Blood-Brain Barrier in Brain Tumors: Biology and Clinical Relevance

Superenhancers as master gene regulators and novel therapeutic targets in brain tumors

Transcriptional deregulation, a cancer cell hallmark, is driven by epigenetic abnormalities in the majority of brain tumors, including adult glioblastoma and pediatric brain tumors. Epigenetic abnormalities can activate epigenetic regulatory elements to regulate the expression of oncogenes. Superenhancers (SEs), identified as novel epigenetic regulatory elements, are clusters of enhancers with cell-type specificity that can drive the aberrant transcription of oncogenes and promote tumor initiation and progression. As gene regulators, SEs are involved in tumorigenesis in a variety of tumors, including brain tumors. SEs are susceptible to inhibition by their key components, such as bromodomain protein 4 and cyclin-dependent kinase 7, providing new opportunities for antitumor therapy. In this review, we summarized the characteristics and identification, unique organizational structures, and activation mechanisms of SEs in tumors, as well as the clinical applications related to SEs in tumor therapy and prognostication. Based on a review of the literature, we discussed the relationship between SEs and different brain tumors and potential therapeutic targets, focusing on glioblastoma.

Microenvironment and the progress of immunotherapy in clinical practice of NSCLC brain metastasis

One of the most frequent distant metastases of lung cancer occurs in the brain. The average natural survival duration for patients with lung cancer who have brain metastases is about 1 to 2 months. Knowledge about brain metastases is currently restricted since they are more difficult to acquire than other metastases. This review begins with an analysis of the immune microenvironment of brain metastases; focuses primarily on the functions of microglia, astrocytes, neurons, and tumor-infiltrating lymphocytes in the microenvironment of brain metastases; and offers an atlas of the immune microenvironment of brain metastases involving significant cells. In an effort to give researchers new research ideas, the study also briefly covers how immunotherapy for non-small cell lung cancer with brain metastases is currently faring.

Brain Metastasis from HER2-Positive Breast Cancer: An Evolving Landscape

Trastuzumab deruxtecan is a HER2-directed antibody-drug conjugate with ability to cross the blood-tumor barrier and activity on brain metastases. To test the activity of new drugs, patient-derived xenograft models from human brain metastases and phase 0 and window-of-opportunity trials are of utmost importance. See related article by Kabraji et al., p. 174.

The role of irreversible pan-HER tyrosine kinase inhibitors in the treatment of HER2-Positive metastatic breast cancer

Human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) is the leading cause of cancer death in women. For patients with HER2-positive MBC, after the failure of multiple lines of treatment, there is no optimal line of therapy. A series of clinical trials confirmed that treatment with irreversible pan-HER tyrosine kinase inhibitors (TKIs) in combination with chemotherapy significantly improves patients' survival outcomes. This review focuses on the pathogenesis of HER2-positive breast cancer, current standard treatments, mechanisms of approved irreversible TKIs, and key clinical trials. The available findings suggest that irreversible pan-HER TKIs, such as pyrotinib and neratinib, in combination with chemotherapy, represent a beneficial salvage therapy for patients with HER2-positive MBC with manageable toxicity. However, further studies are needed to assess the efficacy and safety of this combination therapy.

Convection-enhanced delivery of immunomodulatory therapy for high-grade glioma

The prognosis for glioblastoma has remained poor despite multimodal standard of care treatment, including temozolomide, radiation, and surgical resection. Further, the addition of immunotherapies, while promising in a number of other solid tumors, has overwhelmingly failed in the treatment of gliomas, in part due to the immunosuppressive microenvironment and poor drug penetrance to the brain. Local delivery of immunomodulatory therapies circumvents some of these challenges and has led to long-term remission in select patients. Many of these approaches utilize convection-enhanced delivery (CED) for immunological drug delivery, allowing high doses to be delivered directly to the brain parenchyma, avoiding systemic toxicity. Here, we review the literature encompassing immunotherapies delivered via CED-from preclinical model systems to clinical trials-and explore how their unique combination elicits an antitumor response by the immune system, decreases toxicity, and improves survival among select high-grade glioma patients.

