Emerging nanobiotechnology-encoded relaxation tuning establishes new MRI modes to localize, monitor and predict diseases

Magnetic resonance imaging (MRI) is one of the most important techniques in the diagnosis of many diseases including cancers, where contrast agents (CAs) are usually necessary to improve its precision and sensitivity. Previous MRI CAs are confined to the signal-to-noise ratio (SNR) elevation of lesions for precisely localizing lesions. As nanobiotechnology advances, some new MRI CAs or nanobiotechnology-enabled MRI modes have been established to vary the longitudinal or transverse relaxation of CAs, which are harnessed to detect lesion targets, monitor disease evolution, predict or evaluate curative effect, etc. These distinct cases provide unexpected insights into the correlation of the design principles of these nanobiotechnologies and corresponding MRI CAs with their potential applications. In this review, first, we briefly present the principles, classifications and applications of conventional MRI CAs, and then elucidate the recent advances in relaxation tuning via the development of various nanobiotechnologies with emphasis on the design strategies of nanobiotechnology and the corresponding MRI CAs to target the tumor microenvironment (TME) and biological targets or activities in tumors or other diseases. In addition, we exemplified the advantages of these strategies in disease theranostics and explored their potential application fields. Finally, we analyzed the present limitations, potential solutions and future development direction of MRI after its combination with nanobiotechnology.

68Ga-WRWWWW Is a Potential Positron Emission Tomography Probe for Imaging Inflammatory Diseases by Targeting Formyl Peptide Receptor 2

Inflammation plays a significant role in many physiological and pathological processes. Molecular imaging could provide functional as well as anatomical information for visualizing various inflammatory diseases. Advancements in imaging tracers for inflammation would improve the accuracy of diagnosis and monitoring, thus facilitating patient care. The positron emission tomography (PET) imaging tracer, ⁶⁸Ga-labeled antagonist peptide Trp-Arg-Trp-Trp-Trp-Trp (WRWWWW, WRW⁴), targets formyl peptide receptor 2 (FPR2), which is in turn widely distributed in a variety of tissues and is associated with many inflammatory diseases. In the current study, we aimed to investigate the potential of ⁶⁸Ga-WRW⁴ for detecting and monitoring inflammatory lesions in mice. We established an inflammation mouse model by the intramuscular injection of turpentine oil into the left thigh. WRW⁴ was labeled with ⁶⁸Ga with an overall radiochemical yield >90% and radiochemical purity >99%. ⁶⁸Ga-WRW⁴ uptake in inflamed muscle peaked on day 2 (1.14 ± 0.01 percentage of the injected dose per gram of tissue (%ID/g)) and the uptake ratio of inflammatory/normal muscle also reached a maximum (12.36 ± 2.35). Strong PET signals were detected in the left thigh at 60 min after the injection of ⁶⁸Ga-WRW⁴ in experimental mice, but weak or no signals were detected in mice in the blocking and control groups. ⁶⁸Ga-WRW⁴ uptake was in agreement with the dynamics of immune cell infiltration during the inflammatory reaction. These results suggest that ⁶⁸Ga-WRW⁴ is a promising PET tracer suitable for the noninvasive detection of FPR2 expression and for monitoring inflammatory activity in inflammation-bearing mice.

Tuberculosis: Role of Nuclear Medicine and Molecular Imaging With Potential Impact of Neutrophil-Specific Tracers

