Contrast agents for hepatic MRI

Imaging of the Liver and Pancreas: The Added Value of MRI

MR is a powerful diagnostic tool in the diagnosis and management of most hepatic and pancreatic diseases. Thanks to its multiple sequences, the use of dedicated contrast media and special techniques, it allows a multiparametric approach able to provide both morphological and functional information for many pathological conditions. The knowledge of correct technique is fundamental in order to obtain a correct diagnosis. In this paper, different MR sequences will be illustrated in the evaluation of liver and pancreatic diseases, especially those sequences which provide information not otherwise obtainable with other imaging techniques. Practical MR protocols with the most common indications of MR in the study of the liver and pancreas are provided.

Microwave ablation of multifocal primary liver cancer guided by real-time 3.0T MRI

OBJECTIVE

To investigate the feasibility and efficacy of real-time 3.0 T magnetic resonance imaging (MRI) guided percutaneous microwave ablation (MWA) in the treatment of multifocal liver cancer.

METHODS

A total of 76 lesions in 26 patients with multifocal liver cancer who underwent 3.0 T MRI-guided microwave ablation in our hospital from April 2020 to April 2022 were retrospectively analyzed. The technical success rate, average operation time, average ablation time, and complications were evaluated. The upper abdomen was reviewed by pre- and post-contrast enhanced MRI scan every 1 months after the operation. The short-term curative effect was evaluated according to the modified Response Evaluation Criteria in Solid Tumors (mRECIST) criteria (2020 version), and the local control rate was calculated.

RESULTS

All 76 lesions were successfully operated. The technical success rate was 100%, the average operation time was 103.58 ± 18.57 min, the average ablation time of a single lesion was 11.00 ± 4.05 min, and the average ablation power was 43.03 ± 4.45 W. There were no serious complications such as massive bleeding, liver failure, and infection after the operation, except in one case with a small amount of pleural effusion and one case with right upper abdominal pain. The average follow-up time was 13.88 ± 6.62 months. One patient died due to liver failure, and one lesion developed a local recurrence. The local control rate was 98.7%.

CONCLUSIONS

MWA of multifocal liver cancer guided by real-time 3.0 T MRI is a safe and feasible technique and has excellent short-term efficacy.

Iron Oxide Nanoparticles as Theranostic Agents in Cancer Immunotherapy

Starting from the mid-1990s, several iron oxide nanoparticles (NPs) were developed as MRI contrast agents. Since their sizes fall in the tenths of a nanometer range, after i.v. injection these NPs are preferentially captured by the reticuloendothelial system of the liver. They have therefore been proposed as liver-specific contrast agents. Even though their unfavorable cost/benefit ratio has led to their withdrawal from the market, innovative applications have recently prompted a renewal of interest in these NPs. One important and innovative application is as diagnostic agents in cancer immunotherapy, thanks to their ability to track tumor-associated macrophages (TAMs) in vivo. It is worth noting that iron oxide NPs may also have a therapeutic role, given their ability to alter macrophage polarization. This review is devoted to the most recent advances in applications of iron oxide NPs in tumor diagnosis and therapy. The intrinsic therapeutic effect of these NPs on tumor growth, their capability to alter macrophage polarization and their diagnostic potential are examined. Innovative strategies for NP-based drug delivery in tumors (e.g., magnetic resonance targeting) will also be described. Finally, the review looks at their role as tracers for innovative, and very promising, imaging techniques (magnetic particle imaging-MPI).

Bioimaging Applications of Non-Lamellar Liquid Crystalline Nanoparticles

Self-assembling processes of amphiphilic lipids in water give rise to complex architectures known as lyotropic liquid crystalline (LLC) phases. Particularly, bicontinuous cubic and hexagonal LLC phases can be dispersed in water forming colloidal nanoparticles respectively known as cubosomes and hexosomes. These non-lamellar LLC dispersions are of particular interest for pharmaceutical and biomedical applications as they are potentially non-toxic, chemically stable, and biocompatible, also allowing encapsulation of large amounts of drugs. Furthermore, conjugation of specific moieties enables their targeting, increasing therapeutic efficacies and reducing side effects by avoiding exposure of healthy tissues. In addition, as they can be easy loaded or functionalized with both hydrophobic and hydrophilic imaging probes, cubosomes and hexosomes can be used for the engineering of multifunctional/theranostic nanoplatforms. This review outlines recent advances in the applications of cubosomes and hexosomes for in vitro and in vivo bioimaging.

