Mrinal Joel

Recruited Brain Tumor‐Derived Mesenchymal Stem Cells Contribute to Brain Tumor Progression

The identity of the cells that contribute to brain tumor structure and progression remains unclear. Mesenchymal stem cells (MSCs) have recently been isolated from normal mouse brain. Here, we report the infiltration of MSC‐like cells into the GL261 murine glioma model. These brain tumor‐derived mesenchymal stem cells (BT‐MSCs) are defined with the phenotype (Lin‐Sca‐1+CD9+CD44+CD166+/−) and have multipotent differentiation capacity. We show that the infiltration of BT‐MSCs correlates to tumor progression; furthermore, BT‐MSCs increased the proliferation rate of GL261 cells in vitro. For the first time, we report that the majority of GL261 cells expressed mesenchymal phenotype under both adherent and sphere culture conditions in vitro and that the non‐MSC population is nontumorigenic in vivo. Although the GL261 cell line expressed mesenchymal phenotype markers in vitro, most BT‐MSCs are recruited cells from host origin in both wild‐type GL261 inoculated into green fluorescent protein (GFP)‐transgenic mice and GL261‐GFP cells inoculated into wild‐type mice. We show the expression of chemokine receptors CXCR4 and CXCR6 on different recruited cell populations. In vivo, the GL261 cells change marker profile and acquire a phenotype that is more similar to cells growing in sphere culture conditions. Finally, we identify a BT‐MSC population in human glioblastoma that is CD44+CD9+CD166+ both in freshly isolated and culture‐expanded cells. Our data indicate that cells with MSC‐like phenotype infiltrate into the tumor stroma and play an important role in tumor cell growth in vitro and in vivo. Thus, we suggest that targeting BT‐MSCs could be a possible strategy for treating glioblastoma patients. Stem Cells 2014;32:1110–1123

Combined expressional analysis, bioinformatics and targeted proteomics identify new potential therapeutic targets in glioblastoma stem cells

Ovarian cancer is associated with increased expression of the pro-angiogenic chemokine interleukin-8 (IL-8, CXCL8), which induces tumor cell proliferation, angiogenesis, and metastasis. Even though bortezomib (BZ) has shown remarkable anti-tumor activity in hematological malignancies, it has been less effective in ovarian cancer; however, the mechanisms are not understood. We have recently shown that BZ unexpectedly induces the expression of IL-8 in ovarian cancer cells in vitro, by IκB kinase (IKK)-dependent mechanism. Here, we tested the hypothesis that IKK inhibition reduces the IL-8 production and increases BZ effectiveness in reducing ovarian tumor growth in vivo. Our results demonstrate that the combination of BZ and the IKK inhibitor Bay 117085 significantly reduces the growth of ovarian tumor xenografts in nude mice when compared to either drug alone. Mice treated with the BZ/Bay 117085 combination exhibit smallest tumors, and lowest levels of IL-8. Furthermore, the reduced tumor growth in the combination group is associated with decreased tumor levels of S536P-p65 NFκB and its decreased recruitment to IL-8 promoter in tumor tissues. These data provide the first in vivo evidence that combining BZ with IKK inhibitor is effective, and suggest that using IKK inhibitors may increase BZ effectiveness in ovarian cancer treatment.Glioblastoma (GBM) is both the most common and the most lethal primary brain tumor. It is thought that GBM stem cells (GSCs) are critically important in resistance to therapy. Therefore, there is a strong rationale to target these cells in order to develop new molecular therapies. To identify molecular targets in GSCs, we compared gene expression in GSCs to that in neural stem cells (NSCs) from the adult human brain, using microarrays. Bioinformatic filtering identified 20 genes (PBK/TOPK, CENPA, KIF15, DEPDC1, CDC6, DLG7/DLGAP5/HURP, KIF18A, EZH2, HMMR/RHAMM/CD168, NOL4, MPP6, MDM1, RAPGEF4, RHBDD1, FNDC3B, FILIP1L, MCC, ATXN7L4/ATXN7L1, P2RY5/LPAR6 and FAM118A) that were consistently expressed in GSC cultures and consistently not expressed in NSC cultures. The expression of these genes was confirmed in clinical samples (TCGA and REMBRANDT). The first nine genes were highly co-expressed in all GBM subtypes and were part of the same protein-protein interaction network. Furthermore, their combined up-regulation correlated negatively with patient survival in the mesenchymal GBM subtype. Using targeted proteomics and the COGNOSCENTE database we linked these genes to GBM signalling pathways. Nine genes: PBK, CENPA, KIF15, DEPDC1, CDC6, DLG7, KIF18A, EZH2 and HMMR should be further explored as targets for treatment of GBM.

