Paramagnetic and fluorescent liposomes for target-specific imaging and therapy of tumor angiogenesis

Design and Application of pH-Responsive Liposomes for Site-Specific Delivery of Cytotoxin from Cobra Venom

Background

Current immunotherapies with unexpected severe side effects and treatment resistance have not resulted in the desired outcomes for patients with melanoma, and there is a need to discover more effective medications. Cytotoxin (CTX) from Cobra Venom has been established to have favorable cytolytic activity and antitumor efficacy and is regarded as a promising novel anticancer agent. However, amphiphilic CTX with excellent anionic phosphatidylserine lipid-binding ability may also damage normal cells.

Methods

We developed pH-responsive liposomes with a high CTX load (CTX@PSL) for targeted acidic-stimuli release of drugs in the tumor microenvironment. The morphology, size, zeta potential, drug-release kinetics, and preservation stability were characterized. Cell uptake, apoptosis-promoting effects, and cytotoxicity were assessed using MTT assay and flow cytometry. Finally, the tissue distribution and antitumor effects of CTX@PSL were systematically assessed using an in vivo imaging system.

Results

CTX@PSL exhibited high drug entrapment efficiency, drug loading, stability, and a rapid release profile under acidic conditions. These nanoparticles, irregularly spherical in shape and small in size, can effectively accumulate at tumor sites (six times higher than free CTX) and are rapidly internalized into cancer cells (2.5-fold higher cell uptake efficiency). CTX@PSL displayed significantly stronger cytotoxicity (IC50 0.25 μg/mL) and increased apoptosis in than the other formulations (apoptosis rate 71.78±1.70%). CTX@PSL showed considerably better tumor inhibition efficacy than free CTX or conventional liposomes (tumor inhibition rate 79.78±5.93%).

Conclusion

Our results suggest that CTX@PSL improves tumor-site accumulation and intracellular uptake for sustained and targeted CTX release. By combining the advantages of CTX and stimuli-responsive nanotechnology, the novel CTX@PSL nanoformulation is a promising therapeutic candidate for cancer treatment.

Exploring the Usability of α-MSH-SM-Liposome as an Imaging Agent to Study Biodegradable Bone Implants In Vivo

Novel biodegradable metal alloys are increasingly used as implant materials. The implantation can be accompanied by an inflammatory response to a foreign object. For studying inflammation in the implantation area, non-invasive imaging methods are needed. In vivo imaging for the implanted area and its surroundings will provide beneficiary information to understand implant-related inflammation and help to monitor it. Therefore, inflammation-sensitive fluorescent liposomes in rats were tested in the presence of an implant to evaluate their usability in studying inflammation. The sphingomyelin-containing liposomes carrying alpha-melanocyte-stimulating hormone (α-MSH)-peptide were tested in a rat bone implant model. The liposome interaction with implant material (Mg-10Gd) was analyzed with Mg-based implant material (Mg-10Gd) in vitro. The liposome uptake process was studied in the bone-marrow-derived macrophages in vitro. Finally, this liposomal tracer was tested in vivo. It was found that α-MSH coupled sphingomyelin-containing liposomes and the Mg-10Gd implant did not have any disturbing influence on each other. The clearance of liposomes was observed in the presence of an inert and biodegradable implant. The degradable Mg-10Gd was used as an alloy example; however, the presented imaging system offers a new possible use of α-MSH-SM-liposomes as tools for investigating implant responses.

Preparation of layering-structured magnetic fluorescent liposomes and labeling of HepG2 cells

BACKGROUND

At present, surgical resection and chemotherapy are still the main treatments for hepatocellular carcinoma and other cancers, but the curative effect and survival rate are not ideal.

OBJECTIVE

In this study, we aim to prepare a carrier with low toxicity, high biocompatibility and targeted transport for the treatment of hepatocellular carcinoma.

METHODS

CdSe quantum dots (QDs) modified with oleic acid were synthesized. Then hydrophobic CdSe QDs and hydrophilic super-paramagnetic Fe3O4 particles were encapsulated into different layers of liposomes to form magnetic fluorescent liposomes (MFLs). MFLs in the aqueous would quickly drift towards the external magnet and the entire process was clearly observed with fluorescence microscope. The fluorescence spectra revealed that the fluorescence properties of MFLs were similar to that of CdSe QDs.

RESULTS

QDs had an average size of 3.32 nm with good fluorescence properties. The size of MFLs was about 100 nm (transmission electron microscopy (TEM) analysis showed the average size of MFLs was about 82.8 nm and dynamic light scattering (DLS) detection showed 111.9 nm). After being cultured with MFLs for 8 h, HepG2 cells were labeled by MFLs and good fluorescence images were obtained. MTT analysis also expressed their good biocompatibility.

CONCLUSION

The prepared MFLs had multi-function and could be used as ideal drug carriers.

A Comprehensive Updated Review on Magnetic Nanoparticles in Diagnostics

Magnetic nanoparticles (MNPs) have been studied for diagnostic purposes for decades. Their high surface-to-volume ratio, dispersibility, ability to interact with various molecules and superparamagnetic properties are at the core of what makes MNPs so promising. They have been applied in a multitude of areas in medicine, particularly Magnetic Resonance Imaging (MRI). Iron oxide nanoparticles (IONPs) are the most well-accepted based on their excellent superparamagnetic properties and low toxicity. Nevertheless, IONPs are facing many challenges that make their entry into the market difficult. To overcome these challenges, research has focused on developing MNPs with better safety profiles and enhanced magnetic properties. One particularly important strategy includes doping MNPs (particularly IONPs) with other metallic elements, such as cobalt (Co) and manganese (Mn), to reduce the iron (Fe) content released into the body resulting in the creation of multimodal nanoparticles with unique properties. Another approach includes the development of MNPs using other metals besides Fe, that possess great magnetic or other imaging properties. The future of this field seems to be the production of MNPs which can be used as multipurpose platforms that can combine different uses of MRI or different imaging techniques to design more effective and complete diagnostic tests.

Intricate crosstalk between MYB and noncoding RNAs in cancer

MYB is often overexpressed in malignant tumors and plays a carcinogenic role in the initiation and development of cancer. Deletion of the MYB regulatory C-terminal domain may be a driving mutation leading to tumorigenesis, therefore, different tumor mechanisms produce similar MYB proteins. As MYB is a transcription factor, priority has been given to identifying the genes that it regulates. All previous attention has been focused on protein-coding genes. However, an increasing number of studies have suggested that MYB can affect the complexity of cancer progression by regulating tumor-associated noncoding RNAs (ncRNAs), such as microRNAs, long-non-coding RNAs and circular RNAs. ncRNAs can regulate the expression of numerous downstream genes at the transcription, RNA processing and translation levels, thereby having various biological functions. Additionally, ncRNAs play important roles in regulating MYB expression. This review focuses on the intricate crosstalk between oncogenic MYB and ncRNAs, which play a pivotal role in tumorigenesis, including proliferation, apoptosis, angiogenesis, metastasis, senescence and drug resistance. In addition, we discuss therapeutic strategies for crosstalk between MYB and ncRNAs to prevent the occurrence and development of cancer.

