Thymosin ß 4 gene silencing decreases stemness and invasiveness in glioblastoma.

Thymosin beta 4 is a pleiotropic actin-sequestering polypeptide that is involved in wound healing and developmental processes. Thymosin beta 4 gene silencing promotes differentiation of neural stem cells whereas thymosin beta 4 overexpression initiates cortical folding of developing brain hemispheres. A role of thymosin beta 4 in malignant gliomas has not yet been investigated. We analysed thymosin beta 4 staining on tissue microarrays and performed interrogations of the REMBRANDT and the Cancer Genome Atlas databases. We investigated thymosin beta 4 expression in seven established glioma cell lines and seven glioma-initiating cell lines and induced or silenced thymosin beta 4 expression by lentiviral transduction in LNT-229, U87MG and GS-2 cells to study the effects of altered thymosin beta 4 expression on gene expression, growth, clonogenicity, migration, invasion, self-renewal and differentiation capacity in vitro, and tumorigenicity in vivo. Thymosin beta 4 expression increased with grade of malignancy in gliomas. Thymosin beta 4 gene silencing in LNT-229 and U87MG glioma cells inhibited migration and invasion, promoted starvation-induced cell death in vitro and enhanced survival of glioma-bearing mice. Thymosin beta 4 gene silencing in GS-2 cells inhibited self-renewal and promoted differentiation in vitro and decreased tumorigenicity in vivo. Gene expression analysis suggested a thymosin beta 4-dependent regulation of mesenchymal signature genes and modulation of TGFß and p53 signalling networks. We conclude that thymosin beta 4 should be explored as a novel molecular target for anti-glioma therapy.

Integrin control of the transforming growth factor-ß pathway in glioblastoma.

Transforming growth factor-ß is a central mediator of the malignant phenotype of glioblastoma, the most common and malignant form of intrinsic brain tumours. Transforming growth factor-ß promotes invasiveness and angiogenesis, maintains cancer cell stemness and induces profound immunosuppression in the host. Integrins regulate cellular adhesion and transmit signals important for cell survival, proliferation, differentiation and motility, and may be involved in the activation of transforming growth factor-ß. We report that αvß3, αvß5 and αvß8 integrins are broadly expressed not only in glioblastoma blood vessels but also in tumour cells. Exposure to αv, ß3 or ß5 neutralizing antibodies, RNA interference-mediated integrin gene silencing or pharmacological integrin inhibition using the cyclic RGD peptide EMD 121974 (cilengitide) results in reduced phosphorylation of Smad2 in most glioma cell lines, including glioma-initiating cell lines and reduced transforming growth factor-ß-mediated reporter gene activity, coinciding with reduced transforming growth factor-ß protein levels in the supernatant. Time course experiments indicated that the loss of transforming growth factor-ß bioactivity due to integrin inhibition likely results from two distinct mechanisms: an early effect on activation of preformed inactive protein, and second, major effect on transforming growth factor-ß gene transcription as confirmed by decreased activity of the transforming growth factor-ß gene promoter and decreased transforming growth factor-ß(1) and transforming growth factor-ß(2) messenger RNA expression levels. In vivo, EMD 121974 (cilengitide), which is currently in late clinical development as an antiangiogenic agent in newly diagnosed glioblastoma, was a weak antagonist of pSmad2 phosphorylation. These results validate integrin inhibition as a promising strategy not only to inhibit angiogenesis, but also to block transforming growth factor-ß-controlled features of malignancy including invasiveness, stemness and immunosuppression in human glioblastoma.

Therapeutic Targeting of TGFß Ligands in Glioblastoma Using Novel Antisense Oligonucleotides Reduces the Growth of Experimental Gliomas.

PURPOSE: Transforming growth factor (TGF)-ß is expressed at high levels by glioma cells and contributes to the malignant phenotype of glioblastoma. However, its therapeutic targeting remains challenging. Here, we examined an alternative therapeutic approach of TGFß inhibition using two novel phosphorothioate-locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, ISTH1047 and ISTH0047, which specifically target TGFß1 and TGFß2. EXPERIMENTAL DESIGN: We characterized the effects of ISTH1047 and ISTH0047 on TGFß1/2 expression, downstream signaling and growth of human LN-308, LN-229, and ZH-161 cells as well as murine SMA-560 glioma cells in vitro. Furthermore, we assessed their target inhibition and effects on survival in orthotopic xenogeneic and syngeneic rodent glioma models in vivo. RESULTS: Both antisense oligonucleotides specifically silenced their corresponding target and abrogated SMAD2 phosphorylation in several glioma cell lines. Moreover, inhibition of TGFß1 or TGFß2 expression by ISTH1047 or ISTH0047 reduced the migration and invasiveness of LN-308 and SMA-560 glioma cells. Systemic antisense oligonucleotide administration to glioma-bearing mice suppressed TGFß1 or TGFß2 mRNA expression as well as the expression of the downstream target PAI-1 in orthotopic gliomas. Glioma-bearing mice had significantly prolonged survival upon systemic treatment with ISTH1047 or ISTH0047, which was associated with a reduction of intratumoral SMAD2 phosphorylation and, in a fully immunocompetent model, with increased immune cell infiltration. CONCLUSIONS: Targeting TGFß expression with the novel LNA antisense oligonucleotides ISTH1047 or ISTH0047 results in strong antiglioma activity in vitro and in vivo, which may represent a promising approach to be examined in human patients with glioma.

