Molecular and Clinicopathological Characterization of a Prognostic Immune Gene Signature Associated With MGMT Methylation in Glioblastoma

Background: O6-methylguanine-DNA methyltransferase (MGMT) methylation status affects tumor chemo-resistance and the prognosis of glioblastoma (GBM) patients. We aimed to investigate the role of MGMT methylation in the regulation of GBM immunophenotype and discover an effective biomarker to improve prognosis prediction of GBM patients. Methods: A total of 769 GBM patients with clinical information from five independent cohorts were enrolled in the present study. Samples from the Cancer Genome Atlas (TCGA) dataset were used as the training set, whereas transcriptome data from the Chinese Glioma Genome Atlas (CGGA) RNA-seq, CGGA microarray, GSE16011, and the Repository for Molecular Brain Neoplasia (REMBRANDT) cohort were used for validation. A series of bioinformatics approaches were carried out to construct a prognostic signature based on immune-related genes, which were tightly related to the MGMT methylation status. In silico analyses were performed to investigate the influence of the signature on immunosuppression and remodeling of the tumor microenvironment. Then, the utility of this immune gene signature was analyzed by the development and evaluation of a nomogram. In vitro experiments were further used to verify the immunologic function of the genes in the signature. Results: We found that MGMT unmethylation was closely associated with immune-related biological processes in GBM. Sixty-five immune genes were more highly expressed in the MGMT unmethylated than the MGMT-methylated group. An immune gene-based risk model was further established to divide patients into high and low-risk groups, and the prognostic value of this signature was validated in several GBM cohorts. Functional analyses manifested a universal up-regulation of immune-related pathways in the high-risk group. Furthermore, the risk score was highly correlated to the immune cell infiltration, immunosuppression, inflammatory activities, as well as the expression levels of immune checkpoints. A nomogram was developed for clinical application. Knockdown of the five genes in the signature remodeled the immunosuppressive microenvironment by restraining M2 macrophage polarization and suppressing immunosuppressive cytokines production. Conclusions: MGMT methylation is strongly related to the immune responses in GBM. The immune gene-based signature we identified may have potential implications in predicting the prognosis of GBM patients and mechanisms underlying the role of MGMT methylation.

Immune Checkpoint Inhibitors in Gliomas

PURPOSE OF REVIEW

Malignant gliomas result in disproportionately high morbidity and mortality compared with other primary tumors, and progression of disease is inevitable. Novel therapies to improve outcomes are needed and immune checkpoint inhibitors hold significant promise.

RECENT FINDINGS

A limited body of preclinical evidence suggests that checkpoint inhibitors may be effective treatment for gliomas. Biomarkers to identify characteristics of gliomas responsive to these therapies will be essential. These may include mismatch repair deficiency and high mutational load that might be germline, somatic, or acquired after therapy. Evidence on the use of immune checkpoint inhibitors in gliomas is evolving. Clinical trials are underway and results are eagerly awaited. Understanding the role of immune checkpoint inhibitors in combination with other treatment modalities for gliomas is crucial to the improvement of outcomes. The design and conduct of future clinical trials need to account for increasingly complex treatment options.

Prospect of Immunotherapy for Glioblastoma: Tumor Vaccine, Immune Checkpoint Inhibitors and Combination Therapy

To date, clinical trials of various vaccine therapies using autologous tumor antigens or tumor-associated/specific antigen peptide with adjuvants have been performed to treat patients with high-grade gliomas (HGG). Furthermore, immune checkpoint pathway-targeted therapies including anti- programmed cell death 1 (PD-1) antibody have been remarkably effective in other neoplasms, and various clinical trials with anti-PD-1 antibody in patients with HGG have started to date. It is possible that up-regulation of immune checkpoint molecules in tumor tissues after vaccine therapy may be one of the mechanisms of vaccine failure. Multiple preclinical studies indicate that combination therapy with vaccination and immune checkpoint blockade is effective for the treatment of malignant tumors including HGG. Thus, immunotherapy, especially combination therapy with vaccine and immune checkpoint inhibitors, may be a promising strategy for treatment of patients with HGG.

