Ligand-dependent activation of the hedgehog pathway in glioma progenitor cells

Endocannabinoids are potential inhibitors of glioblastoma multiforme proliferation

Globally, it is evident that glioblastoma multiforme (GBM) is an aggressive malignant cancer with a high mortality rate and no effective treatment options. Glioblastoma is classified as the stage-four progression of a glioma tumor, and its diagnosis results in a shortened life expectancy. Treatment options for GBM include chemotherapy, immunotherapy, surgical intervention, and conventional pharmacotherapy; however, at best, they extend the patient's life by a maximum of 5 years. GBMs are considered incurable due to their high recurrence rate, despite various aggressive therapeutic approaches which can have many serious adverse effects. Ceramides, classified as endocannabinoids, offer a promising novel therapeutic approach for GBM. Endocannabinoids may enhance the apoptosis of GBM cells but have no effect on normal healthy neural cells. Cannabinoids promote atypical protein kinase C, deactivate fatty acid amide hydrolase enzymes, and activate transient receptor potential vanilloid 1 (TRPV1) and TRPV2 to induce pro-apoptotic signaling pathways without increasing endogenous cannabinoids. In previous in vivo studies, endocannabinoids, chemically classified as amide formations of oleic and palmitic acids, have been shown to increase the pro-apoptotic activity of human cancer cells and inhibit cell migration and angiogenesis. This review focuses on the biological synthesis and pharmacology of endogenous cannabinoids for the enhancement of cancer cell apoptosis, which have potential as a novel therapy for GBM. Please cite this article as: Duzan A, Reinken D, McGomery TL, Ferencz N, Plummer JM, Basti MM. Endocannabinoids are potential inhibitors of glioblastoma multiforme proliferation. J Integr Med. 2023; Epub ahead of print.

Signaling pathways governing glioma cancer stem cells behavior

Glioma is the most common malignant brain tumor that develops in the glial tissue. Several studies have identified that glioma cancer stem cells (GCSCs) play important roles in tumor-initiating features in malignant gliomas. GCSCs are a small population in the brain that presents an essential role in the metastasis of glioma cells to other organs. These cells can self-renew and differentiate, which are thought to be involved in the pathogenesis of glioma. Therefore, targeting GCSCs might be a novel strategy for the treatment of glioma. Accumulating evidence revealed that several signaling pathways, including Notch, TGF-β, Wnt, STAT3, AKT, and EGFR mediated GCSC growth, proliferation, migration, and invasion. Besides, non-coding RNAs (ncRNAs), including miRNAs, circular RNAs, and long ncRNAs have been found to play pivotal roles in the regulation of GCSC pathogenesis and drug resistance. Therefore, targeting these pathways could open a new avenue for glioma management. In this review, we summarized critical signaling pathways involved in the stimulation or prevention of GCSCs tumorigenesis and invasiveness.

Hedgehog signaling mechanism and role in cancer

Cell-cell communication through evolutionarily conserved signaling pathways governs embryonic development and adult tissue homeostasis. Deregulation of these signaling pathways has been implicated in a wide range of human diseases including cancer. One such pathway is the Hedgehog (Hh) pathway, which was originally discovered in Drosophila and later found to play a fundamental role in human development and diseases. Abnormal Hh pathway activation is a major driver of basal cell carcinomas (BCC) and medulloblastoma. Hh exerts it biological influence through a largely conserved signal transduction pathway from the activation of the GPCR family transmembrane protein Smoothened (Smo) to the conversion of latent Zn-finger transcription factors Gli/Ci proteins from their repressor (GliR/CiR) to activator (GliA/CiA) forms. Studies from model organisms and human patients have provided deep insight into the Hh signal transduction mechanisms, revealed roles of Hh signaling in a wide range of human cancers, and suggested multiple strategies for targeting this pathway in cancer treatment.

Canonical Hedgehog Pathway and Noncanonical GLI Transcription Factor Activation in Cancer

The Hedgehog signaling pathway is one of the fundamental pathways required for development and regulation of postnatal regeneration in a variety of tissues. The pathway has also been associated with cancers since the identification of a mutation in one of its components, PTCH, as the cause of Basal Cell Nevus Syndrome, which is associated with several cancers. Our understanding of the pathway in tumorigenesis has expanded greatly since that initial discovery over two decades ago. The pathway has tumor-suppressive and oncogenic functions depending on the context of the cancer. Furthermore, noncanonical activation of GLI transcription factors has been reported in a number of tumor types. Here, we review the roles of canonical Hedgehog signaling pathway and noncanonical GLI activation in cancers, particularly epithelial cancers, and discuss an emerging concept of the distinct outcomes that these modes have on cancer initiation and progression.

The scaffolding protein DLG5 promotes glioblastoma growth by controlling Sonic Hedgehog signaling in tumor stem cells

BACKGROUND

Tumor invasion, a hallmark of malignant gliomas, involves reorganization of cell polarity and changes in the expression and distribution of scaffolding proteins associated with polarity complexes. The scaffolding proteins of the DLG family are usually downregulated in invasive tumors and regarded as tumor suppressors. Despite their important role in regulating neurodevelopmental signaling, the expression and functions of DLG proteins have remained almost entirely unexplored in malignant gliomas.

METHODS

Western blot, immunohistochemistry, and analysis of gene expression were used to quantify DLG members in glioma specimens and cancer datasets. Over-expression and knockdown of DLG5, the highest-expressed DLG member in glioblastoma, were used to investigate its effects on tumor stem cells and tumor growth. qRT-PCR, Western blotting, and co-precipitation assays were used to investigate DLG5 signaling mechanisms.

RESULTS

DLG5 was upregulated in malignant gliomas compared to other solid tumors, being the predominant DLG member in all glioblastoma molecular subtypes. DLG5 promoted glioblastoma stem cell invasion, viability, and self-renewal. Knockdown of this protein in vivo disrupted tumor formation and extended survival. At the molecular level, DLG5 regulated Sonic Hedgehog (Shh) signaling, making DLG5-deficient cells insensitive to Shh ligand. Loss of DLG5 increased the proteasomal degradation of Gli1, underlying the loss of Shh signaling and tumor stem cell sensitization.

CONCLUSIONS

The high expression and pro-tumoral functions of DLG5 in glioblastoma, including its dominant regulation of Shh signaling in tumor stem cells, reveal a novel role for this protein that is strikingly different from its proposed tumor-suppressor role in other solid tumors.

Hydrophobic Mismatch Controls the Mode of Membrane-Mediated Interactions of Transmembrane Peptides

Various cellular processes require the concerted cooperative action of proteins. The possibility for such synchronization implies the occurrence of specific long-range interactions between the involved protein participants. Bilayer lipid membranes can mediate protein-protein interactions via relatively long-range elastic deformations induced by the incorporated proteins. We considered the interactions between transmembrane peptides mediated by elastic deformations using the framework of the theory of elasticity of lipid membranes. An effective peptide shape was assumed to be cylindrical, hourglass-like, or barrel-like. The interaction potentials were obtained for membranes of different thicknesses and elastic rigidities. Cylindrically shaped peptides manifest almost neutral average interactions-they attract each other at short distances and repel at large ones, independently of membrane thickness or rigidity. The hourglass-like peptides repel each other in thin bilayers and strongly attract each other in thicker bilayers. On the contrary, the barrel-like peptides repel each other in thick bilayers and attract each other in thinner membranes. These results potentially provide possible mechanisms of control for the mode of protein-protein interactions in membrane domains with different bilayer thicknesses.

