Molecular Pathogenesis of Non-Hodgkin's Lymphoma: the Role of Bcl-6

Selective deletion of E3 ubiquitin ligase FBW7 in VE-cadherin-positive cells instigates diffuse large B-cell lymphoma in mice in vivo

During the maturation of hematopoietic stem/progenitor cells (HSPCs) to fully differentiated mature B lymphocytes, developing lymphocytes may undergo malignant transformation and produce B-cell lymphomas. Emerging evidence shows that through the endothelial-hematopoietic transition, specialized endothelial cells called the hemogenic endothelium can differentiate into HSPCs. However, the contribution of genetic defects in hemogenic endothelial cells to B-cell lymphomagenesis has not yet been investigated. Here, we report that mice with endothelial cell-specific deletion of Fbw7 spontaneously developed diffuse large B-cell lymphoma (DLBCL) following Bcl6 accumulation. Using lineage tracing, we showed that B-cell lymphomas in Fbw7 knockout mice were hemogenic endothelium-derived. Mechanistically, we found that FBW7 directly interacted with Bcl6 and promoted its proteasomal degradation. FBW7 expression levels are inversely correlated with BCL6 expression. Additionally, pharmacological disruption of Bcl6 abolished Fbw7 deletion-induced B-cell lymphomagenesis. We conclude that selective deletion of E3 ubiquitin ligase FBW7 in VE-cadherin positive endothelial cells instigates diffuse large B-cell lymphoma via upregulation of BCL6 stability. In addition, the mice with endothelial cell-specific deletion of Fbw7 provide a valuable preclinical platform for in vivo development and evaluation of novel therapeutic interventions for the treatment of DLBCL.

Preclinical and clinical progress for HDAC as a putative target for epigenetic remodeling and functionality of immune cells

Genetic changes are difficult to reverse; thus, epigenetic aberrations, including changes in DNA methylation, histone modifications, and noncoding RNAs, with potential reversibility, have attracted attention as pharmaceutical targets. The current paradigm is that histone deacetylases (HDACs) regulate gene expression via deacetylation of histone and nonhistone proteins or by forming corepressor complexes with transcription factors. The emergence of epigenetic tools related to HDACs can be used as diagnostic and therapeutic markers. HDAC inhibitors that block specific or a series of HDACs have proven to be a powerful therapeutic treatment for immune-related diseases. Here, we summarize the various roles of HDACs and HDAC inhibitors in the development and function of innate and adaptive immune cells and their implications for various diseases and therapies.

Structure-Based Design of First-Generation Small Molecule Inhibitors Targeting the Catalytic Pockets of AID, APOBEC3A, and APOBEC3B

Activation-induced cytidine deaminase (AID) initiates antibody diversification by mutating immunoglobulin loci in B lymphocytes. AID and related APOBEC3 (A3) enzymes also induce genome-wide mutations and lesions implicated in tumorigenesis and tumor progression. The most prevalent mutation signatures across diverse tumor genomes are attributable to the mistargeted mutagenic activities of AID/A3s. Thus, inhibiting AID/A3s has been suggested to be of therapeutic benefit. We previously used a computational-biochemical approach to gain insight into the structure of AID’s catalytic pocket, which resulted in the discovery of a novel type of regulatory catalytic pocket closure that regulates AID/A3s that we termed the “Schrodinger’s CATalytic pocket”. Our findings were subsequently confirmed by direct structural studies. Here, we describe our search for small molecules that target the catalytic pocket of AID. We identified small molecules that inhibit purified AID, AID in cell extracts, and endogenous AID of lymphoma cells. Analogue expansion yielded derivatives with improved potencies. These were found to also inhibit A3A and A3B, the two most tumorigenic siblings of AID. Two compounds exhibit low micromolar IC₅₀ inhibition of AID and A3A, exhibiting the strongest potency for A3A. Docking suggests key interactions between their warheads and residues lining the catalytic pockets of AID, A3A, and A3B and between the tails and DNA-interacting residues on the surface proximal to the catalytic pocket opening. Accordingly, mutants of these residues decreased inhibition potency. The chemistry and abundance of key stabilizing interactions between the small molecules and residues within and immediately outside the catalytic pockets are promising for therapeutic development.

Molecular Genetics of Relapsed Diffuse Large B-Cell Lymphoma: Insight into Mechanisms of Therapy Resistance

The majority of patients with diffuse large B-cell lymphoma (DLBCL) can be treated successfully with a combination of chemotherapy and the monoclonal anti-CD20 antibody rituximab. Nonetheless, approximately one-third of the patients with DLBCL still experience relapse or refractory (R/R) disease after first-line immunochemotherapy. Whole-exome sequencing on large cohorts of primary DLBCL has revealed the mutational landscape of DLBCL, which has provided a framework to define novel prognostic subtypes in DLBCL. Several studies have investigated the genetic alterations specifically associated with R/R DLBCL, thereby uncovering molecular pathways linked to therapy resistance. Here, we summarize the current state of knowledge regarding the genetic alterations that are enriched in R/R DLBCL, and the corresponding pathways affected by these gene mutations. Furthermore, we elaborate on their potential role in mediating therapy resistance, also in connection with findings in other B-cell malignancies, and discuss alternative treatment options. Hence, this review provides a comprehensive overview on the gene lesions and molecular mechanisms underlying R/R DLBCL, which are considered valuable parameters to guide treatment.

The Role of Microbial Translocation and Immune Activation in AIDS-Associated Non-Hodgkin Lymphoma Pathogenesis: What Have We Learned?

