WDR5 Supports an N-Myc Transcriptional Complex That Drives a Protumorigenic Gene Expression Signature in Neuroblastoma

WD repeat domain 5 (WDR5) inhibitors: a patent review (2016-present)

INTRODUCTION

WDR5 is an epigenetic scaffolding protein that has attracted significant interest as an anti-cancer drug target, especially in MLL-rearranged leukemias. The most druggable 'WIN-site' on WDR5, which tethers WDR5 to chromatin, has been successfully targeted with multiple classes of exquisitely potent small-molecule protein-protein interaction inhibitors. Earlier progress has also been made on the development of WDR5 degraders and inhibitors at the 'WBM-site' on the opposite face of WDR5.

AREAS COVERED

Based on an international survey of the patent literature using SciFinder from 2016-2024, herein we provide a comprehensive account of the chemical matter targeting WDR5, with a particular focus on proprietary compounds that are underreported in the existing academic literature. Our survey illuminates challenges for the field to overcome: a broad lack of chemical diversity, confusion about the molecular mechanism of WIN-site inhibitors, a paucity of brain-penetrant scaffolds despite emerging evidence of activity in brain cancers, sparse pharmacokinetic, metabolic, and disposition characterization, and the absence of safety or efficacy data in humans.

EXPERT OPINION

It is our opinion that the best-in-class WIN-site inhibitors (from the imidazole class) merit advancement into clinical testing, likely against leukemia, which should provide much-needed clarity about the exciting but unproven potential of WDR5 as a next-generation therapeutic target.

Crystal structures of DCAF1-PROTAC-WDR5 ternary complexes provide insight into DCAF1 substrate specificity

Proteolysis-targeting chimeras (PROTACs) have been explored for the degradation of drug targets for more than two decades. However, only a handful of E3 ligase substrate receptors have been efficiently used. Downregulation and mutation of these receptors would reduce the effectiveness of such PROTACs. We recently developed potent ligands for DCAF1, a substrate receptor of EDVP and CUL4 E3 ligases. Here, we focus on DCAF1 toward the development of PROTACs for WDR5, a drug target in various cancers. We report four DCAF1-based PROTACs with endogenous and exogenous WDR5 degradation effects and high-resolution crystal structures of the ternary complexes of DCAF1-PROTAC-WDR5. The structures reveal detailed insights into the interaction of DCAF1 with various WDR5-PROTACs, indicating a significant role of DCAF1 loops in providing needed surface plasticity, and reflecting the mechanism by which DCAF1 functions as a substrate receptor for E3 ligases with diverse sets of substrates.

MBD2 regulates the progression and chemoresistance of cholangiocarcinoma through interaction with WDR5

BACKGROUND

Cholangiocarcinoma (CCA) is a highly malignant, rapidly progressing tumor of the bile duct. Owing to its chemoresistance, it always has an extremely poor prognosis. Therefore, detailed elucidation of the mechanisms of chemoresistance and identification of therapeutic targets are still needed.

METHODS

We analyzed the expression of MBD2 (Methyl-CpG-binding domain 2) in CCA and normal bile duct tissues using the public database and immunohistochemistry (IHC). The roles of MBD2 in CCA cell proliferation, migration, and chemoresistance ability were validated through CCK-8, plate cloning assay, wound healing assays and xenograft mouse model. In addition, we constructed a primary CCA mouse model to further confirm the effect of MBD2. RNA-seq and co-IP-MS were used to identify the mechanisms by how MBD2 leads to chemoresistance.

RESULTS

MBD2 was upregulated in CCA. It promoted the proliferation, migration and chemoresistance of CCA cells. Mechanistically, MBD2 directly interacted with WDR5, bound to the promoter of ABCB1, promoted the trimethylation of H3K4 in this region through KMT2A, and activated the expression of ABCB1. Knocking down WDR5 or KMT2A blocked the transcriptional activation of ABCB1 by MBD2. The molecular inhibitor MM-102 targeted the interaction of WDR5 with KMT2A. MM-102 inhibited the expression of ABCB1 in CCA cells and decreased the chemoresistance of CCA to cisplatin.

CONCLUSION

MBD2 promotes the progression and chemoresistance of CCA through interactions with WDR5. MM-102 can effectively block this process and increase the sensitivity of CCA to cisplatin.

Activation of the Snail transcription factor induces Mdm2 gene expression

Epithelial-like tumor cells can become metastatic by undergoing molecular and phenotypic reprogramming in a process referred to as epithelial-to-mesenchymal transition (EMT). In response to EMT genes that promote migration and condition the tumor microenvironment to permit intravasation into the bloodstream, dissemination and extravasation into new organs are induced. While the mutant p53 has been implicated in extravasation, one negative regulator of p53, the oncogene murine double minute-2 gene (Mdm2), is required in the early stages of metastasis and the driver of EMT. This activity is independent of Mdm2's role in the p53-Mdm2 autoregulatory feedback loop. Herein, we examine the EMT transcription factor Snail as a downstream effector of kinase signaling pathways. We show that the activation of upstream receptors and KRas signaling increase Snail levels. Snail binds to Ebox DNA motifs, and Mdm2 has two Ebox DNA-binding domains in the second promoter. Snail binds to the second Ebox and induces Mdm2 gene expression. Knockdown of endogenous Snail by shRNA shows a decrease in Mdm2 and is associated with reduced migration. The reintroduction of Mdm2 in shSnail cells restores cellular migration. These data integrate upstream pathways that induce Snail-Mdm2 to promote the metastasis of tumor cells.

Structural studies of WDR5 in complex with MBD3C WIN motif reveal a unique binding mode

The nucleosome remodeling and deacetylase (NuRD) complex plays a pivotal role in chromatin regulation and transcriptional repression. In mice, methyl-CpG binding domain 3 isoform C (MBD3C) interacts specifically with the histone H3 binding protein WD repeat-containing protein 5 (WDR5) and forms the WDR5-MBD3C/Norde complex. Despite the functional significance of this interaction on embryonic stem cell gene regulation, the molecular mechanism underlying MBD3C recognition by WDR5 remains elusive. Here, we determined the crystal structure of WDR5 in complex with the peptide (residues 40-51) derived from the MBD3C protein at a resolution of 1.9 Å. Structural analysis revealed that MBD3C utilizes a unique binding mode to interact with WDR5, wherein MBD3C Arg43 and Phe47 are involved in recognizing the WDR5-interacting (WIN) site and Tyr191-related B site on the small surface of WDR5, respectively. Notably, the binding induces a ∼91° rotation of WDR5 Tyr191, generating the hydrophobic B site. Furthermore, mutation experiments combined with isothermal titration calorimetry (ITC) assays confirmed the importance of both Arg43 and Phe47 in mediating WDR5 binding affinity. By determining structures of various peptides bound to WDR5, we demonstrated that the WDR5 WIN site and B site can be concurrently recognized by WIN motif peptides containing ''Arg-Cies/Ser-Arg-Val-Phe'' consensus sequence. Overall, this study reveals the structural basis for the formation of the WDR5-MBD3C subcomplex and provides new insights into the recognition mode of WDR5 for the WIN motif. Moreover, these findings shed light on structural-based designs of WDR5-targeted anti-cancer small molecule inhibitors or peptide-mimic drugs.

MYCN drives oncogenesis by cooperating with the histone methyltransferase G9a and the WDR5 adaptor to orchestrate global gene transcription

MYCN activates canonical MYC targets involved in ribosome biogenesis, protein synthesis, and represses neuronal differentiation genes to drive oncogenesis in neuroblastoma (NB). How MYCN orchestrates global gene expression remains incompletely understood. Our study finds that MYCN binds promoters to up-regulate canonical MYC targets but binds to both enhancers and promoters to repress differentiation genes. MYCN binding also increases H3K4me3 and H3K27ac on canonical MYC target promoters and decreases H3K27ac on neuronal differentiation gene enhancers and promoters. WDR5 facilitates MYCN promoter binding to activate canonical MYC target genes, whereas MYCN recruits G9a to enhancers to repress neuronal differentiation genes. Targeting both MYCN's active and repressive transcriptional activities using both WDR5 and G9a inhibitors synergistically suppresses NB growth. We demonstrate that MYCN cooperates with WDR5 and G9a to orchestrate global gene transcription. The targeting of both these cofactors is a novel therapeutic strategy to indirectly target the oncogenic activity of MYCN.