Noninvasive Imaging for Assessment of the Efficacy of Therapeutic Agents for Hepatocellular Carcinoma

Morphological imaging techniques are typically used in the anti-cancer drug efficacy evaluation process. However, these techniques can evaluate the therapeutic efficacy only when the tumor shows anatomic changes-usually at later stages, when the therapeutic effects are poor. In contrast, molecular imaging allows noninvasive monitoring of tumor growth, assessment of drug metabolism, and evaluation of therapeutic efficacy at the molecular and cellular levels. Multimodality molecular imaging, which combines the advantages of various imaging modalities, provides even more comprehensive therapeutic efficacy assessment in preclinical and clinical studies. This review provides an overview of molecular imaging evaluation of therapeutic efficacy of the anti-tumor drugs in hepatocellular carcinoma (HCC) both in preclinical and clinical research, which holds great promise in guiding HCC treatment into the era of precision medicine.

Detection of U-87 Tumor Cells by RGD-Functionalized/Gd-Containing Giant Unilamellar Vesicles in Magnetization Transfer Contrast Magnetic Resonance Images

OBJECTIVES

The targeting of tumor cells and their visualization with magnetic resonance imaging (MRI) is an important task in biomedicine. The low sensitivity of this technique is a significant drawback and one that may hamper the detection of the imaging reporters used.To overcome this sensitivity issue, this work explores the synergy between 2 strategies: (1) arginine, glycine, aspartic acid peptide (RGD)-functionalized giant unilamellar vesicles (GUVs) loaded with Gd complexes to accumulate large amounts of MRI contrast agent at the targeting site; and (2) the use of magnetization transfer contrast (MTC), which is a sensitive MRI technique for the detection of Gd complexes in the tumor region.

MATERIALS AND METHODS

Giant unilamellar vesicles were prepared using the gentle swelling method, and the cyclic RGD targeting moiety was introduced onto the external membrane. Paramagnetic Gd-containing complexes and the fluorescent probe rhodamine were both part of the vesicle membranes and Gd-complexes were also the payload within the inner aqueous cavity. Giant unilamellar vesicles that were loaded with the imaging reporters, but devoid of the RGD targeting moiety, were used as controls. U-87 MG human glioblastoma cells, which are known to overexpress the targets for RGD moieties, were used. In the in vivo experiments, U-87 MG cells were subcutaneously injected into nu/nu mice, and the generated tumors were imaged using MRI, 15 days after cell administration. Magnetic resonance imaging was carried out at 7 T, and T2W, T1W, and MTC/Z-spectra were acquired. Confocal microscopy images and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used for result validation.

RESULTS

In vitro results show that RGD GUVs specifically bind to U-87 MG cells. Microscopy demonstrates that (1) RGD GUVs were anchored onto the external surface of the tumor cells without any internalization; (2) a low number of GUVs per cell were clustered at specific regions; and (3) there is no evidence for macrophage uptake or cell toxicity. The MRI of cell pellets after incubation with RGD GUVs and untargeted ctrl-GUVs was performed. No difference in T1 signal was detected, whereas a 15% difference in MT contrast is present between the RGD GUV-treated cells and the ctrl-GUV-treated cells.Magnetic resonance imaging scans of tumor-bearing mice were acquired before and after (t = 0, 4 hours and 24 hours) the administration of RGD GUVs and ctrl-GUVs. A roughly 16% MTC difference between the 2 groups was observed after 4 hours. Immunofluorescence analyses and ICP-MS analyses (for Gd-detection) of the explanted tumors confirmed the specific accumulation of RGD GUVs in the tumor region.

CONCLUSIONS

RGD GUVs seem to be interesting carriers that can facilitate the specific accumulation of MRI contrast agents at the tumor region. However, the concentration achieved is still below the threshold needed for T1w-MRI visualization. Conversely, MTC proved to be sufficiently sensitive for the visualization of detectable contrast between pretargeting and posttargeting images.

Nanotechnology for angiogenesis: opportunities and challenges

Angiogenesis plays a critical role within the human body, from the early stages of life (i.e., embryonic development) to life-threatening diseases (e.g., cancer, heart attack, stroke, wound healing). Many pharmaceutical companies have expended huge efforts on both stimulation and inhibition of angiogenesis. During the last decade, the nanotechnology revolution has made a great impact in medicine, and regulatory approvals are starting to be achieved for nanomedicines to treat a wide range of diseases. Angiogenesis therapies involve the inhibition of angiogenesis in oncology and ophthalmology, and stimulation of angiogenesis in wound healing and tissue engineering. This review aims to summarize nanotechnology-based strategies that have been explored in the broad area of angiogenesis. Lipid-based, carbon-based and polymeric nanoparticles, and a wide range of inorganic and metallic nanoparticles are covered in detail. Theranostic and imaging approaches can be facilitated by nanoparticles. Many preparations have been reported to have a bimodal effect where they stimulate angiogenesis at low dose and inhibit it at higher doses.

Design and synthesis of lipid-mimetic cationic iridium complexes and their liposomal formulation for in vitro and in vivo application in luminescent bioimaging

Two iridium [Ir(N^C)₂(N^N)]⁺ complexes with the diimine N^N ligand containing a long polymethylene hydrophobic chain were synthesized and characterized by using NMR and ESI mass-spectrometry: N^N – 2-(1-hexadecyl-1H-imidazol-2-yl)pyridine, N^C – methyl-2-phenylquinoline-4-carboxylate (Ir1) and 2-phenylquinoline-4-carboxylic acid (Ir2). These complexes were used to prepare the luminescent PEGylated DPPC liposomes (DPPC/DSPE-PEG2000/Ir-complex = 95/4.5/1 mol%) using a thin film hydration method. The narrowly dispersed liposomes had diameters of about 110 nm. The photophysics of the complexes and labeled liposomes were carefully studied. Ir1 and Ir2 give red emission (λ_em = 667 and 605 nm) with a lifetime in the microsecond domain and quantum yields of 4.8% and 10.0% in degassed solution. Incorporation of the complexes into the liposome lipid bilayer results in shielding of the emitters from interaction with molecular oxygen and partial suppression of excited state nonradiative relaxation due to the effect of the relatively rigid bilayer matrix. Delivery of labeled liposomes to the cultured ARPE-19 cells demonstrated the usefulness of Ir1 and Ir2 in cellular imaging. Labeled liposomes were then injected intravitreally into rat eyes and imaged successfully with optical coherence tomography and funduscopy. In conclusion, iridium complexes enabled the successful labeling and imaging of liposomes in cells and animals.