With Tuberculosis (TB) affecting millions of people worldwide, novel imaging modalities and tools, particularly nuclear medicine and molecular imaging, have grown with greater interest to assess the biology of the tuberculous granuloma and evolution thereof. Much early work has been performed at the pre-clinical level using gamma single photon emission computed tomography (SPECT) agents exploiting certain characteristics of Mycobacterium tuberculosis (MTb). Both antituberculous SPECT and positron emission tomography (PET) agents have been utilised to characterise MTb. Other PET tracers have been utilised to help to characterise the biology of MTb (including Gallium-68-labelled radiopharmaceuticals). Of all the tracers, 2-[¹⁸F]FDG has been studied extensively over the last two decades in many aspects of the treatment paradigm of TB: at diagnosis, staging, response assessment, restaging, and in potentially predicting the outcome of patients with latent TB infection. Its lower specificity in being able to distinguish different inflammatory cell types in the granuloma has garnered interest in reviewing more specific agents that can portend prognostic implications in the management of MTb. With the neutrophil being a cell type that portends this poorer prognosis, imaging this cell type may be able to answer more accurately questions relating to the tuberculous granuloma transmissivity and may help in characterising patients who may be at risk of developing active TB. The formyl peptide receptor 1(FPR1) expressed by neutrophils is a key marker in this process and is a potential target to characterise these areas. The pre-clinical work regarding the role of radiolabelled N-cinnamoyl –F-(D) L – F – (D) –L F (cFLFLF) (which is an antagonist for FPR1) using Technetium 99m-labelled conjugates and more recently radiolabelled with Gallium-68 and Copper 64 is discussed. It is the hope that further work with this tracer may accelerate its potential to be utilised in responding to many of the current diagnostic dilemmas and challenges in TB management, thereby making the tracer a translatable option in routine clinical care.

Retention of 64Cu-FLFLF, a Formyl Peptide Receptor 1-Specific PET Probe, Correlates with Macrophage and Neutrophil Abundance in Lung Granulomas from Cynomolgus Macaques

Neutrophilic inflammation correlates with severe tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb). Granulomas are lesions that form in TB, and a PET probe for following neutrophil recruitment to granulomas could predict disease progression. We tested the formyl peptide receptor 1 (FPR1)-targeting peptide FLFLF in Mtb-infected macaques. Preliminary studies in mice demonstrated specificity for neutrophils. In macaques, 64Cu-FLFLF was retained in lung granulomas and analysis of lung granulomas identified positive correlations between 64Cu-FLFLF and neutrophil and macrophage numbers (R2 = 0.8681 and 0.7643, respectively), and weaker correlations for T cells and B cells (R2 = 0.5744 and 0.5908, respectively), suggesting that multiple cell types drive 64Cu-FLFLF avidity. By PET/CT imaging, we found that granulomas retained 64Cu-FLFLF but with less avidity than the glucose analog 18F-FDG. These studies suggest that neutrophil-specific probes have potential PET/CT applications in TB, but important issues need to be addressed before they can be used in nonhuman primates and humans.

Smart magnetic resonance imaging-based theranostics for cancer

Smart theranostics are dynamic platforms that integrate multiple functions, including at least imaging, therapy, and responsiveness, in a single agent. This review showcases a variety of responsive theranostic agents developed specifically for magnetic resonance imaging (MRI), due to the privileged position this non-invasive, non-ionising imaging modality continues to hold within the clinical imaging field. Different MRI smart theranostic designs have been devised in the search for more efficient cancer therapy, and improved diagnostic efficiency, through the increase of the local concentration of therapeutic effectors and MRI signal intensity in pathological tissues. This review explores novel small-molecule and nanosized MRI theranostic agents for cancer that exhibit responsiveness to endogenous (change in pH, redox environment, or enzymes) or exogenous (temperature, ultrasound, or light) stimuli. The challenges and obstacles in the design and in vivo application of responsive theranostics are also discussed to guide future research in this interdisciplinary field towards more controllable, efficient, and diagnostically relevant smart theranostics agents.

In vivo assessing colitis severity by topical administration of fluorescent probe against neutrophils

