Magnetic resonance imaging detection of tumor cells by targeting low-density lipoprotein receptors with Gd-loaded low-density lipoprotein particles

Low-density lipoprotein: a versatile nanoscale platform for targeted delivery

Low-density lipoprotein (LDL) is a small lipoprotein that plays a vital role in controlling lipid metabolism. LDL has a delicate nanostructure with unique physicochemical properties: superior payload capacity, long residence time in circulation, excellent biocompatibility, smaller size, and natural targeting. In recent decades, the superiority and feasibility of LDL particles as targeted delivery carriers have attracted much attention. In this review, we introduce the structure, composition, advantages, defects, and reconstruction of LDL delivery systems, summarize their research status and progress in targeted diagnosis and therapy, and finally look forward to the clinical application of LDL as an effective delivery vehicle.

LDL mediated delivery of Paclitaxel and MRI imaging probes for personalized medicine applications

BACKGROUND

The combination of imaging and therapeutic agents in the same smart nanoparticle is a promising option to perform a minimally invasive imaging guided therapy. In this study, Low density lipoproteins (LDL), one of the most attractive biodegradable and biocompatible nanoparticles, were used for the simultaneous delivery of Paclitaxel (PTX), a hydrophobic antitumour drug and an amphiphilic contrast agent, Gd-AAZTA-C17, in B16-F10 melanoma cell line. These cells overexpress LDL receptors, as assessed by flow cytometry analysis.

RESULTS

PTX and Gd-AAZTA-C17 loaded LDLs (LDL-PTX-Gd) have been prepared, characterized and their stability was assessed under 72 h incubation at 37 °C and compared to LDL loaded with Gd-AAZTA-C17 (LDL-Gd) and LDL-PTX. The cytotoxic effect of LDL-PTX-Gd was evaluated by MTT assay. The anti-tumour drug loaded into LDLs showed a significantly higher toxicity on B16-F10 cells with respect to the commercially available formulation Paclitaxel kabi (PTX Kabi) used in clinical applications. Tumour cells uptake was initially assessed by ICP-MS and MRI on B16-F10 cell line. By the analysis of the image signal intensity, it was possible to extrapolate the amount of internalized PTX indirectly by the decrease of relaxation times caused by Gd, proportional to its concentration. Finally, the treatment with PTX loaded LDL on B16-F10 tumour bearing mice resulted in a marked reduction of tumour growth compared to the administration of PTX Kabi alone.

CONCLUSIONS

LDLs are selectively taken-up by tumour cells and can be successfully exploited for the selective delivery of Paclitaxel and imaging agents. For the first time the anon invasive "in vivo" determination of the amount of PTX accumulated in the tumour was possible, thanks to the use of theranostic agents of natural origin.

Lipoproteins-Nanocarriers as a Promising Approach for Targeting Liver Cancer: Present Status and Application Prospects

The prevalence of liver cancer is increasing over the years and it is the fifth leading cause of mortality worldwide. The intrusive features and burden of low survival rate make it a global health issue in both developing and developed countries. The recommended chemotherapy drugs for patients in the intermediate and advanced stages of various liver cancers yield a low response rate due to the nonspecific nature of drug delivery, thus warranting the search for new therapeutic strategies and potential drug delivery carriers. There are several new drug delivery methods available to ferry the targeted molecules to the specific biological environment. In recent years, the nano assembly of lipoprotein moieties (lipidic nanoparticles) has emerged as a promising and efficiently tailored drug delivery system in liver cancer treatment. This increased precision of nano lipoproteins conjugates in chemotherapeutic targeting offers new avenues for the treatment of liver cancer with high specificity and efficiency. This present review is focused on concisely outlining the knowledge of liver cancer diagnosis, existing treatment strategies, lipoproteins, their preparation, mechanism and their potential application in the treatment of liver cancer.

Serum protein-based nanoparticles for cancer diagnosis and treatment

Serum protein as naturally essential biomacromolecules has recently emerged as a versatile carrier for diagnostic and therapeutic drug delivery for cancer nanomedicine with superior biocompatibility, improved pharmacokinetics and enhanced targeting capacity. A variety of serum proteins have been utilized for drug delivery, mainly including albumin, ferritin/apoferritin, transferrin, low-density lipoprotein, high-density lipoprotein and hemoglobin. As evidenced by the success of paclitaxel-bound albumin nanoparticles (Abraxane^TM), serum protein-based nanoparticles have gained attractive attentions for precise biological design and potential clinical application. In this review, we summarize the general design strategies, targeting mechanisms and recent development of serum protein-based nanoparticles in the field of cancer nanomedicine. Moreover, we also concisely specify the current challenges to be addressed for a bright future of serum protein-based nanomedicines.