Exploring promising natural compounds for breast cancer treatment: in silico molecular docking targeting WDR5-MYC protein interaction

Cancer is an aberrant differentiation of normal cells, characterized by uncontrolled growth and the potential to acquire invasive and aggressive properties that ultimately lead to metastasis. In the realm of scientific exploration, a multitude of pathways has been investigated and targeted by researchers, among which one specific pathway is recognized as WDR5-MYC. Continuous investigations and research show that WDR5-MYC is a therapeutic target protein. Hence, the discovery of naturally occurring compounds with anticancer properties has been suggested as a rapid and efficient alternative for the development of anticancerous therapeutics. A virtual screening approach was used to identify the most potent compounds from the NP-lib database at the MTiOpenScreen webserver against WDR5-MYC. This process yielded a total of 304 identified compounds. Subsequently, after screening, four potent compounds, namely Estrone (ZINC000003869899), Ethyl-1,2-benzanthracene (ZINC000003157052), Strychnine (ZINC000000119434) and 7H-DIBENZO [C, G] CARBAZOLE (ZINC000001562130), along with a cocrystallized 5-[4-(trifluoromethyl) phenyl]-1H-tetrazole inhibitor (QBP) as a reference ligand, were considered for stringent molecular docking. Thus, each compound exhibited significant docking energy between -8.2 and -7.7 kcal/mol and molecular contacts with essential residue Asn225, Lys250, Ser267 and Lys272 in the active pocket of WDR5-MYC against the QBP inhibitor (the native ligand QBP serves as a reference in the comparative analysis of docked complexes). The results support the potent compounds for drug-likeness and strong binding affinity with WDR5-MYC protein. Further, the stability of the selected compounds was predicted by molecular dynamics simulation (100 ns) contributed by intermolecular hydrogen bonds and hydrophobic interactions. This demonstrates the potential of the selected compounds to be used against breast cancer treatment.Communicated by Ramaswamy H. Sarma.

Structure-Based Discovery of Potent, Orally Bioavailable Benzoxazepinone-Based WD Repeat Domain 5 Inhibitors

The chromatin-associated protein WDR5 (WD repeat domain 5) is an essential cofactor for MYC and a conserved regulator of ribosome protein gene transcription. It is also a high-profile target for anti-cancer drug discovery, with proposed utility against both solid and hematological malignancies. We have previously discovered potent dihydroisoquinolinone-based WDR5 WIN-site inhibitors with demonstrated efficacy and safety in animal models. In this study, we sought to optimize the bicyclic core to discover a novel series of WDR5 WIN-site inhibitors with improved potency and physicochemical properties. We identified the 3,4-dihydrobenzo[f][1,4]oxazepin-5(2H)-one core as an alternative scaffold for potent WDR5 inhibitors. Additionally, we used X-ray structural analysis to design partially saturated bicyclic P7 units. These benzoxazepinone-based inhibitors exhibited increased cellular potency and selectivity and favorable physicochemical properties compared to our best-in-class dihydroisoquinolinone-based counterparts. This study opens avenues to discover more advanced WDR5 WIN-site inhibitors and supports their development as novel anti-cancer therapeutics.

Discovery of Potent and Selective WDR5 Proteolysis Targeting Chimeras as Potential Therapeutics for Pancreatic Cancer

As a core chromatin-regulatory scaffolding protein, WDR5 mediates numerous protein-protein interactions (PPIs) with other partner oncoproteins. However, small-molecule inhibitors that block these PPIs exert limited cell-killing effects. Here, we report structure-activity relationship studies in pancreatic ductal adenocarcinoma (PDAC) cells that led to the discovery of several WDR5 proteolysis-targeting chimer (PROTAC) degraders, including 11 (MS132), a highly potent and selective von Hippel-Lindau (VHL)-recruiting WDR5 degrader, which displayed positive binding cooperativity between WDR5 and VHL, effectively inhibited proliferation in PDAC cells, and was bioavailable in mice and 25, a cereblon (CRBN)-recruiting WDR5 degrader, which selectively degraded WDR5 over the CRBN neo-substrate IKZF1. Furthermore, by conducting site-directed mutagenesis studies, we determined that WDR5 K296, but not K32, was involved in the PROTAC-induced WDR5 degradation. Collectively, these studies resulted in a highly effective WDR5 degrader, which could be a potential therapeutic for pancreatic cancer and several potentially useful tool compounds.

Epigenetic Dysregulation in MYCN-Amplified Neuroblastoma

Neuroblastoma (NB), a childhood cancer arising from the neural crest, poses significant clinical challenges, particularly in cases featuring amplification of the MYCN oncogene. Epigenetic factors play a pivotal role in normal neural crest and NB development, influencing gene expression patterns critical for tumorigenesis. This review delves into the multifaceted interplay between MYCN and known epigenetic modifications during NB genesis, shedding light on the intricate regulatory networks underlying the disease. We provide an extensive survey of known epigenetic mechanisms, encompassing DNA methylation, histone modifications, non-coding RNAs, super-enhancers (SEs), bromodomains (BET), and chromatin modifiers in MYCN-amplified (MNA) NB. These epigenetic changes collectively contribute to the dysregulated gene expression landscape observed in MNA NB. Furthermore, we review emerging therapeutic strategies targeting epigenetic regulators, including histone deacetylase inhibitors (HDACi), histone methyltransferase inhibitors (HMTi), and DNA methyltransferase inhibitors (DNMTi). We also discuss and summarize current drugs in preclinical and clinical trials, offering insights into their potential for improving outcomes for MNA NB patients.

KMT2A is targeted by miR-361-3p and modulates leukemia cell's abilities to proliferate, migrate and invade

OBJECTIVE

The lives and safety of humans are significantly threatened by acute myeloid leukemia (AML), which is proven to be the most prevalent acute leukemia. This work is therefore intended to investigate and analyze the expressions of miR-361-3p and Histone Lysine Methyltransferase 2A (KMT2A) in tissues and cell lines of AML and identify an advanced and novel target for the therapy of AML.

METHODS

The qRT-PCR and western blot assays were conducted to find expressions of miR-361-3p/KMT2A in AML PB and cell lines. After then, tests using CCK-8 and EdU were run to see how KMT2A affected the growth of AML cells. Transwell migration and invasion assay was conducted to evaluate KMT2A's contribution to the migration and invasion of AML cells. ENCORI and miRWalk predicted the association between KMT2A and miR-361-3p, and the dual-luciferase reporter experiment verified it. Furthermore, rescue studies were used to ascertain how KMT2A affected the miR-361-3p-regulated AML cells' abilities to proliferate, migrate, and invade.

RESULTS

miR-361-3p was poorly expressed while KMT2A was abundantly expressed. Additionally, KMT2A downregulation prevented AML cells from proliferating. PCNA and Ki-67 protein levels fell when KMT2A was silent. Furthermore, AML cells' motility, invasion, and metastasis were inhibited by low KMT2A expression. KMT2A was also identified as a direct target of miR-361-3p and negatively correlated with miR-361-3p. Finally, the over-expression of KMT2A partially reversed the inhibitory effects of up-regulation of miR-361-3p.

CONCLUSION

A potential therapeutic candidate target for the treatment of AML may be miR-361-3p/KMT2A.

