By Nana O 
Researchers at Washington University School of Medicine in St. Louis, in collaboration with scientists at Northwestern University, have unveiled a revolutionary noninvasive strategy to combat glioblastoma, one of the most formidable and deadly forms of brain cancer. This pioneering approach leverages precisely engineered nanostructures, delivered via simple nasal drops, to carry potent cancer-fighting compounds directly into the brain. In preclinical studies involving mice, this innovative method has demonstrated remarkable success in treating glioblastoma by effectively stimulating the brain’s own immune system, offering a significant advancement over current and emerging invasive treatment modalities. The findings, published this month in the prestigious journal Proceedings of the National Academy of Sciences (PNAS), represent a significant leap forward in the quest for more accessible and less burdensome cancer therapies.
The Unyielding Challenge of Glioblastoma
Glioblastoma multiforme (GBM) is a highly aggressive primary brain tumor that originates from astrocytes, a type of glial cell that provides support and nourishment to neurons. It stands as the most prevalent and aggressive malignant brain tumor in adults, affecting approximately three out of every 100,000 individuals in the United States annually. The disease is characterized by its rapid growth and infiltrative nature, making surgical removal exceedingly difficult and often incomplete. Consequently, glioblastoma carries a grim prognosis, with a median survival rate that has historically remained around 15 months even with aggressive treatment.
One of the most significant hurdles in developing effective treatments for glioblastoma lies in the brain’s natural defense mechanisms, particularly the blood-brain barrier (BBB). This highly selective physiological barrier meticulously regulates the passage of substances from the bloodstream into the brain, effectively protecting the central nervous system from toxins and pathogens. While essential for brain health, the BBB also presents a formidable obstacle for the delivery of therapeutic agents, including chemotherapy drugs and immunotherapies, to brain tumors. Traditional drug delivery methods often struggle to achieve therapeutic concentrations within the brain without causing systemic toxicity or requiring highly invasive procedures.
"The reality of glioblastoma has been its relentless progression and the immense challenge in delivering effective treatments," stated Dr. Alexander H. Stegh, a professor and vice chair of research in the Taylor Family Department of Neurosurgery at WashU 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 collaboration between Barnes-Jewish Hospital and WashU Medicine, elaborated, "Our objective was to fundamentally alter this paradigm by devising a noninvasive treatment that harnesses the power of the immune system to eradicate glioblastoma. This research demonstrates that meticulously crafted nanostructures, specifically spherical nucleic acids, possess the capability to safely and efficiently activate potent immune pathways within the brain. This breakthrough fundamentally redefines the possibilities for cancer immunotherapy, particularly for tumors that are notoriously difficult to access."
Harnessing the Immune System: The STING Pathway and Nanomedicine
Glioblastoma is often characterized as a "cold tumor" within the field of oncology. This classification signifies its inherent ability to evade the body’s immune surveillance. Unlike "hot tumors," which display a higher density of immune cells and are generally more receptive to immunotherapies, glioblastoma tumors typically lack significant immune cell infiltration and actively suppress anti-tumor immune responses. This immune-evasive nature poses a substantial challenge for treatments designed to stimulate the immune system to target cancer cells.
Scientists have been actively investigating strategies to overcome this immune suppression, with a particular focus on activating intrinsic cellular defense mechanisms. One such pathway of intense interest is the STING (stimulator of interferon genes) pathway. The STING pathway acts as a critical sensor within cells, recognizing the presence of foreign or aberrant DNA. Upon detection, it triggers a cascade of events that leads to the production of interferons and other signaling molecules, thereby activating a robust immune defense response. Activating the STING pathway has shown considerable potential in "warming up" cold tumors, making them more susceptible to immune-mediated destruction.
Previous research had established that drugs 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 has been their rapid degradation in the body and the necessity for direct intratumoral injection to achieve therapeutic efficacy. Given that multiple doses are often required for optimal effect, these treatments necessitate highly invasive surgical procedures, which can be burdensome for patients already battling a severe illness.
"We were deeply motivated to alleviate the burden on patients who are already facing significant health challenges," explained Akanksha Mahajan, PhD, a postdoctoral research associate in Dr. Stegh’s laboratory and the first author of the study. "The idea was to leverage the unique properties of spherical nucleic acid platforms to deliver these potent STING-activating drugs in a manner that completely bypasses invasive procedures."
The Genesis of Gold-Core Nanostructures for Nose-to-Brain Delivery
To overcome the limitations of current therapies, Dr. Stegh’s team forged a crucial partnership with Dr. Chad A. Mirkin, PhD, a renowned leader in nanotechnology and the director of the International Institute for Nanotechnology and the Rathmann Professor of Chemistry at Northwestern University. Dr. Mirkin’s laboratory pioneered the development of spherical nucleic acids (SNAs), a class of nanoscale particles characterized by a dense arrangement of DNA or RNA strands encircling a core material. These unique structures have demonstrated superior efficacy compared to conventional drug delivery systems due to their enhanced stability, cell penetration, and targeting capabilities.
