Mechanism-based epigenetic chemosensitization therapy of diffuse large B-cell lymphoma

Diagnostic and predictive biomarkers for lymphoma diagnosis and treatment in the era of precision medicine

Lymphomas are a group of hematological malignancies derived from lymphocytes. Lymphomas are clinically and biologically heterogeneous and have overlapping diagnostic features. With the advance of new technologies and the application of efficient and feasible detection platforms, an unprecedented number of novel biomarkers have been discovered or are under investigation at the genetic, epigenetic, and protein level as well as the tumor microenvironment. These biomarkers have enabled new clinical and pathological insights into the mechanisms underlying lymphomagenesis and also have facilitated improvements in the diagnostic workup, sub-classification, outcome stratification, and personalized therapy for lymphoma patients. However, integrating these biomarkers into clinical practice effectively and precisely in daily practice is challenging. More in-depth studies are required to further validate these novel biomarkers and to assess other parameters that can affect the reproducibility of these biomarkers such as the selection of detection methods, biological reagents, interpretation of data, and cost efficiency. Despite these challenges, there are many reasons to be optimistic that novel biomarkers will facilitate better algorithms and strategies as we enter a new era of precision medicine to better refine diagnosis, prognostication, and rational treatment design for patients with lymphomas.

Aberrant methylation of cell-free circulating DNA in plasma predicts poor outcome in diffuse large B cell lymphoma

Background

The prognostic value of aberrant DNA methylation of cell-free circulating DNA in plasma has not previously been evaluated in diffuse large B cell lymphoma (DLBCL). The aim of this study was to investigate if aberrant promoter DNA methylation can be detected in plasma from DLBCL patients and to evaluate this as a prognostic marker. Furthermore, we wanted to follow possible changes in methylation levels during treatment. Seventy-four patients were enrolled in the study, of which 59 received rituximab and CHOP-like chemotherapy. Plasma samples were collected from all patients at the time of diagnosis and from 14 healthy individuals used as controls. In addition, plasma samples were collected during and after treatment for surviving patients. In total, 158 plasma samples were analyzed for DNA methylation in the promoter regions of DAPK (DAPK1), DBC1, MIR34A, and MIR34B/C using pyrosequencing.

Results

Aberrant methylation levels at the time of diagnosis were detected in 19, 16, 8, and 10 % of the DLBCL plasma samples for DAPK1, DBC1, MIR34A, and MIR34B/C, respectively. DAPK1 methylation levels were significantly correlated with DBC1 and MIR34B/C methylation levels (P < 0.001). For the entire cohort, 5-year overall survival (OS) rates were significantly lower in the groups carrying aberrant DAPK1 (P = 0.004) and DBC1 (P = 0.044) methylation, respectively. DAPK1 methylation status were significantly correlated with stage (P = 0.015), as all patients with aberrant DAPK1 methylation were stages III and IV. Multivariate analysis identified DAPK1 as an independent prognostic factor for OS with a hazard ratio of 8.9 (95 % CI 2.7–29.3, P < 0.0007). Patients with DAPK1 methylated cell-free circulating DNA at time of diagnosis, who became long-term survivors, lost the aberrant methylation after treatment initiation. Conversely, patients that maintained or regained aberrant DAPK1 methylation died soon thereafter.

Conclusions

Aberrant promoter methylation of cell-free circulating DNA can be detected in plasma from DLBCL patients and hold promise as an easily accessible marker for evaluating response to treatment and for prognostication. In particular, aberrant DAPK1 methylation in plasma was an independent prognostic marker that may also be used to assess treatment response.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0261-y) contains supplementary material, which is available to authorized users.

An Epigenomic Approach to Improving Response to Neoadjuvant Cisplatin Chemotherapy in Bladder Cancer

Bladder cancer is among the five most common cancers diagnosed in the Western world and causes significant mortality and morbidity rates in affected patients. Therapeutic options to treat the disease in advanced muscle-invasive bladder cancer (MIBC) include cystectomy and chemotherapy. Neoadjuvant cisplatin-based combination chemotherapy is effective in MIBC; however, it has not been widely adopted by the community. One reason is that many patients do not respond to neoadjuvant chemotherapy, and no biomarker currently exists to identify these patients. It is also not clear whether a strategy to sensitize chemoresistant patients may exist. We sought to identify cisplatin-resistance patterns in preclinical models of bladder cancer, and test whether treatment with the epigenetic modifier decitabine is able to sensitize cisplatin-resistant bladder cancer cell lines. Using a screening approach in cisplatin-resistant bladder cancer cell lines, we identified dysregulated genes by RNA sequencing (RNAseq) and DNA methylation assays. DNA methylation analysis of tumors from 18 patients receiving cisplatin-based chemotherapy was used to confirm in vitro results. Cisplatin-resistant bladder cancer cells were treated with decitabine to investigate epigenetic sensitization of resistant cell lines. Our results show that HOXA9 promoter methylation status is associated with response to cisplatin-based chemotherapy in bladder cancer cell lines and in metastatic bladder cancer. Bladder cancer cells resistant to cisplatin chemotherapy can be sensitized to cisplatin by the DNA methylation inhibitor decitabine. Our data suggest that HOXA9 promoter methylation could serve as potential predictive biomarker and decitabine might sensitize resistant tumors in patients receiving cisplatin-based chemotherapy.

Epigenetic Determinants of Cancer

SUMMARYEpigenetic changes are present in all human cancers and are now known to cooperate with genetic alterations to drive the cancer phenotype. These changes involve DNA methylation, histone modifiers and readers, chromatin remodelers, microRNAs, and other components of chromatin. Cancer genetics and epigenetics are inextricably linked in generating the malignant phenotype; epigenetic changes can cause mutations in genes, and, conversely, mutations are frequently observed in genes that modify the epigenome. Epigenetic therapies, in which the goal is to reverse these changes, are now one standard of care for a preleukemic disorder and form of lymphoma. The application of epigenetic therapies in the treatment of solid tumors is also emerging as a viable therapeutic route.

Integrative systems medicine approaches to identify molecular targets in lymphoid malignancies

Although survival rates for lymphoproliferative disorders are steadily increasing both in the US and in Europe, there is need for optimizing front-line therapies and developing more effective salvage strategies. Recent advances in molecular genetics have highlighted the biological diversity of lymphoproliferative disorders. In particular, integrative approaches including whole genome sequencing, whole exome sequencing, and transcriptome or RNA sequencing have been instrumental to the identification of molecular targets for treatment. Herein, we will discuss how genomic, epigenomic and proteomic approaches in lymphoproliferative disorders have supported the discovery of molecular lesions and their therapeutic targeting in the clinic.

