Integrin Targeted MR Imaging

Monoclonal antibody-navigated carbon-encapsulated iron nanoparticles used for MRI-based tracking integrin receptors in murine melanoma

Integrin beta-3 is a cell adhesion molecule that mediate cell-to-cell and cell-to-extracellular matrix communication. The major goal of this study was to explore melanoma cells (B16F10) based upon specific direct targeting of the β3 subunit (CD61) in the integrin αvβ3 receptor using carbon-encapsulated iron nanoparticles decorated with monoclonal antibodies (Fe@C-CONH-anti-CD61 and Fe@C-(CH2)2-CONH-anti-CD61). Both melanoma cells treated with nanoparticles as well as C57BL/6 mice bearing syngeneic B16-F10 tumors intravenously injected with nanoparticles were tested in preclinical MRI studies. The as-synthesized carbon-encapsulated iron nanoparticles functionalized with CD61 monoclonal antibodies have been successfully used as a novel targeted contrast agent for MRI-based tracking melanoma cells expressing the β3 subunit of the integrin αvβ3 receptor.

D-Alpha-Tocopheryl Poly(ethylene Glycol 1000) Succinate-Coated Manganese-Zinc Ferrite Nanomaterials for a Dual-Mode Magnetic Resonance Imaging Contrast Agent and Hyperthermia Treatments

Manganese-zinc ferrite (MZF) is known as high-performance magnetic material and has been used in many fields and development. In the biomedical applications, the biocompatible MZF formulation attracted much attention. In this study, water-soluble amphiphilic vitamin E (TPGS, d-alpha-tocopheryl poly(ethylene glycol 1000) succinate) formulated MZF nanoparticles were synthesized to serve as both a magnetic resonance imaging (MRI) contrast agent and a vehicle for creating magnetically induced hyperthermia against cancer. The MZF nanoparticles were synthesized from a metallic acetylacetonate in an organic phase and further modified with TPGS using an emulsion and solvent-evaporation method. The resulting TPGS-modified MZF nanoparticles exhibited a dual-contrast ability, with a longitudinal relaxivity (35.22 s−1 mM Fe−1) and transverse relaxivity (237.94 s−1 mM Fe−1) that were both higher than Resovist®. Furthermore, the TPGS-assisted MZF formulation can be used for hyperthermia treatment to successfully suppress cell viability and tumor growth after applying an alternating current (AC) electromagnetic field at lower amplitude. Thus, the TPGS-assisted MZF theranostics can not only be applied as a potential contrast agent for MRI but also has potential for use in hyperthermia treatments.

Modular Synthesis of Peptide-Based Single- and Multimodal Targeted Molecular Imaging Agents

A practical, modular synthesis of targeted molecular imaging agents (TMIAs) containing near-infrared dyes for optical molecular imaging (OMI) or chelated metals for magnetic resonance imaging (MRI) and single-photon emission correlation tomography (SPECT) or positron emission tomography (PET) has been developed. In the method, imaging modules are formed early in the synthesis by attaching imaging agents to the side chain of protected lysines. These modules may be assembled to provide a given set of single- or dual-modal imaging agents, which may be conjugated in the last steps of the synthesis under mild conditions to linkers and targeting groups. A key discovery was the ability of a metal such as gadolinium, useful in MRI, to serve as a protecting group for the chelator, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). It was further discovered that two lanthanide metals, La and Ce, can double as protecting groups and placeholder metals, which may be transmetalated under mild conditions by metals used for PET in the final step. The modular method enabled the synthesis of discrete targeted probes with two of the same or different dyes, two same or different metals, or mixtures of dyes and metals. The approach was exemplified by the synthesis of single- or dual-modal imaging modules for MRI-OMI, PET-OMI, and PET-MRI, followed by conjugation to the integrin-seeking peptide, c(RGDyK). For Gd modules, their efficacy for MRI was verified by measuring the NMR spin-lattice relaxivity. To validate functional imaging of TMIAs, dual-modal agents containing Cy5.5 were shown to target A549 cancer cells by confocal fluorescence microscopy.

