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

Loss of CREBBP and KMT2D cooperate to accelerate lymphomagenesis and shape the lymphoma immune microenvironment

Despite regulating overlapping gene enhancers and pathways, CREBBP and KMT2D mutations recurrently co-occur in germinal center (GC) B cell-derived lymphomas, suggesting potential oncogenic cooperation. Herein, we report that combined haploinsufficiency of Crebbp and Kmt2d induces a more severe mouse lymphoma phenotype (vs either allele alone) and unexpectedly confers an immune evasive microenvironment manifesting as CD8+ T-cell exhaustion and reduced infiltration. This is linked to profound repression of immune synapse genes that mediate crosstalk with T-cells, resulting in aberrant GC B cell fate decisions. From the epigenetic perspective, we observe interaction and mutually dependent binding and function of CREBBP and KMT2D on chromatin. Their combined deficiency preferentially impairs activation of immune synapse-responsive super-enhancers, pointing to a particular dependency for both co-activators at these specialized regulatory elements. Together, our data provide an example where chromatin modifier mutations cooperatively shape and induce an immune-evasive microenvironment to facilitate lymphomagenesis.

Challenging our understanding of B-cell lymphomagenesis and risk: Paediatric high-grade B-cell lymphoma, not otherwise specified with a DDX3X::MLLT10 fusion and an IGH deletion

We report a unique case of high-grade B-cell lymphoma, not otherwise specified in a 5-year-old child. Whole-genome sequencing revealed a DDX3X::MLLT10 fusion, usually seen in T-cell acute lymphoblastic leukaemia (ALL). This suggests the novel idea that MLLT10 fusions are capable of driving B-cell malignancies. An IGH deletion usually only seen in adults was also found. These unique genetic findings provide novel insights into B-cell lymphomagenesis. The child remains in remission 7 year post chemotherapy, which demonstrates that novel complex molecular findings do not always denote high-risk disease.

Mouse models of diffuse large B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is a genetically highly heterogeneous disease. Yet, to date, the vast majority of patients receive standardized frontline chemo-immune-therapy consisting of an anthracycline backbone. Using these regimens, approximately 65% of patients can be cured, whereas the remaining 35% of patients will face relapsed or refractory disease, which, even in the era of CAR-T cells, is difficult to treat. To systematically tackle this high medical need, it is important to design, generate and deploy suitable in vivo model systems that capture disease biology, heterogeneity and drug response. Recently published, large comprehensive genomic characterization studies, which defined molecular sub-groups of DLBCL, provide an ideal framework for the generation of autochthonous mouse models, as well as an ideal benchmark for cell line-derived or patient-derived mouse models of DLBCL. Here we discuss the current state of the art in the field of mouse modelling of human DLBCL, with a particular focus on disease biology and genetically defined molecular vulnerabilities, as well as potential targeting strategies.

DLBCL arising from indolent lymphomas: How are they different?

Transformation to diffuse large B-cell lymphoma (DLBCL) is a recognized, but unpredictable, clinical inflection point in the natural history of indolent lymphomas. Large retrospective studies highlight a wide variability in the incidence of transformation across the indolent lymphomas and the adverse outcomes associated with transformed lymphomas. Opportunities to dissect the biology of transformed indolent lymphomas have arisen with evolving technologies and unique tissue collections enabling a growing appreciation, particularly, of their genetic basis, how they relate to the preceding indolent lymphomas and the comparative biology with de novo DLBCL. This review summarizes our current understanding of both the clinical and biological aspects of transformed lymphomas and the outstanding questions that remain.

Personalised therapy in follicular lymphoma - is the dial turning?

Follicular lymphoma is the most common indolent lymphoma accounting for approximately 20%-25% of all new non-Hodgkin lymphoma diagnoses in western countries. Whilst outcomes are mostly favorable, the spectrum of clinical phenotypes includes high-risk groups with significantly inferior outcomes. This review discusses recent updates in risk stratification and treatment approaches from upfront treatment for limited and advanced stage follicular lymphoma to the growing options for relapsed, refractory disease with perspectives on how to approach this from a personalized lens. Notable gaps remain on how one can precisely and prospectively select optimal treatment for patients based on varying risks, with an anticipation that an increased understanding of the biology of these different phenotypes and increasing refinement of imaging- and biomarker-based tools will, in time, allow these gaps to be closed.

