A Responsive Mesoporous Silica Nanoparticle Platform for Magnetic Resonance Imaging-Guided High-Intensity Focused Ultrasound-Stimulated Cargo Delivery with Controllable Location, Time, and Dose

Magnetic resonance imaging (MRI) is an essential modality for clinical diagnosis, and MRI-guided high-intensity focused ultrasound (MRgHIFU) is a powerful technology for targeted therapy. Clinical applications of MRgHIFU primarily utilize hyperthermia and ablation to treat cancerous tissue, but for drug delivery applications thermal damage is undesirable. A biofriendly MRgHIFU-responsive mesoporous silica nanoparticle (MSN) platform that is stimulated within a physiological safe temperature range has been developed, reducing the possibility of thermal damage to the surrounding healthy tissues. Biocompatible polyethylene glycol (PEG) was employed to cap the pores of MSNs, and the release of cargo molecules by HIFU occurs without substantial temperature increase (∼4 °C). To visualize by MRI and measure the stimulated delivery in situ, a U.S. Food and Drug Administration (FDA)-approved gadolinium-based contrast agent, gadopentetate dimeglumine (Gd(DTPA)2–), was used as the imageable cargo. Taking advantage of the three-dimensional (3-D) imaging and targeting capabilities of MRgHIFU, the release of Gd(DTPA)2– stimulated by HIFU was pinpointed at the HIFU focal point in 3-D space in a tissue-mimicking gel phantom. The amount of Gd(DTPA)2– released was controlled by HIFU stimulation times and power levels. A positive correlation between the amount of Gd(DTPA)2– released and T1 was found. The MRgHIFU-stimulated cargo release was further imaged in a sample of ex vivo animal tissue. With this technology, the biodistribution of the nanocarriers can be tracked and the MRgHIFU-stimulated cargo release can be pinpointed, opening up an opportunity for future image-guided theranostic applications.