RGD-Peptide Functionalization Affects the In Vivo Diffusion of a Responsive Trimeric MRI Contrast Agent through Interactions with Integrins

The relevance of MRI as a diagnostic methodology has been expanding significantly with the development of molecular imaging. Partially, the credit for this advancement is due to the increasing potential and performance of targeted MRI contrast agents, which are able to specifically bind distinct receptors or biomarkers. Consequently, these allow for the identification of tissues undergoing a disease, resulting in the over- or underexpression of the particular molecular targets. Here we report a multimeric molecular probe, which combines the established targeting properties of the Arg-Gly-Asp (RGD) peptide sequence toward the integrins with three calcium-responsive, Gd-based paramagnetic moieties. The bifunctional probe showed excellent ¹H MRI contrast enhancement upon Ca²⁺ coordination and demonstrated a longer retention time in the tissue due to the presence of the RGD moiety. The obtained results testify to the potential of combining bioresponsive contrast agents with targeting vectors to develop novel functional molecular imaging methods.

c(RGDfK)- and ZnTriMPyP-Bound Polymeric Nanocarriers for Tumor-Targeted Photodynamic Therapy

Active targeting strategies are currently being extensively investigated in order to enhance the selectivity of photodynamic therapy. The aim of the present research was to evaluate whether the external decoration of nanopolymeric carriers with targeting peptides could add more value to a photosensitizer formulation and increase antitumor therapeutic efficacy and selectivity. To this end, we assessed PLGA-PLA-PEG nanoparticles (NPs) covalently attached to a hydrophilic photosensitizer 5-[4-azidophenyl]-10,15,20-tri-(N-methyl-4-pyridinium)porphyrinato zinc (II) trichloride (ZnTriMPyP) and also to c(RGDfK) peptides, in order to target α_v β₃ integrin-expressing cells. In vitro phototoxicity investigations showed that the ZnTriMPyP-PLGA-PLA-PEG-c(RGDfK) nanosystem is effective at submicromolar concentrations, is devoid of dark toxicity, successfully targets α_v β₃ integrin-expressing cells and is 10-fold more potent than related nanosystems where the PS is occluded instead of covalently bound.

Solid phase synthesis in the development of magnetic resonance imaging probes

We review the use of the solid phase synthesis methodology for the preparation of diverse and potent MRI probes.

Cell-assembled nanoclusters of MSC-targeting Gd-DOTA-peptide as a T2 contrast agent for MRI cell tracking

A cyclic peptide CC9 that targets cell membrane of mesenchymal stem cells (MSCs) is coupled with Gd-DOTA to yield a Gd-DOTA-CC9 complex as MRI contrast agent. It is used to label human MSCs (hMSCs) via electroporation. Electroporation-labeling of hMSCs with Gd-DOTA-CC9 induces cell-assembly of Gd-DOTA-CC9 nanoclusters in the cytoplasm, significantly promotes cell-labeling efficacy and intracellular retention time of the agent. In vitro MRI of labeled hMSCs exhibits significant signal reduction under T₂ -weighted MRI, which can allow long-term tracking of labeled cell transplants in in vivo migration. The labeling strategy is safe in cytotoxicity and differentiation potential.

Molecular Ultrasound Imaging of αvβ3-Integrin Expression in Carotid Arteries of Pigs After Vessel Injury

OBJECTIVES

Interventions such as balloon angioplasty can cause vascular injury leading to platelet activation, thrombus formation, and inflammatory response. This induces vascular smooth muscle cell activation and subsequent re-endothelialization with expression of αvβ3-integrin by endothelial cells and vascular smooth muscle cell. Thus, poly-N-butylcyanoacrylate microbubbles (MBs) targeted to αvβ3-integrin were evaluated for monitoring vascular healing after vessel injury in pigs using molecular ultrasound imaging.

MATERIALS AND METHODS

Approval for animal experiments was obtained. The binding specificity of αvβ3-integrin-targeted MB to human umbilical vein endothelial cells was tested with fluorescence microscopy. In vivo imaging was performed using a clinical ultrasound system and an 8-MHz probe. Six mini pigs were examined after vessel injury in the left carotid artery. The right carotid served as control. Uncoated MB, cDRG-coated MB, and αvβ3-integrin-specific cRGD-coated MB were injected sequentially. Bound MBs were assessed 8 minutes after injection using ultrasound replenishment analysis. Measurements were performed 2 hours, 1 and 5 weeks, and 3 and 6 months after injury. In vivo data were validated by immunohistochemistry.

