HDAC and PI3K Antagonists Cooperate to Inhibit Growth of MYC-Driven Medulloblastoma

Discovery of hydrazide-based PI3K/HDAC dual inhibitors with enhanced pro-apoptotic activity in lymphoma cells

PI3K and HDAC are concurrently upregulated in a variety of cancers, and simultaneous inhibition of PI3K and HDAC may synergistically inhibit tumor proliferation and induce apoptosis, providing a rationale for the study of dual-target PI3K/HDAC inhibitors. In this study, we rationally designed and synthesized a series of novel PI3K/HDAC dual-target inhibitors by combining the morpholino-triazine pharmacophore of PI3K inhibitor ZSTK474 with the hydrazide moiety of HDAC1-3 selective inhibitor 11h. Representative compound 31f possessed both PI3K (IC50 = 2.5-80.5 nM for PI3Kα, β, γ, and δ) and HDAC1-3 inhibitory activities (IC50 = 1.9-75.5 nM for HDAC1-3). 31f showed potent antiproliferative activity against a variety of tumor cell lines. Meanwhile, we designed and synthesized tool molecule 39a, a HDAC inhibitor structurally similar to 31f. In the mantle cell lymphoma Jeko-1 cell line, 31f showed significantly greater efficacy than the single inhibitors in inducing apoptosis. In conclusion, this study provided insights into the development of novel hydrazide-based dual HDAC/PI3K inhibitors.

The dual HDAC/PI3K inhibitor CUDC-907 inhibits the growth and proliferation of MYC-driven Group 3 medulloblastoma

Metastatic Group 3 medulloblastoma (G3 MB) have been shown in several studies to be very high risk, particularly those harboring MYC amplification. More effective therapies are especially important for these patients. CUDC-907, a novel dual inhibitor targeting the MYC upstream pathway (HDAC/PI3K), shows significant antitumor efficacy across multiple cancer types. However, the antitumor effects and underlying mechanisms of CUDC-907 in MB, particularly in very high-risk MB, remain unexplored. In this study, we showed that MYC amplified G3 MB cells, patient-derived organoids and xenograft models were sensitive to CUDC-907. CUDC-907 inhibited MYC expression through the HDAC and PI3K pathways, and then induced G0/G1 phase arrest through the MYC-P21/P27-CDKs/cyclins axis. Furthermore, when CUDC-907 was combined with chemotherapeutic drug cisplatin, G0/G1 phase blocking effect was further enhanced. CUDC-907 in combination with radiotherapy (RT) inhibited DNA damage repair and increased DNA damage. These findings indicate that CUDC-907, either as a monotherapy or in combination with chemoradiotherapy, represents a promising therapeutic strategy for MYC amplified G3 MB, potentially influencing future clinical trials targeting this patient population.

Lactylation in cancer: metabolic mechanism and therapeutic strategies

Recent progress in cancer metabolism research has identified lactylation as a critical post-translational modification influencing tumor development and progression. The process relies on lactate accumulation and the activation of lactate-sensitive acyltransferases. Beyond its role in epigenetic regulation, lactylation has emerged as a significant factor in tumor metabolism and evolution, offering fresh opportunities for developing targeted therapies that transcend traditional approaches. This review explores the growing importance of lactylation in cancer biology and highlights its potential for advancing diagnostic tools and therapeutic strategies.

Recent Advances in Pineoblastoma Research: Molecular Classification, Modelling and Targetable Vulnerabilities

Pineoblastoma (PB) is a rare yet lethal pediatric brain cancer of the pineal gland, a small endocrine organ that secretes melatonin to regulate the circadian rhythm. For PB patients ≤5 years of age, the overall survival rate is approximately 15%; metastatic PB is incurable. Standard treatment, including surgical resection, radiation, and systemic chemotherapy, improves survival but compromises neurocognitive function. A better understanding of the disease and the generation of preclinical models may enable re-evaluation of previous clinical trials, development of precision therapeutic strategies and improve patient outcome. Over the past 5 years, PB has been recognized to include several major subtypes driven by (i) loss of microRNA processing factors DICER and DROSHA characterized by a relatively good prognosis; (ii) loss of the retinoblastoma tumor suppressor RB1; and (iii) amplification or induction of the cMYC protooncogene, with the latter two subtypes exhibiting exceedingly poor prognosis. Recently, mouse models for the major PB subtypes (RB1-, DICER1- and DROSHA-) except MYC- have been established. This progress, including better understanding of the disease, cell of origin, tumor progression, role of autophagy, and targetable vulnerabilities, holds promise for novel therapeutic strategies to combat each subtype of this lethal childhood malignancy.

Targeting protein synthesis pathways in MYC-amplified medulloblastoma

MYC is one of the most deregulated oncogenic transcription factors in human cancers. MYC amplification/or overexpression is most common in Group 3 medulloblastoma and is positively associated with poor prognosis. MYC is known to regulate the transcription of major components of protein synthesis (translation) machinery, leading to promoted rates of protein synthesis and tumorigenesis. MTOR signaling-driven deregulated protein synthesis is widespread in various cancers, including medulloblastoma, which can promote the stabilization of MYC. Indeed, our previous studies demonstrate that the key components of protein synthesis machinery, including mTOR signaling and MYC targets, are overexpressed and activated in MYC-amplified medulloblastoma, confirming MYC-dependent addiction of enhanced protein synthesis in medulloblastoma. Further, targeting this enhanced protein synthesis pathway with combined inhibition of MYC transcription and mTOR translation by small-molecule inhibitors, demonstrates preclinical synergistic anti-tumor potential against MYC-driven medulloblastoma in vitro and in vivo. Thus, inhibiting enhanced protein synthesis by targeting the MYC indirectly and mTOR pathways together may present a highly appropriate strategy for treating MYC-driven medulloblastoma and other MYC-addicted cancers. Evidence strongly proposes that MYC/mTOR-driven tumorigenic signaling can predominantly control the translational machinery to elicit cooperative effects on increased cell proliferation, cell cycle progression, and genome dysregulation as a mechanism of cancer initiation. Several small molecule inhibitors of targeting MYC indirectly and mTOR signaling have been developed and used clinically with immunosuppressants and chemotherapy in multiple cancers. Only a few of them have been investigated as treatments for medulloblastoma and other pediatric tumors. This review explores concurrent targeting of MYC and mTOR signaling against MYC-driven medulloblastoma. Based on existing evidence, targeting of MYC and mTOR pathways together produces functional synergy that could be the basis for effective therapies against medulloblastoma.

Central nervous system distributional kinetics of selected histone deacetylase inhibitors

Histone deacetylase expression and activity are often dysregulated in central nervous system (CNS) tumors, providing a rationale for investigating histone deacetylase inhibitors (HDACIs) in selected brain tumor patients. Although many HDACIs have shown potential in in vitro studies, they have had modest efficacy in vivo. This lack of activity could be due to insufficient CNS exposure to the unbound drug. In this study, we investigated the systemic pharmacokinetics and subsequent CNS distribution of 2 potent HDACIs, vorinostat and quisinostat, in the murine model. Both compounds undergo in vitro degradation in mouse plasma, requiring precautions during sample processing. They also have short half-lives in vivo, in both plasma and the CNS, which may lead to diminished efficacy. Transgenic transporter-deficient mouse models show that the CNS delivery of vorinostat was not limited by the 2 major blood-brain barrier efflux transporters, p-glycoprotein and breast cancer resistance protein. Vorinostat had an unbound CNS tissue-to-plasma partition coefficient of 0.06 ± 0.02. Conversely, the exposure of unbound quisinostat in the brain was only 0.02 ± 0.001 of that in the plasma, and the CNS distribution of quisinostat was limited by the activity of p-glycoprotein. To gain further context for these findings, the CNS distributional kinetics for vorinostat and quisinostat were compared with another hydroxamic acid HDACI, panobinostat. A comprehensive understanding of the CNS target exposure to unbound HDACI, along with known potencies from in vitro testing, can inform the prediction of a therapeutic window for HDACIs that have limited CNS exposure to unbound drug and guide targeted dosing strategies. SIGNIFICANCE STATEMENT: This study indicates that quisinostat and vorinostat are susceptible to enzymatic degradation in the plasma, and to a lesser degree, in the target central nervous system (CNS) tissues. Employing techniques that minimize the postsampling degradation in plasma, brain, and spinal cord, accurate CNS distributional kinetic parameters for these potentially useful compounds were determined. A knowledge of CNS exposure, time to peak, and duration can inform dosing strategies in preclinical and clinical trials in selected CNS tumors.

