Intracranial Glioblastoma Multiforme Xenografts Research Articles

Abstract 2260: Targeting PP2A with LB100 enhances efficacy of CAIX CAR-T cells against GBM

Abstract The need for novel therapies for glioblastoma multiforme (GBM) is well established. Chimeric antigen receptor (CAR)-engineered T cells represent a promising cancer treatment modality for treating GBM. However, CAR-T therapy has limitations, such as low penetration into solid tumors and short duration of CAR-T survival. Protein phosphatase 2A (PP2A) inhibition has been implicated in enhancing T cell anti-tumor activity. LB-100 is a novel, first-in-class, small molecule inhibitor of PP2A recently shown in a Phase I trial to be well-tolerated at doses resulting in stabilization of progressive solid tumors. We set out to overcome limitations of CAR-T therapy by activating the mTOR signaling pathway through inhibition of PP2A by LB-100. GBM highly expresses CAIX due to increased hypoxia signaling. Thus, antitumor CAIX-specific CAR T cells were developed and tested against GBM in vitro and in vivo. CAR-T cells displayed GBM cells cytotoxicity and increased IFN-γ, TNF-α, and IL-2 production. Intra-tumor injection of the CAR-T cells into an intracranial GBM xenograft mouse model efficiently suppressed the tumor growth. We found that PP2A inhibition by LB-100 further enhanced CAIX CAR-T activity and significantly prolonged mouse survival. Herein we demonstrate that CAIX represents a viable target for CAR-T cells and inhibition of PP2A enhances CAR-T efficacy against GBM. Targeting PP2A via inhibition with LB-100 may be a promising therapeutic strategy to improve CAR-T efficacy in other solid tumors. Citation Format: Jing Cui, Qi Zhang, Qi Song, Herui Wang, Pauline Dmitriev, Mitchell Sun, Jared S. Rosenblum, Kaiyong Yang, John Kovach, Mark R. Gilbert, Zhengping Zhuang. Targeting PP2A with LB100 enhances efficacy of CAIX CAR-T cells against GBM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2260.

Targeting Tumor Hypoxia Using Nanoparticle-engineered CXCR4-overexpressing Adipose-derived Stem Cells.

Hypoxia, a hallmark of malignant tumors, often correlates with increasing tumor aggressiveness and poor treatment outcomes. Due to a lack of vasculature, effective drug delivery to hypoxic tumor regions remains challenging. Signaling through the chemokine SDF-1α and its receptor CXCR4 plays a critical role in the homing of stem cells to ischemia for potential use as drug-delivery vehicles. To harness this mechanism for targeting tumor hypoxia, we developed polymeric nanoparticle-induced CXCR4-overexpressing human adipose-derived stem cells (hADSCs). Using glioblastoma multiforme (GBM) as a model tumor, we evaluated the ability of CXCR4-overexpressing hADSCs to target tumor hypoxia in vitro using a 2D migration assay and a 3D collagen hydrogel model. Compared to untransfected hADSCs, CXCR4-overexpressing hADSCs showed enhanced migration in response to hypoxia and penetrated the hypoxic core within tumor spheres. When injected in the contralateral brain in a mouse intracranial GBM xenograft, CXCR4-overexpressing hADSCs exhibited long-range migration toward GBM and preferentially penetrated the hypoxic tumor core. Intravenous injection also led to effective targeting of tumor hypoxia in a subcutaneous tumor model. Together, these results validate polymeric nanoparticle-induced CXCR4-overexpressing hADSCs as a potent cellular vehicle for targeting tumor hypoxia, which may be broadly useful for enhancing drug delivery to various cancer types.

Arsenic trioxide disrupts glioma stem cells via promoting PML degradation to inhibit tumor growth

Glioblastoma multiforme (GBM) is the most lethal brain tumor. Tumor relapse in GBM is inevitable despite maximal therapeutic interventions. Glioma stem cells (GSCs) have been found to be critical players in therapeutic resistance and tumor recurrence. Therapeutic drugs targeting GSCs may significantly improve GBM treatment. In this study, we demonstrated that arsenic trioxide (As2O3) effectively disrupted GSCs and inhibited tumor growth in the GSC-derived orthotopic xenografts by targeting the promyelocytic leukaemia (PML). As2O3 treatment induced rapid degradation of PML protein along with severe apoptosis in GSCs. Disruption of the endogenous PML recapitulated the inhibitory effects of As2O3 treatment on GSCs both in vitro and in orthotopic tumors. Importantly, As2O3 treatment dramatically reduced GSC population in the intracranial GBM xenografts and increased the survival of mice bearing the tumors. In addition, As2O3 treatment preferentially inhibited cell growth of GSCs but not matched non-stem tumor cells (NSTCs). Furthermore, As2O3 treatment or PML disruption potently diminished c-Myc protein levels through increased poly-ubiquitination and proteasome degradation of c-Myc. Our study indicated a potential implication of As2O3 in GBM treatment and highlighted the important role of PML/c-Myc axis in the maintenance of GSCs.

