Opposing Tumor-Promoting and -Suppressive Functions of Rictor/mTORC2 Signaling in Adult Glioma and Pediatric SHH Medulloblastoma

A Neuroimmune-Oncology Microphysiological Analysis Platform (NEO-MAP) for Evaluating Astrocytic Scar Formation and Microgliosis in Glioblastoma Microenvironment

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor, characterized by its heterogeneity in cellular components, including reactive astrocytes and microglia. Since neuroimmune responses like astrogliosis and microgliosis gain recognition as vital factors in brain tumor progression, there is a growing need for clinically relevant models that assess the interactions between astrocytes, microglia, and GBM. Here, a NEuroimmune-Oncology Microphysiological Analysis Platform (NEO-MAP) is presented as a "new map" to observe astrocytic scar formation and microgliosis in response to GBM. NEO-MAP based on pathophysiological principles is designed to replicate the GBM-glia interactions, multi-phenotypic microglia activities, scar-forming astrocytes with chondroitin sulfate proteoglycans (CSPGs) in the extracellular matrix, and the biophysical characteristics of the astrocytic scar barrier. The NEO-MAP reveals that inhibiting mTORC2 in GBM promotes the proinflammatory transformation of astrocytes and enhanced astrocytic scar formation. Astrocytes that form scars prompted microglia to change from the M2 to M1 phenotype, enhancing chemotherapy sensitivity. Tissues from GBM patients show a significant correlation between reduced mTORC2 activity and increased astrogliosis, alongside a decrease in M2-polarized microgliosis, aligning with the NEO-MAP findings. Overall, the NEO-MAP is foreseen as a clinically significant tool for exploring tumor-glia interactions, opening avenues for drug development aimed at the tumor microenvironment.

Targeting gut microbiota: a potential therapeutic approach for tumor microenvironment in glioma

Glioma, being one of the malignant tumors with the highest mortality rate globally, has an unclear pathogenesis, and the existing treatment effects still have certain limitations. The tumor microenvironment (TME) plays an important role in the occurrence, development, and recurrence of glioma. As one of the important regulatory factors of TME, the gut microbiota can regulate the progression of glioma not only by interacting with the brain through the brain-gut axis but also by influencing the tumor immune microenvironment (TIME) and inflammatory microenvironment. Recent studies have identified the gut microbiota and TME as potential therapeutic targets for glioma. This paper aims to summarize the role of the gut microbiota in TME, the association between them and glioma, and the potential of developing new intervention measures by targeting the gut microbiota. Understanding the involvement process of the gut microbiota in glioma may pave the way for the development of effective treatment methods that can regulate TME and prevent disease progression.

RICTOR/mTORC2 downregulation in BRAFV600E melanoma cells promotes resistance to BRAF/MEK inhibition

BACKGROUND

The main drawback of BRAF/MEK inhibitors (BRAF/MEKi)-based targeted therapy in the management of BRAF-mutated cutaneous metastatic melanoma (MM) is the development of therapeutic resistance. We aimed to assess in this context the role of mTORC2, a signaling complex defined by the presence of the essential RICTOR subunit, regarded as an oncogenic driver in several tumor types, including MM.

METHODS

After analyzing The Cancer Genome Atlas MM patients' database to explore both overall survival and molecular signatures as a function of intra-tumor RICTOR levels, we investigated the effects of RICTOR downregulation in BRAFV600E MM cell lines on their response to BRAF/MEKi. We performed proteomic screening to identify proteins modulated by changes in RICTOR expression, and Seahorse analysis to evaluate the effects of RICTOR depletion on mitochondrial respiration. The combination of BRAFi with drugs targeting proteins and processes emerged in the proteomic screening was carried out on RICTOR-deficient cells in vitro and in a xenograft setting in vivo.

