肽基生物可激活的活体自组装纳米材料及生物医学应用

在生理环境下原位构筑自组装纳米材料,由于其生物体内的可控性、相容性及功能性优势,在临床应用方面具有广泛前景.利用病理条件在体内触发响应,能够在多重弱键相互作用下自发形成高级有序结构.其中内源性组装触发因素,如酶、pH、活性氧和配受体相互作用等,通过生物可激活的体内自组装(bioactivated in vivo ass...     

Acetazolamide-based [18F]-PET tracer: In vivo validation of carbonic anhydrase IX as a sole target for imaging of CA-IX expressing hypoxic solid tumors

Carbonic anhydrase IX is overexpressed in many solid tumors including hypoxic tumors and is a potential target for cancer therapy and diagnosis. Reported imaging agents targeting CA-IX are successful mostly in clear cell renal carcinoma as SKRC-52 and no candidate was approved yet in clinical trials for imaging of CA-IX. To validate CA-IX as a valid target for imaging of hypoxic tumor, we designed and synthesized novel [¹⁸F]-PET tracer (1) based on acetazolamide which is one of the well-known CA-IX inhibitors and performed imaging study in CA-IX expressing hypoxic tumor model as 4T1 and HT-29 in vivo models other than SKRC-52. [¹⁸F]-acetazolamide (1) was found to be insufficient for the specific accumulation in CA-IX expressing tumor. This study might be useful to understand in vivo behavior of acetazolamide PET tracer and can contribute to the development of successful PET imaging agents targeting CA-IX in future. Additional study is needed to understand the mechanism of poor targeting of CA-IX, as if CA-IX is not reliable as a sole target for imaging of CA-IX expressing hypoxic solid tumors.     

The Bioconjugation and Radiosynthesis of 89Zr-DFO-labeled Antibodies

The exceptional affinity, specificity, and selectivity of antibodies make them extraordinarily attractive vectors for tumor-targeted PET radiopharmaceuticals. Due to their multi-day biological half-life, antibodies must be labeled with positron-emitting radionuclides with relatively long physical decay half-lives. Traditionally, the positron-emitting isotopes ¹²⁴I (t_1/2 = 4.18 d), ⁸⁶Y (t_1/2 = 14.7 hr), and ⁶⁴Cu (t_1/2 = 12.7 hr) have been used to label antibodies for PET imaging. More recently, however, the field has witnessed a dramatic increase in the use of the positron-emitting radiometal ⁸⁹Zr in antibody-based PET imaging agents. ⁸⁹Zr is a nearly ideal radioisotope for PET imaging with immunoconjugates, as it possesses a physical half-life (t_1/2 = 78.4 hr) that is compatible with the in vivo pharmacokinetics of antibodies and emits a relatively low energy positron that produces high resolution images. Furthermore, antibodies can be straightforwardly labeled with ⁸⁹Zr using the siderophore-derived chelator desferrioxamine (DFO). In this protocol, the prostate-specific membrane antigen targeting antibody J591 will be used as a model system to illustrate (1) the bioconjugation of the bifunctional chelator DFO-isothiocyanate to an antibody, (2) the radiosynthesis and purification of a ⁸⁹Zr-DFO-mAb radioimmunoconjugate, and (3) in vivo PET imaging with an ⁸⁹Zr-DFO-mAb radioimmunoconjugate in a murine model of cancer.     

Au nanostructures: an emerging prospect in cancer theranostics

Au nanoparticles have been used in biomedical applications since ancient times. However, the rapid development of nanotechnology over the past century has led to recognition of the great potential of Au nanoparticles in a wide range of applications. Advanced fabrication techniques allow us to synthesize a variety of Au nanostructures possessing physiochemical properties that can be exploited for different purposes. Functionalization of the surface of Au nanoparticles further eases their application in various roles. These advantages of Au nanoparticles make them particularly suited for cancer treatment and diagnosis. The small size of Au particles enables them to preferentially accumulate at tumor sites to achieve in vivo targeting after systemic administration. Efficient light absorption followed by rapid heat conversion makes them very promising in photothermal therapy. The facile surface chemistry of Au nanoparticles eases delivery of drugs, ligands or imaging contrast agents in vivo. In this review, we summarize recent development of Au nanoparticles in cancer theranostics including imaging-based detection, photothermal therapy, chemical therapy and drug delivery. The multifunctional nature of Au nanoparticles means they hold great promise as novel anti-cancer therapeutics.     