Inflammatory bowel disease has become a global burden given its high incidence and refractory to medical treatment. Improved diagnostic strategies to monitor disease activity more accurately are necessary to conduct and evaluate medical treatment. High level of neutrophil infiltration in colon is associated with poor prognosis and enhanced risk of developing colitis-associated cancer. Herein, to accurately monitor neutrophil levels in colitis condition, we designed and constructed a specific probe (CPM), consisting of a neutrophil formyl peptide receptor targeting group (cFLFLFK), a short PEG linker and a near-infrared fluorescent dye. CPM selectively identified neutrophils in vitro and preferentially recognized neutrophils in vivo with enhanced targeting ability and biodistribution property. After verified the ability to target activated neutrophils, CPM was used to detect neutrophils in experimental colitis by systemic and topical administration. Compared to systemic administration, topical administration of CPM allows lower dosage, higher target-to-background ratio and longer duration of effective monitoring. More importantly, we used CPM to assess neutrophil levels in the course of colitis development. The fluorescence intensity of CPM increased along with colitis progression. Additionally, CPM was used to detected neutrophil levels in colitis-associated cancer and enhanced neutrophil infiltration in the tumor sites was detected. In conclusion, the probe CPM is a promising tool for in vivo improved diagnosis of colitis severity by monitoring the extent of neutrophil infiltration.

Targeting of Formyl Peptide Receptor 2 for in vivo imaging of acute vascular inflammation

Inflammatory conditions are associated with a variety of diseases and can significantly contribute to their pathophysiology. Neutrophils are recognised as key players in driving vascular inflammation and promoting inflammation resolution. As a result, neutrophils, and specifically their surface formyl peptide receptors (FPRs), are attractive targets for non-invasive visualization of inflammatory disease states and studying mechanistic details of the process.

Methods: A small-molecule Formyl Peptide Receptor 2 (FPR2/ALX)-targeted compound was combined with two rhodamine-derived fluorescent tags to form firstly, a targeted probe (Rho-pip-C1) and secondly a targeted, pH-responsive probe (Rho-NH-C1) for in vivo applications. We tested internalization, toxicity and functional interactions with neutrophils in vitro for both compounds, as well as the fluorescence switching response of Rho-NH-C1 to neutrophil activation. Finally, in vivo imaging (fluorescent intravital microscopy [IVM]) and therapeutic efficacy studies were performed in an inflammatory mouse model.

Results: In vitro studies showed that the compounds bound to human neutrophils via FPR2/ALX without causing internalization at relevant concentrations. Additionally, the compounds did not cause toxicity or affect neutrophil functional responses (e.g. chemotaxis or transmigration). In vivo studies using IVM showed Rho-pip-C1 bound to activated neutrophils in a model of vascular inflammation. The pH-sensitive (“switchable”) version termed Rho-NH-C1 validated these findings, showing fluorescent activity only in inflammatory conditions.

Conclusions: These results indicate a viable design of fluorescent probes that have the ability to detect inflammatory events by targeting activated neutrophils.

SPECT imaging of lung ischemia-reperfusion injury using [99mTc]cFLFLF for molecular targeting of formyl peptide receptor 1

Primary graft dysfunction after lung transplantation, a consequence of ischemia-reperfusion injury (IRI), is a major cause of morbidity and mortality. IRI involves acute inflammation and innate immune cell activation, leading to rapid infiltration of neutrophils. Formyl peptide receptor 1 (FPR1) expressed by phagocytic leukocytes plays an important role in neutrophil function. The cell surface expression of FPR1 is rapidly and robustly upregulated on neutrophils in response to inflammatory stimuli. Thus, we hypothesized that use of [^99mTc]cFLFLF, a selective FPR1 peptide ligand, would permit in vivo neutrophil labeling and noninvasive imaging of IRI using single-photon emission computed tomography (SPECT). A murine model of left lung IRI was utilized. Lung function, neutrophil infiltration, and SPECT imaging were assessed after 1 h of ischemia and 2, 12, or 24 h of reperfusion. [^99mTc]cFLFLF was injected 2 h before SPECT. Signal intensity by SPECT and total probe uptake by gamma counts were 3.9- and 2.3-fold higher, respectively, in left lungs after ischemia and 2 h of reperfusion versus sham. These values significantly decreased with longer reperfusion times, correlating with resolution of IRI as shown by improved lung function and decreased neutrophil infiltration. SPECT results were confirmed using Cy7-cFLFLF-based fluorescence imaging of lungs. Immunofluorescence microscopy confirmed cFLFLF binding primarily to activated neutrophils. These results demonstrate that [^99mTc]cFLFLF SPECT enables noninvasive detection of lung IRI and permits monitoring of resolution of injury over time. Clinical application of [^99mTc]cFLFLF SPECT may permit diagnosis of lung IRI for timely intervention to improve outcomes after transplantation.

