Noncanonical Functions of the Polycomb Group Protein EZH2 in Breast Cancer

Innovative sarcoma therapy using multifaceted nano-PROTAC-induced EZH2 degradation and immunity enhancement

Sarcomas are highly malignant tumors characterized by their heterogeneity and resistance to conventional therapies, which significantly limit treatment options. EZH2 is highly expressed in sarcomas, but targeting it is difficult. In this study, we uncovered the non-canonical transcriptional mechanisms of EZH2 in sarcoma and highlighted the essential role of EZH2 in regulating YAP1 through non-canonical transcriptional pathways in the progression of sarcoma. Building on this, we developed YM@VBM, a novel and versatile nano-PROTAC (proteolysis-targeting chimera), by integrating a polyphenol-vanadium oxide system with the EZH2 degrader YM281 PROTAC, encapsulated in methoxy polyethylene glycol-NH2 to enhance biocompatibility. To further facilitate targeted drug delivery to tumors, YM@VBM nano-PROTACs were incorporated into microneedle patches. Our engineered YM@VBM exhibited multiple functionalities, including the peroxidase-like activity to generate reactive oxygen species, depletion of glutathione, and photothermal effects, specifically targeting sarcoma characteristics. YM@VBM significantly enhanced targeting efficacy via inducing potent EZH2 degradation. Most importantly, it can also activate anti-tumor immunity via excluding myeloid-derived suppressor cells, maturing dendritic cells, and forming tertiary lymphoid structures. Hence, we reveal that YM@VBM presents a promising treatment strategy for sarcoma, offering a multifaceted approach to combat this challenging malignancy.

BRD9 functions as a methylarginine reader to regulate AKT-EZH2 signaling

Recognition of methylarginine marks by effector proteins ("readers") is a critical link between arginine methylation and various cellular processes. Recently, we identified methylation of AKT1 at arginine-391 (R391), but the reader for this methylation has yet to be characterized. Here, we show that bromodomain-containing protein 9 (BRD9), a reader of acetylated lysine, unexpectedly recognizes methylated R391 of AKT1 through an aromatic cage in its bromodomain. Disrupting the methylarginine reader function of BRD9 suppresses AKT activation and tumorigenesis. RNA sequencing data show that BRD9 and AKT coregulate a hallmark transcriptional program in part through enhancer of zeste homolog 2 (EZH2)-mediated methylation of histone-3 lysine-27. We also find that inhibitors of BRD9 and EZH2 display synergistic effects on suppression of cell proliferation and tumor growth. Collectively, our study reveals a previously unknown function of BRD9 and a potential therapeutic strategy for cancer treatment by combining BRD9 and EZH2 inhibitors.

ABL Kinases Modulate EZH2 Phosphorylation and Signaling in Metastatic Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) remains a leading cause of cancer associated deaths in women owing to its highly metastatic potential and limited treatment options. Recent studies have shown that expression of proteins associated with epigenetic regulation of gene expression are associated with metastatic relapse, however targeting epigenetic regulatory proteins has not resulted in effective therapies for TNBC in the clinic. The ABL tyrosine kinases promote metastasis of breast cancer cells in mouse models. However, a role of ABL kinases in the regulation of epigenetic processes in solid tumor metastasis remains unexplored. Here we show that inactivation of ABL kinases in bone metastatic TNBC cells led to a significant enrichment in gene signatures associated with the PRC2 protein complex, revealing a functional link between ABL kinases and the PRC2 complex. ABL inactivation promotes EZH2-T487 phosphorylation through the regulation of a FAK-CDK1 signaling axis. We find that phosphorylated EZH2 T487 or a phosphomimic EZH2 T487D mutant exhibit increased binding to non-canonical binding partners of EZH2 including c-MYC and ZMYND8. Notably, we identify a therapeutic vulnerability in TNBC cells whereby combination treatment with ABL allosteric inhibitors and EZH2 inhibitors elicits a synergistic decrease in TNBC cell survival in vitro, and impairs TNBC metastasis, prolonging survival of tumor-bearing mice treated with the combination therapy.

One Sentence Summary

ABL Kinases indirectly impact EZH2 catalytic activity by blocking a signaling cascade that leads to changes in the phosphorylation, protein interactions, and function of the PRC2 catalytic component EZH2 in TNBC.

