EZH2 Cooperates with BRD4-NUT to Drive NUT Carcinoma Growth by Silencing Key Tumor Suppressor Genes

NUT carcinoma is an aggressive carcinoma driven by the BRD4-NUT fusion oncoprotein, which activates chromatin to promote expression of progrowth genes. BET bromodomain inhibitors (BETi) are a promising treatment for NUT carcinoma that can impede BRD4-NUT's ability to activate genes, but the efficacy of BETi as monotherapy is limited. Here, we demonstrated that enhancer of zeste homolog 2 (EZH2), which silences genes through establishment of repressive chromatin, is a dependency in NUT carcinoma. Inhibition of EZH2 with the clinical compound tazemetostat potently blocked growth of NUT carcinoma cells. Epigenetic and transcriptomic analysis revealed that tazemetostat reversed the EZH2-specific H3K27me3 silencing mark and restored expression of multiple tumor suppressor genes while having no effect on key oncogenic BRD4-NUT-regulated genes. Indeed, H3K27me3 and H3K27ac domains were found to be mutually exclusive in NUT carcinoma cells. CDKN2A was identified as the only gene among all tazemetostat-derepressed genes to confer resistance to tazemetostat in a CRISPR-Cas9 screen. Combined inhibition of EZH2 and BET synergized to downregulate cell proliferation genes, resulting in more pronounced growth arrest and differentiation than either inhibitor alone. In preclinical models, combined tazemetostat and BETi synergistically blocked tumor growth and prolonged survival of NUT carcinoma-xenografted mice, with complete remission without relapse in one cohort. Identification of EZH2 as a dependency in NUT carcinoma substantiates the reliance of NUT carcinoma tumor cells on epigenetic dysregulation of functionally opposite, yet highly complementary, chromatin regulatory pathways to maintain NUT carcinoma growth.

SIGNIFICANCE

Repression of tumor suppressor genes, including CDKN2A, by EZH2 provides a mechanistic rationale for combining EZH2 and BET inhibitors for the clinical treatment of NUT carcinoma. See related commentary by Kazansky and Kentsis, p. 3827.

EZH2 synergizes with BRD4-NUT to drive NUT carcinoma growth through silencing of key tumor suppressor genes

NUT carcinoma (NC) is an aggressive carcinoma driven by the BRD4-NUT fusion oncoprotein, which activates chromatin to promote expression of pro-growth genes. BET bromodomain inhibitors (BETi) impede BRD4-NUT's ability to activate genes and are thus a promising treatment but limited as monotherapy. The role of gene repression in NC is unknown. Here, we demonstrate that EZH2, which silences genes through establishment of repressive chromatin, is a dependency in NC. Inhibition of EZH2 with the clinical compound tazemetostat (taz) potently blocked growth of NC cells. Epigenetic and transcriptomic analysis revealed that taz reversed the EZH2-specific H3K27me3 silencing mark, and restored expression of multiple tumor suppressor genes while having no effect on key oncogenic BRD4- NUT-regulated genes. CDKN2A was identified as the only gene amongst all taz-derepressed genes to confer resistance to taz in a CRISPR-Cas9 screen. Combined EZH2 inhibition and BET inhibition synergized to downregulate cell proliferation genes resulting in more pronounced growth arrest and differentiation than either inhibitor alone. In pre-clinical models, combined taz and BETi synergistically blocked growth and prolonged survival of NC-xenografted mice, with all mice cured in one cohort.

STATEMENT OF SIGNIFICANCE

Identification of EZH2 as a dependency in NC substantiates the reliance of NC tumor cells on epigenetic dysregulation of functionally opposite, yet highly complementary chromatin regulatory pathways to maintain NC growth. In particular, repression of CDKN2A expression by EZH2 provides a mechanistic rationale for combining EZH2i with BETi for the clinical treatment of NC.

Influence of climatic parameters on the probabilistic design of green roofs

Green roofs are effective tools for stormwater control in highly urbanized areas since they allow the reduction of peak runoffs and volumes discharged in sewer systems. Their design is quite standardized, except for the thickness of the growing medium layer, which is strictly related to vegetation type and rainfall regime. The paper proposes an analytical probabilistic approach that relates the climatic variables, the growing medium thickness, and the water content in the condition of fulfilled field capacity to the probability that runoff from green roofs exceeds a fixed threshold. The developed equations also consider the possibility of a reduced retention capacity due to previous rainfall events, that strongly influence the performance of these green infrastructures, especially when short dry periods and/or low evapotranspiration rates occur. This feature, neglected by the traditional design storm approach, and only partially considered by previous analytical probabilistic models, represent a great potentiality of the proposed equations that are also more user-friendly and less time-consuming than continuous simulation analysis. The focus of the paper is on the influence of climatic parameters on runoff probability. To this aim to perform the monthly analysis is fundamental, especially when there is a strong variability of the climatic parameters throughout the year. The model was tested in a case study in Milano, Italy. The application presented a good agreement between the results obtained from the proposed equations and those obtained from the continuous simulation of recorded data. The results also highlighted the importance of performing analysis on a monthly scale.

Probabilistic modeling of sustainable urban drainage systems

Sustainable Urban Drainage Systems (SUDS) include strategies and solutions for distributed stormwater management and control. They are strongly encouraged, especially in highly urbanized areas that suffer the combined effect of impervious surfaces and the increase in extreme rainfall events due to urbanization growth and climate change. Their integration into traditional urban drainage systems can mitigate flood risk and pollution of receiving water bodies. The main goal of SUDS is to restore the natural water balance by increasing infiltration and evapotranspiration processes and promoting rainwater harvesting and reuse. This paper proposes an analytical-probabilistic approach for SUDS modeling applicable to different systems. Developed equations allow estimating the runoff and residual storage probability for evaluating the efficiency of the storage volume both in terms of flood control and, depending on SUDS type, in terms of emptying time or water needs supply. The modeling considers the possibility of consecutive chained rainfalls; this feature is relevant for SUDS, often characterized by low outflow rates. Relating characteristic parameters to a probabilistic level (the Average Return Interval, ARI) makes the formulas interesting to be used in the design practice. An application to two case studies confirmed the goodness of the proposed method.

Conformational-Design-Driven Discovery of EZM0414: A Selective, Potent SETD2 Inhibitor for Clinical Studies

SETD2, a lysine N-methyltransferase, is a histone methyltransferase that plays an important role in various cellular processes and was identified as a target of interest in multiple myeloma that features a t(4,14) translocation. We recently reported the discovery of a novel small-molecule SETD2 inhibitor tool compound that is suitable for preclinical studies. Herein we describe the conformational-design-driven evolution of the advanced chemistry lead, which resulted in compounds appropriate for clinical evaluation. Further optimization of this chemical series led to the discovery of EZM0414, which is a potent, selective, and orally bioavailable inhibitor of SETD2 with good pharmacokinetic properties and robust pharmacodynamic activity in a mouse xenograft model.

