Indoximod-based chemo-immunotherapy for pediatric brain tumors: A first-in-children phase I trial

Targeting the kynurenine pathway in gliomas: Insights into pathogenesis, therapeutic targets, and clinical advances

Gliomas, the most prevalent primary brain tumors, continue to present significant challenges in oncology due to poor patient prognosis despite advances in treatment such as immunotherapy and cancer vaccines. Recent research highlights the potential of targeting tryptophan metabolism, particularly the kynurenine pathway (KP) and combinatorial approaches with immunotherapies, as a promising strategy in cancer research. The key enzymes of the kynurenine pathway, such as IDO1, IDO2, and TDO, and metabolites like kynurenine, kynurenic acid, and quinolinic acid, are implicated in fostering an immunosuppressive tumor microenvironment and promoting glioma cell survival. In glioblastoma, a highly aggressive glioma subtype, elevated IDO and TDO expression correlates with reduced survival rates. KP metabolites, such as kynurenine (KYN), 3-hydroxykynurenine (3-HK), kynurenic acid (KYNA), and quinolinic acid (QUIN), are involved in modulating immune responses, oxidative stress, neuroprotection, and neurotoxicity. This review synthesizes recent findings on the kynurenine pathway involvement in glioma pathogenesis, examining potential therapeutic targets within this pathway and discussing ongoing clinical trials that draw attention to treatments based on this pathway. Furthermore, it highlights novel findings on the post-translational modifications of kynurenine pathway enzymes and their regulatory roles, presenting their potential as therapeutic targets in gliomas.

New insights into tryptophan metabolism in cancer

Tryptophan (Trp) is an essential amino acid and key intermediate in a range of biological processes. Early studies identified altered Trp utilization in cancer cells favoring cancer survival and growth. Seminal findings linking Trp metabolism and suppression of immunity led to an explosion of interest ultimately culminating in clinical trials targeting these pathways in melanoma. The failure of these trials led to a clinical retreat in this approach; however, recent insights into the complex interplay of the various Trp circuits and between tumor cells, immune cells, and the microbiota have shown that reconsideration of Trp metabolism is needed. Here, we discuss recent developments in our understanding of Trp metabolism and apparent contradictions in the field. We also discuss adaptations that occur when Trp pathways are manipulated, which may impact therapy responses.

Therapeutic approaches for targeting the pediatric brain tumor microenvironment

Central nervous system (CNS) tumors are the most frequent solid malignant tumors in pediatric patients and are the leading cause of tumor-related death in children. Treatment for this heterogeneous group of tumors consists of various combinations of safe maximal surgical resection, chemotherapy, and radiation therapy which offer a cure for some children but often cause debilitating adverse late effects in others. While therapies targeting the tumor microenvironment (TME) like immune checkpoint inhibition (ICI) have been successful in treating some cancers, these therapies failed to exhibit treatment efficacy in the majority of pediatric brain tumors in the clinic. Importantly, the pediatric TME is unique and distinct from adult brain tumors and designing therapies to effectively target these tumors requires understanding the unique biology of pediatric brain tumors and the use of translational models that recapitulate the TME. Here we describe the TME of medulloblastoma (MB) and diffuse midline glioma (DMG), specifically diffuse intrinsic pontine glioma (DIPG), and further present the current drug delivery approaches and clinical administration routes targeting the TME in these tumors, including preclinical and clinical studies.

Exploring the role of LOX family in glioma progression and immune modulation

Background

Glioma is a major cause of mortality among central nervous system tumors, with a generally poor prognosis. The lysyl oxidase (LOX) family, a group of copper-dependent amine oxidases, has been implicated in the progression of various cancers, but its specific role in glioma and its relationship with immune infiltration remains insufficiently explored. This study aims to investigate the LOX family's expression, prognostic significance, and immune infiltration dynamics in glioma to identify potential therapeutic targets.