Lipoprotein-based drug delivery

Lipoproteins (LPs) are circulating heterogeneous nanoparticles produced by the liver and intestines. LPs play a major role in the transport of dietary and endogenous lipids to target cells through cell membrane receptors or cell surface-bound lipoprotein lipase. The stability, biocompatibility, and selective transport of LPs make them promising delivery vehicles for various therapeutic and imaging agents. This review discusses isolation, manufacturing, and drug loading techniques used for LP-based drug delivery, as well as recent applications for diagnosis and treatment of cancer, atherosclerosis, and other life-threatening diseases.

New nanoprobe for breast cancer cell imaging based on low-density lipoprotein

Many malignant cancers have an increased demand for lipoprotein due to the requirement for lipids for the rapid proliferation of the tumours and which is met by the increased availability of LDL through upregulation of LDL transporters. This unique phenomenon is the basis for the use of LDL based nanoparticles for cell imaging. In this study, a novel MR-active LDL nanoparticle was synthesised as the MRI probes. This MR-active LDL was characterised by using different techniques including scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier-transform infra-red spectroscopy (FTIR) and magnetic resonance imaging (MRI). The intracellular uptake of Gd³⁺ and cytotoxicity was measured by ICP-AES and MTT assay respectively. Results suggest that this nanoprobe with spherical shape and size of 55 nm has reduced relaxation time compared to commercial contrast agent and is introduced as an appropriate imaging probe. The amount of reabsorption of nanoprobe increased up to 6 h and given that the connection of the chelator does not have an effect on reabsorption proves that entry through transporter of APO section has done. This study lays the basis for exploring a personalised medicine strategy by directing a patient's own LDL to cancer cell imaging in the early stages.

Radiolabeled PET/MRI Nanoparticles for Tumor Imaging

The development of integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners opened a new scenario for cancer diagnosis, treatment, and follow-up. Multimodal imaging combines functional and morphological information from different modalities, which, singularly, cannot provide a comprehensive pathophysiological overview. Molecular imaging exploits multimodal imaging in order to obtain information at a biological and cellular level; in this way, it is possible to track biological pathways and discover many typical tumoral features. In this context, nanoparticle-based contrast agents (CAs) can improve probe biocompatibility and biodistribution, prolonging blood half-life to achieve specific target accumulation and non-toxicity. In addition, CAs can be simultaneously delivered with drugs or, in general, therapeutic agents gathering a dual diagnostic and therapeutic effect in order to perform cancer diagnosis and treatment simultaneous. The way for personalized medicine is not so far. Herein, we report principles, characteristics, applications, and concerns of nanoparticle (NP)-based PET/MRI CAs.

Hybrid PET/MRI Methodology

The hybrid PET/MR scanner represents the first implementation of the effective integration of two modalities allowing truly synchronous/simultaneous acquisition of their imaging signals. This integration, resulting from the innovation and development of specific hardware components has paved the way for new approaches in the study of neurodegenerative diseases. This chapter will describe the hardware development that has led to the availability of different clinical solutions for PET/MR imaging as well as the still-open technological challenges and opportunities related to the processing and exploitation of the simultaneous acquisition in neurological studies.

An innovative therapeutic approach for malignant mesothelioma treatment based on the use of Gd/boron multimodal probes for MRI guided BNCT

The aim of this study is to develop an innovative imaging guided approach based on Boron Neutron Capture Therapy, for the treatment of mesothelioma, assisted by the quantification of the in vivo boron distribution by MRI. The herein reported results demonstrate that overexpressed Low Density Lipoproteins receptors can be successfully exploited to deliver to mesothelioma cells a therapeutic dose of boron (26 μg/g), significantly higher than in the surrounding tissue (3.5 μg/g). Boron and Gd cells uptake was assessed by ICP-MS and MRI on two mesothelioma (ZL34, AE17) and two healthy (MRC-5 and NMuMg) cell lines. An in vivo model was prepared by subcutaneous injection of ZL34 cells in Nu/Nu mice. After irradiation with thermal neutrons, tumor growth was evaluated for 40 days by MRI. Tumor masses of boron treated mice showed a drastic reduction of about 80-85%. The obtained results appear very promising providing patients affected by this rare disease with an improved therapeutic option, exploiting LDL transporters.