Expression of activator proteins of SHH/GLI and PI3K/Akt/mTORC1 signaling pathways in human gliomas is associated with high grade tumors

Recent findings have demonstrated a synergic crosstalk between SHH/GLI and PI3K/Akt/mTORC1 signaling in glioblastoma progression cells in vitro and in tumors in mice, but it is not known if this also occurs in human gliomas. We then aimed to investigate the expression of key proteins of these pathways in different human gliomas. The expression of PTEN, phospho-Akt (Ser473), phospho-S6K1 (Thr389), SHH, GLI1, GLI2 and GLI3 was assessed by immunohistochemistry in gliomas and in control brain tissues. The pattern of expression of each protein was established according to glioma type, glioma grade and to cell type; the relative expression of each protein was used to perform statistical analyses. We found that the expression of proteins of both signaling pathways differs between normal brain and glioma tissues. For instance, normal astrocytes had a different protein expression pattern compared with reactive and tumoral astrocytes. Interestingly, we detected a recurrent pattern of expression of GLI3 in oligodendrocytes and of phospho-S6K1 in mitotic neoplastic cells. We also identified differences of cell signaling according to glioma type: oligodendrogliomas and ependymomas are related with the expression of SHH/GLI proteins. Finally, we detected that high grade gliomas statistically correlate with the expression of GLI1 and GLI2, and that GLI1, GLI2, phospho-Akt and phospho-S6K1 are more expressed in patients with less survival, suggesting that activation of these cell signaling influences glioma outcome and patient survival. In summary, our results show that proteins of PI3K/Akt/mTORC1 and SHH/GLI pathways are differentially expressed in human gliomas according to tumor type and grade, and suggest that the activation of these signaling networks is associated with glioma progression.

Epigenetics of glioblastoma multiforme: From molecular mechanisms to therapeutic approaches

Glioblastoma multiforme (GBM) is the most common form of brain cancer and one of the most aggressive cancers found in humans. Most of the signs and symptoms of GBM can be mild and slowly aggravated, although other symptoms might demonstrate it as an acute ailment. However, the precise mechanisms of the development of GBM remain unknown. Due to the improvement of molecular pathology, current researches have reported that glioma progression is strongly connected with different types of epigenetic phenomena, such as histone modifications, DNA methylation, chromatin remodeling, and aberrant microRNA. Furthermore, the genes and the proteins that control these alterations have become novel targets for treating glioma because of the reversibility of epigenetic modifications. In some cases, gene mutations including P16, TP53, and EGFR, have been observed in GBM. In contrast, monosomies, including removals of chromosome 10, particularly q23 and q25-26, are considered the standard markers for determining the development and aggressiveness of GBM. Recently, amid the epigenetic therapies, histone deacetylase inhibitors (HDACIs) and DNA methyltransferase inhibitors have been used for treating tumors, either single or combined. Specifically, HDACIs are served as a good choice and deliver a novel pathway to treat GBM. In this review, we focus on the epigenetics of GBM and the consequence of its mutations. We also highlight various treatment approaches, namely gene editing, epigenetic drugs, and microRNAs to combat GBM.

Targeting CD146 using folic acid-conjugated nanoparticles and suppression of tumor growth in a mouse glioma model

OBJECTIVE

Glioma stem cells (GSCs) are responsible for tumor initiation, therapeutic resistance, and recurrence. CD146 is mainly expressed in dividing GSCs and regulates cell cycle progression. However, the evaluation of the efficacy of targeted therapy against CD146 in vivo remains to be investigated. In this study, the authors aimed to develop gene therapy targeting GSCs using chitosan oligosaccharide lactate (COL) nanoparticles (NPs) conjugated with folic acid-polyethylene glycol (FA-PEG-COL NPs) for in vitro and in vivo delivery of CD146 small-interfering RNA (siCD146) and to determine the effect of CD146 knockdown on tumor growth.

METHODS

To examine the uptake of NPs by tumor cells, immunofluorescence staining, flow cytometry, and in vivo imaging were performed. The knockdown effect of siCD146 was measured by western blot and water-soluble tetrazolium salt-8 assay in mouse glioma cells. The efficacy of siRNA therapy-targeted GSCs was evaluated by monitoring tumor growth through in vivo imaging and histological analysis.

RESULTS

In vivo accumulation of the FA-PEG-COL NPs in subcutaneous and intracranial gliomas following NP administration via a mouse tail vein was observed. Additionally, in vitro delivery of siCD146 ionically cross-linked NPs, reduced CD146 levels, and suppressed growth in the glioma tumor sphere. Evaluation of the in vivo therapeutic effects of siCD146-cross-linked NPs in a mouse glioma model revealed significant suppression of intracranial tumor growth, with complete removal of the tumor observed in some mice on histological examination. Furthermore, delivery of siCD146 significantly reduced the Ki-67 index in residual tumor tissues relative to that in control mice.

CONCLUSIONS

CD146 is a potential therapeutic target, and folic acid-conjugated NPs delivering siRNA may facilitate gene therapy in malignant gliomas.

Hypoxia induced Sonic Hedgehog signaling regulates cancer stemness, epithelial-to-mesenchymal transition and invasion in cholangiocarcinoma

Aberrant activation of Sonic Hedgehog (SHH) pathway has been implicated in a variety of cancers including cholangiocarcinoma (CC); however, the influencing factors are still unknown. Additionally, intratumoral hypoxia is known to contribute towards therapeutic resistance through modulatory effects on various pathways. In this study, we investigated the relationship between hypoxia and SHH pathway activation and the effect of this interplay on cancer stemness and epithelial-to- mesenchymal transition (EMT) during cholangiocarcinogenesis. Hypoxia promoted SHH pathway activation, evidenced by upregulated SHH and SMO levels, and enhanced glioma-associated oncogene homolog 1 (GLI1) nuclear translocation; whereas silencing of HIF-1α impaired SHH upregulation. Hypoxia also enhanced the expression of cancer stem cell (CSC) transcription factors (NANOG, Oct4, SOX2), CD133 and EMT markers (N-cadherin, Vimentin), thereby supporting invasion. Cyclopamine treatment suppressed hypoxia induced SHH pathway activation, consequently reducing invasiveness by downregulating the expression of CSC transcription factors, CD133 and EMT. Cyclopamine induced apoptosis in CC cells under hypoxia, suggesting that hypoxia induced activation of SHH pathway has modulatory effects on CC progression. Therefore, SHH signaling is proposed as a target for CC treatment, which is refractory to standard chemotherapy.

Hedgehog Signaling: An Achilles' Heel in Cancer

Hedgehog signaling pathway originally identified in the fruit fly Drosophila is an evolutionarily conserved signaling mechanism with crucial roles in embryogenesis, growth and patterning. It exerts its biological effect through a signaling mechanism that terminates at glioma-associated oncogene (GLI) transcription factors which alternate between activator and repressor forms and mediate various responses. The important components of the pathway include the hedgehog ligands (SHH), the Patched (PTCH) receptor, Smoothened (SMO), Suppressor of Fused (SuFu) and GLI transcription factors. Activating or inactivating mutations in key genes cause uncontrolled activation of the pathway in a ligand independent manner. The ligand-dependent aberrant activation of the hedgehog pathway causing overexpression of hedgehog pathway components and its target genes occurs in autocrine as well as paracrine fashion. In adults, aberrant activation of hedgehog signaling has been linked to birth defects and multiple solid cancers. In this review, we assimilate data from recent studies to understand the mechanism of functioning of the hedgehog signaling pathway, role in cancer, its association in various solid malignancies and the current strategies being used to target this pathway for cancer treatment.