Methods

A comprehensive analysis was conducted using public databases to assess gene expression, mutation frequency, and immune infiltration patterns related to the LOX family in glioma. The results were validated through survival analysis and immunohistochemistry. Functional assays, including EdU, Transwell, and flow cytometry, were used to evaluate glioma cell proliferation, migration, invasion, and apoptosis. Co-culture experiments with immune cells, ELISA, and a glioma transplantation model were employed to study the immune-modulatory effects of the LOX family. Gene and protein expression levels were further analyzed using qRT-PCR and Western blotting.

Results

The LOX family was significantly upregulated in low-grade gliomas and strongly associated with poor clinical outcomes. Although mutation frequencies were low, the LOX family contributed to glioma progression through pathways involving metastasis, hypoxia response, angiogenesis, and immune cell infiltration. LOX expression correlated with increased infiltration of macrophages and eosinophils and decreased presence of Treg and CD8+ T cells. Knockdown of LOX genes impaired glioma cell functions, induced apoptosis, and altered immune cell behavior by reducing M2 macrophage polarization and enhancing CD8+ T cell activity.

Conclusions

The LOX family is overexpressed in glioma and is associated with poor prognosis and altered immune infiltration patterns. These findings highlight the LOX family as a promising prognostic marker and therapeutic target, particularly for enhancing the effectiveness of immunotherapy in glioma treatment.

Metabolic cross-talk between glioblastoma and glioblastoma-associated microglia/macrophages: From basic insights to therapeutic strategies

Glioblastoma (GBM), a highly malignant "cold" tumor of the central nervous system, is characterized by its ability to remodel the GBM immune microenvironment (GME), leading to significant resistance to immunotherapy. GBM-associated microglia/macrophages (GAMs) are essential components of the GME. Targeting GAMs has emerged as a promising strategy against GBM. However, their highly immunosuppressive nature contributes to GBM progression and drug resistance, significantly impeding anti-GBM immunotherapy. Accumulating evidence suggests that metabolic reprogramming accompanies GBM progression and GAM polarization, which are in turn driven by specific metabolic abnormalities and altered cellular signaling pathways. Importantly, metabolic crosstalk between GBM and GAMs further promotes tumor progression. Clarifying and disrupting this metabolic crosstalk is expected to enhance the antitumor phenotype of GAMs and inhibit GBM malignant progression. This review explores metabolism-based interregulation between GBM and GAMs and summarizes recent therapeutic strategies targeting this crosstalk, offering new insights into GBM immunotherapy.

Targeted therapy for pediatric glioma: RAF(t)ing in the molecular era

BACKGROUND

Pediatric gliomas are the most frequently occurring central nervous system tumors in children. While targeted therapies have been widely applied in the treatment of many adult cancers, their use in pediatric gliomas has lagged behind. However, recent advances in multiomics profiling of pediatric gliomas, coupled with the approval of inhibitors against Raf serine/threonine kinase (RAF), isocitrate dehydrogenase 1/2 (IDH1/2) and neurotrophic receptor tyrosine kinase (NTRK), have spurred significant progress in this field. In light of these developments, this review aims to provide a comprehensive overview of current advancements and the evolving landscape of targeted therapeutic strategies and approaches for pediatric gliomas.

DATA SOURCES

Data analyzed in this study were obtained from the literature from PubMed, as well as other online databases and websites, including ClinicalTrials.gov and the Pediatric Neuro-Oncology Consortium.

RESULTS

Based on findings from multiomics profiling, significant insights have been gained into the genetic and molecular landscape of pediatric gliomas, enabling the identification of key mutations and potentially targetable lesions. These advancements provide rationales for the development of more precise treatment strategies and targeted therapies. Recent approvals of targeted therapies and ongoing clinical trials in pediatric gliomas are converging on the targeting of key signaling molecules and metabolic pathways.

CONCLUSIONS

In the molecular era, targeted therapies offer new hope for more effective and personalized treatment options for pediatric glioma patients. By developing and tailoring treatments to target specific molecular and metabolic vulnerabilities, targeted therapies have the potential to improve the clinical management of pediatric gliomas, ultimately enhancing both the treatment experience and overall prognosis of these patients.