Biomacromolecules as carriers in drug delivery and tissue engineering

Natural biomacromolecules have attracted increased attention as carriers in biomedicine in recent years because of their inherent biochemical and biophysical properties including renewability, nontoxicity, biocompatibility, biodegradability, long blood circulation time and targeting ability. Recent advances in our understanding of the biological functions of natural-origin biomacromolecules and the progress in the study of biological drug carriers indicate that such carriers may have advantages over synthetic material-based carriers in terms of half-life, stability, safety and ease of manufacture. In this review, we give a brief introduction to the biochemical properties of the widely used biomacromolecule-based carriers such as albumin, lipoproteins and polysaccharides. Then examples from the clinic and in recent laboratory development are summarized. Finally the current challenges and future prospects of present biological carriers are discussed.

Overexpression of low-density lipoprotein receptors stimulated by vascular endothelial growth factor in fibroblasts from pterygium

The activation of subconjunctival fibroblasts is believed to be responsible for the pathogenesis of pterygium. Vascular endothelial growth factor (VEGF) appears to be the most potent stimulator of formation and progression of pterygium. Pterygium excision is a common procedure, although the recurrence rates remain high. Various postoperative adjuvant therapies are now attempted to lower the recurrence rate, with severe side effects. To offer a greater therapeutic effect and lower side effects, it's necessary to discover a constant nanoparticle drug delivery targeting to subconjunctival fibroblasts in pterygium (PSFs). This study was designed to investigate the expression of low-density lipoprotein receptor (LDLr) stimulated by VEGF in PSFs. We found that after exposure to VEGF, mRNA and protein levels of LDLr were both increased significantly in PSFs, assessed using relative quantitative real-time RT-PCR and Western blot. Moreover, it's demonstrated that the expression of LDLr were positively correlated with the cells proliferation. Uptake of DiI-LDL via live PSFs was increased with time, estimated by confocal microscopy. The protein expression of LDLr in pterygium subconjunctival tissues was significantly higher than in normal subconjunctival tissues. These results suggest that LDLr in the activated PSFs may become a novel target receptor for controlled drug delivery to lower postsurgical recurrence rate.

Lipoproteins and lipoprotein mimetics for imaging and drug delivery

Lipoproteins are a set of natural nanoparticles whose main role is the transport of fats within the body. While much work has been done to develop synthetic nanocarriers to deliver drugs or contrast media, natural nanoparticles such as lipoproteins represent appealing alternatives. Lipoproteins are biocompatible, biodegradable, non-immunogenic and are naturally targeted to some disease sites. Lipoproteins can be modified to act as contrast agents in many ways, such as by insertion of gold cores to provide contrast for computed tomography. They can be loaded with drugs, nucleic acids, photosensitizers or boron to act as therapeutics. Attachment of ligands can re-route lipoproteins to new targets. These attributes render lipoproteins attractive and versatile delivery vehicles. In this review we will provide background on lipoproteins, then survey their roles as contrast agents, in drug and nucleic acid delivery, as well as in photodynamic therapy and boron neutron capture therapy.

Magnetic resonance imaging of osteosarcoma using a bis(alendronate)-based bone-targeted contrast agent

Magnetic resonance (MR) is currently used for diagnosis of osteosarcoma but not well even though contrast agents are administered. Here, we report a novel bone-targeted MR imaging contrast agent, Gd₂-diethylenetriaminepentaacetate-bis(alendronate) (Gd₂-DTPA-BA) for the diagnosis of osteosarcoma. It is the conjugate of a bone cell-seeking molecule (i.e., alendronate) and an MR imaging contrast agent (i.e., Gd-DTPA). Its physicochemical parameters were measured, including pK_a, complex constant, and T₁ relaxivity. Its bone cell-seeking ability was evaluated by measuring its adsorption on hydroxyapatite. Hemolysis was investigated. MR imaging and biodistribution of Gd₂-DTPA-BA and Gd-DTPA were studied on healthy and osteosarcoma-bearing nude mice. Gd₂-DTPA-BA showed high adsorption on hydroxyapatite, the high MR relaxivity (r₁) of 7.613mM^-1s^-1 (2.6 folds of Gd-DTPA), and no hemolysis. The MR contrast effect of Gd₂-DTPA-BA was much higher than that of Gd-DTPA after intravenous injection to the mice. More importantly, the MR imaging of osteosarcoma was significantly improved by Gd₂-DTPA-BA. The signal intensity of Gd₂-DTPA-BA reached 120.3% at 50min, equal to three folds of Gd-DTPA. The bone targeting index (bone/blood) of Gd₂-DTPA-BA in the osteosarcoma-bearing mice was very high to 130 at 180min. Furthermore, the contrast enhancement could also be found in the lung due to metastasis of osteosarcoma. Gd₂-DTPA-BA plays a promising role in the diagnoses of osteosacomas, including the primary bone tumors and metastases.

