Synthesis and Evaluation of 131I-Skyrin as a Necrosis Avid Agent for Potential Targeted Radionuclide Therapy of Solid Tumors

Target identification and occupancy measurement of necrosis avid agent rhein using bioorthogonal chemistry-enabling probes

Necrosis is an important biomarker, which only occurs in pathological situations. Tracking of necrosis avid agents is of crucial importance toward understanding their mechanisms. Herein, we developed a modular probe strategy based on bioorthogonal copper-free click chemistry. Structural modification of rhein with transcyclooctene (TCO) led to the identification of rhein-TCO2 as the most active probe with specific necrosis affinity. In a systematic evaluation, the colocalization of rhein-TCO2 in the nucleus (exposed DNA and rRNA) of necrotic cells was observed. This work provides a foundation for the development of target-identified of rhein compounds, and binding to exposed DNA and rRNA may be an important target of rhein compounds in necrotic cells.

Structural modification of rhein with transcyclooctene (TCO) led to the identification of rhein-TCO2 as the most active probe with specific necrosis affinity.

Comparison of Cytotoxic, Genotoxic, and DNA-Protective Effects of Skyrin on Cancerous vs. Non-Cancerous Human Cells

Secondary metabolites as a potential source of anticancer therapeutics have been the subject of many studies. Since hypericin, a metabolite isolated from Hypericum perforatum L., shows several biomedical properties applicable in oncology, the aim of our study was to investigate its potential precursor skyrin in terms of genotoxic and DNA-protective effects. These skyrin effects were analyzed by cell-free methods, and cytotoxicity was estimated by an MTT assay and by a trypan blue exclusion test, while the genotoxic/antigenotoxic potential was examined by comet assay using non-cancerous human lymphocytes and the HepG2 cancer cell line. Skyrin did not show DNA-damaging effects but rather exhibited DNA-protectivity using a DNA-topology assay. However, we observed only weak antioxidant and chelating skyrin properties in other cell-free methods. Regarding the cytotoxic activity of skyrin, HepG2 cells were more prone to skyrin-induced death in comparison to human lymphocytes. Skyrin in non-cytotoxic concentrations did not exhibit elevated genotoxicity in both cell types. On the other hand, skyrin displayed moderate DNA-protective effects that were more noticeable in the case of non-cancerous human lymphocytes. The potential genotoxic effects of skyrin were not observed, and its DNA-protective capacity was more prominent in non-cancerous cells. Therefore, skyrin might be a promising agent used in anticancer therapy.

Death Receptor 5 (TNFRSF10B) Is Upregulated and TRAIL Resistance Is Reversed in Hypoxia and Normoxia in Colorectal Cancer Cell Lines after Treatment with Skyrin, the Active Metabolite of Hypericum spp

Skyrin (SKR) is a plant bisanthraquinone secondary metabolite from the Hypericum genus with potential use in anticancer therapy. However, its effect and mechanism of action are still unknown. The negative effect of SKR on HCT 116 and HT-29 cancer cell lines in hypoxic and normoxic conditions was observed. HCT 116 cells were more responsive to SKR treatment as demonstrated by decreased metabolic activity, cellularity and accumulation of cells in the G1 phase. Moreover, an increasing number of apoptotic cells was observed after treatment with SKR. Based on the LC-MS comparative proteomic data from hypoxia and normoxia (data are available via ProteomeXchange with the identifier PXD019995), SKR significantly upregulated Death receptor 5 (DR5), which was confirmed by real-time qualitative PCR (RT-qPCR). Furthermore, multiple changes in the Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-activated cascade were observed. Moreover, the reversion of TRAIL resistance was observed in HCT 116, HT-29 and SW620 cell lines, even in hypoxia, which was linked to the upregulation of DR5. In conclusion, our results propose the use of SKR as a prospective anticancer drug, particularly as an adjuvant to TRAIL-targeting treatment to reverse TRAIL resistance in hypoxia.

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.

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.

Target exploration of rhein as a small-molecule necrosis avid agent by post-treatment click modification

Post-labeling of compound 3 indicated that binding to exposed DNA may be an important mechanism of targeting of rhein compounds to necrotic cells.

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.

Linking secondary metabolites to biosynthesis genes in the fungal endophyte Cyanodermella asteris: The anti-cancer bisanthraquinone skyrin

Fungal aromatic polyketides display a very diverse and widespread group of natural products. Due to their excellent light absorption properties and widely studied biological activities, they offer numerous application for food, textile and pharmaceutical industry. The biosynthetic pathways of fungal aromatic polyketides usually involve a set of successive enzymes, in which a non-reductive polyketide synthase iteratively catalyzes the essential assembly of simple building blocks into (often polycyclic) aromatic compounds. However, only a limited number of such pathways have been described so far and further elucidation of the individual biosynthetic steps is needed to fully exploit the biotechnological and medicinal potential of these compounds. Here, we identified the bisanthraquinone skyrin as the main pigment of the fungus Cyanodermella asteris, an endophyte that has recently been isolated from the traditional Chinese medicinal plant Aster tataricus. The genome of C. asteris was sequenced, assembled and annotated, which enables first insights into a genome from a non-lichenized member of the class Lecanoromycetes. Genetic and in silico analyses led to the identification of a gene cluster of five genes suggested to encode the enzymatic pathway for skyrin. Our study is a starting point for rational pathway engineering in order to drive the production towards higher yields or more active derivatives. Moreover, our investigations revealed a large potential of secondary metabolite production in C. asteris as well as in all Lecanoromycetes of which genomes were available. These findings convincingly emphasize that Lecanoromycetes are prolific producers of secondary metabolites.

Radioiodinated hypericin disulfonic acid sodium salts as a DNA-binding probe for early imaging of necrotic myocardium

Necrotic myocardium imaging can provide great indicators of salvaged myocardial areas for clinical guidances to patients with myocardial infarction (MI). One of the key challenges in necrotic myocardium imaging however, is lack of ideal necrotic imaging tracers for exactly and timely depicting the necrotic myocardium. ¹³¹I-hypericin (¹³¹I-Hyp) is a promising tracer in exact necrotic myocardium delineation. However, it can't clearly image necrotic myocardium until 9h post injection (p.i.) for the high background signals in blood and lung due to the strong lipophilicity. Herein, an optimized ¹³¹I-hypericin-2,5-disulfonic acid sodium salts (¹³¹I-Shyp) probe was synthesized for better pharmacokinetic and biodistribution properties to necrosis imaging. And the related mechanisms of necrotic avidity ability of ¹³¹I-Hyp and ¹³¹I-Shyp were also explored. In the results, ¹³¹I-Shyp still showed selectively high accumulation in both necrotic cells and tissues. Biodistribution data revealed the decreased uptake of ¹³¹I-Shyp in normal organs (lung, spleen and heart) and blood (as shown in pharmacokinetics studies). ¹³¹I-Shyp presented quicker and clearer imaging for necrotic myocardium at 4h p.i. compared with ¹³¹I-Hyp, suggesting that improved hydrophilicity of ¹³¹I-Shyp may be conducive to its better pharmacokinetic and biodistribution properties to imaging. Additionally, DNA competitive binding assays and blocking experiments indicated that E-DNA is the possible target of Shyp and Hyp for their necrosis avidity. ¹³¹I-Shyp may serve as a potential E-DNA targeted probe for necrotic myocardium imaging with molecular specificity for clinical use.