Progress Toward Epigenetic Targeted Therapies for Childhood Cancer

Among the most significant discoveries from cancer genomics efforts has been the critical role of epigenetic dysregulation in cancer development and progression. Studies across diverse cancer types have revealed frequent mutations in genes encoding epigenetic regulators, alterations in DNA methylation and histone modifications, and a dramatic reorganization of chromatin structure. Epigenetic changes are especially relevant to pediatric cancers, which are often characterized by a low rate of genetic mutations. The inherent reversibility of epigenetic lesions has led to an intense interest in the development of epigenetic targeted therapies. Additionally, the recent appreciation of the interplay between the epigenome and immune regulation has sparked interest in combination therapies and synergistic immunotherapy approaches. Further, the recent appreciation of epigenetic variability as a driving force in cancer evolution has suggested new roles for epigenetic therapies in limiting plasticity and resistance. Here, we review recent progress and emerging directions in the development of epigenetic targeted therapeutics and their promise across the landscape of childhood cancers.

Pediatric Central Nervous System Embryonal Tumors: Presentation, Diagnosis, Therapeutic Strategies, and Survivorship-A Review

Central nervous system (CNS) embryonal tumors represent a diverse group of neoplasms and have a peak incidence in early childhood. These tumors can be located anywhere within the CNS, and presenting symptoms typically represent tumor location. These tumors display distinctive findings on neuroimaging and are staged using magnetic resonance imaging of the brain and spine as well as evaluation of cerebrospinal fluid. Diagnosis is made based on an integrated analysis of histologic and molecular features via tissue sampling. Risk stratification is based on integration of clinical staging and extent of resection with histologic and molecular risk factors. The therapeutic approach for these tumors is multimodal and includes surgery, chemotherapy, and radiation, tailored to the individual patient factors (including age) and specific tumor type. Comprehensive supportive care including management of nausea, nutrition support, pain, fertility preservation, and mitigation of therapy-related morbidity (including hearing protection) is imperative through treatment of CNS embryonal tumors. Despite advances in therapy and supportive care, the long-term consequences of current treatment strategies are substantial. Integration of less toxic, molecularly targeted therapies and a comprehensive, multidisciplinary approach to survivorship care are essential to improving survival and the overall quality of life for survivors.

Transcriptional Regulation of Protein Synthesis by Mediator Kinase Represents a Therapeutic Vulnerability in MYC-driven Medulloblastoma

MYC-driven medulloblastoma (MB) is a highly aggressive cancer type with poor prognosis and limited treatment options. Through CRISPR-Cas9 screening of MB cell lines, we identified the Mediator-associated kinase CDK8 as a critical regulator of MYC-driven MB. Loss of CDK8 substantially reduces MYC expression and induces pronounced transcriptional changes, consequently inhibiting MB growth and suppressing monosome assembly, resulting in decreased ribosome biogenesis and protein synthesis. Mechanistically, CDK8 regulates the occupancy of RNA polymerase II at specific chromatin loci, facilitating an epigenetic alteration that promotes the transcriptional regulation of ribosomal genes. Targeting CDK8 effectively diminishes the stem-like neoplastic cells characterized by hyperactive ribosome biogenesis. Furthermore, we demonstrated that the combined inhibition of CDK8 and mTOR synergizes to optimize therapeutic outcomes in vivo and in vivo. Overall, our findings establish a connection between CDK8-mediated transcriptional regulation and mRNA translation, suggesting a promising new therapeutic approach that targets the protein synthesis for MYC-driven MB. .

Practical immunomodulatory landscape of glioblastoma multiforme (GBM) therapy

Glioblastoma multiforme (GBM) is the most common harmful high-grade brain tumor with high mortality and low survival rate. Importantly, besides routine diagnostic and therapeutic methods, modern and useful practical techniques are urgently needed for this serious malignancy. Correspondingly, the translational medicine focusing on genetic and epigenetic profiles of glioblastoma, as well as the immune framework and brain microenvironment, based on these challenging findings, indicates that key clinical interventions include immunotherapy, such as immunoassay, oncolytic viral therapy, and chimeric antigen receptor T (CAR T) cell therapy, which are of great importance in both diagnosis and therapy. Relatively, vaccine therapy reflects the untapped confidence to enhance GBM outcomes. Ongoing advances in immunotherapy, which utilizes different methods to regenerate or modify the resistant body for cancer therapy, have revealed serious results with many different problems and difficulties for patients. Safe checkpoint inhibitors, adoptive cellular treatment, cellular and peptide antibodies, and other innovations give researchers an endless cluster of instruments to plan profoundly in personalized medicine and the potential for combination techniques. In this way, antibodies that block immune checkpoints, particularly those that target the program death 1 (PD-1)/PD-1 (PD-L1) ligand pathway, have improved prognosis in a wide range of diseases. However, its use in combination with chemotherapy, radiation therapy, or monotherapy is ineffective in treating GBM. The purpose of this review is to provide an up-to-date overview of the translational elements concentrating on the immunotherapeutic field of GBM alongside describing the molecular mechanism involved in GBM and related signaling pathways, presenting both historical perspectives and future directions underlying basic and clinical practice.

Identification of tumor rejection antigens and the immunologic landscape of medulloblastoma

BACKGROUND

The current standard of care treatments for medulloblastoma are insufficient as these do not take tumor heterogeneity into account. Newer, safer, patient-specific treatment approaches are required to treat high-risk medulloblastoma patients who are not cured by the standard therapies. Immunotherapy is a promising treatment modality that could be key to improving survival and avoiding morbidity. For an effective immune response, appropriate tumor antigens must be targeted. While medulloblastoma patients with subgroup-specific genetic substitutions have been previously reported, the immunogenicity of these genetic alterations remains unknown. The aim of this study is to identify potential tumor rejection antigens for the development of antigen-directed cellular therapies for medulloblastoma.

METHODS

We developed a cancer immunogenomics pipeline and performed a comprehensive analysis of medulloblastoma subgroup-specific transcription profiles (n = 170, 18 WNT, 46 SHH, 41 Group 3, and 65 Group 4 patient tumors) available through International Cancer Genome Consortium (ICGC) and European Genome-Phenome Archive (EGA). We performed in silico antigen prediction across a broad array of antigen classes including neoantigens, tumor-associated antigens (TAAs), and fusion proteins. Furthermore, we evaluated the antigen processing and presentation pathway in tumor cells and the immune infiltrating cell landscape using the latest computational deconvolution methods.

RESULTS

Medulloblastoma patients were found to express multiple private and shared immunogenic antigens. The proportion of predicted TAAs was higher than neoantigens and gene fusions for all molecular subgroups, except for sonic hedgehog (SHH), which had a higher neoantigen burden. Importantly, cancer-testis antigens, as well as previously unappreciated neurodevelopmental antigens, were found to be expressed by most patients across all medulloblastoma subgroups. Despite being immunologically cold, medulloblastoma subgroups were found to have distinct immune cell gene signatures.

CONCLUSIONS

Using a custom antigen prediction pipeline, we identified potential tumor rejection antigens with important implications for the development of immunotherapy for medulloblastoma.

Mechanistic insights into medulloblastoma relapse

Pediatric brain tumors are the leading cause of cancer-related deaths in children, with medulloblastoma (MB) being the most common type. A better understanding of these malignancies has led to their classification into four major molecular subgroups. This classification not only facilitates the stratification of clinical trials, but also the development of more effective therapies. Despite recent progress, approximately 30% of children diagnosed with MB experience tumor relapse. Recurrent disease in MB is often metastatic and responds poorly to current therapies. As a result, only a small subset of patients with recurrent MB survive beyond one year. Due to its dismal prognosis, novel therapeutic strategies aimed at preventing or managing recurrent disease are urgently needed. In this review, we summarize recent advances in our understanding of the molecular mechanisms behind treatment failure in MB, as well as those characterizing recurrent cases. We also propose avenues for how these findings can be used to better inform personalized medicine approaches for the treatment of newly diagnosed and recurrent MB. Lastly, we discuss the treatments currently being evaluated for MB patients, with special emphasis on those targeting MB by subgroup at diagnosis and relapse.

