Investigating Neural Stem Cell and Glioma Stem Cell Self-renewal Potential Using Extreme Limiting Dilution Analysis (ELDA)

Coordinated Targeting of S6K1/2 and AXL Disrupts Pyrimidine Biosynthesis in PTEN-Deficient Glioblastoma

Intrinsic resistance to targeted therapeutics in PTEN-deficient glioblastoma (GBM) is mediated by redundant signaling networks that sustain critical metabolic functions. Here, we demonstrate that coordinated inhibition of the ribosomal protein S6 kinase 1 (S6K1) and the receptor tyrosine kinase AXL using LY-2584702 and BMS-777607 can overcome network redundancy to reduce GBM tumor growth. This combination of S6K1 and AXL inhibition suppressed glucose flux to pyrimidine biosynthesis. Genetic inactivation studies to map the signaling network indicated that both S6K1 and S6K2 transmit growth signals in PTEN-deficient GBM. Kinome-wide ATP binding analysis in inhibitor-treated cells revealed that LY-2584702 directly inhibited S6K1, and substrate phosphorylation studies showed that BMS-777607 inactivation of upstream AXL collaborated to reduce S6K2-mediated signal transduction. Thus, combination targeting of S6K1 and AXL provides a kinase-directed therapeutic approach that circumvents signal transduction redundancy to interrupt metabolic function and reduce growth of PTEN-deficient GBM.

SIGNIFICANCE

Therapy for glioblastoma would be advanced by incorporating molecularly targeted kinase-directed agents, similar to standard of care strategies in other tumor types. Here, we identify a kinase targeting approach to inhibit the metabolism and growth of glioblastoma.

Hierarchical self-recognition and response in CSC and non-CSC micro-niches for cancer therapy

Cancer stem cells (CSCs) characterized by self-renewal, invasiveness, tumorigenicity and resistance to treatment are regarded as the thorniest issues in refractory tumors. We develop a targeted and hierarchical controlled release nano-therapeutic platform (SEED-NPs) that self-identifies and responds to CSC and non-CSC micro-niches of tumors. In non-CSC micro-niche, reactive oxygen species (ROS) trigger the burst release of the chemotherapeutic drug and photosensitizer to kill tumor cells and reduce tumor volume by combining chemotherapy and photodynamic therapy (PDT). In CSC micro-niche, the preferentially released differentiation drug induces CSC differentiation and transforms CSCs into chemotherapy-sensitive cells. SEED-NPs exhibit an extraordinary capacity for downregulating the stemness of CD44+/CD24- SP (side population) cell population both in vitro and in vivo, and reveal a 4-fold increase of tumor-targeted accumulation. Also, PDT-generated ROS promote the formation of tunneling nanotubes and facilitate the divergent network transport of drugs in deep tumors. Moreover, ROS in turn promotes CSC differentiation and drug release. This positive-feedback-loop strategy enhances the elimination of refractory CSCs. As a result, SEED-NPs achieve excellent therapeutic effects in both 4T1 SP tumor-bearing mice and regular 4T1 tumor-bearing mice without obvious toxicities and eradicate half of mice tumors. SEED-NPs integrate differentiation, chemotherapy and PDT, which proved feasible and valuable, indicating that active targeting and hierarchical release are necessary to enhance antitumor efficacy. These findings provide promising prospects for overcoming barriers in the treatment of CSCs.

Olig1/2-Expressing Intermediate Lineage Progenitors Are Predisposed to PTEN/p53-Loss-Induced Gliomagenesis and Harbor Specific Therapeutic Vulnerabilities

