Interaction of MRI Contrast Agent [Gd(DOTA)]- with Lipid Membranes: A Molecular Dynamics Study

Contrast agents are important imaging probes in clinical MRI, allowing the identification of anatomic changes that otherwise would not be possible. Intensive research on the development of new contrast agents is being made to image specific pathological markers or sense local biochemical changes. The most widely used MRI contrast agents are based on gadolinium(III) complexes. Due to their very high charge density, they have low permeability through tight biological barriers such as the blood-brain barrier, hampering their application in the diagnosis of neurological disorders. In this study, we explore the interaction between the widely used contrast agent [Gd(DOTA)]- (Dotarem) and POPC lipid bilayers by means of molecular dynamics simulations. This metal complex is a standard reference where several chemical modifications have been introduced to improve key properties such as bioavailability and targeting. The simulations unveil detailed insights into the agent's interaction with the lipid bilayer, offering perspectives beyond experimental methods. Various properties, including the impact on global and local bilayer properties, were analyzed. As expected, the results indicate a low partition coefficient (KP) and high permeation barrier for this reference compound. Nevertheless, favorable interactions are established with the membrane leading to moderately long residence times. While coordination of one inner-sphere water molecule is maintained for the membrane-associated chelate, the physical-chemical attributes of [Gd(DOTA)]- as a MRI contrast agent are affected. Namely, increases in the rotational correlation times and in the residence time of the inner-sphere water are observed, with the former expected to significantly increase the water proton relaxivity. This work establishes a reference framework for the use of simulations to guide the rational design of new contrast agents with improved relaxivity and bioavailability and for the development of liposome-based formulations for use as imaging probes or theranostic agents.

Compartmentalized drug localization studies in extracellular vesicles for anticancer therapy

In the development of therapeutic extracellular vesicles (EVs), drug encapsulation efficiencies are significantly lower when compared with synthetic nanomedicines. This is due to the hierarchical structure of the EV membrane and the physicochemical properties of the candidate drug (molecular weight, hydrophilicity, lipophilicity, and so on). As a proof of concept, here we demonstrated the importance of drug compartmentalization in EVs as an additional parameter affecting the therapeutic potential of drug-loaded EVs. In human adipose mesenchymal stem cell (hADSC) derived EVs, we performed a comparative drug loading analysis using two formulations of the same chemotherapeutic molecule - free doxorubicin (DOX) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) lipid-conjugated doxorubicin (L-DOX) - to enhance the intracellular uptake and therapeutic efficacy. By nano surface energy transfer (NSET) and molecular simulation techniques, along with cryo-TEM analysis, we confirmed the differential compartmentalization of these two molecules in hADSC EVs. L-DOX was preferentially adsorbed onto the surface of the EV, due to its higher lipophilicity, whereas free DOX was mostly encapsulated within the EV core. Also, the L-DOX loaded EV (LDOX@EV) returned an almost three-fold higher DOX content as compared to the free DOX loaded EV (DOX@EV), for a given input mass of drug. Based on the cellular investigations, L-DOX@EV showed higher cell internalization than DOX@EV. Also, in comparison with free L-DOX, the magnitude of therapeutic potential enhancement displayed by the surface compartmentalized L-DOX@EV is highly promising and can be exploited to overcome the sensitivity of many potential drugs, which are impermeable in nature. Overall, this study illustrates the significance of drug compartmentalization in EVs and how this could affect intracellular delivery, loading efficiency, and therapeutic effect. This will further lay the foundation for the future systematic investigation of EV-based biotherapeutic delivery platforms for personalized medicine.

Exosome-Modified Liposomes Targeted Delivery of Thalidomide to Regulate Treg Cells for Antitumor Immunotherapy

