The management of brain diseases remains a challenge, particularly because of the difficulty for drugs to cross the blood–brain barrier. Among strategies developed to improve drug delivery, nano-sized emulsions (i.e., nanoemulsions), employed as nanocarriers, have been described. Moreover, focused ultrasound-mediated blood–brain barrier disruption using microbubbles is an attractive method to overcome this barrier, showing promising results in clinical trials. Therefore, nanoemulsions combined with this technology represent a real opportunity to bypass the constraints imposed by the blood–brain barrier and improve the treatment of brain diseases. In this work, a stable freeze-dried emulsion of perfluorooctyl bromide nanodroplets stabilized with home-made fluorinated surfactants able to carry hydrophobic agents is developed. This formulation is biocompatible and droplets composing the emulsion are internalized in multiple cell lines. After intravenous administration in mice, droplets are eliminated from the bloodstream in 24 h (blood half-life (t_1/2) = 3.11 h) and no long-term toxicity is expected since they are completely excreted from mice’ bodies after 72 h. In addition, intracerebral accumulation of tagged droplets is safely and significantly increased after focused ultrasound-mediated blood–brain barrier disruption. Thus, the proposed nanoemulsion appears as a promising nanocarrier for a successful focused ultrasound-mediated brain delivery of hydrophobic agents.

We investigated the in vitro ultrasound-triggered delivery of paclitaxel, a well known anti-cancerous drug, encapsulated in an emulsion and in the presence of CT26 tumor cells. The emulsion was made of nanodroplets, whose volume comprised 95% perfluoro-octyl bromide and 5% tributyl O-acetylcitrate, in which paclitaxel was solubilized. These nanodroplets, prepared using a high-pressure microfluidizer, were stabilized by a tailor-made and recently patented biocompatible fluorinated surfactant. The delivery investigations were performed at 37 °C using a high intensity focused ultrasound transducer at a frequency of 1.1 MHz. The ultrasonic pulse was made of 275 sinusoidal periods and the pulse repetition frequency was 200 Hz with a duty cycle of 5%. The measured viabilities of CT26 cells showed that paclitaxel delivery was achievable for peak-to-peak pressures of 0.4 and 3.5 MPa, without having to vaporize the perfluorocarbon part of the droplet or to induce inertial cavitation.

The effect of micro-droplet concentration on HIFU beam absorption.

Photodynamic therapy (PDT) is a non-invasive therapeutic modality based on the interaction between a photosensitive molecule called photosensitizer (PS) and visible light irradiation in the presence of oxygen molecule. Protoporphyrin IX (PpIX), an efficient and widely used PS, is hampered in clinical PDT by its poor water-solubility and tendency to self-aggregate. These features are strongly related to the PS hydrophilic–lipophilic balance. In order to improve the chemical properties of PpIX, a series of amphiphilic PpIX derivatives endowed with PEG₅₅₀ headgroups and hydrogenated or fluorinated tails was synthetized. Hydrophilic–lipophilic balance (HLB) and log p-values were computed for all of the prepared compounds. Their photochemical properties (spectroscopic characterization, photobleaching, and singlet oxygen quantum yield) were also evaluated followed by the in vitro studies of their cellular uptake, subcellular localization, and photocytotoxicity on three tumor cell lines (4T1, scc-U8, and WiDr cell lines). The results confirm the therapeutic potency of these new PpIX derivatives. Indeed, while all of the derivatives were perfectly water soluble, some of them exhibited an improved photodynamic effect compared to the parent PpIX.

Purpose: Micron-sized perfluorocarbon droplet adjuvants to focused ultrasound therapies allow lower applied power, circumvent unwanted prefocal heating, and enhance thermal dose in highly perfused tissues. The heat enhancement has been shown to saturate at increasing concentrations. Experiments were performed to empirically model the saturating heating effects during focused ultrasound. Materials and methods: The measurements were made at varying concentrations using magnetic resonance thermometry and focused ultrasound by circulating droplets of mean diameter 1.9 to 2.3 µm through a perfused phantom. A simulation was performed to estimate the interaction radius size, empirically. Results: The interaction radius, representing the radius of a sphere encompassing 90% of the probability for the transformation of acoustic energy into heat deposition around a single droplet, was determined experimentally from ultrasonic absorption coefficient measurements The simulations suggest the interaction radius was approximately 12.5-fold larger than the geometrical radius of droplets, corresponding to an interaction volume on the order of 2000 larger than the geometrical volume. Conclusions: The results provide information regarding the dose–response relationship from the droplets, a measure with 15% precision of their interaction radii with focused ultrasound, and subsequent insights into the underlying physical heating mechanism.

Glioblastoma (GBM) remains the most aggressive primary brain tumor, characterized by a high recurrence rate and a poor prognosis, particularly due to the blood-brain/tumor barrier, which severely limits the intracerebral drug delivery. This study evaluates a novel strategy combining a nanomedicine-based drug delivery approach with focused ultrasound-mediated blood–brain barrier disruption (FUS-BBBD) to achieve localized therapeutic drug concentrations to the tumor. Paclitaxel and docetaxel were encapsulated in perfluorooctyl bromide nanodroplets, stabilized with fluorinated surfactants. The formulation was optimized and characterized in terms of drug loading, encapsulation efficiency, size, size distribution and stability. In vivo pharmacokinetics (PK) and safety were assessed in C57BL/6 mice. Therapeutic efficacy was evaluated using an orthotopic syngeneic GL261 glioma model combined with hemispheric 1.5 MHz FUS-BBBD. Docetaxel-loaded nanodroplets (DTX-NDs) emerge as the most promising candidates. Optimized DTX-NDs exhibited a mean diameter of 62 ± 4 nm with an encapsulation efficiency exceeding 90%, a good stability achieved by freeze-drying, and a sustained release profile. PK analysis demonstrated a 28-fold reduction in systemic clearance and a significantly prolonged terminal half-life compared to free docetaxel. Quantitative LC-MS confirmed that FUS-BBBD enhanced docetaxel accumulation 9-fold in healthy brain tissue (p < 0.05) and 6-fold in GL261 glioma-bearing mice (p < 0.05) when using the nanodroplet formulation. An optimized treatment plan with DTX-NDs (20 mg kg⁻¹ every 72 hours) successfully balanced efficacy and safety, extending median survival to 36 days versus 20 days for free DTX (p < 0.05), while achieving a 33% long-term survival rate. Toxicity was limited to transient and reversible hepatotoxicity. This study demonstrates that the repeated combination of DTX-NDs and FUS-BBBD is a biocompatible and effective strategy for enhancing brain drug delivery while minimizing peripheral toxicity, thereby offering a promising translational approach for the treatment of GBM.