Efficacy and activity of PD-1 blockade in patients with advanced esophageal squamous cell carcinoma: a systematic review and meta-analysis with focus on the value of PD-L1 combined positive score

BACKGROUND

Recently, several randomized controlled trials (RCTs) investigated immunotherapy-based regimens versus chemotherapy alone in patients with advanced esophageal squamous cell carcinoma (ESCC). Here we conducted a systematic review and meta-analysis on the efficacy and activity of programmed cell death protein 1 blockade in these patients, with focus on the value of programmed death-ligand 1 combined positive score (CPS) for selecting patients who may benefit the most.

METHODS

RCTs investigating treatment with or without immune checkpoint inhibitors for advanced ESCC were selected. The hazard ratio (HR) and the odds ratio were used to compare the treatment effect on survival outcomes and tumor response, respectively, for immunotherapy-based regimens compared with standard chemotherapy, overall and according to geographic region or treatment line. We carried out a subgroup analysis comparing patients with CPS ≥10 or <10 and the evidence for treatment effect was evaluated by interaction test.

RESULTS

A total of 5257 patients and 10 RCTs were included. Overall, the HR for overall survival benefit with immunotherapy-based regimens was 0.71 [95% confidence interval (CI) 0.66-0.76] compared with chemotherapy alone; such effect was independent from geographical region (Asia versus rest of the world) and treatment line (upfront versus second/further lines). The HR for progression-free survival benefit and the odds ratio for overall response rate increase were 0.78 (95% CI 0.66-0.93) and 1.50 (95% CI 1.22-1.83), respectively. The HR for overall survival benefit with immunotherapy-based treatment was 0.60 (95% CI 0.51-0.70) for CPS ≥10 subgroup versus 0.83 (95% CI 0.69-1.00) for CPS <10 (P for interaction 0.009).

CONCLUSIONS

Immune checkpoint inhibitors have a consistent benefit in reducing the risk of death for ESCC patients which is dependent on programmed death-ligand 1 CPS status. Further investigations of biomarkers for immunotherapy in the subgroup of patients with CPS <10 are needed.

Clinical impact of neutropenia and febrile neutropenia in metastatic colorectal cancer patients treated with FOLFOXIRI/bevacizumab: a pooled analysis of TRIBE and TRIBE2 studies by GONO

BACKGROUND

TRIBE and TRIBE-2 studies demonstrated higher benefit from FOLFOXIRI (fluorouracil, leucovorin, oxaliplatin, and irinotecan)/bevacizumab compared with FOLFIRI (fluorouracil, leucovorin, and irinotecan) or FOLFOX/bevacizumab as an upfront option for metastatic colorectal cancer patients, with more toxicities. We focused on the incidence and longitudinal dynamics of neutropenia and febrile neutropenia (FN) in the two studies, to evaluate their clinical relevance, the magnitude of impact of FOLFOXIRI/bevacizumab, and the role of risk factors in predicting their occurrence.

METHODS

The overall incidence of grade 3-4 (G3-4) neutropenia and FN, the time to their onset, the use of granulocyte colony-stimulating factor, and the association with risk factors were evaluated in the overall population and according to treatment arm. FN episodes were assessed by Multinational Association for Supportive Care in Cancer (MASCC) score.

RESULTS

Among 1155 patients, 568 (49%) received FOLFOXIRI/bevacizumab. Overall, 410 (35%) experienced G3-4 neutropenia and 70 (6%) FN, 21 (2%) at high risk. FOLFOXIRI/bevacizumab was associated with higher incidence of neutropenia (51% versus 21%, P < 0.001), FN (8% versus 4%, P = 0.02), and high-risk FN [18 (3%) versus 3 (1%), P = 0.015]. No related deaths were observed. The first episode of G3-4 neutropenia and FN occurred mainly in the first 2 months in both arms. Longitudinal analysis showed different patterns of evolution over cycles between the arms (P < 0.001) G3-4 neutropenia being more frequent in the first cycles with FOLFOXIRI/bevacizumab. Older patients (P = 0.01) and females (P < 0.001) had a significantly higher risk of G3-4 neutropenia. No significant interaction effect between arm and analysed risk factors in terms of risk of G3-4 neutropenia or FN was observed. The incidence of FN among older females receiving FOLFOXIRI/bevacizumab was 12%. Neither G3-4 neutropenia nor FN impaired efficacy in terms of overall response rate, progression-free survival, and overall survival.

CONCLUSIONS

FOLFOXIRI/bevacizumab has a higher risk of G3-4 neutropenia and FN than doublets/bevacizumab. FN occurred in <10% of patients, mostly as low-risk episodes. A closer monitoring during the first 2 months is recommended; prophylactic use of granulocyte colony-stimulating factor may be considered for older females.

Discovery of a First-in-Class Inhibitor of the Histone Methyltransferase SETD2 Suitable for Preclinical Studies

SET domain-containing protein 2 (SETD2), a histone methyltransferase, has been identified as a target of interest in certain hematological malignancies, including multiple myeloma. This account details the discovery of EPZ-719, a novel and potent SETD2 inhibitor with a high selectivity over other histone methyltransferases. A screening campaign of the Epizyme proprietary histone methyltransferase-biased library identified potential leads based on a 2-amidoindole core. Structure-based drug design (SBDD) and drug metabolism/pharmacokinetics (DMPK) optimization resulted in EPZ-719, an attractive tool compound for the interrogation of SETD2 biology that enables in vivo target validation studies.

Impact of age and gender on the efficacy and safety of upfront therapy with panitumumab plus FOLFOX followed by panitumumab-based maintenance: a pre-specified subgroup analysis of the Valentino study

BACKGROUND

The safety and efficacy outcome of elderly metastatic colorectal cancer (mCRC) patients fit enough to receive combination chemotherapy plus biological agents is an issue of growing interest. Also, gender-specific differential toxicity and efficacy of anti-epidermal growth factor receptor (EGFR)-based upfront treatments need to be explored.

PATIENTS AND METHODS

Valentino was a multicenter, randomized, phase II trial, investigating two panitumumab-based maintenance strategies following first-line panitumumab plus FOLFOX in RAS wild-type mCRC patients. We carried out a subgroup analysis, aimed at assessing the differences in efficacy, safety and quality of life (QoL) according to age (<70 versus ≥70 years) and gender (male versus female). Efficacy endpoints were progression-free survival (PFS), overall survival (OS) and overall response rate (ORR); safety endpoints were rates of any grade and grade 3/4 adverse events (AEs).