Thalidomide (THD), a synthetic derivative of glutamic acid, was initially used as a sedative and antiemetic until the 1960s, when it was found to cause devastating teratogenic effects. However, subsequent studies have clearly demonstrated the anti-inflammatory, anti-angiogenic, and immunomodulatory properties of thalidomide, thus providing a rationale for its current use in the treatment of various autoimmune diseases and cancers. Our group found that thalidomide can suppress the regulatory T cells (Tregs), a minor subset of CD4+ T cells (~10%) with unique immunosuppressive activity that have been shown to accumulate in the tumor microenvironment (TME) and represent a major mechanism of tumor immune evasion. Due to the low solubility of thalidomide in its present form of administration, coupled with its lack of specificity for targeted delivery and controlled drug release, it is an urgent need to find potent delivery methods that can significantly enhance its solubility, optimize the desired site of drug action, and mitigate its toxicity. In this study, the isolated exosomes were incubated with synthetic liposomes to form hybrid exosomes (HEs) that carried THD (HE-THD) with uniform size distribution. The results demonstrated that HE-THD could significantly abrogate the expansion and proliferation of Tregs induced by TNF, and this might result from blocking TNF-TNFR2 interaction. By encapsulating THD in hybrid exosomes, our drug delivery system successfully increased the solubility of THD, laying a foundation for future in vivo experiments that validate the antitumor activity of HE-THD by reducing the Treg frequency within the tumor microenvironment.

How Could Nanomedicine Improve the Safety of Contrast Agents for MRI during Pregnancy?

Pregnancy is a delicate state, during which timely investigation of possible physiological anomalies is essential to reduce the risk of maternal and fetal complications. Medical imaging encompasses different technologies to image the human body for the diagnosis, course of treatment management, and follow-up of diseases. Ultrasound (US) is currently the imaging system of choice for pregnant patients. However, sonographic evaluations can be non-effective or give ambiguous results. Therefore, magnetic resonance imaging (MRI), due to its excellent tissue penetration, the possibility of acquisition of three-dimensional anatomical information, and its high spatial resolution, is considered a valid diagnostical alternative. Nevertheless, currently employed contrast agents to improve the MRI image quality are harmful to the fetus. Because of their ability to cross the placenta, their use on pregnant patients is avoided. This review will firstly recapitulate the most common non-obstetrical, obstetrical, and fetal indications for magnetic resonance imaging on pregnant women. Fetal safety risks, due to the use of strong magnetic fields and exogenous contrast agents, will be presented. Then, possible advantages of nanostructured contrast agents compared to current molecular ones are explored. Nanosystems’ characteristics affecting contrast efficiency, and their potential for improving contrast-enhanced MRI’s safety in pregnant women, are discussed. Lastly, promising examples of nanoparticles as safer alternatives to current MRI contrast agents in pregnancy are discussed.

Re-engineered imaging agent using biomimetic approaches

Recent progress in biomedical technology, the clinical bioimaging, has a greater impact on the diagnosis, treatment, and prevention of disease, especially by early intervention and precise therapy. Varieties of organic and inorganic materials either in the form of small molecules or nano-sized materials have been engineered as a contrast agent (CA) to enhance image resolution among different tissues for the detection of abnormalities such as cancer and vascular occlusion. Among different innovative imaging agents, contrast agents coupled with biologically derived endogenous platform shows the promising application in the biomedical field, including drug delivery and bioimaging. Strategy using biocomponents such as cells or products of cells as a delivery system predominantly reduces the toxic behavior of its cargo, as these systems reduce non-specific distribution by navigating its cargo toward the targeted location. The hypothesis is that depending on the original biological role of the naïve cell, the contrast agents carried by such a system can provide corresponding natural designated behavior. Therefore, by combining properties of conventional synthetic molecules and nanomaterials with endogenous cell body, new solutions in the field of bioimaging to overcome biological barriers have been offered as innovative bioengineering. In this review, we will discuss the engineering of cell and cell-derived components as a delivery system for various contrast agents to achieve clinically relevant contrast for diagnosis and study underlining mechanism of disease progression. This article is categorized under: Nanotechnology Approaches to Biology > Cells at the Nanoscale Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Re-engineering a Liposome with Membranes of Red Blood Cells for Drug Delivery and Diagnostic Applications

