Synthesis and evaluation of nanoglobular macrocyclic Mn(II) chelate conjugates as non-gadolinium(III) MRI contrast agents

Mn-Based MRI Contrast Agents: An Overview

MRI contrast agents are required in the clinic to detect some pathologies, such as cancers. Nevertheless, at the moment, only small extracellular and non-specific gadolinium complexes are available for clinicians. Moreover, safety issues have recently emerged concerning the use of gadolinium complexes; hence, alternatives are urgently needed. Manganese-based MRI contrast agents could be one of these alternatives and increasing numbers of studies are available in the literature. This review aims at synthesizing all the research, from small Mn complexes to nanoparticular agents, including theranostic agents, to highlight all the efforts already made by the scientific community to obtain highly efficient agents but also evidence of the weaknesses of the developed systems.

New opportunities for RGD-engineered metal nanoparticles in cancer

The advent of nanotechnology has opened new possibilities for bioimaging. Metal nanoparticles (such as gold, silver, iron, copper, etc.) hold tremendous potential and offer enormous opportunities for imaging and diagnostics due to their broad optical characteristics, ease of manufacturing technique, and simple surface modification. The arginine-glycine-aspartate (RGD) peptide is a three-amino acid sequence that seems to have a considerably greater ability to adhere to integrin adhesion molecules that exclusively express on tumour cells. RGD peptides act as the efficient tailoring ligand with a variety of benefits including non-toxicity, greater precision, rapid clearance, etc. This review focuses on the possibility of non-invasive cancer imaging using metal nanoparticles with RGD assistance.

Eu3+ and Tb3+ @ PSQ: Dual Luminescent Polyhedral Oligomeric Polysilsesquioxanes

The synthesis and characterization of novel luminescent amorphous POSS-based polysilsesquioxanes (PSQs) with Tb³⁺ and Eu³⁺ ions directly integrated in the polysilsesquioxane matrix is presented. Two different Tb³⁺/Eu³⁺ molar ratios were applied, with the aim of disclosing the relationships between the nature and loading of the ions and the luminescence properties. Particular attention was given to the investigation of site geometry and hydration state of the metal centers in the inorganic framework, and of the effect of the Tb³⁺ → Eu³⁺ energy transfer on the overall optical properties of the co-doped materials. The obtained materials were characterized by high photostability and colors of the emitted light ranging from orange to deep red, as a function of both the Tb³⁺/Eu³⁺ molar ratio and the chosen excitation wavelength. A good energy transfer was observed, with higher efficiency displayed when donor/sensitizer concentration was lower than the acceptor/activator concentration. The easiness of preparation and the possibility to finely tune the photoluminescence properties make these materials valid candidates for several applications, including bioimaging, sensors, ratiometric luminescence-based thermometers, and optical components in inorganic or hybrid light-emitting devices.

Evaluation of Physicochemical Properties, Pharmacokinetics, Biodistribution, Toxicity, and Contrast-Enhanced Cancer MRI of a Cancer-Targeting Contrast Agent, MT218

OBJECTIVES

Preclinical assessments were performed according to the US Food and Drug Administration guidelines to determine the physicochemical properties, pharmacokinetics, clearance, safety, and tumor-specific magnetic resonance (MR) imaging of MT218, a peptidic gadolinium-based MR imaging agent targeting to extradomain B fibronectin for MR molecular imaging of aggressive tumors.

MATERIALS AND METHODS

Relaxivity, chelation stability, binding affinity, safety-related target profiling, and effects on CYP450 enzymes and transporters were evaluated in vitro. Magnetic resonance imaging was performed with rats bearing prostate cancer xenografts, immunocompetent mice bearing murine pancreatic cancer allografts, and mice bearing lung cancer xenografts at different doses of MT218. Pharmacological effects on cardiovascular, respiratory, and central nervous systems were determined in rats and conscious beagle dogs. Pharmacokinetics were tested in rats and dogs. Biodistribution and excretion were studied in rats. Single and repeated dosing toxicity was evaluated in rats and dogs. In vitro and in vivo genotoxicity, in vitro hemolysis, and anaphylactic reactivity were also performed.

