Orthotopic Glioblastoma Model Research Articles

CXCR4-STAT3 Axis Plays a Role in Tumor Cell Infiltration in an Orthotopic Mouse Glioblastoma Model.

Glioblastoma multiforme (GBM) is a fatal malignant tumor that is characterized by diffusive growth of tumor cells into the surrounding brain parenchyma. However, the diffusive nature of GBM and its relationship with the tumor microenvironment (TME) is still unknown. Here, we investigated the interactions of GBM with the surrounding microenvironment in orthotopic xenograft animal models using two human glioma cell lines, U87 and LN229. The GBM cells in our model showed different features on the aspects of cell growth rate during their development, dispersive nature of glioma tumor cells along blood vessels, and invasion into the brain parenchyma. Our results indicated that these differences in the two models are in part due to differences in the expression of CXCR4 and STAT3, both of which play an important role in tumor progression. In addition, the GBM shows considerable accumulation of resident microglia and peripheral macrophages, but polarizes differently into tumor-supporting cells. These results suggest that the intrinsic factors of GBM and their interaction with the TME determine the diffusive nature and probably the responsiveness to non-cancer cells in the TME.

Modulation of inhibitory signals in CAR T cells leads to improved activity against glioblastoma.

3031 Background: Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the immunosuppressive tumor microenvironment. Adoptively transferred CAR T cells remain susceptible to inhibition via the engagement of co-inhibitory receptors on their surface such as PD1, BTLA, CTLA4 and LAG3. The subsequent recruitment of Src homology region 2 containing protein tyrosine phosphatase 2 (SHP2) by these receptors to the immune synapse may represent a common mechanism of T cell inhibition, as SHP2 can de-phosphorylate key signaling molecules that mediate T cell activation (including CD28 and CD3ζ). We hypothesized that SHP2 deletion will simultaneously offset the effects of multiple co-inhibitory receptors, thereby improving the anti-tumor activity of CAR T cells. Methods: Electroporation of sgRNA/Cas9 ribonucleoprotein complexes into human T cells was used to knockout (KO) SHP2. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 endodomain) targeting HER2. The phenotype of wild-type (WT) and SHP2KO CAR T cells was evaluated with mass cytometry and flow cytometry. Their anti-tumor function was tested in vitro using the xCELLigence assay (an impedance-based cytotoxicity assay), and in vivo, in an orthotopic xenograft mouse model of GBM. Results: Efficient and reproducible depletion of the SHP2 protein in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect CAR T cell expansion, proliferation or baseline phenotype. However, following co-culture with HER2+ LN229-GBM cells, the CD8+ central memory (CCR7+ CD45RA-) and effector memory (CCR7- CD45RA-) subsets were enriched to a greater extent in the SHP2KO CAR T cells. The pattern of cytokine co-expression varied between donors in a single-cell analysis comparing SHP2KO to WT CAR T cells after encountering LN229 cells. Functionally, SHP2KO CAR T cells derived from the majority of healthy donor and patient peripheral blood eliminated LN229 cells more rapidly in vitro. In an orthotopic mouse model of GBM, SHP2KO CAR T cells showed better early control of established LN229 xenografts and improved survival in comparison to WT CAR T cells. Conclusions: SHP2 deletion in CD28ζ.CAR T cells improves their anti-tumor activity.

Modulation of inhibitory receptor signaling pathways improves CAR T cell activity against glioblastoma

Background & Aim Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the highly immunosuppressive tumor microenvironment. These adoptively transferred CAR T cells are susceptible to inhibition via the engagement of inhibitory receptors on their surface including PD1, CTLA4, LAG3 and BTLA. The recruitment of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) to the immune synapse upon engagement of these co-inhibitory receptors may represent a common mechanism of T cell inhibition. Upon its recruitment and activation, SHP2 dephosphorylates key stimulatory signaling molecules, thus limiting T cell activation. We hypothesized that disrupting SHP2 expression will simultaneously offset multiple co-inhibitory pathways, thereby improving the anti-tumor activity of CAR T cells. Methods, Results & Conclusion CRISPR/Cas9 technology was used to knockout (KO) SHP2 from human T cells. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 signaling endodomain) targeting HER2. The phenotype of wild-type and edited CAR T cells was investigated using mass cytometry and confirmed with flow cytometry. Their function was tested in vitro using xcelligence (an electrical impedance-based long-term cytotoxicity assay) and in vivo in an orthotopic xenograft mouse model of GBM. Efficient SHP2 KO in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect T cell expansion, proliferation or phenotypic profile. However, SHP2KO CAR T cells eliminated LN229 cells (a GBM cell line) in vitro more efficiently compared to wild-type CAR T cells. In vivo, SHP2KO CAR T cells showed better control of engrafted LN229 tumor cells and improved the survival of treated mice in comparison to wild-type CAR T cells. In conclusion, these results suggest that SHP2 may limit the function of CAR T cells and that SHP2 deletion may improve their anti-GBM activity.