Amino acid metabolism in glioblastoma pathogenesis, immune evasion, and treatment resistance

Glioblastoma (GBM) ranks among the most lethal primary tumors of the central nervous system. This is partly due to its complex intracellular metabolism and interactions with the surrounding tumor microenvironment (TME). Compelling evidence represents that altered amino acids (AAs) metabolism plays a crucial role in both areas. The role of AAs and their metabolites in glioma biology is an emerging topic. Therefore, this review was conducted to summarize the current knowledge about the molecular mechanisms by which AAs participate in the GBM pathogenesis. AAs can directly influence tumor progression by affecting tumor cell metabolism or indirectly by releasing bioactive agents through particular metabolic pathways. This review begins by examining the metabolic pathways of essential AAs, such as tryptophan, tyrosine, and phenylalanine, which contribute to synthesizing critical neurotransmitters and shape tumor metabolism signatures. We explore how these pathways impact tumor growth and immune modulation, focusing on how AAs and their metabolites can promote malignant properties in GBM cells. AAs also play a pivotal role in reprogramming the TME, contributing to immune evasion and resistance to therapy. The review further discusses how tumor metabolism signatures, influenced by AA metabolism, can enhance the immunosuppressive microenvironment, providing new avenues for targeted immunotherapies. Finally, we outline potential therapeutic strategies to modulate AA metabolism and emphasize critical opportunities for future research to improve GBM management.

Blocking Feedback Immunosuppression of Antigen Presentation in Brain Tumor During Oncolytic Virotherapy with oHSV-mshPKR

Glioblastoma (GBM) is the most frequent malignant brain tumor. We recently discovered that oncolytic herpes simplex virus engineered to disable tumor-intrinsic protein kinase R (PKR) signaling (oHSV-shPKR) could increase oHSV oncolysis and antitumor immune response. However, in this study, we show that disabling tumor-intrinsic PKR signaling can also induce the activation of the indoleamine 2,3-dioxygenase (IDO) signaling pathway. Both GBM tumor progression and oHSV intratumoral therapy increased infiltration of IDO+CD11c+ dendritic cells (DC) into the tumor. The coculture of oHSV-infected human GBM neurospheres with monocyte-derived DCs (MoDC) dramatically increased IDO signaling activation in MoDCs through type-I IFN signaling. Addition of IDO inhibitor (indoximod) in the coculture significantly increased MoDC activation and reduced the consumption of tryptophan. Combining indoximod and oHSV significantly inhibited tumor growth and induced antigen-specific CD8+ T-cell activation. These results suggest that inhibition of the IDO pathway could significantly block feedback immunosuppression during oncolytic virotherapy of GBM.

SN-38-indoximod conjugate: carrier free nano-prodrug for cancer therapy

BACKGROUND

The integration of immunotherapy alongside chemotherapy represents a crucial approach in the treatment of cancer. Herein we report the SN-38-indoximod conjugate nano-prodrug to address the difficulties encountered by individuals. In this prodrug, SN-38 is connected to indoximod through a specific disulfide linker, which enables the release of the components in response to the tumor microenvironment characterized by elevated levels of glutathione, thereby facilitating programmed chemoimmunotherapy.

RESULTS

SN-38-indoximod conjugate was synthesized and fabricated to nano-prodrug by reprecipitation method. It showed comparable anti-cancer activity against A549 cells than SN-38 (IC50 = 0.24 ± 0.01 µM) with IC50 value 0.32 ± 0.04 µM. It inhibited 90% A549 cell at very lower concentration (IC90 = 6.07 ± 0.41 µM) as compared with SN-38 (IC90 = 24.60 ± 1.24 µM) and mixture of SN-38: indoximod (1:1, IC90 >30 µM). The nano-prodrug showed better size distribution profile and dispersion stability contains nanoparticles in effective size range (80-160 nm) required for the EPR effect.