Abstract 2562: Dianhydrogalactitol inhibits the growth of glioma stem and non-stem cultures, including temozolomide-resistant cell lines, in vitro and in vivo

Abstract The standard of care for glioblastoma multiforme (GBM) patients is surgical resection followed by temozolomide (TMZ) and irradiation (XRT). However, TMZ-resistance has emerged as a significant unmet medical need, as DNA repair enzyme 0-6-methylguanine DNA methyltransferase (MGMT) removes the methyl-group adducts caused by TMZ. Dianhydrogalactitol (VAL-083) is a structurally unique alkylating agent causing DNA crosslinks at N7 position of guanine. Because VAL-083's N7 adducts are not subject to MGMT mediated repair, it may be an effective chemotherapeutic in the treatment of TMZ-resistant GBM. VAL-083 crosses the blood brain barrier and accumulates in brain tumor tissue. We have recently shown that TMZ activity is similar in cancer stem cells (CSC) and their paired non-CSC from primary GBM tissues, and that the activity is MGMT-dependent. We thus sought to investigate how our CSC and non-CSC panel would respond to VAL-083 alone or in combination with XRT. We further investigated the activity of VAL-083 in in vivo models of drug-resistant GBM in comparison to TMZ. Rag2 mice bearing intracranial human GBM xenograft tumors of either MGMT-positive and TMZ-resistant origin (BT74), or MGMT-negative and TMZ-sensitive origin (U251) were treated. VAL-083 was given i.p. 3 times/week x 3 weeks, and the efficacy of VAL-083 in controlling tumor growth compared to TMZ (30 mg/kg). Disease progression was evaluated by overall survival, clinical observations and body weight measurements. Our in vitro results show that VAL-083 is a potent inhibitor of all tested primary GBM cultures, irrespective of MGMT status. VAL-083 causes cell cycle arrest and loss of cell viability in TMZ-resistant cells, and at lower concentrations than TMZ in TMZ-sensitive cells. Furthermore, VAL-083 is not affected by cell culture condition (Stem vs. Non-Stem). Low dose VAL-083 combined with XRT exhibited an additive effect in all cultures tested, suggesting that VAL-083 might act as a radiosensitizer. In the in vivo U251 model, the median survival time for mice treated with 4 mg/kg VAL-083 was significantly increased to 72 days compared to 48 days for controls (p<0.0001). Median survival time for 3 mg/kg VAL-083 was 54 days. Body weight loss was observed in mice treated with 5 mg/kg and treatment was stopped after 4 doses after which the animals recovered and their median survival was 57 days. Animals treated with TMZ were terminated at day 102 at the end of the study. BT74: study is ongoing, data will be presented at the meeting.In conclusion, VAL-083 is highly efficacious against both stem and non-stem GBM cell cultures in vitro, the activity is independent of MGMT and VAL-083 appears to act as a radiosensitizer in GBM. In vivo xenograft GBM models further validate the benefits of VAL-083 in the treatment of GBM and support ongoing clinical research with VAL-083, which is currently in a clinical trial for GBM patients with recurrent disease. Citation Format: Shaun D. Fouse, Anne Steino, Nicholas Butowski, Jeffrey A. Bacha, Sarath Kanekal, Nancy Dos Santos, Dennis M. Brown, Joseph F. Costello. Dianhydrogalactitol inhibits the growth of glioma stem and non-stem cultures, including temozolomide-resistant cell lines, in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2562. doi:10.1158/1538-7445.AM2015-2562

Selective lentiviral gene delivery to CD133-expressing human glioblastoma stem cells.

