First preclinical evaluation of mono-[123I]iodohypericin as a necrosis-avid tracer agent

Radioiodinated hypericin as a tracer for detection of acute myocardial infarction: SPECT-CT imaging in a swine model

PURPOSE

Hypericin (Hyp) is a natural compound with a newly discovered necrosis-avidity, which can be exploited as a necrosis-avid tracer once labeled with radioactive iodine as has been tested in rodent models. This study was to evaluate the effect of radioiodinated Hyp (131I-Hyp) for imaging detection of acute myocardial infarction (AMI) in conditions closer to clinical scenarios.

METHODS

We established swine AMI models (n = 6) which were intravenously given 131I-Hyp and 99mTc-sestamibi and underwent SPECT-CT imaging with high- and low-energy collimators. The acquired SPECT images were fused with cardiac CT images and correlated with postmortem autoradiography and macro- and microscopic pathology. Tissue γ counting was performed to determine biodistribution of 131I-Hyp.

RESULTS

131I-Hyp based SPECT indicated clearly hot regions on ventricular walls which were all histologically proved as AMI. Complementally, the hot AMI regions on 131I-Hyp SPECT (infarct/myoc ratio of 15.3 ± 7.7) were inversely cold regions on 99mTc-sestamibi SPECT (infarct/myoc ratio of 0.029 ± 0.021). Autoradiography of heart slices showed 9.8 times higher 131I-Hyp uptake in infarcted over normal myocardium. With γ counting, the mean 131I-Hyp uptake in infarcts was 10.69 ID%/g, 12.05 times of that in viable myocardium.

CONCLUSION

131I-Hyp shows a potential for clinical detection of AMI once I-131 is substituted by its isotope like I-124 or I-123 for PET or SPECT, respectively.

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.

Preparation and validation of cyclodextrin-based excipients for radioiodinated hypericin applied in a targeted cancer radiotherapy

BACKGROUND

Iodine-131 labeled hypericin (¹³¹I-Hyp) has been utilized as a necrosis-avid theragnostic tracer in a dual targeting pan-anticancer strategy called OncoCiDia. Widespread use of previously-tested solvent dimethyl sulfoxide (DMSO) is limited by safety concerns. To tackle this, the present study was designed to explore a clinically feasible excipient for the formulation of the hydrophobic ¹³¹I-Hyp for intravenous administration.

METHOD

Solubility of Hyp in serial solutions of already-approved hydroxypropyl-β-cyclodextrin (HP-β-CD) was evaluated by UVspectrophotometry and 50% HP-β-CD was chosen for further experiments. Two novel HP-β-CD-based formulations of ¹³¹I-Hyp were compared with previous DMSO-based formulation, with regards to necrosis-targetability and biodistribution, by magnetic resonance imaging, single-photon emission computed tomography (SPECT), gamma counting, autoradiography, fluorescence microscopy and histopathology.

RESULTS

Hyp solubility was enhanced with increasing HP-β-CD concentrations. The radiochemical purity of ¹³¹I-Hyp was higher than 90% in all formulations. The necrosis-targetability of ¹³¹I-Hyp in the novel formulations was confirmed in vivo by SPECT and in vitro by autoradiography, fluorescence microscopy and histopathology. The plasma clearance of radioactivity was faster in the novel formulations.

CONCLUSION

The novel ¹³¹I-Hyp formulations with HP-β-CD could be a suitable pharmaceutical excipient for ¹³¹I-Hyp for intravenous administration.

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.

Biodegradable Hypericin-Containing Nanoparticles for Necrosis Targeting and Fluorescence Imaging

Necrosis targeting and imaging has significant implications for evaluating tumor growth, therapeutic response, and delivery of therapeutics to perinecrotic tumor zones. Hypericin is a hydrophobic molecule with high necrosis affinity and fluorescence imaging properties. To date, the safe and effective delivery of hypericin to areas of necrosis in vivo remains a challenge because of its incompatible biophysical properties. To address this issue, we have developed a biodegradable nanoparticle (Hyp-NP) for delivery of hypericin to tumors for necrosis targeting and fluorescence imaging. The nanoparticle was developed using methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) and hypericin by a modified solvent evaporation technique. The size of Hyp-NP was 19.0 ± 1.8 nm from cryo-TEM and 37.3 ± 0.7 nm from dynamic light-scattering analysis with a polydispersity index of 0.15 ± 0.01. The encapsulation efficiency of hypericin was 95.05% w/w by UV-vis absorption. After storage for 30 days, 91.4% hypericin was retained in Hyp-NP with nearly no change in hydrodynamic size, representing nanoparticle stability. In an ovarian cancer cell line, Hyp-NP demonstrated cellular internalization with intracellular cytoplasmic localization and preserved fluorescence and necrosis affinity. In a mouse subcutaneous tumor model, tumor accumulation was noted at 8 h postinjection, with near-complete clearance at 96 h postinjection. Hyp-NP was shown to be tightly localized within necrotic tumor zones. Histological analysis of harvested organs demonstrated no gross abnormalities, and in vitro, no hemolysis was observed. This proof-of-concept study demonstrates the potential clinical applications of Hyp-NP for necrosis targeting.

Imaging Cell Death: Focus on Early Evaluation of Tumor Response to Therapy

Cell death plays a prominent role in the treatment of cancer, because most anticancer therapies act by the induction of cell death including apoptosis, necrosis, and other pathways of cell death. Imaging cell death helps to identify treatment responders from nonresponders and thus enables patient-tailored therapy, which will increase the likelihood of treatment response and ultimately lead to improved patient survival. By taking advantage of molecular probes that specifically target the biomarkers/biochemical processes of cell death, cell death imaging can be successfully achieved. In recent years, with the increased understanding of the molecular mechanism of cell death, a variety of well-defined biomarkers/biochemical processes of cell death have been identified. By targeting these established cell death biomarkers/biochemical processes, a set of molecular imaging probes have been developed and evaluated for early monitoring treatment response in tumors. In this review, we mainly present the recent advances in identifying useful biomarkers/biochemical processes for both apoptosis and necrosis imaging and in developing molecular imaging probes targeting these biomarkers/biochemical processes, with a focus on their application in early evaluation of tumor response to therapy.

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.

Predicting Clinical Efficacy of Vascular Disrupting Agents in Rodent Models of Primary and Secondary Liver Cancers: An Overview with Imaging-Histopathology Correlation

Vascular disrupting agents (VDAs) have entered clinical trials for over 15 years. As the leading VDA, combretastatin A4 phosphate (CA4P) has been evaluated in combination with chemotherapy and molecular targeting agents among patients with ovarian cancer, lung cancer and thyroid cancer, but still remains rarely explored in human liver cancers. To overcome tumor residues and regrowth after CA4P monotherapy, a novel dual targeting pan-anticancer theragnostic strategy, i.e., OncoCiDia, has been developed and shown promise previously in secondary liver tumor models. Animal model of primary liver cancer is time consuming to induce, but of value for more closely mimicking human liver cancers in terms of tumor angiogenesis, histopathological heterogeneity, cellular differentiation, tumor components, cancer progression and therapeutic response. Being increasingly adopted in VDA researches, multiparametric magnetic resonance imaging (MRI) provides imaging biomarkers to reflect in vivo tumor responses to drugs. In this article as a chapter of a doctoral thesis, we overview the construction and clinical relevance of primary and secondary liver cancer models in rodents. Target selection for CA4P therapy assisted by enhanced MRI using hepatobiliary contrast agents (CAs), and therapeutic efficacy evaluated by using MRI with a non-specific contrast agent, dynamic contrast enhanced (DCE) imaging, diffusion weighted imaging (DWI) are also described. We then summarize diverse responses among primary hepatocellular carcinomas (HCCs), secondary liver and pancreatic tumors to CA4P, which appeared to be related to tumor size, vascularity, and cellular differentiation. In general, imaging-histopathology correlation studies allow to conclude that CA4P tends to be more effective in secondary liver tumors and in more differentiated HCCs, but less effective in less differentiated HCCs and implanted pancreatic tumor. Notably, cirrhotic liver may be responsive to CA4P as well. All these could be instructive for future clinical trials of VDAs.