Combating Glioblastoma by Codelivering the Small-Molecule Inhibitor of STAT3 and STAT3siRNA with α5β1 Integrin Receptor-Selective Liposomes.

Glioblastoma multiforme (GBM) is one of the most aggressive tumors with a median survival of only 15 months. Effective therapeutics need to overcome the formidable challenge of crossing the blood-brain barrier (BBB). Receptors and transporters overexpressed on BCECs are being used for designing liposomes, polymers, polymeric micelles, peptides, and dendrimer-based drug carriers for combating brain tumors. Herein, using the orthotopic mouse glioblastoma model, we show that codelivering a small-molecule inhibitor of the JAK/STAT pathway (WP1066) and STAT3siRNA with nanometric (100-150 nm) α5β1 integrin receptor-selective liposomes of RGDK-lipopeptide holds therapeutic promise in combating glioblastoma. Rh-PE (red)-labeled liposomes of RGDK-lipopeptide were found to be internalized in GL261 cells via integrin α5β1 receptors. Intravenously administered near-infrared (NIR)-dye-labeled α5β1 integrin receptor-selective liposomes of RGDK-lipopeptide were found to be accumulated preferentially in the mouse brain tumor tissue. Importantly, we show that iv injection of WP1066 (a commercially sold small-molecule inhibitor of the JAK/STAT pathway) and STAT3siRNA cosolubilized within the liposomes of RGDK-lipopeptide leads to significant inhibition (>350% compared to the untreated mice group) of orthotopically growing mouse glioblastoma. The present strategy may find future use in combating GBM.

The oncogene BCL6 is up-regulated in glioblastoma in response to DNA damage, and drives survival after therapy.

The prognosis for people with the high-grade brain tumor glioblastoma is very poor, due largely to low cell death in response to genotoxic therapy. The transcription factor BCL6, a protein that normally suppresses the DNA damage response during immune cell maturation, and a known driver of B-cell lymphoma, was shown to mediate the survival of glioblastoma cells. Expression was observed in glioblastoma tumor specimens and cell lines. When BCL6 expression or activity was reduced in these lines, increased apoptosis and a profound loss of proliferation was observed, consistent with gene expression signatures suggestive of anti-apoptotic and pro-survival signaling role for BCL6 in glioblastoma. Further, treatment with the standard therapies for glioblastoma—ionizing radiation and temozolomide—both induced BCL6 expression in vitro, and an in vivo orthotopic animal model of glioblastoma. Importantly, inhibition of BCL6 in combination with genotoxic therapies enhanced the therapeutic effect. Together these data demonstrate that BCL6 is an active transcription factor in glioblastoma, that it drives survival of cells, and that it increased with DNA damage, which increased the survival rate of therapy-treated cells. This makes BCL6 an excellent therapeutic target in glioblastoma—by increasing sensitivity to standard DNA damaging therapy, BCL6 inhibitors have real potential to improve the outcome for people with this disease.

Poly(ethylene glycol)-Poly(beta-amino ester)-Based Nanoparticles for Suicide Gene Therapy Enhance Brain Penetration and Extend Survival in a Preclinical Human Glioblastoma Orthotopic Xenograft Model.

Glioblastoma (GBM) is the most devastating brain cancer, and cures remain elusive with currently available neurosurgical, pharmacological, and radiation approaches. While retrovirus- and adenovirus-mediated suicide gene therapy using DNA encoding herpes simplex virus-thymidine kinase (HSV-tk) and prodrug ganciclovir has been suggested as a promising strategy, a nonviral approach for treatment in an orthotopic human primary brain tumor model has not previously been demonstrated. Delivery challenges include nanoparticle penetration through brain tumors, efficient cancer cell uptake, endosomal escape to the cytosol, and biodegradability. To meet these challenges, we synthesized poly(ethylene glycol)-modified poly(beta-amino ester) (PEG-PBAE) polymers to improve extracellular delivery and coencapsulated plasmid DNA with end-modified poly(beta-amino ester) (ePBAE) polymers to improve intracellular delivery as well. We created and evaluated a library of PEG-PBAE/ePBAE nanoparticles (NPs) for effective gene therapy against two independent primary human stem-like brain tumor initiating cells, a putative target to prevent GBM recurrence. The optimally engineered PEG-PBAE/ePBAE NP formulation demonstrated 54 and 82% transfection efficacies in GBM1A and BTIC375 cells respectively, in comparison to 37 and 66% for optimized PBAE NPs without PEG. The leading PEG-PBAE NP formulation also maintained sub-250 nm particle size up to 5 h, while PBAE NPs without PEG showed aggregation over time to micrometer-sized complexes. The comparative advantage demonstrated in vitro successfully translated into improved in vivo diffusion, with a higher amount of PEG-PBAE NPs penetrating to a distance of 2 mm from the injection site. A significant increase in median survival from 53.5 to 67 days by PEG-PBAE/pHSV-tk NP and systemic ganciclovir treatment compared to a control group in orthotopic murine model of human glioblastoma demonstrates the potential of PEG-PBAE-based NPs as an effective gene therapy platform for the treatment of human brain tumors.