Development, characterisation and in vitro evaluation of lanthanide-based FPR2/ALX-targeted imaging probes

We report the design, preparation and characterisation of three small-molecule, Formyl Peptide Receptor (FPR)-targeted lanthanide complexes (Tb·14, Eu·14 and Gd·14). Long-lived, metal-based emission was observed from the terbium complex (τH2O = 1.9 ms), whereas only negligible lanthanide signals were detected in the europium analogue. Ligand-centred emission was investigated using Gd·14 at room temperature and 77 K, leading to the postulation that metal emission may be sensitised via a ligand-based charge transfer state of the targeting Quin C1 unit. Comparatively high longitudinal relaxivity values (r1) for octadentate metal complexes of Gd·14 were determined (6.9 mM-1 s-1 at 400 MHz and 294 K), which could be a result of a relative increase in twisted square antiprism (TSAP) isomer prevalence compared to typical DOTA constructs (as evidenced by NMR spectroscopy). In vitro validation of concentration responses of Tb·14via three key neutrophil functional assays demonstrated that the inflammatory responses of neutrophils (i.e. chemotaxis, transmigration and granular release) remained unchanged in the presence of specific concentrations of the compound. Using a time-resolved microscopy set-up we were able to observe binding of the Tb·14 probe to stimulated human neutrophils around the cell periphery, while in the same experiment with un-activated neutrophils, no metal-based signals were detected. Our results demonstrate the utility of Tb·14 for time-resolved microscopy with lifetimes several orders of magnitude longer than autofluorescent signals and a preferential uptake in stimulated neutrophils.

Ln(III) chelates-functionalized carbon quantum dots: Synthesis, optical studies and multimodal bioimaging applications

The carbon quantum dots termined with amine groups (CQDs-NH₂) were synthesized in one-pot hydrothermal method with citric acid as carbon source and branched polyethylenimine (BPEI) as passive agent, which was then covalently linked to 1, 4, 7, 10-tetraazacyclononane (DOTA) framework to yield CQDs-DOTA. The CQDs-DOTA provide excellent ligand scaffolds for the chelation of lanthanide ions, yielding the related complexes CQDs-DOTA-Ln (Ln = Eu, Tb, Yb and Gd). The successful preparation of CQDs-DOTA-Ln was validated by TEM, XRD, XPS, and FT-IR spectroscopy. The CQDs-DOTA-Ln (Ln = Eu, Tb and Yb) exhibited the characteristic emissions of related lanthanide ions, indicating the CQDs could sensitize the luminescence of lanthanide ions. Besides, the CQDs-DOTA-Gd could serve as an excellent T1-weighted MR imaging probe due to the chelation of paramagnetic Gd (III) ions and good hydrophilicity. The cytotoxicity of CQDs-DOTA-Ln was evaluated through MTT assay upon HeLa cells. The images from fluorescence microscopy further verified their applications in bioimaging in vitro. Due to the good biocompatibility, low toxicity, and high contrast efficiency, the CQDs-DOTA-Ln with Vis/NIR fluorescence and MR multi-modal imaging performance could be used as potential contrast agents for clinic applications.

A long-lived peptide-conjugated iridium(iii) complex as a luminescent probe and inhibitor of the cell migration mediator, formyl peptide receptor 2

Formyl peptide receptors play important biological and therapeutic roles in wound repair and inflammatory diseases. In this work, we present a luminescent iridium(iii) complex (6) conjugated with the peptide agonist WKYMVm as a luminescent formyl peptide receptor 2 (FPR2) imaging probe in living cells. Complex 6 displayed ideal cell imaging characteristics, high photostability and low cytotoxicity. Competition assays with a known FPR2 antagonist, WRW4, and siRNA knockdown experiments both revealed that complex 6 selectively targeted FPR2 in living HUVEC cells. Moreover, complex 6 regulated FPR2 signalling in HUVEC cells as shown using a mechanical scratch assay. Finally, complex 6 reduced epithelial cell migration capacity and inhibited lipoxin A4 (LXA4)-triggered cell migration in HUVEC cells, demonstrating the ability of this complex to inhibit FPR2 in living cells. To our knowledge, this is the first long-lived probe for imaging FPR2 in living cells.