Abnormal activity of transcription factors gli in high-grade gliomas

Malignant transformation is associated with loss of cell differentiation, anaplasia. Transcription factors gli, required for embryonic development, may be involved in this process. We studied the activity of transcription factors gli in high-grade gliomas and their role in maintenance of stem cell state and glioma cell survival. 20 glioma cell lines and a sample of a normal adult brain tissue were used in the present study. We found the expression of gli target genes, including GLI1 and FOXM1, in all tested glioma cell lines, but not in the normal tissue. Interestingly, the expression of gli target genes in some glioma cell lines was observed together with a high level of their transcriptional repressor, Gli3R. Knockdown of GLI3 in one of these lines resulted in decrease of gli target gene expression. These data suggest that Gli3R does not prevent the gli target genes transcription, and gli3 acts in glioma cells more as an activator, than a repressor of transcription. We observed that gli regulated the expression of such genes, as SOX2 or OCT4 that maintain stem cell state, and TET1, involving in DNA demethylation. Treatment with GANT61 or siRNA against GLI1, GLI2, or GLI3 could result in complete glioma cell death, while cyclopamine had a weaker and line-specific effect on glioma cell survival. Thus, the gli transcription factors are abnormally active in high-grade gliomas, regulate expression of genes, maintaining the stem cell state, and contribute to glioma cell survival.

Novel-smoothened inhibitors for therapeutic targeting of naïve and drug-resistant hedgehog pathway-driven cancers

The G protein-coupled receptor (GPCR) smoothened (SMO) is a key signaling component of the sonic hedgehog (Hh) pathway and a clinically validated target for cancer treatment. The FDA-approved SMO inhibitors GDC-0449/Vismodegib and LDE225/Sonidegib demonstrated clinical antitumor efficacy. Nevertheless, relatively high percentage of treated patients would eventually develop acquired cross resistance to both drugs. Here, based on published structure and activity of GDC-0449 inhibitor class, we replaced its amide core with benzimidazole which retained bulk of the SMO-targeting activity as measured in our Hh/SMO/Gli1-reporter system. Synthesis and screening of multiple series of benzimidazole derivatives identified HH-1, HH-13, and HH-20 with potent target suppression (IC₅₀: <0.1 μmol/L) in the reporter assays. In NIH3T3 cells stimulated with a secreted Hh (SHH), these inhibitors dose dependently reduced mRNA and protein expression of the endogenous pathway components PTCH-1, Gli1, and cyclin D1 resulting in growth inhibition via G₀/G₁ arrest. Mechanistically, the SMO-targeted growth inhibition involved downregulation of mTOR signaling inputs and readouts consistent with diminished mTORC1/mTORC2 functions and apoptosis. In mice, as with GDC-0449, orally administered HH inhibitors blocked paracrine activation of stromal Hh pathway in Calu-6 tumor microenvironment and attenuated growth of PTCH^+/-/P53^-/- medulloblastoma allograft tumors. Furthermore, HH-13 and HH-20 potently targeted the drug-resistant smoothened SMO-D473H (IC₅₀: <0.2 μmol/L) compared to the poor inhibition by GDC-0449 (IC₅₀: >60 μmol/L). These results identify HH-13 and HH-20 as potent inhibitors capable of targeting naïve and drug-resistant Hh/SMO-driven cancers. The current leads may be optimized to improve pharmaceutical property for potential development of new therapy for treatment of Hh pathway-driven cancers.

GLI2 promotes cell proliferation and migration through transcriptional activation of ARHGEF16 in human glioma cells

BACKGROUND

The Hedgehog (Hh) signaling pathway plays critical roles in modulating embryogenesis and maintaining tissue homeostasis, with glioma-associated oncogene (GLI) transcription factors being the main mediators. Aberrant activation of this pathway is associated with various human malignancies including glioblastoma, although the mechanistic details are not well understood.

METHODS

We performed a microarray analysis of genes that are differentially expressed in glioblastoma U87 cells overexpressing GLI2A, the active form of GLI2, relative to the control cells. Chromatin immunoprecipitation and dual-luciferase assays were used to determine whether Rho guanine nucleotide exchange factor 16 (ARHGEF16) is a downstream target of GLI2. Then, transwell migration, EdU and soft-agar colony formation assays were employed to test effects of ARHGEF16 on glioma cancer cell migration and proliferation, and the effects of GLI2/ARHGEF16 signaling on tumor growth were examined in vivo. Finally, we performed yeast two-hybrid assay, Co-IP and GST-pull down to identify factors that mediate effects of ARHGEF16.

RESULTS

We found that ARHGEF16 mRNA level was upregulated in U87 cells overexpressing GLI2A relative to control cells. GLI2 binds to the ARHGEF16 promoter and activates gene transcription. Glioma cells U87 and U118 overexpressing ARHGEF16 showed enhanced migration and proliferation relative to the control cells, while knockdown of ARHGEF16 in H4 cells led to decreased cell proliferation compared to the control H4 cells. In contrast to the promoting effect of GLI2A overexpression on glioma xenograft growth, both GLI2 inhibition and ARHGEF16 knockdown retarded tumor growth. Cytoskeleton-associated protein 5 (CKAP5) was identified as an interaction protein of ARHGEF16, which is important for the stimulatory effects of ARHGEF16 on glioma cell migration and proliferation.

CONCLUSIONS

These results suggest that therapeutic strategies targeting the GLI2/ARHGEF16/CKAP5 signaling axis could inhibit glioma progression and recurrence.

Targeting GLI Transcription Factors in Cancer

Aberrant activation of hedgehog (Hh) signaling has been observed in a wide variety of tumors and accounts for more than 25% of human cancer deaths. Inhibitors targeting the Hh signal transducer Smoothened (SMO) are widely used and display a good initial efficacy in patients suffering from basal cell carcinoma (BCC); however, a large number of patients relapse. Though SMO mutations may explain acquired therapy resistance, a growing body of evidence suggests that the non-canonical, SMO-independent activation of the Hh pathway in BCC patients can also account for this adverse effect. In this review, we highlight the importance of glioma-associated oncogene (GLI) transcription factors (the main downstream effectors of the canonical and the non-canonical Hh cascade) and their putative role in the regulation of multiple oncogenic signaling pathways. Moreover, we discuss the contribution of the Hh signaling to malignant transformation and propose GLIs as central hubs in tumor signaling networks and thus attractive molecular targets in anti-cancer therapies.

Nucleolar and spindle associated protein 1 promotes the aggressiveness of astrocytoma by activating the Hedgehog signaling pathway

BACKGROUND

The prognosis of human astrocytoma is poor, and the molecular alterations underlying its pathogenesis still needed to be elucidated. Nucleolar and spindle associated protein 1 (NUSAP1) was observed in several types of cancers, but its role in astrocytoma remained unknown.

METHODS

The expression of NUSAP1 in astrocytoma cell lines and tissues were measured with western blotting and Real-Time PCR. Two hundred and twenty-one astrocytoma tissue samples were analyzed by immunochemistry to demonstrate the correlation between the NUSAP1 expression and clinicopathological characteristics. 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay, colony formation, transwell matrix penetration assay, wound healing assay and anchorage-independent growth assay were used to investigate the biological effect of NUSAP1 in astrocytoma. An intracranial brain xenograft tumor model was used to confirm the oncogenic role of NUSAP1 in human astrocytoma. Luciferase reporter assay was used to investigate the effect of NUSAP1 on Hedgehog signaling pathway.

RESULTS

NUSAP1 was markedly overexpressed in astrocytoma cell lines and tissues compared with normal astrocytes and brain tissues. NUSAP1 was found to be overexpressed in 152 of 221 (68.78%) astrocytoma tissues, and was significantly correlated to poor survival. Further, ectopic expression or knockdown of NUSAP1 significantly promoted or inhibited, respectively, the invasive ability of astrocytoma cells. Moreover, intracranial xenografts of astrocytoma cells engineered to express NUSAP1 were highly invasive compared with the parental cells. With regard to its molecular mechanism, upregulation of NUSAP1 in astrocytoma cells promoted the nuclear translocation of GLI family zinc finger 1 (GLI1) and upregulated the downstream genes of the Hedgehog pathway.

