Gadolinium-conjugated dendrimer nanoclusters as a tumor-targeted T1 magnetic resonance imaging contrast agent

Biodegradable polydisulfide dendrimer nanoclusters as MRI contrast agents

Gadolinium-conjugated dendrimer nanoclusters (DNCs) are a promising platform for the early detection of disease; however, their clinical utility is potentially limited due to safety concerns related to nephrogenic systemic fibrosis (NSF). In this paper, biodegradable DNCs were prepared with polydisulfide linkages between the individual dendrimers to facilitate excretion. Further, DNCs were labeled with premetalated Gd chelates to eliminate the risk of free Gd becoming entrapped in dendrimer cavities. The biodegradable polydisulfide DNCs possessed a circulation half-life of >1.6 h in mice and produced significant contrast enhancement in the abdominal aorta and kidneys for as long as 4 h. The DNCs were reduced in circulation as a result of thiol-disulfide exchange, and the degradation products were rapidly excreted via renal filtration. These agents demonstrated effective and prolonged in vivo contrast enhancement and yet minimized Gd tissue retention. Biodegradable polydisulfide DNCs represent a promising biodegradable macromolecular MRI contrast agent for magnetic resonance angiography and can potentially be further developed into target-specific MRI contrast agents.

Multifunctional nanoparticles: cost versus benefit of adding targeting and imaging capabilities

Nanoparticle-based drug delivery systems have been developed to improve the efficacy and reduce the systemic toxicity of a wide range of drugs. Although clinically approved nanoparticles have consistently shown value in reducing drug toxicity, their use has not always translated into improved clinical outcomes. This has led to the development of "multifunctional" nanoparticles, where additional capabilities like targeting and image contrast enhancement are added to the nanoparticles. However, additional functionality means additional synthetic steps and costs, more convoluted behavior and effects in vivo, and also greater regulatory hurdles. The trade-off between additional functionality and complexity is the subject of ongoing debate and the focus of this Review.

Determination of pore sizes and relative porosity in porous nanoshell architectures using dextran retention with single monomer resolution and proton permeation

Unilamellar phospholipid vesicles prepared using the polymerizable lipid bis-sorbylphosphatidylcholine (bis-SorbPC) yield three-dimensional nanoarchitectures that are highly permeable to small molecules. The resulting porous phospholipid nanoshells (PPNs) are potentially useful for a range of biomedical applications including nanosensors and nanodelivery vehicles for cellular assays and manipulations. The uniformity and size distribution of the pores, key properties for sensor design and utilization, have not previously been reported. Fluorophore-assisted carbohydrate electrophoresis (FACE) was utilized to assess the nominal molecular weight cutoff limit (NMCL) of the PPN via analysis of retained dextran with single monomer resolution. The NMCL of PPNs prepared from pure bis-SorbPC was equivalent to a 1800 Da linear dextran, corresponding to a maximum pore diameter of 2.6 nm. Further investigation of PPNs prepared using binary mixtures of bis-SorbPC and dioleoylphosphatidylcholine (DOPC) revealed a similar NMCL when the bis-SorbPC content exceeded 30 mol %, whereas different size-dependent permeation was observed below this composition. Below 30 mol % bis-SorbPC, dextran retention provided insufficient mass resolution (162 Da) to observe porosity on the experimental time scale; however, proton permeability showed a marked enhancement for bis-SorbPC ≥ 10 mol %. Combined, these data suggest that the NMCL for native pores in bis-SorbPC PPNs results from an inherent property within the lipid assembly that can be partially disrupted by dilution of bis-SorbPC below a critical value for domain formation. Additionally, the analytical method described herein should prove useful for the challenging task of elucidating porosity in a range of three-dimensional nanomaterials.

Near-infrared fluorescent imaging of metastatic ovarian cancer using folate receptor-targeted high-density lipoprotein nanocarriers

AIM

The targeting efficiency of folate receptor-α (FR-α)-targeted high-density lipoprotein nanoparticles (HDL NPs) was evaluated in a syngeneic mouse model of ovarian cancer.

MATERIALS & METHODS

Folic acid was conjugated to the surface of fluorescent-labeled HDL NPs. In vivo tumor targeting of folic acid-HDL NPs and HDL NPs were evaluated in mice with metastatic ovarian cancer following intravenous or intraperitoneal (ip.) administration.