Biological Role and Therapeutic Targeting of TGF-ß3 in Glioblastoma.

Transforming growth factor (TGF)-ß contributes to the malignant phenotype of glioblastoma by promoting invasiveness and angiogenesis and creating an immunosuppressive microenvironment. So far, TGF-ß1 and TGF-ß2 isoforms have been considered to act in a similar fashion without isoform-specific function in glioblastoma. A pathogenic role for TGF-ß3 in glioblastoma has not been defined yet. Here, we studied the expression and functional role of endogenous and exogenous TGF-ß3 in glioblastoma models. TGF-ß3 mRNA is expressed in human and murine long-term glioma cell lines as well as in human glioma-initiating cell cultures with expression levels lower than TGF-ß1 or TGF-ß2 in most cell lines. Inhibition of TGF-ß3 mRNA expression by ISTH2020 or ISTH2023, two different isoform-specific phosphorothioate locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, blocks downstream SMAD2 and SMAD1/5 phosphorylation in human LN-308 cells, without affecting TGF-ß1 or TGF-ß2 mRNA expression or protein levels. Moreover, inhibition of TGF-ß3 expression reduces invasiveness in vitro Interestingly, depletion of TGF-ß3 also attenuates signaling evoked by TGF-ß1 or TGF-ß2 In orthotopic syngeneic (SMA-560) and xenograft (LN-308) in vivo glioma models, expression of TGF-ß3 as well as of the downstream target, plasminogen-activator-inhibitor (PAI)-1, was reduced, while TGF-ß1 and TGF-ß2 levels were unaffected following systemic treatment with TGF-ß3 -specific antisense oligonucleotides. We conclude that TGF-ß3 might function as a gatekeeper controlling downstream signaling despite high expression of TGF-ß1 and TGF-ß2 isoforms. Targeting TGF-ß3in vivo may represent a promising strategy interfering with aberrant TGF-ß signaling in glioblastoma. Mol Cancer Ther; 16(6); 1177-86. ©2017 AACR.

Age-associated and therapy-induced alterations in the cellular microenvironment of experimental gliomas.

The poor prognosis associated with advanced age in patients with glioblastoma remains poorly understood. Glioblastoma in the elderly has been particularly associated with vascular endothelial growth factor (VEGF)-dependent angiogenesis, and early uncontrolled studies suggested that the anti-angiogenic agent bevacizumab (BEV), an antibody to VEGF, might be preferentially active in this patient population. Accordingly, we explored host age-dependent differences in survival and benefit from radiotherapy (RT) or BEV in syngeneic mouse glioma models. Survival was inferior in older mice in the SMA-540 and and less so in SMA-560, but not in the SMA-497 or GL-261 models. Detailed flow cytometric studies revealed increased myeloid and decreased effector T cell population frequencies in SMA-540 tumors of old compared to young mice, but no such difference in the SMA-497 model. Bone marrow transplantation (BMT) from young to old mice had no effect, whereas survival was reduced with BMT from old to young mice. BEV significantly decreased vessel densities in gliomas of old, but not young mice. Accordingly, old, but not young SMA-540 tumor-bearing mice benefited from BEV alone or in combination with RT. End-stage tumors of old BEV- and BEV/RT-treated mice exhibited increased infiltration of T helper and cytotoxic T cells compared to tumors of young mice. The SMA-540 model may provide a valuable tool to evaluate the influence of host age on glioblastoma progression and treatment response. The biological host factors that modulate glioma growth in old as opposed to young mice remain to be identified.

Multimodal elucidation of choline metabolism in a murine glioma model using magnetic resonance spectroscopy and 11C-choline positron emission tomography.