Combinatorial epigenetic therapy in diffuse large B cell lymphoma pre-clinical models and patients

BACKGROUND

Refractory and/or relapsed diffuse large B cell lymphoma (RR-DLBCL) patients are incurable with conventional chemotherapy due to the aggressiveness and the chemorefractory state of these tumors. DNA hypermethylation and histone deacetylation are two major epigenetic modifications by which aggressive DLBCL maintain their oncogenic state. We have previously reported that DNA methyltransferase inhibitors (DNMTI) affect RR-DLBCL growth and improve chemosensitivity. Here, we hypothesized that the combination of DNMTI with histone deacetylase inhibitor (HDI) would be an active and feasible therapeutic strategy in RR-DLBCL. Thus, we evaluated the anti-lymphoma activity of the HDI vorinostat (VST) in combination with the DNMTI azacitidine (AZA) or decitabine (DAC) in pre-clinical models of RR-DLBCL, and we determined the feasibility of the combination by conducting a phase Ib trial in RR-DLBCL patients.

RESULTS

Concurrent combination of DNMTI and HDI resulted in synergistic anti-lymphoma effect toward RR-DLBCL cells in vitro and in vivo, with no significant toxicity increase. In a phase Ib trial, a total of 18 patients with a median of three prior therapies were treated with four different dose levels of AZA and VST. The most common toxicities were hematological, followed by gastrointestinal and metabolic. The clinical benefit was low as only one subject had a partial response and three subjects had stable disease. Interestingly, two of the seven patients that received additional chemotherapy post-study achieved a complete response and three others had a significant clinical benefit. These observations suggested that the combination might have a delayed chemosensitization effect that we were able to confirm by using in vitro and in vivo models. These studies also demonstrated that the addition of VST does not improve the chemosensitizing effect of DAC alone.

CONCLUSIONS

Our data supports the strategy of epigenetic priming by employing DNMTI in RR-DLBCL patients in order to overcome resistance and improve their outcomes.

Therapeutic implication of concomitant chromosomal aberrations in patients with aggressive B-cell lymphomas

A subset of diffuse large B-cell lymphomas (DLBCL) harbors concomitant rearrangements of MYC, BCL2 and BCL6 and is characterized by clinical aggressiveness and intrinsic refractoriness to standard chemo-immunotherapy. Commonly identified as "double or triple hit" lymphomas, these diseases represent a therapeutic challenge to chemotherapy-based regimens and likely require a more targeted approach. Herein we summarize the unique biological behavior of double and triple hit lymphomas focusing on the coordinated network of pathways that enable cancer cells to tolerate the oncogenic stress imposed by the co-expression of MYC, BCL2 and BCL6. We discuss how these enabling pathways contribute to the chemo-refractoriness of these tumors. We propose to exploit lymphoma cells' addiction to these oncogenic networks to design combinatorial treatments for this aggressive disease based on the modulation of epigenetically-silenced pathways and decreasing expression and activity of these oncogenic drivers.

Epigenetic changes mediated by polycomb repressive complex 2 and E2a are associated with drug resistance in a mouse model of lymphoma

Background

The genetic origins of chemotherapy resistance are well established; however, the role of epigenetics in drug resistance is less well understood. To investigate mechanisms of drug resistance, we performed systematic genetic, epigenetic, and transcriptomic analyses of an alkylating agent-sensitive murine lymphoma cell line and a series of resistant lines derived by drug dose escalation.

Methods

Dose escalation of the alkylating agent mafosfamide was used to create a series of increasingly drug-resistant mouse Burkitt’s lymphoma cell lines. Whole genome sequencing, DNA microarrays, reduced representation bisulfite sequencing, and chromatin immunoprecipitation sequencing were used to identify alterations in DNA sequence, mRNA expression, CpG methylation, and H3K27me3 occupancy, respectively, that were associated with increased resistance.

Results

Our data suggest that acquired resistance cannot be explained by genetic alterations. Based on integration of transcriptional profiles with transcription factor binding data, we hypothesize that resistance is driven by epigenetic plasticity. We observed that the resistant cells had H3K27me3 and DNA methylation profiles distinct from those of the parental lines. Moreover, we observed DNA methylation changes in the promoters of genes regulated by E2a and members of the polycomb repressor complex 2 (PRC2) and differentially expressed genes were enriched for targets of E2a. The integrative analysis considering H3K27me3 further supported a role for PRC2 in mediating resistance. By integrating our results with data from the Immunological Genome Project (Immgen.org), we showed that these transcriptional changes track the B-cell maturation axis.

Conclusions

Our data suggest a novel mechanism of drug resistance in which E2a and PRC2 drive changes in the B-cell epigenome; these alterations attenuate alkylating agent treatment-induced apoptosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0305-0) contains supplementary material, which is available to authorized users.

Histone deacetylases 1 and 2 regulate DNA replication and DNA repair: potential targets for genome stability-mechanism-based therapeutics for a subset of cancers

Histone deacetylases 1 and 2 (HDAC1,2) belong to the class I HDAC family, which are targeted by the FDA-approved small molecule HDAC inhibitors currently used in cancer therapy. HDAC1,2 are recruited to DNA break sites during DNA repair and to chromatin around forks during DNA replication. Cancer cells use DNA repair and DNA replication as survival mechanisms and to evade chemotherapy-induced cytotoxicity. Hence, it is vital to understand how HDAC1,2 function during the genome maintenance processes (DNA replication and DNA repair) in order to gain insights into the mode-of-action of HDAC inhibitors in cancer therapeutics. The first-in-class HDAC1,2-selective inhibitors and Hdac1,2 conditional knockout systems greatly facilitated dissecting the precise mechanisms by which HDAC1,2 control genome stability in normal and cancer cells. In this perspective, I summarize the findings on the mechanistic functions of class I HDACs, specifically, HDAC1,2 in genome maintenance, unanswered questions for future investigations and views on how this knowledge could be harnessed for better-targeted cancer therapeutics for a subset of cancers.