RESULTS & DISCUSSION

Intravenous FR-α-targeted HDL resulted in high uptake of the fluorescent nanoparticle in host liver and spleen. The ip. injection of fluorescent HDL produced moderate fluorescence throughout the abdomen. Conversely, animals receiving the ip. FR-α-targeted HDL showed a high fluorescence signal in ovarian tumors, surpassing that seen in all of the host tissues.

CONCLUSION

The authors' findings demonstrate that the combination of local-regional ip. administration and FR-α-directed nanoparticles provides an enhanced approach to selectively targeting ovarian cancer cells for drug treatment.

Dendritic nanoparticles: the next generation of nanocarriers?

Dendritic polymers have attracted a great deal of scientific interest due to their well-defined unique structure and capability to be multifunctionalized. Here we present a comprehensive overview of various dendrimer-based nanomaterials that are currently being investigated for therapeutic delivery and diagnostic applications. Through a critical review of the old and new dendritic designs, we highlight the advantages and disadvantages of these systems and their structure-biological property relationships. This article also focuses on the major challenges facing the clinical translation of these nanomaterials and how these challenges are being (or should be) addressed, which will greatly benefit the overall progress of dendritic materials for theranostics.

Gadolinium-encapsulating iron oxide nanoprobe as activatable NMR/MRI contrast agent

Herein we report a novel gadolinium-encapsulating iron oxide nanoparticle-based activatable NMR/MRI nanoprobe. In our design, Gd-DTPA is encapsulated within the poly(acrylic acid) (PAA) polymer coating of a superparamagnetic iron oxide nanoparticle (IO-PAA), yielding a composite magnetic nanoprobe (IO-PAA-Gd-DTPA) with quenched longitudinal spin-lattice magnetic relaxation (T(1)). Upon release of the Gd-DTPA complex from the nanoprobe's polymeric coating in acidic media, an increase in the T(1) relaxation rate (1/T(1)) of the composite magnetic nanoprobe was observed, indicating a dequenching of the nanoprobe with a corresponding increase in the T(1)-weighted MRI signal. When a folate-conjugated nanoprobe was incubated in HeLa cells, a cancer cell line overexpressing folate receptors, an increase in the 1/T(1) signal was observed. This result suggests that, upon receptor-mediated internalization, the composite magnetic nanoprobe degraded within the cell's lysosome acidic (pH 5.0) environment, resulting in an intracellular release of Gd-DTPA complex with subsequent T(1) activation. In addition, when an anticancer drug (Taxol) was coencapsulated with the Gd-DTPA within the folate receptor targeting composite magnetic nanoprobe, the T(1) activation of the probe coincided with the rate of drug release and corresponding cytotoxic effect in cell culture studies. Taken together, these results suggest that our activatable T(1) nanoagent could be of great importance for the detection of acidic tumors and assessment of drug targeting and release by MRI.

Block copolymer-based gadolinium nanoparticles as MRI contrast agents with high T1 relaxivity

AIMS

To synthesize block copolymer-based gadolinium nanoparticles (Gd-NPs) and evaluate their potential as a new MRI contrast agent.

MATERIALS & METHODS

The Gd-NPs were developed through coordination of gadolinium chelates into a pentablock copolymer synthesized by two sequential atom transfer radical polymerizations, and evaluated by measuring their T1 relaxivity in vitro and imaging their T1 contrast in tissue using MRI.

RESULTS

Solution and MRI studies demonstrated that these Gd-NPs exhibit remarkably high T1 relaxivity on both per particle and per gadolinium ion basis, and can generate a much better MRI contrast compared with gadolinium chelates alone.

CONCLUSION

These novel Gd-NPs may have important applications in magnetic resonance-based medical imaging.

New clathrin-based nanoplatforms for magnetic resonance imaging

Background

Magnetic Resonance Imaging (MRI) has high spatial resolution, but low sensitivity for visualization of molecular targets in the central nervous system (CNS). Our goal was to develop a new MRI method with the potential for non-invasive molecular brain imaging. We herein introduce new bio-nanotechnology approaches for designing CNS contrast media based on the ubiquitous clathrin cell protein.