The histone demethylase KDM5C controls female bone mass by promoting energy metabolism in osteoclasts

Women experience osteoporosis at higher rates than men. Aside from hormones, the mechanisms driving sex-dependent bone mass regulation are not well understood. Here, we demonstrate that the X-linked H3K4me2/3 demethylase KDM5C regulates sex-specific bone mass. Loss of KDM5C in hematopoietic stem cells or bone marrow monocytes increases bone mass in female but not male mice. Mechanistically, loss of KDM5C impairs the bioenergetic metabolism, resulting in impaired osteoclastogenesis. Treatment with the KDM5 inhibitor reduces osteoclastogenesis and energy metabolism of both female mice and human monocytes. Our report details a sex-dependent mechanism for bone homeostasis, connecting epigenetic regulation to osteoclast metabolism and positions KDM5C as a potential target for future treatment of osteoporosis in women.

Sequence analyses of relapsed or refractory diffuse large B-cell lymphomas unravel three genetic subgroups of patients and the GNA13 mutant as poor prognostic biomarker, results of LNH-EP1 study

Advances in molecular profiling of newly diagnosed diffuse large B-cell lymphoma (DLBCL) have recently refine genetic subgroups. Genetic subgroups remain undetermined at the time of relapse or refractory (RR) disease. This study aims to decipher genetic subgroups and search for prognostic molecular biomarkers in patients with RR-DLBCL. From 2015 to 2021, targeted next-generation sequencing analyses of germline-matched tumor samples and fresh tissue from RR-DLBCL patients were performed. Unsupervised clustering of somatic mutations was performed and correlations with patient outcome were sought. A number of 120 patients with RR-DLBCL were included in LNH-EP1 study and a molecular tumor landscape was successfully analyzed in 87% of patients (104/120 tumor samples). The median age was 67.5 years (range 27.4-87.4), median number of previous treatments was 2 (range 1-9). The most frequently mutated genes were TP53 (n = 53 mutations; 42% of samples), CREBBP (n = 39; 32%), BCL2 (n = 86; 31%), KMT2D (n = 39; 28%) and PIM1 (n = 54; 22%). Unsupervised clustering separated three genetic subgroups entitled BST (enriched in BCL2, SOCS1, and TNFRSF14 mutations); TKS (enriched in TP53, KMT2D, and STAT6 mutations); and PCM (enriched in PIM1, CD79B, and MYD88 mutations). Median overall survival (OS) was 11.0 (95% confidence interval [CI]: 8.1-12.6) months. OS was not significantly different between the three genetic subgroups. GNA13 mutant was significantly associated with an increased risk of death (hazard ratio: 6.6 [95% CI: 2.1-20.6]; p = .0011) and shorter OS (p = .0340). At the time of relapse or refractory disease, three genetic subgroups of DLBCL patients were delineated, which could help advance precision molecular medicine programs.

Principles of phosphoproteomics and applications in cancer research

Phosphorylation constitutes the most common and best-studied regulatory post-translational modification in biological systems and archetypal signalling pathways driven by protein and lipid kinases are disrupted in essentially all cancer types. Thus, the study of the phosphoproteome stands to provide unique biological information on signalling pathway activity and on kinase network circuitry that is not captured by genetic or transcriptomic technologies. Here, we discuss the methods and tools used in phosphoproteomics and highlight how this technique has been used, and can be used in the future, for cancer research. Challenges still exist in mass spectrometry phosphoproteomics and in the software required to provide biological information from these datasets. Nevertheless, improvements in mass spectrometers with enhanced scan rates, separation capabilities and sensitivity, in biochemical methods for sample preparation and in computational pipelines are enabling an increasingly deep analysis of the phosphoproteome, where previous bottlenecks in data acquisition, processing and interpretation are being relieved. These powerful hardware and algorithmic innovations are not only providing exciting new mechanistic insights into tumour biology, from where new drug targets may be derived, but are also leading to the discovery of phosphoproteins as mediators of drug sensitivity and resistance and as classifiers of disease subtypes. These studies are, therefore, uncovering phosphoproteins as a new generation of disruptive biomarkers to improve personalised anti-cancer therapies.

