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 poised to revolutionize the treatment of glioblastoma, one of the most aggressive and invariably fatal forms of brain cancer. This innovative approach leverages precisely engineered nanostructures, crafted from sub-microscopic materials, capable of delivering potent anti-cancer compounds directly into the brain via simple nasal drops. In preclinical studies conducted on mice, this method demonstrated remarkable success in combating glioblastoma by effectively stimulating the brain’s own immune system, thereby circumventing the considerable invasiveness associated with many current and developing therapeutic interventions. The findings, published this month in the prestigious journal Proceedings of the National Academy of Sciences (PNAS), signal a significant leap forward in the quest for more effective and less burdensome treatments for this devastating disease.
The Elusive Target: Why Glioblastoma Remains a Formidable Challenge
Glioblastoma multiforme (GBM) originates from astrocytes, glial cells that provide support and insulation for neurons in the brain. It stands as the most prevalent and aggressive malignant primary brain tumor, impacting an estimated three out of every 100,000 individuals in the United States annually. The disease is characterized by its rapid proliferation and infiltrative growth, making complete surgical resection exceedingly difficult, if not impossible. Consequently, glioblastoma is almost universally fatal, with a median survival rate often measured in months, even with aggressive multimodal therapy including surgery, radiation, and chemotherapy.
A primary impediment to effective glioblastoma treatment lies in the inherent biological defenses of the brain. The blood-brain barrier (BBB), a highly selective physiological barrier, tightly regulates the passage of substances from the bloodstream into the central nervous system, effectively shielding the brain from potential toxins but also hindering the delivery of therapeutic agents. Conventional systemic drug administration often fails to achieve sufficient concentrations within the brain to be therapeutically effective, necessitating alternative, often more invasive, delivery routes.
"Our fundamental objective was to dismantle this therapeutic barrier and engineer a noninvasive treatment modality capable of harnessing the body’s own immune defenses to actively combat glioblastoma," stated Dr. Alexander H. Stegh, 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 directs research for The Brain Tumor Center at Siteman Cancer Center, a joint enterprise of Barnes-Jewish Hospital and WashU Medicine, elaborated, "This research unequivocally demonstrates that meticulously designed nanostructures, specifically spherical nucleic acids (SNAs), possess the capacity to safely and effectively activate robust immune pathways within the brain. This represents a paradigm shift in how cancer immunotherapy can be applied to tumors that are notoriously difficult to access."
Igniting the Immune Response: The STING Pathway Nanomedicine Approach
Glioblastoma is frequently categorized as a "cold tumor," a term denoting its ability to evade detection and immune attack. Unlike "hot tumors," which exhibit a higher degree of immune cell infiltration and are generally more responsive to immunotherapies, glioblastoma cells often create an immunosuppressive microenvironment, effectively dampening the body’s natural anti-cancer responses. Scientists have been actively investigating strategies to overcome this immune evasion, with a particular focus on pathways that can initiate a robust inflammatory and immune cascade.
One such promising target is the STING (stimulator of interferon genes) pathway. This critical innate immune sensing mechanism is activated when cells detect the presence of foreign or aberrant DNA, triggering a signaling cascade that leads to the production of interferons and other immune-activating molecules, thereby orchestrating a potent defense response. Preclinical evidence has indicated that drugs capable of activating the STING pathway can effectively prime the immune system to recognize and attack glioblastoma. However, a significant limitation of these drugs has been their rapid degradation in the body and the necessity for direct intratumoral injection to achieve therapeutic efficacy. This requirement for repeated, invasive procedures presents a substantial burden on patients already grappling with a severe illness.
"The significant challenges associated with invasive drug delivery for STING agonists were a primary motivator for our research," explained Dr. Akanksha Mahajan, a postdoctoral research associate in Dr. Stegh’s laboratory and the first author of the study. "We were driven by the desire to spare patients from the ordeal of repeated invasive procedures. The hypothesis was that we could leverage the unique properties of spherical nucleic acid platforms to deliver these potent immunomodulatory agents in a completely noninvasive manner."
Crafting Nanostructures for Nose-to-Brain Delivery: A Synergistic Partnership
To surmount the delivery challenges, Dr. Stegh’s team forged a crucial collaboration with Dr. Chad A. Mirkin, director of the International Institute for Nanotechnology and the Rathmann Professor of Chemistry at Northwestern University. Dr. Mirkin is a pioneer in the field of nanotechnology and the inventor of spherical nucleic acids (SNAs). SNAs are nanoscale particles characterized by a dense arrangement of DNA or RNA strands around a core, a configuration that has been shown to confer superior cellular uptake and biological activity compared to traditional linear nucleic acid delivery systems.
The collaborative effort focused on designing a specialized variant of SNAs specifically tailored for glioblastoma immunotherapy. These novel nanostructures featured a gold nanoparticle core, which provides structural integrity and facilitates imaging, surrounded by short DNA fragments engineered to activate the STING pathway within targeted immune cells. The critical innovation lay in utilizing the nasal passages as a direct conduit for delivering these nanostructures into the brain, bypassing the blood-brain barrier entirely.
