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 for combating glioblastoma, one of the most aggressive and lethal forms of brain cancer. This innovative approach leverages precisely engineered nanostructures, designed to ferry potent cancer-fighting compounds directly into the brain via simple nasal drops. In preclinical studies conducted on mice, this novel method not only demonstrated efficacy in treating glioblastoma but also achieved this by stimulating the brain’s own immune system, a significant advancement over current treatment paradigms that often involve highly invasive procedures. The findings, published this month in the esteemed journal PNAS, represent a critical step toward developing safer and more effective therapeutic options for patients battling this devastating disease.
The Formidable Challenge of Glioblastoma
Glioblastoma multiforme (GBM) originates from astrocytes, a critical type of glial cell in the brain responsible for supporting and protecting neurons. It stands as the most prevalent and aggressive malignant primary brain tumor, affecting approximately three out of every 100,000 individuals in the United States annually. The disease is characterized by its rapid progression and a grim prognosis, with median survival rates often measured in months, even with aggressive multimodal treatment. A primary hurdle in treating glioblastoma has historically been the formidable blood-brain barrier (BBB), a highly selective physiological barrier that severely restricts the passage of most therapeutic agents from the bloodstream into the central nervous system. This inherent challenge necessitates invasive delivery methods or the development of specialized drug formulations capable of crossing this biological shield.
"Our overarching goal was to fundamentally alter this challenging therapeutic landscape by devising a noninvasive treatment that could effectively mobilize the immune system to recognize and attack 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 the distinguished position of research director for The Brain Tumor Center at Siteman Cancer Center, a collaboration between Barnes-Jewish Hospital and WashU Medicine, elaborated on the significance of their findings: "Through this pioneering research, we have definitively shown that meticulously engineered nanostructures, specifically spherical nucleic acids (SNAs), possess the capability to safely and potently activate crucial immune pathways within the brain. This breakthrough redefines the possibilities for cancer immunotherapy, particularly for tumors that are notoriously difficult to access."
Reactivating the Immune System Through STING Pathway Nanomedicine
Glioblastoma is frequently characterized as a "cold tumor" within the context of cancer immunology. This designation reflects its intrinsic ability to evade detection and rejection by the immune system, largely due to a lack of pre-existing inflammatory signals that typically attract immune cells to tumor sites. In contrast, "hot tumors" are often infiltrated by immune cells and exhibit a higher susceptibility to immunotherapies. Glioblastoma’s immunosuppressive microenvironment allows it to proliferate unchecked. Consequently, a significant area of research has focused on strategies to "reprogram" these cold tumors into more immunogenic ones.
One promising avenue involves stimulating a critical innate immune pathway known as STING (stimulator of interferon genes). The STING pathway is a key component of the cellular defense system that responds to the presence of foreign or aberrant DNA, such as that found in invading pathogens or damaged host cells. Upon activation, the STING pathway triggers the production of type I interferons and other signaling molecules, initiating a cascade of immune responses designed to eliminate the threat. Previous research had indicated that drugs capable of activating the STING pathway could prime the immune system to recognize and attack glioblastoma. However, a significant limitation of these agents has been their rapid degradation in biological systems and the requirement for direct intratumoral injection to achieve therapeutic concentrations. The necessity for multiple doses, each demanding an invasive surgical procedure, presented a substantial barrier to clinical translation, imposing significant physical and psychological burdens on already critically ill patients.
"We were deeply motivated to alleviate the burden of invasive procedures for patients who are already facing immense health challenges," explained Akanksha Mahajan, PhD, a postdoctoral research associate in Dr. Stegh’s laboratory and the first author of the study. "This sentiment led us to explore the potential of spherical nucleic acid platforms as a means to deliver these potent STING-activating drugs in a noninvasive manner."
Innovative Nanostructure Design for Nose-to-Brain Delivery
To overcome the limitations of existing STING agonists, Dr. Stegh’s team joined forces with Chad A. Mirkin, PhD, a leading figure in nanoscience and a co-corresponding author of the study. Dr. Mirkin, director of the International Institute for Nanotechnology and the Rathmann Professor of Chemistry at Northwestern University, is renowned for his pioneering work on spherical nucleic acids. SNAs are nanoscale particles characterized by a dense arrangement of DNA or RNA molecules densely packed around a core, which has demonstrated superior cellular uptake and efficacy compared to traditional linear DNA or RNA delivery systems.
The collaborative effort resulted in the design of a specialized SNA construct. These nanostructures feature a gold nanoparticle core, which provides structural integrity and facilitates imaging, enveloped by short DNA fragments specifically engineered to activate the STING pathway within targeted immune cells. A critical innovation of this approach lies in its unique delivery route. Recognizing the direct connection between the nasal cavity and the brain via the olfactory and trigeminal nerve pathways, the researchers selected intranasal administration as the noninvasive entry point for these nanostructures. While intranasal drug delivery for central nervous system (CNS) disorders has been explored previously, its application in conjunction with nanoscale therapeutics for activating immune responses against brain tumors had not yet been demonstrated.