Inhibition of COP9-signalosome (CSN) deneddylating activity and tumor growth of diffuse large B-cell lymphomas by doxycycline

In searching for small-molecule compounds that inhibit proliferation and survival of diffuse large B-cell lymphoma (DLBCL) cells and may, therefore, be exploited as potential therapeutic agents for this disease, we identified the commonly used and well-tolerated antibiotic doxycycline as a strong candidate. Here, we demonstrate that doxycycline inhibits the growth of DLBCL cells both in vitro and in mouse xenograft models. In addition, we show that doxycycline accumulates in DLBCL cells to high concentrations and affects multiple signaling pathways that are crucial for lymphomagenesis. Our data reveal the deneddylating activity of COP-9 signalosome (CSN) as a novel target of doxycycline and suggest that doxycycline may exert its effects in DLBCL cells in part through a CSN5-HSP90 pathway. Consistently, knockdown of CSN5 exhibited similar effects as doxycycline treatment on DLBCL cell survival and HSP90 chaperone function. In addition to DLBCL cells, doxycycline inhibited growth of several other types of non-Hodgkin lymphoma cells in vitro. Together, our results suggest that doxycycline may represent a promising therapeutic agent for DLBCL and other non-Hodgkin lymphomas subtypes.

Epigenetics and Lymphoma: Can We Use Epigenetics to Prime or Reset Chemoresistant Lymphoma Programs?

Non-Hodgkin lymphoma is a diverse group of lymphocyte-derived neoplasms. Although a heterogeneous group of malignancies, it has become apparent that epigenetic alterations, such as disturbances of DNA methylation and histone modification, are a common occurrence in both B cell and T cell lymphomas, contributing to lymphomagenesis. As a result, the use of epigenetic targeted therapy has been incorporated into various pre-clinical and clinical studies, demonstrating significant efficacy in lymphoma, with vorinostat becoming the first epigenetic therapy to receive FDA approval in any malignancy. The role of epigenetic drugs is evolving, with its potential use in combination therapy as well as a means of overcoming chemotherapy resistance. In this review, we discuss the epigenetic alterations in non-Hodgkin lymphomas as well as provide an overview of current epigenetic drugs and their role in clinical practice, and on-going clinical trials.

HDAC1,2 inhibition impairs EZH2- and BBAP-mediated DNA repair to overcome chemoresistance in EZH2 gain-of-function mutant diffuse large B-cell lymphoma

Gain-of-function mutations in the catalytic site of EZH2 (Enhancer of Zeste Homologue 2), is observed in about 22% of diffuse large B-cell lymphoma (DLBCL) cases. Here we show that selective inhibition of histone deacetylase 1,2 (HDAC1,2) activity using a small molecule inhibitor causes cytotoxic or cytostatic effects in EZH2 gain-of-function mutant (EZH2^GOF) DLBCL cells. Our results show that blocking the activity of HDAC1,2 increases global H3K27ac without causing a concomitant global decrease in H3K27me3 levels. Our data shows that inhibition of HDAC1,2 is sufficient to decrease H3K27me3 present at DSBs, decrease DSB repair and activate the DNA damage response in these cells. In addition to increased H3K27me3, we found that the EZH2^GOF DLBCL cells overexpress another chemotherapy resistance factor − B-lymphoma and BAL-associated protein (BBAP). BBAP monoubiquitinates histone H4K91, a residue that is also subjected to acetylation. Our results show that selective inhibition of HDAC1,2 increases H4K91ac, decreases BBAP-mediated H4K91 monoubiquitination, impairs BBAP-dependent DSB repair and sensitizes the refractory EZH2^GOF DLBCL cells to treatment with doxorubicin, a chemotherapy agent. Hence, selective HDAC1,2 inhibition provides a novel DNA repair mechanism-based therapeutic approach as it can overcome both EZH2- and BBAP-mediated DSB repair in the EZH2^GOF DLBCL cells.

Epigenetics: A primer for clinicians

With recent advances in cellular biology, we now appreciate that modifications to DNA and histones can have a profound impact on transcription and function, even in the absence of changes to DNA sequence. These modifications, now commonly referred to as "epigenetic" alterations, have changed how we understand cell behavior, reprogramming and differentiation and have provided significant insight into the mechanisms underlying carcinogenesis. Epigenetic alterations, to this point, are largely identified by changes in DNA methylation and hydroxymethylation as well as methylation, acetylation, and phosphorylation of histone tails. These modifications enable significant flexibility in gene expression, rather than just turning genes "ON" or "OFF." Herein we describe the epigenetic landscape in the regulation of gene expression with a particular focus on interrogating DNA methylation in myeloid malignancy.

ZEB1-associated drug resistance in cancer cells is reversed by the class I HDAC inhibitor mocetinostat

Therapy resistance is a major clinical problem in cancer medicine and crucial for disease relapse and progression. Therefore, the clinical need to overcome it, particularly for aggressive tumors such as pancreatic cancer, is very high. Aberrant activation of an epithelial-mesenchymal transition (EMT) and an associated cancer stem cell phenotype are considered a major cause of therapy resistance. Particularly, the EMT-activator ZEB1 was shown to confer stemness and resistance. We applied a systematic, stepwise strategy to interfere with ZEB1 function, aiming to overcome drug resistance. This led to the identification of both its target gene miR-203 as a major drug sensitizer and subsequently the class I HDAC inhibitor mocetinostat as epigenetic drug to interfere with ZEB1 function, restore miR-203 expression, repress stemness properties, and induce sensitivity against chemotherapy. Thereby, mocetinostat turned out to be more effective than other HDAC inhibitors, such as SAHA, indicating the relevance of the screening strategy. Our data encourage the application of mechanism-based combinations of selected epigenetic drugs with standard chemotherapy for the rational treatment of aggressive solid tumors, such as pancreatic cancer.

The Impact of DNA Methylation in Hematopoietic Malignancies

Aberrant DNA methylation is a characteristic feature of cancer including blood malignancies. Mutations in the DNA methylation regulators DNMT3A, TET1/2 and IDH1/2 are recurrent in leukemia and lymphoma. Specific and distinct DNA methylation patterns characterize subtypes of AML and lymphoma. Regulatory regions such as promoter CpG islands, CpG shores and enhancers show changes in methylation during transformation. However, the reported poor correlation between changes in methylation and gene expression in many mouse models and human studies reflects the complexity in the precise molecular mechanism for why aberrant DNA methylation promotes malignancies. This review will summarize current concepts regarding the mechanisms behind aberrant DNA methylation in hematopoietic malignancy and discuss its importance in cancer prognosis, tumor heterogeneity and relapse.

Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics

The 'language' of covalent histone modifications translates environmental and cellular cues into gene expression. This vast array of post-translational modifications on histones are more than just covalent moieties added onto a protein, as they also form a platform on which crucial cellular signals are relayed. The reversible lysine acetylation has emerged as an important post-translational modification of both histone and non-histone proteins, dictating numerous epigenetic programs within a cell. Thus, understanding the complex biology of lysine acetylation and its regulators is essential for the development of epigenetic therapeutics. In this review, we will attempt to address the complexities of lysine acetylation in the context of tumorigenesis, their role in cancer progression and emphasize on the modalities developed to target lysine acetyltransferases towards cancer treatment.

The role of next-generation sequencing in understanding the genomic basis of diffuse large B cell lymphoma and advancing targeted therapies

Next Generation Sequencing (NGS) has redefined the genetic landscape of Diffuse Large B-Cell Lymphoma (DLBCL) by identifying recurrent somatic mutations. Importantly, in some cases these mutations impact potentially actionable targets, thus affording novel personalized therapy opportunities. At the forefront of today's precision therapy era, how to best incorporate NGS into daily clinical practice is of primordial concern, in order to tailor patient's treatment regimens according to their individual mutational profiles. With the advent of cell-free DNA sequencing, which provides a sensitive and less invasive means of monitoring DLBCL patients, the clinical feasibility of NGS has been greatly improved. This article reviews the current landscape of DLBCL mutations, as well as the targeted therapies developed to counter their effects, and discusses how best to utilize NGS data for treatment decision-making.

Epigenetic dysregulation in follicular lymphoma

The adoption of next-generation sequencing technologies has led to a remarkable shift in our understanding of the genetic landscape of follicular lymphoma. While the disease has been synonymous with the t(14;18), the prevalence of alterations in genes that regulate the epigenome has been established as a pivotal hallmark of these lymphomas. Giant strides are being made in unraveling the biological consequences of these alterations in tumorigenesis opening up new opportunities for directed therapies.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin's lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.

Promoter hypermethylation of PTPL1, PTPN6, DAPK, p16 and 5-azacitidine inhibits growth in DLBCL

Aberrant hypermethylation of CpG islands of tumor suppressor is one of the mechanisms for epigenetic loss of gene function. In the present study, the methylation status of the promoter regions of protein tyrosine phosphatase (PTPN) 6, DAPK, and p16 were studied using methylation-specific polymerase chain reaction (MSP) in 26 diffuse large B cell lymphoma (DLBCL) lymphomas. In OCI-LY1 cell line, gene methylation status, expression of PTPL1 and its reactivation by DNA demethylation was determined by PCR and on the protein level by western blotting. ELISA-like reaction was used to detect global DNA methylation measurement. Induction of apoptosis by 5-azacitidine was analyzed by Annexin V/PI staining and flow cytometry. Our results show that hypermethylation of the PTPN6 gene promoter region was found in 15.4% (4/26), the DAPK gene promoter region in 30.8% (8/26), the p16 gene promoter region in 7.7% (2/26). Notably, we identified that PTPL1 was hypermethylated and transcriptionally silenced in OCI-LY1 cell line. The expression of PTPL1 was re-inducible by 5-azacytidine. 5-azacytidine also inhibits the proliferation and decreases the global methylation level of the OCI-LY1 cell line. We can conclude from our study that a higher prevalence of methylation of PTPL1, PTPN6, DAPK and p16 occur in DLBCL. Our data also highlights 5-azacytidine as a potential therapeutic candidate for DLBCL. Further studies are required to substantiate the role of methylation of PTPL1, PTPN6, DAPK and p16 as a marker in diffuse large B cell lymphoma.

Genetic and molecular targets in lymphoma: implications for prognosis and treatment

Lymphomas are the most common hematologic malignancies with approximately 79,000 new cases estimated for 2013 in the USA. Despite improved outcomes, relapse or recurrence remains a common problem with conventional cytotoxic therapy. Recently, many genetic and molecular mechanisms that drive various cellular events like apoptosis, angiogenesis and cell motility have been more clearly delineated. These new findings, coupled with the advent of high-throughput screening technology have led to the discovery of many compounds that can target specific mutations and/or influence deregulated transcription. In this review, we intend to provide a concise overview of genetic and molecular events that drive cellular processes in lymphomas and represent potential therapeutic targets. Additionally, we briefly discuss the prognostic significance of select biological markers.

Ex vivo engineered immune organoids for controlled germinal center reactions

Ex vivo engineered three-dimensional organotypic cultures have enabled the real-time study and control of biological functioning of mammalian tissues. Organs of broad interest where its architectural, cellular, and molecular complexity has prevented progress in ex vivo engineering are the secondary immune organs. Ex vivo immune organs can enable mechanistic understanding of the immune system and more importantly, accelerate the translation of immunotherapies as well as a deeper understanding of the mechanisms that lead to their malignant transformation into a variety of B and T cell malignancies. However, till date, no modular ex vivo immune organ has been developed with an ability to control the rate of immune reaction through tunable design parameter. Here we describe a B cell follicle organoid made of nanocomposite biomaterials, which recapitulates the anatomical microenvironment of a lymphoid tissue that provides the basis to induce an accelerated germinal center (GC) reaction by continuously providing extracellular matrix (ECM) and cell-cell signals to naïve B cells. Compared to existing co-cultures, immune organoids provide a control over primary B cell proliferation with ∼100-fold higher and rapid differentiation to the GC phenotype with robust antibody class switching.

Mechanisms and clinical applications of chromosomal instability in lymphoid malignancy

Lymphocytes are unique among cells in that they undergo programmed DNA breaks and translocations, but that special property predisposes them to chromosomal instability (CIN), a cardinal feature of neoplastic lymphoid cells that manifests as whole chromosome- or translocation-based aneuploidy. In several lymphoid malignancies translocations may be the defining or diagnostic markers of the diseases. CIN is a cornerstone of the mutational architecture supporting lymphoid neoplasia, though it is perhaps one of the least understood components of malignant transformation in terms of its molecular mechanisms. CIN is associated with prognosis and response to treatment, making it a key area for impacting treatment outcomes and predicting prognoses. Here we will review the types and mechanisms of CIN found in Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma and the lymphoid leukaemias, with emphasis placed on pathogenic mutations affecting DNA recombination, replication and repair; telomere function; and mitotic regulation of spindle attachment, centrosome function, and chromosomal segregation. We will discuss the means by which chromosome-level genetic aberrations may give rise to multiple pathogenic mutations required for carcinogenesis and conclude with a discussion of the clinical applications of CIN and aneuploidy to diagnosis, prognosis and therapy.

