Multimodality Imaging of Integrin α(v)β(3) Expression

Advancing cancer theranostics through biomimetics: A comprehensive review

Nanotheranostics, especially those employing biomimetic approaches, are of substantial interest for molecular imaging and cancer therapy. The incorporation of diagnostics and therapeutics, known as cancer theranostics, represents a promising strategy in modern oncology. Biomimetics, inspired by nature, offers a multidisciplinary avenue with potential in advancing cancer theranostics. This review comprehensively analyses recent progress in biomimetics-based cancer theranostics, emphasizing its role in overcoming current treatment challenges, with a focus on breast, prostate, and skin cancers. Biomimetic approaches have been explored to address multidrug resistance (MDR), emphasizing their role in immunotherapy and photothermal therapy. The specific areas covered include biomimetic drug delivery systems bypassing MDR mechanisms, biomimetic platforms for immune checkpoint blockade, immune cell modulation, and photothermal tumor ablation. Pretargeting techniques enhancing radiotherapeutic agent uptake are discussed, along with a comprehensive review of clinical trials of global nanotheranostics. This review delves into biomimetic materials, nanotechnology, and bioinspired strategies for cancer imaging, diagnosis, and targeted drug delivery. These include imaging probes, contrast agents, and biosensors for enhanced specificity and sensitivity. Biomimetic strategies for targeted drug delivery involve the design of nanoparticles, liposomes, and hydrogels for site-specific delivery and improved therapeutic efficacy. Overall, this current review provides valuable information for investigators, clinicians, and biomedical engineers, offering insights into the latest biomimetics applications in cancer theranostics. Leveraging biomimetics aims to revolutionize cancer diagnosis, treatment, and patient outcomes.

Photodynamic therapy for prostate cancer: Recent advances, challenges and opportunities

Over the past two decades, there has been a tendency toward early diagnosis of prostate cancer due to raised awareness among the general public and professionals, as well as the promotion of prostate-specific antigen (PSA) screening. As a result, patients with prostate cancer are detected at an earlier stage. Due to the risks of urine incontinence, erectile dysfunction, etc., surgery is not advised because the tumor is so small at this early stage. Doctors typically only advise active surveillance. However, it will bring negative psychological effects on patients, such as anxiety. And there is a higher chance of cancer progression. Focal therapy has received increasing attention as an alternative option between active monitoring and radical therapy. Due to its minimally invasive, oncological safety, low toxicity, minimal effects on functional outcomes and support by level 1 evidence from the only RCT within the focal therapy literature, photodynamic treatment (PDT) holds significant promise as the focal therapy of choice over other modalities for men with localized prostate cancer. However, there are still numerous obstacles that prevent further advancement. The review that follows provides an overview of the preclinical and clinical published research on PDT for prostate cancer from 1999 to the present. It focuses on clinical applications of PDT and innovative techniques and technologies that address current problems, especially the use of nanoparticle photosensitizers in PDT of prostate cancer.

Radionuclide-based molecular imaging allows CAR-T cellular visualization and therapeutic monitoring

Chimeric antigen receptor T cell (CAR-T) therapy is a new and effective form of adoptive cell therapy that is rapidly entering the mainstream for the treatment of CD19-positive hematological cancers because of its impressive effect and durable responses. Huge challenges remain in achieving similar success in patients with solid tumors. The current methods of monitoring CAR-T, including morphological imaging (CT and MRI), blood tests, and biopsy, have limitations to assess whether CAR-T cells are homing to tumor sites and infiltrating into tumor bed, or to assess the survival, proliferation, and persistence of CAR-T cells in solid tumors associated with an immunosuppressive microenvironment. Radionuclide-based molecular imaging affords improved CAR-T cellular visualization and therapeutic monitoring through either a direct cellular radiolabeling approach or a reporter gene imaging strategy, and endogenous cell imaging is beneficial to reflect functional information and immune status of T cells. Focusing on the dynamic monitoring and precise assessment of CAR-T therapy, this review summarizes the current applications of radionuclide-based noninvasive imaging in CAR-T cells visualization and monitoring and presents current challenges and strategic choices.

A 64 Cu-porphyrin-based dual-modal molecular probe with integrin αv β3 targeting function for tumour imaging

Pyropheophorbide-a (Pyro) is a promising multifunctional molecule for multimodal tumour imaging and photodynamic therapy, but its clinical applications are seriously restricted by the limited tumour accumulation capability. Here, we designed and synthesized a small-molecule probe that achieved specific dual-modal tumour imaging based on Pyro. Briefly, a novel molecule combining Pyro, an RGD dimer peptide (3PRGD2 ) and 64 Cu, was designed and synthesized, and the obtained molecule, 64 Cu-Pyro-3PRGD2 , exhibited high tumour specificity in both positron emission tomography and optical imaging in vivo. c (RGDfk) peptide blocking significantly reduced the efficacy of the probe, which confirmed the integrin αV β3 targeting of this molecular probe. 64 Cu-Pyro-3PRGD2 had very low accumulation in normal organs and could be rapidly cleared through kidney metabolism, which prevented the potential damage to adjacent normal tissues. Overall, combining tumour targeting, dual-modal imaging, and biosafety, 64 Cu-Pyro-3PRGD2 has the potential for clinical use as a molecular imaging probe for tumour diagnosis.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.

