Clinicopathologic and Prognostic Significance of Bruton's Tyrosine Kinase Expression in Diffuse Large B-Cell Lymphoma.

BACKGROUND/AIM: Bruton's tyrosine kinase (BTK)-mediated B-cell-receptor signaling drives lymphomagenesis of diffuse large B-cell lymphoma (DLBCL). We investigated the clinicopathological significance of BTK positivity in DLBCL according to known molecules related to resistance to BTK inhibitors [BCL2 apoptosis regulator (BCL2)/MYC proto-oncogene, bHLH transcription factor (MYC)]. PATIENTS AND METHODS: We evaluated BTK expression immunohistochemically in 106 DLBCLs considering their BCL2/MYC status. RESULTS: Considering the whole cohort, BTK was expressed in 65.1%, including 70.4% (50/71) of non-germinal center B-cell-like (non-GCB) subtype; BCL2 expression was detected in 60.4%, MYC expression in 15.1%, MYC translocation in 4.2% (4/96) and MYC gain/amplification in 7.6% (8/105). Overall and in the non-GCB cohort, BTK positively correlated with high international prognostic index (both p=0.005) and stage (p=0.006 and p=0.002), and with BCL2 intensity (p=0.005 and p=0.026, respectively); MYC gain/amplification total cohort (p=0.038). Moreover, high risk, defined as co-expression of BTK and either or both BCL2/MYC, independently predicted shorter progression-free survival in patients treated with rituximab plus cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) (all R-CHOP-treated patients: hazard ratio=2.565, p=0.044; R-CHOP-treated non-GCB subgroup: HR=3.833, p=0.019). CONCLUSION: BTK expression may be utilized to stratify risk in patients with DLBCL.

Inhibition of Polo-like kinase 4 induces mitotic defects and DNA damage in diffuse large B-cell lymphoma.

Polo-like kinase 4 (PLK4), a key regulator of centriole biogenesis, has recently been shown to play key roles in tumorigenesis. Blocking PLK4 expression by interference or targeted drugs exhibits attractive potential in improving the efficacy of chemotherapy. Nevertheless, the role of PLK4 in diffuse large B-cell lymphoma (DLBCL) is still undefined. In this study, we discover that PLK4 is a potential target for the treatment of DLBCL, and demonstrate the efficacy of a PLK4 inhibitor when used in combination with doxorubicin. Pharmaceutical inhibition of PLK4 with CFI-400945 inhibited DLBCL cell proliferation and induced apoptotic cell death. The anti-tumor effects were accompanied by mitotic defects, including polyploidy and cytokinesis failure. Activation of p53 and Hippo/YAP tumor suppressor signaling pathway was identified as the potential mechanisms driving CFI-400945 activity. Moreover, CFI-400945 treatment resulted in activation of DNA damage response. Combining CFI-400945 with doxorubicin markedly delayed tumor progression in DLBCL xenografts. Finally, PLK4 was increased in primary DLBCL tissues and cell lines. High levels of PLK4 expression were associated with poor survival in the patients receiving CHOP-based treatment, implicating PLK4 as a predictive biomarker of DLBCL chemosensitivity. These results provide the therapeutic potential of CFI-400945 both as monotherapy or in combination with doxorubicin for the treatment of DLBCL.

Downregulation of USP18 reduces tumor-infiltrating activated dendritic cells in extranodal diffuse large B cell lymphoma patients.