Glioblastoma chemotherapeutic agents used in the clinical setting and in clinical trials: Nanomedicine approaches to improve their efficacy.

Even though substantial advances in understanding glioma pathogenesis have prompted a more rational design of potential therapeutic strategies, glioblastoma multiforme remains an incurable disease with the lowest median overall survival among all malignant brain tumours. Therefore, there is a dire need to find novel drug delivery strategies to improve the current dismal survival outcomes. In this context, nanomedicine offers an appealing alternative as it shows potential to improve brain drug delivery. Accordingly, we here review nanomedicine-based drug delivery strategies tested in orthotopic animal models of glioblastoma intended to improve the efficacy of the drug candidates that are currently used in the clinical setting or that have entered clinical trials for the treatment of glioblastoma multiforme. We also outline the future perspectives of nanotechnology to provide emerging glioblastoma treatment with broad translational clinical potential based on the nanocarriers that have already entered the clinical trials stage for the treatment of malignant glioma.

Riluzole enhances the antitumor effects of temozolomide via suppression of MGMT expression in glioblastoma.

Glutamatergic signaling significantly promotes proliferation, migration, and invasion in glioblastoma (GBM). Riluzole, a metabotropic glutamate receptor 1 inhibitor, reportedly suppresses GBM growth. However, the effects of combining riluzole with the primary GBM chemotherapeutic agent, temozolomide (TMZ), are unknown. This study aimed to investigate the efficacy of combinatorial therapy with TMZ/riluzole for GBM in vitro and in vivo. Three GBM cell lines, T98G (human; O6-methylguanine DNA methyltransferase [MGMT] positive), U87MG (human; MGMT negative), and GL261 (murine; MGMT positive), were treated with TMZ, riluzole, or a combination of both. The authors performed cell viability assays, followed by isobologram analysis, to evaluate the effects of combinatorial treatment for each GBM cell line. They tested the effect of riluzole on MGMT, a DNA repair enzyme causing chemoresistance to TMZ, through quantitative real-time reverse transcription polymerase chain reaction in T98G cells. Furthermore, they evaluated the efficacy of combinatorial TMZ/riluzole treatment in an orthotopic mouse allograft model of MGMT-positive GBM using C57BL/6 J mice and GL261 cells. Riluzole displayed significant time- and dose-dependent growth-inhibitory effects on all GBM cell lines assessed independently. Riluzole enhanced the antitumor effect of TMZ synergistically in MGMT-positive but not in MGMT-negative GBM cell lines. Riluzole singularly suppressed MGMT expression, and it significantly suppressed TMZ-induced MGMT upregulation (p < 0.01). Furthermore, combinatorial TMZ/riluzole treatment significantly suppressed tumor growth in the intracranial MGMT-positive GBM model (p < 0.05). Riluzole attenuates TMZ-induced MGMT upregulation and enhances the antitumor effect of TMZ in MGMT-positive GBMs. Therefore, combinatorial TMZ/riluzole treatment is a potentially promising novel therapeutic regimen for MGMT-positive GBMs.

Treatment of an aggressive orthotopic murine glioblastoma model with combination checkpoint blockade and a multivalent neoantigen vaccine.