Sex affects bone morphogenetic protein type II receptor signaling in pulmonary artery smooth muscle cells

RATIONALE

Major pulmonary arterial hypertension (PAH) registries report a greater incidence of PAH in women; mutations in the bone morphogenic protein type II receptor (BMPR-II) occur in approximately 80% of patients with heritable PAH (hPAH).

OBJECTIVES

We addressed the hypothesis that women may be predisposed to PAH due to normally reduced basal BMPR-II signaling in human pulmonary artery smooth muscle cells (hPASMCs).

METHODS

We examined the BMPR-II signaling pathway in hPASMCs derived from men and women with no underlying cardiovascular disease (non-PAH hPASMCs). We also determined the development of pulmonary hypertension in male and female mice deficient in Smad1.

MEASUREMENTS AND MAIN RESULTS

Platelet-derived growth factor, estrogen, and serotonin induced proliferation only in non-PAH female hPASMCs. Female non-PAH hPASMCs exhibited reduced messenger RNA and protein expression of BMPR-II, the signaling intermediary Smad1, and the downstream genes, inhibitors of DNA binding proteins, Id1 and Id3. Induction of phospho-Smad1/5/8 and Id protein by BMP4 was also reduced in female hPASMCs. BMP4 induced proliferation in female, but not male, hPASMCs. However, small interfering RNA silencing of Smad1 invoked proliferative responses to BMP4 in male hPASMCs. In male hPASMCs, estrogen decreased messenger RNA and protein expression of Id genes. The estrogen metabolite 4-hydroxyestradiol decreased phospho-Smad1/5/8 and Id expression in female hPASMCs while increasing these in males commensurate with a decreased proliferative effect in male hPASMCs. Female Smad1(+/-) mice developed pulmonary hypertension (reversed by ovariectomy).

CONCLUSIONS

We conclude that estrogen-driven suppression of BMPR-II signaling in non-PAH hPASMCs derived from women contributes to a pro-proliferative phenotype in hPASMCs that may predispose women to PAH.

Epigenomic evolution in diffuse large B-cell lymphomas

The contribution of epigenomic alterations to tumour progression and relapse is not well characterized. Here we characterize an association between disease progression and DNA methylation in diffuse large B-cell lymphoma (DLBCL). By profiling genome-wide DNA methylation at single-base pair resolution in thirteen DLBCL diagnosis–relapse sample pairs, we show that DLBCL patients exhibit heterogeneous evolution of tumour methylomes during relapse. We identify differentially methylated regulatory elements and determine a relapse-associated methylation signature converging on key pathways such as transforming growth factor-β (TGF-β) receptor activity. We also observe decreased intra-tumour methylation heterogeneity from diagnosis to relapsed tumour samples. Relapse-free patients display lower intra-tumour methylation heterogeneity at diagnosis compared with relapsed patients in an independent validation cohort. Furthermore, intra-tumour methylation heterogeneity is predictive of time to relapse. Therefore, we propose that epigenomic heterogeneity may support or drive the relapse phenotype and can be used to predict DLBCL relapse.

The contribution of epigenomic alterations to tumour progression and relapse is not well characterized. Here the authors characterize epigenetic evolution in aggressive B-cell lymphoma and find that epigenomic heterogeneity may not only support and drive the relapse phenotype but also be used to predict lymphoma relapse.

DUSP4 deficiency caused by promoter hypermethylation drives JNK signaling and tumor cell survival in diffuse large B cell lymphoma

Using DNA methylation and gene expression profiling of diffuse large B cell lymphoma (DLBCL) samples, Schmid et al. find that the dual-specificity phosphatase DUSP4 gene is highly methylated in nodal and extranodal DLBCL cases, which correlates with loss of DUSP4 expression. Low DUSP4 expression represents a negative prognostic factor in patient cohorts. Ectopic DUSP4 expression inhibits JNK signaling and induces apoptosis in DLBCL cells. This effect can be phenocopied by JNK inhibitors in vitro and in vivo.

The epigenetic dysregulation of tumor suppressor genes is an important driver of human carcinogenesis. We have combined genome-wide DNA methylation analyses and gene expression profiling after pharmacological DNA demethylation with functional screening to identify novel tumor suppressors in diffuse large B cell lymphoma (DLBCL). We find that a CpG island in the promoter of the dual-specificity phosphatase DUSP4 is aberrantly methylated in nodal and extranodal DLBCL, irrespective of ABC or GCB subtype, resulting in loss of DUSP4 expression in 75% of >200 examined cases. The DUSP4 genomic locus is further deleted in up to 13% of aggressive B cell lymphomas, and the lack of DUSP4 is a negative prognostic factor in three independent cohorts of DLBCL patients. Ectopic expression of wild-type DUSP4, but not of a phosphatase-deficient mutant, dephosphorylates c-JUN N-terminal kinase (JNK) and induces apoptosis in DLBCL cells. Pharmacological or dominant-negative JNK inhibition restricts DLBCL survival in vitro and in vivo and synergizes strongly with the Bruton’s tyrosine kinase inhibitor ibrutinib. Our results indicate that DLBCL cells depend on JNK signaling for survival. This finding provides a mechanistic basis for the clinical development of JNK inhibitors in DLBCL, ideally in synthetic lethal combinations with inhibitors of chronic active B cell receptor signaling.

The BET Bromodomain Inhibitor OTX015 Affects Pathogenetic Pathways in Preclinical B-cell Tumor Models and Synergizes with Targeted Drugs

PURPOSE

In cancer cells, the epigenome is often deregulated, and inhibition of the bromodomain and extra-terminal (BET) family of bromodomain-containing proteins is a novel epigenetic therapeutic approach. Preliminary results of an ongoing phase I trial have reported promising activity and tolerability with the new BET bromodomain inhibitor OTX015.

EXPERIMENTAL DESIGN

We assessed the preclinical activity of OTX015 as single agent and in combination in mature B-cell lymphoma models and performed in vitro and in vivo experiments to identify the mechanism of action and the genetic features associated with sensitivity to the compound.

RESULTS

OTX015 showed antiproliferative activity in a large panel of cell lines derived from mature B-cell lymphoid tumors with median IC50 of 240 nmol/L, without significant differences among the different histotypes. In vitro and in vivo experiments showed that OTX015 targeted NFKB/TLR/JAK/STAT signaling pathways, MYC- and E2F1-regulated genes, cell-cycle regulation, and chromatin structure. OTX015 presented in vitro synergism with several anticancer agents, especially with mTOR and BTK inhibitors. Gene expression signatures associated with different degrees of sensitivity to OTX015 were identified. Although OTX015 was mostly cytostatic, the compound induced apoptosis in a genetically defined subgroup of cells, derived from activated B-cell-like diffuse large B-cell lymphoma, bearing wtTP53, mutations in MYD88, and CD79B or CARD11.