MLL1 inhibits the neurogenic potential of SCAPs by interacting with WDR5 and repressing HES1

Mesenchymal stem cell (MSC)-based therapy has emerged as a promising treatment for spinal cord injury (SCI), but improving the neurogenic potential of MSCs remains a challenge. Mixed lineage leukemia 1 (MLL1), an H3K4me3 methyltransferases, plays a critical role in regulating lineage-specific gene expression and influences neurogenesis. In this study, we investigated the role and mechanism of MLL1 in the neurogenesis of stem cells from apical papilla (SCAPs). We examined the expression of neural markers, and the nerve repair and regeneration ability of SCAPs using dynamic changes in neuron-like cells, immunofluorescence staining, and a SCI model. We employed a coimmunoprecipitation (Co-IP) assay, real-time RT-PCR, microarray analysis, and chromatin immunoprecipitation (ChIP) assay to investigate the molecular mechanism. The results showed that MLL1 knock-down increased the expression of neural markers, including neurogenic differentiation factor (NeuroD), neural cell adhesion molecule (NCAM), tyrosine hydroxylase (TH), βIII-tubulin and Nestin, and promoted neuron-like cell formation in SCAPs. In vivo, a transplantation experiment showed that depletion of MLL 1 in SCAPs can restore motor function in a rat SCI model. MLL1 can combine with WD repeat domain 5 (WDR5) and WDR5 inhibit the expression of neural markers in SCAPs. MLL1 regulates Hairy and enhancer of split 1 (HES1) expression by directly binds to HES1 promoters via regulating H3K4me3 methylation by interacting with WDR5. Additionally, HES1 enhances the expression of neural markers in SCAPs. Our findings demonstrate that MLL1 inhibits the neurogenic potential of SCAPs by interacting with WDR5 and repressing HES1. These results provide a potential therapeutic target for promoting the recovery of motor function in SCI patients.

LncRNA AC142119.1 facilitates the progression of neuroblastoma by epigenetically initiating the transcription of MYCN

BACKGROUND

Oncogene MYCN is closely related with malignant progression and poor prognosis of neuroblastoma (NB). Recently, long non-coding RNAs (lncRNAs) have been recognized as crucial regulators in various cancers. However, whether lncRNAs contribute to the overexpression of MYCN in NB is unclear.

METHODS

Microarray analysis were applied to analyze the differentially expressed lncRNAs between MYCN-amplified and MYCN-non-amplified NB cell lines. Bioinformatic analyses were utilized to identify lncRNAs nearby MYCN locus. qRT-PCR was used to detect the expression level of lncRNA AC142119.1 in NB cell lines and tissues. Gain- and loss-of-function assays were conducted to investigate the biological effect of AC142119.1 in NB. Fluorescence in situ hybridization, RNA pull-down, RNA immunoprecipitation, mass spectrometry, RNA electrophoretic mobility shift, chromatin immunoprecipitation and chromatin isolation by RNA purification assays were performed to validate the interaction between AC142119.1 and WDR5 protein as well as MYCN promoter.

RESULTS

AC142119.1 was significantly elevated in NB tissues with MYCN amplification, advanced INSS stage and high risk, and associated with poor survival of NB patients. Moreover, enforced expression of AC142119.1 reinforced the proliferation of NB cells in vitro and in vivo. Additionally, AC142119.1 specifically recruited WDR5 protein to interact with MYCN promoter, further initiating the transcription of MYCN and accelerating NB progression.

CONCLUSIONS

We identified a novel lncRNA AC142119.1, which promoted the progression of NB through epigenetically initiating the transcription of MYCN via interacting with both WDR5 protein and the promoter of MYCN, indicating that AC142119.1 might be a potential diagnostic biomarker and therapeutic target for NB.

3D environment controls H3K4 methylation and the mechanical response of the nucleus in acute lymphoblastic leukemia cells

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, and the infiltration of leukemic cells is critical for disease progression and relapse. Nuclear deformability plays a critical role in cancer cell invasion through confined spaces; however, the direct impact of epigenetic changes on the nuclear deformability of leukemic cells remains unclear. Here, we characterized how 3D collagen matrix conditions induced H3K4 methylation in ALL cell lines and clinical samples. We used specific shRNA and chemical inhibitors to target WDR5 (a core subunit involved in H3K4 methylation) and determined that targeting WDR5 reduced the H3K4 methylation induced by the 3D environment and the invasiveness of ALL cells in vitro and in vivo. Intriguingly, targeting WDR5 did not reduce the adhesion or the chemotactic response of leukemia cells, suggesting a different mechanism by which H3K4 methylation might govern ALL cell invasiveness. Finally, we conducted biochemical, and biophysical experiments to determine that 3D environments promoted the alteration of the chromatin, the morphology, and the mechanical behavior of the nucleus in ALL cells. Collectively, our data suggest that 3D environments control an upregulation of H3K4 methylation in ALL cells, and targeting WDR5 might serve as a promising therapeutic target against ALL invasiveness in vivo.

Recent Progress in Modulation of WD40-Repeat Domain 5 Protein (WDR5): Inhibitors and Degraders

WD40-repeat (WDR) domain proteins play a crucial role in mediating protein-protein interactions that sustain oncogenesis in human cancers. One prominent example is the interaction between the transcription factor MYC and its chromatin co-factor, WD40-repeat domain protein 5 (WDR5), which is essential for oncogenic processes. The MYC family of proteins is frequently overexpressed in various cancers and has been validated as a promising target for anticancer therapies. The recruitment of MYC to chromatin is facilitated by WDR5, highlighting the significance of their interaction. Consequently, inhibiting the MYC-WDR5 interaction has been shown to induce the regression of malignant tumors, offering an alternative approach to targeting MYC in the development of anticancer drugs. WDR5 has two protein interaction sites, the "WDR5-binding motif" (WBM) site for MYC interaction and the histone methyltransferases SET1 recognition motif "WDR5-interacting" (WIN) site forming MLL complex. Significant efforts have been dedicated to the discovery of inhibitors that target the WDR5 protein. More recently, the successful application of targeted protein degradation technology has enabled the removal of WDR5. This breakthrough has opened up new avenues for inhibiting the interaction between WDR5 and the binding partners. In this review, we address the recent progress made in targeting WDR5 to inhibit MDR5-MYC and MDR5-MLL1 interactions, including its targeted protein degradation and their potential impact on anticancer drug discovery.

MYCN driven oncogenesis involves cooperation with WDR5 to activate canonical MYC targets and G9a to repress differentiation genes

MYCN activates canonical MYC targets involved in ribosome biogenesis, protein synthesis and represses neuronal differentiation genes to drive oncogenesis in neuroblastoma (NB). How MYCN orchestrates global gene expression remains incompletely understood. Our study finds that MYCN binds promoters to up-regulate canonical MYC targets but binds to both enhancers and promoters to repress differentiation genes. MYCN-binding also increases H3K4me3 and H3K27ac on canonical MYC target promoters and decreases H3K27ac on neuronal differentiation gene enhancers and promoters. WDR5 is needed to facilitate MYCN promoter binding to activate canonical MYC target genes, whereas MYCN recruits G9a to enhancers to repress neuronal differentiation genes. Targeting both MYCN's active and repressive transcriptional activities using both WDR5 and G9a inhibitors synergistically suppresses NB growth. We demonstrate that MYCN cooperates with WDR5 and G9a to orchestrate global gene transcription. The targeting of both these cofactors is a novel therapeutic strategy to indirectly target the oncogenic activity of MYCN.

Defining the landscape of circular RNAs in neuroblastoma unveils a global suppressive function of MYCN

Circular RNAs (circRNAs) are a regulatory RNA class. While cancer-driving functions have been identified for single circRNAs, how they modulate gene expression in cancer is not well understood. We investigate circRNA expression in the pediatric malignancy, neuroblastoma, through deep whole-transcriptome sequencing in 104 primary neuroblastomas covering all risk groups. We demonstrate that MYCN amplification, which defines a subset of high-risk cases, causes globally suppressed circRNA biogenesis directly dependent on the DHX9 RNA helicase. We detect similar mechanisms in shaping circRNA expression in the pediatric cancer medulloblastoma implying a general MYCN effect. Comparisons to other cancers identify 25 circRNAs that are specifically upregulated in neuroblastoma, including circARID1A. Transcribed from the ARID1A tumor suppressor gene, circARID1A promotes cell growth and survival, mediated by direct interaction with the KHSRP RNA-binding protein. Our study highlights the importance of MYCN regulating circRNAs in cancer and identifies molecular mechanisms, which explain their contribution to neuroblastoma pathogenesis.

