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 to combat glioblastoma, one of the most aggressive and lethal forms of brain cancer. This innovative method harnesses precisely engineered nanostructures, delivered via simple nasal drops, to ferry potent cancer-fighting compounds directly into the brain. In preclinical studies utilizing mice, this novel approach demonstrated remarkable success in treating glioblastoma by effectively stimulating the brain’s own immune system, a significant departure from the highly invasive procedures currently under development for similar treatments. The findings, published this month in the esteemed journal Proceedings of the National Academy of Sciences (PNAS), mark a pivotal moment in the quest for more accessible and effective brain tumor therapies.
The Persistent Challenge of Glioblastoma Treatment
Glioblastoma multiforme (GBM) is a formidable adversary in the field of oncology. Originating from astrocytes, a critical type of glial cell in the brain, it stands as the most prevalent and aggressive malignant brain tumor in adults. In the United States, its incidence is approximately three in every 100,000 individuals, a statistic that underscores its rarity but also its devastating impact. The disease is characterized by its rapid proliferation and an overwhelmingly grim prognosis, with median survival rates often measured in months rather than years, even with aggressive treatment regimens.
A fundamental hurdle in effectively treating glioblastoma lies in the inherent biological defenses of the brain itself. The blood-brain barrier (BBB), a highly selective physiological barrier that protects the central nervous system from circulating toxins and pathogens, also severely restricts the passage of most therapeutic agents. This means that even potent chemotherapy drugs or targeted therapies developed in the lab often struggle to reach therapeutic concentrations within the tumor site, rendering them less effective. Conventional treatment often involves a combination of surgery, radiation therapy, and chemotherapy, but the limitations in drug delivery significantly impact treatment efficacy and patient outcomes.
"We were driven by the urgent need to fundamentally alter this challenging landscape," 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 significant role of research director for The Brain Tumor Center at Siteman Cancer Center, a joint venture between Barnes-Jewish Hospital and WashU Medicine, elaborated on the team’s ambitious goal. "Our objective was to devise a noninvasive treatment that could effectively leverage the body’s own immune system to mount an attack against glioblastoma. What we have demonstrated with this research is the remarkable capability of precisely engineered nanostructures, specifically spherical nucleic acids, to safely and effectively activate potent immune pathways within the brain. This represents a paradigm shift in how cancer immunotherapy can be achieved, particularly for tumors that are notoriously difficult to access."
Reawakening the Immune System: Harnessing the STING Pathway
Glioblastoma has long been characterized as a "cold tumor" by oncologists. This designation stems from its inherent ability to evade immune surveillance. Unlike "hot tumors," which exhibit a robust inflammatory infiltrate and are more amenable to immunotherapeutic interventions, glioblastoma tumors typically lack the necessary immune cell activity to trigger a significant anti-tumor response. This immune evasion is a key factor contributing to its aggressive nature and resistance to many conventional treatments.
Scientists have been actively exploring strategies to overcome this immune suppression, with a particular focus on activating specific cellular pathways that can initiate an immune cascade. One such pathway is known as STING, an acronym for stimulator of interferon genes. The STING pathway plays a crucial role in the innate immune system’s defense against viral infections and intracellular pathogens. It is typically activated when cells detect the presence of foreign DNA, prompting the production of interferons and other signaling molecules that alert and mobilize immune cells to combat the threat.
Previous investigations had established that drugs designed to activate the STING pathway held promise for priming the immune system to recognize and attack glioblastoma cells. However, these STING-activating drugs faced significant limitations. They are known for their rapid degradation within the body, meaning they quickly lose their therapeutic potency. Furthermore, to achieve any meaningful therapeutic effect, they had to be administered directly into the tumor through highly invasive surgical procedures. The need for multiple such injections due to the drug’s short half-life and the invasive nature of repeated surgeries presented a formidable barrier to clinical translation and patient tolerability.
"The idea of requiring patients, who are already grappling with a severe illness, to undergo repeated invasive procedures was something we found deeply concerning," explained Akanksha Mahajan, PhD, a postdoctoral research associate in Dr. Stegh’s lab and the first author of the study. "I strongly believed that we could utilize the unique properties of spherical nucleic acid platforms to deliver these potent immune-activating drugs in a manner that was entirely noninvasive."
Engineering Nanostructures for Nose-to-Brain Delivery
To surmount the challenges associated with STING pathway activation and drug delivery, Dr. Stegh’s team forged a critical partnership with Chad A. Mirkin, PhD, a distinguished figure in the field of nanotechnology. Dr. Mirkin, the director of the International Institute for Nanotechnology and the Rathmann Professor of 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 molecules tethered to a core, a structural configuration that has been shown to enhance their cellular uptake and therapeutic efficacy compared to conventional drug delivery systems.
