受体结合实验及其在放射性显像剂研究中的应用进展

受体结合实验是一种重要的药物筛选方法,它通过体外实验来考察配体与受体的结合能力。目前,很多放射性显像剂是利用放射性配体与体内受体结合的高度选择性来进行受体显像的。因此,受体结合实验是放射性显像剂研究中广泛使用的一种体外评价方法,在放射性显像剂设计与筛选中发挥了重要作用。     

正电子放射性显像剂代谢及其研究方法进展

正电子放射性显像剂主要用于PET的研究,能在分子水平上反映细胞代谢、细胞受体活性、细胞核内的核酸合成以及细胞基因的改变,在临床疾病诊断和治疗中有重要的地位和作用.PET显像剂进入生物体内后会发生代谢转化,了解PET显像剂的代谢途径和转化过程,对于准确分析和解释显像结果及设计开发新型PET显像剂非常重要.该文总结了目前PET显像剂代谢研究的现状,并对PET显像剂代谢研究方法以及分析技术等进行了综述.     

肿瘤受体显像

肿瘤受体显像研究包括放射性标记配体的制备、配体与受体的体外分析及体内受体显像,肿瘤受体配体可用18F、123I(或131I)、111In与99Tcm标记,通过放射性受体结合分析、放射性自显影与受体特性分析,对其体外性能进行研究。神经多肽受体显像、类固醇受体显像与σ受体显像等已应用于多种肿瘤的诊断、分期、治疗方案选择与预后评价,其中神经多肽受体显像得到了较广泛的研究与应用。     

肿瘤受体显像

肿瘤受体显像包括放射放射性标记配体的制备、配体与受体的体外分析及体内受体显像,肿瘤受体配体可用＾１８Ｆ、＾１２３Ｉ、＾１１１Ｉｎ与＾９９Ｔｃ＾ｍ标记,放射性受体结分析,放射性自显影与受体特性分析,对其体外性能进行研究。     

梭曼中毒影响γ-氨基丁酸系统吗?

用体外放射性配体结合实验方法检测了梭曼对牛小脑γ-氨基丁酸(GABA)受体和GABA摄取的影响.10~(-3)～10~(-6)M未影响GABA受体结合;对GABA摄取有轻微抑制IC_(50)为1.4×10~(-3)M.这一结果未能支持加拿大学者Lundy关于梭曼中毒有可能影响GABA受体结合的假设.对梭曼中毒与GABA系统的关系进行了讨论.     

肿瘤生长抑素受体显像剂~(99)Tc~m-octreotide的制备及鉴定

目的　建立99Tcm 直接标记octreotide的最佳方法 ,评价其受体介导结合特性以及作为肿瘤生长抑素受体显像剂的可能性。方法　采用抗坏血酸钠和连二亚硫酸钠作为还原剂 ,对oct reotide进行标记 ;用大鼠脑皮质细胞膜进行体外受体结合分析 ;进行动物体内分布、药代动力学、毒性实验和临床受体显像。结果　99Tcm octreotide放化纯达 78 5 % ,纯化后为 93 8% ,室温下放置 4h为92 1%。细胞膜体外放射受体结合分析证实99Tcm octreotide与octreotide具有相同的受体介导结合特性。 3例肺癌患者临床受体显像均获得阳性结果。结论　99Tcm 直接法标记octreotide方法可行 ,稳定性好 ;99Tcm octreotide是一种很有希望的肿瘤生长抑素受体显像剂     

葛根素对β肾上腺素受体结合作用和腺苷酸环化酶活性的影响

本研究采用放射性配体结合分析和腺苷酸环化酶(AC)活性测定,观察了葛根的有效化学成分之一葛根素对大鼠心肌膜中β受体结合作用和北京鸭红细胞膜中AG活性的影响。结果表明,葛根素如同其他β受体拮抗剂一样,能明显地降低β受体的最大结合容量,抑制受体与标记配体结合,阻断肾上腺素对膜剂中AC活性的激动作用,从而证明葛根素是一种β受体的拮抗剂。     

人重组阿片受体样受体在CHO细胞稳定表达系统的建立

目的：在中国仓鼠卵巢（CHO）细胞上稳定转染人重组阿片受体样受体（hORL1）,为体外高通量筛选hORL1受体作用药物及相关药物分子机制研究奠定基础。方法：用脂质体介导法将pcDNA3.1（＋）-hORL1重组质粒稳定转染到缺乏hORL1的CHO细胞中,然后用含G418的选择性培养液进行筛选,挑取耐药克隆;用放射性配体-受体结合实验进一步筛选阳性克隆,对阳性克隆受体亲和力和表达量进行分析,用[35S]GTPγS结合实验分析表达受体的功能。结果与结论：在稳定转染hORL1的克隆细胞中,[3H]伤害感受肽的Kd和Bmax值分别为（0.44±0.21）nmol/L和（0.35±0.06）pmol/mg蛋白。伤害感受肽刺激受体结合[35S]GTPγS的EC50值为3.45nmol/L。以上结果与文献报道的天然hORL1受体的特性相似,说明该细胞株表达的hORL1受体与天然的hORL1受体具有基本一致的生物学特性,证实成功建立了稳定表达人阿片受体样受体的细胞模型。     