Novel lipoidal Ir(iii) phosphorescent labels were embedded into liposomes and used for imaging in cells and animals.

Recent Advancements of Nanomedicine towards Antiangiogenic Therapy in Cancer

Angiogenesis is a process of generation of de-novo blood vessels from already existing vasculature. It has a crucial role in different physiological process including wound healing, embryonic development, and tumor growth. The methods by which therapeutic drugs inhibit tumor angiogenesis are termed as anti-angiogenesis cancer therapy. Developments of angiogenic inhibiting drugs have various limitations causing a barrier for successful treatment of cancer, where angiogenesis plays an important role. In this context, investigators developed novel strategies using nanotechnological approaches that have demonstrated inherent antiangiogenic properties or used for the delivery of antiangiogenic agents in a targeted manner. In this present article, we decisively highlight the recent developments of various nanoparticles (NPs) including liposomes, lipid NPs, protein NPs, polymer NPs, inorganic NPs, viral and bio-inspired NPs for potential application in antiangiogenic cancer therapy. Additionally, the clinical perspectives, challenges of nanomedicine, and future perspectives are briefly analyzed.

Optical and Optoacoustic Imaging

The spatiotemporal determination of molecular events and cells is important for understanding disease processes, especially in oncology, and thus for the development of novel treatments. Equally important is the knowledge of the biodistribution, localization, and targeted accumulation of novel therapies as well as monitoring of tumor growth and therapeutic response. Optical imaging provides an ideal versatile platform for imaging of all these problems and questions.

Hybrid Magnetic Nanostructures For Cancer Diagnosis And Therapy

Cancer is the second disease in the world from the point of view of mortality. The conventional routes of treatment were found to be not sufficient and thus alternative ways are imposed. The use of hybrid, magnetic nanostructures is a promising way for simultaneous targeted diagnosis and treatment of various types of cancer. For this reason, the development of core@shell structures was found to be an efficient way to develop stable, biocompatible, non-toxic carriers with shell-dependent internalization capacity in cancer cells. So, the multicomponent approach can be the most suitable way to assure the multifunctionality of these nanostructures to achieve the desired/necessary properties. The in vivo stability is mostly assured by the coating of the magnetic core with various polymers (including polyethylene glycol, silica etc.), while the targeting capacity is mostly assured by the decoration of these nanostructures with folic acid. Unfortunately, there are also some limitations related to the multilayered approach. For instance, the increasing of the thickness of layers leads to a decrease the magnetic properties, (hyperthermia and guiding ability in the magnetic field, for instance), the outer shell should contain the targeting molecules (as well as the agents helping the internalization into the cancer cells), etc.

Synthesis, Characterization, and Biomedical Applications of an Alkylated Quercetin-Gadolinium Complex

Flavonoids and their derivatives have been extensively studied for their pharmaceutical applications due to their antioxidant and anti-inflammatory properties. The coordination complexes of several flavonoids have demonstrated DNA binding ability that can confer anticancer properties. The structure of the flavonoid has a pronounced influence on its pharmacological properties. Herein we report the synthesis and characterization of alkylated quercetin and its complex with gadolinium. The structure of the complex was confirmed using spectroscopic techniques. The ability of the gadolinium-alkylated quercetin complex to serve as a magnetic contrast agent was compared with gadolinium-quercetin complex. The quercetin-gadolinium complex was found to exhibit better contrast property with a relaxivity of 0.2952 μg mL^-1 s^-1 when compared to the gadolinium complex of alkylated quercetin. This difference primarily arises due to the greater hydrophobicity of the alkylated quercetin complex that restricts access of water. However, the alkylated quercetin was found to exhibit better enzyme mimic activity as the metal ion served as a redox center that enabled quantification of hydrogen peroxide in the concentration range 50-450 μM within 5 s with a sensitivity of 64 nA/μM and limit of detection of 7.3 μM. The better sensing performance of the alkylated quercetin-gadolinium complex, reported here for the first time, when compared to quercetin-gadolinium complex can be attributed to the enhanced electroactive area on the working electrode.

Hydrophilic Quantum Dots Functionalized with Gd(III)-DO3A Monoamide Chelates as Bright and Effective T1-weighted Bimodal Nanoprobes

Magnetic resonance imaging (MRI) is a powerful non-invasive diagnostic tool that enables distinguishing healthy from pathological tissues, with high anatomical detail. Nevertheless, MRI is quite limited in the investigation of molecular/cellular biochemical events, which can be reached by fluorescence-based techniques. Thus, we developed bimodal nanosystems consisting in hydrophilic quantum dots (QDs) directly conjugated to Gd(III)-DO3A monoamide chelates, a Gd(III)-DOTA derivative, allowing for the combination of the advantages of both MRI and fluorescence-based tools. These nanoparticulate systems can also improve MRI contrast, by increasing the local concentration of paramagnetic chelates. Transmetallation assays, optical characterization, and relaxometric analyses, showed that the developed bimodal nanoprobes have great chemical stability, bright fluorescence, and high relaxivities. Moreover, fluorescence correlation spectroscopy (FCS) analysis allowed us to distinguish nanosystems containing different amounts of chelates/QD. Also, inductively coupled plasma optical emission spectrometry (ICP - OES) indicated a conjugation yield higher than 75%. Our nanosystems showed effective longitudinal relaxivities per QD and per paramagnetic ion, at least 5 times [per Gd(III)] and 100 times (per QD) higher than the r1 for Gd(III)-DOTA chelates, suitable for T1-weighted imaging. Additionally, the bimodal nanoparticles presented negligible cytotoxicity, and efficiently labeled HeLa cells as shown by fluorescence. Thus, the developed nanosystems show potential as strategic probes for fluorescence analyses and MRI, being useful for investigating a variety of biological processes.

