Irradiation to Improve the Response to Immunotherapeutic Agents in Glioblastomas

An Update on the Clinical Status, Challenges, and Future Directions of Oncolytic Virotherapy for Malignant Gliomas

OPINION STATEMENT

Malignant gliomas are common central nervous system tumors that pose a significant clinical challenge due to the lack of effective treatments. Glioblastoma (GBM), a grade 4 malignant glioma, is the most prevalent primary malignant brain tumor and is associated with poor prognosis. Current clinical trials are exploring various strategies to combat GBM, with oncolytic viruses (OVs) appearing particularly promising. In addition to ongoing and recently completed clinical trials, one OV (Teserpaturev, Delytact®) received provisional approval for GBM treatment in Japan. OVs are designed to selectively target and eliminate cancer cells while promoting changes in the tumor microenvironment that can trigger and support long-lasting anti-tumor immunity. OVs offer the potential to remodel the tumor microenvironment and reverse systemic immune exhaustion. Additionally, an increasing number of OVs are armed with immunomodulatory payloads or combined with immunotherapy approaches in an effort to promote anti-tumor responses in a tumor-targeted manner. Recently completed oncolytic virotherapy trials can guide the way for future treatment individualization through patient preselection, enhancing the likelihood of achieving the highest possible clinical success. These trials also offer valuable insight into the numerous challenges inherent in malignant glioma treatment, some of which OVs can help overcome.

Radiation-primed TGF-β trapping by engineered extracellular vesicles for targeted glioblastoma therapy

The poor outcome of glioblastoma multiforme (GBM) treated with immunotherapy is attributed to the profound immunosuppressive tumor microenvironment (TME) and the lack of effective delivery across the blood-brain barrier. Radiation therapy (RT) induces an immunogenic antitumor response that is counteracted by evasive mechanisms, among which transforming growth factor-β (TGF-β) activation is the most prominent factor. We report an extracellular vesicle (EV)-based nanotherapeutic that traps TGF-β by expressing the extracellular domain of the TGF-β type II receptor and targets GBM by decorating the EV surface with RGD peptide. We show that short-burst radiation dramatically enhanced the targeting efficiency of RGD peptide-conjugated EVs to GBM, while the displayed TGF-β trap reversed radiation-stimulated TGF-β activation in the TME, offering a synergistic effect in the murine GBM model. The combined therapy significantly increased CD8+ cytotoxic T cells infiltration and M1/M2 macrophage ratio, resulting in the regression of tumor growth and prolongation of overall survival. These results provide an EV-based therapeutic strategy for immune remodeling of the GBM TME and eradication of therapy-resistant tumors, further supporting its clinical translation.

Metabolism/Immunity Dual-Regulation Thermogels Potentiating Immunotherapy of Glioblastoma Through Lactate-Excretion Inhibition and PD-1/PD-L1 Blockade

Intrinsic immunosuppressive tumor microenvironment (ITM) and insufficient tumor infiltration of T cells severely impede the progress of glioblastoma (GBM) immunotherapy. In this study, it is identify that inhibiting the expression of glucose transporter 1 (GLUT1) can facilitate the prevention of lactate excretion from tumor glycolysis, which significantly alleviates the lactate-driven ITM by reducing immunosuppressive tumor-associated macrophages (TAMs) and regulatory T cells (Tregs). Simultaneously, the findings show that the generated inflammatory cytokine IFN-γ during immune activation aggravates the immune escape by upregulating immune checkpoint programmed death-ligand 1 (PD-L1) in tumor cells and TAMs. Therefore, an injectable thermogel loaded with a GLUT1 inhibitor BAY-876 and a PD-1/PD-L1 blocker BMS-1 (Gel@B-B) for dual-regulation of metabolism and immunity of GBM is developed. Consequently, in situ injection of Gel@B-B significantly delays tumor growth and prolongs the survival of the orthotopic GBM mouse model. By actively exposing tumor antigens to antigen-presenting cells, the GBM vaccine combined with Gel@B-B is found to significantly increase the fraction of effector T cells (Th1/CTLs) in the tumor microenvironment, thereby remarkably mitigating tumor recurrence long-term. This study may provide a promising strategy for GBM immunotherapy.

