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肿瘤受体显像及核素靶向治疗是利用放射性核素标记的配体与存在于肿瘤的特异性受体相结合的一种特异性强、灵敏度高的核医学分子诊疗技术,其在精准医学中发挥着越来越重要的作用。用放射性核素标记的分子探针进行显像,因其具有高灵敏度、高特异性、可定量及无创性检测等优势,已经成为在分子水平上进行活体内病变精准诊断和疗效评价的重要手段。
人表皮生长因子受体2(human epidermal growth factor receptor type 2,HER2)在很多恶性肿瘤(如乳腺癌、卵巢癌、前列腺癌)中高表达[1],HER2的表达与肿瘤的侵袭性有关[2],在很大程度上决定了患者的预后,HER2阳性乳腺癌患者的中位生存期较短。对于HER2阳性肿瘤,HER2靶向药物曲妥珠单抗(商品名:赫赛汀,Herceptin)可以明显延长肿瘤患者的生存时间[3-4]。因此,准确筛选出HER2阳性肿瘤并对其进行靶向治疗意义重大。HER2亲和体具有相对较小的分子量、较高的特异性及亲和力,放射性核素标记的HER2亲和体在体内的血液清除速率快、肿瘤摄取明显,在HER2高表达的肿瘤精准诊疗中具有良好的临床应用前景。本文将对放射性核素标记的HER2亲和体分子探针用于分子影像、治疗及疗效评价的研究进展进行综述。
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1995年Nord等[10]首次提出小分子靶向结合蛋白,即亲和体,距今已有20年,亲和体分子现已被证实为一类极具前景的、用于开发不同分子靶向显像试剂或治疗药物的通用平台,且被广泛应用于疾病的诊断、治疗及生物技术等多种领域。亲和体分子蛋白骨架源于葡萄球菌A蛋白IgG结合域中的Z结合域,是由58个氨基酸残基构成的稳定的三螺旋结构,亲和体分子库可由螺旋1和2中的13个氨基酸残基随机组合而成[11-13]。亲和体分子体积小,可以快速穿过生物学屏障,具有较好的生物动力学特征,结构稳定,较易合成,尤其是可与靶分子,如表皮生长因子受体、HER2、人血清白蛋白、TNF-α等高亲和性、高特异性地结合,这些优点使得亲和体分子成为分子影像学研究的焦点。
HER2亲和体分子最基本的氨基酸序列为VD-NKFNKEQQNAFYEILHLPNLNEEQRNAFIQSLKDDPS-QSANLLAEAKKLNDAQAPK,完全可以通过固相合成法合成,可明显降低合成的费用。第一代HER2亲和体分子主要为ZHER2: 4[14],其亲和力较低(50 nmol/L),很难应用于体内靶向显像。第二代HER2亲和体分子为ZHER2: 477和ZHER2: 342[15],通过对成熟的亲和体序列进行定点变异而筛选得到,亲和力提高了3个数量级。第三代HER2亲和体分子为对ZHER2: 342进行改进得到的ZHER2: 2395[16]和ZHER2: 2891[17],具有更高的亲水性、热稳定性及更易于与HER2结合等优点,使体内优良靶向显像成为可能。各代HER2亲和体的氨基酸序列比较见表 1[18]。
亲和体名称 氨基酸序列 ZHER2 V D N K F N K E Q Q N A F Y E I L H L P N L N E E Q R N A F I Q S L K D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:4 V D N K F N K E L R Q A Y W E I Q A L P N L N W T Q S R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:477 V D N K F N K E M R N A Y W E I A L L P N L N V A Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:342 V D N K F N K E M R N A Y W E I A L L P N L N N Q Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:2395 A E N K F N K E M R N A Y W E I A L L P N L T N Q Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:2891 A E A K Y A K E M R N A Y W E I A L L P N L T N Q Q K R A F I R K L Y D D P S Q S S E L L S E A K K L N D S Q A P K 注:表中,HER2:人表皮生长因子受体2;ZHER2表示HER2亲和体基本的氨基酸序列;红色字体标注的为与HER2亲和体基本氨基酸序列相比修改后的氨基酸残基。 表 1 各代HER2亲和体的氨基酸序列比较
Table 1. Comparison of amino acid sequences among different generations of human epidermal growth factor receptor type 2 affibody molecules