Human immunodeficiency virus (HIV) infection is associated with greatly increased risk for development of non-Hodgkin lymphoma (NHL). Nearly all acquired immunodeficiency syndrome (AIDS)-associated NHL (AIDS-NHL) is of B-cell origin. Two major mechanisms are believed to contribute to the genesis of AIDS-NHL: (1) loss of immunoregulation of Epstein-Barr virus (EBV)+ B cells, resulting from impaired T-cell function late in the course of HIV disease and (2) chronic B-cell activation, leading to DNA-modifying events that contribute to oncogene mutations/ translocations. HIV infection has long been known to be associated with chronic inflammation and polyclonal B-cell activation, and more recently, microbial translocation. Microbial translocation is bacterial product leakage from gut lumen into the peripheral circulation, resulting in high levels of lipopolysaccharide (LPS) in the peripheral circulation, leading to chronic immune activation and inflammation. We review recent literature linking microbial translocation to lymphom-agenesis. This includes epidemiological studies of biomarkers of microbial translocation with risk of AIDS-NHL and emerging data on the mechanisms by which microbial translocation may lead to AIDS-NHL development.

From genetics to the clinic: a translational perspective on follicular lymphoma

Follicular lymphoma (FL) is the most frequent indolent B cell lymphoma and is still considered to be incurable. In recent years, whole-exome sequencing studies of large cohorts of patients have greatly improved our knowledge of the FL mutational landscape. Moreover, the prolonged evolution of this disease has enabled some insights regarding the early pre-lymphoma lesions as well as the clonal evolution after treatment, allowing an evolutionary perspective on lymphomagenesis. Deciphering the earliest initiating lesions and identifying the molecular alterations leading to disease progression currently represent important goals; accomplishing these could help identify the most relevant targets for precision therapy.

MicroRNA-187 induces diffuse large B-cell lymphoma cell apoptosis via targeting BCL6

MicroRNAs (miRs) are endogenous non-coding RNAs that serve key functions in a wide range of biological processes, including cell growth, development, apoptosis and carcinogenesis. However, the association between miR-187 and B-cell lymphoma 6 (BCL6) has yet to be fully investigated in lymphoma cell apoptosis. The present study hypothesized that a post-translational mechanism may exist for BCL6 expression, which is regulated by miR-187 in lymphoma cells. The present study demonstrated that the expression of miR-187 in diffuse large B-cell lymphoma (DLBCL) cells was significantly decreased, and its expression was negatively correlated with BCL6 expression. It was also observed that miR-187 directly binds to the 3'-untranslated region of BCL6 mRNA and subsequently suppresses the expression of BCL6. Additionally, the induced expression of miR-187 significantly promoted DLBCL cell apoptosis in vitro. The drug sensitivity of human DLBCL SUDHL2 cells was increased following induction of miR-187 overexpression via an miR-187 mimic. In conclusion, the results of the present study suggest that the modulation of miR-187 expression in DLBCL cells may improve the sensitivity of chemotherapy through BCL6 targeting.

A Critical Role of miR-144 in Diffuse Large B-cell Lymphoma Proliferation and Invasion

MicroRNAs are endogenous noncoding RNAs that play important roles in a wide variety of biologic processes such as apoptosis, development, aging, and tumorigenesis. The B-cell lymphoma 6 (BCL6) transcriptional repressor has emerged as a critical therapeutic target in diffuse large B-cell lymphomas (DLBCL), but the mechanisms regulating BCL6 are still unclear. In the current study, we screened the microRNA expression profiles in DLBCL specimens and cell lines by qRT-PCR and found that the expression of miR-144 was significantly downregulated in DLBCL tissues and cell lines and negatively correlated with BCL6 expression. We further demonstrated that BCL6 was the direct target gene of miR-144, and miR-144 suppressed the expression of BCL6 via binding the 3'untranslated region of BCL6 mRNA. Biologically, forced expression of miR-144 significantly attenuated cell proliferation and invasion of OCI-Ly3 cells in vitro, and the tumor-suppressor effect of miR-144 was also confirmed using a xenograft mouse model in vivo Taken together, our results reveal that miR-144 regulates BCL6 in DLBCL and provide a rationale for developing strategies that target miR-144 as a therapeutic intervention for DLBCL.

IFI16 Expression Is Related to Selected Transcription Factors during B-Cell Differentiation

The interferon-inducible DNA sensor IFI16 is involved in the modulation of cellular survival, proliferation, and differentiation. In the hematopoietic system, IFI16 is consistently expressed in the CD34+ stem cells and in peripheral blood lymphocytes; however, little is known regarding its regulation during maturation of B- and T-cells. We explored the role of IFI16 in normal B-cell subsets by analysing its expression and relationship with the major transcription factors involved in germinal center (GC) development and plasma-cell (PC) maturation. IFI16 mRNA was differentially expressed in B-cell subsets with significant decrease in IFI16 mRNA in GC and PCs with respect to naïve and memory subsets. IFI16 mRNA expression is inversely correlated with a few master regulators of B-cell differentiation such as BCL6, XBP1, POU2AF1, and BLIMP1. In contrast, IFI16 expression positively correlated with STAT3, REL, SPIB, RELA, RELB, IRF4, STAT5B, and STAT5A. ARACNE algorithm indicated a direct regulation of IFI16 by BCL6, STAT5B, and RELB, whereas the relationship between IFI16 and the other factors is modulated by intermediate factors. In addition, analysis of the CD40 signaling pathway showed that IFI16 gene expression directly correlated with NF-κB activation, indicating that IFI16 could be considered an upstream modulator of NF-κB in human B-cells.

Assessment of Tissue Level of Histone Deactylase-2 (HDAC-2) in Patients With Mycosis Fungoides

BACKGROUND

Histone deactylases (HDAC) have a role in the pathogenesis of mycosis fungoides (MF) through their actions on different apoptosis pathways.

OBJECTIVE

To assess the possible role played by HDAC-2 in MF by estimating the tissue expression of HDAC2 mRNA in different stages of MF.

METHODS

This study included 28 MF patients and 30 controls. The HDAC-2 levels were detected by real-time polymerase chain reaction (PCR). Correlations of HDAC-2 levels with clinical presentation and different stages of MF were analyzed.

RESULTS

Mean HDAC-2 level was significantly higher in patients (P < .001) than in controls. HDAC-2 highest mean value was significantly detected in patients with stage IIb, and the lowest mean value was detected in patients with stage Ia (P < .001).