The metabolites, transporters, and enzymes involved in choline metabolism are regarded as biomarkers for disease progression in a variety of cancers, but their in vivo detection is not ideal. Both magnetic resonance spectroscopy [MRS using chemical shift imaging (CSI) total choline (tCho)] and C-choline positron emission tomography (PET) can probe this pathway, but they have not been compared side by side. In this study, we used the spontaneous murine astrocytoma model SMA560 injected intracranially into syngeneic VM/Dk mice, analyzing animals at various postimplantation time points using dynamic microPET imaging and CSI MRS. We observed an increase in tumor volume and C-choline uptake between days 5 and 18. Similarly, tCho levels decreased at days 5 to 18. We found a negative correlation between the tCho and PET results in the tumor and a positive correlation between the tCho tumor-to-brain ratio and choline uptake in the tumor. PCR results confirmed expected increases in expression levels for most of the transporters and enzymes. Using MRS quantification, a good agreement was found between CSI and C-choline PET data, whereas a negative correlation occurred when CSI was not referenced. Thus, C-choline PET and MRS methods seemed to be complementary in strengths. While advancing tumor proliferation caused an increasing C-choline uptake, gliosis and inflammation potentially accounted for a high peritumoral tCho signal in CSI, as supported by histology and secondary ion mass spectrometry imaging. Our findings provide definitive evidence of the use of MRS, CSI, and PET for imaging tumors in vivo.

Monitoring the glioma tropism of bone marrow-derived progenitor cells by 2-photon laser scanning microscopy and positron emission tomography.

Intracerebral experimental gliomas attract intravenously injected murine or human bone marrow-derived hematopoietic progenitor and stem cells (HPC) in vitro, ex vivo, and in vivo, indicating that these progenitor cells might be suitable vehicles for a cell-based delivery of therapeutic molecules to malignant gliomas. With regard to therapeutic application, it is important to investigate cell fates in vivo (i.e., the time-dependent intratumoral and systemic distribution after intravenously injection). Conventional histological analysis has limitations in this regard because longitudinal monitoring is precluded. Here, we used 2-photon laser scanning microscopy (2PLSM), positron emission tomography (PET), and MRI to study the fate of intravenously injected HPC carrying fluorescence, bioluminescence, and PET reporter genes in glioma-bearing mice. Our 2PLSM-based monitoring studies revealed that HPC homing to intracerebral experimental gliomas occurred already within the first 6 h and was most efficient within the first 24 h after intravenous injection. The highest PET signals were detected in intracerebral gliomas, whereas the tracer uptake in other organs, notably spleen, lung, liver, and muscle, remained at background levels. The results have important implications for designing schedules for therapeutic cell-based anti-glioma approaches. Moreover, the PET reporter-based imaging technique will allow noninvasive monitoring of cell fate in future cell-based therapeutic antiglioma approaches.

APO010, a synthetic hexameric CD95 ligand, induces human glioma cell death in vitro and in vivo.

Death receptor targeting has emerged as one of the promising novel approaches of cancer therapy. The activation of one such prototypic death receptor, CD95 (Fas/APO-1), has remained controversial because CD95 agonistic molecules have exhibited either too strong toxicity or too little activity. The natural CD95 ligand (CD95L) is a cytokine, which needs to trimerize to mediate a cell death signal. Mega-Fas-Ligand, now referred to as APO010, is a synthetic hexameric CD95 agonist that exhibits strong antitumor activity in various tumor models. Here, we studied the effects of APO010 in human glioma models in vitro and in vivo. Compared with a cross-linked soluble CD95L or a CD95-agonistic antibody, APO010 exhibited superior activity in glioma cell lines expressing CD95 and triggered caspase-dependent cell death. APO010 reduced glioma cell viability in synergy when combined with temozolomide. The locoregional administration of APO010 induced glioma cell death in vivo and prolonged the survival of tumor-bearing mice. A further exploration of APO010 as a novel antiglioma agent is warranted.

Glioma tropism of lentivirally transduced hematopoietic progenitor cells.

Experimental gliomas attract hematopoietic progenitor cells (HPC) in vivo. HPC are therefore promising candidates for a cell-based delivery of therapeutic molecules to experimental gliomas. A therapeutic application requires efficient genetic manipulation of the cellular vector and a lack of tumorigenicity. Here, we studied the impact of lenti-viral transduction on the glioma tropism of human or murine HPC. Transduction of human or murine HPC with a GFP lentivirus (lenti-GFP) did not interfere with the glioma-mediated attraction of HPC. Bone marrow reconstitution of C57Bl/6 mice with syngeneic GFP-transgenic lineage-depleted bone marrow cells (lin- BM) was as efficient as reconstitution with syngeneic lin- BM transduced ex vivo with lenti-GFP. SMA-560 gliomas growing orthotopically in lenti-GFP-reconstituted VM/Dk mice recruited GFP-positive bone marrow-derived cells. Thus, lentiviral transduction did not interfere with the attraction of exogenously injected HPC or endogenous bone marrow-derived cells by experimental gliomas. Lenti-GFP-HPC implanted directly into tumor-free brains were not tumorigenic. The intravenous injection of lenti-GFP-HPC in glioma-bearing mice did not alter the survival of otherwise untreated animals and had no impact on the survival benefit conferred by cerebral irradiation. Taken together, genetic manipulation of HPC with lenti-GFP neither made these cells tumorigenic nor interfered with their glioma tropism.