CONCLUSION

This research offers valuable insights into the advancement of conjugate nano-prodrugs exhibiting synergistic pharmacological effects, while also presenting novel opportunities for the design of prodrug molecules capable of releasing drugs in response to diverse triggers.

Metabolism of Tryptophan, Glutamine, and Asparagine in Cancer Immunotherapy-Synergism or Mechanism of Resistance?

Amino acids are crucial components of proteins, key molecules in cellular physiology and homeostasis. However, they are also involved in a variety of other mechanisms, such as energy homeostasis, nitrogen exchange, further synthesis of bioactive compounds, production of nucleotides, or activation of signaling pathways. Moreover, amino acids and their metabolites have immunoregulatory properties, significantly affecting the behavior of immune cells. Immunotherapy is one of the oncological treatment methods that improves cytotoxic properties of one's own immune system. Thus, enzymes catalyzing amino acid metabolism, together with metabolites themselves, can affect immune antitumor properties and responses to immunotherapy. In this review, we will discuss the involvement of tryptophan, glutamine, and asparagine metabolism in the behavior of immune cells targeted by immunotherapy and summarize results of the most recent investigations on the impact of amino acid metabolites on immunotherapy.

Biological function of d-tryptophan: a bibliometric analysis and review

Background

d-Tryptophan is recognised for its unique physiological properties. In this study, we aimed to explore the dynamic trends and emerging topics in d-tryptophan research to offer fresh perspectives for future studies.

Methods

Employing bibliometric analysis, we examined the literature on d-tryptophan indexed in the Web of Science Core Collection from January 1987 to December 2023. The "Bibliometrix" R package and CiteSpace were utilised for data processing.

Results

Analyses of 865 publications revealed 2209 keywords, 4068 authors, 2094 institutions, and contributors from 302 regions. The USA was at the forefront of publications concerning d-tryptophan, but the European Journal of Pharmacology, Journal of Biological Chemistry, and Journal of Medicinal Chemistry were notable for their contributions, co-citations, and impact, respectively. This literature review reveals that since 1987, studies have developed from a focus on d-tryptophan metabolism to the exploration of its functions in organic and medicinal chemistry and food science. Recent findings highlight the potential of d-tryptophan as a non-nutritional sweetener and food preservative as well as its role in inhibiting the growth of bacterial biofilms. Additionally, its immunomodulatory properties are being investigated in relation to allergic diseases. Furthermore, d-tryptophan plays a role in the therapy of atherosclerosis, osteoporosis, tuberculosis, and cancer.

Conclusion

The results of bibliometric analysis highlight that future research should focus on the biological functions of d-tryptophan as a food preservative and its use in immunomodulation and drug development, providing strong guidance for future research.

Exploring novel non-opioid pathways and therapeutics for pain modulation

The opioid crisis has highlighted the urgent need for alternative pain management strategies. This review explores novel non-opioid targets and pathways involved in pain modulation, highlighting advancements in understanding and therapeutic potential. Pain, a multifaceted phenomenon with nociceptive, neuropathic, and inflammatory components, involves intricate molecular signaling cascades. Key pathways reviewed include voltage-gated sodium channels (Nav1.7, Nav1.8, Nav1.9), inflammasome complexes (NLRP3), the kynurenine pathway, prostaglandins, and bradykinin-mediated signaling. Emerging therapeutics such as selective Nav channel blockers, NLRP3 inhibitors, kynurenine pathway modulators, EP receptor antagonists, and bradykinin receptor antagonists offer promising alternatives to opioids. Despite challenges in clinical translation, these developments signal a paradigm shift in pain management, with precision-focused therapies poised to address unmet needs. This review emphasizes the importance of integrating molecular insights into the development of safer, more effective analgesics, setting the stage for transformative advancements in non-opioid pain relief.