Potential Pathogenic Impact of Cow’s Milk Consumption and Bovine Milk-Derived Exosomal MicroRNAs in Diffuse Large B-Cell Lymphoma

Epidemiological evidence supports an association between cow’s milk consumption and the risk of diffuse large B-cell lymphoma (DLBCL), the most common non-Hodgkin lymphoma worldwide. This narrative review intends to elucidate the potential impact of milk-related agents, predominantly milk-derived exosomes (MDEs) and their microRNAs (miRs) in lymphomagenesis. Upregulation of PI3K-AKT-mTORC1 signaling is a common feature of DLBCL. Increased expression of B cell lymphoma 6 (BCL6) and suppression of B lymphocyte-induced maturation protein 1 (BLIMP1)/PR domain-containing protein 1 (PRDM1) are crucial pathological deviations in DLBCL. Translational evidence indicates that during the breastfeeding period, human MDE miRs support B cell proliferation via epigenetic upregulation of BCL6 (via miR-148a-3p-mediated suppression of DNA methyltransferase 1 (DNMT1) and miR-155-5p/miR-29b-5p-mediated suppression of activation-induced cytidine deaminase (AICDA) and suppression of BLIMP1 (via MDE let-7-5p/miR-125b-5p-targeting of PRDM1). After weaning with the physiological termination of MDE miR signaling, the infant’s BCL6 expression and B cell proliferation declines, whereas BLIMP1-mediated B cell maturation for adequate own antibody production rises. Because human and bovine MDE miRs share identical nucleotide sequences, the consumption of pasteurized cow’s milk in adults with the continued transfer of bioactive bovine MDE miRs may de-differentiate B cells back to the neonatal “proliferation-dominated” B cell phenotype maintaining an increased BLC6/BLIMP1 ratio. Persistent milk-induced epigenetic dysregulation of BCL6 and BLIMP1 expression may thus represent a novel driving mechanism in B cell lymphomagenesis. Bovine MDEs and their miR cargo have to be considered potential pathogens that should be removed from the human food chain.

KMT2D acetylation by CREBBP reveals a cooperative functional interaction at enhancers in normal and malignant germinal center B cells

Heterozygous inactivating mutations of the KMT2D methyltransferase and the CREBBP acetyltransferase are among the most common genetic alterations in B cell lymphoma and co-occur in 40 to 60% of follicular lymphoma (FL) and 30% of EZB/C3 diffuse large B cell lymphoma (DLBCL) cases, suggesting they may be coselected. Here, we show that combined germinal center (GC)-specific haploinsufficiency of Crebbp and Kmt2d synergizes in vivo to promote the expansion of abnormally polarized GCs, a common preneoplastic event. These enzymes form a biochemical complex on select enhancers/superenhancers that are critical for the delivery of immune signals in the GC light zone and are only corrupted upon dual Crebbp/Kmt2d loss, both in mouse GC B cells and in human DLBCL. Moreover, CREBBP directly acetylates KMT2D in GC-derived B cells, and, consistently, its inactivation by FL/DLBCL-associated mutations abrogates its ability to catalyze KMT2D acetylation. Genetic and pharmacologic loss of CREBBP and the consequent decrease in KMT2D acetylation lead to reduced levels of H3K4me1, supporting a role for this posttranslational modification in modulating KMT2D activity. Our data identify a direct biochemical and functional interaction between CREBBP and KMT2D in the GC, with implications for their role as tumor suppressors in FL/DLBCL and for the development of precision medicine approaches targeting enhancer defects induced by their combined loss.

Clinical advances in epigenetic therapies for lymphoma

BACKGROUND

Advances in understanding of cancer biology, genomics, epigenomics, and immunology have resulted in development of several therapeutic options that expand cancer care beyond traditional chemotherapy or radiotherapy, including individualized treatment strategies, novel treatments based on monotherapies or combination therapy to reduce toxicities, and implementation of strategies for overcoming resistance to anticancer therapy.

RESULTS

This review covers the latest applications of epigenetic therapies for treatment of B cell, T cell, and Hodgkin lymphomas, highlighting key clinical trial results with monotherapies and combination therapies from the main classes of epigenetic therapies, including inhibitors of DNA methyltransferases, protein arginine methyltransferases, enhancer of zeste homolog 2, histone deacetylases, and the bromodomain and extraterminal domain.

CONCLUSION

Epigenetic therapies are emerging as an attractive add-on to traditional chemotherapy and immunotherapy regimens. New classes of epigenetic therapies promise low toxicity and may work synergistically with other cancer treatments to overcome drug resistance mechanisms.