G9a/GLP Modulators: Inhibitors to Degraders

Histone methylation, a crucial aspect of epigenetics, intricately involves specialized enzymes such as G9a, a histone methyltransferase (HMT) catalyzing the methylation of histone H3 lysine 9 (H3K9) and H3K27. Apart from histone modification, G9a regulates essential cellular processes such as deoxyribonucleic acid (DNA) replication, damage repair, and gene expression via modulating DNA methylation patterns. The dysregulation and overexpression of G9a are intricately linked to cancer initiation, progression, and metastasis, making it a compelling target for anticancer therapy. Moreover, aberrant levels of H3K9 dimethylation were identified in Alzheimer's disease (AD), broadening the scope of epigenetic implications across various pathologies. The quest for potent therapy has resulted in the identification of numerous G9a inhibitors/degraders, each demonstrating the potential to disrupt aberrant signaling pathways. This perspective provides valuable insights into the evolving potential and advancement of G9a modulators as promising candidates for treating a spectrum of diseases.

Expression patterns of H3K27me3 for differentiation of breast fibroadenomas and phyllodes tumors

Phyllodes tumors (PTs) are rare breast tumors showing overlapping features with fibroadenomas (FAs). Diagnosis on small biopsies is challenging. New diagnostic markers are needed. Here we evaluated immunohistochemical staining of histone 3 trimethyl-lysine-27 (H3K27me3) as a diagnostic and prognostic marker in a series of PTs. Surgically removed PTs at our institution (September 1990 and July 2022) and control FAs. Tissue micro-arrays (4 cores, 2 mm Ø) stained with H3K27me3, and scored with QuPath-derived H-score. Fisher exact test, Mann-Whitney U-test and chi-squared test used for group comparison. ROC analysis applied to define cutoffs. Cox proportional hazards models were used for assessing disease-free survival (DFS), overall survival (OS), and disease-specific survival (DSS) in PTs. We included 81 patients with PTs and 44 patients with FAs. QuPath-derived H-scores of stromal H3K27me3 were statically significantly lower in PTs than in FAs (p < 0.001). We identified exploratory cutoffs to discriminate FAs from benign and malignant PTs (AUC = 0.78 and 0.73, respectively). No associations between DFS, OS, or DSS and H3K27me3 expression were found. H3K27me3 expression differs between FAs and PTs, indicating potential as diagnostic marker, but it is not predictive for DFS, OS or DSS in PTs. Further validation is needed.

EZH2-associated tumor malignancy: A prominent target for cancer treatment

The discussion in this review centers around the significant relationships between EZH2 and the initiation, progression, metastasis, metabolism, drug resistance, and immune regulation of cancer. Polycomb group (PcG) proteins, which encompass two primary Polycomb repressor complexes (PRC1 and PRC2), have been categorized. PRC2 consists mainly of four subunits, namely EZH2, EED, SUZ12, and RbAp46/48. As the crucial catalytic component within the PRC2 complex, EZH2 plays a pivotal role in controlling a wide range of biological processes. Overexpression/mutations of EZH2 have been detected in a wide variety of tumors. Several mechanisms of EZH regulation have been identified, including regulation EZH2 mRNA by miRNAs, LncRNAs, accessibility to DNA via DNA-binding proteins, post-translational modifications, and transcriptional regulation. EZH2 signaling triggers cancer progression and may intervene with anti-tumor immunity; therefore it has charmed attention as an effective therapeutic target in cancer therapy. Numerous nucleic acid-based therapies have been used in the modification of EZH2. In addition to gene therapy approaches, pharmaceutical compounds can be used to target the EZH2 signaling pathway in the treatment of cancer. EZH2-associated tumor cells and immune cells enhance the effects of the immune response in a variety of human malignancies. The combination of epigenetic modifying agents, such as anti-EZH2 compounds with immunotherapy, could potentially be efficacious even in the context of immunosuppressive tumors. Summary, understanding the mechanisms underlying resistance to EZH2 inhibitors may facilitate the development of novel drugs to prevent or treat relapse in treated patients.

RBM39 Enhances Cholangiocarcinoma Growth Through EZH2-mediated WNT7B/β-catenin Pathway

BACKGROUND & AIMS

The RNA-binding motif protein 39 (RBM39) functions as both an RNA-binding protein and a splicing factor in a variety of cancer types. However, the function of RBM39 in cholangiocarcinoma (CCA) remains undefined. In this study, we aimed to investigate the role of RBM39 in CCA and explore its potential as a therapeutic target.

