SUMMARY MALT1 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.

Integrative genomic and gene-expression analyses have identified amplified onco-genes in B-cell non-Hodgkin lymphoma (B-NHL), but the capability of such technologies to localize tumor suppressor genes within homozygous deletions remains unexplored. Array-based comparative genomic hybridization (CGH) and gene-expression microarray analysis of 48 cell lines derived from patients with different B-NHLs delineated 20 homozy-gous deletions at 7 chromosome areas, all of which contained tumor suppressor gene targets. Further investigation revealed that only a fraction of primary biopsies presented inactivation of these genes by point mutation or intragenic deletion, but instead some of them were frequently silenced by epigenetic mechanisms. Notably, the pattern of genetic and epigenetic inactivation differed among B-NHL subtypes. Thus, the P53-inducible PIG7/LITAF was silenced by homozygous deletion in primary mediastinal B-cell lym-phoma and by promoter hypermethyl-ation in germinal center lymphoma, the proapoptotic BIM gene presented ho-mozygous deletion in mantle cell lym-phoma and promoter hypermethylation in Burkitt lymphoma, the proapoptotic BH3-only NOXA was mutated and preferentially silenced in diffuse large B-cell lym-phoma, and INK4c/P18 was silenced by biallelic mutation in mantle-cell lym-phoma. Our microarray strategy has identified novel candidate tumor suppressor genes inactivated by genetic and epige-netic mechanisms that substantially vary among the B-NHL subtypes. (Blood. 2007; 109:271-280)

In Burkitt lymphoma/leukemia (BL), achievement of complete remission with first-line chemotherapy remains a challenging issue, as most patients who respond remain disease-free, whereas those refractory have few options of being rescued with salvage therapies. The mechanisms underlying BL chemoresistance and how it can be circumvented remain undetermined. We previously reported the frequent inactivation of the proapoptotic BIM gene in B-cell lymphomas. Here we show that BIM epigenetic silencing by concurrent promoter hypermethylation and deacetylation occurs frequently in primary BL samples and BL-derived cell lines. Remarkably, patients with BL with hypermethylated BIM presented lower complete remission rate (24% vs 79%; P ‫؍‬ .002) and shorter overall survival (P ‫؍‬ .007) than those with BIM-expressing lymphomas, indicating that BIM transcriptional repression may mediate tumor chemoresistance. Accordingly, by combining in vitro and in vivo studies of human BL-xenografts grown in immunodeficient RAG2 ؊/؊ ␥c ؊/؊ mice and of murine B220 ؉ IgM ؉ B-cell lymphomas generated in E-MYC and E-MYC-BIM ؉/؊ transgenes, we demonstrate that lymphoma chemoresistance is dictated by BIM gene dosage and is reversible on BIM reactivation by genetic manipulation or after treatment with histone-deacetylase inhibitors. We suggest that the combination of histone-deacetylase inhibitors and high-dose chemotherapy may overcome chemoresistance, achieve durable remission, and improve survival of patients with BL. (Blood. 2010;116(14):2531-2542)

The chromosomal translocation t(11;14)(q13;q32) leading to cyclin-D1 overexpression plays an essential role in the development of mantle cell lymphoma (MCL), an aggressive tumor that remains incurable with current treatment strategies. Cyclin-D1 has been postulated as an effective therapeutic target, but the evaluation of this target has been hampered by our incomplete understanding of its oncogenic functions and by the lack of valid MCL murine models. To address these issues, we generated a cyclin-D1-driven mouse model in which cyclin-D1 expression can be regulated externally. These mice developed cyclin-D1-expressing lymphomas capable of recapitulating features of human MCL. We found that cyclin-D1 inactivation was not sufficient to induce lymphoma regression in vivo; however, using a combination of in vitro and in vivo assays, we identified a novel prosurvival cyclin-D1 function in MCL cells. Specifically, we found that cyclin-D1, besides increasing cell proliferation through deregulation of the cell cycle at the G 1 -S transition, sequestrates the proapoptotic protein BAX in the cytoplasm, thereby favoring BCL2's antiapoptotic function. Accordingly, cyclin-D1 inhibition sensitized the lymphoma cells to apoptosis through BAX release. Thus, genetic or pharmacologic targeting of cyclin-D1 combined with a proapoptotic BH3 mimetic synergistically killed the cyclin-D1-expressing murine lymphomas, human MCL cell lines, and primary lymphoma cells. Our study identifies a role of cyclin-D1 in deregulating apoptosis in MCL cells, and highlights the potential benefit of simultaneously targeting cyclin-D1 and survival pathways in patients with MCL. This effective combination therapy also might be exploited in other cyclin-D1-expressing tumors.antle cell lymphoma (MCL) is a distinct lymphoma entity that accounts for ∼6-8% of all cases of lymphoma (1, 2). MCL is thought to be derived from naïve pregerminal center B lymphocytes localized in primary follicles or in the mantle region of secondary follicles, and thus most tumors do not show somatic hypermutation of the Ig heavy-chain coding (IGH) genes. Cytologically, two major MCL subsets can be distinguished, the classical and blastoid/pleomorphic variants, which share a characteristic CD19 + CD5 + CD23 − immunophenotype (2). Almost all MCL cases show the chromosomal translocation t(11;14)(q13;q32), which juxtaposes the CCND1 gene with IGH gene enhancers and causes overexpression of the cyclin-D1 protein. The best-known function ascribed to cyclin-D1 is in positive regulation of cell cycling. In MCL cells, constitutive cyclin-D1 activation maintains retinoblastoma (RB) protein in a phosphorylated state and promotes cell proliferation, thus likely initiating tumorigenesis (3). However, whether cyclin-D1 has additional oncogenic functions in the lymphoma cells has not been well addressed. In B lymphocytes, cyclin-D1 deregulation seems insufficient to induce neoplastic transformation, given that other genetic changes are required for the development of malignancy (3, 4). Numero...

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