Macromolecules, dendrimers, and nanomaterials in magnetic resonance imaging: the interplay between size, function, and pharmacokinetics

Hyperbranched polyethylenimine based polyamine-N-oxide-carboxylate chelates of gadolinium for high relaxivity MRI contrast agents

Polydentate amine-N-oxide carboxylates were used as ligands for the formation of Gd(iii) complexes with high relaxivity as MRI contrast agents. Cytotoxicity assays revealed good cytocompatibility of these complexes for clinical applications.

Pharmacokinetics of Chiral Dendrimer-Triamine-Coordinated Gd-MRI Contrast Agents Evaluated by in Vivo MRI and Estimated by in Vitro QCM

Recently, we developed novel chiral dendrimer-triamine-coordinated Gd-MRI contrast agents (Gd-MRI CAs), which showed longitudinal relaxivity (r₁) values about four times higher than that of clinically used Gd-DTPA (Magnevist^®, Bayer). In our continuing study of pharmacokinetic differences derived from both the chirality and generation of Gd-MRI CAs, we found that the ability of chiral dendrimer Gd-MRI CAs to circulate within the body can be directly evaluated by in vitro MRI (7 T). In this study, the association constants (K_a) of chiral dendrimer Gd-MRI CAs to bovine serum albumin (BSA), measured and calculated with a quartz crystal microbalance (QCM) in vitro, were found to be an extremely easy means for evaluating the body-circulation ability of chiral dendrimer Gd-MRI CAs. The K_a values of S-isomeric dendrimer Gd-MRI CAs were generally greater than those of R-isomeric dendrimer Gd-MRI CAs, which is consistent with the results of our previous MRI study in vivo.

Optimizing the high-field relaxivity by self-assembling of macrocyclic Gd(III) complexes

Using recognition moieties that bind to the inner co-ordination sphere of a monomeric DO3A-type di-aqua complex, dimeric poly(aminocarboxylate) gadolinium(III) compounds can be formed with greatly enhanced relaxivities, arising from optimized contributions of inner- and second spheres of hydration.

Evaluation of zinc-doped magnetite nanoparticle toxicity in the liver and kidney of mice after sub-chronic intragastric administration

Super-paramagnetic iron oxide nanoparticles (SPIONs) have been approved for clinical use due to their salient super-paramagnetic properties and low toxicity. Zn²⁺ doped SPIONs possess significantly higher magnetic susceptibility than that of conventional SPIONs. Here we evaluated the potential toxicity of Zn²⁺ doped Fe₃O₄ nanoparticles (Zn_0.4Fe_2.6O₄ NPs) in the liver and kidney of mice after repeated intragastric administration for 30 days. Zn_0.4Fe_2.6O₄ NPs did not cause significant changes in their body weights and the coefficients of the liver and kidney, but increased the levels of Fe and Zn in the two organs. Zn_0.4Fe_2.6O₄ NP induced slight oxidative stress in the liver and kidney, which could be successfully counteracted by their intrinsic antioxidant systems and had no observable hazardous effects on the histopathology, ultrastructure and functions of the two organs. These results demonstrated that high-performance magnetic Zn_0.4Fe_2.6O₄ NPs did not produce apparent toxicity in the liver and kidney of mice even after sub-chronic intragastric administration. In addition, Zn²⁺ doping not only markedly enhanced magnetic susceptibility of Zn_0.4Fe_2.6O₄ NPs but also significantly increased the stability of Zn_0.4Fe_2.6O₄ NPs in biological conditions, making them appropriate for use in magnetic resonance imaging and drug delivery by the oral route.

Multifunctional hybrid nanogels for theranostic applications

This paper reviews a wide set of theranostic applications based on the special properties associated with composite nanogels. The nanogels presented here are mostly hybridized with quantum dots, magnetic nanoparticles, and plasmonic metal noble nanoparticles. These inorganic components confer nanogels multifunctional properties that extend their applications from drug delivery systems to diagnosis and therapy. Nanogels can also be surface functionalized with specific ligands to achieve targeted therapy and reduce toxicity. This versatility makes hybrid nanogels very promising agents for imaging, diagnosis and treatment of cancer and other diseases.

