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Notch信号通路是一种普遍存在于从果蝇到哺乳动物等众多生命体中具有高度保守性的关键信号通路,其功能是参与细胞发育、增殖、分化、凋亡、黏附及器官发育。Notch信号通路是由Notch受体、Notch配体和CSL(CBF-1、suppressor of hairless、Lag的合称)-DNA结合蛋白3部分组成。Notch受体和配体均在细胞膜上表达。Notch受体胞外区是配体结合并激活Notch受体的部位,Notch受体胞内区(Notch intracellular domain,NICD)为其活性成分,未成熟的Notch受体与邻近细胞配体结合后被激活,经过3次裂解产生活性成分NICD。而关键的裂解发生在S3位点,即由γ分泌酶介导的切割作用而产生NICD。当NICD进入核内后,激活下游靶基因的转录。近年来,许多研究结果发现Notch信号通路失调与包括胰腺癌在内的多种肿瘤的发生、发展过程密切相关,在这些肿瘤中发现Notch通路持续活化[1-5]。(3,5-二氟苯乙酰基)-L-丙氨酰基-S-苯基甘氨酸叔丁酯(N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester,DAPT)是一种γ分泌酶抑制剂,能够通过阻断Notch信号通路,抑制肿瘤细胞的生长、转移和侵袭[6-7]。本研究以DAPT为前体进行体外细胞学实验,合成11C-N-甲基-DAPT(简称11C-DAPT),初步研究其在正常新西兰兔体内的动态分布,为进一步开展此类肿瘤特异性显像剂的转化研究及指导同类肿瘤分子靶向药物的治疗奠定基础、提供依据。
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人胰腺癌细胞株MiaPaCa-2由德国海德堡大学Freiss.H教授惠赠。DMEM培养液、胎牛血清、胰蛋白酶、PBS均购自美国Hyclone公司;DAPT购自美国Selleck公司;二甲基亚砜购自美国Sigma/Aldrich公司。NucleoCounter NC-100型全自动细胞计数仪购自丹麦chemometec公司;Sep-Pak QMA SPE分离柱购自美国Waters公司。使用美国GE公司的MINItrace Ⅱ回旋加速器、TRACERlab FXC Pro合成模块和Elite PET/CT。
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普通级雄性新西兰兔1只,3月龄,体质量3 kg,许可证编号:SYXK(京,2015-0025)。
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人胰腺癌细胞株MiaPaCa-2培养于DMEM培养液(加10%胎牛血清),在37℃、5% CO2培养箱中传代3代以上进行实验。经传代后的人胰腺癌细胞株MiaPaCa-2用0.25%胰酶进行消化,用DMEM培养液制成单个细胞悬液,用全自动细胞计数仪计数,调整细胞浓度至3×104个/mL,接种于96孔培养板,每孔体积100 μL。在37℃ 5% CO2培养箱中培养24 h,待细胞贴壁后,吸出培养液,分别加入不同浓度梯度的DAPT(30、45、60、70、80、90、 120 μmol/L)和CH3-DAPT(10、20、40、80、120、160、200 μmol/L)溶液,二者均溶于DMEM培养液。同时设置对照组和空白组,对照组加入相同体积的DMEM培养液,空白组无细胞只加培养液。DAPT和CH3-DAPT(实验组)均设5个复孔。37℃ 5% CO2培养箱中培养72 h。CCK-8法测定每组各孔的光密度(optical density,OD)值。
$ {\text{抑制率}}(\%)=1-{\frac{OD{\text{值}({\text{实验}})}-{\rm{OD}}{\text{值}}({\text{空白}})}{OD{\text{值}({\text{对照}})}-{\rm{OD}}{\text{值}}({\text{空白}})}}\times 100\% $ 使用SPSS19.0软件对数据进行logit回归分析,并计算半抑制浓度(half maximal inhibitory concentration,IC50)
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回旋加速器生产11C-CO2,在全自动合成仪上经H2还原得到11C-CH4,11C-CH4与I2反应生成11C-CH3I后转入反应瓶;2 mg前体DAPT溶于0.4 mL二甲基亚砜,预先置于反应瓶中,加入7 μL 5 mol/L NaOH ,充分振荡混匀。11C-CH3I与DAPT混合,标记反应80℃,反应时间3 min,洗脱液终止反应,降温冷却至35°C。产物使用高效液相色谱(high performance liquid chromatography,HPLC)仪进行分离纯化(C18柱,洗脱液300 mL 30%乙醇,流速2.5 mL/min,紫外线254 nm),收集产物,生理盐水稀释,无菌滤膜过滤待用。11C-DAPT的合成路线见图1。
