By Nana O 
Researchers at Washington University School of Medicine in St. Louis, in collaboration with scientists at Northwestern University, have unveiled a groundbreaking noninvasive strategy poised to revolutionize the treatment of glioblastoma, one of the most aggressive and deadliest forms of brain cancer. This innovative method harnesses the power of precisely engineered nanostructures, capable of delivering potent cancer-fighting compounds directly into the brain through simple nasal drops. Early studies in animal models have demonstrated remarkable success, not only by treating glioblastoma but also by effectively stimulating the brain’s own immune system, a critical step in combating this notoriously resilient disease. Crucially, this novel approach circumvents the significant invasiveness associated with many current and experimental brain cancer therapies.
The findings of this pivotal research were published this month in the esteemed scientific journal Proceedings of the National Academy of Sciences (PNAS), a testament to the rigor and significance of the work.
The Elusive Nature of Glioblastoma: A Persistent Therapeutic Challenge
Glioblastoma multiforme (GBM) represents the most prevalent and aggressive primary malignant brain tumor in adults, originating from astrocytes, a type of glial cell that supports and nourishes neurons. In the United States, the incidence of glioblastoma is approximately three in every 100,000 individuals, a statistic that underscores its relative rarity but devastating impact. The disease is characterized by rapid proliferation, diffuse infiltration into surrounding brain tissue, and an exceedingly poor prognosis, with a median survival rate often measured in months.
A primary impediment to effective glioblastoma treatment lies in the formidable biological barriers that protect the brain. The blood-brain barrier (BBB), a highly selective physiological barrier, strictly regulates the passage of substances from the bloodstream into the brain. This protective mechanism, while essential for maintaining brain health, also poses a significant challenge for the delivery of therapeutic agents, including chemotherapy drugs and immunotherapies, directly to tumor sites. Many conventional treatments struggle to cross the BBB in sufficient concentrations to exert a meaningful anti-cancer effect, leading to limited efficacy and significant systemic toxicity.
"Our fundamental goal was to overcome the limitations of current treatment paradigms and develop a noninvasive therapeutic avenue that could effectively harness the immune system to combat glioblastoma," stated Dr. Alexander H. Stegh, a professor and vice chair of research in the Taylor Family Department of Neurosurgery at Washington University School of Medicine and a co-corresponding author of the study. Dr. Stegh, who also directs research for The Brain Tumor Center at Siteman Cancer Center, a renowned institution based at Barnes-Jewish Hospital and WashU Medicine, elaborated, "This research demonstrates that intricately designed nanostructures, specifically spherical nucleic acids (SNAs), possess the capability to safely and efficiently activate potent immune pathways within the brain. This represents a paradigm shift in how cancer immunotherapy can be applied to tumors that are typically inaccessible through conventional means."
Reactivating the Immune System: Targeting the STING Pathway
Glioblastoma is often characterized as a "cold tumor" in the context of immunotherapy. This designation reflects its inherent ability to evade immune surveillance. Unlike "hot tumors," which are typically infiltrated by immune cells and exhibit a robust inflammatory response conducive to immunotherapy, glioblastoma tumors largely lack these features. They employ a variety of mechanisms to suppress anti-tumor immunity, effectively creating an immunosuppressive microenvironment that shields them from immune attack.
Scientists have long sought methods to overcome this immune evasion. One promising avenue of research has focused on activating a critical intracellular signaling pathway known as STING (stimulator of interferon genes). The STING pathway plays a crucial role in innate immunity. It is activated when cells detect the presence of foreign DNA, such as that found in viruses or bacteria, or even aberrant self-DNA within the cytoplasm. Upon activation, STING initiates a cascade of events that leads to the production of type I interferons and other inflammatory cytokines, ultimately orchestrating a potent immune defense response.
Previous studies have indicated that drugs designed to activate the STING pathway could potentially prime the immune system to recognize and attack glioblastoma cells. However, a significant hurdle with these STING-activating drugs has been their inherent instability. They tend to degrade rapidly within the body, necessitating direct injection into the tumor to achieve therapeutic concentrations. Given that multiple doses are often required for efficacy, this approach inherently involves highly invasive surgical procedures, which can be burdensome and risky for patients already grappling with a devastating illness.
"We recognized the significant burden that repeated invasive procedures place on patients who are already critically ill. This realization spurred our motivation to find a less intrusive delivery method," explained Dr. Akanksha Mahajan, a postdoctoral research associate in Dr. Stegh’s laboratory and the first author of the study. "We hypothesized that we could leverage the unique properties of spherical nucleic acid platforms to deliver these STING-activating compounds in a noninvasive manner."
Engineering Nanostructures for Targeted Nose-to-Brain Delivery
To address the limitations of existing STING pathway activators, Dr. Stegh’s team joined forces with Dr. Chad A. Mirkin, a distinguished figure in nanotechnology and the director of the International Institute for Nanotechnology and the Rathmann Professor of Chemistry at Northwestern University. Dr. Mirkin is a pioneer in the development of spherical nucleic acids (SNAs), a class of nanoscale particles characterized by a dense arrangement of nucleic acid (DNA or RNA) molecules surrounding a core. SNAs have demonstrated superior cellular uptake and biological activity compared to conventional nucleic acid delivery systems.