Feasibility and efficacy study of microwave ablation of recurrent small HCC guided by enhanced liver-specific magnetic resonance imaging contrast agent

OBJECTIVES

To investigate the feasibility and efficacy of liver-specific magnetic resonance imaging (MRI) with gadolinium-containing contrast agent guidance for microwave ablation (MWA) of recurrent small hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

The Ethics Committee of the First Affiliated Hospital of Fujian Medical University approved this study. Eighteen patients presented with 30 recurrent small HCCs, at least one lesion per patient was undetectable on unenhanced MRI, but this was clearly demonstrated in the hepatobiliary phase after liver-specific MRI contrast agent administration. Gd-BOPTA (16 cases) or Gd-EOB-DTPA (2 cases) were injected half an hour before the procedure, and MWA was performed by percutaneous puncture of the target lesion with a magnetic resonance-compatible microwave antenna under 1.5 T MRI guidance.

RESULTS

The technical success rate was 100%. The mean maximum diameter of the lesions was 9.7 ± 2.8 mm (5.0-15.4 mm). The mean follow-up time was 11.6 ± 4.7 months (range, 4-19 months), and no local recurrence was observed.

CONCLUSIONS

MWA of small HCCs guided by enhanced liver-specific MRI contrast agent is a safe and effective technique.

Nanoparticle design considerations for molecular imaging of apoptosis: Diagnostic, prognostic, and therapeutic value

The present review analyzes various approaches for the design and synthesis of different nanoparticles for imaging and therapy. Nanoparticles for computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and optical imaging are discussed. The influence of nanoparticle size, shape, surface charge, composition, surface functionalization, active targeting and other factors on imaging and therapeutic efficacy is analyzed. Cyto- and genotoxicity of nanoparticles are also discussed. Special attention in the review is paid to the imaging of apoptotic tissues and cells in different diseases.

Age dependence of spleen- and muscle-corrected hepatic signal enhancement on hepatobiliary phase gadoxetate MRI

OBJECTIVES

To identify correlations of signal enhancements (SE) and SE normalized to reference tissues of the spleen, kidney, liver, musculus erector spinae (MES) and ductus hepatocholedochus (DHC) on hepatobiliary phase gadoxetate-enhanced MRI with patient age in non-cirrhotic patients.

METHODS

A heterogeneous cohort of 131 patients with different clinical backgrounds underwent a standardized 3.0-T gadoxetate-enhanced liver MRI between November 2008 and June 2013. After exclusion of cirrhotic patients, a cohort of 75 patients with no diagnosed diffuse liver disease was selected. The ratio of signal intensity 20 min post- to pre-contrast administration (SE) in the spleen, kidney, liver, MES and DHC, and the SE of the kidney, liver and DHC normalized to the reference tissues spleen or MES were compared to patient age.

RESULTS

Patient age was inversely correlated with the liver SE normalized to the spleen and MES SE (both p < 0.001) and proportionally with the SE of the spleen (p = 0.043), the MES (p = 0.030) and the kidney (p = 0.022). No significant correlations were observed for the DHC (p = 0.347) and liver SE (p = 0.606).

CONCLUSION

The age dependence of hepatic SE normalized to the enhancement in the spleen and MES calls for a cautious interpretation of these quantification methods.

KEY POINTS

• Patient age was inversely correlated with spleen- and MES-corrected liver rSE (p < 0.001). • Patient age was correlated with spleen (p = 0.043) and MES SE (p = 0.030). • Patient age may confound quantitative liver function assessment using gadoxetate-enhanced liver MRI.

Application of iron oxide nanoparticles in glioma imaging and therapy: from bench to bedside

Gliomas are the most common primary brain tumors and have a very dismal prognosis. However, recent advancements in nanomedicine and nanotechnology provide opportunities for personalized treatment regimens to improve the poor prognosis of patients suffering from glioma. This comprehensive review starts with an outline of the current status facing glioma. It then provides an overview of the state-of-the-art applications of iron oxide nanoparticles (IONPs) to glioma diagnostics and therapeutics, including MR contrast enhancement, drug delivery, cell labeling and tracking, magnetic hyperthermia treatment and magnetic particle imaging. It also addresses current challenges associated with the biological barriers and IONP design with an emphasis on recent advances and innovative approaches for glioma targeting strategies. Opportunities for future development are highlighted.

