In vitro treatment of melanoma brain metastasis by simultaneously targeting the MAPK and PI3K signaling pathways

Screening out molecular pathways and prognostic biomarkers of ultraviolet-mediated melanoma through computational techniques

PURPOSE

Ultraviolet radiation causes skin cancer, but the exact mechanism by which it occurs and the most effective methods of intervention to prevent it are yet unknown. For this purpose, our study will use bioinformatics and systems biology approaches to discover potential biomarkers of skin cancer for early diagnosis and prevention of disease with applicable clinical treatments.

METHODS

This study compared gene expression and protein levels in ultraviolet-mediated cultured keratinocytes and adjacent normal skin tissue using RNA sequencing data from the National Center for Biotechnology Information-Gene Expression Omnibus (NCBI-GEO) database. Then, pathway analysis was employed with a selection of hub genes from the protein-protein interaction (PPI) network and the survival and expression profiles. Finally, potential clinical biomarkers were validated by receiver operating characteristic (ROC) curve analysis.

RESULTS

We identified 32 shared differentially expressed genes (DEGs) by analyzing three different subsets of the GSE85443 dataset. Skin cancer development is related to the control of several DEGs through cyclin-dependent protein serine/threonine kinase activity, cell cycle regulation, and activation of the NIMA kinase pathways. The cytoHubba plugin in Cytoscape identified 12 hub genes from PPI; among these 3 DEGs, namely, AURKA, CDK4, and PLK1 were significantly associated with survival (P < 0.05) and highly expressed in skin cancer tissues. For validation purposes, ROC curve analysis indicated two biomarkers: AURKA (area under the curve (AUC) value = 0.8) and PLK1 (AUC value = 0.7), which were in an acceptable range.

CONCLUSIONS

Further translational research, including clinical experiments, teratogenicity tests, and in-vitro or in-vivo studies, will be performed to evaluate the expression of these identified biomarkers regarding the prognosis of skin cancer patients.

A flow cytometry-based protocol for syngenic isolation of neurovascular unit cells from mouse and human tissues

The neurovascular unit (NVU), composed of endothelial cells, pericytes, juxtaposed astrocytes and microglia together with neurons, is essential for proper central nervous system functioning. The NVU critically regulates blood-brain barrier (BBB) function, which is impaired in several neurological diseases and is therefore a key therapeutic target. To understand the extent and cellular source of BBB dysfunction, simultaneous isolation and analysis of NVU cells is needed. Here, we describe a protocol for the EPAM-ia method, which is based on flow cytometry for simultaneous isolation and analysis of endothelial cells, pericytes, astrocytes and microglia. This method is based on differential processing of NVU cell types using enzymes, mechanical homogenization and filtration specific for each cell type followed by combining them for immunostaining and fluorescence-activated cell sorting. The gating strategy encompasses cell-type-specific and exclusion markers for contaminating cells to isolate the major NVU cell types. This protocol takes ~6 h for two sets of one or two animals. The isolation part requires experience in animal handling, fresh tissue processing and immunolabeling for flow cytometry. Sorted NVU cells can be used for downstream applications including transcriptomics, proteomics and cell culture. Multiple cell-type analyses using UpSet can then be applied to obtain robust targets from single or multiple NVU cell types in neurological diseases associated with BBB dysfunction. The EPAM-ia method is also amenable to isolation of several other cell types, including cancer cells and immune cells. This protocol is applicable to healthy and pathological tissue from mouse and human sources and to several cell types compared with similar protocols.