CONCLUSIONS

Together with the data coming from the ongoing phase I study, the in vitro and in vivo data presented here provide the basis for further clinical investigation of OTX015 as single agent and in combination therapies.

Summary and future directions

Our understanding of disease biology and treatment paradigms in diffuse large B-cell lymphoma (DLBCL) is now sufficiently mature that we are poised to enter a new phase of hematological oncology. To achieve the goal of precision medicine and begin to logically deploy the vast array of currently available, novel targeted therapies we must develop a roadmap for clinical research. We urgently need robust biomarkers to inform the results of current and planned randomized, controlled phase III clinical trials. These biomarkers should capitalize on our current understanding of the genetic landscape of DLBCL and will help to define those patients destined to fail R-CHOP. But more importantly, they will inform the molecular correlates of treatment failure for planned clinical trials testing novel agents and combinations. If successful, we can move the field past the vast array of prognostic markers and develop predictive biomarkers that direct future therapy.

Association of downregulation of WWOX with poor prognosis in patients with intrahepatic cholangiocarcinoma after curative resection

BACKGROUND AND AIM

Downregulation of the WW domain containing oxidoreductase (WWOX) has been reported to be involved in tumorigenesis in several neoplasms. This study sought to investigate the expression and role of WWOX in intrahepatic cholangiocarcinoma (ICC).

METHODS

WWOX expression was measured by quantitative real-time polymerase chain reaction (PCR), immunoblot, immunofluorescence, and immunohistochemistry. The prognostic significance was assessed by Kaplan-Meier and Cox regression analyses. The role of WWOX in proliferation, anchorage-independent growth, gene expression regulation, and tumorigenesis was assessed by WWOX re-expression using lentivirus. Methylation-specific PCR was performed to evaluate the methylation status of the WWOX gene regulatory region. A DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (AZA), was used to activate the endogenous WWOX gene in ICC cells both in vitro and in vivo.

RESULTS

The expression of WWOX in ICC tissues was much lower than that in nontumorous samples and showed reverse correlation with proliferative status. Restoration of WWOX expression resulted in suppression of the growth of WWOX-deficient ICC cells through activation of the intrinsic apoptotic signaling pathway, but did not affect growth of WWOX-sufficient human intrahepatic biliary epithelial derived non-cancer cells. Multivariate analyses revealed that downregulation of WWOX was an unfavorable predictor for overall survival and cumulative recurrence rates. The WWOX gene regulatory region was frequently methylated in ICC tissues and cell lines, and intratumoral WWOX restoration, through AZA injection, suppressed tumor growth in nude mice.

CONCLUSION

Downregulation of WWOX may occur as a result of hypermethylation and implies a poor prognosis in ICC; WWOX re-expression may be a potential molecular therapeutic target for ICC.

Emergence of drug tolerance in cancer cell populations: an evolutionary outcome of selection, nongenetic instability, and stress-induced adaptation

In recent experiments on isogenetic cancer cell lines, it was observed that exposure to high doses of anticancer drugs can induce the emergence of a subpopulation of weakly proliferative and drug-tolerant cells, which display markers associated with stem cell-like cancer cells. After a period of time, some of the surviving cells were observed to change their phenotype to resume normal proliferation and eventually repopulate the sample. Furthermore, the drug-tolerant cells could be drug resensitized following drug washout. Here, we propose a theoretical mechanism for the transient emergence of such drug tolerance. In this framework, we formulate an individual-based model and an integro-differential equation model of reversible phenotypic evolution in a cell population exposed to cytotoxic drugs. The outcomes of both models suggest that nongenetic instability, stress-induced adaptation, selection, and the interplay between these mechanisms can push an actively proliferating cell population to transition into a weakly proliferative and drug-tolerant state. Hence, the cell population experiences much less stress in the presence of the drugs and, in the long run, reacquires a proliferative phenotype, due to phenotypic fluctuations and selection pressure. These mechanisms can also reverse epigenetic drug tolerance following drug washout. Our study highlights how the transient appearance of the weakly proliferative and drug-tolerant cells is related to the use of high-dose therapy. Furthermore, we show how stem-like characteristics can act to stabilize the transient, weakly proliferative, and drug-tolerant subpopulation for a longer time window. Finally, using our models as in silico laboratories, we propose new testable hypotheses that could help uncover general principles underlying the emergence of cancer drug tolerance.

The epigenetic basis of diffuse large B-cell lymphoma

The pathogenesis of diffuse large B-cell lymphoma (DLBCL) is strongly linked to perturbation of epigenetic mechanisms. The germinal center (GC) B cells from which DLBCLs arise are prone to instability in their cytosine methylation patterns. DLBCLs inherit this epigenetic instability and display variable degrees of epigenetic heterogeneity. Greater epigenetic heterogeneity is linked with poor clinical outcome. Somatic mutations of histone-modifying proteins have also emerged as a hallmark of DLBCL. The effect of these somatic mutations may be to disrupt epigenetic switches that control the GC phenotype and "lock in" certain oncogenic features of GC B cells, resulting in malignant transformation. DNA methyltransferase and histone methyltransferase inhibitors are emerging as viable therapeutic approaches to erase aberrant epigenetic programming, suppress DLBCL growth, and overcome chemotherapy resistance. This review will discuss these recent advances and their therapeutic implications.

Future directions and targeted therapies in bladder cancer

There are substantial unmet needs for patients with metastatic urothelial carcinoma (UC). First-line cisplatin-based chemotherapy regimens yield a median survival of 12 to 15 months and long-term survival in 5% to 15%. Salvage systemic therapy yields a median survival of 6 to 8 months. Hence, the discovery of novel therapeutic targets is of paramount importance. Recent molecular analyses have provided insights regarding molecular tumor tissue alterations on multiple platforms. A multidisciplinary effort using innovative clinical trial designs and exploiting preclinical signals of robust activity guided by predictive biomarkers may provide much needed clinical advances in therapy for advanced UC.

