Molecular imaging in drug development. Nat Rev Drug Discov. 2008;7:591-607. [PMID: 18591980 DOI: 10.1038/nrd2290]

Synthesis, radiolabelling, and biological assessment of folic acid-conjugated G-3 99mTc-dendrimer as the breast cancer molecular imaging agent

Hence, in this study, the authors aimed to develop a dendrimer-based imaging agent comprised of poly(ethylene glycol) (PEG)-citrate, technetium-99 m (99mTc), and folic acid. The dendrimer-G3 was synthesised and conjugated with folic acid, which confirmed by Fourier transform infrared, proton nuclear magnetic resonance, dynamic light scattering, and transition electron microscopy. 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-Tetrazolium-5-Carboxanilide cytotoxicity assay kit was used to measure the cellular toxicity of dendrimer. Imaging and biodistribution studies were conducted on the mice bearing tumour. The results showed that the fabricated dendrimer-G3 has a size of 90 ± 3 nm, which was increased to 100 ± 4 nm following the conjugation with folic acid. The radiostablity investigation showed that the fabricated dendrimers were stable in the human serum at various times. Toxicity assessment confirmed no cellular toxicity against HEK-293 cells at 0.25, 0.5, 1, 2, 4, and 8 mg/μl concentrations. The in vivo studies demonstrated that the synthesised dendrimers were able to provide a bright SPECT image applicable for tumour detection. In conclusion, the authors' study documented the positive aspects of PEG-citrate dendrimer conjugated with folic acid as the SPECT contrast agent for breast cancer detection.

Quantifying drug tissue biodistribution by integrating high content screening with deep-learning analysis

Quantitatively determining in vivo achievable drug concentrations in targeted organs of animal models and subsequent target engagement confirmation is a challenge to drug discovery and translation due to lack of bioassay technologies that can discriminate drug binding with different mechanisms. We have developed a multiplexed and high-throughput method to quantify drug distribution in tissues by integrating high content screening (HCS) with U-Net based deep learning (DL) image analysis models. This technology combination allowed direct visualization and quantification of biologics drug binding in targeted tissues with cellular resolution, thus enabling biologists to objectively determine drug binding kinetics.

Synthesis and preliminary evaluation of a novel positron emission tomography (PET) ligand for imaging fatty acid amide hydrolase (FAAH)

Fatty acid amide hydrolase (FAAH) exerts its main function in the catabolism of the endogenous chemical messenger anandamide (AEA), thus modulating the endocannabinoid (eCB) pathway. Inhibition of FAAH may serve as an effective strategy to relieve anxiety and possibly other central nervous system (CNS)-related disorders. Positron emission tomography (PET) would facilitate us to better understand the relationship between FAAH in certain disease conditions, and accelerate clinical translation of FAAH inhibitors by providing in vivo quantitative information. So far, most PET tracers show irreversible binding patterns with FAAH, which would result in complicated quantitative processes. Herein, we have identified a new FAAH inhibitor (1-((1-methyl-1H-indol-2-yl)methyl)piperidin-4-yl)(oxazol-2-yl)methanone (8) which inhibits the hydrolysis of AEA in the brain with high potency (IC₅₀ value 11 nM at a substrate concentration of 0.5 µM), and without showing time-dependency. The PET tracer [¹¹C]8 (also called [¹¹C]FAAH-1906) was successfully radiolabeled with [¹¹C]MeI in 17 ± 6% decay-corrected radiochemical yield (n = 7) with >74.0 GBq/μmol (2 Ci/μmol) molar activity and >99% radiochemical purity. Ex vivo biodistribution and blocking studies of [¹¹C]8 in normal mice were also conducted, indicating good brain penetration, high brain target selectivity, and modest to excellent target selectivity in peripheral tissues. Thus, [¹¹C]8 is a potentially useful PET ligand with enzyme inhibitory and target binding properties consistent with a reversible mode of action.

Synthesis and preliminary evaluation of 4-hydroxy-6-(3-[11C]methoxyphenethyl)pyridazin-3(2H)-one, a 11C-labeled d-amino acid oxidase (DAAO) inhibitor for PET imaging

Selective DAAO inhibitors have demonstrated promising therapeutic effects in clinical studies, including clinically alleviating symptoms of schizophrenic patients and ameliorating cognitive function in Alzheimer's patients with early phase. Herein we report the synthesis and preliminary evaluation of a ¹¹C-labeled positron emission tomography ligand based on a DAAO inhibitor, DAO-1903 (8). ¹¹C-Isotopologue of 8 was prepared in high radiochemical yield with high radiochemical purity (>99%) and high molar activity (>37 GBq/µmol). In vitro autoradiography studies indicated that the ligand possessed high in vitro specific binding to DAAO, while in vivo dynamic PET studies demonstrated that [¹¹C]8 failed to cross the blood-brain barrier possibly due to moderate brain efflux mechanism. Further chemical scaffold optimization is necessary to overcome limited brain permeability and improve specific binding.