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新西兰兔1只,耳缘静脉注射125.8 MBq(3.4 mCi)11C-DAPT后用PET/CT进行动态扫描,0、7、14、21、28 min各采集1次,共5次。CT扫描参数:电压120 kV,电流150 mA,层厚5 mm;PET扫描参数:1 min/床位,共4个床位。扫描结束后,对原始图像采用OSEM图像重建技术进行重建。获得CT、PET及二者融合图像。在主要脏器勾画ROI,测量放射性浓度(kBq/mL)及其随时间的变化。
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CCK-8法检测结果显示,DAPT和CH3-DAPT对胰腺癌细胞株MIAPaCa-2增殖的抑制作用呈剂量依赖关系。DAPT和CH3-DAPT作用于胰腺癌细胞株MiaPaCa-2后72 h,细胞增殖的IC50分别为64.2 μmol/L和180.0 μmol/L。
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11C-DAPT整个合成过程大约30 min,放射化学产率25%~35%(未校正,3次重复试验),放射化学纯度>95%。HPLC检测11C-DAPT与12C-DAPT标准品保留时间一致,大约在5.3 min时(图2、3)。
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兔注射11C-DAPT后,体内吸收迅速,以肾脏分布较多,肝脏、肠道、肺、脑等脏器摄取较低。7 min时肝脏、肾脏摄取达到高峰,28 min后降低>50%(表1)。注射后即刻扫描,肠道、脑及肺的放射性摄取达到高峰,随时间延长逐渐降低。0~21 min,随时间延长,膀胱的放射性摄取逐渐增高。兔喉部前方可见放射性摄取增高组织,且随时间延长摄取逐渐降低,但受PET/CT分辨率的影响,无法明确具体器官来源。图4和图5显示注射 11C-DAPT后正常兔的PET/CT图像。
组织 ROI 的放射性浓度 (kBq/mL) 0 min 7 min 14 min 21 min 28 min 脑 38.3±1.53 26.6±0.58 23.3±0.58 16.0±1.00 14.0±0.00 肺 40.6±2.52 28.3±2.08 20.0±2.64 12.6±1.52 12.3±0.58 肝脏 57.0±1.73 66.7±0.58 50.3±0.58 45.3±1.57 30.0±1.00 肠道 43.3±3.51 35.0±3.00 27.3±1.53 21.3±1.53 16.7±0.58 肾脏 83.7±3.06 123.6±5.69 75.3±2.31 65.0±2.65 51.6±3.06 膀胱 2.3±0.58 3.3±1.15 29.7±0.58 60.0±0.00 49.7±0.58 注:表中,DAPT:(3,5-二氟苯乙酰基)-L-丙氨酰基-S-苯基甘氨酸叔丁酯;ROI:感兴趣区。 表 1 11C-DAPT在正常新西兰兔体内的生物学分布(
$\bar x \pm s$ Table 1. Biodistribution of 11C-N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester(DAPT) in normal New Zealand rabbit
Notch信号通路小分子抑制剂DAPT的11C标记及在正常兔体内的初步动态显像研究
11C-labeling DAPT a small-molecular inhibitor of the Notch signaling pathway, and preliminary imaging study of dynamic distribution in a normal rabbit
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摘要:
目的 研究正电子核素11C标记Notch通路抑制剂(3,5-二氟苯乙酰基)-L-丙氨酰基-S-苯基甘氨酸叔丁酯(DAPT)的制备方法,并进行正常兔PET/CT的初步动态显像。 方法 采用细胞计数Kit-8法检测不同浓度DAPT和CH3-DAPT对人胰腺癌细胞株MiaPaCa-2增殖的影响,并计算半抑制浓度(IC50)。以DAPT为前体,使用全自动合成仪进行合成,得到产物11C-N-甲基-DAPT(简称11C-DAPT),并用高效液相色谱(HPLC)仪进行分离纯化。正常新西兰兔静脉注射125.8 MBq(3.4 mCi)11C-DAPT后,用PET/CT进行全身动态扫描。在不同器官勾画感兴趣区,测量放射性浓度随时间的动态变化。 结果 DAPT和CH3-DAPT均可抑制人胰腺癌MiaPaCa-2细胞的增殖,呈浓度依赖关系,72 h的IC50分别为64.2、180.0 μmol/L。11C-DAPT合成过程大约30 min,未校正放射化学产率为25%~35%,放射化学纯度>95%。11C-DAPT主要经肾脏排泄,全身脏器中肾脏摄取最高,肝脏、肠道、肺和脑摄取低。静脉注射后7 min肝脏、肾脏摄取达到高峰,28 min后降低>50%。 结论 11C-DAPT的合成过程简便、快速,放射化学纯度高。PET/CT的初步显像为进一步探索11C-DAPT作为胰腺癌新型靶向分子探针奠定了基础。 -
关键词:
- 同位素标记 /
- 正电子发射断层显像计算机体层摄影术 /
- Notch信号通路 /
- γ分泌酶抑制剂 /
- (3,5-二氟苯乙酰基)-L-丙氨酰基-S-苯基甘氨酸叔丁酯 /
- 分子探针