Malignant gliomas such as glioblastoma are highly heterogeneous with distinct cells of origin and varied genetic alterations. It remains elusive whether the specific states of neural cell lineages are differentially susceptible to distinct genetic alterations during malignant transformation. Here, an analysis of The Cancer Genome Atlas databases revealed that comutations of PTEN and TP53 are most significantly enriched in human high-grade gliomas. Therefore, we selectively ablated Pten and Trp53 in different progenitors to determine which cell lineage states are susceptible to malignant transformation. Mice with PTEN/p53 ablation mediated by multilineage-expressing human GFAP (hGFAP) promoter-driven Cre developed glioma but with incomplete penetrance and long latency. Unexpectedly, ablation of Pten and Trp53 in Nestin+ neural stem cells (NSC) or Pdgfra+/NG2+ committed oligodendrocyte precursor cells (OPC), two major cells of origin in glioma, did not induce glioma formation in mice. Strikingly, mice lacking Pten and Trp53 in Olig1+/Olig2+ intermediate precursors (pri-OPC) prior to the committed OPCs developed high-grade gliomas with 100% penetrance and short latency. The resulting tumors exhibited distinct tumor phenotypes and drug sensitivities from NSC- or OPC-derived glioma subtypes. Integrated transcriptomic and epigenomic analyses revealed that PTEN/p53-loss induced activation of oncogenic pathways, including HIPPO-YAP and PI3K signaling, to promote malignant transformation. Targeting the core regulatory circuitries YAP and PI3K signaling effectively inhibited tumor cell growth. Thus, our multicell state in vivo mutagenesis analyses suggests that transit-amplifying states of Olig1/2 intermediate lineage precursors are predisposed to PTEN/p53-loss-induced transformation and gliomagenesis, pointing to subtype-specific treatment strategies for gliomas with distinct genetic alterations.

SIGNIFICANCE

Multiple progenitor-state mutagenesis reveal that Olig1/2-expressing intermediate precursors are highly susceptible to PTEN/p53-loss-mediated transformation and impart differential drug sensitivity, indicating tumor-initiating cell states and genetic drivers dictate glioma phenotypes and drug responses. See related commentary by Zamler and Hu, p. 807.

Evaluation of CD98 light chain-LAT1 as a potential marker of cancer stem-like cells in glioblastoma

OBJECTIVE

Glioma stem cells (GSCs) are a minority population of glioma cells that regarded as the cause of tumor formation and recurrence. Identifying new molecular strategies targeting GSCs must be urgently developed to treat glioblastoma. In this study, one of CD98 light chain-L type amino acid transporter 1 (LAT1) was found as a potential GSC marker. LAT1 served as EAA transporter has been shown to be closely related with tumor invasion, metastasis, angiogenesis, and radiosensitivity.

METHODS

LAT1⁺ and LAT1^- glioma cells were sorted by flow cytometry. Cellular immunofluorescence, sphere-formation arrays, and in vitro limiting dilution experiments were used to identify cell stemness. Differentiated glioma stem cells were cultured, and the expressions of β-tubulinIII, GFAP, and LAT1 were detected by Western blot. Nude mouse models were constructed to observe tumor formation and metastasis in nude mice.

RESULTS

LAT1⁺ glioma cells were testified a small percentage of all cells and selected as the subsequent sorting marker. LAT1⁺ cells were separated from U87 and U251 cells could express high level of stem cell markers, and possessed GSC properties including self-renewal ability and multi-directional differentiation potential. But LAT1^- cells did not have these characteristics. In addition, LAT1⁺ cells were able to generate tumors in vivo, tumor size of LAT1⁺ cells formed were much bigger than that of LAT1^- cells.

CONCLUSION

Our study, including molecular, cell, vitro and vivo experiments, has shown that LAT1⁺ cells possess GSC properties, and present for the first time that LAT1 can be used as a new marker for GSCs screening.

The Deubiquitinase USP13 Maintains Cancer Cell Stemness by Promoting FASN Stability in Small Cell Lung Cancer

USP13 is significantly amplified in over 20% of lung cancer patients and critical for tumor progression. However, the functional role of USP13 in small cell lung cancer (SCLC) remains largely unclear. In this study, we found that the deubiquitinase USP13 is highly expressed in SCLC tumor samples and positively associated with poor prognosis in multiple cohorts. In vitro and in vivo depletion of USP13 inhibited SCLC cancer stem cells (CSCs) properties and tumorigenesis, and this inhibitory effect was rescued by reconstituted expression of wide type (WT) USP13 but not the enzyme-inactive USP13 mutant. Mechanistically, USP13 interacts with fatty acid synthase (FASN) and enhances FASN protein stability. FASN downregulation suppresses USP13-enhanced cell renewal regulator expression, sphere formation ability, and de novo fatty acids biogenesis. Accordingly, we found FASN expression is upregulated in surgical resected SCLC specimens, positively correlated with USP13, and associated with poor prognosis of SCLC patients. More importantly, the small molecule inhibitor of FASN, TVB-2640, significantly inhibits lipogenic phenotype and attenuates self-renewal ability, chemotherapy resistance and USP13-mediated tumorigenesis in SCLC. Thus, our study highlights a critical role of the USP13-FASN-lipogenesis axis in SCLC cancer stemness maintenance and tumor growth, and reveals a potential combination therapy for SCLC patients.