RESULTS

At 1.4 T, the r1 and r2 relaxivities of MT218 were 5.43 and 7.40 mM -1 s -1 in pure water, 6.58 and 8.87 mM -1 s -1 in phosphate-buffered saline, and 6.54 and 8.70 mM -1 s -1 in aqueous solution of human serum albumin, respectively. The binding affinity of MT218 to extradomain B fragment is 3.45 μM. MT218 exhibited no dissociation of the Gd(III) chelates under physiological conditions. The peptide degradation half-life ( t1/2 ) of MT218 was 1.63, 5.85, and 2.63 hours in rat, dog, and human plasma, respectively. It had little effect on CYP450 enzymes and transporters. MT218 produced up to 7-fold increase of contrast-to-noise ratios in the extradomain B fibronectin-rich tumors with a dose of 0.04 mmol/kg for at least 30 minutes. MT218 had little pharmacological effect on central nervous, cardiovascular, or respiratory systems. MT218 had a mean plasma elimination half-life ( t1/2 ) of 0.31 and 0.89 hours in rats and dogs at 0.1 mmol/kg, respectively. No detectable Gd deposition was observed in the brain at 6 hours postinjection of MT218 at 0.1 mmol/kg in rats. MT218 was not mutagenic and had no mortality or morbidity in the rats or dogs up to 1.39 and 0.70 mmol/kg/d, respectively. The no observed adverse effect level of MT218 in Sprague-Dawley rats was 1.39 mmol/kg for single dosing and 0.46 mmol/kg/d for repeated dosing. The no observed adverse effect level in dogs was 0.07 mmol/kg/d. MT218 exhibited no genotoxicity, hemolysis, and anaphylactic reactivity.

CONCLUSION

The preclinical assessments showed that the targeted contrast agent MT218 has high r1 and r2 relaxivities, satisfactory physicochemical properties, pharmacokinetic, and safety profiles and produces effective tumor enhancement in multiple cancer types in rats and mice at reduced doses.

Double hydrophilic copolymers - synthetic approaches, architectural variety, and current application fields

Solubility and functionality of polymeric materials are essential properties determining their role in any application. In that regard, double hydrophilic copolymers (DHC) are typically constructed from two chemically dissimilar but water-soluble building blocks. During the past decades, these materials have been intensely developed and utilised as, e.g., matrices for the design of multifunctional hybrid materials, in drug carriers and gene delivery, as nanoreactors, or as sensors. This is predominantly due to almost unlimited possibilities to precisely tune DHC composition and topology, their solution behavior, e.g., stimuli-response, and potential interactions with small molecules, ions and (nanoparticle) surfaces. In this contribution we want to highlight that this class of polymers has experienced tremendous progress regarding synthesis, architectural variety, and the possibility to combine response to different stimuli within one material. Especially the implementation of DHCs as versatile building blocks in hybrid materials expanded the range of water-based applications during the last two decades, which now includes also photocatalysis, sensing, and 3D inkjet printing of hydrogels, definitely going beyond already well-established utilisation in biomedicine or as templates.

Use of Polyhedral Oligomeric Silsesquioxane (POSS) in Drug Delivery, Photodynamic Therapy and Bioimaging

Polyhedral oligomeric silsesquioxanes (POSS) have attracted considerable attention in the design of novel organic-inorganic hybrid materials with high performance capabilities. Features such as their well-defined nanoscale structure, chemical tunability, and biocompatibility make POSS an ideal building block to fabricate hybrid materials for biomedical applications. This review highlights recent advances in the application of POSS-based hybrid materials, with particular emphasis on drug delivery, photodynamic therapy and bioimaging. The design and synthesis of POSS-based materials is described, along with the current methods for controlling their chemical functionalization for biomedical applications. We summarize the advantages of using POSS for several drug delivery applications. We also describe the current progress on using POSS-based materials to improve photodynamic therapies. The use of POSS for delivery of contrast agents or as a passivating agent for nanoprobes is also summarized. We envision that POSS-based hybrid materials have great potential for a variety of biomedical applications including drug delivery, photodynamic therapy and bioimaging.

Nanoprobe-mediated precise imaging and therapy of glioma

Gliomas are the most common primary brain tumors in adults, accounting for 80% of primary intracranial tumors. Due to the heterogeneous and infiltrating nature of malignant gliomas and the hindrance of the blood-brain barrier (BBB), it is very difficult to accurately image and differentiate the malignancy grade of gliomas, thus significantly influencing the diagnostic accuracy and subsequent surgery or therapy. In recent years, the rapid development of emerging nanoprobes has provided a promising opportunity for the diagnosis and treatment of gliomas. After rational component regulation and surface modification, functional nanoprobes could efficiently cross the BBB, target gliomas, and realize single-modal or multimodal imaging of gliomas with high clarity. Moreover, these contrast nanoagents could also be conjugated with therapeutic drugs and cure cancerous tissues at the same time. Herein, we focus on the design strategies of nanoprobes for effective crossing of the BBB, and introduce the recent advances in the precise imaging and therapy of gliomas using functional nanoprobes. Finally, we also discuss the challenges and future directions of nanoprobe-based diagnosis and treatment of gliomas.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe , and studied the most important physicochemical properties in vitro. MnLMe displays optimized r1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r1b =21.1 mM-1  s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (Ka =4.2×103  M-1 ). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe, and studied the most important physicochemical properties in vitro. MnLMe displays optimized r 1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r 1 b=21.1 mM-1 s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (K a=4.2×103 M-1). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

