By Nana O 
Researchers at Washington University School of Medicine in St. Louis, collaborating with scientists at Northwestern University, have unveiled a groundbreaking noninvasive strategy for treating glioblastoma, one of the most aggressive and deadly forms of brain cancer. This innovative approach leverages precisely engineered nanostructures, capable of delivering potent cancer-fighting compounds directly into the brain via simple nasal drops. In preclinical studies involving mice, this novel method not only successfully treated glioblastoma but also did so by effectively stimulating the brain’s own immune system, circumventing the significant invasiveness associated with many current and developing treatment modalities. The findings, published this month in the prestigious journal PNAS, represent a significant leap forward in the quest for more effective and less burdensome therapies for this devastating disease.
The Unyielding Challenge of Glioblastoma Treatment
Glioblastoma multiforme (GBM) stands as the most prevalent and deadliest primary malignant brain tumor in adults, originating from astrocytes, a crucial type of glial cell that provides support and insulation to neurons. The incidence rate of glioblastoma is approximately three in every 100,000 individuals in the United States, translating to roughly 12,000 new diagnoses annually. Its insidious nature lies in its rapid progression and a grim prognosis, with a median survival rate often measured in months, even with aggressive treatment regimens.
A primary impediment to effective glioblastoma therapy is the formidable blood-brain barrier (BBB). This highly selective physiological barrier, composed of endothelial cells with tight junctions, astrocytes, and pericytes, acts as a critical gatekeeper, protecting the central nervous system from circulating toxins and pathogens. While essential for brain health, the BBB also severely restricts the passage of most therapeutic agents, including chemotherapy drugs and immunotherapies, from the bloodstream into the brain. This limitation necessitates either highly invasive delivery methods or the use of drugs that can breach the BBB, often with significant systemic side effects.
"We were driven by the urgent need to overcome these treatment barriers and devise a noninvasive method that could harness the body’s own immune defenses to combat glioblastoma," stated Alexander H. Stegh, PhD, a professor and vice chair of research in the WashU Medicine Taylor Family Department of Neurosurgery and a co-corresponding author of the study. Dr. Stegh, who also holds a pivotal role as research director of The Brain Tumor Center at Siteman Cancer Center, a collaboration between Barnes-Jewish Hospital and WashU Medicine, elaborated on the significance of their findings: "Our research demonstrates that exquisitely designed nanostructures, specifically spherical nucleic acids, can safely and effectively engage potent immune pathways within the brain. This breakthrough fundamentally redefines the potential for cancer immunotherapy in tumors that have historically been difficult to access."
Harnessing the STING Pathway: A New Front in Immunotherapy
Glioblastoma is notoriously characterized as a "cold tumor." This classification stems from its inherent ability to evade immune surveillance, meaning it typically fails to elicit a robust inflammatory response from the body’s immune system. Unlike "hot tumors," which are more readily recognized and attacked by immune cells, glioblastomas employ various mechanisms to suppress or deflect immune activity. This immune-evasive nature makes them particularly resistant to conventional immunotherapies that rely on a pre-existing immune response.
Scientists have been intensely exploring strategies to activate dormant immune pathways within the tumor microenvironment. One such promising target is the STING (stimulator of interferon genes) pathway. The STING pathway is a crucial component of the innate immune system, acting as a sensor for the presence of foreign DNA. When cellular damage or infection introduces foreign DNA into the cytoplasm, or when DNA is present in the wrong cellular compartments, the STING pathway is triggered. This activation cascade initiates the production of interferons and other cytokines, which then alert and mobilize various immune cells, including T cells and dendritic cells, to mount an inflammatory and anti-cancer response.
Previous research had established that drugs designed to activate the STING pathway held therapeutic potential for glioblastoma. However, these agents faced significant limitations: they were often unstable, degrading rapidly in the body, and required direct injection into the tumor to achieve sufficient therapeutic concentrations. Given that glioblastomas often necessitate multiple treatment interventions, repeated direct tumor injections translate into highly invasive surgical procedures, imposing a substantial burden on patients who are already critically ill.
"Our primary motivation was to spare patients the ordeal of repeated invasive procedures during an already challenging period of their lives," explained Akanksha Mahajan, PhD, a postdoctoral research associate in Dr. Stegh’s lab and the study’s first author. "I believed that by utilizing spherical nucleic acid platforms, we could achieve noninvasive delivery of these immunomodulatory drugs, thereby revolutionizing their application."
Engineering Nanostructures for Nose-to-Brain Delivery
To translate this vision into reality, Dr. Stegh’s team forged a critical partnership with Chad A. Mirkin, PhD, a renowned expert in nanotechnology and a co-corresponding author on the study. Dr. Mirkin, who directs the International Institute for Nanotechnology and holds a distinguished professorship in Chemistry at Northwestern University, is a pioneer in the development of spherical nucleic acids (SNAs). SNAs are nanoscale particles characterized by a dense arrangement of DNA or RNA strands around a core. This unique architecture has been shown to confer superior cellular uptake and stability compared to traditional nucleic acid delivery systems.