NIR Emitting Nanoprobes Based on Cyclic RGD Motif Conjugated PbS Quantum Dots for Integrin-Targeted Optical Bioimaging

Here, silica-coated PbS quantum dots (QDs) with photoluminescence emission properties in the near-infrared (NIR) region are proposed as potential effective single particle optical nanoprobes for future in vivo imaging of tumors. The dispersibility in aqueous medium of hydrophobic PbS QDs was accomplished by growing a silica shell on their surface by exploiting a base assisted water-in-oil microemulsion method. The silica-coated PbS QDs were then conjugated with a specifically designed cyclic arginine-glycine-aspartic acid (cRGD) peptide that is able to specifically recognize αvβ3 integrins, which are overexpressed in angiogenic tumor-induced vasculatures and on some solid tumors, to achieve tumor-specific targeting. The cRGD peptide PbS silica-coated QDs were systematically characterized, at each step of their preparation, by means of complementary optical and structural techniques, demonstrating appropriate colloidal stability and the maintenance of their optical futures in aqueous solutions. The cellular uptake of cRGD peptide functionalized luminescent nanostructures in human melanoma cells, where overexpression of αvβ3 was observed, was assessed by means of confocal microscopy analysis and cytometric study. The selectivity of the cRGD peptide PbS silica-coated QDs for the αvβ3 integrin was established, consequently highlighting the significant potential of the developed NIR emitting nanostructures as optically traceable nanoprobes for future αvβ3 integrin receptor in vivo targeting in the NIR region.

Radiolabeled, Antibody-Conjugated Manganese Oxide Nanoparticles for Tumor Vasculature Targeted Positron Emission Tomography and Magnetic Resonance Imaging

Manganese oxide nanoparticles (Mn₃O₄ NPs) have attracted a great deal of attention in the field of biomedical imaging because of their ability to create an enhanced imaging signal in MRI as novel potent T₁ contrast agents. In this study, we present tumor vasculature-targeted imaging in mice using Mn₃O₄ NPs through conjugation to the anti-CD105 antibody TRC105 and radionuclide copper-64 (⁶⁴Cu, t_1/2: 12.7 h). The Mn₃O₄ conjugated NPs, ⁶⁴Cu-NOTA-Mn₃O₄@PEG-TRC105, exhibited sufficient stability in vitro and in vivo. Serial positron emission tomography (PET) and magnetic resonance imaging (MRI) studies evaluated the pharmacokinetics and demonstrated targeting of ⁶⁴Cu-NOTA-Mn₃O₄@PEG-TRC105 to 4T1 murine breast tumors in vivo, compared to ⁶⁴Cu-NOTA-Mn₃O₄@PEG. The specificity of ⁶⁴Cu-NOTA-Mn₃O₄@PEG-TRC105 for the vascular marker CD105 was confirmed through in vivo, in vitro, and ex vivo experiments. Since Mn₃O₄ conjugated NPs exhibited desirable properties for T₁ enhanced imaging and low toxicity, the tumor-specific Mn₃O₄ conjugated NPs reported in this study may serve as promising multifunctional nanoplatforms for precise cancer imaging and diagnosis.

Positron emission tomography (PET) guided glioblastoma targeting by a fullerene-based nanoplatform with fast renal clearance

Various carbonaceous nanomaterials, including fullerene, carbon nanotube, graphene, and carbon dots, have attracted increasing attention during past decades for their potential applications in biological imaging and therapy. In this study, we have developed a fullerene-based tumor-targeted positron emission tomography (PET) imaging probe. Water-soluble functionalized C₆₀ conjugates were radio-labeled with ⁶⁴Cu and modified with cyclo (Arg-Gly-Asp) peptides (cRGD) for targeting of integrin α_vβ₃ in glioblastoma. The specificity of fluorescein-labeled C₆₀ conjugates against cellular integrin α_vβ₃ was evaluated in U87MG (integrin α_vβ₃ positive) and MCF-7 cells (integrin α_vβ₃ negative) by confocal fluorescence microscopy and flow cytometry. Our results indicated that cRGD-conjugated C₆₀ derivatives showed better cellular internalization compared with C₆₀ derivatives without the cRGD attachment. Moreover, an interesting finding on intra-nuclei transportation of cRGD-conjugated C₆₀ derivatives was observed in U87MG cells. In vivo serial PET studies showed preferential accumulation of cRGD-conjugated C₆₀ derivatives at in U87MG tumors. In addition, the pharmacokinetic profiles of these fullerene-based nanoparticles conjugated with cRGD and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) fit well with the three compartment model. The renal clearance of C₆₀-based nanoparticles is remarkably fast, which makes this material very promising for safer cancer theranostic applications.

STATEMENT OF SIGNIFICANCE

Safety is one of the major concerns for nanomedicine and nanomaterials with fast clearance profile are highly desirable. Fullerene is a distinct type of zero-dimensional carbon nanomaterial with ultrasmall size, uniform dispersity, and versatile reactivity. Here we have developed a fullerene-based tumor-targeted positron emission tomography imaging probe using water-soluble functionalized C₆₀ conjugates radio-labeled with ⁶⁴Cu and modified with cyclo (Arg-Gly-Asp) peptides (cRGD) for glioblastoma targeting. The improved tumor targeting property along with fast renal clearance behavior of C₆₀-based nanoparticles makes this material very promising for future safer cancer theranostic applications.

Synthesis, Chemical Characterization and Multiscale Biological Evaluation of a Dimeric-cRGD Peptide for Targeted Imaging of α V β 3 Integrin Activity

Cyclic peptides containing the Arg-Gly-Asp (RGD) sequence have been shown to specifically bind the angiogenesis biomarker α_Vβ₃ integrin. We report the synthesis, chemical characterization, and biological evaluation of two novel dimeric cyclic RGD-based molecular probes for the targeted imaging of α_Vβ₃ activity (a radiolabeled version, ⁶⁴Cu-NOTA-PEG₄-cRGD₂, for PET imaging, and a fluorescent version, FITC-PEG₄-cRGD₂, for in vitro work). We investigated the performance of this probe at the receptor, cell, organ, and whole-body levels, including its use to detect diabetes associated impairment of ischemia-induced myocardial angiogenesis. Both versions of the probe were found to be stable, demonstrated fast receptor association constants, and showed high specificity for α_Vβ₃ in HUVECs (K_d ~ 35 nM). Dynamic PET-CT imaging indicated rapid blood clearance via kidney filtration, and accumulation within α_Vβ₃-positive infarcted myocardium. ⁶⁴Cu-NOTA-PEG₄-cRGD₂ demonstrated a favorable biodistribution, slow washout, and excellent performance with respect to the quality of the PET-CT images obtained. Importantly, the ratio of probe uptake in infarcted heart tissue compared to normal tissue was significantly higher in non-diabetic rats than in diabetic ones. Overall, our probes are promising agents for non-invasive quantitative imaging of α_Vβ₃ expression, both in vitro and in vivo.