Macromolecular Drug Carriers for Targeted Glioblastoma Therapy: Preclinical Studies, Challenges, and Future Perspectives

Glioblastoma, the most common, aggressive brain tumor, ranks among the least curable cancers-owing to its strong tendency for intracranial dissemination, high proliferation potential, and inherent tumor resistance to radiation and chemotherapy. Current glioblastoma treatment strategies are further hampered by a critical challenge: adverse, non-specific treatment effects in normal tissue combined with the inability of drugs to penetrate the blood brain barrier and reach the tumor microenvironment. Thus, the creation of effective therapies for glioblastoma requires development of targeted drug-delivery systems that increase accumulation of the drug in the tumor tissue while minimizing systemic toxicity in healthy tissues. As demonstrated in various preclinical glioblastoma models, macromolecular drug carriers have the potential to improve delivery of small molecule drugs, therapeutic peptides, proteins, and genes to brain tumors. Currently used macromolecular drug delivery systems, such as liposomes and polymers, passively target solid tumors, including glioblastoma, by capitalizing on abnormalities of the tumor vasculature, its lack of lymphatic drainage, and the enhanced permeation and retention (EPR) effect. In addition to passive targeting, active targeting approaches include the incorporation of various ligands on the surface of macromolecules that bind to cell surface receptors expressed on specific cancer cells. Active targeting approaches also utilize stimulus responsive macromolecules which further improve tumor accumulation by triggering changes in the physical properties of the macromolecular carrier. The stimulus can be an intrinsic property of the tumor tissue, such as low pH, or extrinsic, such as local application of ultrasound or heat. This review article explores current preclinical studies and future perspectives of targeted drug delivery to glioblastoma by macromolecular carrier systems, including polymeric micelles, nanoparticles, and biopolymers. We highlight key aspects of the design of diverse macromolecular drug delivery systems through a review of their preclinical applications in various glioblastoma animal models. We also review the principles and advantages of passive and active targeting based on various macromolecular carriers. Additionally, we discuss the potential disadvantages that may prevent clinical application of these carriers in targeting glioblastoma, as well as approaches to overcoming these obstacles.

A review on the role of lipid-based nanoparticles in medical diagnosis and imaging

Molecular and diagnostic imaging has been recently a subject of intense research in the treatment of numerous diseases. In medical imaging, there are different modalities with unique strengths including MRI, ultrasound imaging, computed tomography, positron emission tomography and single photon emission computed tomography. These systems need specific contrast agents to achieve a suitable image with the best quality. Nanoparticles represent an innovative tool in imaging field research and diagnostics of various diseases, especially cancerous ones. Among the nanocarriers, lipid-based nanoparticles, such as nanostructured lipid carriers, solid lipid nanoparticles and liposomes, are the most used carriers in imaging because of having many advantageous properties. This review addresses advancements in different lipid-based nanoparticles as tools in medical diagnostic and imaging.

Oxyresveratrol prevents murine H22 hepatocellular carcinoma growth and lymph node metastasis via inhibiting tumor angiogenesis and lymphangiogenesis

The purpose of this study was to investigate the effects and mechanisms of oxyresveratrol (Oxyres) on hepatocellular carcinoma (HCC) in vitro and in vivo. The MTT and Transwell assays were performed to investigate the effects of Oxyres on cell proliferation and migration of two HCC cell lines, QGY-7701 and SMMC-7721 cells. H22 cells were subcutaneously injected into hind foot pads of 70 male mice to establish a lymph node metastasis model. These mice were randomly divided into seven groups as follows, control group, HCC group, Oxyres 20 mg/kg group, Oxyres 40 mg/kg group, Oxyres 60 mg/kg group, Resveratrol (Res) group, and Adriamycin (ADM) group. Oxyres, Res, and ADM were intraperitoneally injected daily for consecutive 21 days. Tumors and popliteal lymph node were isolated and embedded for histology analysis. Expressions of CD31 and vascular endothelial growth factor receptor-3 (VEGFR3) in tumors were detected by immunohistocehmistry. Expressions of vascular endothelial growth factor C (VEGF-C) were measured by Western blot. Oxyres significantly inhibited the proliferation and migration of QGY-7701 and SMMC-7721 cells. Oxyres significantly inhibited tumor growth (p < 0.001) and metastasis to sentinel lymph nodes (70%) in a dose-dependent manner. Oxyres showed a similar inhibition rate as Res. Oxyres also significantly decreased micro-blood vessel density and micro-lymphatic vessel density in tumors (p < 0.05). Expressions of CD31, VEGFR3, and VEGF-C of tumors were also inhibited by Oxyres (p < 0.05). Oxyres exerts anti-tumor effects against HCC through inhibiting both angiogenesis and lymph node metastasis, which suggests Oxyres be a potential therapeutic agent.

Nano-sized and other improved reporters for magnetic resonance imaging of angiogenesis

Magnetic Resonance Imaging (MRI) enables to provide anatomical, functional and molecular information of pathological angiogenesis when used with properly tailored imaging probes. Functional studies have been the domain of Dynamic Contrast Enhancement (DCE) -MRI protocols from which it is possible to extract quantitative estimations on key parameters such as the volumes of vascular and extracellular compartments and the rates of the bidirectional exchange of the imaging reporters across the endothelial barrier. Whereas paramagnetic Gd-complexes able to reversibly bind to serum albumin act better than the clinically used small-sized, hydrophilic species, new findings suggest that an accurate assessment of the vascular volume is possible by analyzing images acquired upon the i.v. administration of Gd-labelled Red Blood Cells (RBCs). As far as it concerns molecular MRI, among the many available biomarkers, α_vβ₃ integrins are the most investigated ones. The low expression of these targets makes mandatory the use of nano-sized systems endowed with the proper signal enhancing capabilities. A number of targeted nano-particles have been investigated including micelles, liposomes, iron oxides and perfluorocarbon containing systems. Finally, a growing attention is devoted to the design and testing of "theranostic" agents based on the exploitation of MRI to monitor drug delivery processes and therapeutic outcome.

Surfactant-Stripped Frozen Pheophytin Micelles for Multimodal Gut Imaging

Edible, surfactant-stripped, frozen micelles are formed from pheophytin (demetallated chlorophyll), a pigment that is naturally consumed in human diets. Pheophytin nanoparticles pass completely and safely through the gastrointestinal tract and enable trimodal gut contrast imaging via photoacoustic, fluorescence, and positron emission tomography techniques.

The evolution of gadolinium based contrast agents: from single-modality to multi-modality

Gadolinium-based contrast agents are extensively used as magnetic resonance imaging (MRI) contrast agents due to their outstanding signal enhancement and ease of chemical modification. However, it is increasingly recognized that information obtained from single modal molecular imaging cannot satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research, due to its limitation and default rooted in single molecular imaging technique itself. To compensate for the deficiencies of single function magnetic resonance imaging contrast agents, the combination of multi-modality imaging has turned to be the research hotpot in recent years. This review presents an overview on the recent developments of the functionalization of gadolinium-based contrast agents, and their application in biomedicine applications.