METHODS

The expression of RBM39 in CCA was investigated by analyzing human CCA tumor specimens. CRISPR/Cas9 or shRNA-mediated depletion of RBM39 was performed in vitro and in vivo to document the oncogenic role of RBM39 in CCA. The anti-tumor effect of the RBM39 inhibitor, Indisulam, in combination with the EZH2 degrader MS177 was assessed in vitro and in vivo.

RESULTS

RBM39 is significantly increased in human CCA tissues and associated with a poor prognosis in patients with CCA. Depletion of RBM39 by CRISPR/Cas9 or shRNA inhibited CCA cell proliferation in vitro and prevented CCA development and tumor growth in mice. Mechanistically, our results showed that depletion of RBM39 suppressed EZH2 expression via disrupting its mRNA splicing. RBM39-regulated EZH2 controls WNT7B/β-catenin activity. Pharmacological co-targeting of RBM39 (with Indisulam) and EZH2 (with MS177) resulted in a synergistic antitumor effect, both in vitro and in vivo.

CONCLUSION

This study discloses a novel RBM39-EZH2-β-catenin signaling axis that is crucial for CCA growth. Our findings suggest that simultaneous inhibition of RBM39 and EZH2 presents a promising therapeutic strategy for CCA treatment.

Immunomodulator-Derived Nanoparticles Induce Neuroprotection and Regulatory T Cell Action to Alleviate Parkinsonism

Post-translational modification, mitochondrial abruptions, neuroinflammation, and α-synuclein (α-Syn) aggregation are considered as major causes of Parkinson's disease (PD) pathogenesis. The recent literature highlights neuroimmune cross talk and the negative role of immune effector T (Teff) and positive regulation by regulatory T (Treg) cells in PD treatment. Herein, a strategy to endow Treg action paves the path for development of PD treatment. Thus, we explored the neuroprotective efficiency of the immunomodulator and PP2A (protein phosphatase 2) activator, FTY720 nanoparticles in in vivo experimental PD models. Repurposing of FTY720 for PD is known due to its protective effect by reducing PD and its camouflaged role in endowing EZH2-mediated epigenetic regulation of PD. EZH2-FOXP3 interaction is necessary for the neuroprotective Treg cell activity. Therefore, we synthesized FTY720 nanoparticles to improve FTY720 protective efficacy in an in vivo PD model to explore the PP2A mediated signaling. We confirmed the formation of FTY720NPs, and the results of the behavioral and protein expression study showed the significant neuroprotective efficiency of our nanoformulations. In the exploration of neuroprotective mechanism, several lines of evidence confirmed FTY720NPs mediated induction of PP2A/EZH2/FOXP3 signaling in the induction of Treg cells effect in in vivo PD treatment. In summary, our nanoformulations have novel potential to alleviate PD by inducing PP2A-induced epigenetic regulation-mediated neuroimmunomodulation at the clinical setup.

Mechanistic insights into cisplatin response in breast tumors: Molecular determinants and drug/nanotechnology-based therapeutic opportunities

Breast cancer continues to be a major global health challenge, driving the need for effective therapeutic strategies. Cisplatin, a powerful chemotherapeutic agent, is widely used in breast cancer treatment. However, its effectiveness is often limited by systemic toxicity and the development of drug resistance. This review examines the molecular factors that influence cisplatin response and resistance, offering crucial insights for the scientific community. It highlights the significance of understanding cisplatin resistance's genetic and epigenetic contributors, which could lead to more personalized treatment approaches. Additionally, the review explores innovative strategies to counteract cisplatin resistance, including combination therapies, nanoparticle-based drug delivery systems, and targeted therapies. These approaches are under intensive investigation and promise to enhance breast cancer treatment outcomes. This comprehensive discussion is a valuable resource to advance breast cancer therapeutics and address the challenge of cisplatin resistance.

Integrative analysis of ultra-deep RNA-seq reveals alternative promoter usage as a mechanism of activating oncogenic programmes during prostate cancer progression

Transcription factor (TF) proteins regulate gene activity by binding to regulatory regions, most importantly at gene promoters. Many genes have alternative promoters (APs) bound by distinct TFs. The role of differential TF activity at APs during tumour development is poorly understood. Here we show, using deep RNA sequencing in 274 biopsies of benign prostate tissue, localized prostate tumours and metastatic castration-resistant prostate cancer, that AP usage increases as tumours progress and APs are responsible for a disproportionate amount of tumour transcriptional activity. Expression of the androgen receptor (AR), the key driver of prostate tumour activity, is correlated with elevated AP usage. We identified AR, FOXA1 and MYC as potential drivers of AP activation. DNA methylation is a likely mechanism for AP activation during tumour progression and lineage plasticity. Our data suggest that prostate tumours activate APs to magnify the transcriptional impact of tumour drivers, including AR and MYC.

