PEGylated Amphiphilic Gd-DOTA Backboned-Bound Branched Polymers as Magnetic Resonance Imaging Contrast Agents

MRI contrast agents with high kinetic stability and relaxivity are the key objectives in the field. We previously reported that Gd-DOTA backboned-bound branched polymers possess high kinetic stability and significantly increased T1 relaxivity than traditional branched polymer contrast agents. In this work, non-PEGylated and PEGylated amphiphilic Gd-DOTA backboned-bound branched polymers [P(GdDOTA-C6), P(GdDOTA-C10), mPEG-P(GdDOTA-C6), and mPEG-P(GdDOTA-C10)] were obtained by sequential introduction of rigid carbon chains (1,6-hexamethylenediamine or 1,10-diaminodecane) and mPEG into the structure of Gd-DOTA backboned-bound branched polymers. It is found that the introduction of both rigid carbon chains, especially the longer one, and mPEG can increase the kinetic stability and T1 relaxivity of Gd-DOTA backboned-bound branched polymers. Among them, mPEG-P(GdDOTA-C10) possesses the highest kinetic stability (significantly higher than those of linear Gd-DTPA and cyclic Gd-DOTA-butrol) and T1 relaxivity (42.9 mM-1 s-1, 1.5 T), 11 times that of Gd-DOTA and 1.4 times that of previously reported Gd-DOTA backboned-bound branched polymers. In addition, mPEG-P(GdDOTA-C10) showed excellent MRA effect in cardiovascular and hepatic vessels at a dose (0.025 or 0.05 mmol Gd/kg BW) far below the clinical range (0.1-0.3 mmol Gd/kg BW). Overall, effective branched-polymer-based contrast agents can be obtained by a strategy in which rigid carbon chains and PEG were introduced into the structure of Gd-DOTA backbone-bound branched polymers, resulting in excellent kinetic stability and enhanced T1 relaxivity.

Gadolinium(III) Complex-Backboned Branched Polymers as Imaging Probes for Contrast-Enhanced Magnetic Resonance Angiography

Compared to traditional branched polymers with Gd(III) chelates conjugated on their surface, branched polymers with Gd(III) chelates as the internal skeleton are considered to be a reasonable strategy for preparing efficient magnetic resonance imaging contrast agents. Herein, the Gd(III) ligand DOTA was chosen as the internal skeleton; four different molecular weights (3.5, 5.3, 8.6, and 13.1 kDa) and degrees of branching poly-DOTA branched polymers (P1, P2, P3, and P4) were synthesized by a simple "A₂ + B₄"-type one-pot polymerization. The Gd(III) chelates of these poly-DOTA branched polymers (P1-Gd, P2-Gd, P3-Gd, and P4-Gd) display excellent kinetic stability, which is significantly higher than those of linear Gd-DTPA and cyclic Gd-DOTA-butrol and slightly lower than that of cyclic Gd-DOTA. The T₁ relaxivities of P1-Gd, P2-Gd, P3-Gd, and P4-Gd are 29.4, 38.7, 44.0, and 47.9 Gd mM^-1 s^-1, respectively, at 0.5 T, which are about 6-11 times higher than that of Gd-DOTA (4.4 Gd mM^-1 s^-1). P4-Gd was selected for in vivo magnetic resonance angiography (MRA) because of its high kinetic stability, T₁ relaxivity, and good biosafety. The results showed excellent MRA effect, sensitive detection of vascular stenosis, and prolonged observation window as compared to Gd-DOTA. Overall, Gd(III) chelates of poly-DOTA branched polymers are good candidates of MRI probes, providing a unique design strategy in which Gd chelation can occur at both the interior and surface of the poly-DOTA branched polymers, resulting in excellent relaxivity enhancement. In vivo animal MRA studies of the probe provide possibilities in discovering small vascular pathologies.