CCT196969 effectively inhibits growth and survival of melanoma brain metastasis cells

Melanomas frequently metastasize to the brain. Despite recent progress in the treatment of melanoma brain metastasis, therapy resistance and relapse of disease remain unsolved challenges. CCT196969 is a SRC family kinase (SFK) and Raf proto-oncogene, serine/threonine kinase (RAF) inhibitor with documented effects in primary melanoma cell lines in vitro and in vivo. Using in vitro cell line assays, we studied the effects of CCT196969 in multiple melanoma brain metastasis cell lines. The drug effectively inhibited proliferation, migration, and survival in all examined cell lines, with viability IC₅₀ doses in the range of 0.18–2.6 μM. Western blot analysis showed decreased expression of p-ERK, p-MEK, p-STAT3 and STAT3 upon CCT196969 treatment. Furthermore, CCT196969 inhibited viability in two B-Raf Proto-Oncogene (BRAF) inhibitor resistant metastatic melanoma cell lines. Further in vivo studies should be performed to determine the treatment potential of CCT196969 in patients with treatment-naïve and resistant melanoma brain metastasis.

Translating pharmacology models effectively to predict therapeutic benefit

Many in vitro and in vivo models are used in pharmacological research to evaluate the role of targeted proteins in a disease. Understanding the translational relevance and limitation of these models for analyzing the disposition, pharmacokinetic/pharmacodynamic (PK/PD) profile, mechanism, and efficacy of a drug, is essential when selecting the most appropriate model of the disease of interest and predicting clinically efficacious doses of the investigational drug. Here, we review selected animal models used in ophthalmology, infectious diseases, oncology, autoimmune diseases, and neuroscience. Each area has specific challenges around translatability and determination of an efficacious dose: new patient-specific dosing methods could help overcome these limitations.

The PIK3CA H1047R Mutation Confers Resistance to BRAF and MEK Inhibitors in A375 Melanoma Cells through the Cross-Activation of MAPK and PI3K-Akt Pathways

The targeting of the Mitogen-Activated Protein Kinase (MAPK) signalling pathway in melanoma improves the prognosis of patients harbouring the V-Raf Murine Sarcoma Viral Oncogene Homolog B1 (BRAF) mutation. However, a fraction of these patients may experience tumour progression due to resistance to targeted therapy. Mutations affecting the Phosphoinositol-3-Kinase (PI3K)–Akt pathway may favour the onset of drug resistance, suggesting the existence of a crosstalk between the MAPK and PI3K–Akt pathways. We hypothesized that the inhibition of both pathways may be a therapeutic option in resistant melanoma. However, conflicting data have been generated in this context. In this study, three different A375 cell melanoma models either overexpressing or not expressing the wild-type or mutated form of the PhosphatidylInositol-4,5-bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) gene were used to clarify the therapeutic response of melanoma to BRAF, Mitogen-Activated Protein Kinase Kinase 1 (MEK), and PI3K inhibitors in the presence of the PIK3CA H1047R mutation. Our data strongly support the notion that the crosstalk between the MAPK and PI3K–Akt pathways is one of the main mechanisms associated with melanoma development and progression and that the combination of MAPK and PI3K inhibitors may sensitize melanoma cells to therapy.

CRISPR/Cas9 Mediated Knockout of Cyclooxygenase-2 Gene Inhibits Invasiveness in A2058 Melanoma Cells

The inducible isoenzyme cyclooxygenase-2 (COX-2) is an important hub in cellular signaling, which contributes to tumor progression by modulating and enhancing a pro-inflammatory tumor microenvironment, tumor growth, apoptosis resistance, angiogenesis and metastasis. In order to understand the role of COX-2 expression in melanoma, we investigated the functional knockout effect of COX-2 in A2058 human melanoma cells. COX-2 knockout was validated by Western blot and flow cytometry analysis. When comparing COX-2 knockout cells to controls, we observed significantly reduced invasion, colony and spheroid formation potential in cell monolayers and three-dimensional models in vitro, and significantly reduced tumor development in xenograft mouse models in vivo. Moreover, COX-2 knockout alters the metabolic activity of cells under normoxia and experimental hypoxia as demonstrated by using the radiotracers [¹⁸F]FDG and [¹⁸F]FMISO. Finally, a pilot protein array analysis in COX-2 knockout cells verified significantly altered downstream signaling pathways that can be linked to cellular and molecular mechanisms of cancer metastasis closely related to the enzyme. Given the complexity of the signaling pathways and the multifaceted role of COX-2, targeted suppression of COX-2 in melanoma cells, in combination with modulation of related signaling pathways, appears to be a promising therapeutic approach.

