Synthesis and Preclinical Evaluation of Radioiodinated Hypericin Dicarboxylic Acid as a Necrosis Avid Agent in Rat Models of Induced Hepatic, Muscular, and Myocardial Necroses

Hypericin: A natural anthraquinone as promising therapeutic agent

BACKGROUND

Hypericin is a prominent secondary metabolite mainly existing in genus Hypericum. It has become a research focus for a quiet long time owing to its extensively pharmacological activities especially the anti-cancer, anti-bacterial, anti-viral and neuroprotective effects. This review concentrated on summarizing and analyzing the existing studies of hypericin in a comprehensive perspective.

METHODS

The literature with desired information about hypericin published after 2010 was gained from electronic databases including PubMed, SciFinder, Science Direct, Web of Science, China National Knowledge Infrastructure databases and Wan Fang DATA.

RESULTS

According to extensive preclinical and clinical studies conducted on the hypericin, an organized and comprehensive summary of the natural and artificial sources, strategies for improving the bioactivities, pharmacological activities, drug combination of hypericin was presented to explore the future therapeutic potential of this active compound.

CONCLUSIONS

Overall, this review offered a theoretical guidance for the follow-up research of hypericin. However, the pharmacological mechanisms, pharmacokinetics and structure activity relationship of hypericin should be further studied in future research.

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.

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.

A novel multimodal nanoplatform for targeting tumor necrosis

Peri-necrotic tumor regions have been found to be a source of cancer stem cells (CSC), important in tumor recurrence. Necrotic and peri-necrotic tumor zones have poor vascular supply, limiting effective exposure to systemically administered therapeutics. Therefore, there is a critical need to develop agents that can effectively target these relatively protected tumor areas. We have developed a multi-property nanoplatform with necrosis avidity, fluorescence imaging and X-ray tracking capabilities to evaluate its feasibility for therapeutic drug delivery. The developed nanoparticle consists of three elements: poly(ethylene glycol)-block-poly(ε-caprolactone) as the biodegradable carrier; hypericin as a natural compound with fluorescence and necrosis avidity; and gold nanoparticles for X-ray tracking. This reproducible nanoparticle has a hydrodynamic size of 103.9 ± 1.7 nm with a uniform spherical morphology (polydispersity index = 0.12). The nanoparticle shows safety with systemic administration and a stable 30 day profile. Intravenous nanoparticle injection into a subcutaneous tumor-bearing mouse and intra-arterial nanoparticle injection into rabbits bearing VX2 orthotopic liver tumors resulted in fluorescence and X-ray attenuation within the tumors. In addition, ex vivo and histological analysis confirmed the accumulation of hypericin and gold in areas of necrosis and peri-necrosis. This nanoplatform, therefore, has the potential to enhance putative therapeutic drug delivery to necrotic and peri-necrotic areas, and may also have an application for monitoring early response to anti-tumor therapies.

Au-Hyp-NP developed by encapsulation of gold and hypericin into PEG-PCL nanoplatform for fluorescence and X-ray tracking with tumor necrosis targeting.

The evolving roles of radiolabeled quinones as small molecular probes in necrotic imaging

Necrosis plays vital roles in living organisms which is related closely with various diseases. Non-invasively necrotic imaging can be of great values in clinical decision-making, evaluation of individualized treatment responses, and prediction of patient prognosis. This narrative review will demonstrate how the evolution of quinones for necrotic imaging has been promoted by searching for their active centers. In this review, we summarized the recent developments of various quinones with the continuous simplified π-conjugated cores in necrotic imaging and speculated their possible molecular mechanisms might be attributed to their intercalations with exposed DNA in necrotic tissues. We discussed their clinical challenges of necrotic imaging with quinones and their future translation studies deserved to be explored in personalized patient treatment.