Imaging blood-brain barrier dysfunction: A state-of-the-art review from a clinical perspective

The blood-brain barrier (BBB) consists of specialized cells that tightly regulate the in- and outflow of molecules from the blood to brain parenchyma, protecting the brain's microenvironment. If one of the BBB components starts to fail, its dysfunction can lead to a cascade of neuroinflammatory events leading to neuronal dysfunction and degeneration. Preliminary imaging findings suggest that BBB dysfunction could serve as an early diagnostic and prognostic biomarker for a number of neurological diseases. This review aims to provide clinicians with an overview of the emerging field of BBB imaging in humans by answering three key questions: (1. Disease) In which diseases could BBB imaging be useful? (2. Device) What are currently available imaging methods for evaluating BBB integrity? And (3. Distribution) what is the potential of BBB imaging in different environments, particularly in resource limited settings? We conclude that further advances are needed, such as the validation, standardization and implementation of readily available, low-cost and non-contrast BBB imaging techniques, for BBB imaging to be a useful clinical biomarker in both resource-limited and well-resourced settings.

Tyrosine Kinase Inhibitors for Glioblastoma Multiforme: Challenges and Opportunities for Drug Delivery

Glioblastoma multiforme (GBM) is an aggressive brain tumor with high mortality rates. Due to its invasiveness, heterogeneity, and incomplete resection, the treatment is very challenging. Targeted therapies such as tyrosine kinase inhibitors (TKIs) have great potential for GBM treatment, however, their efficacy is primarily limited by poor brain distribution due to the presence of the blood-brain barrier (BBB). This review focuses on the potential of TKIs in GBM therapy and provides an insight into the reasons behind unsuccessful clinical trials of TKIs in GBM despite the success in treating other cancer types. The main section is dedicated to the use of promising drug delivery strategies for targeted delivery to brain tumors. Use of brain targeted delivery strategies can help enhance the efficacy of TKIs in GBM. Among various drug delivery approaches used to bypass or cross BBB, utilizing nanocarriers is a promising strategy to augment the pharmacokinetic properties of TKIs and overcome their limitations. This is because of their advantages such as the ability to cross BBB, chemical stabilization of drug in circulation, passive or active targeting of tumor, modulation of drug release from the carrier, and the possibility to be delivered via non-invasive intranasal route.

Ultrasonic-induced reversible blood–brain barrier opening: Safety evaluation into the cellular level

An important function of the blood–brain barrier (BBB) is to protect the central nervous system and maintain its homeostasis, but it is also a major barrier to the intervention and treatment of neurological diseases. Our study aimed at opening the BBB using a noninvasive method, focused ultrasound, screening for 16 different parameter combinations of frequency, peak voltage (Ppeak) and irradiation time. Comparing the results of hematoxylin–eosin staining, serum oxidative damage factor and TUNEL staining under various conditions, we obtained a parameter combination that did not lead to oxidative stress injury and apoptosis: 0.8 mHz + 900 mVpp + 90 s. It will be used as a safety parameter for BBB opening treatment of Parkinson’s disease in our subsequent experiments. In addition, the closing time after the BBB opening was verified in magnetic resonance imaging contrast examination and at the tissue level. It is worth mentioning that, different from previous studies, we focused on damage assessment at cellular and molecular levels.

Oncolytic Viral Therapy for Malignant Glioma and Their Application in Clinical Practice

Glioblastoma is the most common primary malignant brain tumor in adults and outcomes remain poor despite the current standard of care multimodal therapy. Oncolytic virotherapy utilizes engineered viruses to exert an anti-tumor effect via both direct oncolysis and stimulation of an immune response within the tumor microenvironment, turning tumors from "cold" to "hot." This has shown promise as a novel therapeutic modality and attempts to circumvent the challenges associated with traditional treatments. Many oncolytic viruses have been investigated in completed and ongoing clinical trials and while safety has been demonstrated, clinical outcomes have been variable, often with only a subgroup of patients showing a significant response. This review summarizes these studies, addresses relevant technical aspects of oncolytic virus administration, and highlights practical considerations to assist providers in appropriately caring for patients treated with oncolytic virotherapy. Additionally, future directions within the field that may help to maximize efficacy of this modality are discussed.