Evaluation of intracellular labeling with micron-sized particles of iron oxide (MPIOs) as a general tool for in vitro and in vivo tracking of human stem and progenitor cells.

Magnetic resonance imaging (MRI)-based tracking is increasingly attracting attention as a means of better understanding stem cell dynamics in vivo. Intracellular labeling with micrometer-sized particles of iron oxide (MPIOs) provides a practical MRI-based approach due to superior detectability relative to smaller iron oxide particles. However, insufficient information is available about the general utility across cell types and the effects on cell vitality of MPIO labeling of human stem cells. We labeled six human cell types from different sources: mesenchymal stem cells derived from bone marrow (MSCs), mesenchymal stem cells derived from adipose tissue (ASCs), presumptive adult neural stem cells (ad-NSCs), fetal neural progenitor cells (f-NPCs), a glioma cell line (U87), and glioblastoma tumor stem cells (GSCs), with two different sizes of MPIOs (0.9 and 2.84 μm). Labeling and uptake efficiencies were highly variable among cell types. Several parameters of general cell function were tested in vitro. Only minor differences were found between labeled and unlabeled cells with respect to proliferation rate, mitotic duration, random motility, and capacity for differentiation to specific phenotypes. In vivo behavior was tested in chicken embryos and severe combined immunodeficient (SCID) mice. Postmortem histology showed that labeled cells survived and could integrate into various tissues. MRI-based tracking over several weeks in the SCID mice showed that labeled GSCs and f-NPCs injected into the brain exhibited translocations similar to those seen for unlabeled cells and as expected from migratory behavior described in previous studies. The results support MPIO-based cell tracking as a generally useful tool for studies of human stem cell dynamics in vivo.

Expansion of multipotent stem cells from the adult human brain.

The discovery of stem cells in the adult human brain has revealed new possible scenarios for treatment of the sick or injured brain. Both clinical use of and preclinical research on human adult neural stem cells have, however, been seriously hampered by the fact that it has been impossible to passage these cells more than a very few times and with little expansion of cell numbers. Having explored a number of alternative culturing conditions we here present an efficient method for the establishment and propagation of human brain stem cells from whatever brain tissue samples we have tried. We describe virtually unlimited expansion of an authentic stem cell phenotype. Pluripotency proteins Sox2 and Oct4 are expressed without artificial induction. For the first time multipotency of adult human brain-derived stem cells is demonstrated beyond tissue boundaries. We characterize these cells in detail in vitro including microarray and proteomic approaches. Whilst clarification of these cells’ behavior is ongoing, results so far portend well for the future repair of tissues by transplantation of an adult patient’s own-derived stem cells.

A comparative study of the structural organization of spheres derived from the adult human subventricular zone and glioblastoma biopsies

Sphere forming assays have been useful to enrich for stem like cells in a range of tumors. The robustness of this system contrasts the difficulties in defining a stem cell population based on cell surface markers. We have undertaken a study to describe the cellular and organizational composition of tumorspheres, directly comparing these to neurospheres derived from the adult human subventricular zone (SVZ). Primary cell cultures from brain tumors were found to contain variable fractions of cells positive for tumor stem cell markers (CD133 (2-93%)/SSEA1 (3-15%)/CXCR4 (1-72%)). All cultures produced tumors upon xenografting. Tumorspheres contained a heterogeneous population of cells, but were structurally organized with stem cell markers present at the core of spheres, with markers of more mature glial progenitors and astrocytes at more peripheral location. Ultrastructural studies showed that tumorspheres contained a higher fraction of electron dense cells in the core than the periphery (36% and 19%, respectively). Neurospheres also contained a heterogeneous cell population, but did not have an organization similar to tumorspheres. Although tumorspheres clearly display irregular and neoplastic cells, they establish an organized structure with an outward gradient of differentiation. We suggest that this organization is central in maintaining the tumor stem cell pool.

