BET Bromodomain Inhibition Promotes Anti-tumor Immunity by Suppressing PD-L1 Expression

The next-generation BET inhibitor, PLX51107, delays melanoma growth in a CD8-mediated manner

Epigenetic agents such as bromodomain and extra-terminal region inhibitors (BETi) slow tumor growth via tumor intrinsic alterations; however, their effects on antitumor immunity remain unclear. A recent advance is the development of next-generation BETi that are potent and display a favorable half-life. Here, we tested the BETi, PLX51107, for immune-based effects on tumor growth in BRAF V600E melanoma syngeneic models. PLX51107 delayed melanoma tumor growth and increased activated, proliferating, and functional CD8+ T cells in tumors leading to CD8+ T-cell-mediated tumor growth delay. PLX51107 decreased Cox2 expression, increased dendritic cells, and lowered PD-L1, FasL, and IDO-1 expression in the tumor microenvironment. Importantly, PLX51107 delayed the growth of tumors that progressed on anti-PD-1 therapy; a response associated with decreased Cox2 levels, decreased PD-L1 expression on non-immune cells, and increased intratumoral CD8+ T cells. Thus, next-generation BETi represent a potential first-line and secondary treatment strategy for metastatic melanoma by eliciting effects, at least in part, on antitumor CD8+ T cells.

BET protein targeting suppresses the PD-1/PD-L1 pathway in triple-negative breast cancer and elicits anti-tumor immune response

Therapeutic strategies aiming to leverage anti-tumor immunity are being intensively investigated as they show promising results in cancer therapy. The PD-1/PD-L1 pathway constitutes an important target to restore functional anti-tumor immune response. Here, we report that BET protein inhibition suppresses PD-1/PD-L1 in triple-negative breast cancer. BET proteins control PD-1 expression in T cells, and PD-L1 in breast cancer cell models. BET protein targeting reduces T cell-derived interferon-γ production and signaling, thereby suppressing PD-L1 induction in breast cancer cells. Moreover, BET protein inhibition improves tumor cell-specific T cell cytotoxic function. Overall, we demonstrate that BET protein targeting represents a promising strategy to overcome tumor-reactive T cell exhaustion and improve anti-tumor immune responses, by reducing the PD-1/PD-L1 axis in triple-negative breast cancer.

Inhibition of the BET family reduces its new target gene IDO1 expression and the production of L-kynurenine

The bromodomain and extra terminal domain (BET) family members, including BRD2, BRD3, and BRD4, act as epigenetic readers to regulate gene expression. Indoleamine 2,3-dioxygenase 1 (IDO1) is an enzyme that participates in tumor immune escape primarily by catalyzing tryptophan to L-kynurenine. Here, we report that IDO1 is a new target gene of the BET family. RNA profiling showed that compound 9, a new BET inhibitor, reduced IDO1 mRNA up to seven times in Ty-82 cells. IDO1 differentially expressed in tumor cells and its expression could be induced with interferon gamma (IFN-γ). BET inhibitors (ABBV-075, JQ1, and OTX015) inhibited both constitutive and IFN-γ-inducible expression of IDO1. Similarly, reduction of BRD2, BRD3, or BRD4 decreased IDO1 expression. All these BET family members bound to the IDO1 promoter via the acetylated histone H3. JQ1 led to their release and reduced enrichment of RNA polymerase II (Pol II) on the promoter. IFN-γ increased the binding of BRD2, BRD3, BRD4, and Pol II on the IDO1 promoter by increasing the acetylation of histone H3, which could be prevented by JQ1 partially or even completely. Furthermore, both JQ1 and OTX015 decreased the production of L-kynurenine. The combination of BET inhibitors with the IDO1 inhibitor further reduced L-kynurenine, though only marginally. Importantly, the BET inhibitor ABBV-075 significantly inhibited the growth of human Ty-82 xenografts in nude mice and reduced both protein and mRNA levels of IDO1 in the xenografts. This finding lays a basis for the potential combination of BET inhibitors and IDO1 inhibitors for the treatment of IDO1-expressing cancers.

HDAC6 Inhibition Synergizes with Anti-PD-L1 Therapy in ARID1A-Inactivated Ovarian Cancer

ARID1A, encoding a subunit of the SWI/SNF complex, is the most frequently mutated epigenetic regulator in human cancers and is mutated in more than 50% of ovarian clear cell carcinomas (OCCC), a disease that currently has no effective therapy. Inhibition of histone deacetylase 6 (HDAC6) suppresses the growth of ARID1A-mutated tumors and modulates tumor immune microenvironment. Here, we show that inhibition of HDAC6 synergizes with anti-PD-L1 immune checkpoint blockade in ARID1A-inactivated ovarian cancer. ARID1A directly repressed transcription of CD274, the gene encoding PD-L1. Reduced tumor burden and improved survival were observed in ARID1A^flox/flox/PIK3CA^H1047R OCCC mice treated with the HDAC6 inhibitor ACY1215 and anti-PD-L1 immune checkpoint blockade as a result of activation and increased presence of IFNγ-positive CD8 T cells. We confirmed that the combined treatment limited tumor progression in a cytotoxic T-cell-dependent manner, as depletion of CD8⁺ T cells abrogated these antitumor effects. Together, these findings indicate that combined HDAC6 inhibition and immune checkpoint blockade represents a potential treatment strategy for ARID1A-mutated cancers. SIGNIFICANCE: These findings offer a mechanistic rationale for combining epigenetic modulators and existing immunotherapeutic interventions against a disease that has been so far resistant to checkpoint blockade as a monotherapy.See related commentary by Prokunina-Olsson, p. 5476.

Bromodomains: a new target class for drug development

Less than a decade ago, it was shown that bromodomains, acetyl lysine 'reader' modules found in proteins with varied functions, were highly tractable small-molecule targets. This is an unusual property for protein-protein or protein-peptide interaction domains, and it prompted a wave of chemical probe discovery to understand the biological potential of new agents that targeted bromodomains. The original examples, inhibitors of the bromodomain and extra-terminal (BET) class of bromodomains, showed enticing anti-inflammatory and anticancer activities, and several compounds have since advanced to human clinical trials. Here, we review the current state of BET inhibitor biology in relation to clinical development, and we discuss the next wave of bromodomain inhibitors with clinical potential in oncology and non-oncology indications. The lessons learned from BET inhibitor programmes should affect efforts to develop drugs that target non-BET bromodomains and other epigenetic readers.

Recent Findings in the Regulation of Programmed Death Ligand 1 Expression

With the recent approvals for the application of monoclonal antibodies that target the well-characterized immune checkpoints, immune therapy shows great potential against both solid and hematologic tumors. The use of these therapeutic monoclonal antibodies elicits inspiring clinical results with durable objective responses and improvements in overall survival. Agents targeting programmed cell death protein 1 (PD-1; also known as PDCD1) and its ligand (PD-L1) achieve a great success in immune checkpoints therapy. However, the majority of patients fail to respond to PD-1/PD-L1 axis inhibitors. Expression of PD-L1 on the membrane of tumor and immune cells has been shown to be associated with enhanced objective response rates to PD-1/PD-L1 inhibition. Thus, an improved understanding of how PD-L1 expression is regulated will enable us to better define its role as a predictive marker. In this review, we summarize recent findings in the regulation of PD-L1 expression.