Red blood cells (RBCs) make up the overwhelming majority of cells in the vascular system, spending most of their lives wandering the vast network of vessels that permeate every tissue of our bodies. Therefore, the delivery of any class of therapeutic agent that must stay in the circulatory system may benefit from being carried by RBCs. Toward this direction, we have re-engineered a synthetic liposome with the membranes of RBCs and incorporated a magnetic resonance imaging (MRI) contrast agent gadolinium along with the chemotherapeutic drug doxorubicin (DOX) to form a biomimetic liposome (BML). The BMLs proposed herein consist of biocompatible/biodegradable synthetic phospholipids, which include 1,2-distearoyl-sn-glycero-3-phosphoglycerol, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine, and gadolinium-conjugated lipids. These synthetic phospholipids have been fused with a natural RBC membrane and are loaded with DOX using the extrusion technique. BMLs were characterized for their physicochemical properties, stability, fusogenic (between synthetic and natural lipid from RBC), magnetic, drug loading, biocompatibility, and cytotoxicity properties. BMLs had a hydrodynamic diameter of 180 ± 20 nm with a negative surface charge of 29 ± 2 mV. The longitudinal relaxivity (r₁) of BML is 3.71 mM^-1 s^-1, which is comparable to the r₁ of commercial contrast agent, Magnevist. In addition, DOX-loaded BML showed a cytotoxicity pattern similar to that of free DOX. These results showed the potential of using the proposed BML system for both MRI-based diagnostic applications and drug delivery platforms.

Recent advances in development of nanomedicines for multiple sclerosis diagnosis

Multiple sclerosis (MS) is a neurodegenerative disease with a high morbidity and disease burden. It is characterized by the loss of the myelin sheath, resulting in the disruption of neuron electrical signal transmissions and sensory and motor ability deficits. The diagnosis of MS is crucial to its management, but the diagnostic sensitivity and specificity are always a challenge. To overcome this challenge, nanomedicines have recently been employed to aid the diagnosis of MS with an improved diagnostic efficacy. Advances in nanomedicine-based contrast agents in magnetic resonance imaging scanning of MS lesions, and nanomedicine-derived sensors for detecting biomarkers in the cerebrospinal fluid biopsy, or analyzing the composition of exhaled breath gas, have demonstrated the potential of using nanomedicines in the accurate diagnosis of MS. This review aims to provide an overview of recent advances in the application of nanomedicines for the diagnosis of MS and concludes with perspectives of using nanomedicines for the development of safe and effective MS diagnostic nanotools.

Magnetic resonance activatable thermosensitive liposomes for controlled doxorubicin delivery

To limit the massive cytotoxicity of chemotherapeutic agents, it is desirable to establish an appropriate subtle blend of formulation design based on a dual-responsive strategy. In this study, a combined therapeutic platform based on magnetic thermosensitive liposomes (Lip_TS-GD) was developed. The incorporation of chelated-gadolinium imparted magnetic properties to thermosensitive liposomes (Lip_TS). The application of an ultra high field magnetic resonance imaging (UHF-MRI) induced hyperthermia, thus provided an improved chemotherapeutic effect of Doxorubicin (DOX). The paramagnetic platform demonstrated thermal sensitivity over a narrow temperature range starting at 37.8 °C, hence the release of DOX from Lip_TS-GD can be well triggered by inducing hyperthermia using UHF-MRI application. The prepared Lip_TS-GD were below 200 nm in diameter and an adequate release of DOX reaching 68% was obtained after 1 h UHF-MRI exposure. Profoundly, triple-negative breast cancer (TNBC) cells that were treated with Lip_TS-GD and subjected thereafter to UHF-MRI exposure for 60 min showed 36% viability. Hemocompatibility studies of Lip_TS-GD showed a physiological coagulation time and minimal hemolytic potential. Conclusively, Lip_TS-GD guided local delivery of DOX to solid tumors will potentially raise the therapeutic index, thus reducing the required dose and frequency of DOX administered systemically without influencing the adjacent tissues.

Surface functionalization strategies of extracellular vesicles

Extracellular vesicles (EVs) are lipid-protein bilayer vesicular constructs secreted to the extracellular spaces by cells. All cells secrete EVs as a regular biological process that appears to be conserved throughout the evolution. Owing to the rich molecular cargo of EVs with specific lipid and protein content and documented role in cellular communication, EVs have been exploited as a versatile agent in the biomedical arena, including as diagnostic, drug delivery, immunomodulatory, and therapeutic agents. With these multifaceted applications in the biomedical field, the functionalization of EVs to add diverse functionality has garnered rapid attention. EVs can be functionalized with an exogenous imaging and targeting moiety that allows for the target specificity and the real-time tracking of EVs for diagnostic and therapeutic applications. Importantly, such added functionalities can be used to explore EVs' biogenesis pathway and their role in cellular communication, which can lead to a better understanding of EVs' cellular mechanisms and processes. In this report, we have reviewed the existing surface functionalization strategies of EVs and broadly classified them into three major approaches: physical, biological, and chemical approaches. The physical approach of EV functionalization includes methods like sonication, extrusion, and freeze-thaw that can change the surface properties of EVs via membrane rearrangements. The biological approach includes genetically and metabolically engineering cells to express protein or cargo molecules of interest in secreted EVs. The chemical approach includes different facile click type chemistries that can be used to covalently conjugate the EV lipid or protein construct with different linker groups for diverse functionality. Different chemistries like thiol-maleimide, EDC/NHS, azide-alkyne cycloaddition, and amidation chemistry have been discussed to functionalize EVs. Finally, a comparative discussion of all approaches has been done focusing on the significance of each approach. The collective knowledge of the major approach of surface functionalization can be used to improve the limitation of one technique by combining it with another. An optimized surface functionalization approach developed accordingly can efficiently add required functionality to EVs while maintaining their natural integrity.