RESULTS

Low RICTOR levels in BRAF-mutated MM correlate with a worse clinical outcome. Gene Set Enrichment Analysis of low-RICTOR tumors display gene signatures suggestive of activation of the mitochondrial Electron Transport Chain (ETC) energy production. RICTOR-deficient BRAFV600E cells are intrinsically tolerant to BRAF/MEKi and anticipate the onset of resistance to BRAFi upon prolonged drug exposure. Moreover, in drug-naïve cells we observed a decline in RICTOR expression shortly after BRAFi exposure. In RICTOR-depleted cells, both mitochondrial respiration and expression of nicotinamide phosphoribosyltransferase (NAMPT) are enhanced, and their pharmacological inhibition restores sensitivity to BRAFi.

CONCLUSIONS

Our work unveils an unforeseen tumor-suppressing role for mTORC2 in the early adaptation phase of BRAFV600E melanoma cells to targeted therapy and identifies the NAMPT-ETC axis as a potential therapeutic vulnerability of low RICTOR tumors. Importantly, our findings indicate that the evaluation of intra-tumor RICTOR levels has a prognostic value in metastatic melanoma and may help to guide therapeutic strategies in a personalized manner.

mTOR hyperactivity and RICTOR amplification as targets for personalized treatments in malignancies

The increasing knowledge of molecular alterations in malignancies, including mutations and regulatory failures in the mTOR (mechanistic target of rapamycin) signaling pathway, highlights the importance of mTOR hyperactivity as a validated target in common and rare malignancies. This review summarises recent findings on the characterization and prognostic role of mTOR kinase complexes (mTORC1 and mTORC2) activity regarding differences in their function, structure, regulatory mechanisms, and inhibitor sensitivity. We have recently identified new tumor types with RICTOR (rapamycin-insensitive companion of mTOR) amplification and associated mTORC2 hyperactivity as useful potential targets for developing targeted therapies in lung cancer and other newly described malignancies. The activity of mTOR complexes is recommended to be assessed and considered in cancers before mTOR inhibitor therapy, as current first-generation mTOR inhibitors (rapamycin and analogs) can be ineffective in the presence of mTORC2 hyperactivity. We have introduced and proposed a marker panel to determine tissue characteristics of mTOR activity in biopsy specimens, patient materials, and cell lines. Ongoing phase trials of new inhibitors and combination therapies are promising in advanced-stage patients selected by genetic alterations, molecular markers, and/or protein expression changes in the mTOR signaling pathway. Hopefully, the summarized results, our findings, and the suggested characterization of mTOR activity will support therapeutic decisions.

Novel RICTOR amplification harbouring entities: FISH validation of RICTOR amplification in tumour tissue after next-generation sequencing

Alterations in mTOR signalling molecules, including RICTOR amplification, have been previously described in many cancers, particularly associated with poor prognosis. In this study, RICTOR copy number variation (CNV) results of diagnostic next-generation sequencing (NGS) were analysed in 420 various human malignant tissues. RICTOR amplification was tested by Droplet Digital PCR (ddPCR) and validated using the "gold standard" fluorescence in situ hybridisation (FISH). Additionally, the consequences of Rictor protein expression were also studied by immunohistochemistry. RICTOR amplification was presumed in 37 cases with CNV ≥ 3 by NGS, among these, 16 cases (16/420; 3.8%) could be validated by FISH, however, ddPCR confirmed only 11 RICTOR-amplified cases with lower sensitivity. Based on these, neither NGS nor ddPCR could replace traditional FISH in proof of RICTOR amplification. However, NGS could be beneficial to highlight potential RICTOR-amplified cases. The obtained results of the 14 different tumour types with FISH-validated RICTOR amplification demonstrate the importance of RICTOR amplification in a broad spectrum of tumours. The newly described RICTOR-amplified entities could initiate further collaborative studies with larger cohorts to analyse the prevalence of RICTOR amplification in rare diseases. Finally, our and further work could help to improve and expand future therapeutic opportunities for mTOR-targeted therapies.