Optical Imaging Modalities: Principles and Applications in Preclinical Research and Clinical Settings

With the ability to noninvasively image and monitor molecular processes within tumors, molecular imaging represents a fundamental tool for cancer scientists. In the current review, we describe emergent optical technologies for molecular imaging. We aim to provide the reader with an overview of the fundamental principles on which each imaging strategy is based, to introduce established and future applications, and to provide a rationale for selecting optical technologies for molecular imaging depending on disease location, biology, and anatomy. To accelerate clinical translation of imaging techniques, we also describe examples of practical applications in patients. Elevating these techniques into standard-of-care tools will transform patient stratification, disease monitoring, and response evaluation.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Near-Infrared Multipurpose Lanthanide-Imaging Nanoprobes

Optical imaging plays a growing role in modern biomedical research and clinical applications due to its high sensitivity, superb spatiotemporal resolution and minimal hazards. Lanthanide-doped nanoparticles (LDNPs), as a classical category of luminescent materials, exhibit promising photostability, near-infrared (NIR)-excited frequency up-/down-converting capabilities, emission fine-tuning and multispectral features, which have greatly promoted the endeavors of deeper and clearer diagnostics in complex living conditions. This review focuses on the recent advances of LDNP-based multipurpose imaging studies using upconversion, downshifting, lifetime, photoacoustic and multimodal nanoprobes in the NIR (650-1000 nm) and the second near-infrared window (NIR-II, 1000-1700 nm). The principle and design of various functional, activatable, multiplexing or multimodal lanthanide-imaging nanoprobes (LINPs) as well as representative biophotonic applications are summarized in detail. In addition, the future perspectives and challenges for facilitating LINPs to clinical translations are discussed.

Recent Advances in Rare-Earth-Doped Nanoparticles for NIR-II Imaging and Cancer Theranostics

Fluorescence imaging in the second near infrared window (NIR-II, 1,000-1,700 nm) has been widely used in cancer diagnosis and treatment due to its high spatial resolution and deep tissue penetration depths. In this work, recent advances in rare-earth-doped nanoparticles (RENPs)-a novel kind of NIR-II nanoprobes-are presented. The main focus of this study is on the modification of RENPs and their applications in NIR-II in vitro and in vivo imaging and cancer theranostics. Finally, the perspectives and challenges of NIR-II RENPs are discussed.

Rapid Syntheses of [11C]Arylvinyltrifluoromethanes through Treatment of (E)-Arylvinyl(phenyl)iodonium Tosylates with [11C]Trifluoromethylcopper(I)

We report a method for labeling arylvinyltrifluoromethanes with carbon-11 (t_1/2 = 20.4 min) as representatives of a new radiolabeled chemotype that has potential for developing radiotracers for biomedical imaging with positron emission tomography. Treatment of (E)-arylvinyl(phenyl)iodonium tosylates (1a-1k) with [¹¹C[CuCF₃ gave the corresponding [¹¹C]arylvinyltrifluoromethanes ([¹¹C]2a-[¹¹C]2k) in high radiochemical yields (90-97%) under rapid (2 min) and mild (60 °C) conditions.

Hybrid reconstruction method for multispectral bioluminescence tomography with log-sum regularization

Bioluminescence tomography (BLT) has important applications in the in vivo visualization of a pathological process for preclinical studies. However, the reconstruction of BLT is severely ill-posed. To recover the bioluminescence source stably and efficiently, we use a log-sum regularization term in the objective function and utilize a hybrid optimization algorithm for solving the nonconvex regularized problems (HONOR). The hybrid optimization scheme of HONOR merges second-order information and first-order information to reconstruction by choosing either the quasi-Newton (QN) or gradient descent step at each iteration. The QN step uses the limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm (L-BFGS) to acquire second-order information. Simulations and in vivo experiments based on multispectral measurements demonstrated the remarkable performance of the proposed hybrid method in the sparse reconstruction of BLT.

Development of an Integrated Tissue Pretreatment Protocol for Enhanced MALDI MS Imaging of Drug Distribution in the Brain

The matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) technique has attracted intense interest in the visualization of drug distribution in tissues. Its capability to spatially resolve individual molecules makes it a unique tool in drug development and research. However, low drug content and severe ion suppression in tissues hinder its broader application to resolve drug tissue distribution, especially small molecule drugs with a molecular weight below 500 Da. In this work, an integrated tissue pretreatment protocol was developed to enhance the detection of central nervous system drugs in the mouse brain using MALDI MSI. To evaluate the protocol, brain sections from mice dosed intraperitoneally with donepezil, tacrine, clozapine, haloperidol, and aripiprazole were used. The tissue sections were pretreated serially by washing with ammonium acetate solution, incubation with trifluoroacetic acid vapor, and n-hexane washing before MALDI MSI. Compared with the untreated sample, the signal intensities for the test drugs increased by 4.7- to 31.5-fold after pretreatment. Besides the enhancement of signal intensity, fine optimization of pretreatment time and washing solvents preserved the spatial distribution of target drug molecules. The utility of the developed protocol also provided tissue-specific distribution for five drugs which were well resolved when imaged by MALDI MS.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

A Dual-Emissive Phosphorescent Polymeric Probe for Exploring Drug-Induced Liver Injury via Imaging of Peroxynitrite Elevation In Vivo

