PEGylated nanocapsules of perfluorooctyl bromide: Mechanism of formation, influence of polymer concentration on morphology and mechanical properties.

PEGylated nanocapsules containing a liquid core of perfluorooctyl bromide (PFOB) were formulated by an emulsion-evaporation process to be further used as ultrasound contrast agents (UCAs). In an attempt to modulate their acoustic response, related to their shell thickness-to-radius ratio, the initial concentration of polymer was varied in the formulation. Indeed, thinner shells may lead to higher echogenicity. PEGylated nanocapsules morphology was studied by electron microscopy, Small Angle Neutron Scattering and (19)F NMR spectroscopy and related to their mechanical properties to allow a better understanding of their mechanism of formation. We show that the variation of polymer concentration in the formulation impacts the formation mechanism of nanocapsules, and consequently their morphology and mechanical properties. Using low concentration of Poly(ethylene glycol)-b-poly(dl-lactide-co-glycolide) (PLGA-b-PEG), it is impossible to reduce the shell thickness of the UCA, most probably due to dewetting of the polymer layer at the PFOB/water interface. This leads to the coexistence of thick shells along with free PFOB droplets. On the other hand, for high polymer concentration, PEGylated nanocapsules with thick shells were produced with high encapsulation efficiency.

Properties of theranostic nanoparticles determined in suspension by ultrasonic spectroscopy.

In the context of growing use of nanoparticles, it is important to be able to characterize all their physical properties in order to understand their behavior, to optimize them, and to control their quality. We showed that ultrasonic spectroscopy provides many of the desired properties. To do so, we used as an example nanocapsules made of a polymer shell encaspulating a liquid perfluorocarbon core and designed them for theranostic applications. Frequency-dependent measurements of both ultrasound velocity and attenuation were performed on nanocapsule suspensions. Then the desired properties were extracted by analyzing the experimental data using a recently developed model that relates the speed of sound and attenuation of a suspension to the geometrical and viscoelastic properties of the nanocapsules.

High-frequency (20 to 40 MHz) acoustic response of liquid-filled nanocapsules.

Liquid-core nanoparticles are promising candidates for targeted ultrasound-controlled therapy, but their acoustic detection remains challenging. High-frequency (20 to 40 MHz) tone burst sequences were implemented with a programmable ultrasound biomicroscope to characterize acoustic response from perfluorooctyl bromide-core nanoparticles with thick poly(lactide-coglycolide) (PLGA) shells. Radio-frequency signals were acquired from flowing solutions of nanoparticles with two different shell-thickness-to-particle-radius ratios, solid PLGA nanoparticles, and latex nanobeads (linear controls). Normalized fundamental (20 MHz) and second-harmonic power spectral density (PSD) increased with particle concentration and was highest for the thinnest shelled particles. The second- harmonic PSD was detectable from the nanoparticles for peak rarefactional pressures (PRP) from 0.97 to 2.01 MPa at 23 cycles and for tone bursts from 11 to 23 cycles at 2.01 MPa. Their second-harmonic¿to¿fundamental ratio increased as a function of PRP and number of cycles. Within the same PRP and cycle ranges, the second-harmonic¿to¿fundamental ratios from matched concentration solutions of latex nanobeads and solid PLGA nanoparticles was more weakly detectable but also increased with PRP and number of cycles. Nanoparticles were detectable under flow conditions in vitro using the contrast agent mode of a high-frequency commercial scanner. These results characterize linear acoustic response from the nanoparticles (20 to 40 MHz) and demonstrate potential for their highfrequency detection.

RGD decoration of PEGylated polyester nanocapsules of perfluorooctyl bromide for tumor imaging: influence of pre or post-functionalization on capsule morphology.

PEGylated polyester nanocapsules of perfluorooctyl bromide (PFOB) were surface-decorated with a RGD (arginine-glycine-aspartic acid) peptide by either pre-functionalization or post-functionalization strategies using carbodiimide-assisted chemistry. Both strategies allowed successful linkage of RGD at the surface of nanocapsules with up to 600-950 peptide units per nanocapsule without modifying the encapsulation efficacy of PFOB used as the (19)F MRI imaging moiety. Cryo-Transmission Electron Microscopy images evidence that slight changes of the polymer used to form the capsule shell strongly influence nanocapsule morphology. While, the use of copolymer blends induces the formation of acorn morphologies, PLA-b-PEG-COOH leads to elongated and "tears of wine"-like nanoconstructs. In vivo evaluation in mice bearing CT26 tumors by (19)F MRI reveals no significant difference of accumulation between PEGylated and RGD-decorated nanocapsules obtained by the post-functionalization approach (highest RGD density/capsule).

