Water-Mediated Nanostructures for Enhanced MRI: Impact of Water Dynamics on Relaxometric Properties of Gd-DTPA

Artificial neural network modelling hydrodenticity for optimal design by microfluidics of polymer nanoparticles to apply in magnetic resonance imaging

The engineering of nanoparticles impacts the control of their nano-bio interactions at each level of the delivery pathway. Therefore, optimal nanoparticle physicochemical properties should be identified to favour on-target interactions and deliver efficiently active compounds to a specific target. To date, traditional batch processes do not guarantee the reproducibility of results and low polydispersity index of the nanostructures, while microfluidics has emerged as cost effectiveness, short-production time approach to control the nanoparticle size and size distribution. Several thermodynamic processes have been implemented in microfluidics, such as nanoprecipitation, ionotropic gelation, self-assembly, etc., to produce nanoparticles in a continuous mode and high throughput way.   In this work, we show how the Artificial Neural Network (ANN) can be adopted to model the impact of microfluidic parameters (namely, flow rates and polymer concentrations) on the size of the nanoparticles. Promising results have been obtained, with the highest model accuracy reaching 98.9 %, thus confirming the proposed approach's potential applicability for an ANN-guided biopolymer nanoparticle design for biomedical applications. Nanostructures with different degrees of complexity are analysed, and a proof-of-concept machine learning approach is proposed to evaluate Hydrodenticity in biopolymer matrices. STATEMENT OF SIGNIFICANCE: Size, shape and surface charge determine nano-bio interactions of nanoparticles and their ability to target diseases. The ideal nanoparticle design avoids off-target interactions and favours on-target interactions. So, tools enabling the identification of the optimal nanoparticle physicochemical properties for delivery to a specific target are required. In this work, we evaluate the use of Artificial Neural Network (ANN) to analyse the role of microfluidic parameters in predicting the optimal size of the different hydrogel nanoparticles and their ability to trigger Hydrodenticity.

Single-Atom Gadolinium Nano-Contrast Agents with High Stability for Tumor T1 Magnetic Resonance Imaging

Gadolinium chelates for tumor magnetic resonance imaging (MRI) face challenges such as inadequate sensitivity, lack of selectivity, and risk of Gd leakage. This study presents a single-atom Gd nano-contrast agent (Gd-SA) that enhances tumor MRI. Isolated Gd atoms coordinated by six N atoms and two O atoms are atomically dispersed on a hollow carbon nanosphere, allowing the maximum utilization of Gd atoms with reduced risk of toxic Gd ion leakage. Owning to the large surface area and fast exchange of relaxed water molecules, Gd-SA shows excellent T₁-weighted magnetic resonance enhancement with a r₁ value of 11.05 mM^-1 s^-1 at 7 T, which is 3.6 times that of the commercial gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). In vivo MRI results show that the Gd-SA has a higher spatial resolution and a wider imaging time window for tumors than Gd-DTPA, with low hematological, hepatic, and nephric toxicities. These advantages demonstrate the great potential of single-atom Gd-based nanomaterials as safe, efficient, and long-term MRI contrast agents for cancer diagnosis.

Facile Synthesis of Weakly Ferromagnetic Organogadolinium Macrochelates-Based T1 -Weighted Magnetic Resonance Imaging Contrast Agents

To surmount the major concerns of commercial small molecule Gd chelates and reported Gd-based contrast agents (GBCAs) for magnetic resonance imaging (MRI), a new concept of organogadolinium macrochelates (OGMCs) constructed from the coordination between Gd3+ and macromolecules is proposed. A library of macromolecules were screened for Gd3+ coordination, and two candidates [i.e., poly(acrylic acid) (PAA), and poly(aspartic acid) (PASP)] succeeded in OGMC formation. Under optimized synthesis conditions, both Gd-PAA12 and Gd-PASP11 OGMCs are outstanding T1 -weighted CAs owing to their super high r1 values (> 50 mm-1  s-1 , 3.0 T) and ultralow r2 /r1 ratios (< 1.6, 3.0 T). The ferromagnetism of OGMCs is completely different from the paramagnetism of commercial and reported GBCAs. The ferromagnetism is very weak (Ms  < 1.0 emu g-1 ) leading to a low r2 , which is preferred for T1 MRI. Gd3+ is not released from the OGMC Gd-PAA12 and Gd-PASP11, ensuring biosafety for in vivo applications. The safety and T1 -weighted MRI efficiencies of the OGMC Gd-PAA12 and Gd-PASP11 are tested in cells and mice. The synthesis method of the OGMCs is facile and easy to be scaled up. Consequently, the OGMC Gd-PAA12 and Gd-PASP11 are superior T1 -weighted CAs with promising translatability to replace the commercial Gd chelates.