RESULTS

No significant differences in terms of PFS, OS and ORR were observed between patients aged <70 or ≥70 years and the effect of the maintenance treatment arm on survival outcomes was similar in the two subgroups. The safety profile of both induction and maintenance treatment and the impact on QoL were similar in elderly and younger patients. No significant differences in PFS, OS, ORR or clinical benefit rate were observed according to gender. A significantly higher rate of overall grade 3/4 AEs (P = 0.008) and of grade 3/4 thrombocytopenia (P = 0.017), any grade and grade 3/4 neutropenia (P < 0.0001) and any grade conjunctivitis (P = 0.033) was reported in female as compared to male patients. Conversely, we reported a significantly higher incidence of any grade skin rash (P = 0.0007) and hypomagnesemia (P = 0.029) in male patients.

CONCLUSIONS

The upfront choice of an anti-EGFR-based doublet chemotherapy followed by a maintenance strategy represents a valuable option in RAS wild-type mCRC irrespective of gender and age, though a careful evaluation of patients to maximize the risk/benefit ratio is warranted.

Abstract 1161: EZH2 inhibitor tazemetostat demonstrates activity in preclinical models of Bruton's tyrosine kinase inhibitor-resistant relapsed/refractory mantle cell lymphoma

Tazemetostat (EZM6438) is a potent, orally bioavailable small molecule inhibitor of EZH2, the enzymatic subunit of the polycomb repressive complex 2, which has been approved for treatment of epithelioid sarcoma and relapsed/refractory follicular lymphoma. EZH2 has been shown to play a key role in B-cell maturation and multiple B-cell malignancies are dependent on EZH2 for survival. Mantle cell lymphoma (MCL) is a rare subtype of mature B cell non-Hodgkin lymphoma characterized by the t(11;14)(q13;q32) translocation leading to overexpression of cyclin D1, which plays a significant role in tumor cell proliferation via cell cycle dysregulation, chromosomal instability, and epigenetic regulation. This disease most often presents at an advanced stage and while initial responses occur, most cases relapse to frontline therapy, including Bruton's Tyrosine Kinase (BTK) inhibitors. The rate of intrinsic and acquired resistance to these treatments results in a high unmet medical need. We previously reported that treatment with EZH2 inhibitors, as monotherapy or in combination with BTK inhibitors, elicited in vitro anti-proliferative activity and in vivo tumor growth inhibition in MCL models, demonstrating that EZH2 may be a promising therapeutic target in this indication. To extend our previous in vitro combination studies, we demonstrated that the recently approved BTK inhibitor, zanubrutinib synergized with tazemetostat and demonstrated that tazemetostat resensitized a subset of cell lines intrinsically resistant to BTK inhibitors. In vivo studies confirmed these findings, showing a significant tumor growth delay when tazemetostat was combined with zanubrutinib in the MCL MINO cell line-derived murine xenograft model compared to the single agent treatments. To understand if EZH2 inhibition offered potential therapeutic benefit to the MCL BTK inhibitor-resistant population, we generated in vitro MCL models of acquired resistance to the BTK inhibitors ibrutinib and zanubrutinib. These cell lines retained the in vitro sensitivity to tazemetostat observed in the parental cell line, suggesting a potential therapeutic option for tazemetostat in the setting of acquired resistance to BTK inhibitors. Additionally, we showed that tazemetostat induced anti-proliferative effects ex vivo in samples derived from MCL patients that were relapsed or refractory to one or more current standard of care agents, including the BTK inhibitor ibrutinib. Subsequent studies aim to identify the mechanisms of growth inhibition driven by tazemetostat in MCL models sensitive and resistant to BTK inhibitors. In summary, these data suggest that tazemetostat treatment (alone or in combination with a BTK inhibitor) could be a potential therapeutic option in the treatment of the MCL patient population that is relapsed/refractory to BTK inhibitor therapy.

Citation Format: Jeffrey A. Keats, Arleide Lee, Jeremy C. Cunniff, Weiqing Chen, Revonda Mehovic, Vania Estanek, Crag Markwood, Cuyue Tang, Daniel T. Dransfield, Veronica Gibaja, Alejandra Raimondi. EZH2 inhibitor tazemetostat demonstrates activity in preclinical models of Bruton's tyrosine kinase inhibitor-resistant relapsed/refractory mantle cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1161.

The importance of respecting accreditation indicators to improve quality of care

Issue

The health and social-care facilities (HSF) of the Lombardy Region provide services specifically conceived for fragile populations, including elderly, disabled, addicts etc. Through its Accreditation Units, the Agency for Health Protection (ATS) in the Metropolitan City of Milan is responsible for overseeing authorization and accreditation indicators of HSFs in all afferent districts. Assessed requirements include the qualitative standard (presence of mandatory professional figures) and the quantitative standard (guaranteed weekly minimum time of care per patient) of operating staff, based on current legislation.

Description of the problem

These standards are evaluated at site-inspection by examining staff qualifications and by matching staff working hours to actual daily presence of patients, randomly selecting a recent past week. The resulting standards may thus not be fully representative of the whole year. In 2019, the Health and Social-care facilities Accreditation Unit of ATS began a retrospective quali-quantitative analysis of health service staffing data for 2017 and 2018. Data were extrapolated from two main databases: “Scheda Struttura”, a data collection tool regarding work hours, qualifications, waiting lists etc. compiled yearly by HSF managers; and economic data detailing reimbursements by the regional health service, based on effective daily presence of patients at the HSF.

Results

Preliminary results relating to 2017 showed that around 4% of HSFs do not guarantee qualitative staffing standards, and almost 30% do not guarantee quantitative staffing standards throughout the year.

Lessons

The proposed tool is useful for emphasizing potentially critical situations and may help define the annual inspection schedule with the aim of continuously improving quality of care among regional HSFs.

Key messages

Data management tools can help local health authorities monitor and identify facilities at risk of falling below the defined standards of care. Qualitative and quantitative analysis of health service staffing is useful for emphasizing potentially critical situations and may help define the annual inspection schedule.

Activation of 574 new Alzheimer’s special care unit beds in the Metropolitan City of Milan

Issue

Dementia is among the main causes of disability and dependency in the elderly. It was defined a public health priority by the WHO. The health and social-care system of the Lombardy region (SSR) plays a key role in implementing assistance and care pathways specifically designed for fragile populations, including those affected by dementia and Alzheimer's disease, its most common form.