Key actors in cancer therapy: epigenetic modifiers

Epigenetic reprogramming plays a crucial role in the tumorigenicity and maintenance of tumor-specific gene expression that especially occurs through DNA methylation and/or histone modifications. It has well-defined mechanisms. It is known that alterations in the DNA methylation pattern and/or the loss of specific histone acetylation/methylation markers are related to several hallmarks of cancer, such as drug resistance, stemness, epithelial-mesenchymal transition, and metastasis. It has also recently been highlighted that epigenetic alterations are critical for the regulation of the stemlike properties of cancer cells (tumor-initiating cells; cancer stem cells). Cancer stem cells are thought to be responsible for the recurrence of cancer which makes the patient return to the clinic with metastatic tumor tissue. Hence, the dysregulation of epigenetic machinery represents potential new therapeutic targets. Therefore, compounds with epigenetic activities have become crucial for developing new therapy regimens (e.g., antimetastatic agents) in the fight against cancer. Here, we review the epigenetic modifiers that have already been used in the clinic and/or in clinical trials, related preclinical studies in cancer therapy, and the smart combination strategies that target cancer stem cells along with the other cancer cells. The emerging role of epitranscriptome (RNA epigenetic) in cancer therapy has also been included in this review as a new avenue and potential target for the better management of cancer-beneficial epigenetic machinery.

Macrophage migration inhibitory factor-CD74 interaction regulates the expression of programmed cell death ligand 1 in melanoma cells

Expression of programmed cell death ligand 1 (PD‐L1) on tumor cells contributes to cancer immune evasion by interacting with programmed cell death 1 on immune cells. γ‐Interferon (IFN‐γ) has been reported as a key extrinsic stimulator of PD‐L1 expression, yet its mechanism of expression is poorly understood. This study analyzed the role of CD74 and its ligand macrophage migration inhibitory factor (MIF) on PD‐L1 expression, by immunohistochemical analysis of melanoma tissue samples and in vitro analyses of melanoma cell lines treated with IFN‐γ and inhibitors of the MIF‐CD74 interaction. Immunohistochemical analyses of 97 melanoma tissue samples showed significant correlations between CD74 and the expression status of PD‐L1 (P < .01). In vitro analysis of 2 melanoma cell lines, which are known to secrete MIF constitutively and express cell surface CD74 following IFN‐γ stimulation, showed upregulation of PD‐L1 levels by IFN‐γ stimulation. This was suppressed by further treatment with the MIF‐CD74 interaction inhibitor, 4‐iodo‐6‐phenylpyrimidine. In the analysis of melanoma cell line WM1361A, which constitutively expresses PD‐L1, CD74, and MIF in its non‐treated state, treatment with 4‐iodo‐6‐phenylpyrimidine and transfection of siRNAs targeting MIF and CD74 significantly suppressed the expression of PD‐L1. Together, the results indicated that MIF‐CD74 interaction directly regulated the expression of PD‐L1 and helps tumor cells escape from antitumorigenic immune responses. In conclusion, the MIF‐CD74 interaction could be a therapeutic target in the treatment of melanoma patients.

Reprogramming Tumor Immune Microenvironment (TIME) and Metabolism via Biomimetic Targeting Codelivery of Shikonin/JQ1

Remodeling tumor immune microenvironment (TIME) is an important strategy to lift the immunosuppression and achieve immune normalization. In this work, a mannosylated lactoferrin nanoparticulate system (Man-LF NPs) is developed for dual-targeting biomimetic codelivery of shikonin and JQ1 via the mannose receptor and LRP-1 that are overexpressed in both cancer cells and tumor-associated macrophages. The Man-LF NPs can serve as multitarget therapy for inducing immune cell death in the cancer cells, repressing glucose metabolism and repolarizing tumor-associated macrophages, and consequently, lead to remodeling the TIME (e.g., promotion of dendritic cell maturation and CD8⁺ T cell infiltration, as well as suppression of Treg). Moreover, JQ1 is a suppressor of PD-L1, and the Man-LF NPs can also work on PD-L1 checkpoint blockage. The results reveal the synergistic combination of shikonin and JQ1 and the treatment potency of the Man-LF NPs. Importantly, it is demonstrated that the interaction between the tumor metabolism and immunity plays an essential role in immunotherapy, and the developed drug combination and nanoformulation can target the multiple components in the complicated network of TIME, providing a potential therapeutic strategy.

The BD2 domain of BRD4 is a determinant in EndoMT and vein graft neointima formation

BACKGROUND

Vein-graft bypass is commonly performed to overcome atherosclerosis but is limited by high failure rates, principally due to neointimal wall thickening. Recent studies reveal that endothelial-mesenchymal transition (EndoMT) is critical for vein-graft neointima formation. BETs are a family of Bromo/ExtraTerminal domains-containing epigenetic reader proteins (BRD2, BRD3, BRD4). They bind acetylated histones through their unique tandem bromodomains (BD1, BD2), facilitating transcriptional complex formation and cell-state transitions. The role for BETs, including individual BRDs and their unique BDs, is not well understood in EndoMT and neointimal formation.

METHODS AND RESULTS

Repression of BRD4 expression abrogated TGFβ1-induced EndoMT, with greater effects than BRD2 or BRD3 knockdown. An inhibitor selective for BD2 in all BETs, but not that for BD1, blocked EndoMT. Moreover, expression of a dominant-negative BRD4-specific BD2 fully abolished EndoMT. Concordantly, BRD4 knockdown repressed TGFβ1-stimulated increase of ZEB1 protein - a transcription factor integral in EndoMT. In vivo, lentiviral gene transfer of either BRD4 shRNA or dominant negative BRD4-specific BD2 mitigated neointimal development in rat jugular veins grafted to carotid arteries.

CONCLUSIONS

Our data reveal the BD2 domain of BRD4 as a determinant driving EndoMT in vitro and neointimal formation in vivo. These findings provide new insight into BET biology, while offering prospects of specific BET domain targeting as an approach to limiting neointima and extending vein graft patency.

NUT midline carcinoma of the head and neck: current perspectives

Abstract: NUT midline carcinoma (NMC) is a rare and aggressive subtype of squamous carcinoma that typically arises from midline supradiaphragmatic structures, frequently from the head and neck area. NMC is genetically driven by a chromosomal rearrangement involving the NUT gene, which forms oncoproteins considered major pathogenic drivers of cellular transformation. Diagnosis of NMC has been made remarkably easier with the availability of a commercial antibody against NUT, and can be established through positive nuclear immunohistochemical staining. Although NMC remains an underrecognized malignancy, in recent years there has appeared to be increasing awareness of disease and frequency of diagnosis in adults. To date, a standard treatment for head and neck NMC has not been established and a multimodal approach with systemic chemotherapy, surgery and radiation therapy is currently adopted in clinical practice. Recently, BET inhibitors and histone deacetylase inhibitors have emerged as two promising classes of targeted agents, currently investigated in clinical trials for adults with head and neck NMC. At the same time, combination approaches and novel targeted agents, such as next-generation BET inhibitors and CDK9 inhibitors, have shown preclinical activity. The present review explores the clinical pathological characteristics of NMC of the head and neck and presents the current state of the art on diagnosis, prognosis, and treatment of this rare but lethal disease.

SF2523: Dual PI3K/BRD4 Inhibitor Blocks Tumor Immunosuppression and Promotes Adaptive Immune Responses in Cancer

Macrophages (MΘs) are key immune infiltrates in solid tumors and serve as major drivers behind tumor growth, immune suppression, and inhibition of adaptive immune responses in the tumor microenvironment (TME). Bromodomain and extraterminal (BET) protein, BRD4, which binds to acetylated lysine on histone tails, has recently been reported to promote gene transcription of proinflammatory cytokines but has rarely been explored for its role in IL4-driven MΘ transcriptional programming and MΘ-mediated immunosuppression in the TME. Herein, we report that BET bromodomain inhibitor, JQ1, blocks association of BRD4 with promoters of arginase and other IL4-driven MΘ genes, which promote immunosuppression in TME. Pharmacologic inhibition of BRD4 using JQ1 and/or PI3K using dual PI3K/BRD4 inhibitor SF2523 (previously reported by our group as a potent inhibitor to block tumor growth and metastasis in various cancer models) suppresses tumor growth in syngeneic and spontaneous murine cancer models; reduces infiltration of myeloid-derived suppressor cells; blocks polarization of immunosuppressive MΘs; restores CD8⁺ T-cell activity; and stimulates antitumor immune responses. Finally, our results suggest that BRD4 regulates the immunosuppressive myeloid TME, and BET inhibitors and dual PI3K/BRD4 inhibitors are therapeutic strategies for cancers driven by the MΘ-dependent immunosuppressive TME.