Improving the Anti-Tumor Effect of Indoleamine 2,3-Dioxygenase Inhibitor CY1-4 by CY1-4 Nano-Skeleton Drug Delivery System

Background: CY1-4, 9-nitropyridine [2',3':4,5] pyrimido [1,2-α] indole -5,11- dione, is an indoleamine 2,3-dioxygenase (IDO) inhibitor and a poorly water-soluble substance. It is very important to increase the solubility of CY1-4 to improve its bioavailability and therapeutic effect. In this study, the mesoporous silica nano-skeleton carrier material Sylysia was selected as the carrier to load CY1-4, and then the CY1-4 nano-skeleton drug delivery system (MSNM@CY1-4) was prepared by coating the hydrophilic polymer material Hydroxypropyl methylcellulose (HPMC) and the lipid material Distearoylphosphatidyl-ethanolamine-poly(ethylene glycol)2000 (DSPE-PEG2000) to improve the anti-tumor effect of CY1-4. Methods: The solubility and dissolution of MSNM@CY1-4 were investigated, and its bioavailability, anti-tumor efficacy, IDO inhibitory ability and immune mechanism were evaluated in vivo. Results: CY1-4 was loaded in MSNM@CY1-4 in an amorphous form, and MSNM@CY1-4 could significantly improve the solubility (up to about 200 times) and dissolution rate of CY1-4. In vivo studies showed that the oral bioavailability of CY1-4 in 20 mg/kg MSNM@CY1-4 was about 23.9-fold more than that in 50 mg/kg CY1-4 suspension. In B16F10 tumor-bearing mice, MSNM@CY1-4 significantly inhibited tumor growth, prolonged survival time, significantly inhibited IDO activity in blood and tumor tissues, and reduced Tregs in tumor tissues and tumor-draining lymph nodes to improve anti-tumor efficacy. Conclusions: The nano-skeleton drug delivery system (MSNM@CY1-4) constructed in this study is a potential drug delivery platform for improving the anti-tumor effect of oral poorly water-soluble CY1-4.

Tumor energy metabolism: implications for therapeutic targets

Tumor energy metabolism plays a crucial role in the occurrence, progression, and drug resistance of tumors. The study of tumor energy metabolism has gradually become an emerging field of tumor treatment. Recent studies have shown that epigenetic regulation is closely linked to tumor energy metabolism, influencing the metabolic remodeling and biological traits of tumor cells. This review focuses on the primary pathways of tumor energy metabolism and explores therapeutic strategies to target these pathways. It covers key areas such as glycolysis, the Warburg effect, mitochondrial function, oxidative phosphorylation, and the metabolic adaptability of tumors. Additionally, this article examines the role of the epigenetic regulator SWI/SNF complex in tumor metabolism, specifically its interactions with glucose, lipids, and amino acids. Summarizing therapeutic strategies aimed at these metabolic pathways, including inhibitors of glycolysis, mitochondrial-targeted drugs, exploitation of metabolic vulnerabilities, and recent developments related to SWI/SNF complexes as potential targets. The clinical significance, challenges, and future directions of tumor metabolism research are discussed, including strategies to overcome drug resistance, the potential of combination therapy, and the application of new technologies.

Oncolytic Virotherapies and Adjuvant Gut Microbiome Therapeutics to Enhance Efficacy Against Malignant Gliomas

Glioblastoma (GBM) is the most prevalent malignant brain tumor. Current standard-of-care treatments offer limited benefits for patient survival. Virotherapy is emerging as a novel strategy to use oncolytic viruses (OVs) for the treatment of GBM. These engineered and non-engineered viruses infect and lyse cancer cells, causing tumor destruction without harming healthy cells. Recent advances in genetic modifications to OVs have helped improve their targeting capabilities and introduce therapeutic genes, broadening the therapeutic window and minimizing potential side effects. The efficacy of oncolytic virotherapy can be enhanced by combining it with other treatments such as immunotherapy, chemotherapy, or radiation. Recent studies suggest that manipulating the gut microbiome to enhance immune responses helps improve the therapeutic efficacy of the OVs. This narrative review intends to explore OVs and their role against solid tumors, especially GBM while emphasizing the latest technologies used to enhance and improve its therapeutic and clinical responses.