Description of the Problem

The SSR provides residential care options especially conceived for dementia patients, known as Alzheimer's special care units (ASCU). However, waiting lists are concerning, and distribution of these facilities is inconsistent throughout the region. In 2018 there were 981 accredited and SSR-covered ASCU beds in the Metropolitan City of Milan (MCM), translating in 1.26 beds/1000 people aged ≥ 65. With regional legislation (DGR 1046/2018), the SSR proposed activation of new ASCU beds in all territories with less than 2 beds/1000 people aged ≥ 65. The MCM Agency for Health Protection (ATS) thus analyzed the distribution of ASCU beds in afferent districts, defining specific needs for each district. The aim was to fund and activate 574 new ASCU beds homogenously among previously accredited and SSR-covered residential care facilities, reaching the targeted 2 ASCU beds/1000 people aged ≥ 65. Applicant facilities had to respond to specific personnel, technological, therapeutic and structural requirements.

Results

Preliminary results indicate 29 residential care facilities applied for evaluation in 2019. The ATS received and evaluated all applications. Following site-inspection, 8 facilities were deemed inappropriate.

Lessons

In 2019, 21 residential care facilities were approved for funding and activation of 558 new ASCU beds. Residual beds will be funded in 2020. Main messages: Activation of new ASCU beds in 2019 and 2020 increased specialized long-term care beds for dementia patients by almost 60%, allowing a more homogenous distribution among MCM districts.

Key messages

The health and social-care system of the Lombardy region proposed activation of new Alzheimer’s special care units beds in all territories with less than 2 beds/1000 people aged ≥ 65. Activation of 574 new Alzheimer’s special care units beds increased by almost 60%, allowing a more homogenous distribution among Metropolitan City of Milan districts.

Abstract 1768: Identification of a potent, orally-available SMARCA2/4 inhibitor with in vitro and in vivo activity in preclinical models of SMARCA4-mutant NSCLC

SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily A member 2 (SMARCA2) is an ATP-dependent DNA helicase and a catalytic component of the SWI/SNF complex. SWI/SNF-mediated nucleosome remodeling is a critical regulator of chromatin accessibility resulting in transcriptional regulation of gene sets that determine and maintain cell state. The role of SMARCA2 as the catalytic driver of SWI/SNF activity is mutually exclusive with that of its close paralog, SMARCA4. Loss of functional SMARCA4, as is reported in a subset of NSCLC and other cancer types generally confers a dependency on SMARCA2. Cancers lacking functional SMARCA4 have been shown to be sensitive to loss of SMARCA2 function either through genetic ablation or the use of a small molecule SMARCA2/4 inhibitor. We describe the identification and characterization of a small molecule SMARCA2/4 inhibitor Compound 1 and its selective activity in the SMARCA4-mutant setting both in in vitro and in vivo model systems. The compound demonstrates inhibition of SMARCA2 and SMARCA4 enzymatic activity in biochemical assays and broad selectivity against other helicases. Selective sensitivity in anti-proliferative assays of 15-fold was observed in NSCLC cell lines with SMARCA4 protein loss compared to those harboring WT SMARCA4 protein. Oral dosing demonstrates dose-dependent in vivo SMARCA2 inhibition and anti-tumor activity in SMARCA4-mutant NSCLC xenograft models. This compound is suitable for further exploration of the role of SMARCA2/4 and SWI/SNF in vitro and in vivo in cancer and other indications.

Citation Format: Allison E. Drew, Suzanne L. Jacques, Lindsey W. Eichinger, Chloe Pantano, Vinny Motwani, Cuyue Tang, Cuyue Tang, Neil Farrow, Dorothy Brach, Selene Howe, Alejandra Raimondi, Daniel T. Dransfield, Kenneth W. Duncan, Kim Stickland, Liyue Huang, John Lampe. Identification of a potent, orally-available SMARCA2/4 inhibitor with in vitro and in vivo activity in preclinical models of SMARCA4-mutant NSCLC [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1768.

Abstract 2924: Aberrant SWI/SNF complexes lacking SMARCA2 or SMARCA4 differentially affect cell state and response to a novel SMARCA2/4 inhibitor

SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily A member 2 (SMARCA2) is an ATP-dependent DNA helicase and a catalytic component of the SWI/SNF complex. SWI/SNF-mediated nucleosome remodeling is a critical regulator of chromatin accessibility resulting in transcriptional regulation of gene sets that determine and maintain cell state. SMARCA2's role as the catalytic driver of SWI/SNF activity is mutually exclusive with that of its close paralog, SMARCA4. Here, we show that the synthetic lethal relationship between SMARCA2 and SMARCA4 can be genetically engineered bi-directionally in SMARCA2/SMARCA4 wild type (WT) cell lines. While knockout (KO) of either protein individually minimally affects cell growth, a genetically engineered cell line with loss of either SMARCA2 or SMARCA4 becomes sensitive to loss of its paralog. While SMARCA2 is infrequently lost through genetic mutation, SMARCA4 mutations occur in a wide variety of cancer types. We present CRISPR-Cas9 pooled screening data showing that cell lines with SMARCA4 mutations have a selective sensitivity to loss of SMARCA2 across multiple cancer indications, including NSCLC and ovarian carcinoma. SMARCA2 and SMARCA4, though partially redundant, also play unique roles within the cell as is evidenced by the unique set of transcriptional changes that occur in the SMARCA2/4 isogeneic cell lines, including the differential modulation of genes involved in TGFB signaling, regulation of angiogenesis, and in determinants of epithelial or mesenchymal cell state. ChIP-seq studies show changes in SWI/SNF occupancy as well as in the chromatin landscape that are specific to the loss of either SMARCA2 or SMARCA4. These isogenic cell lines also respond differently to treatment with a novel SMARCA2/4 inhibitor, Compound 1, in transcriptional as well as functional effects, providing evidence that dual inhibition with a small molecule may not be equivalent to the complete genetic ablation of these two proteins The NCI-H358 NCSLC cell line expresses WT SMARCA2 and SMARCA4 and is weakly sensitive to treatment with Compound 1. CRISPR-Cas9 mediated KO of SMARCA4 confers several-fold greater sensitivity to treatment with the novel inhibitor compared to the parental cell line. Surprisingly, KO of SMARCA2 does not confer sensitivity to inhibitor treatment. This selectivity sensitivity to treatment with Compound 1 that we observe in the SMARCA4-KO cell line is also observed across a panel of SMARCA4-mutant NSCLC. The relationship between the transcriptional and phenotypic changes that occur in these isogenic knockout lines as well as in SMARCA4-mutated NSCLC cell lines in response to SMARCA2/4 inhibitor treatment have revealed novel mechanisms driven by specific SWI/SNF complexes. These data have allowed us to better understand the potential therapeutic utility of a SMARCA2/4 inhibitor in both a SMARCA4-mut and SMARCA4-wt NSCLC patient population.