The histone demethylase KDM5C controls female bone mass by promoting energy metabolism in osteoclasts

Women experience osteoporosis at higher rates than men. Aside from hormones, the mechanisms driving sex-dependent bone mass regulation are not well-understood. Here, we demonstrate that the X-linked H3K4me2/3 demethylase KDM5C regulates sex-specific bone mass. Loss of KDM5C in hematopoietic stem cells or bone marrow monocytes (BMM) increases bone mass in female but not male mice. Mechanistically, loss of KDM5C impairs the bioenergetic metabolism resulting in impaired osteoclastogenesis. Treatment with the KDM5 inhibitor reduces osteoclastogenesis and energy metabolism of both female mice and human monocytes. Our report details a novel sex-dependent mechanism for bone homeostasis, connecting epigenetic regulation to osteoclast metabolism, and positions KDM5C as a target for future treatment of osteoporosis in women.

One-Sentence Summary

KDM5C, an X-linked epigenetic regulator, controls female bone homeostasis by promoting energy metabolism in osteoclasts.

Cooperative super-enhancer inactivation caused by heterozygous loss of CREBBP and KMT2D skews B cell fate decisions and yields T cell-depleted lymphomas

Mutations affecting enhancer chromatin regulators CREBBP and KMT2D are highly co-occurrent in germinal center (GC)-derived lymphomas and other tumors, even though regulating similar pathways. Herein, we report that combined haploinsufficiency of Crebbp and Kmt2d (C+K) indeed accelerated lymphomagenesis. C+K haploinsufficiency induced GC hyperplasia by altering cell fate decisions, skewing B cells away from memory and plasma cell differentiation. C+K deficiency particularly impaired enhancer activation for immune synapse genes involved in exiting the GC reaction. This effect was especially severe at super-enhancers for immunoregulatory and differentiation genes. Mechanistically, CREBBP and KMT2D formed a complex, were highly co-localized on chromatin, and were required for each-other's stable recruitment to enhancers. Notably, C+K lymphomas in mice and humans manifested significantly reduced CD8 ⁺ T-cell abundance. Hence, deficiency of C+K cooperatively induced an immune evasive phenotype due at least in part to failure to activate key immune synapse super-enhancers, associated with altered immune cell fate decisions.

SIGNIFICANCE

Although CREBBP and KMT2D have similar enhancer regulatory functions, they are paradoxically co-mutated in lymphomas. We show that their combined loss causes specific disruption of super-enhancers driving immune synapse genes. Importantly, this leads to reduction of CD8 cells in lymphomas, linking super-enhancer function to immune surveillance, with implications for immunotherapy resistance.

Combined Reverse-Transcriptase Multiplex Ligation-Dependent Probe Amplification and Next-Generation Sequencing Analyses to Assign Unclassified BCL2-/BCL6- Nonrearranged Small B-Cell Lymphoid Neoplasms as Follicular or Nodal Marginal Zone Lymphoma

Distinguishing between follicular lymphoma (FL) and nodal marginal zone lymphoma (NMZL) can be difficult when morphologic and phenotypic features are unusual and characteristic cytogenetic rearrangements are absent. We evaluated the diagnostic contribution of ancillary techniques-including fluorescence in situ hybridization (FISH)-detected 1p36 deletion; reverse-transcriptase, multiplex, ligation-dependent probe amplification (RT-MLPA); and next-generation sequencing (NGS)-for tumors that remain unclassified according to standard criteria. After review, 50 CD5-negative small B-cell lymphoid neoplasms without BCL2 and BCL6 FISH rearrangements were diagnosed as FLs (n = 27), NMZLs (n = 5), or unclassified (n = 18) based on the 2016 World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. FISH helped identify the 1p36 deletion in 3 FLs and 1 unclassified tumor. Most classified FLs had an RT-MLPA germinal center B-cell (GCB) signature (93%) or were noncontributive (7%). Classified NMZLs had an RT-MLPA activated B-cell signature (20%), had an unassigned signature (40%), or were noncontributive (40%). Among unclassified tumors, the RT-MLPA GCB signature was associated with mutations most commonly found in FLs (CREBBP, EZH2, STAT6, and/or TNFRSF14) (90%). An RT-MLPA-detected GCB signature and/or NGS-detected gene mutations were considered as FL identifiers for 13 tumors. An activated B-cell signature or NOTCH2 mutation supported NMZL diagnosis in 3 tumors. Combining the RT-MLPA and NGS findings successfully discriminated 89% of unclassified tumors in favor of one or the other diagnosis. NGS-detected mutations may be of therapeutic interest. Herein, we detected 3 EZH2 and 8 CREBBP mutations that might be eligible for targeted therapies.