Multimodal targeted high relaxivity thermosensitive liposome for in vivo imaging

Liposomes are spherical, self-closed structures formed by lipid bilayers that can encapsulate drugs and/or imaging agents in their hydrophilic core or within their membrane moiety, making them suitable delivery vehicles. We have synthesized a new liposome containing gadolinium-DOTA lipid bilayer, as a targeting multimodal molecular imaging agent for magnetic resonance and optical imaging. We showed that this liposome has a much higher molar relaxivities r1 and r2 compared to a more conventional liposome containing gadolinium-DTPA-BSA lipid. By incorporating both gadolinium and rhodamine in the lipid bilayer as well as biotin on its surface, we used this agent for multimodal imaging and targeting of tumors through the strong biotin-streptavidin interaction. Since this new liposome is thermosensitive, it can be used for ultrasound-mediated drug delivery at specific sites, such as tumors, and can be guided by magnetic resonance imaging.

Evaluation of GX1 and RGD-GX1 peptides as new radiotracers for angiogenesis evaluation in experimental glioma models

Gliomas are the most common type among all central nervous system tumors. The aggressiveness of gliomas is correlated with the level of angiogenesis and is often associated with prognosis. The aim of this study is to evaluate the novel GX1 peptide and the heterodimer RGD-GX1 radiolabeled with technetium-99m, for angiogenesis detection in glioma models. Radiolabeling and radiochemical controls were assessed for both radioconjugates. In vitro binding studies in glioma tumor cells were performed, as well as biodistribution in SCID mice bearing tumor cells, in order to evaluate the biological behavior and tumor uptake of the radiocomplexes. Blocking and imaging studies were also conducted. MicroSPECT/CT images were acquired in animals with experimentally implanted intracranial tumor. Open field activity was performed to evaluate behavior, as well as perfusion and histology analysis. The radiochemical purity of both radiotracers was greater than 96 %. In vitro binding studies revealed rather similar binding profi le for each molecule. The highest binding was for RGD-GX1 peptide at 120 min in U87MG cells (1.14 ± 0.35 %). Tumor uptake was also favorable for RGD-GX1 peptide in U87MG cells, reaching 2.96 ± 0.70 % at 1 h p.i. with 47 % of blocking. Imaging studies also indicated better visualization for RGD-GX1 peptide in U87MG cells. Behavior evaluation pointed brain damage and histology studies confirmed actual tumor in the uptake site. The results with the angiogenesis seeking molecule (99m)Tc-HYNIC-E-[c(RGDfk)-c(GX1)] were successful, and better than with (99m)Tc-HYNIC-PEG4-c(GX1). Future studies targeting angiogenesis in other glioma and nonglioma tumor models are recommended.

MRI-visible liposome nanovehicles for potential tumor-targeted delivery of multimodal therapies

Real-time diagnosis and monitoring of disease development, and therapeutic responses to treatment, are possible by theranostic magnetic resonance imaging (MRI). Here we report the synthesis of a multifunctional liposome, which contains Gd-DOTA (an MRI probe), paclitaxel and c(RGDyk) (a targeted peptide). This nanoparticle overcame the insolubility of paclitaxel, reduced the side effects of FDA-approved formulation of PTX-Cre (Taxol®) and improved drug delivery efficiency to the tumor. c(RGDyk) modification greatly enhanced the cytotoxicity of the drug in tumor cells A549. The T1 relaxivity in tumor cells treated with the targeted liposome formulation was increased 16-fold when compared with the non-targeted group. In vivo, the tumors in mice were visualized using T1-weighted imaging after administration of the liposome. Also the tumor growth could be inhibited well after the treatment. Fluorescence images in vitro and ex vivo also showed the targeting effect of this liposome in tumor cells, indicating that this nanovehicle could limit the off-target side effects of anticancer drugs and contrast agents. These findings lay the foundation for further tumor inhibition study and application of this delivery vehicle in cancer therapy settings.

Multifunctional calcium phosphate nanoparticles for combining near-infrared fluorescence imaging and photodynamic therapy

Photodynamic therapy (PDT) of tumors causes skin photosensitivity as a result of unspecific accumulation behavior of the photosensitizers. PDT of tumors was improved by calcium phosphate nanoparticles conjugated with (i) Temoporfin as a photosensitizer, (ii) the RGDfK peptide for favored tumor targeting and (iii) the fluorescent dye molecule DY682-NHS for enabling near-infrared fluorescence (NIRF) optical imaging in vivo. The nanoparticles were characterized with regard to size, spectroscopic properties and uptake into CAL-27 cells. The nanoparticles had a hydrodynamic diameter of approximately 200 nm and a zeta potential of around +22mV. Their biodistribution at 24h after injection was investigated via NIRF optical imaging. After treating tumor-bearing CAL-27 mice with nanoparticle-PDT, the therapeutic efficacy was assessed by a fluorescent DY-734-annexin V probe at 2 days and 2 weeks after treatment to detect apoptosis. Additionally, the contrast agent IRDye® 800CW RGD was used to assess tumor vascularization (up to 4 weeks after PDT). After nanoparticle-PDT in mice, apoptosis in the tumor was detected after 2 days. Decreases in tumor vascularization and tumor volume were detected in the next few days. Calcium phosphate nanoparticles can be used as multifunctional tools for NIRF optical imaging, PDT and tumor targeting as they exhibited a high therapeutic efficacy, being capable of inducing apoptosis and destroying tumor vascularization.

Phase separation behavior of mixed lipid systems at neutral and low pH: coarse-grained simulations with DMD/LIME

We extend LIME, an intermediate resolution, implicit solvent model for phospholipids previously used in discontinuous molecular dynamics simulations of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer formation at 325 K, to the description of the geometry and energetics of 1,2-distearoyl-sn-glycero-3-phospho-L-serine (DSPS) and 1,2-dihenarachidoyl-sn-glycero-3-phosphocholine (21PC) and mixtures thereof at both neutral and low pH at 310 K. A multiscale modeling approach is used to calculate the LIME parameters from atomistic simulation data on a mixed DPPC/DSPS system at different pH values. In the model, 17 coarse-grained sites represent DSPS and 18 coarse-grained sites represent 21PC. Each of these coarse-grained sites is classified as 1 of 9 types. LIME/DMD simulations of equimolar bilayers show the following: (1) 21PC/DSPS bilayers with and without surface area restrictions separate faster at low pH than at neutral pH, (2) 21PC/DSPS systems separate at approximately the same rate regardless of whether they are subjected to surface area restrictions, and (3) bilayers with a molar ratio of 9:1 (21PC:DSPS) phase separate to form heterogeneous domains faster at low pH than at neutral pH. Our results are consistent with experimental findings of Sofou and co-workers (Bandekar et al. Mol. Pharmaceutics, 2013, 10, 152-160; Karve et al. Biomaterials, 2010, 31, 4409-4416) that more doxorubicin is released from 21PC/DSPS liposomes at low pH than at neutral pH, presumably because greater phase separation is achieved at low pH than at neutral pH. These are the first molecular-level simulations of the phase separation in mixed lipid bilayers induced by a change in pH.