Manganese(III) porphyrin oligomers as high-relaxivity MRI contrast agents

Manganese(III) porphyrins (Mn^IIIPs) as MRI contrast agents (CAs) have drawn particular attention due to their high longitudinal relaxivity (r₁) and unique biodistribution. In this work, two Mn^IIIP-based oligomers, MnPD and MnPT, were designed to further improve the relaxivity with ease of synthesis. The two compounds were fully characterized and their nuclear magnetic relaxation dispersion (NMRD) profiles were acquired with a fast field cycling NMR relaxometer. Both of the compounds exhibited extended high molar r₁ at high fields, higher than that of Gd-DTPA, the first clinical gadolinium(III)-based MRI CA. The r₁ value of per manganese atom increased with the increasing number of Mn^IIIP building blocks, suggesting rotational correlation time (τ_R) played dominant role in the r₁ dispersion. The toxicity of the two Mn^IIIPs and the imaging effectiveness were estimated in vitro and in vivo. With good biocompatibility, significant contrast enhancement, and complete excretion in 24 h, MnPD and MnPT are both promising for high field clinical applications. The applied strategy also potentially provided a facile approach for creation of more Mn^IIIP oligomer as efficient T₁ MRI CAs.

Synthesis, modification and bioapplications of nanoscale copper chalcogenides

Copper chalcogenides have a simple general formula, variable atomic ratios, and complicated crystal structures, which lead to their wealth of optical, electrical, and magnetic properties with great potential for wide applications ranging from energy conversion to the biomedical field. Herein, we summarize the recent advances in (1) the synthesis of size- and morphology tunable nanostructures by different methods; (2) surface modification and functionalization for different purposes; and (3) bioapplications for diagnosis and treatment of tumors by different imaging and therapy methods, as well as antibacterial applications. We also briefly discuss the future directions and challenges of copper chalcogenide nanoparticles in the biomedical field.

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

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.

Polymeric Hybrid Nanomicelles for Cancer Theranostics: An Efficient and Precise Anticancer Strategy for the Codelivery of Doxorubicin/miR-34a and Magnetic Resonance Imaging

To realize precise tumor therapy, a versatile oncotherapy nanoplatform integrating both diagnostic and therapeutic functions is necessary. Herein, we fabricated a hybrid micelle (HM) utilizing two amphiphilic diblock copolymers, polyethylenimine-polycaprolactone (PEI-PCL) and diethylenetriaminepentaacetic acid gadolinium(III)  (Gd-DTPA)-conjugated polyethyleneglycol-polycaprolactone (Gd-PEG-PCL), to codeliver the small-molecule chemotherapy drugs doxorubicin (Dox) and microRNA-34a (miR-34a), denoted as Gd-HM-Dox/34a. Conjugating Gd-DTPA on the surface of hybrid micelles, leading the relaxation rate of Gd-DTPA increased more than 1.4 times (13.6 mM^-1 S^-1). Furthermore, hybrid micelles enhanced the ability of miR-34a to escape from lysosomes/endosomes and Dox release to the nucleus. In addition, the released miR-34a subsequently downregulates Bcl-2, cyclin D1, CDK6, and Bax expression and inhibits proliferation and migration of MDA-MB-231 breast cancer cells. Moreover, the suitable micelle size improved the penetration of Dox into three-dimensional (3D) multicellular spheroids compared with Gd-HM-Dox and Free Dox, generating efficient cell killing in the 3D multicellular spheroids. Furthermore, the Gd-HM-Dox/34a exhibited augmented accumulation in the tumor tissue, which improved the magnetic resonance (MR) imaging contrast of solid tumors and enhanced the combined efficiency of chemotherapeutic drugs Dox and therapeutic gene miR-34a in suppressing tumor growth on MDA-MB-231 tumor-bearing mice. Therefore, we established a hybrid micelle to offer a promising theranostic approach that inhibits tumor growth and enhances MR imaging.