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.

Photoacoustic-Based Multimodal Nanoprobes: from Constructing to Biological Applications

Multimodal nanoprobes have attracted intensive attentions since they can integrate various imaging modalities to obtain complementary merits of single modality. Meanwhile, recent interest in laser-induced photoacoustic imaging is rapidly growing due to its unique advantages in visualizing tissue structure and function with high spatial resolution and satisfactory imaging depth. In this review, we summarize multimodal nanoprobes involving photoacoustic imaging. In particular, we focus on the method to construct multimodal nanoprobes. We have divided the synthetic methods into two types. First, we call it “one for all” concept, which involves intrinsic properties of the element in a single particle. Second, “all in one” concept, which means integrating different functional blocks in one particle. Then, we simply introduce the applications of the multifunctional nanoprobes for in vivo imaging and imaging-guided tumor therapy. At last, we discuss the advantages and disadvantages of the present methods to construct the multimodal nanoprobes and share our viewpoints in this area.

Heat-induced-radiolabeling and click chemistry: A powerful combination for generating multifunctional nanomaterials

A key advantage of nanomaterials for biomedical applications is their ability to feature multiple small reporter groups (multimodality), or combinations of reporter groups and therapeutic agents (multifunctionality), while being targeted to cell surface receptors. Here a facile combination of techniques for the syntheses of multimodal, targeted nanoparticles (NPs) is presented, whereby heat-induced-radiolabeling (HIR) labels NPs with radiometals and so-called click chemistry is used to attach bioactive groups to the NP surface. Click-reactive alkyne or azide groups were first attached to the nonradioactive clinical Feraheme (FH) NPs. Resulting "Alkyne-FH" and "Azide-FH" intermediates, like the parent NP, tolerated 89Zr labeling by the HIR method previously described. Subsequently, biomolecules were quickly conjugated to the radioactive NPs by either copper-catalyzed or copper-free click reactions with high efficiency. Synthesis of the Alkyne-FH or Azide-FH intermediates, followed by HIR and then by click reactions for biomolecule attachment, provides a simple and potentially general path for the synthesis of multimodal, multifunctional, and targeted NPs for biomedical applications.

Photodynamic Therapy Induced Enhancement of Tumor Vasculature Permeability Using an Upconversion Nanoconstruct for Improved Intratumoral Nanoparticle Delivery in Deep Tissues

Photodynamic therapy (PDT) has recently emerged as an approach to enhance intratumoral accumulation of nanoparticles. However, conventional PDT is greatly limited by the inability of the excitation light to sufficiently penetrate tissue, rendering PDT ineffective in the relatively deep tumors. To address this limitation, we developed a novel PDT platform and reported for the first time the effect of deep-tissue PDT on nanoparticle uptake in tumors. This platform employed c(RGDyK)-conjugated upconversion nanoparticles (UCNPs), which facilitate active targeting of the nanoconstruct to tumor vasculature and achieve the deep-tissue photosensitizer activation by NIR light irradiation. Results indicated that our PDT system efficiently enhanced intratumoral uptake of different nanoparticles in a deep-seated tumor model. The optimal light dose for deep-tissue PDT (34 mW/cm²) was determined and the most robust permeability enhancement was achieved by administering the nanoparticles within 15 minutes following PDT treatment. Further, a two-step treatment strategy was developed and validated featuring the capability of improving the therapeutic efficacy of Doxil while simultaneously reducing its cardiotoxicity. This two-step treatment resulted in a tumor inhibition rate of 79% compared with 56% after Doxil treatment alone. These findings provide evidence in support of the clinical application of deep-tissue PDT for enhanced nano-drug delivery.

Conformationally Strained trans-Cyclooctene (sTCO) Enables the Rapid Construction of (18)F-PET Probes via Tetrazine Ligation

The bioorthogonal reaction between tetrazines and trans-cyclooctenes is a method for the rapid construction of F-18 probes for PET imaging. Described here is a second generation ¹⁸F-labeling system based on a conformationally strained trans-cyclooctene (sTCO)—a dienophile that is approximately 2 orders of magnitude more reactive than conventional TCO dienophiles. Starting from a readily prepared tosylate precursor, an ¹⁸F labeled sTCO derivative (¹⁸F-sTCO) could be synthesized in 29.3 +/- 5.1% isolated yield and with high specific activity. Tetrazine ligation was carried out with a cyclic RGD-conjugate of a diphenyl-s-tetrazine analogue (RGD-Tz) chosen from a diene class with an excellent combination of fast reactivity and stability both for the diene as well as the Diels-Alder adduct. For both the tetrazine and the sTCO, mini-PEG spacers were included to enhance solubility and improve the in vivo distribution profile of the resulting probe. Extremely fast reactivity (up to 2.86 x 10⁵ M^-1s^-1 at 25 °C in water) has been observed in kinetic studies in the reaction of sTCO with diphenyl-s-tetrazine derivatives. A kinetic study on sTCO diastereomers in 55:45 MeOH:water showed that the syn-diastereomer displayed slightly faster reactivity than the anti-diastereomer. An ¹⁸F-sTCO conjugate with RGD-Tz demonstrated prominent and persistent tumor uptake in vivo with good tumor-to-background contrast. Unlike most radiolabeled RGD peptides, the tumor uptake of this PET agent increased from 5.3 +/- 0.2% ID/g at 1 h post injection (p.i.), to 8.9 +/- 0.5% ID/g at 4 h p.i., providing evidence for prolonged blood circulation. These findings suggest that tetrazine ligations employing ¹⁸F-sTCO should serve as a powerful and general platform for the rapid construction of peptide or protein derived PET agents.