LncRNA MBNL1-AS1 Represses Proliferation and Cancer Stem-Like Properties of Breast Cancer through MBNL1-AS1/ZFP36/CENPA Axis

Background

Emerging studies have revealed long noncoding RNAs (lncRNAs) were key regulators of cancer progression. In this research, the expression and roles of MBNL1-AS1 were explored in breast cancer (BC).

Methods

In this study, the MBNL1-AS1 expression in breast cancer tissue, as well as in cell line, was studied by qRT-PCR assays. The effects of MBNL1-AS1 on proliferation and stemness were evaluated by MTT assays, colony formation assays, orthotopic breast tumor mice models, extreme limiting dilution analysis (ELDA), fluorescence in situ hybridization (FISH), flow cytometry assays, and sphere formation assays. Flexmap 3D assays were performed to show that MBNL1-AS1 downregulated the centromere protein A (CENPA) secretion in BC cells. Western blot, RNA pull-down assays, RNA immunoprecipitation (RIP) assays, and FISH were conducted to detect the mechanism.

Results

The results showed that the expression levels of MBNL1-AS1 were downregulated in breast cancer tissues and cell lines. In vitro and in vivo studies demonstrated that overexpression of MBNL1-AS1 markedly inhibited BC cells proliferation and stemness. RNA pull-down assay, RIP assay, western blot assay, and qRT-PCR assay showed that MBNL1-AS1 downregulated CENPA mRNA via directly interacting with Zinc Finger Protein 36 (ZFP36) and subsequently decreased the stability of CENPA mRNA. Restoration assays also confirmed that MBNL1-AS1 suppressed the CENPA-mediated proliferation and stemness in breast cancer cells.

Conclusions

The new mechanism of how MBNL1-AS1 regulates BC phenotype is elucidated, and the MBNL1-AS1/ZFP36/CENPA axis may be served as a therapeutic target for BC patients.

Subventricular zone adult mouse neural stem cells require insulin receptor for self-renewal

The insulin receptor (INSR) is an evolutionarily conserved signaling protein that regulates development and cellular metabolism. INSR signaling promotes neurogenesis in Drosophila; however, a specific role for the INSR in maintaining adult neural stem cells (NSCs) in mammals has not been investigated. We show that conditionally deleting the Insr gene in adult mouse NSCs reduces subventricular zone NSCs by ∼70% accompanied by a corresponding increase in progenitors. Insr deletion also produced hyposmia caused by aberrant olfactory bulb neurogenesis. Interestingly, hippocampal neurogenesis and hippocampal-dependent behaviors were unperturbed. Highly aggressive proneural and mesenchymal glioblastomas had high INSR/insulin-like growth factor (IGF) pathway gene expression, and isolated glioma stem cells had an aberrantly high ratio of INSR:IGF type 1 receptor. Moreover, INSR knockdown inhibited GBM tumorsphere growth. Altogether, these data demonstrate that the INSR is essential for a subset of normal NSCs, as well as for brain tumor stem cell self-renewal.

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Insulin receptor (INSR) is essential for adult SVZ neural stem cell self-renewal

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INSR deletion causes hyposmia with increased olfactory bulb neurogenesis

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Hippocampal stem cells (and associated behaviors) do not require INSR

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Glioblastomas overexpress INSR pathway components required for tumorsphere growth

MELK Inhibition Effectively Suppresses Growth of Glioblastoma and Cancer Stem-Like Cells by Blocking AKT and FOXM1 Pathways

