SELEX技术及核酸适配子在临床诊断中的应用前景

指数富集配体的系统进化技术是一种新的组合化学技术,它利用人工合成的随机寡核苷酸文库,通过体外多轮筛选与扩增,获得能与靶物质特异性结合的寡核苷酸适配子。适配子的靶分子广泛,与靶物质结合的亲和力高、特异性强,在制备及稳定性等方面优于抗体。基于适配子的生物芯片、生物传感器、分子信标等检测新技术已初步显示出良好的敏感性和特异性,在人类疾病诊断中具有良好的应用前景。     

泡沫细胞靶向适配子的体外筛选

目的筛选巨噬细胞源性泡沫细胞的寡核苷酸适配子,为动脉粥样硬化的靶向治疗提供实验依据。方法以80 mg/L氧化型低密度脂蛋白孵育THP-1巨噬细胞72 h,建立泡沫细胞模型;利用指数富集配基的系统进化技术,从体外合成的随机单链DNA文库中筛选特异性寡核苷酸适配子;荧光显微镜观察寡核苷酸文库与泡沫细胞结合的特异性;克隆、测序确定适配子的序列并进行一级结构和二级结构分析。结果通过油红O染色和高效液相色谱分析,确定成功建立泡沫细胞模型;经过18轮的循环筛选,寡核苷酸文库仅与泡沫细胞结合,不再结合巨噬细胞、血管平滑肌细胞。测序鉴定出的所有适配子序列可以分为12个家族,没有共同的同源序列。二级结构分析表明,适配子主要形成茎环结构,这可能是适配子与巨噬细胞源性泡沫细胞结合的结构基础。结论利用复合靶指数富集配基的系统进化技术成功筛选出巨噬细胞源性泡沫细胞的寡核苷酸适配子。     

骨肉瘤特异生物诊断探针制备

目的构建与骨肉瘤细胞高亲和性与特异性结合的DNA寡核苷酸适配体库,用于骨肉瘤临床特异性诊断。方法体外合成40 nt高通量随机序列的单链DNA寡核苷酸文库(ssDNAs);骨肉瘤细胞(U-2 OS)作为目标细胞与文库ssDNAs反应;指数富集配体的系统进化(SELEX)技术用于筛选富集与靶细胞结合的寡核苷酸;聚合酶链反应(PCR)技术与亲和层析技术用于次轮反应文库的制备;应用荧光光谱跟踪筛选过程;对最后的筛选序列进行克隆、测序与保存。结果十一轮至十三轮筛选后的ssDNAs荧光光谱曲线显示了有意义重叠,因此结束筛选;对十三轮筛选的ssDNAs进行了克隆测序,依据一级结构的同源序列建立了寡核苷酸探针组群。结论应用SELEX技术最终从高通量的随机文库中获得了与U-2 OS具有高度亲和性的寡核苷酸适配体,适配体库的建立不仅仅用于骨肉瘤的特异性诊断,也将为探针-载体-抗肿瘤药物复合体的研制与实施骨肉瘤定向治疗搭建了可行性平台。     

抗体基因芯片应用于检测鼻咽癌组织切片蛋白质表达谱的研究

目的研究应用抗体基因芯片检测鼻咽癌组织特异性蛋白质表达谱的新技术方案。方法利用噬菌体抗体库筛选出抗鼻咽癌的特异性抗体库,以扩增抗体基因V-D-J片段作为标识分子用于制备抗体基因芯片;通过特异性抗体库与鼻咽癌肿瘤组织结合后,使标记引物扩增的V-D-J序列与抗体基因芯片进行杂交后显示癌组织的蛋白质表达谱,从而选择性通过免疫组织化学显示其中关键性蛋白质原位表达状况。结果肿瘤组织结合的抗体滴度可达到106～108数量级,标记的DNA分子效价约为10-6～10-8,以该文一次检测20个抗体为例,基因芯片检出有10～14个阳性蛋白质表达谱;免疫组织化学可显示阳性抗体在细胞中的结合部位。结论以抗体基因芯片为核心的技术方案,能在组织切片上同时检测含多个蛋白质表达谱,可以广泛应用于基础研究和临床诊疗过程。     

核酸适配子在消化系统肿瘤诊治的应用研究进展

核酸适配子是一类寡核苷酸配基,由指数富集配体系统进化技术从寡核苷酸文库中筛选合成所得.核酸适配子的配体种类丰富,其亲和力及特异性较蛋白抗体高、性质稳定及合成简便,有望成为生物医药领域的花魁.核酸适配子在疾病尤其是肿瘤诊治的应用中已表现出很大潜力.此文就核酸适配子在消化系肿瘤诊治的应用研究进展作一综述.     