Trifunctional Polymeric Nanocomposites Incorporated with Fe₃O₄/Iodine-Containing Rare Earth Complex for Computed X-ray Tomography, Magnetic Resonance, and Optical Imaging

In this study, a novel polymerizable CT contrast agent integrating iodine with europium(III) has been developed by a facile and universal coordination chemistry method. The Fe3O4 nanoparticles are then incorporated into this iodine-containing europium complex by seed-emulsifier-free polymerization. The nanocomposites combining the difunctional complex and superparamagnetic Fe3O4 nanoparticles, which have uniform size dispersion and high encapsulation rate, are suitable for computed X-ray tomography (CT), magnetic resonance imaging (MRI), and optical imaging. They possess good paramagnetic properties with a maximum saturation magnetization of 2.16 emu/g and a transverse relaxivity rate of 260 mM(-1) s(-1), and they exhibit obvious contrast effects with an iodine payload less than 4.8 mg I/mL. In the in vivo optical imaging assessment, vivid fluorescent dots can be observed in the liver and spleen by two-photon confocal scanning laser microscopy (CLSM). All the results showed that nanocomposites as polymeric trifunctional contrast agents have great clinical potential in CT, MR, and optical imaging.

Gd(3+)-Based Magnetic Resonance Imaging Contrast Agent Responsive to Zn(2+)

We report the heteroditopic ligand H5L, which contains a DO3A unit for Gd(3+) complexation connected to an NO2A moiety through a N-propylacetamide linker. The synthesis of the ligand followed a convergent route that involved the preparation of 1,4-bis(tert-butoxycarbonylmethyl)-1,4,7-triazacyclononane following the orthoamide strategy. The luminescence lifetimes of the Tb((5)D4) excited state measured for the TbL complex point to the absence of coordinated water molecules. Density functional theory calculations and (1)H NMR studies indicate that the EuL complex presents a square antiprismatic coordination in aqueous solution, where eight coordination is provided by the seven donor atoms of the DO3A unit and the amide oxygen atom of the N-propylacetamide linker. Addition of Zn(2+) to aqueous solutions of the TbL complex provokes a decrease of the emission intensity as the emission lifetime becomes shorter, which is a consequence of the coordination of a water molecule to the Tb(3+) ion upon Zn(2+) binding to the NO2A moiety. The relaxivity of the GdL complex recorded at 7 T (25 °C) increases by almost 150% in the presence of 1 equiv of Zn(2+), while Ca(2+) and Mg(2+) induced very small relaxivity changes. In vitro magnetic resonance imaging experiments confirmed the ability of GdL to provide response to the presence of Zn(2+).

Gd3+-1,4,7,10-Tetraazacyclododecane-1,4,7-triacetic-2-hydroxypropyl-β-cyclodextrin/Pluronic Polyrotaxane as a Long Circulating High Relaxivity MRI Contrast Agent

A multivalent magnetic resonance imaging agent based on a 2-hydroxypropyl-β-cyclodextrin (HPCD):Pluronic F127 polyrotaxane carrier has been synthesized, and its blood pool contrast properties have been characterized. This Gd3+-DO3A-HPCD/Pluronic polyrotaxane construct is shown to circulate for more than 30 min and provide >100-fold vascular enhancement relative to the monomeric Gd3+-DO3A-HPCD control that is rapidly cleared via the kidney. The high r1 relaxivity at 37 °C (23.83 mM(-1) s(-1) at 1.5 T; 34.08 mM(-1) s(-1) at 0.5 T), extended blood circulation, well-known pharmacology of the polyrotaxane precursors, and absence of acute toxicity make it a highly attractive blood pool contrast agent candidate.