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.

Supramolecular aggregates from polyacrylates and Gd(iii)-containing cationic surfactants as high-relaxivity MRI contrast agents

The assembly behavior of narrowly dispersed poly(sodium acrylate) (PAAS) of different molecular weights with Gd(iii)-containing cationic metallosurfactants (MS) was investigated by DLS, TEM and relaxivity plotting.

Carborane–β-cyclodextrin complexes as a supramolecular connector for bioactive surfaces

The supramolecular carborane–β-cyclodextrin system allows for effective monovalent immobilization of biologically active peptides resulting in efficient cell adhesion and spreading.

Non-invasive molecular imaging for preclinical cancer therapeutic development

Molecular and non-invasive imaging are rapidly emerging fields in preclinical cancer drug discovery. This is driven by the need to develop more efficacious and safer treatments, the advent of molecular-targeted therapeutics, and the requirements to reduce and refine current preclinical in vivo models. Such bioimaging strategies include MRI, PET, single positron emission computed tomography, ultrasound, and optical approaches such as bioluminescence and fluorescence imaging. These molecular imaging modalities have several advantages over traditional screening methods, not least the ability to quantitatively monitor pharmacodynamic changes at the cellular and molecular level in living animals non-invasively in real time. This review aims to provide an overview of non-invasive molecular imaging techniques, highlighting the strengths, limitations and versatility of these approaches in preclinical cancer drug discovery and development.

Nanotechnology applications in diagnosis and treatment of metastasis

The lethality of solid tumors is in large part dependent on their ability to metastasize through hematologic and lymphatic transport pathways. The dissemination of cancer cells from the primary tumor to undergo transport, their ability to survive in transit and then to subsequently form metastatic colonies, is facilitated by a complex concert of signaling pathways and cell–cell and cell–matrix interactions. Elucidating these mechanistic components is highly valuable to guide the development of technologies for efficiently detecting and treating metastasis. To this end, in recent years nanotechnology approaches have provided several unique detection, characterization and treatment strategies. The current article will review these approaches to discuss their promise and challenges, specifically in metastatic cancer, above and beyond the usual nanomedicine applications in cancer therapy.

Molecular imaging of angiogenesis to delineate the tumor margins in glioma rat model with endoglin-targeted paramagnetic liposomes using 3T MRI

PURPOSE

To evaluate the use of endoglin-targeted paramagnetic liposomes in delineating the glioma margins using magnetic resonance (MR) angiogenesis imaging in a rat model.

MATERIALS AND METHODS

Four liposome preparations, including nontargeted paramagnetic liposomes (Gd-SLs), isotype control IgG-coupled paramagnetic liposomes (IgG-Gd-SLs), endoglin monoclonal antibody coupled paramagnetic liposomes (MAb-Gd-SLs), and biotinylated antibodies (Bio-MAb)/streptavidin-coupled paramagnetic liposomes (SAv-Gd-SLs) for two-step pretargeting imaging, were formulated. All animal experiments were carried out with the approval of the Shanghai Animal Care. C6 glioma-bearing Sprague-Dawley rats were intravenously injected with gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) or the previously mentioned liposomes (n = 5) and imaged with MR. T1 -weighted MRI was performed before and dynamically repeated after different contrast agents were injected. The enhancement features of the tumors were compared.

RESULTS

The signal enhancement of the tumor in the two-step pretargeting group increased by 117.9 ± 5.3% at the periphery and 109.2 ± 3.5% in the center (P = 0.032) at the 8-hour timepoint after SAv-Gd-SLs injection. Ring-like enhancement margins were demonstrated at the periphery of the tumor in the two-step targeted group. The specificity of the targeted liposomes was supported by the competitive study. The signal of peak enhancement using MAb-Gd-SLs was 59% less than that of the two-step group and only slightly higher than the non-targeted groups.

CONCLUSION

The two-step endoglin-targeted imaging using biotin-streptavidin interaction was demonstrated to induce intense enhancement of the tumor periphery, which implies that this advanced MR molecular contrast agent may be suitable for accurately delineating glioma tumor margins. J. Magn. Reson. Imaging 2015;41:1056-1064. © 2014 Wiley Periodicals, Inc.

A diaCEST MRI approach for monitoring liposomal accumulation in tumors

Nanocarrier-based chemotherapy allows preferential delivery of therapeutics to tumors and has been found to improve the efficacy of cancer treatment. However, difficulties in tracking nanocarriers and evaluating their pharmacological fates in patients have limited judicious selection of patients to those who might most benefit from nanotherapeutics. To enable the monitoring of nanocarriers in vivo, we developed MRI-traceable diamagnetic Chemical Exchange Saturation Transfer (diaCEST) liposomes. The diaCEST liposomes were based on the clinical formulation of liposomal doxorubicin (i.e. DOXIL®) and were loaded with barbituric acid (BA), a small, organic, biocompatible diaCEST contrast agent. The optimized diaCEST liposomal formulation with a BA-to-lipid ratio of 25% exhibited 30% contrast enhancement at B1=4.7μT in vitro. The contrast was stable, with ~80% of the initial CEST signal sustained over 8h in vitro. We used the diaCEST liposomes to monitor the response to tumor necrosis factor-alpha (TNF-α), an agent in clinical trials that increases vascular permeability and uptake of nanocarriers into tumors. After systemic administration of diaCEST liposomes to mice bearing CT26 tumors, we found an average diaCEST contrast at the BA frequency (5ppm) of 0.4% at B1=4.7μT while if TNF-α was co-administered the contrast increased to 1.5%. This novel approach provides a non-radioactive, non-metallic, biocompatible, semi-quantitative, and clinically translatable approach to evaluate the tumor targeting of stealth liposomes in vivo, which may enable personalized nanomedicine.

Molecular imaging of tumor-associated angiogenesis using a novel magnetic resonance imaging contrast agent targeting αvβ 3 integrin

BACKGROUND

The recent introduction of biological anticancer therapy has renewed the interest in functional imaging of tumor-associated angiogenesis (TAA) as a tool to monitor early therapy response. The present study evaluated imaging of TAA using P1227, a novel, small molecular magnetic resonance imaging (MRI) probe targeting αvβ3 integrin.

METHODS

HT29 human colorectal cancers were grown in athymic mice. Dynamic MRI was performed using a three-dimensional VIBE sequence up to 110 min after injection of P1227 or gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA). Specificity was assessed by using P1227 1 h after intravenous administration of the αvβ3 inhibitor cilengitide. Regions of interest were drawn encompassing the tumor rim and normal muscle. Imaging data were compared with microvessel density and αvβ3 expression.