Biofunctionalized Prussian Blue Nanoparticles for Multimodal Molecular Imaging Applications

Multimodal, molecular imaging allows the visualization of biological processes at cellular, subcellular, and molecular-level resolutions using multiple, complementary imaging techniques. These imaging agents facilitate the real-time assessment of pathways and mechanisms in vivo, which enhance both diagnostic and therapeutic efficacy. This article presents the protocol for the synthesis of biofunctionalized Prussian blue nanoparticles (PB NPs) - a novel class of agents for use in multimodal, molecular imaging applications. The imaging modalities incorporated in the nanoparticles, fluorescence imaging and magnetic resonance imaging (MRI), have complementary features. The PB NPs possess a core-shell design where gadolinium and manganese ions incorporated within the interstitial spaces of the PB lattice generate MRI contrast, both in T₁ and T₂-weighted sequences. The PB NPs are coated with fluorescent avidin using electrostatic self-assembly, which enables fluorescence imaging. The avidin-coated nanoparticles are modified with biotinylated ligands that confer molecular targeting capabilities to the nanoparticles. The stability and toxicity of the nanoparticles are measured, as well as their MRI relaxivities. The multimodal, molecular imaging capabilities of these biofunctionalized PB NPs are then demonstrated by using them for fluorescence imaging and molecular MRI in vitro.     

Split-Cre Complementation Indicates Coincident Activity of Different Genes In Vivo

Cre/LoxP recombination is the gold standard for conditional gene regulation in mice in vivo. However, promoters driving the expression of Cre recombinase are often active in a wide range of cell types and therefore unsuited to target more specific subsets of cells. To overcome this limitation, we designed inactive “split-Cre” fragments that regain Cre activity when overlapping co-expression is controlled by two different promoters. Using transgenic mice and virus-mediated expression of split-Cre, we show that efficient reporter gene activation is achieved in vivo. In the brain of transgenic mice, we genetically defined a subgroup of glial progenitor cells in which the Plp1- and the Gfap-promoter are simultaneously active, giving rise to both astrocytes and NG2-positive glia. Similarly, a subset of interneurons was labelled after viral transfection using Gad67- and Cck1 promoters to express split-Cre. Thus, split-Cre mediated genomic recombination constitutes a powerful spatial and temporal coincidence detector for in vivo targeting.     

“Velcro” Engineering of High Affinity CD47 Ectodomain as Signal Regulatory Protein α (SIRPα) Antagonists That Enhance Antibody-dependent Cellular Phagocytosis

CD47 is a cell surface protein that transmits an anti-phagocytic signal, known as the “don''t-eat-me” signal, to macrophages upon engaging its receptor signal regulatory protein α (SIRPα). Molecules that antagonize the CD47-SIRPα interaction by binding to CD47, such as anti-CD47 antibodies and the engineered SIRPα variant CV1, have been shown to facilitate macrophage-mediated anti-tumor responses. However, these strategies targeting CD47 are handicapped by large antigen sinks in vivo and indiscriminate cell binding due to ubiquitous expression of CD47. These factors reduce bioavailability and increase the risk of toxicity. Here, we present an alternative strategy to antagonize the CD47-SIRPα pathway by engineering high affinity CD47 variants that target SIRPα, which has restricted tissue expression. CD47 proved to be refractive to conventional affinity maturation techniques targeting its binding interface with SIRPα. Therefore, we developed a novel engineering approach, whereby we augmented the existing contact interface via N-terminal peptide extension, coined “Velcro” engineering. The high affinity variant (Velcro-CD47) bound to the two most prominent human SIRPα alleles with greatly increased affinity relative to wild-type CD47 and potently antagonized CD47 binding to SIRPα on human macrophages. Velcro-CD47 synergizes with tumor-specific monoclonal antibodies to enhance macrophage phagocytosis of tumor cells in vitro, with similar potency as CV1. Finally, Velcro-CD47 interacts specifically with a subset of myeloid-derived cells in human blood, whereas CV1 binds all myeloid, lymphoid, and erythroid populations interrogated. This is consistent with the restricted expression of SIRPα compared with CD47. Herein, we have demonstrated that “Velcro” engineering is a powerful protein-engineering tool with potential applications to other systems and that Velcro-CD47 could be an alternative adjuvant to CD47-targeting agents for cancer immunotherapy.     