CONCLUSION

These findings indicate that NUSAP1 contributes to the progression of astrocytoma by enhancing tumor cell invasiveness via activation of the Hedgehog signaling pathway, and that NUSAP1 might be a potential prognostic biomarker as well as a target in astrocytoma.

mTORC2 regulates hedgehog pathway activity by promoting stability to Gli2 protein and its nuclear translocation

mTORC2 is aberrantly activated in cancer and therefore is considered to be an important therapeutic target. The hedgehog pathway, which is also often hyperactivated, regulates transcription of several genes associated with angiogenesis, metastasis, cellular proliferation and cancer stem cell (CSC) regeneration. However, the contribution of mTORC2 toward hedgehog pathway activity has not been explored yet. Here we have addressed the molecular cross talk between mTORC2 and hedgehog pathway activities in the context of glioblastoma multiforme, a malignant brain tumor using as a model system. We observed that higher mTORC2 activity enhanced the expression of a few hedgehog pathway molecules (Gli1, Gli2 and Ptch1) and amplified its target genes (Cyclin D1, Cyclin D2, Cyclin E, Snail, Slug and VEGF) both in mRNA and protein levels as corroborated by increased metastasis, angiogenesis, cellular proliferation and stem cell regeneration. Inhibition of mTORC2 formation decreased hedgehog pathway activity and attenuated all these above-mentioned events, suggesting their cross talk with each other. Further investigations revealed that mTORC2 inhibited ubiquitination of Gli2 by inactivating GSK3β, and thus it promotes stability to Gli2 and its nuclear translocation. Moreover, enhanced mTORC2 activity led to the increased clonogenic properties and CD133+ cells, indicating its role in CSC regeneration. mTORC2 inhibitor directed the reduction of hedgehog pathway proteins and also reduced CSCs. Thus, our observations support a role for elevated mTORC2 activity in regulating angiogenesis, metastasis, cellular proliferation and CSC regeneration via hedgehog pathway activity. Taken together, it provides a rationale for including the mTOR2 inhibitor as part of the therapeutic regimen for CSCs.

Anti-Cancer Phytometabolites Targeting Cancer Stem Cells

Medicinal plants are a plentiful source of bioactive molecules with much structural diversity. In cancer treatment, molecules obtained from plants represent an attractive alternative to other treatments because several plant-derived compounds have exhibited lower toxicity and higher selectivity against cancer cells. In this review, we focus on the possible application of bioactive molecules obtained from plants against more primitive cell populations in cancers, cancer stem cells. Cancer stem cells are present in several kinds of tumors and are responsible for recurrences and metastases. Common anti-cancer drugs exhibit lower effectiveness against cancer stem cells because of their biological features. However, recently discovered natural phytometabolites exert cytotoxic effects on this rare population of cells in cancers. Therefore, this review presents the latest research on promising compounds from plants that can act as antitumor drugs and that mainly affect stem cell populations in cancers.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

The Crossroads of Neural Stem Cell Development and Tumorigenesis

Isolated brain tumors contain cells that exhibit stem cell features and a tissue microenvironment bearing remarkable similarities to the normal neurogenic niche. This supports the idea that neural stem (NSCs) or progenitor cells, and their progeny are the likely tumor cell(s) of origin. This prompted the investigation of the relationship between NSCs/progenitors and the initiation of tumorigenesis. These studies led to the identification of common signaling machineries underlying NSC development and tumor formation, particularly those with known roles in proliferation and cell fate determination. This review will explore the molecular mechanisms that regulate NSC behavior in the neurogenic niche of the forebrain, and how deregulation of the developmental potential of NSCs might contribute to tumorigenesis.

The Anti-Cancer Effect of Polyphenols against Breast Cancer and Cancer Stem Cells: Molecular Mechanisms

The high incidence of breast cancer in developed and developing countries, and its correlation to cancer-related deaths, has prompted concerned scientists to discover novel alternatives to deal with this challenge. In this review, we will provide a brief overview of polyphenol structures and classifications, as well as on the carcinogenic process. The biology of breast cancer cells will also be discussed. The molecular mechanisms involved in the anti-cancer activities of numerous polyphenols, against a wide range of breast cancer cells, in vitro and in vivo, will be explained in detail. The interplay between autophagy and apoptosis in the anti-cancer activity of polyphenols will also be highlighted. In addition, the potential of polyphenols to target cancer stem cells (CSCs) via various mechanisms will be explained. Recently, the use of natural products as chemotherapeutics and chemopreventive drugs to overcome the side effects and resistance that arise from using chemical-based agents has garnered the attention of the scientific community. Polyphenol research is considered a promising field in the treatment and prevention of breast cancer.

Metabolic Precursor of Cholesterol Causes Formation of Chained Aggregates of Liquid-Ordered Domains

7-Dehydrocholesterol, an immediate metabolic predecessor of cholesterol, can accumulate in tissues due to some metabolic abnormalities, causing an array of symptoms known as Smith-Lemli-Opitz syndrome. Enrichment of cellular membranes with 7-dehydrocholesterol interferes with normal cell-signaling processes, which involve interaction between rafts and formation of the so-called signaling platforms. In model membranes, cholesterol-based ordered domains usually merge upon contact. According to our experimental data, ordered domains in the model systems where cholesterol is substituted for 7-dehydrocholesterol never merge on the time scale of the experiment, but clusterize into necklace-like aggregates. We attribute such different dynamical behavior to altered properties of the domain boundary. In the framework of thickness mismatch model, we analyzed changes of interaction energy profiles of two approaching domains caused by substitution of cholesterol by 7-dehydrocholesterol. The energy barrier for domain merger is shown to increase notably, with simultaneous appearance of another distinct local energy minimum. Such energy profile is in perfect qualitative agreement with the experimental observations. The observed change of domain dynamics can impair proper interaction between cellular rafts underlying pathologies associated with deviations in cholesterol metabolism.

DYNAMICS OF GLI REGULATION AND A STRATEGY TO CONTROL CANCEROUS SITUATION: HEDGEHOG SIGNALING PATHWAY REVISITED

The hedgehog signaling cascade generates highly diverse, fine-tuned responses in response to the external stimulus by the sonic hedgehog (SHH) protein. This is required for the flawless functioning of the cell, its development, survival and proliferation; maintained through production of Glioma protein (GLI) and transcriptional activation of its target genes. Any change in the behavior of GLI response by ectopic expression of SHH or mutations in the core pathway components may cause serious consequences in the cell fate through rapid, uncontrolled and elevated production of GLI. Here, we present a simple but extensive computational model that considers the detailed reaction mechanisms involved in the hedgehog signal transduction and provides a detailed insight into regulation of GLI. For the first time, by explicit involvement of suppressor of fused (SUFU) and Hedgehog interacting protein (HHIP) reaction kinetics in the model, we try to demonstrate the vital importance of HHIP and SUFU in maintaining the graded response of GLI in response to SHH. By performing parameter variations, we capture the conversion of a graded response of GLI to an ultrasensitive switch under SUFU-deficient conditions that might predispose abnormal embryonic development and the irreversible switching response of GLI that corresponds to signal-independent pathway activation observed in cancers.

Epigenetic pathways and glioblastoma treatment: insights from signaling cascades

There is an urgent need to identify novel therapies for glioblastoma (GBM) as most therapies are ineffective. A first step in this process is to identify and validate targets for therapeutic intervention. Epigenetic modulators have emerged as attractive drug targets in several cancers including GBM. These epigenetic regulators affect gene expression without changing the DNA sequence. Recent studies suggest that epigenetic regulators interact with drivers of GBM cell and stem-like cell proliferation. These drivers include components of the Notch, Hedgehog, and Wingless (WNT) pathways. We highlight recent studies connecting epigenetic and signaling pathways in GBM. We also review systems and big data approaches for identifying patient specific therapies in GBM. Collectively, these studies will identify drug combinations that may be effective in GBM and other cancers.

Cancer stem cells in glioblastoma

Glioblastoma is the most prevalent and malignant primary brain tumor, containing self-renewing, tumorigenic cancer stem cells (CSCs) that contribute to tumor initiation and therapeutic resistance. In this review, Lathia et al. discuss how the integration of genetics, epigenetics, and metabolism has shaped our understanding of how CSCs function to drive GBM growth.