Citation Format: Lindsey W. Eichinger, Chloe Pantano, Vinny Motwani, Dorothy Brach, Selene Howe, Alejandra Raimondi, Daniel T. Dransfield, Kenneth W. Duncan, Kim Stickland, Cuyue Tang, Neil A. Farrow, John Lampe, Suzanne L. Jacques, Allison E. Drew. Aberrant SWI/SNF complexes lacking SMARCA2 or SMARCA4 differentially affect cell state and response to a novel SMARCA2/4 inhibitor [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2924.

Temozolomide and irinotecan (TEMIRI regimen) as salvage treatment of irinotecan-sensitive advanced colorectal cancer patients bearing MGMT methylation

Background

Non-randomized studies showed that temozolomide (TMZ) achieves an average 10% response rate in heavily pretreated metastatic colorectal cancer (mCRC) patients with promoter methylation of the DNA repair gene O6-methylguanine-DNA methyltransferase (MGMT). In this phase II trial, irinotecan and temozolomide (TEMIRI) combination regimen was assessed in irinotecan-sensitive, MGMT methylated/microsatellite stable (MSS) pretreated mCRC patients.

Patients and methods

Key inclusion criteria were centrally confirmed MGMT methylation by methylation-specific PCR, MSS mCRC, progression after at least two prior chemotherapy regimens for advanced disease and irinotecan-free interval >3 months. TEMIRI (TMZ 150 mg/m2 on days 1-5 plus irinotecan 100 mg/m2 on days 1, 15 q28 days) was administered for six cycles, followed by maintenance with TMZ. The primary end point was overall response rate (ORR). Exploratory translational analyses included MGMT immunohistochemistry (IHC) and methyl-BEAMing (MB).

Results

Between December 2014 and June 2017, 25 patients were enrolled. The primary end point was met, since six patients achieved a partial response [ORR 24%, 95% confidence interval (CI) 11% to 43%]. At a median follow-up of 15.6 months, median progression-free survival (mPFS) and overall survival (mOS) were 4.4 and 13.8 months, respectively. Only four (16%) patients had ≥ grade 3 (CTCAE 4.0) adverse events. All patients whose cancer was MGMT-positive IHC were non-responders. Consistently, patients with MGMT-negative/low tumors had a significantly longer mPFS than others (6.9 versus 2.0 months; hazard ratio = 0.29, 95% CI 0.02-0.41; P = 0.003) and a non-significant trend for longer mOS. MB testing showed similar accuracy.

Conclusions

TEMIRI regimen is a safe and active option in pre-treated, irinotecan-sensitive mCRC patients with MGMT methylation.

Anti-tumor Activity of the Type I PRMT Inhibitor, GSK3368715, Synergizes with PRMT5 Inhibition through MTAP Loss

Type I protein arginine methyltransferases (PRMTs) catalyze asymmetric dimethylation of arginines on proteins. Type I PRMTs and their substrates have been implicated in human cancers, suggesting inhibition of type I PRMTs may offer a therapeutic approach for oncology. The current report describes GSK3368715 (EPZ019997), a potent, reversible type I PRMT inhibitor with anti-tumor effects in human cancer models. Inhibition of PRMT5, the predominant type II PRMT, produces synergistic cancer cell growth inhibition when combined with GSK3368715. Interestingly, deletion of the methylthioadenosine phosphorylase gene (MTAP) results in accumulation of the metabolite 2-methylthioadenosine, an endogenous inhibitor of PRMT5, and correlates with sensitivity to GSK3368715 in cell lines. These data provide rationale to explore MTAP status as a biomarker strategy for patient selection.

Abstract 808: Opportunity for therapeutic expansion in mantle cell lymphoma: Tazemetostat combination synergy status in preclinical MCL models

Tazemetostat (EPZ-6438) is a potent, selective, orally bioavailable small molecule inhibitor of EZH2, the enzymatic subunit of the polycomb repressive complex 2, which is currently being evaluated in multiple phase II clinical trials for the treatment of non-Hodgkin lymphoma, mesothelioma and molecularly defined solid tumors. Objective clinical responses have been observed in phase II studies of tazemetostat, including patients with B-cell lymphomas.

EZH2 has been shown to play a key role in the maturation of B-cells and, consistent with this phenomenon, multiple B-cell malignancies are dependent on EZH2 for survival. In preclinical studies in mantle cell lymphoma (MCL), a disease arising from mantle zone cells surrounding germinal centers, treatment with EZH2 inhibitors, in in vitro and in vivo models demonstrated antiproliferative activity, suggesting EZH2 may be a promising therapeutic target for MCL.

MCL is a distinct B-cell non-Hodgkin lymphoma characterized by the chromosomal translocation t(11;14) that leads to overexpression of cyclin D1. The disease most often presents at an advanced stage, and while initial responses occur, nearly all cases relapse or become resistant to frontline therapy and progress with poor prognosis. Novel targeted therapies are currently entering the clinic in combination with standard of care treatments, but heterogeneous response rates and durations of response show that there remains an unmet medical need in this population.

The most widely used MCL treatment regimens include combinations of two or more Standard of Care (SOC) agents. In order to support potential future clinical investigations with tazemetostat we established in vitro assays to assess its combinatorial activity with 24 traditional and emerging therapies across seven MCL cell lines. All compounds were evaluated for their single agent activity in order to determine the appropriate starting doses to investigate synergy. We then looked at both a seven-day pretreatment with tazemetostat alone followed by a four-day cotreatment with combination partner as well as a seven-day cotreatment including both drugs simultaneously. Synergy status was determined via Loewe, BLISS and additional mathematical models. Robust synergy was observed with glucocorticoid receptor agonists, immunomodulatory drugs, venetoclax and a variety of B-cell receptor pathway modulators in both dosing regimens. In addition, we show that EPZ011989 (an EZH2 tool compound) induces tumor growth inhibition in a MCL xenograft model, and has combination benefit with ibrutinib.

Preclinical data suggest that the sensitivity to tazemetostat as a single agent in MCL cell lines can be greatly enhanced in combination with new and emerging therapies. These combination approaches may be worthy of exploration in the clinic for the treatment of MCL.

Citation Format: Tami L. Hood, Kat Cosmopoulos, Allison Drew, Kelli Armstrong, Jennifer Johnson, Smith Jesse, Alejandra Raimondi. Opportunity for therapeutic expansion in mantle cell lymphoma: Tazemetostat combination synergy status in preclinical MCL models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 808.