Construction of Paramagnetic Manganese-Chelated Polymeric Nanoparticles Using Pyrene-End-Modified Double-Hydrophilic Block Copolymers for Enhanced Magnetic Resonance Relaxivity: A Comparative Study with Cisplatin Pharmacophore

Cationic metal-mediated self-assembly of double-hydrophilic block copolymers (DHBCs) has been of great interest for the preparation of hybrid nanoparticles for versatile applications. Among many functional transition-metal ions, manganese (Mn^II) is a highly attractive element due to its paramagnetic property with a high coordination number. However, Mn^II does not lead to the efficient self-assembly of DHBCs because of the relatively high aqueous solubility of coordinated Mn^II. This article reports a facile method for direct conjugation of Mn^II ions inside sterically stabilized polymer assemblies, composed of pyrene-end-modified DHBCs. Nitroxide-mediated radical polymerization was used to prepare the poly(ethylene glycol)- b-poly(acrylate) DHBC precursor, followed by the end-modification with pyrene maleimide via the radical-exchange reaction. Employing the self-associated DHBC as the nanoscale template, the simple addition of Mn^II enables a large number of polyvalent Mn^II ions to be immobilized at the chelating blocks of DHBCs, which can be readily monitored by the excimeric fluorescence emission change of the terminal pyrene fluorophore. The resulting Mn^II-loaded polymeric nanoparticles (Mn^II-PNPs) possess nanogel-like scaffolds, which allow for efficient water permeation at the Mn^II-incorporated interior for enhanced magnetic resonance contrasting effect. Additionally, by comparing the coordination properties of Mn^II and cisplatin, we endeavor to understand the internal structures and the relevant physicochemical features of metal-chelated nanoparticles.

Fe3O4 Nanoparticles Functionalized with Polymer Ligand for T1-Weighted MRI In Vitro and In Vivo

Magnetic resonance imaging (MRI) has gained wide interest in early accurate diagnoses due to the high resolution and low toxicity of magnetic nanoparticles. In order to develop potential alternatives of toxic Gd- or Mn-based chelating agents, we report the synthesis of water soluble ultra-small Fe3O4 nanoparticles by a modified co-precipitation method as T1-weighted positive contrast agents. The magnetic iron oxide nanoparticles (MIONs) were functionalized by polymer ligand dodecanthiol-polymethacrylic acid (DDT-PMAA) to enhance their colloidal stability. These MIONs have high longitudinal relaxivity (r1 = 8.18 mM-1·S-1) and exhibited good results in the in vitro and in vivo MR imaging. No toxicity was observed in cytotoxicity assay and histology toxicity analysis. The MIONs@DDT-PMAA(magnetic iron oxide nanoparticles @ dodecanthiol-polymethacrylic acid) present great potential as positive contrast agents for tumor diagnosis.

A multifunctional low-generation dendrimer-based nanoprobe for the targeted dual mode MR/CT imaging of orthotopic brain gliomas

An RGD peptide-targeted low-generation dendrimer nanoprobe can cross the blood-brain barrier for dual-modal MR/CT imaging of an orthotopic brain glioma.

Dendrimer- and copolymer-based nanoparticles for magnetic resonance cancer theranostics

Cancer theranostics is one of the most important approaches for detecting and treating patients at an early stage. To develop such a technique, accurate detection, specific targeting, and controlled delivery are the key components. Various kinds of nanoparticles have been proposed and demonstrated as potential nanovehicles for cancer theranostics. Among them, polymer-like dendrimers and copolymer-based core-shell nanoparticles could potentially be the best possible choices. At present, magnetic resonance imaging (MRI) is widely used for clinical purposes and is generally considered the most convenient and noninvasive imaging modality. Superparamagnetic iron oxide (SPIO) and gadolinium (Gd)-based dendrimers are the major nanostructures that are currently being investigated as nanovehicles for cancer theranostics using MRI. These structures are capable of specific targeting of tumors as well as controlled drug or gene delivery to tumor sites using pH, temperature, or alternating magnetic field (AMF)-controlled mechanisms. Recently, Gd-based pseudo-porous polymer-dendrimer supramolecular nanoparticles have shown 4-fold higher T1 relaxivity along with highly efficient AMF-guided drug release properties. Core-shell copolymer-based nanovehicles are an equally attractive alternative for designing contrast agents and for delivering anti-cancer drugs. Various copolymer materials could be used as core and shell components to provide biostability, modifiable surface properties, and even adjustable imaging contrast enhancement. Recent advances and challenges in MRI cancer theranostics using dendrimer- and copolymer-based nanovehicles have been summarized in this review article, along with new unpublished research results from our laboratories.

Synthesis and Evaluation of Manganese(II)-Based Ethylenediaminetetraacetic Acid-Ethoxybenzyl Conjugate as a Highly Stable Hepatobiliary Magnetic Resonance Imaging Contrast Agent

In this study, we designed and synthesized a highly stable manganese (Mn²⁺)-based hepatobiliary complex by tethering an ethoxybenzyl (EOB) moiety with an ethylenediaminetetraacetic acid (EDTA) coordination cage as an alternative to the well-established hepatobiliary gadolinium (Gd³⁺) chelates and evaluated its usage as a T₁ hepatobiliary magnetic resonance imaging (MRI) contrast agent (CA). This new complex exhibits higher r₁ relaxivity (2.3 mM^-1 s^-1) than clinically approved Mn²⁺-based hepatobiliary complex Mn-DPDP (1.6 mM^-1 s^-1) at 1.5 T. Mn-EDTA-EOB shows much higher kinetic inertness than that of clinically approved Gd³⁺-based hepatobiliary MRI CAs, such as Gd-DTPA-EOB and Gd-BOPTA. In addition, in vivo biodistribution and MRI enhancement patterns of this new Mn²⁺ chelate are comparable to those of Gd³⁺-based hepatobiliary MRI CAs. The diagnostic efficacy of the new complex was demonstrated by its enhanced tumor detection sensitivity in a liver cancer model using in vivo MRI.