Biology of follicular lymphoma: insights and windows of clinical opportunity

Follicular lymphoma (FL) is a heterogeneous disease, both clinically and biologically. The biological behavior and development of FL is a culmination of complex multistep processes underpinned by genetic and nongenetic determinants. Epigenetic deregulation through recurrent genetic alterations is now a recognized major biological hallmark of FL, alongside the t(14;18) translocation. In parallel, there is a strong interplay between the lymphoma B cells and the immune microenvironment, with the microenvironment serving as a critical enabler by creating a tumor-supportive niche and modulating the immune response to favor survival of the malignant B cells. A further layer of complexity arises from the biological heterogeneity that occurs between patients and within an individual, both over the course of the disease and at different sites of disease involvement. Altogether, taking the first steps to bridge the understanding of these various biological components and how to evaluate these clinically may aid and inform future strategies, including logical therapeutic interventions, risk stratification, therapy selection, and disease monitoring.

Squamous cell lung cancer: Current landscape and future therapeutic options

Squamous cell lung cancers (lung squamous cell carcinomas [LUSCs]) are associated with high mortality and a lack of therapies specific to this disease. Although recurrent molecular aberrations are present in LUSCs, efforts to develop targeted therapies against receptor tyrosine kinases, signaling transduction, and cell cycle checkpoints in LUSCs were met with significant challenges. The present therapeutic landscape focuses on epigenetic therapies to modulate the expression of lineage-dependent survival pathways and undruggable oncogenes. Another important therapeutic approach is to exploit metabolic vulnerabilities unique to LUSCs. These novel therapies may synergize with immune checkpoint inhibitors in the right therapeutic context. For example, the recognition that alterations in KEAP1-NFE2L2 in LUSCs affected antitumor immune responses created unique opportunities for targeted, metabolic, and immune combinations. This article provides a perspective on how lessons learned from the past influence the current therapeutic landscape and opportunities for future drug development for LUSCs.

The multifaceted role of micronuclei in tumour progression: A whole organism perspective

Within most tumour types, cancerous cells exist in a state of aneuploidy, an incorrect chromosome number or structure. Additionally, tumour cells frequently exhibit chromosomal instability; the ongoing loss or gain of whole or parts of chromosomes during cell division. Chromosomal instability results in a high rate of chromosome segregation defects, and a constantly changing genomic landscape. A second consequence of recurrent chromosome segregation defects is the exclusion of mis-segregated chromatin from the newly reforming nucleus. Chromosomes, or chromosome fragments that are not incorporated into the main nucleus are often packaged into extranuclear structures called micronuclei. While the initial impact of micronucleus formation is an imbalance or loss of genetic material in the resulting daughter cells, several other downstream consequences are now known to result from this process. In this review, we discuss the further consequences of micronucleus formation, including how structural changes to the micronuclear envelope, and the rupturing of micronuclear membranes can contribute to metastasis, immune cell activation and overall, tumour progression.

The genomic landscape of canine diffuse large B-cell lymphoma identifies distinct subtypes with clinical and therapeutic implications

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoid neoplasm in dogs and in humans. It is characterized by a remarkable degree of clinical heterogeneity that is not completely elucidated by molecular data. This poses a major barrier to understanding the disease and its response to therapy, or when treating dogs with DLBCL within clinical trials. We performed an integrated analysis of exome (n = 77) and RNA sequencing (n = 43) data in a cohort of canine DLBCL to define the genetic landscape of this tumor. A wide range of signaling pathways and cellular processes were found in common with human DLBCL, but the frequencies of the most recurrently mutated genes (TRAF3, SETD2, POT1, TP53, MYC, FBXW7, DDX3X and TBL1XR1) differed. We developed a prognostic model integrating exonic variants and clinical and transcriptomic features to predict the outcome in dogs with DLBCL. These results comprehensively define the genetic drivers of canine DLBCL and can be prospectively utilized to identify new therapeutic opportunities.