EZH2: The roles in targeted therapy and mechanisms of resistance in breast cancer

Drug resistance presents a formidable challenge in the realm of breast cancer therapy. Accumulating evidence suggests that enhancer of zeste homolog 2 (EZH2), a component of the polycomb repressive complex 2 (PRC2), may serve as a key regulator in controlling drug resistance. EZH2 overexpression has been observed in breast cancer and many other malignancies, showing a strong correlation with poor outcomes. This review aims to summarize the mechanisms by which EZH2 regulates drug resistance, with a specific focus on breast cancer, in order to provide a comprehensive understanding of the underlying molecular processes. Additionally, we will discuss the current strategies and outcomes of targeting EZH2 using both single agents and combination therapies, with the goal of offering improved guidance for the clinical treatment of breast cancer patients who have developed drug resistance.

Genetic analysis of PALB2 gene WD40 domain in canine mammary tumour patients

BACKGROUND

DNA repair mechanisms are essential for tumorigenesis and disruption of HR mechanism is an important predisposing factor of human breast cancers (BC). PALB2 is an important part of the HR. There are similarities between canine mammary tumours (CMT) and BCs. As its human counterpart, PALB2 mutations could be a predisposing factor of CMT.

OBJECTIVES

In this study, we aimed to investigate the impacts of PALB2 variants on tumorigenesis and canine mammary tumor (CMT) malignancy.

METHODS

We performed Sanger sequencing to detect germline mutations in the WD40 domain of the canine PALB2 gene in CMT patients. We conducted in silico analysis to investigate the variants, and compared the germline PALB2 mutations in humans that cause breast cancer (BC) with the variants detected in dogs with CMT.

RESULTS

We identified an intronic (c.3096+8C>G) variant, two exonic (p.A1050V and p.R1354R) variants, and a 3' UTR variant (c.4071T>C). Of these, p.R1354R and c.4071T>C novel variants were identified for the first time in this study. We found that the p.A1050V mutation had a significant effect. However, we could not determine sufficient similarity due to the differences in nucleotide/amino acid sequences between two species. Nonetheless, possible variants of human sequences in the exact location as their dog counterparts are associated with several cancer types, implying that the variants could be crucial for tumorigenesis in dogs. Our results did not show any effect of the variants on tumor malignancy.

CONCLUSIONS

The current project is the first study investigating the relationship between the PALB2 gene WD40 domain and CMTs. Our findings will contribute to a better understanding of the pathogenic mechanism of the PALB2 gene in CMTs. In humans, variant positions in canines have been linked to cancer-related phenotypes such as familial BC, endometrial tumor, and hereditary cancer predisposition syndrome. The results of bioinformatics analyses should be investigated through functional tests or case-control studies.

Molecular hybridization: a powerful tool for multitarget drug discovery

INTRODUCTION

The current drug discovery paradigm of 'one drug, multiple targets' has gained attention from both the academic medicinal chemistry community and the pharmaceutical industry. This is in response to the urgent need for effective agents to treat multifactorial chronic diseases. The molecular hybridization strategy is a useful tool that has been widely explored, particularly in the last two decades, for the design of multi-target drugs.

AREAS COVERED

This review examines the current state of molecular hybridization in guiding the discovery of multitarget small molecules. The article discusses the design strategies and target selection for a multitarget polypharmacology approach to treat various diseases, including cancer, Alzheimer's disease, cardiac arrhythmia, endometriosis, and inflammatory diseases.

EXPERT OPINION

Although the examples discussed highlight the importance of molecular hybridization for the discovery of multitarget bioactive compounds, it is notorious that the literature has focused on specific classes of targets. This may be due to a deep understanding of the pharmacophore features required for target binding, making targets such as histone deacetylases and cholinesterases frequent starting points. However, it is important to encourage the scientific community to explore diverse combinations of targets using the molecular hybridization strategy.