Functional and Mechanistic Interrogation of BET Bromodomain Degraders for the Treatment of Metastatic Castration-resistant Prostate Cancer

PURPOSE

The bromodomain and extraterminal (BET)-containing proteins (BRD2/3/4) are essential epigenetic coregulators for prostate cancer growth. BRD inhibitors have shown promise for treatment of metastatic castration-resistant prostate cancer (mCRPC), and have been shown to function even in the context of resistance to next-generation AR-targeted therapies such as enzalutamide and abiraterone. Their clinical translation, however, has been limited by off-target effects, toxicity, and rapid resistance.

EXPERIMENTAL DESIGN

We have developed a series of molecules that target BET bromodomain proteins through their proteasomal degradation, improving efficacy and specificity of standard inhibitors. We tested their efficacy by utilizing prostate cancer cell lines and patient-derived xenografts, as well as several techniques including RNA-sequencing, mass spectroscopic proteomics, and lipidomics.

RESULTS

BET degraders function in vitro and in vivo to suppress prostate cancer growth. These drugs preferentially affect AR-positive prostate cancer cells (22Rv1, LNCaP, VCaP) over AR-negative cells (PC3 and DU145), and proteomic and genomic mechanistic studies confirm disruption of oncogenic AR and MYC signaling at lower concentrations than BET inhibitors. We also identified increases in polyunsaturated fatty acids (PUFA) and thioredoxin-interacting protein (TXNIP) as potential pharmacodynamics biomarkers for targeting BET proteins.

CONCLUSIONS

Compounds inducing the pharmacologic degradation of BET proteins effectively target the major oncogenic drivers of prostate cancer, and ultimately present a potential advance in the treatment of mCRPC. In particular, our compound dBET-3, is most suited for further clinical development.

The BET-bromodomain inhibitor JQ1 renders neuroblastoma cells more resistant to NK cell-mediated recognition and killing by downregulating ligands for NKG2D and DNAM-1 receptors

Low expression of ligands for NK cell-activating receptors contributes to neuroblastoma (NB) aggressiveness. Recently, we demonstrated that the expression of MYCN, a poor prognosis marker in NB, inversely correlates with that of activating ligands. This indicates that MYCN expression level can predict the susceptibility of NB cells to NK cell-mediated immunotherapy and that its downregulation can be exploited as a novel therapeutic strategy to induce the expression of activating ligands. Here we evaluated the effect of the BET-bromodomain inhibitor JQ1 on the expression of ligands for NK cell-activating receptors in NB cell lines. Although downmodulating MYCN, JQ1 impaired the expression of ligands for NK cell-activating receptors, rendering NB cell lines more resistant to NK cell-mediated killing. The downregulation of activating ligands was due to JQ1-mediated impaired functions of both c-MYC and p53, two transcription factors known to regulate the expression of ULBP1-3 ligands for NKG2D activating receptor. Moreover JQ1 strongly downregulated the levels of ROS, a stress-induced signaling event associated with the induction of ligands for NK cell-activating receptors. These results suggest that the use of JQ1 should be discourage in combination with NK cell-based immunotherapy in a perspective chemotherapeutic treatment of NB. Thus, further investigations, exploiting molecular strategies aimed to boost the NK cell-mediated killing of NB cells, are warranted.

Targeting epigenetic modifications in cancer therapy: erasing the roadmap to cancer

Epigenetic dysregulation is a common feature of most cancers, often occurring directly through alteration of epigenetic machinery. Over the last several years, a new generation of drugs directed at epigenetic modulators have entered clinical development, and results from these trials are now being disclosed. Unlike first-generation epigenetic therapies, these new agents are selective, and many are targeted to proteins which are mutated or translocated in cancer. This review will provide a summary of the epigenetic modulatory agents currently in clinical development and discuss the opportunities and challenges in their development. As these drugs advance in the clinic, drug discovery has continued with a focus on both novel and existing epigenetic targets. We will provide an overview of these efforts and the strategies being employed.

HDAC3 Inhibition Upregulates PD-L1 Expression in B-Cell Lymphomas and Augments the Efficacy of Anti-PD-L1 Therapy

Programmed cell-death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) pathway blockade is a promising therapy for the treatment of advanced cancers, including B-cell lymphoma. The clinical response to PD-1/PD-L1 immunotherapy correlates with PD-L1 levels on tumor cells and other cells in the tumor microenvironment. Hence, it is important to understand the molecular mechanisms that regulate PD-L1 expression. Here, we report that histone deacetylase 3 (HDAC3) is a crucial repressor of PD-L1 transcription in B-cell lymphoma. Pan-HDACs or selective HDAC3 inhibitors could rapidly increase histone acetylation and recruitment of bromodomain protein BRD4 at the promoter region of PD-L1 gene, leading to activation of its transcription. Mechanically, HDAC3 and its putative associated corepressor SMRT were recruited to the PD-L1 promoter by the transcriptional repressor BCL6. In addition, HDAC3 inhibition reduced DNA methyltransferase 1 protein levels to indirectly activate PD-L1 transcription. Finally, HDAC3 inhibition increased PD-L1 expression on dendritic cells in the tumor microenvironment. Combining selective HDAC3 inhibitor with anti-PD-L1 immunotherapy enhanced tumor regression in syngeneic murine lymphoma model. Our findings identify HDAC3 as an important epigenetic regulator of PD-L1 expression and implicate combination of HDAC3 inhibition with PD-1/PD-L1 blockade in the treatment of B-cell lymphomas.

Acetyl-CoA Metabolism Supports Multistep Pancreatic Tumorigenesis

Pancreatic ductal adenocarcinoma (PDA) has a poor prognosis, and new strategies for prevention and treatment are urgently needed. We previously reported that histone H4 acetylation is elevated in pancreatic acinar cells harboring Kras mutations prior to the appearance of premalignant lesions. Because acetyl-CoA abundance regulates global histone acetylation, we hypothesized that altered acetyl-CoA metabolism might contribute to metabolic or epigenetic alterations that promote tumorigenesis. We found that acetyl-CoA abundance is elevated in KRAS-mutant acinar cells and that its use in the mevalonate pathway supports acinar-to-ductal metaplasia (ADM). Pancreas-specific loss of the acetyl-CoA-producing enzyme ATP-citrate lyase (ACLY) accordingly suppresses ADM and tumor formation. In PDA cells, growth factors promote AKT-ACLY signaling and histone acetylation, and both cell proliferation and tumor growth can be suppressed by concurrent BET inhibition and statin treatment. Thus, KRAS-driven metabolic alterations promote acinar cell plasticity and tumor development, and targeting acetyl-CoA-dependent processes exerts anticancer effects. SIGNIFICANCE: Pancreatic cancer is among the deadliest of human malignancies. We identify a key role for the metabolic enzyme ACLY, which produces acetyl-CoA, in pancreatic carcinogenesis. The data suggest that acetyl-CoA use for histone acetylation and in the mevalonate pathway facilitates cell plasticity and proliferation, suggesting potential to target these pathways.See related commentary by Halbrook et al., p. 326.This article is highlighted in the In This Issue feature, p. 305.