Effects of RNA methylation N6-methyladenosine regulators on malignant progression and prognosis of melanoma

Background

Melanoma is an extremely aggressive type of skin cancer and experiencing a expeditiously rising mortality in a current year. Exploring new potential prognostic biomarkers and therapeutic targets of melanoma are urgently needed. The ambition of this research was to identify genetic markers and assess prognostic performance of N6-methyladenosine (m6A) regulators in melanoma.

Methods

Gene expression data and corresponding clinical informations of melanoma patients as well as sequence data of normal controls are collected from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) databases. Quantitative real-time PCR (qRT-PCR) analysis was carried out to detect the RNA expression of IGF2BP3 in A375 cell line, melanoma tissues, and normal tissues. Western blot, cell proliferation, and migration assays were performed to assess the ability of IGF2BP3 in A375 cell line.

Results

Differently expressed m6A regulators between tumor samples and normal samples were analyzed. A three-gene prognostic signature including IGF2BP3, RBM15B, and METTL16 was constructed, and the risk score of this signature was identified to be an independent prognostic indicator for melanoma. In addition, IGF2BP3 was verified to promote melanoma cell proliferation and migration in vitro and associate with lymph node metastasis in clinical samples. Moreover, risk score and the expression of IGF2BP3 were positively associated with the infiltrating immune cells and these hub genes made excellent potential drug targets in melanoma.

Conclusion

We identified the genetic changes in m6A regulatory genes and constructed a three-gene risk signature with distinct prognostic value in melanoma. This research provided new insights into the epigenetic understanding of m6A regulators and novel therapeutic strategies in melanoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02163-9.

FB-15 inhibits MGC-803 cells growth by regulating energy metabolism

In this study, we scrutinized the anticancer effects of FB-15 on human gastric carcinoma MGC-803 cells in vitro and vivo, and its preliminary effect on tubulin and HIF-1α. We confirmed that FB-15 not only inhibited the proliferation of a large number of cells in a concentration and time-dependent manner but also inhibited proliferation of a single cell to form clones. FB-15 manifested little cytotoxicity for normal stomach cells GES-1. The flow cytometry analysis displayed that FB-15 induced apoptosis MGC-803 cells and mainly arrested cells in the S phase in a concentration-dependent manner. The results of the wound healing assay indicated that FB-15 suppressed cell migration. Furthermore, the western blotting showed that FB-15 down-regulated the expression of β3-tubulin and HIF-1α, consistent with Immunohistochemical assay. The binding modes of FB-15 with tubulin were clarified by molecular docking. FB-15 significantly suppressed the growth of MGC-803 gastric cancer tumors. The inhibitory effect of FB-15 on tumor growth was superior to 5-Fu. Taken together, these results provided evidence for FB-15 to be used as an effective anticancer drug candidate for gastric cancer.

Effective Treatment of Metastatic Melanoma by Combining MAPK and PI3K Signaling Pathway Inhibitors