Amino acid metabolic reprogramming in the tumor microenvironment and its implication for cancer therapy

Amino acids are essential building blocks for proteins, crucial energy sources for cell survival, and key signaling molecules supporting the resistant growth of tumor cells. In tumor cells, amino acid metabolic reprogramming is characterized by the enhanced uptake of amino acids as well as their aberrant synthesis, breakdown, and transport, leading to immune evasion and malignant progression of tumor cells. This article reviews the altered amino acid metabolism in tumor cells and its impact on tumor microenvironment, and also provides an overview of the current clinical applications of amino acid metabolism. Innovative drugs targeting amino acid metabolism hold great promise for precision and personalized cancer therapy.

Molecular mechanisms and therapeutic significance of Tryptophan Metabolism and signaling in cancer

Tryptophan (Trp) metabolism involves three primary pathways: the kynurenine (Kyn) pathway (KP), the 5-hydroxytryptamine (serotonin, 5-HT) pathway, and the indole pathway. Under normal physiological conditions, Trp metabolism plays crucial roles in regulating inflammation, immunity, and neuronal function. Key rate-limiting enzymes such as indoleamine-2,3-dioxygenase (IDO), Trp-2,3-dioxygenase (TDO), and kynurenine monooxygenase (KMO) drive these metabolic processes. Imbalances in Trp metabolism are linked to various cancers and often correlate with poor prognosis and adverse clinical characteristics. Dysregulated Trp metabolism fosters tumor growth and immune evasion primarily by creating an immunosuppressive tumor microenvironment (TME). Activation of the KP results in the production of immunosuppressive metabolites like Kyn, which modulate immune responses and promote oncogenesis mainly through interaction with the aryl hydrocarbon receptor (AHR). Targeting Trp metabolism therapeutically has shown significant potential, especially with the development of small-molecule inhibitors for IDO1, TDO, and other key enzymes. These inhibitors disrupt the immunosuppressive signals within the TME, potentially restoring effective anti-tumor immune responses. Recently, IDO1 inhibitors have been tested in clinical trials, showing the potential to enhance the effects of existing cancer therapies. However, mixed results in later-stage trials underscore the need for a deeper understanding of Trp metabolism and its complex role in cancer. Recent advancements have also explored combining Trp metabolism inhibitors with other treatments, such as immune checkpoint inhibitors, chemotherapy, and radiotherapy, to enhance therapeutic efficacy and overcome resistance mechanisms. This review summarizes the current understanding of Trp metabolism and signaling in cancer, detailing the oncogenic mechanisms and clinical significance of dysregulated Trp metabolism. Additionally, it provides insights into the challenges in developing Trp-targeted therapies and future research directions aimed at optimizing these therapeutic strategies and improving patient outcomes.

Brain macrophage senescence in glioma

Gliomas are a diverse group of primary central nervous system neoplasms with no curative therapies available. Brain macrophages comprise microglia in the brain parenchyma, border-associated macrophages in the meningeal-choroid plexus-perivascular space and monocyte-derived macrophages infiltrating the brain. With the great improvement of our recognition of brain macrophages, diverse macrophage populations have been found in the context of glioma, which exhibit functional and phenotypic heterogeneity. We have long thought that brain macrophage senescence is detrimental, manifested by specialized forms of persistent cell cycle arrest and chronic low-grade inflammation. Persistent senescence of macrophages may result in immune dysfunction, potentially contributing to glioma initiation and development. Given the crucial roles played by brain macrophages in glioma, we unravel how brain macrophages undergo reprogramming and their contribution to glioma. We outline general molecular alterations and specific biomarkers in senescent brain macrophages, as well as functional changes (such as metabolism, autophagy, phagocytosis, antigen presentation, and infiltration and recruitment). In addition, recent advances in genetic regulation and mechanisms linked to senescent brain macrophages are discussed. In particular, this review emphasizes the contribution of senescent brain macrophages to glioma, which may drive translational efforts to utilize brain macrophages as a prognostic marker or/and treatment target in glioma. An in-depth comprehending of how brain macrophage senescence functionally influences the tumor microenvironment will be key to our development of innovative therapeutics for glioma.