A tumor microenvironment dual responsive contrast agent for contrary contrast-magnetic resonance imaging and specific chemotherapy of tumors

Development of magnetic resonance imaging (MRI) contrast agents (CAs) is still one of the research hotspots due to the inherent limitations of T₁- or T₂-weighted CAs and T₁/T₂ dual-mode CAs. To dramatically enhance the MRI contrast between tumors and normal tissues, we propose a new concept of contrary contrast-MRI (CC-MRI), whose specific definition is that CC-MRI CAs present a positive or negative signal at normal tissues, but show contrary signals at diseased tissues. To realize CC-MRI of tumors, we designed and developed a tumor microenvironment (TME) dual responsive CA (i.e., SA-FeGdNP-DOX@mPEG), which is almost not responsive under normal physiological conditions, but highly responsive to the acidic and reductive TME. Our SA-FeGdNP-DOX@mPEG shows a negative MRI signal under normal physiological conditions due to the high r₂ value (336.9 mM^-1 s^-1) and high r₂/r₁ ratio (18.4), but switches to a positive MRI signal in the TME because of the high r₁ value (20.32 mM^-1 s^-1) and low r₂/r₁ ratio (7.2). Our TME dual responsive SA-FeGdNP-DOX@mPEG significantly enhanced the contrast of MR images between tumors and livers, and the ΔSNR difference reached 501%. In addition, our SA-FeGdNP-DOX2@mPEG2 with tumor targetability and controlled DOX release responding to the TME was also used for tumor-specific chemotherapy with reduced side effects.

Tuning of Hydrogel Architectures by Ionotropic Gelation in Microfluidics: Beyond Batch Processing to Multimodal Diagnostics

Microfluidics is emerging as a promising tool to control physicochemical properties of nanoparticles and to accelerate clinical translation. Indeed, microfluidic-based techniques offer more advantages in nanomedicine over batch processes, allowing fine-tuning of process parameters. In particular, the use of microfluidics to produce nanoparticles has paved the way for the development of nano-scaled structures for improved detection and treatment of several diseases. Here, ionotropic gelation is implemented in a custom-designed microfluidic chip to produce different nanoarchitectures based on chitosan-hyaluronic acid polymers. The selected biomaterials provide biocompatibility, biodegradability and non-toxic properties to the formulation, making it promising for nanomedicine applications. Furthermore, results show that morphological structures can be tuned through microfluidics by controlling the flow rates. Aside from the nanostructures, the ability to encapsulate gadolinium contrast agent for magnetic resonance imaging and a dye for optical imaging is demonstrated. In conclusion, the polymer nanoparticles here designed revealed the dual capability of enhancing the relaxometric properties of gadolinium by attaining Hydrodenticity and serving as a promising nanocarrier for multimodal imaging applications.