Origin of Glycosylated Hemoglobin Al in Chronic Renal Failure

In chronic renal failure both HbAI and HbAlc levels have been reported to be elevated. In order to investigate the causes of such increase we measured HbAI (cation-exchange chromatography), blood urea nitrogen, arterial blood pH, plasma bicarbonate, phosphatemia, serum iron and serum ferritin before dialysis in 60 uremic patients receiving long term hemodialysis. The increased levels of HbAI do not correlate with glucose intolerance, phosphatemia, blood urea nitrogen, time averaged concentration of urea, serum iron and serum ferritin. On the contrary the presence of a highly significant correlation between HbAI and arterial blood pH (p < 0.001) and between HbAI and plasma bicarbonate (p < 0.001) seems to emphasize a major role for acidosis in increasing the HbAI levels in uremic patients on long term hemodialysis.

Identification of a CARM1 Inhibitor with Potent In Vitro and In Vivo Activity in Preclinical Models of Multiple Myeloma

CARM1 is an arginine methyltransferase with diverse histone and non-histone substrates implicated in the regulation of cellular processes including transcriptional co-activation and RNA processing. CARM1 overexpression has been reported in multiple cancer types and has been shown to modulate oncogenic pathways in in vitro studies. Detailed understanding of the mechanism of action of CARM1 in oncogenesis has been limited by a lack of selective tool compounds, particularly for in vivo studies. We describe the identification and characterization of, to our knowledge, the first potent and selective inhibitor of CARM1 that exhibits anti-proliferative effects both in vitro and in vivo and, to our knowledge, the first demonstration of a role for CARM1 in multiple myeloma (MM). EZM2302 (GSK3359088) is an inhibitor of CARM1 enzymatic activity in biochemical assays (IC₅₀ = 6 nM) with broad selectivity against other histone methyltransferases. Treatment of MM cell lines with EZM2302 leads to inhibition of PABP1 and SMB methylation and cell stasis with IC₅₀ values in the nanomolar range. Oral dosing of EZM2302 demonstrates dose-dependent in vivo CARM1 inhibition and anti-tumor activity in an MM xenograft model. EZM2302 is a validated chemical probe suitable for further understanding the biological role CARM1 plays in cancer and other diseases.

Abstract 3345: Selective killing of SMARCA2- and SMARCA4-deficient tumors by inhibition of EZH2: In vitro and in vivo preclinical models

The histone methyltransferase EZH2 is the enzymatic subunit of the polycomb repressive complex 2 (PRC2) that catalyzes the methylation of H3K27 thereby repressing target gene transcription. EZH2 is amplified, overexpressed, or mutated in multiple cancer types, most notably Follicular Lymphoma (FL) and germinal center Diffuse Large B-cell Lymphoma (GCB-DLBCL). We previously reported that preclinical models of malignant rhabdoid tumors, which are deficient in the SWI/SNF core component INI1 (SNF5, SMARCB1), are selectively killed by potent and selective inhibitors of EZH2. Here we report another class of SWI/SNF-altered cancers named small cell carcinoma of the ovary hypercalcemic type (SCCOHT) that is dependent on EZH2 activity. SCCOHT is a very aggressive form of cancer that responds poorly to conventional therapy with a one-year overall survival rate of only 50%. Very few novel agents have been approved for this indication; thus there is a need for targeted therapeutics in SCCOHT. SMARCA4 and SMARCA2 are co-inactivated in this tumor type that has many rhabdoid features. We demonstrate that tazemetostat, an EZH2 inhibitor currently in phase 2 clinical trials, induces potent and selective killing in SMARCA2 and SMARCA4-deficient ovarian cell lines. In addition to small molecule inhibitor data, we conducted functional genomics studies with CRISPR pooled screening, and confirmed that SCCOHT is also sensitive to CRISPR-mediated EZH2 gene ablation. Dose-dependent anti-tumor effects were observed upon tazemetostat treatment in SCCOHT xenografts deficient in both SMARCA2 and SMARCA4. We also report on additional non-ovarian tumor types with dual SMARCA2/SMARCA4 loss including NSCLC that exhibit EZH2 dependence representing additional potential therapeutic indications for tazemetostat treatment.

Citation Format: Elayne Chan-Penebre, Kelli Armstrong, Allison Drew, Alexandra R. Grassian, Igor Feldman, Maria Roche, Peter Ho, Dorothy Brach, Alejandra Raimondi, Robert A. Copeland, Richard Chesworth, Jesse J. Smith, Scott A. Ribich. Selective killing of SMARCA2- and SMARCA4-deficient tumors by inhibition of EZH2: In vitro and in vivo preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3345. doi:10.1158/1538-7445.AM2017-3345

Abstract 1944: Tazemetostat displays synergistic antiproliferative activity with backbone therapies in preclinical models of AT/RT and MRT

Malignant Rhabdoid Tumors (MRT) and Atypical Teratoid Rhabdoid Tumors (AT/RT) are typically pediatric cancers which are rare and aggressive with extremely high unmet medical need. At a molecular level MRT and AT/RT tumors are almost universally characterized by loss of the INI1 protein (also known as SNF5 or SMARCB1), a component of the Switch Sucrose Non-fermentable (SWI/SNF) multimeric chromatin modifying complex. In many cell types, the SWI/SNF complex and the PRC2 complex have an antagonistic relationship in the regulation of tumor suppressor genes, cell cycle checkpoints, hedgehog and myc pathway genes, among others [Wilson et al, Cancer Cell. 2010 Oct 19;18(4):316-28.]. This explicated the possibility of a novel treatment modality for these tumors, based on inhibition of EZH2 - the catalytic subunit of PRC2. Tazemetostat (EPZ-6438) is a potent and orally bioavailable small molecule inhibitor of EZH2 currently in phase 2 clinical trials in adult patients with non-Hodgkin lymphoma, INI1-negative tumors and mesothelioma. Dependency of INI1-negative tumors on EZH2 catalytic activity was demonstrated in preclinical models of MRT, where robust tumor regressions were induced with tazemetostat treatment [Knutson et al, Proc Natl Acad Sci USA. 2013 May 7;110(19):7922-7]. Consistent with this, tazemetostat demonstrated activity in relapsed or refractory patients with INI1-negative tumors enrolled in the adult phase 1 clinical trial. In addition, a phase 1 dose escalation study in pediatric patients with INI1-negative solid tumors is currently ongoing. Backbone therapies for MRT and AT/RT are comprised of cytotoxic chemotherapy which may or may not be administered in the context of stem cell transplant, in addition to surgical resection and radiation therapy. In support of combination clinical scenarios including EZH2 inhibition in this setting, we sought to explore the antiproliferative effects of combining tazemetostat with current small molecule treatment therapies in cell line models of AT/RT and MRT. Synergistic activity was observed when tazometostat was combined with individual components of chemotherapeutic regimens and targeted therapies such as vincristine, doxorubicin, alisertib and HDAC inhibitors.Further, we investigated the effects of ionizing radiation together with tazemetostat treatment. Application of X-ray irradiation concomitantly or after tazemetostat treatment, induced robust antiproliferative activity and reduction in clonogenic potential of both AT/RT cell lines tested.Taken together these results suggest that pharmacological inhibition of EZH2 enhances the activity of backbone therapy and may have an advantage over monotherapy in INI1-negative cancers supporting the therapeutic potential of combination regimens that include tazemetostat in these tumors.