Advances in the therapeutic delivery and applications of functionalized Pluronics: A critical review

Pluronic (PEO-PPO-PEO) block copolymers can form nano-sized micelles with a structure composed of a hydrophobic PPO core and hydrophilic PEO shell layer. Pluronics are U.S. Food and Drug Administration approved polymers, which are widely used for solubilization of drugs and their delivery, gene/therapeutic delivery, diagnostics, and tissue engineering applications due to their non-ionic properties, non-toxicity, micelle forming ability, excellent biocompatibility and biodegradability. Although Pluronics have been employed as drug carrier systems for several decades, numerous issues such as rapid dissolution, shorter residence time in biological media, fast clearance and weak mechanical strength have hindered their efficacy. Pluronics have been functionalized with pH-sensitive, biological-responsive moieties, antibodies, aptamers, folic acid, drugs, different nanoparticles, and photo/thermo-responsive hydrogels. These functionalization strategies enable Pluronics to act as stimuli responsive and targeted drug delivery vehicles. Moreover, Pluronics have emerged in nano-emulsion formulations and have been utilized to improve the properties of cubosomes, dendrimers and nano-sheets, including their biocompatibility and aqueous solubility. Functionalization of Pluronics results in the significant improvement of target specificity, loading capacity, biocompatibility of nanoparticles and stimuli responsive hydrogels for the promising delivery of a range of drugs. Therefore, this review presents an overview of all advancements (from the last 15 years) in functionalized Pluronics, providing a valuable tool for industry and academia in order to optimize their use in drug or therapeutic delivery, in addition to several other biomedical applications.

Structural changes in lipid mesophases due to intercalation of dendritic polymer nanoparticles: Swollen lamellae, suppressed curvature, and augmented structural disorder

Understanding interactions between nanoparticles and model membranes is relevant to functional nano-composites and the fundamentals of nanotoxicity. In this study, the effect of polyamidoamine (PAMAM) dendrimers as model nanoparticles (NP) on the mesophase behaviour of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) has been investigated using high-pressure small-angle X-ray scattering (HP-SAXS). The pressure-temperature (p-T) diagrams for POPE mesophases in excess water were obtained in the absence and presence of G2 and G4 polyamidoamine (PAMAM) dendrimers (29 Å and 45 Å in diameter, respectively) at varying NP-lipid number ratio (ν = 0.0002-0.02) over the pressure range p = 1-3000 bar and temperature range T = 20-80 °C. The p-T phase diagram of POPE exhibited the L_β, L_α and H_II phases. Complete analysis of the phase diagrams, including the relative area pervaded by different phases, phase transition temperatures (T_t) and pressures (p_t), the lattice parameters (d-spacing), the pressure-dependence of d-spacing (Δd/Δp), and the structural ordering in the mesophase as gauged by the Scherrer coherence length (L) permitted insights into the size- and concentration-dependent interactions between the dendrimers and the model membrane system. The addition of dendrimers changed the phase transition pressure and temperature and resulted in the emergence of highly swollen lamellar phases, dubbed L_β-den and L_α-den. G4 PAMAM dendrimers at the highest concentration ν = 0.02 suppressed the formation of the H_II phase within the temperature range studied, whereas the addition of G2 PAMAM dendrimers at the same concentration promoted an extended mixed lamellar region in which L_α and L_β phases coexisted. STATEMENT OF SIGNIFICANCE: Using high pressure small angle X-ray scattering in the pressure range 1-3000 bar and temperature range 20-60 °C, we have studied interactions between PAMAM dendrimers (as model nanoparticles) and POPE lipid mesophases (as model membranes). We report the pressure-temperature phase diagrams for the dendrimer-lipid mesophases for the first time. We find that the dendrimers alter the phase transition temperatures (T_t) and pressures (p_t), the lattice parameters (d-spacing), and the structural order in the mesophase. We interpret these unprecedented results in terms of the fluidity of the lipid membranes and the interactions between the dendrimers and the membranes. Our findings are of fundamental relevance to the field of nanotoxicity and functional nanomaterials that integrate nanoparticles and organized lipid structures.

Dendrimeric calcium-sensitive MRI probes: the first low-field relaxometric study

In the present work the first investigation ever of calcium sensitive dendrimer relaxation mechanisms at low fields is reported.

AS1411 aptamer-modified theranostic liposomes co-encapsulating manganese oxide nano-contrast agent and paclitaxel for MRI and therapy of cancer

With the advantages and development of MRI nano-contrast agents (CAs), increasing number of MRI-based theranostic nanoparticles have emerged. Liposome, as a biosafe nanocarrier has been used phase III trial for cancer treatment. In this study, liposome was employed as a nanocarrier to co-encapsulate MRI nano-contrast agent poly(ethylene glycol)-grafted manganese oxide (PEG-MnO) and anticancer drug paclitaxel (PTX) for the fabrication of a novel theranostic nanocomplex. After being further modified with AS1411 aptamer, the obtained nanoprobe AS1411-liposome-PEG-MnO-PTX displayed the potential of simultaneous MRI diagnosis and therapy of renal carcinoma in vitro and in vivo. It was found that compared with PEG-MnO nano-CA, liposome-PEG-MnO and AS1411-liposome-PEG-MnO presented a stronger MR contrast enhancement effect in the tumor and longer retention time in the tumor region. More importantly, the introduction of AS1411 aptamer further enhanced the MRI effect and the tumor growth inhibition effect, showing its potential use as a theranostic nanoprobe for renal carcinoma.