Validation of Nanobody and Antibody Based In Vivo Tumor Xenograft NIRF-imaging Experiments in Mice Using Ex Vivo Flow Cytometry and Microscopy

This protocol outlines the steps required to perform ex vivo validation of in vivo near-infrared fluorescence (NIRF) xenograft imaging experiments in mice using fluorophore labelled nanobodies and conventional antibodies.First we describe how to generate subcutaneous tumors in mice, using antigen-negative cell lines as negative controls and antigen-positive cells as positive controls in the same mice for intraindividual comparison. We outline how to administer intravenously near-infrared fluorophore labelled (AlexaFluor680) antigen-specific nanobodies and conventional antibodies. In vivo imaging was performed with a small-animal NIRF-Imaging system. After the in vivo imaging experiments the mice were sacrificed. We then describe how to prepare the tumors for parallel ex vivo analyses by flow cytometry and fluorescence microscopy to validate in vivo imaging results.The use of the near-infrared fluorophore labelled nanobodies allows for non-invasive same day imaging in vivo. Our protocols describe the ex vivo quantification of the specific labeling efficiency of tumor cells by flow cytometry and analysis of the distribution of the antibody constructs within the tumors by fluorescence microscopy. Using near-infrared fluorophore labelled probes allows for non-invasive, economical in vivo imaging with the unique ability to exploit the same probe without further secondary labelling for ex vivo validation experiments using flow cytometry and fluorescence microscopy.     

The Practicality of Mesoporous Silica Nanoparticles as Drug Delivery Devices and Progress Toward This Goal

Mesoporous silica nanoparticles (MSNs) have been proposed as drug delivery devices for approximately 15 years. The history of in vitro studies has been promising, demonstrating that MSNs have the capability for stimulus-responsive controlled release, good cellular uptake, cell specific targeting, and the ability to carry a variety of cargoes from hydrophobic drug molecules to imaging agents. However, the translation of the in vitro findings to in vivo conditions has been slow. Herein, we review the current state-of-the-art in the use of MSN for systemic drug delivery in vivo and provide critical insight into the future of MSNs as systemic drug delivery devices and directions that should be undertaken to improve their practicality.     

In vivo uses of aptamers selected against cell surface biomarkers for therapy and molecular imaging

Nucleic acid Aptamers are ligands that are selected by a process of molecular evolution to bind with high affinities and specificities to a specific target. Recently, an increasing number of aptamers have been selected against biomarkers expressed at the surface of human cells or infectious pathogens. This class of targets, mostly proteins, is associated with several pathologies including cancer, inflammation and infection diseases. Several of these cell surface specific aptamers were tested in vivo as drugs or as targeting agents for nanocarriers, siRNA or contrast agents. Strikingly, they were used to develop a wide variety of new treatments or new approaches for molecular imaging and they were also able to improve current therapies such as chemotherapy, radiotherapy or immunotherapy. This review presents these different applications and the different studies conducted in vivo with this class of aptamers, predominantly in pre-clinical models.     

