Preparation and long-term biodistribution studies of a PAMAM dendrimer G5-Gd-BnDOTA conjugate for lymphatic imaging

Unsupervised Fusion of Misaligned PAT and MRI Images via Mutually Reinforcing Cross-Modality Image Generation and Registration

Photoacoustic tomography (PAT) and magnetic resonance imaging (MRI) are two advanced imaging techniques widely used in pre-clinical research. PAT has high optical contrast and deep imaging range but poor soft tissue contrast, whereas MRI provides excellent soft tissue information but poor temporal resolution. Despite recent advances in medical image fusion with pre-aligned multimodal data, PAT-MRI image fusion remains challenging due to misaligned images and spatial distortion. To address these issues, we propose an unsupervised multi-stage deep learning framework called PAMRFuse for misaligned PAT and MRI image fusion. PAMRFuse comprises a multimodal to unimodal registration network to accurately align the input PAT-MRI image pairs and a self-attentive fusion network that selects information-rich features for fusion. We employ an end-to-end mutually reinforcing mode in our registration network, which enables joint optimization of cross-modality image generation and registration. To the best of our knowledge, this is the first attempt at information fusion for misaligned PAT and MRI. Qualitative and quantitative experimental results show the excellent performance of our method in fusing PAT-MRI images of small animals captured from commercial imaging systems.

Dendrimers: Advancements and Potential Applications in Cancer Diagnosis and Treatment-An Overview

Cancer is a leading cause of death worldwide, and the main treatment methods for this condition are surgery, chemotherapy, and radiotherapy. These treatment methods are invasive and can cause severe adverse reactions among organisms, so nanomaterials are increasingly used as structures for anticancer therapies. Dendrimers are a type of nanomaterial with unique properties, and their production can be controlled to obtain compounds with the desired characteristics. These polymeric molecules are used in cancer diagnosis and treatment through the targeted distribution of some pharmacological substances. Dendrimers have the ability to fulfill several objectives in anticancer therapy simultaneously, such as targeting tumor cells so that healthy tissue is not affected, controlling the release of anticancer agents in the tumor microenvironment, and combining anticancer strategies based on the administration of anticancer molecules to potentiate their effect through photothermal therapy or photodynamic therapy. The purpose of this review is to summarize and highlight the possible uses of dendrimers regarding the diagnosis and treatment of oncological conditions.

Mechanical relaxation of functionalized carbosilane dendrimer melts

Functionalizing the internal structure of classical dendrimers is a new way of tailoring their properties. Using atomistic molecular dynamics simulations, we investigate the rheological behavior of functionalized dendrimer (FD) melts obtained by modifying the branching of carbosilane dendrimers (CSD). The time (relaxation modulus G(t)) and frequency (storage G' and loss G'' moduli) dependencies of the dynamic modulus are obtained. Fourth generation FD melts present a region where G' > G''. In contrast, their non-functionalized counterparts (i.e., classical dendrimers with regular branching) do not show such a region. The comparative analysis of FD and CSD suggests that the internal densification due to functionalization prevents the penetration of branches and causes FD to behave like colloidal particles in a crowded environment. Since CSD have no special interactions, we expect that this effect will be common for other dendrimer macromolecules.

Dendrimers based cancer nanotheranostics: An overview

Cancer is a known deadliest disease that requires a judicious diagnostic, targeting, and treatment strategy for an early prognosis and selective therapy. The major pitfalls of the conventional approach are non-specificity in targeting, failure to precisely monitor therapy outcome, and cancer progression leading to malignancies. The unique physicochemical properties offered by nanotechnology derived nanocarriers have the potential to radically change the landscape of cancer diagnosis and therapeutic management. An integrative approach of utilizing both diagnostic and therapeutic functionality using a nanocarrier is termed as nanotheranostic. The nanotheranostics platform is designed in such a way that overcomes various biological barriers, efficiently targets the payload to the desired locus, and simultaneously supports planning, monitoring, and verification of treatment delivery to demonstrate an enhanced therapeutic efficacy. Thus, a nanotheranostic platform could potentially assist in drug targeting, image-guided focal therapy, drug release and distribution monitoring, predictionof treatment response, and patient stratification. A class of highly branched nanocarriers known as dendrimers is recognized as an advanced nanotheranostic platform that has the potential to revolutionize the oncology arena by its unique and exciting features. A dendrimer is a well-defined three-dimensional globular chemical architecture with a high level of monodispersity, amenability of precise size control, and surface functionalization. All the dendrimer properties exhibit a reproducible pharmacokinetic behavior that could ensure the desired biodistribution and efficacy. Dendrimers are thus being exploited as a nanotheranostic platform embodying a diverse class of therapeutic, imaging, and targeting moieties for cancer diagnosis and treatment.