Tissues with defined cellular hierarchies in development and homeostasis give rise to tumors with cellular hierarchies, suggesting that tumors recapitulate specific tissues and mimic their origins. Glioblastoma (GBM) is the most prevalent and malignant primary brain tumor and contains self-renewing, tumorigenic cancer stem cells (CSCs) that contribute to tumor initiation and therapeutic resistance. As normal stem and progenitor cells participate in tissue development and repair, these developmental programs re-emerge in CSCs to support the development and progressive growth of tumors. Elucidation of the molecular mechanisms that govern CSCs has informed the development of novel targeted therapeutics for GBM and other brain cancers. CSCs are not self-autonomous units; rather, they function within an ecological system, both actively remodeling the microenvironment and receiving critical maintenance cues from their niches. To fulfill the future goal of developing novel therapies to collapse CSC dynamics, drawing parallels to other normal and pathological states that are highly interactive with their microenvironments and that use developmental signaling pathways will be beneficial.

The Role of Hedgehog Signaling in Tumor Induced Bone Disease

Despite significant progress in cancer treatments, tumor induced bone disease continues to cause significant morbidities. While tumors show distinct mutations and clinical characteristics, they behave similarly once they establish in bone. Tumors can metastasize to bone from distant sites (breast, prostate, lung), directly invade into bone (head and neck) or originate from the bone (melanoma, chondrosarcoma) where they cause pain, fractures, hypercalcemia, and ultimately, poor prognoses and outcomes. Tumors in bone secrete factors (interleukins and parathyroid hormone-related protein) that induce RANKL expression from osteoblasts, causing an increase in osteoclast mediated bone resorption. While the mechanisms involved varies slightly between tumor types, many tumors display an increase in Hedgehog signaling components that lead to increased tumor growth, therapy failure, and metastasis. The work of multiple laboratories has detailed Hh signaling in several tumor types and revealed that tumor establishment in bone can be controlled by both canonical and non-canonical Hh signaling in a cell type specific manner. This review will explore the role of Hh signaling in the modulation of tumor induced bone disease, and will shed insight into possible therapeutic interventions for blocking Hh signaling in these tumors.

Hedgehog Signaling in the Maintenance of Cancer Stem Cells

Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.

Cooperative integration between HEDGEHOG-GLI signalling and other oncogenic pathways: implications for cancer therapy

The HEDGEHOG-GLI (HH-GLI) signalling is a key pathway critical in embryonic development, stem cell biology and tissue homeostasis. In recent years, aberrant activation of HH-GLI signalling has been linked to several types of cancer, including those of the skin, brain, lungs, prostate, gastrointestinal tract and blood. HH-GLI signalling is initiated by binding of HH ligands to the transmembrane receptor PATCHED and is mediated by transcriptional effectors that belong to the GLI family, whose activity is finely tuned by a number of molecular interactions and post-translation modifications. Several reports suggest that the activity of the GLI proteins is regulated by several proliferative and oncogenic inputs, in addition or independent of upstream HH signalling. The identification of this complex crosstalk and the understanding of how the major oncogenic signalling pathways interact in cancer is a crucial step towards the establishment of efficient targeted combinatorial treatments. Here we review recent findings on the cooperative integration of HH-GLI signalling with the major oncogenic inputs and we discuss how these cues modulate the activity of the GLI proteins in cancer. We then summarise the latest advances on SMO and GLI inhibitors and alternative approaches to attenuate HH signalling through rational combinatorial therapies.

Hedgehog signaling in the pathogenesis of neuro-oncology diseases

The review summarizes current knowledge on the Hedgehog signaling pathway, its role in normal embryogenesis and/or initiation and progression of neuro-oncological diseases, especially of high-grade gliomas, the most malignant neuroepithelial tumors. The main proteins forming the Hedgehog signaling pathway include Shh, PTCH1, SMO, HHIP, SUFU and GLI1 isoforms. Effects of other signaling pathways on the family of transcription factors GLI and other proteins are described. The review summarizes modern data about the impact of the Hedgehog signaling pathway on proliferation, migration activity and invasiveness, and also on tumor neoangiogenesis and tumor cell chemoresistance. The role of the Hedgehog signaling pathway in origin of cancer stem cells and epithelial-mesenchymal transition is also analyzed. Some prospects for new anticancer drugs acting on components of the Hedgehog signaling pathway inhibitors are demonstrated.

CSNK1A1 and Gli2 as Novel Targets Identified Through an Integrative Analysis of Gene Expression Data, Protein-Protein Interaction and Pathways Networks in Glioblastoma Tumors: Can These Two Be Antagonistic Proteins?

Glioblastoma (GBM) is the malignant form of glioma, and the interplay of different pathways working in concert in GBM development and progression needs to be fully understood. Wnt signaling and sonic hedgehog (SHH) signaling pathways, having basic similarities, are among the major pathways aberrantly activated in GBM, and hence, need to be targeted. It becomes imperative, therefore, to explore the functioning of these pathways in context of each other in GBM. An integrative approach may help provide new biological insights, as well as solve the problem of identifying common drug targets for simultaneous targeting of these pathways. The beauty of this approach is that it can recapitulate several known facts, as well as decipher new emerging patterns, identifying those targets that could be missed when relying on one type of data at a time. This approach can be easily extended to other systems to discover key patterns in the functioning of signaling molecules. Studies were designed to assess the relationship between significant differential expression of genes of the Wnt (Wnt/β-catenin canonical and Wnt non-canonical) and SHH signaling pathways and their connectivity patterns in interaction and signaling networks. Further, the aim was to decipher underlying mechanistic patterns that may be involved in a more specific way and to generate a ranked list of genes that can be used as markers or drug targets. These studies predict that Wnt pathway plays a relatively more pro-active role than the SHH pathway in GBM. Further, CTNNB1, CSNK1A1, and Gli2 proteins may act as key drug targets common to these pathways. While CTNNB1 is a widely studied molecule in the context of GBM, the likely roles of CSNK1A1 and Gli2 are found to be relatively novel. It is surmised that Gli2 may be antagonistic to CSNK1A1, preventing the phosphorylation of CTNNB1 and SMO proteins in Wnt and SHH signaling pathway, respectively, by CSNK1A1, and thereby, aberrant activation. New insights into the possible behavior of these pathway molecules relative to each other in GBM reveal some key interesting patterns.

Targeting the SMO oncogene by miR-326 inhibits glioma biological behaviors and stemness

BACKGROUND

Few studies have associated microRNAs (miRNAs) with the hedgehog (Hh) pathway. Here, we investigated whether targeting smoothened (SMO) with miR-326 would affect glioma biological behavior and stemness.

METHODS

To investigate the expression of SMO and miR-326 in glioma specimens and cell lines, we utilized quantitative real-time (qRT)-PCR, Western blot, immunohistochemistry, and fluorescence in situ hybridization. The luciferase reporter assay was used to verify the relationship between SMO and miR-326. We performed cell counting kit-8, transwell, and flow cytometric assays using annexin-V labeling to detect changes after transfection with siRNA against SMO or miR-326. qRT-PCR assays, neurosphere formation, and immunofluorescence were utilized to detect the modification of self-renewal and stemness in U251 tumor stem cells. A U251-implanted intracranial model was used to study the effect of miR-326 on tumor volume and SMO suppression efficacy.

RESULTS

SMO was upregulated in gliomas and was associated with tumor grade and survival period. SMO inhibition suppressed the biological behaviors of glioma cells. SMO expression was inversely correlated with miR-326 and was identified as a novel direct target of miR-326. miR-326 overexpression not only repressed SMO and downstream genes but also decreased the activity of the Hh pathway. Moreover, miR-326 overexpression decreased self-renewal and stemness and partially prompted differentiation in U251 tumor stem cells. In turn, the inhibition of Hh partially elevated miR-326 expression. Intracranial tumorigenicity induced by the transfection of miR-326 was reduced and was partially mediated by the decreased SMO expression.

