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噬菌体展示(phage display)技术是一项研究生物活性肽、肽类药物筛选和抗体制备等非常有用的手段[1]。近年发展起来的噬菌体随机肽库体内筛选方法(phage display in vivo),是寻找与组织、器官特异性结合多肽的有效手段[2-3]。此法可在受体分子尚不清楚的情况下,以受体天然存在的环境组织器官为配基,利用噬菌体短肽的抗原特异性寻找未知的靶分子,确定其结构域,具有特异结合活体组织器官、在体内稳定性好、特异性高、缩短了研究周期等优点,而且筛选与治疗在相同条件下进行,避免了体外筛选得到的配体在体内试验无效或活性低的缺点,最大程度保证了筛选到的短肽的靶向特异性[4]。目前,国际上已经通过噬菌体体内筛选技术成功得到了几组特异肿瘤组织结合的多肽[5-8],将多肽与阿霉素和肿瘤坏死因子α耦联后,在小鼠肿瘤模型中起到了良好的抗肿瘤作用[9-10];将放射性核素标记该类多肽也可应用于肿瘤的显像和放射治疗的研究中[11-13]。本研究通过噬菌体体内筛选技术筛选与肺癌组织特异结合的七肽,并用125I标记后进行肺癌显像,结果如下。
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IRM-2小鼠是我所自主培育的肿瘤易感小鼠,已经成功接种了多种肿瘤。接种Lewis肺癌后10 d左右,肿瘤直径可达0. 5 cm,用于后续噬菌体体内七肽筛选。
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对收集的噬菌体进行滴度测定,第一轮未扩增的噬菌体每10μl滴度为5×105 pfu,扩增后的噬菌体每10μl滴度为1.55×1011 pfu。此后每轮筛选的噬菌体未扩增,滴度逐渐增大。挑取20个单菌落,测序外源插入七肽序列,其中一管测序错误、两管信号弱而未测出,其余17个样品测定的序列推导出的多肽序列结果见表 1。结果显示,出现频率最高的七肽序列为谷氨酰胺-酪氨-甘氨酸-谷氨酰胺-苯丙氨酸-丙氨酸-酪氨酸,即:QYGQFAY。
多肽序列 出现频率 1 YSGKPGW 2/20 2 QYGQFAY 13/20 3 LMLRDVC 1/20 4 CREAGNY 1/20 注:表中多肽序列的代号为相应的氨基酸缩写。 表 1 T7噬菌体展示文库筛选的靶向结合Lewis肺癌的七肽序列
通过化学合成法合成QYGQFAY七肽,并进行高效液相层析法纯化和质谱鉴定,结果:合成的七肽纯度为98%,质谱结果与QYGQFAY分子质量相吻合。
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纸层析测定标记率时,游离125I的比移值为0.8~0.9,125I-QYGQFAY的比移值为0.1~0.2,标记率约为85 %(图 1)。对标记的QYGQFAY七肽进行Sephedex G-75柱层析分离,对洗脱液进行放射性计数可知,QYGQFAY峰出现在第12~15管,游离125I峰出现在第36 ~ 38管(图 2)。纯化产物的纸层析结果显示,125I-QYGQFAY七肽的放化纯度 > 99%(图 3)。72 h后再次进行放化纯度的检测,放化纯度 > 95%,说明125I-QYGQFAY七肽在室温下放置3 d仍可稳定的存在。
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经Lewis肺癌小鼠尾静脉注射125I-QYGQFAY七肽后0.5、2、6 h用小动物活体成像系统测定荷瘤鼠体内放射性分布的结果见图 4。0.5 h时几乎全身分布,主要集中在肝脏等部位,肿瘤部位有部分分布,但是聚集的量较少(A3);2 h时放射性几乎都聚集于肿瘤部位,其他器官基本无分布(B3);6 h时放射性仍然主要集中在肿瘤部位,但体内总的放射性已经较低,已基本代谢完。
多肽类肺癌显像剂的制备及其初步鉴定
The preparation and identification of peptide imaging agent of lung cancer
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摘要:
目的 通过噬菌体随机七肽文库筛选出与体内肺癌组织特异结合的七肽,并制备肽类肺癌早期诊断试剂。 方法 通过噬菌体展示体内筛选技术获得与肺癌特异结合的噬菌体,进行序列测定,合成特异结合的多肽,125I标记后经静脉注射入小鼠体内,观察其在小鼠Lewis肺癌模型中的分布。 结果 通过4轮筛选获得了QYGQFAY七肽,该七肽经125I标记后可以很好地与肺癌组织特异结合,在体内2 h左右与肿瘤结合得最充分,而且体内代谢较快,6 h左右体内分布明显减少,基本代谢完毕。 结论 该七肽可以较好地对Lewis肺癌进行显像和诊断。 Abstract:Objective To screen in vivo lung cancer specific binding 7-peptide from T7 phage display random peptide library and prepare peptide imaging agent in early diagnosis of lung cancer. Methods Used phage display in vivo technology to get the 7-peptide phage that can bind the lung cancer specifically, then sequenced and synthesized 7-peptide. After being labeled by 125I, this 7-peptide was injected into mice via vein and the distribution in the mice tumor mold was observed. Results One 7-peptide was obtained after four rounds of screening, and the peptide could bind lung cancer tissue specifically. Metabolism of this peptide in mice was fast and imaging of lung cancer was best two hours later after injection. The distribution in vivo decreased and almost disappeared after six hours. Conclusion This 7-peptide could be used to image and diagnose of lung cancer effectively. -
Key words:
- Phage display /
- Peptides /
- Peptide library /
- Lung neoplasms
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表 1 T7噬菌体展示文库筛选的靶向结合Lewis肺癌的七肽序列
多肽序列 出现频率 1 YSGKPGW 2/20 2 QYGQFAY 13/20 3 LMLRDVC 1/20 4 CREAGNY 1/20 注:表中多肽序列的代号为相应的氨基酸缩写。 -
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