Chidamide represses MYC expression and might improve survival for patients with double expressor lymphoma

Double expressor lymphoma (DEL), characterized by high expressions of both MYC and BCL-2, displays poor prognosis after current therapies. The HDAC inhibitor chidamide has been approved for treatment of T cell lymphoma, but its efficacy on B cell lymphoma is unclear. Here, by combining inhibition screening and transcriptomic analyses, we found that the sensitivity of B lymphoma cells to chidamide was positively correlated with the expression levels of MYC. Chidamide treatment reduced MYC protein levels and repressed MYC pathway in B lymphoma cells with high MYC expressions. Ectopic expression of MYC in chidamide-insensitive B lymphoma cells increased their response to chidamide. Thus, we proposed that adding chidamide into R-CHOP (CR-CHOP) might be effective for DEL, and retrospectively analyzed 185 DEL patients treated in West China Hospital. 80% of patients showed response to CR-CHOP treatment. In the median follow-up of 42 months, CR-CHOP significantly improve the survival for DEL patients with R-IPI ≤2. Totally 35 patients underwent autologous stem cell transplantation (ASCT) in remission and demonstrated a trend for better survival. Combining CR-CHOP with ASCT resulted in the most superior PFS and OS above all. For response patients, CR-CHOP reduced relapse with better PFS than R-CHOP-like regimens with or without ASCT. Taken together, our data indicated that chidamide repressed the MYC pathway in B lymphoma and is potentially efficacious to treat DEL.

Orthogonal proteogenomic analysis identifies the druggable PA2G4-MYC axis in 3q26 AML

The overexpression of the ecotropic viral integration site-1 gene (EVI1/MECOM) marks the most lethal acute myeloid leukemia (AML) subgroup carrying chromosome 3q26 abnormalities. By taking advantage of the intersectionality of high-throughput cell-based and gene expression screens selective and pan-histone deacetylase inhibitors (HDACis) emerge as potent repressors of EVI1. To understand the mechanism driving on-target anti-leukemia activity of this compound class, here we dissect the expression dynamics of the bone marrow leukemia cells of patients treated with HDACi and reconstitute the EVI1 chromatin-associated co-transcriptional complex merging on the role of proliferation-associated 2G4 (PA2G4) protein. PA2G4 overexpression rescues AML cells from the inhibitory effects of HDACis, while genetic and small molecule inhibition of PA2G4 abrogates EVI1 in 3q26 AML cells, including in patient-derived leukemia xenografts. This study positions PA2G4 at the crosstalk of the EVI1 leukemogenic signal for developing new therapeutics and urges the use of HDACis-based combination therapies in patients with 3q26 AML.

Defeating MYC with drug combinations or dual-targeting drugs

Members of the MYC family of proteins are a major target for cancer drug discovery, but the development of drugs that block MYC-driven cancers has not yet been successful. Approaches to achieve success may include the development of combination therapies or dual-acting drugs that target MYC at multiple nodes. Such treatments hold the possibility of additive or synergistic activity, potentially reducing side effect profiles and the emergence of resistance. In this review, we examine the prominent MYC-related targets and highlight those that have been targeted in combination and/or dual-target approaches. Finally, we explore the challenges of combination and dual-target approaches from a drug development perspective.

Advances in targeting histone deacetylase for treatment of solid tumors

Histone deacetylase (HDAC) serves as a critical molecular regulator in the pathobiology of various malignancies and have garnered attention as a viable target for therapeutic intervention. A variety of HDAC inhibitors (HDACis) have been developed to target HDACs. Many preclinical studies have conclusively demonstrated the antitumor effects of HDACis, whether used as monotherapy or in combination treatments. On this basis, researchers have conducted various clinical studies to evaluate the potential of selective and pan-HDACis in clinical settings. In our work, we extensively summarized and organized current clinical trials, providing a comprehensive overview of the current clinical advancements in targeting HDAC therapy. Furthermore, we engaged in discussions about several clinical trials that did not yield positive outcomes, analyzing the factors that led to their lack of anticipated therapeutic effectiveness. Apart from the experimental design factors, issues such as toxicological side effects, tumor heterogeneity, and unexpected off-target effects also contributed to these less-than-expected results. These challenges have naturally become significant barriers to the application of HDACis. Despite these challenges, we believe that advancements in HDACi research and improvements in combination therapies will pave the way or lead to a broad and hopeful future in the treatment of solid tumors.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Drivers Underlying Metastasis and Relapse in Medulloblastoma and Targeting Strategies

Medulloblastomas comprise a molecularly diverse set of malignant pediatric brain tumors in which patients are stratified according to different prognostic risk groups that span from very good to very poor. Metastasis at diagnosis is most often a marker of poor prognosis and the relapse incidence is higher in these children. Medulloblastoma relapse is almost always fatal and recurring cells have, apart from resistance to standard of care, acquired genetic and epigenetic changes that correlate with an increased dormancy state, cell state reprogramming and immune escape. Here, we review means to carefully study metastasis and relapse in preclinical models, in light of recently described molecular subgroups. We will exemplify how therapy resistance develops at the cellular level, in a specific niche or from therapy-induced secondary mutations. We further describe underlying molecular mechanisms on how tumors acquire the ability to promote leptomeningeal dissemination and discuss how they can establish therapy-resistant cell clones. Finally, we describe some of the ongoing clinical trials of high-risk medulloblastoma and suggest or discuss more individualized treatments that could be of benefit to specific subgroups.

Pharmacokinetics of Panobinostat: Interspecies Difference in Metabolic Stability

The deregulation of histone deacetylase (HDAC) expression is often seen in many cancers, and HDAC inhibitors have shown potency against a variety of cancer types. Panobinostat is a potent pan-HDAC inhibitor that has been tested in multiple studies for the treatment of brain tumors. There have been contrasting views surrounding its efficacy for the treatment of tumors in the central nervous system (CNS) following systemic administration when examined in different models or species. We conducted experiments using three different mouse strains or genotypes to have a more comprehensive understanding of the systemic as well as the CNS distributional kinetics of panobinostat. Our study found that panobinostat experienced rapid degradation in vitro in Friend leukemia virus strain B mouse matrices and a faster degradation rate was observed at 37°C compared with room temperature and 4°C, suggesting that the in vitro instability of panobinostat was due to enzymatic metabolism. Panobinostat also showed interstrain and interspecies differences in the in vitro plasma stability and was stable in human plasma. The objective of this study was to examine the in vitro metabolic stability of panobinostat in different matrices and assess the influence of that metabolic stability on the in vivo pharmacokinetics and CNS delivery of panobinostat. Importantly, the plasma stability in various mouse strains was not reflected in the in vivo systemic pharmacokinetic behavior of panobinostat. Several hypotheses arise from this finding, including: the binding of panobinostat to red blood cells, the existence of competing endogenous compounds to enzyme(s), the distribution into tissues with a lower level of enzymatic activity or the metabolism occurring in the plasma is a small fraction of the total metabolism in vivo. SIGNIFICANCE STATEMENT: Panobinostat showed different in vitro degradation in plasma from different mouse strains and genotypes. However, despite the differences surrounding in vitro plasma stability, panobinostat showed similar in vivo pharmacokinetic behavior in different mouse models. This suggests that the interstrain difference in enzymatic activity did not affect the in vivo pharmacokinetic behavior of panobinostat and its central nervous system distribution in mice. This lack of translation between in vitro metabolism assays and in vivo disposition can confound drug development.

A Benzarone Derivative Inhibits EYA to Suppress Tumor Growth in SHH Medulloblastoma

Medulloblastoma is one of the most common malignant brain tumors of children, and 30% of medulloblastomas are driven by gain-of-function genetic lesions in the Sonic Hedgehog (SHH) signaling pathway. EYA1, a haloacid dehalogenase phosphatase and transcription factor, is critical for tumorigenesis and proliferation of SHH medulloblastoma (SHH-MB). Benzarone and benzbromarone have been identified as allosteric inhibitors of EYA proteins. Using benzarone as a point of departure, we developed a panel of 35 derivatives and tested them in SHH-MB. Among these compounds, DS-1-38 functioned as an EYA antagonist and opposed SHH signaling. DS-1-38 inhibited SHH-MB growth in vitro and in vivo, showed excellent brain penetrance, and increased the lifespan of genetically engineered mice predisposed to fatal SHH-MB. These data suggest that EYA inhibitors represent promising therapies for pediatric SHH-MB.