Drug-induced liver injury (DILI) is a widespread clinical problem. The pathophysiological mechanisms of DILI are complicated, and the traditional diagnostic methods for DILI have their limitations. Owing to its convenient operation, high sensitivity, and high specificity, luminescent sensing and imaging as an indispensable tool in biological research and clinical trials may provide an important means for DILI study. Herein, we report the rational design and preparation of a near-infrared dual-phosphorescent polymeric probe (P-ONOO) for exploring the DILI via specific imaging of peroxynitrite (ONOO^-) elevation in vivo, which was one of early markers of DILI and very difficult to be detected due to its short half-life and high reactive activity. With the utilization of P-ONOO, the raised ONOO^- was visualized successfully in the drug-treated hepatocytes with a high signal-to-noise ratio via ratiometric and time-resolved photoluminescence imaging. Importantly, the ONOO^- boost in the acetaminophen-induced liver injury in real time was verified, and the direct observation of the elevated ONOO^- production in ketoconazole-induced liver injury was achieved for the first time. Our findings may contribute to understanding the exact mechanism of ketoconazole-induced hepatotoxicity that is still ambiguous. Notably, this luminescent approach for revealing the liver injury works fast and conveniently.

A novel natural product, britanin, inhibits tumor growth of pancreatic cancer by suppressing nuclear factor-κB activation

Pancreatic cancer has a high mortality rate and poor prognosis. The development of novel medicines for pancreatic cancer therapy is urgently need. Britanin is a bioactive sesquiterpene lactone, that exhibits excellent anti-inflammatory and antioxidant effects. However, the potential anti-tumour activity of britanin is also considerable. Hence, in this study, the in vitro and in vivo anti-pancreatic cancer effects of britanin were investigated. Several pancreatic cancer cell lines were applied to evaluate inhibition of proliferation, migration and NF-κB pathway in vitro. Then in vivo toxicity of britanin was evaluated in BALB/c mice. The in vivo inhibitory effects of britanin were investigated by bioluminescence imaging, traditional methods and histological analysis in a pancreatic cancer xenograft mouse model. The results showed that britanin exhibited effective anti-tumour actions both in vitro and in vivo. The IC₅₀ values in PANC-1, BxPC-3 and MIA CaPa-2 cell lines were 1.348, 3.367 and 3.104 μmol/L, respectively, and cell proliferation and migration were significantly inhibited by britanin treatment. Western blotting demonstrated that NF-κB family proteins, such as P50, P65, and P-P65 were affected by britanin treatment. It is worth noting that the P-P65 protein, which regulates the expression of multiple factors downstream, was significantly decreased in britanin treated group. In vivo experiments verified that britanin could suppress the tumour progression in a pancreatic cancer xenograft mouse model, while the compound did not exhibit intolerable toxicity. In conclusion, britanin has remarkable potential treatment effects against pancreatic cancer, and it could be developed as a new agent for pancreatic cancer chemotherapy.

Polymeric Core-Shell Nanoparticles Prepared by Spontaneous Emulsification Solvent Evaporation and Functionalized by the Layer-by-Layer Method

The aim of our study was to develop a novel method for the preparation of polymeric core-shell nanoparticles loaded with various actives for biomedical applications. Poly(caprolactone) (PCL), poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) nanoparticles were prepared using the spontaneous emulsification solvent evaporation (SESE) method. The model active substance, Coumarin-6, was encapsulated into formed polymeric nanoparticles, then they were modified/functionalized by multilayer shells' formation. Three types of multilayered shells were formed: two types of polyelectrolyte shell composed of biocompatible and biodegradable polyelectrolytes poly-L-lysine hydrobromide (PLL), fluorescently-labeled poly-L-lysine (PLL-ROD), poly-L-glutamic acid sodium salt (PGA) and pegylated-PGA (PGA-g-PEG), and hybrid shell composed of PLL, PGA, and SPIONs (superparamagnetic iron oxide nanoparticles) were used. Multilayer shells were constructed by the saturation technique of the layer-by-layer (LbL) method. Properties of our polymeric core-shell nanoparticle were optimized for bioimaging, passive and magnetic targeting.

Synthesis and pharmacokinetic study of a 11C-labeled cholesterol 24-hydroxylase inhibitor using 'in-loop' [11C]CO2 fixation method

Cholesterol 24-hydroxylase, also known as CYP46A1 (EC 1.14.13.98), is a monooxygenase and a member of the cytochrome P450 family. CYP46A1 is specifically expressed in the brain where it controls cholesterol elimination by producing 24S-hydroxylcholesterol (24-HC) as the major metabolite. Modulation of CYP46A1 activity may affect Aβ deposition and p-tau accumulation by changing 24-HC formation, which thereafter serves as potential therapeutic pathway for Alzheimer's disease. In this work, we showcase the efficient synthesis and preliminary pharmacokinetic evaluation of a novel cholesterol 24-hydroxylase inhibitor 1 for use in positron emission tomography.

Imaging of the immune system - towards a subcellular and molecular understanding

Immune responses involve many types of leukocytes that traffic to the site of injury, recognize the insult and respond appropriately. Imaging of the immune system involves a set of methods and analytical tools that are used to visualize immune responses at the cellular and molecular level as they occur in real time. We will review recent and emerging technological advances in optical imaging, and their application to understanding the molecular and cellular responses of neutrophils, macrophages and lymphocytes. Optical live-cell imaging provides deep mechanistic insights at the molecular, cellular, tissue and organism levels. Live-cell imaging can capture quantitative information in real time at subcellular resolution with minimal phototoxicity and repeatedly in the same living cells or in accessible tissues of the living organism. Advanced FRET probes allow tracking signaling events in live cells. Light-sheet microscopy allows for deeper tissue penetration in optically clear samples, enriching our understanding of the higher-level organization of the immune response. Super-resolution microscopy offers insights into compartmentalized signaling at a resolution beyond the diffraction limit, approaching single-molecule resolution. This Review provides a current perspective on live-cell imaging in vitro and in vivo with a focus on the assessment of the immune system.