Extranodal diffuse large B cell lymphoma (EN DLBCL) often leads to poor outcomes, while the underlying mechanism remains unclear. As immune imbalance plays an important role in lymphoma pathogenesis, we hypothesized that immune genes might be involved in the development of EN DLBCL. Ninety-three differentially expressed immune genes (DEIGs) were identified from 1168 differentially expressed genes (DEGs) between tumor tissues of lymph node DLBCL (LN DLBCL) and EN DLBCL patients in TCGA database. Nine prognostic immune genes were further identified from DEIGs by univariate Cox regression analysis. A multivariate predictive model was established based on these prognostic immune genes. Patients were divided into high- and low-risk groups according to the median model-based risk score. Kaplan-Meier survival curves showed that patients in the high-risk group had a shorter survival time than those in the low-risk group (P < 0.001). Ubiquitin-specific peptidase 18 (USP18) was further recognized as the key immune gene in EN DLBCL on the basis of coexpression of differentially expressed transcription factors (DETFs) and prognostic immune genes. USP18 exhibited low expression in EN DLBCL, which was regulated by LIM homeobox 2 (LHX2) (R = 0.497, P < 0.001, positive). The potential pathway downstream of USP18 was the MAPK pathway, identified by gene set variation analysis (GSVA), gene set enrichment analysis (GSEA) and Pearson correlation analysis (R = 0.294, P < 0.05, positive). The "ssGSEA" algorithm and Pearson correlation analysis identified that activated dendritic cells (aDCs) were the cell type mostly associated with USP18 (R = 0.694, P < 0.001, positive), indicating that USP18 participated in DC-modulating immune responses. The correlations among key biomarkers were supported by multiomics database validation. Indeed, the USP18 protein was confirmed to be expressed at lower levels in tumor tissues in patients with EN DLBCL than in those with LN DLBCL by immunohistochemistry. In short, our study illustrated that the downregulation of USP18 was associated with reduced aDC number in the tumor tissues of EN DLBCL patients, indicating that targeting USP18 might serve as a promising therapy.

KDM5 inhibition offers a novel therapeutic strategy for the treatment of KMT2D mutant lymphomas.

Loss-of-function mutations in KMT2D are a striking feature of germinal center (GC) lymphomas, resulting in decreased histone 3 lysine 4 (H3K4) methylation and altered gene expression. We hypothesized that inhibition of the KDM5 family, which demethylates H3K4me3/me2, would reestablish H3K4 methylation and restore the expression of genes repressed on loss of KMT2D. KDM5 inhibition increased H3K4me3 levels and caused an antiproliferative response in vitro, which was markedly greater in both endogenous and gene-edited KMT2D mutant diffuse large B-cell lymphoma cell lines, whereas tumor growth was inhibited in KMT2D mutant xenografts in vivo. KDM5 inhibition reactivated both KMT2D-dependent and -independent genes, resulting in diminished B-cell signaling and altered expression of B-cell lymphoma 2 (BCL2) family members, including BCL2 itself. KDM5 inhibition may offer an effective therapeutic strategy for ameliorating KMT2D loss-of-function mutations in GC lymphomas.

Phosphatase PP2A enhances MCL-1 protein half-life in multiple myeloma cells.

Multiple myeloma (MM), a treatable but incurable malignancy, is characterized by the growth of clonal plasma cells in protective niches in the bone marrow. MM cells depend on expression of BCL-2 family proteins, in particular MCL-1, for survival. The regulation of MCL-1 is complex and cell type-dependent. Unraveling the exact mechanism by which MCL-1 is overexpressed in MM may provide new therapeutic strategies for inhibition in malignant cells, preferably limiting side effects in healthy cells. In this study, we reveal that one cause of overexpression could be stabilization of the MCL-1 protein. We demonstrate this in a subset of MM and diffuse large B cell lymphoma (DLBCL) cell lines and MM patient samples. We applied a phosphatase siRNA screen to identify phosphatases responsible for MCL-1 stabilization in MM, and revealed PP2A as the MCL-1 stabilizing phosphatase. Using the PP2A inhibitor okadaic acid, we validated that PP2A dephosphorylates MCL-1 at Ser159 and/or Thr163, and thereby stabilizes MCL-1 in MM cells with long MCL-1 half-life, but not in DLBCL cells. Combined kinase and phosphatase inhibition experiments suggest that the MCL-1 half-life in MM is regulated by the counteracting functions of JNK and PP2A. These findings increase the understanding of the mechanisms by which MCL-1 is post-translationally regulated, which may provide novel strategies to inhibit MCL-1 in MM cells.

Activation-induced cytidine deaminase overexpression in double-hit lymphoma: potential target for novel anticancer therapy.

