Quantitative (1)H MRI, (19)F MRI, and (19)F MRS of cell-internalized perfluorocarbon paramagnetic nanoparticles

In vivo molecular imaging with targeted MRI contrast agents will require sensitive methods to quantify local concentrations of contrast agent, enabling not only imaging-based recognition of pathological biomarkers but also detection of changes in expression levels as a consequence of disease development, therapeutic interventions or recurrence of disease. In recent years, targeted paramagnetic perfluorocarbon emulsions have been frequently applied in this context, permitting high-resolution (1)H MRI combined with quantitative (19)F MR imaging or spectroscopy, under the assumption that the fluorine signal is not altered by the local tissue and cellular environment. In this in vitro study we have investigated the (19)F MR-based quantification potential of a paramagnetic perfluorocarbon emulsion conjugated with RGD-peptide to target the cell-internalizing α(ν)β(3)-integrin expressed on endothelial cells, using a combination of (1)H MRI, (19)F MRI and (19)F MRS. The cells took up the targeted emulsion to a greater extent than nontargeted emulsion. The targeted emulsion was internalized into large 1-7 µm diameter vesicles in the perinuclear region, whereas nontargeted emulsion ended up in 1-4 µm diameter vesicles, which were more evenly distributed in the cytoplasm. Association of the targeted emulsion with the cells resulted in different proton longitudinal relaxivity values, r(1), for targeted and control nanoparticles, prohibiting unambiguous quantification of local contrast agent concentration. Upon cellular association, the fluorine R(1) was constant with concentration, while the fluorine R(2) increased nonlinearly with concentration. Even though the fluorine relaxation rate was not constant, the (19)F MRI and (19)F MRS signals for both targeted nanoparticles and controls were linear and quantifiable as function of nanoparticle concentration.

Temperature-sensitive liposomes for doxorubicin delivery under MRI guidance

Local drug delivery of doxorubicin holds promise to improve the therapeutic efficacy and to reduce toxicity profiles. Here, we investigated the release of doxorubicin and [Gd(HPDO3A)(H(2)O)] from different temperature-sensitive liposomes for applications in temperature-induced drug delivery under magnetic resonance image guidance. In particular, two temperature-sensitive systems composed of DPPC:MPPC:DPPE-PEG2000 (low temperature-sensitive liposomes, LTSL) and DPPC:HSPC:cholesterol:DPPE-PEG2000 (traditional temperature-sensitive liposomes, TTSL) were investigated. The co-encapsulation of [Gd(HPDO3A)(H(2)O)], a clinically approved MRI contrast agent, did not influence the encapsulation and release of doxorubicin. The LTSL system showed a higher leakage of doxorubicin at 37 degrees C, but a faster release of doxorubicin at 42 degrees C compared to the TTSL system. Furthermore, the rapid release of both doxorubicin and the MRI contrast agent from the liposomes occurred near the melting phase transition temperature, making it possible to image the release of doxorubicin using MRI.

A high relaxivity Gd(III)DOTA-DSPE-based liposomal contrast agent for magnetic resonance imaging

The field of molecular imaging aims to visualize and quantify (patho)physiological processes at the cellular and molecular level. Sensitive and site-targeted contrast agents are employed to visualize molecular constituents of processes of interest. The principal aim of this study was to develop a magnetic resonance imaging (MRI) detectable liposome with high relaxivity and stability. To this end, Gd(III)DOTA-DSPE was synthesized and incorporated in a liposomal formulation. The resulting liposomes were extensively characterized in vitro in terms of contrast agent efficiency and structural properties. The liposomes were shown to have a high longitudinal relaxivity, which is crucial for the detection of low concentration molecular markers in molecular imaging studies. We also demonstrated that Gd(III)DOTA-DSPE exhibits no detectable transmetallation upon incubation with Zn(II). This is important as it significantly contributes to the biocompatibility of the contrast agent. The present liposome preparation will serve as versatile and well characterized platform for molecular imaging and targeted drug delivery studies.

A doxorubicin prodrug activated by the staudinger reaction

Much effort has been devoted to prodrug systems that effect drug release at the tumor through enzymatic action. To widen the scope of prodrug therapy, the use of the selective Staudinger reaction as prodrug activator, instead of relying on enzymatic action, was investigated. Doxorubicin was conjugated to a p-azidobenzyl trigger that is cleaved after reacting with the chemical activator, triphenylphosphine. The prodrug activation was confirmed in water, cell growth medium, and serum, using HPLC and LCMS. Next, this approach was tested in a cell proliferation assay with A431 human vulvar skin squamous carcinoma cells. The doxorubicin prodrug was shown to exhibit a 176-fold higher IC50 of 15.1 microM vs 0.086 microM for the parent drug, doxorubicin. Addition of triphenylphosphine (5 x 60 microM in 72 h) to the prodrug in cell culture effected the complete recovery of the activity of the parent drug as evidenced by an IC50 value of 0.074 microM. Furthermore, high levels of triphenylphosphine were tolerated well by the cells. The demonstrated usefulness of the Staudinger reaction in cell culture and its in vivo potential opens up new avenues for prodrug therapy.

Dendritic PARACEST contrast agents for magnetic resonance imaging

MRI contrast agents based on chemical exchange-dependent saturation transfer (CEST), such as Yb(III)DOTAM complexes, are highly suitable for pH mapping. In this paper, the synthesis of Yb(III)DOTAM-functionalized poly(propylene imine) dendrimers is described. The applicability of these dendritic PARACEST MRI agents for pH mapping has been evaluated on a 7 T NMR spectrometer and on a 3 T clinical MRI scanner. As expected, based on the different numbers of exchangeable amide protons, the lowest detectable concentration of the first and third generation dendritic PARACEST agents is by a respective factor of about 4 and 16 lower than that of a mononuclear reference complex. The pH dependence of the CEST effect observed for these compounds depends on the generation of the poly(propylene imine) dendrimer. Upon going to higher generations of the Yb(III)DOTAM-terminated dendrimer, a shift of the maximum CEST effect towards lower pH values was observed. This allows for a fine-tuning of the responsive pH region by varying the dendritic framework.

Wetting behavior of water droplets on hydrophobic microtextures of comparable size

The wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The effect of structure geometry, roughness, and relative pore fraction on the contact angles was investigated experimentally for droplets of size comparable to the size of the structures. It was found that surface geometry may induce a transition from groove-filling and Wenzel-like behavior to nonfilling of surface grooves and consequential Cassie-Baxter behavior. Numerical calculations of the free energy of these systems suggest that the equilibrium behavior is in line with the experimental observations. The observations may serve as guidelines for the design of surfaces with the desired wetting behavior.