Inter-observer agreement on the assessment of relative liver lesion signal intensity on hepatobiliary phase imaging with gadoxetate (Gd-EOB-DTPA)

PURPOSE

The purpose of the study was to assess the inter-observer agreement on the qualitative and quantitative evaluation of relative signal intensity of liver lesions on delayed hepatobiliary phase (HBP) MRI with gadoxetate (Gd-EOB-DTPA).

METHODS

105 patients with liver lesions, who had delayed HPB MRI using gadoxetate were reviewed retrospectively. For each patient, four readers (two fellows in training and two attending radiologists) qualitatively assessed the relative SI of the largest representative lesion on a five point scale, and quantitatively measured the relative SI of the lesion to adjacent liver parenchyma using region of interests (ROI). Intra-class correlation (ICC) and kappa statistics with quadratic weights (k) analysis, and maximally selected rank statistic were performed.

RESULTS

Substantial agreement between fellows (k = 0.719; ICC = 0.705) and almost perfect agreement between attending radiologists (k = 0.853; ICC = 0.849) were found for both qualitative and quantitative assessments of relative SI on delayed HPB imaging. A cut-off ratio to differentiate between hypointense and iso- to hyperintense lesions by ROI was calculated to be 0.90.

CONCLUSION

Inter-observer agreement of liver lesion relative SI on delayed HBP imaging is high and may improve with radiologist experience. A cut-off ratio of relative SI at 0.90 may be useful to quantitatively distinguish hypointense from iso- to hyperintense liver lesions.

USPIO-loaded red blood cells as a biomimetic MR contrast agent: a relaxometric study

Red blood cells (RBCs) loaded with iron oxide nanoparticles have been proposed as biomimetic constructs with long half-life (ca. 20 days) in the blood compartment and potentially interesting properties (such as relaxivity) as intravascular contrast agents for magnetic resonance imaging. However, the encapsulation of nanoparticles into RBCs might affect their magnetic properties and relaxivity, which may be significantly different from the native suspension. Here, we present a relaxometric study of P904, a novel ultra small iron oxide nanoparticle developed by Guerbet, enclosed in human RBCs. We measured longitudinal (r1 ) and transverse (r2 ) relaxivity over a wide range of Larmor frequencies (0.01-300 MHz) in samples of P904-loaded RBCs, and in control samples with P904 nanoparticles dispersed in blood. Internalization of P904 into RBCs resulted in smaller r1 , and in a very high r2 /r1 ratio (232) at the highest field. Moreover, a shift of the Curie peak to high fields was observed in P904-loaded RBCs, possibly the result of nanoparticle size selection caused by the internalization process. High r2 relaxivity together with a high r2 /r1 ratio and a very long blood half-life make P904-loaded RBCs a promising blood-pool negative contrast agent for MR diagnostic applications.

MRI-detectable polymeric micelles incorporating platinum anticancer drugs enhance survival in an advanced hepatocellular carcinoma model

Hepatocellular carcinoma (HCC) is one of the most intractable and lethal cancers; most cases are diagnosed at advanced stages with underlying liver dysfunction and are frequently resistant to conventional chemotherapy and radiotherapy. The development of tumor-targeting systems may improve treatment outcomes. Nanomedicine platforms are of particular interest for enhancing chemotherapeutic efficiency, and they include polymeric micelles, which enable targeting of multiple drugs to solid tumors, including imaging and therapeutic agents. This allows concurrent diagnosis, targeting strategy validation, and efficacy assessment. We used polymeric micelles containing the T1-weighted magnetic resonance imaging contrast agent gadolinium-diethylenetriaminpentaacetic acid (Gd-DTPA) and the parent complex of the anticancer drug oxaliplatin [(1,2-diaminocyclohexane)platinum(II) (DACHPt)] for simultaneous imaging and therapy in an orthotopic rat model of HCC. The Gd-DTPA/DACHPt-loaded micelles were injected into the hepatic artery, and magnetic resonance imaging performance and antitumor activity against HCC, as well as adverse drug reactions were assessed. After a single administration, the micelles achieved strong and specific tumor contrast enhancement, induced high levels of tumor apoptosis, and significantly suppressed tumor size and growth. Moreover, the micelles did not induce severe adverse reactions and significantly improved survival outcomes in comparison to oxaliplatin or saline controls. Our results suggest that Gd-DTPA/DACHPt-loaded micelles are a promising approach for effective diagnosis and treatment of advanced HCC.