Agents described in the Molecular Imaging and Contrast Agent Database for imaging carbonic anhydrase IX expression

Abstract

Carbonic anhydrase IX (CA IX) is selectively expressed in a range of hypoxic tumours and is a validated endogenous hypoxia marker with prognostic significance; hence, CA IX is of great interest as a molecular imaging target in oncology. In this review, we present an overview of the different imaging agents and imaging modalities that have been applied for the in vivo detection of CA IX. The imaging agents reviewed are all entries in the Molecular Imaging and Contrast Agent Database (MICAD) and comprise antibody, antibody fragments and small molecule imaging agents. The effectiveness of these agents for imaging CA IX in vivo gave variable performance; however, a number of agents proved very capable. As molecular imaging has become indispensable in current medical practice we anticipate that the clinical significance of CA IX will see continued development and improvements in imaging agents for targeting this enzyme.     

Folate/NIR 797-Conjugated Albumin Magnetic Nanospheres: Synthesis,Characterisation, and In Vitro and In Vivo Targeting Evaluation

A practical and effective strategy for synthesis of Folate-NIR 797-conjugated Magnetic Albumin Nanospheres (FA-NIR 797-MAN) was developed. For this strategy, Magnetic Albumin Nanospheres (MAN), composed of superparamagnetic iron oxide nanoparticles (SPIONs) and bovine serum albumin (BSA), were covalently conjugated with folic acid (FA) ligands to enhance the targeting capability of the particles to folate receptor (FR) over-expressing tumours. Subsequently, a near-infrared (NIR) fluorescent dye NIR 797 was conjugated with FA-conjugated MAN for in vivo fluorescence imaging. The FA-NIR 797-MAN exhibited low toxicity to a human nasopharyngeal epidermal carcinoma cell line (KB cells). Additionally, in vitro and in vivo evaluation of the dynamic behaviour and targeting ability of FA-NIR 797-MAN to KB tumours validated the highly selective affinity of FA-NIR 797-MAN for FR-positive tumours. In summary, the FA-NIR 797-MAN prepared here exhibited great potential for tumour imaging, since the near-infrared fluorescence contrast agents target cells via FR-mediated endocytosis. The high fluorescence intensity together with the targeting effect makes FA-NIR 797-MAN a promising candidate for imaging, monitoring, and early diagnosis of cancer at the molecular and cellular levels.     

Development of Human-Like scFv-Fc Neutralizing Botulinum Neurotoxin E

BackgroundBotulinum neurotoxins (BoNTs) are considered to be the most toxic substances known on earth and are responsible for human botulism, a life-threatening disease characterized by flaccid muscle paralysis that occurs naturally by food-poisoning or colonization of the gastrointestinal tract by BoNT-producing clostridia. BoNTs have been classified as category A agent by the Centers of Disease Control and Prevention (CDC) and are listed among the six agents with the highest risk to be used as bioweapons. Neutralizing antibodies are required for the development of effective anti-botulism therapies to deal with the potential risk of exposure.ResultsIn this study, a macaque (Macaca fascicularis) was immunized with recombinant light chain of BoNT/E3 and an immune phage display library was constructed. After a multi-step panning, several antibody fragments (scFv, single chain fragment variable) with nanomolar affinities were isolated, that inhibited the endopeptidase activity of pure BoNT/E3 in vitro by targeting its light chain. Furthermore, three scFv were confirmed to neutralize BoNT/E3 induced paralysis in an ex vivo mouse phrenic nerve-hemidiaphragm assay. The most effective neutralization (20LD₅₀/mL, BoNT/E3) was observed with scFv ELC18, with a minimum neutralizing concentration at 0.3 nM. Furthermore, ELC18 was highly effective in vivo when administered as an scFv-Fc construct. Complete protection of 1LD₅₀ BoNT/E3 was observed with 1.6 ng/dose in the mouse flaccid paralysis assay.ConclusionThese scFv-Fcs antibodies are the first recombinant antibodies neutralizing BoNT/E by targeting its light chain. The human-like nature of the isolated antibodies is predicting a good tolerance for further clinical development.     