Imaging technology of the lymphatic system

The lymphatic system plays critical roles in tissue fluid homeostasis and immunity and has been implicated in the development of many different pathologies, ranging from lymphedema, the spread of cancer to chronic inflammation. In this review, we first summarize the state-of-the-art of lymphatic imaging in the clinic and the advantages and disadvantages of these existing techniques. We then detail recent progress on imaging technology, including advancements in tracer design and injection methods, that have allowed visualization of lymphatic vessels with excellent spatial and temporal resolution in preclinical models. Finally, we describe the different approaches to quantifying lymphatic function that are being developed and discuss some emerging topics for lymphatic imaging in the clinic. Continued advancements in lymphatic imaging technology will be critical for the optimization of diagnostic methods for lymphatic disorders and the evaluation of novel therapies targeting the lymphatic system.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

Iron Oxide Nanoparticles: An Alternative for Positive Contrast in Magnetic Resonance Imaging

Iron oxide nanoparticles have been extensively utilised as negative (T2) contrast agents in magnetic resonance imaging. In the past few years, researchers have also exploited their application as positive (T1) contrast agents to overcome the limitation of traditional Gd3+ contrast agents. To provide T1 contrast, these particles must present certain physicochemical properties with control over the size, morphology and surface of the particles. In this review, we summarise the reported T1 iron oxide nanoparticles and critically revise their properties, synthetic protocols and application, not only in MRI but also in multimodal imaging. In addition, we briefly summarise the most important nanoparticulate Gd and Mn agents to evaluate whether T1 iron oxide nanoparticles can reach Gd/Mn contrast capabilities.

Opportunities in Interventional and Diagnostic Imaging by Using High-Performance Low-Field-Strength MRI

Background Commercial low-field-strength MRI systems are generally not equipped with state-of-the-art MRI hardware, and are not suitable for demanding imaging techniques. An MRI system was developed that combines low field strength (0.55 T) with high-performance imaging technology. Purpose To evaluate applications of a high-performance low-field-strength MRI system, specifically MRI-guided cardiovascular catheterizations with metallic devices, diagnostic imaging in high-susceptibility regions, and efficient image acquisition strategies. Materials and Methods A commercial 1.5-T MRI system was modified to operate at 0.55 T while maintaining high-performance hardware, shielded gradients (45 mT/m; 200 T/m/sec), and advanced imaging methods. MRI was performed between January 2018 and April 2019. T1, T2, and T2* were measured at 0.55 T; relaxivity of exogenous contrast agents was measured; and clinical applications advantageous at low field were evaluated. Results There were 83 0.55-T MRI examinations performed in study participants (45 women; mean age, 34 years ± 13). On average, T1 was 32% shorter, T2 was 26% longer, and T2* was 40% longer at 0.55 T compared with 1.5 T. Nine metallic interventional devices were found to be intrinsically safe at 0.55 T (<1°C heating) and MRI-guided right heart catheterization was performed in seven study participants with commercial metallic guidewires. Compared with 1.5 T, reduced image distortion was shown in lungs, upper airway, cranial sinuses, and intestines because of improved field homogeneity. Oxygen inhalation generated lung signal enhancement of 19% ± 11 (standard deviation) at 0.55 T compared with 7.6% ± 6.3 at 1.5 T (P = .02; five participants) because of the increased T1 relaxivity of oxygen (4.7e-4 mmHg-1sec-1). Efficient spiral image acquisitions were amenable to low field strength and generated increased signal-to-noise ratio compared with Cartesian acquisitions (P < .02). Representative imaging of the brain, spine, abdomen, and heart generated good image quality with this system. Conclusion This initial study suggests that high-performance low-field-strength MRI offers advantages for MRI-guided catheterizations with metal devices, MRI in high-susceptibility regions, and efficient imaging. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Grist in this issue.