Glioblastoma multiforme (GBM) is a deadly primary brain malignancy. Glioblastoma stem cells (GSC), which have the ability to self-renew and differentiate into tumor lineages, are believed to cause tumor recurrence due to their resistance to current therapies. A subset of GSCs is marked by cell surface expression of CD133, a glycosylated pentaspan transmembrane protein. The study of CD133-expressing GSCs has been limited by the relative paucity of genetic tools that specifically target them. Here, we present CD133-LV, a lentiviral vector presenting a single chain antibody against CD133 on its envelope, as a vehicle for the selective transduction of CD133-expressing GSCs. We show that CD133-LV selectively transduces CD133+ human GSCs in dose-dependent manner and that transduced cells maintain their stem-like properties. The transduction efficiency of CD133-LV is reduced by an antibody that recognizes the same epitope on CD133 as the viral envelope and by shRNA-mediated knockdown of CD133. Conversely, the rate of transduction by CD133-LV is augmented by overexpression of CD133 in primary human GBM cultures. CD133-LV selectively transduces CD133-expressing cells in intracranial human GBM xenografts in NOD.SCID mice, but spares normal mouse brain tissue, neurons derived from human embryonic stem cells and primary human astrocytes. Our findings indicate that CD133-LV represents a novel tool for the selective genetic manipulation of CD133-expressing GSCs, and can be used to answer important questions about how these cells contribute to tumor biology and therapy resistance.

AI-05 * IMPACT OF GBM MICROENVIRONMENT ON EXPRESSION PROFILE OF BONE MARROW DERIVED PROGENITOR CELLS

We have recently shown that bone marrow derived cells (BMDC) provide a distinct tumor region dependent contribution to glioblastoma multiforme (GBM) neovascularization. The influence of GBM microenvironment on differentiation and modulation of expression factors by BMDC however remains unknown. In this study we establish the differential expression profile of BMDC as a consequence of recruitment and interaction with the GBM microenvironment and in response to radiation (RTx) and anti-angiogenic therapy (AATx). Chimeric mice with reconstituted green-fluorescent bone marrow were used to create intracranial GBM xenografts, by implanting red fluorescent glioma stem cells or U87 into the frontal lobes. Subsequently, BMDC recruited to the GBM were isolated from the GBM cells using FACS during GBM growth, and following treatment (RTx and AATx). RNA was extracted from both FACS-purified BMDC and GBM cells, and mRNA and miRNA array analyses were performed. We compared the expression profiles to systemic BMDC derived from control donor mice. BMDCs were found to exhibit significant plasticity and altered their expression profiles based on stage of GBM growth and in response to therapy. TGFb was significantly upregulated in BMDCs following recruitment to GBMs, with a compensatory increase in expression of IL6,4,8 by GBM cells. BMDC up-regulate cytokines, IFNG, CXCL and TNF pathways, and transcriptional regulators, SMAD2, all of which are able to influence the tumor microenvironment. BMDCs also prove to express angiogenic factors and angioMIRs, with a distinct differential expression pattern based on stage of GBM growth and in response to therapy. We demonstrate that a significant cross-talk exists between BMDC in the tumor microenvironment and GBM cells. There is a distinct angiogenic and invasive profile of BMDC once recruited to the GBM. Furthermore, recruited BMDC provide a source of angiogenic factors, that are differentially expressed based on the stage of GBM growth and in response to therapy.

SC-16 * DIVERGENT CELL CYCLE REGULATION IN GBM CELLS PROVIDES A UNIQUE POINT OF INTERVENTION IN POLARIZED CD133+ CELLS

Recent studies in distinct glioma types have separately identified phenotypically distinct populations of tumor propagating cells (TPCs). Enrichment of TPCs by cell surface marker expression (CD133 [PMID:17051156], NG2 [PMID: 21907924]) has revealed the possibility of multiple TPC populations, within a single tumor, that have distinct properties and therapy sensitivities. Here we identify and compare the coexisting populations of glioblastoma multiforme (GBM) cells expressing the stem marker CD133 and the progenitor marker NG2. We compare the proliferative properties of CD133+ and NG2+ cells, and investigate how polarity and mode of division may determine other functional properties including cell cycle regulation and therapy sensitivity. Established and primary GBM cell cultures were analyzed by immunofluorescence and flow cytometry for expression of CD133 and NG2, alongside markers of polarity and proliferation. We showed that CD133+ and NG2+ GBM cells coexist as predominantly separate subpopulations. CD133+ cells are highly polarized and, compared to NG2+ or marker-negative subpopulations, are slower dividing. Cell cycle and gene expression analyses showed that the increase in cell cycle length in CD133+ cells is due to an extended G2-M period. As expected CD133+ cells have increased expression of DNA-damage response genes, however paradoxically we also detected increased activation of polo-like kinase 1 (PLK1). CD133+ cells were uniquely sensitive to the PLK1 inhibitor BI2536 in vivo, and treatment of intracranial GBM xenografts with the BRAF inhibitor PLX4720 and BI2536 showed greater anti-tumor activity than either alone. Our studies identified two putative TPC subpopulations in GBM with distinct cell cycle dynamics, DNA damage response and cell division mode. Ongoing work will investigate the role of Plk1 activity in linking these divergent phenotypes. Understanding this phenotypic heterogeneity in adjacent TPC types will allow the design of treatment strategies that eradicate multiple putative TPC populations.

