University of Utah researchers have achieved a significant breakthrough in targeted drug delivery, successfully demonstrating ultrasound-activated nanoparticles that can release medications in specific deep brain regions of non-human primates. The proof-of-concept study, published in the Journal of Controlled Release, represents a critical step toward clinical translation of precision medicine for neurological disorders.
Multilayered Nanoparticle Design Overcomes Stability Challenges
The research team, led by Jan Kubanek, Ph.D., assistant professor in biomedical engineering at the University of Utah, engineered innovative three-layer nanoparticles to address previous stability concerns. The design features an inner core containing a contrast agent that responds to ultrasound activation, a second layer that encapsulates the drug, and an outer protective shell.
"The main benefit of using ultrasound-sensitive nanoparticles is that they encapsulate the drug so that it has minimal interaction with the body, except where it's released by focused ultrasound," Kubanek explained. "This could potentially allow us to treat under-regulated or malfunctioning circuits in the brain without exposing the entire brain and the body to drugs."
The enhanced design builds upon previous rodent research but addresses critical limitations. Earlier nanoparticles were unstable in the bloodstream, raising safety concerns. Kubanek's team improved stability by selecting a different contrast agent and adding the outer shell, while encapsulating the drug to prevent unwanted interactions with surrounding tissues until ultrasound activation.
Behavioral Evidence Confirms Targeted Brain Delivery
To evaluate their system's safety and effectiveness, researchers loaded the nanocarriers with low-dose propofol, an anesthetic that suppresses neural circuits. They chose propofol because it produces well-defined neural inhibition with rapid effects, allowing precise assessment of drug release.
The team focused on the lateral geniculate nuclei (LGN), small brain structures crucial for vision. Using an established visual choice experiment, they tested whether releasing propofol in specific LGN regions would impact the monkeys' behavior. Animals were shown light flashes on both sides and indicated which appeared first through eye movements.
After injecting propofol-loaded nanoparticles into the bloodstream, researchers delivered 1-minute ultrasound pulses to either the right or left LGN. As predicted, animals showed behavioral bias corresponding to the targeted brain side. When propofol was released in the right LGN, animals chose right-side targets, and vice versa for left LGN targeting.
The selective propofol release successfully modulated visual choice behavior specific to the targeted brain side, demonstrating precise spatial control. The study found that low propofol doses achieved targeted brain delivery when ultrasound-activated, minimizing interaction with other tissues and organs.
Clinical Translation Potential and Safety Profile
The nanoparticles circulated in the blood for approximately 30 minutes, providing a practical time window for human applications. This circulation time offers sufficient opportunity for targeted ultrasound activation while limiting systemic exposure.
"This study is important because it demonstrated a safe and effective approach to releasing drugs on demand in awake, behaving primates, as opposed to previous studies that used rodents, thus providing a critical step toward future clinical translation," said Guoying Liu, Ph.D., director of NIBIB's Division of Applied Science and Technology.
The researchers acknowledged two study limitations: drug release was not validated using imaging modalities, and behavioral effects could be subject to adaptation or other cognitive influences. However, these limitations were mitigated by contrasting drug release across different brain sites and comparing propofol-filled nanoparticles with saline and empty nanoparticles.
Complementary Framework Technology Advances Precision Control
Parallel research from The University of Texas at Austin has developed hydrogen-bonded organic frameworks that can be programmed for ultrasound-triggered drug release. The team, led by Huiliang "Evan" Wang, created a visualization model showing mechanochemical scission—the severing of bonds between hydrogen frameworks using sound waves.
"We aim to make the experience easier for patients through these non-invasive techniques while simultaneously improving the accuracy and effectiveness of treatments," Wang explained. Their research, published in Nature, demonstrated the technology using designer drug clozapine N-oxide embedded in nanoparticles, activated by focused ultrasound to control specific neuronal activity in deep brain regions.
Broad Therapeutic Applications on the Horizon
Both research teams envision extensive clinical applications. The Utah system could potentially treat cancer, pain, or addiction, as the nanoparticles are designed to carry various drugs and release them upon ultrasound activation. The team is currently testing targeted chemotherapy delivery in a mouse model of glioblastoma, the most aggressive brain cancer.
The UT Austin technology shows promise for treating neurological conditions including depression, anxiety, and Parkinson's disease through precise neural activity control. Targeted tumor drug delivery could improve chemotherapy efficacy while minimizing side effects, and ultrasound-triggered local anesthesia could provide chronic pain relief without invasive procedures.
"A major strength of this approach is that the nanoparticles are designed to carry any drug and release it upon ultrasound activation so this system could be used to treat cancer, pain, or addiction," Kubanek noted. The UT Austin team plans to advance their technology into clinical trials while continuing computational design refinements for enhanced drug delivery capabilities.