Targeted nanotheranostics for personalized cancer therapy.

INTRODUCTION: The development of nanomedicine, during the last 10 years have given rise to novel delivery systems among which multifunctional platforms called nanotheranostics that are designed to simultaneously diagnose and cure cancer. These systems can be built using the large panel of biocompatible and biodegradable materials. The recent advances of imaging modalities even enable targeted nanotheranostics to probe molecular structures on specific cells opening the doors to personalized cancer therapy. AREAS COVERED: This review presents the different requirements nanotheranostics should fulfill to achieve an optimized anticancer therapy. It focuses on two imaging modalities: MRI and ultrasonography used to visualize drug delivery, release, and efficacy. The advantages and limitations of these two methods are considered. The review will enable the readers to virtually tune a nanotheranostic system according to the nature of the targeting tissue and the availability of imaging modality. EXPERT OPINION: Despite great perspectives, described for nanotheranostic systems in personalized cancer therapy, the imaging techniques still face technological issues, such as high sensitivity and good spatial and temporal resolutions. Active targeting should consider better specificity and low immunogenicity of the ligand selected, to be more efficient.

Long-circulating perfluorooctyl bromide nanocapsules for tumor imaging by 19FMRI.

PLGA-PEG nanocapsules containing a liquid core of perfluorooctyl bromide were synthesized by an emulsion-evaporation process and designed as contrast agents for (19)F MRI. Physico-chemical properties of plain and PEGylated nanocapsules were compared. The encapsulation efficiency of PFOB, estimated by (19)F NMR spectroscopy, is enhanced when using PLGA-PEG instead of PLGA. PLGA-PEG nanocapsule diameter, measured by Dynamic Light Scattering is around 120 nm, in agreement with Transmission Electron microscopy (TEM) observations. TEM and Scanning Electron Microscopy (SEM) reveal that spherical core-shell morphology is preserved. PEGylation is further confirmed by Zeta potential measurements and X-ray Photoelectron Spectroscopy. In vitro, stealthiness of the PEGylated nanocapsules is evidenced by weak complement activation. Accumulation kinetics in the liver and the spleen was performed by (19)F MRI in mice, during the first 90 min after intravenous injection. In the liver, plain nanocapsules accumulate faster than their PEGylated counterparts. We observe PEGylated nanocapsule accumulation in CT26 xenograft tumor 7 h after administration to mice, whereas plain nanocapsules remain undetectable, using (19)F MRI. Our results validate the use of diblock copolymers for PEGylation to increase the residence time of nanocapsules in the blood stream and to reach tumors by the Enhanced Permeation and Retention (EPR) effect.

Doxorubicin loaded magnetic polymersomes: theranostic nanocarriers for MR imaging and magneto-chemotherapy.

Hydrophobically modified maghemite (γ-Fe(2)O(3)) nanoparticles were encapsulated within the membrane of poly(trimethylene carbonate)-b-poly(l-glutamic acid) (PTMC-b-PGA) block copolymer vesicles using a nanoprecipitation process. This formation method gives simple access to highly magnetic nanoparticles (MNPs) (loaded up to 70 wt %) together with good control over the vesicles size (100-400 nm). The simultaneous loading of maghemite nanoparticles and doxorubicin was also achieved by nanoprecipitation. The deformation of the vesicle membrane under an applied magnetic field has been evidenced by small angle neutron scattering. These superparamagnetic hybrid self-assemblies display enhanced contrast properties that open potential applications for magnetic resonance imaging. They can also be guided in a magnetic field gradient. The feasibility of controlled drug release by radio frequency magnetic hyperthermia was demonstrated in the case of encapsulated doxorubicin molecules, showing the viability of the concept of magneto-chemotherapy. These magnetic polymersomes can be used as efficient multifunctional nanocarriers for combined therapy and imaging.