RESULTS

Significantly stronger binding of cRGD-MB than MB and cDRG-MB to human umbilical vein endothelial cells was found (P < 0.01). As vessel injury leads to upregulation of αvβ3-integrin, cRGD-MBs bound significantly stronger (P < 0.05) in injured carotid arteries than at the counter side 1 week after vessel injury and significant differences could also be observed after 5 weeks. After 3 months, αvβ3-integrin expression decreased to baseline and binding of cRGD-MB was comparable in both vessels. Values remained at baseline also after 6 months.

CONCLUSIONS

Ultrasound imaging with RGD-MB is promising for monitoring vascular healing after vessel injury. This may open new perspectives to assess vascular damage after radiological interventions.

RGD-Modified Albumin Nanoconjugates for Targeted Delivery of a Porphyrin Photosensitizer

Advances in photodynamic therapy of cancer have been restrained by lack of cancer specificity and side effects to normal tissues. Molecularly targeted photodynamic therapy can achieve higher cancer specificity by combination of active cancer targeting and localized laser activation. We aimed to use albumin as a carrier to prepare targeted nanoconjugates that are selective to cancer cells and smaller than conventional nanoparticles for superior tumor penetration. IRDye 700DX (IR700), a porphyrin photosensitizer, was covalently conjugated to human serum albumin that was also linked with tumor-targeting RGD peptides. With multiple IR700 and RGD molecules in a single albumin molecule, the resultant nanoconjugates demonstrated monodispersed and uniform size distribution with a diameter of 10.9 nm. These targeted nanoconjugates showed 121-fold increase in cellular delivery of IR700 into TOV21G ovarian cancer cells compared to control nanoconjugates. Mechanistic studies revealed that the integrin specific cellular delivery was achieved through dynamin-mediated caveolae-dependent endocytosis pathways. They produced massive cell killing in TOV21G cells at low nanomolar concentrations upon light irradiation, while NIH/3T3 cells that do not express integrin αvβ3 were not affected. Because of their small size, targeted albumin nanoconjugates could penetrate tumor spheroids of SKOV-3 ovarian cancer cells and produced strong phototoxicity in this 3-D model. Owing to their cancer-specific delivery and small size, these targeted nanoconjugates may become an effective drug delivery system for enabling molecularly targeted photodynamic therapy of cancer.

Molecular imaging of the tumor microenvironment

The tumor microenvironment plays a critical role in tumor initiation, progression, metastasis, and resistance to therapy. It is different from normal tissue in the extracellular matrix, vascular and lymphatic networks, as well as physiologic conditions. Molecular imaging of the tumor microenvironment provides a better understanding of its function in cancer biology, and thus allowing for the design of new diagnostics and therapeutics for early cancer diagnosis and treatment. The clinical translation of cancer molecular imaging is often hampered by the high cost of commercialization of targeted imaging agents as well as the limited clinical applications and small market size of some of the agents. Because many different cancer types share similar tumor microenvironment features, the ability to target these biomarkers has the potential to provide clinically translatable molecular imaging technologies for a spectrum of cancers and broad clinical applications. There has been significant progress in targeting the tumor microenvironment for cancer molecular imaging. In this review, we summarize the principles and strategies of recent advances made in molecular imaging of the tumor microenvironment, using various imaging modalities for early detection and diagnosis of cancer.

Tuning of synthesis conditions by thermal decomposition towards gadolinium-doped manganese carbonate nanoparticles with uniform size and high relaxivity

A low temperature thermal decomposition method has been developed to synthesize uniform-sized Gd-doped MnCO₃ nanoparticles.

Gelatinase activity imaged by activatable cell-penetrating peptides in cell-based and in vivo models of stroke

Matrix metalloproteinases (MMPs), particularly gelatinases (MMP-2/-9), are involved in neurovascular impairment after stroke. Detection of gelatinase activity in vivo can provide insight into blood-brain barrier disruption, hemorrhage, and nerve cell injury or death. We applied gelatinase-activatable cell-penetrating peptides (ACPP) with a cleavable l-amino acid linker to examine gelatinase activity in primary neurons in culture and ischemic mouse brain in vivo We found uptake of Cy5-conjugated ACPP (ACPP-Cy5) due to gelatinase activation both in cultured neurons exposed to n-methyl-d-aspartate and in mice after cerebral ischemia. Fluorescence intensity was significantly reduced when cells or mice were treated with MMP inhibitors or when a cleavage-resistant ACPP-Cy5 was substituted. We also applied an ACPP dendrimer (ACPPD) conjugated with multiple Cy5 and/or gadolinium moieties for fluorescence and magnetic resonance imaging (MRI) in intact animals. Fluorescence analysis showed that ACPPD was detected in sub-femtomole range in ischemic tissues. Moreover, MRI and inductively coupled plasma mass spectrometry revealed that ACPPD produced quantitative measures of gelatinase activity in the ischemic region. The resulting spatial pattern of gelatinase activity and neurodegeneration were very similar. We conclude that ACPPs are capable of tracing spatiotemporal gelatinase activity in vivo, and will therefore be useful in elucidating mechanisms of gelatinase-mediated neurodegeneration after stroke.