Synthesis and Bioevaluation of 3-(Arylmethylene)indole Derivatives: Discovery of a Novel ALK Modulator with Antiglioblastoma Activities

Glioblastoma is the most common brain tumor, with high recurrence and low survival rates. An integrative bioinformatics analysis demonstrated that anaplastic lymphoma kinase (ALK) is a promising therapeutic target for glioblastoma. We designed and synthesized a series of 3-(arylmethylene)indole derivatives, which were further evaluated for antiproliferative activity using glioma cell lines. Among them, compound 4a significantly inhibited the viability of glioblastoma cells. With favorable pharmacokinetic characteristics and blood-brain barrier permeability, 4a improved the survival rate and inhibited the growth of orthotopic glioblastoma. The Phospho-Totum system revealed that ALK was a potential target for the antiglioblastoma activity of 4a. Further experiments indicated that 4a might be a novel ALK modulator, which interacted with the extracellular ligand-binding domain of ALK, thus selectively induced ERK-mediated autophagy and apoptosis. Our findings provide an alternative ALK-based targeting strategy and a new drug candidate for glioblastoma therapy.

Swimming training and herbal nanoformulations as natural remedies to improve sensory-motor impairment in rat midbrain tumor models: system biology, behavioral test, and experimental validation

Motor impairment worsens health-related quality of life in patients with primary and metastatic midbrain tumors. Here, 56-male-Wistar rats were divided into eight groups: Normal group, Midbrain Tomur Model group, Model + Exe group, Model + Lipo, Model + Extract, Model + Lipo-Extract, Model + Extract-Exe, Model + Lipo-Extract + Exe. According to the aim, mid-brain tumor models were conducted by injections of the C6 glioma cell line (5 × 105 cell suspension) and stereotaxic techniques in the substantia nigra area. Furthermore, consumption of nanoformulation of herbals extract (100 mg/kg/day), crude extract (100 mg/kg/day), and swimming training (30 min, 3 days/week) as interventional protocols were performed for 6 weeks. In addition, we evaluated the effect of polyherbal nanoliposomes containing four plant extracts and swimming training on the GABArα1/TRKB/DRD2/DRD1a/TH network in the substantia nigra of the midbrain tumor rat model. Data emphasized that DRD2 might be a druggable protein with the network's highest significance cut-point effect that could modulate sensory-motor impairment. Furthermore, we found Quercetin, Ginsenosides, Curcumin, and Rutin, as bioactive compounds present in Ginseng, Matthiola incana, Turmeric, and Green-Tea extracts, could bind over the DRD2 protein with approved binding affinity scores. Based on our data, swimming training, and nanoliposome-enriched combined supplements could consider effective complementary medicine for motor impairment recovery induced by the midbrain tumor in the substantia nigra area. Hence, regular swimming training and natural medicines rich in polyphenolic bioactive components and antioxidative effects could modify and improve the dopamine receptors' function.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03574-3.

Injury primes mutation-bearing astrocytes for dedifferentiation in later life

Despite their latent neurogenic potential, most normal parenchymal astrocytes fail to dedifferentiate to neural stem cells in response to injury. In contrast, aberrant lineage plasticity is a hallmark of gliomas, and this suggests that tumor suppressors may constrain astrocyte dedifferentiation. Here, we show that p53, one of the most commonly inactivated tumor suppressors in glioma, is a gatekeeper of astrocyte fate. In the context of stab-wound injury, p53 loss destabilized the identity of astrocytes, priming them to dedifferentiate in later life. This resulted from persistent and age-exacerbated neuroinflammation at the injury site and EGFR activation in periwound astrocytes. Mechanistically, dedifferentiation was driven by the synergistic upregulation of mTOR signaling downstream of p53 loss and EGFR, which reinstates stemness programs via increased translation of neurodevelopmental transcription factors. Thus, our findings suggest that first-hit mutations remove the barriers to injury-induced dedifferentiation by sensitizing somatic cells to inflammatory signals, with implications for tumorigenesis.

miR-199a-3p promotes gastric cancer progression by promoting its stemness potential via DDR2 mediation

BACKGROUND

Peritoneal metastasis (PM) is an independent prognostic factor in gastric cancer (GC), however, the underlying mechanisms of PM occurrence remain unclear.

METHOD

The roles of DDR2 were investigated in GC and its potential relationship to PM, and orthotopic implants into nude mice were performed to assess the biological effects of DDR2 on PM.