Targeting Nanostrategies for Imaging of Atherosclerosis

Despite the progress in cardiovascular research, atherosclerosis still represents the main cause of death worldwide. Clinically, the diagnosis of Atherosclerotic Cardiovascular Disease (ASCVD) relies on imaging methodologies including X-ray angiography and computed tomography (CT), which however still fails in the identification of patients at high risk of plaque rupture, the main cause of severe clinical events as stroke and heart attack. Magnetic resonance imaging, which is characterized by very high spatial resolution, could provide a better characterization of atherosclerotic plaque (AP) anatomy and composition, aiding in the identification of “vulnerable” plaques. In this context, hydrogel matrices, which have been demonstrated able to boost relaxometric properties of Gd-based contrast agents (CAs) by the effect of Hydrodenticity, represent a valuable tool towards the precision imaging of ASCVD improving the performance of this class of CAs while reducing systemic toxicity. In particular, hydrogel nanoparticles encapsulating Gd-DTPA can further contribute to providing CA-specific accumulation in the AP by nanoparticle surface decoration triggering an active targeting of the AP with the overall effect of allowing an earlier and more accurate diagnosis. In this work, we tested crosslinked Hyaluronic Acid Nanoparticles (cHANPs) in the complex environment of human atherosclerotic plaque. In addition, the surface of cHANPs was decorated with the antibody anti-CD36 (Ab36-cHANPs) for the active targeting of AP-associated macrophages. Results demonstrate that the Hydrodenticity of cHANPs and Ab36-cHANPs is preserved in this complex system and, preliminarily, that interaction of these probes with the AP is present.

Theranostic Design of Angiopep-2 Conjugated Hyaluronic Acid Nanoparticles (Thera-ANG-cHANPs) for Dual Targeting and Boosted Imaging of Glioma Cells

Simple Summary

Glioblastoma multiforme is the most aggressive malignant brain tumor with poor patient prognosis. The presence of the blood-brain barrier and the complex tumor microenvironment impair the efficient accumulation of drugs and contrast agents, causing late diagnosis, inefficient treatment and monitoring. Functionalized theranostic nanoparticles are a valuable tool to modulate biodistribution of active agents, promoting their active delivery and selective accumulation for an earlier diagnosis and effective treatment, and provide simultaneous therapy and imaging for improved evaluation of treatment efficacy. In this work, we developed angiopep-2 functionalized crosslinked hyaluronic acid nanoparticles encapsulating gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and irinotecan (Thera-ANG-cHANPs) that were shown to boost relaxometric properties of Gd-DTPA by the effect of Hydrodenticity, improve the uptake of nanoparticles by the exploitation of angiopep-2 improved transport properties, and accelerate the therapeutic effect of Irinotecan.

Abstract

Glioblastoma multiforme (GBM) has a mean survival of only 15 months. Tumour heterogeneity and blood-brain barrier (BBB) mainly hinder the transport of active agents, leading to late diagnosis, ineffective therapy and inaccurate follow-up. The use of hydrogel nanoparticles, particularly hyaluronic acid as naturally occurring polymer of the extracellular matrix (ECM), has great potential in improving the transport of drug molecules and, furthermore, in facilitatating the early diagnosis by the effect of hydrodenticity enabling the T₁ boosting of Gadolinium chelates for MRI. Here, crosslinked hyaluronic acid nanoparticles encapsulating gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and the chemotherapeutic agent irinotecan (Thera-cHANPs) are proposed as theranostic nanovectors, with improved MRI capacities. Irinotecan was selected since currently repurposed as an alternative compound to the poorly effective temozolomide (TMZ), generally approved as the gold standard in GBM clinical care. Also, active crossing and targeting are achieved by theranostic cHANPs decorated with angiopep-2 (Thera-ANG-cHANPs), a dual-targeting peptide interacting with low density lipoprotein receptor related protein-1(LRP-1) receptors overexpressed by both endothelial cells of the BBB and glioma cells. Results showed preserving the hydrodenticity effect in the advanced formulation and internalization by the active peptide-mediated uptake of Thera-cHANPs in U87 and GS-102 cells. Moreover, Thera-ANG-cHANPs proved to reduce ironotecan time response, showing a significant cytotoxic effect in 24 h instead of 48 h.