Synthesis and evaluation of a [18F]formyl-Met-Leu-Phe derivative: A positron emission tomography imaging probe for bacterial infections

The tripeptide formyl-Met-Leu-Phe (fMLF) is a prototype of N-formylated chemotactic peptides for neutrophils owing to its ability to bind and activate the G protein-coupled formyl peptide receptor (FPR). Here, we developed an ¹⁸F-labeled fMLF derivative targeting FPR as a positron emission tomography (PET) imaging probe for bacterial infections. The study demonstrates that the fMLF derivative fMLFXYk(FB)k (X = Nle) has a high affinity for FPR (Ki = 0.62 ± 0.13 nM). The radiochemical yield and purity of [¹⁸F]fMLFXYk(FB)k were 16% and >96%, respectively. The in vivo biodistribution study showed that [¹⁸F]fMLFXYk(FB)k uptake was higher in the bacterial infected region than in the non-infected region. We observed considerably higher infection-to-muscle ratio of 4.6 at 60 min after [¹⁸F]fMLFXYk(FB)k injection. Furthermore, small-animal PET imaging studies suggested that [¹⁸F]fMLFXYk(FB)k uptake in the bacterial infected region was clearly visualized 60 min after injection.

Targeting formyl peptide receptor 1 of activated macrophages to monitor inflammation of experimental osteoarthritis in rat

Macrophages play a crucial role in the pathogenesis of osteoarthritis (OA). In this study, the feasibility of a formyl peptide receptor 1 (Fpr1)-targeting peptide probe cFLFLF-PEG-(64) Cu via positron emission tomography (PET) imaging was investigated for detection of macrophage activity during development of OA. Monoiodoacetate (MIA) was intraarticularly injected into the knee joint of Sprague-Dawley rats to induce OA. Five days later, cFLFLF-PEG-(64) Cu (∼7,400 kBq/rat) was injected into the tail vein and microPET/CT imaging was performed to assess the OA inflammation by detecting infiltration of macrophages by Fpr1 expression. In addition, a murine macrophage cell line RAW264.7 and two fluorescent probes cFLFLF-PEG-cyanine 7 (cFLFLF-PEG-Cy7) and cFLFLF-PEG-cyanine 5 (cFLFLF-PEG-Cy5) were used to define the binding specificity of the peptide to macrophages. It was found with the MIA model that the maximal standard uptake values (SUVmax ) for right (MIA treated) and left (control) knees were 17.96 ± 5.45 and 3.00 ± 1.40, respectively. Histological evaluation of cryomicrotome sections showed that Fpr1 expression, cFLFLF-PEG-Cy5 binding, and tartrate-resistant acid phosphatase activity were elevated in the injured synovial membranes. The in vitro experiments demonstrated that both fluorescent peptide probes could bind specifically to RAW264.7 cells, which was blocked by cFLFLF but not by the scramble peptide. The findings highlighted the use of cFLFLF-PEG-(64) Cu/PET as an effective method potentially applied for detection and treatment evaluation of OA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1529-1538, 2016.

A review of UHMWPE wear-induced osteolysis: the role for early detection of the immune response

In a world where increasing joint arthroplasties are being performed on increasingly younger patients, osteolysis as the leading cause of failure after total joint arthroplasty (TJA) has gained considerable attention. Ultra-high molecular weight polyethylene wear-induced osteolysis is the process by which prosthetic debris mechanically released from the surface of prosthetic joints induces an immune response that favors bone catabolism, resulting in loosening of prostheses with eventual failure or fracture. The immune response initiated is innate in that it is nonspecific and self-propagating, with monocytic cells and osteoclasts being the main effectors. To date, detecting disease early enough to implement effective intervention without unwanted systemic side effects has been a major barrier. These barriers can be overcome using newer in vivo imaging techniques and modules linked with fluorescence and/or chemotherapies. We discuss the pathogenesis of osteolysis, and provide discussion of the challenges with imaging and therapeutics. We describe a positron emission tomography imaging cinnamoyl-Phe-(D)-Leu-Phe-(D)-Leu-Phe-Lys module, specific to macrophages, which holds promise in early detection of disease and localization of treatment. Further research and increased collaboration among therapeutic and three-dimensional imaging researchers are essential in realizing a solution to clinical osteolysis in TJA.