SIGNIFICANCE

Development of a benzarone derivative that inhibits EYA1 and impedes the growth of SHH medulloblastoma provides an avenue for improving treatment of this malignant pediatric brain cancer.

Transcriptional Regulation of Protein Synthesis by Mediator Kinase in MYC-driven Medulloblastoma

MYC-driven medulloblastoma (MB) is a highly aggressive cancer type with poor prognosis and limited treatment options. Through CRISPR-Cas9 screening across MB cell lines, we identified the Mediator-associated kinase CDK8 as the top dependence for MYC-driven MB. Loss of CDK8 markedly reduces MYC expression and impedes MB growth. Mechanistically, we demonstrate that CDK8 depletion suppresses ribosome biogenesis and mRNA translation. CDK8 regulates occupancy of phospho-Polymerase II at specific chromatin loci facilitating an epigenetic alteration that promotes transcriptional regulation of ribosome biogenesis. Additionally, CDK8-mediated phosphorylation of 4EBP1 plays a crucial role in initiating eIF4E-dependent translation. Targeting CDK8 effectively suppresses cancer stem and progenitor cells, characterized by increased ribosome biogenesis activity. We also report the synergistic inhibition of CDK8 and mTOR in vivo and in vitro . Overall, our findings establish a connection between transcription and translation regulation, suggesting a promising therapeutic approach targets multiple points in the protein synthesis network for MYC-driven MB.

Development of a high-throughput screening platform to identify new therapeutic agents for Medulloblastoma Group 3

Pediatric brain tumors (PBTs) represent about 25 % of all pediatric cancers and are the most common solid tumors in children and adolescents. Medulloblastoma (MB) is the most frequently occurring malignant PBT, accounting for almost 10 % of all pediatric cancer deaths. MB Group 3 (MB G3) accounts for 25-30 % of all MB cases and has the worst outcome, particularly when associated with MYC amplification. However, no targeted treatments for this group have been developed so far. Here we describe a unique high throughput screening (HTS) platform specifically designed to identify new therapies for MB G3. The platform incorporates optimized and validated 2D and 3D efficacy and toxicity models, that account for tumor heterogenicity, limited efficacy and unacceptable toxicity from the very early stage of drug discovery. The platform has been validated by conducting a pilot HTS campaign with a 1280 lead-like compound library. Results showed 8 active compounds, targeting MB reported targets and several are currently approved or in clinical trials for pediatric patients with PBTs, including MB. Moreover, hits were combined to avoid tumor resistance, identifying 3 synergistic pairs, one of which is currently under clinical study for recurrent MB and other PBTs.

Heterogeneity and tumoral origin of medulloblastoma in the single-cell era

Medulloblastoma is one of the most common malignant pediatric brain tumors derived from posterior fossa. The current treatment includes maximal safe surgical resection, radiotherapy, whole cranio-spinal radiation and adjuvant with chemotherapy. However, it can only limitedly prolong the survival time with severe side effects and relapse. Defining the intratumoral heterogeneity, cellular origin and identifying the interaction network within tumor microenvironment are helpful for understanding the mechanisms of medulloblastoma tumorigenesis and relapse. Due to technological limitations, the mechanisms of cellular heterogeneity and tumor origin have not been fully understood. Recently, the emergence of single-cell technology has provided a powerful tool for achieving the goal of understanding the mechanisms of tumorigenesis. Several studies have demonstrated the intratumoral heterogeneity and tumor origin for each subtype of medulloblastoma utilizing the single-cell RNA-seq, which has not been uncovered before using conventional technologies. In this review, we present an overview of the current progress in understanding of cellular heterogeneity and tumor origin of medulloblastoma and discuss novel findings in the age of single-cell technologies.

Fimepinostat Impairs NF-κB and PI3K/AKT Signaling and Enhances Gemcitabine Efficacy in H3.3K27M-Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is the most aggressive pediatric brain tumor, and the oncohistone H3.3K27M mutation is associated with significantly worse clinical outcomes. Despite extensive research efforts, effective approaches for treating DIPG are lacking. Through drug screening, we identified the combination of gemcitabine and fimepinostat as a potent therapeutic intervention for H3.3K27M DIPG. H3.3K27M facilitated gemcitabine-induced apoptosis in DIPG, and gemcitabine stabilized and activated p53, including increasing chromatin accessibility for p53 at apoptosis-related loci. Gemcitabine simultaneously induced a prosurvival program in DIPG through activation of RELB-mediated NF-κB signaling. Specifically, gemcitabine induced the transcription of long terminal repeat elements, activated cGAS-STING signaling, and stimulated noncanonical NF-κB signaling. A drug screen in gemcitabine-treated DIPG cells revealed that fimepinostat, a dual inhibitor of HDAC and PI3K, effectively suppressed the gemcitabine-induced NF-κB signaling in addition to blocking PI3K/AKT activation. Combination therapy comprising gemcitabine and fimepinostat elicited synergistic antitumor effects in vitro and in orthotopic H3.3K27M DIPG xenograft models. Collectively, p53 activation using gemcitabine and suppression of RELB-mediated NF-κB activation and PI3K/AKT signaling using fimepinostat is a potential therapeutic strategy for treating H3.3K27M DIPG.

SIGNIFICANCE

Gemcitabine activates p53 and induces apoptosis to elicit antitumor effects in H3.3K27M DIPG, which can be enhanced by blocking NF-κB and PI3K/AKT signaling with fimepinostat, providing a synergistic combination therapy for DIPG.

SALL4 is a CRL3REN/KCTD11 substrate that drives Sonic Hedgehog-dependent medulloblastoma

The Sonic Hedgehog (SHH) pathway is crucial regulator of embryonic development and stemness. Its alteration leads to medulloblastoma (MB), the most common malignant pediatric brain tumor. The SHH-MB subgroup is the best genetically characterized, however the molecular mechanisms responsible for its pathogenesis are not fully understood and therapeutic benefits are still limited. Here, we show that the pro-oncogenic stemness regulator Spalt-like transcriptional factor 4 (SALL4) is re-expressed in mouse SHH-MB models, and its high levels correlate with worse overall survival in SHH-MB patients. Proteomic analysis revealed that SALL4 interacts with REN/KCTD11 (here REN), a substrate receptor subunit of the Cullin3-RING ubiquitin ligase complex (CRL3REN) and a tumor suppressor lost in ~30% of human SHH-MBs. We demonstrate that CRL3REN induces polyubiquitylation and degradation of wild type SALL4, but not of a SALL4 mutant lacking zinc finger cluster 1 domain (ΔZFC1). Interestingly, SALL4 binds GLI1 and cooperates with HDAC1 to potentiate GLI1 deacetylation and transcriptional activity. Notably, inhibition of SALL4 suppresses SHH-MB growth both in murine and patient-derived xenograft models. Our findings identify SALL4 as a CRL3REN substrate and a promising therapeutic target in SHH-dependent cancers.

Current and future therapeutic strategies for high-grade gliomas leveraging the interplay between epigenetic regulators and kinase signaling networks

Targeted therapies, including small molecule inhibitors directed against aberrant kinase signaling and chromatin regulators, are emerging treatment options for high-grade gliomas (HGG). However, when translating these inhibitors into the clinic, their efficacy is generally limited to partial and transient responses. Recent studies in models of high-grade gliomas reveal a convergence of epigenetic regulators and kinase signaling networks that often cooperate to promote malignant properties and drug resistance. This review examines the interplay between five well-characterized groups of chromatin regulators, including the histone deacetylase (HDAC) family, bromodomain and extraterminal (BET)-containing proteins, protein arginine methyltransferase (PRMT) family, Enhancer of zeste homolog 2 (EZH2), and lysine-specific demethylase 1 (LSD1), and various signaling pathways essential for cancer cell growth and progression. These specific epigenetic regulators were chosen for review due to their targetability via pharmacological intervention and clinical relevance. Several studies have demonstrated improved efficacy from the dual inhibition of the epigenetic regulators and signaling kinases. Overall, the interactions between epigenetic regulators and kinase signaling pathways are likely influenced by several factors, including individual glioma subtypes, preexisting mutations, and overlapping/interdependent functions of the chromatin regulators. The insights gained by understanding how the genome and epigenome cooperate in high-grade gliomas will guide the design of future therapeutic strategies that utilize dual inhibition with improved efficacy and overall survival.

