New Research Points to HDAC3 Inhibition as a Potential Game-Changing Treatment for Specific Lymphoma Subtypes

By Sucharita Mistry, PhD

B-cell lymphomas such as diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) are blood cancers of the immune cells. A vast majority of B-cell lymphomas typically display a high frequency of genetic alterations. Since lymphomas show remarkable genetic diversity, a big challenge for scientists is not only to determine which genes are mutated in these diseases, but also to identify “actionable” genetic alterations that can respond to targeted therapies.

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“Discovering how different mutations are involved in causing the disease is a major key to advancing novel mechanism-based precision therapies and immunotherapies for lymphomas, with potentially less toxic side-effects,” says Dr. Ari Melnick, a world-renowned physician-scientist at Weill Cornell Medicine.

Dr. Melnick led groundbreaking research that defines the genetic underpinnings of CREBBP mutation in lymphomas, paving the way for new therapeutic avenues. The findings of this study were recently published in Cancer Discovery.

The CREBBP gene encodes a kind of histone acetyltransferase (HAT), an enzyme that introduces small chemical tags called acetyl groups on histones, which are the major structural proteins of chromosomes. The chemical modifications on histones are termed as epigenetic changes, and they determine whether genes are turned on or off. The CREBBP gene, which is an epigenetic modifier, is frequently mutated in DLBCL and FL.

The Melnick research team, in collaboration with scientists at the MD Anderson Cancer Center, characterized the functional consequences of CREBBP mutation in lymphomas. Using a powerful CRISPR gene-editing technology, the researchers engineered lymphoma cell lines that differed only in the CREBBP mutation status. The research team discovered two different types of CREBBP mutations that either truncate the protein or inactivate the HAT domain, the latter associated with poor clinical outcomes.

This study showed that CREBBP mutation disrupts key biological pathways resulting in abnormal silencing of tumor-suppressive and antigen-presenting pathway genes. This disruption allows lymphoma cells to hide from the immune system so that they cannot be recognized and attacked by the T-cells that play an essential role in the body’s immune response.

More importantly, the malfunction in immune surveillance was restored by an HDAC3 inhibitor, a drug that specifically reverses the histone acetylation defect caused by CREBBP mutation. Notably, selective inhibition of HDAC3 reversed the epigenetic abnormalities, halted lymphoma growth and induced the expression of major histocompatibility (MHC) class II protein, enabling the T cells of the immune system to recognize and kill lymphoma cells. The research team also demonstrated that combination of an HDAC3 inhibitor with an immune checkpoint inhibitor (PD-1/PD-L1 blockade) results in synergistic anti-lymphoma immunity effects.

These findings uncover a novel mechanistic link between CREBBP mutation and immune surveillance dysfunction in lymphomas that can be counteracted by an HDAC3 inhibitor, providing a potentially game-changing approach for restoring anti-tumor immunity.

“HDAC3 inhibition provides an attractive therapeutic avenue for DLBCL and FL and may have enhanced potency in CREBBP-mutant tumors,” says Dr. Melnick. “We are very excited to translate this research into clinical trials that could potentially lead to the development of novel mechanism-based immune epigenetic therapy for CREBBP-mutant lymphomas.”

 

Precision Medicine Combination Treatment Shows Anti-Tumor Activity in Preclinical DLBCL Models

By Sucharita Mistry, PhD

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma in adults. DLBCLs are aggressive and typically represent a heterogeneous collection of diseases that can be grouped into different subtypes depending on their particular genetic lesions.

One such subtype, described as the C3 or EZB cluster, features alterations in the BCL2 gene and mutations in chromatin remodeling genes such as EZH2. The malignant growth of this particular subtype of DLBCL is likely dependent on genetic abnormalities in EZH2 and BCL2. Both these oncogenes (genes with the potential to cause cancer) mediate their effects on tumor growth through distinct mechanisms, providing new opportunities for rational therapeutic strategies that inhibit EZH2 and BCL2 concurrently.

Dr. Lisa Roth and colleagues from the Weill Cornell Medicine and NewYork-Presbyterian Hospital Lymphoma Program evaluated the efficacy of EZH2 inhibitor tazemetostat and BCL2 inhibitor venetoclax as single agents and in combination using different preclinical models.