Activation-induced cytidine deaminase (AID) is one kind of the mutant enzymes, which target regulating the immunoglobulin (Ig) gene in Burkitt's lymphoma to initiate class switch recombination (CSR), resulting in c-Myc chromosomal translocation. However, it is not clear that whether AID induces c-Myc/IgH translocation in double-hit lymphoma (DHL) with c-Myc gene translocation. In this study, the AID in DHL tissues and classical diffuse large b-cell lymphoma (DLBCL) tissues were compared. The results suggested that AID is of important value in predicting DHL, stronger CSR of AID was observed in DHL patients, which exhibited AID overexpression and c-Myc gene translocation of DHL after CSR induction. It is concluded that AID directly induces CSR in DHL and may result in c-Myc gene translocation. Targeting AID may be a good treatment regimen for DHL.

LUBAC accelerates B-cell lymphomagenesis by conferring resistance to genotoxic stress on B cells.

The linear ubiquitin chain assembly complex (LUBAC) is a key regulator of NF-κB signaling. Activating single-nucleotide polymorphisms of HOIP, the catalytic subunit of LUBAC, are enriched in patients with activated B-cell-like (ABC) diffuse large B-cell lymphoma (DLBCL), and expression of HOIP, which parallels LUBAC activity, is elevated in ABC-DLBCL samples. Thus, to clarify the precise roles of LUBAC in lymphomagenesis, we generated a mouse model with augmented expression of HOIP in B cells. Interestingly, augmented HOIP expression facilitated DLBCL-like B-cell lymphomagenesis driven by MYD88-activating mutation. The developed lymphoma cells partly shared somatic gene mutations with human DLBCLs, with increased frequency of a typical AID mutation pattern. In vitro analysis revealed that HOIP overexpression protected B cells from DNA damage-induced cell death through NF-κB activation, and analysis of the human DLBCL database showed that expression of HOIP positively correlated with gene signatures representing regulation of apoptosis signaling, as well as NF-κB signaling. These results indicate that HOIP facilitates lymphomagenesis by preventing cell death and augmenting NF-κB signaling, leading to accumulation of AID-mediated mutations. Furthermore, a natural compound that specifically inhibits LUBAC was shown to suppress the tumor growth in a mouse transplantation model. Collectively, our data indicate that LUBAC is crucially involved in B-cell lymphomagenesis through protection against DNA damage-induced cell death and is a suitable therapeutic target for B-cell lymphomas.

Antitumor effects of rafoxanide in diffuse large B cell lymphoma via the PTEN/PI3K/Akt and JNK/c-Jun pathways.

AIMS: Diffuse large B-cell lymphoma (DLBCL) is one of the most aggressive lymphoid malignancies, which remains incurable, thus warranting the development of new therapies. Our previous study determined that rafoxanide is very effective in treating multiple myeloma (MM). In the present study, we tried to evaluate the effects of rafoxanide on DLBCL, as well as the potential underlying molecular mechanisms. MAIN METHODS: We used CCK-8 assay and flow cytometry to assess cell viability and apoptosis. The proteins and pathways associated with apoptosis and proliferation were evaluated through western blot, and xenograft mice were used as the experimental animal model. We also used the TUNEL assay and immunofluorescence for further analyses. KEY FINDINGS: Treatment with different doses of rafoxanide significantly inhibited cell viability and apoptosis. Additionally, the compound induced cell cycle arrest, reduced mitochondrial membrane potential (Δψm), and stimulated reactive oxygen species (ROS) generation without the influence of normal peripheral blood monocytes (PBMCs). As expected, rafoxanide played a role in regulating these proteins and the PTEN/PI3K/AKT and JNK/c-Jun pathways. Furthermore, immunofluorescence and western blot results showed that rafoxanide upregulated H2AX phosphorylation and then inhibited DNA repair in DLBCL. In the xenograft mouse model, tumor volumes were reduced after intraperitoneal injection with rafoxanide. We also observed that TUNEL positive cells were remarkably increased in rafoxanide-treated tumor tissues. SIGNIFICANCE: These results collectively provide a novel choice to regular treatment for DLBCL patients with poor prognosis.