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.

131I-Evans blue: evaluation of necrosis targeting property and preliminary assessment of the mechanism in animal models

Necrosis is a form of cell death, which is related to various serious diseases such as cardiovascular disease, cancer, and neurodegeneration. Necrosis-avid agents (NAAs) selectively accumulated in the necrotic tissues can be used for imaging and/or therapy of related diseases. The aim of this study was to preliminarily investigate necrosis avidity of ¹³¹I-evans blue (¹³¹I-EB) and its mechanism. The biodistribution of ¹³¹I-EB at 24 h after intravenous administration showed that the radioactivity ratio of necrotic to viable tissue was 3.41 in the liver and 11.82 in the muscle as determined by γ counting in model rats. Autoradiography and histological staining displayed preferential uptake of ¹³¹I-EB in necrotic tissues. In vitro nuclear extracts from necrotic cells exhibited 82.3% of the uptake in nuclei at 15 min, as well as 79.2% of the uptake at 2 h after ¹³¹I-EB incubation. The DNA binding study demonstrated that evans blue (EB) has strong binding affinity with calf-thymus DNA (CT-DNA) (K_sv=5.08×10⁵ L/(mol/L)). Furthermore, the accumulation of ¹³¹I-EB in necrotic muscle was efficiently blocked by an excess amount of unlabeled EB. In conclusion, ¹³¹I-EB can not only detect necrosis by binding the DNA released from necrotic cells, but also image necrotic tissues generated from the disease clinically.

Improved therapeutic outcomes of thermal ablation on rat orthotopic liver allograft sarcoma models by radioiodinated hypericin induced necrosis targeted radiotherapy

Residual tumor resulting in tumor recurrence after various anticancer therapies is an unmet challenge in current clinical oncology. This study aimed to investigate the hypothesis that radioiodinated hypericin (131I-Hyp) may inhibit residual tumor recurrence after microwave ablation (MWA) on rat orthotopic liver allograft sarcoma models.Thirty Sprague-Dawley (SD) rats with hepatic tumors were divided into three groups: Group A received laparotomy MWA and sequential intravenous injection (i.v.) of 131I labelled hypericin (131I-Hyp) in a time interval of 24 h; Group B received only laparotomy MWA; Group C was a blank control. Tumor inhibitory effects were monitored with in vivo magnetic resonance imaging (MRI) and these findings were compared to histopathology data before (baseline, day 0) and 1, 4, and 8 days after MWA. In addition, biodistribution of 131I-Hyp was assessed with in vivo single-photon emission computed tomography-computed tomography (SPECT-CT) imaging, in vitro autoradiography, fluorescent microscopy, and gamma counting.A fast clearance of 131I-Hyp and increasing deposit in necrotic tumors appeared over time, with a significantly higher radioactivity than other organs (0.9169 ± 1.1138 % ID/g, P < 0.01) on day 9. Tumor growth was significantly slowed down in group A compared to group B and C according to MRI images and corresponding tumor doubling time (12.13 ± 1.99, 4.09 ± 0.97, 3.36 ± 0.72 days respectively). The crescent tagerability of 131I-Hyp to necrosis was visualized consistently by autoradiography and fluorescence microscopy.In conclusion, 131I-Hyp induced necrosis targeted radiotherapy improved therapeutic outcomes of MWA on rat orthotopic liver allograft sarcoma models.

Biodistribution and tolerance of intravenous iodine-131-labelled hypericin in healthy dogs

Hypericin (Hyp) is a necrosis-avid compound that can be efficiently labelled with radioiodine for both diagnostic and therapeutic purposes. Before ¹³¹ I-Hyp can be considered as a clinically useful drug in a combination therapy for canine cancer patients, evaluation of its toxicity is necessary. The aim of this study was to investigate the biodistribution and tolerance of a single dose administration of ¹³¹ I-Hyp. Three healthy dogs were included. ¹³¹ I-Hyp at a dose of 0.2 mg/kg and an activity of 185 MBq was intravenously injected. The effects on physical, haematological and biochemical parameters were characterized and the biodistribution and elimination pattern, the effective half-life and dose rate were assessed. Drug-related adverse events were limited to mild gastrointestinal signs, resolving within 48 hours. No significant differences were found in blood haematology and serum biochemistry before and after treatment. Following administration, highest percentage of injected dose (%ID ± SD) was found in the liver (5.5 ± 0.33), the lungs (4.17 ± 0.14) and the heart (3.11 ± 0.78). After 24 hours, highest %ID was found in colon (4.25 ± 1.45) and liver (3.45 ± 0.60). Clearance from all organs was effective within 7 days. Effective half-life was established at 80 hours, and the dose rate fell below <20 μSv/h at 1 m within 1 day. The current study reveals that single dose treatment with ¹³¹ I-Hyp at the described dose is well tolerated by healthy dogs and supports the use of radioiodinated hypericin in a combination therapy for canine cancer patients.

Effects of Glycosylation on Biodistribution and Imaging Quality of Necrotic Myocardium of Iodine-131-Labeled Sennidins

PURPOSE

Sennidins are necrosis-avid agents for noninvasive assessment of myocardial viability which is important for patients with myocardial infarction (MI). However, high accumulation of radioactivity in the liver interferes with the assessment of myocardial viability. In this study, we compared sennidins with sennosides to investigate the effects of glycosylation on biodistribution and imaging quality of sennidins.

PROCEDURES

Sennidin A (SA), sennidin B (SB), sennoside A (SSA), and sennoside B (SSB) were labeled with I-131. In vitro binding to necrotic cells and hepatic cells and in vivo biodistribution in rats with muscular necrosis were evaluated by gamma counting, autoradiography, and histopathology. Single photon emission computed tomography/computed tomography (SPECT/CT) images were acquired in rats with acute MI.

RESULTS

The uptake of [¹³¹I]SA, [¹³¹I]SSA, [¹³¹I]SB, and [¹³¹I]SSB in necrotic cells was significantly higher than that in viable cells (p < 0.05). Hepatic cells uptake of [¹³¹I]SSA and [¹³¹I]SSB were 7-fold and 10-fold lower than that of corresponding [¹³¹I]SA and [¹³¹I]SB, respectively. The biodistribution data showed that the radioactivities in the liver and feces were significantly lower with [¹³¹I]sennosides than those with [¹³¹I]sennidins (p < 0.01). Autoradiography showed preferential accumulation of these four radiotracers in necrotic areas of muscle, confirmed by histopathology. SPECT/CT imaging studies showed better image quality with [¹³¹I]SSB than with [¹³¹I]SB due to less liver interference.

CONCLUSIONS

Glycosylation significantly decreased the liver uptake and improved the quality of cardiac imaging. [¹³¹I]SSB may serve as a promising necrosis-avid agent for noninvasive assessment of myocardial viability.