Direct Administration of Chemotherapy and Other Agents into the Fourth Ventricle to Treat Recurrent Malignant Brain Tumors in Children

Direct administration of chemotherapy and other agents into the fourth ventricle of the brain is a novel approach to treating recurrent malignant posterior fossa brain tumors in children. Candidates for this treatment approach include patients with recurrent medulloblastoma, ependymoma, atypical teratoid/rhabdoid tumor, and potentially other neoplasms that originate in the fourth ventricle or elsewhere in the posterior fossa. In this chapter, the authors first explain the rationale for considering fourth ventricular drug infusions in patients with recurrent malignant posterior fossa tumors. We then summarize the results of translational experiments conducted in piglets and non-human primates that demonstrated safety and favorable pharmacokinetics. These translational experiments led to several pilot human clinical trials, and the results of these trials are reviewed. Finally, currently open clinical trials testing infusion of various agents into the fourth ventricle are discussed, and thoughts about potential future directions are shared.

Combination drug screen identifies synergistic drug interaction of BCL-XL and class I histone deacetylase inhibitors in MYC-amplified medulloblastoma cells

PURPOSE

Patients with MYC-amplified Group 3 medulloblastoma (MB) (subtype II) show poor progression-free survival rates. Class I histone deacetylase inhibitors (HDACi) are highly effective for the treatment of MYC-amplified MB in vitro and in vivo. Drug combination regimens including class I HDACi may represent an urgently needed novel treatment approach for this high risk disease.

METHODS

A medium-throughput in vitro combination drug screen was performed in three MYC-amplified and one non-MYC-amplified MB cell line testing 75 clinically relevant drugs alone and in combination with entinostat. The drug sensitivity score (DSS) was calculated based on metabolic inhibition quantified by CellTiter-Glo. The six top synergistic combination hits were evaluated in a 5 × 5 combination matrix and a seven-ray design. Synergy was validated and characterized by cell counts, caspase-3-like-activity and poly-(ADP-ribose)-polymerase-(PARP)-cleavage. On-target activity of drugs was validated by immunoprecipitation and western blot. BCL-XL dependency of the observed effect was explored with siRNA mediated knockdown of BCL2L1, and selective inhibition with targeted compounds (A-1331852, A-1155463).

RESULTS

20/75 drugs effectively reduced metabolic activity in combination with entinostat in all three MYC-amplified cell lines (DSS ≥ 10). The combination entinostat and navitoclax showed the strongest synergistic interaction across all MYC-amplified cell lines. siRNA mediated knockdown of BCL2L1, as well as targeted inhibition with selective inhibitors showed BCL-XL dependency of the observed effect. Increased cell death was associated with increased caspase-3-like-activity.

CONCLUSION

Our study identifies the combination of class I HDACi and BCL-XL inhibitors as a potential new approach for the treatment of MYC-amplified MB cells.

Technologies of targeting histone deacetylase in drug discovery: Current progress and emerging prospects

Histone deacetylases (HDACs) catalyze the hydrolysis of acetyl-l-lysine side chains in histones and non-histones, which are key to epigenetic regulation in humans. Targeting HDACs has emerged as a promising strategy for treating various types of cancer, including myeloma and hematologic malignancies. At present, numerous small molecule inhibitors targeting HDACs are actively being investigated in clinical trials. Despite their potential efficacy in cancer treatment, HDAC inhibitors suffer from multi-directional selectivity and preclinical resistance issues. Hence, developing novel inhibitors based on cutting-edge medicinal chemistry techniques is essential to overcome these limitations and improve clinical outcomes. This manuscript presents an extensive overview of the properties and biological functions of HDACs in cancer, provides an overview of the current state of development and limitations of clinical HDAC inhibitors, and analyzes a range of innovative medicinal chemistry techniques that are applied. These techniques include selective inhibitors, dual-target inhibitors, proteolysis targeting chimeras, and protein-protein interaction inhibitors.

Central Nervous System Distribution of Panobinostat in Preclinical Models to Guide Dosing for Pediatric Brain Tumors

Achieving adequate exposure of the free therapeutic agent at the target is a critical determinant of efficacious chemotherapy. With this in mind, a major challenge in developing therapies for central nervous system (CNS) tumors is to overcome barriers to delivery, including the blood-brain barrier (BBB). Panobinostat is a nonselective pan-histone deacetylase inhibitor that is being tested in preclinical and clinical studies, including for the treatment of pediatric medulloblastoma, which has a propensity for leptomeningeal spread and diffuse midline glioma, which can infiltrate into supratentorial brain regions. In this study, we examined the rate, extent, and spatial heterogeneity of panobinostat CNS distribution in mice. Transporter-deficient mouse studies show that panobinostat is a dual substrate of P-glycoprotein (P-gp) and breast cancer resistant protein (Bcrp), which are major efflux transporters expressed at the BBB. The CNS delivery of panobinostat was moderately limited by P-gp and Bcrp, and the unbound tissue-to-plasma partition coefficient of panobinostat was 0.32 and 0.21 in the brain and spinal cord in wild-type mice. In addition, following intravenous administration, panobinostat demonstrated heterogeneous distribution among brain regions, indicating that its efficacy would be influenced by tumor location or the presence and extent of leptomeningeal spread. Simulation using a compartmental BBB model suggests inadequate exposure of free panobinostat in the brain following a recommended oral dosing regimen in patients. Therefore, alternative approaches to CNS delivery may be necessary to have adequate exposure of free panobinostat for the treatment of a broad range of pediatric brain tumors. SIGNIFICANCE STATEMENT: This study shows that the central nervous system (CNS) penetration of panobinostat is limited by P-gp and Bcrp, and its efficacy may be limited by inadequate distribution to the tumor. Panobinostat has heterogeneous distribution into various brain regions, indicating that its efficacy might depend on the anatomical location of the tumors. These distributional parameters in the mouse CNS can inform both preclinical and clinical trial study design and may guide treatment for these devastating brain tumors in children.

MYC overexpression and SMARCA4 loss cooperate to drive medulloblastoma formation in mice

Group 3 medulloblastoma is one of the most aggressive types of childhood brain tumors. Roughly 30% of cases carry genetic alterations in MYC, SMARCA4, or both genes combined. While overexpression of MYC has previously been shown to drive medulloblastoma formation in mice, the functional significance of SMARCA4 mutations and their suitability as a therapeutic target remain largely unclear. To address this issue, we combined overexpression of MYC with a loss of SMARCA4 in granule cell precursors. Both alterations did not increase proliferation of granule cell precursors in vitro. However, combined MYC overexpression and SMARCA4 loss successfully induced tumor formation in vivo after orthotopic transplantation in recipient mice. Resulting tumors displayed anaplastic histology and exclusively consisted of SMARCA4-negative cells although a mixture of recombined and non-recombined cells was injected. These observations provide first evidence for a tumor-promoting role of a SMARCA4 deficiency in the development of medulloblastoma. In comparing the transcriptome of tumors to the cells of origin and an established Sonic Hedgehog medulloblastoma model, we gathered first hints on deregulated gene expression that could be specifically involved in SMARCA4/MYC driven tumorigenesis. Finally, an integration of RNA sequencing and DNA methylation data of murine tumors with human samples revealed a high resemblance to human Group 3 medulloblastoma on the molecular level. Altogether, the development of SMARCA4-deficient medulloblastomas in mice paves the way to deciphering the role of frequently occurring SMARCA4 alterations in Group 3 medulloblastoma with the perspective to explore targeted therapeutic options.

