MicroRNA-155靶向的放射性标记探针对乳腺癌小鼠模型的活体显像

目的：microRNA-155（miR-155）显著高表达于乳腺癌、肺癌、肝癌等多种恶性肿瘤，本研究旨在构建靶向miR-155的放射性示踪探针对乳腺肿瘤的活体显像。方法：体外化学合成靶向miR-155的反义互补寡核苷酸探针（AMO-155），并对其进行5′端乙酰基修饰及2′ 甲氧基修饰,进而与双功能螯合剂NHS MAG3偶联后，在氯化亚锡的还原作用下对其标记 99mTc，评价血清稳定性，并对乳腺癌荷瘤裸鼠进行活体显像，对比反义、无义及阻断组的显像差异，并通过实时定量PCR（quantitative real-time PCR, qRT-PCR）鉴定肿瘤的miR-155水平。结果：99mTc-AMO-155的制备标记率达97%（n=5），放射化学纯度大于98%（n=5），放射比活度约为3.75 GBq/μg。通过对比无义对照组及阻断组，99mTc-AMO-155能够在活体水平特异性地显示miR-155高表达的恶性肿瘤。此外，针对miR-155不同表达水平的肿瘤，99mTc-AMO-155亦可在活体水平反映其表达差异。结论：经化学修饰的99mTc标记的AMO-155探针具有良好的血清稳定性及活体肿瘤靶向识别作用，为肿瘤显像提供了潜在的新型探针。

In vivo imaging of breast tumors by a 99mTc radiolabeled probe targeting microRNA-155 in mice models

Objective:MicroRNA-155 (miR-155) is significantly highly expressed in breast cancer,lung cancer,liver cancer and other malignant tumors.This study was to design and construct a radiolabeled probe targeting miR-155 for in vivo imaging in breast cancer.Methods:Anti-miR-155 oligonucleotide (AMO-155) was chemically synthesized with 2'-OMe modification.Its 5'end was linked with acetyl amine group.After chelated with a bifunctional chelator NHS-MAG3,AMO-155 was radiolabeled with 99mTc using stannous chloride.The serum stability was evaluated at cellular level.In vivo imaging was performed in MCF-7 tumor bearing mice after the administration of 99mTc radiolabeled AMO-155 and scramble control probes,respectively.Furthermore,the blocked imaging of tumor bearing mice was obtained after the injection of unlabeled AMO-155 2 hours ahead.MCF-7 and MDA-MB-231 tumor bearing mice with different expression level of miR-155 were imaged,respectively.Quantitative real-time PCR (qRT-PCR) was used to identify the expression level of miR-155 in the bearing tumors.Results:99mTc-AMO-155 was prepared with high radiolabeled efficiency (97％),radiochemical purity (greater than 98％),and radioactive specific activity (3.75 GBq/μg).99mTc-AMO-155 was stable in fresh human serum for 12 hours.After the administration via tail vein,99mTc-AMO-155 displayed significant accumulation in MCF-7 bearing tumors with high expression level of miR-155,whereas 99mTc-control showed little accumulation.After blocked with unlabeled AMO-155,the tumor could not be visualized clearly after the administration of 99mTc-AMO-155.Furthermore,99mTc-AMO-155 could show the differential expression of miR-155 in vivo.MCF-7 tumor was shown with significantly higher radioactive accumulation than MDA-MB-231,based on its higher expression level of miR-155,which was verified by qRT-PCR.Conclusion:99mTc-labeled AMO-155 with chemical modification showed good serum stability and in vivo tumor targeting ability.This study provides a potential probe for in vivo imaging of breast cancer.