Fluorous Tagged Peptides for Intracellular Delivery and Biomedical Imaging

Fluorous tagged peptides have shown promising features for biomedical applications such as drug delivery and multimodal imaging. The bioconjugation of fluoroalkyl ligands onto cargo peptides greatly enhances their proteolytic stability and membrane penetration via a proposed “fluorine effect”. The tagged peptides also efficiently deliver other biomolecules such as DNA and siRNA into cells via a co-assembly strategy. The fluoroalkyl chains on peptides with antifouling properties enable efficient gene delivery in the presence of serum proteins. Besides intracellular biomolecule delivery, the amphiphilic peptides can be used to stabilized perfluorocarbon-filled microbubbles for ultrasound imaging. The fluorine nucleus on fluoroalkyls provides intrinsic probes for background-free magnetic resonance imaging. Labeling of fluorous tags with radionuclide ¹⁸F also allows tracing the biodistribution of peptides via positron emission tomography imaging. This mini-review will discuss properties and mechanism of the fluorous tagged peptides in these applications.     

On a class of Riemann surfaces

It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary.     

扩展基于AD9874数字接收机谱宽的二次抽取算法

针对基于AD9874芯片的数字接收机的最小谱宽和谱宽允许设置的数目均不能满足常规临床用磁共振成像技术的要求,本文从软件角度提出了一种扩展数字接收机谱宽的二次抽取算法. 该算法具体实现过程主要包括两个步骤：(1) 自适应过采样倍率和自动谱宽调整;(2) 数字滤波和抽取. 为了验证这个二次抽取算法的有效性,本文分别用单脉冲实验和磁共振成像实验加以了验证.     

一种应用于活细胞中检测Hg(Ⅱ)的苯并噻唑类荧光探针

合成和表征了一种苯并噻唑类的荧光探针(YH1),并用光谱法研究了它对不同金属离子的响应。结果表明:YH1对Hg2+显示出好的选择性和灵敏度,与Hg2+作用后,在紫外光的激发下它的溶液颜色由蓝色变为无色。在1.4~8.8μmol·L-1浓度的范围内,YH1的荧光强度与Hg2+浓度有线性关系,其对Hg2+的检出限为0.56μmol·L-1。此外,YH1可跨过细胞膜,细胞毒性低,还可应用于He La活细胞中对Hg2+进行荧光成像。     

Cysteine‐Mediated Intracellular Building of Luciferin to Enhance Probe Retention and Fluorescence Turn‐On

The development of sensitive and selective small molecular probes that enable real‐time detection of endogenous cysteine (Cys) has become an attractive topic because of the essential roles played by Cys in controlling the cellular nitrogen balance and in maintaining biological redox homeostasis. Herein, we report a Cys‐specific probe, 2‐cyanobenzothiazol‐6‐yl acrylate (CBTOA), that shows not only fluorescence turn‐on for sensitive detection of endogenous Cys but also enhanced probe retention inside cells for real‐time monitoring of Cys levels upon external stimulation. Cys‐mediated intracellular formation of luciferin from CBTOA was the key strategy leading to this new type of fluorogenic probe. CBTOA showed fast response to Cys in living cells and liver tissue slices with high sensitivity and selectivity. By using CBTOA as a real‐time probe, we were able to monitor the change in Cys levels in living HeLa cells under ROS‐induced oxidative stress as well as in human mesenchymal stem cells during adipogenic differentiation.     

Surface‐Functionalized Nanoparticles by Olefin Metathesis: A Chemoselective Approach for In Vivo Characterization of Atherosclerosis Plaque

The use of click chemistry reactions for the functionalization of nanoparticles is particularly useful to modify the surface in a well‐defined manner and to enhance the targeting properties, thus facilitating clinical translation. Here it is demonstrated that olefin metathesis can be used for the chemoselective functionalization of iron oxide nanoparticles with three different examples. This approach enables, in one step, the synthesis and functionalization of different water‐stable magnetite‐based particles from oleic acid‐coated counterparts. The surface of the nanoparticles was completely characterized showing how the metathesis approach introduces a large number of hydrophilic molecules on their coating layer. As an example of the possible applications of these new nanocomposites, a focus was taken on atherosclerosis plaques. It is also demonstrated how the in vitro properties of one of the probes, particularly its Ca²⁺‐binding properties, mediate their final in vivo use; that is, the selective accumulation in atherosclerotic plaques. This opens promising new applications to detect possible microcalcifications associated with plaque vulnerability. The accumulation of the new imaging tracers is demonstrated by in vivo magnetic resonance imaging of carotids and aorta in the ApoE^?/? mouse model and the results were confirmed by histology.     