EGFR mutation prevalence, real-world treatment patterns, and outcomes among patients with resected, early-stage, non-small cell lung cancer in Canada

OBJECTIVES

The ADAURA trial demonstrated the benefit of adjuvant osimertinib among patients with resected, early-stage, epidermal growth factor receptor-mutated (EGFRm) non-small cell lung cancer (NSCLC). To understand the potential population impact, it is critical to deduce the prevalence, management, and outcomes of this patient population in the real-world setting before use of adjuvant osimertinib.

MATERIALS AND METHODS

Using PALEOS (Pan-cAnadian Lung cancEr Observational Study) data (2012-2019), a retrospective, multi-center, observational cohort study was conducted among patients with early-stage (IB-IIIA) resected NSCLC who had not received neoadjuvant therapy. Study outcomes included EGFRm prevalence, treatment patterns, recurrence outcomes, and overall and disease-free survival (OS/DFS).

RESULTS

Among patients undergoing reflexive EGFRm testing by a pathologist at time of diagnosis irrespective of disease stage (N = 535), 23 % were EGFRm-positive; 15.9 % had common mutations and 5.6 % had uncommon mutations. Within the EGFRm-positive cohort (N = 156), mean age at diagnosis was 68 years, 65 % of patients were female, and 35 % were of Asian descent. At diagnosis, 48 %, 31 %, and 21 % had stage IB, II, or IIIA disease, respectively; 46 % received adjuvant therapy after resection. Half of patients experienced disease recurrence, typically involving distant sites; central nervous system metastasis varied from 12 % to 15.0 % across disease stages. EGFR tyrosine kinase inhibitors were the most commonly received therapy after first metastatic recurrence. Median OS (DFS) was not reached, 71.2 (22.8) months, and 50.1 (18.0) months among stage IB, II, and IIIA patients. Patients with uncommon EGFRm had a lower probability of survival than those with common EGFRm (2 years: 87 % vs 91 %-94 %; 4 years: 56 % vs 73 %-82 %).

CONCLUSION

Approximately-one-quarter of patients with resected, early-stage NSCLC were EGFRm-positive in this study. These patients had high recurrence rates and suboptimal long-term survival after treatment with current therapies. New adjuvant treatments are warranted.

New Advances in Biomedical Application of Polymeric Micelles

In the last decade, nanomedicine has arisen as an emergent area of medicine, which studies nanometric systems, namely polymeric micelles (PMs), that increase the solubility and the stability of the encapsulated drugs. Furthermore, their application in dermal drug delivery is also relevant. PMs present unique characteristics because of their unique core-shell architecture. They are colloidal dispersions of amphiphilic compounds, which self-assemble in an aqueous medium, giving a structure-type core-shell, with a hydrophobic core (that can encapsulate hydrophobic drugs), and a hydrophilic shell, which works as a stabilizing agent. These features offer PMs adequate steric protection and determine their hydrophilicity, charge, length, and surface density properties. Furthermore, due to their small size, PMs can be absorbed by the intestinal mucosa with the drug, and they transport the drug in the bloodstream until the therapeutic target. Moreover, PMs improve the pharmacokinetic profile of the encapsulated drug, present high load capacity, and are synthesized by a reproducible, easy, and low-cost method. In silico approaches have been explored to improve the physicochemical properties of PMs. Based on this, a computer-aided strategy was developed and validated to enable the delivery of poorly soluble drugs and established critical physicochemical parameters to maximize drug loading, formulation stability, and tumor exposure. Poly(2-oxazoline) (POx)-based PMs display unprecedented high loading concerning water-insoluble drugs and over 60 drugs have been incorporated in POx PMs. Among various stimuli, pH and temperature are the most widely studied for enhanced drug release at the site of action. Researchers are focusing on dual (pH and temperature) responsive PMs for controlled and improved drug release at the site of action. These dual responsive systems are mainly evaluated for cancer therapy as certain malignancies can cause a slight increase in temperature and a decrease in the extracellular pH around the tumor site. This review is a compilation of updated therapeutic applications of PMs, such as PMs that are based on Pluronics^®, micelleplexes and Pox-based PMs in several biomedical applications.

