By Nana O 
Researchers at Washington University School of Medicine in St. Louis, in collaboration with scientists from Northwestern University, have pioneered a groundbreaking noninvasive strategy to combat glioblastoma, one of the most aggressive and lethal forms of brain cancer. This innovative method utilizes precisely engineered nanostructures, crafted from minute materials, capable of delivering potent anti-cancer compounds directly into the brain through simple nasal drops. Preclinical studies conducted on mice have demonstrated remarkable success in treating glioblastoma by effectively stimulating the brain’s own immune system. Crucially, this novel technique circumvents the need for invasive procedures that are often associated with current and emerging treatments for brain tumors, offering a significant leap forward in patient care.
The transformative findings of this research were published this month in the esteemed scientific journal Proceedings of the National Academy of Sciences (PNAS), signaling a significant advancement in the field of neuro-oncology and nanomedicine.
The Elusive Nature of Glioblastoma: A formidable Therapeutic Challenge
Glioblastoma multiforme (GBM) is a devastating diagnosis. Originating from astrocytes, a type of glial cell that supports nerve cells, it stands as the most prevalent and aggressive malignant primary brain tumor. In the United States, it affects approximately three out of every 100,000 individuals annually, a stark statistic that underscores its rarity yet profound impact. The disease is characterized by its rapid proliferation and relentless progression, leading to a grim prognosis with a median survival rate that has historically remained around 15 months, even with aggressive treatment regimens.
A principal impediment to effectively treating glioblastoma lies in the inherent protective mechanisms of the brain. The blood-brain barrier (BBB), a highly selective physiological barrier, tightly regulates the passage of substances from the bloodstream into the brain parenchyma. While essential for safeguarding the delicate neural environment from toxins and pathogens, the BBB also presents a formidable obstacle for the delivery of therapeutic agents, including chemotherapy drugs and immunotherapy agents, to brain tumors. Conventional systemic administration of anti-cancer drugs often results in insufficient drug concentrations reaching the tumor site, while simultaneously exposing the rest of the body to potentially debilitating side effects.
"Our fundamental goal was to fundamentally alter this challenging landscape and to conceive of a noninvasive treatment paradigm capable of galvanizing the body’s own immune system to actively target and eradicate glioblastoma," stated Alexander H. Stegh, PhD, a distinguished professor and vice chair of research in the Taylor Family Department of Neurosurgery at WashU Medicine. Dr. Stegh also holds the pivotal role of research director for The Brain Tumor Center at Siteman Cancer Center, a collaborative effort between Barnes-Jewish Hospital and WashU Medicine. "Through this rigorous research, we have definitively demonstrated that meticulously designed nanostructures, specifically spherical nucleic acids, possess the remarkable capacity to safely and efficiently activate potent immune pathways within the brain. This breakthrough fundamentally redefines the potential for achieving cancer immunotherapy in tumors that have traditionally been exceedingly difficult to access and treat."
Reactivating the Immune System: The STING Pathway Nanomedicine Approach
Glioblastoma is frequently categorized as a "cold tumor." This designation reflects its inherent ability to evade immune surveillance and recognition. Unlike "hot tumors," which exhibit a greater propensity to elicit a robust immune response and are thus more amenable to existing immunotherapies, glioblastoma cells often employ sophisticated mechanisms to suppress immune cell infiltration and activity within the tumor microenvironment. This immune evasion is a critical factor contributing to the disease’s recalcitrance to treatment.
Scientists have long been investigating strategies to overcome this immune suppression, with a particular focus on pathways that can initiate and amplify anti-tumor immunity. One such promising pathway is known as STING (stimulator of interferon genes). The STING pathway plays a crucial role in the innate immune system’s response to intracellular pathogens. It is activated when cellular sensors detect the presence of foreign DNA, such as that from viruses or bacteria, within the cell’s cytoplasm. Upon activation, STING triggers a cascade of signaling events that lead to the production of type I interferons and other pro-inflammatory cytokines, ultimately orchestrating a potent immune defense.
Previous research had indicated that pharmacological agents capable of activating the STING pathway could prime the immune system to recognize and attack glioblastoma cells. However, a significant limitation of these existing STING agonists was their rapid degradation in the body and the necessity for direct intratumoral injection to achieve therapeutic efficacy. Given that multiple doses are typically required for sustained effect, this approach necessitates highly invasive surgical procedures, posing substantial risks and burdens for patients already grappling with a severe illness.
"We were deeply motivated to alleviate the significant burden placed on patients undergoing such arduous treatments when they are already in a vulnerable state," explained Akanksha Mahajan, PhD, a postdoctoral research associate in Dr. Stegh’s laboratory and the first author of the study. "It was this desire that spurred our investigation into leveraging the unique properties of spherical nucleic acid platforms to facilitate the noninvasive delivery of these potent immune-activating drugs."
Engineering Nanostructures for Nose-to-Brain Delivery: A Gold-Core Strategy
To surmount the challenges posed by invasive delivery methods and rapid drug degradation, Dr. Stegh’s team forged a critical partnership with Chad A. Mirkin, PhD, a renowned leader in nanotechnology and 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 DNA or RNA molecules on their surface, often encircling a core material. SNAs have demonstrated superior cellular uptake and biological activity compared to conventional linear nucleic acid delivery systems.
The collaborative effort led to the design of a specialized iteration of SNAs. These novel nanostructures feature a gold nanoparticle core, providing structural integrity and facilitating imaging, enveloped by short DNA fragments engineered to specifically activate the STING pathway within targeted immune cells. The critical innovation in this approach lies in the chosen route of administration: intranasal delivery. This method capitalizes on the direct pathway from the nasal cavity to the brain via the olfactory and trigeminal nerves, bypassing the restrictive blood-brain barrier.