Synthesis, relaxivity, and in vitro fluorescence imaging studies of a novel d-f heterometallic trinuclear complex as a potential bimodal imaging probe for MRI and optical imaging

A new trinuclear heterometallic Ru(II)-Gd complex of 4-aminopyridine appended DO3A (DO3A = 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane) with 2,2'-bipyridine as ancillary ligands is synthesized and its relaxometry and in vitro fluorescence imaging studies are reported. The complex [Ru(bpy)2{Gd(DOTA-AMpy)(H2O)}2]Cl2 (7) exhibits a "per Gd" longitudinal relaxivity (r1p) of 5.80 and 14.30 mM(-1) s(-1) in aqueous solution and in the presence of HSA, respectively (20 MHz, pH = 7.4, PBS, 37 °C). The complex 7 exhibits an intense (1)MLCT absorption band at 480 nm and luminesces at 595 nm with a luminescence quantum yield of 3.2%. The fluorescence microscopy imaging study of HeLa cells incubated with 7 and stained with ethidium bromide and acridine orange confirms that the cells are viable throughout the imaging experiments and its cytotoxicity against HeLa cells, studied by the MTT assay, demonstrates its use for bioimaging studies. HeLa cell lines treated with the complex 7 and stained with Hoechst-33342 showed marked morphological signs of apoptosis in a dose-dependent manner by inducing changes in cell cycle arrest at the G2/M phase. Furthermore, apoptosis of HeLa cells, studied by the DNA ladder assay, indicates apoptotic cell death lending support for the antitumor activity of 7. A molecular docking study reveals that the complex 7 intercalates into the major groove of the DNA stabilized by hydrogen bonding and it binds with HSA by electrostatic- and hydrogen bonding interactions. The relaxometry, luminescence and fluorescence imaging studies indicate that the Ru(II)-Gd complex 7 has a good cell membrane permeability and could be considered as a potential bimodal imaging probe.

Dendrimer-Assisted Formation of Fe3O4/Au Nanocomposite Particles for Targeted Dual Mode CT/MR Imaging of Tumors

A unique dendrimer-assisted approach is reported to create Fe3O4/Au nanocomposite particles (NCPs) for targeted dual mode computed tomography/magnetic resonance (CT/MR) imaging of tumors. In this approach, preformed Fe3O4 nanoparticles (NPs) are assembled with multilayers of poly(γ-glutamic acid) (PGA)/poly(L-lysine)/PGA/folic acid (FA)-modified dendrimer-entrapped gold nanoparticles via a layer-by-layer self-assembly technique. The interlayers are crosslinked via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide chemistry, the assembled Au core NPs are then used as seed particles for subsequent seed-mediated growth of Au shells via iterative Au salt reduction process, and subsequent acetylation of the remaining amines of dendrimers leads to the formation of Fe3O4/Au(n.)Ac-FA NCPs with a tunable molar ratio of Au/Fe3O4. It is shown that the Fe3O4/Au(n.)Ac-FA NCPs at an optimized Au/Fe3O4 molar ratio of 2.02 display a relatively high R2 relaxivity (92.67 × 10(-3) M(-1) s(-1)) and good X-ray attenuation property, and are cytocompatible and hemocompatible in the given concentration range. Importantly, with the FA-mediated targeting, the Fe3O4/Au(n.)Ac-FA NCPs are able to be specifically uptaken by cancer cells overexpressing FA receptors, and be used as an efficient nanoprobe for targeted dual mode CT/MR imaging of a xenografted tumor model. With the versatile dendrimer chemistry, the developed Fe3O4/Au NCPs may be differently functionalized, thereby providing a unique platform for diagnosis and therapy of different biological systems.

Facile Phase Transfer and Surface Biofunctionalization of Hydrophobic Nanoparticles Using Janus DNA Tetrahedron Nanostructures

Hydrophobic nanoparticles have shown substantial potential for bioanalysis and biomedical applications. However, their use is hindered by complex phase transfer and inefficient surface modification. This paper reports a facile and universal strategy for phase transfer and surface biofunctionalization of hydrophobic nanomaterials using aptamer-pendant DNA tetrahedron nanostructures (Apt-tet). The Janus DNA tetrahedron nanostructures are constructed by three carboxyl group modified DNA strands and one aptamer sequence. The pendant linear sequence is an aptamer, in this case AS1411, known to specifically bind nucleolin, typically overexpressed on the plasma membranes of tumor cells. The incorporation of the aptamers adds targeting ability and also enhances intracellular uptake. Phase-transfer efficiency using Apt-tet is much higher than that achieved using single-stranded DNA. In addition, the DNA tetrahedron nanostructures can be programmed to permit the incorporation of other functional nucleic acids, such as DNAzymes, siRNA, or antisense DNA, allowing, in turn, the construction of promising theranostic nanoagents for bioanalysis and biomedical applications. Given these unique features, we believe that our strategy of surface modification and functionalization may become a new paradigm in phase-transfer-agent design and further expand biomedical applications of hydrophobic nanomaterials.

