AACR 2014: How deregulation of histone methyltransferases drive malignant transformation of B-cells

wendybeguelinBy Wendy Béguelin, PhD

DLBCLs are a heterogeneous group of diseases initiating from germinal center (GC) B cells. GC B cells are uniquely specialized to tolerate rapid proliferation, and physiological genomic instability, thus generating a diverse set of clones of cells encoding high affinity antibodies. The GC phenotype poses a significant risk in the malignant transformation to B cells, with epigenetic regulatory complexes playing a critical role in lymphomagenesis. During a symposium session at the recent American Association for Cancer Research, the Melnick Lab, reported how the deregulation of histone methyltransferases causes the malignant transformation of B-cells.

EZH2, which epigenetically silences genes through histone 3 lysine 27 methylation is upregulated in normal and malignant GC B cells. EZH2 is often affected by gain of function mutations in lymphomas that alter its enzymatic specificity. EZH2 mediates GC formation by transiently suppressing checkpoint genes and terminal differentiation genes through formation of bivalent chromatin domains. EZH2 somatic mutations induce germinal center hyperplasia and malignant transformation, and cooperate with other oncogenes such as BCL2. EZH2 specific inhibitors can suppress the growth of GC derived lymphoma cells in vitro and in vivo, and are currently being evaluated in early phase clinical trials. DNA methyltransferase 1 (DNMT1) is required for B cells to form GC, and GC B cells display cytosine methylation redistribution as compared to resting or naïve B cells. DLBCL in turn exhibit prominent and heterogeneous disruption of cytosine methylation distribution, with specific and distinct DNA methylation profiles occurring in different lymphoma subtypes.

Epigenetic heterogeneity is associated with unfavorable outcomes in B-cell lymphoma. This suggests that epigenetic diversity may provide a survival advantage to lymphoma cell populations. DNA methyltransferase inhibitors can reprogram lymphoma cells to develop a form of incomplete senescence that allows for a more complete response to chemotherapy treatment. These DNA methyltransferase inhibitors can be safely combined with standard lymphoma therapies for first line treatment of patients with DLBCL. However, further research will be required to confirm this targeted therapy approach for clinical use in patients.


AACR 2014: IL10 autoregulatory loop displays promise as new therapeutic target for DLBCL

shaknovich_rBy Rita Shaknovich MD, PHD

Diffuse large B cell lymphoma (DLBCL) is a common aggressive lymphoma that represents 30-40% of newly diagnosed cases of non-Hodgkin lymphoma, but accounts for up to 80% of lymphoma-related deaths. Although R-CHOP remains the standard first line therapy, it has more recently been associated with a frequent lack of response in DLBCL patients. This lack of response has enforced the necessity for finding alternate therapeutic targets.

At the 2014 meeting of the American Association for Cancer Research researchers from Weill Cornell Medical College reported on their recent findings. In a late breaking abstract the Shaknovich Lab reported on the potential of the IL10 receptor as a new biomarker and therapeutic target in DLBCL. The  hypothesis is that DLBCL is dependent on the feed-forward autostimulatory loop that begins from the autocrine IL10 secretion and stimulation of overexpressed receptors leading to cell proliferation and that blocking the receptor would lead to cell death.

The research team of postdoctoral fellow Wendy Beguelin and research associate Seema Sawh determined that blocking IL10R results in specific inhibition of signaling through JAK1/2 and loss of phosphorylation at STAT3Y705 immediately after treatment. The inhibition of signaling through MAPK and phosphorylation of STAT3S727 came at a later time in treatment. The inhibition of signaling was sustained for days with only one drug treatment leading to induction of apoptosis. Anti-IL10R treatment resulted in significant downregulation of IL10 and IL10RA transcription, leading to interruption of IL10-IL10R autostimulatory loop.

IL10R is a novel therapeutic target in DLBCL that allows for easy detection and targeting. Shaknovich Lab is planning further animal studies and hopes to develop therapeutic antibody for clinical use in patients.


Novel Therapeutic Strategies for Targeting the Lymphoma Microenvironment

Ruan Face By Jia Ruan, MD, PhD

Although conventional chemotherapy is primarily aimed at tumor cells, we now know of the importance of neighborhood cells, included within the tumor mass. These include endothelial cells and pericytes that form blood vessels, macrophages that mediate inflammation, and fibroblasts and extracellular matrix proteins that build matrix and scar tissues. The interaction between the tumor cells and their neighborhood is collectively known as the tumor microenvironment. Given the importance of the tumor microenvironment in maintaining tumor growth and developing resistance to conventional chemotherapy, novel strategies that target the microenvironment are under active investigation. Clinical researchers led by, Dr. Jia Ruan, have recently published 2 important studies on developing novel therapeutic strategies that target lymphoma angiogenesis (blood vessel formation) and lymphangiogenesis (lymphatic vessel formation) within the tumor microenvironment.