While intranasal delivery has been explored previously for delivering therapeutics to the brain, this research marks a significant advancement by demonstrating, for the first time, the ability of a nanoscale therapy delivered via this route to effectively activate immune responses against brain tumors.
"This represents a landmark achievement, as it is the inaugural instance where we have successfully demonstrated the capacity to enhance immune cell activation within glioblastoma tumors through the intranasal administration of nanoscale therapeutics designed for nose-to-brain delivery," Mahajan emphasized.
Tracing the Nanodrops: From Nasal Passage to Brain Tumors
The researchers meticulously designed their experiments to validate both the targeted delivery of the nanostructures to the brain and the subsequent activation of the intended immune cells within the tumor microenvironment. To enable precise tracking, they incorporated a molecular tag into the spherical nucleic acid constructs that emits a fluorescent signal when exposed to near-infrared light. Following the administration of the nanodrops to mice engineered to develop glioblastoma, the research team observed the particles traversing the neural pathways, specifically along the olfactory nerve that connects the nasal region to the brain.
Upon reaching the brain, the immune response elicited by the nanomedicine was observed to be concentrated within specific immune cells residing in and around the tumor. This localized activation is crucial for maximizing therapeutic effect while minimizing off-target effects. Furthermore, some immune activity was also detected in the nearby lymph nodes, suggesting a broader engagement of the immune system. Importantly, the study found that the therapy did not disseminate widely throughout the body, a critical finding that greatly reduces concerns about systemic toxicity and potential adverse side effects.
Subsequent histological and molecular analyses provided definitive evidence that immune cells within and surrounding the glioblastoma tumors had indeed activated the STING pathway. This pathway activation empowered these immune cells to mount a more robust and coordinated attack against the cancer cells, leading to tumor regression in the animal models.
A Synergistic Approach: Eradicating Tumors and Preventing Recurrence
The therapeutic potential of this nanotherapy was further amplified when it was combined with agents designed to activate T lymphocytes, another critical component of the adaptive immune system. This dual-pronged therapeutic strategy, involving a two-dose regimen of the STING-activating nanomedicine followed by immune-boosting T-cell therapy, resulted in the complete eradication of tumors in the majority of the treated mice. Critically, this combination therapy also induced a durable anti-tumor immune memory, which conferred long-lasting protection against cancer recurrence. These outcomes significantly surpassed the efficacy observed with current STING-targeting therapies in preclinical models.
Dr. Stegh cautioned that activating the STING pathway alone may not be sufficient to achieve a complete cure for glioblastoma in all cases. He highlighted that glioblastoma tumors are adept at employing multiple defense mechanisms to suppress or even shut down the immune response. To address this, his research group is actively exploring strategies to engineer their nanostructures with additional immune-activating functionalities. This multi-pronged approach could enable the simultaneous targeting of multiple immune-suppressive pathways within a single therapeutic intervention, thereby enhancing overall efficacy.
"This innovative approach holds immense promise for the development of safer and more effective treatments for glioblastoma and potentially for other cancers that are resistant to current immunotherapies," Dr. Stegh asserted. "It represents a pivotal stride towards translating these promising preclinical findings into clinical applications that can benefit patients."
The Broader Implications and Future Directions
The successful demonstration of noninvasive, nose-to-brain delivery of immune-stimulating nanostructures for glioblastoma treatment has far-reaching implications. It offers a potential paradigm shift away from the highly invasive surgical interventions that have long been the standard for delivering therapeutics directly to brain tumors. The ability to stimulate the brain’s immune system locally, without widespread systemic exposure, could significantly improve the quality of life for patients undergoing treatment and reduce the incidence of severe side effects.
This research opens doors for the application of similar nanotechnological strategies to other neurological conditions and brain cancers that are currently difficult to treat due to the blood-brain barrier. The modular design of the SNAs also allows for customization, enabling the incorporation of different therapeutic payloads and targeting moieties, paving the way for personalized medicine approaches.
The long-term immunity observed in the mouse models is particularly encouraging, suggesting that this approach could not only treat existing tumors but also prevent their insidious return, a common and devastating characteristic of glioblastoma. Future research will likely focus on further optimizing the nanostructure design, refining the dosing regimens, and conducting rigorous clinical trials to evaluate the safety and efficacy of this therapy in human patients. The collaborative nature of this research, bridging expertise in neurosurgery, immunology, and nanotechnology, exemplifies the power of interdisciplinary science in tackling complex medical challenges.
Funding and Disclosure
This groundbreaking research was made possible through substantial support from various national and institutional funding bodies. Key financial contributions were provided by the National Cancer Institute (NCI) of the National Institutes of Health (NIH) under grant numbers P50CA221747 and R01CA275430, as well as the NIH through grants R01CA120813, R01NS120547, and R01CA272639. Additional support was received from the Melanoma Research Foundation and the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University. Grants from industry partners Cellularity, Alnylam, and AbbVie also played a role in advancing this work. Imaging facilities at the Siteman Cancer Center Small Animal Cancer Imaging, supported by NIH instrumentation grants S10OD027042 and S10OD025264, along with the National Cancer Institute Cancer Center grant P30CA091842, were instrumental. PET and MRI imaging services were funded 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 or other funding organizations.
Furthermore, certain financial disclosures have been made by the principal investigators. Alexander Stegh holds a shareholder position in Exicure Inc., a company actively involved in the development of SNA therapeutic platforms. 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 outlines the application of SNA nanoconjugates for crossing the blood-brain barrier. These disclosures are provided to ensure transparency regarding potential conflicts of interest within the research and development process.