A Neutralization Epitope in the Hepatitis C Virus E2 Glycoprotein Interacts with Host Entry Factor CD81

The identification of a specific immunogenic candidate that will effectively activate the appropriate pathway for neutralizing antibody production is fundamental for vaccine design. By using a monoclonal antibody (1H8) that neutralizes HCV in vitro, we have demonstrated here that 1H8 recognized an epitope mapped between residues A524 and W529 of the E2 protein. We also found that the epitope residues A524, P525, Y527 and W529 were crucial for antibody binding, while the residues T526, Y527 and W529 within the same epitope engaged in the interaction with the host entry factor CD81. Furthermore, we detected “1H8-like” antibodies, defined as those with amino acid-specificity similar to 1H8, in the plasma of patients with chronic HCV infection. The time course study of plasma samples from Patient H, a well-characterized case of post-transfusion hepatitis C, showed that “1H8-like” antibodies could be detected in a sample collected almost two years after the initial infection, thus confirming the immunogenicity of this epitope in vivo. The characterization of this neutralization epitope with a function in host entry factor CD81 interaction should enhance our understanding of antibody-mediated neutralization of HCV infections.     

Imaging gene expression in the brain with peptide nucleic acid (PNA) antisense radiopharmaceuticals and drug targeting technology

Antisense oligomers are potential pharmaceutical and radiopharmaceutical agents that can be used to modulate and image gene expression. Progress with in vivogene targeting using antisense-based therapeutics has been slower than expected during the last decade, owing to poor trans-cellular delivery of antisense agents. This chapter suggests that if antisense pharmacology is merged with drug targeting technology, then membrane barriers can be circumvented and antisense agents can be delivered to tissues in vivo. Without the application of drug targeting, the likelihood of success for an antisense drug development program is low, particularly for the brain which is protected by the blood-brain barrier (BBB). Among the different classes of antisense agents, peptide nucleic acids (PNA) present advantages for in vivoapplications over conventional and modified oligodeoxynucleotides (ODN), including phosphorothioates (PS)-ODN. Some advantages of PNAs include their electrically neutral backbone, low toxicity to neural cells, resistance to nucleases and peptidases, and lack of binding to plasma proteins. PNAs are poorly transported through cellular membranes, however, including the BBB and the brain cell membrane (BCM). Because the mRNA target for the antisense agent lies within the cytosol of the target cell, the BBB and the BCM must be circumvented in vivo, which ispossible with the use of chimeric peptide drug targeting technology. Chimeric peptides are formed by conjugation of a non-transportable drug, such as a PNA, to a drug delivery vector. The vector undergoes receptor-mediated transcytosis (RMT) through the BBB and receptor-mediated endocytosis through the BCM in vivo. When labeled with a radioisotope (e.g., ¹²⁵I or ¹¹¹In), the antisense chimeric peptide provides imaging of gene expressionin the brain in vivoin a sequence-specific manner. Further development of antisense radiopharmaceutical agents may allow for in vivoimaging of genes in pathological states, and may provide tools for the analysis of novel genes with functional genomics.     

Method for Assessing the Reliability of Molecular Diagnostics Based on Multiplexed SERS-Coded Nanoparticles

Surface-enhanced Raman scattering (SERS) nanoparticles have been engineered to generate unique fingerprint spectra and are potentially useful as bright contrast agents for molecular diagnostics. One promising strategy for biomedical diagnostics and imaging is to functionalize various particle types (“flavors”), each emitting a unique spectral signature, to target a large multiplexed panel of molecular biomarkers. While SERS particles emit narrow spectral features that allow them to be easily separable under ideal conditions, the presence of competing noise sources and background signals such as detector noise, laser background, and autofluorescence confounds the reliability of demultiplexing algorithms. Results obtained during time-constrained in vivo imaging experiments may not be reproducible or accurate. Therefore, our goal is to provide experimentalists with a metric that may be monitored to enforce a desired bound on accuracy within a user-defined confidence level. We have defined a spectral reliability index (SRI), based on the output of a direct classical least-squares (DCLS) demultiplexing routine, which provides a measure of the reliability of the computed nanoparticle concentrations and ratios. We present simulations and experiments to demonstrate the feasibility of this strategy, which can potentially be utilized for a range of instruments and biomedical applications involving multiplexed SERS nanoparticles.     