Although clinical trials testing immunotherapies in glioblastoma (GBM) have yielded mixed results, new strategies targeting tumor-specific somatic coding mutations, termed "neoantigens," represent promising therapeutic approaches. We characterized the microenvironment and neoantigen landscape of the aggressive CT2A GBM model in order to develop a platform to test combination checkpoint blockade and neoantigen vaccination. Flow cytometric analysis was performed on intracranial CT2A and GL261 tumor-infiltrating lymphocytes (TILs). Whole-exome DNA and RNA sequencing of the CT2A murine GBM was employed to identify expressed, somatic mutations. Predicted neoantigens were identified using the pVAC-seq software suite, and top-ranking candidates were screened for reactivity by interferon-gamma enzyme linked immunospot assays. Survival analysis was performed comparing neoantigen vaccination, anti-programmed cell death ligand 1 (αPD-L1), or combination therapy. Compared with the GL261 model, CT2A exhibited immunologic features consistent with human GBM including reduced αPD-L1 sensitivity and hypofunctional TILs. Of the 29 CT2A neoantigens screened, we identified neoantigen-specific CD8+ T-cell responses in the intracranial TIL and draining lymph nodes to two H2-Kb restricted (Epb4H471L and Pomgnt1R497L) and one H2-Db restricted neoantigen (Plin2G332R). Survival analysis showed that therapeutic neoantigen vaccination with Epb4H471L, Pomgnt1R497L, and Plin2G332R, in combination with αPD-L1 treatment was superior to αPD-L1 alone. We identified endogenous neoantigen specific CD8+ T cells within an αPD-L1 resistant murine GBM and show that neoantigen vaccination significantly augments survival benefit in combination with αPD-L1 treatment. These observations provide important preclinical correlates for GBM immunotherapy trials and support further investigation into the effects of multimodal immunotherapeutic interventions on antiglioma immunity. 1. Neoantigen vaccines combined with checkpoint blockade may be promising treatments.2. CT2A tumors exhibit features of human GBM microenvironments.3. Differential scanning fluorimetry assays may complement in silico neoantigen prediction tools.

Correction: Arming an Oncolytic Herpes Simplex Virus Type 1 with a Single-chain Fragment Variable Antibody against PD-1 for Experimental Glioblastoma Therapy

Purpose: Glioblastoma (GBM) is resistant to standard of care. Immune checkpoints inhibitors (such as anti-PD-1 mAbs) efficiently restore antitumor T-cell activity. We engineered a new oncolytic herpes simplex virus (oHSV) expressing a single-chain antibody against PD-1 (scFvPD-1) to evaluate its efficacy in mouse models of GBM. Experimental Design: NG34scFvPD-1 expresses the human GADD34 gene transcriptionally controlled by the Nestin promoter to allow replication in GBM cells and a scFvPD-1 cDNA transcriptionally controlled by the CMV promoter. ELISA assays were performed to detect binding of scFvPD-1 to mouse and human PD-1. In vitro cytotoxicity and replication assays were performed to measure NG34scFvPD-1 oncolysis, and scFvPD-1 expression and secretion were determined. In vivo survival studies using orthotopic mouse GBM models were performed to evaluate the therapeutic potency of NG34scFvPD-1. Results: NG34scFvPD-1–infected GBM cells express and secrete scFvPD-1 that binds mouse PD-1. The introduction of the scFvPD-1 sequence in the viral backbone does not alter the oncolytic properties of NG34scFvPD-1. In situ NG34scFvPD-1 treatment improved the survival with a tail of durable survivorship in 2 syngeneic immunocompetent mouse models of GBM. Mice that survived the first GBM challenge rejected the second challenge of GBM when implanted in the contralateral hemisphere. However, this was not true when athymic mice were employed as the recipients of the second challenge, consistent with the need for an intact immune system to obtain a memory response. Conclusions: NG34scFvPD-1 treatment induces a durable antitumor response in 2 preclinical mouse models of GBM with evidence for antitumor memory.

Contrast-enhanced, conebeam CT-based, fractionated radiotherapy and follow-up monitoring of orthotopic mouse glioblastoma: a proof-of-concept study