Drug screening approach combines epigenetic sensitization with immunochemotherapy in cancer.

BACKGROUND: The epigenome plays a key role in cancer heterogeneity and drug resistance. Hence, a number of epigenetic inhibitors have been developed and tested in cancers. The major focus of most studies so far has been on the cytotoxic effect of these compounds, and only few have investigated the ability to revert the resistant phenotype in cancer cells. Hence, there is a need for a systematic methodology to unravel the mechanisms behind epigenetic sensitization. RESULTS: We have developed a high-throughput protocol to screen non-simultaneous drug combinations, and used it to investigate the reprogramming potential of epigenetic inhibitors. We demonstrated the effectiveness of our protocol by screening 60 epigenetic compounds on diffuse large B-cell lymphoma (DLBCL) cells. We identified several histone deacetylase (HDAC) and histone methyltransferase (HMT) inhibitors that acted synergistically with doxorubicin and rituximab. These two classes of epigenetic inhibitors achieved sensitization by disrupting DNA repair, cell cycle, and apoptotic signaling. The data used to perform these analyses are easily browsable through our Results Explorer. Additionally, we showed that these inhibitors achieve sensitization at lower doses than those required to induce cytotoxicity. CONCLUSIONS: Our drug screening approach provides a systematic framework to test non-simultaneous drug combinations. This methodology identified HDAC and HMT inhibitors as successful sensitizing compounds in treatment-resistant DLBCL. Further investigation into the mechanisms behind successful epigenetic sensitization highlighted DNA repair, cell cycle, and apoptosis as the most dysregulated pathways. Altogether, our method adds supporting evidence in the use of epigenetic inhibitors as sensitizing agents in clinical settings.

Ruxolitinib shows activity against Hodgkin lymphoma but not primary mediastinal large B-cell lymphoma.

BACKGROUND: The upregulated expression of the JAK/STAT pathway promotes tumor growth in Hodgkin lymphoma (HL) and primary mediastinal large B-cell lymphoma (PMBCL). Based on the hypothesis that JAK2 is a therapeutic target, we performed a prospective pilot study using ruxolitinib. METHODS: Relapsed or refractory patients with HL or PMBCL were eligible for this study, and JAK2 amplification was assessed by fluorescence in situ hybridization. Ruxolitinib was administered orally at a dose of 20 mg twice daily for a 28-day cycle. Treatment was continued for up to 16 cycles or until progressive disease or intolerability. The primary objective was to assess the overall disease control rate comprising complete response (CR), partial response (PR), or stable disease (SD). RESULTS: We analyzed 13 HL patients and six PMBCL patients. All responders (one CR, five PR, and one SD) had HL whereas all cases of PMBCL progressed after first or second cycle. The disease control rate for HL was 54% (7/13) with median response duration of 5.6 months. JAK2 amplification was present in six of nine patients tested (four HL, two PMBCL), and three of these HL patients showed PR (n = 2) or SD (n = 1). None of the three HL patients shown to not have JAK2 amplification responded to ruxolitinib. Most treatment-related adverse events were grade 1 or 2 and manageable. CONCLUSIONS: Ruxolitinib has single-agent activity against HL but does not act against PMBCL with or without JAK2 amplification. TRIAL REGISTRATION: The study population was patients who had relapsed or refractory HL or PMBCL, and patients were registered for our pilot study after providing written informed consent between November 2013 and November 2015 (CilinicalTrials.gov: NCT01965119).

Glycolytic enzyme hexokinase II is a putative therapeutic target in B-cell malignant lymphoma.