有机磷毒剂对人脑谷氨酸受体的作用

本工作采用放射性配体结合实验方法，用健康意外死亡的人大脑额叶皮层突触膜作为受体源，３Ｈ－谷氨酸和３Ｈ－ＭＫ８０１作为标记配体在体外研究了人脑皮层ＮＭＤＡ受体的特性及有机磷毒剂对受体结合的影响。人大脑皮层膜与３Ｈ－谷氨酸有一特异性的可饱合性结合。特异性结合表现为单一结合位点，ＫＤ值和Ｂｍａｘ值分别为１０３ｎｍｏｌ／Ｌ和１．６７ｐｍｏｌ／ｍｇ蛋白。谷氨酸受体激动剂对人大脑皮层与谷氨酸结合的抑制强度依次为Ｌ－Ｇｌｕ＞ＤＬ－Ｇｌｕ＞ＫＡ＞ＮＭＤＡ＞Ｄ－Ｇｌｕ。谷氨酸受体亚型拮抗剂ＡＰ５和ＤＮＱＸ（１μｍ…     

99Tcm N核类心肌灌注显像剂的研究进展

放射性核素MPI是无创性诊断冠心病的重要手段.目前临床使用的201 Tl、99 Tcm标记的心肌灌注显像剂均存在一定的局限性.99TcmN核化学稳定性较高,使用已知配体与99TcmN核结合已成为制备新型心肌灌注显像剂的一条重要途径.笔者对以99TcmN核类新型心肌灌注显像剂的结构、生物学分布特性及显像特点进行总结,并介绍几种应用前景比较好的99TcmN核类心肌灌注显像剂.     

Radiochemical purity of routinely prepared 99Tcm radiopharmaceuticals: a retrospective study

Radiochemical purity is an important quality parameter for radiopharmaceuticals. In this study, the radiochemical purity of 2090 samples out of 7000 routine preparations of 20 different 99Tcm radiopharmaceuticals was tested using standard methods over a period of more than 7 years. The mean radiochemical purity was 96.92% (standard deviation = 6.71%). Seventy-four preparations failed to meet radiochemical purity limits; that is, 3.54% of all preparations tested or 1.06% of all preparations in the observation period. The reasons for substandard preparations were mainly related to laboratory-specific conditions. The introduction of a dedicated quality control protocol allowed the elimination of many sources of labelling failures and could reduce the number of administered preparations with an insufficient radiochemical purity. We stress the need for quality control in the preparation of radiopharmaceuticals and provide original radiochemical purity values of routinely prepared 99Tcm radiopharmaceuticals.     

Effect of protein binding on renal extraction of 131I-OIH and 99mTc-labeled tubular agents.

The clearance of 99mTc-mercaptoacetyltriglycine (MAG3) is less than the clearances of o-131I-iodohippurate (OIH) and 99mTc-labeled DD- and LL-ethylenedicysteine (EC). This difference could be associated with the lower affinity of MAG3 for the tubular transport receptor, but MAG3 is more highly protein bound than OIH and the EC isomers; protein binding could also be an important factor governing tubular extraction. To separate the effects of protein binding from tubular receptor affinity, the extraction fractions (EFs) of MAG3, OIH, and the DD, LL, and DL isomers of 99mTc-EC were measured in an isolated perfused rat kidney model using a protein-free perfusate and perfusates containing bovine serum albumin. METHODS: The right kidney was removed from the rat and perfused with modified Krebs-Henseleit buffers containing 7.5 or 2.5 g/dL bovine serum albumin or a protein-free perfusate. OIH was coinjected into the renal artery with each of the 99mTc-tracers. Protein binding was measured in each of the perfusates, and the venous outflow was collected to determine the EF. RESULTS: The protein binding of MAG3 in the albumin perfusates ranged from 87% to 95%, significantly higher than the 20%-34% range of protein binding observed with the three EC complexes (P < 0.05). In the 2.5 g/dL albumin perfusate, the EF of MAG3 was 44%, significantly less than the 57%-77% EF of the three EC complexes; in the 7.5 g/dL perfusate, the MAG3 EF fell to 18% versus 39%-45% for the EC complexes (P < 0.05). However, in the protein-free perfusate, the EF of MAG3 was 64%, equal to or higher than the 46%-62% EF of the three EC complexes. CONCLUSION: Protein binding modulates the tubular extraction of renal tracers. Protein binding and receptor affinity must be considered in the design of future renal radiopharmaceuticals as well as radiopharmaceuticals targeting other receptors.     