Targeting activated hepatic stellate cells (aHSCs) for liver fibrosis imaging

Following injurious stimuli, quiescent hepatic stellate cells (qHSCs) transdifferentiate into activated HSCs (aHSCs). aHSCs play pivotal roles in the onset and progression of liver fibrosis. Therefore, molecular imaging of aHSCs in liver fibrosis will facilitate early diagnosis, prognosis prediction, and instruction and evaluation of aHSC-targeted treatment. To date, several receptors, such as integrin αvβ3, mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR), collagen type VI receptor (CVIR), platelet-derived growth factor receptor-β (PDGFR-β), vimentin, and desmin, have been identified as biomarkers of aHSCs. Corresponding ligands to these receptors have also been developed. This review will discuss strategies for developing aHSC-targeted imaging in liver fibrosis.

Main applications of hybrid PET-MRI contrast agents: a review

In medical imaging, the continuous quest to improve diagnostic performance and optimize treatment strategies has led to the use of combined imaging modalities. Positron emission tomography (PET) and computed tomography (CT) is a hybrid imaging existing already for many years. The high spatial and contrast resolution of magnetic resonance imaging (MRI) and the high sensitivity and molecular information from PET imaging are leading to the development of this new hybrid imaging along with hybrid contrast agents. To create a hybrid contrast agent for PET-MRI device, a PET radiotracer needs to be combined with an MRI contrast agent. The most common approach is to add a radioactive isotope to the surface of a small superparamagnetic iron oxide (SPIO) particle. The resulting agents offer a wide range of applications, such as pH variation monitoring, non-invasive angiography and early imaging diagnosis of atherosclerosis. Oncology is the most promising field with the detection of sentinel lymph nodes and the targeting of tumor neoangiogenesis. Oncology and cardiovascular imaging are thus major areas of development for hybrid PET-MRI imaging systems and hybrid contrast agents. The aim is to combine high spatial resolution, high sensitivity, morphological and functional information. Future prospects include the use of specific antibodies and hybrid multimodal PET-MRI-ultrasound-fluorescence imaging with the potential to provide overall pre-, intra- and postoperative patient care.

TYR as a multifunctional reporter gene regulated by the Tet-on system for multimodality imaging: an in vitro study

The human tyrosinase gene TYR is a multifunctional reporter gene with potential use in photoacoustic imaging (PAI), positron emission tomography (PET), and magnetic resonance imaging (MRI). We sought to establish and evaluate a reporter gene system using TYR under the control of the Tet-on gene expression system (gene expression induced by doxycycline [Dox]) as a multimodality imaging agent. We transfected TYR into human breast cancer cells (MDA-MB-231), naming the resulting cell line 231-TYR. Using non-transfected MDA-MB-231 cells as a control, we verified successful expression of TYR by 231-TYR after incubation with Dox using western blot, cellular tyrosinase activity, Masson-Fontana silver staining, and a cell immunofluorescence study, while the control cells and 231-TYR cells without Dox exposure revealed no TYR expression. Detected by its absorbance at 405 nm, increasing concentrations of melanin correlated positively with Dox concentration and incubation time. TYR expression by Dox-induced transfected cells shortened MRI T1 and T2 relaxation times. Photoacoustic signals were easily detected in these cells. (18)F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide ((18)F-5-FPN), which targets melanin, quickly accumulated in Dox-induced 231-TYR cells. These show that TYR induction of melanin production is regulated by the Tet-on system, and TYR-containing indicator cells may have utility in multimodality imaging.

Synthesis and Evaluation of 64Cu-DOTA-NT-Cy5.5 as a Dual-Modality PET/Fluorescence Probe to Image Neurotensin Receptor-Positive Tumor

Overexpression of neurotensin receptors (NTRs) has been suggested to play important roles in the growth and survival of a variety of tumor types. The aim of this study is to develop a dual-modality probe (64Cu -DOTA-NT-Cy5.5) for imaging NTR1 expression in vivo with both positron emission tomography (PET) and fluorescence. In this approach, the thiol group and N terminal amino group of neurotensin analogue (Cys-NT) were chemically modified with Cy5.5 dye and DOTA chelator, respectively. After radiolabeling with 64Cu, the resulting probe (64Cu-DOTA-NT-Cy5.5) was evaluated in NTR1 positive HT-29 tumor model. Small animal PET quantification analysis demonstrated that the tumor uptake was 1.91±0.22 and 1.79±0.16%ID/g at 1 and 4 h postinjection (p.i.), respectively. The tumor-to-muscle ratio was 17.44±3.25 at 4 h p.i. based on biodistribution. Receptor specificity was confirmed by the successful blocking experiment at 4 h p.i. (0.42±0.05%ID/g). In parallel with PET experiment, fluorescence imaging was also performed, which demonstrated prominent tumor uptake in HT-29 model. As a proof of concept, an imaging guided surgery was performed to the fluorescent moiety of this probe and could provide potential surgery guidance for NTR positive patients. In summary, our results clearly indicated that the dual-modality probe, 64Cu-DOTA-NT-Cy5.5, could serve as a promising agent to image NTR positive tumors in vivo.

Superparamagnetic core/shell GoldMag nanoparticles: size-, concentration- and time-dependent cellular nanotoxicity on human umbilical vein endothelial cells and the suitable conditions for magnetic resonance imaging

Background

GoldMag nanoparticles (GMNPs) possess the properties of colloid gold and superparamagnetic iron oxide nanoparticles, which make them useful for delivery, separation and molecular imaging. However, because of the nanometer effect, GMNPs are highly toxic. Thus, the biosafety of GMNPs should be fully studied prior to their use in biomedicine. The main purpose of this study was to evaluate the nanotoxicity of GMNPs on human umbilical vein endothelial cells (HUVECs) and determine a suitable size, concentration and time for magnetic resonance imaging (MRI).