The first study was published in the leading hematology journal Blood in collaboration with Dr. Leandro Cerchietti, a lymphoma biologist, and Dr. Katherine Hajjar, a vascular biology expert, both at Weill Cornell Medical College. The study found that pericytes, the vascular accessory cells surrounding the endothelial cells, are important players in lymphoma tumor angiogenesis, and represent potentially novel therapeutic targets for anti-lymphoma therapy. Specifically, the Weill Cornell lymphoma researchers treated human diffuse large B-cell lymphoma (DLBCL) growing in mouse models with an oral drug called imatinib. This incapacitated a critical cell surface receptor within the pericytes, namely platelet-derived growth factor receptor β (PDGFRβ), which is important for the survival of the pericytes and its communication with the endothelial cells. As a result, lymphoma-associated microvascular blood vessel formation was reduced due to programmed-cell death of both pericytes and endothelial cells. This ultimately translated into therapeutic effect of lymphoma growth impairment. This study provided proof of principal that targeting non-tumor vascular cells within the lymphoma microenvironment can result in significant inhibition of lymphoma growth, providing the basis for more refined consideration of anti-angiogenesis as a treatment strategy for lymphoma patients.

The second study published in Cancer Research, in collaboration with Dr. Lijun Xia, a glycoprotein and vascular biology expert at the Oklahoma Research Foundation. The researchers found that 1) lymphatic vessels, which form the vascular network known as lymphangiogenesis, contributed to the growth and spreading of lymphomas in an experimental model of mantle cell lymphoma (MCL), and 2) treatment with the immunomodulatory drug lenalidomide potently inhibited the growth and spreading of MCL by disabling tumor lymphangiogenesis. Mechanistically the researchers demonstrated that treatment with lenalidomide reduced the number of MCL-associated macrophages and their production of a growth factor important for the formation of lymphatic vessels, namely vascular endothelial growth factor-C (VEGF-C). This is the first study to address the potential importance of lymphangiogenesis in lymphoma growth, and provided a novel perspective of the mechanisms of action of lenalidomide in lymphoma therapy. This pre-clinical study synergizes with our recent clinical data displaying high response rates and durable remissions with the biologic combination of lenalidomide + rituximab in patients with previously untreated MCL.

Both studies open potentially new novel paths to treating lymphoma, exemplifying the Lymphoma Program’s commitment to the bench-to-bedside translational research that brings cutting-edge science to patient care.

References

1. Blood. 2013 Jun 27:121(26):5192-202. Imatinib disrupts lymphoma angiogenesis by targeting vascular pericytes.

2. Cancer Res. 2013 Dec 15:73(24):7254-64. Lenalidomide inhibits lymphangiogenesis in preclinical models of mantle cell lymphoma.


Dr. Ari Melnick Discusses EZH2 as a Potential Target in Diffuse Large B Cell Lymphoma

Last week Weill Cornell researcher Dr. Ari Melnick sat down with Targeted Oncology to briefly summarize the potential of EZH2 in treating diffuse large B-cell lymphoma.

 


Two Modes of DLBCL Relapse

Yanwen JiangBy Yanwen Jiang PhD 

Despite improvements in care for patients with diffuse large B-cell lymphoma (DLBCL), roughly one-third of patients do not respond to initial therapy or relapse within the first 2-3 years after treatment. Unfortunately, our current understanding of the molecular mechanisms of relapse is extremely poor.

During the recent 2013 American Society of Hematology meeting, we reported for the first time that there exist at least two distinct scenarios of DLBCL relapse.  In the first scenario, the tumor cells at diagnosis are almost genetically identical to tumor cells at relapse. Both tumors harbor the same set of mutations with the relapsed tumor possessing a few additional mutations, suggesting that the relapsed tumor evolved continuously from the tumor present at diagnosis. We termed this scenario “linear” mode.  In the second scenario, the tumors at diagnosis and relapse carry different mutations, suggesting that an early divergent event occurred and that the tumors developed in parallel.  Therefore, we named this scenario the “divergent” mode.  Moreover, we observed that tumors with higher genetic heterogeneity at diagnosis were more likely to relapse through the divergent mode. This may provide a foundation for evaluation of different treatment strategies for different relapse modes.

Currently, we are expanding our study to investigate the role of epigenetics, particularly DNA methylation, in DLBCL relapse.  For more research information on DLBCL, and relapsed DLBCL, please visit our websites at the Elemento Lab and the Melnick lab.