Hexokinase II (HXKII) is a key regulator of glucose metabolism that converts glucose to glucose 6-phosphate. Furthermore, HXKII blocks mitochondria-dependent apoptosis by inhibiting the release of cytochrome c. HXKII overexpression is frequently observed in several types of cancer and confers chemoresistance to cancer cells. In the present study, we found that compared with cell lines generated from diffuse large-B-cell lymphoma (DLBCL) patients, cell lines with features of Burkitt lymphoma have higher levels of HXKII because of the activation of both c-MYC and HIF-1. Under normoxia, HXKII levels were correlated with the growth ability of each B-cell lymphoma cell line. HXKII levels were further enhanced when the B-cell lymphoma cells were cultured under hypoxia. The high levels of HXKII induced by hypoxia conferred cisplatin resistance in all tested B-cell lymphoma cell lines. The HDAC inhibitor panobinostat significantly suppressed HXKII expression under both normoxic and hypoxic conditions. Importantly, panobinostat reversed the anti-lymphoma action of cisplatin, and this effect was diminished by hypoxia. These data suggest that HXKII plays different roles, including in the regulation of glycolysis and inhibition of apoptosis, depending on its expression levels. Furthermore, inhibition of HXKII expression by panobinostat may represent a new and attractive strategy to overcome cisplatin resistance.

Primary Cutaneous Anaplastic Lymphoma Kinase-Positive Large B-Cell Lymphoma.

Large B-cell lymphomas include several subtypes. Recently, anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma has been delineated as a distinct entity involving mostly lymph nodes and rarely affecting extranodal sites. We describe the first case of a primary cutaneous ALK-positive large B-cell lymphoma in a 48-year-old man with a solitary nodule on the back, and describe the histologic and phenotypic features. Accurate staging confirmed the absence of other lesions, and so surgical excision and postoperative local radiation therapy were initiated and resulted in complete remission. Two years later, extracutaneous spread with involvement of axillary lymph nodes occurred. Complete remission was achieved again by multiagent chemotherapy. Our case demonstrates that a primary cutaneous form of ALK-positive large B-cell lymphoma exists. The immunophenotypic analysis of cutaneous large B-cell lymphomas affecting the skin primarily or secondarily should include the assessment of ALK expression.

Non-oncogene Addiction to SIRT3 Plays a Critical Role in Lymphomagenesis.

Diffuse large B cell lymphomas (DLBCLs) are genetically heterogeneous and highly proliferative neoplasms derived from germinal center (GC) B cells. Here, we show that DLBCLs are dependent on mitochondrial lysine deacetylase SIRT3 for proliferation, survival, self-renewal, and tumor growth in vivo regardless of disease subtype and genetics. SIRT3 knockout attenuated B cell lymphomagenesis in VavP-Bcl2 mice without affecting normal GC formation. Mechanistically, SIRT3 depletion impaired glutamine flux to the TCA cycle via glutamate dehydrogenase and reduction in acetyl-CoA pools, which in turn induce autophagy and cell death. We developed a mitochondrial-targeted class I sirtuin inhibitor, YC8-02, which phenocopied the effects of SIRT3 depletion and killed DLBCL cells. SIRT3 is thus a metabolic non-oncogene addiction and therapeutic target for DLBCLs.

TAK1 is a druggable kinase for diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most common form of lymphoma, and up to 30% DLBCL patients eventually died by using first-line chemotherapy regimens. Currently, Bruton tyrosine kinase (BTK) inhibitor (ibrutinib) is one of the most promising medicine in clinical trials for DLBCL, to which about 25% of patients with relapsed or refractory DLBCL are responsive. Thus, it is urgent to discover new druggable targets for DLBCL, especially for patients who are unresponsive to first-line chemotherapy and ibrutinib. Here, we found that MAP 3K7 (TAK1) is required for DLBCL survival. Inhibition of TAK1 by small molecule 5Z7 or genetic silence could massively induce deaths of DLBCL cells. Mechanistically, TAK1 inhibition could dramatically reduce the nuclear factor kappa B (NF-κB) activity. Notably, ibrutinib-resistant DLBCL cells also respond to TAK1 inhibition. Database analysis showed that high expression of TAK1 in patients with DLBCL shows poor survival. A subtype of DLBCL patients showed that high expression of both TAK1 and BTK1 is poorly responsive to the current chemotherapy. Moreover, DLBCL cell line with high expression of both TAK1 and BTK1 is resistant to Dox. Simultaneously targeting TAK1 and BTK not only increases cellular toxicity of individual drug but also enhances the sensitivity to Dox. Taken together, we provide convincing evidence to show that kinase TAK1 is a druggable target in DLBCL. SIGNIFICANCE OF THE STUDY: Currently, there is still a significant portion of patients with DLBCL who are unresponsive to first-line chemotherapy. Thus, identification of novel druggable targets such as kinase is critical important. Here, we found that TAK1 inhibition promotes death of DLBCL cells through inhibition of chronic NF-κB signalling. Importantly, TAK1 inhibition overcomes ibrutinib resistance in DLBCL cells. Finally, DLBCL patients with high expression of both TAK1 and BTK showed extremely poor survival. In summary, we provide convincing results to demonstrate a potential important druggable kinase in DLBCL.