Malignant melanoma is the most aggressive type of skin cancer and is closely associated with the development of brain metastases. Despite aggressive treatment, the prognosis has traditionally been poor, necessitating improved therapies. In melanoma, the mitogen activated protein kinase and the phosphoinositide 3-kinase signaling pathways are commonly altered, and therapeutically inhibiting one of the pathways often upregulates the other, leading to resistance. Thus, combined treatment targeting both pathways is a promising strategy to overcome this. Here, we studied the in vitro and in vivo effects of the PI3K inhibitor buparlisib and the MEK1/2 inhibitor trametinib, used either as targeted monotherapies or in combination, on patient-derived melanoma brain metastasis cell lines. Scratch wound and trans-well assays were carried out to assess the migratory capacity of the cells upon drug treatment, whereas flow cytometry, apoptosis array and Western blots were used to study apoptosis. Finally, an in vivo treatment experiment was carried out on NOD/SCID mice. We show that combined therapy was more effective than monotherapy. Combined treatment also more effectively increased apoptosis, and inhibited tumor growth in vivo. This suggests a clinical potential of combined treatment to overcome ceased treatment activity which is often seen after monotherapies, and strongly encourages the evaluation of the treatment strategy on melanoma patients with brain metastases.

Concentration-Dependent Dual Effects of Ciprofloxacin on SB-590885-Resistant BRAFV600E A375 Melanoma Cells

BRAF inhibitors (BRAFi) have been applied to treat melanoma harboring V600E mutations. Several studies showed that BRAFi-resistant melanomas are dependent on mitochondrial biogenesis. Therefore, the present study aimed to investigate the influence of ciprofloxacin (CIP), a mitochondria-targeting antibiotic, on SB-590885-resistant BRAF^V600E A375 melanoma (A375/SB) cells. The cytotoxicity activity of CIP and SB-590885, a potent and specific BRAFi, on A375 and A375/SB cells was evaluated by MTT, colony formation, migration, and spheroid formation assays. Moreover, SB-590885-induced cell death in A375 cells was analyzed. SB-590885 showed time- and concentration-dependent cytotoxic effects on A375 cells. Twenty-five μg/mL CIP decreased the cell viability of A375 and A375/SB cells in a time-dependent manner. This concentration of CIP markedly decreased clonogenicity in both cells and caused a reduction in the growth of A375/SB spheroids. The cytotoxicity of 5 μg/mL CIP on A375/SB cells was less than that of A375 cells. The colony formation and migration ability of A375/SB cells was increased in the presence of 5 μg/mL CIP. Ten μM SB-590885 induced a massive vacuolization in A375 cells. Cell death assays suggested a simultaneous activation of autophagy, paraptosis, apoptosis, and necrosis. For the first time, this study reveals that CIP at the maximum concentration in serum (5 μg/mL) can enhance the colony formation and migration abilities in BRAFi-resistant melanoma cells, while it has cytotoxic activity against these cells at a higher concentration than serum level. This study suggests that CIP may promote aggressive growth properties in BRAFi-resistant melanomas, at a concentration present in serum.

Emerging findings into molecular mechanism of brain metastasis

Brain metastasis is an important cause of morbidity and mortality in cancer patients. Hence, the need to develop improved therapies to prevent and treat metastasis to the brain is becoming urgent. Recent studies in this area are bringing about some advanced progress on brain metastasis. It was concluded that the occurrence and poor prognosis of brain metastasis have been mostly attributed to the exclusion of anticancer drugs from the brain by the blood-brain barrier. And several highly potent new generation targeted drugs with enhanced CNS distribution have been developed constantly. However, the noted "seed and soil" hypothesis also suggests that the outcome of metastasis depends on the relationship between unique tumor cells and the specific organ microenvironment. Moreover, increasing studies in multiple tumor types demonstrated that brain metastasis has great molecular differences between primary tumors and extracranial metastasis to a large extent. Here, the authors summarized the most common malignancies that could lead to brain metastasis-lung cancer, breast cancer and melanoma and their related mutated factors. Only by comprehending a deeper understanding of the molecular mechanisms, more effective brain-specific therapies will be developed for brain metastasis.

