Magnetic nanobeads as potential contrast agents for magnetic resonance imaging

Molecular Parameters Promoting High Relaxivity in Cluster-Nanocarrier Magnetic Resonance Imaging Contrast Agents

We have investigated the mechanism of relaxivity for two magnetic resonance imaging contrast agents that both employ a cluster-nanocarrier design. The first system termed Mn8Fe4-coPS comprises the cluster Mn8Fe4O12(L)16(H2O)4 or Mn8Fe4 (1) (L = carboxylate) co-polymerized with polystyrene to form ∼75 nm nanobeads. The second system termed Mn3Bpy-PAm used the cluster Mn3(O2CCH3)6(Bpy)2 or Mn3Bpy (2) where Bpy = 2,2'-bipyridine, entrapped in ∼180 nm polyacrylamide nanobeads. Here, we investigate the rate of water exchange of the two clusters, and corresponding cluster-nanocarriers, in order to elucidate the mechanism of relaxivity in the cluster-nanocarrier. Swift-Connick analysis of O-17 NMR was used to determine the water exchange rates of the clusters and cluster-nanocarriers. We found distinct differences in the water exchange rate between Mn8Fe4 and Mn8Fe4-coPS, and we utilized these differences to elucidate the nanobead structure. Using the transverse relaxivity from O-17 NMR line widths, we were able to determine the hydration state of the Mn3Bpy (2) cluster as well as Mn3Bpy-PAm. Using these hydration states in the Swift-Connick analysis of O-17 NMR, we found the water exchange rate to be extremely close in value for the cluster Mn3Bpy and cluster-nanocarrier Mn3Bpy-PAm.

Porous Silica Nanospheres with a Confined Mono(aquated) Mn(II)-Complex: A Potential T1-T2 Dual Contrast Agent for Magnetic Resonance Imaging

Magnetic resonance imaging has emerged as an indispensable imaging modality for the early-stage diagnosis of many diseases. The imaging in the presence of a contrast agent is always advantageous, as it mitigates the low-sensitivity issue of the measurements and provides excellent contrast in the acquired images even in a short acquisition time. However, the stability and high relaxivity of the contrast agents remained a challenge. Here, molecules of a mononuclear, mono(aquated), thermodynamically stable [log K_MnL = 14.80(7) and pMn = 8.97] Mn(II)-complex (1), based on a hexadentate pyridine-picolinate unit-containing ligand (H₂PyDPA), were confined within a porous silica nanosphere in a noncovalent fashion to render a stable nanosystem, complex 1@SiO₂NP. The entrapped complex 1 (complex 1@SiO₂) exhibited r₁ = 8.46 mM^-1 s^-1 and r₂ = 33.15 mM^-1 s^-1 at pH = 7.4, 25 °C, and 1.41 T in N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The values were about 2.9 times higher compared to the free (unentrapped)-complex 1 molecules. The synthesized complex 1@SiO₂NP interacted significantly with albumin protein and consequently boosted both the relaxivity values to r₁ = 24.76 mM^-1 s^-1 and r₂ = 63.96 mM^-1 s^-1 at pH = 7.4, 37 °C, and 1.41 T. The kinetic inertness of the entrapped molecules was established by recognizing no appreciable change in the r₁ value upon challenging complex 1@SiO₂NP with 30 and 40 times excess of Zn(II) ions at pH 6 and 25 °C. The water molecule coordinated to the Mn(II) ion in complex 1@SiO₂ was also impervious to the physiologically relevant anions (bicarbonate, biphosphate, and citrate) and pH of the medium. Thus, it ensured the availability of the inner-coordination site of complex 1 for the coordination of water molecules in the biological media. The concentration-dependent changes in image intensities in T₁- and T₂-weighted phantom images and uptake of the nanoparticles by the HeLa cell put forward the biocompatible complex 1@SiO₂NP as a potential dual-mode MRI contrast agent, an alternative to Gd(III)-containing contrast agents.