Results

Transmission electron microscopy showed that GMNPs had a typical shell/core structure, and the shell was confirmed to be gold using energy dispersive spectrometer analysis. The average sizes of the 30 and 50 nm GMNPs were 30.65 ± 3.15 and 49.23 ± 5.01 nm, respectively, and the shell thickness were 6.8 ± 0.65 and 8.5 ± 1.36 nm, respectively. Dynamic light scattering showed that the hydrodynamic diameter of the 30 and 50 nm GMNPs were 33.2 ± 2.68 and 53.12 ± 4.56 nm, respectively. The r₂ relaxivity of the 50 nm GMNPs was 98.65 mM⁻¹ s⁻¹, whereas it was 80.18 mM⁻¹ s⁻¹ for the 30 nm GMNPs. The proliferation, cytoskeleton, migration, tube formation, apoptosis and ROS generation of labeled HUVECs depended on the size and concentration of GMNPs and the time of exposure. Because of the higher labeling rate, the 50 nm GMNPs exhibited a significant increase in nanotoxicity compared with the 30 nm GMNPs at the same concentration and time. At no more than 25 μg/mL and 12 hours, the 50 nm GMNPs exhibited no significant nanotoxicity in HUVECs, whereas no toxicity was observed at 50 μg/mL and 24 hours for the 30 nm GMNPs.

Conclusions

These results demonstrated that the nanotoxicity of GMNPs in HUVECs depended on size, concentration and time. Exposure to larger GMNPs with a higher concentration for a longer period of time resulted in a higher labeling rate and ROS level for HUVECs. Coupled with r₂ relaxivity, it was suggested that the 50 nm GMNPs are more suitable for HUVEC labeling and MRI, and the suitable concentration and time were 25 μg/mL and 12 hours.

Detection of vulnerable atherosclerosis plaques with a dual-modal single-photon-emission computed tomography/magnetic resonance imaging probe targeting apoptotic macrophages

Atherosclerosis (AS), especially the vulnerable AS plaque rupture-induced acute obstructive vascular disease, is a leading cause of death. Accordingly, there is a need for an effective method to draw accurate predictions about AS progression and plaque vulnerability. Herein we report on an approach to constructing a hybrid nanoparticle system using a single-photon-emission computed tomography (SPECT)/magnetic resonance imaging (MRI) multimodal probe, aiming for a comprehensive evaluation of AS progression by achieving high sensitivity along with high resolution. Ultrasmall superparamagnetic iron oxide (USPIO) was covered by aminated poly(ethylene glycol) (PEG) and carboxylated PEG simultaneously and then functionalized with diethylenetriaminepentacetate acid for (99m)Tc coordination and subsequently Annexin V for targeting apoptotic macrophages abundant in vulnerable plaques. The in vivo accumulations of imaging probe reflected by SPECT and MRI were consistent and accurate in highlighting lesions. Intense radioactive signals detected by SPECT facilitated focus recognization and quantification, while USPIO-based T2-weighted MRI improved the focal localization and volumetry of AS plaques. For subsequent ex vivo planar images, targeting effects were further confirmed by immunohistochemistry, including CD-68 and TUNEL staining; meanwhile, the degree of concentration was proven to be statistically correlated with the Oil Red O staining results. In conclusion, these results indicated that the Annexin V-modified hybrid nanoparticle system specifically targeted the vulnerable AS plaques containing apoptotic macrophages and could be of great value in the invasively accurate detection of vulnerable plaques.

The role of molecular imaging in diagnosis of deep vein thrombosis

Venous thromboembolism (VTE) mostly presenting as deep venous thrombosis (DVT) and pulmonary embolism (PE) affects up to 600,000 individuals in United States each year. Clinical symptoms of VTE are nonspecific and sometimes misleading. Additionally, side effects of available treatment plans for DVT are significant. Therefore, medical imaging plays a crucial role in proper diagnosis and avoidance from over/under diagnosis, which exposes the patient to risk. In addition to conventional structural imaging modalities, such as ultrasonography and computed tomography, molecular imaging with different tracers have been studied for diagnosis of DVT. In this review we will discuss currently available and newly evolving targets and tracers for detection of DVT using molecular imaging methods.

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.

Iodinated oil-loaded, fluorescent mesoporous silica-coated iron oxide nanoparticles for magnetic resonance imaging/computed tomography/fluorescence trimodal imaging

In this study, a novel magnetic resonance imaging (MRI)/computed tomography (CT)/fluorescence trifunctional probe was prepared by loading iodinated oil into fluorescent mesoporous silica-coated superparamagnetic iron oxide nanoparticles (i-fmSiO4@SPIONs). Fluorescent mesoporous silica-coated superparamagnetic iron oxide nanoparticles (fmSiO4@SPIONs) were prepared by growing fluorescent dye-doped silica onto superparamagnetic iron oxide nanoparticles (SPIONs) directed by a cetyltrimethylammonium bromide template. As prepared, fmSiO4@SPIONs had a uniform size, a large surface area, and a large pore volume, which demonstrated high efficiency for iodinated oil loading. Iodinated oil loading did not change the sizes of fmSiO4@SPIONs, but they reduced the MRI T2 relaxivity (r2) markedly. I-fmSiO4@SPIONs were stable in their physical condition and did not demonstrate cytotoxic effects under the conditions investigated. In vitro studies indicated that the contrast enhancement of MRI and CT, and the fluorescence signal intensity of i-fmSiO4@SPION aqueous suspensions and macrophages, were intensified with increased i-fmSiO4@SPION concentrations in suspension and cell culture media. Moreover, for the in vivo study, the accumulation of i-fmSiO4@SPIONs in the liver could also be detected by MRI, CT, and fluorescence imaging. Our study demonstrated that i-fmSiO4@SPIONs had great potential for MRI/CT/fluorescence trimodal imaging.

Fe5C2 nanoparticles with high MRI contrast enhancement for tumor imaging

An ancient material for magnetic resonance (MR) imaging: For the first time, Fe5C2 is prepared as colloidal stable nanoparticles with good aqueous stability. The nanoparticles boast strong magnetization, excellent chemical inertness, low toxicity, and one of the highest r2 relaxivities reported to date. These nanoparticles hold great potential in MR imaging as well as in other biomedical areas.