WDR5 facilitates recruitment of N-MYC to conserved WDR5 gene targets in neuroblastoma cell lines

Collectively, the MYC family of oncoprotein transcription factors is overexpressed in more than half of all malignancies. The ability of MYC proteins to access chromatin is fundamental to their role in promoting oncogenic gene expression programs in cancer and this function depends on MYC-cofactor interactions. One such cofactor is the chromatin regulator WDR5, which in models of Burkitt lymphoma facilitates recruitment of the c-MYC protein to chromatin at genes associated with protein synthesis, allowing for tumor progression and maintenance. However, beyond Burkitt lymphoma, it is unknown whether these observations extend to other cancers or MYC family members, and whether WDR5 can be deemed as a "universal" MYC recruiter. Here, we focus on N-MYC amplified neuroblastoma to determine the extent of colocalization between N-MYC and WDR5 on chromatin while also demonstrating that like c-MYC, WDR5 can facilitate the recruitment of N-MYC to conserved WDR5-bound genes. We conclude based on this analysis that N-MYC and WDR5 colocalize invariantly across cell lines at predicted sites of facilitated recruitment associated with protein synthesis genes. Surprisingly, we also identify N-MYC-WDR5 cobound genes that are associated with DNA repair and cell cycle processes. Dissection of chromatin binding characteristics for N-MYC and WDR5 at all cobound genes reveals that sites of facilitated recruitment are inherently different than most N-MYC-WDR5 cobound sites. Our data reveals that WDR5 acts as a universal MYC recruiter at a small cohort of previously identified genes and highlights novel biological functions that may be coregulated by N-MYC and WDR5 to sustain the neuroblastoma state.

Discovery, evaluation and mechanism study of WDR5-targeted small molecular inhibitors for neuroblastoma

Neuroblastoma is the most common and deadliest tumor in infancy. WDR5 (WD Repeat Domain 5), a critical factor supporting an N-myc transcriptional complex via its WBM site and interacting with chromosome via its WIN site, promotes the progression of neuroblastoma, thus making it a potential anti-neuroblastoma drug target. So far, a few WIN site inhibitors have been reported, and the WBM site disruptors are rare to see. In this study we conducted virtual screening to identify candidate hit compounds targeting the WBM site of WDR5. As a result, 60 compounds were selected as candidate WBM site inhibitors. Cell proliferation assay demonstrated 6 structurally distinct WBM site inhibitors, numbering as compounds 4, 7, 11, 13, 19 and 22, which potently suppressed 3 neuroblastoma cell lines (MYCN-amplified IMR32 and LAN5 cell lines, and MYCN-unamplified SK-N-AS cell line). Among them, compound 19 suppressed the proliferation of IMR32 and LAN5 cells with EC50 values of 12.34 and 14.89 μM, respectively, and exerted a moderate inhibition on SK-N-AS cells, without affecting HEK293T cells at 20 μM. Analysis of high-resolution crystal complex structure of compound 19 against WDR5 revealed that it competitively occupied the hydrophobic pocket where V264 was located, which might disrupt the interaction of MYC with WDR5 and further MYC-medicated gene transcription. By performing RNA-seq analysis we demonstrated the differences in molecular action mechanisms of the compound 19 and a WIN site inhibitor OICR-9429. Most interestingly, we established the particularly high synergy rate by combining WBM site inhibitor 19 and the WIN site inhibitor OICR-9429, providing a novel therapeutic avenue for neuroblastoma.

A Review of the Regulatory Mechanisms of N-Myc on Cell Cycle

Neuroblastoma has obvious heterogeneity. It is one of the few undifferentiated malignant tumors that can spontaneously degenerate into completely benign tumors. However, for its high-risk type, even with various intensive treatment options, the prognosis is still unsatisfactory. At the same time, a large number of research data show that the abnormal amplification and high-level expression of the MYCN gene are positively correlated with the malignant progression, poor prognosis, and mortality of neuroblastoma. In this context, this article explores the role of the N-Myc, MYCN gene expression product on its target genes related to the cell cycle and reveals its regulatory network in promoting tumor proliferation and malignant progression. We hope it can provide ideas and direction for the research and development of drugs targeting N-Myc and its downstream target genes.

Discovery of Potent Small-Molecule Inhibitors of WDR5-MYC Interaction

WD repeat domain 5 (WDR5) is a member of the WD40-repeat protein family that plays a critical role in multiple processes. It is also a prominent target for pharmacological inhibition in diseases such as cancer, aging, and neurodegenerative disorders. Interactions between WDR5 and various partners are essential for sustaining its function. Most drug discovery efforts center on the WIN (WDR5 interaction motif) site of WDR5 that is responsible for the recruitment of WDR5 to chromatin. Here, we describe the discovery of novel WDR5 inhibitors for the other WBM (WDR5 binding motif) pocket on this scaffold protein, to disrupt WDR5 interaction with its binding partner MYC by high-throughput biochemical screening, subsequent molecule optimization, and biological assessment. These new WDR5 inhibitors provide useful probes for future investigations of WDR5 and an avenue for targeting WDR5 as a therapeutic strategy.

FOXQ1 recruits the MLL complex to activate transcription of EMT and promote breast cancer metastasis

Aberrant expression of the Forkhead box transcription factor, FOXQ1, is a prevalent mechanism of epithelial-mesenchymal transition (EMT) and metastasis in multiple carcinoma types. However, it remains unknown how FOXQ1 regulates gene expression. Here, we report that FOXQ1 initiates EMT by recruiting the MLL/KMT2 histone methyltransferase complex as a transcriptional coactivator. We first establish that FOXQ1 promoter recognition precedes MLL complex assembly and histone-3 lysine-4 trimethylation within the promoter regions of critical genes in the EMT program. Mechanistically, we identify that the Forkhead box in FOXQ1 functions as a transactivation domain directly binding the MLL core complex subunit RbBP5 without interrupting FOXQ1 DNA binding activity. Moreover, genetic disruption of the FOXQ1-RbBP5 interaction or pharmacologic targeting of KMT2/MLL recruitment inhibits FOXQ1-dependent gene expression, EMT, and in vivo tumor progression. Our study suggests that targeting the FOXQ1-MLL epigenetic axis could be a promising strategy to combat triple-negative breast cancer metastatic progression.

Inhibition of Wdr5 Attenuates Ang-II-Induced Fibroblast-to-Myofibroblast Transition in Cardiac Fibrosis by Regulating Mdm2/P53/P21 Pathway

Cardiac fibrosis is an important pathological process in many diseases. Wdr5 catalyzes the trimethylation of lysine K4 on histone H3. The effects of Wdr5 on the cardiac fibrosis phenotype and the activation or transformation of cardiac fibroblasts were investigated by Ang-II-infused mice by osmotic mini-pump and isolated primary neonatal rat cardiac fibroblasts. We found that the Wdr5 expression and histone H3K4me3 modification were significantly increased in Ang-II-infused mice. By stimulating primary neonatal rat cardiac fibroblasts with Ang II, we detected that the expression of Wdr5 and H3K4me3 modification were also significantly increased. Two Wdr5-specific inhibitors, and the lentivirus that transfected Sh-Wdr5, were used to treat primary mouse cardiac fibroblasts, which not only inhibited the histone methylation by Wdr5 but also significantly reduced the activation and migration ability of Ang-II-treated fibroblasts. To explore its mechanism, we found that the inhibition of Wdr5 increased the expression of P53, P21. Cut&Tag-qPCR showed that the inhibition of Wdr5 significantly reduced the enrichment of H3K4me3 in the Mdm2 promoter region. For in vivo experiments, we finally proved that the Wdr5 inhibitor OICR9429 significantly reduced Ang-II-induced cardiac fibrosis and increased the expression of P21 in cardiac fibroblasts. Inhibition of Wdr5 may mediate cardiac fibroblast cycle arrest through the Mdm2/P53/P21 pathway and alleviate cardiac fibrosis.