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.

Necrosis targeted radiotherapy with iodine-131-labeled hypericin to improve anticancer efficacy of vascular disrupting treatment in rabbit VX2 tumor models

A viable rim of tumor cells surrounding central necrosis always exists and leads to tumor recurrence after vascular disrupting treatment (VDT). A novel necrosis targeted radiotherapy (NTRT) using iodine-131-labeled hypericin (131I-Hyp) was specifically designed to treat viable tumor rim and improve tumor control after VDT in rabbit models of multifocal VX2 tumors. NTRT was administered 24 hours after VDT. Tumor growth was significantly slowed down by NTRT with a smaller tumor volume and a prolonged tumor doubling time (14.4 vs. 5.7 days), as followed by in vivo magnetic resonance imaging over 12 days. The viable tumor rims were well inhibited in NTRT group compared with single VDT control group, as showed on tumor cross sections at day 12 (1 vs. 3.7 in area). High targetability of 131I-Hyp to tumor necrosis was demonstrated by in vivo SPECT as high uptake in tumor regions lasting over 9 days with 4.26 to 98 times higher radioactivity for necrosis versus the viable tumor and other organs by gamma counting, and with ratios of 7.7-11.7 and 10.5-13.7 for necrosis over peri-tumor tissue by autoradiography and fluorescence microscopy, respectively. In conclusion, NTRT improved the anticancer efficacy of VDT in rabbits with VX2 tumors.

Hypericin in the Light and in the Dark: Two Sides of the Same Coin

Hypericin (4,5,7,4',5',7'-hexahydroxy-2,2'-dimethylnaphtodianthrone) is a naturally occurring chromophore found in some species of the genus Hypericum, especially Hypericum perforatum L. (St. John's wort), and in some basidiomycetes (Dermocybe spp.) or endophytic fungi (Thielavia subthermophila). In recent decades, hypericin has been intensively studied for its broad pharmacological spectrum. Among its antidepressant and light-dependent antiviral actions, hypericin is a powerful natural photosensitizer that is applicable in the photodynamic therapy (PDT) of various oncological diseases. As the accumulation of hypericin is significantly higher in neoplastic tissue than in normal tissue, it can be used in photodynamic diagnosis (PDD) as an effective fluorescence marker for tumor detection and visualization. In addition, light-activated hypericin acts as a strong pro-oxidant agent with antineoplastic and antiangiogenic properties, since it effectively induces the apoptosis, necrosis or autophagy of cancer cells. Moreover, a strong affinity of hypericin for necrotic tissue was discovered. Thus, hypericin and its radiolabeled derivatives have been recently investigated as potential biomarkers for the non-invasive targeting of tissue necrosis in numerous disorders, including solid tumors. On the other hand, several light-independent actions of hypericin have also been described, even though its effects in the dark have not been studied as intensively as those of photoactivated hypericin. Various experimental studies have revealed no cytotoxicity of hypericin in the dark; however, it can serve as a potential antimetastatic and antiangiogenic agent. On the contrary, hypericin can induce the expression of some ABC transporters, which are often associated with the multidrug resistance (MDR) of cancer cells. Moreover, the hypericin-mediated attenuation of the cytotoxicity of some chemotherapeutics was revealed. Therefore, hypericin might represent another St. John's wort metabolite that is potentially responsible for negative herb-drug interactions. The main aim of this review is to summarize the benefits of photoactivated and non-activated hypericin, mainly in preclinical and clinical applications, and to uncover the "dark side" of this secondary metabolite, focusing on MDR mechanisms.

Tumor resistance to vascular disrupting agents: mechanisms, imaging, and solutions

The emergence of vascular disrupting agents (VDAs) is a significant advance in the treatment of solid tumors. VDAs induce rapid and selective shutdown of tumor blood flow resulting in massive necrosis. However, a viable marginal tumor rim always remains after VDA treatment and is a major cause of recurrence. In this review, we discuss the mechanisms involved in the resistance of solid tumors to VDAs. Hypoxia, tumor-associated macrophages, and bone marrow-derived circulating endothelial progenitor cells all may contribute to resistance. Resistance can be monitored using magnetic resonance imaging markers. The various solutions proposed to manage tumor resistance to VDAs emphasize combining these agents with other approaches including antiangiogenic agents, chemotherapy, radiotherapy, radioimmunotherapy, and sequential dual-targeting internal radiotherapy.

Discovery of Radioiodinated Monomeric Anthraquinones as a Novel Class of Necrosis Avid Agents for Early Imaging of Necrotic Myocardium

Assessment of myocardial viability is deemed necessary to aid in clinical decision making whether to recommend revascularization therapy for patients with myocardial infarction (MI). Dianthraquinones such as hypericin (Hyp) selectively accumulate in necrotic myocardium, but were unsuitable for early imaging after administration to assess myocardial viability. Since dianthraquinones can be composed by coupling two molecules of monomeric anthraquinone and the active center can be found by splitting chemical structure, we propose that monomeric anthraquinones may be effective functional groups for necrosis targetability. In this study, eight radioiodinated monomeric anthraquinones were evaluated as novel necrosis avid agents (NAAs) for imaging of necrotic myocardium. All (131)I-anthraquinones showed high affinity to necrotic tissues and (131)I-rhein emerged as the most promising compound. Infarcts were visualized on SPECT/CT images at 6 h after injection of (131)I-rhein, which was earlier than that with (131)I-Hyp. Moreover, (131)I-rhein showed satisfactory heart-to-blood, heart-to-liver and heart-to-lung ratios for obtaining images of good diagnostic quality. (131)I-rhein was a more promising "hot spot imaging" tracer for earlier visualization of necrotic myocardium than (131)I-Hyp, which supported further development of radiopharmaceuticals based on rhein for SPECT/CT ((123)I and (99m)Tc) or PET/CT imaging ((18)F and (124)I) of myocardial necrosis.

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

Myocardial infarction (MI) leads to substantial morbidity and mortality around the world. Accurate assessment of myocardial viability is essential to assist therapies and improve patient outcomes. (131)I-hypericin dicarboxylic acid ((131)I-HDA) was synthesized and evaluated as a potential diagnostic agent for earlier assessment of myocardium viability compared to its preceding counterpart (131)I-hypericin ((131)I-Hyp) with strong hydrophobic property, long plasma half-life, and high uptake in mononuclear phagocyte system (MPS). Herein, HDA was synthesized and characterized, and self-aggregation constant Kα was analyzed by spectrophotometry. Plasma half-life was determined in healthy rats by γ-counting. (131)I-HDA and (131)I-Hyp were prepared with iodogen as oxidant. In vitro necrosis avidity of (131)I-HDA and (131)I-Hyp was evaluated in necrotic cells induced by hyperthermia. Biodistribution was determined in rat models of induced necrosis using γ-counting, autoradiography, and histopathology. Earlier imaging of necrotic myocardium to assess myocardial viability was performed in rat models of reperfused myocardium infarction using single photon emission computed tomography/computed tomography (SPECT/CT). As a result, the self-aggregation constant Kα of HDA was lower than that of Hyp (105602 vs 194644, p < 0.01). (131)I-HDA displayed a shorter blood half-life compared with (131)I-Hyp (9.21 vs 31.20 h, p < 0.01). The necrotic-viable ratio in cells was higher with (131)I-HDA relative to that with (131)I-Hyp (5.48 vs 4.63, p < 0.05). (131)I-HDA showed a higher necrotic-viable myocardium ratio (7.32 vs 3.20, p < 0.01), necrotic myocardium-blood ratio (3.34 vs 1.74, p < 0.05), and necrotic myocardium-lung ratio (3.09 vs 0.61, p < 0.01) compared with (131)I-Hyp. (131)I-HDA achieved imaging of necrotic myocardium at 6 h postinjection (p.i.) with SPECT/CT, earlier than what (131)I-Hyp did. Therefore, (131)I-HDA may serve as a promising necrosis-avid diagnostic agent for earlier imaging of necrotic myocardium compared with (131)I-Hyp. This may support further development of radiopharmaceuticals ((123)I and (99m)Tc) based on HDA for SPECT/CT of necrotic myocardium.