Impact of Epigenetic Regulation on Head and Neck Squamous Cell Carcinoma

The most common type of head and neck cancer, head and neck squamous cell carcinoma (HNSCC), can develop therapeutic resistance that complicates its treatment. The 5-y survival rate for HNSCC remains at ~50%, and improving these outcomes requires a better understanding of the pathogenesis of HNSCC. Studies of HNSCC using in vitro, ex vivo, and in vivo approaches provide a novel conceptual framework based on epigenetic mechanisms for developing future clinical applications. Normal oral tissues are influenced by environmental factors that induce pathological changes affecting the network of epigenetic enzymes and signaling pathways to induce HNSCC growth and metastasis. Although various epigenetic regulator families, such as DNA methyltransferases, ten-eleven translocation proteins, histone acetyltransferases, histone deacetylases, BET bromodomain proteins, protein arginine methyltransferases, histone lysine methyltransferases, and histone lysine demethylases, have a role in diverse cancers, specific members have a function in HNSCC. Recently, lysine-specific demethylases have been identified as a potential, attractive, and novel target of HNSCC. Lysine-specific demethylase 1 (LSD1) expression is inappropriately upregulated in HNSCC and an orthotopic HNSCC mouse model. LSD1 can demethylate lysine at specific histone positions to repress gene expression or stimulate transcription, indicating a dual and context-dependent role in transcriptional regulation. Our study showed that LSD1 promotes HNSCC growth and metastasis. Pharmacological attenuation of LSD1 inhibits orthotopic and patient-derived HNSCC xenograft growth-specific target genes and signaling pathways. This review provides recent evidence demonstrating the function of epigenetic regulator enzymes in HNSCC progression, including potential therapeutic applications for such enzymes in combination and immunotherapy.

HDAC3 modulates cancer immunity via increasing PD-L1 expression in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the second leading cause of cancer-related deaths worldwide. Despite immune checkpoints based immunotherapy highlights a new therapeutic strategy and achieves a remarkable therapeutic effect in various types of malignant tumors. Pancreatic cancer is one of the non-immunogenic cancers and is resistant to immunotherapy. Programmed death ligand 1 (PD-L1) is expressed on the surface of tumor cells and its level is a key determinant of the checkpoint immunotherapy efficacy. Here, we reported that the specific inhibitor of histone deacetylase 3 (HDAC3) decreased the protein and mRNA level of PD-L1 in pancreatic cancer cells. Furthermore, we showed that HDAC3 was critical for PD-L1 regulation and positively correlated with PD-L1 in PDAC patient specimens. Finally, we demonstrated that HDAC3/signal transducer and activator of transcription 3 (STAT3) pathway transcriptionally regulated PD-L1 expression. Collectively, our data contributes to a better understanding of the function of HDAC3 in cancer immunity and the regulatory mechanism of PD-L1. More importantly, these data suggest that the HDAC3 inhibitors might be used to improve immunotherapy in pancreatic cancer.

Therapeutic targeting of immune checkpoints with small molecule inhibitors

Immune checkpoints are known to contribute to tumor progression by enhancing cancer's ability to evade the immune system and metastasize. Immunotherapies, including monoclonal antibodies, have been developed to target specific immunosuppressive molecules on the membranes of cancer cells and have proven revolutionary in the field of oncology. Recently, small molecule inhibitors (SMIs) have gained increased attention in cancer research with potential applications in immunotherapy. SMIs have desirable benefits over large-molecule inhibitors, such as monoclonal antibodies, including greater cell permeability, organ specificity, longer half-lives, cheaper production costs, and the possibility for oral administration. This paper will review the mechanisms by which noteworthy and novel immune checkpoints contribute to tumor progression, and how they may be targeted by SMIs and epigenetic modifiers to offer possible adjuvants to established therapeutic regimens. SMIs target immune checkpoints in several ways, such as blocking signaling between tumorigenic factors, building immune tolerance, and direct inhibition via epigenetic repression of immune inhibitory molecules. Further investigation into combination therapies utilizing SMIs and conventional cancer therapies will uncover new treatment options that may provide better patient outcomes across a range of cancers.

Emerging roles of and therapeutic strategies targeting BRD4 in cancer

The Bromodomain and Extra-terminal (BET) family of proteins were first recognized as important epigenetic regulators in inflammatory processes; however, there is increasing evidence to support the notion that BET proteins also play a critical role in 'reading' chromatin and recruiting chromatin-regulating enzymes to control gene expression in a number of pathologic processes, including cancer. To this end, the mechanisms by which BET proteins regulate chromatin remodeling and promote tumor-associated inflammation have been heavily studied over the past decade. This article to review the biology of BET protein dysfunction in promoting tumor-associated inflammation and cancer progression and the application of small molecule inhibitors that target specific BET proteins, alone or in combination with immunomodulatory agents as a novel therapeutic strategy for cancer patients.

BET and EZH2 Inhibitors: Novel Approaches for Targeting Cancer

PURPOSE OF REVIEW

Increasing evidence suggests that epigenome plays a central role in cancer development making it a promising target for anticancer treatments. Here, we review two new classes of epigenome-targeting agents: the bromodomain and extraterminal domain proteins (BET) inhibitors and the enhancer of zeste homolog (EZH2) inhibitors.

RECENT FINDINGS

Clinical research evaluating BET and EZH2 inhibitors is still at an early stage; however, both classes of drugs have demonstrated activity among different hematologic malignancies and solid tumors. Several studies on BETi and EZH2i are ongoing to better define their potential role in cancer treatment, which patients are most likely to benefit and if the association with other drugs can improve their efficacy.

Combinatorial Approach to Improve Cancer Immunotherapy: Rational Drug Design Strategy to Simultaneously Hit Multiple Targets to Kill Tumor Cells and to Activate the Immune System

Cancer immunotherapy, including immune checkpoint blockade and adoptive CAR T-cell therapy, has clearly established itself as an important modality to treat melanoma and other malignancies. Despite the tremendous clinical success of immunotherapy over other cancer treatments, this approach has shown substantial benefit to only some of the patients while the rest of the patients have not responded due to immune evasion. In recent years, a combination of cancer immunotherapy together with existing anticancer treatments has gained significant attention and has been extensively investigated in preclinical or clinical studies. In this review, we discuss the therapeutic potential of novel regimens combining immune checkpoint inhibitors with therapeutic interventions that (1) increase tumor immunogenicity such as chemotherapy, radiotherapy, and epigenetic therapy; (2) reverse tumor immunosuppression such as TAMs, MDSCs, and Tregs targeted therapy; and (3) reduce tumor burden and increase the immune effector response with rationally designed dual or triple inhibitory chemotypes.

Overexpressed histone acetyltransferase 1 regulates cancer immunity by increasing programmed death-ligand 1 expression in pancreatic cancer

BACKGROUND

Pancreatic ductal adenocarcinoma is one of the leading causes of cancer-related death worldwide. Immune checkpoint blockade therapy, including anti-PD-1 and anti-PD-L1, is a new therapeutic strategy for cancer treatment but the monotherapy with PD-L1 inhibitors for pancreatic cancer is almost ineffective for pancreatic cancer. Thus, exploring the regulatory mechanism of PD-L1 in cancer cells, especially in pancreatic cancer cells, is one of the key strategies to improving cancer patient response to PD-L1 blockade therapy. Histone acetyltransferase 1(HAT1) is a classic type B histone acetyltransferase and the biological role of HAT1 in pancreatic cancer is unclear.

METHODS

The clinical relevance of HAT1 was examined by the GEPIA web tool, Western blotting and immunohistochemistry of pancreatic cancer tissue microarray slides. Tumor cell motility was investigated by MTS assay, colony formation assay and xenografts. The relationship between HAT1 and PD-L1 was examined by Western blot analysis, RT-qPCR and immunohistochemistry.

RESULTS

HAT1 was upregulated in PDAC and associated with poor prognosis in PDAC patients. The knockdown of HAT1 decreased the proliferation of pancreatic cancer cells in vivo and in vitro. Strikingly, we showed that HAT1 transcriptionally regulated PD-L1, and this process was mainly mediated by BRD4 in pancreatic cancer. The knockdown of HAT1 improved the efficacy of immune checkpoint blockade by decreasing the PD-L1.