CONCLUSION

Up-regulation of tissue HDAC-2 in MF patients might develop a new approach in the understanding of the pathogenesis of MF. Histone deactylases are important targets for molecular cancer therapeutics.

Pellino 1 promotes lymphomagenesis by deregulating BCL6 polyubiquitination

The signal-responsive E3 ubiquitin ligase pellino 1 (PELI1) regulates TLR and T cell receptor (TCR) signaling and contributes to the maintenance of autoimmunity; however, little is known about the consequence of mutations that result in upregulation of PELI1. Here, we developed transgenic mice that constitutively express human PELI1 and determined that these mice have a shorter lifespan due to tumor formation. Constitutive expression of PELI1 resulted in ligand-independent hyperactivation of B cells and facilitated the development of a wide range of lymphoid tumors, with prominent B cell infiltration observed across multiple organs. PELI1 directly interacted with the oncoprotein B cell chronic lymphocytic leukemia (BCL6) and induced lysine 63-mediated BCL6 polyubiquitination. In samples from patients with diffuse large B cell lymphomas (DLBCLs), PELI1 expression levels positively correlated with BCL6 expression, and PELI1 overexpression was closely associated with poor prognosis in DLBCLs. Together, these results suggest that increased PELI1 expression and subsequent induction of BCL6 promotes lymphomagenesis and that this pathway may be a potential target for therapeutic strategies to treat B cell lymphomas.

B-cell lymphoma 6 protein stimulates oncogenicity of human breast cancer cells

Background

B-cell lymphoma 6 (BCL6) protein, an evolutionarily conserved zinc finger transcription factor, showed to be highly expressed in various human cancers in addition to malignancies in the lymphoid system. This study investigated the role of BCL6 expression in breast cancer and its clinical significance in breast cancer patients.

Methods

Expression of BCL6 protein was assessed using in situ hybridization and immunohistochemistry in 127 breast cancer patients and 50 patients with breast benign disease as well as in breast cell lines. Expression of BCL6 was restored or knocked down in two breast cancer cell lines (MCF-7 and T47D) using BCL6 cDNA and siRNA, respectively. The phenotypic change of these breast cancer cell lines was assessed using cell viability MTT, Transwell invasion, colony formation, and flow cytometry assays and in a xenograft mice model. Luciferase reporter gene, immunoblot, and qRT-PCR were used to investigate the molecular events after manipulated BCL6 expression in breast cancer cells.

Results

BCL6 protein was highly expressed in breast cancer cell lines and tissue specimens and expression of BCL6 protein was associated with disease progression and poor survival of breast cancer patients. In vitro, the forced expression of BCL6 results in increased proliferation, anchorage-independent growth, migration, invasion and survival of breast cancer cell lines, whereas knockdown of BCL6 expression reduced these oncogenic properties of breast cancer cells. Moreover, forced expression of BCL6 increased tumor growth and invasiveness in a nude mouse xenograft model. At the gene level, BCL6 was a target gene of miR-339-5p. Expression of BCL6 induced expression of CXCR4 and cyclinD1 proteins.

Conclusions

The current study demonstrated the oncogenic property of BCL6 in breast cancer and further study could target BCL6 as a novel potential therapeutic strategy for breast cancer.

Fluorescence Immunophenotyping and Interphase Cytogenetics (FICTION) Detects BCL6 Abnormalities, Including Gene Amplification, in Most Cases of Nodular Lymphocyte-Predominant Hodgkin Lymphoma

Context.— BCL6 translocations are a frequent finding in B-cell lymphomas of diverse subtypes, including some cases of nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL). However, reliable analysis of BCL6 rearrangements using fluorescence in situ hybridization is difficult in NLPHL because of the relative paucity of neoplastic cells. Combined immunofluorescence microscopy and fluorescence in situ hybridization, or fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms (FICTION), permits targeted analysis of neoplastic cells.

Objective.—To better define the spectrum of BCL6 abnormalities in NLPHL using FICTION analysis.

Design.—We performed an optimized FICTION analysis of 24 lymph nodes, including 11 NLPHL, 5 follicular hyperplasia with prominent progressive transformation of germinal centers, and 8 follicular hyperplasia without progressive transformation of germinal centers.

Results.— BCL6 rearrangement was identified in 5 of 11 cases of NLPHL (46%). In addition, BCL6 gene amplification, with large clusters of BCL6 signals in the absence of chromosome 3 aneuploidy, was detected in 3 of 11 cases of NLPHL (27%). One NLPHL showed extra copies of BCL6 present in conjunction with multiple copies of chromosome 3. Altogether, we detected BCL6 abnormalities in 9 of 11 cases of NLPHL (82%). None of the progressive transformation of germinal centers or follicular hyperplasia cases showed BCL6 abnormalities by FICTION.

Conclusions.—To our knowledge, this is the first report of BCL6 gene amplification in NLPHL. Our optimized protocol for FICTION permits detection of cytogenetic abnormalities in most NLPHL cases and may represent a useful ancillary diagnostic technique.

Is rheumatoid arthritis a B-cell haematological disease with a predilection for the joints? Following the B cell thread to its logical conclusion

B-cell depleting therapy (BCDT) is effective in suppressing synovitis and erosions in rheumatoid arthritis suggesting that a cell of the B-lymphocyte lineage is critical in the pathogenesis of this disease. Non-Hodgkins lymphoma (NHL) also responds to BCDT but multiple myeloma (MM), does not as cells have differentiated beyond the CD20-bearing stage. However, there are similarities between B-NHL, MM and RA that suggest all 3 conditions could be initiated and perpetuated by the same cellular players. Numerous plasma cells and B cells are present within rheumatoid synovial membrane, and subarticular bone where they contribute to osteitis. On MRI scans this appears as bone oedema, which has been demonstrated to precede the development of bone erosions. Plasma cell clonality has been detected within RA synovial membrane and bone marrow. It is proposed that RA could represent a "forme fruste" of a B cell neoplastic condition, with production of autoantibodies that target a self-antigen within the joint. The activation of rheumatoid bone osteoclasts by anticitrullinated protein antibodies supports this theory. The erosions of RA would have parallels with the lytic lesions of MM but autoantigen targeting dictates that erosions occur at joint margins. This theory is discussed from rheumatologic and haematologic perspectives.