靶向寄生虫的核酸适配体应用研究进展

核酸适配体是人工合成的单链DNA或RNA寡核苷酸,经指数富集的配体系统进化技术体外筛选获得。核酸适配体可与病毒、细菌、寄生虫等生物体的蛋白质与其他小分子靶标进行高亲和力和特异性结合。与抗体相比,核酸适配体具有无免疫原性、制备简单、易于批量生产、便于修饰、性能稳定、价格低廉等优点,在疾病诊断和治疗领域具有重要的应用潜力。本文综述了靶向疟原虫、锥虫、利什曼原虫等寄生虫的核酸适配体的研究进展,以期为寄生虫感染的检测和防治提供新策略。     

结核分枝杆菌MPT64蛋白适配子的筛选与鉴定

目的 利用指数富集配体系统进化(SELEX)技术筛选能与结核分枝杆菌分泌蛋白MPT64特异性结合的寡核苷酸适配子,寻找早期诊断结核病的方法.方法 体外合成随机单链DNA(ssDNA)文库,以MPT64蛋白为靶物质,采取SELEX技术进行12轮筛选,将适配子库克隆、测序后,用DNAMAN软件对其结构进行分析,经生物素-链亲和素-辣根过氧化物酶显色系统测定亲和力,并利用捕获适配子与检测适配子组成的"三明治"夹心法对获得的适配子进行初步验证.将13个非结核分枝杆菌菌株和BCG菌株作为阴性组计为0,将结核分枝杆菌和牛结核分枝杆菌组作为阳性组计为1,采用MedCalc软件分析受试者操作特征曲线,确定最佳阳性判定值,并构建散点图.结果 经12轮筛选后,随机挑选15个适配子与MPT64蛋白的亲和性进行分析,吸光度值为0.492～1.243,73.3％的适配子的吸光度值在1.0以上;二级结构分析显示,适配子与MPT64蛋白亲和性的基础主要是大口袋茎环结构,口袋与环之间的茎桥含有不同数量的GC碱基对;"三明治"夹心法对阴性组[非结核分枝杆菌标准菌株及卡介苗(BCG)株]和阳性组(结核分枝杆菌实验室H37Rv株及临床株、牛结核分枝杆菌标准株)共47个菌株培养上清的检测结果显示,在临界(cut-off)值为0.61时,H37Rv、牛结核分枝杆菌组为阳性,BCG株为阴性;阴性组标本的阴性检出率为85.7％,阳性组标本的阳性检出率为87.9％,表现出一定的检测价值.结论 已初步筛选到与MPT64蛋白具有高亲和性的DNA适配子.     

丙型肝炎病毒相关适配分子的研究进展

指数富集配基的系统进化(systematic evolution of ligand by exponential enrichment,SELEX)技术是一类新的组合化学技术,应用人工合成的随机寡核苷酸文库,通过体外筛选、分离、富集获得能与靶物质特异性结合的寡核苷酸适配子.具有实用范围广、筛选过程简便、适配子有高特异性和高亲和性等特点.适配子的选择性在很多方面优于抗体,在分子识别研究中具有重要价值,可用于靶物质的测定、阻断靶物质的生物活性.本文综述SELEX技术及寡核苷酸适配子在丙型肝炎病毒诊断和治疗领域的最新进展,并且对其前景进行分析和预测.     

紫外线致弱童虫免疫家兔血清筛选日本血吸虫成虫cDNA文库

目的　用致弱疫苗免疫血清、感染血清筛选文库获取新的日本血吸虫特异性未知抗原基因。　方法　用紫外线致弱童虫免疫兔血清、感染血清免疫筛选日本血吸虫成虫cD?鄄NA文库 ,对阳性重组子进行克隆、测序 ,利用软件对核酸序列进行分析 ,确定目的基因。　结果　筛选出 6种蛋白分子基因 :3-磷酸甘油醛脱氢酶 (GAPDH) ,丝氨酸蛋白酶抑制剂 (serpin) ,线粒体编码蛋白 ,肌球蛋白 (myosin)部分重链基因以及两个未知新基因。　结论　紫外线致弱疫苗免疫血清筛选cDNA文库为寻找新的抗血吸虫病疫苗提供了又一途径。     