Long-term in vivo clearance of gadolinium-based AGuIX nanoparticles and their biocompatibility after systemic injection

We previously reported the synthesis of gadolinium-based nanoparticles (NPs) denoted AGuIX (activation and guiding of irradiation by X-ray) NPs and demonstrated their potential as an MRI contrast agent and their efficacy as radiosensitizing particles during X-ray cancer treatment. Here we focus on the elimination kinetics of AGuIX NPs from the subcellular to whole-organ scale using original and complementary methods such as laser-induced breakdown spectroscopy (LIBS), intravital two-photon microscopy, inductively coupled plasma optical emission spectrometry (ICP-OES), transmission electron microscopy (TEM), and electrospray ionization mass spectrometry (ESI-MS). This combination of techniques allows the exact mechanism of AGuIX NPs elimination to be elucidated, including their retention in proximal tubules and their excretion as degraded or native NPs. Finally, we demonstrated that systemic AGuIX NP administration induced moderate and transient effects on renal function. These results provide useful and promising preclinical information concerning the safety of theranostic AGuIX NPs.

Nanoparticles for imaging: top or flop?

Nanoparticles are frequently suggested as diagnostic agents. However, except for iron oxide nanoparticles, diagnostic nanoparticles have been barely incorporated into clinical use so far. This is predominantly due to difficulties in achieving acceptable pharmacokinetic properties and reproducible particle uniformity as well as to concerns about toxicity, biodegradation, and elimination. Reasonable indications for the clinical utilization of nanoparticles should consider their biologic behavior. For example, many nanoparticles are taken up by macrophages and accumulate in macrophage-rich tissues. Thus, they can be used to provide contrast in liver, spleen, lymph nodes, and inflammatory lesions (eg, atherosclerotic plaques). Furthermore, cells can be efficiently labeled with nanoparticles, enabling the localization of implanted (stem) cells and tissue-engineered grafts as well as in vivo migration studies of cells. The potential of using nanoparticles for molecular imaging is compromised because their pharmacokinetic properties are difficult to control. Ideal targets for nanoparticles are localized on the endothelial luminal surface, whereas targeted nanoparticle delivery to extravascular structures is often limited and difficult to separate from an underlying enhanced permeability and retention (EPR) effect. The majority of clinically used nanoparticle-based drug delivery systems are based on the EPR effect, and, for their more personalized use, imaging markers can be incorporated to monitor biodistribution, target site accumulation, drug release, and treatment efficacy. In conclusion, although nanoparticles are not always the right choice for molecular imaging (because smaller or larger molecules might provide more specific information), there are other diagnostic and theranostic applications for which nanoparticles hold substantial clinical potential.

The status of neuroendocrine tumor imaging: from darkness to light?

Diagnostic imaging plays a pivotal role in the diagnosis, staging, treatment selection and follow-up for neuroendocrine tumors. The available diagnostic strategies are morphologic imaging, including computed tomography, magnetic resonance imaging (MRI) and ultrasound techniques, and molecular imaging, including scintigraphy with (111)In-pentetreotide and positron emission tomography with (68)Ga-DOTA-peptides, (18)F-DOPA and (11)C-5-HTP. A combination of anatomic and functional techniques is routinely performed to optimize sensitivity and specificity. The introduction of diffusion-weighted MRI and dynamic contrast-enhanced techniques represents a promising advance in radiologic imaging, whereas new receptor-binding peptides, including somatostatin agonists and antagonists, represent the recent most favorable innovation in molecular imaging. Future development includes the short-term validation of these techniques, but in extension also a more comprehensive multilevel integration of biologic information pertaining to a specific tumor and patient, possibly encompassing genomic considerations, currently evolving as a new entity denoted 'precision medicine'. The ideal is a diagnostic sequence that captures the global status of an individual's tumor and encompasses a multidimensional characterization of tumor location, metabolic performance and target identification. To date, advances in imagery have focused on increasing resolution, discrimination and functional characterization. In the future, the fusion of imagery with the parallel analysis of biological and genomic information has the potential to considerably amplify diagnosis.

Insight into hepatocellular carcinoma biology with gadoxetate disodium-enhanced MRI

The current algorithm for the imaging diagnosis of hepatocellular carcinoma accurately detects large, progressed tumors displaying the classical imaging features of arterial hyperenhancement with 'washout' and/or 'capsule' appearance. Liver MRI with the relatively newer hepatobiliary agent, gadoxetate disodium, provides information on hepatocellular function in addition to vascularity, facilitates detection of small progressed tumors, as well as early/vaguely nodular tumors, and shows promise for characterizing hepatocellular carcinoma biology. Prediction of tumor grade, presence of biliary and stem cell markers, microvascular invasion, future hypervascularization and post-treatment recurrence have all been studied with gadoxetate disodium-enhanced MRI with encouraging results. Incorporation of gadoxetate disodium-enhanced MRI into standard diagnostic and management algorithms will likely unfold in the future.