Radiofluorination of a Pre‐formed Gallium(III) Aza‐macrocyclic Complex: Towards Next‐Generation Positron Emission Tomography (PET) Imaging Agents

As part of a study to investigate the factors influencing the development of new, more effective metal‐complex‐based positron emission tomography (PET) imaging agents, the distorted octahedral complex, [GaCl(L)]?2 H₂O has been prepared by reaction of 1‐benzyl‐1,4,7‐triazacyclononane‐4,7‐dicarboxylic acid hydrochloride (H₂L?HCl) with Ga(NO₃)₃?9 H₂O, which is a convenient source of Ga^III for reactions in water. Spectroscopic and crystallographic data for [GaCl(L)]?2 H₂O are described, together with the crystal structure of [GaCl(L)]?MeCN. Fluorination of this complex by Cl^?/F^? exchange was achieved in high yield by treatment with KF in water at room temperature over 90 minutes, although the reaction was complete in approximately 30 minutes if heated to 80 °C, giving [GaF(L)]?2 H₂O in good yield. The same complex was obtained by hydrothermal synthesis from GaF₃?3 H₂O and Li₂L, and has been characterised by single‐crystal X‐ray analysis, IR, ¹H and ¹⁹F{¹H} NMR spectroscopy and ESI⁺ MS. Radiofluorination of the pre‐formed [GaCl(L)]?2 H₂O has been demonstrated on a 210 nanomolar scale in aqueous NaOAc at pH 4 by using carrier‐free ¹⁸F^?, leading to 60–70 % ¹⁸F‐incorporation after heating to 80 °C for 30 minutes. The resulting radioproduct was purified easily by using a solid‐phase extraction (SPE) cartridge, leading to 98–99 % radiochemical purity. The [Ga¹⁸F(L)] is stable for at least 90 minutes in 10 % EtOH/NaOAc solution at pH 6, but defluorinates over this time scale at pH of approximately 7.5 in phosphate buffered saline (PBS) or human serum albumin (HSA). The subtle role of the Group 13 metal ion and co‐ligand donor set in influencing the pH dependence of this system is discussed in the context of developing potential new imaging agents for PET.     

Phosphorescent Ruthenium Complexes with a Nitroimidazole Unit that Image Oxygen Fluctuation in Tumor Tissue

Understanding oxygen fluctuation in a cancerous tumor is important for effective treatment, especially during radiotherapy. In this paper, ruthenium complexes bearing a nitroimidazole group are shown to report the oxygen status in tumor tissue directly. The nitroimidazole group was known to be accumulated in hypoxic tumor tissues. On the other hand, the ruthenium complex showed strong phosphorescence around 600 nm. The emission of ruthenium is quenched instantaneously by molecular oxygen due to energy transfer between triplet states of oxygen and ruthenium complex, but the emission is then recovered by the removal of oxygen. Thus, we could observe oxygen fluctuation in tumor tissue in a real‐time manner by monitoring the phosphorescence of the ruthenium complex. The versatility of the probe is demonstrated by monitoring oxygen fluctuation in living cells and tumor tissue planted in mice. The ruthenium complex promptly penetrated plasma membrane and accumulated in cells to emit its oxygen‐dependent phosphorescence. In vivo experiments revealed that the oxygen level in tumor tissue seems to fluctuate at the sub‐minute timescale.     

Dual‐Modal Magnetic Resonance/Fluorescent Zinc Probes for Pancreatic β‐Cell Mass Imaging

Despite the contribution of changes in pancreatic β‐cell mass to the development of all forms of diabetes mellitus, few robust approaches currently exist to monitor these changes prospectively in vivo. Although magnetic‐resonance imaging (MRI) provides a potentially useful technique, targeting MRI‐active probes to the β cell has proved challenging. Zinc ions are highly concentrated in the secretory granule, but they are relatively less abundant in the exocrine pancreas and in other tissues. We have therefore developed functional dual‐modal probes based on transition‐metal chelates capable of binding zinc. The first of these, Gd ?1 , binds Zn^II directly by means of an amidoquinoline moiety (AQA), thus causing a large ratiometric Stokes shift in the fluorescence from λ_em=410 to 500 nm with an increase in relaxivity from r₁=4.2 up to 4.9 mM ^?1 s^?1. The probe is efficiently accumulated into secretory granules in β‐cell‐derived lines and isolated islets, but more poorly by non‐endocrine cells, and leads to a reduction in T₁ in human islets. In vivo murine studies of Gd ?1 have shown accumulation of the probe in the pancreas with increased signal intensity over 140 minutes.     

Cyclometalated Iridium(III) Complexes as Two‐Photon Phosphorescent Probes for Specific Mitochondrial Dynamics Tracking in Living Cells

Five cyclometalated iridium(III) complexes with 2‐phenylimidazo[4,5‐f][1,10]phenanthroline derivatives ( IrL1 – IrL5 ) were synthesized and developed to image and track mitochondria in living cells under two‐photon (750 nm) excitation, with two‐photon absorption cross‐sections of 48.8–65.5 GM at 750 nm. Confocal microscopy and inductive coupled plasma‐mass spectrometry (ICP‐MS) demonstrated that these complexes selectively accumulate in mitochondria within 5 min, without needing additional reagents for membrane permeabilization, or replacement of the culture medium. In addition, photobleaching experiments and luminescence measurements confirmed the photostability of these complexes under continuous laser irradiation and physiological pH resistance. Moreover, results using 3D multicellular spheroids demonstrate the proficiency of these two‐photon luminescent complexes in deep penetration imaging. Two‐photon excitation using such novel complexes of iridium(III) for exclusive visualization of mitochondria in living cells may substantially enhance practical applications of bioimaging and tracking.