Heteronuclear Ir(III)-Ln(III) Luminescent Complexes: Small-Molecule Probes for Dual Modal Imaging and Oxygen Sensing

Luminescent, mixed metal d-f complexes have the potential to be used for dual (magnetic resonance imaging (MRI) and luminescence) in vivo imaging. Here, we present dinuclear and trinuclear d-f complexes, comprising a rigid framework linking a luminescent Ir center to one (Ir·Ln) or two (Ir·Ln2) lanthanide metal centers (where Ln = Eu(III) and Gd(III), respectively). A range of physical, spectroscopic, and imaging-based properties including relaxivity arising from the Gd(III) units and the occurrence of Ir(III) → Eu(III) photoinduced energy-transfer are presented. The rigidity imposed by the ligand facilitates high relaxivities for the Gd(III) complexes, while the luminescence from the Ir(III) and Eu(III) centers provide luminescence imaging capabilities. Dinuclear (Ir·Ln) complexes performed best in cellular studies, exhibiting good solubility in aqueous solutions, low toxicity after 4 and 18 h, respectively, and punctate lysosomal staining. We also demonstrate the first example of oxygen sensing in fixed cells using the dyad Ir·Gd, via two-photon phosphorescence lifetime imaging (PLIM).

(13) C-TmDOTA as versatile thermometer compound for solid-state NMR of hydrated lipid bilayer membranes

Recent advances in solid-state nuclear magnetic resonance (NMR) techniques, such as magic angle spinning and high-power decoupling, have dramatically increased the sensitivity and resolution of NMR. However, these NMR techniques generate extra heat, causing a temperature difference between the sample in the rotor and the variable temperature gas. This extra heating is a particularly crucial problem for hydrated lipid membrane samples. Thus, to develop an NMR thermometer that is suitable for hydrated lipid samples, thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA) was synthesized and labeled with (13) C (i.e., (13) C-TmDOTA) to increase the NMR sensitivity. The complex was mixed with a hydrated lipid membrane, and the system was subjected to solid-state NMR and differential scanning calorimetric analyses. The physical properties of the lipid bilayer and the quality of the NMR spectra of the membrane were negligibly affected by the presence of (13) C-TmDOTA, and the (13) C chemical shift of the complex exhibited a large-temperature dependence. The results demonstrated that (13) C-TmDOTA could be successfully used as a thermometer to accurately monitor temperature changes induced by (1) H decoupling pulses and/or by magic angle spinning and the temperature distribution of the sample inside the rotor. Thus, (13) C-TmDOTA was shown to be a versatile thermometer for hydrated lipid assemblies. Copyright © 2015 John Wiley & Sons, Ltd.

A gadolinium(iii) complex based dual-modal probe for MRI and fluorescence sensing of fluoride ions in aqueous medium and in vivo

A novel Gd(iii) complex based dual-modal probe, Gd(TTA)₃-DPPZ was designed and assembled for the simultaneous fluoride ion in aqueous media and in vivo.