The WD repeat-containing protein 5 (WDR5) antagonist WDR5-0103 restores the efficacy of cytotoxic drugs in multidrug-resistant cancer cells overexpressing ABCB1 or ABCG2

The development of multidrug resistance (MDR) is one of the major challenges in the treatment of cancer which is caused by the overexpression of the ATP-binding cassette (ABC) transporters ABCB1 (P-glycoprotein) and/or ABCG2 (BCRP/MXR/ABCP) in cancer cells. These transporters are capable of reducing the efficacy of cytotoxic drugs by actively effluxing them out of cancer cells. Since there is currently no approved treatment for patients with multidrug-resistant tumors, the drug repurposing approach provides an alternative route to identify agents to reverse MDR mediated by ABCB1 and/or ABCG2 in multidrug-resistant cancer cells. WDR5-0103 is a histone H3 lysine 4 (H3K4) methyltransferase inhibitor that disrupts the interaction between the WD repeat-containing protein 5 (WDR5) and mixed-lineage leukemia (MLL) protein. In this study, the effect of WDR5-0103 on MDR mediated by ABCB1 and ABCG2 was determined. We found that in a concentration-dependent manner, WDR5-0103 could sensitize ABCB1- and ABCG2-overexpressing multidrug-resistant cancer cells to conventional cytotoxic drugs. Our results showed that WDR5-0103 reverses MDR and improves drug-induced apoptosis in multidrug-resistant cancer cells by inhibiting the drug-efflux function of ABCB1 and ABCG2, without altering the protein expression of ABCB1 or ABCG2. The potential sites of interactions of WDR5-0103 with the drug-binding pockets of ABCB1 and ABCG2 were predicted by molecular docking. In conclusion, the MDR reversal activity of WDR5-0103 demonstrated here indicates that it could be used in combination therapy to provide benefits to a subset of patients with tumor expressing high levels of ABCB1 or ABCG2.

Discovery of a dual WDR5 and Ikaros PROTAC degrader as an anti-cancer therapeutic

WD repeat domain 5 (WDR5), an integral component of the MLL/KMT2A lysine methyltransferase complex, is critically involved in oncogenesis and represents an attractive onco-target. Inhibitors targeting protein-protein interactions (PPIs) between WDR5 and its binding partners, however, do not inhibit all of WDR5-mediated oncogenic functions and exert rather limited antitumor effects. Here, we report a cereblon (CRBN)-recruiting proteolysis targeting chimera (PROTAC) of WDR5, MS40, which selectively degrades WDR5 and the well-established neo-substrates of immunomodulatory drugs (IMiDs):CRBN, the Ikaros zinc finger (IKZF) transcription factors IKZF1 and IKZF3. MS40-induced WDR5 degradation caused disassociation of the MLL/KMT2A complex off chromatin, resulting in decreased H3K4me2. Transcriptomic profiling revealed that targets of both WDR5 and IMiDs:CRBN were significantly repressed by treatment of MS40. In MLL-rearranged leukemias, which exhibit IKZF1 high expression and dependency, co-suppression of WDR5 and Ikaros by MS40 is superior in suppressing oncogenesis to the WDR5 PPI inhibitor, to MS40's non-PROTAC analog controls (MS40N1 and MS40N2, which do not bind CRBN and WDR5, respectively), and to a matched VHL-based WDR5 PROTAC (MS169, which degrades WDR5 but not Ikaros). MS40 suppressed the growth of primary leukemia patient cells in vitro and patient-derived xenografts in vivo. Thus, dual degradation of WDR5 and Ikaros is a promising anti-cancer strategy.

Discovery of Potent Orally Bioavailable WD Repeat Domain 5 (WDR5) Inhibitors Using a Pharmacophore-Based Optimization

WD repeat domain 5 (WDR5) is a nuclear scaffolding protein that forms many biologically important multiprotein complexes. The WIN site of WDR5 represents a promising pharmacological target in a variety of human cancers. Here, we describe the optimization of our initial WDR5 WIN-site inhibitor using a structure-guided pharmacophore-based convergent strategy to improve its druglike properties and pharmacokinetic profile. The core of the previous lead remained constant while a focused SAR effort on the three pharmacophore units was combined to generate a new in vivo lead series. Importantly, this new series of compounds has picomolar binding affinity, improved cellular antiproliferative activity and selectivity, and increased kinetic aqueous solubility. They also exhibit a desirable oral pharmacokinetic profile with manageable intravenous clearance and high oral bioavailability. Thus, these new leads are useful probes toward studying the effects of WDR5 inhibition.

Targeting Oncogenic Transcriptional Networks in Neuroblastoma: From N-Myc to Epigenetic Drugs

Neuroblastoma (NB) is one of the most frequently occurring neurogenic extracranial solid cancers in childhood and infancy. Over the years, many pieces of evidence suggested that NB development is controlled by gene expression dysregulation. These unleashed programs that outline NB cancer cells make them highly dependent on specific tuning of gene expression, which can act co-operatively to define the differentiation state, cell identity, and specialized functions. The peculiar regulation is mainly caused by genetic and epigenetic alterations, resulting in the dependency on a small set of key master transcriptional regulators as the convergence point of multiple signalling pathways. In this review, we provide a comprehensive blueprint of transcriptional regulation bearing NB initiation and progression, unveiling the complexity of novel oncogenic and tumour suppressive regulatory networks of this pathology. Furthermore, we underline the significance of multi-target therapies against these hallmarks, showing how novel approaches, together with chemotherapy, surgery, or radiotherapy, can have substantial antineoplastic effects, disrupting a wide variety of tumorigenic pathways through combinations of different treatments.

MYCN in Neuroblastoma: "Old Wine into New Wineskins"

MYCN Proto-Oncogene, BHLH Transcription Factor (MYCN) has been one of the most studied genes in neuroblastoma. It is known for its oncogenetic mechanisms, as well as its role in the prognosis of the disease and it is considered one of the prominent targets for neuroblastoma therapy. In the present work, we attempted to review the literature, on the relation between MYCN and neuroblastoma from all possible mechanistic sites. We have searched the literature for the role of MYCN in neuroblastoma based on the following topics: the references of MYCN in the literature, the gene's anatomy, along with its transcripts, the protein's anatomy, the epigenetic mechanisms regulating MYCN expression and function, as well as MYCN amplification. MYCN plays a significant role in neuroblastoma biology. Its functions and properties range from the forming of G-quadraplexes, to the interaction with miRNAs, as well as the regulation of gene methylation and histone acetylation and deacetylation. Although MYCN is one of the most primary genes studied in neuroblastoma, there is still a lot to be learned. Our knowledge on the exact mechanisms of MYCN amplification, etiology and potential interventions is still limited. The knowledge on the molecular mechanisms of MYCN in neuroblastoma, could have potential prognostic and therapeutic advantages.

Targeting Myc Interacting Proteins as a Winding Path in Cancer Therapy

MYC, as a well-known oncogene, plays essential roles in promoting tumor occurrence, development, invasion and metastasis in many kinds of solid tumors and hematologic neoplasms. In tumors, the low expression and the short half-life of Myc are reversed, cause tumorigenesis. And proteins that directly interact with different Myc domains have exerted a significant impact in the process of Myc-driven carcinogenesis. Apart from affecting the transcription of Myc target genes, Myc interaction proteins also regulate the stability of Myc through acetylation, methylation, phosphorylation and other post-translational modifications, as well as competitive combination with Myc. In this review, we summarize a series of Myc interacting proteins and recent advances in the related inhibitors, hoping that can provide new opportunities for Myc-driven cancer treatment.