RESULTS

Herein, DDR2 level is more significantly observed to elevate in PM lesion than the primary lesion. GC with DDR2-high expression evokes a worse overall survival (OS) in TCGA, similar results of the gloomy OS with high DDR2 levels are clarified via the stratifying stage of TNM. The conspicuously increased expression of DDR2 was found in GC cell lines, luciferase reporter assays verified that miR-199a-3p directly targeted DDR2 gene, which was correlated to tumor progression. We ulteriorly observed DDR2 participated in GC stemness maintenance via mediating pluripotency factor SOX2 expression and implicated in autophagy and DNA damage of cancer stem cells (CSCs). In particular, DDR2 dominated EMT programming through recruiting NFATc1-SOX2 complex to Snai1 in governing cell progression, controlling by DDR2-mTOR-SOX2 axis in SGC-7901 CSCs. Furthermore, DDR2 promoted the tumor peritoneal dissemination in gastric xenograft mouse model.

CONCLUSION

Phenotype screens and disseminated verifications incriminating in GC exposit the miR-199a-3p-DDR2-mTOR-SOX2 axis as a clinically actionable target for tumor PM progression. The herein-reported DDR2-based underlying axis in GC represents novel and potent tools for studying the mechanisms of PM.

The role of metabolic ecosystem in cancer progression — metabolic plasticity and mTOR hyperactivity in tumor tissues

Despite advancements in cancer management, tumor relapse and metastasis are associated with poor outcomes in many cancers. Over the past decade, oncogene-driven carcinogenesis, dysregulated cellular signaling networks, dynamic changes in the tissue microenvironment, epithelial-mesenchymal transitions, protein expression within regulatory pathways, and their part in tumor progression are described in several studies. However, the complexity of metabolic enzyme expression is considerably under evaluated. Alterations in cellular metabolism determine the individual phenotype and behavior of cells, which is a well-recognized hallmark of cancer progression, especially in the adaptation mechanisms underlying therapy resistance. In metabolic symbiosis, cells compete, communicate, and even feed each other, supervised by tumor cells. Metabolic reprogramming forms a unique fingerprint for each tumor tissue, depending on the cellular content and genetic, epigenetic, and microenvironmental alterations of the developing cancer. Based on its sensing and effector functions, the mechanistic target of rapamycin (mTOR) kinase is considered the master regulator of metabolic adaptation. Moreover, mTOR kinase hyperactivity is associated with poor prognosis in various tumor types. In situ metabolic phenotyping in recent studies highlights the importance of metabolic plasticity, mTOR hyperactivity, and their role in tumor progression. In this review, we update recent developments in metabolic phenotyping of the cancer ecosystem, metabolic symbiosis, and plasticity which could provide new research directions in tumor biology. In addition, we suggest pathomorphological and analytical studies relating to metabolic alterations, mTOR activity, and their associations which are necessary to improve understanding of tumor heterogeneity and expand the therapeutic management of cancer.

Regulation of Chemosensitivity in Human Medulloblastoma Cells by p53 and the PI3 Kinase Signaling Pathway

In medulloblastoma, p53 expression has been associated with chemoresistance and radiation resistance and with poor long-term outcomes in the p53-mutated sonic hedgehog, MYC-p53, and p53-positive medulloblastoma subgroups. We previously established a direct role for p53 in supporting drug resistance in medulloblastoma cells with high basal protein expression levels (D556 and DAOY). We now show that p53 genetic suppression in medulloblastoma cells with low basal p53 protein expression levels (D283 and UW228) significantly reduced drug responsiveness, suggesting opposing roles for low p53 protein expression levels. Mechanistically, the enhanced cell death by p53 knockdown in high-p53 cells was associated with an induction of mTOR/PI3K signaling. Both mTOR inhibition and p110α/PIK3CA induction confirmed these findings, which abrogated or accentuated the enhanced chemosensitivity response in D556 cells respectively while converse was seen in D283 cells. Co-treatment with G-actin-sequestering peptide, thymosin β4 (Tβ4), induced p-AKT^S473 in both p53-high and p53-low cells, enhancing chemosensitivity in D556 cells while enhancing chemoresistance in D283 and UW228 cells. IMPLICATIONS: Collectively, we identified an unexpected role for the PI3K signaling in enhancing cell death in medulloblastoma cells with high basal p53 expression. These studies indicate that levels of p53 immunopositivity may serve as a diagnostic marker of chemotherapy resistance and for defining therapeutic targeting.