While intranasal delivery has been explored for various brain-targeted therapies in the past, no nanoscale therapeutic agent had previously demonstrated the capability to elicit a significant immune response against brain tumors via this route. This novel approach offered a promising avenue for overcoming the limitations of previous strategies.
"This represents a pivotal breakthrough, as it is the first demonstration that nanoscale therapeutics delivered via the nasal route can successfully enhance immune cell activation within glioblastoma tumors," Dr. Mahajan affirmed. "This validates the potential of intranasal nanomedicine for treating brain cancers."
Tracing the Nanodrops: Visualizing Brainward Migration and Immune Engagement
A key aspect of the research involved rigorously demonstrating both the selective transport of the nanostructures to the brain and their targeted engagement with the intended immune cells. To achieve this, the researchers incorporated a molecular tag into the SNAs that emits a fluorescent signal detectable under near-infrared light. Following the administration of the nanodrops to mice engineered to develop glioblastoma, sophisticated imaging techniques were employed to track the particles’ journey.
The imaging studies revealed that the nanostructures successfully navigated the olfactory and trigeminal pathways, which connect the nasal cavity directly to the brain. The fluorescent signal confirmed the particles’ migration along the primary nerve tracts leading from the facial region into the central nervous system.
Upon reaching their destination, the nanomedicine-induced immune response was observed to be concentrated within specific immune cells residing in and around the tumor microenvironment. A notable degree of immune activation was also detected in nearby lymph nodes, suggesting a systemic priming of the immune system in response to the localized brain treatment. Crucially, the therapy did not exhibit widespread dissemination throughout the body, a critical factor in minimizing the risk of off-target effects and systemic toxicity.
Further detailed histological and molecular analyses confirmed that immune cells within and adjacent to the tumor had indeed activated the STING pathway. This activation empowered these immune cells to mount a more potent and coordinated attack against the glioblastoma cells, leading to tumor suppression.
A Synergistic Assault: Combining Nanotherapy with T-Cell Activation for Tumor Eradication and Long-Term Immunity
The researchers then explored the potential of combining this novel nanotherapy with other immune-boosting agents. When the STING-activating nanotherapy was administered in conjunction with drugs designed to activate T lymphocytes – another critical component of the adaptive immune system – the results were profoundly encouraging. This two-pronged approach led to the complete eradication of glioblastoma tumors in the majority of treated mice.
Furthermore, the combination therapy induced a durable, long-lasting immune memory, effectively preventing the recurrence of cancer. This outcome significantly surpassed the efficacy observed with existing STING-targeting therapies alone, highlighting the synergistic power of combining innate and adaptive immune stimulation.
Dr. Stegh cautioned that stimulating the STING pathway in isolation may not be sufficient to achieve a complete cure for glioblastoma. He acknowledged that glioblastoma employs a multifaceted array of immune-evasive strategies that can ultimately suppress anti-tumor immunity. Consequently, his research group is actively investigating ways to engineer their nanostructures with additional immune-activating functionalities. This would enable a single therapeutic intervention to simultaneously target multiple immunosuppressive mechanisms within the tumor microenvironment.
"This innovative nanotherapy approach offers tangible hope for the development of safer, more effective treatments for glioblastoma and potentially for other cancers that exhibit resistance to current immunotherapies," Dr. Stegh emphasized. "It represents a critical and exciting step forward on the path toward clinical translation and eventual patient benefit."
Funding and Disclosure: A Collaborative Endeavor with Industry Ties
This pioneering research was generously supported by multiple national funding bodies and research institutions. Key financial contributions were provided by the National Cancer Institute (NCI) of the National Institutes of Health (NIH) through grant numbers P50CA221747 and R01CA275430. Additional support from the NIH included grants R01CA120813, R01NS120547, and R01CA272639. The Melanoma Research Foundation and the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University also provided crucial funding. Furthermore, grants from Cellularity, Alnylam, and AbbVie contributed to the advancement of this work.
Specialized imaging services essential for the study were facilitated by the Siteman Cancer Center Small Animal Cancer Imaging facility, which received support from NIH instrumentation grants S10OD027042 and S10OD025264, as well as the NCI Cancer Center grant P30CA091842. Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) were supported by the Robert H. Lurie Comprehensive Cancer Center Grant P30CA060553.
It is important to note that the content presented in this article is solely the responsibility of the authors and does not necessarily reflect the official views or policies of the NIH.
The researchers have disclosed potential competing interests relevant to their work. Dr. Alexander Stegh is a shareholder in Exicure Inc., a company actively involved in developing SNA therapeutic platforms. Dr. Chad Mirkin is a shareholder in Flashpoint, a company focused on developing SNA-based therapeutics. Both Dr. Stegh and Dr. Mirkin are co-inventors on patent US20150031745A1, which details the use of SNA nanoconjugates for crossing the blood-brain barrier. These disclosures underscore the significant translational potential of the research and the active development of related technologies within the scientific and commercial spheres.