BackgroundDespite aggressive treatment regimens comprising surgery and radiochemotherapy, glioblastoma (GBM) remains a cancer entity with very poor prognosis. The development of novel, combined modality approaches necessitates adequate preclinical model systems and therapy regimens that closely reflect the clinical situation. So far, image-guided, fractionated radiotherapy of orthotopic GBM models represents a major limitation in this regard.MethodsGL261 mouse GBM cells were inoculated into the right hemispheres of C57BL/6 mice. Tumor growth was monitored by contrast-enhanced conebeam CT (CBCT) scans. When reaching an average volume of approximately 7 mm3, GBM tumors were irradiated with daily fractions of 2 Gy up to a cumulative dose of 20 Gy in different beam collimation settings. For treatment planning and tumor volume follow-up, contrast-enhanced CBCT scans were performed twice per week. Daily repositioning of animals was achieved by alignment of bony structures in native CBCT scans. When showing neurological symptoms, mice were sacrificed by cardiac perfusion. Brains, livers, and kidneys were processed into histologic sections. Potential toxic effects of contrast agent administration were assessed by measurement of liver enzyme and creatinine serum levels and by histologic examination.ResultsTumors were successfully visualized by contrast-enhanced CBCT scans with a detection limit of approximately 2 mm3, and treatment planning could be performed. For daily repositioning of the animals, alignment of bony structures in native CT scans was well feasible. Fractionated irradiation caused a significant delay in tumor growth translating into significantly prolonged survival in clear dependence of the beam collimation setting and margin size. Brain sections revealed tumors of similar appearance and volume on the day of euthanasia. Importantly, the repeated contrast agent injections were well tolerated, as liver enzyme and creatinine serum levels were only subclinically elevated, and liver and kidney sections displayed normal histomorphology.ConclusionsContrast-enhanced, CT-based, fractionated radiation of orthotopic mouse GBM represents a versatile preclinical technique for the development and evaluation of multimodal radiotherapeutic approaches in combination with novel therapeutic agents in order to accelerate translation into clinical testing.

Deliver anti-PD-L1 into brain by p-hydroxybenzoic acid to enhance immunotherapeutic effect for glioblastoma

In glioblastoma with typical immunosuppressive characteristics, immune checkpoint inhibitors treatment showed unsatisfactory clinical effects, attributable to the exclusion of antibodies by blood-brain barrier (BBB) to a large extent. Herein, a conjugate of anti-programmed death ligand 1 antibody (αPDL1) and the targeting moiety p-hydroxybenzoic acid (pHA) was designed to realize crossing BBB of antibody based on the dopamine receptor mediated transcytosis. Conjugation with pHA did not influence the binding affinity of αPDL1 with PD-L1 protein, thus maintaining the capability of PD pathway blockade. Importantly, pHA-αPDL1 crossed BBB, demonstrated by the increased distribution in both the brain and the glioma after intravenous administration of pHA-αPDL1. Compared with the unmodified αPDL1, pHA-αPDL1 prolonged the survival time and suppressed tumor growth more effectively in an orthotopic glioblastoma model by activating glioma-infiltrating T cells. Our results suggested the potential of the antibody-pHA conjugate to improve efficacy for cerebral diseases by providing a potential platform for macromolecules to play therapeutics role in the brain.

Low-dose oncolytic adenovirus therapy overcomes tumor-induced immune suppression and sensitizes intracranial gliomas to anti-PD-1 therapy.

BackgroundThe tumor-selective human adenovirus Delta24-RGD is currently under investigation in phase II clinical trials for patients with recurrent glioblastoma (GBM). To improve treatments for patients with GBM, we explored the potential of combining Delta24-RGD with antibodies targeting immune checkpoints.MethodsC57BL/6 mice were intracranially injected with GL261 cells and treated with a low dose of Delta24-RGD virus. The expression dynamics of 10 co-signaling molecules known to affect immune activity was assessed in tumor-infiltrating immune cells by flow cytometry after viral injection. The antitumor activity was measured by tumor cell killing and IFNγ production in co-cultures. Efficacy of the combination viro-immunotherapy was tested in vitro and in the GL261 and CT2A orthotopic mouse GBM models. Patient-derived GBM cell cultures were treated with Delta24-RGD to assess changes in PD-L1 expression induced by virus infection.ResultsDelta24-RGD therapy increased intratumoral CD8+ T cells expressing Inducible T-cell co-stimulator (ICOS) and PD-1. Functionality assays confirmed a significant positive correlation between tumor cell lysis and IFNγ production in ex vivo cultures (Spearman r = 0.9524; P < .01). Co-cultures significantly increased IFNγ production upon treatment with PD-1 blocking antibodies. In vivo, combination therapy with low-dose Delta24-RGD and anti-PD-1 antibodies significantly improved outcome compared to single-agent therapy in both syngeneic mouse glioma models and increased PD-1+ tumor-infiltrating CD8+ T cells. Delta24-RGD infection induced tumor-specific changes in PD-L1 expression in primary GBM cell cultures.ConclusionsThis study demonstrates the potential of using low-dose Delta24-RGD therapy to sensitize glioma for combination with anti-PD-1 antibody therapy.

MerTK inhibition decreases immune suppressive glioblastoma-associated macrophages and neoangiogenesis in glioblastoma microenvironment.