Discovery of a novel, highly potent EZH2 PROTAC degrader for targeting non-canonical oncogenic functions of EZH2

Aberrant expression of EZH2, the main catalytic subunit of PRC2, has been implicated in numerous cancers, including leukemia, breast, and prostate. Recent studies have highlighted non-catalytic oncogenic functions of EZH2, which EZH2 catalytic inhibitors cannot attenuate. Therefore, proteolysis-targeting chimera (PROTAC) degraders have been explored as an alternative therapeutic approach to suppress both canonical and non-canonical oncogenic activity. Here we present MS8847, a novel, highly potent EZH2 PROTAC degrader that recruits the E3 ligase von Hippel-Lindau (VHL). MS8847 degrades EZH2 in a concentration-, time-, and ubiquitin-proteasome system (UPS)-dependent manner. Notably, MS8847 induces superior EZH2 degradation and anti-proliferative effects in MLL-rearranged (MLL-r) acute myeloid leukemia (AML) cells compared to previously published EZH2 PROTAC degraders. Moreover, MS8847 degrades EZH2 and inhibits cell growth in triple-negative breast cancer (TNBC) cell lines, displays efficacy in a 3D TNBC in vitro model, and has a pharmacokinetic (PK) profile suitable for in vivo efficacy studies. Overall, MS8847 is a valuable chemical tool for the biomedical community to investigate canonical and non-canonical oncogenic functions of EZH2.

Design, synthesis, and evaluation of VHL-based EZH2 degraders for breast cancer

EZH2 (enhancer of zeste homolog 2) is one of the most important histone methyltransferases (HMTs), and overexpression of EZH2 can lead to proliferation, migration and angiogenesis of tumor cells. But most of EZH2 inhibitors are only effective against some hematologic malignancies and have poor efficacy against solid tumors. Here, we report the design, synthesis, and evaluation of highly potent proteolysis targeting chimeric (PROTACs) small molecules targeting EZH2. We developed a potent and effective EZH2 degrader P4, which effectively induced EZH2 protein degradation and inhibited breast cancer cell growth. Further studies showed that P4 can significantly decrease the degree of H3K27me3 in MDA-MB-231 cell line, induce apoptosis and G0/G1 phase arrest in Pfeiffer and MDA-MB-231 cell lines. Therefore, P4 is a potential anticancer molecule for breast cancer treatment.

Non-canonical functions of EZH2 in cancer

Mutations in chromatin modifying genes frequently occur in many kinds of cancer. Most mechanistic studies focus on their canonical functions, while therapeutic approaches target their enzymatic activity. Recent studies, however, demonstrate that non-canonical functions of chromatin modifiers may be equally important and therapeutically actionable in different types of cancer. One epigenetic regulator that demonstrates such a dual role in cancer is the histone methyltransferase EZH2. EZH2 is a core component of the polycomb repressive complex 2 (PRC2), which plays a crucial role in cell identity, differentiation, proliferation, stemness and plasticity. While much of the regulatory functions and oncogenic activity of EZH2 have been attributed to its canonical, enzymatic activity of methylating lysine 27 on histone 3 (H3K27me3), a repressive chromatin mark, recent studies suggest that non-canonical functions that are independent of H3K27me3 also contribute towards the oncogenic activity of EZH2. Contrary to PRC2's canonical repressive activity, mediated by H3K27me3, outside of the complex EZH2 can directly interact with transcription factors and oncogenes to activate gene expression. A more focused investigation into these non-canonical interactions of EZH2 and other epigenetic/chromatin regulators may uncover new and more effective therapeutic strategies. Here, we summarize major findings on the non-canonical functions of EZH2 and how they are related to different aspects of carcinogenesis.

An EZH2-NF-κB regulatory axis drives expression of pro-oncogenic gene signatures in triple negative breast cancer

The histone methyltransferase EZH2 has been studied most extensively in the context of PRC2-dependent gene repression. Accumulating evidence indicates non-canonical functions for EZH2 in cancer contexts including promoting paradoxical gene expression through interactions with transcription factors, including NF-κB in triple negative breast cancer (TNBC). We profile EZH2 and NF-κB factor co-localization and positive gene regulation genome-wide, and define a subset of NF-κB targets and genes associated with oncogenic functions in TNBC that is enriched in patient datasets. We demonstrate interaction between EZH2 and RelA requiring the recently identified transactivation domain (TAD) which mediates EZH2 recruitment to, and activation of certain NF-κB-dependent genes, and supports downstream migration and stemness phenotypes in TNBC cells. Interestingly, EZH2-NF-κB positive regulation of genes and stemness does not require PRC2. This study provides new insight into pro-oncogenic regulatory functions for EZH2 in breast cancer through PRC2-independent, and NF-κB-dependent regulatory mechanisms.