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.

Efficient construction of PET/fluorescence probe based on sarcophagine cage: an opportunity to integrate diagnosis with treatment

PURPOSE

Due to the shortage of established platforms/methods for multimodality probe construction, in this study, we developed a heterofunctional chelator, BaAn(Boc)Sar, from sarcophagine cage as a general platform for dual-modality probe construction.

PROCEDURES

A dual-modality probe for positron-emission tomography (PET) and fluorescence imaging was synthesized using the developed BaAn(Boc)Sar chelator. The c(RGDyK)(2) peptide (denoted as RGD(2)) and fluorescence dye Cy5.5 were conjugated with BaAn(Boc)Sar to form BaAnSar-RGD(2)-Cy5.5. Then, BaAnSar-RGD(2)-Cy5.5 was labeled with (64)Cu in ammonium acetate buffer. PET and fluorescent imaging were carried out to evaluate (64)Cu-BaAnSar-RGD(2)-Cy5.5 in nude mice bearing U87MG glioblastoma xenograft.

RESULTS

The BaAnSar-RGD(2)-Cy5.5 was labeled with (64)Cu very efficiently in 0.1 M NH(4)OAc buffer within 10 min at 37 °C in the yield of 86.7 ± 4.4 % (n = 3). The specific activity of (64)Cu-BaBaSar-RGD(2) was controlled at 50-200 mCi/μmol for the consideration of both PET and optical imaging. MicroPET quantification analysis shows that the U87MG tumor uptake is 6.41 ± 0.28, 6.51 ± 1.45, and 5.92 ± 1.57 %ID/g at 1, 4, and 20 h postinjection, respectively. Good correlation was obtained between the tumor to muscle ratios measured by the radioactivity and fluorescence intensity. As a proof of concept, an animal surgery study demonstrated that this dual-modality probe would greatly benefit the patients because the PET moiety could be used for tumor detection, and the fluorescent moiety would allow image-guided surgery.

CONCLUSIONS

Our findings demonstrated the effectiveness and feasibility of preparing dual-modality imaging probes based on the sarcophagine scaffold. The resulting PET and fluorescent imaging probe also holds a great potential for clinical translation.

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.

RGD-based PET tracers for imaging receptor integrin αv β3 expression

Positron emission tomography (PET) imaging of receptor integrin αv β3 expression may play a key role in the early detection of cancer and cardiovascular diseases, monitoring disease progression, evaluating therapeutic response, and aiding anti-angiogenic drugs discovery and development. The last decade has seen the development of new PET tracers for in vivo imaging of integrin αv β3 expression along with advances in PET chemistry. In this review, we will focus on the radiochemistry development of PET tracers based on arginine-glycine-aspartic acid (RGD) peptide, present an overview of general strategies for preparing RGD-based PET tracers, and review the recent advances in preparations of (18) F-labeled, (64) Cu-labeled, and (68) Ga-labeled RGD tracers, RGD-based PET multivalent probes, and RGD-based PET multimodality probes for imaging receptor integrin αv β3 expression.

Optical imaging of tumor microenvironment

Tumor microenvironment plays important roles in tumor development and metastasis. Features of the tumor microenvironment that are significantly different from normal tissues include acidity, hypoxia, overexpressed proteases and so on. Therefore, these features can serve as not only biomarkers for tumor diagnosis but also theraputic targets for tumor treatment. Imaging modalities such as optical, positron emission tomography (PET) and magnetic resonance imaging (MRI) have been intensively applied to investigate tumor microenvironment. Various imaging probes targeting pH, hypoxia and proteases in tumor microenvironment were thus well developed. In this review, we will focus on recent examples on fluorescent probes for optical imaging of tumor microenvironment. Construction of these fluorescent probes were based on characteristic feature of pH, hypoxia and proteases in tumor microenvironment. Strategies for development of these fluorescent probes and applications of these probes in optical imaging of tumor cells or tissues will be discussed in this review paper.

Folic acid-conjugated LaF3:Yb,Tm@SiO2 nanoprobes for targeting dual-modality imaging of upconversion luminescence and X-ray computed tomography

Development of multimodal contrast agents for in vivo simultaneous multimodality imaging is an emerging interdiscipline that is paving the avenue toward the goal of personalized medicine. Herein, folic acid-conjugated silica-modified LaF(3):Yb,Tm upconversion nanoparticles (UCNPs@SiO(2)-FA) with high La content in a single particle were strategically designed and prepared for simultaneously targeting dual-modality imaging of upconversion luminescence (UCL) and X-ray computed tomography (CT). LaF(3) UCNPs were synthesized by a novel oleic acid (OA)/ionic liquid (IL) two-phase system. Afterward, a folic acid molecule was covalently anchored on the surface of UCNPs with a silane coupling agent. The UCNPs@SiO(2)-FA exhibits good stability, water dispersibility and solubility, low cytotoxicity, good biocompatibility, highly selective targeting, excellent X-ray attenuation, and UCL emission under excitation at 980 nm. In vivo UCL and CT images of mice show the UCNPs@SiO(2)-FA can be used in targeting dual-modality imaging. These results suggest that the as-prepared nanoprobe is a good candidate with excellent imaging and targeting ability for targeting dual-modality imaging of UCL and CT.