Erythrocyte membrane concealed paramagnetic polymeric nanoparticle for contrast-enhanced magnetic resonance imaging

Recent progress in bioimaging nanotechnology has a great impact on the diagnosis, treatment, and prevention of diseases by enabling early intervention. Among different types of bioimaging modalities, contrast-enhanced magnetic resonance imaging using paramagnetic gadolinium-based molecular contrast agents (GBCAs) are most commonly used in clinic. However, molecular GBCAs distribute rapidly between plasma and interstitial spaces with short half-lives limiting its clinical impacts. To improve the properties of GBCAs, herein an effort has been put forth by incorporating GBCA into nanoscale system mimicking the property of red blood cell (RBC) that could facilitate contrast enhancement and prolong intraluminal retention in the body. The proposed nanoconstruct is made up of polymeric-core labeled with lipid conjugated GBCA followed by the imprint of the RBC membrane concealment layer to enhance stability and biocompatibility. Meanwhile, the confinement strategy of GBCA was implemented to accelerate magnetic properties of nanoconstruct providing longitudinal-relaxivity (r₁) to 12.78 ± 0.29 (mM s)^-1. Such improvement in r₁ was further confirmed by enhanced contrast in the vascular angiography of the murine model. Given higher colloidal stability and tunable magnetic properties, nanoconstruct proposed herein is a promising platform technology for the applications where enhanced plasma residence time and magnetic properties are necessary for diagnosis and therapy.

Strategic reconstruction of macrophage-derived extracellular vesicles as a magnetic resonance imaging contrast agent

Reconstruction of extracellular vesicles with imaging agents allows precise downstream analysis using clinical imaging modalities, for example, MRI. This will further improve the biocompatibility of agents thereby enhancing clinical investigations.

Integration of gadolinium in nanostructure for contrast enhanced-magnetic resonance imaging

Magnetic resonance imaging (MRI) is a routinely used imaging technique in medical diagnostics, which is further enhanced with the use of contrast agents (CAs). The most commonly used CAs are gadolinium-based contrast agents (GBCAs), in which gadolinium (Gd) is chelated with organic chelating agents (linear or cyclic). However, the use of GBCA is related to toxic side effect due to the release of free Gd³⁺ ions from the chelating agents. The repeated use of GBCAs has led to Gd deposition in various major organs including bone, brain, and kidneys. As a result, the use of GBCA has been linked to the development of nephrogenic systemic fibrosis (NSF). Due to the GBCA associated toxicities, some clinically approved GBCAs have been limited or revoked recently. Therefore, there is an urgent need for the development of new strategies to chelate and stabilize Gd³⁺ ions for contrast enhancement, safety profile, and selective imaging of a pathological site. Toward this endeavor, GBCAs have been engineered using different nanoparticulate systems to improve their stability, biocompatibility, and pharmacokinetics. Throughout this review, some of the important strategies for engineering small molecular Gd³⁺ chelates into a nanoconstruct is discussed. We focus on the development of GBCAs as liposomes, mesoporous silica nanoparticles (MSNs), polymeric nanocarriers, and plasmonic nanoparticles-based design strategies to improve safety and contrast enhancement for contrast enhanced-magnetic resonance imaging (Ce-MRI). We also discuss the in-vitro/in-vivo properties of strategically designed nanoscale MRI CAs, its potentials, and limitations. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Diagnostic Tools > Diagnostic Nanodevices Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Macrophage-derived exosome-mimetic hybrid vesicles for tumor targeted drug delivery