Investigation of expressions of PDK1, PLK1 and c-Myc in diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma. Because the prognosis of DLBCL patients varies considerably, there is an urgent need to identify novel prognostic factors. In this study, we investigated the expression levels of the signalling enzyme 3-phosphoinositide-dependent protein kinase-1 (PDK1), the cell cycle regulatory enzyme Polo-like kinase 1 (PLK1) and the transcription factor (c-Myc) in DLBCL tissues and evaluated their clinical and prognostic significance. PDK1, PLK1 and c-Myc were detected by immunohistochemical staining of paraffin-embedded specimens from 152 DLBCL and 48 lymphadenitis patients. Expression levels were correlated with clinicopathological factors. PDK1, PLK1 and c-Myc were more commonly expressed in DLBCL specimens than in lymphadenitis specimens, and the expression of each protein correlated positively with that of the other two molecules. High PDK1, PLK1 and c-Myc expression, high international prognostic index score, high lactate dehydrogenase levels and late Ann Arbor stage were shown to correlate with shorter overall survival time. A multivariate Cox regression model showed that high expression levels of PLK1 and c-Myc were independent prognostic factors for DLBCL. Our findings indicate that PLK1 and c-Myc expression might be promising predictive biomarkers for DLBCL patients.

KLHL6 is a tumor suppressor gene in diffuse large B-cell lymphoma.

The ubiquitin proteasome system (UPS) plays a critical function in cellular homeostasis. The misregulation of UPS is often found in human diseases, including cancer. Kelch-like protein 6 (KLHL6) is an E3 ligase gene mutated in diffused large B-cell lymphoma (DLBCL). This review discusses the function of KLHL6 as a cullin3-RING ligase and how cancer-associated mutations disrupt the interaction with the cullin3, resulting in the loss of KLHL6 function. Furthermore, the mRNA decay factor Roquin2 is discussed as the first bona fide substrate of KLHL6 in the context of B-cell receptor activation and B-cell lymphoma. Importantly, the tumor-suppressing mechanism of KLHL6 via the degradation of Roquin2 and the mRNA decay in the context of the NF-κB pathway is summarized.

Targeting NEDD8-activating enzyme is a new approach to treat canine diffuse large B-cell lymphoma.

Canine diffuse large B-cell lymphoma (DLBCL), the most common hematologic malignancy of dogs, is associated with poor overall survival. The lack of conventional chemotherapies with sustainable efficacy warrants investigation of novel therapies. Pevonedistat (MLN4924) is a potent and selective small molecule NEDD8-activating enzyme inhibitor. In human activated B-cell-like (ABC) diffuse large B-cell lymphoma, pevonedistat induces lymphoma cell apoptosis, DNA damage and G1 cell cycle arrest by inhibiting the nuclear factor-κB (NF-κB) pathway. Genomic and transcriptomic studies showed that the NF-κB pathway is deregulated in canine DLBCL. Our results showed that pevonedistat treatment significantly reduces the viability of canine DLBCL cells by inducing G1 cell cycle arrest and apoptosis. Pevonedistat treatment inhibits NF-κB pathway activation and downregulates NF-κB target genes in canine DLBCL. Moreover, administration of pevonedistat to mice bearing canine DLBCL xenograft tumours resulted in tumour regression. Our in vivo and in vitro studies provide justification for future clinical application of pevonedistat as a potential new anti-cancer therapy that may benefit both canine and human species.