A novel solid lipid nanoparticle formulation for active targeting to tumor α(v) β(3) integrin receptors reveals cyclic RGD as a double-edged sword

The overexpression of α(v) β(3) integrin receptors on tumor cells and tumor vascular endothelium makes it a useful target for imaging, chemotherapy and anti-angiogenic therapy. However integrin-targeted delivery of therapeutics by nanoparticles have provided only marginal, if any, enhancement of therapeutic effect. This work was thus focused on the development of novel α(v) β(3) -targeted near infrared light-emitting solid lipid nanoparticles (SLN) through conjugation to the α(v) β(3) integrin-specific ligand cyclic Arg-Gly-Asp (cRGD), and the assessment of the effects of α(v) β(3) targeting on nanoparticle biodistribution. Since our previously developed non-targeted "stealth" SLN showed little hepatic accumulation, unlike most reported liposomes and micelles, they served as a reference for quantifying the effects of cRGD-conjugation on tumor uptake and whole animal biodistribution of SLN. Non-targeted SLN, actively targeted (RGD-SLN) and blocked RGD-SLN were prepared to contain near infrared quantum dots for live animal imaging. They were injected intravenously to nude mice bearing xenograft orthotopic human breast tumors or dorsal window chamber breast tumors. Tumor micropharmacokinetics of various SLN formulations were determined using intravital microscopy, and whole animal biodistribution was followed over time by optical imaging. The active tumor targeting with cRGD was found to be a "double-edged sword": while the specificity of RGD-SLN accumulation in tumor blood vessels and their tumor residence time increased, their distribution in the liver, spleen, and kidneys was significantly greater than the non-targeted SLN, leaving a smaller amount of nanoparticles in the tumor tissue. Nevertheless the enhanced specificity and retention of RGD-SLN in tumor neovasculature could make this novel formulation useful for tumor neovascular-specific therapies and imaging applications.

Gold Nanorods Conjugated with Doxorubicin and cRGD for Combined Anticancer Drug Delivery and PET Imaging

A multifunctional gold nanorod (GNR)-based nanoplatform for targeted anticancer drug delivery and positron emission tomography (PET) imaging of tumors was developed and characterized. An anti-cancer drug (i.e., doxorubicin (DOX)) was covalently conjugated onto PEGylated (PEG: polyethylene glycol) GNR nanocarriers via a hydrazone bond to achieve pH-sensitive controlled drug release. Tumor-targeting ligands (i.e., the cyclo(Arg-Gly-Asp-D-Phe-Cys) peptides, cRGD) and ⁶⁴Cu-chelators (i.e., 1,4,7-triazacyclononane-N, N', N''-triacetic acid (NOTA)) were conjugated onto the distal ends of the PEG arms to achieve active tumor-targeting and PET imaging, respectively. Based on flow cytometry analysis, cRGD-conjugated nanocarriers (i.e., GNR-DOX-cRGD) exhibited a higher cellular uptake and cytotoxicity than non-targeted ones (i.e., GNR-DOX) in vitro. However, GNR-DOX-cRGD and GNR-DOX nanocarriers had similar in vivo biodistribution according to in vivo PET imaging and biodistribution studies. Due to the unique optical properties of GNRs, this multifunctional GNR-based nanoplatform can potentially be optimized for combined cancer therapies (chemotherapy and photothermal therapy) and multimodality imaging (PET, optical, X-ray computed tomography (CT), etc.).

The efficient synthesis and biological evaluation of novel bi-functionalized sarcophagine for (64)cu radiopharmaceuticals

Purpose We and others have reported that Sarcophagine-based bifunctional chelators could be effectively used in the syntheses of ⁶⁴Cu radiopharmaceuticals. The resulted ⁶⁴Cu-Sarcophagine complexes demonstrated great in vivo stability. The goal of this study was to further derivatize Sarcophagine cage with amino and maleimide functional groups for conjugation with bioligands.

Methods Starting from DiAmSar, three novel chelators (AnAnSar, BaMalSar, and Mal₂Sar) with two functional groups have been synthesized. Among those, BaMalSar and Mal₂Sar have been conjugated with cyclic peptide c(RGDyC) (denoted as RGD) and the resulted conjugates, BaMalSar-RGD and Mal₂Sar-RGD₂ have been labeled with ⁶⁴Cu. The tumor targeting efficacy of ⁶⁴Cu-labeled RGD peptides were evaluated in a subcutaneous U87MG glioblastoma xenograft model.

Results The conjugates, BaMalSar-RGD and Mal₂Sar-RGD₂ could be labeled with ⁶⁴CuCl₂ in 10 min with high purity (>98%) and high radiochemical yield (>90%). Both ⁶⁴Cu-BaMalSar-RGD and ⁶⁴Cu-Mal₂Sar-RGD₂ exhibited high tumor uptake and tumor-to-normal tissue ratios.

Conclusion Three novel chelators with two functional groups have been developed based on Sarcophagine cage. The platform developed in this study could have broad applications in the design and synthesis of ⁶⁴Cu-radiopharmaceuticals.

Long-term multimodal imaging of tumor draining sentinel lymph nodes using mesoporous silica-based nanoprobes

The imaging of sentinel lymph nodes (SLNs), the first defense against primary tumor metastasis, has been considered as an important strategy for noninvasive tracking tumor metastasis in clinics. In this study, we report the development and application of mesoporous silica-based triple-modal nanoprobes that integrate multiple functional moieties to facilitate near-infrared optical, magnetic resonance (MR) and positron emission tomography (PET) imaging. After embedding near-infrared dye ZW800, the nanoprobe was labeled with T(1) contrast agent Gd(3+) and radionuclide (64)Cu through chelating reactions. High stability and long intracellular retention time of the nanoprobes was confirmed by in vitro characterization, which facilitate long-term in vivo imaging. Longitudinal multimodal imaging was subsequently achieved to visualize tumor draining SLNs up to 3 weeks in a 4T1 tumor metastatic model. Obvious differences in uptake rate, amount of particles, and contrast between metastatic and contra-lateral sentinel lymph nodes were observed. These findings provide very helpful guidance for the design of robust multifunctional nanomaterials in SLNs' mapping and tumor metastasis diagnosis.