CONCLUSIONS

The recognition of HAT1 in regulating tumor cell proliferation and cancer immunity indicated that HAT1 might be employed as a new diagnostic and prognostic marker and a predictive marker for pancreatic cancer therapy, especially in immune checkpoint blockade therapy. Targeting HAT1 highlights a novel therapeutic approach to overcome immune evasion by tumor cells.

Clinicopathological and Preclinical Findings of NUT Carcinoma: A Multicenter Study

BACKGROUND

NUT carcinoma is a rare aggressive disease caused by BRD4/3-NUT fusion, and C-MYC upregulation plays a key role in the pathogenesis. Here, we report on the clinicopathological characteristics of Korean patients with NUT carcinoma and the in vitro efficacy of MYC-targeting agents against patient-derived NUT carcinoma cell lines.

MATERIALS AND METHODS

Thirteen patients with NUT carcinoma were evaluated for p53, C-MYC, epidermal growth factor receptor (EGFR), HER2, and programmed cell death ligand 1 (PD-L1) by immunohistochemistry. The half maximal inhibitory concentration (IC₅₀) values of NUT carcinoma cell lines (SNU-2972-1, SNU-3178S, HCC2429, and Ty-82) were determined using MYC-targeting agents, including bromodomain and extraterminal (BET) inhibitors (I-BET, OTX-015, AZD5153) and histone deacetylase (HDAC) inhibitors (vorinostat, romidepsin, panobinostat, CUDC-907).

RESULTS

Primary tumor sites included head and neck (n = 9) and lung (n = 4). The patient age ranged from 8 to 73 years with the male/female ratio of 1.2:1. Nine patients died at 3-23.6 months (median, 10.6) after diagnosis. Eight patients had been misdiagnosed initially with other diseases. One patient with metastatic NUT carcinoma who received mass excision plus metastasectomy followed by chemoradiotherapy was a long-term survivor (>27 months). Although expressions of C-MYC (8/12, 73%) and p53 (12/12, 100%) were commonly observed, EGFR, HER2, and PD-L1 expressions were observed in 2 of 7 (29%), 2 of 8 (25%), and 1 of 12 (8.3%) patients, respectively. BET and HDAC inhibitors showed variable but limited in vitro efficacy. However, a dual HDAC/PI3K inhibitor, CUDC-907, was most potent against NUT carcinoma cells, with an IC₅₀ of 5.5-9.0 pmol/L. Consistent with these findings, kinome short interfering RNA screening showed a positive hit for PI3KCA in NUT carcinoma cells. Panobinostat (IC₅₀, 0.4-1.3 nmol/L) and a bivalent BET inhibitor, AZD5153 (IC₅₀, 3.7-8.2 nmol/L), also showed remarkable efficacies.

CONCLUSION

East Asian patients with NUT carcinoma showed dismal survival outcomes like Western patients, and CUDC-907 might be promising in NUT carcinoma treatment.

IMPLICATIONS FOR PRACTICE

NUT carcinoma (NC) is a disease caused by BRD-NUT fusion leading to C-MYC upregulation. NC is often misdiagnosed and very aggressive, requiring development of effective therapeutic strategy. This article presents the clinicopathological features of the largest series of NCs in East Asians and preclinical sensitivities to MYC-targeting agents in NC cell lines. Patients with NC had grave outcomes and poor response to treatment. Among MYC-targeting agents, including BET and HDAC inhibitors, CUDC-907 (a dual PI3K/HDAC inhibitor) was most effective against NC cells, followed by panobinostat (an HDAC inhibitor) and AZD5153 (a bivalent BET inhibitor). CUDC-907 might be promising in NC treatment.

Targeting c-Myc: JQ1 as a promising option for c-Myc-amplified esophageal squamous cell carcinoma

c-Myc amplification-induced cell cycle dysregulation is a common cause for esophageal squamous cell carcinoma (ESCC), but no approved targeted drug is available so far. The bromodomain inhibitor JQ1, which targets c-Myc, exerts anti-tumor activity in multiple cancers. However, the role of JQ1 in ESCC remains unknown. In this study, we reported that JQ1 had potent anti-proliferative effects on ESCC cells in both time- and dose-dependent manners by inducing cell cycle arrest at G1 phase, cell apoptosis, and the mesenchymal-epithelial transition. Follow-up studies revealed that both c-Myc/cyclin/Rb and PI3K/AKT signaling pathways were inactivated by JQ1, as indicated by the downregulation of c-Myc, cyclin A/E, and phosphorylated Rb, AKT and S6. Tumor suppression induced by JQ1 in c-Myc amplified or highly expressed xenografts was higher than that in xenografts with low expression, suggesting its potential role in prediction. In conclusion, targeting c-Myc by JQ1 could cause significant tumor suppression in ESCC both in vitro and in vivo. Also, c-Myc amplification or high expression might serve as a potential biomarker and provide a promising therapeutic option for ESCC.

Therapeutic Cancer Vaccines-T Cell Responses and Epigenetic Modulation

There is great interest in developing efficient therapeutic cancer vaccines, as this type of therapy allows targeted killing of tumor cells as well as long-lasting immune protection. High levels of tumor-infiltrating CD8⁺ T cells are associated with better prognosis in many cancers, and it is expected that new generation vaccines will induce effective production of these cells. Epigenetic mechanisms can promote changes in host immune responses, as well as mediate immune evasion by cancer cells. Here, we focus on epigenetic modifications involved in both vaccine-adjuvant-generated T cell immunity and cancer immune escape mechanisms. We propose that vaccine-adjuvant systems may be utilized to induce beneficial epigenetic modifications and discuss how epigenetic interventions could improve vaccine-based therapies. Additionally, we speculate on how, given the unique nature of individual epigenetic landscapes, epigenetic mapping of cancer progression and specific subsequent immune responses, could be harnessed to tailor therapeutic vaccines to each patient.

Elevated H3K27me3 levels sensitize osteosarcoma to cisplatin

BACKGROUND

In osteosarcoma (OS), chemotherapy resistance has become one of the greatest issues leading to high mortality among patients. However, the mechanisms of drug resistance remain elusive, limiting therapeutic efficacy. Here, we set out to explore the relationship between dynamic histone changes and the efficacy of cisplatin against OS.

RESULTS

First, we found two histone demethylases associated with histone H3 lysine 27 trimethylation (H3K27me3) demethylation, KDM6A, and KDM6B that were upregulated after cisplatin treatment. Consistent with the clinical data, cisplatin-resistant OS specimens showed lower H3K27me3 levels than sensitive specimens. Then, we evaluated the effects of H3K27me3 alteration on OS chemosensitivity. In vitro inhibition of the histone methyltransferase EZH2 in OS cells decreased H3K27me3 levels and led to cisplatin resistance. Conversely, inhibition of the demethylases KDM6A and KDM6B increased H3K27me3 levels in OS and reversed cisplatin resistance in vitro and in vivo. Mechanistically, with the help of RNA sequencing (RNAseq), we found that PRKCA and MCL1 directly participated in the process by altering H3K27me3 on their gene loci, ultimately inactivating RAF/ERK/MAPK cascades and decreasing phosphorylation of BCL2.

CONCLUSIONS

Our study reveals a new epigenetic mechanism of OS resistance and indicates that elevated H3K27me3 levels can sensitize OS to cisplatin, suggesting a promising new strategy for the treatment of OS.

HDAC is indispensable for IFN-γ-induced B7-H1 expression in gastric cancer

Background

B7 homolog 1 (B7-H1) overexpression on tumor cells is an important mechanism of immune evasion in gastric cancer (GC). Elucidation of the regulation of B7-H1 expression is urgently required to guide B7-H1-targeted cancer therapy. Interferon gamma (IFN-γ) is thought to be the main driving force behind B7-H1 expression, and epigenetic factors including histone acetylation are recently linked to the process. Here, we investigated the potential role of histone deacetylase (HDAC) in IFN-γ-induced B7-H1 expression in GC. The effect of Vorinostat (SAHA), a small molecular inhibitor of HDAC, on tumor growth and B7-H1 expression in a mouse GC model was also evaluated.

