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 transform the treatment landscape for glioblastoma, one of the most aggressive and lethal forms of brain cancer. This innovative approach leverages precisely engineered nanostructures, delivered via simple nasal drops, to ferry potent cancer-fighting compounds directly into the brain. In preclinical studies utilizing mouse models, this novel method not only successfully treated glioblastoma but also did so by ingeniously harnessing and amplifying the brain’s own immune system, a stark departure from the highly invasive procedures that characterize many current and developing therapeutic interventions.
The Unyielding Challenge of Glioblastoma
Glioblastoma, a devastating malignancy originating from astrocytes – critical support cells within the brain – stands as the most prevalent and deadliest primary malignant brain tumor. Affecting approximately three out of every 100,000 individuals in the United States annually, its rapid progression and grim prognosis have long presented an insurmountable hurdle for medical science. A primary obstacle to effective treatment lies in the formidable blood-brain barrier, a highly selective physiological barrier that severely restricts the passage of most therapeutic agents from the bloodstream into the brain parenchyma. This inherent biological defense mechanism, while crucial for protecting the central nervous system, complicates the delivery of life-saving drugs to cancerous growths within the brain.
"Our fundamental goal was to fundamentally alter this challenging reality by developing a treatment that bypasses invasive methods and instead empowers 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 initiative of Barnes-Jewish Hospital and WashU Medicine, further elaborated on the significance of their findings: "This research unequivocally demonstrates that meticulously designed nanostructures, specifically spherical nucleic acids, possess the capability to safely and efficiently activate potent immune pathways within the brain. This represents a paradigm shift in how we can achieve cancer immunotherapy, particularly for tumors that have historically been exceptionally difficult to access."
Reawakening the Immune System: The STING Pathway Nanomedicine
Glioblastoma is frequently characterized as a "cold tumor" due to its remarkable ability to evade the body’s natural immune surveillance. Unlike "hot tumors," which exhibit a heightened immune response and are generally more amenable to immunotherapy, glioblastoma often operates under the radar of immune cells. Scientists have, for years, been exploring ways to stimulate a critical cellular signaling pathway known as STING, which stands for stimulator of interferon genes. This pathway is a fundamental component of the innate immune system, designed to detect foreign DNA, thereby triggering a cascade of immune defenses aimed at neutralizing threats.
Previous research had indicated that drugs capable of activating the STING pathway held promise for priming the immune system to recognize and attack glioblastoma cells. However, a significant limitation of these existing STING agonists was their inherent instability, leading to rapid degradation within the body. Consequently, to achieve therapeutic efficacy, they necessitated direct injection into the tumor itself. Given that multiple doses are often required for optimal impact, this approach translated into a series of highly invasive surgical procedures, placing considerable burden on already gravely ill patients.
"We were deeply motivated to find a less burdensome alternative for patients, minimizing the need for invasive interventions during their already difficult journey with illness," explained Dr. Akanksha Mahajan, a postdoctoral research associate in Dr. Stegh’s laboratory and the study’s first author. "I believed that we could leverage the unique properties of spherical nucleic acid platforms to deliver these STING-activating drugs in a noninvasive manner."
Architecting Gold-Core Nanostructures for Direct Nose-to-Brain Delivery
In pursuit of this ambitious goal, Dr. Stegh’s team forged a crucial partnership with Dr. Chad A. Mirkin, PhD, 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, particularly renowned for his development of spherical nucleic acids (SNAs). These intricate nanoscale particles feature a core structure densely functionalized with DNA or RNA strands, a design that has been shown to confer superior delivery efficiency and cellular uptake compared to conventional drug delivery systems.
The collaborative effort led to the design of a specialized iteration of SNAs. These advanced nanostructures incorporated gold nanoparticle cores, chosen for their biocompatibility and ease of functionalization, and were adorned with short DNA fragments engineered to specifically activate the STING pathway within targeted immune cells. The critical innovation was the route of administration: the nasal passages. This route offers a direct pathway from the nasal cavity to the brain, bypassing the blood-brain barrier for certain types of molecules.