Multifunctional gap-enhanced Raman tags for preoperative and intraoperative cancer imaging

Multi-modality imaging agents are desirable for tumor diagnosis because they can provide more alternative and reliable information for accurate detection and therapy of diseases than single imaging technique. However, most reported conventional imaging agents have not been found to successfully overcome the disadvantages of traditional diagnoses such as sensitivity, spatial resolution, short half-decay time and complexity. Therefore, exploring a multifunctional nanocomposite with the combination of their individual modality characteristics has great impact on preoperative imaging and intraoperative diagnosis of cancer. In our study, mesoporous silica gadolinium-loaded gap-enhanced Raman tags (Gd-GERTs) specifically for preoperative and intraoperative imaging are designed and their imaging capability and biosafety are examined. They exhibit strong attenuation property for computed X-ray tomography (CT) imaging, high T₁ relaxivity for magnetic resonance (MR) imaging capability and surface-enhanced Raman spectroscopy (SERS) signal with good dispersity and stability, which presents CT/MR/SERS multi-mode imaging performance of the tumor of mice within a given time. Furthermore, in vivo biodistribution and long-term toxicity studies reveal that the Gd-GERTs have good biocompatibility and bio-safety. Therefore, Gd-GERTs are of great potential as a multifunctional nanoplatform for accurate preoperative CT/MRI diagnosis and intraoperative Raman imaging-guide resection of cancers. STATEMENT OF SIGNIFICANCE: Recent advances in molecular imaging technology have provided a myriad of opportunities to prepare various nanomaterials for accurate diagnosis and response evaluation of cancer via different imaging modalities. However, single bioimaging modality is still challenging to overcome the issues such as sensitivity, spatial resolution, imaging speed and complexity for clinicians. In this work, we designed a kind of unique multifunctional nanoprobes with computed X-ray tomography/magnetic resonance/surface-enhanced Raman spectroscopy (CT/MR/SERS) triple-modal imaging capabilities. Multifunctional nanotags offer the capabilities of preoperative noninvasive CT/MR imaging for identification of tumors as well as intraoperative real-time SERS imaging for guidance of complete resection of tumors. These multifunctional nanoprobes show critical clinical significance on the improvement of tumor diagnosis and therapy.

Ultrasound molecular imaging: insights into cardiovascular pathology

Similar to what has already occurred in cancer medicine, the management of cardiovascular conditions will likely be improved by non-invasive molecular imaging technologies that can provide earlier or more accurate diagnosis. These techniques are already having a positive impact in pre-clinical research by providing insight into pathophysiology or efficacy of new therapies. Contrast enhanced ultrasound (CEU) molecular imaging is a technique that relies on the ultrasound detection of targeted microbubble contrast agents to examine molecular or cellular events that occur at the blood pool-endothelial interface. CEU molecular imaging techniques have been developed that are able to provide unique information on atherosclerosis, ischemia reperfusion injury, angiogenesis, vascular inflammation, and thrombus formation. Accordingly, CEU has the potential to be used in a wide variety of circumstances to detect disease early or at the bedside, and to guide appropriate therapy based on vascular phenotype. This review will describe the physical basis for CEU molecular imaging, and the specific disease processes for the pre-clinical translational research experience.

Use of imaging to assess the activity of hepatic transporters

Introduction: Membrane transporters of the SLC and ABC families are abundantly expressed in the liver, where they control the transfer of drugs/drug metabolites across the sinusoidal and canalicular hepatocyte membranes and play a pivotal role in hepatic drug clearance. Noninvasive imaging methods, such as PET, SPECT or MRI, allow for measuring the activity of hepatic transporters in vivo, provided that suitable transporter imaging probes are available.Areas covered: We give an overview of the working principles of imaging-based assessment of hepatic transporter activity. We discuss different currently available PET/SPECT radiotracers and MRI contrast agents and their applications to measure hepatic transporter activity in health and disease. We cover mathematical modeling approaches to obtain quantitative parameters of transporter activity and provide a critical assessment of methodological limitations and challenges associated with this approach.Expert opinion: PET in combination with pharmacokinetic modeling can be potentially applied in drug development to study the distribution of new drug candidates to the liver and their clearance mechanisms. This approach bears potential to mechanistically assess transporter-mediated drug-drug interactions, to assess the influence of disease on hepatic drug disposition and to validate and refine currently available in vitro-in vivo extrapolation methods to predict hepatic clearance of drugs.