Results

RNA-seq data from The Cancer Genome Atlas revealed that expression of B7-H1, HDAC1–3, 6–8, and 10 and SIRT1, 3, 5, and 6 was higher, and expression of HDAC5 and SIRT4 was lower in GC compared to that in normal gastric tissues; that HDAC3 and HDAC1 expression level significantly correlated with B7-H1 in GC with a respective r value of 0.42 (p < 0.001) and 0.21 (p < 0.001). HDAC inhibitor (Trichostatin A, SAHA, and sodium butyrate) pretreatment suppressed IFN-γ-induced B7-H1 expression on HGC-27 cells. HDAC1 and HDAC3 gene knockdown had the same effect. SAHA pretreatment or HDAC knockdown resulted in impaired IFN-γ signaling, demonstrated by the reduction of JAK2, p-JAK1, p-JAK2, and p-STAT1 expression and inefficient STAT1 nuclear translocation. Furthermore, SAHA pretreatment compromised IFN-γ-induced upregulation of histone H3 lysine 9 acetylation level in B7-H1 gene promoter. In the grafted mouse GC model, SAHA treatment suppressed tumor growth, inhibited B7-H1 expression, and elevated the percentage of tumor-infiltrating CD8+ T cells.

Conclusion

HDAC is indispensable for IFN-γ-induced B7-H1 in GC. The study suggests the possibility of targeting B7-H1 using small molecular HDAC inhibitors for cancer treatment.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0589-6) contains supplementary material, which is available to authorized users.

Immunotherapy and Epigenetic Pathway Modulation in Glioblastoma Multiforme

Glioblastoma Multiforme (GBM) is the most common malignant primary brain tumor. Despite aggressive multimodality treatment it remains one of the most challenging and intractable cancers (1]. While current standard of care treatment for GBM is maximal safe surgical resection, systemic chemotherapy with Temozolimide (TMZ), and radiation therapy, the current prognosis of GBM patients remains poor, with a median overall survival of 12–15 months (2, 3). Therefore, other treatments are needed to provide better outcomes for GBM patients. Immunotherapy is one of the most promising new cancer treatment approaches. Immunotherapy drugs have obtained regulatory approval in a variety of cancers including melanoma (4), Hodgkin lymphoma (5), and non-small cell lung cancer (6). The basis of immunotherapy in cancer treatment is linked to stimulating the immune system to recognize cancer cells as foreign, thereby leading to the eventual elimination of the tumor. One form of immunotherapy utilizes vaccines that target tumor antigens (7), while other approaches utilize T-cells in patients to stimulate them to attack tumor cells (8). Despite intensive efforts all approaches have not been overtly successful (9), suggesting that we need to better understand the underlying biology of tumor cells and their environment as they respond to immunotherapy. Recent studies have elucidated epigenetic pathway regulation of GBM tumor expansion (10), suggesting that combined epigenetic pathway inhibition with immunotherapy may be feasible. In this review, we discuss current GBM clinical trials and how immune system interactions with epigenetic pathways and signaling nodes can be delineated to uncover potential combination therapies for this incurable disease.

Bromodomain Drug Discovery - the Past, the Present, and the Future

With the bromodomain (BRD) inhibitor JQ1, a remarkable success story of BRD4 as a novel drug target has been set off that yielded many anti-cancer drugs that are now in clinical trials. But not all of the great prospects of BRDs as drug targets may become true. First evaluations of ongoing clinical trials revealed that treatment with BET-inhibitors can be accompanied with significant toxic side effects and the validation of the therapeutic benefit of BET-inhibitors compared to existing therapies is still pending. New strategies that may overcome possible obstacles in BRD drug discovery include combination therapies with other agents, dual target inhibitors, and proteolysis targeting chimeras (PROTACs). Furthermore, non-BET proteins seem promising drug targets as well. Most recently, BRDs have been identified as putative targets to treat parasitic diseases such as malaria. Milestones in BRD drug discovery are reviewed and promising new developments are evaluated.

Emerging role of precision medicine in biliary tract cancers

Biliary tracts cancers (BTCs) are a diverse group of aggressive malignancies with an overall poor prognosis. Genomic characterization has uncovered many putative clinically actionable aberrations that can also facilitate the prognostication of patients. As such, comprehensive genomic profiling is playing a growing role in the clinical management of BTCs. Currently however, there is only one precision medicine approved by the US Food and Drug Administration (FDA) for the treatment of BTCs. Herein, we highlight the prevalence and prognostic, diagnostic, and predictive significance of recurrent mutations and other genomic aberrations with current clinical implications or emerging relevance to clinical practice. Some ongoing clinical trials, as well as future areas of exploration for precision oncology in BTCs are highlighted.

The application of nanotechnology in immune checkpoint blockade for cancer treatment

Cancer immunotherapy, which could utilize the host's immune system to kill tumor cells, has great potential in long-term inhibition of tumor growth and recurrence compared to chemotherapy and radiotherapy. As we know, tumors exhibit powerful adaption to escape the destruction of immune system at the late stage of diseases due to overactivation of immune checkpoint pathways which function as natural "brakes" for immune responses. The newly emerging immune checkpoint inhibitors are regarded as the breakthrough for cancer immunotherapy as they can re-boost the host's immune system by restoring T cells function and promoting cytotoxic T lymphocytes (CTLs) responses. However, there is still scope for improvement in enhancing the clinical efficacy and reducing side effects of these immune modulators. In this review, we mainly introduce the basic mechanisms of the immune checkpoint pathways and outline the recent successes of immune checkpoint blockade (ICB) therapy in combination with nanoparticle delivery system. Furthermore, the underexplored potential in application of nanotechnology to enhance the efficacy of immune checkpoint therapy and overcome the limits of immune checkpoint inhibitors is also discussed.

Biochemical Aspects of PD-L1 Regulation in Cancer Immunotherapy

PD-L1, frequently expressed in human cancers, engages with PD-1 on immune cells and contributes to cancer immune evasion. As such, antibodies blocking the PD-1/PD-L1 interaction reactivate cytotoxic T cells to eradicate cancer cells. However, a majority of cancer patients fail to respond to PD-1/PD-L1 blockade with unclear underlying mechanism(s). Recent studies revealed that PD-L1 expression levels on tumor cells might affect the clinical response to anti-PD-1/PD-L1 therapies. Hence, understanding molecular mechanisms for controlling PD-L1 expression will be important to improve the clinical response rate and efficacy of PD-1/PD-L1 blockade. In this review, we primarily focus on summarizing PD-L1 regulation and its potential roles in regulating antitumor immune response, with purpose to optimize anti-PD-1/PD-L1 therapies, benefiting a wider cancer patient population.

Regulatory mechanisms of PD-L1 expression in cancer cells

Immunotherapy targeting the PD-L1/PD-1 pathway using antibodies is effective in the clinical treatment of a multitude of cancers. This makes research of the regulatory mechanisms of PD-1 expression in cancer cells intriguing. PD-L1 expression can be categorized into inducible expression, attributed to extrinsic factors in the microenvironment, and constitutive expression, attributed to intrinsic cancer-driving gene alteration. The mechanisms of PD-L1 expression in cancer cells operate at multiple levels, including gene amplification, chromatin modification, transcription, posttranscription, translation and posttranslation. Moreover, some open questions in this field that need to be answered in future research are proposed. Studies of regulatory mechanisms of PD-L1 expression pave the way for the application of more effective approaches in the future of cancer immunotherapy.