Lipoprotein-Related and Apolipoprotein-Mediated Delivery Systems for Drug Targeting and Imaging

The integration of lipoprotein-related or apolipoprotein-targeted nanoparticles as pharmaceutical carriers opens new therapeutic and diagnostic avenues in nanomedicine. The concept is to exploit the intrinsic characteristics of lipoprotein particles as being the natural transporter of apolar lipids and fat in human circulation. Discrete lipoprotein assemblies and lipoprotein-based biomimetics offer a versatile nanoparticle platform that can be manipulated and tuned for specific medical applications. This article reviews the possibilities for constructing drug loaded, reconstituted or artificial lipoprotein particles. The advantages and limitations of lipoproteinbased delivery systems are critically evaluated and potential future challenges, especially concerning targeting specificity, concepts for lipoprotein rerouting and design of innovative lipoprotein mimetic particles using apolipoprotein sequences as targeting moieties are discussed. Finally, the review highlights potential medical applications for lipoprotein-based nanoparticle systems in the fields of cardiovascular research, cancer therapy, gene delivery and brain targeting focusing on representative examples from literature.

Evaluation of the dose enhancement of combined ¹⁰B + ¹⁵⁷Gd neutron capture therapy (NCT)

An innovative molecule, GdBLDL, for boron neutron capture therapy (BNCT) has been developed and its effectiveness as a BNCT carrier is currently under evaluation using in vivo experiments on small animal tumour models. The molecule contains both (10)B (the most commonly used NCT agent) and (157)Gd nuclei. (157)Gd is the second most studied element to perform NCT, mainly thanks to its high cross section for the capture of low-energy neutrons. The main drawback of (157)Gd neutron capture reaction is the very short range and low-energy secondary charged particles (Auger electrons), which requires (157)Gd to be very close to the cellular DNA to have an appreciable biological effect. Treatment doses were calculated by Monte Carlo simulations to ensure the optimised tumour irradiation and the sparing of the healthy organs of the irradiated animals. The enhancement of the absorbed dose due to the simultaneous presence of (10)B and (157)Gd in the experimental set-up was calculated and the advantage introduced by the presence of (157)Gd was discussed.

Glypican-3 antibody functionalized Prussian blue nanoparticles for targeted MR imaging and photothermal therapy of hepatocellular carcinoma

MRI-guided photothermal therapy is becoming a more widely accepted minimally invasive technique.

Gold nanocrystal labeling allows low-density lipoprotein imaging from the subcellular to macroscopic level

Low-density lipoprotein (LDL) plays a critical role in cholesterol transport and is closely linked to the progression of several diseases. This motivates the development of methods to study LDL behavior from the microscopic to whole-body level. We have developed an approach to efficiently load LDL with a range of diagnostically active nanocrystals or hydrophobic agents. We performed focused experiments on LDL labeled with gold nanocrystals (Au-LDL). The labeling procedure had minimal effect on LDL size, morphology, or composition. Biological function was found to be maintained from both in vitro and in vivo experiments. Tumor-bearing mice were injected intravenously with LDL, DiR-LDL, Au-LDL, or a gold-loaded nanoemulsion. LDL accumulation in the tumors was detected with whole-body imaging methods, such as computed tomography (CT), spectral CT, and fluorescence imaging. Cellular localization was studied with transmission electron microscopy and fluorescence techniques. This LDL labeling procedure should permit the study of lipoprotein biointeractions in unprecedented detail.

Lipoprotein lipase in non-small cell lung cancer tissue is highly expressed in a subpopulation of tumor-associated macrophages

High lipoprotein lipase (LPL) activity in non-small cell lung cancer (NSCLC) tissue strongly predicts shorter patient survival. We tested the hypothesis that in NSCLC tissue, macrophages are the major site of LPL expression. LPL expression in the entire NSCLC tissue and in the adjacent non-cancer lung tissue was compared to the expression of genes preferentially expressed in macrophages. LPL expression at the cellular level was analyzed by mRNA fluorescence in situ hybridization. In the whole cancer tissue (but not in the adjacent non-cancer tissue), expression of LPL correlated with expression of genes preferentially expressed in macrophages (MSR1, CD163, FOLR2), but not with expression of genes preferentially expressed in tumor cells. All cells in the cancer and adjacent non-cancer tissue exhibit low LPL expression. However, in cancer tissue only, there were individual highly LPL-expressing cells which were macrophages. These LPL-overexpressing cells were approximately 10 times less abundant than anti-CD163-stained, tumor-associated macrophages. To conclude, in NSCLC tissue, a subpopulation of tumor-associated macrophages highly expresses LPL. Because tumor-associated macrophages are pro-tumorigenic, these cells should be further characterized to better understand the underlying nature of the close relationship between high LPL activity in NSCLC tissue and shorter patient survival.