Abstract:Objective To label N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester(DAPT), an inhibitor of the Notch signaling pathway, with 11C and perform preliminarily dynamic imaging in normal rabbit. Methods Proliferation of human pancreatic cancer cell line MiaPaCa-2 were assessed by cell counting kit-8 method after treatment with various concentrations of DAPT and CH3-DAPT. Half-maximal inhibitory concentration(IC50) was calculated. DAPT was then used as a precursor to prepare 11C-N-methyl-DAPT(11C-DAPT) with a fully automatic synthesizer. The final product was purified through semipreparative high performance liquid chromatography(HPLC). After intravenous injection of 125.8 MBq(3.4 mCi) 11C-DAPT, a normal New Zealand rabbit was subjected to dynamic whole-body PET/CT scanning. The dynamic changes in radioactivity were measured by drawing regions of interest over different organs. Results DAPT and CH3-DAPT concentration-dependently inhibited the growth of the human pancreatic cancer cell line MiaPaCa-2. The IC50 values were 64.2 and 180.0 μmol/L at 72 h after administration, respectively. 11C-DAPT was synthesized for approximately 30 min. The uncorrected radiochemical yield was 25%–35%. Radiochemical purity was above 95%. 11C-DAPT was mainly excreted through the kidney, the highest uptake was in the kidneys, and the uptake in the liver, intestine, lung, and brain was relatively low. The tracer uptake in the kidneys and liver peaked at 7 min after injection and decreased to >50% at 28 min. Conclusions 11C-DAPT can be easily and rapidly synthesized with high radiochemical purity. Preliminary PET/CT imaging can lay a foundation for further investigating 11C-DAPT as a novel molecular probe. -
表 1 11C-DAPT在正常新西兰兔体内的生物学分布(
$\bar x \pm s$ Table 1. Biodistribution of 11C-N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester(DAPT) in normal New Zealand rabbit
组织 ROI 的放射性浓度 (kBq/mL) 0 min 7 min 14 min 21 min 28 min 脑 38.3±1.53 26.6±0.58 23.3±0.58 16.0±1.00 14.0±0.00 肺 40.6±2.52 28.3±2.08 20.0±2.64 12.6±1.52 12.3±0.58 肝脏 57.0±1.73 66.7±0.58 50.3±0.58 45.3±1.57 30.0±1.00 肠道 43.3±3.51 35.0±3.00 27.3±1.53 21.3±1.53 16.7±0.58 肾脏 83.7±3.06 123.6±5.69 75.3±2.31 65.0±2.65 51.6±3.06 膀胱 2.3±0.58 3.3±1.15 29.7±0.58 60.0±0.00 49.7±0.58 注:表中,DAPT:(3,5-二氟苯乙酰基)-L-丙氨酰基-S-苯基甘氨酸叔丁酯;ROI:感兴趣区。 -
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