Treatment during a developmental window prevents NF1-associated optic pathway gliomas by targeting Erk-dependent migrating glial progenitors

The mechanism of vulnerability to pediatric low-grade gliomas (pLGGs)-the most common brain tumor in children-during development remains largely unknown. Using mouse models of neurofibromatosis type 1 (NF1)-associated pLGGs in the optic pathway (NF1-OPG), we demonstrate that NF1-OPG arose from the vulnerability to the dependency of Mek-Erk/MAPK signaling during gliogenesis of one of the two developmentally transient precursor populations in the optic nerve, brain-derived migrating glial progenitors (GPs), but not local progenitors. Hyperactive Erk/MAPK signaling by Nf1 loss overproduced GPs by disrupting the balance between stem-cell maintenance and gliogenesis of hypothalamic ventricular zone radial glia (RG). Persistence of RG-like GPs initiated NF1-OPG, causing Bax-dependent apoptosis in retinal ganglion cells. Removal of three Mek1/Mek2 alleles or transient post-natal treatment with a low-dose MEK inhibitor normalized differentiation of Nf1^-/- RG-like GPs, preventing NF1-OPG formation and neuronal degeneration. We provide the proof-of-concept evidence for preventing pLGGs before tumor-associated neurological damage enters an irreversible phase.

Genomic Characterization and Therapeutic Targeting of HPV Undetected Cervical Carcinomas

Simple Summary

Persistent HPV infection is a known driver of cervical carcinogenesis, but the existence and biological relevance of HPV undetected (HPV^U) cervical cancer has been debated. Here we report the results of detailed molecular classification of HPV^U cervical cancer, and validate HPV^U as a biomarker of poor outcomes. We identify that HPV^U cervical cancer tumors harbor mutations affecting cell cycle progression, and in vitro experiments reveal HPV^U, but not HPV⁺, cells are sensitive to palbociclib monotherapy. HPV^U status can be translated into the clinic as a predictive biomarker of poor patient response to standard of care treatments and these patients may benefit from personalized treatment plans. Our results identify palbociclib as a lead candidate as an alternative treatment strategy for HPV^U cervical cancer patients. We also suggest that primary cervix tumors be routinely tested for HPV prior to treatment to identify patients who will benefit from more aggressive precision-driven therapy.

Abstract

Cervical cancer tumors with undetectable HPV (HPV^U) have been underappreciated in clinical decision making. In this study, two independent CC datasets were used to characterize the largest cohort of HPV^U tumors to date (HPV^U = 35, HPV⁺ = 430). Genomic and transcriptome tumor profiles and patient survival outcomes were compared between HPV⁺ and HPV^U tumors. In vitro analyses were done to determine efficacy of the selective CDK4/6 inhibitor palbociclib on HPV^U cancer cell lines. Patients with HPV^U CC tumors had worse progression-free and overall survival outcomes compared to HPV⁺ patients. TP53, ARID1A, PTEN, ARID5B, CTNNB1, CTCF, and CCND1 were identified as significantly mutated genes (SMGs) enriched in HPV^U tumors, with converging functional roles in cell cycle progression. In vitro HPV^U, but not HPV⁺, cancer cell lines with wild type RB1 were sensitive to palbociclib monotherapy. These results indicate that HPV^U status can be translated into the clinic as a predictive biomarker of poor patient response to standard of care treatments. We suggest primary cervix tumors be routinely tested for HPV prior to treatment to identify patients who will benefit from more aggressive precision-driven therapy. Our results identify palbociclib as a lead candidate as an alternative treatment strategy for HPV^U CC patients.