Glioblastoma-associated macrophages and microglia (GAMs) are the predominant immune cells in the tumor microenvironment. Activation of MerTK, a receptor tyrosine kinase, polarizes GAMs to an immunosuppressive phenotype, promoting tumor growth. Here, the role of MerTK inhibition in the glioblastoma microenvironment is investigated in vitro and in vivo. Effects of MRX-2843 in glioblastoma microenvironment regulation were determined in vitro by cell viability, cytokine array, in vitro tube formation, Western blotting, and wound healing assays. A syngeneic GL261 orthotopic glioblastoma mouse model was used to evaluate the survival benefit of MRX-2843 treatment. Multiplex fluorescent immunohistochemistry was used to evaluate the expression of CD206, an anti-inflammatory marker on GAMs, and angiogenesis in murine brain tumor tissues. MRX-2843 inhibited cell growth and induced apoptosis in human glioblastoma cells and decreased protein expression of phosphorylated MerTK, AKT, and ERK, which are essential for cell survival signaling. Interleukin-8 and C-C motif chemokine ligand 2, the pro-glioma and pro-angiogenic cytokines, were decreased by MRX-2843. Decreased vascular formation and numbers of immunosuppressive (CD206+) GAMs were observed following MRX-2843 treatment in vivo, suggesting that in addition to alleviating immunosuppression, MRX-2843 also inhibits neoangiogenesis in the glioma microenvironment. These results were supported by a prolonged survival in the syngeneic mouse orthotopic GL261 glioblastoma model following MRX-2843 treatment. Our findings suggest that MRX-2843 has a therapeutic benefit via promoting GAM polarization away from immunosuppressive condition, inhibiting neoangiogenesis in the glioblastoma microenvironment and inducing tumor cell death.

Intravital imaging reveals synergistic effect of CAR T-cells and radiation therapy in a preclinical immunocompetent glioblastoma model

ABSTRACT Recent advances in novel immune strategies, particularly chimeric antigen receptor (CAR)-bearing T-cells, have shown limited efficacy against glioblastoma (GBM) in clinical trials. We currently have an incomplete understanding of how these emerging therapies integrate with the current standard of care, specifically radiation therapy (RT). Additionally, there is an insufficient number of preclinical studies monitoring these therapies with high spatiotemporal resolution. To address these limitations, we report the first longitudinal fluorescence-based intravital microscopy imaging of CAR T-cells within an orthotopic GBM preclinical model to illustrate the necessity of RT for complete therapeutic response. Additionally, we detail the first usage of murine-derived CAR T-cells targeting the disialoganglioside GD2 in an immunocompetent tumor model. Cell culture assays demonstrated substantial GD2 CAR T-cell-mediated killing of murine GBM cell lines SB28 and GL26 induced to overexpress GD2. Complete antitumor response in advanced syngeneic orthotopic models of GBM was achieved only when a single intravenous dose of GD2 CAR T-cells was following either sub-lethal whole-body irradiation or focal RT. Intravital microscopy imaging successfully visualized CAR T-cell homing and T-cell mediated apoptosis of tumor cells in real-time within the tumor stroma. Findings indicate that RT allows for rapid CAR T-cell extravasation from the vasculature and expansion within the tumor microenvironment, leading to a more robust and lasting immunologic response. These exciting results highlight potential opportunities to improve intravenous adoptive T-cell administration in the treatment of GBM through concurrent RT. Additionally, they emphasize the need for advancements in immunotherapeutic homing to and extravasation through the tumor microenvironment.

2-[18F]FELP, a novel LAT1-specific PET tracer, for the discrimination between glioblastoma, radiation necrosis and inflammation