The investigation of ceranib-2 on apoptosis and drug interaction with carboplatin in human non small cell lung cancer cells in vitro

Ceramide is found to be involved in inhibition of cell division and induction of apoptosis in certain tumour cells. Ceranib-2 is an agent that increases ceramide levels by inhibiting ceramidase in cancer cells. Therefore, we aimed to investigate the effects of ceranib-2 on cell survival, apoptosis and interaction with carboplatin in human non-small cell lung cancer cells. The cytotoxic effect of ceranib-2 (1-100 µM) was determined by MTT assay in human lung adenocarcinoma (A549) and large cell lung carcinoma (H460) cells. Carboplatin (1-100 µM) and lung bronchial epithelial cells (BEAS-2B) were used as positive controls. Morphological and ultrastructural changes were analysed by light microscope and TEM. Apoptotic/necrotic cell death and acid ceramidase activity were analysed by ELISA. Combination effects of ceranib-2 and carboplatin were investigated by MTT. The expression levels of CASP3, CASP9, BAX and BCL-2 were examined by qRT-PCR. The IC₅₀ of ceranib-2 was determined as 22 μM in A549 cells and 8 μM in H460 cells for 24 h. Morphological changes and induction of DNA fragmentation have revealed apoptotic effects of ceranib-2 in both cell lines. Ceranib-2 and carboplatin has shown synergism in combined treatment at 10 and 25 μM doses in H460 cells for 24 h. Ceranib-2 inhibited acid ceramidase activity by 44% at 25 µM in H460 cells. Finally, CASP3, CASP9 and BAX expressions were increased while BCL-2 expression was reduced in both cells. Our results obtained some preliminary results about the cytotoxic and apoptotic effects of ceranib-2 for the first time in NSCLC cell lines.

SOX4 promotes melanoma cell migration and invasion though the activation of the NF-κB signaling pathway

SOX4 has been reported to be abnormally expressed in many types of cancer, including melanoma. However, its role in cell proliferation and metastasis remains controversial. In this study, SOX4 was downregulated or overexpressed in A375, A2058 and A875 melanoma cells by siRNA or lentivirus transfection, respectively. Cell metastasis was observed by Transwell assay. In an aim to elucidate the underlying mechanisms, we determined the expression of nuclear factor-κB (NF-κB) by real-time PCR assay and western blot analysis. Our data indicated that SOX4 knockdown inhibited melanoma cell migration and invasion. In the melanoma cells in which SOX4 was downregulated, the expression levels of NF-κB/p65, matrix metalloproteinase (MMP)2 and MMP9 were suppressed at both the mRNA and protein levels. Conversely, the overexpression of SOX4 promoted melanoma cell migration and invasion. In the melanoma cells in which SOX4 was overexpressed, the expression levels of NF-κB/p65, MMP2 and MMP9 were increased at both the mRNA and protein level. On the whole, our findings indicate that SOX4 promotes melanoma cell migration and invasion through the activation of the NF-κB/p65 signaling pathway. Thus, SOX4 may prove to be a potential therapeutic target for the treatment of melanoma.

PTEN status is a crucial determinant of the functional outcome of combined MEK and mTOR inhibition in cancer

Combined MAPK/PI3K pathway inhibition represents an attractive, albeit toxic, therapeutic strategy in oncology. Since PTEN lies at the intersection of these two pathways, we investigated whether PTEN status determines the functional response to combined pathway inhibition. PTEN (gene, mRNA, and protein) status was extensively characterized in a panel of cancer cell lines and combined MEK/mTOR inhibition displayed highly synergistic pharmacologic interactions almost exclusively in PTEN-loss models. Genetic manipulation of PTEN status confirmed a mechanistic role for PTEN in determining the functional outcome of combined pathway blockade. Proteomic analysis showed greater phosphoproteomic profile modification(s) in response to combined MEK/mTOR inhibition in PTEN-loss contexts and identified JAK1/STAT3 activation as a potential mediator of synergistic interactions. Overall, our results show that PTEN-loss is a crucial determinant of synergistic interactions between MAPK and PI3K pathway inhibitors, potentially exploitable for the selection of cancer patients at the highest chance of benefit from combined therapeutic strategies.