(99m)Tc SPECT imaging agent based on cFLFLFK for the detection of FPR1 in inflammation

Non-invasive imaging of the inflammatory process can provide great insight into a wide variety of disease states, aiding diagnosis, evaluation and effective targeted treatment. During inflammation, blood borne leukocytes are recruited, through a series of activation and adhesion steps, to the site of injury or infection where they migrate across the blood vessel wall into the tissue. Thus, tracking leukocyte recruitment and accumulation provides a dynamic and localised read out of inflammatory events. Current leukocyte imaging techniques require ex vivo labelling of patient blood, involving laborious processing and potential risks to both patient and laboratory staff. Utilising high affinity ligands for leukocyte specific receptors may allow for injectable tracers that label leukocytes in situ, omitting potentially hazardous ex vivo handling. Formyl peptide receptors (FPRs) are a group of G-protein coupled receptors involved in the chemotaxis and inflammatory functioning of leukocytes. Highly expressed on leukocytes, and up-regulated during inflammation, these receptors provide a potential target for imaging inflammatory events. Herein we present the synthesis and initial in vitro testing of a potential Single Photon Emission Computed Tomography (SPECT) leukocyte tracer. The FPR1 antagonist cFLFLFK-NH2, which displays high affinity with little physiological effect, has been linked via a PEG motif to a (99m)Tc chelate. This tracer shows in vitro binding to human embryonic kidney cells expressing the FPR1 receptor, and functional in vitro tests reveal cFLFLFK-NH2 compounds to have no effect on inflammatory cell functioning. Overall, these data show that (99m)Tc.cFLFLFK-NH2 may be a useful tool for non-invasive imaging of leukocyte accumulation in inflammatory disease states.

Cell tracking technologies for acute ischemic brain injury

Stem cell therapy has showed considerable potential in the treatment of stroke over the last decade. In order that these therapies may be optimized, the relative benefits of growth factor release, immunomodulation, and direct tissue replacement by therapeutic stem cells are widely under investigation. Fundamental to the progress of this research are effective imaging techniques that enable cell tracking in vivo. Direct analysis of the benefit of cell therapy includes the study of cell migration, localization, division and/or differentiation, and survival. This review explores the various imaging tools currently used in clinics and laboratories, addressing image resolution, long-term cell monitoring, imaging agents/isotopes, as well as safety and costs associated with each technique. Finally, burgeoning tracking techniques are discussed, with emphasis on multimodal imaging.

Final step gallium-68 radiolabelling of silica-coated iron oxide nanorods as potential PET/MR multimodal imaging agents

The investigation of iron oxide-based positron emission tomography/magnetic resonance (PET/MR) multimodal imaging agents is an expanding field in which a variety of nanoparticle sizes, shapes, surface coatings and radioisotopes are open for exploration. This study develops iron oxide nanorods which are coated with various mixtures of poly(ethylene glycol) (PEG) and macrocyclic ligand (DO3A) via the formation of a silica layer on the surface. Gallium-68 radiolabelling of the nanorods was carried out in high radiochemical yields (RCY) and their stability in human serum was demonstrated for all constructs, even in the absence of the macrocyclic chelating unit. Further studies were carried out in an attempt to determine the appropriate amount of PEG coating to give optimal properties for future in vivo studies.

Recognition of Immune Response for the Early Diagnosis and Treatment of Osteoarthritis

Osteoarthritis is a common and debilitating joint disease that affects up to 30 million Americans, leading to significant disability, reduction in quality of life, and costing the United States tens of billions of dollars annually. Classically, osteoarthritis has been characterized as a degenerative, wear-and-tear disease, but recent research has identified it as an immunopathological disease on a spectrum between healthy condition and rheumatoid arthritis. A systematic literature review demonstrates that the disease pathogenesis is driven by an early innate immune response which progressively catalyzes degenerative changes that ultimately lead to an altered joint microenvironment. It is feasible to detect this infiltration of cells in the early, and presumably asymptomatic, phase of the disease through noninvasive imaging techniques. This screening can serve to aid clinicians in potentially identifying high-risk patients, hopefully leading to early effective management, vast improvements in quality of life, and significant reductions in disability, morbidity, and cost related to osteoarthritis. Although the diagnosis and treatment of osteoarthritis routinely utilize both invasive and non-invasive strategies, imaging techniques specific to inflammatory cells are not commonly employed for these purposes. This review discusses this paradigm and aims to shift the focus of future osteoarthritis-related research towards early diagnosis of the disease process.