Stem-Like Cell Populations, p53-Pathway Activation and Mechanisms of Recurrence in Sonic Hedgehog Medulloblastoma

While most Sonic Hedgehog-associated medulloblastomas (SHH-MBs) respond to therapeutic intervention, radiation therapy often causes deleterious long-term neurocognitive defects, especially in infants and young children. To limit neurological comorbidities, the development of a reduction-of-therapy treatment or de-escalation approach was investigated. Although retrospective analysis of MBs indicated low-dose therapy was potentially effective, clinical de-escalation trials showed poor outcomes in infant SHH-MBs and was prematurely terminated. Recent studies suggest the existence of cancer-stem-cell (CSC)-like cell populations that are more resistant to therapies and drive tumor recurrence. This review will discuss the mechanism of these CSC-like cells in SHH-MBs in resisting to p53-pathway activation, which may contribute to the disappointing outcomes of the recent de-escalation trials.

Targeting of the Hedgehog/GLI and mTOR pathways in advanced pancreatic cancer, a phase 1 trial of Vismodegib and Sirolimus combination

BACKGROUND/OBJECTIVES

Preclinical data indicated a functional and molecular interaction between Hedgehog (HH)/GLI and PI3K-AKT-mTOR pathways promoting pancreatic ductal adenocarcinoma (PDAC). A phase I study was conducted of Vismodegib and Sirolimus combination to evaluate maximum tolerated dose (MTD) and preliminary anti-tumor efficacy.

METHODS

Cohort I included advanced solid tumors patients following a traditional 3 + 3 design. Vismodegib was orally administered at 150 mg daily with Sirolimus starting at 3 mg daily, increasing to 6 mg daily at dose level 2. Cohort II included only metastatic PDAC patients. Anti-tumor efficacy was evaluated every two cycles and target assessment at pre-treatment and after a single cycle.

RESULTS

Nine patient were enrolled in cohort I and 22 patients in cohort II. Twenty-eight patients were evaluated for dose-limiting toxicities (DLTs). One DLT was observed in each cohort, consisting of grade 2 mucositis and grade 3 thrombocytopenia. The MTD for Vismodegib and Sirolimus were 150 mg daily and 6 mg daily, respectively. The most common grade 3-4 toxicities were fatigue, thrombocytopenia, dehydration, and infections. A total of 6 patients had stable disease. No partial or complete responses were observed. Paired biopsy analysis before and after the first cycle in cohort II consistently demonstrated reduced GLI1 expression. Conversely, GLI and mTOR downstream targets were not significantly affected.

CONCLUSIONS

The combination of Vismodegib and Sirolimus was well tolerated. Clinical benefit was limited to stable disease in a subgroup of patients. Targeting efficacy demonstrated consistent partial decreases in HH/GLI signaling with limited impact on mTOR signaling. These findings conflict with pre-clinical models and warrant further investigations.

Murine models of IDH-wild-type glioblastoma exhibit spatial segregation of tumor initiation and manifestation during evolution

Recent characterization of spatiotemporal genomic architecture of IDH-wild-type multifocal glioblastomas (M-GBMs) suggests a clinically unobserved common-ancestor (CA) with a less aggressive phenotype, generating highly genetically divergent malignant gliomas/GBMs in distant brain regions. Using serial MRI/3D-reconstruction, whole-genome sequencing and spectral karyotyping-based single-cell phylogenetic tree building, we show two distinct types of tumor evolution in p53-mutant driven mouse models. Malignant gliomas/GBMs grow as a single mass (Type 1) and multifocal masses (Type 2), respectively, despite both exhibiting loss of Pten/chromosome 19 (chr19) and PI3K/Akt activation with sub-tetraploid/4N genomes. Analysis of early biopsied and multi-segment tumor tissues reveals no evidence of less proliferative diploid/2N lesions in Type 1 tumors. Strikingly, CA-derived relatively quiescent tumor precursors with ancestral diploid/2N genomes and normal Pten/chr19 are observed in the subventricular zone (SVZ), but are distantly segregated from multi focal Type 2 tumors. Importantly, PI3K/Akt inhibition by Rictor/mTORC2 deletion blocks distant dispersal, restricting glioma growth in the SVZ.