CONCLUSIONS

This work suggests a possible molecular mechanism of the miR- 326/SMO axis, which can be a potential alternative therapeutic pathway for gliomas.

G protein-coupled receptors as oncogenic signals in glioma: emerging therapeutic avenues

Gliomas are the most common malignant intracranial tumors. Newly developed targeted therapies for these cancers aim to inhibit oncogenic signals, many of which emanate from receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor receptor (VEGFR). Unfortunately, the first-generation treatments targeting these oncogenic signals provide little survival benefit in both mouse xenograft models and human patients. The search for new treatment options has uncovered several G protein-coupled receptor (GPCR) candidates and generated a growing interest in this class of proteins as alternative therapeutic targets for the treatment of various cancers, including glioblastoma multiforme (GBM). GPCRs constitute a large family of membrane receptors that influence oncogenic pathways through canonical and non-canonical signaling. Accordingly, evidence indicates that GPCRs display a unique ability to crosstalk with receptor tyrosine kinases, making them important molecular components controlling tumorigenesis. This review summarizes the current research on GPCR functionality in gliomas and explores the potential of modulating these receptors to treat this devastating disease.

Endothelial cells promote stem-like phenotype of glioma cells through activating the Hedgehog pathway

Microenvironmental regulation of cancer stem cells (CSCs) strongly influences the onset and spread of cancer. The way in which glioma cells interact with their microenvironment and acquire the phenotypes of CSCs remains elusive. We investigated how communication between vascular endothelial cells and glioma cells promoted the properties of glioma stem cells (GSCs). We observed that CD133⁺ GSCs were located closely to Shh⁺ endothelial cells in specimens of human glioblastoma multiforme (GBM). In both in vitro and in vivo studies, we found that endothelial cells promoted the appearance of CSC-like glioma cells, as demonstrated by increases in tumourigenicity and expression of stemness genes such as Sox2, Olig2, Bmi1 and CD133 in glioma cells that were co-cultured with endothelial cells. Knockdown of Smo in glioma cells led to a significant reduction of their CSC-like phenotype formation in vitro and in vivo. Endothelial cells with Shh knockdown failed to promote Hedgehog (HH) pathway activation and CSC-like phenotype formation in co-cultured glioma cells. By examination of glioma tissue specimens from 65 patients, we found that the survival of glioma patients was closely correlated with the expression of both Shh by endothelial cells and Gli1 by perivascular glioma cells. Taken together, our study demonstrates that endothelial cells in the tumour microenvironment provide Shh to activate the HH signalling pathway in glioma cells, thereby promoting GSC properties and glioma propagation. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Expression of Hedgehog ligand and signal transduction components in mutually distinct isocitrate dehydrogenase mutant glioma cells supports a role for paracrine signaling

Hedgehog (Hh) signaling regulates the growth of malignant gliomas by a ligand-dependent mechanism. The cellular source of Sonic Hh ligand and mode of signaling have not been clearly defined due to the lack of methods to definitively identify neoplastic cells in glioma specimens. Using an antibody specific for mutant isocitrate dehydrogenase protein expression to identify glioma cells, we demonstrate that Sonic Hh ligand and the pathway components Patched1 (PTCH1) and GLI1 are expressed in neoplastic cells. Further, Sonic Hh ligand and its transcriptional targets, PTCH1 and GLI1, are expressed in mutually distinct populations of neoplastic cells. These findings support a paracrine mode of intratumoral Hh signaling in malignant gliomas.

Arsenic trioxide inhibits Hedgehog, Notch and stem cell properties in glioblastoma neurospheres

Background

Notch and Hedgehog signaling have been implicated in the pathogenesis and stem-like characteristics of glioblastomas, and inhibitors of the pathways have been suggested as new therapies for these aggressive tumors. It has also been reported that targeting both pathways simultaneously can be advantageous in treating glioblastoma neurospheres, but this is difficult to achieve in vivo using multiple agents. Since arsenic trioxide has been shown to inhibit both Notch and Hedgehog in some solid tumors, we examined its effects on these pathways and on stem cell phenotype in glioblastoma.

Results

We found that arsenic trioxide suppresses proliferation and promotes apoptosis in three stem-like glioblastoma neurospheres lines, while inhibiting Notch and Hedgehog target genes. Importantly, arsenic trioxide markedly reduced clonogenic capacity of the tumor neurospheres, and the stem-like CD133-positive fraction was also diminished along with expression of the stem cell markers SOX2 and CD133.

Conclusions

Our results suggest that arsenic trioxide may be effective in targeting stem-like glioblastoma cells in patients by inhibiting Notch and Hedgehog activity.

On the Genesis of Neuroblastoma and Glioma

As the emergence of cancer is most frequent in proliferating tissues, replication errors are considered to be at the base of this disease. This review concentrates mainly on two neural cancers, neuroblastoma and glioma, with completely different backgrounds that are well documented with respect to their ontogeny. Although clinical data on other cancers of the nervous system are available, usually little can be said about their origins. Neuroblastoma is initiated in the embryo at a moment when the nervous system (NS) is in full expansion and occasionally genomic damage can lead to neoplasia. Glioma, to the contrary, occurs in the adult brain supposed to be mostly in a postmitotic state. According to current consensus, neural stem cells located in the subventricular zone (SVZ) in the adult are thought to accumulate enough genomic mutations to diverge on a carcinogenic course leading to diverse forms of glioma. After weighing the pros and cons of this current hypothesis in this review, it will be argued that this may be improbable, yielding to the original old concept of glial origin of glioma.

Pathway modulations and epigenetic alterations in ovarian tumorbiogenesis

Cellular pathways are numerous and are highly integrated in function in the control of cellular systems. They collectively regulate cell division, proliferation, survival and apoptosis of cells and mutagenesis of key genes that control these pathways can initiate neoplastic transformations. Understanding these pathways is crucial to future therapeutic and preventive strategies of the disease. Ovarian cancers are of three major types; epithelial, germ-cell, and stromal. However, ovarian cancers of epithelial origin, arising from the mesothelium, are the predominant form. Of the subtypes of ovarian cancer, the high-grade serous tumors are fatal, with low survival rate due to late detection and poor response to treatments. Close examination of preserved ovarian tissues and in vitro studies have provided insights into the mechanistic changes occurring in cells mediated by a few key genes. This review will focus on pathways and key genes of the pathways that are mutated or have aberrant functions in the pathology of ovarian cancer. Non-genetic mechanisms that are gaining prominence in the pathology of ovarian cancer, miRNAs and epigenetics, will also be discussed in the review.

Primary orthotopic glioma xenografts recapitulate infiltrative growth and isocitrate dehydrogenase I mutation

Malignant gliomas constitute a heterogeneous group of highly infiltrative glial neoplasms with distinct clinical and molecular features. Primary orthotopic xenografts recapitulate the histopathological and molecular features of malignant glioma subtypes in preclinical animal models. To model WHO grades III and IV malignant gliomas in transplantation assays, human tumor cells are xenografted into an orthotopic site, the brain, of immunocompromised mice. In contrast to secondary xenografts that utilize cultured tumor cells, human glioma cells are dissociated from resected specimens and transplanted without prior passage in tissue culture to generate primary xenografts. The procedure in this report details tumor sample preparation, intracranial transplantation into immunocompromised mice, monitoring for tumor engraftment and tumor harvesting for subsequent passage into recipient animals or analysis. Tumor cell preparation requires 2 hr and surgical procedure requires 20 min/animal.