Transmembrane Protein-Based Risk Model and H3K4me3 Modification Characteristics in Lung Adenocarcinoma

The role and mechanism of transmembrane proteins (TMEMs) in tumorigenesis remain unclear. Based on 4 independent cohorts containing 1,208 cases, we identified 3 TMEMs (TMEM273, TMEM164, and TMEM125), which were used to construct a risk model to predict the prognosis of LUAD. The two patterns based on the risk score exhibited a high degree of consistency with the characteristics of immune cell infiltration and epigenetic distribution. Patients with a low-risk score, characterized by an increased activation of immunity, H3K4me3 modification, tumor cell apoptosis, chemokine secretion, and TMB, had better disease-free survival (DFS) and overall survival (OS). Obvious immunosuppression, increased epithelial–mesenchymal transition, a low H3K4me3 level, shortened cell cycle, and accelerated cell division manifested in high-risk patients, with poorer DFS and OS. The model showed a better prognostic value than the tumor immune dysfunction and exclusion score. Correlation analysis told us that patients with high scores were suitable for treatment with CD276 inhibitors for their higher levels of CD276 expression. The risk score had a strong negative correlation with HAVCR2 and ICOS among patients with EGFR-WT, KRAS-WT, STK11-WT, or TP53-MUT, and patients with these mutation types with low scores were suitable for treatment with HAVCR2 or ICOS inhibitors. This work comprehensively analyzed the role and mechanism of TMEMs in LUAD and revealed the characteristics of histone methylation modification. The TMEM-based signature gave us deep insight into immune cell infiltration profiles and provided an individualized immunotherapy strategy.

Immune Epigenetic Crosstalk Between Malignant B Cells and the Tumor Microenvironment in B Cell Lymphoma

Epigenetic reprogramming is a hallmark of lymphomagenesis, however its role in reshaping the tumor microenvironment is still not well understood. Here we review the most common chromatin modifier mutations in B cell lymphoma and their effect on B cells as well as on T cell landscape. We will also discuss precision therapy strategies to reverse their aberrant signaling by targeting mutated proteins or counterbalance epigenetic mechanisms.

Epigenetic, Metabolic, and Immune Crosstalk in Germinal-Center-Derived B-Cell Lymphomas: Unveiling New Vulnerabilities for Rational Combination Therapies

B-cell non-Hodgkin lymphomas (B-NHLs) are highly heterogenous by genetic, phenotypic, and clinical appearance. Next-generation sequencing technologies and multi-dimensional data analyses have further refined the way these diseases can be more precisely classified by specific genomic, epigenomic, and transcriptomic characteristics. The molecular and genetic heterogeneity of B-NHLs may contribute to the poor outcome of some of these diseases, suggesting that more personalized precision-medicine approaches are needed for improved therapeutic efficacy. The germinal center (GC) B-cell like diffuse large B-cell lymphomas (GCB-DLBCLs) and follicular lymphomas (FLs) share specific epigenetic programs. These diseases often remain difficult to treat and surprisingly do not respond advanced immunotherapies, despite arising in secondary lymphoid organs at sites of antigen recognition. Epigenetic dysregulation is a hallmark of GCB-DLBCLs and FLs, with gain-of-function (GOF) mutations in the histone methyltransferase EZH2, loss-of-function (LOF) mutations in histone acetyl transferases CREBBP and EP300, and the histone methyltransferase KMT2D representing the most prevalent genetic lesions driving these diseases. These mutations have the common effect to disrupt the interactions between lymphoma cells and the immune microenvironment, via decreased antigen presentation and responsiveness to IFN-γ and CD40 signaling pathways. This indicates that immune evasion is a key step in GC B-cell lymphomagenesis. EZH2 inhibitors are now approved for the treatment of FL and selective HDAC3 inhibitors counteracting the effects of CREBBP LOF mutations are under development. These treatments can help restore the immune control of GCB lymphomas, and may represent optimal candidate agents for more effective combination with immunotherapies. Here, we review recent progress in understanding the impact of mutant chromatin modifiers on immune evasion in GCB lymphomas. We provide new insights on how the epigenetic program of these diseases may be regulated at the level of metabolism, discussing the role of metabolic intermediates as cofactors of epigenetic enzymes. In addition, lymphoma metabolic adaptation can negatively influence the immune microenvironment, further contributing to the development of immune cold tumors, poorly infiltrated by effector immune cells. Based on these findings, we discuss relevant candidate epigenetic/metabolic/immune targets for rational combination therapies to investigate as more effective precision-medicine approaches for GCB lymphomas.

