A total of 298 articles were identified until 26 April 2021. After completion of the full-text review, 20 studies were included for the purpose of this systematic review.
Numerous preclinical and clinical trials have been conducted for DMG. Here we summarize the results of the clinical trials available in the scientific literature as well as promising treatments that are in development. Table 1, found in Appendix A, presents a summary of past clinical trials and promising preclinical studies for DMG.
Park (2021)
This study demonstrated that a progression free survival at 6 months after radiotherapy significantly improved survival in adult patients with DMG while surgical extent did not improve survival, suggesting the important role of radiotherapy in patients with adult brain DMG [23].
Chi (2019)
ONC 201 is a selective dopamine D2 receptor antagonist that can cross the blood-brain barrier. This study was of 14 patients (7 adults and 7 children) with K27M mutant DMG or DIPG with prior radiotherapy. They were given adjuvant ONC201 therapy once weekly. The progression free survival rate was 14 weeks, and the overall survival was 17 weeks. 4 of the adults are continuing therapy. Clinical and radiographic improvements were appreciated [24].
Li (2020)
Retrospective institutional review between 1984 to 2019 of 108 patients with DMG, 62 of which need ventricular shunting for treatment of HCP. VAD (ventricular access device) placement was shown to adequately manage HCP in patients with DMG while also showing promise as a method of disease monitoring via CSF analysis [19].
ONC201
ONC201 is a selective DRD2 antagonist capable of crossing the blood brain barrier and exhibits p53-independent anti-cancer efficacy in preclinical models of high-grade glioma. Furthermore, ONC201 activates the integrated stress response (ISR) and inactivates Akt/ERK along with other pro-survival signaling pathways. In one case study, ONC201 was administered to a 10-year-old female following unsuccessful radiotherapy. Treatment with ONC201 proved to be effective as it decreased tumor volume by 44% and significantly improved the patient’s hearing and grade IV facial palsy. Another study with 18 patients aged 3 to 42 years also showed promising outcomes. The median overall survival for patients with recurrent disease (n=14) was 17 weeks. Some patients experienced a stabilization and subsequent reduction in tumor size with one adult patient even experiencing a full response after 10 months of treatment.2,4 While these results are promising, these studies did not account for prior therapies in some patients potentially confounding interpretation. More research will need to be conducted to evaluate the true effect of OCN201 on DMG [24, 25].
Olaparib in combination with Bevacizumab
Olaparib is a poly-adenosine diphosphate-ribose polymerase (PARP) inhibitor shown to inhibit gliomas in preclinical trials. Preliminary studies have demonstrated that PARP inhibitors elicit a therapeutic response independent of BRCA1/2 status or homologous recombination deficiency (HRD). Furthermore, olaparib is believed to be effective against tumors harboring TP53 mutations. Olaparib has been used in combination with bevacizumab for patients with advanced ovarian cancer and has resulted in favorable outcomes. One case study of a 37-year-old female treated with olaparib and bevacizumab reported the complete remission of DMG after approximately 7 months of treatment. Unfortunately, the patient relapsed the following month and died two months later resulting in an overall survival of 16 months. Though the patient passed, this case study demonstrated the potential to use olaparib and bevacizumab for the treatment of DMG. Clinical trials investigating the efficacy of Olaparib for tumors harboring TP53 mutations are currently being conducted [26].
Nimotuzumab
Nimotuzumab is a recombinant monoclonal antibody for the epidermal growth factor (EGF) receptor. 80 to 85% of pediatric high-grade gliomas overexpress the EGF receptor. Nimotuzumab mediates anti-neoplastic effects by antagonizing the intrinsic tyrosine kinase activity of the EGF receptor. A phase III clinical study with 42 patients aged 3 to 20-years-old administered nimotuzumab in combination with radiotherapy. The resulting median overall survival was 9.4 months. The longest overall survival period was 47.4 months. While this treatment method may not have favorable outcomes when compared with other treatments described in this paper, it is worth noting because of the low toxicity of the drug.
Ribociclib
Ribociclib is an orally bioavailable inhibitor of cyclin D-CDK4/6, which induces cell-cycle arrest by maintaining the tumor suppressor protein retinoblastoma (RB) in a hypophosphorylated, active state. In one study, ribociclib was administered to 10 RB+ patients, 9 diagnosed with diffuse intrinsic pontine glioma (DIPG) and 1 diagnosed with DMG, following their radiotherapy. The ages of the 10 patients ranged from 3.7 to 19.8 years old. The outcomes for the DIPG patients were a 1-year overall survival of 89% and a mean overall survival of 16.1 months with a range of 10–30 months. The overall survival for the DMG patient was 6 months. The results from this study have spurred additional clinical trials investigating the efficacy of a combination study with everolimus, and a second study evaluating how effectively ribociclib reaches target tissues in pediatric brain tumors [28].
H3.3K27M-Specific Vaccines
The H3.3K27M mutation is seen in most patients with DMG and more than 70% of patients with DIPG. The H3.3K27M protein contains a 10 mer peptide sequence, spanning position 26–35, that can function as an HLA-A*02:01–restricted cytotoxic T lymphocyte (CTL) epitope. In one clinical trial, a synthetic H3.3K27M26–35 peptide vaccine was administered to 29 patients following completion of radiotherapy. 39% of patients developed an immunological response and generated sufficient levels of H3.3K27M-reactive CD8+ T cells. The median OS of immunological responders was 16.3 months compared with 9.9 months for nonresponders. This data suggests that patients who mount a sufficient immune response will have a better prognosis when treated with this vaccine. As such, concurrent administration of corticosteroids, such as dexamethasone, should be avoided when utilizing this treatment regimen [29].