Biofunctionalized gadolinium-containing prussian blue nanoparticles as multimodal molecular imaging agents

Molecular imaging agents enable the visualization of phenomena with cellular and subcellular level resolutions and therefore have enormous potential in improving disease diagnosis and therapy assessment. In this article, we describe the synthesis, characterization, and demonstration of core-shell, biofunctionalized, gadolinium-containing Prussian blue nanoparticles as multimodal molecular imaging agents. Our multimodal nanoparticles combine the advantages of MRI and fluorescence. The core of our nanoparticles consists of a Prussian blue lattice with gadolinium ions located within the lattice interstices that confer high relaxivity to the nanoparticles providing MRI contrast. The relaxivities of our nanoparticles are nearly nine times those observed for the clinically used Magnevist. The nanoparticle MRI core is biofunctionalized with a layer of fluorescently labeled avidin that enables fluorescence imaging. Biotinylated antibodies are attached to the surface avidin and confer molecular specificity to the nanoparticles by targeting cell-specific biomarkers. We demonstrate our nanoparticles as multimodal molecular imaging agents in an in vitro model consisting of a mixture of eosinophilic cells and squamous epithelial cells. Our nanoparticles specifically detect eosinophilic cells and not squamous epithelial cells, via both fluorescence imaging and MRI in vitro. These results suggest the potential of our biofunctionalized Prussian blue nanoparticles as multimodal molecular imaging agents in vivo.

In vivo hepatocyte MR imaging using lactose functionalized magnetoliposomes

The aim of this study was to assess a novel lactose functionalized magnetoliposomes (MLs) as an MR contrast agent to target hepatocytes as well as to evaluate the targeting ability of MLs for in vivo applications. In the present work, 17 nm sized iron oxide cores functionalized with anionic MLs bearing lactose moieties were used for targeting the asialoglycoprotein receptor (ASGP-r), which is highly expressed in hepatocytes. Non-functionalized anionic MLs were tested as negative controls. The size distribution of lactose and anionic MLs was determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). After intravenous administration of both MLs, contrast enhancement in the liver was observed by magnetic resonance imaging (MRI). Label retention was monitored non-invasively by MRI and validated with Prussian blue staining and TEM for up to eight days post MLs administration. Although the MRI signal intensity did not show significant differences between functionalized and non-functionalized particles, iron-specific Prussian blue staining and TEM analysis confirmed the uptake of lactose MLs mainly in hepatocytes. In contrast, non-functionalized anionic MLs were mainly taken up by Kupffer and sinusoidal cells. Target specificity was further confirmed by high-resolution MR imaging of phantoms containing isolated hepatocytes, Kupffer cell (KCs) and hepatic stellate cells (HSCs) fractions. Hypointense signal was observed for hepatocytes isolated from animals which received lactose MLs but not from animals which received anionic MLs. These data demonstrate that galactose-functionalized MLs can be used as a hepatocyte targeting MR contrast agent to potentially aid in the diagnosis of hepatic diseases if the non-specific uptake by KCs is taken into account.

Use of contrast agents in oncological imaging: magnetic resonance imaging

Magnetic resonance plays a leading role in the management of oncology patients, providing superior contrast resolution and greater sensitivity compared with other techniques, which enables more accurate tumor identification, characterization and staging. Contrast agents are widely used in clinical magnetic resonance imaging; approximately 40-50% of clinical scans are contrast enhanced. Most contrast agents are based on the paramagnetic gadolinium ion Gd3+, which is chelated to avoid the toxic effects of free gadolinium. Multiple factors such as molecule structure, molecule concentration, dose, field strength and temperature determine the longitudinal and transverse relaxation rates (R1 and R2, respectively) and thus the T1- and T2-relaxivities of these chelates. These T1- and T2-relaxivities, together with their pharmacokinetic properties (i.e. distribution and concentration in the area of interest), determine the radiologic efficacy of the gadolinium-based contrast agents.