Knockdown of NAT12/NAA30 reduces tumorigenic features of glioblastoma- initiating cells

BackgroundGlioblastoma (GBM) is the most common primary brain malignancy and confers a dismal prognosis. GBMs harbor glioblastoma-initiating cells (GICs) that drive tumorigenesis and contribute to therapeutic resistance and tumor recurrence. Consequently, there is a strong rationale to target this cell population in order to develop new molecular therapies against GBM. Accumulating evidence indicates that Nα-terminal acetyltransferases (NATs), that are dysregulated in numerous human cancers, can serve as therapeutic targets.MethodsMicroarrays were used to study the expression of several NATs including NAT12/NAA30 in clinical samples and stem cell cultures. The expression of NAT12/NAA30 was analyzed using qPCR, immunolabeling and western blot. We conducted shRNA-mediated knockdown of NAT12/NAA30 gene in GICs and studied the effects on cell viability, sphere-formation and hypoxia sensitivity. Intracranial transplantation to SCID mice enabled us to investigate the effects of NAT12/NAA30 depletion in vivo. Using microarrays we identified genes and biochemical pathways whose expression was altered upon NAT12/NAA30 down-regulation.ResultsWhile decreased expression of the distal 3’UTR of NAT12/NAA30 was generally observed in GICs and GBMs, this gene was strongly up-regulated at the protein level in GBM and GICs. The increased protein levels were not caused by increased levels of the steady state mRNA but rather by other mechanisms. Also, shorter 3’UTR of NAT12/NAA30 correlated with poor survival in glioma patients.As well, we observed previously not described nuclear localization of this typically cytoplasmic protein. When compared to non-silencing controls, cells featuring NAT12/NAA30 knockdown exhibited reduced cell viability, sphere-forming ability, and mitochondrial hypoxia tolerance. Intracranial transplantation showed that knockdown of NAT12/NAA30 resulted in prolonged animal survival.Microarray analysis of the knockdown cultures showed reduced levels of HIF1α and altered expression of several other genes involved in the hypoxia response. Furthermore, NAT12/NAA30 knockdown correlated with expressional dysregulation of genes involved in the p53 pathway, ribosomal assembly and cell proliferation. Western blot analysis revealed reduction of HIF1α, phospho-MTOR(Ser2448) and higher levels of p53 and GFAP in these cultures.ConclusionNAT12/NAA30 plays an important role in growth and survival of GICs possibly by regulating hypoxia response (HIF1α), levels of p-MTOR (Ser2448) and the p53 pathway.

Combined inhibition of Wee1 and Chk1 gives synergistic DNA damage in S-phase due to distinct regulation of CDK activity and CDC45 loading

Recent studies have shown synergistic cytotoxic effects of simultaneous Chk1- and Wee1-inhibition. However, the mechanisms behind this synergy are not known. Here, we present a flow cytometry-based screen for compounds that cause increased DNA damage in S-phase when combined with the Wee1-inhibitor MK1775. Strikingly, the Chk1-inhibitors AZD7762 and LY2603618 were among the top candidate hits of 1664 tested compounds, suggesting that the synergistic cytotoxic effects are due to increased S-phase DNA damage. Combined Wee1- and Chk1-inhibition caused a strong synergy in induction of S-phase DNA damage and reduction of clonogenic survival. To address the underlying mechanisms, we developed a novel assay measuring CDK-dependent phosphorylations in single S-phase cells. Surprisingly, while Wee1-inhibition alone induced less DNA damage compared to Chk1-inhibition, Wee1-inhibition caused a bigger increase in S-phase CDK-activity. However, the loading of replication initiation factor CDC45 was more increased after Chk1- than Wee1-inhibition and further increased by the combined treatment, and thus correlated well with DNA damage. Therefore, when Wee1 alone is inhibited, Chk1 suppresses CDC45 loading and thereby limits the extent of unscheduled replication initiation and subsequent S-phase DNA damage, despite very high CDK-activity. These results can explain why combined treatment with Wee1- and Chk1-inhibitors gives synergistic anti-cancer effects.