Imaging gene expression in the brain with peptide nucleic acid (PNA) antisense radiopharmaceuticals and drug targeting technology

Summary Antisense oligomers are potential pharmaceutical and radiopharmaceutical agents that can be used to modulate and image gene expression. Progress with in vivo gene targeting using antisense-based therapeutics has been slower than expected during the last decade, owing to poor trans-cellular delivery of antisense agents. This chapter suggests that if antisense pharmacology is merged with drug targeting technology, then membrane barriers can be circumvented and antisense agents can be delivered to tissues in vivo. Without the application of drug targeting, the likelihood of success for an antisense drug development program is low, particularly for the brain which is protected by the blood-brain barrier (BBB). Among the different classes of antisense agents, peptide nucleic acids (PNA) present advantages for in vivo applications over conventional and modified oligodeoxynucleotides (ODN), including phosphorothioates (PS)-ODN. Some advantages of PNAs include their electrically neutral backbone, low toxicity to neural cells, resistance to nucleases and peptidases, and lack of binding to plasma proteins. PNAs are poorly transported through cellular membranes, however, including the BBB and the brain cell membrane (BCM). Because the mRNA target for the antisense agent lies within the cytosol of the target cell, the BBB and the BCM must be circumvented in vivo, which is possible with the use of chimeric peptide drug targeting technology. Chimeric peptides are formed by conjugation of a non-transportable drug, such as a PNA, to a drug delivery vector. The vector undergoes receptor-mediated transcytosis (RMT) through the BBB and receptor-mediated endocytosis through the BCM in vivo. When labeled with a radioisotope (e.g., ¹²⁵I or ¹¹¹In), the antisense chimeric peptide provides imaging of gene expression in the brain in vivo in a sequence-specific manner. Further development of antisense radiopharmaceutical agents may allow for in vivo imaging of genes in pathological states, and may provide tools for the analysis of novel genes with functional genomics.     

Imaging gene expression in the brain with peptide nucleic acid (PNA) antisense radiopharmaceuticals and drug targeting technology

Summary Antisense oligomers are potential pharmaceutical and radiopharmaceutical agents that can be used to modulate and image gene expression. Progress within vivo gene targeting using antisense-based therapeutics has been slower than expected during the last decade, owing to poor trans-cellular delivery of antisense agents. This chapter suggests that if antisense pharmacology is merged with drug targeting technology, then membrane barriers can be circumvented and antisense agents can be delivered to tissuesin vivo. Without the application of drug targeting, the likelihood of success for an antisense drug development program is low, particularly for the brain which is protected by the blood-brain barrier (BBB). Among the different classes of antisense agents, peptide nucleic acids (PNA) present advantages forin vivo applications over conventional and modified oligodeoxynucleotides (ODN), including phosphorothioates (PS)-ODN. Some advantages of PNAs include their electrically neutral backbone, low toxicity to neural cells, resistance to nucleases and peptidases, and lack of binding to plasma proteins. PNAs are poorly transported through cellular membranes, however, including the BBB and the brain cell membrane (BCM). Because the mRNA target for the antisense agent lies within the cytosol of the target cell, the BBB and the BCM must be circumventedin vivo, which is possible with the use of chimeric peptide drug targeting technology. Chimeric peptides are formed by conjugation of a non-transportable drug, such as a PNA, to a drug delivery vector. The vector undergoes receptor-mediated transcytosis (RMT) through the BBB and receptor-mediated endocytosis through the BCMin vivo. When labeled with a radioisotope (e.g.,¹²⁵I or¹¹¹In), the antisense chimeric peptide provides imaging of gene expression in the brainin vivo in a sequence-specific manner. Further development of antisense radiopharmaceutical agents may allow forin vivo imaging of genes in pathological states, and may provide tools for the analysis of novel genes with functional genomics.     