6-Thioguanine and zebularine down-regulate DNMT1 and globally demethylate canine malignant lymphoid cells

Background

The antimetabolite 6-thioguanine (6-TG) has been used to treat both human and canine lymphoid malignancies. 6-TG has been shown to be epigenetically active as a demethylating agent in a human lymphoma cell line, causing downregulation of DNA methyltransferase 1 (DNMT1) through ubiquitin-targeted degradation. Zebularine (Zeb), a similar cytidine analog, also has demethylating activity as well as oral bioavailability. The hypothesis of the present study was that 6-TG and Zeb would cause downregulation of DNMT1 and globally demethylate the genomic DNA of canine lymphoma cells. The secondary hypothesis was that these agents would cause a dose-dependent decrease in cell proliferation in canine lymphoma cells. Canine CLGL-90 malignant T cells and CLL 17–7 cells were incubated in modified RPMI media. They were treated with 6-TG, Zeb, or control media at biologically relevant concentrations.

Results

Following treatment with each agent, DNMT1 protein and global DNA methylation were significantly decreased. A dose-dependent decrease in cell survival was also observed, with apoptosis being the primary mode of cell death in the CLGL-90 cell line.

Conclusions

These results confirm the demethylating action of 6-TG and Zeb in canine cells which is similar to that shown in human cell lines. Confirmation of this mechanism supports the clinical application of these compounds as demethylating drugs in veterinary patients.

Inhibiting DNA Methylation by 5-Aza-2'-deoxycytidine ameliorates atherosclerosis through suppressing macrophage inflammation

Inflammation marks all stages of atherogenesis. DNA hypermethylation in the whole genome or specific genes is associated with inflammation and cardiovascular diseases. Therefore, we aimed to study whether inhibiting DNA methylation by DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) ameliorates atherosclerosis in low-density lipoprotein receptor knockout (Ldlr(-/-)) mice. Ldlr(-/-) mice were fed an atherogenic diet and adminisered saline or 5-aza-dC (0.25 mg/kg) for up to 30 weeks. 5-aza-dC treatment markedly decreased atherosclerosis development in Ldlr(-/-) mice without changes in body weight, plasma lipid profile, macrophage cholesterol levels and plaque lipid content. Instead, this effect was associated with decreased macrophage inflammation. Macrophages with 5-aza-dC treatment had downregulated expression of genes involved in inflammation (TNF-α, IL-6, IL-1β, and inducible nitric oxidase) and chemotaxis (CD62/L-selectin, chemokine [C-C motif] ligand 2/MCP-1 [CCL2/MCP-1], CCL5, CCL9, and CCL2 receptor CCR2). This resulted in attenuated macrophage migration and adhesion to endothelial cells and reduced macrophage infiltration into atherosclerotic plaques. 5-aza-dC also suppressed macrophage endoplasmic reticulum stress, a key upstream signal that activates macrophage inflammation and apoptotic pathways. Finally, 5-aza-dC demethylated liver X receptor α (LXRα) and peroxisome proliferator-activated receptor γ1 (PPARγ1) promoters, which are both enriched with CpG sites. This led to overexpression of LXRα and PPARγ, which may be responsible for 5-aza-dC's anti-inflammatory and atheroprotective effect. Our findings provide strong evidence that DNA methylation may play a significant role in cardiovascular diseases and serve as a therapeutic target for prevention and treatment of atherosclerosis.

Investigational epigenetically targeted drugs in early phase trials for the treatment of haematological malignancies

INTRODUCTION

For decades, cancer research has focussed on the genetic defects that drive tumourigenesis. However, recent high-resolution sequencing studies have uncovered mounting evidence for the complementary role of epigenetic deregulation as a hallmark of haematological malignancies. The reversibility of epigenetic changes makes them suitable candidates for pharmacological manipulation and therapeutic targeting.

AREAS COVERED

This review summarises the mechanisms of normal epigenetic regulation and how these are perturbed in haematological malignancies as a result of genetic alterations. The article concludes with how these can be reversed and appraises the investigational epigenetically targeted therapies in preclinical and clinical use.

EXPERT OPINION

The identification of recurring alterations in components of the epigenome of leukaemia and lymphoma has driven the rapid development of highly potent epigenetically targeted therapies. This rapid development has alluded to the possibility of a personalised therapeutic approach in selected patient populations. An enhanced understanding of the biological effects of these epigenetic alterations in initiation and progression of haematological malignancies, together with a clear mechanistic insight into how the drugs reverse the phenotypes, will define their translation into routine clinical use.

Correlation of long non-coding RNA expression with metastasis, drug resistance and clinical outcome in cancer

The therapeutic response and clinical outcome of patients diagnosed with the same cancer type and that receive identical treatment is highly variable to reflect the genetic heterogeneity within tumor cells. Non-coding RNAs (ncRNAs) are recently discovered molecules that regulate eukaryotic gene expression and represent a significant advance towards a better understanding of the mechanisms that govern cellular growth. NcRNAs are essential for the proper regulation of cell proliferation and survival under physiologic conditions and are deregulated in many pathologies, e.g., human cancers. NcRNAs have been associated with cancer diagnosis, staging, treatment response, metastasis and survival and include distinct subtypes, e.g., long ncRNAs (lncRNAs) and microRNAs (miRNAs). LncRNAs have been linked to essential growth-promoting activities and their deregulation contributes to tumor cell survival. A prominent example is the Hox transcript antisense intergenic lncRNA, HOTAIR, that cooperates with the polycomb repressive complex to reprogram chromatin organization. HOTAIR expression is deregulated in a spectrum of cancers and HOTAIR expression correlates with patient survival. Here, we highlight emerging evidence that supports a role for lncRNAs in cancer with implications for the development of novel diagnostics and therapeutics.

Epigenetic diversity in hematopoietic neoplasms

Tumor cell populations display a remarkable extent of variability in non-genetic characteristics such as DNA methylation, histone modification patterns, and differentiation levels of individual cells. It remains to be elucidated whether non-genetic heterogeneity is simply a byproduct of tumor evolution or instead a manifestation of a higher-order tissue organization that is maintained within the neoplasm to establish a differentiation hierarchy, a favorable microenvironment, or a buffer against changing selection pressures during tumorigenesis. Here, we review recent findings on epigenetic diversity, particularly heterogeneity in DNA methylation patterns in hematologic malignancies. We also address the implications of epigenetic heterogeneity for the clonal evolution of tumors and discuss its effects on gene expression and other genome functions in cancer.