Recent Progress in NIR-II Contrast Agent for Biological Imaging

Fluorescence imaging technology has gradually become a new and promising tool for in vivo visualization detection. Because it can provide real-time sub-cellular resolution imaging results, it can be widely used in the field of biological detection and medical detection and treatment. However, due to the limited imaging depth (1-2 mm) and self-fluorescence background of tissue emitted in the visible region (400-700 nm), it fails to reveal biological complexity in deep tissues. The traditional near infrared wavelength (NIR-I, 650-950 nm) is considered as the first biological window, because it reduces the NIR absorption and scattering from blood and water in organisms. NIR fluorescence bioimaging's penetration is larger than that of visible light. In fact, NIR-I fluorescence bioimaging is still interfered by tissue autofluorescence (background noise), and the existence of photon scattering, which limits the depth of tissue penetration. Recent experimental and simulation results show that the signal-to-noise ratio (SNR) of bioimaging can be significantly improved at the second region near infrared (NIR-II, 1,000-1,700 nm), also known as the second biological window. NIR-II bioimaging is able to explore deep-tissues information in the range of centimeter, and to obtain micron-level resolution at the millimeter depth, which surpass the performance of NIR-I fluorescence imaging. The key of fluorescence bioimaging is to achieve highly selective imaging thanks to the functional/targeting contrast agent (probe). However, the progress of NIR-II probes is very limited. To date, there are a few reports about NIR-II fluorescence probes, such as carbon nanotubes, Ag2S quantum dots, and organic small molecular dyes. In this paper, we surveyed the development of NIR-II imaging contrast agents and their application in cancer imaging, medical detection, vascular bioimaging, and cancer diagnosis. In addition, the hotspots and challenges of NIR-II bioimaging are discussed. It is expected that our findings will lay a foundation for further theoretical research and practical application of NIR-II bioimaging, as well as the inspiration of new ideas in this field.

Preclinical validation of [18F]2FNQ1P as a specific PET radiotracer of 5-HT6 receptors in rat, pig, non-human primate and human brain tissue

INTRODUCTION

The aim of this study was to perform in-vitro and in-vivo radiopharmacological characterizations of [¹⁸F]2FNQ1P, a new PET radiotracer of 5-HT₆ receptors, in rat, pig, non-human primate and human tissues. The 5-HT₆ receptor is one of the more recently identified serotonin receptors in central nervous system and, because of its role in memory and cognitive processes, is considered as a promising therapeutic target.

METHODS

In-vitro autoradiography and saturation binding assays were performed in postmortem brain tissues from rat, pig, non-human primate and human caudate nucleus, completed by serum stability assessment in all species and cerebral radiometabolite and biodistribution studies in rat.

RESULTS

In all species, autoradiography data revealed high binding levels of [¹⁸F]2FNQ1P in cerebral regions with high 5-HT₆ receptor density. Binding was blocked by addition of SB258585 as a specific antagonist. Binding assays provided K_D and B_max values of respectively 1.34 nM and 0.03 pmol·mg^-1 in rat, 0.60 nM and 0.04 pmol·mg^-1 in pig, 1.38 nM and 0.07 pmol·mg^-1 in non-human primate, and 1.39 nM and 0.15 pmol·mg^-1 in human caudate nucleus. In rat brain, the proportion of unmetabolized [¹⁸F]2FNQ1P was >99% 5 min after iv injection and 89% at 40 min. The biodistribution studies found maximal radioactivity in lungs and kidneys (3.5 ± 1.2% ID/g and 2.0 ± 0.7% ID/g, respectively, 15 min post-injection).

CONCLUSION

These radiopharmacological data confirm that [¹⁸F]2FNQ1P is a specific radiotracer for molecular imaging of 5-HT₆ receptors and suggest that it could be used as a radiopharmaceutical in humans.

18F-Trifluoromethanesulfinate Enables Direct C-H 18F-Trifluoromethylation of Native Aromatic Residues in Peptides

18F labeling strategies for unmodified peptides with [18F]fluoride require 18F-labeled prosthetics for bioconjugation more often with cysteine thiols or lysine amines. Here we explore selective radical chemistry to target aromatic residues applying C-H 18F-trifluoromethylation. We report a one-step route to [18F]CF3SO2NH4 from [18F]fluoride and its application to direct [18F]CF3 incorporation at tryptophan or tyrosine residues using unmodified peptides as complex as recombinant human insulin. The fully automated radiosynthesis of octreotide[Trp(2-CF218F)] enables in vivo positron emission tomography imaging.

Glutathione-responsive disassembly of disulfide dicyanine for tumor imaging with reduction in background signal intensity

Near-infrared (NIR) fluorescence imaging has been proved as an effective modality in identifying the tumor border and distinguishing the tumor cells from healthy tissue during the oncological surgery. Developing NIR fluorescent probes with high tumor to background (T/B) signal is essential for the complete debulking of the tumor, which will prolong the survival rate of tumor patients. However, the nonspecific binding and "always-on" properties of the conventional fluorescent probes leads to high background signals and poor specificity. Method: To address this problem, glutathione (GSH)-responsive, two disulfide-bonded dicyanine dyes (ss-diCy5 and ss-diNH800CW) were synthesized. As synthesized dyes are quenched under normal physiological conditions, however, once reached to the tumor site, these dyes are capable of emitting strong fluorescence signals primarily because of the cleavage of the disulfide bond in the tumor microenvironment with high GSH concentration. Besides, the GSH-responsive behavior of these dyes was monitored using the UV-vis and fluorescence spectroscopy. The diagnostic accuracy of the aforementioned dyes was also tested both in tumor cells and 4T1-bearing mice. Results: The fluorescence signal intensity of disulfide dicyanine dyes was quenched up to 89% compared to the mono cyanine dyes, thus providing a very low fluorescence background. However, when the disulfide dicyanine dye reaches the tumor site, the dicyanine is cleaved by GSH into two mono-dyes with high fluorescence strength, thus producing strong fluorescent signals upon excitation. The fluorescent signal of the dicyanine was enhanced by up to 27-fold after interacting with the GSH solution. In vivo xenografts tumor studies further revealed that the fluorescence signals of aforementioned dyes can be quickly recovered in the solid tumor. Conclusion: In summary, the disulfide dicyanines dyes can provide a promising platform for specific tumor-activatable fluorescence imaging with improved T/B value.