ECM Protein Nanofibers and Nanostructures Engineered Using Surface-initiated Assembly

The extracellular matrix (ECM) in tissues is synthesized and assembled by cells to form a 3D fibrillar, protein network with tightly regulated fiber diameter, composition and organization. In addition to providing structural support, the physical and chemical properties of the ECM play an important role in multiple cellular processes including adhesion, differentiation, and apoptosis. In vivo, the ECM is assembled by exposing cryptic self-assembly (fibrillogenesis) sites within proteins. This process varies for different proteins, but fibronectin (FN) fibrillogenesis is well-characterized and serves as a model system for cell-mediated ECM assembly. Specifically, cells use integrin receptors on the cell membrane to bind FN dimers and actomyosin-generated contractile forces to unfold and expose binding sites for assembly into insoluble fibers. This receptor-mediated process enables cells to assemble and organize the ECM from the cellular to tissue scales. Here, we present a method termed surface-initiated assembly (SIA), which recapitulates cell-mediated matrix assembly using protein-surface interactions to unfold ECM proteins and assemble them into insoluble fibers. First, ECM proteins are adsorbed onto a hydrophobic polydimethylsiloxane (PDMS) surface where they partially denature (unfold) and expose cryptic binding domains. The unfolded proteins are then transferred in well-defined micro- and nanopatterns through microcontact printing onto a thermally responsive poly(N-isopropylacrylamide) (PIPAAm) surface. Thermally-triggered dissolution of the PIPAAm leads to final assembly and release of insoluble ECM protein nanofibers and nanostructures with well-defined geometries. Complex architectures are possible by engineering defined patterns on the PDMS stamps used for microcontact printing. In addition to FN, the SIA process can be used with laminin, fibrinogen and collagens type I and IV to create multi-component ECM nanostructures. Thus, SIA can be used to engineer ECM protein-based materials with precise control over the protein composition, fiber geometry and scaffold architecture in order to recapitulate the structure and composition of the ECM in vivo.     

New Dual Mode Gadolinium Nanoparticle Contrast Agent for Magnetic Resonance Imaging

Background

Liposomal-based gadolinium (Gd) nanoparticles have elicited significant interest for use as blood pool and molecular magnetic resonance imaging (MRI) contrast agents. Previous generations of liposomal MR agents contained gadolinium-chelates either within the interior of liposomes (core-encapsulated gadolinium liposomes) or presented on the surface of liposomes (surface-conjugated gadolinium liposomes). We hypothesized that a liposomal agent that contained both core-encapsulated gadolinium and surface-conjugated gadolinium, defined herein as dual-mode gadolinium (Dual-Gd) liposomes, would result in a significant improvement in nanoparticle-based T1 relaxivity over the previous generations of liposomal agents. In this study, we have developed and tested, both in vitro and in vivo, such a dual-mode liposomal-based gadolinium contrast agent.

Methodology/Principal Findings

Three types of liposomal agents were fabricated: core-encapsulated, surface-conjugated and dual-mode gadolinium liposomes. In vitro physico-chemical characterizations of the agents were performed to determine particle size and elemental composition. Gadolinium-based and nanoparticle-based T1 relaxivities of various agents were determined in bovine plasma. Subsequently, the agents were tested in vivo for contrast-enhanced magnetic resonance angiography (CE-MRA) studies. Characterization of the agents demonstrated the highest gadolinium atoms per nanoparticle for Dual-Gd liposomes. In vitro, surface-conjugated gadolinium liposomes demonstrated the highest T1 relaxivity on a gadolinium-basis. However, Dual-Gd liposomes demonstrated the highest T1 relaxivity on a nanoparticle-basis. In vivo, Dual-Gd liposomes resulted in the highest signal-to-noise ratio (SNR) and contrast-to-noise ratio in CE-MRA studies.

Conclusions/Significance

The dual-mode gadolinium liposomal contrast agent demonstrated higher particle-based T1 relaxivity, both in vitro and in vivo, compared to either the core-encapsulated or the surface-conjugated liposomal agent. The dual-mode gadolinium liposomes could enable reduced particle dose for use in CE-MRA and increased contrast sensitivity for use in molecular imaging.