Ipilimumab and Bevacizumab in Glioblastoma

The median survival in glioblastoma is just over a year, with no standard second-line therapy. Ipilimumab is an immune checkpoint inhibitor that activates the anti-tumour immune response by cytotoxic T-lymphocyte antigen-4 blockade. There is significant evidence supporting its role in the treatment of malignant melanoma, including in patients with brain metastases. The addition of the anti-angiogenesis agent, bevacizumab, seems to offer additional benefit and limit the immune-related side-effects of ipilimumab in melanoma. To date there have been no clinical trials investigating this combination in glioblastoma. In this single practice case series, 20 patients with glioblastoma were consented for and treated with ipilimumab and bevacizumab in combination. Safety, tolerability and the response to treatment were reviewed for all patients. Three patients were treated after palliative first-line radiotherapy, one patient after first-line chemoradiation and 16 patients were treated with recurrent disease. Sixty-five per cent of patients completed four cycles of 3 weekly ipilimumab therapy, administered with 2 weekly bevacizumab. Radiographic responses for patients with recurrent disease were evaluated by Response Assessment in Neuro-oncology (RANO) criteria; 31% of patients showed a partial response, 31% had stable disease and 38% had disease progression. The treatment combination was well tolerated, with treatment terminated before completion due to adverse events in two patients. Autoimmune toxicity was manageable with systemic corticosteroid therapy. Ipilimumab and bevacizumab in combination show promising activity with a predictable and manageable toxicity profile, warranting further clinical studies.

Developing immunotherapeutic strategies to target brain tumors

INTRODUCTION

Recent years have seen rapid growth in cancer treatments that enhance the anti-tumor activities of the immune system. Collectively known as immunotherapy, modulation of the immune system has shown success treating some hematological malignancies, but has yet to be successfully applied to the treatment of patients with brain tumors.

AREAS COVERED

This review highlights mechanistic insights from murine studies and compiled recent clinical trial data, focusing on the most aggressive brain tumor, glioblastoma (GBM). The field has recently accumulated a critical mass of data, and we discuss past treatment failures in the context of newly developed approaches now entering clinical trials. This article provides an overview of the immunotherapeutic armamentarium currently in development for the treatment of patients with GBM, who are in dire need of safe and effective therapies. Expert commentary: Themes that emerge include the importance of mitigating the effects of an immunosuppressive tumor microenvironment and the potential for innate immune cell activation to enhance cytotoxic anti-tumor activity. Consideration of these studies as a collective may inform the design of new immunotherapies, as well as the immune monitoring protocols for patients participating in clinical trials.

Recurrent glioblastoma: Current patterns of care in an Australian population

This retrospective population-based survey examined current patterns of care for patients with recurrent glioblastoma (rGBM) who had previously undergone surgery and post-operative therapy at original diagnosis. The patients were identified from the Victorian Cancer Registry (VCR) from 2006 to 2008. Patient demographics, tumour characteristics and oncological management were extracted using a standardised survey by the treating clinicians/VCR staff and results analysed by the VCR. Kaplan-Meier estimates of overall survival (OS) at diagnosis and progression were calculated. A total of 95 patients (48%) received treatment for first recurrence; craniotomy and post-operative treatment (38), craniotomy only (34) and non-surgical treatment (23). Patients receiving treatment at first progression had a higher median OS than those who did not (7 versus 3 months, p<0.0001). All patients progressed after treatment for first progression with 43 patients (45%) receiving treatment at second progression. To our knowledge this is the first population-based pattern of care survey of treatment for rGBM in an era where post-operative "Stupp" chemo-radiation is standard. First and second line therapy for rGBM is common and associated with significant benefit. Treatment generally includes re-resection and/or systemic therapy.