Extracellular vesicles (EVs) are phospholipid and protein constructs which are continuously secreted by cells in the form of smaller (30-200 nm) and larger (micron size) particles. While all of these vesicles are called as EVs, the smaller size are normally called as exosomes. Small EVs (sEVs) have now been explored as a potential candidate in therapeutics delivery owing to their endogenous functionality, intrinsic targeting property, and ability to cooperate with a host defense mechanism. Considering these potentials, we hypothesize that immune cell-derived sEVs can mimic immune cell to target cancer. However, different sEVs isolation technique reported poor yield and loss of functional properties. To solve this problem, herein we hybridized sEVs with synthetic liposome to engineer vesicles with size less than 200 nm to mimic the size of exosome and named as hybrid exosome (HE). To achieve this goal, sEVs from mouse macrophage was hybridized with synthetic liposome to engineer HE. The fluorescence-based experiment confirmed the successful hybridization process yielding HE with the size of 177 ± 21 nm. Major protein analysis from Blot techniques reveal the presence of EV marker proteins CD81, CD63, and CD9. Differential cellular interaction of HE was observed when treated with normal and cancerous cells thereby supporting our hypothesis. Moreover, a water-soluble doxorubicin was loaded in HE. Drug-loaded HE showed enhanced toxicity against cancer cells and pH-sensitive drug release in acidic condition, benefiting drug delivery to acidic cancer environment. These results suggest that the engineered HE would be an exciting platform for tumor-targeted drug delivery. STATEMENT OF SIGNIFICANCE: Extracellular vesicles (EVs) are phospholipid and protein constructs which are continuously secreted by cells in the human body. These vesicles can efficiently deliver their parental biomolecules to the recipient cells and assist in intracellular communication without a direct cell-to-cell contact. Moreover, they have the ability to perform some of the molecular task similar to that of its parent cells. For example, exosome derived from immune cells can seek for diseased and/or inflammatory cells by reading the cell surface proteins. However, different EVs isolation techniques reported poor yield and loss of functional properties. Therefore, to overcome this limitation, we herein propose to re-engineer immuno-exosome with a synthetic liposome as a refined biomimetic nanostructure for the delivery of doxorubicin (clinical drug) for breast cancer treatment.

Biomimetic surface modification of discoidal polymeric particles

The rationale for the design of drug delivery nanoparticles is traditionally based on co-solvent self-assembly following bottom-up approaches or in combination with top-down approaches leading to tailored physiochemical properties to regulate biological responses. However, the optimal design and control of material properties to achieve specific biological responses remain the central challenge in drug delivery research. Considering this goal, we herein designed discoidal polymeric particles (DPPs) whose surfaces are re-engineered with isolated red blood cell (RBC) membranes to tailor their pharmacokinetics. The RBC membrane-coated DPPs (RBC-DPPs) were found to be biocompatible in cell-based in vitro experiments and exhibited extended blood circulation half-life. They also demonstrated unique kinetics at later time points in a mouse model compared to that of bare DPPs. Our results suggested that the incorporation of biomimicry would enable the biomimetic particles to cooperate with systems in the body such as cells and biomolecules to achieve specific biomedical goals.

The influence of polyethylene glycol passivation on the surface plasmon resonance induced photothermal properties of gold nanorods