Potential roles for efferocytosis in glioblastoma immune evasion

Glioblastoma is an aggressive and incurable brain cancer. This cancer establishes both local and systemic immunosuppression that creates a major obstacle to effective immunotherapies. Many studies point to tumor-resident myeloid cells (primarily microglia and macrophages) as key mediators of this immunosuppression. Myeloid cells exhibit a high level of plasticity with respect to their phenotype and are capable of both stimulating and repressing immune responses. How glioblastomas recruit myeloid cells and exploit them to avoid the immune system is an active area of research. Macrophages can acquire an immunosuppressive phenotype as a consequence of exposure to cytokines such as TGFB1 or IL4; in addition, macrophages can acquire an immunosuppressive phenotype as a consequence of the engulfment of apoptotic cells, a process referred to as efferocytosis. There is substantial evidence that glioblastoma cells are able to secrete cytokines and other factors that induce an immunosuppressive phenotype in macrophages and microglia. However, less is known about the contribution of efferocytosis to immunosuppression in glioblastoma. Here I review the literature in this area and discuss the potential of efferocytosis inhibition to improve glioblastoma response to immunotherapy.

Synergistically Enhancing Immunotherapy Efficacy in Glioblastoma with Gold-Core Silica-Shell Nanoparticles and Radiation

Purpose

Glioblastoma is a highly aggressive brain tumor with universally poor outcomes. Recent progress in immune checkpoint inhibitors has led to increased interest in their application in glioblastoma. Nonetheless, the unique immune milieu in the brain has posed remarkable challenges to the efficacy of immunotherapy. We aimed to leverage the radiation-induced immunogenic cell death to overcome the immunosuppressive network in glioblastoma.

Methods

We developed a novel approach using the gold-core silica-shell nanoparticles (Au@SiO2 NPs) in combination with low-dose radiation to enhance the therapeutic efficacy of the immune checkpoint inhibitor (atezolizumab) in brain tumors. The biocompatibility, immune cell recruitment, and antitumor ability of the combinatorial strategy were determined using in vitro assays and in vivo models.

Results

Our approach successfully induced the migration of macrophages towards brain tumors and promoted cancer cell apoptosis. Subcutaneous tumor models demonstrated favorable safety profiles and significantly enhanced anticancer effects. In orthotopic brain tumor models, the multimodal therapy yielded substantial prognostic benefits over any individual modalities, achieving an impressive 40% survival rate.

Conclusion

In summary, the combination of Au@SiO2 NPs and low-dose radiation holds the potential to improve the clinical efficacy of immune checkpoint inhibitors. The synergetic strategy modulates tumor microenvironments and enhances systemic antitumor immunity, paving a novel way for glioblastoma treatment.

Establishing Imaging Biomarkers of Host Immune System Efficacy during Glioblastoma Therapy Response: Challenges, Obstacles and Future Perspectives

This hypothesis proposal addresses three major questions: (1) Why do we need imaging biomarkers for assessing the efficacy of immune system participation in glioblastoma therapy response? (2) Why are they not available yet? and (3) How can we produce them? We summarize the literature data supporting the claim that the immune system is behind the efficacy of most successful glioblastoma therapies but, unfortunately, there are no current short-term imaging biomarkers of its activity. We also discuss how using an immunocompetent murine model of glioblastoma, allowing the cure of mice and the generation of immune memory, provides a suitable framework for glioblastoma therapy response biomarker studies. Both magnetic resonance imaging and magnetic resonance-based metabolomic data (i.e., magnetic resonance spectroscopic imaging) can provide non-invasive assessments of such a system. A predictor based in nosological images, generated from magnetic resonance spectroscopic imaging analyses and their oscillatory patterns, should be translational to clinics. We also review hurdles that may explain why such an oscillatory biomarker was not reported in previous imaging glioblastoma work. Single shot explorations that neglect short-term oscillatory behavior derived from immune system attack on tumors may mislead actual response extent detection. Finally, we consider improvements required to properly predict immune system-mediated early response (1–2 weeks) to therapy. The sensible use of improved biomarkers may enable translatable evidence-based therapeutic protocols, with the possibility of extending preclinical results to human patients.

