptation evoked by arginine enhances the effect of radiation in brain metastases

Selected patients with brain metastases (BM) are candidates for radiotherapy. A lactatogenic metabolism, common in BM, has been associated with radioresistance. We demonstrated that BM express nitric oxide (NO) synthase 2 and that administration of its substrate l-arginine decreases tumor lactate in BM patients. In a placebo-controlled trial, we showed that administration of l-arginine before each fraction enhanced the effect of radiation, improving the control of BM. Studies in preclinical models demonstrated that l-arginine radiosensitization is a NO-mediated mechanism secondary to the metabolic adaptation induced in cancer cells. We showed that the decrease in tumor lactate was a consequence of reduced glycolysis that also impacted ATP and NAD+ levels. These effects were associated with NO-dependent inhibition of GAPDH and hyperactivation of PARP upon nitrosative DNA damage. These metabolic changes ultimately impaired the repair of DNA damage induced by radiation in cancer cells while greatly sparing tumor-infiltrating lymphocytes.Fil: Marullo, Rossella. Cornell University; Estados UnidosFil: Castro, Monica. Universidad de Buenos Aires; ArgentinaFil: Yomtoubian, Shira. Cornell University; Estados UnidosFil: Nieves Calvo Vidal, M.. Cornell University; Estados UnidosFil: Revuelta, María Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Krumsiek, Jan. Cornell University; Estados UnidosFil: Nicholas, Andrew P.. Cornell University; Estados UnidosFil: Cresta Morgado, Pablo. Universidad de Buenos Aires; ArgentinaFil: Yang, ShaoNing. Cornell University; Estados UnidosFil: Medina, Vanina Araceli. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas; ArgentinaFil: Roth, Berta María Cristina. Universidad de Buenos Aires; ArgentinaFil: Bonomi, Marcelo. Ohio State University; Estados UnidosFil: Keshari, Kayvan R.. Memorial Sloan Kettering Cancer Center; Estados UnidosFil: Mittal, Vivek. Cornell University; Estados UnidosFil: Navigante, Alfredo Hugo. Universidad de Buenos Aires; ArgentinaFil: Cerchietti, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; Argentin

Integrin αvβ3 acting as membrane receptor for thyroid hormones mediates angiogenesis in malignant T cells

The interaction of lymphoid tumor cells with components of the extracellular matrix via integrin αvβ3 allows tumor survival and growth. This integrin was demonstrated to be the membrane receptor for thyroid hormones (THs) in several tissues. We found that THs, acting as soluble integrin αvβ3 ligands, activated growth-related signaling pathways in T-cell lymphomas (TCLs). Specifically, TH-activated αvβ3 integrin signaling promoted TCL proliferation and angiogenesis, in part, via the upregulation of vascular endothelial growth factor (VEGF). Consequently, genetic or pharmacologic inhibition of integrin αvβ3 decreased VEGF production and induced TCL cell death in vitro and in human xenograft models. In sum, we show that integrin αvβ3 transduces prosurvival signals into TCL nuclei, suggesting a novel mechanism for the endocrine modulation of TCL pathophysiology. Targeting this mechanism could constitute an effective and potentially low-toxicity chemotherapy-free treatment of TCL patients.Fil: Cayrol, Maria Florencia. Pontificia Universidad Católica Argentina ; ArgentinaFil: Díaz Flaqué, María Celeste. Pontificia Universidad Católica Argentina ; ArgentinaFil: Tharu, Fernando. Cornell University; Estados UnidosFil: Yang, Shao Ning. Cornell University; Estados UnidosFil: Sterle, Helena Andrea. Pontificia Universidad Católica Argentina ; ArgentinaFil: Bolontrade, Marcela Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Amorós, Mariana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Isse, Blanca Alicia de Los Angeles G.. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Farias, Ricardo Norberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Biológica; ArgentinaFil: Ahn, Haelee. Cornell University; Estados UnidosFil: Tian, Ye F.. Cornell University; Estados UnidosFil: Tabbò, Fabrizio. Cornell University; Estados UnidosFil: Singh, Ajnesh. Cornell University; Estados UnidosFil: Inghirami, Giorgio. Cornell University; Estados UnidosFil: Cerchietti, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Cornell University; Estados UnidosFil: Cremaschi, Graciela Alicia. Pontificia Universidad Católica Argentina ; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentin

BCL6 is critical for the development of a diverse primary B cell repertoire

BCL6 protects germinal center (GC) B cells against DNA damage–induced apoptosis during somatic hypermutation and class-switch recombination. Although expression of BCL6 was not found in early IL-7–dependent B cell precursors, we report that IL-7Rα–Stat5 signaling negatively regulates BCL6. Upon productive VH-DJH gene rearrangement and expression of a μ heavy chain, however, activation of pre–B cell receptor signaling strongly induces BCL6 expression, whereas IL-7Rα–Stat5 signaling is attenuated. At the transition from IL-7–dependent to –independent stages of B cell development, BCL6 is activated, reaches expression levels resembling those in GC B cells, and protects pre–B cells from DNA damage–induced apoptosis during immunoglobulin (Ig) light chain gene recombination. In the absence of BCL6, DNA breaks during Ig light chain gene rearrangement lead to excessive up-regulation of Arf and p53. As a consequence, the pool of new bone marrow immature B cells is markedly reduced in size and clonal diversity. We conclude that negative regulation of Arf by BCL6 is required for pre–B cell self-renewal and the formation of a diverse polyclonal B cell repertoire

Inhibition of Anaplastic Lymphoma Kinase (ALK) Activity Provides a Therapeutic Approach for CLTC-ALK-Positive Human Diffuse Large B Cell Lymphomas

ALK positive diffuse large B-cell lymphomas (DLBCL) are a distinct lymphoma subtype associated with a poor outcome. Most of them feature a t(2;17) encoding a clathrin (CLTC)-ALK fusion protein. The contribution of deregulated ALK-activity in the pathogenesis and maintenance of these DLBCLs is not yet known. We established and characterized the first CLTC-ALK positive DLBCL cell line (LM1). LM1 formed tumors in NOD-SCID mice. The selective ALK inhibitor NVP-TAE684 inhibited growth of LM1 cells in vitro at nanomolar concentrations. NVP-TAE684 repressed ALK-activated signalling pathways and induced apoptosis of LM1 DLBCL cells. Inhibition of ALK-activity resulted in sustained tumor regression in the xenotransplant tumor model. These data indicate a role of CLTC-ALK in the maintenance of the malignant phenotype thereby providing a rationale therapeutic target for these otherwise refractory tumors