Combating the epigenome: epigenetic drugs against non-Hodgkin's lymphoma

Non-Hodgkin's lymphomas (NHLs) comprise a large and diverse group of neoplasms of lymphocyte origin with heterogeneous molecular features and clinical manifestations. Current therapies are based on standard chemotherapy, immunotherapy, radiation or stem cell transplantation. The discovery of recurrent mutations in epigenetic enzymes, such as chromatin modifiers and DNA methyltransferases, has provided researchers with a rationale to develop novel inhibitors targeting these enzymes. Several clinical and preclinical studies have demonstrated the efficacy of epigenetic drugs in NHL therapy and a few specific inhibitors have already been approved for clinical use. Here, we provide an overview of current NHL classification and a review of the present literature describing epigenetic alterations in NHL, including a summary of different epigenetic drugs, and their use in preclinical and clinical studies.

Overexpression of the transcriptional repressor complex BCL-6/BCoR leads to nuclear aggregates distinct from classical aggresomes

Nuclear inclusions of aggregated proteins have primarily been characterized for molecules with aberrant poly-glutamine repeats and for mutated or structurally altered proteins. They were termed “nuclear aggresomes” and misfolding was shown to promote association with molecular chaperones and proteasomes. Here, we report that two components of a transcriptional repressor complex (BCL-6 and BCoR) of wildtype amino acid sequence can independently or jointly induce the formation of nuclear aggregates when overexpressed. The observation that the majority of cells rapidly downregulate BCL-6/BCoR levels, supports the notion that expression of these proteins is under tight control. The inclusions occur when BCL-6/BCoR expression exceeds 150-fold of endogenous levels. They preferentially develop in the nucleus by a gradual increase in aggregate size to form large, spheroid structures which are not associated with heat shock proteins or marked by ubiquitin. In contrast, we find the close association of BCL-6/BCoR inclusions with PML bodies and a reduction in aggregation upon the concomitant overexpression of histone deacetylases or heat shock protein 70. In summary, our data offer a perspective on nuclear aggregates distinct from classical “nuclear aggresomes”: Large complexes of spheroid structure can evolve in the nucleus without being marked by the cellular machinery for protein refolding and degradation. However, nuclear proteostasis can be restored by balancing the levels of chaperones.

Sirtuin and pan-class I/II deacetylase (DAC) inhibition is synergistic in preclinical models and clinical studies of lymphoma

Understanding the molecular pathogenesis of lymphoma has led to paradigm-changing treatment opportunities. One example involves tailoring specific agents based on the cell of origin in aggressive lymphomas. Germinal center (GC)-derived diffuse large B-cell lymphoma (DLBCL) is known to be driven by an addiction to Bcl6, whereas the activated B-cell (ABC) subtype is driven by nuclear factor κB. In the GC subtype, there is a critical inverse relationship between Bcl6 and p53, the functional status of which is linked to each transcription factor's degree of acetylation. Deacetylation of Bcl6 is required for its transcriptional repressor effects allowing for the oncogene to drive lymphomagenesis. Conversely, acetylation of p53 is activating when class III deacetylases (DACs), or sirtuins, are inhibited by niacinamide. Treatment of DLBCL cell lines with pan-DAC inhibitors in combination with niacinamide produces synergistic cytotoxicity in GC over ABC subtypes. This correlated with acetylation of both Bcl6 and p53. This combination also produced remissions in a spontaneous aggressive B-cell lymphoma mouse model expressing Bcl6. In a phase 1 proof-of-principle clinical trial, 24% of patients with relapsed or refractory lymphoma attained a response to vorinostat and niacinamide, and 57% experienced disease stabilization. We report herein on the preclinical and clinical activity of this targeted strategy in aggressive lymphomas. This trial was registered at www.clinicaltrials.gov as #NCT00691210.

Notch-regulated periphery B cell differentiation involves suppression of E protein function

Notch signaling pathway plays important roles in promoting the generation of marginal zone (MZ) B cells at the expense of follicular (FO) B cells during periphery B cell maturation, but the underlying molecular mechanisms are not well understood. We hypothesize that Notch favors the generation of MZ B cells by downregulating E protein activity. In this study, we demonstrated that expression of Id2 and ankyrin-repeat SOCS box-containing protein 2 was elevated in MZ B cells and by Notch signaling. Id2 inhibits the DNA binding activity of E proteins, whereas ankyrin-repeat SOCS box-containing protein 2 facilitates E protein ubiquitination. Next, we examined the phenotypes of splenic B cells in mice expressing constitutively active Notch1 and/or two gain-of-function mutants of E proteins that counteract Id2-mediated inhibition or Notch-induced degradation. We found that upregulation of E proteins promoted the formation of FO B cells, whereas it suppressed the maturation of MZ B cells. In contrast, excessive amounts of Notch1 stimulated the differentiation of MZ B cells and inhibited the production of FO B cells. More interestingly, the effects of Notch1 were reversed by gain of E protein function. Furthermore, high levels of Bcl-6 expression in FO B cells was shown to be diminished by Notch signaling and restored by E proteins. In addition, E proteins facilitated and Notch hindered the differentiation of transitional B cells. Taken together, it appears that Notch regulates peripheral B cell differentiation, at least in part, through opposing E protein function.