Mini-pillar array for hydrogel-supported 3D culture and high-content histologic analysis of human tumor spheroids

Three-dimensional (3D) cancer cell culture models mimic the complex 3D organization and microenvironment of human solid tumor tissue and are thus considered as highly predictive models representing avascular tumor regions. Confocal laser scanning microscopy is useful for monitoring drug penetration and therapeutic responses in 3D tumor models; however, photonic attenuation at increasing imaging depths and limited penetration of common fluorescence tracers are significant technical challenges to imaging. Immunohistological staining would be a good alternative, but the preparation of tissue sections from rather fragile spheroids through fixing and embedding procedures is challenging. Here we introduce a novel 3 × 3 mini-pillar array chip that can be utilized for 3D cell culturing and sectioning for high-content histologic analysis. The mini-pillar array chip facilitated the generation of 3D spheroids of human cancer cells within hydrogels such as alginate, collagen, and Matrigel. As expected, visualization of the 3D distribution of calcein AM and doxorubicin by optical sectioning was limited by photonic attenuation and dye penetration. The integrity of the 3D microtissue section was confirmed by immunostaining on paraffin sections and cryo-sections. The applicability of the mini-pillar array for drug activity evaluation was tested by measuring viability changes in spheroids exposed to anti-cancer agents, 5-fluorouracil and tirapazamine. Thus, our novel mini-pillar array platform can potentially promote high-content histologic analysis of 3D cultures and can be further optimized for field-specific needs.

Cortactin and Exo70 mediated invasion of hepatoma carcinoma cells by MMP-9 secretion

This study was aimed to evaluate the regulation mechanism of cortactin (CTTN) on matrix metalloproteinases 9 (MMP-9) and its relations with Exo70 in invasion of hepatoma carcinoma (HCC) cells. The expression levels of CTTN, Exo70 and MMP-9 were detected in normal hepatocytes and various HCC cells by real-time PCR. Then the migration and invasion ability of these cells was revealed by scratch and invasion assay. The effects of CTTN on MMP-9 and the ability of migration and invasion were evaluated by silence and overexpress CTTN. During this process, the expression of CTTN was detected by Western blot, the activity and concentration of MMP-9 in supernatant of culture medium was detected by zymography and ELISA assay. Besides, Exo70 was also inhibited to reveal its effects on MMP-9 and the migration and invasion ability of LM3. Increased expression of CTTN, MMP-9, Exo70, reduced scratch area and increased puncture cell numbers were found in HCC cells (p < 0.05). The expression of CTTN was significantly correlated with Exo70 and the migration and invasion ability of HCC (p < 0.05). In addition, the activity and concentration of MMP-9 were significantly affected by the expression level of CTTN, while the expression of MMP-9 was not influenced. Besides, Exo70-si also exhibited significantly inhibition effects on the activity and concentration of MMP-9 and puncture cell numbers (p < 0.05). A synergistic reaction may exhibited on CTTN and Exo70, which could mediate the secretion of MMPs thereby regulate tumor invasion.

Metabotropic glutamate receptors in cancer

Metabotropic glutamate receptors (mGluRs) are widely known for their roles in synaptic signaling. However, accumulating evidence suggests roles of mGluRs in human malignancies in addition to synaptic transmission. Somatic cell homeostasis presents intriguing possibilities of mGluRs and glutamate signaling as novel targets for human cancers. More recently, aberrant glutamate signaling has been shown to participate in the transformation and maintenance of various cancer types, including glioma, melanoma skin cancer, breast cancer, and prostate cancer, indicating that genes encoding mGluRs, GRMs, can function as oncogenes. Here, we provide a review on the interactions of mGluRs and their ligand, glutamate, in processes that promote the growth of tumors of neuronal and non-neuronal origins. Further, we discuss the evolution of riluzole, a glutamate release inhibitor approved for amyotrophic lateral sclerosis (ALS), but now fashioned as an mGluR1 inhibitor for melanoma therapy and as a radio-sensitizer for tumors that have metastasized to the brain. With the success of riluzole, it is not far-fetched to believe that other drugs that may act directly or indirectly on other mGluRs can be beneficial for multiple applications. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