Virus-based nanomaterials as positron emission tomography and magnetic resonance contrast agents: from technology development to translational medicine

Viruses have recently emerged as ideal protein scaffolds for a new class of contrast agents that can be used in medical imaging procedures such as positron emission tomography (PET) and magnetic resonance imaging (MRI). Whereas synthetic nanoparticles are difficult to produce as homogeneous formulations due to the inherently stochastic nature of the synthesis process, virus-based nanoparticles are genetically encoded and are therefore produced as homogeneous and monodisperse preparations with a high degree of quality control. Because the virus capsids have a defined chemical structure that has evolved to carry cargoes of nucleic acids, they can be modified to carry precisely defined cargoes of contrast agents and can be decorated with spatially defined contrast reagents on the internal or external surfaces. Viral nanoparticles can also be genetically programed or conjugated with targeting ligands to deliver contrast agents to specific cells, and the natural biocompatibility of viruses means that they are cleared rapidly from the body. Nanoparticles based on bacteriophages and plant viruses are safe for use in humans and can be produced inexpensively in large quantities as self-assembling recombinant proteins. Based on these considerations, a new generation of contrast agents has been developed using bacteriophages and plant viruses as scaffolds to carry positron-emitting radioisotopes such as [(18) F] fluorodeoxyglucose for PET imaging and iron oxide or Gd(3+) for MRI. Although challenges such as immunogenicity, loading efficiency, and regulatory compliance remain to be address, virus-based nanoparticles represent a promising new enabling technology for a new generation of highly biocompatible and biodegradable targeted imaging reagents.

Enhancing magnetic resonance imaging with contrast agents for ultra-high field strengths

Contrast agents are diagnostic tools that often complement magnetic resonance imaging. At ultra-high field strengths (≥7 T), magnetic resonance imaging is capable of generating desirable high signal-to-noise ratios, but clinically available contrast agents are less effective at ultra-high field strengths relative to lower fields. This gap in effectiveness demands the development of contrast agents for ultra-high field strengths. In this minireview, we summarize contrast agents reported during the last three years that focused on ultra-high field strengths.

Assembly of near infra-red emitting upconverting nanoparticles and multiple Gd(III)-chelates as a potential bimodal contrast agent for MRI and optical imaging

Linking multiple paramagnetic gadolinium(III)-chelates based on the 2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl]acetate (DOTA) ligand to the surface of NaGdF4:Yb(3+),Tm(3+) upconverting nanoparticles with an average particle size of 20 nm resulted in an assembly that has favorable properties for bimodal Magnetic Resonance Imaging (MRI) and Optical Imaging (OI). An improved synthetic pathway was used to couple the paramagnetic precursor to the nanoparticles. The nanoparticles were rendered water dispersible via citrate capping, leaving one acid group free for amide coupling with the mono-amino precursor of the DOTA ligand. Luminescence spectroscopy measurements have shown that the excitation of the nanoconstruct at 980 nm resulted in intense upconverted emission of thulium(III) at 800 nm. The assembly of several paramagnetic centers on the nanoparticle scaffold reduces the overall tumbling rate, resulting in enhanced longitudinal relaxation times and improved relaxivity. The proton NMRD profiles show a characteristic hump at higher frequencies, which is caused by the slow rotation of the nanoconstruct, resulting in r1 values of 25 mM(-1) s(-1) per gadolinium(III)-ion at 60 MHz and 310 K. This is a significant improvement compared to the Gd-DO3A-ethylamine precursor (4) for which a value of r1 of 3.23 mM(-1) s(-1) was observed under the same conditions. Theoretical fitting by two different approaches showed an increase of τR from 57.3 ps for the Gd-DO3A-ethylamine precursor (4) to 392.0 ps for the nanoconstruct, which is responsible for the overall substantial increase in relaxivity.