Dual inhibition of EZH2 and G9A/GLP histone methyltransferases by HKMTI-1-005 promotes differentiation of acute myeloid leukemia cells

All-trans-retinoic acid (ATRA)-based differentiation therapy of acute promyelocytic leukemia (APL) represents one of the most clinically effective examples of precision medicine and the first example of targeted oncoprotein degradation. The success of ATRA in APL, however, remains to be translated to non-APL acute myeloid leukemia (AML). We previously showed that aberrant histone modifications, including histone H3 lysine 4 (H3K4) and lysine 27 (H3K27) methylation, were associated with this lack of response and that epigenetic therapy with small molecule inhibitors of the H3K4 demethylase LSD1/KDM1A could reprogram AML cells to respond to ATRA. Serving as the enzymatic component of Polycomb Repressive Complex 2, EZH2/KMT6A methyltransferase plays a critical role in normal hematopoiesis by affecting the balance between self-renewal and differentiation. The canonical function of EZH2 is methylation of H3K27, although important non-canonical roles have recently been described. EZH2 mutation or deregulated expression has been conclusively demonstrated in the pathogenesis of AML and response to treatment, thus making it an attractive therapeutic target. In this study, we therefore investigated whether inhibition of EZH2 might also improve the response of non-APL AML cells to ATRA-based therapy. We focused on GSK-343, a pyridone-containing S-adenosyl-L-methionine cofactor-competitive EZH2 inhibitor that is representative of its class, and HKMTI-1-005, a substrate-competitive dual inhibitor targeting EZH2 and the closely related G9A/GLP H3K9 methyltransferases. We found that treatment with HKMTI-1-005 phenocopied EZH2 knockdown and was more effective in inducing differentiation than GSK-343, despite the efficacy of GSK-343 in terms of abolishing H3K27 trimethylation. Furthermore, transcriptomic analysis revealed that in contrast to treatment with GSK-343, HKMTI-1-005 upregulated the expression of differentiation pathway genes with and without ATRA, while downregulating genes associated with a hematopoietic stem cell phenotype. These results pointed to a non-canonical role for EZH2, which was supported by the finding that EZH2 associates with the master regulator of myeloid differentiation, RARα, in an ATRA-dependent manner that was enhanced by HKMTI-1-005, possibly playing a role in co-regulator complex exchange during transcriptional activation. In summary, our results strongly suggest that addition of HKMTI-1-005 to ATRA is a new therapeutic approach against AML that warrants further investigation.

Discovery of IHMT-337 as a potent irreversible EZH2 inhibitor targeting CDK4 transcription for malignancies

Enhancer of zeste homolog 2 (EZH2), an enzymatic subunit of PRC2 complex, plays an important role in tumor development and progression through its catalytic and noncatalytic activities. Overexpression or gain-of-function mutations of EZH2 have been significantly associated with tumor cell proliferation of triple-negative breast cancer (TNBC) and diffuse large B-cell lymphoma (DLBCL). As a result, it has gained interest as a potential therapeutic target. The currently available EZH2 inhibitors, such as EPZ6438 and GSK126, are of benefit for clinical using or reached clinical trials. However, certain cancers are resistant to these enzymatic inhibitors due to its noncatalytic or transcriptional activity through modulating nonhistone proteins. Thus, it may be more effective to synergistically degrade EZH2 in addition to enzymatic inhibition. Here, through a rational design and chemical screening, we discovered a new irreversible EZH2 inhibitor, IHMT-337, which covalently bounds to and degrades EZH2 via the E3 ligase CHIP-mediated ubiquitination pathway. Moreover, we revealed that IHMT-337 affects cell cycle progression in TNBC cells through targeting transcriptional regulating of CDK4, a novel PRC2 complex- and enzymatic activity-independent function of EZH2. More significantly, our compound inhibits both DLBCL and TNBC cell proliferation in different preclinical models in vitro and in vivo. Taken together, our findings demonstrate that in addition to enzymatic inhibition, destroying of EZH2 by IHMT-337 could be a promising therapeutic strategy for TNBC and other malignancies that are independent of EZH2 enzymatic activity.