Differential propagation of stroma and cancer stem cells dictates tumorigenesis and multipotency

Glioblastoma Multiforme (GBM) is characterized by high cancer cell heterogeneity and the presence of a complex tumor microenvironment. Those factors are a key obstacle for the treatment of this tumor type. To model the disease in mice, the current strategy is to grow GBM cells in serum-free non-adherent condition, which maintains their tumor-initiating potential. However, the so-generated tumors are histologically different from the one of origin. In this work, we performed high-throughput marker expression analysis and investigated the tumorigenicity of GBM cells enriched under different culture conditions. We identified a marker panel that distinguished tumorigenic sphere cultures from non-tumorigenic serum cultures (high CD56, SOX2, SOX9, and low CD105, CD248, αSMA). Contrary to previous work, we found that ‘mixed cell cultures’ grown in serum conditions are tumorigenic and express cancer stem cell (CSC) markers. As well, 1% serum plus bFGF and TGF-α preserved the tumorigenicity of sphere cultures and induced epithelial-to-mesenchymal transition gene expression. Furthermore, we identified 12 genes that could replace the 840 genes of The Cancer Genome Atlas (TCGA) used for GBM-subtyping. Our data suggest that the tumorigenicity of GBM cultures depend on cell culture strategies that retain CSCs in culture rather than the presence of serum in the cell culture medium.

EGF signalling and rapamycin-mediated mTOR inhibition in glioblastoma multiforme evaluated by phospho-specific flow cytometry

Development of novel patient stratification tools for cancer is a challenge that require advanced molecular screening and a detailed understanding of tumour signalling networks. Here, we apply phospho-specific flow cytometry for signal profiling of primary glioblastoma tumours after preservation of single-cell phosphorylation status as a strategy for evaluation of tumour signalling potential and assessment of rapamycin-mediated mTOR inhibition. The method has already enhanced insight into cancers and disorders of the immune system, and our study demonstrate a great potential to improve the understanding of aberrant signalling in glioblastoma and other solid tumours.

Inhibition of tumor formation and redirected differentiation of glioblastoma cells in a xenotypic embryonic environment

Background: Tissue microenvironment plays key roles in regulating the progression of aggressive tumors. Tumors are uncommon in the early embryo, suggesting that embryonic tissue microenvironments are nonpermissive for tumors. Yet, the effects of embryonic tissue microenvironments on tumor cells have not been extensively studied. We have, therefore, tested the behavior of human glioblastoma multiforme (GBM) cells transplanted into a central neural tissue microenvironment in the chicken embryo. Results: GBM cells were cultured as spheres to enrich for GBM stem cells (GSCs) and transduced with GFP for identification. Within the proliferative embryonic neural tissue, GSC‐enriched GBM cells exhibited reduced proliferation and survival, altered gene expression, and formed no tumors, in marked contrast to their aggressive behavior in vitro and tumor formation in other tissue microenvironments including the chorioallantoic membrane of the chicken embryo and the brain of adult severe combined immunodeficiency (SCID) mice. Surviving cells in the spinal neural tube exhibited tumor‐atypical expression profiles of neuron‐, glia‐, stem cell‐, and tumor‐related genes. Conclusions: Embryonic neural tissue provides a poor environment for GBM cell survival and tumor formation, and redirects differentiation toward a more benign phenotype. Understanding the anti‐tumorigenic effects of this embryonic tissue microenvironment could provide opportunities to develop novel therapies for GBM treatment. Developmental Dynamics 242:1078‐1093, 2013.