Immune System-Related Changes in Preclinical GL261 Glioblastoma under TMZ Treatment: Explaining MRSI-Based Nosological Imaging Findings with RT-PCR Analyses

Glioblastomas (GB) are brain tumours with poor prognosis even after aggressive therapy. Previous work suggests that magnetic resonance spectroscopic imaging (MRSI) could act as a biomarker of efficient immune system attack onto GB, presenting oscillatory changes. Glioma-associated microglia/macrophages (GAMs) constitute the most abundant non-tumour cell type within the GB and can be polarised into anti-tumour (M1) or pro-tumour (M2) phenotypes. One of the mechanisms to mediate immunosuppression in brain tumours is the interaction between programmed cell death-1 ligand 1 (PD-L1) and programmed cell death-1 receptor (PD-1). We evaluated the subpopulations of GAMs in responding and control GB tumours to correlate PD-L1 expression to GAM polarisation in order to explain/validate MRSI-detected findings. Mice were evaluated by MRI/MRSI to assess the extent of response to treatment and with qPCR for GAMs M1 and M2 polarisation analyses. M1/M2 ratios and PD-L1 expression were higher in treated compared to control tumours. Furthermore, PD-L1 expression was positively correlated with the M1/M2 ratio. The oscillatory change in the GAMs prevailing population could be one of the key causes for the differential MRSI-detected pattern, allowing this to act as immune system activity biomarker in future work.

Tumor cell-targeting radiotherapy in the treatment of glioblastoma multiforme using linear accelerators

Although boron neuron capture therapy (BNCT) has enabled the delivery of stronger radiation dose to glioblastoma multiforme (GBM) cells for precision radiotherapy (RT), patients in need are almost unable to access the treatment due to insufficient operating devices. Therefore, we developed targeted sensitization-enhanced radiotherapy (TSER), a strategy that could achieve precision cell-targeted RT using common linear accelerators. TSER, which involves the combination of GoldenDisk (GD; a spherical radioenhancer), 5-aminolevulinic acid (5-ALA), low-intensity ultrasound (US), and low-dose RT, exhibited synergized radiosensitization effects. Both 5-ALA and hyaluronic-acid-immobilized GD can selectively accumulate in GBM to induce chemical and biological enhancement of radiosensitization, resulting in DNA damage, escalation of reactive oxygen species levels, and cell cycle redistribution, in turn sensitizing GBM cells to radiation under US. TSER showed an enhanced therapeutic effect and survival in the treatment of an orthotropic GBM model with only 20% of the radiation dose compared to that of a 10-Gy RT. The strategy with the potential to inhibit GBM progress and rescue the organ at risk using low-dose RT, thereby improving the quality of life of GBM patients, shedding light on achieving cell-targeted RT using universally available linear accelerators. STATEMENT OF SIGNIFICANCE: We invented GoldenDisk (GD), a radioenhancer with hyaluronic-acid (HAc)-coated gold nanoparticle (AuNP)-core/silica shell nanoparticle, to make radiotherapy (RT) safer and smarter. The surface modification of HAc and silica allows GD to target CD44-overexpressed glioblastoma multiforme (GBM) cells and stay structurally stable in cytoplasm throughout the course of RT. By combining GD with low-energy ultrasound and an FDA-approved imaging agent, 5-aminolevulinic acid (5-ALA), GBM cells were sensitized to RT leaving healthy tissues in the vicinity unaffected. The ionized radiation can further be transferred to photoelectronic products with higher cytotoxicity by GD upon collision, achieving higher therapeutic efficacy. With the newly-developed strategy, we are able to achieve low-dose precision RT with the use of only 20% radiation dose.

Preclinical Modeling of Surgery and Steroid Therapy for Glioblastoma Reveals Changes in Immunophenotype that are Associated with Tumor Growth and Outcome

PURPOSE

Glioblastoma (GBM) immunotherapy clinical trials are generally initiated after standard-of-care treatment-including surgical resection, perioperative high-dose steroid therapy, chemotherapy, and radiation treatment-has either begun or failed. However, the impact of these interventions on the antitumoral immune response is not well studied. While discoveries regarding the impact of chemotherapy and radiation on immune response have been made and translated into clinical trial design, the impact of surgical resection and steroids on the antitumor immune response has yet to be determined.