The collaborative effort between the Washington University and Northwestern teams resulted in the design of a specialized iteration of SNAs. These nanostructures feature a core composed of gold nanoparticles, chosen for their biocompatibility and ease of functionalization, densely coated with short DNA fragments specifically engineered to activate the STING pathway. The critical innovation lay in the method of delivery. Instead of resorting to systemic injection or direct tumor injection, the researchers ingeniously utilized the nasal passages as a direct conduit for delivering these nanostructures to the brain.
Intranasal delivery has been explored in the past as a potential route for delivering therapeutics to the central nervous system, aiming to circumvent the BBB. However, previous attempts have largely focused on larger molecules or simpler drug formulations. The novel aspect of this research is the demonstration of a nanoscale therapy that can successfully activate immune responses against brain tumors via this noninvasive nasal route.
"This represents a significant milestone," Mahajan emphasized. "It is the first time we have been able to demonstrate that nanoscale therapeutics, delivered via the nose, can effectively enhance immune cell activation specifically within glioblastoma tumors in the brain."
Tracing the Nanodrops: From Nasal Passage to Neural Pathways
A key objective of the study was to rigorously validate both the selective delivery of the nanostructures to the brain and their precise activation of the intended immune cells within the tumor microenvironment. To achieve this, the researchers incorporated a molecular tag into the spherical nucleic acids. This tag, when exposed to near-infrared light, emits a detectable fluorescence, allowing for real-time tracking of the nanodrops’ journey.
Following the administration of the nanodrops to mice engineered with glioblastoma tumors, the research team meticulously observed the distribution of the fluorescently tagged particles. Their imaging studies revealed that the nanostructures traveled along a well-established pathway: the olfactory nerve, which directly connects the nasal cavity to the olfactory bulb in the brain. From there, the particles diffused into other brain regions, including the tumor site.
Crucially, the immune response triggered by the nanomedicine was found to be highly localized, concentrating within specific immune cells situated within and around the glioblastoma tumor. A secondary site of immune activity was also noted in nearby lymph nodes, suggesting a systemic priming of the immune system. Importantly, the therapy did not exhibit widespread dissemination throughout the rest of the body, a factor that significantly mitigates concerns about potential off-target effects and systemic toxicity.
Subsequent microscopic examination of the tumor tissue confirmed the intended mechanism of action. Immune cells in and around the tumor had successfully activated the STING pathway, leading to a heightened state of alert and enabling them to mount a more potent and coordinated attack against the cancerous cells. This enhanced immune surveillance and cytotoxic activity are critical for tumor regression.
Synergistic Therapies: Eradicating Tumors and Forging Long-Term Immunity
The researchers further explored the potential of combining their novel nanotherapy with other immunomodulatory agents to achieve even more profound therapeutic outcomes. They found that when the STING-activating nanodrops were administered in conjunction with drugs designed to activate T lymphocytes – another vital component of the adaptive immune system – the results were exceptionally promising. This dual-action approach led to the complete eradication of glioblastoma tumors in the treated mice.
Moreover, the combination therapy not only eliminated existing tumors but also induced a durable and long-lasting immune memory. This immunological memory prevented the cancer from recurring in the animal models, a critical factor in achieving long-term remission and improving survival rates. These outcomes significantly outperformed those observed with conventional STING-targeting therapies, underscoring the enhanced efficacy of the noninvasive nanodrop approach.
Dr. Stegh cautioned that while stimulating the STING pathway is a crucial step, it is unlikely to be sufficient on its own to cure glioblastoma. Glioblastoma tumors are notoriously adept at employing a variety of sophisticated mechanisms to suppress or disarm the immune response. To address this, his team is actively investigating ways to engineer their nanostructures with additional immune-activating functionalities. The goal is to create a single therapeutic agent capable of simultaneously targeting multiple immunosuppressive pathways within the tumor microenvironment.
"This therapeutic strategy holds immense promise for developing safer and more effective treatments for glioblastoma," Dr. Stegh concluded. "Furthermore, it opens up new avenues for treating other cancers that are resistant to current immunotherapies. This work represents a significant and critical step towards translating these findings into clinical applications for patients."
Funding and Disclosure Landscape
This groundbreaking research was made possible through substantial financial support from various national and institutional grants. Key funding sources include the National Cancer Institute (NCI) of the National Institutes of Health (NIH) under grant numbers P50CA221747 and R01CA275430, as well as additional NIH grants R01CA120813, R01NS120547, and R01CA272639. Support was also provided by the Melanoma Research Foundation, the Chicago Cancer Baseball Charities at the Lurie Cancer Center of Northwestern University, and grants from commercial entities Cellularity, Alnylam, and AbbVie. The imaging infrastructure at the Siteman Cancer Center Small Animal Cancer Imaging facility received support from NIH instrumentation grants S10OD027042 and S10OD025264, and 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 of this publication is solely the responsibility of the authors and does not necessarily reflect the official views of the NIH.
The research also involves potential conflicts of interest. Dr. Alexander Stegh is a shareholder in Exicure Inc., a company actively involved in developing 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 co-inventors on U.S. Patent US20150031745A1, which describes the use of SNA nanoconjugates for crossing the blood-brain barrier. These disclosures are standard practice in scientific publications and are intended to ensure transparency in research.