Sox2+ cells in Sonic Hedgehog-subtype medulloblastoma resist p53-mediated cell-cycle arrest response and drive therapy-induced recurrence

BACKGROUND

High-intensity therapy effectively treats most TP53 wild-type (TP53-WT) Sonic Hedgehog-subgroup medulloblastomas (SHH-MBs), but often cause long-term deleterious neurotoxicities in children. Recent clinical trials investigating reduction/de-escalation of therapy for TP53-WT SHH-MBs caused poor overall survival. Here, we investigated whether reduced levels of p53-pathway activation by low-intensity therapy potentially contribute to diminished therapeutic efficacy.

METHODS

Using mouse SHH-MB models with different p53 activities, we investigated therapeutic efficacy by activating p53-mediated cell-cycle arrest versus p53-mediated apoptosis on radiation-induced recurrence.

RESULTS

Upon radiation treatment, p53WT-mediated apoptosis was sufficient to eliminate all SHH-MB cells, including Sox2+ cells. The same treatment eliminated most Sox2- bulk tumor cells in SHH-MBs harboring p53 R172P, an apoptosis-defective allele with cell-cycle arrest activity, via inducing robust neuronal differentiation. Rare quiescent Sox2+ cells survived radiation-enhanced p53R172P activation and entered a proliferative state, regenerating tumors. Transcriptomes of Sox2+ cells resembled quiescent Nestin-expressing progenitors in the developing cerebellum, expressing Olig2 known to suppress p53 and p21 expression. Importantly, high SOX2 expression is associated with poor survival of all four SHH-MB subgroups, independent of TP53 mutational status.

CONCLUSIONS

Quiescent Sox2+ cells are efficiently eliminated by p53-mediated apoptosis, but not cell-cycle arrest and differentiation. Their survival contributes to tumor recurrence due to insufficient p53-pathway activation.

Intratumoural Heterogeneity Underlies Distinct Therapy Responses and Treatment Resistance in Glioblastoma

Glioblastomas are the most common and lethal neoplasms of the central nervous system. Neighbouring glioma cells maintain extreme degrees of genetic and phenotypic variation that form intratumoural heterogeneity. This genetic diversity allows the most adaptive tumour clones to develop treatment resistance, ultimately leading to disease recurrence. We aimed to model this phenomenon and test the effectiveness of several targeted therapeutic interventions to overcome therapy resistance. Heterogeneous tumour masses were first deconstructed into single tumour cells, which were expanded independently as single-cell clones. Single nucleotide polymorphism arrays, whole-genome and RNA sequencing, and CpG methylation analysis validated the unique molecular profile of each tumour clone, which displayed distinct pathologic features, including cell morphology, growth rate, and resistance to temozolomide and ionizing radiation. We also identified variable sensitivities to AURK, CDK, and EGFR inhibitors which were consistent with the heterogeneous molecular alterations that each clone harboured. These targeted therapies effectively eliminated the temozolomide- and/or irradiation-resistant clones and also parental polyclonal cells. Our findings indicate that polyclonal tumours create a dynamic environment that consists of diverse tumour elements and treatment responses. Designing targeted therapies based on a range of molecular profiles can be a more effective strategy to eradicate treatment resistance, recurrence, and metastasis.

Defective DNA damage repair leads to frequent catastrophic genomic events in murine and human tumors

Chromothripsis and chromoanasynthesis are catastrophic events leading to clustered genomic rearrangements. Whole-genome sequencing revealed frequent complex genomic rearrangements (n = 16/26) in brain tumors developing in mice deficient for factors involved in homologous-recombination-repair or non-homologous-end-joining. Catastrophic events were tightly linked to Myc/Mycn amplification, with increased DNA damage and inefficient apoptotic response already observable at early postnatal stages. Inhibition of repair processes and comparison of the mouse tumors with human medulloblastomas (n = 68) and glioblastomas (n = 32) identified chromothripsis as associated with MYC/MYCN gains and with DNA repair deficiencies, pointing towards therapeutic opportunities to target DNA repair defects in tumors with complex genomic rearrangements.

Chromothripsis and chromoanasynthesis lead to locally clustered rearrangements affecting one or a few chromosomes, but their impact on cancer development and progression is unclear. Here the authors analyse the role of DNA repair factors in brain tumors by whole-genome sequencing of tumors from mouse models of medulloblastoma or high grade gliomas.