Mn(2+)-doped silica nanoparticles for hepatocyte-targeted detection of liver cancer in T1-weighted MRI

With an aim to examine the possibility of developing a liver-specific MRI contrast agent that takes advantages of brightly enhanced MR images by Mn²⁺ whilst making up the limitations of the pre-developed contrast agent, the Mn²⁺-doped SiO₂ nanoparticles (Mn-SiO₂) were synthesized and their characteristics as MR contrast agents were investigated. The in vitro and in vivo investigations showed that Mn-SiO₂ has unique MR contrast-enhancing characteristics that activate positive contrast enhancement in T1-weighted MR images only under low pH conditions by liberating Mn²⁺ ions from MR inactive nanoparticles. The administration of Mn-SiO₂ to an orthotopic xenograft model of human hepatocellular carcinoma (HCC) resulted in a differentiation of enhancement periods between HCC and normal parenchyma tissues on T1-weighted MR images and consequently presented the duplicates of the highly contrast-enhanced liver image with an equal liver-to-HCC contrast ratio but opposite contrast. The Mn-SiO₂-enhanced MR imaging therefore allowed for the repetitive detection of the HCC within a single MR imaging session, which can help us to achieve more reliable diagnosis and characterization of liver lesions than is possible with any currently used Mn²⁺-based contrast agent. In addition, the in vivo biodistribution study also supported the effectiveness of Mn-SiO₂ nanoparticles as a liver-specific MRI contrast agent, which efficiently delivers and releases the T1-contrasting Mn²⁺ ions to targeted hepatocytes.

Applications and potential toxicity of magnetic iron oxide nanoparticles

Owing to their unique physical and chemical properties, magnetic iron oxide nanoparticles have become a powerful platform in many diverse aspects of biomedicine, including magnetic resonance imaging, drug and gene delivery, biological sensing, and hyperthermia. However, the biomedical applications of magnetic iron oxide nanoparticles arouse serious concerns about their pharmacokinetics, metabolism, and toxicity. In this review, the updated research on the biomedical applications and potential toxicity of magnetic iron oxide nanoparticles is summarized. Much more effort is required to develop magnetic iron oxide nanoparticles with improved biocompatible surface engineering to achieve minimal toxicity, for various applications in biomedicine.

Investigation and management of hepatic incidentalomas

With the widespread use of medical imaging has come the detection of incidental liver lesions that are, by and large, asymptomatic prior to their discovery. These lesions may become a source of anxiety and often require further investigation to reassure the patient of their usually benign nature. Use of contemporary hepatobiliary imaging and simple laboratory tests often allow a definite diagnosis to be made without resorting to exhaustive investigation or inappropriate surgery. The goal of this paper is to review the clinical features and imaging characteristics of common and important liver incidentalomas, their natural course, complications, and indications for surgical or other intervention.

Anticancer nanomedicine and tumor vascular permeability; Where is the missing link?

Anticancer nanomedicine was coined to describe anticancer delivery systems such as polymer conjugates, liposomes, micelles, and metal nanoparticles. These anticancer delivery platforms have been developed with the enhanced permeability and retention (EPR) effect as a central mechanism for tumor targeting. EPR based nanomedicine has demonstrated, beyond doubt, to selectively target tumor tissues in animal models. However, over the last two decades, only nine anticancer agents utilizing this targeting strategy have been approved for clinical use. In this review, we systematically analyze various aspects that explain the limited clinical progress yet achieved. The influence of nanomedicine physicochemical characteristics, animal tumor models, and variations in tumor biology, on EPR based tumor targeting is closely examined. Furthermore, we reviewed results from over one hundred publications to construct patterns of factors that can influence the transition of EPR based anticancer nanomedicine to the clinic.

In vivo bio-imaging using chlorotoxin-based conjugates

Surgical resection remains the primary component of cancer therapy. The precision required to successfully separate cancer tissue from normal tissue relies heavily on the surgeon's ability to delineate the tumor margins. Despite recent advances in surgical guidance and monitoring systems, intra-operative identification of these margins remains imprecise and directly influences patient prognosis. If the surgeon had improved tools to distinguish these margins, tumor progression and unacceptable morbidity could be avoided. In this article, we review the history of chlorotoxin and its tumor specificity and discuss the research currently being generated to target optical imaging agents to cancer tissue.

Encapsulation of superparamagnetic nanoparticles into red blood cells as new carriers of MRI contrast agents

AIMS

The half-life of superparamagnetic iron oxide nanoparticles in the bloodstream is very short since they are rapidly taken up by the reticuloendothelial system. In this article, we report the encapsulation of different magnetic nanoparticles into human erythrocytes to increase their blood circulation time.