RESULTS

Using P1227, specific enhancement of the angiogenic tumor rim, but not of normal muscle, was observed, whereas Gd-DOTA enhanced tumor and normal muscle. After administering cilengitide, enhancement with P1227, but not with DOTA, was significantly suppressed during the first 20 min. When using P1227, a significant correlation was observed between normalized enhancement of the tumor rim and immunohistochemical αvβ3 integrin expression.

CONCLUSIONS

Molecular MRI using a small monogadolinated tracer targeting αvβ3 integrin and moderate magnetic field strength holds promise in assessing colorectal TAA.

Accumulation of nano-sized particles in a murine model of angiogenesis

PURPOSE

To evaluate the ability of nm-scaled iron oxide particles conjugated with Azure A, a classic histological dye, to accumulate in areas of angiogenesis in a recently developed murine angiogenesis model.

MATERIALS AND METHODS

We characterised the Azure A particles with regard to their hydrodynamic size, zeta potential, and blood circulation half-life. The particles were then investigated by Magnetic Resonance Imaging (MRI) in a recently developed murine angiogenesis model along with reference particles (Ferumoxtran-10) and saline injections.

RESULTS

The Azure A particles had a mean hydrodynamic diameter of 51.8 ± 43.2 nm, a zeta potential of -17.2 ± 2.8 mV, and a blood circulation half-life of 127.8 ± 74.7 min. Comparison of MR images taken pre- and 24-h post-injection revealed a significant increase in R2(*) relaxation rates for both Azure A and Ferumoxtran-10 particles. No significant difference was found for the saline injections. The relative increase was calculated for the three groups, and showed a significant difference between the saline group and the Azure A group, and between the saline group and the Ferumoxtran-10 group. However, no significant difference was found between the two particle groups.

CONCLUSION

Ultrahigh-field MRI revealed localisation of both types of iron oxide particles to areas of neovasculature. However, the Azure A particles did not show any enhanced accumulation relative to Ferumoxtran-10, suggesting the accumulation in both cases to be passive.

Tumor targeting and imaging with dual-peptide conjugated multifunctional liposomal nanoparticles

BACKGROUND

The significant progress in nanotechnology provides a wide spectrum of nanosized material for various applications, including tumor targeting and molecular imaging. The aim of this study was to evaluate multifunctional liposomal nanoparticles for targeting approaches and detection of tumors using different imaging modalities. The concept of dual-targeting was tested in vitro and in vivo using liposomes derivatized with an arginine-glycine-aspartic acid (RGD) peptide binding to αvβ3 integrin receptors and a substance P peptide binding to neurokinin-1 receptors.

METHODS

For liposome preparation, lipids, polyethylene glycol building blocks, DTPA-derivatized lipids for radiolabeling, lipid-based RGD and substance P building blocks and imaging labels were combined in defined molar ratios. Liposomes were characterized by photon correlation spectroscopy and zeta potential measurements, and in vitro binding properties were tested using fluorescence microscopy. Standardized protocols for radiolabeling were developed to perform biodistribution and micro-single photon emission computed tomography/computed tomography (SPECT/CT) studies in nude mice bearing glioblastoma and/or melanoma tumor xenografts. Additionally, an initial magnetic resonance imaging study was performed.

RESULTS

Liposomes were radiolabeled with high radiochemical yields. Fluorescence microscopy showed specific cellular interactions with RGD-liposomes and substance P-liposomes. Biodistribution and micro-SPECT/CT imaging of (111)In-labeled liposomal nanoparticles revealed low tumor uptake, but in a preliminary magnetic resonance imaging study with a single-targeted RGD-liposome, uptake in the tumor xenografts could be visualized.

CONCLUSION

The present study shows the potential of liposomes as multifunctional targeted vehicles for imaging of tumors combining radioactive, fluorescent, and magnetic resonance signaling. Specific in vitro tumor targeting by fluorescence microscopy and radioactivity was achieved. However, biodistribution studies in an animal tumor model revealed only moderate tumor uptake and no additive effect using a dual-targeting approach.

Passive targeting of lipid-based nanoparticles to mouse cardiac ischemia-reperfusion injury

Reperfusion therapy is commonly applied after a myocardial infarction. Reperfusion, however, causes secondary damage. An emerging approach for treatment of ischemia-reperfusion (IR) injury involves the delivery of therapeutic nanoparticles to the myocardium to promote cell survival and constructively influence scar formation and myocardial remodeling. The aim of this study was to provide detailed understanding of the in vivo accumulation and distribution kinetics of lipid-based nanoparticles (micelles and liposomes) in a mouse model of acute and chronic IR injury. Both micelles and liposomes contained paramagnetic and fluorescent lipids and could therefore be visualized with magnetic resonance imaging (MRI) and confocal laser scanning microscopy (CLSM). In acute IR injury both types of nanoparticles accumulated massively and specifically in the infarcted myocardium as revealed by MRI and CLSM. Micelles displayed faster accumulation kinetics, probably owing to their smaller size. Liposomes occasionally co-localized with vessels and inflammatory cells. In chronic IR injury only minor accumulation of micelles was observed with MRI. Nevertheless, CLSM revealed specific accumulation of both micelles and liposomes in the infarct area 3 h after administration. Owing to their specific accumulation in the infarcted myocardium, lipid-based micelles and liposomes are promising vehicles for (visualization of) drug delivery in myocardial infarction.

Paramagnetic liposomes for molecular MRI and MRI-guided drug delivery

Liposomes are a versatile class of nanoparticles with tunable properties, and multiple liposomal drug formulations have been clinically approved for cancer treatment. In recent years, an extensive library of gadolinium (Gd)-containing liposomal MRI contrast agents has been developed for molecular and cellular imaging of disease-specific markers and for image-guided drug delivery. This review discusses the advances in the development and novel applications of paramagnetic liposomes in molecular and cellular imaging, and in image-guided drug delivery. A high targeting specificity has been achieved in vitro using ligand-conjugated paramagnetic liposomes. On targeting of internalizing cell receptors, the effective longitudinal relaxivity r1 of paramagnetic liposomes is modulated by compartmentalization effects. This provides unique opportunities to monitor the biological fate of liposomes. In vivo contrast-enhanced MRI studies with nontargeted liposomes have shown the extravasation of liposomes in diseases associated with endothelial dysfunction, such as tumors and myocardial infarction. The in vivo use of targeted paramagnetic liposomes has facilitated the specific imaging of pathophysiological processes, such as angiogenesis and inflammation. Paramagnetic liposomes loaded with drugs have been utilized for therapeutic interventions. MR image-guided drug delivery using such liposomes allows the visualization and quantification of local drug delivery.