Polycomb Repressive Complex 2 in Oncology

Dynamic regulation of the chromatin state by Polycomb Repressive Complex 2 (PRC2) provides an important mean for epigenetic gene control that can profoundly influence normal development and cell lineage specification. PRC2 and PRC2-induced methylation of histone H3 lysine 27 (H3K27) are critically involved in a wide range of DNA-templated processes, which at least include transcriptional repression and gene imprinting, organization of three-dimensional chromatin structure, DNA replication and DNA damage response and repair. PRC2-based genome regulation often goes wrong in diseases, notably cancer. This chapter discusses about different modes-of-action through which PRC2 and EZH2, a catalytic subunit of PRC2, mediate (epi)genomic and transcriptomic regulation. We will also discuss about how alteration or mutation of the PRC2 core or axillary component promotes oncogenesis, how post-translational modification regulates functionality of EZH2 and PRC2, and how PRC2 and other epigenetic pathways crosstalk. Lastly, we will briefly touch on advances in targeting EZH2 and PRC2 dependence as cancer therapeutics.

EZH2 Protein Expression in Estrogen Receptor Positive Invasive Breast Cancer Treated With Neoadjuvant Endocrine Therapy: An Exploratory Study of Association With Tumor Response

INTRODUCTION

Neoadjuvant endocrine therapy (NET) can be used to treat estrogen receptor positive (ER+) invasive breast cancer (IBC). Tumors with Ki67>10% after 2 to 4 weeks of NET are considered resistant to endocrine therapy. Enhancer of Zeste Homolog 2 (EZH2) is a targetable oncoprotein and overexpression in ER+ IBC has been linked to resistance to endocrine therapy. We examined whether EZH2 expression levels in ER+ IBC could be used to predict response to NET.

MATERIALS AND METHODS

We retrospectively identified 46 patients with localized ER+ HER2/neu negative IBC treated with a minimum of 4 weeks of NET. We quantified EZH2 nuclear expression in pretherapy core biopsies using a score that included intensity and percent of cells staining. Ki67 was evaluated in both pretherapy core biopsies and posttherapy tumor resections and scored according to the guidelines of the International Ki67 Working Groups, with a global weighted score. Ki67≤10% after NET was considered endocrine responsive. Logistic regression analysis was performed to determine the association between EZH2 expression and response to NET.

RESULTS

We found significant associations of tumor grade ( P =0.011), pretherapy Ki67 ( P =0.003), and EZH2 ( P <0.001), with response to NET. On logistic regression adjusted for tumor grade and pretherapy Ki67, increased EZH2 scores were associated with decreased odds of endocrine responsiveness, defined as posttreatment Ki67≤10% (odds ratio=0.976, 95% CI, 0.956 to 0.997; P =0.026). In addition, with EZH2 score in the model, associations of tumor grade and pretreatment Ki67 with posttreatment Ki67≤10% response to NET became not significant.

CONCLUSIONS

Our results suggest that EZH2 might be a useful biomarker to predict response to NET.

Targeting Triple-Negative Breast Cancer by a Novel Proteolysis Targeting Chimera Degrader of Enhancer of Zeste Homolog 2

Enhancer of zeste homolog 2 (EZH2), a catalytic subunit of polycomb repressive complex 2 (PRC2), is overexpressed in triple-negative breast cancer (TNBC), correlating with poor prognosis. However, EZH2 catalytic inhibitors are ineffective in suppressing the growth of TNBC cells that are dependent on EZH2. Knockdown of EZH2 inhibits the proliferation of these cells, suggesting that EZH2 protein overexpression but not its catalytic activity is critical for driving TNBC progression. Several proteolysis targeting chimera (PROTAC) degraders of EZH2, including the von Hippel-Lindau (VHL)-recruiting PROTAC YM281, have been reported. However, the effects of these EZH2 PROTACs in TNBC cells were not investigated. Here, we report the discovery and characterization of a novel, potent, and selective EZH2 PROTAC degrader, MS8815 (compound 16), which induced robust EZH2 degradation in a concentration-, time-, and proteasome-dependent manner in TNBC cells. Importantly, 16 effectively suppressed the cell growth in multiple TNBC cell lines and primary patient TNBC cells.

EZH2 Protein Expression in Triple-negative Breast Cancer Treated With Neoadjuvant Chemotherapy: An Exploratory Study of Association With Tumor Response and Prognosis

INTRODUCTION

Neaodjuvant chemotherapy is used to treat high risk triple-negative breast cancer (TNBC). Residual cancer burden (RCB) is used to predict risk of relapse after neoadjuvant chemotherapy (NAC); however, it cannot predict disease recurrence with certainty. EZH2 is a targetable oncogenic protein overexpressed in TNBC and associated with metastasis and stem cell expansion. We quantified EZH2 protein expression in TNBC before NAC to examine potential utility as a predictive and prognostic biomarker.