Prospects in the management of patients with follicular lymphoma beyond first-line therapy

The management of patients with relapsed or refractory follicular lymphoma has evolved markedly in the last decade, with the availability of new classes of agents (phosphoinositide 3-kinase inhibitors, immunomodulators, epigenetic therapies, and chimeric antigen receptor T cells) supplementing the multiple approaches already available (cytotoxic agents, anti-CD20 antibodies, radiation therapy, radioimmunotherapy, and autologous and allogeneic transplants). The diversity of clinical scenarios, the flood of data derived from phase II studies, and the lack of randomized studies comparing treatment strategies preclude firm recommendations and require personalized decisions. Patients with early progression require specific attention given the risk of histological transformation and their lower response to standard therapies. In sequencing therapies, one must consider prior treatment regimens and the potential need for future lines of therapy. Careful evaluation of risks and expected benefits of available options, which vary depending on location and socioeconomics, should be undertaken, and should incorporate the patient's goals. Preserving quality of life for these patients is essential, given the likelihood of years to decades of survival and the possibility of multiple lines of therapy. The current landscape is likely to continue evolving rapidly with other effective agents emerging (notably bispecific antibodies and other targeted therapies), and multiple combinations being evaluated. It is hoped that new treatments under development will achieve longer progression-free intervals and minimize toxicity. A better understanding of disease biology and the mechanisms of these different agents should provide further insights to select the optimal therapy at each stage of disease.

Tazemetostat: a treatment option for relapsed/refractory follicular lymphoma

INTRODUCTION

Follicular lymphoma (FL) is the second most common form of B cell lymphoma and generally presents as an indolent and relatively slow-growing tumor. However, most FLs are incurable with a shortening of subsequent responses. Therefore, novel and more effective treatments are desperately needed. Tazemetostat is a first-in-class, selective, oral inhibitor of EZH2, a lysine methyltransferase that is mutated in about 25% of FL. Tazemetostat has been recently approved for relapsed/refractory FL after two or more lines of therapy in the presence of an EZH2 mutation or independent of an EZH2 mutation in the absence of other options.

AREAS COVERED

Here, the authors provide a review focusing on the molecular mechanisms of EZH2, clinical development of tazemetostat and other EZH2 inhibitors (EZH2i), as single-agent therapy and in combinatorial regimens. Finally, they provide a futuristic look at therapeutic approaches for this disease.

EXPERT OPINION

Tazemetostat monotherapy showed clinically meaningful and durable responses with a favorable toxicity profile, especially in EZH2 mutant lymphoma. Future studies should explore mechanism-based combinatorial regimens to maximize and prolong the anti-lymphoma effect.

7-[[(4-methyl-2-pyridinyl)amino](2-pyridinyl)methyl]-8-quinolinol (compound 30666) inhibits enhancer activity and reduces B-cell lymphoma growth - A question of specificity

B-cell non-Hodgkin lymphoma (NHL) is among the ten most common malignancies. Survival rates range from very poor to over 90% and highly depend on the stage and subtype. Characteristic features of NHL are recurrent translocations juxtaposing an oncogene (e.g. MYC, BCL2) to the enhancers in the immunoglobulin heavy chain (IGH) locus. Survival and proliferation of many B-cell lymphomas depend on the expression of the translocated oncogene. Thus, targeting IGH enhancers as an anti-lymphoma treatment seems a promising strategy. Recently, a small molecule - 7-[[(4-methyl-2-pyridinyl)amino](2-pyridinyl)methyl]-8-quinolinol (compound 30666) was identified to decrease activity of the Eμ enhancer and reduce the expression of translocated oncogenes in multiple myeloma and some NHL cell lines (Dolloff, 2019). Here, we aimed to test the effect of compound 30666 in Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) and shed light on its mechanism of action. We report that both IGH-translocation positive NHL cells as well as IGH-translocation negative B cells and non-B cell controls treated with compound 30666 exhibited consistent growth inhibition. A statistically significant increase in cell percentage in sub-G1 phase of cell cycle was observed, suggesting induction of apoptosis. Compound 30666 downregulated MYC levels in BL cell lines and altered IGH enhancer RNA expression. Moreover, a global decrease of H3K27ac and an increase of H3K4me1 was observed upon 30666 treatment, which suggests switching enhancers to a poised or primed state. Altogether, our findings indicate that 30666 inhibitor affects enhancer activity but might not be as specific for IGH enhancers as previously reported.