Paramagnetic Mn8Fe4-co-Polystyrene Nanobeads as a Potential T1-T2 Multimodal Magnetic Resonance Imaging Contrast Agent with In Vivo Studies

In developing a cluster-nanocarrier design, as a magnetic resonance imaging contrast agent, we have investigated the enhanced relaxivity of a manganese and iron-oxo cluster grafted within a porous polystyrene nanobead with increased relaxivity due to a higher surface area. The synthesis of the cluster-nanocarrier for the cluster Mn8Fe4O12(O2CC6H4CH═CH2)16(H2O)4, cross-linked with polystyrene (the nanocarrier), under miniemulsion conditions is described. By including a branched hydrophobe, iso-octane, the resulting nanobeads are porous and ∼70 nm in diameter. The increased surface area of the nanobeads compared to nonporous nanobeads leads to an enhancement in relaxivity; r1 increases from 3.8 to 5.2 ± 0.1 mM-1 s-1, and r2 increases from 11.9 to 50.1 ± 4.8 mM-1 s-1, at 9.4 teslas, strengthening the potential for T1 and T2 imaging. Several metrics were used to assess stability, and the porosity produced no reduction in metal stability. Synchrotron X-ray fluorescence microscopy was used to demonstrate that the nanobeads remain intact in vivo. In depth, physicochemical characteristics were determined, including extensive pharmacokinetics, in vivo imaging, and systemic biodistribution analysis.

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization - a Thomas Dougherty Award for Excellence in PDT paper

Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemical, photosensitizer, which preferentially accumulates in tissues/cells and, upon irradiation with the appropriate wavelength of light, confers cytotoxicity by generation of reactive molecular species. The preferential accumulation however is not universal and, depending on the anatomical site, the ratio of tumor to normal tissue may be reversed in favor of normal tissue. Under such circumstances, control of the volume of light illumination provides a second handle of selectivity. Singlet oxygen is the putative favorite reactive molecular species although other entities such as nitric oxide have been credibly implicated. Typically, most photosensitizers in current clinical use have a finite quantum yield of fluorescence which is exploited for surgery guidance and can also be incorporated for monitoring and treatment design. In addition, the photodynamic process alters the cellular, stromal, and/or vascular microenvironment transiently in a process termed photodynamic priming, making it more receptive to subsequent additional therapies including chemo- and immunotherapy. Thus, photodynamic priming may be considered as an enabling technology for the more commonly used frontline treatments. Recently, there has been an increase in the exploitation of the theranostic potential of photodynamic therapy in different preclinical and clinical settings with the use of new photosensitizer formulations and combinatorial therapeutic options. The emergence of nanomedicine has further added to the repertoire of photodynamic therapy's potential and the convergence and co-evolution of these two exciting tools is expected to push the barriers of smart therapies, where such optical approaches might have a special niche. This review provides a perspective on current status of photodynamic therapy in anti-cancer and anti-microbial therapies and it suggests how evolving technologies combined with photochemically-initiated molecular processes may be exploited to become co-conspirators in optimization of treatment outcomes. We also project, at least for the short term, the direction that this modality may be taking in the near future.

Renal-clearable zwitterionic conjugated hollow ultrasmall Fe3O4 nanoparticles for T1-weighted MR imaging in vivo

Monodispersed hollow Fe₃O₄ nanoparticles with the diameters of 7 and 10 nm were prepared via a high-temperature pyrolysis method and the Kirkendall effect by regulating the ratio of oleylamine to oleic acid.