MATERIALS AND METHODS

We retrospectively identified 63 patients with localized TNBC treated with NAC. We quantified EZH2 nuclear expression in pretherapy biopsies using a score which included intensity and percent of positive cells at each intensity. EZH2 expression was evaluated as a continuous variable and dichotomized at a score of 210. Logistic regression analysis was used to determine association between EZH2 expression and RCB, tumor-infiltrating lymphocytes, clinicopathologic features and disease-free survival.

RESULTS

There was no significant association between EZH2 score and posttreatment RCB class evaluated as a continuous variable (P=0.831) or dichotomized at 210 (P=0.546). On multivariable logistic regression, adjusted for covariates including RCB, EZH2 >210 was associated with development of metastasis (odds ratio=14.35, 95% confidence interval: 2.69-76.66; P=0.002). Logistic regression was run with EZH2 scores as a continuous variable and increased EZH2 score was associated with metastasis (odds ratio=1.10, 95% confidence interval: 1.00-1.03; P=0.047).

CONCLUSION

In our study of TNBC treated with NAC, high EZH2 expression in pretherapy core biopsies was significantly associated with metastatic recurrence independent of RCB. The potential value of EZH2 as a biomarker to improve stratification of outcome after NAC should be explored further.

TPH1 and 5-HT7 Receptor Overexpression Leading to Gemcitabine-Resistance Requires Non-Canonical Permissive Action of EZH2 in Pancreatic Ductal Adenocarcinoma

In the present study, we investigated the regulatory mechanisms underlying overexpression of EZH2, tryptophan hydroxylase 1 (TPH1), and 5-HT7, in relation to gemcitabine resistance and CSC survival in PDAC cells. In aggressive PANC-1 and MIA PaCa-2 cells, knock-down (KD) of EZH2, TPH1, or HTR7 induced a decrease in CSCs and recovery from gemcitabine resistance, while preconditioning of less aggressive Capan-1 cells with 5-HT induced gemcitabine resistance with increased expression of EZH2, TPH1, and 5-HT7. Such effects of the gene KD and 5-HT treatment were mediated through PI3K/Akt and JAK2/STAT3 signaling pathways. EZH2 KD or GSK-126 (an EZH2 inhibitor) inhibited activities of these signaling pathways which altered nuclear level of NF-kB, Sp1, and p-STAT3, accompanied by downregulation of TPH1 and 5-HT7. Co-immunoprecipation with EZH2 and pan-methyl lysine antibodies revealed that auto-methylated EZH2 served as a scaffold for binding with methylated NF-kB and Sp1 as well as unmethylated p-STAT3. Furthermore, the inhibitor of EZH2, TPH1, or 5-HT7 effectively regressed pancreatic tumor growth in a xenografted mouse tumor model. Overall, the results revealed that long-term exposure to 5-HT upregulated EZH2, and the noncanonical action of EZH2 allowed the expression of TPH1-5-HT7 axis leading to gemcitabine resistance and CSC population in PDAC.

Proteomic and molecular dynamic investigations of PTM-induced structural fluctuations in breast and ovarian cancer

Post-translational processing leads to conformational changes in protein structure that modulate molecular functions and change the signature of metabolic transformations and immune responses. Some post-translational modifications (PTMs), such as phosphorylation and acetylation, are strongly related to oncogenic processes and malignancy. This study investigated a PTM pattern in patients with gender-specific ovarian or breast cancer. Proteomic profiling and analysis of cancer-specific PTM patterns were performed using high-resolution UPLC-MS/MS. Structural analysis, topology, and stability of PTMs associated with sex-specific cancers were analyzed using molecular dynamics modeling. We identified highly specific PTMs, of which 12 modified peptides from eight distinct proteins derived from patients with ovarian cancer and 6 peptides of three proteins favored patients from the group with breast cancer. We found that all defined PTMs were localized in the compact and stable structural motifs exposed outside the solvent environment. PTMs increase the solvent-accessible surface area of the modified moiety and its active environment. The observed conformational fluctuations are still inadequate to activate the structural degradation and enhance protein elimination/clearance; however, it is sufficient for the significant modulation of protein activity.