Discovery of necrosis avidity of rhein and its applications in necrosis imaging

Necrosis-avid agents possess exploitable theragnostic utilities including evaluation of tissue viability, monitoring of therapeutic efficacy as well as diagnosis and treatment of necrosis-related disorders. Rhein (4,5-dihydroxyl-2-carboxylic-9,10-dihydrodiketoanthracene), a naturally occurring monomeric anthraquinone compound extensively found in medicinal herbs, was recently demonstrated to have a newly discovered necrosis-avid trait and to show promising application in necrosis imaging. In this overview, we present the discovering process of rhein as a new necrosis-avid agent as well as its potential imaging applications in visualisation of myocardial necrosis and early evaluation of tumour response to therapy. Moreover, the molecular mechanism exploration of necrosis avidity behind rhein are also presented. The discovery of necrosis avidity with rhein and the development of rhein-based molecular probes may further expand the scope of necrosis-avid compounds and highlight the potential utility of necrosis-avid molecular probes in necrosis imaging.

Molecular imaging of myocardial necrosis: an updated mini-review

Acute myocardial infarction (AMI) remains the most severe and common cardiac emergency among various ischaemic heart diseases. Both unregulated (necrosis) and regulated (apoptosis, autophagy and necroptosis et al.) forms of cell death can occur during AMI. Non-invasive imaging of cardiomyocyte death represents an attractive approach to acquire insights into the pathophysiology of AMI, track the temporal and spatial evolution of MI, guide therapeutic decision-making, evaluate response to therapeutic intervention and predict prognosis. Although several forms of cell death have been identified during AMI, to date, only apoptosis- and necrosis-detecting probes compatible with currently available tomographic imaging modalities have been successfully developed for non-invasive visualisation of cardiomyocyte death. Myocardial apoptosis imaging has gained more attention because of its potential controllability while less attention has been paid to myocardial necrosis imaging. In our opinion, although cardiomyocyte necrosis is unsalvageable, imaging necrosis can play an important role in early diagnosis, risk stratification, prognostic prediction and guidance in therapeutic decision-making of AMI. In this mini-review, we summarise the updated advances achieved by us and others and discuss the challenges in the development of molecular imaging probes for visualisation of myocardial necrosis.

A Model In Vitro Study Using Hypericin: Tumor-Versus Necrosis-Targeting Property and Possible Mechanisms

Hypericin (Hyp) had been explored as a tumor-seeking agent for years; however, more recent studies showed its necrosis-avidity rather than cancer-seeking property. To further look into this discrepancy, we conducted an in vitro study on Hyp retention in vital and dead cancerous HepG2 and normal LO2 cell lines by measuring the fluorescence intensity and concentration of Hyp in cells. To question the DNA binding theory for its necrosis-avidity, the subcellular distribution of Hyp was also investigated to explore the possible mechanisms of the necrosis avidity. The fluorescence intensity and concentration are significantly higher in dead cells than those in vital cells, and this difference did not differ between HepG2 and LO2 cell lines. Hyp was taken up in vital cells in the early phase and excreted within hours, whereas it was retained in dead cells for more than two days. Confocal microscopy showed that Hyp selectively accumulated in lysosomes rather than cell membrane or nuclei. Hyp showed a necrosis-avid property rather than cancer-targetability. The long-lasting retention of Hyp in dead cells may be associated with halted energy metabolism and/or binding with certain degraded cellular substrates. Necrosis-avidity of Hyp was confirmed, which may be associated with halted energy metabolism in dead LO2 or HepG2 cells.

Hypericin-Loaded Carbon Nanohorn Hybrid for Combined Photodynamic and Photothermal Therapy in Vivo