How can nanotechnology help the fight against breast cancer?

In this review we provide a broad overview on the use of nanotechnology for the fight against breast cancer (BC). Nowadays, detection, diagnosis, treatment, and prevention may be possible thanks to the application of nanotechnology to clinical practice. Taking into consideration the different forms of BC and the disease status, nanomaterials can be designed to meet the most forefront objectives of modern therapy and diagnosis. We have analyzed in detail three main groups of nanomaterial applications for BC treatment and diagnosis. We have identified several types of drugs successfully conjugated with nanomaterials. We have analyzed the main important imaging techniques and all nanomaterials used to help the non-invasive, early detection of the lesions. Moreover, we have examined theranostic nanomaterials as unique tools, combining imaging, detection, and therapy for BC. This state of the art review provides a useful guide depicting how nanotechnology can be used to overcome the current barriers in BC clinical practice, and how it will shape the future scenario of treatments, prevention, and diagnosis, revolutionizing the current approaches, e.g., reducing the suffering related to chemotherapy.

A promising magnetic resonance stem cell tracer based on natural biomaterials in a biological system: manganese(II) chelated to melanin nanoparticles

Background

Melanin and manganese are both indispensable natural substances that play crucial roles in the human body. Melanin has been used as a multimodality imaging nanoplatform for biology science research because of its natural binding ability with metal ions (eg, ⁶⁴Cu²⁺, Fe³⁺, and Gd³⁺). Because of its effects on T1 signal enhancement, Mn-based nanoparticles have been used in magnetic resonance (MR) quantitative cell tracking in vivo. Stem cell tracking in vivo is an essential technology used to characterize engrafted stem cells, including cellular viability, biodistribution, differentiation capacity, and long-term fate.

Methods

In the present study, manganese(II) ions chelated to melanin nanoparticles [MNP-Mn(II)] were synthesized. The characteristics, stem cell labeling efficiency, and cytotoxicity of the nanoparticles were evaluated. MR imaging of the labeled stem cells in vivo and in vitro were also further performed. In T1 relaxivity (r1), MNP-Mn(II) were significantly more abundant than Omniscan. Bone marrow-derived stem cells (BMSCs) can be labeled easily by coincubating with MNP-Mn(II), suggesting that MNP-Mn(II) had high biocompatibility.

Results

Cell Counting Kit-8 assays revealed that MNP-Mn(II) had almost no cytotoxicity when used to label BMSCs, even with a very high concentration (1,600 µg/mL). BMSCs labeled with MNP-Mn(II) could generate a hyperintense T1 signal both in vitro and in vivo, and the hyperintense T1 signal in vivo persisted for at least 28 days.

Conclusion

Taken together, our results showed that MNP-Mn(II) possessed many excellent properties for potential quantitative stem cell tracking in vivo.

A New Bis(aquated) High Relaxivity Mn(II) Complex as an Alternative to Gd(III)-Based MRI Contrast Agent

Disclosed here are a piperazine, a pyridine, and two carboxylate groups containing pentadentate ligand H₂pmpa and its corresponding water-soluble Mn(II) complex (1). DFT-based structural optimization implied that the complex had pentagonal bipyramidal geometry where the axial positions were occupied by two water molecules, and the equatorial plane was constituted by the ligand ON₃O donor set. Thus, a bis(aquated) disc-like Mn(II) complex has been synthesized. The complex showed higher stability compared with Mn(II)-EDTA complex [log K_MnL = 14.29(3)] and showed a very high r₁ relaxivity value of 5.88 mM^-1 s^-1 at 1.41 T, 25 °C, and pH = 7.4. The relaxivity value remained almost unaffected by the pH of the medium in the range of 6-10. Although the presence of 200 equiv of fluoride and bicarbonate anions did not affect the relaxivity value appreciably, an increase in the value was noticed in the presence of phosphate anion due to slow tumbling of the complex. Cell viability measurements, as well as phantom MR images using clinical MRI imager, consolidated the possible candidature of complex 1 as a positive contrast agent.