Citation Format: Christine R. Klaus, Jeffrey A. Keats, Jesse J. Smith, Richard Chesworth, Robert A. Copeland, Scott Ribich, Alejandra Raimondi. Tazemetostat displays synergistic antiproliferative activity with backbone therapies in preclinical models of AT/RT and MRT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1944. doi:10.1158/1538-7445.AM2017-1944

Novel Oxindole Sulfonamides and Sulfamides: EPZ031686, the First Orally Bioavailable Small Molecule SMYD3 Inhibitor

SMYD3 has been implicated in a range of cancers; however, until now no potent selective small molecule inhibitors have been available for target validation studies. A novel oxindole series of SMYD3 inhibitors was identified through screening of the Epizyme proprietary histone methyltransferase-biased library. Potency optimization afforded two tool compounds, sulfonamide EPZ031686 and sulfamide EPZ030456, with cellular potency at a level sufficient to probe the in vitro biology of SMYD3 inhibition. EPZ031686 shows good bioavailability following oral dosing in mice making it a suitable tool for potential in vivo target validation studies.

Abstract C85: Identification of a novel potent selective SMYD3 inhibitor with oral bioavailability

SMYD3 (Set and Mynd Domain containing 3) is a lysine methyltransferase overexpressed in several cancer types including breast, prostrate, pancreatic, and lung, and this overexpression is associated with poor clinical prognosis. Genetic knockdown of SMYD3 by shRNA has been shown to decrease proliferation in a range of cancer cell lines suggesting that inhibition of SMYD3 may have therapeutic utility.

In this presentation we describe the discovery and optimization of a novel series of oxindole sulfonamides and sulfamides with SMYD3 inhibitory activity. One of these compounds, EPZ030456, has a SMYD3 biochemical IC50 of 4 nM and is active in cells with an IC50 of 48 nM in a trimethyl MAP3K2 (MEKK2) in-cell western (ICW) assay. The crystal structure of this compound was solved with SMYD3 and the nucleotide substrate, S-adenosylmethionine and shows the oxindole portion of the molecule extends into the SMYD3 lysine binding channel. EPZ030456 shows &lt; 30% inhibition at a 10 uM screening concentration against 17 histone methyltransferase targets tested, including SMYD2.

Further optimization within the series resulted in EPZ031686 which has similar potency to EPZ030456 with a biochemical IC50 of 3 nM and an ICW IC50 of 36 nM and in addition exhibits good bioavailability following oral dosing in mice. Hence, EPZ031686 is a suitable tool to study the role of SMYD3 in cancer and other therapeutic areas, using both in vitro and in vivo models.

Citation Format: Lorna H. Mitchell, Paula A. Boriack-Sjodin, Sherri Smith, Michael Thomenius, Nathalie Rioux, Michael Munchhof, James E. Mills, Christine Klaus, Jennifer Totman, Thomas V. Riera, Alejandra Raimondi, Suzanne L. Jacques, Megan Foley, Nigel J. Waters, Kevin W. Kuntz, Tim J. Wigle, Margaret Porter Scott, Robert A. Copeland, Jesse J. Smith, Richard Chesworth. Identification of a novel potent selective SMYD3 inhibitor with oral bioavailability. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C85.

Abstract 5383: DOT1L inhibitor EPZ-5676 synergizes with cytarabine and azacitidine in preclinical models of MLL-rearranged leukemia

EPZ-5676 is a small molecule inhibitor of the histone methyltransferase DOT1L currently in clinical development and represents a first in class novel therapeutic agent for the treatment of MLL-rearranged (MLL-r) leukemia. In preclinical studies, EPZ-5676 selectively inhibited intracellular histone H3K79 methylation, downstream target gene expression and demonstrated complete tumor regression in a MLL-r leukemia xenograft model. We previously reported synergistic and durable anti-proliferative activity when EPZ-5676 was combined with current AML standard of care drugs, cytarabine and daunorubicin in MLL-r leukemia models MOLM-13 (MLL-AF9) and MV4-11 (MLL-AF4). Combination benefit was also observed when MLL-r cells were treated with cytarabine, prior to co-treatment with EPZ-5676. Additionally, both cytarabine and the DNA methyltransferase inhibitor azacitidine, displayed synergistic anti-leukemic activity in MLL-r rearranged cells in a 7 day co-treatment model (7 days of continuous treatment with EPZ-5676 and second agent; see Klaus et al, JPET, 2014). In this report we discuss results of investigating additional treatment schedules using EPZ-5676 in combination with azacitidine in MLL-r cells. Cells were pretreated with azacitidine at nanomolar concentrations known to reverse promoter DNA-hypermethylation and alter the chromatin state (Tsai et al., Cancer Cell, 2012). We found treating MV4-11 and MOLM-13 cells once daily for three consecutive days followed by sequential treatment with EPZ-5676 elicited a synergistic anti-proliferative effect using the Chou-Talalay method (Chou, Pharmacol Rev., 2006). Results of studies to investigate the mechanism of this synergistic cell killing, including evaluation of differentiation markers and Annexin V staining will be reported. To determine if combinations of EPZ-5676 with cytarabine or azacitidine were tolerable and efficacious in vivo, nude rats implanted subcutaneously with MV4-11 tumors were treated using a range of doses and schedules. Azacitidine and cytarabine were delivered by intraperitoneal injection once daily for 14 days at their respective maximum tolerated doses of 2 and 200 mg/kg. Dosing at the established MTD, these agents inhibited the subcutaneous MV4-11 tumor growth by 50% compared to vehicle controls. Efficacy results from the EPZ-5676 combination studies with cytarabine or azacitidine will be presented. In summary, our results indicate that EPZ-5676 in combination with cytarabine or azacitidine revealed a synergistic effect, regardless of the treatment schedule used in preclinical models of MLL-r leukemia. Tolerable in vivo rat combination doses for EPZ-5676 with both cytarabine and azacitidine have been determined in support of potential future assessment of these combinations in MLL-r leukemia patients.