Paramagnetic Clusters of Mn3(O2CCH3)6(Bpy)2 in Polyacrylamide Nanobeads as a New Design Approach to a T1- T2 Multimodal Magnetic Resonance Imaging Contrast Agent

There is an increasing need for gadolinium-free magnetic resonance imaging (MRI) contrast agents, particularly for patients suffering from chronic kidney disease. Using a cluster-nanocarrier combination, we have identified a novel approach to the design of biomedical nanomaterials and report here the criteria for the cluster and the nanocarrier and the advantages of this combination. We have investigated the relaxivity of the following manganese oxo clusters: the parent cluster Mn₃(O₂CCH₃)₆(Bpy)₂ (1) where Bpy = 2,2'-bipyridine and three new analogs, Mn₃(O₂CC₆H₄CH═CH₂)₆(Bpy)₂ (2), Mn₃(O₂CC(CH₃)═CH₂)₆(Bpy)₂ (3), and Mn₃O(O₂CCH₃)₆(Pyr)₂ (4) where Pyr = pyridine. The parent cluster, Mn₃(O₂CCH₃)₆(Bpy)₂ (1), had impressive relaxivity ( r₁ = 6.9 mM^-1 s^-1, r₂ = 125 mM^-1 s^-1) and was found to be the most amenable for the synthesis of cluster-nanocarrier nanobeads. Using the inverse miniemulsion polymerization technique (1) in combination with the hydrophilic monomer acrylamide, we synthesized nanobeads (∼125 nm diameter) with homogeneously dispersed clusters within the polyacrylamide matrix (termed Mn₃Bpy-PAm). The nanobeads were surface-modified by co-polymerization with an amine-functionalized monomer. This enabled various postsynthetic modifications, for example, to attach a near-IR dye, Cyanine7, as well as a targeting agent. When evaluated as a potential multimodal MRI contrast agent, high relaxivity and contrast were observed with r₁ = 54.4 mM^-1 s^-1 and r₂ = 144 mM^-1 s^-1, surpassing T₁ relaxivity of clinically used Gd-DTPA chelates as well as comparable T₂ relaxivity to iron oxide microspheres. Physicochemical properties, cellular uptake, and impacts on cell viability were also investigated.

Quantum Monte Carlo simulations of a giant {Ni21Gd20} cage with a S = 91 spin ground state

The detailed analysis of magnetic interactions in a giant molecule is difficult both because the synthesis of such compounds is challenging and the number of energy levels increases exponentially with the magnitude and number of spins. Here, we isolated a {Ni₂₁Gd₂₀} nanocage with a large number of energy levels (≈5 × 10³⁰) and used quantum Monte Carlo (QMC) simulations to perform a detailed analysis of magnetic interactions. Based on magnetization measurements above 2 K, the QMC simulations predicted very weak ferromagnetic interactions that would give a record S = 91 spin ground state. Low-temperature measurements confirm the spin ground state but suggest a more complex picture due to the single ion anisotropy; this has also been modeled using the QMC approach. The high spin and large number of low-lying states lead to a large low-field magnetic entropy (14.1 J kg^-1 K^-1 for ΔH = 1 T at 1.1 K) for this material.

Metal-Phenolic Encapsulated Mesoporous Silica Nanoparticles for pH-Responsive Drug Delivery and Magnetic Resonance Imaging

The anticancer drug doxorubicin (DOX) is locked in the mesoporous silica nanoparticle by coating FeIII-TA polymer, and its burst release can be achieved under acidic environment, along with the decreased longitudinal relaxivity. This nanoplatform shows great potential to monitoring the drug delivery process and the fate of the nanocarrier.

Magnetic nanoformulations for prostate cancer

Magnetic nanoparticles (MNPs) play a vital role for improved imaging applications. Recently, a number of studies demonstrate MNPs can be applied for targeted delivery, sustained release of therapeutics, and hyperthermia. Based on stable particle size and shape, biocompatibility, and inherent contrast enhancement characteristics, MNPs have been encouraged for pre-clinical studies and human use. As a theranostic platform development, MNPs need to balance both delivery and imaging aspects. Thus, this review provides significant insight and advances in the theranostic role of MNPs through the documentation of unique magnetic nanoparticles used in prostate cancer, their interaction with prostate cancer cells, in vivo fate, targeting, and biodistribution. Specific and custom-made applications of various novel nanoformulations in prostate cancer are discussed.