Photosensitizer (PS)/polyhedral oligomeric silsesquioxane (POSS)-crosslinked nanohybrids for enhanced imaging-guided photodynamic cancer therapy

Photodynamic therapy (PDT) has drawn extensive attention as a promising cancer treatment modality. However, most PDT nanoagents suffer from insufficient drug loading capacity, a severe self-quenching effect, premature release of drugs and/or potential toxicity. Herein, we rationally designed an inorganic-organic nanohybrid with high drug loading capacity and superior chemical stability for enhanced PDT. Polyhedral oligomeric silsesquioxane (POSS), an amine-containing cage-shaped building block, was crosslinked with chlorin e6 (Ce6), a carboxyl-containing photosensitizer, via the amine-carboxyl reaction. Polyethylene glycol (PEG) polymers were further modified on the surface of the nanoparticle to improve the aqueous dispersibility and prolong the circulation time of the final nanoconstruct (POSS-Ce6-PEG). The as-prepared POSS-Ce6-PEG has a considerably high loading rate of Ce6 (19.8 wt%) with desirable fluorescence emission and singlet oxygen generation. Besides, in vitro experiments revealed that the nanoagent exhibited enhanced cellular uptake and a preferred intracellular accumulation within mitochondria and the endoplasmic reticulum, resulting in high anticancer efficiency under light irradiation. Furthermore, in vivo imaging-guided PDT was also successfully achieved, showing the effective tumor targeting and ablation ability of POSS-Ce6-PEG. More importantly, the nanoagent possesses negligible dark cytotoxicity and systemic side effects. Therefore, POSS-Ce6-PEG as an eligible PDT theranostic agent holds great potential in clinical applications.

Targeting Fibronectin for Cancer Imaging and Therapy

During cancer progression, the extracellular matrix (ECM) undergoes dramatic changes, which promote cancer cell migration and invasion. In the remodeled tumor ECM, fibronectin (FN) level is upregulated to assist tumor growth, progression, and invasion. FN serves as a central organizer of ECM molecules and mediates the crosstalk between the tumor microenvironment and cancer cells. Its upregulation is correlated with angiogenesis, cancer progression, metastasis, and drug resistance. A number of FN-targeting ligands have been developed for cancer imaging and therapy. Thus far, FN-targeting imaging agents have been tested for nuclear imaging, MRI, and fluorescence imaging, for tumor detection and localization. FN-targeting therapeutics, including nuclear medicine, chemotherapy drugs, cytokines, and photothermal moieties, were also developed in cancer therapy. Because of the prevalence of FN overexpression in cancer, FN targeting imaging agents and therapeutics have the promise of broad applications in the diagnosis, treatment, and image-guided interventions of many types of cancers. This review will summarize current understanding on the role of FN in cancer, discuss the design and development of FN-targeting agents, and highlight the applications of these FN-targeting agents in cancer imaging and therapy.

The design of a multifunctional dendrimer-based nanoplatform for targeted dual mode SPECT/MR imaging of tumors

A multifunctional dendrimer-based nanoplatform labeled with ^99mTc can be synthesized for targeted SPECT/MR dual mode imaging of tumors.

RGD-functionalized ultrasmall iron oxide nanoparticles for targeted T₁-weighted MR imaging of gliomas

We report a convenient approach to prepare ultrasmall Fe3O4 nanoparticles (NPs) functionalized with an arginylglycylaspartic acid (RGD) peptide for in vitro and in vivo magnetic resonance (MR) imaging of gliomas. In our work, stable sodium citrate-stabilized Fe3O4 NPs were prepared by a solvothermal route. Then, the carboxylated Fe3O4 NPs stabilized with sodium citrate were conjugated with polyethylene glycol (PEG)-linked RGD. The formed ultrasmall RGD-functionalized nanoprobe (Fe3O4-PEG-RGD) was fully characterized using different techniques. We show that these Fe3O4-PEG-RGD particles with a size of 2.7 nm are water-dispersible, stable, cytocompatible and hemocompatible in a given concentration range, and display targeting specificity to glioma cells overexpressing αvβ3 integrin in vitro. With the relatively high r1 relaxivity (r1 = 1.4 mM(-1) s(-1)), the Fe3O4-PEG-RGD particles can be used as an efficient nanoprobe for targeted T1-weighted positive MR imaging of glioma cells in vitro and the xenografted tumor model in vivo via an active RGD-mediated targeting pathway. The developed RGD-functionalized Fe3O4 NPs may hold great promise to be used as a nanoprobe for targeted T1-weighted MR imaging of different αvβ3 integrin-overexpressing cancer cells or biological systems.