Methodology/Principal Findings

The first approach utilizes three-legged clathrin triskelia modified to carry 81 gadolinium chelates. The second approach uses clathrin cages self-assembled from triskelia and designed to carry 432 gadolinium chelates. Clathrin triskelia and cages were characterized by size, structure, protein concentration, and chelate and gadolinium contents. Relaxivity was evaluated at 0.47 T. A series of studies were conducted to ascertain whether fluorescent-tagged clathrin nanoplatforms could cross the blood brain barriers (BBB) unaided following intranasal, intravenous, and intraperitoneal routes of administration. Clathrin nanoparticles can be constituted as triskelia (18.5 nm in size), and as cages assembled from them (55 nm). The mean chelate: clathrin heavy chain molar ratio was 27.04±4.8: 1 for triskelia, and 4.2±1.04: 1 for cages. Triskelia had ionic relaxivity of 16 mM⁻¹s⁻¹, and molecular relaxivity of 1,166 mM⁻¹s⁻¹, while cages had ionic relaxivity of 81 mM⁻¹s⁻¹ and molecular relaxivity of 31,512 mM⁻¹s⁻¹. Thus, cages exhibited 20 times higher ionic relaxivity and 8,000-fold greater molecular relaxivity than gadopentetate dimeglumine. Clathrin nanoplatforms modified with fluorescent tags were able to cross or bypass the BBB without enhancements following intravenous, intraperitoneal and intranasal administration in rats.

Conclusions/Significance

Use of clathrin triskelia and cages as carriers of CNS contrast media represents a new approach. This new biocompatible protein-based nanotechnology demonstrated suitable physicochemical properties to warrant further in vivo imaging and drug delivery studies. Significantly, both nanotransporters crossed and/or bypassed the BBB without enhancers. Thus, clathrin nanoplatforms could be an appealing alternative to existing CNS bio-nanotechnologies.

A novel clinically translatable fluorescent nanoparticle for targeted molecular imaging of tumors in living subjects

The use of quantum dots (QDs) in biomedical research has grown tremendously, yet successful examples of clinical applications are absent due to many clinical concerns. Here, we report on a new type of stable and biocompatible dendron-coated InP/ZnS core/shell QD as a clinically translatable nanoprobe for molecular imaging applications. The QDs (QD710-Dendron) were demonstrated to hold several significant features: near-infrared (NIR) emission, high stability in biological media, suitable size with possible renal clearance, and ability of extravasation. More importantly, a pilot mouse toxicity study confirmed that QD710-Dendron lacks significant toxicity at the doses tested. The acute tumor uptake of QD710-Dendron resulted in good contrast from the surrounding nontumorous tissues, indicating the possibility of passive targeting of the QDs. The highly specific targeting of QD710-Dendron-RGD(2) to integrin α(v)β(3)-positive tumor cells resulted in high tumor uptake and long retention of the nanoprobe at tumor sites. In summary, QD710-Dendron and RGD-modified nanoparticles demonstrate small size, high stability, biocompatibility, favorable in vivo pharmacokinetics, and successful tumor imaging properties. These features satisfy the requirements for clinical translation and should promote efforts to further investigate the possibility of using QD710-Dendron-based nanoprobes in the clinical setting in the near future.

Synthesis and application of superparamagnetic iron oxide nanoparticles in targeted therapy and imaging of cancer

Superparamagnetic iron oxide (SPIO) nanoparticles have become a popular strategy of cancer treatment and molecular imaging because of their versatile properties and biocompatibility. A variety of studies have shown the exciting potential of functionalized SPIO nanoparticles, such as surface-coated, targeted ligandconjugated, and/or drug-loaded SPIO nanoparticles, as powerful tools for targeted imaging and therapy. Moreover, the applications of SPIO nanoparticles that integrate diagnosis and therapy in SPIO nanoparticles facilitate the monitoring of therapeutic efficacy during treatment. In the present review, we primarily concentrate on the recent advancements in the field of SPIO nanoparticles in terms of synthesis, targeted therapy, and cancer imaging.

MR molecular imaging of prostate cancer with a peptide-targeted contrast agent in a mouse orthotopic prostate cancer model

PURPOSE

To study the effectiveness of a peptide targeted nanoglobular Gd-DOTA complexes for MR molecular imaging of prostate cancer in a mouse orthotopic PC-3 prostate cancer model.

METHODS

A CLT1 (CGLIIQKNEC) peptide-targeted generation 2 nanoglobular Gd-DOTA monoamide conjugate [CLT1-G2-(Gd-DOTA)] was used for imaging fibrin-fibronectin complexes in prostate tumor using a non-specific peptide KAREC modified conjugate, KAREC-G2-(Gd-DOTA) as a control. Cy5 conjugates of CLT1 and KAREC were synthesized for binding studies. Orthotopic PC-3 prostate tumors were established in the prostate of athymic male nude mice. MRI study was performed on a Bruker 7T small animal MRI system.