Influence of Molecular Mobility on Contrast Efficiency of Branched Polyethylene Glycol Contrast Agent

For a water-soluble polyethylene glycol (PEG) magnetic resonance imaging (MRI) contrast agent, it has been demonstrated that the contrast efficiency was increased with increased branched structure of the contrast agent. However, the cause of enhanced contrast efficiency by the branched structure has not been clarified. Hence, we investigate the cause of the contrast agent enhancement by changing the Gd introduction ratio of the eight-arm PEG from 1.97 to 4.07; furthermore, the terminal mobility of the contrast agents with different structures was evaluated using proton nuclear magnetic resonance (¹H-NMR) spectroscopy. It was shown that the relaxivity and contrast luminance of the synthesized branched PEG-Gd contrast agents are larger than those of linear PEG-Gd and commercially available contrast agents. Additionally, the change in the Gd introduction ratio did not affect the contrast efficiency. The terminal mobility results measured by NMR show that the linewidth at half height became broader with an increased number of branches, implying that the mobility of branched PEG-Gd is slower than that of linear PEG-Gd. Interestingly, the linewidth at half height of different structures did not change in an organic solvent; this phenomenon appeared specifically in water. It is suggested that the stable branched structure enabled the improvement in the relaxivity and contrast luminance.

Modular synthesis and modification of novel bifunctional dendrons

The modular synthesis of two generations of highly branched bifunctional dendrons is reported. The first generation dendron–antibody conjugate is shown to selectively detect CD4⁺ T cells in the PBMC culture.

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.

Superfine Magnetic Resonance Imaging of the Cerebrovasculature Using Self-Assembled Branched Polyethylene Glycol-Gd Contrast Agent

Magnetic resonance angiography is an attractive method for the visualization of the cerebrovasculature, but small-sized vessels are hard to visualize with the current clinically approved agents. In this study, a polymeric contrast agent for the superfine imaging of the cerebrovasculature is presented. Eight-arm polyethylene glycol with a molecular weight of ≈17 000 Da conjugated with a Gd chelate and fluorescein (F-8-arm PEG-Gd) is used. The relaxivity rate is 9.3 × 10^-3 m^-1 s^-1 , which is threefold higher than that of free Gd chelate. Light scattering analysis reveals that F-8-arm PEG-Gd is formed by self-assembly. When the F-8-arm PEG-Gd is intravenously injected, cerebrovasculature as small as 100 µm in diameter is clearly visualized. However, signals are not enhanced when Gd chelate and Gd chelate-conjugated 8-arm PEG are injected. Furthermore, small vasculature around infarct region in rat stroke model can be visualized. These results suggest that F-8-arm PEG-Gd enhances the MR imaging of cerebrovasculature.

Biodistribution, pharmacokinetics, and toxicity of dendrimer-coated iron oxide nanoparticles in BALB/c mice

Background

The possibility of using a specific nanoparticle in nanomedicine highly depends on its biodistribution profile and biocompatibility. Due to growing demand for iron oxide nanoparticles (IONPs) and dendrimers in biomedical applications, this study was performed to assess the biodistribution, pharmacokinetics, and toxicity of dendrimer-coated iron oxide nanoparticles (G₄@IONPs).

Materials and methods

IONPs were synthesized via co-precipitation and coated with the fourth generation (G₄) of polyamidoamine (PAMAM) dendrimer. To determine the biodistribution, 5 mg/mL G₄@IONPs suspension was intraperitoneally injected into tumor-bearing BALB/c mice, and iron levels in blood and various organs, including the lung, liver, brain, heart, tumor, and kidney, were measured by inductively coupled plasma mass spectrometry (ICP-MS) at 4, 8, 12, and 24 h after injection. Also, to investigate the toxicity of G₄@IONPs, different concentrations of G₄@IONPs were injected into BALB/c mice, and blood, renal, and hepatic factors were measured. Furthermore, histopathological staining was performed to investigate the effect of G₄@IONPs on the liver and kidney tissues.

Results

The results showed that the iron content was higher in the kidney, liver, and lung tissues 24 h after injection. Toxicity assessments revealed a significant increase in blood urea nitrogen (BUN) and direct bilirubin at the concentration of 10 mg/kg. Also, in this concentration, histopathological abnormalities were detected in liver tissue.