Hyaluronic Acid-Chitosan Nanoparticles to Deliver Gd-DTPA for MR Cancer Imaging

Molecular imaging is essential to increase the sensitivity and selectivity of cancer diagnosis especially at the early stage of tumors. Recently, polyionic nanocomplexes (PICs), which are composed of polyanions and opposite polycations, have been demonstrated to be a promising strategy for biomedical applications. In this work, chitosan-hyaluronic acid nanoparticles (GCHN) were developed to deliver Gd-DTPA as MRI contrast agents for tumor diagnosis. The Gd-labeled conjugates (CS-DTPA-Gd) were successfully synthesized by carbodiimide reaction, and then GCHN were prepared by ionic gelation using the obtained CS-DTPA-Gd and hyaluronic acid. The morphology of GCHN was spherical or ellipsoidal, which is observed by transmission electronic microscopy (TEM). The mean particle size and zeta potential of GCHN were 213.8 ± 2.6 nm and 19.92 ± 1.69 mV, respectively. The significant enhancement of signal intensity induced by GCHN was observed both in vitro and in vivo. Also, compared with Magnevist, GCHN was witnessed for a prolonged imaging time in the B16 tumor-bearing mice model. Furthermore, GCHN were verified as below toxic both in vitro and in vivo. These results indicated that GCHN could potentially be an alternative to current MRI contrast agents for tumor diagnosis.

Manganese (II) Chelate Functionalized Copper Sulfide Nanoparticles for Efficient Magnetic Resonance/Photoacoustic Dual-Modal Imaging Guided Photothermal Therapy

The integration of diagnostic and therapeutic functionalities into one nanoplatform shows great promise in cancer therapy. In this research, manganese (II) chelate functionalized copper sulfide nanoparticles were successfully prepared using a facile hydrothermal method. The obtained ultrasmall nanoparticles exhibit excellent photothermal effect and photoaoustic activity. Besides, the high loading content of Mn(II) chelates makes the nanoparticles attractive T₁ contrast agent in magnetic resonance imaging (MRI). In vivo photoacoustic imaging (PAI) results showed that the nanoparticles could be efficiently accumulated in tumor site in 24 h after systematic administration, which was further validated by MRI tests. The subsequent photothermal therapy of cancer in vivo was achieved without inducing any observed side effects. Therefore, the copper sulfide nanoparticles functionalized with Mn(II) chelate hold great promise as a theranostic nanomedicine for MR/PA dual-modal imaging guided photothermal therapy of cancer.

Manganese doped iron oxide theranostic nanoparticles for combined T1 magnetic resonance imaging and photothermal therapy

Photothermal therapy (PTT) is a noninvasive and convenient way to ablate tumor tissues. Integrating PTT with imaging technique could precisely identify the location and the size of tumor regions, thereby significantly improving the therapeutic efficacy. Magnetic resonance imaging (MRI) is widely used in clinical diagnosis due to its superb spatial resolution and real-time monitoring feature. In our work, we developed a theranostic nanoplatform based on manganese doped iron oxide (MnIO) nanoparticles modified with denatured bovine serum albumin (MnIO-dBSA). The in vitro experiment revealed that the MnIO nanoparticles exhibited T1-weighted MRI capability (r1 = 8.24 mM(-1) s(-1), r2/r1 = 2.18) and good photothermal effect under near-infrared laser irradiation (808 nm). Using 4T1 tumor-bearing mice as an animal model, we further demonstrated that the MnIO-dBSA composites could significantly increase T1 MRI signal intensity at the tumor site (about two times) and effectively ablate tumor tissues with photoirradiation. Taken together, this work demonstrates the great potential of the MnIO nanoparticles as an ideal theranostic platform for efficient tumor MR imaging and photothermal therapy.

Solution thermodynamics, computational and relaxometric studies of ditopic DO3A-based Mn(ii) complexes

The structure, stability and magnetic properties of novel ditopic Mn(ii)-complexes were studied by molecular modeling, potentiometric and relaxometric techniques.

Dendritic nanoglobules with polyhedral oligomeric silsesquioxane core and their biomedical applications

Dendrimers have been recognized as promising materials for biomedical applications due to their unique properties, such as well-defined unimolecular structures, precise molecular weights and high degrees of branching and surface functionality. The dendrimers with a polyhedral oligomeric silsesquioxane core – nanoglobules – have many advantageous features over traditional dendrimers, including more functional groups at the same generation of dendrimers, well-defined 3D structures and relatively compact morphologies. Various nanoglobules of polyhedral oligomeric silsesquioxane-core dendrimers have been synthesized and investigated for biomedical applications. Nanoglobules have been used as carriers for developing drug-delivery systems, gene-delivery systems and imaging contrast agents with precisely defined structures and sizes. This article summarizes the recent developments in nanoglobules for biomedical applications.