Androgen deprivation therapy in the treatment of locally advanced, nonmetastatic prostate cancer: practical experience and a review of the clinical trial evidence

Following new scientific insights, initial management for patients with high-risk nonmetastatic prostate cancer has changed considerably and rapidly over the last few years. Several clinical and pathologic variables should be taken into account when deciding the best treatment choice for those patients. These variables are summarized and discussed in detail. High radiation doses to the prostate are essential to achieve good local control in patients with high-risk nonmetastatic disease. Addition of androgen deprivation therapy (ADT) to radiation therapy has significantly improved overall survival and cancer-specific survival compared with radiation therapy alone without significantly increasing toxicity. Long-term neo(adjuvant) ADT (2-3 years) to radiation therapy significantly improved cancer-specific survival compared with short-term ADT (4-6 months). Radical prostatectomy with extended pelvic lymph node dissection is considered a reasonable option in experienced hands. ADT alone is an inappropriate treatment option for patients with high-risk nonmetastatic disease. Management decisions for these patients should be discussed by a multidisciplinary team.

Zinc-oxide-silica-silver nanocomposite: Unique one-pot synthesis and enhanced catalytic and anti-bacterial performance

We describe herein a unique approach to synthesize zinc oxide-silica-silver (ZnO-SiO2-Ag) nanocomposite, in a simple, one-pot process. The typical process for ZnO synthesis by alkaline precipitation of zinc salts has been tweaked to replace alkali by alkaline sodium silicate. The free acid from zinc salts helps in the synthesis of silica nanoparticles, whereas the alkalinity of sodium silicate precipitates the zinc salts. Addition of silver ions into the reaction pot prior to addition of sodium silicate, and subsequent reduction by borohydride, gives additional functionality of metallic centres for catalytic applications. The synthesis strategy is based on our recent work typically involving acid-base type of cross-reactions and demonstrates a novel strategy to synthesize nanocomposites in a one-pot approach. Each component in the composite offers a unique feature. ZnO besides displaying mild catalytic and anti-bacterial behaviour is an excellent and a cheap 3-D support for heterogeneous catalysis. Silver nanoparticles enhance the catalytic & anti-bacterial properties of ZnO. Silica is an important part of the composite; which not only "glues" the two nanoparticles thereby stabilizing the nanocomposite, but also significantly enhances the surface area of the composite; which is an attractive feature of any catalyst composite. The nanocomposite is found to show excellent catalytic performance with very high turnover frequencies (TOFs) when studied for catalytic reduction of Rhodamine B (RhB) and 4-Nitrophenol (4-NP). Additionally, the composite has been tested for its anti-bacterial properties on three different bacterial strains i.e. E. coli, B. Cereus and Bacillus firmus. The mechanism for enhancement of catalytic performance has been probed by understanding the role of silica in offering accessibility to the catalyst via its porous high surface area network. The nanocomposite has been characterized by a host of different analytical techniques. The uniqueness of our product and process stems from the novel synthesis strategy, the choice and combination of the three moieties, increased surface area offered by silica, and cost effectiveness, thereby making our product and process commercially viable and sustainable for industrial applications.

EDTA capped iron oxide nanoparticles magnetic micelles: drug delivery vehicle for treatment of chronic myeloid leukemia and T1–T2 dual contrast agent for magnetic resonance imaging

This study shows that multiple functionalities like drug delivery and T₁–T₂ dual modalities can be achieved by a proper surface architecture.