Targeted Dual pH-Sensitive Lipid ECO/siRNA Self-Assembly Nanoparticles Facilitate In Vivo Cytosolic sieIF4E Delivery and Overcome Paclitaxel Resistance in Breast Cancer Therapy

RNAi-mediated knockdown of oncogenes associated with drug resistance can potentially enhance the efficacy of chemotherapy. Here, we have designed and developed targeted dual pH-sensitive lipid-siRNA self-assembly nanoparticles, RGD-PEG(HZ)-ECO/siRNA, which can efficiently silence the oncogene, eukaryotic translation initiation factor 4E (eIF4E), and consequently resensitize triple-negative breast tumors to paclitaxel. The dual pH-sensitive function of these nanoparticles facilitates effective cytosolic siRNA delivery in cancer cells, both in vitro and in vivo. Intravenous injection of RGD-PEG(HZ)-ECO/siRNA nanoparticles (1.0 mg-siRNA/kg) results in effective gene silencing for at least one week in MDA-MB-231 tumors. In addition, treatment of athymic nude mice with RGD-PEG(HZ)-ECO/sieIF4E every 6 days for 6 weeks down-regulates the overexpression of eIF4E and resensitizes paclitaxel-resistant MDA-MB-231 tumors to paclitaxel, resulting in significant tumor regression at a low dose, with negligible side effects. Moreover, repeated injections of the RGD-PEG(HZ)-ECO/siRNA nanoparticles in immunocompetent mice result in minimal immunogenicity, demonstrating their safety and low toxicity. These multifunctional lipid/siRNA nanoparticles constitute a versatile platform of delivery of therapeutic siRNA for treating cancer and other human diseases.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

Dual-targeting superparamagnetic iron oxide nanoprobes with high and low target density for brain glioma imaging

A major limit of superparamagnetic iron oxide nanoparticles (SPIONs) as a magnetic resonance (MR) imaging nanoprobe in clinical applications is that the SPIONs are unable to reach sufficient concentrations at the tumor site by passive targeting to produce an obvious contrast effect for tumor imaging. Single-targeting SPIONs systems have been applied to improve the contrast effect. However, they still suffer from a lack of efficiency and specificity of the SPIONs to tumors. Herein, we developed folic acid (FA) and cyclic Arg-Gly-Asp-D-Tyr-Lys (c(RGDyK)) dual-targeting nanoprobes based on Cy5.5 labeled Fe3O4 nanoparticles (NPs). The synergistic targeting ability of the dual-targeting Fe3O4 NPs and the effect of the dual-target density on targeting specificity were investigated in brain glioma-bearing mice. In vivo T2-weighted MR imaging of brain glioma-bearing mice and ex vivo near-infrared imaging of brains harboring gliomas suggested that the combination of dual-target increased the uptake of NPs by glioma, consequently, enhanced the contrast effect. Moreover, it was revealed that the density of dual-target plays an important role in targeting specificity.

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.

Improved tumor-targeting MRI contrast agents: Gd(DOTA) conjugates of a cycloalkane-based RGD peptide

Two new MRI contrast agents, Gd-DOTA-c(RGD-ACP-K) (1) and Gd-DOTA-c(RGD-ACH-K) (2), which were designed by incorporating aminocyclopentane (ACP)- or aminocyclohexane (ACH)-carboxylic acid into Gd-DOTA (gadolinium-tetraazacyclo dodecanetetraacetic acid) and cyclic RGDK peptides, were synthesized and evaluated for tumor-targeting ability in vitro and in vivo. Binding affinity studies showed that both 1 and 2 exhibited higher affinity for integrin receptors than cyclic RGDyK peptides, which were used as a reference. These complexes showed high relaxivity and good stability in human serum and have the potential to improve target-specific signal enhancement in vivo MR images.