MATERIALS & METHODS

Newly synthesized and commercially available nanoparticles were evaluated for the encapsulation into red blood cells through the transient opening of membrane pores by controlled hypotonic dialysis and successive isotonic resealing and reannealing of cells.

RESULTS

Commercial superparamagnetic iron oxide nanoparticles (SHU 555A, AMI 227 and PMP-50) dextran or carboxydextran coated can be successfully loaded into red blood cells; similarly, some of the new nanomaterials, such as Np-1 nanoparticles dispersed in the Disperbyk®-190 agent, can be efficiently encapsulated into red blood cells.

CONCLUSION

A careful consideration of magnetic nanoparticles parameters, such as size, synthesis protocols, coating and/or dispersant agents, is required in order to obtain efficient loading through the cell membrane pores.

Magnetic nanoparticles as targeted delivery systems in oncology

BACKGROUND

Many different types of nanoparticles, magnetic nanoparticles being just a category among them, offer exciting opportunities for technologies at the interfaces between chemistry, physics and biology. Some magnetic nanoparticles have already been utilized in clinical practice as contrast enhancing agents for magnetic resonance imaging (MRI). However, their physicochemical properties are constantly being improved upon also for other biological applications, such as magnetically-guided delivery systems for different therapeutics. By exposure of magnetic nanoparticles with attached therapeutics to an external magnetic field with appropriate characteristics, they are concentrated and retained at the preferred site which enables the targeted delivery of therapeutics to the desired spot.

CONCLUSIONS

The idea of binding chemotherapeutics to magnetic nanoparticles has been around for 30 years, however, no magnetic nanoparticles as delivery systems have yet been approved for clinical practice. Recently, binding of nucleic acids to magnetic nanoparticles has been demonstrated as a successful non-viral transfection method of different cell lines in vitro. With the optimization of this method called magnetofection, it will hopefully become another form of gene delivery for the treatment of cancer.

Gadoxetate Acid-Enhanced MR Imaging for HCC: A Review for Clinicians

Hepatocellular carcinoma (HCC) is increasingly being detected at an earlier stage, owing to the screening programs and regular imaging follow-up in high-risk populations. Small HCCs still pose diagnostic challenges on imaging due to decreased sensitivity and increased frequency of atypical features. Differentiating early HCC from premalignant or benign nodules is important as management differs and has implications on both the quality of life and the overall survival for the patients. Gadoxetate acid (Gd-EOB-DTPA, Primovist(®), Bayer Schering Pharma) is a relatively new, safe and well-tolerated liver-specific contrast agent for magnetic resonance (MR) imaging of the liver that has combined perfusion- and hepatocyte-specific properties, allowing for the acquisition of both dynamic and hepatobiliary phase images. Its high biliary uptake and excretion improves lesion detection and characterization by increasing liver-to-lesion conspicuity in the added hepatobiliary phase imaging. To date, gadoxetate acid-enhanced MRI has been mostly shown to be superior to unenhanced MRI, computed tomography, and other types of contrast agents in the detection and characterization of liver lesions. This review article focuses on the evolving role of gadoxetate acid in the characterization of HCC, differentiating it from other mimickers of HCC.

Magnetic resonance imaging of the liver: New imaging strategies for evaluating focal liver lesions

The early detection of focal liver lesions, particularly those which are malignant, is of utmost importance. The resection of liver metastases of some malignancies (including colorectal cancer) has been shown to improve the survival of patients. Exact knowledge of the number, size, and regional distribution of liver metastases is essential to determine their resectability. Almost all focal liver lesions larger than 10 mm are demonstrated with current imaging techniques but the detection of smaller focal liver lesions is still relatively poor. One of the advantages of magnetic resonance imaging (MRI) of the liver is better soft tissue contrast (compared to other radiologic modalities), which allows better detection and characterization of the focal liver lesions in question. Developments in MRI hardware and software and the availability of novel MRI contrast agents have further improved the diagnostic yield of MRI in lesion detection and characterization. Although the primary modalities for liver imaging are ultrasound and computed tomography, recent studies have suggested that MRI is the most sensitive method for detecting small liver metastatic lesions, and MRI is now considered the pre-operative standard method for diagnosis. Two recent developments in MRI sequences for the upper abdomen comprise unenhanced diffusion-weighted imaging (DWI), and keyhole-based dynamic contrast-enhanced (DCE) MRI (4D THRIVE). DWI allows improved detection (b = 10 s/mm²) of small (< 10 mm) focal liver lesions in particular, and is useful as a road map sequence. Also, using higher b-values, the calculation of the apparent diffusion coefficient value, true diffusion coefficient, D, and the perfusion fraction, f, has been used for the characterization of focal liver lesions. DCE 4D THRIVE enables MRI of the liver with high temporal and spatial resolution and full liver coverage. 4D THRIVE improves evaluation of focal liver lesions, providing multiple arterial and venous phases, and allows the calculation of perfusion parameters using pharmacokinetic models. 4D THRIVE has potential benefits in terms of detection, characterization and staging of focal liver lesions and in monitoring therapy.