EXPERIMENTAL DESIGN

We developed a murine model integrating tumor resection and steroid treatment and used flow cytometry to analyze systemic and local immune changes. These mouse model findings were validated in a cohort of 95 patients with primary GBM.

RESULTS

Using our murine resection model, we observed a systemic reduction in lymphocytes corresponding to increased tumor volume and decreased circulating lymphocytes that was masked by dexamethasone treatment. The reduction in circulating T cells was due to reduced CCR7 expression, resulting in T-cell sequestration in lymphoid organs and the bone marrow. We confirmed these findings in a cohort of patients with primary GBM and found that prior to steroid treatment, circulating lymphocytes inversely correlated with tumor volume. Finally, we demonstrated that peripheral lymphocyte content varies with progression-free survival and overall survival, independent of tumor volume, steroid use, or molecular profiles.

CONCLUSIONS

These data reveal that prior to intervention, increased tumor volume corresponds with reduced systemic immune function and that peripheral lymphocyte counts are prognostic when steroid treatment is taken into account.

3,3'-Diindolylmethane Enhances Tumor Regression After Radiation Through Protecting Normal Cells to Modulate Antitumor Immunity

Purpose

Preclinical and clinical data indicate that radiation therapy acts as an immune modifier, having both immune-stimulatory and immunosuppressive effects on the tumor-immune microenvironment (TIME). 3.3’-diindolylmethane (DIM) sensitizes tumor cells to radiation and protects mice from lethal doses of total body irradiation. We hypothesize that protecting nontumoral cells from the adverse effects of radiation treatment (RT) may help to correct immunosuppression resulting from radiation.

Methods and Materials

We generated tumor graft models using immune-competent and immune-deficient mouse strains. Narrow-beamed radiation was targeted to tumor sites using shielding. Tumor regression was monitored after DIM and RT versus RT alone. The effects of DIM on the efficacy of RT were assessed using immunohistochemistry staining and gene expression profiling. Complete blood counts, clonogenic cell survival assays, and global gene expression profiling of cultured cells were performed to study DIM’s radioprotective effects on normal cells.

Results

DIM enhanced tumor regression after RT in immune-competent but not immune-deficient mice. Data indicated that DIM increased intratumoral immune cells after RT, contributing to enhanced immunologic responses such as adhesion and antigen processing. DIM protected normal cells from radiation-induced immediate injuries in vitro and in vivo. Transcriptomic profiling of cultured cells showed that DIM treatment mildly increased expression of some genes that are normally induced after radiation, such as genes involved in cell cycle arrest and apoptosis.

Conclusions

In this study, using cultured cells and preclinical breast cancer models, we show that DIM protects normal cells from radiation-induced immediate cellular injury and combination treatment of DIM and radiation potentiates antitumor immune responses and enhances the efficacy of RT.

The Change of Soluble Programmed Cell Death-Ligand 1 in Glioma Patients Receiving Radiotherapy and Its Impact on Clinical Outcomes

Background

The programmed cell death ligand 1 (PD-L1) plays a key role in glioma development. However, due to the specificity of glioma's anatomical position, the role of its expression as a tumor biomarker is limited. It has been proven that the levels of soluble programmed death-ligand 1 (sPD-L1) are associated with prognosis in many malignancies including glioma. However, the expression of sPD-L1 in glioma patients receiving radiotherapy (RT) remains unclear. The purpose of this study was to evaluate the concentration of sPD-L1 in the plasma of glioma patients before and after RT and to explore its relationship with clinical outcomes.

Methods

Between October 2017 and September 2018, glioma patients treated with RT (30 ± 10 Gy, 2 Gy/f) were enrolled, and blood samples were collected before and after RT. We quantified the sPD-L1 levels by enzyme-linked immunosorbent assay (ELISA). The isocitrate dehydrogenase-1 (IDH-1) mutational status and Ki-67 expression of tumors were evaluated by immunohistochemistry. Glioma murine model were used to address whether circulating sPD-L1 molecules are directly targeted by an anti-PD-L1 antibody. The associations between sPD-L1 and clinical features were assessed with Pearson's or Spearman's correlation analysis. The progression-free survival (PFS) and overall survival (OS) were determined by the Kaplan-Meier method.