Finely crafted quasi-core–shell gadolinium/layered double hydroxide hybrids for switching on/off bimodal CT/MRI contrasting nanodiagnostic platforms

Quasi core–shell structure of LDH platetes and Gd(OH)₃ nanorods were synthesized to control water approach to Gd(OH)₃ depending on pH.

Scoping Review of Targeted Ultrasound Contrast Agents in the Detection of Angiogenesis

A systematic search was conducted to categorize targeted ultrasound contrast agents (UCAs) used in cancer-related angiogenesis detection. We identified 15 unique contrast agents from 2008 to March 2018. Most primary research articles studied UCAs targeted to vascular endothelial growth factor receptor or α_v β₃ -integrin. Breast cancer and colon cancer are the most common neoplastic processes in which these agents were studied. BR55 (Bracco Research SA, Geneva, Switzerland), a vascular endothelial growth factor receptor-targeting UCA, is the first targeted UCA that has completed phase 0 trials. Our review identifies a gap in the literature regarding the application of targeted UCAs in cancer models beyond breast and colon cancers and identifies other promising UCAs.

Recent advances of polyoxometalates in multi-functional imaging and photothermal therapy

The recent advances of polyoxometalate clusters in terms of near infrared photothermal properties for targeted tumor therapy have been summarized while the combined applications with various bio-imaging techniques and chemotherapies are reviewed.

Stem Cell Tracking with Nanoparticle-Based Ultrasound Contrast Agents

Cell therapy is revolutionizing modern medicine. To promote this emerging therapy, the ability to image and track therapeutic cells is critical to monitor the progress of the treatment. Ultrasound imaging is promising in tracking therapeutic cells but suffers from poor contrast against local tissues. Therefore, it is critical to increase the ultrasound contrast of therapeutic cells over local tissue at the injection site. Here, we describe a method to increase the ultrasound intensity of therapeutic cells with nanoparticles to make the injected therapeutic cells more visible.

The fluorescent dye 3,3'-diethylthiatricarbocyanine iodide is unsuitable for in vivo imaging of myelination in the mouse

There is a growing interest to use non-invasive optical imaging methods to study central nervous system diseases. The application of a myelin-binding fluorescent dye, 3,3-diethylthiatricarbocyanine iodide (DBT) was recently described for in vivo optical imaging of demyelination in the mouse. In the present study we aimed at adapting the method to our optical imaging systems, the IVIS Lumina II to measure epifluorescence and the fluorescent molecular tomograph (FMT) for 3-dimensional quantification of the fluorophore. Epifluorescent imaging was performed 5-30 min after DBT injection which was followed by FMT imaging at 40 min. Two mice also underwent micro-CT imaging in the FMT cassette for the purpose of FMT-CT co-registration. Ex vivo imaging of the brain and other tissues of the head and neck was carried out 1 h after injection. Both the FMT-CT co-registration and the ex vivo imaging of organs proved that DBT poorly crossed the blood-brain barrier. The dye did not accumulate in the myelin sheath of the sciatic nerve. In contrast, there was an intense accumulation in the pituitary and salivary glands. The FMT-CT co-registration unequivocally demonstrated that the signal localized to the head did not originate from beyond the blood-brain barrier. No myelin binding was demonstrated by the ex vivo imaging either. In conclusion, DBT is unsuitable for in vivo imaging of myelination due to its poor BBB penetration, accumulation in other structures of the head and neck region and lack of selective binding towards myelin in vivo.

NIR nanoprobe-facilitated cross-referencing manifestation of local disease biology for dynamic therapeutic response assessment

Pharmacological interventions for effective treatment require opportune, dynamic and accurate manifestation of pathological status. Traditional clinical techniques relying on biopsy-based histological examinations and blood tests are dramatically restricted due to their invasiveness, unsatisfactory precision, non-real-time reporting and risk of complications. Although current strategies through molecular imaging enable non-invasive and spatiotemporal mapping of pathological changes in intact organisms, environment-activatable, sensitive and quantitative sensing platforms, especially for dynamic feedback of the therapeutic response, are still urgently desired in practice. Herein, we innovatively integrate deep-tissue penetrable multispectral optoacoustic tomography (MSOT) and near-infrared (NIR) optical imaging based technology by tailoring a free radical-responsive chromophore with photon-upconverting nanocrystals. During the therapeutic process, the specific reactions between the drug-stimulated reactive oxygen species (ROS) and radical-sensitive probes result in an absorption shift, which can be captured by MSOT. Meanwhile, the radical-triggered reaction also induces multispectral upconversion luminescence (UCL) responses that exhibit the opposite trend in comparison to MSOT. Such reversed-ratiometric dual-modal imaging outcomes provide an ideal cross-referencing system that guarantees the maximum sensing specificity and sensitivity, thus enabling precise disease biology evaluation and treatment assessments in vivo.