Interplay between interferon regulatory factor 1 and BRD4 in the regulation of PD-L1 in pancreatic stellate cells

The fibrotic reaction is a characteristic feature of human pancreatic ductal adenocarcinoma (PDAC) tumors. It is associated with activation and proliferation of pancreatic stellate cells (PSCs), which are key regulators of fibrosis in vivo. While there is increasing interest in the regulation of PD-L1 expression in cancer and immune cells, the expression and regulation of PD-L1 in other stromal cells, such as PSCs, has not been fully evaluated. Here we show that PSCs in vitro express higher PD-L1 mRNA and protein levels compared to the levels present in PDAC cells. We show that inhibitors targeting bromodomain and extra-terminal (BET) proteins and BRD4 knockdown decrease interferon-γ (IFN-γ)-induced PD-L1 expression in PSCs. We also show that c-MYC, one of the well-established targets of BET inhibitors, does not mediate IFN-γ-regulated PD-L1 expression in PSCs. Instead we show that interferon regulatory factor 1 (IRF1) mediates IFN-γ-induced PD-L1 expression in PSCs. Finally, while we show that BET inhibitors do not regulate IFN-γ-induced IRF1 expression in PSCs, BET inhibitors decrease binding of IRF1 and BRD4 to the PD-L1 promoter. Together, these results demonstrate the interplay between IRF1 and BRD4 in the regulation of PD-L1 in PSCs.

Green Tea Catechin Is an Alternative Immune Checkpoint Inhibitor that Inhibits PD-L1 Expression and Lung Tumor Growth

The anticancer activity of immune checkpoint inhibitors is attracting attention in various clinical sites. Since green tea catechin has cancer-preventive activity in humans, whether green tea catechin supports the role of immune checkpoint inhibitors was studied. We here report that (−)-epigallocatechin gallate (EGCG) inhibited programmed cell death ligand 1 (PD-L1) expression in non–small-cell lung cancer cells, induced by both interferon (IFN)-γ and epidermal growth factor (EGF). The mRNA and protein levels of IFN-γ–induced PD-L1 were reduced 40–80% after pretreatment with EGCG and green tea extract (GTE) in A549 cells, via inhibition of JAK2/STAT1 signaling. Similarly, EGF-induced PD-L1 expression was reduced about 37–50% in EGCG-pretreated Lu99 cells through inhibition of EGF receptor/Akt signaling. Furthermore, 0.3% GTE in drinking water reduced the average number of tumors per mouse from 4.1 ± 0.5 to 2.6 ± 0.4 and the percentage of PD-L1 positive cells from 9.6% to 2.9%, a decrease of 70%, in lung tumors of A/J mice given a single intraperitoneal injection of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In co-culture experiments using F10-OVA melanoma cells and tumor-specific CD3+ T cells, EGCG reduced PD-L1 mRNA expression about 30% in F10-OVA cells and restored interleukin-2 mRNA expression in tumor-specific CD3+ T cells. The results show that green tea catechin is an immune checkpoint inhibitor.

Targeting the Microenvironment in High Grade Serous Ovarian Cancer

Cancer⁻stroma interactions play a key role in cancer progression and response to standard chemotherapy. Here, we provide a summary of the mechanisms by which the major cellular components of the ovarian cancer (OC) tumor microenvironment (TME) including cancer-associated fibroblasts (CAFs), myeloid, immune, endothelial, and mesothelial cells potentiate cancer progression. High-grade serous ovarian cancer (HGSOC) is characterized by a pro-inflammatory and angiogenic signature. This profile is correlated with clinical outcomes and can be a target for therapy. Accumulation of malignant ascites in the peritoneal cavity allows for secreted factors to fuel paracrine and autocrine circuits that augment cancer cell proliferation and invasiveness. Adhesion of cancer cells to the mesothelial matrix promotes peritoneal tumor dissemination and represents another attractive target to prevent metastasis. The immunosuppressed tumor milieu of HGSOC is permissive for tumor growth and can be modulated therapeutically. Results of emerging preclinical and clinical trials testing TME-modulating therapeutics for the treatment of OC are highlighted.

BET Bromodomain Inhibition Cooperates with PD-1 Blockade to Facilitate Antitumor Response in Kras-Mutant Non-Small Cell Lung Cancer

KRAS mutation is present in approximately 30% of human lung adenocarcinomas. Although recent advances in targeted therapy have shown great promise, effective targeting of KRAS remains elusive, and concurrent alterations in tumor suppressors render KRAS-mutant tumors even more resistant to existing therapies. Contributing to the refractoriness of KRAS-mutant tumors are immunosuppressive mechanisms, such as increased presence of suppressive regulatory T cells (Treg) in tumors and elevated expression of the inhibitory receptor PD-1 on tumor-infiltrating T cells. Treatment with BET bromodomain inhibitors is beneficial for hematologic malignancies, and they have Treg-disruptive effects in a non-small cell lung cancer (NSCLC) model. Targeting PD-1-inhibitory signals through PD-1 antibody blockade also has substantial therapeutic impact in lung cancer, although these outcomes are limited to a minority of patients. We hypothesized that the BET bromodomain inhibitor JQ1 would synergize with PD-1 blockade to promote a robust antitumor response in lung cancer. In the present study, using Kras^+/LSL-G12D ; Trp53^L/L (KP) mouse models of NSCLC, we identified cooperative effects between JQ1 and PD-1 antibody. The numbers of tumor-infiltrating Tregs were reduced and activation of tumor-infiltrating T cells, which had a T-helper type 1 (Th1) cytokine profile, was enhanced, underlying their improved effector function. Furthermore, lung tumor-bearing mice treated with this combination showed robust and long-lasting antitumor responses compared with either agent alone, culminating in substantial improvement in the overall survival of treated mice. Thus, combining BET bromodomain inhibition with immune checkpoint blockade offers a promising therapeutic approach for solid malignancies such as lung adenocarcinoma. Cancer Immunol Res; 6(10); 1234-45. ©2018 AACR.

BET proteins in abnormal metabolism, inflammation, and the breast cancer microenvironment

Obesity and its associated pathology Type 2 diabetes are two chronic metabolic and inflammatory diseases that promote breast cancer progression, metastasis, and poor outcomes. Emerging critical opinion considers unresolved inflammation and abnormal metabolism separately from obesity; settings where they do not co-occur can inform disease mechanism. In breast cancer, the tumor microenvironment is often infiltrated with T effector and T regulatory cells programmed by metabolic signaling. The pathways by which tumor cells evade immune surveillance, immune therapies, and take advantage of antitumor immunity are poorly understood, but likely depend on metabolic inflammation in the microenvironment. Immune functions are abnormal in metabolic disease, and lessons learned from preclinical studies in lean and metabolically normal environments may not translate to patients with obesity and metabolic disease. This problem is made more urgent by the rising incidence of breast cancer among women who are not obese but who have metabolic disease and associated inflammation, a phenotype common in Asia. The somatic BET proteins, comprising BRD2, BRD3, and BRD4, are new critical regulators of metabolism, coactivate transcription of genes that encode proinflammatory cytokines in immune cell subsets infiltrating the microenvironment, and could be important targets in breast cancer immunotherapy. These transcriptional coregulators are well known to regulate tumor cell progression, but only recently identified as critical for metabolism, metastasis, and expression of immune checkpoint molecules. We consider interrelationships among metabolism, inflammation, and breast cancer aggressiveness relevant to the emerging threat of breast cancer among women with metabolic disease, but without obesity.