Tumor vasculature targeted photodynamic therapy for enhanced delivery of nanoparticles

Delivery of nanoparticle drugs to tumors relies heavily on the enhanced permeability and retention (EPR) effect. While many consider the effect to be equally effective on all tumors, it varies drastically among the tumors' origins, stages, and organs, owing much to differences in vessel leakiness. Suboptimal EPR effect represents a major problem in the translation of nanomedicine to the clinic. In the present study, we introduce a photodynamic therapy (PDT)-based EPR enhancement technology. The method uses RGD-modified ferritin (RFRT) as "smart" carriers that site-specifically deliver (1)O2 to the tumor endothelium. The photodynamic stimulus can cause permeabilized tumor vessels that facilitate extravasation of nanoparticles at the sites. The method has proven to be safe, selective, and effective. Increased tumor uptake was observed with a wide range of nanoparticles by as much as 20.08-fold. It is expected that the methodology can find wide applications in the area of nanomedicine.

Fluorescent PEGylation agent by a thiolactone-based one-pot reaction: a new strategy for theranostic combinations

A new strategy to facilely synthesize multifunctional polymers with both fluorescent and protein reactive groups has been successfully developed using the thiolactone-based one-pot reaction.

Ferritin nanocages to encapsulate and deliver photosensitizers for efficient photodynamic therapy against cancer

Photodynamic therapy is an emerging treatment modality that is under intensive preclinical and clinical investigations for many types of disease including cancer. Despite the promise, there is a lack of a reliable drug delivery vehicle that can transport photosensitizers (PSs) to tumors in a site-specific manner. Previous efforts have been focused on polymer- or liposome-based nanocarriers, which are usually associated with a suboptimal PS loading rate and a large particle size. We report herein that a RGD4C-modified ferritin (RFRT), a protein-based nanoparticle, can serve as a safe and efficient PS vehicle. Zinc hexadecafluorophthalocyanine (ZnF16Pc), a potent PS with a high (1)O2 quantum yield but poor water solubility, can be encapsulated into RFRTs with a loading rate as high as ~60 wt % (i.e., 1.5 mg of ZnF16Pc can be loaded on 1 mg of RFRTs), which far exceeds those reported previously. Despite the high loading, the ZnF16Pc-loaded RFRTs (P-RFRTs) show an overall particle size of 18.6 ± 2.6 nm, which is significantly smaller than other PS-nanocarrier conjugates. When tested on U87MG subcutaneous tumor models, P-RFRTs showed a high tumor accumulation rate (tumor-to-normal tissue ratio of 26.82 ± 4.07 at 24 h), a good tumor inhibition rate (83.64% on day 12), as well as minimal toxicity to the skin and other major organs. This technology can be extended to deliver other metal-containing PSs and holds great clinical translation potential.

Polymeric materials for theranostic applications

Nanotechnology has continuously contributed to the fast development of diagnostic and therapeutic agents. Theranostic nanomedicine has encompassed the ongoing efforts on concurrent molecular imaging of biomarkers, delivery of therapeutic agents, and monitoring of therapy response. Among these formulations, polymer-based theranostic agents hold great promise for the construction of multifunctional agents for translational medicine. In this article, we reviewed the state-of-the-art polymeric nanoparticles, from preparation to application, as potential theranostic agents for diagnosis and therapy. We summarized several major polymer formulas, including polymeric conjugate complexes, nanospheres, micelles, and dendrimers for integrated molecular imaging and therapeutic applications.

Nanotheranostics for personalized medicine

Nanotheranostics, the integration of diagnostic and therapeutic function in one system using the benefits of nanotechnology, is extremely attractive for personalized medicine. Because treating cancer is not a one-size-fits-all scenario, it requires therapy to be adapted to the patient's specific biomolecules. Personalized and precision medicine (PM) does just that. It identifies biomarkers to gain an understanding of the diagnosis and in turn treating the specific disorder based on the precise diagnosis. By predominantly utilizing the unique properties of nanoparticles to achieve biomarker identification and drug delivery, nanotheranostics can be applied to noninvasively discover and target image biomarkers and further deliver treatment based on the biomarker distribution. This is a large and hopeful role theranostics must fill. However, as described in this expert opinion, current nanotechnology-based theranostics systems engineered for PM applications are not yet sufficient. PM is an ever-growing field that will be a driving force for future discoveries in biomedicine, especially cancer theranostics. In this article, the authors dissect the requirements for successful nanotheranostics-based PM.