ME-03 * BONE MARROW DERIVED MICROGLIA AND THEIR FUNCTION WITHIN TUMOR MICROENVIRONMENT

We have previously demonstrated that BMDC are recruited to Glioblastoma Multiforme (GBM), in a highly tumor-growth and region-dependent pattern, demonstrating that the majority of BMDCs differentiate into inflammatory cells, MAC3 + , and CD11b+ IBA1+ microglia-like cells. The majority of microglia seen in GBM microenvironment are derived from the BMDC rather than being resident brain microglia. The role of microglial cells in GBMs remains unknown, with evidence supporting both an anti- and pro- tumorgenic function. In this study we aimed to understand the contribution of microglia to GBM growth and tumor vascularity. Chimeric mice with reconstituted green-fluorescent bone marrow were used to create intracranial GBM xenografts, by implanting red fluorescent glioma stem cells or U87 into the frontal lobe. Using a known inhibitor of microglial activation, minocycline, we show that treatment with this agent increased tumor cell growth and invasiveness and reduced animal survival compared to controls. We show that Minocycline decreases activation of microglia, inhibits the phagocytic activity of microglia in GBMs and decreases the perivascular localization of microglia. The mRNA expression profile of microglia isolated from the GBM microenvironment showed, through Ingenuity Pathway Analysis (IPA), a loss of engulfment and migration of cells and phaocytotic pathways in BM-derived microglia, additionally we see a reorganization of cytoskeletal pathways leading to an increase in the migration and invasiveness of GBM cells following treatment with Minocycline. We also have preliminary data to suggest that this property of Minocycline is dependent on VEGF levels, where in the context of low VEGF Minocycline does not provide a significant anti-angiogenic role. We demonstrate that microglia in GBM microenvironment, are primarily recruited and differentiated from the BM and not resident, and that these cells have an anti-tumorgenic functions, and inhibition of the activated microglia by Minocycline, results in a more invasive phenotype of GBM cells.

A nanoparticle carrying the p53 gene targets tumors including cancer stem cells, sensitizes glioblastoma to chemotherapy and improves survival.

Temozolomide (TMZ)-resistance in glioblastoma multiforme (GBM) has been linked to upregulation of O6-methylguanine-DNA methyltransferase (MGMT). Wild-type (wt) p53 was previously shown to down-modulate MGMT. However, p53 therapy for GBM is limited by lack of efficient delivery across the blood brain barrier (BBB). We have developed a systemic nanodelivery platform (scL) for tumor-specific targeting (primary and metastatic), which is currently in multiple clinical trials. This self-assembling nanocomplex is formed by simple mixing of the components in a defined order and a specific ratio. Here, we demonstrate that scL crosses the BBB and efficiently targets GBM, as well as cancer stem cells (CSCs), which have been implicated in recurrence and treatment resistance in many human cancers. Moreover, systemic delivery of scL-p53 down-modulates MGMT and induces apoptosis in intracranial GBM xenografts. The combination of scL-p53 and TMZ increased the antitumor efficacy of TMZ with enhanced survival benefit in a mouse model of highly TMZ-resistant GBM. scL-p53 also sensitized both CSCs and bulk tumor cells to TMZ, increasing apoptosis. These results suggest that combining scL-p53 with standard TMZ treatment could be a more effective therapy for GBM.