Active Targeting of Sorafenib: Preparation, Characterization, and In Vitro Testing of Drug-Loaded Magnetic Solid Lipid Nanoparticles

Sorafenib is an anticancer drug approved by the Food and Drug Administration for the treatment of hepatocellular and advanced renal carcinoma. The clinical application of sorafenib is promising, yet limited by its severe toxic side effects. The aim of this study is to develop sorafenib-loaded magnetic nanovectors able to enhance the drug delivery to the disease site with the help of a remote magnetic field, thus enabling cancer treatment while limiting negative effects on healthy tissues. Sorafenib and superparamagnetic iron oxide nanoparticles are encapsulated in solid lipid nanoparticles by a hot homogenization technique using cetyl palmitate as lipid matrix. The obtained nanoparticles (Sor-Mag-SLNs) have a sorafenib loading efficiency of about 90% and are found to be very stable in an aqueous environment. Plain Mag-SLNs exhibit good cytocompatibility, whereas an antiproliferative effect against tumor cells (human hepatocarcinoma HepG2) is observed for drug-loaded Sor-Mag-SLNs. The obtained results show that it is possible to prepare stable Sor-Mag-SLNs able to inhibit cancer cell proliferation through the sorafenib cytotoxic action, and to enhance/localize this effect in a desired area thanks to a magnetically driven accumulation of the drug. Moreover, the relaxivity properties observed in water suspensions hold promise for Sor-Mag-SLN tracking through clinical magnetic resonance imaging.

Electrostatic Polyion Micelles with Fluorescence and MRI Dual Functions

We report in this work the formation of fluorescence and MRI bimodal imaging nanoparticles achieved by electrostatic self-assembly. The nanoparticles are micelles formed with Gd(3+) ion, a bisligand that contains aggregation induced emission (AIE) group, and a block copolymer. The coordination between the Gd(3+) ion and the bisligand produces a negatively charged coordination complex, which interacted with the positive-neutral block copolymer to form polyion micelles. The micelles exhibit considerable fluorescence owing to the rotation restriction of the AIE group; meanwhile, the longitudinal relaxation of water was significantly slowed down which provide T1 contrast for magnetic resonance imaging. In vitro fluorescence imaging and in vivo MRI measurements verified this micelle indeed exhibit dual imaging ability. We expect that this orthogonal imaging may provide more accurate diagnosis in practical applications and will pave the way for the development of an advanced technique for diagnosis.

Magnetic resonance imaging of tumor with a self-traceable polymer conjugated with an antibody fragment

A (13)C-enriched phosphorylcholine polymer ((13)C-PMPC) as a self-traceable MR (magnetic resonance) tag was conjugated with a fragment (scFv) of Herceptin, a clinical antibody against antigen Her2. When injected in model mice bearing Her2(+) (gastric) and Her2(-) (pancreatic) tumors, the antibody-tag conjugate (13)C-PMPC-scFv selectively accumulated in the Her2(+) tumor with a rapid build-up/decay (accumulation/clearance) profile and, with the use of the (1)H-(13)C double-resonance (heteronuclear correlation) technique, the Her2(+) gastric tumor was clearly MR imaged.

Potential theranostic and multimodal iron oxide nanoparticles decorated with rhenium-bipyridine and -phenanthroline complexes