A focus on the preclinical development and clinical status of the histone deacetylase inhibitor, romidepsin (depsipeptide, Istodax(®))

Romidepsin (Istodax(®), depsipeptide, FR901228, FK228, NSC 630176) is a cyclic peptide, broad-spectrum, potent histone deacetylase inhibitor, with activity mainly against class I histone deacetylase enzymes. In this article, we give an overview of the putative modes of action, such as effects on gene expression, cell cycle regulation, apoptosis induction, DNA repair, protein acetylation and induction of autophagy. Romidepsin has mainly been developed as a therapy for hematologic malignancies and is approved by the US FDA for the treatment of cutaneous T-cell lymphomas. This report outlines the laboratory and clinical development of the compound as a single agent that has more recently been evaluated in combination with other anticancer therapeutics, such as proteasome inhibitors.

Conditional inactivation of Blimp1 in adult mice promotes increased bone mass

Bone resorption, which is regulated by osteoclasts, is excessively activated in bone destructive diseases such as osteoporosis. Thus, controlling osteoclasts would be an effective strategy to prevent pathological bone loss. Although several transcription factors that regulate osteoclast differentiation and function could serve as molecular targets to inhibit osteoclast formation, those factors have not yet been characterized using a loss of function approach in adults. Here we report such a study showing that inactivation of B-lymphocyte induced maturation protein 1 (Blimp1) in adult mice increases bone mass by suppressing osteoclast formation. Using an ex vivo assay, we show that osteoclast differentiation is significantly inhibited by Blimp1 inactivation at an early stage of osteoclastogenesis. Conditional inactivation of Blimp1 inhibited osteoclast formation and increased bone mass in both male and female adult mice. Bone resorption parameters were significantly reduced by Blimp1 inactivation in vivo. Blimp1 reportedly regulates immune cell differentiation and function, but we detected no immune cell failure following Blimp1 inactivation. These data suggest that Blimp1 is a potential target to promote increased bone mass and prevent osteoclastogenesis.

Promising personalized therapeutic options for diffuse large B-cell Lymphoma Subtypes with oncogene addictions

Currently, two major classification systems segregate diffuse large B-cell lymphoma (DLBCL) into subtypes based on gene expression profiles and provide great insights about the oncogenic mechanisms that may be crucial for lymphomagenesis as well as prognostic information regarding response to current therapies. However, these current classification systems primarily look at expression and not dependency and are thus limited to inductive or probabilistic reasoning when evaluating alternative therapeutic options. The development of a deductive classification system that identifies subtypes in which all patients with a given phenotype require the same oncogenic drivers, and would therefore have a similar response to a rational therapy targeting the essential drivers, would significantly advance the treatment of DLBCL. This review highlights the putative drivers identified as well as the work done to identify potentially dependent populations. These studies integrated genomic analysis and functional screens to provide a rationale for targeted therapies within defined populations. Personalizing treatments by identifying patients with oncogenic dependencies via genotyping and specifically targeting the responsible drivers may constitute a novel approach for the treatment of DLBCL.

POZ-, AT-hook-, and zinc finger-containing protein (PATZ) interacts with human oncogene B cell lymphoma 6 (BCL6) and is required for its negative autoregulation

The PATZ1 gene encoding a POZ/AT-hook/Kruppel zinc finger (PATZ) transcription factor, is considered a cancer-related gene because of its loss or misexpression in human neoplasias. As for other POZ/domain and Kruppel zinc finger (POK) family members, the transcriptional activity of PATZ is due to the POZ-mediated oligomer formation, suggesting that it might be not a typical transactivator but an architectural transcription factor, thus functioning either as activator or as repressor depending on the presence of proteins able to interact with it. Therefore, to better elucidate PATZ function, we searched for its molecular partners. By yeast two-hybrid screenings, we found a specific interaction between PATZ and BCL6, a human oncogene that plays a key role in germinal center (GC) derived neoplasias. We demonstrate that PATZ and BCL6 interact in germinal center-derived B lymphoma cells, through the POZ domain of PATZ. Moreover, we show that PATZ is able to bind the BCL6 regulatory region, where BCL6 itself acts as a negative regulator, and to contribute to negatively modulate its activity. Consistently, disruption of one or both Patz1 alleles in mice causes focal expansion of thymus B cells, in which BCL6 is up-regulated. This phenotype was almost completely rescued by crossing Patz1(+/-) with Bcl6(+/-) mice, indicating a key role for Bcl6 expression in its development. Finally, a significant number of Patz1 knock-out mice (both heterozygous and homozygous) also develop BCL6-expressing lymphomas. Therefore, the disruption of one or both Patz1 alleles may favor lymphomagenesis by activating the BCL6 pathway.

Pathogenesis of human B cell lymphomas

The mechanisms that drive normal B cell differentiation and activation are frequently subverted by B cell lymphomas for their unlimited growth and survival. B cells are particularly prone to malignant transformation because the machinery used for antibody diversification can cause chromosomal translocations and oncogenic mutations. The advent of functional and structural genomics has greatly accelerated our understanding of oncogenic mechanisms in lymphomagenesis. The signaling pathways that normal B cells utilize to sense antigens are frequently derailed in B cell malignancies, leading to constitutive activation of prosurvival pathways. These malignancies co-opt transcriptional regulatory systems that characterize their normal B cell counterparts and frequently alter epigenetic regulators of chromatin structure and gene expression. These mechanistic insights are ushering in an era of targeted therapies for these cancers based on the principles of pathogenesis.

Screening for Compounds That Modulate Epigenetic Regulation of the Transcriptome

Epigenetic control of the transciptome is a complex and highly coordinated cellular process. One critical mechanism involves DNA methylation, mediated by distinct but related DNA methyltransferases (DNMTs). Although several DNMT inhibitors are available, most are nonselective; selective DNMT inhibitors, therefore, could be optimal as therapeutics, as well acting as chemical probes to elucidate the fundamental biology of individual DNMTs. DNA methylation is a stable chemical modification, yet posttranslational modification of histones is transitory, with reversible effects on gene expression. Histone posttranslational modifications influence access of transcription factors to DNA target sites to affect gene activity. Histones are regulated by several enzymes, including acetylases (HATs), deacetylases (HDACs), methyltransferases (HMTs), and demethylases (HDMTs). Generally, HATs activate, whereas HDACs suppress gene activity. Specifically, HMTs and HDMTs can either activate or inhibit gene expression, depending on the site and extent of the methylation pattern. There is growing interest in drugs that target enzymes involved in epigenetic control. Currently, a range of high-throughput screening (HTS) technologies are used to identify selective compounds against these enzymes. This review focuses on the rationale for drug development of these enzymes, as well the utility of HTS methods used in identifying and optimizing novel selective compounds that modulate epigenetic control of the human transcriptome.