Medulloblastoma targeted therapy: From signaling pathways heterogeneity and current treatment dilemma to the recent advances in development of therapeutic strategies

Medulloblastoma (MB) is a major pediatric malignant brain tumor that arises in the cerebellum. MB tumors exhibit highly heterogeneous driven by diverse genetic alterations and could be divided into four major subgroups based on their different biological drivers and molecular features (Wnt, Sonic hedgehog (Shh), group 3, and group 4 MB). Even though the therapeutic strategies for each MB subtype integrate their pathogenesis and were developed to focus on their specific target sites, the unexpected drug non-selective cytotoxicity, low drug accumulation in the brain, and complexed MB tumor microenvironment still be huge obstacles to achieving satisfied MB therapeutic efficiency. This review discussed the current advances in modern MB therapeutic strategy development. Through the recent advances in knowledge of the origin, molecular pathogenesis of MB subtypes and their current therapeutic barriers, we particularly reviewed the current development in advanced MB therapeutic strategy committed to overcome MB treatment obstacles, focusing on novel signaling pathway targeted therapeutic agents and their combination discovery, advanced drug delivery systems design, and MB immunotherapy strategy development.

Discovery of (S)-N1-(thiazol-2-yl) pyrrolidine-1,2-dicarboxamide derivatives targeting PI3Ka/HDAC6 for the treatment of cancer

Recently, PI3K and HDAC have been considered as promising targets for the cancer therapy. A couple of pan-PI3K/HDAC dual inhibitors have been developed as a new class of anticancer agents. Herein, we discovered a new series of (S)-N1-(thiazol-2-yl) pyrrolidine-1,2-dicarboxamide derivatives targeting PI3Kα/HDAC6. All the derivatives exerted dual-target inhibitory activities. Particularly, in the enzymatic selectivity assay, compound 21j was identified as a subtype-selective PI3Kα/HDAC6 dual inhibitor (IC50 = 2.9 and 26 nM against PI3Kα and HDAC6, respectively), which displayed high potency against L-363 cell line with IC50 value of 0.17 μM. In addition, 21j significantly inhibited phosphorylation of pAkt(Ser473) and induced accumulation of acetylated α-tubulin while having a negligible effect on the levels of acetylated Histone H3 and H4 at nanomolar level. Attributed to its favorable in vitro performance, 21j has the potential to alleviate the adverse effects resulted from pan-PI3K inhibition and pan-HDAC inhibition. It is valuable for further functional investigation as an anti-cancer agent.

SCARB2 drives hepatocellular carcinoma tumor initiating cells via enhanced MYC transcriptional activity

CSCs (Cancer stem cells) with distinct metabolic features are considered to cause HCC (hepatocellular carcinoma) initiation, metastasis and therapeutic resistance. Here, we perform a metabolic gene CRISPR/Cas9 knockout library screen in tumorspheres derived from HCC cells and find that deletion of SCARB2 suppresses the cancer stem cell-like properties of HCC cells. Knockout of Scarb2 in hepatocytes attenuates HCC initiation and progression in both MYC-driven and DEN (diethylnitrosamine)-induced HCC mouse models. Mechanistically, binding of SCARB2 with MYC promotes MYC acetylation by interfering with HDCA3-mediated MYC deacetylation on lysine 148 and subsequently enhances MYC transcriptional activity. Screening of a database of FDA (Food and Drug Administration)-approved drugs shows Polymyxin B displays high binding affinity for SCARB2 protein, disrupts the SCARB2-MYC interaction, decreases MYC activity, and reduces the tumor burden. Our study identifies SCARB2 as a functional driver of HCC and suggests Polymyxin B-based treatment as a targeted therapeutic option for HCC.

Advances of antitumor drug discovery in traditional Chinese medicine and natural active products by using multi-active components combination

The antitumor efficacy of Chinese herbal medicines has been widely recognized. Leading compounds such as sterols, glycosides, flavonoids, alkaloids, terpenoids, phenylpropanoids, and polyketides constitute their complex active components. The antitumor monomers derived from Chinese medicine possess an attractive anticancer activity. However, their use was limited by low bioavailability, significant toxicity, and side effects, hindering their clinical applications. Recently, new chemical entities have been designed and synthesized by combining natural drugs with other small drug molecules or active moieties to improve the antitumor activity and selectivity, and reduce side effects. Such a novel conjugated drug that can interact with several vital biological targets in cells may have a more significant or synergistic anticancer activity than a single-molecule drug. In addition, antitumor conjugates could be obtained by combining pharmacophores containing two or more known drugs or leading compounds. Based on these studies, the new drug research and development could be greatly shortened. This study reviews the research progress of conjugates with antitumor activity based on Chinese herbal medicine. It is expected to serve as a valuable reference to antitumor drug research and clinical application of traditional Chinese medicine.

Surviving the hunger games: Metabolic reprogramming in medulloblastoma

Medulloblastoma is a highly malignant pediatric brain tumor characterized by its aggressive nature and limited treatment options. Metabolic changes have recently emerged as key factors in the development, progression, and response to therapy in various types of cancer. Cancer cells exhibit remarkable adaptability by modulating glucose, lipids, amino acids, and nucleotide metabolism to survive in nutrient- and oxygen-deprived environments. Although medulloblastoma has been extensively studied from a genomic perspective, leading to the identification of four subgroups and their respective subcategories, the investigation of its metabolic phenotype has remained relatively understudied. This review focus on the available literature, aiming to summarize the current knowledge about the main metabolic pathways that are deregulated in medulloblastoma tumors, while emphasizing the controversial aspects and the progress that is yet to be made. Furthermore, we underscored the insights gained so far regarding the impact of metabolism on the development of drug resistance in medulloblastoma and the therapeutic strategies employed to target specific metabolic pathways.

Class I HDAC inhibition reduces DNA damage repair capacity of MYC-amplified medulloblastoma cells

PURPOSE

MYC-driven Group 3 medulloblastoma (MB) (subtype II) is a highly aggressive childhood brain tumor. Sensitivity of MYC-driven MB to class I histone deacetylase inhibitors (HDACi) has been previously demonstrated in vitro and in vivo. In this study we characterize the transcriptional effects of class I HDACi in MYC-driven MB and explore beneficial drug combinations.

METHODS

MYC-amplified Group 3 MB cells (HD-MB03) were treated with class I HDACi entinostat. Changes in the gene expression profile were quantified on a microarray. Bioinformatic assessment led to the identification of pathways affected by entinostat treatment. Five drugs interfering with these pathways (olaparib, idasanutlin, ribociclib, selinexor, vinblastine) were tested for synergy with entinostat in WST-8 metabolic activity assays in a 5 × 5 combination matrix design. Synergy was validated in cell count and flow cytometry experiments. The effect of entinostat and olaparib on DNA damage was evaluated by γH2A.X quantification in immunoblotting, fluorescence microscopy and flow cytometry.

RESULTS

Entinostat treatment changed the expression of genes involved in 22 pathways, including downregulation of DNA damage response. The PARP1 inhibitors olaparib and pamiparib showed synergy with entinostat selectively in MYC-amplified MB cells, leading to increased cell death, decreased viability and increased formation of double strand breaks, as well as increased sensitivity to additional induction of DNA damage by doxorubicin. Non-MYC-amplified MB cells and normal human fibroblasts were not susceptible to this triple treatment.

CONCLUSION

Our study identifies the combination of entinostat with olaparib as a new potential therapeutic approach for MYC-driven Group 3 MB.

Quatramer™ encapsulation of dual-targeted PI3-Kδ/HDAC6 inhibitor, HSB-510, suppresses growth of breast cancer

Multiple studies have shown that the progression of breast cancer depends on multiple signaling pathways, suggesting that therapies with multitargeted anticancer agents will offer improved therapeutic benefits through synergistic effects in inhibiting cancer growth. Dual-targeted inhibitors of phosphoinositide 3-kinase (PI3-K) and histone deacetylase (HDAC) have emerged as promising cancer therapy candidates. However, poor aqueous solubility and bioavailability limited their efficacy in cancer. The present study investigates the encapsulation of a PI3-Kδ/HDAC6 dual inhibitor into hybrid block copolymers (polylactic acid-methoxy polyethylene glycol; polylactic acid-polyethylene glycol-polypropylene glycol-polyethylene glycol-polylactic acid) (HSB-510) as a delivery system to target PI3-Kδ and HDAC6 pathways in breast cancer cells. The prepared HSB-510 showed an average diameter of 96 ± 3 nm, a zeta potential of -17 ± 2 mV, and PDI of ˂0.1 with a slow and sustained release profile of PI3-Kδ/HDAC6 inhibitors in a nonphysiological buffer. In vitro studies with HSB-510 have demonstrated substantial growth inhibition of breast cancer cell lines, MDA-MB-468, SUM-149, MCF-7, and Ehrlich ascites carcinoma (EAC) as well as downregulation of phospho-AKT, phospho-ERK, and c-Myc levels. Importantly, bi-weekly treatment of Balb/c wild-type mice harboring EAC cells with HSB-510 at a dose of 25 mg/kg resulted in significant tumor growth inhibition. The treatment with HSB-510 was without any significant effect on the body weights of the mice. These results demonstrate that a novel Quatramer encapsulation of a PI3-Kδ/HDAC6 dual inhibitor (HSB-510) represents an approach for the successful targeting of breast cancer and potentially other cancer types.