The current management of brain metastasis in melanoma: a focus on riluzole

Brain metastasis is a common endpoint in human malignant melanoma, and the prognosis for patients remains poor despite advancements in therapy. Current treatment for melanoma metastatic to the brain is grouped into those providing symptomatic relief such as corticosteroids and antiepileptic agents, to those that are disease modifying. Related to the latter group, recent studies have demonstrated that aberrant glutamate signaling plays a role in the transformation and maintenance of various cancer types, including melanoma. Glutamate secretion from these and surrounding cells have been found to stimulate regulatory pathways that control tumor growth, proliferation and survival in vitro and in vivo. The antiglutamatergic actions of an inhibitor of glutamate release, riluzole, have been detected by its ability to clear glutamate from the synapse, and it has been shown to inhibit glutamate release rather than directly inhibiting glutamate receptors. Preclinical studies have demonstrated the ability of riluzole to act as a radiosensitizing agent in melanoma. The effect of riluzole on downstream glutamatergic signaling has pointed to cross talk between the metabotropic G-protein-coupled glutamate receptors implicated in a subset of human melanomas with other signaling pathways, including apoptotic, angiogenic, ROS and cell invasion mechanisms, thus establishing its potential to be further explored in combination therapy regimens for both primary human melanoma and melanoma metastatic to the brain.

PTEN expression and function in adult cancer stem cells and prospects for therapeutic targeting

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a non-redundant lipid phosphatase that restrains and fine tunes the phosphatidylinositol-3-kinase (PI3K) signaling pathway. PTEN is involved in inherited syndromes, which predispose to different types of cancers and is among the most frequently inactivated tumor suppressor genes in sporadic cancers. Indeed, loss of PTEN function occurs in a wide spectrum of human cancers through a variety of mechanisms, including mutations, deletions, transcriptional silencing, or protein instability. PTEN prevents tumorigenesis through multiple mechanisms and regulates a plethora of cellular processes, including survival, proliferation, energy metabolism and cellular architecture. Moreover, recent studies have demonstrated that PTEN is able to exit, exist, and function outside the cell, allowing for inhibition of the PI3K pathway in neighboring cells in a paracrine fashion. Most recently, studies have shown that PTEN is also critical for stem cell maintenance and that PTEN loss can lead to the emergence and proliferation of cancer stem cell (CSC) clones. Depending on the cellular and tissue context of origin, PTEN deletion may result in increased self-renewal capacity or normal stem cell exhaustion and PTEN-defìcient stem and progenitor cells have been reported in prostate, lung, intestinal, and pancreatic tissues before tumor formation; moreover, reversible or irreversible PTEN loss is frequently observed in CSC from a variety of solid and hematologic malignancies, where it may contribute to the functional phenotype of CSC. In this review, we will focus on the role of PTEN expression and function and downstream pathway activation in cancer stem cell biology and regulation of the tumorigenic potential; the emerging role of PTEN in mediating the crosstalk between the PI3K and MAPK pathways will also be discussed, together with prospects for the therapeutic targeting of tumors lacking PTEN expression.

The mTOR signaling pathway as a treatment target for intracranial neoplasms

Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has become an attractive target for human cancer therapy. Hyperactivation of mTOR has been reported in both sporadic and syndromic (hereditary) brain tumors. In contrast to the large number of successful clinical trials employing mTOR inhibitors in different types of epithelial neoplasms, their use to treat intracranial neoplasms is more limited. In this review, we summarize the role of mTOR activation in brain tumor pathogenesis and growth relevant to new human brain tumor trials currently under way using mTOR inhibitors.