The collaborative effort led to the design of a specialized SNA construct. These nanostructures featured a gold nanoparticle core, providing a stable scaffold, and were densely functionalized with short DNA fragments engineered to specifically activate the STING pathway within targeted immune cells. The critical innovation, however, lay in the chosen route of administration: the nasal passages.
Intranasal delivery has emerged as a promising strategy for brain-targeted drug delivery in various research contexts. The nasal cavity offers a direct conduit to the brain via the olfactory and trigeminal nerve pathways, bypassing the BBB. While this route has been explored for delivering therapeutics to the brain, no nanoscale therapy had previously demonstrated the capacity to effectively activate immune responses against brain tumors using this noninvasive approach.
"This research marks a significant milestone as it represents the first demonstration that nanoscale therapeutics, delivered via the nasal route, can effectively enhance immune cell activation within glioblastoma tumors," Dr. Mahajan emphasized. "This opens up entirely new possibilities for treating brain cancers."
Tracking the Nanodrops: From Nasal Cavity to Brain Tumor
A key objective of the study was to validate both the selective delivery of the engineered nanostructures to the brain and their intended biological activity – the activation of target immune cells. To facilitate this tracking, the researchers incorporated a molecular tag into the SNA constructs that emitted a fluorescent signal under near-infrared light.
Following the administration of the nanodrop formulation to mice bearing glioblastoma tumors, the research team meticulously tracked the movement of the fluorescently tagged nanostructures. Their observations confirmed that the particles traveled along the established pathways of the olfactory and trigeminal nerves, which connect the nasal cavity to various regions of the brain, including those harboring the tumors.
Upon reaching the brain, the nanomedicine’s impact was localized. The immune response triggered by the SNAs was concentrated within specific immune cell populations residing in and around the tumor microenvironment. Evidence of this immune activation was also observed in nearby lymph nodes, suggesting a systemic priming effect. Crucially, the study found minimal off-target distribution of the nanotherapy throughout the rest of the body, a finding that significantly reduces concerns about widespread systemic toxicity and adverse side effects.
Further histological and molecular analyses confirmed that immune cells infiltrating the tumor and its periphery had successfully engaged the STING pathway. This activation empowered these immune cells to mount a more robust and coordinated attack against the glioblastoma cells, leading to a reduction in tumor burden.
Synergistic Therapies: Eradicating Tumors and Preventing Recurrence
The researchers went a step further by investigating the potential of combining their novel nanotherapy with other immunomodulatory agents. When the STING-activating nanodrops were administered in conjunction with therapies designed to activate T lymphocytes – another critical component of the anti-cancer immune response – the results were particularly striking. This two-pronged approach led to the complete eradication of glioblastoma tumors in the treated mice.
Moreover, the combination therapy induced a durable, long-lasting immune memory. This immunological memory proved effective in preventing the recurrence of cancer, a common and devastating challenge in glioblastoma treatment. These outcomes significantly surpassed the efficacy observed with current STING-targeting therapies administered through more invasive routes, highlighting the superior therapeutic potential of this noninvasive nanodrop approach.
Dr. Stegh cautioned that while STING pathway activation is a crucial step, it is unlikely to be a standalone cure for glioblastoma. The tumor’s sophisticated defense mechanisms, which include actively suppressing immune cell function, require a multifaceted therapeutic strategy. To this end, his research group is actively exploring ways to engineer their nanostructures with additional immune-activating functionalities. This could enable a single therapeutic agent to simultaneously target multiple immunosuppressive pathways, thereby enhancing its anti-tumor potency.
"This innovative approach holds immense promise for developing safer and more effective treatments for glioblastoma, and potentially for other cancers that exhibit resistance to immunotherapy," Dr. Stegh concluded. "It represents a critical advancement that brings us closer to clinical application and offers tangible hope for patients facing these devastating diagnoses."
Funding and Disclosure: A Collaborative Effort
The research underpinning this breakthrough was generously supported by grants from several esteemed organizations, including the National Cancer Institute (NCI) of the National Institutes of Health (NIH) under grant numbers P50CA221747 and R01CA275430, and the NIH with grants R01CA120813, R01NS120547, and R01CA272639. Additional support was provided by the Melanoma Research Foundation, the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University, and grants from Cellularity, Alnylam, and AbbVie. Imaging services at the Siteman Cancer Center Small Animal Cancer Imaging facility were made possible by NIH instrumentation grants S10OD027042 and S10OD025264, as well as the National Cancer Institute Cancer Center grant P30CA091842. PET and MRI imaging 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 study’s authors and does not necessarily reflect the official views or policies of the NIH.
Furthermore, the researchers disclosed potential competing interests. Dr. Alexander Stegh is a shareholder of Exicure Inc., a company involved in the development of SNA therapeutic platforms. Dr. Chad Mirkin is a shareholder in Flashpoint, a company developing SNA-based therapeutics. Both Dr. Stegh and Dr. Mirkin are co-inventors on U.S. Patent US20150031745A1, which describes SNA nanoconjugates designed to cross the blood-brain barrier. These disclosures ensure transparency and adherence to ethical standards in scientific reporting.