Two structurally similar nanoparticles were designed for multimodal imaging and possible radiotherapy. The assembly consists of ultrasmall superparamagnetic iron oxide nanoparticles that act as contrast agents for MRI with a luminescent rhenium complex, for optical imaging, attached to the surface. Rhenium has the advantage of being luminescent and carries two radio-isotopes ¹⁸⁶Re and ¹⁸⁸Re making it possible to act as a contrast agent for SPECT (γ) and to be used for radiotherapy (β). The iron oxide nanoparticles were treated with a silane and further functionalized with picolyl. This picolyl was used to capture rhenium(i)(CO)₃-1,10-phenanthroline (ReL₁) or rhenium(i)(CO)₃-2,2'-bipyridine (ReL₂) and forms the final product Fe₃O₄-picolyl-rhenium(i)(CO)₃-1,10-phenanthroline (IO-ReL₁) or Fe₃O₄-silica-picolyl-rhenium(i)(CO)₃-2,2'-bipyridine (IO-ReL₂), respectively. All products were characterized properly (TEM, XRD, NMR, IR and TXRF) and a full investigation of the relaxometric and optical properties was conducted. Although iron oxide nanoparticles suffer from strong Rayleigh scattering, an efficient sensitized luminescence was observed and the orange emission wavelength was found to be 585 nm for IO-ReL₁ and 592 nm for IO-ReL₂ after irradiation at 395 nm. The relaxometric study of these ultrasmall nanoparticles showed very promising results. The r₂ values measured at a magnetic field strength of 60 MHz of the nanoparticles being 92.9 mM^-1 s^-1 and 97.5 mM^-1 s^-1 for IO-ReL₁ and IO-ReL₂, respectively, were at least 1.5 times larger than Sinerem®.

Synthesis and characterization of gadolinium-Peptidomimetic complex as an αvβ3 integrin targeted MR contrast agent

There is growing interest in small and rigid peptidomimetic αvβ3 integrin antagonists that are readily synthesized and characterized and amenable to physiological conditions. Peptidomimetic 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-β-alanine (IAC) was successfully conjugated to DOTA, complexed with Gd(III) and radiolabeled with (153)Gd. Radioassay results demonstrated specificity of the labeled conjugate by blocking ∼95% binding with the addition of a 50-fold molar excess of cold IAC to the reaction solution. Relaxometry was used to support the hypothesis that the specificity of the Gd-peptidomimetic targeting αvβ3 integrin would increase the contrast and therefore enhance the sensitivity of an MRI scan of αvβ3 integrin positive tissues. Magnetic resonance imaging of cell pellets (M21 human melanoma) was also performed, and the images clearly show that cells reacted with Gd(III)-DOTA-IAC display a brighter image than cells without the Gd(III)-DOTA-IAC contrast agent. In addition, Gd(III)-DOTA-IAC and IAC, with IC50 of 300nM and 230nM, respectively, are 2.1 and 2.7 times more potent than c(RGDfK) whose IC50 is 625nM. This promising preliminary data fuels further investigation of DOTA-IAC conjugates for targeting tumor associated angiogenesis and αvβ3 integrin positive tumors using magnetic resonance imaging.

The Present and the Future of Degradable Dendrimers and Derivatives in Theranostics

Interest in dendrimer-based nanomedicines has been growing recently, as it is possible to precisely manipulate the molecular weight, chemical composition, and surface functionality of dendrimers, tuning their properties according to the desired biomedical application. However, one important concern about dendrimer-based therapeutics remains-the nondegradability under physiological conditions of the most commonly used dendrimers. Therefore, biodegradable dendrimers represent an attractive class of nanomaterials, since they present advantages over conventional nondegradable dendrimers regarding the release of the loaded molecules and the prevention of bioaccumulation of synthetic materials and subsequent cytotoxicity. Here, we present an overview of the state-of-the-art of the design of biodegradable dendritic structures, with particular focus on the hurdles regarding the use of these as vectors of drugs and nucleic acids, as well as macromolecular contrast agents.

High relaxivity Gd(III)-DNA gold nanostars: investigation of shape effects on proton relaxation