Gold nanorods (AuNRs) possess unique photothermal properties due to their strong plasmonic absorption in the near-infrared region of the electromagnetic spectrum. They have been explored widely as an alternative or a complement to chemotherapy in cancer treatment. However, the use of AuNRs as an injectable medicine is greatly hindered by their stability in biological media. Therefore, studies have been focused on improving the stability of AuNRs by introducing biocompatible surface functionalizations such as polyethylene glycol (PEG) coatings. However, these coatings can affect heat conduction and alter their photothermal behavior. Herein, we studied how functionalization of AuNRs with PEG chains of different molecular weights determined the temperature distribution of suspensions under near-infrared irradiation, cell uptake in vitro, and hyperthermia-induced cytotoxicity. Thermogravimetric analysis of the PEG-conjugated AuNRs exhibited slightly different PEG mass fractions of 12.0%, 12.7%, and 18.5% for PEG chains with molecular weights of 2, 5, and 10 kDa, respectively, implying distinct structures for PEG brushes. When exposed to near-infrared radiation, we found greater temperatures and temperature gradients for longer PEG chains, while rapid aggregation was observed in unmodified (raw) AuNRs. The effect of the PEG coating on heat transport was investigated using molecular dynamics simulations, which revealed the atomic scale structure of the PEG brushes and demonstrated lower thermal conductivity for PEG-coated AuNRs than for unmodified AuNRs. We also characterized the uptake of the AuNRs into mouse melanoma cells in vitro and determined their ability to kill these cells when subjected to near-infrared radiation. For all PEG-coated AuNRs, exposure to 10 s of near-infrared radiation significantly reduced cell viability relative to unirradiated controls, with this viability further decreasing with increasing AuNR doses, indicating potential phototherapeutic effects. The 5 kDa PEG coating appeared to yield the best performance, yielding significant phototoxicity at even the lowest dose considered (0.5 μg mL-1), while also exhibiting high colloidal stability, which could help in rational design consideration of AuNRs for NIR induced photothermal therapy.

Natural killer cell membrane infused biomimetic liposomes for targeted tumor therapy

Therapeutic efficacy of a systemic drug delivery largely depends on the targeting design of the delivery system, which tackles with circulatory traffic and prevents the nonspecific distribution of the drug in the wide range of vital organs. A drawing attention has been given to a biomimetic cloaking of the synthetic drug delivery nanoparticle using mammalian cell-ghosts, which has shown the installment of the biological complexity of the original cells thereby acting as naïve cells, to precisely delivery drug to the intended target. Align towards this direction; we developed a membrane camouflage fusogenic liposomal delivery system "NKsome" for targeted tumor therapy using Natural Killer (NK) cell-ghost, which naturally undergoes immunosurveillance of diseased/stress cells. The engineered NKsome shows successful retention of NK cell membrane-associated targeting protein on its surface. With its excellent biocompatibility, NKsome shows a higher affinity towards cancer than normal cells as demonstrated by in vitro flow-passage assay, and exhibits enhanced tumor homing efficiency in-vivo with an extended plasma residence time of 18 h. Moreover, the therapeutic potential of doxorubicin-loaded NKsome shows promising antitumor activity in vivo against MCF-7 induced tumor model. Overall results illustrate the therapeutic advantages of NK cell biomimicry capable of communicating like immune cells for cooperative drug delivery.

Nano-confinement-driven enhanced magnetic relaxivity of SPIONs for targeted tumor bioimaging

Superparamagnetic iron oxide nanoparticles (SPIONs) are highly biocompatible and have a versatile synthetic technique based on coprecipitation, reduction-precipitation, and hydrothermal methods, where Fe³⁺ and Fe²⁺ react in aqueous solutions; both these ions are present in our body and have clear metabolic pathways; therefore, they have attracted extensive research interest and development in the field of diagnostic imaging and therapy. However, most SPION-based clinical diagnostic contrast agents are discontinued due to severe pain, low transverse magnetic relaxivity range of 80-180 mM^-1 s^-1, shorter circulation half-life, and lack of disease specificity. Therefore, in this study, we engineered a bone cancer-targeted hybrid nanoconstruct (HNC) with a high transverse magnetic relaxivity of 625 mM^-1 s^-1, which was significantly higher than that of clinical contrast agents. The engineered HNC is peripherally decorated with a bone-seeking agent, alendronic acid-conjugated phospholipid, exhibiting a hydrodynamic size of 80 nm with a negative surface potential, -35 mV. The interior skeleton of the HNC is composed of biodegradable and biocompatible poly(l-lactic-co-glycolic acid) (PLGA), in which 5 nm SPIONs are confined. We have successfully tuned the distance between the confined SPIONs from 0.5 to 4 nm, as revealed by transmission electron microscopy (TEM) images and magnetic resonance image (MRI) phantoms. This cluster confinement dramatically enhances magnetic relaxivity possibly due to the increase in net local magnetization due to proximal field inhomogeneity. In an in vitro examination, 80% of HNC is found to bind with hydroxyapatite (HAp), which when characterized by TEM shows a painting of SPIONs over a HAp crystal. HNC is found to accumulate in mouse osteosarcoma tumor (K7M2 tumor model); both MRI and histological examination of the tumor show the potential of HNC as targeting agents for diagnosis of tumor in the bone.