Radio-labeled receptor-binding peptides: a new class of radiopharmaceuticals

Radio-labeled receptor-binding peptides have emerged as an important class of radiopharmaceuticals. In vertebrates, these peptides transmit their biological function by binding to their specific receptor on the target cell surface. This specific receptor-binding property is exploited when the radio-labeled peptide is used as a radiopharmaceutical. The high-binding affinity for its receptor facilitates retention of the peptide in receptor-expressing tissues, whereas its relatively small size facilitates rapid clearance from the blood and other nontarget tissues. Receptor-binding peptides labeled with gamma-emitters can be used to visualize receptor-positive cells in vivo. In addition, when labeled with beta- or alpha-emitters, these peptides can be used for peptide-receptor radionuclide therapy. Various receptors are overexpressed on particular tumor types, and peptides binding to these receptors can be used to visualize tumor lesions scintigraphically. Furthermore, peptides binding receptors on granulocytes can be used to image infectious and inflammatory foci, whereas peptides binding receptors on activated thrombocytes can be used for thrombus imaging. Here, the peptide analogs that are under development for these applications are reviewed.     

Radiopharmaceuticals for renal positron emission tomography imaging

Radiopharmaceuticals for functional renal imaging, including renal blood flow, renal blood volume, glomerular excretion, and metabolism have been available for some time. This review outlines radiopharmaceuticals for functional renal imaging as well as those that target pertinent molecular constituents of renal injury and repair. The angiotensin and endothelin receptors are particularly appealing molecular targets for renal imaging because of their association with renal physiology and pathology. Other targets such as the vascular endothelial growth factor (VEGF) receptor, integrin, or phosphatidylserine have been investigated at length for cancer imaging, but they are just as important constituents of the renal injury/repair process. Various diseases can involve identical mechanisms, such as angiogenesis and apoptosis, and radiopharmaceuticals developed for these processes in other organs can also be used for renal imaging. The sensitivity and spatial resolution of positron emission tomography makes it an ideal tool for molecular and functional kidney imaging. Radiopharmaceutical development for the kidneys must focus on achieving high target selectivity and binding affinity, stability and slow metabolism in vivo, and minimal nonspecific accumulation and urinary excretion.     

Quantitative in vivo and in vitro comparison between radiolabelled colloids, biomolecules and blood cells in their ability to diagnose deep venous thrombosis

Three radiopharmaceutical groups (colloids, specific biomolecules and blood cells) and a control group were investigated with regard to their ability to rapidly diagnose deep venous thrombosis in an experimental rabbit model. An artificial thrombus was induced in the jugular vein and the radiopharmaceuticals were injected either homolaterally or contralaterally relative to the thrombus. The accumulation of the radioactivity in the thrombus 30 min after the induction was determined in vivo from scintillation camera images. After dissection of the jugular vein, the radioactivity of the thrombus was measured in vitro. None of the investigated radiopharmaceutical groups showed any marked high thrombus uptake after contralateral injections, not even the groups that consisted of substances known to be actively involved in coagulation and fibrinolysis. The results exclude a high degree of specific interaction between the radiopharmaceuticals and the thrombus in our model. After homolateral injection only colloids and reduced 99Tcm-pertechnetate showed a high thrombus uptake, thus also excluding a specific binding to thrombus. This investigation shows that none of the specific radiopharmaceuticals had a greater ability to accumulate in the thrombus than the colloids, and it is therefore suggested that the clinical usefulness is due to other mechanisms, like circulatory changes secondary to the DVT.     

Development of new radiopharmaceuticals based on N-substitution of iminodiacetic acid.

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labeled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.     

The use of tritium labeled compounds to develop gamma-emitting receptor-binding radiotracers

In an effort to evaluate receptor binding drugs for their potential as gamma labeled radiopharmaceuticals suitable for clinical heart scanning, in vivo data were compared with the results obtained from a theoretical model. The distribution of selected tritium-labeled, receptor-binding radiotracers was studied in animals to determine if the heart to blood ratios agree with those obtained using a theoretical model of receptor binding. In general, the in vivo studies agree with the theoretical model when the concentration of the radiotracer in the heart is due to specific receptor binding. The use of the theoretical model for a first approximation followed by in vivo biodistribution studies is an efficient strategy to select those few from among the large number of receptor binding compounds that will ultimately yield an efficacious radiopharmaceutical to study receptor changes in the intact human heart.