Chromatin Memory in the Development of Human Cancers

Cancer is a complex disease with acquired genomic and epigenomic alterations that affect cell proliferation, viability and invasiveness. Almost all the epigenetic mechanisms including cytosine methylation and hydroxymethylation, chromatin remodeling and non-coding RNAs have been found associate with carcinogenesis and cancer specific expression profile. Altered histone modification as an epigenetic hallmark is frequently found in tumors. Understanding the epigenetic alterations induced by carcinogens or infectious agents may help us understand early epigenetic changes prior to the development of cancer. In this review, we focus on chromatin remodeling and the associated histone modifiers in the development of cancer; the application of these modifiers as a cancer therapy target in different clinical trial phases is also discussed.

Current and investigational drug strategies for glioblastoma

Medical treatments for glioblastoma face several challenges. Lipophilic alkylators remain the mainstay of treatment, emphasising the primacy of good blood-brain barrier penetration. Temozolomide has emerged as a major contributor to improved patient survival. The roles of procarbazine and vincristine in the procarbazine, lomustine and vincristine (PCV) schedule have attracted scrutiny and several lines of evidence now support the use of lomustine as effective single-agent therapy. Bevacizumab has had a convoluted development history, but clearly now has no major role in first-line treatment, and may even be detrimental to quality of life in this setting. In later disease, clinically meaningful benefits are achievable in some patients, but more impressively the combination of bevacizumab and lomustine shows early promise. Over the last decade, investigational strategies in glioblastoma have largely subscribed to the targeted kinase inhibitor paradigm and have mostly failed. Low prevalence dominant driver lesions such as the FGFR-TACC fusion may represent a niche role for this agent class. Immunological, metabolic and radiosensitising approaches are being pursued and offer more generalised efficacy. Finally, trial design is a crucial consideration. Progress in clinical glioblastoma research would be greatly facilitated by improved methodologies incorporating: (i) routine pharmacokinetic and pharmacodynamic assessments by preoperative dosing; and (ii) multi-stage, multi-arm protocols incorporating new therapy approaches and high-resolution biology in order to guide necessary improvements in science.

Manipulating the epigenome in germinal center lymphomas: is it getting easier and ezier?

Mutations affecting key epigenetic modifiers tend to cluster in malignancies in which cells of origin lie in the germinal center (GC). EZH2, as transcriptional repressor, is mutated in high frequency in Chinese and Western patients with follicular lymphoma and may represent a rational target for GC-derived lymphomas. .

Epigenetic silencing of TFPI-2 in canine diffuse large B-cell lymphoma

Epigenetic modifications are important early events during carcinogenesis. In particular, hypermethylation of CpG islands in the promoter region of tumor suppressor genes is a well-known mechanism of gene silencing that contributes to cancer development and progression. Tissue factor pathway inhibitor 2 (TFPI-2) is a tumor suppressor involved in invasiveness inhibition. Although TFPI-2 transcriptional silencing, through promoter hypermethylation, has been widely reported in several human malignancies, it has never been explored in lymphoma. In the present study TFPI-2 methylation and gene expression have been investigated in canine Diffuse Large B-cell lymphomas (cDLBCL). The methylation level of 23 CpGs located within the TFPI-2 promoter was investigated by bisulfite-specific PCR and next generation amplicon deep sequencing (GS Junior 454, Roche) in 22 cDLBCLs and 9 controls. For the same specimens, TFPI-2 gene expression was assessed by means of Real-time RT-PCR. Sequence analysis clearly demonstrated that TFPI2 is frequently hypermethylated in cDLBCL. Hypermethylation of the TFPI-2 promoter was found in 77% of DLBCLs (17 out of 22) and in one normal lymph node. Globally, dogs with DLBCL showed a mean methylation level significantly increased compared to controls (p<0.01) and analysis of hypermethylation by site identified 19 loci out of 23 (82%) with mean methylation levels from 2- to 120-fold higher in cDLBCL. Gene expression analysis confirmed a significant down-regulation of TFPI-2 (p<0.05) in DLBCLs compared with normal lymph nodes, suggesting that TFPI-2 hypermethylation negatively regulates its transcription. In addition, a significant positive correlation (p<0.01) was found between TFPI-2 methylation levels and age providing the first indication of age-associated epigenetic modifications in canine DLBCL. To conclude, our findings demonstrated that epigenetic dysregulation of TFPI-2, leading to its reduced expression, is frequently detected in canine DLBCL. In the next future, the aberrant TFPI-2 promoter hypermethylation may be considered in association with prognosis and therapy.

Epigenetic approaches for chemosensitization of refractory diffuse large B-cell lymphomas

Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma, with the greatest challenge for improving patient survival being the management of chemorefractory disease upon relapse. Epigenetic dysregulation has been correlated with more-aggressive malignancies and chemoresistance. In this issue of Cancer Discovery, Clozel and colleagues show the potential for low-dose DNA methyltransferase inhibitors as both a rational and an effective neoadjuvant approach for chemosensitization in DLBCL.

Integrative genomic analysis of temozolomide resistance in diffuse large B-cell lymphoma

PURPOSE

Despite advances, there is an urgent need for effective therapeutics for relapsed diffuse large B-cell lymphoma, particularly in elderly patients and primary central nervous system (CNS) lymphoma. Temozolomide (TMZ), an oral DNA-alkylating agent routinely used in the therapy of glioblastoma multiforme, is active in patients with primary CNS lymphoma but the response rates are low. The mechanisms contributing to TMZ resistance are unknown.

EXPERIMENTAL DESIGN

We undertook an unbiased and genome-wide approach to understand the genomic methylation and gene expression profiling differences associated with TMZ resistance in diffuse large B-cell lymphoma cell lines and identify mechanisms to overcome TMZ resistance.

RESULTS

TMZ was cytotoxic in a subset of diffuse large B-cell lymphoma cell lines, independent of MGMT promoter methylation or protein expression. Using Connectivity Map (CMAP), we identified several compounds capable of reversing the gene expression signature associated with TMZ resistance. The demethylating agent decitabine (DAC) is identified by CMAP as capable of reprogramming gene expression to overcome TMZ resistance. Treatment with DAC led to increased expression of SMAD1, a transcription factor involved in TGF-β/bone morphogenetic protein (BMP) signaling, previously shown to be epigenetically silenced in resistant diffuse large B-cell lymphoma. In vitro and in vivo treatment with a combination of DAC and TMZ had greater antilymphoma activity than either drug alone, with complete responses in TMZ-resistant diffuse large B-cell lymphoma murine xenograft models.

CONCLUSIONS

Integrative genome-wide methylation and gene expression analysis identified novel genes associated with TMZ resistance and demonstrate potent synergy between DAC and TMZ. The evidence from cell line and murine experiments supports prospective investigation of TMZ in combination with demethylating agents in diffuse large B-cell lymphoma.