Functionalized low-density lipoprotein nanoparticles for in vivo enhancement of atherosclerosis on magnetic resonance images

To allow visualization of macrophage-rich and miniature-sized atheromas by magnetic resonance (MR) imaging, we have converted low-density lipoprotein (LDL) into MR-active nanoparticles via the intercalation of a 1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (DO3A) derivative and the subsequent coordination reaction with Gd(3+). After careful removal of nonchelated Gd(3+), an MR-active LDL (Gd(3+)-LDL) with a remarkably high payload of Gd(3+) (in excess of 200 Gd(3+) atoms per particle) and a high relaxivity (r(1) = 20.1 s(-1) mM(-1) per Gd(3+) or 4040 s(-1) mM(-1) per LDL) was obtained. Dynamic light-scattering photon correlation spectroscopy (DLS) and cryo transmission electron microscope (cryoTEM) images showed that Gd(3+)-LDL particles did not aggregate and remained of a similar size (25-30 nm) to native LDL. Intravenous injection of Gd(3+)-LDL into an atherosclerotic mouse model (ApoE(-/-)) resulted in an extremely high enhancement of the atheroma-bearing aortic walls at 48 h after injection. Free Gd(3+) dissociation from Gd(3+)-LDL was not detected over the imaging time window (96 h). Because autologous LDL can be isolated, modified, and returned to the same patient, our results suggest that MR-active LDL can potentially be used as a noninfectious and nonimmunogenic imaging probe for the enhancement of atheroplaques presumably via the uptake into macrophages inside the plaque.

Drug delivery via lipoprotein-based carriers: answering the challenges in systemic therapeutics

Plasma lipoproteins are transporters of lipids and other hydrophobic molecules in the mammalian circulation. Lipoproteins also have a strong potential to serve as drug-delivery vehicles due to their small size, long residence time in the circulation and high-drug payload. Consequently, lipoproteins and synthetic/reconstituted lipoprotein preparations have been evaluated with increasing interest towards clinical applications, particularly for cancer diagnostics/imaging and chemotherapy. In this review, past and current studies on lipoproteins and similar alternative drug carriers are discussed regarding their suitability as agents to deliver drugs, primarily to cancer cells and tumors. A lipoprotein-based delivery strategy may also provide a novel platform for improving the therapeutic efficacy of drugs that have previously been judged unsuitable or had only limited application due to poor solubility. An additional, and perhaps the most important aspect of the drug-delivery process via lipoprotein-type carriers, is the receptor-mediated uptake of the payload from the lipoprotein complex. Monitoring the expression of specific receptors prior to treatment could, thus, give rise to efficient selection of optimally responsive patients, resulting in a successful personalized therapy regimen.

Recombinant high-density lipoprotein nanoparticles containing gadolinium-labeled cholesterol for morphologic and functional magnetic resonance imaging of the liver

Background

Natural high-density lipoproteins (HDL) possess important physiological functions to the transport of cholesterol from the peripheral tissues to the liver for metabolic degradation and excretion in the bile.

Methods and results

In this work, we took advantage of this pathway and prepared two different gadolinium (Gd)-DTPA-labeled cholesterol-containing recombinant HDL nanoparticles (Gd-chol-HDL) and Gd-(chol)₂-HDL as liver-specific magnetic resonance imaging (MRI) contrast agents. The reconstituted HDL nanoparticles had structural similarity to native HDL, and could be taken up by HepG2 cells via interaction with HDL receptors in vitro. In vivo MRI studies in rats after intravenous injections of 10 μmol gadolinium per kg of recombinant HDL nanoparticles indicated that both nanoparticles could provide signal enhancement in the liver and related organs. However, different T₁-weighted image details suggested that they participated in different cholesterol metabolism and excretion pathways in the liver.

Conclusion

Such information could be highly useful to differentiate functional changes as well as anatomic differences in the liver. These cholesterol-derived contrast agents and their recombinant HDL preparations may warrant further development as a new class of contrast agents for MRI of the liver and related organs.

MRI of cells and mice at 1 and 7 Tesla with Gd-targeting agents: when the low field is better!