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.

cRGD peptide-conjugated icosahedral closo-B12(2-) core carrying multiple Gd3+-DOTA chelates for α(v)β3 integrin-targeted tumor imaging (MRI)

A vertex-differentiated icosahedral closo-B(12)(2-) core was utilized to construct a α(v)β(3) integrin receptor-targeted (via cRGD peptide) high payload MRI contrast agent (CA-12) carrying 11 copies of Gd(3+)-DOTA chelates attached to the closo-B(12)(2-) surface via suitable linkers. The resulting polyfunctional MRI contrast agent possessed a higher relaxivity value per-Gd compared to Omniscan, a small molecular contrast agent commonly used in clinical settings. The α(v)β(3) integrin receptor specificity of CA-12 was confirmed via in vitro cellular binding experiments and in vivo MRI of mice bearing human PC-3 prostate cancer xenografts. Integrin α(v)β(3)-positive MDA-MB-231 cells exhibited 300% higher uptake of CA-12 than α(v)β(3)-negative T47D cells. Serial T1-weighted MRI showed superior contrast enhancement of tumors by CA-12 compared to both a nontargeted 12-fold Gd(3+)-DOTA closomer control (CA-7) and Omniscan. Contrast enhancement by CA-12 persisted for 4 h postinjection, and subsequent enhancement of kidney tissue indicated a renal elimination route similar to Omniscan. No toxic effects of CA-12 were apparent in any mice for up to 24 h postinjection. Post-mortem ICP-OES analysis at 24 h detected no residual Gd in any of the tissue samples analyzed.

SPPS resins impact the PNA-syntheses' improvement

The personalized medicine, also documented as "individualized medicine", is an effective and therapeutic approach. It is designed to treat the disease of the individual patient whose precise differential gene expression profile is well known. The trend in the biomedical and biophysical research shows important consequences for the pharmaceutical drug and diagnostics research. It requires a high variability in the design and safety of target-specific pharmacologically active molecules and diagnostic components for imaging of metabolic processes. A key technology which may fulfill the highest demands during synthesis of these individual drugs and diagnostics is the solid phase synthesis which is congenial to automated manufacturing. Additionally the choice of tools like resins and reagents is pivotal to synthesize drugs and diagnostics in high quality and yields. Here we demonstrate the solid phase synthesis effects dependent on the choice of resin and of the deprotection agent.

Assessment and comparison of magnetic nanoparticles as MRI contrast agents in a rodent model of human hepatocellular carcinoma

The purpose of this study was to synthesize, characterize and tailor the surface properties of magnetic nanoparticles with biocompatible copolymer coatings and to evaluate the efficiency of the resulting nanoconjugates as magnetic resonance imaging (MRI) contrast agents for liver imaging. Magnetic nanoparticles with core diameters of 10 and 30 nm were synthesized by pyrolysis and were subsequently coated with a copolymer containing either carboxyl (SHP) or methoxy groups as termini. All four formulas, and ferumoxides (Feridex I.V.(®)), were individually injected intravenously into separate, normal Balb/C mice (at 2.5, 1.0 and 0.56 mg Fe kg(-1)), and the animals underwent T(2)-weighted MRI at multiple time points post injection (p.i.) to evaluate the hepatic uptake and clearance. Furthermore, we compared the abilities of the new formulas and Feridex to detect tumors in an orthotropic Huh7 tumor model. Transmission electron microscopy (TEM) revealed a narrow size distribution of both the 10 and 30 nm nanoparticles, in contrast to a wide size distribution of Feridex. MTT, apoptosis and cyclin/DNA flow cytometry assays showed that the polymer coated nanoparticles had no adverse effect on cell growth. Among all the tested formulas, including Feridex, SHP-30 showed the highest macrophage uptake at the in vitro level. In vivo MRI studies on normal mice confirmed the superiority of SHP-30 in inducing hypointensities in the liver tissue, especially at clinical dose (0.56 mg Fe kg(-1)) and 3 T field. SHP-30 showed better contrast-to-noise ratio than Feridex on the orthotropic Huh7 tumor model. SHP-30 was found to be an efficient contrast agent for liver MR imaging. The success of this study suggests that, by improving the synthetic approach and by tuning the surface properties of IONPs, one can arrive at better formulas than Feridex for clinical practice.