Glycosaminoglycans and Contrast Agents: The Role of Hyaluronic Acid as MRI Contrast Enhancer

A comprehensive understanding of the behaviour of Glycosaminoglycans (GAGs) combined with imaging or therapeutic agents can be a key factor for the rational design of drug delivery and diagnostic systems. In this work, physical and thermodynamic phenomena arising from the complex interplay between GAGs and contrast agents for Magnetic Resonance Imaging (MRI) have been explored. Being an excellent candidate for drug delivery and diagnostic systems, Hyaluronic acid (HA) (0.1 to 0.7%w/v) has been chosen as a GAG model, and Gd-DTPA (0.01 to 0.2 mM) as a relevant MRI contrast agent. HA samples crosslinked with divinyl sulfone (DVS) have also been investigated. Water Diffusion and Isothermal Titration Calorimetry studies demonstrated that the interaction between HA and Gd-DTPA can form hydrogen bonds and coordinate water molecules, which plays a leading role in determining both the polymer conformation and the relaxometric properties of the contrast agent. This interaction can be modulated by changing the GAG/contrast agent molar ratio and by acting on the organization of the polymer network. The fine control over the combination of GAGs and imaging agents could represent an enormous advantage in formulating novel multifunctional diagnostic probes paving the way for precision nanomedicine tools.

New Strategies in the Design of Paramagnetic CAs

Nowadays, magnetic resonance imaging (MRI) is the first diagnostic imaging modality for numerous indications able to provide anatomical information with high spatial resolution through the use of magnetic fields and gradients. Indeed, thanks to the characteristic relaxation time of each tissue, it is possible to distinguish between healthy and pathological ones. However, the need to have brighter images to increase differences and catch important diagnostic details has led to the use of contrast agents (CAs). Among them, Gadolinium-based CAs (Gd-CAs) are routinely used in clinical MRI practice. During these last years, FDA highlighted many risks related to the use of Gd-CAs such as nephrotoxicity, heavy allergic effects, and, recently, about the deposition within the brain. These alerts opened a debate about the opportunity to formulate Gd-CAs in a different way but also to the use of alternative and safer compounds to be administered, such as manganese- (Mn-) based agents. In this review, the physical principle behind the role of relaxivity and the T₁ boosting will be described in terms of characteristic correlation times and inner and outer spheres. Then, the recent advances in the entrapment of Gd-CAs within nanostructures will be analyzed in terms of relaxivity boosting obtained without the chemical modification of CAs as approved in the chemical practice. Finally, a critical evaluation of the use of manganese-based CAs will be illustrated as an alternative ion to Gd due to its excellent properties and endogenous elimination pathway.

Biocompatible superparamagnetic core-shell nanoparticles for potential use in hyperthermia-enabled drug release and as an enhanced contrast agent

Superparamagnetic iron oxide nanoparticles (SPIONs) and core-shell type nanoparticles, consisting of SPIONs coated with mesoporous silica and/or lipid, were synthesised and tested for their potential theranostic applications in drug delivery, magnetic hyperthermia and as a contrast agent. Transmission Electron Microscopy (TEM) confirmed the size of bare and coated SPIONs was in the range of 5-20 nm and 100-200 nm respectively. The superparamagnetic nature of all the prepared nanomaterials as indicated by Vibrating Sample Magnetometry (VSM) and their heating properties under an AC field confirm their potential for hyperthermia applications. Scanning Column Magnetometry (SCM) data showed that extrusion of bare-SPION (b-SPION) dispersions through a 100 nm polycarbonate membrane significantly improved the dispersion stability of the sample. No sedimentation was apparent after 18 h compared to a pre-extrusion estimate of 43% settled at the bottom of the tube over the same time. Lipid coating also enhanced dispersion stability. Transversal relaxation time (T2) measurements for the nanoparticles, using a bench-top relaxometer, displayed a significantly lower value of 46 ms, with a narrow relaxation time distribution, for lipid silica coated SPIONs (Lip-SiSPIONs) as compared to that of 1316 ms for the b-SPIONs. Entrapment efficiency of the anticancer drug, Doxorubicin (DOX) for Lip-SPIONs was observed to be 35% which increased to 58% for Lip-SiSPIONs. Moreover, initial in-vitro cytotoxicity studies against human breast adenocarcinoma, MCF-7 cells showed that % cell viability increased from 57% for bSPIONs to 82% for Lip-SPIONs and to 87% for Lip-SiSPIONs. This suggests that silica and lipid coatings improve the biocompatibility of bSPIONs significantly and enhance the suitability of these particles as drug carriers. Hence, the magnetic nanomaterials prepared in this work have potential theranostic properties as a drug carrier for hyperthermia cancer therapy and also offer enhancement of contrast agent efficacy and a route to a significant increase in dispersion stability.