Follicular lymphoma: stillSix characters in search of an author?

Follicular lymphoma (FL) is regarded as a distinct entity in the literature as well as in the 2008 edition of the WHO classification of tumours of haematopoietic and lymphoid tissues. Nevertheless, there are still several issues that are matters of controversy such as the grading system or the exact biological location of grade 3B FL. This makes FL somewhat like the Six characters in search of an author of Pirandello's comedy. Here, we revise the morphology and pathobiology of FL by highlighting both the areas remaining critical and future perspectives. This review was inspired by the reappraisal of Professor Lennert's personal archive that represents a unique legacy for the entire scientific community.

Mechanisms that promote and suppress chromosomal translocations in lymphocytes

Recurrent chromosomal translocations are characteristic features of many types of cancers, especially lymphomas and leukemias. Several basic mechanistic factors are required for the generation of most translocations. First, DNA double-strand breaks (DSBs) must be present simultaneously at the two participating loci. Second, the two broken loci must either be in proximity or be moved into proximity to be joined. Finally, cellular DNA repair pathways must be available to join the two broken loci to complete the translocation. These mechanistic factors can vary in different normal and mutant cells and, as a result, substantially influence the frequency at which particular translocations are generated in a given cell type. Ultimately, however, appearance of recurrent oncogenic translocations in tumors is, in most cases, strongly influenced by selection for the translocated oncogene during the tumorigenesis process. In this review, we discuss in depth the factors and pathways that contribute to the generation of translocations in lymphocytes and other cell types. We also discuss recent findings regarding mechanisms that underlie the appearance of recurrent translocations in tumors.

Prognostic impact of MUM1 expression by immunohistochemistry on primary mediastinal large B-cell lymphoma

Diffuse large B-cell lymphoma can be classified into two prognostically distinct subgroups with germinal center B-cell-like (CG) and activated B-cell-like (post-CG) characteristics, based on CD10, BCL-6, and MUM1 expression. We performed a retrospective analysis of the clinical variables of 37 patients with primary mediastinal large B-cell lymphoma and the expression of BCL-6 and MUM1 in 22 patients with available tissue. The median age was 30 years, and 70% of the patients were female. BCL-6 and MUM1 were expressed in 64% and 45% of cases, respectively. Five-year overall survival (OS) and disease-free survival (DFS) were 47% and 81%, respectively. In univariate analysis, complete response (p = 0.0001), radiation therapy (p = 0.01), International Prognostic Index (p = 0.001), and MUM1 expression (p = 0.002) correlated with OS. For this group of patients with homogeneous clinical characteristics, response to initial chemotherapy and MUM1 expression were associated with prognosis.

B-cell stimulatory cytokines and markers of immune activation are elevated several years prior to the diagnosis of systemic AIDS-associated non-Hodgkin B-cell lymphoma

BACKGROUND

The risk of developing non-Hodgkin lymphoma (NHL) is greatly increased in HIV infection. The aim of this study was to determine whether elevated serum levels of molecules associated with B-cell activation precede the diagnosis of AIDS-associated NHL (AIDS-NHL).

METHODS

Serum levels of B-cell activation-associated molecules, interleukin (IL)6, IL10, soluble CD23 (sCD23), sCD27, sCD30, C-reactive protein (CRP), and immunoglobulin E were determined in 179 NHL cases and HIV+ controls in the Multicenter AIDS Cohort Study, collected at up to 3 time points per subject, 0 to 5 years prior to AIDS-NHL diagnosis.

RESULTS

Serum IL6, IL10, CRP, sCD23, sCD27, and sCD30 levels were all significantly elevated in the AIDS-NHL group, when compared with HIV+ controls or with AIDS controls, after adjusting for CD4 T-cell number. Elevated serum levels of B-cell activation-associated molecules were seen to be associated with the development of systemic [non-CNS (central nervous system)] NHL, but not with the development of primary CNS lymphoma.

CONCLUSIONS

Levels of certain B-cell stimulatory cytokines and molecules associated with immune activation are elevated for several years preceding the diagnosis of systemic AIDS-NHL. This observation is consistent with the hypothesis that chronic B-cell activation contributes to the development of these hematologic malignancies.

IMPACT

Marked differences in serum levels of several molecules are seen for several years prediagnosis in those who eventually develop AIDS-NHL. Some of these molecules may serve as candidate biomarkers and provide valuable information to better define the etiology of NHL.

The biology of HDAC in cancer: the nuclear and epigenetic components

Traditionally, cancer has been regarded to originate from genetic alterations such as mutations, deletions, rearrangements as well as gene amplifications, leading to abnormal expression of tumor suppressor genes and oncogenes. An increasing body of evidence indicates that in addition to changes in DNA sequence, epigenetic alterations contribute to cancer initiation and progression. In contrast to genetic mutations, epigenetic changes are reversible and therefore an attractive target for cancer therapy. Many epi-drugs such as histone deacetylase (HDAC) inhibitors showed anticancer activity in cell culture and animal models of carcinogenesis. Recently, the two HDAC inhibitors suberoylanilide hydroxamic acid (SAHA, Vorinostat) and Romidepsin (Depsipeptide, FK228) were FDA approved for the treatment of cutaneous T-cell lymphoma (CTCL). Although HDAC inhibitors are potent anticancer agents, these compounds act against several HDAC family members potentially resulting in numerous side effects. This stems from the fact that HDACs play crucial roles in a variety of biological processes including cell cycle progression, proliferation, differentiation, and development. Consistently, mice deficient in single HDACs mostly exhibit severe phenotypes. Therefore, it is necessary to specify the cancer-relevant HDACs in a given tumor type in order to design selective inhibitors that target only cancer cells without affecting normal cells. In this chapter, we summarize the current state of knowledge of individual nuclear HDAC family members in development and tumorigenesis, their contribution to the hallmarks of cancer, and the involvement of HDAC family members in different types of human malignancies.