AS1411 aptamer modified theranostic liposomes co-encapsulating manganese oxide nano-contrast agent and paclitaxel for MRI and therapy of cancer was realized.

PAMAM dendrimer - cell membrane interactions

PAMAM dendrimers have been conjectured for a wide range of biomedical applications due to their tuneable physicochemical properties. However, their application has been hindered by uncertainties in their cytotoxicity, which is influenced by dendrimer generation (i.e. size and surface group density), surface chemistry, and dosage, as well as cell specificity. In this review, biomedical applications of polyamidoamine (PAMAM) dendrimers and some related cytotoxicity studies are first outlined. Alongside these in vitro experiments, lipid membranes such as supported lipid bilayers (SLBs), liposomes, and Langmuir monolayers have been used as cell membrane models to study PAMAM dendrimer-membrane interactions. Related experimental and theoretical studies are summarized, and the physical insights from these studies are discussed to shed light on the fundamental understanding of PAMAM dendrimer-cell membrane interactions. We conclude with a summary of some questions that call for further investigations.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Polymeric 1 H MRI Probes for Visualizing Tumor In Vivo

Magnetic resonance imaging (MRI) has become a prominent non- or low-invasive imaging technique, providing high-resolution, three-dimensional images as well as physiological information about tissues. Low-molecular-weight Gd-MRI contrast agents (CAs), such as Gd-DTPA (DTPA: diethylenetriaminepentaacetic acid), are commonly used in the clinical diagnosis, while macromolecular Gd-MRI CAs have several advantages over low-molecular-weight Gd-MRI CAs, which help minimize the dose of CAs and the risk of side effects. Accordingly, we developed chiral dendrimer Gd-MRI CAs, which showed high r₁ values. The association constant values (K_a ) of S-isomeric dendrimer CAs to bovine serum albumin (BSA) were higher than those of R-isomeric dendrimer CAs. Besides, based on a totally new concept, we developed ¹³ C/¹⁵ N-enriched multiple-resonance NMR/MRI probes, which realized highly selective observation of the probes and analysis of metabolic reactions of interest. This account summarizes our recent study on developing both chiral dendrimer Gd-MRI CAs, and self-traceable ¹³ C/¹⁵ N-enriched phosphorylcholine polymer probes for early detection of tumors.

LAPONITE®-stabilized iron oxide nanoparticles for in vivo MR imaging of tumors

We report the synthesis, characterization and utilization of LAPONITE®-stabilized magnetic iron oxide nanoparticles (LAP-Fe3O4 NPs) as a high performance contrast agent for in vivo magnetic resonance (MR) detection of tumors. In this study, Fe3O4 NPs were synthesized by a facile controlled coprecipitation route in LAP solution, and the formed LAP-Fe3O4 NPs have great colloidal stability and about 2-fold increase of T2 relaxivity than Fe3O4 NPs (from 247.6 mM(-1) s(-1) to 475.9 mM(-1) s(-1)). Moreover, cytotoxicity assay and cell morphology observation demonstrate that LAP-Fe3O4 NPs display good biocompatibility in the given Fe concentration range, and in vivo biodistribution results prove that NPs can be metabolized and cleared out of the body. Most importantly, LAP-Fe3O4 NPs can not only be used as a contrast agent for MR imaging of cancer cells in vitro due to the effective uptake by tumor cells, but also significantly enhance the contrast of a xenografted tumor model. Therefore, the developed LAP-based Fe3O4 NPs with good colloidal stability and exceptionally high transverse relaxivity may have tremendous potential in MR imaging applications.

Contrast agents for cardiovascular magnetic resonance imaging: an overview

Contrast agents for Cardiovascular Magnetic Resonance (CMR) play a major role in research and clinical cardiology.

Asymmetric Michael addition in an aqueous environment with the assistance of optically active hyperbranched polymers

A novel optically active hyperbranched polymer can serve as the chiral scaffolds to promote asymmetric Michael addition reaction in an aqueous environment with a high product yield and enantioselectivity.