A selective WDR5 degrader inhibits acute myeloid leukemia in patient-derived mouse models

Interactions between WD40 repeat domain protein 5 (WDR5) and its various partners such as mixed lineage leukemia (MLL) and c-MYC are essential for sustaining oncogenesis in human cancers. However, inhibitors that block protein-protein interactions (PPIs) between WDR5 and its binding partners exhibit modest cancer cell killing effects and lack in vivo efficacy. Here, we present pharmacological degradation of WDR5 as a promising therapeutic strategy for treating WDR5-dependent tumors and report two high-resolution crystal structures of WDR5-degrader-E3 ligase ternary complexes. We identified an effective WDR5 degrader via structure-based design and demonstrated its in vitro and in vivo antitumor activities. On the basis of the crystal structure of an initial WDR5 degrader in complex with WDR5 and the E3 ligase von Hippel–Lindau (VHL), we designed a WDR5 degrader, MS67, and demonstrated the high cooperativity of MS67 binding to WDR5 and VHL by another ternary complex structure and biophysical characterization. MS67 potently and selectively depleted WDR5 and was more effective than WDR5 PPI inhibitors in suppressing transcription of WDR5-regulated genes, decreasing the chromatin-bound fraction of MLL complex components and c-MYC, and inhibiting the proliferation of cancer cells. In addition, MS67 suppressed malignant growth of MLL-rearranged acute myeloid leukemia patient cells in vitro and in vivo and was well tolerated in vivo. Collectively, our results demonstrate that structure-based design can be an effective strategy to identify highly active degraders and suggest that pharmacological degradation of WDR5 might be a promising treatment for WDR5-dependent cancers.

MYC protein interactors in gene transcription and cancer

The transcription factor and oncoprotein MYC is a potent driver of many human cancers and can regulate numerous biological activities that contribute to tumorigenesis. How a single transcription factor can regulate such a diverse set of biological programmes is central to the understanding of MYC function in cancer. In this Perspective, we highlight how multiple proteins that interact with MYC enable MYC to regulate several central control points of gene transcription. These include promoter binding, epigenetic modifications, initiation, elongation and post-transcriptional processes. Evidence shows that a combination of multiple protein interactions enables MYC to function as a potent oncoprotein, working together in a 'coalition model', as presented here. Moreover, as MYC depends on its protein interactome for function, we discuss recent research that emphasizes an unprecedented opportunity to target protein interactors to directly impede MYC oncogenesis.

Neuroblastoma Risk Assessment and Treatment Stratification with Hybrid Capture-Based Panel Sequencing

For many years, the risk-based therapy stratification of children with neuroblastoma has relied on clinical and molecular covariates. In recent years, genome analysis has revealed further alterations defining risk, tumor biology, and therapeutic targets. The implementation of a robust and scalable method for analyzing traditional and new molecular markers in routine diagnostics is an urgent clinical need. Here, we investigated targeted panel sequencing as a diagnostic approach to analyze all relevant genomic neuroblastoma risk markers in one assay. Our "neuroblastoma hybrid capture sequencing panel" (NB-HCSP) assay employs a technology for the high-coverage sequencing (>1000×) of 55 selected genes and neuroblastoma-relevant genomic regions, which allows for the detection of single nucleotide changes, structural rearrangements, and copy number alterations. We validated our assay by analyzing 15 neuroblastoma cell lines and a cohort of 20 neuroblastomas, for which reference routine diagnostic data and genome sequencing data were available. We observed a high concordance for risk markers identified by the NB-HSCP assay, clinical routine diagnostics, and genome sequencing. Subsequently, we demonstrated clinical applicability of the NB-HCSP assay by analyzing routine clinical samples. We conclude that the NB-HCSP assay may be implemented into routine diagnostics as a single assay that covers all essential covariates for initial neuroblastoma classification, extended risk stratification, and targeted therapy selection.

Targeting WD Repeat-Containing Protein 5 (WDR5): A Medicinal Chemistry Perspective

WD repeat-containing protein 5 (WDR5) is a member of the WD40 protein family, and it is widely involved in various biological activities and not limited to epigenetic regulation in vivo. WDR5 is also involved in the initiation and development of many diseases and plays a key role in these diseases. Since WDR5 was discovered, it has been suggested as a potential disease treatment target, and a large number of inhibitors targeting WDR5 have been discovered. In this review, we discussed the development of inhibitors targeting WDR5 over the years, and the biological mechanisms of these inhibitors based on previous mechanistic studies were explored. Finally, we describe the development potential of inhibitors targeting WDR5 and prospects for further applications.

Structural insights into the recognition of histone H3Q5 serotonylation by WDR5

Serotonylation of histone H3Q5 (H3Q5ser) is a recently identified posttranslational modification of histones that acts as a permissive marker for gene activation in synergy with H3K4me3 during neuronal cell differentiation. However, any proteins that specifically recognize H3Q5ser remain unknown. Here, we found that WDR5 interacts with the N-terminal tail of histone H3 and functions as a "reader" for H3Q5ser. Crystal structures of WDR5 in complex with H3Q5ser and H3K4me3Q5ser peptides revealed that the serotonyl group is accommodated in a shallow surface pocket of WDR5. Experiments in neuroblastoma cells demonstrate that H3K4me3 modification is hampered upon disruption of WDR5-H3Q5ser interaction. WDR5 colocalizes with H3Q5ser in the promoter regions of cancer-promoting genes in neuroblastoma cells, where it promotes gene transcription to induce cell proliferation. Thus, beyond revealing a previously unknown mechanism through which WDR5 reads H3Q5ser to activate transcription, our study suggests that this WDR5-H3Q5ser-mediated epigenetic regulation apparently promotes tumorigenesis.

Design, Synthesis, and Evaluation of WD-Repeat-Containing Protein 5 (WDR5) Degraders

Histone H3K4 methylation serves as a post-translational hallmark of actively transcribed genes and is introduced by histone methyltransferase (HMT) and its regulatory scaffolding proteins. One of these is the WD-repeat-containing protein 5 (WDR5) that has also been associated with controlling long noncoding RNAs and transcription factors including MYC. The wide influence of dysfunctional HMT complexes and the typically upregulated MYC levels in diverse tumor types suggested WDR5 as an attractive drug target. Indeed, protein-protein interface inhibitors for two protein interaction interfaces on WDR5 have been developed. While such compounds only inhibit a subset of WDR5 interactions, chemically induced proteasomal degradation of WDR5 might represent an elegant way to target all oncogenic functions. This study presents the design, synthesis, and evaluation of two diverse WDR5 degrader series based on two WIN site binding scaffolds and shows that linker nature and length strongly influence degradation efficacy.

The roles and regulation of MDM2 and MDMX: it is not just about p53

In this review, Klein et al. discuss the p53-independent roles of MDM2 and MDMX. First, they review the structural and functional features of MDM2 and MDMX proteins separately and together that could be relevant to their p53-independent activities. Following this, they summarize how these two proteins are regulated and how they can function in cells that lack p53.

Most well studied as proteins that restrain the p53 tumor suppressor protein, MDM2 and MDMX have rich lives outside of their relationship to p53. There is much to learn about how these two proteins are regulated and how they can function in cells that lack p53. Regulation of MDM2 and MDMX, which takes place at the level of transcription, post-transcription, and protein modification, can be very intricate and is context-dependent. Equally complex are the myriad roles that these two proteins play in cells that lack wild-type p53; while many of these independent outcomes are consistent with oncogenic transformation, in some settings their functions could also be tumor suppressive. Since numerous small molecules that affect MDM2 and MDMX have been developed for therapeutic outcomes, most if not all designed to prevent their restraint of p53, it will be essential to understand how these diverse molecules might affect the p53-independent activities of MDM2 and MDMX.

p53 Integrates Temporal WDR5 Inputs during Neuroectoderm and Mesoderm Differentiation of Mouse Embryonic Stem Cells

How ubiquitous transcription factors (TFs) coordinate temporal inputs from broadly expressed epigenetic factors to control cell fate remains poorly understood. Here, we uncover a molecular relationship between p53, an abundant embryonic TF, and WDR5, an essential member of the MLL chromatin modifying complex, that regulates mouse embryonic stem cell fate. Wild-type Wdr5 or transient Wdr5 knockout promotes a distinct pattern of global chromatin accessibility and spurs neuroectodermal differentiation through an RbBP5-dependent process in which WDR5 binds to, and activates transcription of, neural genes. Wdr5 rescue after its prolonged inhibition targets WDR5 to mesoderm lineage-specifying genes, stimulating differentiation toward mesoderm fates in a p53-dependent fashion. Finally, we identify a direct interaction between WDR5 and p53 that enables their co-recruitment to, and regulation of, genes known to control cell proliferation and fate. Our results unmask p53-dependent mechanisms that temporally integrate epigenetic WDR5 inputs to drive neuroectoderm and mesoderm differentiation from pluripotent cells.