Tumor-specific chromosome mis-segregation controls cancer plasticity by maintaining tumor heterogeneity

Aneuploidy with chromosome instability is a cancer hallmark. We studied chromosome 7 (Chr7) copy number variation (CNV) in gliomas and in primary cultures derived from them. We found tumor heterogeneity with cells having Chr7-CNV commonly occurs in gliomas, with a higher percentage of cells in high-grade gliomas carrying more than 2 copies of Chr7, as compared to low-grade gliomas. Interestingly, all Chr7-aneuploid cell types in the parental culture of established glioma cell lines reappeared in single-cell-derived subcultures. We then characterized the biology of three syngeneic glioma cultures dominated by different Chr7-aneuploid cell types. We found phenotypic divergence for cells following Chr7 mis-segregation, which benefited overall tumor growth in vitro and in vivo. Mathematical modeling suggested the involvement of chromosome instability and interactions among cell subpopulations in restoring the optimal equilibrium of tumor cell types. Both our experimental data and mathematical modeling demonstrated that the complexity of tumor heterogeneity could be enhanced by the existence of chromosomes with structural abnormality, in addition to their mis-segregations. Overall, our findings show, for the first time, the involvement of chromosome instability in maintaining tumor heterogeneity, which underlies the enhanced growth, persistence and treatment resistance of cancers.

Curcumin suppresses malignant glioma cells growth and induces apoptosis by inhibition of SHH/GLI1 signaling pathway in vitro and vivo

AIMS

To study the role of curcumin on glioma cells via the SHH/GLI1 pathway in vitro and vivo.

METHODS

The effects of curcumin on proliferation, migration, apoptosis, SHH/GLI1 signaling, and GLI1 target genes expression were evaluated in multiple glioma cell lines in vitro. A U87-implanted nude mice model was used to study the role of curcumin on tumor volume and the suppression efficacy of GLI1.

RESULTS

Curcumin showed cytotoxic effects on glioma cell lines in vitro. Both mRNA and protein levels of SHH/GLI1 signaling (Shh, Smo, GLI1) were downregulated in a dose- and time-dependent manner. Several GLI1-dependent target genes (CyclinD1, Bcl-2, Foxm1) were also downregulated. Curcumin treatment prevented GLI1 translocating into the cell nucleus and reduced the concentration of its reporter. Curcumin suppressed cell proliferation, colony formation, migration, and induced apoptosis which was mediated partly through the mitochondrial pathway after an increase in the ratio of Bax to Bcl2. Intraperitoneal injection of curcumin in vivo reduced tumor volume, GLI1 expression, the number of positively stained cells, and prolonged the survival period compared with the control group.

CONCLUSION

This study shows that curcumin holds a great promise for SHH/GLI1 targeted therapy against gliomas.

Inhibition of monocarboxylate transporter-4 depletes stem-like glioblastoma cells and inhibits HIF transcriptional response in a lactate-independent manner

Hypoxic regions are frequent in glioblastoma (GBM), the most common type of malignant adult brain tumor, and increased levels of tumor hypoxia have been associated with worse clinical outcomes. To unmask genes important in hypoxia, we treated GBM neurospheres in hypoxia and identified monocarboxylate transporter-4 (MCT4) as one of the most upregulated genes. To investigate the clinical importance of MCT4 in GBM, we examined clinical outcomes and found that MCT4 overexpression is associated with shorter patient survival. Consistent with this, MCT4 upregulation correlated with the aggressive mesenchymal subset of GBM, and MCT4 downregulation correlated with the less aggressive G-CIMP (Glioma CpG Methylator Phenotype) subset of GBM. Immunohistochemical analysis of tissue microarrays confirmed that MCT4 protein levels were increased in high-grade as compared with lower-grade astrocytomas, further suggesting that MCT4 is a clinically relevant target. To test the requirement for MCT4 in vitro, we transduced neurospheres with lentiviruses encoding short-hairpin RNAs (shRNAs) against MCT4, resulting in growth inhibition of 50-80% under hypoxia in two lines. MCT4 knockdown was associated with a decreased percentage of cells expressing the stem-cell marker CD133 and increased apoptotic fraction. We also found that flow-sorted CD133-positive cells had almost sixfold higher MCT4 levels than CD133-negative cells, suggesting that the stem-like population might have a greater requirement for MCT4. Most importantly, MCT4 silencing also slowed GBM intracranial xenograft growth in vivo. Interestingly, whereas MCT4 is a well-characterized lactate exporter, we found that both intracellular and extracellular lactate levels did not change following MCT4 silencing, suggesting a novel lactate export-independent mechanism for growth inhibition in GBMs. To identify this potential mechanism, we performed microarray analysis on control and shMCT4-expressing neurospheres and found a dramatic reduction in the expression of multiple Hypoxia-Inducible Factor (HIF)-regulated genes following MCT4 knockdown. The overall reduction in HIF transcriptional response was further validated using a hypoxia response element (HRE)-dependent green-fluorescent protein (GFP) reporter line.

Brain tumor stem cells: Molecular characteristics and their impact on therapy

Glioblastoma (GBM) is the most prevalent primary brain tumor and ranks among the most lethal of human cancers with conventional therapy offering only palliation. Great strides have been made in understanding brain cancer genetics and modeling these tumors with new targeted therapies being tested, but these advances have not translated into substantially improved patient outcomes. Multiple chemotherapeutic agents, including temozolomide, the first-line treatment for glioblastoma, have been developed to kill cancer cells. However, the response to temozolomide in GBM is modest. Radiation is also moderately effective but this approach is plagued by limitations due to collateral radiation damage to healthy brain tissue and development of radioresistance. Therapeutic resistance is attributed at least in part to a cell population within the tumor that possesses stem-like characteristics and tumor propagating capabilities, referred to as cancer stem cells. Within GBM, the intratumoral heterogeneity is derived from a combination of regional genetic variance and a cellular hierarchy often regulated by distinct cancer stem cell niches, most notably perivascular and hypoxic regions. With the recent emergence as a key player in tumor biology, cancer stem cells have symbiotic relationships with the tumor microenvironment, oncogenic signaling pathways, and epigenetic modifications. The origins of cancer stem cells and their contributions to brain tumor growth and therapeutic resistance are under active investigation with novel anti-cancer stem cell therapies offering potential new hope for this lethal disease.

Integrative analysis of cancer-related signaling pathways

Identification and classification of cancer types and subtypes is a major issue in current cancer research. Whole genome expression profiling of cancer tissues is often the basis for such subtype classifications of tumors and different signatures for individual cancer types have been described. However, the search for best performing discriminatory gene-expression signatures covering more than one cancer type remains a relevant topic in cancer research as such a signature would help understanding the common changes in signaling networks in these disease types. In this work, we explore the idea of a top down approach for sample stratification based on a module-based network of cancer relevant signaling pathways. For assembly of this network, we consider several of the most established cancer pathways. We evaluate our sample stratification approach using expression data of human breast and ovarian cancer signatures. We show that our approach performs equally well to previously reported methods besides providing the advantage to classify different cancer types. Furthermore, it allows to identify common changes in network module activity of those cancer samples.

New prospects for drug development: the hedgehog pathway revealed. Focus on hematologic malignancies

The hedgehog (Hh) pathway is a critical regulator of vertebrate embryonic development and is involved in the function of processes such as stem cell maintenance and differentiation, tissue polarity and cell proliferation. Given how critical these functions are, it is not surprising that mutations in Hh pathway components are often implicated in the tumorigenesis of a variety of human cancers. Promotion of tumor growth has recently been shown by activated Hh signaling in the tumor itself, as well as by pathway activation within surrounding cells comprising the tumor microenvironment. Targeted disruption of various Hh pathway proteins has been successfully employed as an anticancer strategy with several synthetic Hh antagonists now available. Here, the molecular basis of Hh signaling, the therapeutic rationales for targeting this pathway and the current status of Hh pathway inhibitors in the clinic are reviewed.

Phase I study of the Hedgehog pathway inhibitor IPI-926 in adult patients with solid tumors

PURPOSE

To conduct a first-in-human phase I study to determine the dose-limiting toxicities (DLT), characterize the pharmacokinetic profile, and document the antitumor activity of IPI-926, a new chemical entity that inhibits the Hedgehog pathway (HhP).