Cancer-epigenetic function of the histone methyltransferase KMT2D and therapeutic opportunities for the treatment of KMT2D-deficient tumors

Epigenetic mechanisms are central to understanding the molecular basis underlying tumorigenesis. Aberrations in epigenetic modifiers alter epigenomic landscapes and play a critical role in tumorigenesis. Notably, the histone lysine methyltransferase KMT2D (a COMPASS/ Set1 family member; also known as MLL4, ALR, and MLL2) is among the most frequently mutated genes in many different types of cancer. Recent studies have demonstrated how KMT2D loss induces abnormal epigenomic reprograming and rewires molecular pathways during tumorigenesis. These findings also have clinical and therapeutic implications for cancer treatment. In this review, we summarize recent advances in understanding the role of KMT2D in regulating tumorigenesis and discuss therapeutic opportunities for the treatment of KMT2D-deficient tumors.

Follicular lymphoma dynamics

Follicular lymphoma (FL) is an indolent yet challenging disease. Despite a generally favorable response to immunochemotherapy regimens, a fraction of patients does not respond or relapses early with unfavorable prognosis. For the vast majority of those who initially respond, relapses will repeatedly occur with increasing refractoriness to available treatments. Addressing the clinical challenges in FL warrants deep understanding of the nature of treatment-resistant FL cells seeding relapses, and of the biological basis of early disease progression. Great progress has been made in the last decade in the description and interrogation of the (epi)genomic landscape of FL cells, of their major dependency to the tumor microenvironment (TME), and of the stepwise lymphomagenesis process, from healthy to subclinical disease and to overt FL. A new picture is emerging, in which an ever-evolving tumor-TME duo sparks a complex and multilayered clonal and functional heterogeneity, blurring the discovery of prognostic biomarkers, patient stratification and reliable designs of risk-adapted treatments. Novel technological approaches allowing to decipher both tumor and TME heterogeneity at the single-cell level are beginning to unravel unsuspected cell dynamics and plasticity of FL cells. The upcoming drawing of a comprehensive functional picture of FL within its ecosystem holds great promise to address the unmet medical needs of this complex lymphoma.

Bivalent chromatin as a therapeutic target in cancer: An in silico predictive approach for combining epigenetic drugs

Tumour cell heterogeneity is a major barrier for efficient design of targeted anti-cancer therapies. A diverse distribution of phenotypically distinct tumour-cell subpopulations prior to drug treatment predisposes to non-uniform responses, leading to the elimination of sensitive cancer cells whilst leaving resistant subpopulations unharmed. Few strategies have been proposed for quantifying the variability associated to individual cancer-cell heterogeneity and minimizing its undesirable impact on clinical outcomes. Here, we report a computational approach that allows the rational design of combinatorial therapies involving epigenetic drugs against chromatin modifiers. We have formulated a stochastic model of a bivalent transcription factor that allows us to characterise three different qualitative behaviours, namely: bistable, high- and low-gene expression. Comparison between analytical results and experimental data determined that the so-called bistable and high-gene expression behaviours can be identified with undifferentiated and differentiated cell types, respectively. Since undifferentiated cells with an aberrant self-renewing potential might exhibit a cancer/metastasis-initiating phenotype, we analysed the efficiency of combining epigenetic drugs against the background of heterogeneity within the bistable sub-ensemble. Whereas single-targeted approaches mostly failed to circumvent the therapeutic problems represented by tumour heterogeneity, combinatorial strategies fared much better. Specifically, the more successful combinations were predicted to involve modulators of the histone H3K4 and H3K27 demethylases KDM5 and KDM6A/UTX. Those strategies involving the H3K4 and H3K27 methyltransferases MLL2 and EZH2, however, were predicted to be less effective. Our theoretical framework provides a coherent basis for the development of an in silico platform capable of identifying the epigenetic drugs combinations best-suited to therapeutically manage non-uniform responses of heterogenous cancer cell populations.

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.