Developing immunotherapeutic strategies to target brain tumors

PEGylated Nanoliposomal Doxorubicin Conjugated with Specific TREM2 Peptides for Glioma-Targeting Therapy

PEGylated liposomes can deliver anti-cancer drugs to brain tumors, and achieve enhanced permeability and retention effects. Triggering receptor expressed on myeloid cells 2 (TREM2) is an excellent biomarker for precise therapy of glioma. The present study is aimed at designing PEGylated nanoliposomal doxorubicin (PLD) conjugated with peptides targeting TREM2 for glioma-targeting therapy. The specific peptides are designed with the Rosetta Peptiderive Protocol. Schrodinger's peptide-specific version of Glide is used for molecular docking. PLD modified with peptides (peptide-PLD) are engineered and prepared. Cell cycle, apoptosis, cell invasion and migration, cell viability, and colony-formation assays are performed to analyze glioma cell functions. The anti-tumor effects of peptide-PLD are validated in an intracranial U87-MG cells orthotopic glioma model. The targeting peptides HLRKLRKR and LRKLRLRL showed specific affinity for TREM2 and better cellular uptake in U87-MG cells. PLD with peptide modification demonstrated stable doxorubicin loading, small sizes (<60 nm), and enrichment in the mouse brain. Peptide-PLD treatment inhibited the Akt/GSK3β/β-catenin pathway, thereby inhibiting cell invasion and migration, and colony-forming ability in U87-MG cells. The peptide modification of PLD achieved better suppression of glioma development than PLD. Overall, TREM2-targeting peptides are successfully designed, and peptide-PLD served as a potent drug delivery carrier for glioma-targeting therapy.

Considerations when treating high-grade pediatric glioma patients with immunotherapy

INTRODUCTION

Children with high-grade gliomas (pHGGs) represent a clinical population in substantial need of new therapeutic options given the inefficacy and toxicity of current standard-of-care modalities. Although immunotherapy has emerged as a promising modality, it has yet to elicit a significant survival benefit for pHGG patients. While preclinical studies address a variety of underlying challenges, translational clinical trial design and management also need to reflect the most updated progress and lessons from the field.

AREAS COVERED

The authors will focus our discussion on the design of clinical trials, the management of potential toxicities, immune monitoring, and novel biomarkers. Clinical trial design should integrate appropriate patient populations, novel, and preclinically optimized trial design, and logical treatment combinations, particularly those which synergize with standard of care modalities. However, there are caveats due to the nature of immunotherapy trials, such as patient selection bias, evidenced by the frequent exclusion of patients on high-dose corticosteroids. Robust immune-modulating effects of modern immunotherapy can have toxicities. As such, it is important to understand and manage these, especially in pHGG patients.

EXPERT OPINION

Adequate integration of these considerations should allow us to effectively gain insights on biological activity, safety, and biomarkers associated with benefits for patients.

Identification of myeloid-derived suppressor cells that have an immunosuppressive function in NF2 patients

PURPOSE

There is no targeted drug therapy for NF2 patients, and surgery or radiosurgery is not always effective. Therefore, the exploration of new therapeutic pathways is urgently needed.

METHODS

We analyzed the expression of cytokines in the serum of NF2 patients and determined the percentage of HLA-DR^-CD33⁺CD11b⁺ cells in blood and NF2-associated schwannomas. Furthermore, we analyzed the role of HLA-DR^-CD33⁺CD11b⁺ cells in inhibiting T-cell proliferation, cytokine production, and transforming growth factor expression.

RESULTS

NF2 patients are in an immunosuppressed state with elevated IL-10 and TGF-β expression in plasma and the lymphocytes from NF2 patients secrete less IFN-γ and CD3⁺ T cells proliferate slower than normal healthy donors. HLA-DR^-CD33⁺CD11b⁺ cells frequency significantly increased in the PBMCs and infiltrated in the tumor, these cells express higher iNOS, NOX2 and TGF-β, and induce TGF-β secretion to inhibit CD8⁺ T-cell proliferation, and induce T-cell transformation to a CD4⁺CD25⁺Foxp3⁺ regulatory T cells phenotype. NF2-associated schwannoma cells induced monocytes transformation into an HLA-DR^-CD33⁺CD11b⁺ phenotype, and surgical removal of the tumor reduced the percentage of these cells.

CONCLUSIONS

HLA-DR^-CD33⁺CD11b⁺ cells may represent a population of MDSCs in NF2 patients. Dissecting the mechanisms behind these suppressive mechanisms will be helpful for the design of effective immunotherapeutic protocols and likely provide a new effective treatment for NF2 patients.

Hitting the nail on the head: combining oncolytic adenovirus-mediated virotherapy and immunomodulation for the treatment of glioma

Glioblastoma is a highly aggressive malignant brain tumor with a poor prognosis and the median survival 14.6 months. Immunomodulatory proteins and oncolytic viruses represent two treatment approaches that have recently been developed for patients with glioblastoma that could extend patient survival and result in better treatment outcomes for patients with this disease. Together, these approaches could potentially augment the treatment efficacy and strength of these anti-tumor therapies. In addition to oncolytic activities, this combinatory approach introduces immunomodulation locally only where cancerous cells are present. This thereby results in the change of the tumor microenvironment from immune-suppressive to immune-vulnerable via activation of cytotoxic T cells or through the removal of glioma cells immune-suppressive capability. This review discusses the strengths and weaknesses of adenoviral oncolytic therapy, and highlights the genetic modifications that result in more effective and targeted viral agents. Additionally, the mechanism of action of immune-activating agents is described and the results of previous clinical trials utilizing these treatments in other solid tumors are reviewed. The feasibility, synergy, and limitations for treatments that combine these two approaches are outlined and areas for which more work is needed are considered.

Nanoparticulate Tetrac Inhibits Growth and Vascularity of Glioblastoma Xenografts

Thyroid hormone as L-thyroxine (T₄) stimulates proliferation of glioma cells in vitro and medical induction of hypothyroidism slows clinical growth of glioblastoma multiforme (GBM). The proliferative action of T₄ on glioma cells is initiated nongenomically at a cell surface receptor for thyroid hormone on the extracellular domain of integrin αvβ3. Tetraiodothyroacetic acid (tetrac) is a thyroid hormone derivative that blocks T₄ action at αvβ3 and has anticancer and anti-angiogenic activity. Tetrac has been covalently bonded via a linker to a nanoparticle (Nanotetrac, Nano-diamino-tetrac, NDAT) that increases the potency of tetrac and broadens the anticancer properties of the drug. In the present studies of human GBM xenografts in immunodeficient mice, NDAT administered daily for 10 days subcutaneously as 1 mg tetrac equivalent/kg reduced tumor xenograft weight at animal sacrifice by 50%, compared to untreated control lesions (p < 0.01). Histopathological analysis of tumors revealed a 95% loss of the vascularity of treated tumors compared to controls at 10 days (p < 0.001), without intratumoral hemorrhage. Up to 80% of tumor cells were necrotic in various microscopic fields (p < 0.001 vs. control tumors), an effect attributable to devascularization. There was substantial evidence of apoptosis in other fields (p < 0.001 vs. control tumors). Induction of apoptosis in cancer cells is a well-described quality of NDAT. In summary, systemic NDAT has been shown to be effective by multiple mechanisms in treatment of GBM xenografts.