Pretreating DLBCL with Targeted Therapy Improves Patient Outcomes and Chemotherapy Effectivenes

Diffuse large B-cell lymphoma (DLBCL) is an aggressive lymphoma with high rates of relapse and survival rates that rarely extend beyond two years. However, researchers from the Weill Cornell Lymphoma Program have recently published a study in Cancer Discovery, with the potential to change the standard of care for patients with DLBCL. This study focused on the use of azacitidine (Vidaza), a targeting therapy designed to reawaken the molecular mechanisms that typically trigger cell death but are switched off as lymphoma progresses. Researchers found a resurgence in the death signal on the resumption of chemotherapy for those DLBCL patients treated with azacitidine in advance of chemotherapy. 

As the study’s senior investigator Dr. Leandro Cerchietti, the Raymond and Beverly Sackler Research Scholar and assistant professor of medicine at Weill Cornell Medical College noted, “To have any hope for helping patients with aggressive lymphoma, we need to make this resistant cancer sensitive to treatment. We found we could do this by reprogramming the cancer to a more benign disease, which can then respond to chemotherapy…By pre-treating patients with a low-dose of azacitidine — a targeted drug approved for use in myelodysplastic syndrome — we achieved a profound and stable degree of reprogramming and chemosensitization that was very surprising to us.”

In the proof of concept, phase 3 study led by Dr. Peter Martin, patients received low doses of azacitidine five days in advance of standard chemotherapy. 11 patients achieved a complete remission of cancer, while 10 remained cancer-free for up to 28 months. 

Study collaborator, Dr. Ari Melnick commented, “In this remarkable study, Dr. Cerchietti discovered an important new disease mechanism that causes chemotherapy resistance in aggressive lymphomas, developed a new treatment regimen and completed the first clinical trial, demonstrating that his findings are true and directly relevant to those patients with the most severe forms of this tumor.” 

The implications for this study are far ranging. Dr. Cerchietti explained, “Oncologists have long believed that using high doses of an anti-cancer drug is the best strategy. Our study shows that is not the case in this kind of lymphoma, and suggests this new approach can potentially be translated to other tumor types.”

Researchers plan on expanding the study to additional DLBCL patients in a multi-center clinical trial, while studying pre-treatment strategy options in other tumor types and lymphomas. 

Please look to this space for further updates. A full listings of available clinical trials can be found here


Novel Weill Cornell Drug Displays Promise in Treating DLBCL

Following up on an earlier breakthrough confirming the feasibility of shutting down the Bc16 protein — an important master regulatory transcription factor that is the key to survival for diffuse large-B cell lymphoma and other aggressive B-cell lymphomas– Weill Cornell’s Dr. Ari Melnick and other researchers recently completed a study where five doses of the experimental drug eradicated human lymphoma in mice.

Published online in the journal Cell Reports, the researchers described specifically how Bc16 promotes the survival of DLBCL, before detailing how the Weill Cornell developed Bc16 inhibitor effectively gums up the protein. Initially developed by Dr. Melnick nine years ago, the interim period has seen him working to improve the design for use by DLBCL and other lymphoma patients, collaborating with other world class researchers to understand how both Bc16 and its inhibitor functions.

The researchers found that Bc16 has two independent functions required for the survival of DLBCL. Dr. Melnick described how the first function, “builds a huge shopping mall-style complex”. This complex rests on top of a stretch of the genome. Through this binding Bcl6 deactivates the DNA, prohibiting genes from producing RNA and proteins. As Dr. Melnick noted, “Bcl6 acts like a barcode reader. When it sees that barcode — the DNA sequence — it attaches there”.

He went on, “Normally, the protein complex goes away after an immune reaction has been successfully mounted against the pathogen. But when it doesn’t, and remains stuck to the genes, DLBCL can result. That’s because Bcl6 is inhibiting genes that stop cells from dividing and that sense damage to the genome. We now know the genes that Bcl6 is repressing and how that helps lymphoma develop and survive.”

According to Dr. Melnick the second function, “acts like a switch on railroad track that routes a train in one direction or another. One track is needed when antibodies are required for an immune response, while the other keeps B cells in a constant state of division.”

Importantly the researchers were surprised to find that both the complex and the train switch attach to the Bcl6 protein at the same site. “They fit into the same keyholes on Bcl6,” Dr. Melnick said. “There are two identical binding sites on the protein surface.”

As Dr. Melnick exclaimed, “This is wonderfully serendipitous — our drug just happens to be able to overcome both of the biological mechanisms that are key to survival of aggressive lymphoma,” before adding that the inhibitor completely eradicated DLBCL in mice in a short time, with no detectable side effects.

The team is conducting additional research toward an investigational new drug application from the federal Food and Drug Admission.


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