Cell uptake and in vitro toxicity of magnetic nanoparticles suitable for drug delivery

Magnetic targeting is useful for intravascular or intracavitary drug delivery, including tumor chemotherapy or intraocular antiangiogenic therapy. For all such in vivo applications, the magnetic drug carrier must be biocompatible and nontoxic. In this work, we investigated the toxic properties of magnetic nanoparticles coated with polyethylenoxide (PEO) triblock copolymers. Such coatings prevent the aggregation of magnetic nanoparticles and guarantee consistent magnetic and nonmagnetic flow properties. It was found that the PEO tail block length inversely correlates with toxicity. The nanoparticles with the shortest 0.75 kDa PEO tails were the most toxic, while particles coated with the 15 kDa PEO tail block copolymers were the least toxic. Toxicity responses of the tested prostate cancer cell lines (PC3 and C4-2), human umbilical vein endothelial cells (HUVECs), and human retinal pigment epithelial cells (HRPEs) were similar. Furthermore, all cell types took up the coated magnetic nanoparticles. It is concluded that magnetite nanoparticles coated with triblock copolymers containing PEO tail lengths of above 2 kDa are biocompatible and appropriate for in vivo application.

MR imaging of hypervascular liver masses: a review of current techniques

Major technologic advances in magnetic resonance (MR) imaging, including the advent of novel pulse sequences (eg, diffusion-weighted and steady-state free precession sequences) and the use of hepatocyte-specific contrast agents, have led to better image quality and shorter acquisition times, resulting in dramatic improvements in the noninvasive detection and characterization of hepatic lesions, particularly hypervascular neoplasms. However, as the role of MR imaging in clinical evaluation of the liver continues to evolve, keeping abreast of new developments can be daunting as well as confusing. A systematic approach that makes use of a simple decision algorithm can help differentiate hypervascular hepatic lesions on the basis of their distinguishing MR imaging characteristics and related clinical information.

An in vivo transmission electron microscopy study of injected dextran-coated iron-oxide nanoparticle location in murine breast adenocarcinoma tumors versus time

Investigators are just beginning to use hyperthermia generated by alternating magnetic field (AMF) activated iron oxide nanoparticles (IONPs) as a promising avenue for targeted cancer therapy. An important step in understanding cell death mechanisms in nanoparticle AMF treatments is to determine the location of these nanoparticles in relation to cellular organelles. In this paper, we report on transmission electron microscopy (TEM) studies designed to define the position of 100 nm diameter dextran-coated iron oxide nanoparticles in murine breast adenocarcinoma (MTG-B)and human colon adenocarcinoma tumors propagated in mice.

METHODS

Iron oxide nanoparticles (5 mg/g tumor) were injected into intradermal MTG-B flank tumors on female C3H/HEJ mice and into HT-29 flank tumors on female Nu/Nu mice. The IONPs were allowed to incubate for various times. The tumors were then excised and examined using TEM.

RESULTS

In the MTG-B tumors, most of the nanoparticles reside in aggregates adjacent to cell plasma membranes prior to three hours post-injection. By four hours post injection, however, most of the nanoparticles have been endocytosed by the cells. At time periods after four hours post injection, few visible extracellular nanoparticles remain and intracellular nanoparticles have densely aggregated within endosomes. In the HT-29 tumor, however, endocytosis of nanoparticles has not progressed to the same extent as in the MTG-B tumors by four hours post injection.

CONCLUSIONS

The time at which most of the nanoparticles transition from being extracellular to intracellular in the MTG-B system appears to be between two and four hours. The HT-29 cells, however, display different and delayed uptake pattern. These data show that there are IONP uptake differences between tumor types (cell lines) and that, based on known uptake kinetics, nanoparticle hyperthermia can be employed as an extracellular or intracellular modality. These data will be important in guiding future nanoparticle hyperthermia cancer treatments.