Tazemetostat and venetoclax were administered alone and in combination in a panel of DLBCL cell lines with and without mutations in EZH2 and translocation (a genetic abnormality in which a chromosome breaks and reattaches to a different chromosome) in BCL2. In DLBCL cells harboring EZH2 mutation and BCL2 translocation, the combination treatment markedly enhanced cell killing compared to either drug alone. Although these findings are encouraging, cell culture models are limited as lymphoma cells grown on a plastic surface in liquid cultures cannot recapitulate the physiologic environment within the human body.

To test the efficacy of the drugs in models with increased clinical relevance, Weill Cornell researchers established three-dimensional (3D) organoids that closely mimic the lymph node architecture in humans. The tazemetostat/venetoclax combination therapy was tested in two different novel organoid systems 1) organoids derived from lymphoma cells, and 2) patient-derived xenograft (PDX) organoids generated from a patient tumor and propagated in mice. The PDX tumor carried both EZH2 mutation and BCL2 translocation. In both types of organoids, tazemetostat and venetoclax had minimal activity as single agents, whereas the tazemetostat/venetoclax combination resulted in significant cell killing.

Using novel model systems, this study demonstrated that EZH2 inhibition combined with BCL2 inhibition results in synergistic anti-tumor effects. Learn more about the findings here.

Lisa“The synergistic anti-lymphoma activity mediated by the combination of tazemetostat and venetoclax is quite promising,” says Dr. Roth. “This combination therapy is anticipated to be especially effective as precision therapy for DLBCL patients with EZH2 mutation and BCL2 alteration.”

A clinical trial of this combination treatment is currently in development in collaboration with Drs. Ari Melnick, John Leonard and Peter Martin.

 

Novel Three-Drug Combination of Ibrutinib plus Lenalidomide and Rituximab Shows Promising Anti-Lymphoma Activity in Relapsed/Refractory DLBCL

Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma, rising in incidence among older populations. The standard of care for the approximate one-third of DLBCL patients who do not achieve remission with R-CHOP (rituximab plus cyclophosphamide, doxorubicin, vincristine and prednisone) is salvage high-dose chemotherapy followed by consolidative autologous stem cell transplant, which leads to long-term disease-free survival for only 10-20 percent of relapsed/refractory patients. Patients who relapse within a year of initial therapy, those who relapse after transplant, and those who are ineligible for transplant due to age or comorbidities face the most significant unmet treatment need.

With an eye toward improving therapeutic options and outcomes for this patient population, the Lymphoma Program team, led by Dr. Jia Ruan, collaborated with colleagues nationwide and contributed significantly to a study examining the maximum tolerated dose and preliminary safety and activity of a novel three-drug combination – ibrutinib plus lenalidomide and rituximab – in treatment of relapsed/refractory DLBCL. The team’s encouraging findings were published in the American Society of Hematology’s Blood journal.

The study population consisted of 45 transplant-ineligible DLBCL patients whose disease returned after at least one prior therapy. Patients received oral ibrutinib daily, intravenous rituximab on every first day of six 28-day cycles, and oral lenalidomide on the first 21 days of each cycle. The treatment was provided as continuous chronic therapy in an outpatient clinic setting for as long as patients could derive benefit.

Forty-four percent of patients responded to the triplet, and 28 percent achieved a complete response. The combination performed particularly well (ORR: 65%, CR: 41%) in patients with non-germinal center b cell (non-GCB) DLBCL, a molecular subtype based on disease cell of origin that is not typically associated with favorable prognosis. Common treatment side effects included gastrointestinal complications, fatigue, myelosuppression (reduced blood cell production), hypokalemia (low blood potassium), peripheral edema and skin rash. Side effects could be monitored and mitigated by dose adjustment in the outpatient setting.

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Dr. Jia Ruan

“This novel treatment consists of two oral agents typically used to treat B-cell lymphoma, plus the anti-CD20 antibody rituximab, and can be easily administered in the clinic or patient’s home,” said Dr. Jia Ruan. “This effective low-intensity approach makes it very appealing to a broad range of R/R DLBCL patients in need of treatment.”