Conclusion

Although more systematic studies are still required, our results encouraged the future investigations of G₄@IONPs in biomedical applications.

Toxicology of Engineered Nanoparticles: Focus on Poly(amidoamine) Dendrimers

Engineered nanomaterials are increasingly being developed for paints, sunscreens, cosmetics, industrial lubricants, tyres, semiconductor devices, and also for biomedical applications such as in diagnostics, therapeutics, and contrast agents. As a result, nanomaterials are being manufactured, transported, and used in larger and larger quantities, and potential impacts on environmental and human health have been raised. Poly(amidoamine) (PAMAM) dendrimers are specifically suitable for biomedical applications. They are well-defined nanoscale molecules which contain a 2-carbon ethylenediamine core and primary amine groups at the surface. The systematically variable structural architecture and the large internal free volume make these dendrimers an attractive option for drug delivery and other biomedical applications. Due to the wide range of applications, the Organisation for Economic Co-Operation and Development (OECD) have included them in their list of nanoparticles which require toxicological assessment. Thus, the toxicological impact of these PAMAM dendrimers on human health and the environment is a matter of concern. In this review, the potential toxicological impact of PAMAM dendrimers on human health and environment is assessed, highlighting work to date exploring the toxicological effects of PAMAM dendrimers.

Hydrodenticity to enhance relaxivity of gadolinium-DTPA within crosslinked hyaluronic acid nanoparticles

AIM

The efficacy of gadolinium (Gd) chelates as contrast agents for magnetic resonance imaging remains limited owing to poor relaxivity and toxic effects. Here, the effect of the hydration of the hydrogel structure on the relaxometric properties of Gd-DTPA is explained for the first time and called Hydrodenticity.

RESULTS

The ability to tune the hydrogel structure is proved through a microfluidic flow-focusing approach able to produce crosslinked hyaluronic acid nanoparticles, analyzed regarding the crosslink density and mesh size, and connected to the characteristic correlation times of the Gd-DTPA.

CONCLUSION

Hydrodenticity explains the boosting (12-times) of the Gd-DTPA relaxivity by tuning hydrogel structural parameters, potentially enabling the reduction of the administration dosage as approved for clinical use. [Formula: see text].

Encapsulation of Gadolinium Oxide Nanoparticle (Gd2O3) Contrasting Agents in PAMAM Dendrimer Templates for Enhanced Magnetic Resonance Imaging in Vivo

There has been growing interest in the research of nanomaterials for biomedical applications in recent decades. Herein, a simple approach to synthesize the G4.5-Gd₂O₃-poly(ethylene glycol) (G4.5-Gd₂O₃-PEG) nanoparticles (NPs) that demonstrate potential as dual (T₁ and T₂) contrasting agents in magnetic resonance imaging (MRI) has been reported in this study. Compared to the clinically popular Gd-DTPA contrasting agents, G4.5-Gd₂O₃-PEG NPs exhibited a longer longitudinal relaxation time (T₁) and better biocompatibility when incubated with macrophage cell line RAW264.7 in vitro. Furthermore, the longitudinal relaxivity (r₁) of G4.5-Gd₂O₃-PEG NPs was 53.9 s^-1 mM^-1 at 7T, which is equivalent to 4.8 times greater than to the Gd-DTPA contrasting agents. An in vivo T₁-weighted MRI results revealed that G4.5-Gd₂O₃-PEG NPs significantly enhanced signals in the intestines, kidney, liver, bladder, and spleen. In addition, the T₂-weighted MRI results revealed darker contrast in the kidney, which proves that G4.5-Gd₂O₃-PEG NPs can be exploited as T₁ and T₂ contrasting agents. In summary, these findings suggest that the G4.5-Gd₂O₃-PEG NPs synthesized by an alternative approach can be used as dual MRI contrasting agents.

Enhancing MRI of liver metastases with a zwitterionized biodegradable dendritic contrast agent

The MRI enhanced by a zwitterionized dendritic contrast agent clearly indicates metastatic tumors in the liver.

Multi-arm star-branched polymer as an efficient contrast agent for tumor-targeted magnetic resonance imaging

Contrast agents with high efficiency and safety are excellent candidates as magnetic resonance imaging probes.