Differential effects of low‐ and high‐dose GW2974, a dual epidermal growth factor receptor and HER2 kinase inhibitor, on glioblastoma multiforme invasion

Aberrant expression of epidermal growth factor receptor (EGFR; ErbB1) and HER2 (ErbB2) tyrosine kinases frequently occurs in glioblastoma multiforme (GBM) patients and is considered to be associated with tumor malignancy and poor patient prognosis. In the present study, a dual EGFR and HER2 inhibitor (GW2974) was evaluated for its effects in GBM in vitro and in vivo. Results showed that low-concentration GW2974 inhibited GBM cell invasion, whereas a high concentration of the same compound counteracted this effect. Similar results were observed in an intracranial GBM xenograft model, in which, although both doses of GW2974 slowed tumor growth, no improvement in survival was observed in mice treated with high-dose GW2974, presumably because of the augmentation of tumor invasion. By protein microarray and Western blot analyses, the p38 mitogen-activated protein kinase (MAPK) pathway was found to be activated in GBM cells under high-concentration GW2974. Additionally, blockage of the p38 MAPK pathway reproduced the inhibitory effect of low-concentration GW2974 on cell invasion. These data suggest that the p38 MAPK pathway might contribute to the differential regulation of cell invasion by GW2974. Taken together, our results indicate that GW2974 exerts different effects in GBM depending on drug dosage. This offers a new perspective on the role of GW2974 in tumor progression, providing a potential strategy for GBM treatment based on precise prescription.

A First-Generation Multi-Functional Cytokine for Simultaneous Optical Tracking and Tumor Therapy

Creating new molecules that simultaneously enhance tumor cell killing and permit diagnostic tracking is vital to overcoming the limitations rendering current therapeutic regimens for terminal cancers ineffective. Accordingly, we investigated the efficacy of an innovative new multi-functional targeted anti-cancer molecule, SM7L, using models of the lethal brain tumor Glioblastoma multiforme (GBM). Designed using predictive computer modeling, SM7L incorporates the therapeutic activity of the promising anti-tumor cytokine MDA-7/IL-24, an enhanced secretory domain, and diagnostic domain for non-invasive tracking. In vitro assays revealed the diagnostic domain of SM7L produced robust photon emission, while the therapeutic domain showed marked anti-tumor efficacy and significant modulation of p38MAPK and ERK pathways. In vivo, the unique multi-functional nature of SM7L allowed simultaneous real-time monitoring of both SM7L delivery and anti-tumor efficacy. Utilizing engineered stem cells as novel delivery vehicles for SM7L therapy (SC-SM7L), we demonstrate that SC-SM7L significantly improved pharmacokinetics and attenuated progression of established peripheral and intracranial human GBM xenografts. Furthermore, SC-SM7L anti-tumor efficacy was augmented in vitro and in vivo by concurrent activation of caspase-mediated apoptosis induced by adjuvant SC-mediated S-TRAIL delivery. Collectively, these studies define a promising new approach to treating highly aggressive cancers, including GBM, using the optimized therapeutic molecule SM7L.

Gene therapy-mediated delivery of targeted cytotoxins for glioma therapeutics

Restricting the cytotoxicity of anticancer agents by targeting receptors exclusively expressed on tumor cells is critical when treating infiltrative brain tumors such as glioblastoma multiforme (GBM). GBMs express an IL-13 receptor (IL13Rα2) that differs from the physiological IL4R/IL13R receptor. We developed a regulatable adenoviral vector (Ad.mhIL-4.TRE.mhIL-13-PE) encoding a mutated human IL-13 fused to Pseudomonas exotoxin (mhIL-13-PE) that specifically binds to IL13Rα2 to provide sustained expression, effective anti-GBM cytotoxicity, and minimal neurotoxicity. The therapeutic Ad also encodes mutated human IL-4 that binds to the physiological IL4R/IL13R without interacting with IL13Rα2, thus inhibiting potential binding of mhIL-13-PE to normal brain cells. Using intracranial GBM xenografts and syngeneic mouse models, we tested the Ad.mhIL-4.TRE.mhIL-13-PE and two protein formulations, hIL-13-PE used in clinical trials (Cintredekin Besudotox) and a second-generation mhIL-13-PE. Cintredekin Besudotox doubled median survival without eliciting long-term survival and caused severe neurotoxicity; mhIL-13-PE led to ∼40% long-term survival, eliciting severe neurological toxicity at the high dose tested. In contrast, Ad-mediated delivery of mhIL-13-PE led to tumor regression and long-term survival in over 70% of the animals, without causing apparent neurotoxicity. Although Cintredekin Besudotox was originally developed to target GBM, when tested in a phase III trial it failed to achieve clinical endpoints and revealed neurotoxicity. Limitations of Cintredekin Besudotox include its short half-life, which demanded frequent or continued administration, and binding to IL4R/IL13R, present in normal brain cells. These shortcomings were overcome by our therapeutic Ad, thus representing a significant advance in the development of targeted therapeutics for GBM.