Applications of magnetic microbubbles for theranostics

Compared with other diagnostic methods, ultrasound is proven to be a safe, simple, non-invasive and cost-effective imaging technique, but the resolution is not comparable to that of magnetic resonance imaging (MRI). Contrast-enhanced ultrasound employing microbubbles can gain a better resolution and is now widely used to diagnose a number of diseases in the clinic. For the last decade, microbubbles have been widely used as ultrasound contrast agents, drug delivery systems and nucleic acid transfection tools. However, microbubbles are not fairly stable enough in some conditions and are not well administrated distributed in the circulation system. On the other hand, magnetic nanoparticles, as MRI contrast agents, can non-specifically penetrate into normal tissues because of their relatively small sizes. By taking advantage of these two kinds of agents, the magnetic microbubbles which couple magnetic iron oxides nanoparticles in the microbubble structure have been explored. The stability of microbubbles can be raised by encapsulating magnetic nanoparticles into the bubble shells and with the guidance of magnetic field, magnetic microbubbles can be delivered to regions of interest, and after appropriate ultrasound exposure, the nanoparticles can be released to the desired area while the magnetic microbubbles collapse. In this review, we summarize magnetic microbubbles used in diagnostic and therapeutic fields, and predict the potential applications of magnetic microbubbles in the future.

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.

Trackable and Targeted Phage as Positron Emission Tomography (PET) Agent for Cancer Imaging

The recent advancement of nanotechnology has provided unprecedented opportunities for the development of nanoparticle enabled technologies for detecting and treating cancer. Here, we reported the construction of a PET trackable organic nanoplatform based on phage particle for targeted tumor imaging. Method: The integrin α_vβ₃ targeted phage nanoparticle was constructed by expressing RGD peptides on its surface. The target binding affinity of this engineered phage particle was evaluated in vitro. A bifunctional chelator (BFC) 1,4,7,10-tetraazadodecane-N,N',N",N"'-tetraacetic acid (DOTA) or 4-((8-amino-3,6,10,13,16,19-hexaazabicyclo [6.6.6] icosane-1-ylamino) methyl) benzoic acid (AmBaSar) was then conjugated to the phage surface for ⁶⁴Cu²⁺ chelation. After ⁶⁴Cu radiolabeling, microPET imaging was performed in U87MG tumor model and the receptor specificity was confirmed by blocking experiments. Results: The phage-RGD demonstrated target specificity based on ELISA experiment. According to the TEM images, the morphology of the phage was unchanged after the modification with BFCs. The labeling yield was 25 ± 4% for ⁶⁴Cu-DOTA-phage-RGD and 46 ± 5% for ⁶⁴Cu-AmBaSar-phage-RGD, respectively. At 1 h time point, ⁶⁴Cu-DOTA-phage-RGD and ⁶⁴Cu-AmBaSar-phage-RGD have comparable tumor uptake (~ 8%ID/g). However, ⁶⁴Cu-AmBaSar-phage-RGD showed significantly higher tumor uptake (13.2 ± 1.5 %ID/g, P<0.05) at late time points compared with ⁶⁴Cu-DOTA-phage-RGD (10 ± 1.2 %ID/g). ⁶⁴Cu-AmBaSar-phage-RGD also demonstrated significantly lower liver uptake, which could be attributed to the stability difference between these chelators. There is no significant difference between two tracers regarding the uptake in kidney and muscle at all time points tested. In order to confirm the receptor specificity, blocking experiment was performed. In the RGD blocking experiment, the cold RGD peptide was injected 2 min before the administration of ⁶⁴Cu-AmBaSar-phage-RGD. Tumor uptake was partially blocked at 1 h time point. Phage-RGD particle was also used as the competitive ligand. In this case, the tumor uptake was significantly reduced and the value was kept at low level consistently. Conclusion: In this report, we constructed a PET trackable nanoplatform based on phage particle and demonstrated the imaging capability of these targeted agents. We also demonstrated that the choice of chelator could have significant impact on imaging results of nano-agents. The method established in this research may be applicable to other receptor/ligand systems for theranostic agent construction, which could have an immediate and profound impact on the field of imaging/therapy and lay the foundation for the construction of next generation cancer specific theranostic agents.

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.

Transforming a Targeted Porphyrin Theranostic Agent into a PET Imaging Probe for Cancer

Porphyrin based photosensitizers are useful agents for photodynamic therapy (PDT) and fluorescence imaging of cancer. Porphyrins are also excellent metal chelators forming highly stable metallo-complexes making them efficient delivery vehicles for radioisotopes. Here we investigated the possibility of incorporating (64)Cu into a porphyrin-peptide-folate (PPF) probe developed previously as folate receptor (FR) targeted fluorescent/PDT agent, and evaluated the potential of turning the resulting (64)Cu-PPF into a positron emission tomography (PET) probe for cancer imaging. Noninvasive PET imaging followed by radioassay evaluated the tumor accumulation, pharmacokinetics and biodistribution of (64)Cu-PPF. (64)Cu-PPF uptake in FR-positive tumors was visible on small-animal PET images with high tumor-to-muscle ratio (8.88 ± 3.60) observed after 24 h. Competitive blocking studies confirmed the FR-mediated tracer uptake by the tumor. The ease of efficient (64)Cu-radiolabeling of PPF while retaining its favorable biodistribution, pharmacokinetics and selective tumor uptake, provides a robust strategy to transform tumor-targeted porphyrin-based photosensitizers into PET imaging probes.

Multimodal bacteriochlorophyll theranostic agent

The complimentary ability of different noninvasive imaging technologies with therapeutic modalities can be used in tandem providing high-resolution and highly sensitive imaging of events at the molecular and cellular level providing a means for image-guided therapy. There is increasing interest in using porphyrin-based photosensitizers as theranostics to take advantages of their near-infrared fluorescent properties for imaging and their strong singlet oxygen generation abilities for photodynamic therapy. Here we report a targeted multimodal bacteriochlorophyll theranostic probe. This probe consists of a bacteriochlorophyll derivative, a pharmacokinetics modification peptide linker and folate for targeted delivery to folate receptor expressing cancer cells. We demonstrate its multimodal theranostic capability, its folate receptor targeting ability and its utility for both NIR fluorescence imaging and photodynamic therapy purposes both in vitro and in vivo.

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.

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.