Gadolinium labeled polyelectrolyte nanocarriers for theranostic application

Here, we designed a novel Gadolinium (Gd) labeled drug-loaded polyelectrolyte nanocarriers for theranostics. The nanocarriers were formed via layer-by-layer technique with biodegradable polyelectrolytes: PLL (Poly-L-lysine), PLL-Gd (Gadolinium-labeled Poly-L-lysine) and PGA (Poly-L-glutamic acid). Anticancer drug (Paclitaxel) was encapsulated in the formed nanocarriers. The average size of synthesized nanocarriers was around 150 nm. The empty gadolinium labeled nanocarriers did not show any deleterious effects on tested cells (CT26-CEA, B16F10, 4T1 and PBMC), whereas encapsulated paclitaxel retained its cytotoxic/cytostatic activity. Using T₂ and T₁ NMR relaxation measurements with 9.4 T preclinical MRI scanner, we demonstrated that gadolinium labeled nanocarriers can be detected due to a locally altered contrast in the MR image. Thus, they may become a promising platform for future theranostic applications.

Recent Progress of Rare-Earth Doped Upconversion Nanoparticles: Synthesis, Optimization, and Applications

Upconversion is a nonlinear optical phenomenon that involves the emission of high-energy photons by sequential absorption of two or more low-energy excitation photons. Due to their excellent physiochemical properties such as deep penetration depth, little damage to samples, and high chemical stability, upconversion nanoparticles (UCNPs) are extensively applied in bioimaging, biosensing, theranostic, and photochemical reactions. Here, recent achievements in the synthesis, optimization, and applications of UCNP-based nanomaterials are reviewed. The state-of-the-art approaches to synthesize UCNPs in the past few years are introduced first, followed by a summary of several strategies to optimize upconversion emissive properties and various applications of UCNPs. Lastly, the challenges and future perspectives of UCNPs are provided as a conclusion.

Synthesis Of PEG-Coated, Ultrasmall, Manganese-Doped Iron Oxide Nanoparticles With High Relaxivity For T1/T2 Dual-Contrast Magnetic Resonance Imaging

BACKGROUND

Beyond magnetic resonance imaging (MRI), which has been widely used clinically, molecular MRI (mMRI) can further provide qualitative and quantitative information at the cellular and molecular levels. However, the diagnostic accuracy may not be satisfactory via single-contrast mMRI due to some interferences in vivo. T1/T2 dual-contrast MRI using the same contrast agent (CA) could significantly improve the detection accuracy. Therefore, in this study, we fabricated poly(ethylene glycol) (PEG)-coated, manganese-doped iron oxide nanocomposites (Mn-IONPs@PEG) as T1/T2 dual-contrast CA, and evaluated its feasibility of T1/T2 dual-contrast MRI in vitro and in vivo.

METHODS

Mn-IONPs were prepared by the thermal decomposition of iron-eruciate and manganese-oleate complexes and were coated with 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy[polyethylene glycol]-2000) (DSPE-PEG 2000). The physicochemical properties and cytotoxicity of the Mn-IONPs were fully characterized, followed by MRI in vitro and in vivo.

RESULTS

Ultrasmall 3 nm-sized nanoparticles were successfully prepared and were identified using transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction. After coating with DSPE-PEG, the Mn-IONPs@PEG displayed excellent hydrophilicity and good biocompatibility. Due to the manganese-doping and PEG coating, the Mn-IONPs@PEG showed good relaxivity in vitro. Especially, the Mn-IONPs@PEG coated with DSPE-PEG following a mass ratio to Mn-IONPs of 1:20 showed harmonious longitudinal relaxivity (r 1 = 7.1 mM-1s-1) and transversal relaxivity (r 2 = 120.9 mM-1s-1), making it a better candidate for T1/T2 dual-contrast mMRI. After administrated via a caudal vein, the Mn-IONPs@PEG can induce significant enhancement in both T1-weighted and T2-weighted MR images and the time at 10 mins after injection was regarded as a suitable time for imaging because both the T1 and T2 enhancement were optimum at that time.

CONCLUSION

The obtained Mn-IONPs@PEG exhibited good r 1 and r 2 and was a reasonable candidate for T1/T2 dual-contrast mMRI.

Molecular optical imaging probes for early diagnosis of drug-induced acute kidney injury

Drug-induced acute kidney injury (AKI) with a high morbidity and mortality is poorly diagnosed in hospitals and deficiently evaluated in drug discovery. Here, we report the development of molecular renal probes (MRPs) with high renal clearance efficiency for in vivo optical imaging of drug-induced AKI. MRPs specifically activate their near-infrared fluorescence or chemiluminescence signals towards the prodromal biomarkers of AKI including the superoxide anion, N-acetyl-β-D-glucosaminidase and caspase-3, enabling an example of longitudinal imaging of multiple molecular events in the kidneys of living mice. Importantly, they in situ report the sequential occurrence of oxidative stress, lysosomal damage and cellular apoptosis, which precedes clinical manifestation of AKI (decreased glomerular filtration). Such an active imaging mechanism allows MRPs to non-invasively detect the onset of cisplatin-induced AKI at least 36 h earlier than the existing imaging methods. MRPs can also act as exogenous tracers for optical urinalysis that outperforms typical clinical/preclinical assays, demonstrating their clinical promise for early diagnosis of AKI.