Mammalian models of chemically induced primary malignancies exploitable for imaging-based preclinical theragnostic research

Compared with transplanted tumor models or genetically engineered cancer models, chemically induced primary malignancies in experimental animals can mimic the clinical cancer progress from the early stage on. Cancer caused by chemical carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical carcinogens can be classified upon their origins such as environmental pollutants, cooked meat derived carcinogens, N-nitroso compounds, food additives, antineoplastic agents, naturally occurring substances and synthetic carcinogens, etc. Carcinogen-induced models of primary cancers can be used to evaluate the diagnostic/therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in tumor initiation, promotion and progression. Among commonly adopted cancer models, chemically induced primary malignancies in mammals have several advantages including the easy procedures, fruitful tumor generation and high analogy to clinical human primary cancers. However, in addition to the time-consuming process, the major drawback of chemical carcinogenesis for translational research is the difficulty in noninvasive tumor burden assessment in small animals. Like human cancers, tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse contrast agents, now a workable solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary cancers. Moreover, it is foreseeable that the combined use of chemically induced primary cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and therapeutics.

Exploring diagnostic potentials of radioiodinated sennidin A in rat model of reperfused myocardial infarction

Non-invasive "hot spot imaging" and localization of necrotic tissue may be helpful for definitive diagnosis of myocardial viability, which is essential for clinical management of ischemic heart disease. We labeled Sennidin A (SA), a naturally occurring median dianthrone compound, with (131)I and evaluated (131)I SA as a potential necrosis-avid diagnostic tracer agent in rat model of reperfused myocardial infarction. Magnetic resonance imaging (MRI) was performed to determine the location and dimension of infarction. (131)I-SA was evaluated in rat model of 24-hour old reperfused myocardial infarction using single-photon emission computed tomography/computed tomography (SPECT/CT), biodistribution, triphenyltetrazolium chloride (TTC) histochemical staining, serial sectional autoradiography and microscopy. Gamma counting revealed high uptake and prolonged retention of (131)I SA in necrotic myocardium and fast clearance from non-targeted tissues. On SPECT/CT images, myocardial infarction was persistently visualized as well-defined hotspots over 24h, which was confirmed by perfect matches of images from post-mortem TTC staining and autoradiography. Radioactivity concentration in infarcted myocardium was over 9 times higher than that of the normal myocardium at 24h. With favorable hydrophilicity and stability, radioiodinated SA may serve as a necrosis-avid diagnostic agent for assessment of myocardial viability.

Evaluation of a metalloporphyrin (THPPMnCl) for necrosis-affinity in rat models of necrosis

The combination of an (13I)I-labeled necrosis-targeting agent (NTA) with a vascular disrupting agent is a novel and potentially powerful technique for tumor necrosis treatment (TNT). The purpose of this study was to evaluate a NTA candidate, THPPMnCl, using (131)I isotope for tracing its biodistribution and necrosis affinity. (131)I-THPPMnCl was intravenously injected in rat models with liver, muscle, and tumor necrosis and myocardial infarction (MI), followed by investigations with macroscopic autoradiography, triphenyltetrazolium chloride (TTC) histochemical staining, fluorescence microscopy and H&E stained histology for up to 9 days. (131)I-THPPMnCl displayed a long-term affinity for all types of necrosis and accumulation in the mononuclear phagocytic system especially in the liver. Autoradiograms and TTC staining showed a good targetability of (131)I-THPPMnCl for MI. These findings indicate the potential of THPPMnCl for non-invasive imaging assessment of necrosis, such as in MI. However, (13I)I-THPPMnCl is unlikely suitable for TNT due to its long-term retention in normal tissues.

Radiopharmaceutical evaluation of (131)I-protohypericin as a necrosis avid compound

Hypericin is a necrosis avid agent useful for nuclear imaging and tumor therapy. Protohypericin, with a similar structure to hypericin except poorer planarity, is the precursor of hypericin. In this study, we aimed to investigate the impact of this structural difference on self-assembly, and evaluate the necrosis affinity and metabolism in the rat model of reperfused hepatic infarction. Protohypericin appeared less aggregative in solution compared with hypericin by fluorescence analysis. Biodistribution data of (131)I-protohypericin showed the percentage of injected dose per gram of tissues (%ID/g) increased with time and reached to the maximum of 7.03 at 24 h in necrotic liver by gamma counting. The maximum ratio of target/non-target tissues was 11.7-fold in necrotic liver at 72 h. Pharmacokinetic parameters revealed that the half-life of (131)I-protohypericin was 14.9 h, enabling a long blood circulation and constant retention in necrotic regions. SPECT-CT, autoradiography, and histological staining showed high uptake of (131)I-protohypericin in necrotic tissues. These results suggest that (131)I-protohypericin is a promising necrosis avid compound with a weaker aggregation tendency compared with hypericin and it may have a broad application in imaging and oncotherapy.

Necrosis targeted combinational theragnostic approach using radioiodinated Sennidin A in rodent tumor models

Residual cancer cells and subsequent tumor relapse is an obstacle for curative cancer treatment. Tumor necrosis therapy (TNT) has recently been developed to cause residual tumor regression or destruction. Here, we exploited the avidity of the sennidin A (SA) tracer and radioiodinated SA (¹³¹I-SA) to necrotic tumors in order to further empower TNT. We showed high uptake and prolonged retention of SA in necrotic tumors and a quick clearance in other non-targeted tissues including the liver. On SPECT-CT images, tumor mass appeared persistently as a hotspot. Based on the prominent targetability of ¹³¹I-SA to the tumor necrosis, we designed a combinational theragnostic modality. The vascular disrupting agent (VDA) combretastatin A4 phosphate (CA4P) was used to cause massive tumor necrosis, which formed the target of ¹³¹I-SA that subsequently killed the residual tumor cells by cross-fire irradiation of beta particles. Consequently, ¹³¹I-SA combined with CA4P significantly inhibited tumor growth, extended tumor doubling time and prolonged mean animal survival. In conclusion, ¹³¹I-SA in combination with necrosis inducing drugs/therapies may generate synergetic tumoricidal effects on solid malignancies by means of primary debulking and secondary cleansing process.