Glioblastoma multiforme (GBM) is a devastating disease yet no effective drug treatment has been established to date. Glioblastoma stem-like cells (GSCs) are insensitive to treatment and may be one of the reasons for the relapse of GBM. Maternal embryonic leucine zipper kinase gene (MELK) plays an important role in the malignant proliferation and the maintenance of GSC stemness properties of GBM. However, the therapeutic effect of targeted inhibition of MELK on GBM remains unclear. This study analyzed the effect of a MELK oral inhibitor, OTSSP167, on GBM proliferation and the maintenance of GSC stemness. OTSSP167 significantly inhibited cell proliferation, colony formation, invasion, and migration of GBM. OTSSP167 treatment reduced the expression of cell cycle G2/M phase-related proteins, Cyclin B1 and Cdc2, while up-regulation the expression of p21 and subsequently induced cell cycle arrest at the G2/M phase. OTSSP167 effectively prolonged the survival of tumor-bearing mice and inhibited tumor cell growth in in vivo mouse models. It also reduced protein kinase B (AKT) phosphorylation levels by OTSSP167 treatment, thereby disrupting the proliferation and invasion of GBM cells. Furthermore, OTSSP167 inhibited the proliferation, neurosphere formation and self-renewal capacity of GSCs by reducing forkhead box M1 (FOXM1) phosphorylation and transcriptional activity. Interestingly, the inhibitory effect of OTSSP167 on the proliferation of GSCs was 4-fold more effective than GBM cells. In conclusion, MELK inhibition suppresses the growth of GBM and GSCs by double-blocking AKT and FOXM1 signals. Targeted inhibition of MELK may thus be potentially used as a novel treatment for GBM.

The Dopamine D2 Receptor Contributes to the Spheroid Formation Behavior of U87 Glioblastoma Cells

BACKGROUND

Glioblastoma multiforme (GBM) is a common and lethal cancer of the central nervous system. This cancer is difficult to treat because most anticancer therapeutics do not readily penetrate into the brain due to the tight control at the cerebrovascular barrier. Numerous studies have suggested that dopamine D2 receptor (D2R) antagonists, such as first generation antipsychotics, may have anticancer efficacy in vivo and in vitro. The role of the D2R itself in the anticancer effects is unclear, but there is evidence suggesting that D2R activation promotes stem-like and spheroid forming behaviors in GBM.

OBJECTIVES

We aimed to observe the role of the dopamine D2R and its modulators (at selective concentrations) in spheroid formation and stemness of GBM cell line, U87MG, to clarify the validity of the D2R as a therapeutic target for cancer therapy.

METHODS

Spheroid formation assays and Western blotting of the glioblastoma cell line, U87MG, were used to observe responses to treatment with the D2R agonists sumanirole, ropinirole, and 4-propyl-9-hydroxynaphthoxazine (PHNO); and the D2R antagonists thioridazine, pimozide, haloperidol, and remoxipride. Extreme limiting dilution analysis was done to determine the impact of sumanirole and remoxipride treatment on sphere-forming cell frequency. Proliferation was also measured by crystal violet staining. Stable lentiviral transduction of DRD2 or shDRD2 was used to validate the role of the D2R in assay behaviors.

RESULTS

D2R antagonists thioridazine, pimozide, haloperidol, and remoxipride decrease spheroid formation behaviors at a selective 100 nmol/L concentration, while D2R agonists PHNO, sumanirole, and ropinirole increase the formation of spheroids. Similarly, 100 nmol/L remoxipride decreased sphere-forming cell frequency. These results were recapitulated with genetic overexpression and knockdown of the D2R, and combination experiments indicate that the D2R is required for the effects of the pharmacological modulators. Furthermore, spheroid proliferation and invasive capacity increased under treatment with 100 nmol/L sumanirole and decreased under treatment with 100 nmol/L thioridazine. Expression levels of the stemness markers Nestin and Sox2, as well as those of differentiation marker glial fibrillary acidic protein, were not altered by 100 nmol/L thioridazine or sumanirole for 72 h or continuous treatment with these compounds for 7 days during a spheroid formation assay.

CONCLUSIONS

Signaling activity of the dopamine D2R may be involved in the spheroid formation phenotype in the context of the U87MG cell line. However, this modulation may not be due to alterations in stemness marker expression, but due to other factors that may contribute to spheroid formation, such as cell-cell adhesion or EGFR signaling.