Hyperbranched poly(glycerol) as a T1 contrast agent for tumor-targeted magnetic resonance imaging in vivo

To explore a convenient and efficient strategy for constructing tumor-targeted T₁ mCAs for MRI, hyperbranched poly(glycerol) prepared in one-pot was used to conjugate gadolinium chelates and folic acid ligands through “click chemistry”.

Arginine-glycine-aspartic acid-polyethylene glycol-polyamidoamine dendrimer conjugate improves liver-cell aggregation and function in 3-D spheroid culture

The polyamidoamine (PAMAM) dendrimer, a type of macromolecule material, has been used in spheroidal cell culture and drug delivery in recent years. However, PAMAM is not involved in the study of hepatic cell-spheroid culture or its biological activity, particularly in detoxification function. Here, we constructed a PAMAM-dendrimer conjugate decorated by an integrin ligand: arginine-glycine-aspartic acid (RGD) peptide. Our studies demonstrate that RGD-polyethylene glycol (PEG)-PAMAM conjugates can promote singly floating hepatic cells to aggregate together in a sphere-like growth with a weak reactive oxygen species. Moreover, RGD-PEG-PAMAM conjugates can activate the AKT-MAPK pathway in hepatic cells to promote cell proliferation and improve basic function and ammonia metabolism. Together, our data support the hepatocyte sphere treated by RGD-PEG-PAMAM conjugates as a potential source of hepatic cells for a biological artificial liver system.

Salicylic Acid Conjugated Dendrimers Are a Tunable, High Performance CEST MRI NanoPlatform

Chemical exchange saturation transfer (CEST) is a novel MRI contrast mechanism that is well suited for imaging, however, existing small molecule CEST agents suffer from low sensitivity. We have developed salicylic acid conjugated dendrimers as a versatile, high performance nanoplatform. In particular, we have prepared nanocarriers based on generation 5-poly(amidoamine) (PAMAM) dendrimers with salicylic acid covalently attached to their surface. The resulting conjugates produce strong CEST contrast 9.4 ppm from water with the proton exchange tunable from ∼1000 s(-1) to ∼4500 s(-1) making these dendrimers well suited for sensitive detection. Furthermore, we demonstrate that these conjugates can be used for monitoring convection enhanced delivery into U87 glioblastoma bearing mice, with the contrast produced by these nanoparticles persisting for over 1.5 h and distributed over ∼50% of the tumors. Our results demonstrate that SA modified dendrimers present a promising new nanoplatform for medical applications.

Analysis of the isomer ratios of polymethylated-DOTA complexes and the implications on protein structural studies

A rigidified and symmetrical polymethylated 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligand bearing four SSSS methyl groups in both the tetraaza ring and the acetate arms (SSSS-SSSS-M4DOTMA) was prepared. The isomer ratio of SSSS-SSSS-M4DOTMA complexed with a series of lanthanide ions was carefully investigated using RP-HPLC and NMR. A square antiprismatic (SAP) configuration was exclusively observed for the early lanthanides, while the twisted square antiprismatic (TSAP) geometry was preferred as the lanthanide ion size decreases. The late lanthanides preferentially adopted the TSAP geometry. One of the pendant arms was modified with a pyridyl disulfide group (SSSS-SSSS-M8SPy) for cysteine attachment and displayed a similar isomer trend as the parent compound, Ln-SSSS-SSSS-M4DOTMA. Covalent attachment to the ubiquitin S57C mutant showed resonances whose intensities are in agreement with the isomeric population observed by RP-HPLC. Furthermore, the NOE experiments combined with quantum chemical calculations have unequivocally demonstrated that the SAP of Pr-SSSS-SSSS-M4DOTMA and Pr-SSSS-SSSS-M8SPy, as well as the TSAP of Yb-SSSS-SSSS-M8SPy are more stable than their corresponding isomers.

Facile synthesis of zwitterionic polyglycerol dendrimers with a β-cyclodextrin core as MRI contrast agent carriers

A facile synthesis method of a zwitterionic polyglycerol dendrimer was developed, providing an ideal carrier for drug and imaging probe delivery.

Preparation of linear poly(glycerol) as a T1 contrast agent for tumor-targeted magnetic resonance imaging

Macromolecular contrast agents (CAs) labeled with targeting molecules are gaining remarkable interest as promising materials overcoming the defects of small-molecule CAs.