Biodistribution and anti-tumor efficacy of intratumorally injected necrosis-avid theranostic agent radioiodinated hypericin in rodent tumor models

Hypericin has an excellent necrosis-specific targeting capacity; thus, we explored small-molecular tumor necrosis therapy (SMTNT) for inhibiting tumor growth in rodent tumor models. H22 and S180 tumor-bearing Kunming (KM) mice were intratumorally injected with (131)I-monoiodohypericin ((131)I-MIH) to investigate the biodistribution of (131)I-MIH as a function of time. Single-photon emission computed tomography (SPECT), autoradiography, fluorescence microscopy and hematoxylin and eosin (H&E) staining were performed to determine the intra-tumoral distribution of (131)I-MIH. A therapeutic evaluation study was also performed in the tumor-bearing KM mice using saline and a positive drug as controls. Gamma counting, SPECT images, autoradiography and fluorescence microscopy and H&E staining results revealed intense retention of (131)I-MIH in the necrotic tumor over 168 h and good in vivo stability of the agent. Therapy with a single dose of intra-tumoral administration of (131)I-MIH caused significant tumor growth delay. A histopathological analysis of the tumors and normal organs further validated the therapeutic efficacy and limited systemic toxicity of (131)I-MIH. The prolonged tumor retention and effective therapy indicated that (131)I-MIH may be a promising intratumorally injected SMTNT agent.

Evaluation of hypericin: effect of aggregation on targeting biodistribution

Hypericin (Hy) has shown great promise as a necrosis-avid agent in cancer imaging and therapy. Given the highly hydrophobic and π-conjugated planarity characteristics, Hy tends to form aggregates. To investigate the effect of aggregation on targeting biodistribution, nonaggregated formulation (Non-Ag), aggregated formulation with overconcentrated Hy in dimethyl sulfoxide (Ag-DMSO) solution, and aggregated formulation in water solution (Ag-water) were selected by fluorescence measurement. They were labeled with ¹³¹I and evaluated for the necrosis affinity in rat model of reperfused hepatic infarction by gamma counting and autoradiography. The radioactivity ratio of necrotic liver/normal liver was 17.1, 7.9, and 6.4 for Non-Ag, Ag-DMSO, and Ag-water, respectively. The accumulation of two aggregated formulations (Ag-DMSO and Ag-water) in organs of mononuclear phagocyte system (MPS) was 2.62 ± 0.22 and 3.96 ± 0.30 %ID/g in the lung, and 1.44 ± 0.29 and 1.51 ± 0.23 %ID/g in the spleen, respectively. The biodistribution detected by autoradiography showed the same trend as by gamma counting. In conclusion, the Non-Ag showed better targeting biodistribution and less accumulation in MPS organs than aggregated formulations of Hy. The two aggregated formulations showed significantly lower and higher accumulation in targeting organ and MPS organs, respectively.

Experimental evaluation of radioiodinated sennoside B as a necrosis-avid tracer agent

Necrosis-avid agents are a class of compounds that selectively accumulate in the necrotic tissues after systemic administration, which can be used for in vivo necrosis imaging and targeted therapies. In order to search for a necrosis-avid tracer agent with improved drugability, we labelled iodine-131 on sennoside B (SB) as a naturally occurring median dianthrone compound. The necrosis targetability and clearance properties of (131)I-SB were evaluated in model rats with liver and muscle necrosis. On SPECT/CT images, a "hot spot" in the infarcted liver lobe and necrotic muscle was persistently observed at 24 h and 72 h post-injection (p.i.). Gamma counting of the tissues of interest revealed a radioactivity ratio of necrotic to viable liver at 4.6 and 3.4 and of necrotic to viable muscle at 7.0 and 8.8 at 24 h and 72 h p.i., respectively. The good match of autoradiographs and fluoromicroscopic images with corresponding histochemical staining suggested preferential uptake of (131)I-SB in necrotic tissue. Pharmacokinetic study revealed that (131)I-SB has an elimination half-life of 8.6 h. This study indicates that (131)I-SB shows not only prominent necrosis avidity but also favourable pharmacokinetics, which may serve as a potential necrosis-avid diagnostic agent for assessment of tissue viability.

An authentic imaging probe to track cell fate from beginning to end

Accurate tracing of cell viability is critical for optimizing delivery methods and evaluating the efficacy and safety of cell therapeutics. A nanoparticle-based cell tracker is developed to image cell fate from live to dead. The particle is fabricated from two types of optically quenched polyelectrolytes, a life indicator and a death indicator, through electrostatic interactions. On incubation with cells, the fabricated bifunctional nanoprobes are taken up efficiently and the first colour is produced by normal intracellular proteolysis, reflecting the healthy status of the cells. Depending on the number of coated layers, the signal can persist for several replication cycles. However, as the cells begin dying, the second colour appears quickly to reflect the new cell status. Using this chameleon-like cell tracker, live cells can be distinguished from apoptotic and necrotic cells instantly and definitively.

An overview on development and application of an experimental platform for quantitative cardiac imaging research in rabbit models of myocardial infarction

To exploit the advantages of using rabbits for cardiac imaging research and to tackle the technical obstacles, efforts have been made under the framework of a doctoral research program. In this overview article, by cross-referencing the current literature, we summarize how we have developed a preclinical cardiac research platform based on modified models of reperfused myocardial infarction (MI) in rabbits; how the in vivo manifestations of cardiac imaging could be closely matched with those ex vivo macro- and microscopic findings; how these imaging outcomes could be quantitatively analyzed, validated and demonstrated; and how we could apply this cardiac imaging platform to provide possible solutions to certain lingering diagnostic and therapeutic problems in experimental cardiology. In particular, tissue components in acute cardiac ischemia have been stratified and characterized, post-infarct lipomatous metaplasia (LM) as a common but hardly illuminated clinical pathology has been identified in rabbit models, and a necrosis avid tracer as well as an anti-ischemic drug have been successfully assessed for their potential utilities in clinical cardiology. These outcomes may interest the researchers in the related fields and help strengthen translational research in cardiovascular diseases.

Radiopharmaceutical study on Iodine-131-labelled hypericin in a canine model of hepatic RFA-induced coagulative necrosis

PURPOSE

Hypericin (HYP) has been found avid to necrosis in small animal studies. We sought to evaluate the tissue distribution of (131)I-HYP in a large animal model and to explore the theranostic utilities of (131)I-HYP after radiofrequency ablation (RFA).

MATERIALS AND METHODS

This animal experiment was approved by the institutional ethics committee. Twenty-five male dogs were enrolled and subjected to transabdominal hepatic RFA. (131)I-HYP was prepared by an electrophilic substitution method and intravenously administered at 0.5 mCi/kg. Systemic and regional distributions of (131)I-HYP were monitored dynamically by single-photon emission computed tomography/computed tomography (SPECT-CT), gamma counting, autoradiography, and fluorescent and light microscopy at different time points up to 14 days. Experimental data were quantified and statistically analysed.

RESULTS

Most of the tissues and organs retained (131)I-HYP only transiently. (131)I-HYP was mainly metabolised in the liver and excreted into the bile. (131)I-HYP gradually accumulated in the RFA-induced necrosis with a peak concentration occurring within 2 days and lasting over 2 weeks as visualised by in vivo SPECT-CT and ex vivo autoradiography and fluorescent microscopy, and quantified by radioactivity and fluorescence measurements. Accumulation of (131)I-HYP was low in both the necrosis centre and normal liver tissue.

CONCLUSION

(131)I-HYP showed persistent high affinity to hepatic thermo-coagulative necrosis, but only a transient uptake by normal liver in dogs. Necrosis caused by RFA could be indicated by (131)I-HYP on nuclear imaging, which suggests a supplementary measure for tumour detection and therapy.