Pharmacologic inhibition of cyclin-dependent kinases 4 and 6 arrests the growth of glioblastoma multiforme intracranial xenografts.

Activation of cyclin-dependent kinases 4 and 6 (cdk4/6) occurs in the majority of glioblastoma multiforme (GBM) tumors, and represents a promising molecular target for the development of small molecule inhibitors. In the current study, we investigated the molecular determinants and in vivo response of diverse GBM cell lines and xenografts to PD-0332991, a cdk4/6-specific inhibitor. In vitro testing of PD-0332991 against a panel of GBM cell lines revealed a potent G(1) cell cycle arrest and induction of senescence in each of 16 retinoblastoma protein (Rb)-proficient cell lines regardless of other genetic lesions, whereas 5 cell lines with homozygous inactivation of Rb were completely resistant to treatment. Short hairpin RNA depletion of Rb expression conferred resistance of GBM cells to PD-0332991, further demonstrating a requirement of Rb for sensitivity to cdk4/6 inhibition. PD-0332991 was found to efficiently cross the blood-brain barrier and proved highly effective in suppressing the growth of intracranial GBM xenograft tumors, including those that had recurred after initial therapy with temozolomide. Remarkably, no mice receiving PD-0332991 died as a result of disease progression while on therapy. Additionally, the combination of PD-0332991 and radiation therapy resulted in significantly increased survival benefit compared with either therapy alone. In total, our results support clinical trial evaluation of PD-0332991 against newly diagnosed as well as recurrent GBM, and indicate that Rb status is the primary determinant of potential benefit from this therapy.

Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice

Despite the high doses of radiation delivered in the treatment of patients with glioblastoma multiforme (GBM), the tumors invariably recur within the irradiation field, resulting in a low cure rate. Understanding the mechanism of such recurrence is therefore important. Here we have shown in an intracranial GBM xenograft model that irradiation induces recruitment of bone marrow-derived cells (BMDCs) into the tumors, restoring the radiation-damaged vasculature by vasculogenesis and thereby allowing the growth of surviving tumor cells. BMDC influx was initiated by induction of HIF-1 in the irradiated tumors, and blocking this influx prevented tumor recurrence. Previous studies have indicated that BMDCs are recruited to tumors in part through the interaction between the HIF-1-dependent stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4. Pharmacologic inhibition of HIF-1 or of the SDF-1/CXCR4 interaction prevented the influx of BMDCs, primarily CD11b+ myelomonocytes, and the postirradiation development of functional tumor vasculature, resulting in abrogation of tumor regrowth. Similar results were found using neutralizing antibodies against CXCR4. Our data therefore suggest a novel approach for the treatment of GBM: in addition to radiotherapy, the vasculogenesis pathway needs to be blocked, and this can be accomplished using the clinically approved drug AMD3100, a small molecule inhibitor of SDF-1/CXCR4 interactions.

Role of Ang1 and its interaction with VEGF-A in astrocytomas.

Angiopoietins (Ang1 and Ang2) modulate the activity of the endothelial cell (EC)-specific receptor tyrosine kinase Tie2, which together with vascular endothelial growth factor (VEGF-A) and its EC-specific receptors, VEGFR1 and VEGFR2, regulate normal physiological vessel development. The functional role of angiopoietins in tumor angiogenesis, in particular astrocytoma angiogenesis, remains unclear. In this study, we focus on the specific contribution of Ang1 to the vascular growth of glioblastoma multiforme (GBM) and its interactive role with VEGF-A. Subcutaneous and intracranial GBM xenografts were generated using 3 established astrocytoma cell lines (U87, U373, and U343) that were transfected to stably over-express Ang1. GBM xenografts were also generated to express low levels of VEGF-A and high Angl. We found that Ang1 increases the vascular growth of both subcutaneous and intracranial xenografts of GBM by approximately 3-fold. However, the increased vascular growth was only seen in xenografts with concurrent VEGF-A elevation, since decreasing VEGF-A expression resulted in a loss of the pro-angiogenic growth advantage seen with Ang1. Collectively, our data suggest that Ang1 regulates GBM vascularity in a VEGF-A dependent manner, synergizing the initial pro-angiogenic response that is triggered by VEGF-A and promoting the vascular growth of GBM.