Radioiodinated Pentixather for SPECT Imaging of Expression of the Chemokine Receptor CXCR4 in Rat Myocardial-Infarction-Reperfusion Models

Micro-SPECT Imaging of Acute Ischemic Stroke with Radioiodinated Riboflavin in Rat MCAO Models via Riboflavin Transporter Targeting

Riboflavin transporter-3 (RFVT3) is a recently discovered and novel biomarker for the theranostics of nervous system diseases. RFVT3 is significantly overexpressed in cerebral injury after ischemic stroke. Herein, we first reported an RFVT3-targeted tracer ¹³¹I-riboflavin (¹³¹I-RFLA) for SPECT imaging of ischemic stroke in vivo. ¹³¹I-RFLA was radiosynthesized by the iodogen-coating method. ¹³¹I-RFLA possessed a radiochemical yield of 69.2 ± 3.7% and greater than 95% radiochemical purity. The representative SPECT/CT images using ¹³¹I-RFLA demonstrated the conspicuously increased tracer uptake in the cerebral injury by comparison with the contralateral normal brain at 1 h and 3 and 7 d after stroke. Ex vivo autoradiography demonstrated that the ratio of infarcted to normal brain uptake was 3.63 and it was decreased to 1.98 after blocking, which reconfirmed the results of SPECT images. Importantly, a significant correlation was identified between RFVT3 expression and brain injury by H&E and immunohistochemistry staining. Therefore, RFVT3 is a new and potential biomarker for the early diagnosis of ischemic stroke. In addition, ¹³¹I-RFLA is a promising SPECT tracer for imaging RFVT3-related ischemic cerebral injury in vivo.

China’s radiopharmaceuticals on expressway: 2014–2021

This review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Nuclear Molecular Imaging of Cardiac Remodeling after Myocardial Infarction

The role of molecular imaging technologies in detecting, evaluating, and monitoring cardiovascular disease and their treatment is expanding rapidly. Gradually replacing the conventional anatomical or physiological approaches, molecular imaging strategies using biologically targeted markers provide unique insight into pathobiological processes at molecular and cellular levels and allow for cardiovascular disease evaluation and individualized therapy. This review paper will discuss currently available and developing molecular-based single-photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging strategies to evaluate post-infarction cardiac remodeling. These approaches include potential targeted methods of evaluating critical biological processes, such as inflammation, angiogenesis, and scar formation.

Molecular imaging of cardiac CXCR4 expression in a mouse model of acute myocardial infarction using a novel 68Ga-mCXCL12 PET tracer

BACKGROUND

The chemokine receptor CXCR4 and its ligand CXCL12 have been shown to be a possible imaging and therapeutic target after myocardial infarction (MI). The murine-based and mouse-specific 68Ga-mCXCL12 PET tracer could be suitable for serial in vivo quantification of cardiac CXCR4 expression in a murine model of MI.

METHODS AND RESULTS

At days 1-6 after MI, mice were intravenously injected with 68Ga-mCXCL12. Autoradiography was performed and the infarct-to-remote ratio (I/R) was determined. In vivo PET imaging with 68Ga-mCXCL12 was conducted on days 1-6 after MI and the percentage of the injected dose (%ID/g) of the tracer uptake in the infarct area was calculated. 18F-FDG-PET was performed for anatomical landmarking. Ex vivo autoradiography identified CXCR4 upregulation in the infarct region with an increasing I/R after 12 hours (1.4 ± 0.3), showing a significant increase until day 2 (4.5 ± 0.6), followed by a plateau phase (day 4) and decrease after 10 days (1.3 ± 1.0). In vivo PET imaging identified similar CXCR4 upregulation in the infarct region which peaked around day 3 post MI (9.7 ± 5.0 %ID/g) and then subsequently decreased by day 6 (2.8 ± 1.0 %ID/g).

CONCLUSION

Noninvasive molecular imaging of cardiac CXCR4 expression using a novel, murine-based, and specific 68Ga-mCXCL12 tracer is feasible both ex vivo and in vivo.