IntroductionConsidering the need for rapid change of treatment in recurrent glioblastoma (GB), it is of utmost importance to characterize PET radiopharmaceuticals that allow early discrimination of tumor from therapy-related effects. In this study, we examined the value of 2-[18F]FELP as a LAT1 tumor-specific PET tracer in comparison with [18F]FDG and [18F]FET in a combined orthotopic rat radiation necrosis and glioblastoma model. A second experiment compared 2-[18F]FELP to [18F]FDG in a mouse glioblastoma - inflammation model. MethodsUsing the small animal radiation research platform (SARRP), radiation necrosis (RN) was induced in the left frontal lobe of the rat brain. When radiation-induced changes were visible on MRI, F98 rat glioblastoma cells were stereotactically inoculated in the contralateral right frontal lobe. When tumor growth was confirmed on MRI, 2-[18F]FELP, [18F]FET and [18F]FDG PET scans were acquired on three consecutive days. In an inflammation experiment, mice were inoculated in the left thigh with U87 human glioblastoma cells. After heterotopic tumor growth was confirmed macroscopically, inflammation was induced by injection of turpentine subcutaneously in the right thigh. Subsequently, 2-[18F]FELP and [18F]FDG scans were acquired on two consecutive days. ResultsThe in vivo PET images demonstrated that 2-[18F]FELP could differentiate glioblastoma and radiation necrosis using SUVmean (p = 0.0016) and LNRmean (p = 0.009), while [18F]FET was only able to differentiate both lesions by means of the SUVmean. (p = 0.047) Delayed [18F]FDGlate PET (4 h postinjection) was also able to distinguish glioblastoma from radiation necrosis, but smaller lesion-to-normal brain ratios were observed (SUVmean: p = 0.009; LNRmean: p = 0.028). In the inflammation study, 2-[18F]FELP showed no significant uptake in the inflammation lesion when compared to the control group (SUVmean: p = 0.149; LNRmean: p = 0.083). In contrast, both conventional and delayed [18F]FDG displayed significant uptake in the turpentine-invoked lesion (SUVmean: p = 0.021; LNRmean: p = 0.021). ConclusionThis study suggests that the 2-[18F]FELP PET is able to differentiate glioblastoma from radiation necrosis and that the 2-[18F]FELP uptake is less likely to be contaminated by the presence of inflammation than the [18F]FDG signal. Advances in knowledgeThese results are clinically relevant for the differential diagnosis between tumor and radiation necrosis because radiation necrosis always contains a certain amount of inflammatory cells. Hence, 2-[18F]FELP is preferred to discriminate tumor from radiation necrosis.

Tumor Vessel Normalization, Immunostimulatory Reprogramming, and Improved Survival in Glioblastoma with Combined Inhibition of PD-1, Angiopoietin-2, and VEGF.

Glioblastoma (GBM) is a non-T-cell-inflamed cancer characterized by an immunosuppressive microenvironment that impedes dendritic cell maturation and T-cell cytotoxicity. Proangiogenic cytokines such as VEGF and angiopoietin-2 (Ang-2) have high expression in glioblastoma in a cell-specific manner and not only drive tumor angiogenesis and vascular permeability but also negatively regulate T-lymphocyte and innate immune cell responses. Consequently, the alleviation of immunosuppression might be a prerequisite for successful immune checkpoint therapy in GBM. We here combined antiangiogenic and immune checkpoint therapy and demonstrated improved therapeutic efficacy in syngeneic, orthotopic GBM models. We observed that blockade of VEGF, Ang-2, and programmed cell death protein-1 (PD-1) significantly extended survival compared with vascular targeting alone. In the GBM microenvironment, triple therapy increased the numbers of CTLs, which inversely correlated with myeloid-derived suppressor cells and regulatory T cells. Transcriptome analysis of GBM microvessels indicated a global vascular normalization that was highest after triple therapy. Our results propose a rationale to overcome tumor immunosuppression and the current limitations of VEGF monotherapy by integrating the synergistic effects of VEGF/Ang-2 and PD-1 blockade to reinforce antitumor immunity through a normalized vasculature.

64Cu-ATSM/64Cu-Cl2 and their relationship to hypoxia in glioblastoma: a preclinical study

BackgroundDiacetyl-bis(N4-methylthiosemicarbazone), labeled with 64Cu (64Cu-ATSM) has been suggested as a promising tracer for imaging hypoxia. However, various controversial studies highlighted potential pitfalls that may disable its use as a selective hypoxic marker. They also highlighted that the results may be tumor location dependent. Here, we first analyzed uptake of Cu-ATSM and its less lipophilic counterpart Cu-Cl2 in the tumor over time in an orthotopic glioblastoma model. An in vitro study was also conducted to investigate the hypoxia-dependent copper uptake in tumor cells. We then further performed a comprehensive ex vivo study to compare 64Cu uptake to hypoxic markers, specific cellular reactions, and also transporter expression.MethodsμPET was performed 14 days (18F-FMISO), 15 days (64Cu-ATSM and 64Cu-Cl2), and 16 days (64Cu-ATSM and 64Cu-Cl2) after C6 cell inoculation. Thereafter, the brains were withdrawn for further autoradiography and immunohistochemistry. C6 cells were also grown in hypoxic workstation to analyze cellular uptake of Cu complexes in different oxygen levels.ResultsIn vivo results showed that Cu-ASTM and Cu-Cl2 accumulated in hypoxic areas of the tumors. Cu-ATSM also stained, to a lesser extent, non-hypoxic regions, such as regions of astrogliosis, with high expression of copper transporters and in particular DMT-1 and CTR1, and also characterized by the expression of elevated astrogliosis. In vitro results show that 64Cu-ATSM showed an increase in the uptake only in severe hypoxia at 0.5 and 0.2% of oxygen while for 64Cu-Cl2, the cell retention was significantly increased at 5% and 1% of oxygen with no significant rise at lower oxygen percentages.ConclusionIn the present study, we show that Cu-complexes undoubtedly accumulate in hypoxic areas of the tumors. This uptake may be the reflection of a direct dependency to a redox metabolism and also a reflection of hypoxic-induced overexpression of transporters. We also show that Cu-ATSM also stained non-hypoxic regions such as astrogliosis.