RESULTS

CLT1 peptide showed specific binding in the prostate tumor with no binding in normal tissues. The control peptide had little binding in normal and tumor tissues. CLT1-G2-(Gd-DOTA) resulted in stronger contrast enhancement in tumor tissue than KAREC-G2-(Gd-DOTA). CLT1-G2-(Gd-DOTA) generated ~100% increase in contrast-to-noise ratio (CNR) in the tumor compared to precontrast CNR at 1 min post-injection, while KAREC-G2-(Gd-DOTA) resulted in 8% increase.

CONCLUSION

CLT1-G2-(Gd-DOTA) is a promising molecular MRI contrast agent for fibrin-fibronectin complexes in tumor stroma. It has potential for diagnosis and assessing prognosis of malignant tumors with MRI.

X-ROS signaling: rapid mechano-chemo transduction in heart

We report that in heart cells, physiologic stretch rapidly activates reduced-form nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) to produce reactive oxygen species (ROS) in a process dependent on microtubules (X-ROS signaling). ROS production occurs in the sarcolemmal and t-tubule membranes where NOX2 is located and sensitizes nearby ryanodine receptors (RyRs) in the sarcoplasmic reticulum (SR). This triggers a burst of Ca(2+) sparks, the elementary Ca(2+) release events in heart. Although this stretch-dependent "tuning" of RyRs increases Ca(2+) signaling sensitivity in healthy cardiomyocytes, in disease it enables Ca(2+) sparks to trigger arrhythmogenic Ca(2+) waves. In the mouse model of Duchenne muscular dystrophy, hyperactive X-ROS signaling contributes to cardiomyopathy through aberrant Ca(2+) release from the SR. X-ROS signaling thus provides a mechanistic explanation for the mechanotransduction of Ca(2+) release in the heart and offers fresh therapeutic possibilities.

Layer-by-layer capsules for magnetic resonance imaging and drug delivery

Layer-by-layer (LbL) self-assembled polyelectrolyte capsules have demonstrated their unique advantages and capability in drug delivery applications. These ordered micro/nano-structures are also promising candidates as imaging contrast agents for diagnostic and theranostic applications. Magnetic resonance imaging (MRI), one of the most powerful clinical imaging modalities, is moving forward to the molecular imaging field and requires the availability of advanced imaging probes. In this review, we are focusing on the design of MRI visible LbL capsules, which incorporate either paramagnetic metal-ligand complexes or superparamagnetic iron oxide (SPIO) nanoparticles. The design criteria cover the topics of probe sensitivity, biosafety, long-circulation property, targeting ligand decoration, and drug loading strategies. Examples of MRI visible LbL capsules with paramagnetic or superparamagnetic moieties were given and discussed. This carrier platform can also be chosen for other imaging modalities.

Strategies for the preparation of bifunctional gadolinium(III) chelators

The development of gadolinium chelators that can be easily and readily linked to various substrates is of primary importance for the development high relaxation efficiency and/or targeted magnetic resonance imaging (MRI) contrast agents. Over the last 25 years a large number of bifunctional chelators have been prepared. For the most part, these compounds are based on ligands that are already used in clinically approved contrast agents. More recently, new bifunctional chelators have been reported based on complexes that show a more potent relaxation effect, faster complexation kinetics and in some cases simpler synthetic procedures. This review provides an overview of the synthetic strategies used for the preparation of bifunctional chelators for MRI applications.

Conjugation effects of various linkers on Gd(III) MRI contrast agents with dendrimers: optimizing the hydroxypyridinonate (HOPO) ligands with nontoxic, degradable esteramide (EA) dendrimers for high relaxivity

One essential requirement for more sensitive gadolinium-based MRI contrast agents is to slow the molecular tumbling of the gadolinium(III) ion, which increases the gadolinium's relaxivity (i.e., its ability to speed up the NMR relaxation of nearby water molecules). One route to this is through conjugation to high-molecular-weight polymers such as dendrimers. In this work, amine-functionalized TREN-bis(1,2-HOPO)-TAM-ethylamine and TREN-bis(1-Me-3,2-HOPO)-TAM-ethylamine ligands have been synthesized and attached to biocompatible 40 kDa esteramide (EA)- and poly-l-lysine (PLL)-based dendrimers capable of binding up to eight gadolinium complexes. These conjugates have T(1) relaxivities of up to 38.14 ± 0.02 mM(-1) s(-1) per gadolinium at 37 °C, corresponding to relaxivities of up to 228 mM(-1) s(-1) per dendrimer molecule. This relaxivity expressed on a "per Gd" basis is several times that of the small-molecule complexes and an order of magnitude higher than that of current commercial agents. Because of their high performance and low toxicity, these macromolecules may constitute an attractive complement to currently available gadolinium(III)-based contrast agents.