Results

Sixty glioma patients were included, with a median age of 52 years. The proportions of grade I, II, III, and IV gliomas were 6.7%, 23.3%, 28.4%, and 41.6%, respectively. The baseline sPD-L1 levels were significantly associated with tumor grade, IDH-1 mutation status and Ki-67 expression. Using 14.35 pg/ml as the cutoff, significantly worse PFS and OS were both observed in patients with higher baseline levels of sPD-L1 (P = 0.027 and 0.008, respectively). RT significantly increased the mean level of sPD-L1 (P < 0.001). Further analysis showed that the level of sPD-L1 in IDH-1 mutation patients was higher than that in wild-type patients. Furthermore, an analysis of glioma murine model indicated that anti-PD-L1 antibody combine with RT can be a potentially powerful cancer therapy.

Conclusion

This study reported that sPD-L1 might be a potential biomarker to predict the outcome in glioma patients receiving RT. The elevated level of sPD-L1 after RT suggested that the strategy of a combination of immune checkpoint inhibitors and RT might be promising for glioma patients, especially for those with IDH-1 mutations.

Revealing and Harnessing Tumour-Associated Microglia/Macrophage Heterogeneity in Glioblastoma

Abstract: Cancer heterogeneity and progression are subject to complex interactions between neoplastic cells and their microenvironment, including the immune system. Although glioblastomas (GBMs) are classified as 'cold tumours' with very little lymphocyte infiltration, they can contain up to 30-40% of tumour-associated macrophages, reported to contribute to a supportive microenvironment that facilitates tumour proliferation, survival and migration. In GBM, tumour-associated macrophages comprise either resident parenchymal microglia, perivascular macrophages or peripheral monocyte-derived cells. They are recruited by GBMs and in turn release growth factors and cytokines that affect the tumour. Notably, tumour-associated microglia/macrophages (TAMs) acquire different expression programs, which shape the tumour microenvironment and contribute to GBM molecular subtyping. Further, emerging evidence highlights that TAM programs may adapt to specific tumour features and landscapes. Here, we review key evidence describing TAM transcriptional and functional heterogeneity in GBM. We propose that unravelling the intricate complexity and diversity of the myeloid compartment as well as understanding how different TAM subsets may affect tumour progression will possibly pave the way to new immune therapeutic avenues for GBM patients.

Somatic copy number alterations are associated with EGFR amplification and shortened survival in patients with primary glioblastoma

Glioblastoma (GBM) is the most common malignant primary tumor of the central nervous system. With no effective therapy, the prognosis for patients is terrible poor. It is highly heterogeneous and EGFR amplification is its most frequent molecular alteration.

In this light, we aimed to examine the genetic heterogeneity of GBM and to correlate it with the clinical characteristics of the patients. For that purpose, we analyzed the status of EGFR and the somatic copy number alterations (CNAs) of a set of tumor suppressor genes and oncogenes.

Thus, we found GBMs with high level of EGFR amplification, low level and with no EGFR amplification. Highly amplified tumors showed histological features of aggressiveness. Interestingly, accumulation of CNAs, as a measure of tumor mutational burden, was frequent and significantly associated to shortened survival. EGFR-amplified GBMs displayed both a higher number of concrete CNAs and a higher global tumor mutational burden than their no EGFR-amplified counterparts. In addition to genetic changes previously described in GBM, we found PARK2 and LARGE1 CNAs associated to EGFR amplification. The set of genes analyzed allowed us to explore relevant signaling pathways on GBM. Both PARK2 and LARGE1 are related to receptor tyrosine kinase/PI3K/PTEN/AKT/mTOR-signaling pathway. Finally, we found an association between the molecular pathways altered, EGFR amplification and a poor outcome.

Our results underline the potential interest of categorizing GBM according to their EGFR amplification level and the usefulness of assessing the tumor mutational burden. These approaches would open new knowledge possibilities related to GBM biology and therapy.