While intranasal delivery has been explored in the past for brain-targeted therapies, no nanoscale therapeutic had previously demonstrated the capacity to elicit a robust immune response against brain tumors via this administration route. This study marks a significant breakthrough in validating this novel delivery mechanism for immunotherapy.
"This is, to our knowledge, the first time we have conclusively shown that we can enhance immune cell activation within glioblastoma tumors by delivering nanoscale therapeutics directly from the nose to the brain," Dr. Mahajan emphasized, underscoring the novelty and potential impact of their work.
Tracing the Nanodrops: A Journey to the Brain and Immune Activation
A critical aspect of the research was to rigorously validate both the targeted delivery of the nanostructures to the brain and their efficacy in activating the intended immune cells. To achieve this, the researchers incorporated a molecular tag into the spherical nucleic acids that emitted a detectable glow under near-infrared light. Following the administration of these "nanodrops" to mice bearing glioblastoma tumors, the researchers meticulously tracked the particles’ trajectory. They observed the nanostructures migrating along the olfactory nerve pathway, the primary neural connection linking the facial region to the brain, confirming their intended route of travel.
Upon reaching the brain, the immune response instigated by the nanomedicine was observed to be highly concentrated within specific immune cells residing within the tumor microenvironment. Detectable immune activity was also noted in nearby lymph nodes, suggesting a systemic amplification of the immune response. Crucially, the therapy did not disseminate widely throughout the body, a factor that significantly mitigates the risk of off-target effects and potential systemic toxicity.
Further in-depth analysis revealed that key immune cells located both within and surrounding the tumor had successfully activated the STING pathway. This activation equipped these immune cells with enhanced capabilities to mount a more potent and effective attack against the glioblastoma cells.
Synergistic Therapies: Eradicating Tumors and Preventing Relapse
The therapeutic potential of this nanodrop strategy was further amplified when combined with additional immunotherapies. In the mouse models, pairing the STING-activating nanotherapy with agents designed to invigorate T lymphocytes – another critical class of immune cells central to adaptive immunity – resulted in the complete eradication of tumors. Moreover, this dual-therapy approach induced a durable, long-lasting immune memory, effectively preventing the cancer from recurring. These remarkable outcomes surpassed those achieved with existing STING-targeting therapies, highlighting the synergistic benefits of this combined approach.
Dr. Stegh cautioned that while stimulating the STING pathway is a crucial step, it is unlikely to be a standalone cure for glioblastoma. The complex biology of glioblastoma involves multiple mechanisms that can suppress or disable the immune response. His research team is actively investigating strategies to incorporate additional immune-activating functionalities directly into their nanostructures. This would enable a single therapeutic intervention to address multiple immune evasion tactics employed by the tumor, thereby enhancing its overall efficacy.
"This represents a promising avenue that offers tangible hope for developing safer and more potent treatments for glioblastoma, and potentially for other cancers that have proven resistant to current immunotherapies," Dr. Stegh concluded. "It marks a significant and critical stride toward the eventual translation of this research into clinical applications for patients."
Funding and Disclosure Landscape
The groundbreaking research underpinning this innovative treatment strategy was made possible through substantial financial support from various national and institutional bodies. Key funding was 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 was also secured through grants R01CA120813, R01NS120547, and R01CA272639. Further financial contributions were received from the Melanoma Research Foundation, the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University, and grants from leading biotechnology companies including Cellularity, Alnylam, and AbbVie. Specialized imaging facilities at the Siteman Cancer Center’s Small Animal Cancer Imaging program benefited from NIH instrumentation grants S10OD027042 and S10OD025264, alongside the NCI Cancer Center grant P30CA091842. PET and MRI imaging services 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 policies or viewpoints of the NIH.
In terms of potential conflicts of interest, Dr. Alexander Stegh holds shares in Exicure Inc., a company actively engaged in the development of SNA-based therapeutic platforms. Similarly, Dr. Chad A. 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 details the use of SNA nanoconjugates for crossing the blood-brain barrier. These disclosures are provided to ensure transparency regarding the researchers’ affiliations and intellectual property related to the technology discussed.