Synthesis and evaluation of radioactive/fluorescent peptide probes for imaging of legumain activity

Legumain or asparaginyl endopeptidase is an enzyme overexpressed in some cancers and involved in cancer migration, invasion, and metastasis. We have developed radioiodine- ([¹²⁵I]I-LCP) or fluorescein-labeled peptides (FL-LCP) with a cell-permeable d-Arg nonamer fused to an anionic d-Glu nonamer via a legumain-cleavable linker, to function as peptide probes that measure and monitor legumain activity. Non-cleavable probes of FL-NCP and [¹²⁵I]I-NCP were similarly prepared and evaluated as negative control probes by altering their non-cleavable sequence. Model peptides with the legumain-cleavable or non-cleavable sequence (LCP and NCP, respectively) reacted with recombinant human legumain, and only LCP was digested by this enzyme. [¹²⁵I]I-LCP uptake in legumain-positive HCT116 cells was significantly higher than that of [¹²⁵I]I-NCP (11.2 ± 0.44% vs 1.75 ± 0.06% dose/mg). The accumulation of FL-LCP in the HCT116 cells was rather low (4.75 ± 0.29% dose/mg protein), but not significantly different from the levels of FL-NCP. It is possible that low concentrations of [¹²⁵I]I-LCP (40 pM) can be effectively internalized after legumain cleavage. On the other hand, the cellular uptake of much higher concentrations of the FL-LCP derivative (1 mM) may be restricted by high concentrations of polyanions. The in vivo biodistribution studies in tumor-bearing mice demonstrated that the tumor uptake of [¹²⁵I]I-LCP was 1.34% injected dose per gram (% ID/g) at 30 min. The tumor/blood and tumor/muscle ratios at 30 min were 0.63 and 1.77, respectively, indicating that the [¹²⁵I]I-LCP accumulation in tumors was inadequate for in vivo imaging. Although further structural modifications are necessary to improve pharmacokinetic properties, [¹²⁵I]I-LCP has been demonstrated to be an effective scaffold for the development of nuclear medicine imaging probes to monitor legumain activity in living subjects.

Design, Synthesis, and Evaluation of 18F-Labeled Monoacylglycerol Lipase Inhibitors as Novel Positron Emission Tomography Probes

Dysfunction of monoacylglycerol lipase (MAGL) is associated with several psychopathological disorders, including drug addiction and neurodegenerative diseases. Herein we design, synthesize, and evaluate several irreversible fluorine-containing MAGL inhibitors for positron emission tomography (PET) ligand development. Compound 6 (identified from a therapeutic agent) was advanced for ¹⁸F-labeling via a novel spirocyclic iodonium ylide (SCIDY) strategy, which demonstrated high brain permeability and excellent specific binding. This work supports further development of novel ¹⁸F-labeled MAGL PET probes.

Renal-clearable Molecular Semiconductor for Second Near-Infrared Fluorescence Imaging of Kidney Dysfunction

Real-time imaging of kidney function is important to assess the nephrotoxicity of drugs and monitor the progression of renal diseases; however, it remains challenging because of the lack of optical agents with high renal clearance and high signal-to-background ratio (SBR). Herein, a second near-infrared (NIR-II) fluorescent molecular semiconductor (CDIR2) is synthesized for real-time imaging of kidney dysfunction in living mice. CDIR2 not only has a high renal clearance efficiency (≈90 % injection dosage at 24 h post-injection), but also solely undergoes glomerular filtration into urine without being reabsorbed and secreted in renal tubules. Such a unidirectional renal clearance pathway of CDIR2 permits real-time monitoring of kidney dysfunction in living mice upon nephrotoxic exposure. Thus, this study not only introduces a molecular renal probe but also provides useful molecular guidelines to increase the renal clearance efficiency of NIR-II fluorescent agents.

Synthesis and Preliminary Evaluation of [11 C]GNE-1023 as a Potent PET Probe for Imaging Leucine-Rich Repeat Kinase 2 (LRRK2) in Parkinson's Disease

Leucine-rich repeat kinase 2 (LRRK2) is a large protein involved in the pathogenesis of Parkinson's disease (PD). It has been demonstrated that PD is mainly conferred by LRRK2 mutations that bring about increased kinase activity. As a consequence, selective inhibition of LRRK2 may help to recover the normal functions of LRRK2, thereby serving as a promising alternative therapeutic target for PD treatment. The mapping of LRRK2 by positron emission tomography (PET) studies allows a thorough understanding of PD and other LRRK2-related disorders; it also helps to validate and translate novel LRRK2 inhibitors. However, no LRRK2 PET probes have yet been reported in the primary literature. Herein we present a facile synthesis and preliminary evaluation of [¹¹ C]GNE-1023 as a novel potent PET probe for LRRK2 imaging in PD. [¹¹ C]GNE-1023 was synthesized in good radiochemical yield (10 % non-decay-corrected RCY), excellent radiochemical purity (>99 %), and high molar activity (>37 GBq μmol^-1 ). Excellent in vitro binding specificity of [¹¹ C]GNE-1023 toward LRRK2 was demonstrated in cross-species studies, including rat and nonhuman primate brain tissues by autoradiography experiments. Subsequent whole-body biodistribution studies indicated limited brain uptake and urinary and hepatobiliary elimination of this radioligand. This study may pave the way for further development of a new generation of LRRK2 PET probes.