Histone deacetylase (HDAC) inhibitors in recent clinical trials for cancer therapy

Heritable changes in gene expression that are not based upon alterations in the DNA sequence are defined as epigenetics. The most common mechanisms of epigenetic regulation are the methylation of CpG islands within the DNA and the modification of amino acids in the N-terminal histone tails. In the last years, it became evident that the onset of cancer and its progression may not occur only due to genetic mutations but also because of changes in the patterns of epigenetic modifications. In contrast to genetic mutations, which are almost impossible to reverse, epigenetic changes are potentially reversible. This implies that they are amenable to pharmacological interventions. Therefore, a lot of work in recent years has focussed on the development of small molecule enzyme inhibitors like DNA-methyltransferase inhibitors or inhibitors of histone-modifying enzymes. These may reverse misregulated epigenetic states and be implemented in the treatment of cancer or other diseases, e.g., neurological disorders. Today, several epigenetic drugs are already approved by the FDA and the EMEA for cancer treatment and around ten histone deacetylase (HDAC) inhibitors are in clinical development. This review will give an update on recent clinical trials of the HDAC inhibitors used systemically that were reported in 2009 and 2010 and will present an overview of different biomarkers to monitor the biological effects.

TGFbeta signalling: a complex web in cancer progression

The distortion of growth factor signalling is the most important prerequisite in tumour progression. Transforming growth factor-beta (TGFbeta) signalling regulates tumour progression by a tumour cell-autonomous mechanism or through tumour-stroma interaction, and has either a tumour-suppressing or tumour-promoting function depending on cellular context. Such inherent complexity of TGFbeta signalling results in arduous, but promising, assignments for developing therapeutic strategies against malignant tumours. As numerous cellular context-dependent factors tightly maintain the balance of TGFbeta signalling and contribute to the regulation of TGFbeta-induced cell responses, in this Review we discuss how they maintain the balance of TGFbeta signalling and how their collapse leads to tumour progression.

Immunohistochemical profile and fluorescence in situ hybridization analysis of diffuse large B-cell lymphoma in northern China

CONTEXT

Gene expression profiling of diffuse large B-cell lymphoma using complementary DNA microarrays has revealed 2 major prognostic groups in Western countries: germinal center B-cell-like and nongerminal center B-cell-like lymphomas. Immunohistochemical analysis using antibodies specific for CD10, BCL6, and MUM1 has been proposed as a surrogate for gene expression profiling.

OBJECTIVE

To study the immunohistochemical features of diffuse large B-cell lymphoma cases from northern China because geographic differences for this disease are known to exist.

DESIGN

Morphologic, immunohistochemical, and fluorescence in situ hybridization analyses of 63 cases of diffuse large B-cell lymphoma from northern China.

RESULTS

There were 38 men and 25 women with a median age of 57 years (range, 12-87 years). CD10 was positive in 19 cases (30%), BCL6 was positive in 22 cases (35%), and MUM1 was positive in 32 cases (51%). Twenty-one (33%) cases were germinal center B-cell-like lymphoma, and 42 (67%) were nongerminal center B-cell-like lymphoma. BCL2 was expressed more often in nongerminal center B-cell-like disease versus germinal center B-cell-like disease (60% versus 24%, P = .01) and in nodal versus extranodal (64% versus 30%, P = .01) cases. Fluorescence in situ hybridization analysis showed BCL6, MYC , and BCL2 rearrangements in 11 of 32 (34%), 8 of 27 (30%), and 11 of 50 (22%) cases, respectively.

CONCLUSIONS

These results add to what is known about the geographic variation of diffuse large B-cell lymphomas. In northern China, the frequency of the germinal center B-cell-like type and BCL6 expression and/or BCL6 rearrangement is less and the frequency of MYC rearrangement is greater than have been reported in Western countries.

BCL6 canalizes Notch-dependent transcription, excluding Mastermind-like1 from selected target genes during left-right patterning

Although the Notch signaling pathway is one of the most intensely studied intracellular signaling pathways, the mechanisms by which Notch signaling regulates transcription remain incompletely understood. Here, we report that B cell leukemia/lymphoma 6 (BCL6), a transcriptional repressor, is a Notch-associated factor. BCL6 is necessary to maintain the expression of Pitx2 in the left lateral plate mesoderm during the patterning of left-right asymmetry in Xenopus embryos. For this process, BCL6 forms a complex with BCL6 corepressor (BCoR) on the promoters of selected Notch target genes such as enhancer of split related 1. BCL6 also inhibits the transcription of these genes by competing for the Notch1 intracellular domain, preventing the coactivator Mastermind-like1 (MAM1) from binding. These results define a mechanism restricting Notch-activated transcription to cell-type-appropriate subsets of target genes, and elucidate its relevance in vivo during left-right asymmetric development.

BCL6 and BCoR gang up on Notch to regulate left-right patterning

In this issue of Developmental Cell, Sakano et al. describe a novel mechanism of how a key lymphocyte transcription factor crosstalks to Notch signaling during embryonic development and thereby selectively inhibits Notch-activated target genes to allow proper left-right patterning.