A concise review of magnetic resonance molecular imaging of tumor angiogenesis by targeting integrin αvβ3 with magnetic probes

Angiogenesis is an essential step for the growth and spread of malignant tumors. Accurate detection and quantification of tumor angiogenesis is important for early diagnosis of cancers as well as post therapy assessment of antiangiogenic drugs. The cell adhesion molecule integrin αvβ3 is a specific marker of angiogenesis, which is highly expressed on activated and proliferating endothelial cells, but generally not on quiescent endothelial cells. Therefore, in recent years, many different approaches have been developed for imaging αvβ3 expression, for the detection and characterization of tumor angiogenesis. The present review provides an overview of the current status of magnetic resonance molecular imaging of integrin αvβ3, including the new development of high sensitive contrast agents and strategies for improving the specificity of targeting probes and the biological effects of imaging probes on αvβ3 positive cells.

Design and Application of Magnetic-based Theranostic Nanoparticle Systems

Recently, magnetic-based theranostic nanoparticle (MBTN) systems have been studied, researched, and applied extensively to detect and treat various diseases including cancer. Theranostic nanoparticles are advantageous in that the diagnosis and treatment of a disease can be performed in a single setting using combinational strategies of targeting, imaging, and/or therapy. Of these theranostic strategies, magnetic-based systems containing magnetic nanoparticles (MNPs) have gained popularity because of their unique ability to be used in magnetic resonance imaging, magnetic targeting, hyperthermia, and controlled drug release. To increase their effectiveness, MNPs have been decorated with a wide variety of materials to improve their biocompatibility, carry therapeutic payloads, encapsulate/bind imaging agents, and provide functional groups for conjugation of biomolecules that provide receptor-mediated targeting of the disease. This review summarizes recent patents involving various polymer coatings, imaging agents, therapeutic agents, targeting mechanisms, and applications along with the major requirements and challenges faced in using MBTN for disease management.

Multifunctional magnetic resonance imaging probes

Magnetic resonance imaging (MRI) is a key imaging modality in cancer diagnostics and therapy monitoring. MRI-based tumor detection and characterization is commonly achieved by exploiting the compositional, metabolic, cellular, and vascular differences between malignant and healthy tissue. Contrast agents are frequently applied to enhance this contrast. The last decade has witnessed an increasing interest in novel multifunctional MRI probes. These multifunctional constructs, often of nanoparticle design, allow the incorporation of multiple imaging agents for complementary imaging modalities as well as anti-cancer drugs for therapeutic purposes. The composition, size, and surface properties of such constructs can be tailored as to improve biodistribution and ensure optimal delivery to the tumor microenvironment by passive or targeted mechanisms. Multifunctional MRI probes hold great promise to facilitate more specific tumor diagnosis, patient-specific treatment planning, the monitoring of local drug delivery, and the early evaluation of therapy. This chapter reviews the state-of-the-art and new developments in the application of multifunctional MRI probes in oncology.

Incorporation of paramagnetic, fluorescent and PET/SPECT contrast agents into liposomes for multimodal imaging

A series of metal-chelating lipid conjugates has been designed and synthesized. Each member of the series bears a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) macrocycle attached to the lipid head group, using short n-ethylene glycol (n-EG) spacers of varying length. Liposomes incorporating these lipids, chelated to Gd(3+), (64)Cu(2+), or (111)In(3+), and also incorporating fluorescent lipids, have been prepared, and their application in optical, magnetic resonance (MR) and single-photon emission tomography (SPECT) imaging of cellular uptake and distribution investigated in vitro and in vivo. We have shown that these multimodal liposomes can be used as functional MR contrast agents as well as radionuclide tracers for SPECT, and that they can be optimized for each application. When shielded liposomes were formulated incorporating 50% of a lipid with a short n-EG spacer, to give nanoparticles with a shallow but even coverage of n-EG, they showed good cellular internalization in a range of tumour cells, compared to the limited cellular uptake of conventional shielded liposomes formulated with 7% 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethyleneglycol)(2000)] (DSPE-PEG2000). Moreover, by matching the depth of n-EG coverage to the length of the n-EG spacers of the DOTA lipids, we have shown that similar distributions and blood half lives to DSPE-PEG2000-stabilized liposomes can be achieved. The ability to tune the imaging properties and distribution of these liposomes allows for the future development of a flexible tri-modal imaging agent.

Functional imaging in adult and paediatric brain tumours

Imaging is a key component in the management of brain tumours, with MRI being the preferred modality for most clinical scenarios. However, although conventional MRI provides mainly structural information, such as tumour size and location, it leaves many important clinical questions, such as tumour type, aggressiveness and prognosis, unanswered. An increasing number of studies have shown that additional information can be obtained using functional imaging methods (which probe tissue properties), and that these techniques can give key information of clinical importance. These techniques include diffusion imaging, which can assess tissue structure, and perfusion imaging and magnetic resonance spectroscopy, which measures tissue metabolite profiles. Tumour metabolism can also be investigated using PET, with 18F-deoxyglucose being the most readily available tracer. This Review discusses these methods and the studies that have investigated their clinical use. A strong emphasis is placed on the measurement of quantitative parameters, which is a move away from the qualitative nature of conventional radiological reporting and presents major challenges, particularly for multicentre studies.

Internalization of paramagnetic phosphatidylserine-containing liposomes by macrophages

Background

Inflammation plays an important role in many pathologies, including cardiovascular diseases, neurological conditions and oncology, and is considered an important predictor for disease progression and outcome. In vivo imaging of inflammatory cells will improve diagnosis and provide a read-out for therapy efficacy. Paramagnetic phosphatidylserine (PS)-containing liposomes were developed for magnetic resonance imaging (MRI) and confocal microscopy imaging of macrophages. These nanoparticles also provide a platform to combine imaging with targeted drug delivery.

Results

Incorporation of PS into liposomes did not affect liposomal size and morphology up to 12 mol% of PS. Liposomes containing 6 mol% of PS showed the highest uptake by murine macrophages, while only minor uptake was observed in endothelial cells. Uptake of liposomes containing 6 mol% of PS was dependent on the presence of Ca²⁺ and Mg²⁺. Furthermore, these 6 mol% PS-containing liposomes were mainly internalized into macrophages, whereas liposomes without PS only bound to the macrophage cell membrane.

Conclusions

Paramagnetic liposomes containing 6 mol% of PS for MR imaging of macrophages have been developed. In vitro these liposomes showed specific internalization by macrophages. Therefore, these liposomes might be suitable for in vivo visualization of macrophage content and for (visualization of) targeted drug delivery to inflammatory cells.