In Vivo Bioluminescence Tomography Center of Mass-Guided Conformal Irradiation

The cone-beam computed tomography (CBCT)-guided small animal radiation research platform (SARRP) has provided unique opportunities to test radiobiologic hypotheses. However, CBCT is less adept to localize soft tissue targets growing in a low imaging contrast environment. Three-dimensional bioluminescence tomography (BLT) provides strong image contrast and thus offers an attractive solution. We introduced a novel and efficient BLT-guided conformal radiation therapy and demonstrated it in an orthotopic glioblastoma (GBM) model. A multispectral BLT system was integrated with SARRP for radiation therapy (RT) guidance. GBM growth curve was first established by contrast CBCT/magnetic resonance imaging (MRI) to derive equivalent sphere as approximated gross target volume (aGTV). For BLT, mice were subject to multispectral bioluminescence imaging, followed by SARRP CBCT imaging and optical reconstruction. The CBCT image was acquired to generate anatomic mesh for the reconstruction and RT planning. To ensure high accuracy of the BLT-reconstructed center of mass (CoM) for target localization, we optimized the optical absorption coefficients μa by minimizing the distance between the CoMs of BLT reconstruction and contrast CBCT/MRI-delineated GBM volume. The aGTV combined with the uncertainties of BLT CoM localization and target volume determination was used to generate estimated target volume (ETV). For conformal irradiation procedure, the GBM was first localized by the predetermined ETV centered at BLT-reconstructed CoM, followed by SARRP radiation. The irradiation accuracy was qualitatively confirmed by pathologic staining. Deviation between CoMs of BLT reconstruction and contrast CBCT/MRI-imaged GBM is approximately 1 mm. Our derived ETV centered at BLT-reconstructed CoM covers >95% of the tumor volume. Using the second-week GBM as an example, the ETV-based BLT-guided irradiation can cover 95.4% ± 4.7% tumor volume at prescribed dose. The pathologic staining demonstrated the BLT-guided irradiated area overlapped well with the GBM location. The BLT-guided RT enables 3-dimensional conformal radiation for important orthotopic tumor models, which provides investigators a new preclinical research capability.

DRES-01. EFFICACY OF EGFR PLUS TNF INHIBITION IN A PRECLINICAL MODEL OF GLIOBLASTOMA

Abstract EGFR gene amplification and mutation are common in glioblastoma (GBM), but EGFR inhibition is not effective in treating this tumor. EGFR inhibition may fail because EGFR is not a driver of the malignant phenotype in GBM, or because adaptive compensatory mechanisms are triggered by EGFR inhibition that prevent cell death from a loss of EGFR signaling. We have recently identified a TNFα-JNK-Axl-ERK signaling axis that mediates primary resistance to EGFR inhibition in GBM. Temozolomide (TMZ) is the most effective chemotherapy in GBM, although it has only a modest effect on overall survival. The efficacy of TMZ depends on the absence of the DNA repair protein O6-alkylguanine DNA alkyltransferase (MGMT) which reverses the DNA damage induced by TMZ. The MGMT promoter is hypermethylated in about 45% of GBMs, resulting in lack of MGMT expression. TMZ is less effective in MGMT unmethylated GBMs. Moreover, even initially responsive tumors develop a secondary resistance to TMZ. No treatment is effective in recurrent TMZ-resistant GBM. In this study, we compare the efficacy of temozolomide versus EGFR plus TNF inhibition in an orthotopic model of GBM. We find that efficacy of the two treatments is similar in MGMT-methylated GBMs. However, in MGMT-unmethylated GBMs, a combination of EGFR plus TNF inhibition is more effective. We demonstrate that the two treatment approaches target distinct and non-overlapping pathways. Furthermore, and importantly, EGFR plus TNF inhibition remains effective in TMZ-resistant recurrent GBMs and in GBMs rendered experimentally resistant to TMZ. Since the EGFR is expressed in the majority of GBMs, EGFR inhibition combined with a blunting of the accompanying TNF-driven adaptive response could be a broadly applicable and viable therapeutic approach in primary GBMs with MGMT unmethylation and in recurrent GBMs.