EXPERIMENTAL DESIGN

Patients with solid tumors refractory to standard therapy were given IPI-926 once daily (QD) by mouth in 28-day cycles. The starting dose was 20 mg, and an accelerated titration schedule was used until standard 3 + 3 dose-escalation cohorts were implemented. Pharmacokinetics were evaluated on day -7 and day 22 of cycle 1.

RESULTS

Ninety-four patients (32F, 62M; ages, 39-87) received doses ranging from 20 to 210 mg QD. Dose levels up to and including 160 mg administered QD were well tolerated. Toxicities consisted of reversible elevations in aspartate aminotransferase (AST), alanine aminotransferase (ALT) and bilirubin, fatigue, nausea, alopecia, and muscle spasms. IPI-926 was not associated with hematologic toxicity. IPI-926 pharmacokinetics were characterized by a slow absorption (T(max) = 2-8 hours) and a terminal half-life (t(1/2)) between 20 and 40 hours, supporting QD dosing. Of those HhP inhibitor-naïve patients with basal cell carcinoma (BCC) who received more than one dose of IPI-926 and had a follow-up clinical or Response Evaluation Criteria in Solid Tumors (RECIST) assessment, nearly a third (8 of 28 patients) showed a response to IPI-926 at doses ≥130 mg.

CONCLUSIONS

IPI-926 was well tolerated up to 160 mg QD within 28-day cycles, which was established as the recommended phase II dose and schedule for this agent. Single-agent activity of IPI-926 was observed in HhP inhibitor-naïve patients with BCC.

NPV-LDE-225 (Erismodegib) inhibits epithelial mesenchymal transition and self-renewal of glioblastoma initiating cells by regulating miR-21, miR-128, and miR-200

BACKGROUND

Glioblastoma multiforme is the most common form of primary brain tumor, often characterized by poor survival. Glioblastoma initiating cells (GICs) regulate self-renewal, differentiation, and tumor initiation properties and are involved in tumor growth, recurrence, and resistance to conventional treatments. The sonic hedgehog (SHH) signaling pathway is essential for normal development and embryonic morphogenesis. The objectives of this study were to examine the molecular mechanisms by which GIC characteristics are regulated by NPV-LDE-225 (Smoothened inhibitor; (2,2'-[[dihydro-2-(4-pyridinyl)-1,3(2H,4H)-pyrimidinediyl]bis(methylene)]bis[N,N-dimethylbenzenamine).

METHODS

Cell viability and apoptosis were measured by XTT and annexin V-propidium iodide assay, respectively. Gli translocation and transcriptional activities were measured by immunofluorescence and luciferase assay, respectively. Gene and protein expressions were measured by quantitative real-time PCR and Western blot analyses, respectively.

RESULTS AND CONCLUSION

NPV-LDE-225 inhibited cell viability, neurosphere formation, and Gli transcriptional activity and induced apoptosis by activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase. NPV-LDE-225 increased the expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-R1/DR4, TRAIL-R2/DR5, and Fas and decreased the expression of platelet derived growth factor receptor-α and Bcl2, and these effects were abrogated by Gli1 plus Gli2 short hairpin RNAs. NPV-LDE-225 enhanced the therapeutic potential of FasL and TRAIL by upregulating Fas and DR4/5, respectively. Interestingly, NPV-LDE-225 induced expression of programmed cell death 4 and apoptosis and inhibited cell viability by suppressing micro RNA (miR)-21. Furthermore, NPV-LDE-225 inhibited pluripotency-maintaining factors Nanog, Oct4, Sox2, and cMyc. The inhibition of Bmi1 by NPV-LDE-225 was regulated by induction of miR-128. Finally, NPV-LDE-225 suppressed epithelial-mesenchymal transition by upregulating E-cadherin and inhibiting N-cadherin, Snail, Slug, and Zeb1 through modulating the miR-200 family. Our data highlight the importance of the SHH pathway for self-renewal and early metastasis of GICs.

Modulation of the Wnt/beta-catenin pathway in human oligodendroglioma cells by Sox17 regulates proliferation and differentiation

Oligodendrogliomas originate from oligodendrocyte progenitor cells (OPCs), whose development is regulated by the Sonic hedgehog and Wnt/beta-catenin pathways. We investigated the contribution of these pathways in the proliferation and differentiation of human oligodendroglioma cells (HOG). Inhibition of Hedgehog signaling with cyclopamine decreased cell survival and increased phosphorylated beta-catenin without altering myelin protein levels. Conversely, treatment of HOG with the Wnt antagonist secreted frizzled related protein (SFRP1), led to increased myelin protein levels and reduced cell proliferation, suggesting cell cycle arrest and differentiation. Unlike normal primary human OPCs, beta-catenin in HOG cells is not associated with endogenous Sox17 protein despite high levels of both proteins. Retroviral overexpression of recombinant Sox17 increased HOG cell cycle exit and apoptosis, and raised myelin protein levels and the percentage of O4(+) cells, indicating increased differentiation. Recombinant Sox17 also increased beta-catenin-TCF4-Sox17 complex formation and decreased total cellular levels of beta-catenin. These changes were associated with increased SFRP1, and reduced expression of Wnt-1 and Frizzled-1, -3 and -7 RNA, indicating that Sox17 induced a Hedgehog target, and regulated Wnt signaling at multiple levels. Our studies indicate that Wnt signaling regulates HOG cell cycle arrest and differentiation, and that recombinant Sox17 mediates modulation of the Wnt pathway through changes in beta-catenin, SFRP1 and Wnt/Frizzled expression. Our results thus identify Sox17 as a potential molecular target to include in HOG therapeutic strategies.

Hedgehog signaling pathway in ovarian cancer

Despite advances in surgical and chemotherapeutic treatment options, less than 50% of patients with advanced-stage ovarian cancer survive five years after initial diagnosis. In this regard, novel treatment approaches are warranted utilizing molecularly targeted therapies directed against particular components of specific signaling pathways which are required for tumor development and progression. One molecular pathway of interest is the hedgehog (Hh) signaling pathway. Activation of the Hh pathway has been observed in several cancer types, including ovarian cancer. This review highlights the crucial role of Hh signaling in the development and progression of ovarian cancer and might lead to a better understanding of the Hh signaling in ovarian tumorigenesis, thus encouraging the investigation of novel targeted therapies.

Cathepsin B and uPAR regulate self-renewal of glioma-initiating cells through GLI-regulated Sox2 and Bmi1 expression

Cancer-initiating cells comprise a heterogeneous population of undifferentiated cells with the capacity for self-renewal and high proliferative potential. We investigated the role of uPAR and cathepsin B in the maintenance of stem cell nature in glioma-initiating cells (GICs). Simultaneous knockdown of uPAR and cathepsin B significantly reduced the expression of CD133, Nestin, Sox2 and Bmi1 at the protein level and GLI1 and GLI2 at the messenger RNA level. Also, knockdown of uPAR and cathepsin B resulted in a reduction in the number of GICs as well as sphere size. These changes are mediated by Sox2 and Bmi1, downstream of hedgehog signaling. Addition of cyclopamine reduced the expression of Sox2 and Bmi1 along with GLI1 and GLI2 expression, induced differentiation and reduced subsphere formation of GICs thereby indicating that hedgehog signaling acts upstream of Sox2 and Bmi1. Further confirmation was obtained from increased luciferase expression under the control of a GLI-bound Sox2 and Bmi1 luciferase promoter. Simultaneous knockdown of uPAR and cathepsin B also reduced the expression of Nestin Sox2 and Bmi1 in vivo. Thus, our study highlights the importance of uPAR and cathepsin B in the regulation of malignant stem cell self-renewal through hedgehog components, Bmi1 and Sox2.