Bone marrow aspirate and biopsy: a pathologist's perspective. II. interpretation of the bone marrow aspirate and biopsy

Bone marrow examination has become increasingly important for the diagnosis and treatment of hematologic and other illnesses. Morphologic evaluation of the bone marrow aspirate and biopsy has recently been supplemented by increasingly sophisticated ancillary assays, including immunocytochemistry, cytogenetic analysis, flow cytometry, and molecular assays. With our rapidly expanding knowledge of the clinical and biologic diversity of leukemia and other hematologic neoplasms, and an increasing variety of therapeutic options, the bone marrow examination has became more critical for therapeutic monitoring and planning optimal therapy. Sensitive molecular techniques, in vitro drug sensitivity testing, and a number of other special assays are available to provide valuable data to assist these endeavors. Fortunately, improvements in bone marrow aspirate and needle technology has made the procurement of adequate specimens more reliable and efficient, while the use of conscious sedation has improved patient comfort. The procurement of bone marrow specimens was reviewed in the first part of this series. This paper specifically addresses the diagnostic interpretation of bone marrow specimens and the use of ancillary techniques.

Histone deacetylase 1, 2, 6 and acetylated histone H4 in B- and T-cell lymphomas

AIMS

Histone deacetylase (HDAC) inhibitors are novel therapeutics in the treatment of peripheral T-cell lymphoma, unspecified (PTCL) and diffuse large B-cell lymphoma (DLBCL), where, for unknown reasons, T-cell malignancies appear to be more sensitive than B-cell malignancies. The aim was to determine HDAC expression in DLBCL and PTCL which has not previously been investigated.

METHODS AND RESULTS

The expression of HDAC1, HDAC2, HDAC6 and acetylated histone H4 was examined immunohistochemically in 31 DLBCL and 45 PTCL. All four markers showed high expression in both DLBCL and PTCL compared with normal lymphoid tissue. HDAC1 was more abundantly expressed in PTCL than in DLBCL (P = 0.0046), whereas acetylated H4 was more frequent in DLBCL (P < 0.0001), the latter suggesting a mechanism for T-cell lymphoma sensitivity to HDAC inhibitors. Moderate to strong HDAC6 expression was significantly correlated with favourable outcome (P = 0.016) in DLBCL patients, whereas the opposite effect was observed in PTCL patients (P < 0.0001). The other markers did not correlate with survival (P > 0.05).

CONCLUSIONS

HDAC1, HDAC2, HDAC6 and acetylated H4 are overexpressed in DLBCL and PTCL relative to normal lymphoid tissue. Furthermore, HDAC6 may be an important prognostic marker associated with favourable outcome in DLBCL and a more aggressive course in PTCL.

B-cell differentiation immunophenotypes in classical Hodgkin lymphomas

The bcl6/CD10/MUM1/CD138 B-cell differentiation immunophenotypes were analysed in 101 cases of classical Hodgkin lymphomas (cHL) aiming to elucidate their histogenesis. Three major bcl6/CD10/MUM1/CD138 immunophenotypes were distinguished on the basis of the immunohistochemical positivity of Hodgkin and Reed-Sternberg (H/RS) cells: (a) the late germinal center (GC)/early post-GC B-cell-like immunophenotype (bcl6-/CD10-/MUM1+/CD138-); 59/101 cases (59%), (b) the post-GC B-cell-like immunophenotype (bcl6-/CD10-/MUM1+/CD138+); 24/101 cases (24%) and (c) the indeterminate immunophenotype (bcl6+/CD10-/MUM1+/CD138-: 14 cases and bcl6+/CD10-/MUM1+/CD138+: four cases); 18/101 cases (18%). The above findings indicate that H/RS cells in most cHL display bcl6/CD10/MUM1/CD138 immunophenotypes consistent with late GC/early post-GC or post-GC B-cell differentiation. In addition, H/RS cells in a small fraction of cHL display indeterminate bcl6/CD10/MUM1/CD138 immunophenotypic profiles which are characterized by simultaneous expression of GC, late GC/early post-GC and post-GC B-cell differentiation proteins. These immunophenotypic profiles do not correspond to the differentiation immunophenotypes of normal B-cells and their identification in a part of cHL suggests that the differentiation process of H/RS cells is not complete in a fraction of these cells and/or is still ongoing at the time of observation.

Phase I pharmacokinetic and pharmacodynamic study of LAQ824, a hydroxamate histone deacetylase inhibitor with a heat shock protein-90 inhibitory profile, in patients with advanced solid tumors

PURPOSE

To determine the safety, maximum tolerated dose, and pharmacokinetic-pharmacodynamic profile of a histone deacetylase inhibitor, LAQ824, in patients with advanced malignancy.

PATIENTS AND METHODS

LAQ824 was administered i.v. as a 3-h infusion on days 1, 2, and 3 every 21 days. Western blot assays of peripheral blood mononuclear cell lysates and tumor biopsies pretherapy and posttherapy evaluated target inhibition and effects on heat shock protein-90 (HSP90) client proteins and HSP72.

RESULTS

Thirty-nine patients (22 male; median age, 53 years; median Eastern Cooperative Oncology Group performance status 1) were treated at seven dose levels (mg/m(2)): 6 (3 patients), 12 (4 patients), 24 (4 patients), 36 (4 patients), 48 (4 patients), 72 (19 patients), and 100 (1 patient). Dose-escalation used a modified continual reassessment method. Dose-limiting toxicities were transaminitis, fatigue, atrial fibrillation, raised serum creatinine, and hyperbilirubinemia. A patient with pancreatic cancer treated at 100 mg/m(2) died on course one at day 18 with grade 3 hyperbilirubinemia and neutropenia, fever, and acute renal failure. The area under the plasma concentration curve increased proportionally with increasing dose; median terminal half-life ranged from 8 to 14 hours. Peripheral blood mononuclear cell lysates showed consistent accumulation of acetylated histones posttherapy from 24 mg/m(2); higher doses resulted in increased and longer duration of pharmacodynamic effect. Changes in HSP90 client protein and HSP72 levels consistent with HSP90 inhibition were observed at higher doses. No objective response was documented; 3 patients had stable disease lasting up to 14 months. Based on these data, future efficacy trials should evaluate doses ranging from 24 to 72 mg/m(2).

CONCLUSIONS

LAQ824 was well tolerated at doses that induced accumulation of histone acetylation, with higher doses inducing changes consistent with HSP90 inhibition.