Photodynamic therapy (PDT) of hypericin (Hyp) is hampered by poor water solubility and photostability. Incorporation of photosensitizers into nanocarriers has been designed to solve these issues. Herein, SWNH-Hyps nanohybrids were first fabricated by loading hypericin on the surface of single-walled carbon nanohorns (SWNHs) through ??? interaction and exhibited high solubility and stability in aqueous water. SWNH-Hyps could be utilized for a single platform for cancer therapy because it could simultaneously generate enough reactive oxygen species and hyperthermia using light irradiation. Moreover, the SWNHs not only improved water solubility, photostability, and therapy effects of Hyp but also protected it from light degradation. SWNH-Hyps could effectively ablate 4T1 cells by photodynamic/photothermal synergistic therapy upon 590 and 808 nm light irradiations compared with PDT. Furthermore, remarkable tumor cell death as well as tumor growth inhibition was proved via photothermal therapy and PDT of SWNH-Hyps under 590 and 808 nm light irradiations, which demonstrated that synergistic anticancer ability of SWNH-Hyps was better than that of free Hyp in vivo. Such a simple and facile adsorption method improved water solubility of Hyp and then enhanced its therapy effect, which displays that SWNHs can be hopefully used in medicines in the future.

Updated developments on molecular imaging and therapeutic strategies directed against necrosis

Cell death plays important roles in living organisms and is a hallmark of numerous disorders such as cardiovascular diseases, sepsis and acute pancreatitis. Moreover, cell death also plays a pivotal role in the treatment of certain diseases, for example, cancer. Noninvasive visualization of cell death contributes to gained insight into diseases, development of individualized treatment plans, evaluation of treatment responses, and prediction of patient prognosis. On the other hand, cell death can also be targeted for the treatment of diseases. Although there are many ways for a cell to die, only apoptosis and necrosis have been extensively studied in terms of cell death related theranostics. This review mainly focuses on molecular imaging and therapeutic strategies directed against necrosis. Necrosis shares common morphological characteristics including the rupture of cell membrane integrity and release of cellular contents, which provide potential biomarkers for visualization of necrosis and necrosis targeted therapy. In the present review, we summarize the updated joint efforts to develop molecular imaging probes and therapeutic strategies targeting the biomarkers exposed by necrotic cells. Moreover, we also discuss the challenges in developing necrosis imaging probes and propose several biomarkers of necrosis that deserve to be explored in future imaging and therapy research.

Evaluation of Necrosis Avidity and Potential for Rapid Imaging of Necrotic Myocardium of Radioiodinated Hypocrellins

PURPOSE

Rapid noninvasive delineation of necrotic myocardium in ischemic regions is very critical for risk stratification and clinical decision-making but still challenging. This study aimed to evaluate the necrosis avidity of radioiodinated hypocrellins and its potential for rapidly imaging necrotic myocardium.

PROCEDURES

The aggregation constants of four natural hypocrellins were analyzed by UV/vis spectroscopy. Then, they were radiolabeled with iodine-131 by iodogen oxidation method. Necrosis avidity of iodine-131-labeled hypocrellins was evaluated in rat models with reperfused liver infarction and muscular necrosis by gamma counting, autoradiography, and histopathology. Their pharmacokinetic properties were examined in normal rats. The potential of iodine-131-labeled hypomycin A ([¹³¹I]HD) for early imaging of necrotic myocardium was explored in rat models with reperfused myocardial infarction. Finally, the possible mechanism of necrosis avidity was investigated by in vitro DNA binding and in vivo blocking experiments.

RESULTS

The aggregation constants of four hypocrellins were all much smaller than that of hypericin, a most studied necrosis avid agent. The radiochemical purities of the four radiotracers after purification were all greater than 95 %, and more than 90 % of tracers remained intact after incubation in rat serum for 24 h. Among the four tracers, [¹³¹I]HD exhibited the highest necrotic to viable tissue uptake ratio and the fastest blood clearance. The necrotic myocardium could be clearly visualized 4 h after injection of [¹³¹I]HD by single-photon emission computed tomography/X-ray computed tomography (SPECT/CT). DNA binding studies suggested that HD could bind to DNA through intercalation. Blocking studies demonstrated that uptake of [¹³¹I]HD in necrotic muscle could be significantly blocked by excess unlabeled HD and ethidium bromide with 67 and 60 % decline at 6 h after coinjection, respectively.

CONCLUSIONS

[¹³¹I]HD can be used to rapidly visualize necrotic myocardium. The necrosis avidity mechanism of [¹³¹I]HD may be attributed to its binding to the exposed DNA in necrotic tissues.