Smart 131 I-Labeled Self-Illuminating Photosensitizers for Deep Tumor Therapy

Stimulating photosensitizers (PS) by Cerenkov radiation (CR) can overcome the light penetration limitation in traditional photodynamic therapy. However, separate injection of radiopharmaceuticals and PS cannot guarantee their efficient interaction in tumor areas, while co-delivery of radionuclides and PS face the problem of nonnegligible phototoxicity in normal tissues. Here, we describe a ¹³¹ I-labeled smart photosensitizer, composed of pyropheophorbide-a (photosensitizer), a diisopropylamino group (pH-sensitive group), an ¹³¹ I-labeled tyrosine group (CR donor), and polyethylene glycol, which can self-assemble into nanoparticles (¹³¹ I-sPS NPs). The ¹³¹ I-sPS NPs showed low phototoxicity in normal tissues due to aggregation-caused quenching effect, but could self-produce reactive oxygen species in tumor sites upon disassembly. Upon intravenous injection, ¹³¹ I-sPS NPs showed great tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice and orthotopic VX2 liver tumor bearing rabbits. We believed ¹³¹ I-sPS NPs could expand the application of CR and provide an effective strategy for deep tumor theranostics.

Exploring Solvent Effects in the Radiosynthesis of 18F-Labeled Thymidine Analogues toward Clinical Translation for Positron Emission Tomography Imaging

Thymidine analogues, 5-substituted 2'-deoxy-2'-[¹⁸F]fluoro-arabinofuranosyluracil derivatives, are promising positron emission tomography (PET) tracers being evaluated for noninvasive imaging of cancer cell proliferation and/or reporter gene expression. We report the radiosynthesis of 2'-deoxy-2'-[¹⁸F]fluoro-5-methyl-1-β-d-arabinofuranosyluracil ([¹⁸F]FMAU) and other 2'-deoxy-2'-[¹⁸F]fluoro-5-substituted-1-β-d-arabinofuranosyluracil analogues using 1,4-dioxane to replace the currently used 1,2-dichloroethane. Compared to 1,2-dichloroethane, 1,4-dioxane is analyzed as a better solvent in terms of radiochemical yield and toxicity concern. The use of a less toxic solvent allows for the translation of the improved approach to clinical production. The new radiolabeling method can be applied to an extensive range of uses for ¹⁸F-labeling of other nucleoside analogues.

Preparation and Characterization of Protein-loaded PFC Nanoemulsions for the Treatment of Heart Diseases by Pulmonary Administration

In the treatment of heart disease, strategies for the targeted delivery of protein therapeutics to the heart by inhalation are still immature. Perfluorocarbons (PFCs) are inert chemicals with good biocompatibility, and unique physico-chemical properties that have recently led to their applications in numerous fields. In this study, we combined the advantages of protein-phospholipid complexes and PFC emulsions and then synthesized protein-loaded PFC nanoemulsions (PNEs) to test whether, after inhalation, these nanoemulsions could deliver therapeutic proteins to the heart. After preparing protein-phospholipid complexes by lyophilization, we obtained PNEs by extrusion. The particle size and surface charge of PNEs were about 140 nm and -50 mV, respectively. In vitro results showed that the PNEs had a fine particle fraction of 35% and exhibited sustained protein release. Translocation studies were done using three types of pulmonary epithelial cells, and ~7% translocation was observed in the Calu-3 cell line. Further, they were easily absorbed by cells and had therapeutic effects in culture. In vivo results showed that the PNEs successfully delivered proteins to the myocardial tissue of rats and reduced ischemic myocardial injury caused by acute myocardial infarction (AMI). This study suggests that inhalation of PNEs is a new potential strategy to deliver proteins to cardiac tissues for treating heart diseases.