How ubiquitous chromatin-associated proteins and transcription factors (TFs) regulate cell fate determination is poorly understood. Li et al. show that regulation of the broadly expressed TF p53 by the chromatin-associated protein WDR5 is required for neuroectoderm versus mesoderm lineage determination in mouse embryonic stem cells (ESCs).

Targeting MYCN in Pediatric and Adult Cancers

The deregulation of the MYC family of oncogenes, including c-MYC, MYCN and MYCL occurs in many types of cancers, and is frequently associated with a poor prognosis. The majority of functional studies have focused on c-MYC due to its broad expression profile in human cancers. The existence of highly conserved functional domains between MYCN and c-MYC suggests that MYCN participates in similar activities. MYC encodes a basic helix-loop-helix-leucine zipper (bHLH-LZ) transcription factor (TF) whose central oncogenic role in many human cancers makes it a highly desirable therapeutic target. Historically, as a TF, MYC has been regarded as “undruggable”. Thus, recent efforts focus on investigating methods to indirectly target MYC to achieve anti-tumor effects. This review will primarily summarize the recent progress in understanding the function of MYCN. It will explore efforts at targeting MYCN, including strategies aimed at suppression of MYCN transcription, destabilization of MYCN protein, inhibition of MYCN transcriptional activity, repression of MYCN targets and utilization of MYCN overexpression dependent synthetic lethality.

Reciprocal Induction of MDM2 and MYCN in Neural and Neuroendocrine Cancers

MYC family oncoproteins MYC, MYCN, and MYCL are deregulated in diverse cancers and via diverse mechanisms. Recent studies established a novel form of MYCN regulation in MYCN-overexpressing retinoblastoma and neuroblastoma cells in which the MDM2 oncoprotein promotes MYCN translation and MYCN-dependent proliferation via a p53-independent mechanism. However, it is unclear if MDM2 also promotes expression of other MYC family members and has similar effects in other cancers. Conversely, MYCN has been shown to induce MDM2 expression in neuroblastoma cells, yet it is unclear if MYC shares this ability, if MYC family proteins upregulate MDM2 in other malignancies, and if this regulation occurs during tumorigenesis as well as in cancer cell lines. Here, we report that intrinsically high MDM2 expression is required for high-level expression of MYCN, but not for expression of MYC, in retinoblastoma, neuroblastoma, small cell lung cancer, and medulloblastoma cells. Conversely, ectopic overexpression of MYC as well as MYCN induced high-level MDM2 expression and gave rise to rapidly proliferating and MDM2-dependent cone-precursor-derived masses in a cultured retinoblastoma genesis model. These findings reveal a highly specific collaboration between the MDM2 and MYCN oncoproteins and demonstrate the origin of their oncogenic positive feedback circuit within a normal neuronal tissue.

Targeted Therapy of TERT-Rearranged Neuroblastoma with BET Bromodomain Inhibitor and Proteasome Inhibitor Combination Therapy

PURPOSE

TERT gene rearrangement with transcriptional superenhancers leads to TERT overexpression and neuroblastoma. No targeted therapy is available for clinical trials in patients with TERT-rearranged neuroblastoma.

EXPERIMENTAL DESIGN

Anticancer agents exerting the best synergistic anticancer effects with BET bromodomain inhibitors were identified by screening an FDA-approved oncology drug library. The synergistic effects of the BET bromodomain inhibitor OTX015 and the proteasome inhibitor carfilzomib were examined by immunoblot and flow cytometry analysis. The anticancer efficacy of OTX015 and carfilzomib combination therapy was investigated in mice xenografted with TERT-rearranged neuroblastoma cell lines or patient-derived xenograft (PDX) tumor cells, and the role of TERT reduction in the anticancer efficacy was examined through rescue experiments in mice.

RESULTS

The BET bromodomain protein BRD4 promoted TERT-rearranged neuroblastoma cell proliferation through upregulating TERT expression. Screening of an approved oncology drug library identified the proteasome inhibitor carfilzomib as the agent exerting the best synergistic anticancer effects with BET bromodomain inhibitors including OTX015. OTX015 and carfilzomib synergistically reduced TERT protein expression, induced endoplasmic reticulum stress, and induced TERT-rearranged neuroblastoma cell apoptosis which was blocked by TERT overexpression and endoplasmic reticulum stress antagonists. In mice xenografted with TERT-rearranged neuroblastoma cell lines or PDX tumor cells, OTX015 and carfilzomib synergistically blocked TERT expression, induced tumor cell apoptosis, suppressed tumor progression, and improved mouse survival, which was largely reversed by forced TERT overexpression.

CONCLUSIONS

OTX015 and carfilzomib combination therapy is likely to be translated into the first clinical trial of a targeted therapy in patients with TERT-rearranged neuroblastoma.

Aberrant Activity of Histone-Lysine N-Methyltransferase 2 (KMT2) Complexes in Oncogenesis

KMT2 (histone-lysine N-methyltransferase subclass 2) complexes methylate lysine 4 on the histone H3 tail at gene promoters and gene enhancers and, thus, control the process of gene transcription. These complexes not only play an essential role in normal development but have also been described as involved in the aberrant growth of tissues. KMT2 mutations resulting from the rearrangements of the KMT2A (MLL1) gene at 11q23 are associated with pediatric mixed-lineage leukemias, and recent studies demonstrate that KMT2 genes are frequently mutated in many types of human cancers. Moreover, other components of the KMT2 complexes have been reported to contribute to oncogenesis. This review summarizes the recent advances in our knowledge of the role of KMT2 complexes in cell transformation. In addition, it discusses the therapeutic targeting of different components of the KMT2 complexes.

The Development of Inhibitors Targeting the Mixed Lineage Leukemia 1 (MLL1)-WD Repeat Domain 5 Protein (WDR5) Protein- Protein Interaction

Mixed Lineage Leukemia 1 (MLL1), an important member of Histone Methyltransferases (HMT) family, is capable of catalyzing mono-, di-, and trimethylation of Histone 3 lysine 4 (H3K4). The optimal catalytic activity of MLL1 requires the formation of a core complex consisting of MLL1, WDR5, RbBP5, and ASH2L. The Protein-Protein Interaction (PPI) between WDR5 and MLL1 plays an important role in abnormal gene expression during tumorigenesis, and disturbing this interaction may have a potential for the treatment of leukemia harboring MLL1 fusion proteins. In this review, we will summarize recent progress in the development of inhibitors targeting MLL1- WDR5 interaction.

PHF20 Promotes Glioblastoma Cell Malignancies Through a WISP1/BGN-Dependent Pathway

Glioblastoma (GBM) stem cells are resistant to cancer therapy, and therefore responsible for tumor progression and recurrence after conventional therapy. However, the molecular mechanisms driving the maintenance of stemness and dedifferentiation are poorly understood. In this study, we identified plant homeodomain finger-containing protein 20 (PHF20) as a crucial epigenetic regulator for sustaining the stem cell-like phenotype of GBM. It is highly expressed in GBM and tightly associated with high levels of aggressiveness of tumors and potential poor prognosis in GBM patients. Knockout of PHF20 inhibits GBM cell proliferation, as well as its invasiveness and stem cell-like traits. Mechanistically, PHF20 interacts with WDR5 and binds to the promoter regions of WISP1 for its expression. Subsequently, WISP1 and BGN act in concert to regulate the degradation of β-Catenin. Our findings have identified PHF20 as a key driver of GBM malignant behaviors, and provided a potential target for developing prognosis and therapy.