Nanotechnology-Based Combinatorial Anti-Glioblastoma Therapies: Moving from Terminal to Treatable

Aggressive glioblastoma (GBM) has no known treatment as a primary brain tumor. Since the cancer is so heterogeneous, an immunosuppressive tumor microenvironment (TME) exists, and the blood–brain barrier (BBB) prevents chemotherapeutic chemicals from reaching the central nervous system (CNS), therapeutic success for GBM has been restricted. Drug delivery based on nanocarriers and nanotechnology has the potential to be a handy tool in the continuing effort to combat the challenges of treating GBM. There are various new therapies being tested to extend survival time. Maximizing therapeutic effectiveness necessitates using many treatment modalities at once. In the fight against GBM, combination treatments outperform individual ones. Combination therapies may be enhanced by using nanotechnology-based delivery techniques. Nano-chemotherapy, nano-chemotherapy–radiation, nano-chemotherapy–phototherapy, and nano-chemotherapy–immunotherapy for GBM are the focus of the current review to shed light on the current status of innovative designs.

Brain Cancer Chemotherapy through a Delivery System across the Blood-Brain Barrier into the Brain Based on Receptor-Mediated Transcytosis Using Monoclonal Antibody Conjugates

Advances in pharmacotherapy have brought extraordinary benefits to humanity. However, unmet medical needs in patients remain, particularly in the treatment of central nervous system (CNS) diseases and cancers. CNS drug delivery into the brain across the endothelium is difficult due to the blood-brain barrier (BBB), which is composed mainly of tight junctions and efflux transporters, such as multiple drug resistance 1 (MDR1) (P-glycoprotein). On the other hand, the development of anti-cancer drugs is a challenging task due to their frequent off-target side effects and the complicated mechanisms of cancer pathogenesis and progression. Brain cancer treatment options are surgery, radiation therapy, and chemotherapy. It is difficult to remove all tumor cells, even by surgical removal after a craniotomy. Accordingly, innovative brain cancer drugs are needed. Currently, antibody (Ab) drugs that show high therapeutic effects are often used clinically. Furthermore, antibody-drug conjugates (ADCs), such as trastuzumab deruxtecan, an anti-HER2 (human epidermal receptor 2) ADC with low-molecular cancer drugs through the suitable linker, have been developed. In the case of trastuzumab deruxtecan, it is internalized into cancer cells across the membrane via receptor-mediated endocytosis. Moreover, it is reported that drug delivery into the brain across the BBB was carried out via receptor-mediated transcytosis (RMT), using anti-receptor Abs as a vector against the transferrin receptor (TfR) or insulin receptor (InsR). Thus, anti-TfR ADCs with cancer drugs are promising brain cancer agents due to their precise distribution and low side effects. In this review, I introduce the implementations and potential of brain cancer drug delivery into the brain across the BBB, based on RMT using ADCs.

Hypermutation as a potential predictive biomarker of immunotherapy efficacy in high-grade gliomas: a broken dream?

A high tumor mutational burden and mismatch repair deficiency are observed in 'hypermutated' high-grade gliomas (HGGs); however, the molecular characterization of this distinct subtype and whether it predicts the response to immune checkpoint inhibitors (ICIs) are largely unknown. Pembrolizumab is a valid therapeutic option for the treatment of hypermutated cancers of diverse origin, but only a few clinical trials have explored the activity of ICIs in hypermutated HGGs. HGGs appear to differ from other cancers, likely due to the prevalence of subclonal versus clonal neoantigens, which are unable to elicit an immune response with ICIs. The main aim of this review is to summarize the current knowledge on hypermutation in HGGs, focusing on the broken promises of tumor mutational burden and mismatch repair deficiency as potential biomarkers of response to ICIs.