MRI detection of VEGFR2 in vivo using a low molecular weight peptoid-(Gd)8-dendron for targeting

The synthesis of a polylysine dendron containing eight GdDOTA units conjugated to a peptoid dimer known to have a high affinity for the vascular endothelial growth factor receptor 2 (VEGFR2) is described. This simple low molecular weight system with a molecular r(1) relaxivity of ∼48 mM(-1) s(-1) is shown to enhance MR images of tumors grown in mice in vivo.

A small MRI contrast agent library of gadolinium(III)-encapsulated supramolecular nanoparticles for improved relaxivity and sensitivity

We introduce a new category of nanoparticle-based T(1) MRI contrast agents (CAs) by encapsulating paramagnetic chelated gadolinium(III), i.e., Gd(3+)·DOTA, through supramolecular assembly of molecular building blocks that carry complementary molecular recognition motifs, including adamantane (Ad) and β-cyclodextrin (CD). A small library of Gd(3+)·DOTA-encapsulated supramolecular nanoparticles (Gd(3+)·DOTA⊂SNPs) was produced by systematically altering the molecular building block mixing ratios. A broad spectrum of relaxation rates was correlated to the resulting Gd(3+)·DOTA⊂SNP library. Consequently, an optimal synthetic formulation of Gd(3+)·DOTA⊂SNPs with an r(1) of 17.3 s(-1) mM(-1) (ca. 4-fold higher than clinical Gd(3+) chelated complexes at high field strengths) was identified. T(1)-weighted imaging of Gd(3+)·DOTA⊂SNPs exhibits an enhanced sensitivity with a contrast-to-noise ratio (C/N ratio) ca. 3.6 times greater than that observed for free Gd(3+)·DTPA. A Gd(3+)·DOTA⊂SNPs solution was injected into foot pads of mice, and MRI was employed to monitor dynamic lymphatic drainage of the Gd(3+)·DOTA⊂SNPs-based CA. We observe an increase in signal intensity of the brachial lymph node in T(1)-weighted imaging after injecting Gd(3+)·DOTA⊂SNPs but not after injecting Gd(3+)·DTPA. The MRI results are supported by ICP-MS analysis ex vivo. These results show that Gd(3+)·DOTA⊂SNPs not only exhibits enhanced relaxivity and high sensitivity but also can serve as a potential tool for diagnosis of cancer metastasis.

Cytochrome C encapsulating theranostic nanoparticles: a novel bifunctional system for targeted delivery of therapeutic membrane-impermeable proteins to tumors and imaging of cancer therapy

The effective administration of therapeutic proteins has received increased attention for the treatment of various diseases. Encapsulation of these proteins in various matrices, as a method of protein structure and function preservation, is a widely used approach that results in maintenance of the protein's function. However, targeted delivery and tracking of encapsulated therapeutic proteins to the affected cells is still a challenge. In an effort to advance the targeted delivery of a functional apoptosis-initiating protein (cytochrome c) to cancer cells, we formulated theranostic polymeric nanoparticles for the simultaneous encapsulation of cytochrome c and a near-infrared dye to folate-expressing cancer cells. The polymeric nanoparticles were prepared using a novel water-soluble hyperbranched polyhydroxyl polymer that allows for dual encapsulation of a hydrophilic protein and an amphiphilic fluorescent dye. Our protein therapeutic cargo is the endogenous protein cytochrome c, which upon cytoplasmic release, initiates an apoptotic response leading to programmed cell death. Results indicate that encapsulation of cytochrome c within the nanoparticle's cavities preserved the protein's enzymatic activity. The potential therapeutic property of these nanoparticles was demonstrated by the induction of apoptosis upon intracellular delivery. Furthermore, targeted delivery of cytochrome c to folate-receptor-positive cancer cells was achieved via conjugation of folic acid to the nanoparticle's surface, whereas the nanoparticle's theranostic properties were conferred via the coencapsulation of cytochrome c and a fluorescent dye. Considering that these theranostic nanoparticles can carry an endogenous cellular apoptotic initiator (cytochrome c) and a fluorescent tag (ICG) commonly used in the clinic, their use and potential translation into the clinic is anticipated, facilitating the monitoring of tumor regression.