Comparative study of iodine-123-labeled hypericin and (99m)Tc-labeled hexakis [2-methoxy isobutyl isonitrile] in a rabbit model of myocardial infarction

Identification of myocardial infarction (MI) by imaging is critical for clinical management of ischemic heart disease. Iodine-123-labeled hypericin (¹²³I-Hyp) is a new potent infarct avid agent. We sought to compare target selectivity and organ distribution between ¹²³I-Hyp and the myocardial perfusion agent, technetium-99m-labeled hexakis [2-methoxy isobutyl isonitrile] ((99m)Tc-Sestamibi) in rabbits with acute MI. Hypericin was radiolabeled with I using iodogen as oxidant, and (99m)Tc-Sestamibi was prepared from a commercial kit and radioactive sodium pertechnetate. Rabbits (n = 6) with 24-hour-old MI received ¹²³I-Hyp intravenously and received (99m)Tc-Sestamibi 9 hours later. They were studied by dual-isotope simultaneous acquisition micro single photon emission computed tomography/computed tomography (DISA-μSPECT/CT), tissue gamma counting (TGC), autoradiography, and histology. After purification, ¹²³I-Hyp was obtained with radiochemical purity around 99%. DISA-μSPECT/CT images showed ¹²³I-Hyp retention in infarcted but not in normal myocardium. By TGC, accumulation values reached 1.175 ± 0.096 percentage of injected dose per gram (%ID/g) and 0.028 ± 0.007%ID/g in infarcted myocardium and normal myocardium with high tracer concentration in liver, intestines, and gallbladder. (99m)Tc-Sestamibi was prepared with radiochemical purity over 95%. DISA-μSPECT/CT showed no accumulation in MI and high initial radioactivity levels in normal myocardium that were rapidly cleared as confirmed by TGC (0.011 ± 0.003%ID/g). Liver and intestines were clearly visualized. By TGC, gallbladder and kidneys show moderate (99m)Tc-Sestamibi uptake. The selectivity of ¹²³I-Hyp for infarcted myocardium and (99m)Tc-Sestamibi for normal myocardium was confirmed. ¹²³I-Hyp distribution in rabbits is characterized by hepatobiliary excretion. (99m)Tc-Sestamibi undergoes hepatorenal elimination.

An overview of translational (radio)pharmaceutical research related to certain oncological and non-oncological applications

Translational medicine pursues the conversion of scientific discovery into human health improvement. It aims to establish strategies for diagnosis and treatment of diseases. Cancer treatment is difficult. Radio-pharmaceutical research has played an important role in multiple disciplines, particularly in translational oncology. Based on the natural phenomenon of necrosis avidity, OncoCiDia has emerged as a novel generic approach for treating solid malignancies. Under this systemic dual targeting strategy, a vascular disrupting agent first selectively causes massive tumor necrosis that is followed by iodine-131 labeled-hypericin (¹²³I-Hyp), a necrosis-avid compound that kills the residual cancer cells by crossfire effect of beta radiation. In this review, by emphasizing the potential clinical applicability of OncoCiDia, we summarize our research activities including optimization of radioiodinated hypericin Hyp preparations and recent studies on the biodistribution, dosimetry, pharmacokinetic and, chemical and radiochemical toxicities of the preparations. Myocardial infarction is a global health problem. Although cardiac scintigraphy using radioactive perfusion tracers is used in the assessment of myocardial viability, searching for diagnostic imaging agents with authentic necrosis avidity is pursued. Therefore, a comparative study on the biological profiles of the necrosis avid ¹²³I-Hyp and the commercially available ^99mTc-Sestamibi was conducted and the results are demonstrated. Cholelithiasis or gallstone disease may cause gallbladder inflammation, infection and other severe complications. While studying the mechanisms underlying the necrosis avidity of Hyp and derivatives, their naturally occurring fluorophore property was exploited for targeting cholesterol as a main component of gallstones. The usefulness of Hyp as an optical imaging agent for cholelithiasis was studied and the results are presented. Multiple uses of automatic contrast injectors may reduce costs and save resources. However, cross-contaminations with blood-borne pathogens of infectious diseases may occur. We developed a radioactive method for safety evaluation of a new replaceable patient-delivery system. By mimicking pathogens with a radiotracer, we assessed the feasibility of using the system repeatedly without septic risks. This overview is deemed to be interesting to those involved in the related fields for translational research.

Radioiodinated hypericin: its biodistribution, necrosis avidity and therapeutic efficacy are influenced by formulation

PURPOSE

To study whether formulation influences biodistribution, necrosis avidity and tumoricidal effects of the radioiodinated hypericin, a necrosis avid agent for a dual-targeting anticancer radiotherapy.

METHODS

Iodine-123- and 131-labeled hypericin ((123)I-Hyp and (131)I-Hyp) were prepared with Iodogen as oxidant, and formulated in dimethyl sulfoxide (DMSO)/PEG400 (polyethylene glycol 400)/water (25/60/15, v/v/v) or DMSO/saline (20:80, v/v). The formulations with excessive Hyp were optically characterized. Biodistribution, necrosis avidity and tumoricidal effects were studied in rats (n = 42) without and with reperfused liver infarction and implanted rhabdomyosarcomas (R1). To induce tumor necrosis, R1-rats were pre-treated with a vascular disrupting agent. Magnetic resonance imaging, tissue-gamma counting, autoradiography and histology were used.

RESULTS

The two formulations differed significantly in fluorescence and precipitation. (123)I-Hyp/Hyp in DMSO/PEG400/water exhibited high uptake in necrosis but lower concentration in the lung, spleen and liver (p < 0.01). Tumor volumes of 0.9 ± 0.3 cm(3) with high radioactivity (3.1 ± 0.3% ID/g) were detected 6 days post-treatment. By contrast, (131)I-Hyp/Hypin DMSO/saline showed low uptake in necrosis but high retention in the spleen and liver (p < 0.01). Tumor volumes reached 2.6 ± 0.7 cm(3) with low tracer accumulation (0.1 ± 0.04%ID/g).

CONCLUSIONS

The formulation of radioiodinated hypericin/hypericin appears crucial for its physical property, biodistribution, necrosis avidity and tumoricidal effects.

Necrosis affinity evaluation of 131I-hypericin in a rat model of induced necrosis

Cancers are often with spontaneous or therapeutic necrosis that could be utilized as a generic target for developing new treatments. The purpose of this study was to investigate the biodistribution and pharmacokinetics of radioiodinated hypericin (Hyp), a naturally occurring compound, after intravenous (i.v.) injection in a rat model of liver and muscle necrosis (n = 42), and evaluate its necrosis affinity. Hyp was labeled with (131)I with labeling efficiency >99%. After incubating in solution/rat plasma for 8 days, radiochemical purity of (131)I-Hyp remained 98.1 and 97.1%, respectively, indicating good in vitro stability. SPECT-CT images at 24 h after i.v. injection of (131)I-Hyp in rats with induced liver and muscle necrosis showed obvious tracer absorption in necrotic tissues. Biodistribution studies revealed that the percentage of the injected dose per gram of tissue (%ID/g) evolved from 1.9 %ID/g at 6 h, through a maximum 3.0 %ID/g at 12 h, to 1.0 %ID/g at 192 h in necrotic liver. Pharmacokinetics studies revealed that the terminal elimination half-life, total body clearance and area under the curve of (131)I-Hyp were 32.7 h, 9.2 L/h/kg and 1.6 MBq/L*h, respectively. These results demonstrated that (131)I-Hyp features a long blood circulation in animals and persistent retention in necrotic tissues. Therefore, (131)I-labeled Hyp could be a broad-spectrum anti-tumor agent with a cost much cheaper relative to the biological agents such as monoclonal antibodies.