Adoptive Cell Therapy in Pediatric and Young Adult Solid Tumors: Current Status and Future Directions

Advances from novel adoptive cellular therapies have yet to be fully realized for the treatment of children and young adults with solid tumors. This review discusses the strategies and preliminary results, including T-cell, NK-cell and myeloid cell-based therapies. While each of these approaches have shown some early promise, there remain challenges. These include poor trafficking to the tumor as well as a hostile tumor microenvironment with numerous immunosuppressive mechanisms which result in exhaustion of cellular therapies. We then turn our attention to new strategies proposed to address these challenges including novel clinical trials that are ongoing and in development.

Antibody-Based Formats to Target Glioblastoma: Overcoming Barriers to Protein Drug Delivery

Glioblastoma (GB) is recognized as the most aggressive form of primary brain cancer. Despite advances in treatment strategies that include surgery, radiation, and chemotherapy, the median survival time (∼15 months) of patients with GB has not significantly improved. The poor prognosis of GB is also associated with a very high chance of tumor recurrence (∼90%), and current treatment measures have failed to address the complications associated with this disease. However, targeted therapies enabled through antibody engineering have shown promise in countering GB when used in combination with conventional approaches. Here, we discuss the challenges in conventional as well as future GB therapeutics and highlight some of the known advantages of using targeted biologics to overcome these impediments. We also review a broad range of potential alternative routes that could be used clinically to administer anti-GB biologics to the brain through evasion of its natural barriers.

Towards standardization of the parameters for opening the blood-brain barrier with focused ultrasound to treat glioblastoma multiforme: A systematic review of the devices, animal models, and therapeutic compounds used in rodent tumor models

Glioblastoma multiforme (GBM) is a deadly and aggressive malignant brain cancer that is highly resistant to treatments. A particular challenge of treatment is caused by the blood-brain barrier (BBB), the relatively impermeable vasculature of the brain. The BBB prevents large molecules from entering the brain parenchyma. This protective characteristic of the BBB, however, also limits the delivery of therapeutic drugs for the treatment of brain tumors. To address this limitation, focused ultrasound (FUS) has been safely utilized to create transient openings in the BBB, allowing various high molecular weight drugs access to the brain. We performed a systematic review summarizing current research on treatment of GBMs using FUS-mediated BBB openings in in vivo mouse and rat models. The studies gathered here highlight how the treatment paradigm can allow for increased brain and tumor perfusion of drugs including chemotherapeutics, immunotherapeutics, gene therapeutics, nanoparticles, and more. Given the promising results detailed here, the aim of this review is to detail the commonly used parameters for FUS to open the BBB in rodent GBM models.

Endovascular Chemotherapy: Selective Targeting for Brain Cancer

Establishing an effective and robust management option for brain cancers has proven to bean elusive challenge for the fields of neurosurgery and neuro-oncology. Despite decades of research efforts to improve treatment outcomes and increase patient survivability, brain cancer remains among the most fatal of all cancer classes. A significant barrier to this endeavor is the blood-brain barrier, a major protective border for brain tissue that primarily precludes the optimal delivery of chemotherapeutic drugs to the patient's brain circulation through tight junction formations and selective transporter proteins. This issue is often compounded by tumor location, particularly in inoperable regions near functional brain parenchyma. These obstacles necessitate the development of selectively targeted delivery of chemotherapeutic agents, such as endovascular super-selective intra-arterial injections. Recent experimental studies demonstrate the effectiveness of focused ultrasound to unseal the blood-brain barrier selectively and reversibly. Together, these new technologies can be leveraged to circumvent the limited permeability of the blood-brain barrier, thus improving drug delivery to tumoral locations and potentially enabling a more effective treatment alternative to surgical resection. This review attempts to place into context the necessity of these newer selective chemotherapeutic modalities by briefly highlighting commonly encountered brain cancers and explaining the prominent challenges that face chemotherapy delivery, as well as describing the current preclinical and clinical progress in the development of facilitatory focused ultrasound with selective endovascular chemotherapy.