Gadolinium(III) nanoconjugate contrast agents (CAs) have distinct advantages over their small-molecule counterparts in magnetic resonance imaging. In addition to increased Gd(III) payload, a significant improvement in proton relaxation efficiency, or relaxivity (r1), is often observed. In this work, we describe the synthesis and characterization of a nanoconjugate CA created by covalent attachment of Gd(III) to thiolated DNA (Gd(III)-DNA), followed by surface conjugation onto gold nanostars (DNA-Gd@stars). These conjugates exhibit remarkable r1 with values up to 98 mM(-1) s(-1). Additionally, DNA-Gd@stars show efficient Gd(III) delivery and biocompatibility in vitro and generate significant contrast enhancement when imaged at 7 T. Using nuclear magnetic relaxation dispersion analysis, we attribute the high performance of the DNA-Gd@stars to an increased contribution of second-sphere relaxivity compared to that of spherical CA equivalents (DNA-Gd@spheres). Importantly, the surface of the gold nanostar contains Gd(III)-DNA in regions of positive, negative, and neutral curvature. We hypothesize that the proton relaxation enhancement observed results from the presence of a unique hydrophilic environment produced by Gd(III)-DNA in these regions, which allows second-sphere water molecules to remain adjacent to Gd(III) ions for up to 10 times longer than diffusion. These results establish that particle shape and second-sphere relaxivity are important considerations in the design of Gd(III) nanoconjugate CAs.

MR imaging probes: design and applications

This perspective outlines strategies towards the development of MR imaging probes that our lab has explored over the last 15 years. Namely, we discuss methods to enhance the signal generating capacity of MR probes and how to achieve tissue specificity through protein targeting or probe activation within the tissue microenvironment.

Nanoparticles based on star polymers as theranostic vectors: endosomal-triggered drug release combined with MRI sensitivity

Dual-functional star polymers (diameters 15 nm) are synthesized producing nanoparticles with excellent colloidal stability in both water and serum. The nanoparticles are built with aldehyde groups in the core and activated esters in the arms. The different reactivity of the two functional groups to sequentially react with different amino compounds is exploited; doxorubicin (DOX) and 1-(5-amino-3-aza-2-oxypentyl)-4,7,10-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane (DO3A-tBu-NH2 )-a chelating agent effective for the complexation of Gadolinium ions (Gd). The activated ester group is employed to attach the DO3A chelating agent, while the aldehyde groups are exploited for DOX conjugation, providing a controlled release mechanism for DOX in acidic environments. DOX/Gd-loaded nanoparticles are rapidly taken up by MCF-7 breast cancer cells, subsequently releasing DOX as demonstrated using in vitro fluorescence lifetime imaging microscopy (FLIM). Endosomal, DOX release is observed, using a phasor plot representation of the fluorescence lifetime data, showing an increase of native DOX with time. The MRI properties of the stars are assessed and the relaxivity of Gd loaded in stars is three times higher than conventional organic Gd/DO3A complexes. The DOX/Gd-conjugated nanoparticles yield a similar IC50 to native DOX for breast cancer cell lines, confirming that DOX integrity is conserved during nanoparticle attachment and release.

Radiolabeled dendritic probes as tools for high in vivo tumor targeting: application to melanoma

A small-sized and bifunctional¹¹¹In-radiolabeled dendron shows highin vivotargeting efficiency towards an intracellular target in a murine melanoma model.

Radiopaque poly(ε-caprolactone) as additive for X-ray imaging of temporary implantable medical devices

A family of radiopaque PCL, poly(ε-caprolactone-co-α-triiodobenzoate-ε-caprolactone), has been designed, used and evaluated as macromolecular contrast agent for X-ray imaging of implantable polymeric biomaterials.

Facile preparation and bifunctional imaging of Eu-doped GdPO4 nanorods with MRI and cellular luminescence

Eu-doped GdPO₄ NRs coated by silk fibroin have been prepared in a template of silk fibroin (SF) peptides via a mineralization process. A growth mechanism of SF-NRs is proposed to explain their stronger luminescence, better cyto-compatibility and higher longitudinal relaxivity r₁.

A multiple gadolinium complex decorated fullerene as a highly sensitive T1 contrast agent

A multiple gadolinium complex decorated fullerene (CGD_n) as an enhanced T₁ contrast agent was presented.

Imaging agents based on lanthanide doped nanoparticles

This review summarizes the recent progress of single and multimodal imaging agents based on lanthanide doped nanoparticles.

Silica-based nanoparticles: a versatile tool for the development of efficient imaging agents

In this review a selection of the most recent examples of imaging techniques applied to silica-based NPs for imaging is reported.