Sequential systemic administrations of combretastatin A4 Phosphate and radioiodinated hypericin exert synergistic targeted theranostic effects with prolonged survival on SCID mice carrying bifocal tumor xenografts

Objectives: Based on the soil-to-seeds principle, we explored the small-molecular sequential dual-targeting theranostic strategy (SMSDTTS) for prolonged survival and imaging detectability in a xenograft tumor model.

Materials and Methods: Thirty severe combined immunodeficiency (SCID) mice bearing bilateral radiation-induced fibrosarcoma-1 (RIF-1) subcutaneously were divided into group A of SMSDTTS with sequential intravenous injections of combretastatin A4 phosphate (CA4P) and ¹³¹I-iodohypericin (¹³¹I-Hyp) at a 24 h interval; group B of single targeting control with CA4P and vehicle of ¹³¹I-Hyp; and group C of vehicle control (10 mice per group). Tumoricidal events were monitored by in vivo magnetic resonance imaging (MRI) and planar gamma scintiscan, and validated by ex vivo autoradiography and histopathology. Besides, 9 mice received sequential intravenous injections of CA4P and ¹³¹I-Hyp were subjected to biodistribution analysis at 24, 72 and 120 h.

Results: Gamma counting revealed fast clearance of ¹³¹I-Hyp from normal organs but intense accumulation in necrotic tumor over 120 h. After only one treatment, significantly prolonged survival (p<0.001) was found in group A compared to group B and C with median survival of 33, 22, and 21 days respectively. Tumor volume on day 15 was 2.0 ± 0.89, 5.66 ± 1.66, and 5.02 ± 1.0 cm³ with tumor doubling time 7.8 ± 2.8, 4.4 ± 0.67, and 4.5 ± 0.5 days respectively. SMSDTTS treated tumors were visualized as hot spots on gamma scintiscans, and necrosis over tumor ratio remained consistently high on MRI, autoradiography and histology.

Conclusion: The synergistic antitumor effects, multifocal targetability, simultaneous theranostic property, and good tolerance of the SMSDTTS were evident in this experiment, which warrants further development for preclinical and clinical applications.

Small Molecule Sequential Dual-Targeting Theragnostic Strategy (SMSDTTS): from Preclinical Experiments towards Possible Clinical Anticancer Applications

Hitting the evasive tumor cells proves challenging in targeted cancer therapies. A general and unconventional anticancer approach namely small molecule sequential dual-targeting theragnostic strategy (SMSDTTS) has recently been introduced with the aims to target and debulk the tumor mass, wipe out the residual tumor cells, and meanwhile enable cancer detectability. This dual targeting approach works in two steps for systemic delivery of two naturally derived drugs. First, an anti-tubulin vascular disrupting agent, e.g., combretastatin A4 phosphate (CA4P), is injected to selectively cut off tumor blood supply and to cause massive necrosis, which nevertheless always leaves peripheral tumor residues. Secondly, a necrosis-avid radiopharmaceutical, namely ¹³¹I-hypericin (¹³¹I-Hyp), is administered the next day, which accumulates in intratumoral necrosis and irradiates the residual cancer cells with beta particles. Theoretically, this complementary targeted approach may biologically and radioactively ablate solid tumors and reduce the risk of local recurrence, remote metastases, and thus cancer mortality. Meanwhile, the emitted gamma rays facilitate radio-scintigraphy to detect tumors and follow up the therapy, hence a simultaneous theragnostic approach. SMSDTTS has now shown promise from multicenter animal experiments and may demonstrate unique anticancer efficacy in upcoming preliminary clinical trials. In this short review article, information about the two involved agents, the rationale of SMSDTTS, its preclinical antitumor efficacy, multifocal targetability, simultaneous theragnostic property, and toxicities of the dose regimens are summarized. Meanwhile, possible drawbacks, practical challenges and future improvement with SMSDTTS are discussed, which hopefully may help to push forward this strategy from preclinical experiments towards possible clinical applications.

A safety study on single intravenous dose of tetrachloro-diphenyl glycoluril [iodogen] dissolved in dimethyl sulphoxide (DMSO)

1. Iodogen (tetrachloro-diphenyl glycoluril) dissolved in DMSO (dimethyl sulphoxide) appears indispensable in radioiodination of hypericin for a new anticancer strategy. We studied the safety of intravenously administered iodogen/DMSO in mice (n = 132). 2. Median lethal dose (LD50) of iodogen/DMSO was determined with doses of 40.0, 50.0, 55.0, 60.0, 65.0 and 70.0 mg/kg. Next, toxicity of iodogen/DMSO at 30.0 mg/kg was evaluated using saline and DMSO as controls. Changes in behaviour, body weight and serum biochemistry were evaluated. Histopathology of lungs, heart, liver and kidney was performed. 3. LD50 values of iodogen/DMSO were 59.5 mg/kg (95% confidence limits (CI): 54.1-65.4 mg/kg) and 61.0 mg/kg (95%CI: 56.2-66.2 mg/kg) for female and male mice, respectively. Similar to that of control groups, no animal deaths were encountered after iodogen/DMSO administration at 30.0 mg/kg. Body weights over 24 h were not altered in all groups, but significantly higher in iodogen/DMSO and DMSO groups (p < 0.05) 14 d post-injection. Blood urea nitrogen and alkaline phosphatase increased (p < 0.05) in iodogen/DMSO group without clinical symptoms. No pathologies were found by gross and microscopic inspection. 4. A single dose of iodogen/DMSO up to 30.0 mg/kg, over 3000 times the dose in potential human applications, appears safe, with an LD50 doubling that dose in mice.

A single-dose toxicity study on non-radioactive iodinated hypericin for a targeted anticancer therapy in mice

AIM

Hypericin (Hyp) and its radio-derivatives have been investigated in animal models with ischemic heart diseases and malignancies for diagnostic and therapeutic purposes. Before radioiodinated Hyp ((123)I-Hyp or (131)I-Hyp) can be considered as a clinically useful drug, vigorous evaluations on its chemotoxicity are necessary. In the present study, we examined the toxicity of a single dose of non-radioactive (127)I-Hyp in normal mice for 24 h and 14 d.

METHODS

Studies were performed on 132 normal mice. (127)I -Hyp at a clinically relevant dose of 0.1 mg/kg body weight and a 100-times higher dose of 10 mg/kg was intravenously injected into 40 mice. The safety aspects of clinical manifestations, serological biochemistry, and histopathology were assessed. In another 72 mice, (127)I-Hyp was administered intravenously at assumed values to bracket the value of LD(50). The rest 20 mice were used in the control groups.

RESULTS

At 24 h and 14 d following the injection of (127)I -Hyp at either 0.1 or 10 mg/kg, all mice tolerated well without mortality or any observable treatment-related symptoms. No significant differences were found in blood biochemical parameters between the test and control groups. All organs presented normal appearances upon histopathological inspection. The value of LD(50) of (127)I-Hyp in mice through intravenous injection was 20.26 mg/kg, with the 95% confidence interval between 18.90 and 21.55 mg/kg.

CONCLUSION

The current study reveals a broad safety range of (127)I-Hyp, which not only supports the use of (123)I-Hyp or (131)I-Hyp in the necrosis targeting theragnostic strategy, but also serves as a valuable reference for exploring other possible applications for iodinated Hyp.

Exploring theranostic potentials of radioiodinated hypericin in rodent necrosis models

Objectives: The present animal experiments were conducted to evaluate radioiodinated Hypericin (Hyp) for its regional distribution as well as theranostic potentials.