The collaborative effort focused on designing a specialized iteration of SNAs. These nanostructures featured a gold nanoparticle core, chosen for its biocompatibility and ease of functionalization, surrounded by short DNA fragments engineered to activate the STING pathway specifically within targeted immune cells. The ingenuity of the approach lay in its chosen route of administration: the nasal passages.
The olfactory and trigeminal nerve pathways, which connect the nasal cavity directly to the brain, have long been recognized as potential conduits for noninvasive, brain-targeted drug delivery. While intranasal delivery has been explored for various neurological conditions, its application for activating immune responses within the brain, particularly against tumors, remained largely unproven for nanoscale therapeutics.
"This research marks a pivotal moment, demonstrating for the first time that nanoscale therapeutics delivered via the nose can effectively enhance immune cell activation within glioblastoma tumors," Mahajan emphasized. "This opens up entirely new avenues for treating brain cancers."
Tracing the Journey: Nanodrops Navigate to the Brain
A critical aspect of the study involved validating both the targeted delivery of the nanostructures to the brain and their subsequent activation of the intended immune cells. To achieve this, the researchers incorporated a molecular tag into the spherical nucleic acids that emitted a fluorescent signal detectable under near-infrared light.
Following the administration of the nanodrops to mice bearing glioblastoma tumors, the research team meticulously tracked the particles’ movement. Imaging studies revealed that the nanostructures successfully traversed the olfactory pathway, migrating along the major nerve connecting the nasal region to the brain. Crucially, upon reaching their destination, the immune response triggered by the nanomedicine was observed to be concentrated within specific immune cells residing in the tumor microenvironment. A secondary but significant level of immune activity was also detected in nearby lymph nodes, suggesting a broader engagement of the immune system. Importantly, the therapeutic agent did not disseminate widely throughout the rest of the body, a factor that significantly mitigates the risk of off-target and potentially harmful side effects.
Further histological and molecular analyses confirmed that the STING pathway had been successfully activated in immune cells both within and surrounding the glioblastoma tumors. This activation primed these immune cells, enabling them to mount a more potent and coordinated attack against the cancerous cells.
Synergistic Therapies: Eradicating Tumors and Building Lasting Immunity
The therapeutic potential of this nanotherapy was further amplified when it was combined with other immunomodulatory agents. Specifically, when the STING-activating nanodrops were administered in conjunction with drugs designed to activate T lymphocytes – another critical class of immune cells that play a central role in adaptive immunity – the results were remarkably promising. This two-dose combination therapy not only led to the complete eradication of established glioblastoma tumors in the mouse models but also generated a durable, long-lasting immune memory. This immunological memory was sufficient to prevent the recurrence of the cancer, a significant challenge in glioblastoma treatment.
These outcomes significantly surpassed those observed with existing STING-targeting therapies, underscoring the enhanced efficacy and strategic advantage of this nanostructure-based, noninvasive approach.
Dr. Stegh cautioned that while stimulating the STING pathway is a crucial step, it may not be sufficient on its own to achieve a complete cure for glioblastoma. Glioblastomas are known to employ a complex array of immunosuppressive mechanisms designed to subvert or shut down the immune response. To address this, his research group is actively investigating ways to engineer their nanostructures with additional immune-activating functionalities. This could potentially allow a single nanodrop treatment to simultaneously target multiple immunosuppressive pathways, thereby enhancing its overall therapeutic impact.
"This innovative nanotherapy approach offers a beacon of hope for developing safer and more effective treatments for glioblastoma, and potentially for other cancers that exhibit resistance to current immunotherapies," Dr. Stegh concluded. "It represents a critical and exciting stride toward translating these laboratory breakthroughs into tangible clinical applications that can benefit patients."
Funding and Declarations
This pioneering research was made possible through substantial funding from various governmental and private organizations. Key support was provided by the National Cancer Institute (NCI) of the National Institutes of Health (NIH) under grant numbers P50CA221747 and R01CA275430, as well as additional NIH grants R01CA120813, R01NS120547, and R01CA272639. Further support was received from the Melanoma Research Foundation, the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University, and grants from industry partners Cellularity, Alnylam, and AbbVie. Imaging services at the Siteman Cancer Center Small Animal Cancer Imaging facility were supported by NIH instrumentation grants S10OD027042 and S10OD025264, and the National Cancer Institute Cancer Center grant P30CA091842. Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) were facilitated by the Robert H. Lurie Comprehensive Cancer Center Grant P30CA060553.
The content presented in this article is solely the responsibility of the study authors and does not necessarily reflect the official views or policies of the NIH.
It is important to note the existence of competing interests among some of the study’s key personnel. Dr. Alexander Stegh holds a shareholder position in Exicure Inc., a company actively developing therapeutic platforms based on spherical nucleic acid technology. Dr. Chad Mirkin is a shareholder in Flashpoint, a company that also develops SNA-based therapeutics. Furthermore, both Dr. Stegh and Dr. Mirkin are co-inventors on patent US20150031745A1, which describes the application of SNA nanoconjugates for crossing the blood-brain barrier. These disclosures highlight the commercial interest and ongoing development within the field of SNA therapeutics, while also underscoring the potential for future clinical translation.