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.

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.

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.

Molecular platform for design and synthesis of targeted dual-modality imaging probes

We report a versatile dendritic structure based platform for construction of targeted dual-modality imaging probes. The platform contains multiple copies of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) branching out from a 1,4,7-triazacyclononane-N,N′,N″-triacetic acid (NOTA) core. The specific coordination chemistries of the NOTA and DOTA moieties offer specific loading of ^68/67Ga³⁺ and Gd³⁺, respectively, into a common molecular scaffold. The platform also contains three amino groups which can potentiate targeted dual-modality imaging of PET/MRI or SPECT/MRI (PET: positron emission tomography; SPECT: single photon emission computed tomography; MRI: magnetic resonance imaging) when further functionalized by targeting vectors of interest. To validate this design concept, a bimetallic complex was synthesized with six peripheral Gd-DOTA units and one Ga-NOTA core at the center, whose ion T₁ relaxivity per gadolinium atom was measured to be 15.99 mM^–1 s^–1 at 20 MHz. Further, the bimetallic agent demonstrated its anticipated in vivo stability, tissue distribution, and pharmacokinetic profile when labeled with ⁶⁷Ga. When conjugated with a model targeting peptide sequence, the trivalent construct was able to visualize tumors in a mouse xenograft model by both PET and MRI via a single dose injection.

Functional supramolecular polymers for biomedical applications

As a novel class of dynamic and non-covalent polymers, supramolecular polymers not only display specific structural and physicochemical properties, but also have the ability to undergo reversible changes of structure, shape, and function in response to diverse external stimuli, making them promising candidates for widespread applications ranging from academic research to industrial fields. By an elegant combination of dynamic/reversible structures with exceptional functions, functional supramolecular polymers are attracting increasing attention in various fields. In particular, functional supramolecular polymers offer several unique advantages, including inherent degradable polymer backbones, smart responsiveness to various biological stimuli, and the ease for the incorporation of multiple biofunctionalities (e.g., targeting and bioactivity), thereby showing great potential for a wide range of applications in the biomedical field. In this Review, the trends and representative achievements in the design and synthesis of supramolecular polymers with specific functions are summarized, as well as their wide-ranging biomedical applications such as drug delivery, gene transfection, protein delivery, bio-imaging and diagnosis, tissue engineering, and biomimetic chemistry. These achievements further inspire persistent efforts in an emerging interdisciplin-ary research area of supramolecular chemistry, polymer science, material science, biomedical engineering, and nanotechnology.

Fabrication of AS1411 aptamer functionalized Gd2O3-based molecular magnetic resonance imaging (mMRI) nanoprobe for renal carcinoma cell imaging

A molecular MRI nanoprobe for the sensitive and specific MRI of renal carcinoma cells with BSA-Gd₂O₃nanoparticles as MRI contrast agents, mesoporous silica nanoparticles as nanocarriers and AS1411 aptamer as targeting molecule was developed.

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.

Bioapplications of hyperbranched polymers

The recent research progress in biological and biomedical applications of hyperbranched polymers has been summarized in this review.

Designing New Scaffolds Consisting of Hepta-annulated Heterocycles

The syntheses of hexa and tetra-propargylated pyrido[4′,3′:4,5]thieno[2,3- d]-pyrido[4″’,3″’:4″,5″]thieno[2″,3″:4′,5′] pyrimido[1′,2′:4,5]pyrazino[1,2- a]pyrimidines, are described by the reaction of hepta-annulated heterocyclic systems with propargyl bromide. Multiple alkyne-azide click reaction of these alkyne cores established them as a scaffold for six and four functionalised 1,2,3-triazoles and attached biomolecules.

Visualizing the atherosclerotic plaque: a chemical perspective

Atherosclerosis is the major underlying pathologic cause of coronary artery disease. An early detection of the disease can prevent clinical sequellae such as angina, myocardial infarction, and stroke. The different imaging techniques employed to visualize the atherosclerotic plaque provide information of diagnostic and prognostic value. Furthermore, the use of contrast agents helps to improve signal-to-noise ratio providing better images. For nuclear imaging techniques and optical imaging these agents are absolutely necessary. We report on the different contrast agents that have been used, are used or may be used in future in animals, humans, or excised tissues for the distinct imaging modalities for atherosclerotic plaque imaging.