Yolk-shell nanovesicles endow glutathione-responsive concurrent drug release and T1 MRI activation for cancer theranostics

The effort of incorporating therapeutic drugs with imaging agents has been one of the mainstreams of nanomedicine, which holds great promise in cancer treatment in terms of monitoring therapeutic drug activity and evaluating prognostic index. However, it is still technically challenging to develop nanomedicine endowing a spatiotemporally controllable mechanism of drug release and activatable imaging capability. Here, we developed a yolk-shell type of GSH-responsive nanovesicles (NVs) in which therapeutic drug (Doxorubicin, DOX) and magnetic resonance imaging (MRI) contrast agent (ultrasmall paramagnetic iron oxide nanoparticles, USPIO NPs) formed complexes (denoted as USD) and were encapsulated inside the NVs. The formation of USD complexes is mediated by both the electrostatic adsorption between DOX and poly(acrylic acid) (PAA) polymers and the DOX-iron coordination effect on USPIO NPs. The obtained USD NVs showed a unique yolk-shell structure with restrained drug activity and quenched T1 MRI contrast ability which, on the other hand, can respond to glutathione (GSH) and lead to drug release and T1 contrast activation in a spatiotemporally concurrent manner. Furthermore, the USD NVs exhibited great potential to kill HCT116 cancer cells in vitro and effectively inhibit the tumor growth in vivo. This study may shed light on the design of sophisticated nanotheranostics in precision nanomedicine.

A Microfluidic Platform to design Multimodal PEG - crosslinked Hyaluronic Acid Nanoparticles (PEG-cHANPs) for diagnostic applications

The combination of different imaging modalities can allow obtaining simultaneously morphological and functional information providing a more accurate diagnosis. This advancement can be reached through the use of multimodal tracers, and nanotechnology-based solutions allow the simultaneous delivery of different diagnostic compounds moving a step towards their safe administration for multimodal imaging acquisition. Among different processes, nanoprecipitation is a consolidate method for the production of nanoparticles and its implementation in microfluidics can further improve the control over final product features accelerating its potential clinical translation. A Hydrodynamic Flow Focusing (HFF) approach is proposed to produce through a ONE-STEP process Multimodal Pegylated crosslinked Hyaluronic Acid NanoParticles (PEG-cHANPs). A monodisperse population of NPs with an average size of 140 nm is produced and Gd-DTPA and ATTO488 compounds are co-encapsulated, simultaneously. The results showed that the obtained multimodal nanoparticle could work as MRI/Optical imaging probe. Furthermore, under the Hydrodenticity effect, a boosting of the T1 values with respect to free Gd-DTPA is preserved.

Relaxivity of Gd-Based MRI Contrast Agents in Crosslinked Hyaluronic Acid as a Model for Tissues

The efficiency of MRI contrast agents depends on the relaxation rate enhancement that they can induce at imaging fields. It is well known that, at these fields, large relaxation rates are obtained by binding of gadolinium(III) ions to large molecules. By the same token, the interaction of the gadolinium(III) complexes with macromolecules that are found in biological tissues can be responsible for an increase of the relaxation rate with respect to the value observed in liquids. We investigate here the relaxation enhancement of gadoteridol (Gd-HP-DO3A) in crosslinked hyaluronic acid, taken as model tissue, using fast field-cycling relaxometry. The analysis of the relaxation profiles as a function of the magnetic fields indicates that a sizable increase in the relaxation rates is due to a modest interaction of the contrast agent with the hydrogel and to the slower mobility of the water molecules outside the first-coordination sphere of the gadolinium(III) ion.