Citation Format: Christine R. Klaus, Scott R. Daigle, Vivek Chopra, Jeffrey A. Keats, Carly T. Campbell, Dorothy Iwanowicz, Edward J. Olhava, Margaret P. Scott, Roy M. Pollock, Robert A. Copeland, Jesse J. Smith, Jorge DiMartino, Stephen J. Blakemore, Alejandra Raimondi. DOT1L inhibitor EPZ-5676 synergizes with cytarabine and azacitidine in preclinical models of MLL-rearranged leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5383. doi:10.1158/1538-7445.AM2015-5383

EPZ011989, A Potent, Orally-Available EZH2 Inhibitor with Robust in Vivo Activity

Inhibitors of the protein methyltransferase Enhancer of Zeste Homolog 2 (EZH2) may have significant therapeutic potential for the treatment of B cell lymphomas and other cancer indications. The ability of the scientific community to explore fully the spectrum of EZH2-associated pathobiology has been hampered by the lack of in vivo-active tool compounds for this enzyme. Here we report the discovery and characterization of EPZ011989, a potent, selective, orally bioavailable inhibitor of EZH2 with useful pharmacokinetic properties. EPZ011989 demonstrates significant tumor growth inhibition in a mouse xenograft model of human B cell lymphoma. Hence, this compound represents a powerful tool for the expanded exploration of EZH2 activity in biology.

Synergistic Anti-Tumor Activity of EZH2 Inhibitors and Glucocorticoid Receptor Agonists in Models of Germinal Center Non-Hodgkin Lymphomas

Patients with non-Hodgkin lymphoma (NHL) are treated today with a cocktail of drugs referred to as CHOP (Cyclophosphamide, Hydroxyldaunorubicin, Oncovin, and Prednisone). Subsets of patients with NHL of germinal center origin bear oncogenic mutations in the EZH2 histone methyltransferase. Clinical testing of the EZH2 inhibitor EPZ-6438 has recently begun in patients. We report here that combining EPZ-6438 with CHOP in preclinical cell culture and mouse models results in dramatic synergy for cell killing in EZH2 mutant germinal center NHL cells. Surprisingly, we observe that much of this synergy is due to Prednisolone - a glucocorticoid receptor agonist (GRag) component of CHOP. Dramatic synergy was observed when EPZ-6438 is combined with Prednisolone alone, and a similar effect was observed with Dexamethasone, another GRag. Remarkably, the anti-proliferative effect of the EPZ-6438+GRag combination extends beyond EZH2 mutant-bearing cells to more generally impact germinal center NHL. These preclinical data reveal an unanticipated biological intersection between GR-mediated gene regulation and EZH2-mediated chromatin remodeling. The data also suggest the possibility of a significant and practical benefit of combining EZH2 inhibitors and GRag that warrants further investigation in a clinical setting.

DOT1L inhibitor EPZ-5676 displays synergistic antiproliferative activity in combination with standard of care drugs and hypomethylating agents in MLL-rearranged leukemia cells

EPZ-5676 [(2R,3R,4S,5R)-2-(6-amino-9H-purin-9-yl)-5-((((1r,3S)-3-(2-(5-(tert-butyl)-1H-benzo[d]imidazol-2-yl)ethyl)cyclobutyl)(isopropyl)amino)methyl)tetrahydrofuran-3,4-diol], a small-molecule inhibitor of the protein methyltransferase DOT1L, is currently under clinical investigation for acute leukemias bearing MLL-rearrangements (MLL-r). In this study, we evaluated EPZ-5676 in combination with standard of care (SOC) agents for acute leukemias as well as other chromatin-modifying drugs in cellular assays with three human acute leukemia cell lines: MOLM-13 (MLL-AF9), MV4-11 (MLL-AF4), and SKM-1 (non-MLL-r). Studies were performed to evaluate the antiproliferative effects of EPZ-5676 combinations in a cotreatment model in which the second agent was added simultaneously with EPZ-5676 at the beginning of the assay, or in a pretreatment model in which cells were incubated for several days in the presence of EPZ-5676 prior to the addition of the second agent. EPZ-5676 was found to act synergistically with the acute myeloid leukemia (AML) SOC agents cytarabine or daunorubicin in MOLM-13 and MV4-11 MLL-r cell lines. EPZ-5676 is selective for MLL-r cell lines as demonstrated by its lack of effect either alone or in combination in the nonrearranged SKM-1 cell line. In MLL-r cells, the combination benefit was observed even when EPZ-5676 was washed out prior to the addition of the chemotherapeutic agents, suggesting that EPZ-5676 sets up a durable, altered chromatin state that enhances the chemotherapeutic effects. Our evaluation of EPZ-5676 in conjunction with other chromatin-modifying drugs also revealed a consistent combination benefit, including synergy with DNA hypomethylating agents. These results indicate that EPZ-5676 is highly efficacious as a single agent and synergistically acts with other chemotherapeutics, including AML SOC drugs and DNA hypomethylating agents in MLL-r cells.

Selective inhibition of EZH2 by EPZ-6438 leads to potent antitumor activity in EZH2-mutant non-Hodgkin lymphoma

Mutations within the catalytic domain of the histone methyltransferase EZH2 have been identified in subsets of patients with non-Hodgkin lymphoma (NHL). These genetic alterations are hypothesized to confer an oncogenic dependency on EZH2 enzymatic activity in these cancers. We have previously reported the discovery of EPZ005678 and EPZ-6438, potent and selective S-adenosyl-methionine-competitive small molecule inhibitors of EZH2. Although both compounds are similar with respect to their mechanism of action and selectivity, EPZ-6438 possesses superior potency and drug-like properties, including good oral bioavailability in animals. Here, we characterize the activity of EPZ-6438 in preclinical models of NHL. EPZ-6438 selectively inhibits intracellular lysine 27 of histone H3 (H3K27) methylation in a concentration- and time-dependent manner in both EZH2 wild-type and mutant lymphoma cells. Inhibition of H3K27 trimethylation (H3K27Me3) leads to selective cell killing of human lymphoma cell lines bearing EZH2 catalytic domain point mutations. Treatment of EZH2-mutant NHL xenograft-bearing mice with EPZ-6438 causes dose-dependent tumor growth inhibition, including complete and sustained tumor regressions with correlative diminution of H3K27Me3 levels in tumors and selected normal tissues. Mice dosed orally with EPZ-6438 for 28 days remained tumor free for up to 63 days after stopping compound treatment in two EZH2-mutant xenograft models. These data confirm the dependency of EZH2-mutant NHL on EZH2 activity and portend the utility of EPZ-6438 as a potential treatment for these genetically defined cancers.