Genetic, transcriptional and post-translational regulation of the programmed death protein ligand 1 in cancer: biology and clinical correlations

The programmed death protein 1 (PD-1) and its ligand (PD-L1) represent a well-characterized immune checkpoint in cancer, effectively targeted by monoclonal antibodies that are approved for routine clinical use. The regulation of PD-L1 expression is complex, varies between different tumor types and occurs at the genetic, transcriptional and post-transcriptional levels. Copy number alterations of PD-L1 locus have been reported with varying frequency in several tumor types. At the transcriptional level, a number of transcriptional factors seem to regulate PD-L1 expression including HIF-1, STAT3, NF-κΒ, and AP-1. Activation of common oncogenic pathways such as JAK/STAT, RAS/ERK, or PI3K/AKT/MTOR, as well as treatment with cytotoxic agents have also been shown to affect tumoral PD-L1 expression. Correlative studies of clinical trials with PD-1/PD-L1 inhibitors have so far shown markedly discordant results regarding the value of PD-L1 expression as a marker of response to treatment. As the indications for immune checkpoint inhibition broaden, understanding the regulation of PD-L1 in cancer will be of utmost importance for defining its role as predictive marker but also for optimizing strategies for cancer immunotherapy. Here, we review the current knowledge of PD-L1 regulation, and its use as biomarker and as therapeutic target in cancer.

IL-6 augments IL-4-induced polarization of primary human macrophages through synergy of STAT3, STAT6 and BATF transcription factors

Macrophages in the tumor microenvironment respond to complex cytokine signals. How these responses shape the phenotype of tumor-associated macrophages (TAMs) is incompletely understood. Here we explored how cytokines of the tumor milieu, interleukin (IL)-6 and IL-4, interact to influence target gene expression in primary human monocyte-derived macrophages (hMDMs). We show that dual stimulation with IL-4 and IL-6 synergistically modified gene expression. Among the synergistically induced genes are several targets with known pro-tumorigenic properties, such as CC-chemokine ligand 18 (CCL18), transforming growth factor alpha (TGFA) or CD274 (programmed cell death 1 ligand 1 (PD-L1)). We found that transcription factors of the signal transducer and activator of transcription (STAT) family, STAT3 and STAT6 bind regulatory regions of synergistically induced genes in close vicinity. STAT3 and STAT6 co-binding further induces the basic leucine zipper ATF-like transcription factor (BATF), which participates in synergistic induction of target gene expression. Functional analyses revealed increased MCF-7 and MDA-MB 231 tumor cell motility in response to conditioned media from co-treated hMDMs compared to cells incubated with media from single cytokine-treated hMDMs. Flow cytometric analysis of T cell populations upon co-culture with hMDMs polarized by different cytokines indicated that dual stimulation promoted immunosuppressive properties of hMDMs in a PD-L1-dependent manner. Analysis of clinical data revealed increased expression of BATF together with TAM markers in tumor stroma of breast cancer patients as compared to normal breast tissue stroma. Collectively, our findings suggest that IL-4 and IL-6 cooperate to alter the human macrophage transcriptome, endowing hMDMs with pro-tumorigenic properties.

SWI/SNF Complexes in Ovarian Cancer: Mechanistic Insights and Therapeutic Implications

Ovarian cancer remains the most lethal gynecologic malignancy in the developed world. Despite the unprecedented progress in understanding the genetics of ovarian cancer, cures remain elusive due to a lack of insight into the mechanisms that can be targeted to develop new therapies. SWI/SNF chromatin remodeling complexes are genetically altered in approximately 20% of all human cancers. SWI/SNF alterations vary in different histologic subtypes of ovarian cancer, with ARID1A mutation occurring in approximately 50% of ovarian clear cell carcinomas. Given the complexity and prevalence of SWI/SNF alterations, ovarian cancer represents a paradigm for investigating the molecular basis and exploring therapeutic strategies for SWI/SNF alterations. This review discusses the recent progress in understanding SWI/SNF alterations in ovarian cancer and specifically focuses on: (i) ARID1A mutation in endometriosis-associated clear cell and endometrioid histologic subtypes of ovarian cancer; (ii) SMARCA4 mutation in small cell carcinoma of the ovary, hypercalcemic type; and (iii) amplification/upregulation of CARM1, a regulator of BAF155, in high-grade serous ovarian cancer. Understanding the molecular underpinning of SWI/SNF alterations in different histologic subtypes of ovarian cancer will provide mechanistic insight into how these alterations contribute to ovarian cancer. Finally, the review discusses how these newly gained insights can be leveraged to develop urgently needed therapeutic strategies in a personalized manner.

BET bromodomain inhibitor JQ1 preferentially suppresses EBV-positive nasopharyngeal carcinoma cells partially through repressing c-Myc

The management of advanced nasopharyngeal carcinoma (NPC) remains a challenge. The ubiquitous nature of Epstein–Barr virus (EBV) infection in nonkeratinizing NPC has forced us to investigate novel drugs for NPC in the presence of EBV. In this study, we performed a small-scale screening of a library of compounds that target epigenetic regulators in paired EBV-positive and EBV-negative NPC cell lines. We found that bromodomain and extra-terminal (BET) inhibitor JQ1 preferentially inhibits the growth of EBV-positive NPC cells. JQ1 induces apoptosis, decreases cell proliferation and enhances the radiosensitivity in NPC cells, especially EBV-positive cells. Significantly, JQ1-induced cell death is c-Myc-dependent. Notably, RNA-seq analysis demonstrated that JQ1 represses TP63, TP53 and their targets. JQ1 also lessens the expression of PD-L1 in NPC. Moreover, the high potency of JQ1 in NPC cells was further confirmed in vivo in CNE2-EBV+ tumor-bearing mice. These findings indicate that JQ1 is a promising therapeutic candidate for advanced NPC.

Modeling combination therapy for breast cancer with BET and immune checkpoint inhibitors

CTLA-4 is an immune checkpoint expressed on active anticancer T cells. When it combines with its ligand B7 on dendritic cells, it inhibits the activity of the T cells. The Bromo- and Extra-Terminal (BET) protein family includes proteins that regulate the expression of key oncogenes and antiapoptotic proteins. BET inhibitor (BETi) has been shown to reduce the expression of MYC by suppressing its transcription factors and to down-regulate the hypoxic transcriptome response to VEGF-A. This paper develops a mathematical model of the treatment of cancer by combination therapy of BETi and CTLA-4 inhibitor. The model shows that the two drugs are positively correlated in the sense that the tumor volume decreases as the dose of each of the drugs is increased. The model also considers the effect of the combined therapy on levels of myeloid-derived suppressor cells (MDSCs) and the overexpression of TNF-α, which may predict gastrointestinal side effects of the combination.

BET inhibitors: a novel epigenetic approach

Epigenetics has been defined as 'the structural adaptation of chromosomal regions so as to register, signal or perpetuate altered activity states.' Currently, several classes of anticancer drugs function at the epigenetic level, including inhibitors of DNA methyltransferase, histone deacetylase (HDAC), lysine-specific demethylase 1, zeste homolog 2, and bromodomain and extra-terminal motif (BET) proteins.BET proteins have multiple functions, including the initiation and elongation of transcription and cell cycle regulation. In recent years, inhibitors of BET proteins have been developed as anticancer agents. These inhibitors exhibit selectivity for tumor cells by preferentially binding to superenhancers, noncoding regions of DNA critical for the transcription of genes that determine a cell's identity. Preclinical research on BET inhibitors has identified them as a potential means of targeting MYC.Early clinical trials with BET inhibitors have had mixed results, with few responses in both hematologic and solid tumors that tend to be short-lived. Toxicities have included severe, thrombocytopenia, fatigue, nausea, vomiting, and diarrhea; GI side-effects, fatigue, and low-grade dysgeusia have limited compliance. However, preclinical data suggest that BET inhibitors may have a promising future in combination with other agents. They appear to be able to overcome resistance to targeted agents and have strong synergy with immune checkpoint inhibitors as well as with multiple epigenetic agents, particularly HDAC inhibitors. In many instances, BET and HDAC inhibitors were synergistic at reduced doses, suggesting a potential means of avoiding the overlapping toxicities of the two drug classes.BET inhibitors provide a novel approach to epigenetic anticancer therapy. However, to date they appear to have limited efficacy as single agents. A focus on BET inhibitors in combination with other drugs such as targeted and/or as other epigenetic agents is warranted, due to limited monotherapy activity, including pharmacodynamic correlatives differential activity amongst select drug combinations.