Development of small molecule non-peptide formyl peptide receptor (FPR) ligands and molecular modeling of their recognition

Formyl peptide receptors (FPRs) are G protein-coupled receptors (GPCRs) expressed on a variety of cell types. These receptors play an important role in the regulation of inflammatory reactions and sensing cellular damage. They have also been implicated in the pathogenesis of various diseases, including neurodegenerative diseases, cataract formation, and atherogenesis. Thus, FPR ligands, both agonists and antagonists, may represent novel therapeutics for modulating host defense and innate immunity. A variety of molecules have been identified as receptor subtype-selective and mixed FPR agonists with potential therapeutic value during last decade. This review describes our efforts along with recent advances in the identification, optimization, biological evaluation, and structure-activity relationship (SAR) analysis of small molecule non-peptide FPR agonists and antagonists, including chiral molecules. Questions regarding the interaction at the molecular level of benzimidazoles, pyrazolones, pyridazin-3(2H)-ones, N-phenylureas and other derivatives with FPR1 and FPR2 are discussed. Application of computational models for virtual screening and design of FPR ligands is also considered.

Critical design issues in the targeted molecular imaging of cell surface receptors

The molecular imaging of cell-surface receptors draws closer to reality.

Imaging Neuroinflammation - from Bench to Bedside

Neuroinflammation plays a central role in a variety of neurological diseases, including stroke, multiple sclerosis, Alzheimer’s disease, and malignant CNS neoplasms, among many other. Different cell types and molecular mediators participate in a cascade of events in the brain that is ultimately aimed at control, regeneration and repair, but leads to damage of brain tissue under pathological conditions. Non-invasive molecular imaging of key players in the inflammation cascade holds promise for identification and quantification of the disease process before it is too late for effective therapeutic intervention. In this review, we focus on molecular imaging techniques that target inflammatory cells and molecules that are of interest in neuroinflammation, especially those with high translational potential. Over the past decade, a plethora of molecular imaging agents have been developed and tested in animal models of (neuro)inflammation, and a few have been translated from bench to bedside. The most promising imaging techniques to visualize neuroinflammation include MRI, positron emission tomography (PET), single photon emission computed tomography (SPECT), and optical imaging methods. These techniques enable us to image adhesion molecules to visualize endothelial cell activation, assess leukocyte functions such as oxidative stress, granule release, and phagocytosis, and label a variety of inflammatory cells for cell tracking experiments. In addition, several cell types and their activation can be specifically targeted in vivo, and consequences of neuroinflammation such as neuronal death and demyelination can be quantified. As we continue to make progress in utilizing molecular imaging technology to study and understand neuroinflammation, increasing efforts and investment should be made to bring more of these novel imaging agents from the “bench to bedside.”

The ubiquitous DOTA and its derivatives: the impact of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid on biomedical imaging

Over the last twenty-five years 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) has made a significant impact on the field of diagnostic imaging. DOTA is not the only metal chelate in use in medical diagnostics, but it is the only one to significantly impact on all of the major imaging modalities Magnetic Resonance (MR), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and Fluorescence imaging. This crossover of modalities has been possible due to the versatility of DOTA firstly, to complex a variety of metal ions and secondly, the ease with which it can be modified for different disease states. This has driven research over the last two decades into the chemistry of DOTA and the modification of the substituent pendant arms of this macrocycle to create functional, targeted and dual-modal imaging agents. The primary use of DOTA has been with the lanthanide series of metals, gadolinium for MRI, europium and terbium for fluorescence and neodymium for near infra-red imaging. There are now many research groups dedicated to the use of lanthanides with DOTA although other chelates such as DTPA and NOTA are being increasingly employed. The ease with which DOTA can be conjugated to peptides has given rise to targeted imaging agents seen in the PET, SPECT and radiotherapy fields. These modalities use a variety of radiometals that complex with DOTA, e.g.(64)Cu and (68)Ga which are used in clinical PET scans, (111)In, and (90)Y for SPECT and radiotherapy. In this article, we will demonstrate the remarkable versatility of DOTA, how it has crossed the imaging modality boundaries and how it has been successfully transferred into the clinic.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.