Current Strategies for Management of Medulloblastoma

Medulloblastoma (MB) is the most common malignant central nervous system tumor of childhood, which includes multiple molecular subgroups (4) and subtypes (8 to 12), each with different outcomes and potential therapy options. Long-term survival remains poor for many of the subtypes, with high late mortality risks and poor health-related quality of life. Initial treatment strategies integrate molecular subgroup information with more standard clinical and phenotypic factors to risk stratify newly diagnosed patients. Clinical trials treating relapsed disease, often incurable, now include multiple new approaches in an attempt to improve progression-free and overall survival.

The Neurodevelopmental and Molecular Landscape of Medulloblastoma Subgroups: Current Targets and the Potential for Combined Therapies

Medulloblastoma is the most common malignant pediatric brain tumor and is associated with significant morbidity and mortality in the pediatric population. Despite the use of multiple therapeutic approaches consisting of surgical resection, craniospinal irradiation, and multiagent chemotherapy, the prognosis of many patients with medulloblastoma remains dismal. Additionally, the high doses of radiation and the chemotherapeutic agents used are associated with significant short- and long-term complications and adverse effects, most notably neurocognitive delay. Hence, there is an urgent need for the development and clinical integration of targeted treatment regimens with greater efficacy and superior safety profiles. Since the adoption of the molecular-based classification of medulloblastoma into wingless (WNT) activated, sonic hedgehog (SHH) activated, group 3, and group 4, research efforts have been directed towards unraveling the genetic, epigenetic, transcriptomic, and proteomic profiles of each subtype. This review aims to delineate the progress that has been made in characterizing the neurodevelopmental and molecular features of each medulloblastoma subtype. It further delves into the implications that these characteristics have on the development of subgroup-specific targeted therapeutic agents. Furthermore, it highlights potential future avenues for combining multiple agents or strategies in order to obtain augmented effects and evade the development of treatment resistance in tumors.

An effective kinase inhibition strategy for metastatic recurrent childhood medulloblastoma

PURPOSE

Medulloblastomas (MBs) constitute the most common malignant brain tumor in children and adolescents. MYC-amplified Group 3 MBs are characterized by disease recurrence, specifically in the leptomeninges, whereby patients with these metastatic tumors have a mortality rate nearing 100%. Despite limited research on such tumors, studies on MB metastases at diagnosis suggest targeting kinases to be beneficial.

METHODS

To identify kinase inhibitors that eradicate cells driving therapy evasion and tumor dissemination, we utilized our established patient-derived xenograft (PDX) mouse-adapted therapy platform that models human MB metastatic recurrences following standard chemoradiotherapy. High-throughput screens of 640 kinase inhibitors were conducted against cells isolated from mouse spines in the PDX model and human fetal neural stem cells to reveal compounds that targeted these treatment-refractory, metastatic cells, whilst sparing healthy cells. Blood-brain barrier permeability assays and additional in vitro experimentation helped select top candidates for in vivo studies.

RESULTS

Recurrent Group 3 MB PDX spine cells were therapeutically vulnerable to a selective checkpoint kinase 1 (CHK1) inhibitor and small molecular inhibitor of platelet-derived growth factor receptor beta (PDGFRβ). Inhibitor-treated cells showed a significant reduction in MB stem cell properties associated with treatment failure. Mice also demonstrated survival advantage when treated with a CHK1 inhibitor ex vivo.

CONCLUSION

We identified CHK1 and PDGFRβ inhibitors that effectively target MB cells fueling treatment-refractory metastases. With limited research on effective therapies for Group 3 MB metastatic recurrences, this work highlights promising therapeutic options to treat these aggressive tumors. Additional studies are warranted to investigate these inhibitors' mechanisms and recommended in vivo administration.

Single-cell transcriptomics uncovers cellular architecture and developmental trajectories in hepatoblastoma

BACKGROUND AND AIMS

Hepatoblastoma (HB) is the predominant type of childhood liver cancer. Treatment options for the clinically advanced HB remain limited. We aimed to dissect the cellular and molecular basis underlying HB oncogenesis and heterogeneity at the single-cell level, which could facilitate a better understanding of HB at both the biological and clinical levels.

APPROACH AND RESULTS

Single-cell transcriptome profiling of tumor and paired distal liver tissue samples from five patients with HB was performed. Deconvolution analysis was used for integrating the single-cell transcriptomic profiles with the bulk transcriptomes of our HB cohort of post-neoadjuvant chemotherapy tumor samples. A single-cell transcriptomic landscape of early human liver parenchymal development was established for exploring the cellular root and hierarchy of HB oncogenesis. As a result, seven distinct tumor cell subpopulations were annotated, and an effective HB subtyping method was established based on their compositions. A HB tumor cell hierarchy was further revealed to not only fit with the classical cancer stem cell (CSC) model but also mirror the early human liver parenchymal development. Moreover, FACT inhibition, which could disrupt the oncogenic positive feedback loop between MYC and SSRP1 in HB, was identified as a promising epigenetic-targeted therapeutic strategy against the CSC-like HB1-Pro-like1 subpopulation and its related high-risk "Pro-like1" subtype of HB.

CONCLUSIONS

Our findings illustrate the cellular architecture and developmental trajectories of HB via integrative bulk and single-cell transcriptome analyses, thus establishing a resourceful framework for the development of targeted diagnostics and therapeutics in the future.

Class I HDAC inhibitor entinostat synergizes with PLK1 inhibitors in MYC-amplified medulloblastoma cells

PURPOSE

We and others have demonstrated that MYC-amplified medulloblastoma (MB) cells are susceptible to class I histone deacetylase inhibitor (HDACi) treatment. However, single drug treatment with HDACi has shown limited clinical efficacy. We hypothesized that addition of a second compound acting synergistically with HDACi may enhance efficacy.

METHODS

We used a gene expression dataset to identify PLK1 as a second target in MB cells and validated the relevance of PLK1 in MB. We measured cell metabolic activity, viability, and cycle progression in MB cells after treatment with PLK1-specific inhibitors (PLK1i). Chou-Talalay synergy calculations were used to determine the nature of class I HDACi entinostat and PLK1i interaction which was validated. Finally, the clinical potential of the combination was assessed in the in vivo experiment.

RESULTS

MYC-amplified tumor cells are highly sensitive towards treatment with ATP-competitive PLK1i as a monotherapy. Entinostat and PLK1i in combination act synergistically in MYC-driven MB cells, exerting cytotoxic effects at clinically relevant concentrations. The downstream effect is exerted via MYC-related pathways, pointing out the potential of MYC amplification as a clinically feasible predictive biomarker for patient selection. While entinostat significantly extended survival of mice implanted with orthotopic MYC-amplified MB PDX, there was no evidence of the improvement of survival when treating the animals with the combination.

CONCLUSION

The combination of entinostat and PLK1i showed synergistic interaction in vitro, but not in vivo. Therefore, further screening of blood-brain barrier penetrating PLK1i is warranted to determine the true potential of the combination as no on-target activity was observed after PLK1i volasertib treatment in vivo.

Childhood Brain Tumors: A Review of Strategies to Translate CNS Drug Delivery to Clinical Trials

Brain and spinal tumors affect 1 in 1000 people by 25 years of age, and have diverse histological, biological, anatomical and dissemination characteristics. A mortality of 30-40% means the majority are cured, although two-thirds have life-long disability, linked to accumulated brain injury that is acquired prior to diagnosis, and after surgery or chemo-radiotherapy. Only four drugs have been licensed globally for brain tumors in 40 years and only one for children. Most new cancer drugs in clinical trials do not cross the blood-brain barrier (BBB). Techniques to enhance brain tumor drug delivery are explored in this review, and cover those that augment penetration of the BBB, and those that bypass the BBB. Developing appropriate delivery techniques could improve patient outcomes by ensuring efficacious drug exposure to tumors (including those that are drug-resistant), reducing systemic toxicities and targeting leptomeningeal metastases. Together, this drug delivery strategy seeks to enhance the efficacy of new drugs and enable re-evaluation of existing drugs that might have previously failed because of inadequate delivery. A literature review of repurposed drugs is reported, and a range of preclinical brain tumor models available for translational development are explored.