The Promise for Histone Methyltransferase Inhibitors for Epigenetic Therapy in Clinical Oncology: A Narrative Review

Epigenetic processes are essential for normal development and the maintenance of tissue-specific gene expression in mammals. Changes in gene expression and malignant cellular transformation can result from disruption of epigenetic mechanisms, and global disruption in the epigenetic landscape is a key feature of cancer. The study of epigenetics in cancer has revealed that human cancer cells harbor both genetic alterations and epigenetic abnormalities that interplay at all stages of cancer development. Unlike genetic mutations, epigenetic aberrations are potentially reversible through epigenetic therapy, providing a therapeutically relevant treatment option. Histone methyltransferase inhibitors are emerging as an epigenetic therapy approach with great promise in the field of clinical oncology. The recent accelerated approval of the enhancer of zeste homolog 2 (EZH2; also known as histone-lysine N-methyltransferase EZH2) inhibitor tazemetostat for metastatic or locally advanced epithelioid sarcoma marks the first approval of such a compound for the treatment of cancer. Many other histone methyltransferase inhibitors are currently in development, some of which are being tested in clinical studies. This review focuses on histone methyltransferase inhibitors, highlighting their potential in the treatment of cancer. We also discuss the role for such epigenetic drugs in overcoming epigenetically driven drug resistance mechanisms, and their value in combination with other therapeutic approaches such as immunotherapy.

LncRNA ANRIL acts as a modular scaffold of WDR5 and HDAC3 complexes and promotes alteration of the vascular smooth muscle cell phenotype

Many studies have shown that long-noncoding RNA (lncRNA) is associated with cardiovascular disease, but its molecular mechanism is still unclear. In this study, we explored the role of lncRNA ANRIL in ox-LDL-induced phenotypic transition of human aortic smooth muscle cells (HASMC). The results of quantitative fluorescence PCR showed that the expression of ANRIL in patients with coronary atherosclerotic heart disease (CAD) was significantly higher than that in normal subjects. RNA-FISH detection showed that the ANRIL expression increased in HASMC treated by ox-LDL. Ox-LDL could upregulate the expression of ANRIL and ROS and promote the phenotypic transition of HASMC. After downregulation of ANRIL by siRNA, ROS level decreased and HASMC phenotypic transition alleviated. ANRIL could act as a molecular scaffold to promote the binding of WDR5 and HDAC3 to form WDR5 and HDAC3 complexes, they regulated target genes such as NOX1 expression by histone modification, upregulated ROS level and promote HASMC phenotype transition. Therefore, we found a new epigenetic regulatory mechanism for phenotype transition of VSMC, ANRIL was a treatment target of occlusive vascular diseases.

The complex activities of the SET1/MLL complex core subunits in development and disease

In mammalian cells, the SET1/MLL complexes are the main writers of the H3K4 methyl mark that is associated with active gene expression. The activities of these complexes are critically dependent on the association of the catalytic subunit with their shared core subunits, WDR5, RBBP5, ASH2L, and DPY30, collectively referred as WRAD. In addition, some of these core subunits can bind to proteins other than the SET1/MLL complex components. This review starts with discussion of the molecular activities of these core subunits, with an emphasis on DPY30 in organizing the assembly of the SET1/MLL complexes with other associated factors. This review then focuses on the roles of the core subunits in stem cells and development, as well as in diseased cell states, mainly cancer, and ends with discussion on dissecting the responsible activities of the core subunits and how we may target them for potential disease treatment. This article is part of a Special Issue entitled: The MLL family of proteins in normal development and disease edited by Thomas A Milne.

WDR5 is a conserved regulator of protein synthesis gene expression

WDR5 is a highly-conserved nuclear protein that performs multiple scaffolding functions in the context of chromatin. WDR5 is also a promising target for pharmacological inhibition in cancer, with small molecule inhibitors of an arginine-binding pocket of WDR5 (the 'WIN' site) showing efficacy against a range of cancer cell lines in vitro. Efforts to understand WDR5, or establish the mechanism of action of WIN site inhibitors, however, are stymied by its many functions in the nucleus, and a lack of knowledge of the conserved gene networks-if any-that are under its control. Here, we have performed comparative genomic analyses to identify the conserved sites of WDR5 binding to chromatin, and the conserved genes regulated by WDR5, across a diverse panel of cancer cell lines. We show that a specific cohort of protein synthesis genes (PSGs) are invariantly bound by WDR5, demonstrate that the WIN site anchors WDR5 to chromatin at these sites, and establish that PSGs are bona fide, acute, and persistent targets of WIN site blockade. Together, these data reveal that WDR5 plays a predominant transcriptional role in biomass accumulation and provide further evidence that WIN site inhibitors act to repress gene networks linked to protein synthesis homeostasis.

Combination therapy with the CDK7 inhibitor and the tyrosine kinase inhibitor exerts synergistic anticancer effects against MYCN-amplified neuroblastoma

Patients with neuroblastoma due to MYCN oncogene amplification and consequent N-Myc oncoprotein overexpression have very poor prognosis. The cyclin-dependent kinase 7 (CDK7)/super-enhancer inhibitor THZ1 suppresses MYCN gene transcription, reduces neuroblastoma cell proliferation, but does not cause significant cell death. The protein kinase phosphatase 1 nuclear targeting subunit (PNUTS) has recently been shown to interact with c-Myc protein and suppresses c-Myc protein degradation. Here we screened the U.S. Food and Drug Administration-Approved Oncology Drugs Set V from the National Cancer Institute, and identified tyrosine kinase inhibitors (TKIs), including ponatinib and lapatinib, as the Approved Oncology Drugs exerting the best synergistic anticancer effects with THZ1 in MYCN-amplified neuroblastoma cells. Combination therapy with THZ1 and ponatinib or lapatinib synergistically induced neuroblastoma cell apoptosis, while having little effects in normal nonmalignant cells. Differential gene expression analysis identified PNUTS as one of the genes most synergistically reduced by the combination therapy. Reverse transcription polymerase chain reaction and immunoblot analyses confirmed that THZ1 and the TKIs synergistically downregulated PNUTS mRNA and protein expression and reduced N-Myc protein but not N-Myc mRNA expression. In addition, PNUTS knockdown resulted in decreased N-Myc protein but not mRNA expression and decreased MYCN-amplified neuroblastoma cell proliferation and survival. As CDK7 inhibitors are currently under clinical evaluation in patients, our data suggest the addition of the TKI ponatinib or lapatinib in CDK7 inhibitor clinical trials in patients.

Discovery and Structure-Based Optimization of Potent and Selective WD Repeat Domain 5 (WDR5) Inhibitors Containing a Dihydroisoquinolinone Bicyclic Core

WD repeat domain 5 (WDR5) is a member of the WD40-repeat protein family that plays a critical role in multiple chromatin-centric processes. Overexpression of WDR5 correlates with a poor clinical outcome in many human cancers, and WDR5 itself has emerged as an attractive target for therapy. Most drug-discovery efforts center on the WIN site of WDR5 that is responsible for the recruitment of WDR5 to chromatin. Here, we describe discovery of a novel WDR5 WIN site antagonists containing a dihydroisoquinolinone bicyclic core using a structure-based design. These compounds exhibit picomolar binding affinity and selective concentration-dependent antiproliferative activities in sensitive MLL-fusion cell lines. Furthermore, these WDR5 WIN site binders inhibit proliferation in MYC-driven cancer cells and reduce MYC recruitment to chromatin at MYC/WDR5 co-bound genes. Thus, these molecules are useful probes to study the implication of WDR5 inhibition in cancers and serve as a potential starting point toward the discovery of anti-WDR5 therapeutics.