The collaborative effort led to the design of a specialized iteration of SNAs tailored for glioblastoma immunotherapy. These nanostructures featured a core composed of gold nanoparticles, chosen for their biocompatibility and ability to serve as a stable scaffold. Attached to this gold core were short DNA fragments specifically engineered to activate the STING pathway within targeted immune cells. The innovative aspect of this approach lay in the chosen delivery route: the nasal passages.
Intranasal delivery has been explored in previous research as a potential route for delivering therapeutic agents directly to the brain, bypassing the BBB. The olfactory and trigeminal nerves offer direct pathways from the nasal cavity to the central nervous system. However, despite these explorations, no nanoscale therapy had previously demonstrated the ability to elicit a robust immune response against brain tumors using this noninvasive route.
"This is a truly significant milestone because it marks the first time we have successfully demonstrated that delivering nanoscale therapeutics from the nose to the brain can effectively enhance immune cell activation within glioblastoma tumors," Mahajan emphasized. This achievement opens up a new frontier in brain cancer treatment, moving away from highly invasive methods towards a simpler, more patient-friendly approach.
Tracing the Nanodrops: From Nasal Cavity to Brain Tumors
A crucial aspect of validating this novel therapeutic strategy involved meticulously tracking the nanostructures and confirming their intended biological activity. The research team incorporated a molecular tag into the spherical nucleic acids, which emitted a fluorescent signal detectable under near-infrared light. This allowed for real-time visualization of the nanodrops’ journey within the animal models.
Following the administration of the nanodrops to mice bearing glioblastoma tumors, researchers observed a clear and directed migration of the particles. The fluorescent signal indicated that the nanostructures traveled along the pathway of the olfactory nerve, the primary neural connection linking the nasal region to the brain. Crucially, upon reaching the brain, the immune response triggered by the nanomedicine was found to be concentrated within specific immune cells localized within the tumor microenvironment. Evidence of immune activity was also detected in nearby lymph nodes, suggesting a broader engagement of the immune system.
Of paramount importance, the study found that the therapy did not disseminate widely throughout the body. This limited systemic distribution is a critical factor in minimizing the risk of off-target effects and adverse side effects, a common concern with many potent therapeutic agents. Further microscopic examination confirmed that immune cells residing in and around the tumor had successfully activated the STING pathway. This activation equipped these immune cells with enhanced capabilities to recognize and launch a more potent attack against the cancerous glioblastoma cells.
A Synergistic Approach: Enhancing Tumor Eradication and Long-Term Immunity
The researchers went a step further by investigating the potential synergistic effects of combining their nanotherapy with other immunomodulatory agents. In a series of experiments, the STING-activating nanotherapy was administered in conjunction with drugs designed to activate T lymphocytes, another vital component of the adaptive immune system. This combination therapy yielded exceptionally promising results.
In the mouse models, the two-dose treatment regimen not only led to the complete eradication of existing glioblastoma tumors but also generated a robust and long-lasting immune memory. This immunological memory proved effective in preventing the recurrence of the cancer, a significant challenge in glioblastoma treatment where residual cancer cells can lead to relapse. These outcomes significantly surpassed those observed with existing STING-targeting therapies, underscoring the superior efficacy of the nanostructure-based delivery system.
Dr. Stegh cautioned that while stimulating the STING pathway is a crucial step, it is unlikely to be a standalone cure for glioblastoma. He highlighted that glioblastoma tumors possess sophisticated mechanisms to subvert or suppress the immune response. To address this, his group is actively exploring strategies to incorporate additional immune-activating functionalities into their nanostructures. The aim is to develop single treatments capable of targeting multiple immunosuppressive pathways simultaneously, thereby creating a more comprehensive and formidable anti-cancer assault.
"This represents a promising new direction that offers genuine hope for developing safer and more effective treatments for glioblastoma," Dr. Stegh concluded. "Furthermore, this approach holds significant potential for treating other types of cancers that are resistant to current immunotherapies. It is a critical step forward on the path toward eventual clinical application and widespread patient benefit."
Funding and Declarations: A Collaborative Effort
This pioneering research was made possible through substantial financial support from several prestigious organizations. Key funding was provided by the National Cancer Institute (NCI) of the National Institutes of Health (NIH) under grant numbers P50CA221747 and R01CA275430. Additional support from the NIH came through grants R01CA120813, R01NS120547, and R01CA272639. The Melanoma Research Foundation, the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University, and grants from commercial entities including Cellularity, Alnylam, and AbbVie also contributed significantly to the project’s success.
Specialized imaging services 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. Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) capabilities were facilitated by the Robert H. Lurie Comprehensive Cancer Center Grant P30CA060553.
It is important to note that the content presented in this article solely reflects the responsibility of the study’s authors and does not necessarily represent the official viewpoints or policies of the NIH.
The research team also disclosed potential competing interests. Dr. Alexander Stegh holds shares in Exicure Inc., a company actively involved in the development of 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 listed as co-inventors on patent US20150031745A1, which pertains to SNA nanoconjugates designed to traverse the blood-brain barrier. These disclosures are provided to ensure transparency and adherence to scientific and ethical standards.