Materials and Methods: Rat models of reperfused liver infarction (RLI) and hepatic rhabdomyosarcoma (R1) were surgically induced. R1 models received Combretastatin A4 phosphate (CA4P) intravenously at 10 mg/kg 24 h prior to radioiodinated Hyp. Three groups of 6 rats each containing 3 RLI and 3 R1 models received iv injections of ¹²³I-Hyp at 37, 74, and 185 MBq/kg respectively and followed by 0.1 ml of 1% Evans blue solution were sacrificed at 4, 24 and 48 hour post injection immediately after in vivo examination of MRI and planar gamma scintigraphy. Besides, two groups of 6 R1 models that received either 300 MBq/kg of ¹³¹I-Hyp or vehicle intravenously were examined using MRI to compare tumor growth for 12 days. Autoradiography, gamma counting, and histopathology were performed for postmortem verifications and quantification.

Results: Necrosis as seen in vivo on contrast-enhanced MRI corresponded well with the hot spots on planar scintigraphy. Autoradiography and gamma counting revealed intense accumulation of ¹²³I-Hyp in necrotic liver (3.94 ± 1.60, 5.38 ± 1.04, and 6.03 ± 2.09 %ID/g ± SD) and necrotic tumor (4.27 ± 0.76, 5.57 ± 0.76, and 5.68 ± 1.33 %ID/g ± SD) relative to normal liver (1.76 ± 0.54, 0.41 ± 0.18, and 0.16 ± 0.07 %ID/g ± SD), with a high necrosis-to-liver ratio of 2.3, 14.0, and 37.0 at 4, 24 and 48 h respectively. Tumor volumes in R1 models that received ¹³¹I-Hyp and vehicle changed from 0.45 ± 0.09, and 0.47 ± 0.12 cm³ (p > 0.05) on day 0 to1.32 ± 0.76 and 3.63 ± 0.72 cm³ (p < 0.001) on day 12, with the corresponding necrosis ratios from 73 ± 12 %, and 76 ± 17 % to 47 ± 18% and 17 ± 13 % (p < 0.01), and with the tumor DT of 7.3 ± 1.0 and 4.2 ± 0.7 days, respectively.

Conclusions: Radioiodinated Hyp as a necrosis avid tracer appears promising for non-invasive imaging diagnosis of necrosis-related pathologies. Its prominent targetability to necrosis allows targeted radiotherapy for malignancies on top of a prior necrosis-inducing treatment.

Biomarkers and molecular probes for cell death imaging and targeted therapeutics

Cell death is a critically important biological process. Disruption of homeostasis, either by excessive or deficient cell death, is a hallmark of many pathological conditions. Recent research advances have greatly increased our molecular understanding of cell death and its role in a range of diseases and therapeutic treatments. Central to these ongoing research and clinical efforts is the need for imaging technologies that can locate and identify cell death in a wide array of in vitro and in vivo biomedical samples with varied spatiotemporal requirements. This review article summarizes community efforts over the past five years to identify useful biomarkers for dead and dying cells, and to develop molecular probes that target these biomarkers for optical, radionuclear, or magnetic resonance imaging. Apoptosis biomarkers are classified as either intracellular (caspase enzymes, mitochondrial membrane potential, cytosolic proteins) or extracellular (plasma membrane phospholipids, membrane potential, surface exposed histones). Necrosis, autophagy, and senescence biomarkers are described, as well as unexplored cell death biomarkers. The article discusses possible chemotherapeutic and theranostic strategies, and concludes with a summary of current challenges and expected eventual rewards of clinical cell death imaging.

A review on various targeted anticancer therapies

Translational oncology aims to translate laboratory research into new anticancer therapies. Contrary to conventional surgery, chemotherapy, and radiotherapy, targeted anticancer therapy (TAT) refers to systemic administration of drugs with particular mechanisms that specifically act on well-defined targets or biologic pathways that, when activated or inactivated, may cause regression or destruction of the malignant process, meanwhile with minimized adverse effects on healthy tissues. In this article, we intend to first give a brief review on various known TAT approaches that are deemed promising for clinical applications in the current trend of personalized medicine, and then we will introduce our newly developed approach namely small molecular sequential dual targeting theragnostic strategy as a generalized class of TAT for the management of most solid malignancies, which, after optimization, is expected to help improve overall cancer treatability and curability.

Radiolabeled iodohypericin as tumor necrosis avid tracer: diagnostic and therapeutic potential

It is estimated that 30-80% of solid tumor mass represents necrotic tissue that consists out of a significant number of dead and dying cells. The fact that these necrotic zones are restricted to dysplastic and malignant tissue and are rarely present in normal tissue makes necrosis an interesting target both for cancer diagnosis and therapy. In this study, the avidity of hypericin, [(123) I]iodohypericin and [(131) I]iodohypericin to tumor necrosis was explored for both diagnosis and therapy of experimental malignancies. The intratumoral distribution in RIF-1 tumors was investigated by means of fluorescence microscopy (hypericin) and autoradiography ([(123) I]iodohypericin). Results show high uptake of the tracers in necrosis at 24 hr, lasting for up to 72 hr p.i. Ratios of activity of [(123) I]iodohypericin in necrotic tissue over viable tumor reached up to 19.63 ± 4.66, correlating with 9.20% ID/g in necrosis. Nude mice bearing RIF-1 tumors that received three injections of 300 μCi over a 3-week treatment period showed stabilization in tumor growth for 5 days, as measured by caliper and micro-positron emission tomography using [(18) F]fluorodeoxyglucose. Based on these results, we suggest the potentials of radiolabeled hypericin (1) in diagnostic aspects including prognosis or staging assessment of bulky necrotic cancers, monitoring of treatments and therapeutic follow-up; and (2) in cancer treatment based on tumor necrosis. In conclusion, we showed that hypericin radiolabeled with iodine is a necrosis avid tracer that can be used both as a tumor diagnostic and therapeutic.

Pretargeting of necrotic tumors with biotinylated hypericin using 123I-labeled avidin: evaluation of a two-step strategy

As an alternative to directly targeting of necrotic tissue using hypericin, we synthesized a conjugate of hypericin to biotin for use in a pretargeting approach. With this conjugate, we explored the possibility of a two-step pretargeting strategy using (123)I-labeled avidin as effector molecule directed against necrotic RIF-1 tumors. Hypericin was conjugated to biotin-ethylenediamine in a straightforward coupling method using n-hydroxysuccinimide and dicyclohexylcarbodiimide. The necrosis avidity of the conjugate was first confirmed in necrotic liver tissue by means of fluorescence microscopy. Using autoradiography imaging and whole body-biodistribution, the accumulation of (123)I-avidin in necrotic tumor tissue was evaluated 24 h after administration and 48 h after pretargeting with hypericin-biotin. Analysis of autoradiography images show a higher accumulation of (123)I-avidin in pretargeted compared to nontargeted tissue. However, absolute accumulation of (123)I-avidin in necrotic tumors was low as shown by biodistribution experiments. Direct injection of hypericin-biotin or biotin-fluorescein did not substantially improve (123)I-avidin accumulation after pretargeting, pointing towards a poor penetration of avidin in necrotic tissue. Our results show the feasibility of a pretargeting technique using a small molecule as targeting agent. However, for a more efficient accumulation of the effector molecule in necrotic tissue, other pretargeting strategies need to be investigated.