"This research marks a significant first: it is the inaugural demonstration that nanoscale therapeutics delivered via the nasal route can effectively enhance immune cell activation within glioblastoma tumors," Mahajan emphasized. This accomplishment opens a new frontier in noninvasive brain tumor immunotherapy.
Tracking Nanodrops: Tracing the Pathway to the Brain
A crucial aspect of validating any novel therapeutic strategy is to meticulously track the delivery and localization of the therapeutic agent. The research team incorporated a molecular tag into the SNA nanostructures that emitted a fluorescent signal when exposed to near-infrared light. This enabled real-time monitoring of the nanodrops’ journey after intranasal administration to mice bearing glioblastoma tumors.
The imaging studies provided compelling evidence of selective brain targeting. The researchers observed the nanostructures traveling along the path of the olfactory nerve, the primary neural conduit connecting the nasal passages to the olfactory bulb in the brain. Upon reaching their intended destination, the nanomedicine-induced immune response was observed to be concentrated within specific immune cells residing in the tumor microenvironment. Notably, some degree of immune activation was also detected in nearby lymph nodes, suggesting a systemic priming of the immune system. Crucially, the therapy did not exhibit widespread distribution throughout the rest of the body, a characteristic that significantly mitigates concerns about off-target toxicities and potential systemic side effects.
Further detailed histological and molecular analyses confirmed that immune cells within and surrounding the tumor had successfully activated the STING pathway. This activation empowered these immune cells to mount a more robust and coordinated attack against the cancerous cells, underscoring the therapeutic efficacy of the nanostructure-mediated immune stimulation.
Synergistic Therapies for Tumor Eradication and Long-Term Immunity
The researchers explored the potential of combining their STING-activating nanotherapy with other immunomodulatory agents to enhance therapeutic outcomes. In a critical set of experiments, the nanotherapy was administered in conjunction with drugs designed to activate T lymphocytes, a vital class of immune cells that play a central role in adaptive immunity and cancer surveillance. This dual-therapy approach yielded remarkable results in the mouse models. A two-dose regimen was sufficient to completely eliminate established glioblastoma tumors. Furthermore, the treatment elicited a durable, long-lasting immune response that effectively prevented tumor recurrence, a significant achievement given the aggressive nature of glioblastoma and its propensity for relapse. These outcomes surpassed those observed with current STING-targeting therapies, highlighting the superior efficacy of the novel nanostructure-based approach.
Dr. Stegh cautioned that while stimulating the STING pathway is a powerful strategy, it is unlikely to be a standalone cure for glioblastoma. He elaborated on the tumor’s complex evasion mechanisms: "Glioblastoma employs a multifaceted repertoire of tactics to suppress or completely shut down the immune response. To achieve complete eradication and prevent relapse, we need to overcome these sophisticated defenses." His team is actively investigating strategies to engineer their nanostructures with additional immune-activating functionalities. This could enable a single therapeutic agent to simultaneously target multiple immunosuppressive pathways within the tumor microenvironment, thereby increasing the likelihood of a complete and sustained response.
"This innovative approach holds immense promise for delivering safer, more effective treatments for glioblastoma and potentially for other cancers that have proven resistant to current immunotherapies," Dr. Stegh concluded. "It represents a significant stride forward on the path toward clinical application, offering renewed hope to patients and their families."
Funding and Declarations
This groundbreaking research was made possible through substantial financial support from several key institutions. The National Cancer Institute (NCI) of the National Institutes of Health (NIH) provided crucial funding through grant numbers P50CA221747 and R01CA275430. Additional support from the NIH was provided by grants R01CA120813, R01NS120547, and R01CA272639. The Melanoma Research Foundation and the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University also contributed vital funding. Furthermore, grants from industry partners Cellularity, Alnylam, and AbbVie played a role in advancing this work. Imaging capabilities at the Siteman Cancer Center Small Animal Cancer Imaging facility were supported by NIH instrumentation grants S10OD027042 and S10OD025264, as well as the National Cancer Institute Cancer Center grant P30CA091842. PET and MRI imaging services were supported by the Robert H. Lurie Comprehensive Cancer Center Grant P30CA060553. The content of this publication is solely the responsibility of the authors and does not necessarily reflect the official views of the NIH.
The researchers have disclosed potential conflicts of interest. Alexander Stegh is a shareholder of Exicure Inc., a company involved in the development of SNA therapeutic platforms. Chad A. Mirkin is a shareholder in Flashpoint, a company that develops SNA-based therapeutics. Both Dr. Stegh and Dr. Mirkin are co-inventors on U.S. Patent US20150031745A1, which details SNA nanoconjugates designed to cross the blood-brain barrier. These disclosures are standard practice in scientific publications to ensure transparency regarding potential influences on research outcomes.