阪崎克罗诺菌特异性适配子筛选研究

目的 通过SELEX(指数富集配基系统进化技术)筛选阪崎克罗诺菌特异性DNA适配子, 为建立基于适配子技术的阪崎克罗诺菌快速检测方法奠定基础。方法 在阪崎克罗诺菌比较基因组分析、蛋白亚细胞定位预测、蛋白跨膜区预测分析、基因mRNA表达量分析、基因克隆表达和蛋白纯化基础上,制备用于适配子筛选的靶蛋白。利用靶蛋白偶联羧基磁珠,筛选ssDNA适配子。并对适配子的靶蛋白结合亲和力和目标菌捕获特异性进行分析。结果 适配子S1与靶蛋白结合亲和力较高,对阪崎克罗诺菌有较好捕获能力,捕获率最高为23.1%。对大肠埃希氏菌、沙门氏菌等非目标菌不具有明显的捕获能力,具有较好的阪崎克罗诺菌捕获特异性。结论 适配子S1和S2的二级结构以茎环结构和发夹结构为主。     

筛选结核分枝杆菌CFP-10抗原适体的研究

目的建立SELEX技术筛选结核分枝杆菌CFP-10抗原适体的方法,并获得CFP-10的高亲和性适体。方法体外构建长度为78个碱基的随机单链DNA（ssDNA）文库,以微孔板为筛选介质,采用SELEX技术筛选获得CFP-10的适体库。将适体库克隆、测序,用DNAMAN软件对其结构进行分析,利用酶联寡核苷酸吸附试验（enzyme-linkedoligonucleotide sorbent assay,ELOSA）测定亲和力。结果构建的ssDNA文库经过14轮筛选与CFP-10亲和力从0.273提高到1.265;克隆子测序,大多数长度与预期值相符。二级结构显示,口袋和茎环结构可能是适体与CFP-10结合的结构基础。结论成功建立了SELEX筛选技术,并初步获得了CFP-10的高亲和性适体。     

抗甲状腺刺激性免疫球蛋白单链抗体噬菌体抗体库的初建

目的 建立抗甲状腺刺激性免疫球蛋白单链抗体噬体抗体库,为进一步获得功能性抗体可变区基因,制备单链抗体和单链抗体－辣根过氧化物酶融合蛋白,用于甲状腺自身免疫性疾病的治疗和检测打下基础,方法 利用ＲＴ－ＰＣＲ技术从分泌抗甲状腺刺激性免疫球蛋白的杂交瘤细胞中扩增出轻重链可变区基因,与噬粒表达载体ｐ３ＳＣＭＨ连接,转化大肠杆菌,以甲状腺刺激性免疫球蛋白阳性患者血清ＩｇＧ为抗原对表达的噬菌体抗体进行筛选,结     

Isolation of peptide aptamers that inhibit intracellular processes

We have developed a method for isolation of random peptides that inhibit intracellular processes in bacteria. A library of random peptides expressed as fusions to Escherichia coli thioredoxin (aptamers) were expressed under the tight control of the arabinose-inducible P(BAD) promoter. A selection was applied to the library to isolate aptamers that interfered with the activity of thymidylate synthase (ThyA) in vivo. Expression of an aptamer isolated by this method resulted in a ThyA(-) phenotype that was suppressed by simultaneous overexpression of ThyA. Two-hybrid analysis showed that this aptamer is likely to interact with ThyA in vivo. The library also was screened for aptamers that inhibited growth of bacteria expressing them, and five such aptamers were characterized. Four aptamers were bacteriostatic when expressed, whereas one showed a bactericidal effect. Introduction of translational stop codons into various aptamers blocked their activity, suggesting that their biological effects were likely to be due to protein aptamer rather than RNA. Combinatorial aptamers provide a new genetic and biochemical tool for identifying targets for antibacterial drug development.     

Aptamers evolved from live cells as effective molecular probes for cancer study

Using cell-based aptamer selection, we have developed a strategy to use the differences at the molecular level between any two types of cells for the identification of molecular signatures on the surface of targeted cells. A group of aptamers have been generated for the specific recognition of leukemia cells. The selected aptamers can bind to target cells with an equilibrium dissociation constant (K(d)) in the nanomolar-to-picomolar range. The cell-based selection process is simple, fast, straightforward, and reproducible, and, most importantly, can be done without prior knowledge of target molecules. The selected aptamers can specifically recognize target leukemia cells mixed with normal human bone marrow aspirates and can also identify cancer cells closely related to the target cell line in real clinical specimens. The cell-based aptamer selection holds a great promise in developing specific molecular probes for cancer diagnosis and cancer biomarker discovery.     