Tumor cells were targeted with Gd-loaded/LDL (low density lipoproteins) adducts consisting of ca 300 Gd(III) amphiphilic complexes incorporated in the lipophilic LDL particles. The long reorientational time of the Gd(III) complex in the supramolecular adduct yielded a relaxivity peak at ca 1 T, whereas its relaxivity at 7 T was 5 times less. The field-dependent relaxivity markedly affected the signal enhancement attainable at the two magnetic fields. As tumor cells showed up-regulation of LDL transporters, B16 melanoma cells were labeled with the Gd-loaded/LDL adduct. Each cell contained ca 2 × 10(9) Gd atoms. Upon dispersion of 5000 labeled cells in 1 μl of agar, signal intensity (SI) enhancements of about 30 and 7% were observed at 1 and 7 T, respectively. The results obtained on cellular systems were confirmed in vivo upon the administration of Gd-loaded/LDL particles to C57 mice bearing a transplanted melanoma (B16) tumor. From the herein reported results, one may conclude that, for slowly moving Gd complexes, it is possible to obtain in vivo sensitivity enhancements at 1 T several times higher than that attained at high fields.

Preparation and in vitro studies of MRI-specific superparamagnetic iron oxide antiGPC3 probe for hepatocellular carcinoma

BACKGROUND

The aim of this study was to develop an antiGPC3-ultrasuperparamagnetic iron oxide (USPIO) probe for early detection of hepatocellular carcinoma.

METHODS

GPC3 and AFP receptors were selected as biomarkers and conjugated with USPIO nanoparticles coated by dextran with carboxylate groups to synthesize antiGPC3-USPIO and antiAFP-USPIO probes. HepG2 cells (a human hepatocellular carcinoma cell model with high expression of GPC3) were used along with SMMC-7721 cells (a hepatocellular carcinoma cell model with no expression of GPC3), HeLa cells (a cervical cancer model), and HL-7702 (normal hepatocytes) which were used as controls. After incubation with the probes, the iron content in the cells was calculated, USPIO nanoparticles in cells were observed using transmission electron microscopy, and T1 and T2 relaxation times were measured with a 1.5 T magnetic resonance scanner.

RESULTS

AntiGPC3-USPIO probes with a mean hydrodynamic diameter of 47 nm showed good biological compatibility. Transmission electron microscopic images indicated that the amount of USPIO nanoparticles taken up was significantly higher in HepG2 cells incubated with antiGPC3-USPIO than that in HepG2 cells incubated with antiAFP-USPIO or USPIO nanoparticles and that in the SMMC-7721 or HeLa cells incubated with antiGPC3-USPIO probes, antiAFP-USPIO probes, or USPIO nanoparticles. The higher the concentration and the longer the incubation time, the greater the number of USPIO nanoparticles found in the cells. No USPIO nanoparticles were found in the HL-7702 cells. All of the HepG2, SMMC-7721, and HeLa cells incubated with antiGPC3-USPIO, antiAFP-USPIO, or USPIO nanoparticles were able to shorten the T1 and T2 values in agar solution, especially the T2 images of HepG2 cells incubated with antiGPC3-USPIO probes.

CONCLUSION

AntiGPC3-USPIO probes can be utilized as a specific magnetic resonance targeting contrast agent for early detection of hepatocellular carcinoma. Using a 1.5 T magnetic resonance scanner, the optimal time for imaging HepG2 cells was around 2-4 hours after incubation with antiGPC3-USPIO probes.

Lipoprotein-inspired nanoparticles for cancer theranostics

Over hundreds of millions of years, animals have evolved endogenous lipoprotein nanoparticles for shuttling hydrophobic molecules to different parts of the body. In the last 70 years, scientists have developed an understanding of lipoprotein function, often in relationship to lipid transport and heart disease. Such biocompatible, lipid–protein complexes are also ideal for loading and delivering cancer therapeutic and diagnostic agents, which means that lipoprotein and lipoprotein-inspired nanoparticles also offer opportunities for cancer theranostics. By mimicking the endogenous shape and structure of lipoproteins, the nanocarrier can remain in circulation for an extended period of time, while largely evading the reticuloendothelial cells in the body’s defenses. The small size (less than 30 nm) of the low-density (LDL) and high-density (HDL) classes of lipoproteins allows them to maneuver deeply into tumors. Furthermore, lipoproteins can be targeted to their endogenous receptors, when those are implicated in cancer, or to other cancer receptors.