放射性核素标记HER2亲和体的方法分为直接标记与间接标记。直接标记是将放射性核素直接与HER2亲和体相连接,此方法标记率低,标记物不稳定。间接标记是利用螯合剂将放射性核素与HER2亲和体进行连接,此方法标记率高,标记物稳定。近年来,螯合剂的种类多种多样,而基于肽结构的螯合剂因其结构简单、易与生物物质合成、标记率高、无需纯化、易于制备等优点,已引起研究者的高度重视。早期的螯合剂如MAG3(巯乙酰基三甘氨酸)等,因标记后的探针分子量较大,无法通过肾脏清除而只能通过肝胆分泌途径清除,但因肝胆分泌较慢,导致探针的血液清除较慢,显像本底高,从而导致图像的对比度较低,图像质量不高。进一步的研究将HYNIC(联肼尼克酰胺)、DTPA、DOTA(1, 4, 7, 10-四氮杂环十二烷基-1, 4, 7, 10-四乙酸)、maESE-(巯基乙酰基-谷氨酰-丝氨酰-谷氨酰)和maSKS-(巯基乙酰基-丝氨酰-赖氨酰-丝氨酰)作为螯合剂,使分子探针主要经肾脏清除,减少了经肝脏代谢的量,从而提高了图像质量,但肾内滞留明显[19-21]。通过在HER2亲和体的C端或者N端进行肽螯合剂修饰,对构成的不同分子结构进行核素标记,体内和体外的研究表明,N端的不同氨基酸序列肽结构螯合剂会影响肝脏摄取,而在C端时该影响不明显[22]。当基于N3S结构的螯合剂在C端时,血液循环中无明显游离锝,而当该螯合剂在N端时,放射性核素锝在血中易游离。当AEN-在N端,同时基于N3S结构的螯合剂GGGC-、GGSC-、GGEC-、GGKC-在C端时,HER2特异性结合较好,血中清除较快,经肾脏排泄,并在肾中滞留较少。这些研究结果对制备优良的HER2分子核素探针并促进其临床转化具有重要的价值。
放射性核素标记HER2亲和体分子探针精准诊疗的研究进展
Advances in radionuclide-labeled HER2 affibody molecular probes for precise diagnosis and treatment
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摘要: 人表皮生长因子受体2(HER2)亲和体分子因具有对靶组织亲和力高、特异性强、分子量小、制备简单、生物动力学特征良好等特点, 近年来在肿瘤分子影像方面的研究中显示出了较好的临床应用前景。放射性核素标记HER2亲和体分子探针不仅可以进行肿瘤受体显像及疗效评价, 还可以用于靶向治疗。笔者就目前放射性核素标记HER2亲和体分子探针精准诊疗的研究进展作简要综述。
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关键词:
- 受体, 表皮生长因子 /
- 放射性核素显像 /
- 亲和体分子
Abstract: Human epidermal growth factor receptor type 2(HER2) affibody molecules hold the advantage of high specificity and affinity, small size, simple synthesis, and excellent biological dynamics. It has been widely used in molecular imaging and treatment of tumor, with an eye towards clinical translation. The molecular probes of radionuclide-labeled HER2 affibody can not only be used in receptor imaging and response evaluation of tumor, but also in targeted therapy. This article reviewed the latest researches on radionuclide-labeled HER2 affibody. -
表 1 各代HER2亲和体的氨基酸序列比较
Table 1. Comparison of amino acid sequences among different generations of human epidermal growth factor receptor type 2 affibody molecules
亲和体名称 氨基酸序列 ZHER2 V D N K F N K E Q Q N A F Y E I L H L P N L N E E Q R N A F I Q S L K D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:4 V D N K F N K E L R Q A Y W E I Q A L P N L N W T Q S R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:477 V D N K F N K E M R N A Y W E I A L L P N L N V A Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:342 V D N K F N K E M R N A Y W E I A L L P N L N N Q Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:2395 A E N K F N K E M R N A Y W E I A L L P N L T N Q Q K R A F I R S L Y D D P S Q S A N L L A E A K K L N D A Q A P K ZHER2:2891 A E A K Y A K E M R N A Y W E I A L L P N L T N Q Q K R A F I R K L Y D D P S Q S S E L L S E A K K L N D S Q A P K 注:表中,HER2:人表皮生长因子受体2;ZHER2表示HER2亲和体基本的氨基酸序列;红色字体标注的为与HER2亲和体基本氨基酸序列相比修改后的氨基酸残基。 -
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