Chiral Dinuclear Vanadium Complex-Mediated Oxidative Coupling of Resorcinols

A method for the highly regio- and enantioselective oxidative coupling of resorcinols has been established by using dibrominated dinuclear vanadium(V) catalyst 1c under air. When resorcinols bearing an aryl substituent were applied as substrates to the coupling, axially chiral biresorcinols were obtained as single regioisomers in high yield with up to 98% ee.

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

The purpose of this study is to develop a specific CXCR4-targeting radioiodinated agent (¹²⁵I- or ¹³¹I-pentixather) for single-photon-emission-computed-tomography (SPECT) imaging of CXCR4 expression in myocardial-infarction-reperfusion (MI/R) rat models. After SPECT-CT imaging with ¹²⁵I-pentixather at 4, 12, and 36 h and 3 and 7 days after MI/R, the models were validated by ex vivo autoradiography, TTC staining, and immunohistochemistry and in vivo echocardiography and classical ^99mTc-MIBI perfusion imaging. The SPECT-CT images showed that the infarcted myocardium (IM) could be visualized with high quality as early as 4 h and reached the maximum at 3 days after MI/R and that CXCR4 upregulation was still visible at 7 days after MI/R. In the biodistribution study, high uptakes in the IM (0.99 ± 0.13, 1.52 ± 0.29, 1.75 ± 0.22, 1.94 ± 0.27, and 0.61 ± 0.14% ID/g at 4, 12, and 36 h and 3 and 7 days after MI/R, respectively) were observed that were much higher than that of normal myocardium. The highest uptake was reached at 3 days after MI/R, which agreed well with the SPECT results. In addition, the radioactivity uptakes of the IM in both the biodistribution and SPECT imaging could be blocked effectively by excess amounts of AMD3465, indicating the high specificity of radioiodinated pentixather to CXCR4. On the basis of its promising properties, ¹²⁵I-pentixather may serve as a powerful CXCR4-expression diagnostic probe for evaluating lesions and monitoring therapy responses in patients with cardiovascular diseases.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Excretion and toxicity evaluation of 131I-Sennoside A as a necrosis-avid agent

1. Sennoside A (SA) is a newly identified necrosis-avid agent that shows capability for imaging diagnosis and tumor necrosis targeted radiotherapy. As a water-soluble compound, ¹³¹I-Sennoside A (¹³¹I-SA) might be excreted predominately through the kidneys with the possibility of nephrotoxicity. 2. To further verify excretion pathway and examine nephrotoxicity of ¹³¹I-SA, excretion and nephrotoxicity were appraised. The pharmacokinetics, hepatotoxicity and hematotoxicity of ¹³¹I-SA were also evaluated to accelerate its possible clinical translation. All these studies were conducted in mice with ethanol-induced muscular necrosis following a single intravenous administration of 131I-SA at 18.5 MBq/kg or 370 MBq/kg. 3. Excretion data revealed that ¹³¹I-SA was predominately (73.5% of the injected dose (% ID)) excreted via the kidneys with 69.5% ID detected in urine within 72 h post injection. Biodistribution study indicated that ¹³¹I-SA exhibited initial high distribution in the kidneys but subsequently a fast renal clearance, which was further confirmed by the results of autoradiography and single-photon emission computed tomography-computed tomography (SPECT-CT) imaging. The maximum necrotic to normal muscle ratio reached to 7.9-fold at 48 h post injection, which further verified the necrosis avidity of ¹³¹I-SA. Pharmacokinetic parameters showed that ¹³¹I-SA had fast blood clearance with an elimination half-life of 6.7 h. Various functional indexes were no significant difference (p > 0.05) between before administration and 1 d, 8 d, 16 d after administration. Histopathology showed no signs of tissue damage. 4. These data suggest ¹³¹I-SA is a safe and promising necrosis-avid agent applicable in imaging diagnosis and tumor necrosis targeted radiotherapy.