Emerging EZH2 Inhibitors and Their Application in Lymphoma.

PURPOSE OF REVIEW: Enhancer of Zeste Homolog 2 (EZH2) is histone methyltransferase and catalyzes the methylation of histone 3 lysine 27, a mark of transcriptional repression. Various studies have elucidated the complex role of EZH2 in both normal biology and tumorigenesis. Here, we critically review the emerging role of EZH2 in malignancies, the development of small molecule inhibitors of EZH2, and their application in lymphoma. RECENT FINDINGS: Activating mutations and overexpression of EZH2 are found in non-Hodgkin lymphoma (NHL). As a result, several EZH2 inhibitors have been developed and entered clinical investigation. Tazemetostat, first-in-class EZH2 inhibitor, demonstrated enhanced clinical activity in mutant follicular lymphoma and diffuse large B cell lymphoma. With the early activity noted by tazemetostat in B cell lymphomas, the role of EZH2 inhibition in NHL is becoming more evident. This can be leveraged in future rationale combinations to enhance the activity of EZH2 inhibitors.

Specific covalent inhibition of MALT1 paracaspase suppresses B cell lymphoma growth.

The paracaspase MALT1 plays an essential role in activated B cell-like diffuse large B cell lymphoma (ABC DLBCL) downstream of B cell and TLR pathway genes mutated in these tumors. Although MALT1 is considered a compelling therapeutic target, the development of tractable and specific MALT1 protease inhibitors has thus far been elusive. Here, we developed a target engagement assay that provides a quantitative readout for specific MALT1-inhibitory effects in living cells. This enabled a structure-guided medicinal chemistry effort culminating in the discovery of pharmacologically tractable, irreversible substrate-mimetic compounds that bind the MALT1 active site. We confirmed that MALT1 targeting with compound 3 is effective at suppressing ABC DLBCL cells in vitro and in vivo. We show that a reduction in serum IL-10 levels exquisitely correlates with the drug pharmacokinetics and degree of MALT1 inhibition in vitro and in vivo and could constitute a useful pharmacodynamic biomarker to evaluate these compounds in clinical trials. Compound 3 revealed insights into the biology of MALT1 in ABC DLBCL, such as the role of MALT1 in driving JAK/STAT signaling and suppressing the type I IFN response and MHC class II expression, suggesting that MALT1 inhibition could prime lymphomas for immune recognition by cytotoxic immune cells.

Activation of MET signaling by HDAC6 offers a rationale for a novel ricolinostat and crizotinib combinatorial therapeutic strategy in diffuse large B-cell lymphoma.

Some histone deacetylases (HDACs) promote tumor cell growth and pan- or selective HDAC inhibitors are active in some cancers; however, the pivotal HDAC enzyme and its functions in human diffuse large B-cell lymphoma (DLBCL) remain largely unknown. Using NanoString nCounter assays, we profiled HDAC mRNA expression and identified HDAC6 as an upregulated HDAC family member in DLBCL tissue samples. We then found that HDAC6 plays an oncogenic role in DLBCL, as evidenced by its promotion of cell proliferation in vitro and tumor xenograft growth in vivo. Mechanistically, the interaction between HDAC6 and HR23B downregulated HR23B expression, thereby reducing the levels of casitas B-lineage lymphoma (c-Cbl), an E3 ubiquitin ligase for hepatocyte growth factor receptor (MET), which resulted in the inhibition of MET ubiquitination-dependent degradation. In addition, enhanced HDAC6 expression and decreased HR23B expression were correlated with poor overall survival rates among patients with DLBCL. Taken together, these results establish an HDAC6-HR23B-MET axis and indicate that HDAC6 is a potent promoter of lymphomagenesis in DLBCL. Thus, a therapeutic strategy based on HDAC6 inhibitors in combination with MET inhibitors is promising. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.