Ultra-high relaxivity iron oxide nanoparticles confined in polymer nanospheres for tumor MR imaging

Superparamagnetic iron oxide nanoparticles encapsulated in hydrophilic chitosan nanospheres were prepared by nonsolvent-aided counterion complexation completely in an aqueous solution. The T₂ relaxation of these hybrid nanospheres in vitro and in vivo was investigated. It was found that the molar transverse relaxivity rate r₂ of hybrid nanospheres highly depends upon the payload of iron oxide nanoparticles within hybrid nanospheres. Compared to free iron oxide nanoparticles, the molar transverse relaxivity rate, r₂ of hybrid nanospheres shows an approximately 8-fold increase and reaches the maximum of 533 Fe mM^-1 s^-1. Such a high r₂ value is probably associated with the clustering effect of iron oxide nanoparticles, which are confined in the chitosan nanospheres. The in vivo magnetic resonance imaging (MRI) demonstrates that the hybrid nanospheres shorten transverse relaxation time, T₂ and significantly decrease the signal intensity of the tumor area, giving rise to high contrast tumor MR imaging at a relatively low dose.

Comparative evaluation of the impact on endothelial cells induced by different nanoparticle structures and functionalization

In the research field of nanoparticles, many studies demonstrated a high impact of the shape, size and surface charge, which is determined by the functionalization, of nanoparticles on cell viability and internalization into cells. This work focused on the comparison of three different nanoparticle types to give a better insight into general rules determining the biocompatibility of gold, Janus and semiconductor (quantum dot) nanoparticles. Endothelial cells were subject of this study, since blood is the first barrier after intravenous nanoparticle application. In particular, stronger effects on the viability of endothelial cells were found for nanoparticles with an elongated shape in comparison to spherical ones. Furthermore, a positively charged nanoparticle surface (NH2, CyA) leads to the strongest reduction in cell viability, whereas neutral and negatively charged nanoparticles are highly biocompatible to endothelial cells. These findings are attributed to a rapid internalization of the NH2-functionalized nanoparticles in combination with the damage of intracellular membranes. Interestingly, the endocytotic pathway seems to be a size-dependent process whereas nanoparticles with a size of 20 nm are internalized by caveolae-mediated endocytosis and nanoparticles with a size of 40 nm are taken up by clathrin-mediated internalization and macropinocytosis. Our results can be summarized to formulate five general rules, which are further specified in the text and which determine the biocompatibility of nanoparticles on endothelial cells. Our findings will help to design new nanoparticles with optimized properties concerning biocompatibility and uptake behavior with respect to the respective intended application.

Mesoscale assemblies of iron oxide nanocubes as heat mediators and image contrast agents

Iron oxide nanocubes (IONCs) represent one of the most promising iron-based nanoparticles for both magnetic resonance image (MRI) and magnetically mediated hyperthermia (MMH). Here, we have set a protocol to control the aggregation of magnetically interacting IONCs within a polymeric matrix in a so-called magnetic nanobead (MNB) having mesoscale size (200 nm). By the comparison with individual coated nanocubes, we elucidate the effect of the aggregation on the specific adsorption rates (SAR) and on the T1 and T2 relaxation times. We found that while SAR values decrease as IONCs are aggregated into MNBs but still keeping significant SAR values (200 W/g at 300 kHz), relaxation times show very interesting properties with outstanding values of r2/r1 ratio for the MNBs with respect to single IONCs.

Hybrid Materials Based on the Embedding of Organically Modified Transition Metal Oxoclusters or Polyoxometalates into Polymers for Functional Applications: A Review

The covalent incorporation of inorganic building blocks into a polymer matrix to obtain stable and robust materials is a widely used concept in the field of organic-inorganic hybrid materials, and encompasses the use of different inorganic systems including (but not limited to) nanoparticles, mono- and polynuclear metal complexes and clusters, polyhedral oligomeric silsesquioxanes (POSS), polyoxometalates (POM), layered inorganic systems, inorganic fibers, and whiskers. In this paper, we will review the use of two particular kinds of structurally well-defined inorganic building blocks, namely transition metals oxoclusters (TMO) and polyoxometalates (POM), to obtain hybrid materials with enhanced functional (e.g., optical, dielectric, magnetic, catalytic) properties.