Evaluation of 99mTc-CN5DG as a broad-spectrum SPECT probe for tumor imaging

Previously, we reported a [^99mTc(ǀ)]⁺ labeled d-glucoamine derivative (^99mTc-CN5DG) and evaluated it as a tumor imaging agent in mice bearing A549 tumor xenografts. In this paper, ^99mTc-CN5DG was further studied in U87 MG (human glioma cells), HCT-116 (human colon cancer cells), PANC-1 (human pancreatic cancer cells) and TE-1 (human esophageal cancer cells) tumor xenografts models to verify its potential application for imaging of different kinds of tumors. The biodistribution data showed that ^99mTc-CN5DG had a similar biodistribution pattern in four tumor models at 2 h post-injection with high accumulation in tumors and kidneys. The tumor/muscle ratios (from 4.08 ± 0.42 to 9.63 ± 3.53) and tumor/blood ratios (from 17.18 ± 7.40 to 53.17 ± 16.16) of ^99mTc-CN5DG in four tumor models were high. All four kinds of tumors could be clearly seen on their corresponding SPECT/CT images. Pharmacokinetic study in healthy CD-1 mice demonstrated that ^99mTc-CN5DG cleared fast from blood (2 min, 12.97 ± 0.88%ID/g; 60 min, 0.33 ± 0.06%ID/g) and the blood distribution, elimination half-life was 5.81 min and 21.16 min, respectively. No abnormality was observed through the abnormal toxicity study. All of the above results demonstrated that ^99mTc-CN5DG could be a broad-spectrum SPECT probe for tumor imaging and its further clinical application is warranted.

Small molecules as theranostic agents in cancer immunology

With further research into the molecular mechanisms and roles linking immune suppression and restraint of (pre)malignancies, immunotherapies have revolutionized clinical strategies in the treatment of cancer. However, nearly 70% of patients who received immune checkpoint therapeutics showed no response. Complementary and/or synergistic effects may occur when extracellular checkpoint antibody blockades combine with small molecules targeting intracellular signal pathways up/downstream of immune checkpoints or regulating the innate and adaptive immune response. After radiolabeling with radionuclides, small molecules can also be used for estimating treatment efficacy of immune checkpoint blockades. This review not only highlights some significant intracellular pathways and immune-related targets such as the kynurenine pathway, purinergic signaling, the kinase signaling axis, chemokines, etc., but also summarizes some attractive and potentially immunosuppression-related small molecule agents, which may be synergistic with extracellular immune checkpoint blockade. In addition, opportunities for small molecule-based theranostics in cancer immunology will be discussed.

Radioiodinated progesterone derivative for progesterone receptor targeting with enhanced nucleus uptake via phenylboronic acid conjugation

A novel ¹³¹ I-radiolabeled probe with aromatic boronate motif (¹³¹ I-EIPBA) was designed to target progesterone receptor (PR)-positive breast cancer with enhanced nucleus uptake. Acetylene progesterone was conjugated with pegylated phenylboronic acid via click reaction and radiolabeled with ¹³¹ I to afford ¹³¹ I-EIPBA. Meanwhile, ¹³¹ I-EIPB without boronate was prepared as control agent. After determination of the lipophilicity and stability of these tracers, in vitro cell uptake studies and in vivo biodistribution in rats were performed to verify the enhanced nucleus uptake and PR targeting ability of ¹³¹ I-EIPBA. ¹³¹ I-EIPBA was obtained with moderate radiochemical yield (40.35 ± 3.52%) and high radiochemical purity (>98%). As expected, the high binding affinity (39.58 nM) of ¹³¹ I-EIPBA for PR was determined by cell binding assay. The internalization ratio of ¹³¹ I-EIPBA was remarkably higher than that of ¹³¹ I-EIPB in PR-positive MCF-7 cells. Furthermore, the enhanced nucleus uptake of ¹³¹ I-EIPBA (0.59 ± 0.02%) was found to be significantly higher than that of ¹³¹ I-EIPB (0.13 ± 0.01%) in MCF-7 cells. A novel ¹³¹ I-EIPBA compound was developed for PR targeting with improved cellular nucleus uptake. Furthermore, the introduction of aromatic boronate motif provides a worthwhile strategy for enhancing the nuclear receptor targeting of tracers.

Robust organic nanoparticles for noninvasive long-term fluorescence imaging

Organic nanoparticles obtained from fluorophores with aggregation-caused quenching and aggregation-induced emission features for noninvasive long-term bioimaging are summarized and highlighted.