Design, synthesis, and in vitro evaluation of a binary targeting MRI contrast agent for imaging tumor cells

A binary targeting vector that consists of peptide sequences of Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) motifs has been designed and synthesized using solid-phase peptide synthesis procedure. The vector is then coupled with Gd-DOTA to work as a targeting contrast agent (CA1) for magnetic resonance imaging of human lung adenocarcinoma cells A549. Its longitudinal relaxivity is measured to be 7.55 mM(-1) s(-1) in aqueous solution at a magnetic field of 11.7 T, which is higher than that of Magnevist (4.25 mM(-1) s(-1)) in the same conditions. The cell experiment shows, at the same concentration, uptake quantity of CA1 by A549 is much more than Magnevist and also superior over CA2 (a single targeting contrast agent contains only RGD). The uptake can be blocked by the targetable peptide containing RGD or NGR without coupling Gd. To summarize, CA1 has very good ability to target A549 and higher relaxivity than that of Magnevist. So CA1 is promising MRI contrast agent for high-resolution MR molecular imaging of human lung adenocarcinoma A549 cells.

Self-assembly of supramolecularly engineered polymers and their biomedical applications

Self-assembly behavior of supramolecularly engineered polymers and their biomedical applications have been summarized.

A facile synthetic approach to a biodegradable polydisulfide MRI contrast agent

A biodegradable novel polydisulfide MRI contrast agent forming self-assembly in aqueous solution with a low cytotoxicity and a higherr₁is promising for producing better MRI imaging with fewer side effects.

Gadolinium complexes of monophosphinic acid DOTA derivatives conjugated to cyclodextrin scaffolds: efficient MRI contrast agents for higher magnetic fields

Middle-molecular-weight MRI contrast agents based on conjugates of a phosphinic acid DOTA analogue, 1,4,7,10-tetraazacyclododecane-4,7,10-triacetic-1-{methyl[(4-aminophenyl)methyl]phosphinic acid} (DO3AP(ABn)), with amino-substituted cyclodextrins were prepared and studied by a variety of physico-chemical methods. The conjugates were formed by reaction of the corresponding isothiocyanate with per-6-amino-α/β-cyclodextrin and were complexed with the Ln(III) ion to get the final complexes, (LnL)(6)-α-CD and (LnL)(7)-β-CD. Solution structure of the complexes was estimated by investigation of the Eu(III) complexes. The Gd(III) conjugate complexes are endowed with a short water residence time (τ(M) ∼ 10-15 ns at 298 K) and a high abundance of the twisted-square antiprismatic diastereoisomer. They show a high (1)H relaxivity at high fields due to a convenient combination of the fast water exchange rate and the slow rate of the molecular tumbling given by their macromolecular nature. The (1)H relaxation enhancements per molecule of a contrast agent (CA) are very high reaching for a larger (GdL)(7)-β-CD conjugate ∼140 s(-1) mM(-1) and ∼100 s(-1) mM(-1) at 25 °C and magnetic fields 1.5 T and 3 T, respectively, which is the highest reported longitudinal relaxivity for kinetically stable contrast agents of an intermediate molecular mass (<10 kDa) with one water molecule in the first coordination sphere.

Paramagnetic liposomes for molecular MRI and MRI-guided drug delivery

Liposomes are a versatile class of nanoparticles with tunable properties, and multiple liposomal drug formulations have been clinically approved for cancer treatment. In recent years, an extensive library of gadolinium (Gd)-containing liposomal MRI contrast agents has been developed for molecular and cellular imaging of disease-specific markers and for image-guided drug delivery. This review discusses the advances in the development and novel applications of paramagnetic liposomes in molecular and cellular imaging, and in image-guided drug delivery. A high targeting specificity has been achieved in vitro using ligand-conjugated paramagnetic liposomes. On targeting of internalizing cell receptors, the effective longitudinal relaxivity r1 of paramagnetic liposomes is modulated by compartmentalization effects. This provides unique opportunities to monitor the biological fate of liposomes. In vivo contrast-enhanced MRI studies with nontargeted liposomes have shown the extravasation of liposomes in diseases associated with endothelial dysfunction, such as tumors and myocardial infarction. The in vivo use of targeted paramagnetic liposomes has facilitated the specific imaging of pathophysiological processes, such as angiogenesis and inflammation. Paramagnetic liposomes loaded with drugs have been utilized for therapeutic interventions. MR image-guided drug delivery using such liposomes allows the visualization and quantification of local drug delivery.