Combination of Ribociclib with BET-Bromodomain and PI3K/mTOR Inhibitors for Medulloblastoma Treatment In Vitro and In Vivo

Despite improvement in the treatment of medulloblastoma over the last years, numerous patients with MYC- and MYCN-driven tumors still fail current therapies. Medulloblastomas have an intact retinoblastoma protein RB, suggesting that CDK4/6 inhibition might represent a therapeutic strategy for which drug combination remains understudied. We conducted high-throughput drug combination screens in a Group3 (G3) medulloblastoma line using the CDK4/6 inhibitor (CDK4/6i) ribociclib at IC20, referred to as an anchor, and 87 oncology drugs approved by FDA or in clinical trials. Bromodomain and extra terminal (BET) and PI3K/mTOR inhibitors potentiated ribociclib inhibition of proliferation in an established cell line and freshly dissociated tumor cells from intracranial xenografts of G3 and Sonic hedgehog (SHH) medulloblastomas in vitro. A reverse combination screen using the BET inhibitor JQ1 as anchor, revealed CDK4/6i as the most potentiating drugs. In vivo, ribociclib showed single-agent activity in medulloblastoma models whereas JQ1 failed to show efficacy due to high clearance and insufficient free brain concentration. Despite in vitro synergy, combination of ribociclib with the PI3K/mTOR inhibitor paxalisib did not significantly improve the survival of G3 and SHH medulloblastoma-bearing mice compared with ribociclib alone. Molecular analysis of ribociclib and paxalisib-treated tumors revealed that E2F targets and PI3K/AKT/MTORC1 signaling genes were depleted, as expected. Importantly, in one untreated G3MB model HD-MB03, the PI3K/AKT/MTORC1 gene set was enriched in vitro compared with in vivo suggesting that the pathway displayed increased activity in vitro. Our data illustrate the difficulty in translating in vitro findings in vivo. See related article in Mol Cancer Ther (2022) 21(8):1306-1317.

Tacedinaline (CI-994), a class I HDAC inhibitor, targets intrinsic tumor growth and leptomeningeal dissemination in MYC-driven medulloblastoma while making them susceptible to anti-CD47-induced macrophage phagocytosis via NF-kB-TGM2 driven tumor inflammation

BACKGROUND

While major advances have been made in improving the quality of life and survival of children with most forms of medulloblastoma (MB), those with MYC-driven tumors (Grp3-MB) still suffer significant morbidity and mortality. There is an urgent need to explore multimodal therapeutic regimens which are effective and safe for children. Large-scale studies have revealed abnormal cancer epigenomes caused by mutations and structural alterations of chromatin modifiers, aberrant DNA methylation, and histone modification signatures. Therefore, targeting epigenetic modifiers for cancer treatment has gained increasing interest, and inhibitors for various epigenetic modulators have been intensively studied in clinical trials. Here, we report a cross-entity, epigenetic drug screen to evaluate therapeutic vulnerabilities in MYC amplified MB, which sensitizes them to macrophage-mediated phagocytosis by targeting the CD47-signal regulatory protein α (SIRPα) innate checkpoint pathway.

METHODS

We performed a primary screen including 78 epigenetic inhibitors and a secondary screen including 20 histone deacetylase inhibitors (HDACi) to compare response profiles in atypical teratoid/rhabdoid tumor (AT/RT, n=11), MB (n=14), and glioblastoma (n=14). This unbiased approach revealed the preferential activity of HDACi in MYC-driven MB. Importantly, the class I selective HDACi, CI-994, showed significant cell viability reduction mediated by induction of apoptosis in MYC-driven MB, with little-to-no activity in non-MYC-driven MB, AT/RT, and glioblastoma in vitro. We tested the combinatorial effect of targeting class I HDACs and the CD47-SIRPa phagocytosis checkpoint pathway using in vitro phagocytosis assays and in vivo orthotopic xenograft models.

RESULTS

CI-994 displayed antitumoral effects at the primary site and the metastatic compartment in two orthotopic mouse models of MYC-driven MB. Furthermore, RNA sequencing revealed nuclear factor-kB (NF-κB) pathway induction as a response to CI-994 treatment, followed by transglutaminase 2 (TGM2) expression, which enhanced inflammatory cytokine secretion. We further show interferon-γ release and cell surface expression of engulfment ('eat-me') signals (such as calreticulin). Finally, combining CI-994 treatment with an anti-CD47 mAb targeting the CD47-SIRPα phagocytosis checkpoint enhanced in vitro phagocytosis and survival in tumor-bearing mice.

CONCLUSION

Together, these findings suggest a dynamic relationship between MYC amplification and innate immune suppression in MYC amplified MB and support further investigation of phagocytosis modulation as a strategy to enhance cancer immunotherapy responses.

Current studies and future directions for medulloblastoma: A review from the pacific pediatric neuro-oncology consortium (PNOC) disease working group

Medulloblastoma (MB) is the most common malignant central nervous system tumor of childhood, comprising a heterogenous group of tumors each with distinct biology, clinical behavior, and prognosis. Long-term survival remains unacceptable, and those who do survive face high late mortality risk, new chronic treatment-related medical conditions, neurocognitive impairments, and poor health-related quality of life. Up-front treatment strategies now integrate molecular subgrouping with standard clinico-radiological factors to more actually risk stratify newly-diagnosed patients. To what extent this new stratification will lead to improvements in treatment outcome will be determined in the coming years. In parallel, discovery and appreciation for medulloblastoma's inter- and intra-tumoral heterogeneity continues growing. Clinical trials treating relapsed disease now encompass precision medicine, epigenetic modification, and immune therapy approaches. The Pacific Pediatric Neuro-Oncology (PNOC) Medulloblastoma Working Group is committed to developing clinical trials based on these evolving therapeutic strategies and supports translational efforts by PNOC researchers and the multi-stakeholder medulloblastoma community at large.

A novel dual epigenetic approach targeting BET proteins and HDACs in Group 3 (MYC-driven) Medulloblastoma

Background

Medulloblastoma (MB) patients with MYC oncogene amplification or overexpression exhibit extremely poor clinical outcomes and respond poorly to current therapies. Epigenetic deregulation is very common in MYC-driven MB. The bromodomain extra-terminal (BET) proteins and histone deacetylases (HDACs) are epigenetic regulators of MYC transcription and its associated tumorigenic programs. This study aimed to investigate the therapeutic potential of inhibiting the BET proteins and HDACs together in MB.

Methods

Using clinically relevant BET inhibitors (JQ1 or OTX015) and a pan-HDAC inhibitor (panobinostat), we evaluated the effects of combined inhibition on cell growth/survival in MYC-amplified MB cell lines and xenografts and examined underlying molecular mechanism(s).

Results

Co-treatment of JQ1 or OTX015 with panobinostat synergistically suppressed growth/survival of MYC-amplified MB cells by inducing G2 cell cycle arrest and apoptosis. Mechanistic investigation using RNA-seq revealed that co-treatment of JQ1 with panobinostat synergistically modulated global gene expression including MYC/HDAC targets. SYK and MSI1 oncogenes were among the top 50 genes synergistically downregulated by JQ1 and panobinostat. RT-PCR and western blot analyses confirmed that JQ1 and panobinostat synergistically inhibited the mRNA and protein expression of MSI1/SYK along with MYC expression. Reduced SYK/MSI expression after BET (specifically, BRD4) gene-knockdown further confirmed the epigenetic regulation of SYK and MSI1 genes. In addition, the combination of OTX015 and panobinostat significantly inhibited tumor growth in MYC-amplified MB xenografted mice by downregulating expression of MYC, compared to single-agent therapy.

Conclusions

Together, our findings demonstrated that dual-inhibition of BET and HDAC proteins of the epigenetic pathway can be a novel therapeutic approach against MYC-driven MB.