Synergistic effect of TRAIL and irradiation in elimination of glioblastoma stem-like cells

Immunosuppressive cells in oncolytic virotherapy for glioma: challenges and solutions

Glioblastoma is a highly aggressive form of brain cancer characterized by the abundance of myeloid lineage cells in the tumor microenvironment. Tumor-associated macrophages and microglia (TAM) and myeloid-derived suppressor cells (MDSCs), play a pivotal role in promoting immune suppression and tumor progression. Oncolytic viruses (OVs) are self-amplifying cytotoxic agents that can stimulate local anti-tumor immune responses and have the potential to suppress immunosuppressive myeloid cells and recruit tumor-infiltrating T lymphocytes (TILs) to the tumor site, leading to an adaptive immune response against tumors. However, the impact of OV therapy on the tumor-resident myeloid population and the subsequent immune responses are not yet fully understood. This review provides an overview of how TAM and MDSC respond to different types of OVs, and combination therapeutics that target the myeloid population to promote anti-tumor immune responses in the glioma microenvironment.

Radiation dose-escalation and dose-fractionation modulate the immune microenvironment, cancer stem cells and vasculature in experimental high-grade gliomas

BACKGROUND

In the context of high-grade gliomas (HGGs), very little evidence is available concerning the optimal radiotherapy (RT) schedule to be used in radioimmunotherapy combinations. This studied was aimed at shedding new light in this field by analyzing the effects of RT dose escalation and dose fractionation on the tumor microenvironment of experimental HGGs.

METHODS

Neurospheres (NS) CT-2A HGG-bearing C57BL/6 mice were treated with stereotactic RT. For dose-escalation experiments, mice received 2, 4 or 8 Gy as single administrations. For dose-fractionation experiments, mice received 4 Gy as a single fraction or multiple (1.33x3 Gy) fractions. The impact of the RT schedule on murine survival and tumor immunity was evaluated. Modifications of glioma stem cells (GSCs), tumor vasculature and tumor cell replication were also assessed.

RESULTS

RT dose-escalation was associated with an improved immune profile, with higher CD8⁺ T cells and CD8⁺ T cells/regulatory T cells (Tregs) ratio (P=0.0003 and P=0.0022, respectively) and lower total tumor associated microglia/macrophages (TAMs), M2 TAMs and monocytic myeloid derived suppressor cells (mMDSCs) (P=0.0011, P=0.0024 and P<0.0001, respectively). The progressive increase of RT dosages prolonged survival (P<0.0001) and reduced tumor vasculature (P=0.069), tumor cell proliferation (P<0.0001) and the amount of GSCs (P=0.0132 or lower). Compared to the unfractionated regimen, RT dose-fractionation negatively affected tumor immunity by inducing higher total TAMs, M2 TAMs and mMDSCs (P=0.0051, P=0.0036 and P=0.0436, respectively). Fractionation also induced a shorter survival (P=0.0078), a higher amount of GSCs (P=0.0015 or lower) and a higher degree of tumor cell proliferation (P=0.0003).

CONCLUSIONS

This study demonstrates that RT dosage and fractionation significantly influence survival, tumor immunity and GSCs in experimental HGGs. These findings should be taken into account when aiming at designing more synergistic and effective radio-immunotherapy combinations.

Current approaches in enhancing TRAIL therapies in glioblastoma

Glioblastoma (GBM) is the most prevalent, aggressive, primary brain cancer in adults and continues to pose major medical challenges due in part to its high rate of recurrence. Extensive research is underway to discover new therapies that target GBM cells and prevent the inevitable recurrence in patients. The pro-apoptotic protein tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted attention as an ideal anticancer agent due to its ability to selectively kill cancer cells with minimal toxicity in normal cells. Although initial clinical evaluations of TRAIL therapies in several cancers were promising, later stages of clinical trial results indicated that TRAIL and TRAIL-based therapies failed to demonstrate robust efficacies due to poor pharmacokinetics, resulting in insufficient concentrations of TRAIL at the therapeutic site. However, recent studies have developed novel ways to prolong TRAIL bioavailability at the tumor site and efficiently deliver TRAIL and TRAIL-based therapies using cellular and nanoparticle vehicles as drug loading cargos. Additionally, novel techniques have been developed to address monotherapy resistance, including modulating biomarkers associated with TRAIL resistance in GBM cells. This review highlights the promising work to overcome the challenges of TRAIL-based therapies with the aim to facilitate improved TRAIL efficacy against GBM.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

IFN‑β sensitizes TRAIL‑induced apoptosis by upregulation of death receptor 5 in malignant glioma cells

Tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL), a member of the tumor necrosis factor (TNF) family, induces apoptosis in cancer cells by binding to its receptors, death receptor 4 (DR4) and DR5, without affecting normal cells, and is therefore considered to be a promising antitumor agent for use in cancer treatment. However, several studies have indicated that most glioma cell lines display resistance to TRAIL‑induced apoptosis. To overcome such resistance and to improve the efficacy of TRAIL‑based therapies, identification of ideal agents for combinational treatment is important for achieving rational clinical treatment in glioblastoma patients. The main aim of this study was to investigate whether interferon‑β (IFN‑β) (with its pleiotropic antitumor activities) could sensitize malignant glioma cells to TRAIL‑induced apoptosis using glioma cell lines. TRAIL exhibited a dose‑dependent antitumor effect in all of the 7 types of malignant glioma cell lines, although the intensity of the effect varied among the cell lines. In addition, combined treatment with TRAIL (low clinical dose: 1 ng/ml) and IFN‑β (clinically relevant concentration: 10 IU/ml) in A‑172, AM‑38, T98G, U‑138MG and U‑251MG demonstrated a more marked antitumor effect than TRAIL alone. Furthermore, the antitumor effect of the combined treatment with TRAIL and IFN‑β may be enhanced via an extrinsic apoptotic system, and upregulation of DR5 was revealed to play an important role in this process in U‑138MG cells. These findings provide an experimental basis to suggest that combined treatment with TRAIL and IFN‑β may offer a new therapeutic strategy for malignant gliomas.