Pediatric Hemispheric High-Grade Gliomas and H3.3-G34 Mutation: A Review of the Literature on Biological Features and New Therapeutic Strategies

Pediatric high-grade glioma (pHGG) encompasses a wide range of gliomas with different genomic, epigenomic, and transcriptomic features. Almost 50% of pHGGs present a mutation in genes coding for histone 3, including the subtype harboring the H3.3-G34 mutation. In this context, histone mutations are frequently associated with mutations in TP53 and ATRX, along with PDGFRA and NOTCH2NL amplifications. Moreover, the H3.3-G34 histone mutation induces epigenetic changes in immune-related genes and exerts modulatory functions on the microenvironment. Also, the functionality of the blood-brain barrier (BBB) has an impact on treatment response. The prognosis remains poor with conventional treatments, thus eliciting the investigation of additional and alternative therapies. Promising molecular targets include PDGFRA amplification, BRAF mutation, EGFR amplification, NF1 loss, and IDH mutation. Considering that pHGGs harboring the H3.3-G34R mutation appear to be more susceptible to immunotherapies (ITs), different options have been recently explored, including immune checkpoint inhibitors, antibody mediated IT, and Car-T cells. This review aims to summarize the knowledge concerning cancer biology and cancer-immune cell interaction in this set of pediatric gliomas, with a focus on possible therapeutic options.

Current immunotherapeutic approaches to diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is an aggressive brain tumour that occurs in the pons of the brainstem and accounts for over 80% of all brainstem gliomas. The median age at diagnosis is 6-7 years old, with less than 10% overall survival 2 years after diagnosis and less than 1% after 5 years. DIPGs are surgically inaccessible, and radiation therapy provides only transient benefit, with death ensuing from relentless local tumour infiltration. DIPGs are now the leading cause of brain tumour deaths in children, with a societal cancer burden in years of life lost (YLL) of more than 67 per individual, versus approximately 14 and 16 YLL for lung and breast cancer respectively. More than 95 clinical drug trials have been conducted on children with DIPGs, and all have failed to improve survival. No single or combination chemotherapeutic strategy has been successful to date because of our inability to identify targeted drugs for this disease and to deliver these drugs across an intact blood-brain barrier (BBB). Accordingly, there has been an increased focus on immunotherapy research in DIPG, with explorations into treatments such as chimeric antigen receptor T (CAR-T) cells, immune checkpoint blockades, cancer vaccines, and autologous cell transfer therapy. Here, we review the most recent advances in identifying genetic factors influencing the development of immunotherapy for DIPG. Additionally, we explore emerging technologies such as Magnetic Resonance-guided Focused Ultrasound (MRgFUS) in potential combinatorial approaches to treat DIPG.

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.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

Small Molecule Tyrosine Kinase Inhibitors (TKIs) for Glioblastoma Treatment

In the last decade, many small molecules, usually characterized by heterocyclic scaffolds, have been designed and synthesized as tyrosine kinase inhibitors (TKIs). Among them, several compounds have been tested at preclinical and clinical levels to treat glioblastoma multiforme (GBM). GBM is the most common and aggressive type of cancer originating in the brain and has an unfavorable prognosis, with a median survival of 15-16 months and a 5-year survival rate of 5%. Despite recent advances in treating GBM, it represents an incurable disease associated with treatment resistance and high recurrence rates. For these reasons, there is an urgent need for the development of new pharmacological agents to fight this malignancy. In this review, we reported the compounds published in the last five years, which showed promising activity in GBM preclinical models acting as TKIs. We grouped the compounds based on the targeted kinase: first, we reported receptor TKIs and then, cytoplasmic and peculiar kinase inhibitors. For each small molecule, we included the chemical structure, and we schematized the interaction with the target for some representative compounds with the aim of elucidating the mechanism of action. Finally, we cited the most relevant clinical trials.