Strategies for Target-Specific Contrast Agents for Magnetic Resonance Imaging

This review describes recent research efforts focused on increasing the specificity of contrast agents for proton magnetic resonance imaging (MRI). Contrast agents play an indispensable role in MRI by enhancing the inherent contrast of images; however, the non-specific nature of current clinical contrast agents limits their usefulness. This limitation can be addressed by conjugating contrast agents or contrast-agent-loaded carriers-including polymers, nanoparticles, dendrimers, and liposomes-to molecules that bind to biological sites of interest. An alternative approach to conjugation is synthetically mimicking biological structures with metal complexes that are also contrast agents. In this review, we describe the advantages and limitations of these two targeting strategies with respect to translation from in vitro to in vivo imaging while focusing on advances from the last ten years.

Development of manganese-based nanoparticles as contrast probes for magnetic resonance imaging

MRI is one of the most important imaging tools in clinics. It interrogates nuclei of atoms in a living subject, providing detailed delineation with high spatial and temporal resolutions. To compensate the innate low sensitivity, MRI contrast probes were developed and widely used. These are typically paramagnetic or superparamagnetic materials, functioning by reducing relaxation times of nearby protons. Previously, gadolinium(Gd)-based T₁ contrast probes were dominantly used. However, it was found recently that their uses are occasionally associated with nephrogenic system fibrosis (NSF), which suggests a need of finding alternatives. Among the efforts, manganese-containing nanoparticles have attracted much attention. By careful engineering, manganese nanoparticles with comparable r₁ relaxivities can be yielded. Moreover, other functionalities, be a targeting motif, a therapeutic agent or a second imaging component, can be loaded onto these nanoparticles, resulting in multifunctional nanoplatforms.

Theranostic cRGD-BioShuttle Constructs Containing Temozolomide- and Cy7 For NIR-Imaging and Therapy

Innovative and personalized therapeutic approaches result from the identification and control of individual aberrantly expressed genes at the transcriptional and post-transcriptional level. Therefore, it is of high interest to establish diagnostic, therapeutic and theranostic strategies at these levels. In the present study, we used the Diels-Alder Reaction with inverse electron demand (DAR_inv) click chemistry to prepare a series of cyclic RGD-BioShuttle constructs. These constructs carry the near-infrared (NIR) imaging agent Cy7 and the chemotherapeutic agent temozolomide (TMZ). We evaluated their uptake by and their efficacy against integrin α_vβ₃-expressing MCF7 human breast carcinoma cells. In addition, using a mouse phantom, we analyzed the suitability of this targeted theranostic agent for NIR optical imaging. We observed that the cyclic RGD-based carriers containing TMZ and/or Cy7 were effectively taken up by α_vβ₃-expressing cells, that they were more effective than free TMZ in inducing cell death, and that they could be quantitatively visualized using NIR fluorescence imaging. Therefore, these targeted theranostic agents are considered to be highly suitable systems for improving disease diagnosis and therapy.

Surface-engineered magnetic nanoparticle platforms for cancer imaging and therapy

Enormous efforts have been made toward the translation of nanotechnology into medical practice, including cancer management. Generally the applications have fallen into two categories: diagnosis and therapy. Because the targets are often the same, the development of separate approaches can miss opportunities to improve efficiency and effectiveness. The unique physical properties of nanomaterials enable them to serve as the basis for superior imaging probes to locate and report cancerous lesions and as vehicles to deliver therapeutics preferentially to those lesions. These technologies for probes and vehicles have converged in the current efforts to develop nanotheranostics, nanoplatforms with both imaging and therapeutic functionalities. These new multimodal platforms are highly versatile and valuable components of the emerging trend toward personalized medicine, which emphasizes tailoring treatments to the biology of individual patients to optimize outcomes. The close coupling of imaging and treatment within a theranostic agent and the data about the evolving course of an illness that these agents provide can facilitate informed decisions about modifications to treatment. Magnetic nanoparticles, especially superparamagnetic iron oxide nanoparticles (IONPs), have long been studied as contrast agents for magnetic resonance imaging (MRI). Owing to recent progress in synthesis and surface modification, many new avenues have opened for this class of biomaterials. Such nanoparticles are not merely tiny magnetic crystals, but potential platforms with large surface-to-volume ratios. By taking advantage of the well-developed surface chemistry of these materials, researchers can load a wide range of functionalities, such as targeting, imaging and therapeutic features, onto their surfaces. This versatility makes magnetic nanoparticles excellent scaffolds for the construction of theranostic agents, and many efforts have been launched toward this goal. In this Account, we introduce the surface engineering techniques that we and others have developed, with an emphasis on how these techniques affect the role of nanoparticles as imaging or therapeutic agents. We and others have developed a set of chemical methods to prepare magnetic nanoparticles that possess accurate sizes, shapes, compositions, magnetizations, relaxivities, and surface charges. These features, in turn, can be harnessed to adjust the toxicity and stability of the nanoparticles and, further, to load functionalities, via various mechanisms, onto the nanoparticle surfaces.