Production of a human single-chain variable fragment antibody against esophageal carcinoma

AIM: To construct a phage display library of human singlechain variable fragment (scFv) antibodies associated with esophageal cancer and to preliminarily screen a scFvantibody against esophageal cancer.METHODS: Total RNA extracted from metastatic lymph nodes of esophageal cancer patients was used to construct a scFv gene library. Rescued by M13K07 helper phage, the scFv phage display library was constructed, esophageal cancer cell line Eca 109 and normal human esophageal epithelial cell line (NHEEC) were used for panning and subtractive panning of the scFv phage display library to obtain positive phage clones. Soluble scFv was expressed in E.coliHB2151 which was transfected with the positive phage clone, then purified by affinity chromatography.Relative molecular mass of soluble scFv was estimated by Western blotting, its bioactivity was detected by cell ELISA assay. Sequence of scFv was determined using the method of dideoxynucleotide sequencing.RESULTS: The size of scFv gene library was approximately 9×10^6 clones. After four rounds of panning with Eca109 and three rounds of subtractive panning with NHEEC cells,25 positive phage clones were obtained. Soluble scFv was found to have a molecular mass of 31 ku and was able to bind to Ecal09 cells, but not to HeLa and NHEEC cells.Variable heavy (VH) gene from one of the positive clones was shown to be derived from the γ chain subgroup IV of immunoglobulin, and variable light (VL) gene from the κ chain subgroup I of immunoglobulin.CONCLUSION: A human scFv phage display library can be constructed from the metastatic lymph nodes of esophageal cancer patients. A whole human scFv against esophageal cancer shows some bioactivity.     

Generation and Characterization of a Novel Recombinant Antibody against LMP1-TES1 of Epstein-Barr Virus Isolated by Phage Display

Latent Membrane Protein 1 (LMP1) is a primary target for controlling tumorigenesis in Epstein-Barr virus related malignancies; in this study, we aimed to develop a specific antibody against the TES1 domain of the oncogenic LMP1. We screened a full human naïve Fab phage library against TES1 peptide, which consisted of C terminal-activating regions proximal 44 amino acids. After three rounds of panning, enrichment and testing by phage ELISA and further analyzed by DNA sequencing, we selected a phage clone with the highest affinity to LMP1-TES1 and designated it as htesFab. The positive clone was expressed in Escherichia coli and the purified htesFab was characterized for its binding specificity and affinity to LMP1. ELISA, immunofluorescence and FACS analysis confirmed that htesFab could recognize LMP1 TES1 both in vitro and in LMP1 expressing HNE2-LMP1 cells. Furthermore, MTT assay showed that htesFab inhibited the proliferation of HNE2-LMP1 cells in a dose-dependent manner. In summary, this study reported the isolation and characterization of human Fab, which specifically targets the C terminal region/TES1 of LMP1, and has potential to be developed as novel tool for the diagnosis and therapy of Epstein-Barr virus related carcinoma.     

Light-switching excimer probes for rapid protein monitoring in complex biological fluids

Quantitative protein bioanalysis in complex biological fluids presents considerable challenges in biological studies and disease diagnosis. The major obstacles are the background signals from both the probe and the biological fluids where the proteins reside. We have molecularly engineered light-switching excimer aptamer probes for rapid and sensitive detection of a biomarker protein, platelet-derived growth factor (PDGF). Labeled with one pyrene at each end, the aptamer switches its fluorescence emission from approximately 400 nm (pyrene monomer) to 485 nm (pyrene excimer) upon PDGF binding. This fluorescence wavelength change from monomer to excimer emission is a result of aptamer conformation rearrangement induced by target binding. The excimer probe is able to effectively detect picomolar PDGF in homogeneous solutions. Because the excimer has a much longer fluorescence lifetime (approximately 40 ns) than that of the background (approximately 5 ns), time-resolved measurements were used to eliminate the biological background. We thus were able to detect PDGF in a cell sample quantitatively without any sample pretreatment. This molecular engineering strategy can be used to develop other aptamer probes for protein monitoring. Combined with lifetime-based measurements and molecular engineering, light-switching excimer aptamer probes hold great potential in protein analysis for biomedical studies.