In this Account, we review the field of lipoprotein-inspired nanoparticles related to the delivery of cancer imaging and therapy agents. LDL has innate cancer targeting potential and has been used to incorporate diverse hydrophobic molecules and deliver them to tumors. Nature’s method of rerouting LDL in atherosclerosis provides a strategy to extend the cancer targeting potential of lipoproteins beyond its narrow purview. Although LDL has shown promise as a drug nanocarrier for cancer imaging and therapy, increasing evidence indicates that HDL, the smallest lipoprotein, may also be of use for drug targeting and uptake into cancer cells. We also discuss how synthetic HDL-like nanoparticles, which do not include human or recombinant proteins, can deliver molecules directly to the cytoplasm of certain cancer cells, effectively bypassing the endosomal compartment. This strategy could allow HDL-like nanoparticles to be used to deliver drugs that have increased activity in the cytoplasm. Lipoprotein nanoparticles have evolved to be ideal delivery vehicles, and because of that specialized function, they have the potential to improve cancer theranostics.

MRI-guided neutron capture therapy by use of a dual gadolinium/boron agent targeted at tumour cells through upregulated low-density lipoprotein transporters

The upregulation of low-density lipoprotein (LDL) transporters in tumour cells has been exploited to deliver a sufficient amount of gadolinium/boron/ligand (Gd/B/L) probes for neutron capture therapy, a binary chemio-radiotherapy for cancer treatment. The Gd/B/L probe consists of a carborane unit (ten B atoms) bearing an aliphatic chain on one side (to bind LDL particles), and a Gd(III)/1,4,7,10-tetraazacyclododecane monoamide complex on the other (for detection by magnetic resonance imaging (MRI)). Up to 190 Gd/B/L probes were loaded per LDL particle. The uptake from tumour cells was initially assessed on cell cultures of human hepatoma (HepG2), murine melanoma (B16), and human glioblastoma (U87). The MRI assessment of the amount of Gd/B/L taken up by tumour cells was validated by inductively coupled plasma-mass-spectrometric measurements of the Gd and B content. Measurements were undertaken in vivo on mice bearing tumours in which B16 tumour cells were inoculated at the base of the neck. From the acquisition of magnetic resonance images, it was established that after 4-6 hours from the administration of the Gd/B/L-LDL particles (0.1 and 1 mmol kg(-1) of Gd and (10)B, respectively) the amount of boron taken up in the tumour region is above the threshold required for successful NCT treatment. After neutron irradiation, tumour growth was followed for 20 days by MRI. The group of treated mice showed markedly lower tumour growth with respect to the control group.

Dose estimation in B16 tumour bearing mice for future irradiation in the thermal column of the TRIGA reactor after B/Gd/LDL adduct infusion

To test the efficacy of a new (10)B-vector compound, the B/Gd/LDL adduct synthesised at Torino University, in vivo irradiations of murine tumours are in progress at the TRIGA Mark II reactor of the Pavia University. A localised B16 melanoma tumour is generated in C57BL/6 mice and subsequently infused with the adduct. During the irradiation, the mouse will be put in a shield to protect the whole body except the tumour in the back-neck area. To optimise the treatment set-up, MCNP simulations were performed. A very simplified mouse model was built using MCNP geometry capabilities, as well as the geometry of the shield made of 99% (10)B enriched boric acid. A hole in the shield is foreseen in correspondence of the back-neck region. Many configurations of the shield were tested in terms of neutron flux, dose distribution and mean induced activity in the tumour region and in the radiosensitive organs of the mouse. In the final set-up, up to five mice can be treated simultaneously in the reactor thermal column and the neutron fluence in the tumour region for 10 min of irradiation is of about 5×10(12) cm(-2).

Contrast agents and mechanisms

MRI contrast agents are routinely used in clinical settings. Important advances in their design have been attained in the past few years to overcome sensitivity issues and to make possible molecular imaging applications by means of this modality. Besides the sensitivity enhancement of paramagnetic relaxation probes, outstanding results have been obtained in the development of novel classes of frequency-encoding agents such as chemical exchange saturation transfer and hyperpolarized (13)C-enriched molecules.:

In vitro assessment of poly-iodinated triglyceride reconstituted low-density lipoprotein: initial steps toward CT molecular imaging

RATIONALE AND OBJECTIVES

Targeted molecular probes offer the potential for greater specificity in cancer imaging with contrast-enhanced computed tomography (CT). We investigate a low-density lipoprotein (LDL) nanoparticle loaded with poly-iodinated triglyceride (ITG) in a proof of concept study of targeted x-ray imaging. LDLs are targeted to the LDL cell surface receptor (LDLR), which is overexpressed in several tumor types. The LDL-LDLR pathway presents a high-capacity and self-renewing transport system for molecular imaging in CT.