New Methods for Labeling RGD Peptides with Bromine-76

Direct bromination of the tyrosine residues of peptides and antibodies with bromine-76, to create probes for PET imaging, has been reported. For peptides that do not contain tyrosine residues, however, a prosthetic group is required to achieve labeling via conjugation to other functional groups such as terminal α-amines or lysine ε-amines. The goal of this study was to develop new strategies for labeling small peptides with Br-76 using either a direct labeling method or a prosthetic group, depending on the available functional group on the peptides. A new labeling agent, N-succinimidyl-3-[(76)Br]bromo-2,6-dimethoxybenzoate ([(76)Br]SBDMB) was prepared for cyclic RGD peptide labeling. N-succinimidyl-2, 6-dimethoxybenzoate was also used to pre-attach a 2, 6-dimethoxybenzoyl (DMB) moiety to the peptide, which could then be labeled with Br-76. A competitive cell binding assay was performed to determine the binding affinity of the brominated peptides. PET imaging of U87MG human glioblastoma xenografted mice was performed using [(76)Br]-BrE[c(RGDyK)](2) and [(76)Br]-BrDMB-E[c(RGDyK)](2). An ex vivo biodistribution assay was performed to confirm PET quantification. The mechanisms of bromination reaction between DMB-c(RGDyK) and the brominating agent CH(3)COOBr were investigated with the SCRF-B3LYP/6-31G* method with the Gaussian 09 program package. The yield for direct labeling of c(RGDyK) and E[c(RGDyK)](2) using chloramine-T and peracetic acid at ambient temperature was greater than 50%. The yield for [(76)Br]SBDMB was over 60% using peracetic acid. The conjugation yields for labeling c(RGDfK) and c(RGDyK) were over 70% using the prosthetic group at room temperature. Labeling yield for pre-conjugated peptides was over 60%. SDMB conjugation and bromination did not affect the binding affinity of the peptides with integrin receptors. Both [(76)Br]Br-E[c(RGDyK)](2) and [(76)Br]BrDMB-E[c(RGDyK)](2) showed high tumor uptake in U87MG tumor bearing mice. The specificity of the imaging tracers was confirmed by decreased tumor uptake after co-administration of unlabeled dimeric RGD peptides. The energy barrier of the transition state of bromination for the dimethoxybenzoyl group was about 9 kcal/mol lower than that for the tyrosine residue. In conclusion, the newly developed N-succinimidyl-2, 6-dimethoxybenzoate molecule can be used either for one step labeling through pre-conjugation or as the precursor for a Br-76 labeled prosthetic group for indirect labeling. Radiobromination on a dimethoxybenzoyl group has selectivity over radiobromination on tyrosine. The energy barrier difference of the transition states of bromination between the dimethoxybenzoyl group and the tyrosine residue may account for the reaction selectivity when both groups are present in the same molecule.

Targeted nanoprobes reveal early time point kinetics in vivo by time-resolved MRI

This commentary highlights the findings by Kessinger et al. (Theranostics 2011; 1: 263-275) that dynamic T₂*-weighted magnetic resonance imaging (MRI) of cyclic RGD peptide-encoded superparamagnetic polymeric micelle (SPPM) nanoparticles allows quantitative analysis of tumor integrin αvβ3 expression, which can exclude the effect of blood volume and extravascular signal components and thus provide less biased tumor contrast and receptor specificity of probes.

Integrin Targeted Imaging and Therapy

This theme issue provides an overview on the biology and pathology of various integrins as well as in-depth discussion on the use of integrin as targeting molecules for molecular imaging and molecular therapy.