Convection-Enhanced Delivery
One of the challenges of administrating chemotherapeutic agents is the difficulty of crossing the blood brain barrier (BBB). Even drugs that cross the BBB may not be distributed in the desired manner. Convection-enhanced delivery (CED) is a new therapeutic strategy that allows for targeted release of a drug into a specific region via a cannula thereby bypassing the BBB. CED also allows for the continuous infusion of drugs at a steady rate over a prolonged period, which has been shown to be more effective than single dose administration systems.8 In a phase 1 clinical trial, omburtamab was administered via CED. Omburtamab is a monoclonal antibody that binds the membrane-bound protein CD276, an immune modulator, which is frequently overexpressed in DMG. Although the trial is still incomplete, the children treated at the time of the paper have a median overall survival of 17.5 months and a 1-year survival rate of 58.5%. There are currently other trials underway examining the efficacy of delivering other agents such as IL13-Pseudomonas toxin, Panobinostat, and DNX-2401 via CED [30, 31].
Role of Imaging and Treatment Outcomes in Pediatric DMG Patients
The association and role of metabolic imaging in relation to diagnosis and treatment within diffuse intrinsic pontine gliomas (DIPGs), a DMG subgroup, is not currently well understood. Investigation of 11C-methionine uptake intensity after baseline and post-treatment 11C-methionine PET/CT scans in a group of 22 pediatric patients with a diagnosis of DIPG was conducted. While the 11C-methionine uptake was correlated with an elevated risk of recurrence, no strong correlation was found between uptake and treatment outcomes among the pediatric patients in this study [32].
H3.3 K27M Mutation Impact on DMG Prognosis
The H3.3 K27M mutation is found in certain rare Diffuse Midline Gliomas (DMGs). The 2016 guidelines set by the World Health Organization (WHO) reclassified DMG H3.3 K27M mutants as grade IV spinal cord gliomas, and as such the prognostic factors for this new classification were explored by analyzing data among 25 patients diagnosed with a grade IV spinal cord glioma. The H3.3 K27M mutation was found to not be a major poor prognostic factor among these patients [33].
DIPG Intratumoral Pharmacokinetics Investigation
An absence or lack of intratumoral penetration has been suspected in the failure of many systemic chemotherapy trials. Utilization of gemcitabine as a model agent for assessment of DIPG intratumoral pharmacokinetics in a small Phase 0 clinical trial among pediatric patients has shown otherwise. Models of orthotopic patient-derived xenograft (PDX) models of DIPG and H3K27M pediatric glioblastomas were shown to have comparable levels and clearance of gemcitabine. This finding supports the idea that orthotopic PDX models may be utilized to successfully model human DIPG [34].
Treatment and survival of DMG relapse
This is a discussion of DMG relapse and a comparison of factors influencing long and short-term survival. Receiving a second radiotherapy at the time of relapse improved survival. Additionally, Steroid-independent patients had better survival after relapse, potentially due to the relapse disease being lesser in severity. Majority of long survivors had a lansky play score above 50% [35].
Use of F-DOPA PET in predicting DMG treatment response
The role of F-DOPA PET and MRI in predicting treatment response of DMG was studied. It was found that a ratio of F-DOPA uptake of tumor/uptake of striatum greater than 1 showed an overall survival less than or equal to 1 year. This ratio also presented a smaller reduce in tumor volume following treatment [36].
Efficacy of biopsy in diagnosis and treatment decision
Analysis of seven pediatric patients undergoing biopsy for intrinsic brainstem lesions was conducted to clarify who would benefit from biopsy. Based on MRI findings, the cases analyzed were considered atypical for DMGs. Patients with intrinsic pontine lesions that expand beyond the pons or with localized enhancing portion benefit from the biopsy [37].
DMG Subclasses based on oncogenic pathways
The differences between DMG and supratentorial HGG and the two subgroups of DMG were examined. The study found different patterns of expression of HLH genes and upregulation of GAL3ST1, MAFB, OLIG2 and HOXA2, 3 and 4 in DMG compared to HGG.
DMG arises from two distinct oncogenic pathways. The first group of DMG exhibited an oligodendroglial phenotype associated with PDGFRA gain/amplification. The second group of DMG exhibited a mesenchymal and pro-angiogenic phenotype. The first group had worse survival [38].
DMG mutations, clinical features, surgical treatments and survival analysis
Analysis of 43 cases of DMG and examination of clinical features, surgical treatment, molecular characteristics and survival was conducted. Limb weakness or numbness was the most frequently observed symptom. Partial resection and subtotal resection were performed in the majority of patients. Loss of expression of H3K27me3 and ATRX while p53 was overexpressed and demonstrated worse prognosis. Better preoperative Preoperative Karnofsky Performance Score and treatment with adjuvant radiotherapy showed better prognosis [39].
Response to chemotherapy/predict prognosis based on T2-FLAIR mismatch
T2-FLAIR mismatch in DMG could indicate better outcome of radiotherapy. 21 patients with DIPG were included in the study and T2-FLAIR mismatch was found in 5. All patients received radiotherapy. Response rate of radiotherapy in patients positive for T2-FLAIR mismatch was 100%, while it was 25.0% in patients negative for T2-FLAIR mismatch [40].