MR imaging techniques for nano-pathophysiology and theranostics

The advent of nanoparticle DDSs (drug delivery systems, nano-DDSs) is opening new pathways to understanding physiology and pathophysiology at the nanometer scale. A nano-DDS can be used to deliver higher local concentrations of drugs to a target region and magnify therapeutic effects. However, interstitial cells or fibrosis in intractable tumors, as occurs in pancreatic or scirrhous stomach cancer, tend to impede nanoparticle delivery. Thus, it is critical to optimize the type and size of nanoparticles to reach the target. High-resolution 3D imaging provides a means of "seeing" the nanoparticle distribution and therapeutic effects. We introduce the concept of "nano-pathophysiological imaging" as a strategy for theranostics. The strategy consists of selecting an appropriate nano-DDS and rapidly evaluating drug effects in vivo to guide the next round of therapy. In this article we classify nano-DDSs by component carrier materials and present an overview of the significance of nano-pathophysiological MRI.

Self-organized Mn2+-Block Copolymer Complexes and Their Use for In Vivo MR Imaging of Biological Processes

Manganese-block copolymer complexes (MnBCs) that contain paramagnetic Mn ions complexed with ionic-nonionic poly(ethylene oxide-b-poly(methacrylate) have been developed for use as a T1-weighted MRI contrast agent. By encasing Mn ion within ionized polymer matrices, r1 values could be increased by 250-350 % in comparison with free Mn ion at relative high fields of 4.7 to 11.7 T. MnBCs were further manipulated by treatment with NaOH to achieve more stable complexes (iMnBCs). iMnBCs delayed release of Mn2+ which could be accelerated by low pH, indeed by cellular uptake via endocytosis into acidic compartments. Both complexes exhibited good T1 contrast signal enhancement in liver following intravenous infusion. The contrast was observed in gallbladder due to the clearance of Mn ion from liver to biliary process. iMnBCs, notably, showed a delayed contrast enhancement profile in gallbladder, which was interpreted to be due to degradation and excretion of Mn2+ ions into the gallbladder. Intracortical injection of iMnBCs into the rat brain also led to delayed neuronal transport to thalamus. The delayed enhancement feature may have benefits for targeting MRI contrast to specific cells and surface receptors that are known to be internalized by endocytosis.

Synthesis and characterisation of a novel europium(iii)-containing heptaisobutyl-POSS

A novel Eu(iii)-containing POSS with good light quantum efficiency and high photostability was designed and characterized by a multidisciplinary approach.

Flow cytometry evidence of human granulocytes interaction with polyhedral oligomeric silsesquioxanes: effect of nanoparticle charge

Nanoparticles (NPs) entering the human body are immediately confronted with the innate part of human immune system. In particular, monocyte and neutrophil granulocytes readily clear particles by phagocytosis, even if in the case of NPs the uptake mechanism may be classified as macropinocytosis. Among engineered nanoparticles, in the last years, siliceous materials have emerged as promising materials for several applications ranging from catalysis to biomedical. The polyhedral oligomeric silsesquioxanes (POSS) are nanodimensional, easily synthesizable molecular compounds and POSS-based systems are promising carriers for biological molecules. In this work, the ability of human granulocytes to uptake positively and negatively charged POSS was measured using a simple flow cytometry analysis based on cell size modifications. The data obtained showed that after a 30 min exposure only positive NPs were uptaken by human granulocyte using both macropinocytosis and clathrin-mediated mechanisms as demonstrated by uptake inhibition mediated by amiloride and chlorpromazine.

Polydisulfide manganese(II) complexes as non-gadolinium biodegradable macromolecular MRI contrast agents

PURPOSE

To develop safe and effective manganese(II) -based biodegradable macromolecular MRI contrast agents.

MATERIALS AND METHODS

In this study, we synthesized and characterized two polydisulfide manganese(II) complexes, Mn-DTPA cystamine copolymers and Mn-EDTA cystamine copolymers, as new biodegradable macromolecular MRI contrast agents. The contrast enhancement of the two manganese-based contrast agents were evaluated in mice bearing MDA-MB-231 human breast carcinoma xenografts, in comparison with MnCl(2) .

RESULTS

The T(1) and T(2) relaxivities were 4.74 and 10.38 mM(-1) s(-1) per manganese at 3T for Mn-DTPA cystamine copolymers (M(n) = 30.50 kDa) and 6.41 and 9.72 mM(-1) s(-1) for Mn-EDTA cystamine copolymers (M(n) = 61.80 kDa). Both polydisulfide Mn(II) complexes showed significant liver, myocardium and tumor enhancement.

CONCLUSION

The manganese-based polydisulfide contrast agents have a potential to be developed as alternative non-gadolinium contrast agents for MR cancer and myocardium imaging.