MATERIALS AND METHODS

ITG was synthesized and loaded into the core of LDL particles to form a reconstituted nanoparticle, hereafter referred to as (rITG)LDL. Particle size was measured by dynamic light scattering. The x-ray attenuation of the (rITG)LDL solution was measured with CT imaging and signal enhancement was calibrated for equivalent iodine concentration. Cultured human hepatoblastoma G2 (HepG2) cells, which overexpress LDLR, were incubated with (rITG)LDL with or without native LDL. The cells were imaged with CT to characterize particle sequestration.

RESULTS

Reconstitution of LDL with ITG was successful and did not compromise the targeting function of the particle. Measurement of the x-ray attenuation properties of the (rITG)LDL solution revealed an effective iodine concentration of 0.78 mg/mL. In vitro studies of HepG2 cells demonstrated a significant increase in CT image intensity over control cells when incubated with (rITG)LDL.

CONCLUSION

The in vitro results of this study suggest that (rITG)LDL can provide adequate image enhancement for CT molecular imaging. Potential applications include breast imaging and small animal imaging at low x-ray energies. In vivo experiments will be required to verify that tumor uptake of (rITG)LDL is sufficient for enhanced detection. Use at higher x-ray energies, as used in conventional CT, will require a further increase in iodine loading.

The War on Cancer rages on

In 1971, the "War on Cancer" was launched by the US government to cure cancer by the 200-year anniversary of the founding of the United States of America, 1976. This article briefly looks back at the progress that has been made in cancer research and compares progress made in other areas of human affliction. While progress has indeed been made, the battle continues to rage on.

Modified natural nanoparticles as contrast agents for medical imaging

The development of novel and effective contrast agents is one of the drivers of the ongoing improvement in medical imaging. Many of the new agents reported are nanoparticle-based. There are a variety of natural nanoparticles known, e.g. lipoproteins, viruses or ferritin. Natural nanoparticles have advantages as delivery platforms such as biodegradability. In addition, our understanding of natural nanoparticles is quite advanced, allowing their adaptation as contrast agents. They can be labeled with small molecules or ions such as Gd(3+) to act as contrast agents for magnetic resonance imaging, (18)F to act as positron emission tomography contrast agents or fluorophores to act as contrast agents for fluorescence techniques. Additionally, inorganic nanoparticles such as iron oxide, gold nanoparticles or quantum dots can be incorporated to add further contrast functionality. Furthermore, these natural nanoparticle contrast agents can be re-routed from their natural targets via the attachment of targeting molecules. In this review, we discuss the various modified natural nanoparticles that have been exploited as contrast agents.

HDL as a contrast agent for medical imaging

Contrast-enhanced MRI of atherosclerosis can provide valuable additional information on a patient's disease state. As a result of the interactions of HDL with atherosclerotic plaque and the flexibility of its reconstitution, it is a versatile candidate for the delivery of contrast-generating materials to this pathogenic lesion. We herein discuss the reports of HDL modified with gadolinium to act as an MRI contrast agent for atherosclerosis. Furthermore, HDL has been modified with fluorophores and nanocrystals, allowing it to act as a contrast agent for fluorescent imaging techniques and for computed tomography. Such modified HDL has been found to be macrophage specific, and, therefore, can provide macrophage density information via noninvasive MRI. As such, modified HDL is currently a valuable contrast agent for probing preclinical atherosclerosis. Future developments may allow the application of this particle to further diseases and pathological or physiological processes in both preclinical models as well as in patients.

High-relaxivity gadolinium-modified high-density lipoproteins as magnetic resonance imaging contrast agents

There is an ongoing desire to produce high-relaxivity, Gd-based magnetic resonance imaging (MRI) contrast agents. These may allow for lower doses to be used, which is especially important in view of the current safety concerns surrounding Gd in patients. Here we report the synthesis of a high-relaxivity MRI contrast agent, by incorporating Gd-chelating lipids that coordinate two water molecules into high-density lipoprotein (q = 2 HDL). We compared the properties of q = 2 HDL with those of an analogous HDL particle labeled with Gd-chelating lipids that coordinate only one water molecule (q = 1 HDL). We found that the q = 2 HDL possessed an elevated r(1) of 41 mM(-1) s(-1) compared to 9 mM(-1) s(-1) for q = 1 HDL at 20 MHz, but the q = 2 HDL exhibited high R(2)* values at high fields, precluding imaging above 128 MHz. While carrying out this investigation we observed that enlarged, disrupted particles were formed when the synthesis was carried out above the lipid critical micelle concentration (cmc), indicating the importance of synthesis below the cmc when modifying lipoproteins in this manner. The high relaxivity of q = 2 HDL means it will be an efficacious contrast agent for future MR imaging studies.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.